CH-1996-R-No. 3171
CH 1996 R NO. 5680
CH 1996 R No. 3170
Neutral Citation Number: [1997] EWHC 372 (Pat)
IN THE HIGH COURT OF JUSTICE
CHANCERY DIVISION

Date: 12 June 1997

Before:

THE HON. MR. JUSTICE LADDIE

IN THE MATTER OF The Patents Act 1977
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IN THE MATTER OF United Kingdom Patents numbers 2 036 754, 2 038 550 and 2 038 549 in the name of Raychem Corporation
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IN THE MATTER OF United Kingdom Patent number 2 042 789 in the name of Raychem Corporation
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IN THE MATTER OF European Patent (UK) number 0 223 404 in the name of Raychem Corporation
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B E T W E E N

	Bourns inc.
	Petitioner	
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	RAYCHEM CORPORATION	Respondent	
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Mr. Michael Silverleaf QC instructed by  Linklaters & Paines for the Petitioner
Mr. Christopher Floyd QC and Mr. Iain Purvis instructed by Hobson Audley Hopkins & Wood for the Respondent

Hearing date: 2, 6 - 9 May, 1997
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JUDGMENT

Mr. Justice Laddie:
The petitioner, Bourns Inc., have petitioned to revoke 5 patents granted to and registered in the name of the respondent, Raychem Corporation. Before the petitions came on for trial, Raychem acknowledged that one of its patents had been prior used and therefore agreed to its revocation. This judgment is therefore concerned with the validity of the remaining four. Those patents are (i) GB No. 2,036,754 - referred to during the trial and in this judgment as the “Compositions Patent”, (ii) GB No. 2,038,550 - referred to as the “Circuit Protection Patent”, (iii) GB No. 2,038,549 - referred to as the “Oxygen Barrier Patent” and (iv) GB No. 2,042,789 - referred to as the “Battery Protection Patent”. All four appear to have arisen out of one piece of research conducted by Raychem. The first three have the same priority date, 1 December 1978. The Battery Protection Patent was applied for on 26 January 1979. For the purpose of these proceedings, it was not suggested by either party that anything turned on the differences between these dates and they were treated as contemporaneous.
The technology involved.
All the patents are concerned with what is known as “positive temperature coefficient” or “PTC” compositions, devices and applications. As a general rule, ceramics, rubbers and plastics are insulating materials. That is to say they exhibit a high resistance to the passage of an electrical current. However some decades ago it was found that if a conductive material, like a metal, was incorporated into a ceramic material in sufficient quantity, the electrical resistance of the resultant composite material was lowered and it could pass an electrical current. In the early 1960’s it was shown that the same technique could be applied so as to make rubbers and crystalline plastics conductive. In particular it was found that conductive composites could be produced by incorporating carbon black into rubber or crystalline plastics. These composites have been called conductive rubbers and plastics. By 1970, they were well known. One of the books pleaded in these proceedings as constituting or evidencing the common general knowledge is entitled “Conductive Rubbers and Plastics” by R. H. Norman (referred to as “Norman”) which was published in the United Kingdom in 1970. Conductive rubber has been used, for example, on aircraft wheels to ensure that any static charge built up on the body of the vehicle during flight is discharged through the wheels on landing rather than through the first passenger to disembark. They have also been used in other anti-static applications.

It is easy to visualise how the use of a suitable filler renders ceramics, plastics or rubbers conductive. The mother material’s inherent insulating properties are not changed but the distribution of significant quantities of finely divided conductive material in it allows electrons through. The electrons find a path from one particle of conductive material to another and thereby find a more or less tortuous way around the insulating matrix in which the particles are embedded. Although this may be a somewhat simplified explanation, it is sufficient, and sufficiently accurate, for present purposes. It will be appreciated that, as a generality, the smaller the amount of conductive material incorporated into the matrix, the harder it is for the electrons to find a way through. On the other hand if very large quantities of conductive material are used, the passage of electrons is facilitated. In other words, as a generality, the greater the quantity of conductive material incorporated into the composite, the greater its conductivity and the lower its electrical resistance. 

In 1971, the Cabot Corporation, one of the major suppliers of carbon black for use in conductive plastics, issued a technical report. As one of Bourns’ witnesses stated, and was not seriously or effectively challenged, it contains a helpful but brief summary of the general understanding of the processing, use and operation of conductive plastics. Among other things it records that the electrical characteristics of the composite are affected by the size, shape and structure of the carbon black aggregates incorporated into the polymer. It says that smaller size aggregates mean more aggregates per unit volume of composite. This reduces inter-aggregate distances resulting in higher conductivity (i.e. lower resistivity). Carbon black of irregular shaped aggregates provide more effective  electron paths through the composite thereby also causing higher conductivity. As part of its basic summary, Cabot also confirms that in order to maintain maximum conductivity, processing should be kept to a minimum. Excessive processing during manufacture results in the deterioration of the conductive properties of the finished product.

The incorporation of conductive fillers into an insulating matrix may produce a group of conductive composites exhibiting a more complex and interesting effect. A composite which is conductive, i.e. has low electrical resistance, at room temperatures may develop low conductivity, i.e. have high electrical resistance, at high temperatures. This is what is signified by the expression “positive temperature coefficient”. An explanation for how this effect is caused was put forward in the 1960’s by Mr. Fred Kohler, the  inventor of two of the pieces of prior art pleaded in this case. Although the precise mechanism at work is not known even now, Mr. Kohler’s theory is sufficient to explain some of those features of PTC material behaviour which are relevant to these proceedings. Electrons pass from particle to particle of conductive material when they touch or are very close to each other. As the composite is heated up, expansion of the insulating matrix has the effect of increasing the distance between the conductive particles. More and more of them are separated by a distance which is too great for the electrons to jump. The conductivity of the composite therefore falls as it is heated up. However this effect is less noticeable when the composite has a very high conductive filler content. In such cases, even when heated, numerous particles are still close enough to each other to continue to provide an electrical path through the composite. The result is that the electrical resistance of the composite does not rise, or rise as markedly, as is the case with composites having a lower conductive filler content. From this discussion it can be seen that incorporation of conductive filler into, say, a suitable plastics material will increase the conductivity, i.e. reduce the electrical resistance, of the composite so formed but, when the quantities so added are particularly high, this may result in suppression of the PTC effect.

Since PTC materials change their electrical characteristics significantly when there is a change in temperature, they can be employed in electrical circuits designed to be sensitive to temperature variations. For example they can be employed in over-temperature protection circuits designed to reduce or eliminate the electrical supply to a device which is overheating. By 1973, Dr. J. Meyer, one of the leading workers in the field, was able to report in one of his articles that PTC devices could be found in widely varying commercial applications such as baby food warmers, television screen degaussing systems and automatic chokes for cars. These PTC devices were of the then commercially available ceramics type. As Meyer reported, and was not disputed before me, the use of ceramic PTC devices was restricted by the relatively low conductivity (i.e. a relatively high resistance to the flow of electricity) at normal operating temperatures and their high materials and fabrication costs. He went on to report:

“The most successful work to date has involved crystalline polymers which have been loaded with finely divided conductive materials such as carbon black or silver powder. These loaded polymers have been found to exhibit a PTC phenomenon identical in appearance to that found with ceramic materials with the exception that it is not sensitive to the magnitude of the applied filed. There is a characteristic transition temperature for each polymer, similar to the Curie temperature of the ceramic, which is normally a few degrees below the peak crystalline melting point.”

The use of crystalline polymers loaded with conductive particles, particularly carbon black, as PTC materials was the subject of research commencing in the 1960’s. Although all the claims in the patents in suit encompass such polymeric PTC materials (PPTCs), most of the ones now maintained by Raychem as having independent validity are restricted to such materials and their applications. 

With this basic history and technology in mind, it is convenient to turn to the patents in suit.
The patents in suit
The four patents remaining in issue in these petitions contain in total 110 claims. Even the Oxygen Barrier Patent, which seeks to claim protection for the use of an oxygen impervious cover to protect PTC devices from the adverse effects of oxygen in the air, runs to 24 claims. In accordance with modern practice, the patentee was obliged to indicate which claims it maintained were independently valid. By the beginning of the trial it had come down to some 39 claims. On the morning of the last day of the trial, Mr. Floyd QC, who appeared for Raychem, informed the court and Mr. Silverleaf QC, Counsel for Bourns, that his client was prepared to restrict further the list of claims asserted to be independently valid. This confined consideration of independent validity to about 17 claims (depending on how you counted some of the interdependent claims). Half way through his speech, Mr. Floyd abandoned claim 1 of the Battery Protection Patent. 

Those who have experience of the patent field are well aware of the practice of including in patents numerous subsidiary claims of ever narrower scope. This is usually more an exercise in  drafting skills than a reflection of a proliferation of inventive concepts. However once such claims are included in the patent and have passed scrutiny in the Patent Office, the onus is on the opponent to prove them invalid. Maintaining independent validity for subsidiary claims has, in substance, a similar effect to the patentee asserting that he has an equivalent number of separate inventions or patents. The party attacking validity has to direct his evidence to proving invalidity of all of them. The result is that the greater the number of subsidiary claims, the greater the volume of evidence, including experiments, which will be put before the court. Although the patentee cannot be prevented from asserting independent validity for numerous subsidiary claims, it must not be forgotten that the court has the power to penalise, at least in costs, a party who abuses the system in a way which inflates the duration and expense of litigation unreasonably.
Parametritis
One of the arguments advanced by Mr. Silverleaf was that Raychem’s patents were an exercise in what has become known amongst patent lawyers as parametritis. This is the practice of seeking to repatent the prior art by limiting claims by reference to a series of parameters which were not mentioned in the prior art. Sometimes it includes reference to parameters measured on test equipment which did not exist at the time of the prior art. The attraction of this to a patentee is that it may be impossible to prove now that the prior art inevitably exhibited the parameters and therefore it is impossible for an opponent to prove anticipation. Even if that is what has happened here, it does not alter the task of the court. It must decide whether the opponent has proved anticipation or some other statutory ground of invalidity. Parametritis may make the court’s task more difficult, but at the end of the day the test of invalidity must be the same, whatever the form of the claims.

There is another practice which can be used to obscure the patentee’s contribution, if any, to the art. This takes the form of drafting claims in an unnecessarily complicated way so that they are difficult to work through. Since the claims in a granted patent prima facie are valid and the onus is on the party attacking validity to make out his case, this obscurity may help the patentee. This practice has been deployed extensively in this case. Many of the primary claims in the patents have been drafted in a way which is calculated, in the legal sense, to make them difficult to understand. In some of them, simple known concepts have been dressed up in an elaborate clothing of quasi-science and complicated terminology. Unnecessary obscurity is not a separate ground for invalidating a claim. Within wide limits a patentee can use what language he likes to define his invention. But the court has to guard against being impressed by the form and language of the claims rather than the substance of the patentee’s alleged technical contribution. 

In all cases, and no matter what the nature of the attack on validity or arguments on infringement, the court must have in mind the first of the four steps set out in Windsurfing International Inc. v. Tabur Marine (Great Britain) [1985] RPC 59. It must identify the inventive concept embodied in the claims. In many cases the claim will state that concisely. That is what a properly drafted claim should do. The first step in Windsurfing does not require the court to substitute its own language for that of the patentee if the latter is clear. But where, as here, the claims are prolix and opaque it should break free of the language and concern itself with what the claims really mean. 
The attacks on validity
Bourns only relies on anticipation and obviousness. As far as anticipation is concerned, it was accepted by Mr. Silverleaf, at least by the time of his reply speech, that where the prior art does not actually describe something falling within the scope of the claims his client would need to prove that by following the teaching of the art one would inevitably produce something falling within the claims. With a view to proving inevitable result, certain experiments were conducted by Bourns and responded to by Raychem. Because it was only during the course of the trial that Raychem restricted its assertions of independent validity to 16 or so claims, inevitably most of these experiments were directed primarily at showing the invalidity of claims not now in issue.

Additionally, where the prior art describes a product or process falling within the claims, it will not anticipate unless the description is enabling. As the House of Lords said in Asahi Kasei Kogyo’s Application [1991] RPC 485, an invention cannot be said to have been made available to the public, and therefore invalid for anticipation, merely by a published statement of its existence, unless the method of working is so self-evident as to require no explanation to a man skilled in the art. Because Raychem said that certain pieces of the prior art were non-enabling, experiments were conducted in relation to this issue as well. Once again, reduction of the list of allegedly independent claims and the exclusion thereby of most of those claims against which a strong case of anticipation had been levelled, reduced the importance of this point.

During the trial there was also a dispute between the parties as to what constituted common general knowledge. Bourns argued that certain books, patents and trade catalogues and publications were common general knowledge so that the pleaded prior art could be read in the light of anything contained in them. This approach was illustrated by the following passage in the witness statement of Professor Runt, one of the Bourns’ witnesses:

“For the reasons I have explained in sections 1 and 2 above I consider that a person skilled in the art of PTC devices would have been aware of or had readily available the information in Cabot and the other documents to which I have referred and that it should be regarded as common general knowledge in 1978.”

This was developed by Mr. Silverleaf in the course of argument. He said that material was common general knowledge if it was contained in a document to which people in the industry had frequent reference. He relied on a statement given by Mr. Longhurst, another witness called by Bourns, in relation to a particular document:

"If you are a designer of electronic equipment and batteries, you would certainly refer to these frequently."

Based on this Mr. Silverleaf went on to say that such a document is common general knowledge because it is the kind of thing which is not only on the shelf but to which the man in the art looks. He knows what to look for and where to look. In relation to one document issued by a battery manufacturer as a technical explanation of the performance of its product, Mr. Silverleaf said that it is common general knowledge because it is a designers' guide. It is something which the man in the art is expected to pick up when he wants to use a battery. It is a booklet published by the battery manufacturer to tell you how to use its products. If one is designing equipment to be used with such products, the relevant technical booklet is the first port of call since its existence and that it contained the necessary technical information was well known. Mr. Silverleaf was prepared to go as far as to suggest that common general knowledge would include a reference to an obscure piece of foreign research referred to in a footnote of a reference book.

Mr Floyd said that Mr. Silverleaf’s approach encompassed material which was not common general knowledge. He drew my attention to the following passage in General Tire & Rubber Company v. Firestone Tyre & Rubber Company Limited [1972] RPC 457:

“As regards scientific papers generally, it was said by Luxmoore J. in British Acoustic Films (53 RPC 22, at 250): 
“In my judgment it is not sufficient to prove common general knowledge that a particular disclosure is made in an article, or series of articles, in a scientific journal, no matter how wide the circulation of that journal may be, in the absence of any evidence that the disclosure is accepted generally by those who are engaged in the art to which the disclosure relates. A piece of particular knowledge as disclosed in a scientific paper does not become common general knowledge merely because it is widely read, and still less because it is widely circulated. Such a piece of knowledge only becomes general knowledge when it is generally known and accepted without question by the bulk of those who are engaged in the particular art; in other words, when it becomes part of their common stock of knowledge relating to the art.”
And a little later, distinguishing between what had been written and what has been used, he said:
“It is certainly difficult to appreciate how the use of something which has in fact never been used in a particular art can ever be held to be common general knowledge in the art.”
Those passages have often been quoted, and there has not been cited to us any case in which they have been criticised. We accept them as correctly stating in general the law on this point, though reserving for further consideration whether the words “accepted without question” may not be putting the position rather high: for the purposes of this case we are disposed, without wishing to put forward any full definition, to substitute the words “generally regarded as a good basis for further action”.” 

In my view Mr. Silverleaf was casting the common general knowledge net too widely. It is not enough to say that a document is available to be referred to. Nor is it enough to show that it has been referred to frequently. That is inherent in the quotation from British Acoustic Films referred to above. On the other hand, as Mr. Floyd accepted, for something to qualify as common general knowledge it is not necessary to show that all or a majority of the workers in the field knew it, in the sense of having memorised it. For example in the days before the ready availability of pocket calculators, most technicians needed to use log tables for mathematical calculations. Few if any of them could memorise any of the log conversions in such a table yet those conversions would be common general knowledge in the patent sense. Mr. Floyd did not disagree with this. It seems to me that another passage in the General Tire sets out the rationale for treating data as common general knowledge:

“As regards patent specifications it is the somewhat artificial concept of patent law that each and every specification, of the last 50 years, however unlikely to be looked at and in whatever language written, is part of the relevant public knowledge if it is resting anywhere in the shelves of the Patent Office. On the other hand, common general knowledge is a different concept derived from a commonsense approach to the practical question of what would in fact be known to an appropriately skilled addressee - the sort of man, good at his job, that could be found in real life.”

This emphasises the difference between pleaded prior art and common general knowledge. The court is trying to determine in a common sense way how the average skilled but non-inventive technician would have reacted to the pleaded prior art if it had been put before him in his work place or laboratory. The common general knowledge is the technical background of the notional man in the art against which the prior art must be considered. This is not limited to material he has memorised and has at the front of his mind. It includes all that material in the field he is working in which he knows exists, which he would refer to as a matter of course if he cannot remember it and which he understands is generally regarded as sufficiently reliable to use as a foundation for further work or to help understand the pleaded prior art. This does not mean that everything on the shelf which is capable of being referred to without difficulty is common general knowledge nor does it mean that every word in a common text book is either. In the case of standard textbooks, it is likely that all or most of the main text will be common general knowledge. In many cases common general knowledge will include or be reflected in readily available trade literature which a man in the art would be expected to have at his elbow and regard as basic reliable information. In this case, for example, the general technical discussion of conductive polymers in the Cabot technical report was common general knowledge well before the priority date. So too would be the general teaching in the leading articles and textbooks on the subject. In particular, Professor Runt expressed the view;

“The possibility of making conductive components based on insulating rubbers and plastics has long been known.  Norman, to which I have referred above, is one of the standard works on this subject.  It contains extensive discussion of all the key issues arising in formulating and using such materials.”

Dr. Whitney also agreed that Norman was a standard work in this area of technology. I took him to accept that it was well known. 
Claims to known or obvious desiderata
Allied to Mr. Silverleaf’s objection that the claims in these patents were exercises in parametritis was his argument that most of them were also merely claims to known or obvious desiderata. When stripped of their linguistic camouflage they were claims to compositions or products with characteristics which a man in the art would realise would make them suitable for some known or obvious application. This rendered them invalid for obviousness. He said that the patentee had done nothing but select out of the wide range of PTC compositions and devices which could be made from known materials by known fabrication processes those which happened to have, at least for some commercial applications, obviously desirable properties. He said that this was all that the patentee had done was confirmed when the teachings of the patents were examined. He said that in many cases there was no general teaching which would enable the reader to make the range of products or devices with the specified properties. The patents merely set out known materials and fabrication processes which, if used in the known way, would give the worker compositions or products, some of which would and some of which would not fall within the claims. Raychem had selected out of the range of products or processes so made those which, from a commercial point of view, had attractive properties. Mr. Floyd said that this argument was inadmissible. In reality it was an attack of insufficiency not obviousness and it was only the latter which had been pleaded and which his client had come to court to answer. 

Mr. Silverleaf said that this criticism was misplaced. He drew my attention to a decision of the Technical Board of Appeal in AGREVO [1996] EPOR 171 and, in particular, to the following passage:

“... it has long been a generally accepted legal principle that the extent of the patent monopoly should correspond to and be justified by the technical contribution to the art (see T409/91, OJ EPO, No. 3.3 and 3.4 of the Reasons, and T435/91, OJ EPO 1995, 188, Reasons No. 2.2.1 and 2.2.2). Now, whereas in both the above decisions this general legal principle was applied in relation to the extent of the patent protection that was justified by reference to the requirements of Articles 83 and 84 EPC [i.e. sufficiency], the same legal principle also governs the decision that is required to be made under Article 56 EPC [i.e. obviousness], for everything falling within a valid claim has to be inventive. If this is not the case, the claim must be amended so as to exclude the obvious subject-matter in order to justify the monopoly.” 

I think this is helpful. I do not accept Mr. Floyd’s pleading point. What has to be determined is what technical contribution to the art has been made by the patentee. If that contribution is obvious then it is not protectable under patent law. If the patent claim consists of no more than a product or process selected by reference to a set of obviously desirable parameters, then the technical contribution is the selection of those parameters. Since that selection is obvious, so is the claim. It is permissible to look at the teaching in the specification to see what the patentee has put forward as his technical contribution. Where, as Mr. Silverleaf argues is the case here, the teaching indicates that nothing novel by way of materials or processing has been used, it reinforces the conclusion that the patentee has done no more than select the obviously useful products out of the range of those which can be made with existing technology. In such a case, the patent is just for any good product. On the other hand, where the invention involves the use of new materials or a new process, such as a new way of using known materials, to achieve a known or obvious goal, the inventive concept (per Windsurfing) or technical contribution (per AGREVO) is the materials or process. If the materials or process are not obvious, a claim of permissible width directed to or dependent on the materials or process is not obvious either. Although the claims will give protection to products or processes which meet obvious desiderata, it is the materials or methods for getting there which supports that protection. Here also, the teaching in the specification will be directed at the new materials or processes and will reinforce the conclusion that the claims are directed to a protectable technical contribution.
Witnesses
Before turning to the patents, it is convenient to deal with my assessment of the witnesses who appeared at the trial. Bourns relied on a number of Civil Evidence Act notices together with the evidence of Professor Runt and Messrs Forney, Lau and Longhurst. In fact only Professor Runt, Mr. Forney and Mr. Longhurst were called for cross-examination. Not much turned on the evidence of Mr. Forney and his credibility and reliability was not attacked.

Professor Runt is the Professor of Polymer Science at the Department of Materials Science and Engineering at the Pennsylvania State University. He has held this post since 1993.  He has studied and worked for nearly all his professional life at this University.  He took his first degree in Polymer Science in 1975. During 1974/5 he was taking a course called Polymer Science 409 in which the electrical properties of polymers were studied.  During that course, two of the most important pieces of prior art referred to in these proceedings, referred to as Meyer 1 and Kohler 1 were referred to. Since he graduated he has been a practising materials scientist. He has studied the properties of a wide variety of polymers and polymer composites and has undertaken studies of their electrical properties.  In particular, he has investigated the PTC effect and co-authored papers on this subject. His view was that he had a good working knowledge of the properties of polymer composites, including their electrical properties, in 1978.  At that time his work was on crystalline polymers, but not their electrical properties.  His interest in dielectric spectroscopy of polymers and PTC composites began a little later.  However, he felt able to assess the typical extent of the knowledge of someone ordinarily skilled in the field of polymer composites in 1978.  I did not understand there to be any significant attack from Raychem on his knowledge or his ability to put himself into the state of knowledge which existed in 1978. I found him to be a knowledgeable, careful witness who gave his evidence fairly.

Mr. Longhurst’s expertise is in the field of batteries. Having spent four years with Mullard Research Laboratories, he joined Duracell in 1968 and stayed with that company until his retirement in the autumn of last year. His evidence was directed solely at issues arising in relation to the Battery Patent. Like Professor Runt, he was a knowledgeable and fair witness.

Raychem served witness statements of Drs. Whitney, Cook, Meyer and Chiang. Bourns indicated that they wanted to cross-examine the first two of these. Dr. Whitney covered the same areas of technology as were dealt with by Professor Runt. Dr. Cook’s witness statement related to battery technology. On the morning of the penultimate day of the trial, Raychem withdrew his evidence with the result that the only oral evidence given on behalf of Raychem was that of Dr. Whitney.

Dr. Whitney is a chief scientist of Raychem. He received a degree in chemistry from Harvard University in 1955. He then attended the Massachusetts Institute of Technology (MIT) where he received MS (1962) and ScD (1964) degrees in Materials Science and Engineering. His professional career has been in industry, having held research and development positions at Monsanto Chemical Co., Celanese Research Co., Reprographic Materials Inc., and (since 1972) at Raychem. Within Raychem he has held various positions, both in research and development  and in technical management. He has been closely involved in Raychem's conductive polymer research and development program, especially in the years 1972-1983. He has directed conductive polymer research and development work and has worked closely with most the Raychem scientists and engineers involved in this work during those years. For at least part of the time, he led  and was close to the development effort in Raychem which resulted in the patents in suit. His closeness to Raychem and these patents was evident throughout his evidence. The abiding impression I received while watching and listening to him in the witness box was that he considered it his primary task to support his employer’s case. Balanced and fair answers to technical questions came second.  It was apparent on a number of occasions that he was reluctant to answer questions the response to which might benefit the petitioners. This has reduced the reliance I have felt able to put on his evidence.
The Compositions Patent (2,036,754)
This is concerned with PPTC materials and really represents the core invention of all four patents in suit. As mentioned above, well before the priority date, ceramic PTC devices had found commercial applications. The perceived disadvantages of these was their relatively high resistivities and their cost of fabrication. PTC devices which were cheaper to make and, at least for some applications, had lower operating resistivity might be commercially attractive. Well before the priority date a number of workers in the art, including in particular Meyer and Kohler, had shown that it was possible to get away from expensive ceramics and make good PTC compositions using polymers. 

In a standard electric switch, such as those used to turn on and off an electric light, when the switch is closed, it allows the passage of electricity with little resistance. When it is opened, the flow of electricity is effectively stopped by introducing an extremely high resistance (created by the air gap between the electrical contacts in the switch) into the circuit. In a PTC composition or device, resistance changes from a low figure to a high figure, not by mechanical means as in a domestic light switch, but as  a result of the effect of temperature. Before the priority date, PTC devices were regarded as switches. Obviously, for some applications a PTC device would be attractive if it exhibited particularly low resistance (i.e. it is made of a material exhibiting low resistivity) in one state and a particularly high resistance in another. Since in PTC materials it is a change in temperature which causes a change in resistivity, this temperature is referred to as the switching temperature. It is designated in the patent specification by the symbol Ts. 

Raychem eventually only sought to support the validity of claims 7, 9 and 11 as dependent on claims 1 or 4. This, effectively, meant that Raychem were relying on 6 independent claims. Although Raychem limited its assertion of independent validity in this way, in relation to this and the other patents it did not concede that the other claims, and in particular the claims on which the independently valid claims were dependent, were invalid or, if they were, invalid on any particular basis. It did not concede that those other claims were obvious. Therefore in considering the validity of the claims on which Raychem did rely, it is necessary to consider the status of all the features of those claims, including the parameters from other claims which have been incorporated by dependency.

It is convenient to start with claim 11. It is dependent on, inter alia, claims 1 or 4. It is necessary therefore to consider the latter claims first. 

Claim 1 is for:

“A conductive polymer composition which exhibits PTC behaviour with a switching temperature Ts above 0oC, characterised in that it has a resistivity of less than 7 ohm. cm at least one temperature between Ts and -40oC; and comprises
(1) a polymer component having at least 10% crystallinity and
(2) a particulate filler component which has been dispersed in said polymer component and which comprises carbon black having a particle size, D, which is from 20 to 150 millimicrons and a surface area, S, in m2/gram such that S/D is not more than 10.”

This covers a very wide range of PTC compositions. First, they must switch from low to high resistivity above freezing point. It was not suggested that there was anything unusual about that requirement. Many if not all PTC compositions, particularly those with commercial applications, had switching temperatures above freezing point. All of the PTC compositions disclosed in the pleaded prior art exhibited this feature. The patent contains no teaching as to how to determine in advance the Ts to be exhibited by any particular composition. Further as Professor Runt said, and is not disputed;

“As I explain below the materials as described in both Meyer 1 and Isogai meet all these requirements so that this discovery is not new. Even without that information, all polymeric PTC devices prepared with polymers that melt above 0°C have switching temperatures above 0°C and many carbon blacks meet the S/D ratio laid down in the patent.  All the carbon blacks discussed in Cabot do so.”

As far as this feature is concerned, the claim merely covers PTC compositions which operate in the known useful temperature range.

Secondly, the composition must have a low resistivity below its switching temperature. Although the claim says that this low resistivity must be at a temperature between Ts and -40oC, this covers, of course, room temperature. Again there is no teaching of how to select a particular temperature at which low resistivity is achieved. Once again in this respect the claim merely covers PTC compositions displaying useful resistivity at useful temperatures.

The reference in the claim to having a resistivity of less than 7 ohm.cm sets an upper limit on the resistivity when the composition is in its conductive state. It is not suggested in the patent, nor has it been shown, that there is anything special or significantly different about the compositions falling within this numerical range as compared with those falling just outside it. It appears to be nothing more than an arbitrary limit on resistivity. This view is consistent with the following passage in the specification: 

“The amount of carbon black in the composition should be such that the composition has a resistivity less than 7 ohm.cm, preferably less than 5 ohm.cm, especially less than 2 ohm.cm, particularly less than 1 ohm.cm ...”

All the materials and processing directions are known. Other than general directions to choose something which works, there is no teaching of how to make predictably anything falling within this limit. In fact, the examples set out in the patent include ones which fail to meet  this parameter (see, amongst others, examples 19, 20, 21, 27, 29, and 58). There is nothing which indicates why these examples fall outside the limit in the claim whereas other similar examples fall within. When reduced to essentials this merely limits the claim to PTC compositions of good low resistivity. There is nothing in the claim which a man in the art must use or include to achieve such low resistivity, nor is there any teaching in the specification other than to use known ingredients in the known way and to chose those products which happen to fall within the limit. 7 ohm.cm is arbitrary in the sense that it restricts the claim to compositions which are good for some commercial applications from others which may not be quite so good. It could just as well have been set at 5 ohm.cm or 10 ohm.cm.

Thirdly the polymer must have at least 10% crystallinity. As Professor Runt says, and was not disputed;

“HDPE is typically 60-70% crystalline and virtually all practical crystalline polymers exceed 10% crystallinity.”

This limit excludes virtually nothing. It is a parameter designed to cover all useable polymers.

Fourthly the claim stipulates the characteristics of the carbon black to be used. The limits chosen are very wide. As Professor Runt said in one of the passage quoted above, and is not disputed, many carbon blacks meet the S/D ratio laid down in the patent. All the carbon blacks referred to in the Cabot technical report do so. It can be seen that they all fall well within the 20 - 150 millimicron range. There is nothing in the patent to suggest that these parameters do anything more than cover a very large range of carbon blacks of the type which were known to work in PTC compositions and of the type which a man in the art would be likely to want to use. There is nothing in the evidence suggesting otherwise.

Against this claim Bourns advanced a case of anticipation based on documents referred to as Meyer 1 and Isogai, and obviousness. It is not necessary to determine that issue because Raychem eventually conceded invalidity. However the features of this claim are incorporated into subsequent claims on which Raychem continues to rely. Whether anticipated or not, this claim covers a wide range of compositions which a man skilled in the art would have realised at the priority date had, in some commercial applications, desirable properties. It is a claim for known desiderata.

Alternatively the patentee puts forward independent validity of claims 7, 9 and 11 as dependent on claim 4. This, in turn, is dependent on claim 3. These are in the following terms;

Claim 3:
“A composition according to claim 1 or 2 characterised in that the amount of said filler component is such that the quantity
		 x 
is less than 1”

Claim 4:
“A composition according to claim 3 characterised in that said quantity is less than 0.5”

Neither of these is now asserted to be valid. As Professor Runt explained, it was obvious that;

“... if one is seeking to achieve a  carbon black loaded polymer composite which has an initial low resistivity coupled with a strong PTC effect it is necessary to use a carbon black with a sufficiently small particle size and a sufficiently high structure and porosity to achieve low room temperature resistivity and to use a sufficiently low loading of carbon black to allow disruption of a sufficient proportion of the conductive pathways at the PTC switching temperature.  If either the carbon black is inherently too conductive or it is used at a loading which ensures that the adjacent particles will always be in close proximity, then there will be little or no PTC effect.”

He points out that that is what the S/D volume ratio in claims 3 and 4 is directed to. He goes on to explain that these ratios however do not ensure that the compositions made to them meet the electrical requirements of claim 1 and that compositions with ratios outside these limits may well meet the electrical requirement of claim 1. None of this is disputed. In view of the fact that the examples in the patent support what Professor Runt says on this issue, it would be difficult to do so.

These claims therefore add nothing but a parameter which is likely to be exhibited by many PTC compositions which are of value and many which are not. It will also exclude many PTC compositions which are of value and many which are not.  It is essentially arbitrary and has little technical significance. The selection of a group of compositions by reference to such a parameter does not involve any inventive step. Although it may not be obvious, in the common use of that word, to limit a claim by reference to this particular meaningless and arbitrary parameter, that has nothing to do with patentability. Patents are not given for skill in inventing technically meaningless parameters. Many PTC compositions having obviously desirable characteristics will happen to fall within the limits of these claims. As such they cover what is obvious and would be invalid for this reason.

Claim 11 provides:

“A composition according to any one of the preceding claims characterised by having a resistivity of less than 2 ohm.cm at least one temperature between Ts and -40oC.”

Like claim 1, it is not suggested either in the specification or the evidence that the compositions within this claim should be treated as a type of selection. The chosen limits select out of the wider group of compositions covered by claim 1 those which have lower resistivity below the switching temperature. Where a PTC composition is to be used for switching purposes, it was obvious that in many applications it should have as high a conductivity and therefore as low a resistivity as possible during operation below the switching temperature. Raychem accepted that in 1978, a stable, low resistivity PPTC device (i.e. one made of low resistivity PPTC material) for use in a circuit without excessive power wastage was an obviously desirable goal. This claim is directed to covering PTC compositions with obviously desirable electrical characteristics. Although the specification discloses a number of examples which produce compositions exhibiting the claim 11 properties, many examples do not. There is no general teaching of how to adjust the materials or fabrication conditions used so as to obtain compositions within claim 11 as opposed to those outside claim 11. The patentee has selected those compositions made with known materials and processing which happen to be commercially useful in some applications. The claim is to obvious desiderata only. It is, for that reason, obvious and therefore invalid. 

In the light of this finding, it is not necessary to consider Bourns’ additional argument that following the teaching of Isogai inevitably produces materials falling within claim 11, thereby rendering the claim bad for anticipation. 

To understand claim 7, which is said to be valid, it is useful to start with claim 5, which is not. The latter provides;
 
“A composition according to any one of the preceding claims, characterised in that, after having been subjected to a thermal ageing treatment which consists of maintaining the composition, by external heating thereof, for 25 hours at a temperatures at which the resistivity of the composition is between 100 ohm.cm and the peak resistivity, the composition (a) exhibits PTC behaviour, (b) has a resistivity at at least one temperature between Ts and -40oC which is between 0.5 times and 2 times the resistivity at the same temperature before said thermal ageing treatment, and (c) has a peak resistivity of at least 1000 ohm.cm.”

Essentially this claim is directed at compositions having good PTC characteristics which are stable to heat treatment so that, after such treatment they still display PTC characteristics which are similar, within fairly wide limits, to those exhibited before the treatment. Since the very point of PTC compositions is that their resistivity changes from one temperature to another, it is apparent that they will be used in environments where they will be subject to heat from time to time. As mentioned already, Raychem accepts that in 1978 it was known to be desirable to have stable PTC compositions. Page 9 of the Cabot Report touches on this subject in relation to conductive polymers in general. This, then is a claim to compositions which will be used in hot environments which exhibit relative heat stability.

Once again it is not suggested that there is anything in the nature of a selection invention in any of the parameters in the claim. It covers a fairly wide range of compositions which for some commercial applications are useful. There is no general teaching in the specification of how to achieve any particular level of heat stability. The patentee has simply selected from the range of PTC compositions made with known materials and processes those which have heat stability which will make them useful in some applications. Although until the beginning of the last day of the trial this claim was said to be valid, it is not now. 

Claim 7, which is said to be valid, is very similar to and is dependent on claim 5. It provides;

“A composition according to claim 5 characterised in that, after having been subjected to a voltage ageing treatment which consists of passing current through the composition for 25 hours so that I2R heating thereof maintains the composition at a temperature between Ts  and (Ts + 50)oC, the composition (a) exhibits PTC behaviour, (b) has a resistivity at at least one temperature between Ts and -40oC which is between 0.5 times and 2 times the resistivity at the same temperature before said voltage ageing treatment and (c) has a peak resistivity of at least 1000 ohm.cm.”

To understand this claim, it is necessary to have some more basic science in mind. When electricity passes through an electrical circuit or device, the energy used up in overcoming electrical resistance shows itself usually as heat. For a given electrical current, a low resistance circuit will consume less electrical energy and therefore will produce less heat than a high resistance circuit. This type of heat generation is called I2R heating. The amount of heat produced is proportional to the current (I) squared times the resistance (R). Hence I2R heating. Raising the current or the resistance or both will increase heat production. I2R heating is what is made use of in electric blankets, toasters and heaters. It is also used in simple wire-type electrical fuses which used to be common in the fuse box on the domestic electricity supply to a house or flat. If the current through the fuse rises, so will the heat it produces. If the current rises a lot, for example because there is a short circuit somewhere, the heat generated may be so large that the wire filament in the fuse glows red hot and burns or melts, thereby breaking the circuit.

In PTC compositions the resistivity will usually be orders of magnitude higher above the switching temperature than below it. If the compositon is subject to an electrical current it will therefore generate much more heat above its switching temperature than below it (unless, of course, the effect of the increase in resistance is cancelled out by any drop in current in the circuit).  This is an inherent and inevitable characteristic of all PTC compositions. A device made from PTC composition used in a circuit which makes use of its PTC characteristics will generate heat when it is in its high resistivity state if a current flows through it. As Professor Runt said, it is self evident that for a PTC device to have any practical application it must retain its electrical properties when used. This is also confirmed by one of the pieces of pleaded prior art, referred to as Meyer 1I. In a paragraph headed “PTC Stability”, Dr. Meyer wrote;

“One fact of great importance in any application of composite PTC materials is their stability under operating conditions. Most PTC applications to date involve either the constant cycling of the device through the anomaly point or the holding of the device close to the anomaly temperature [i.e. Ts ]. Thus we are concerned with the stability of the PTC phenomenon both during long term cycling and long term heating.”

The advantage of having temperature stability was well known at the priority date. In the light of this material it will be appreciated that claim 7 is directed to compositions which remain relatively stable (to the same extent as in claim 5) when subject to a particular ageing regime at elevated temperature, that temperature being caused, at least in part, by the passage of electricity through the composition. It is not suggested either in the specification or in the evidence that this ageing regime distinguishes particularly effective PTC compositions from those which are not. It simply sets out a set of ageing characteristics which may be met by PTC compositions, including some of commercial interest. This claim does no more than seek to monopolise a wide group of PTC compositions which happen to have  convenient voltage ageing properties. The particular ageing regime selected, such as treating for 25 hours as opposed to, say, 15 or 30 hours and maintaining the temperature at between Ts and (Ts + 50)oC as opposed to, say, between Ts and (Ts + 40)oC or (Ts + 60)oC, is essentially arbitrary. Furthermore the specification gives no general teaching which would enable a man in the art to make PTC compositions which predictably meat the ageing parameters of the claim. The patentee has done no more than seek to monopolise a group of PTC compositions displaying obviously useful characteristics. The alleged inventive concept of this claim is the idea of having compositions which age well. It is a claim to an obvious desideratum. 

Finally, claim 9 provides;

 “A composition according to any one of the preceding claims characterised in that said polymeric component has at least 40% crystallinity and comprises at least one polymer selected from polyolefins, copolymers of at least one olefin and at least one polar comonomer, polyarylenes, polyesters, polyamides, polycarbonates and fluorine-containing polymers, and said carbon black has a particle size of 20 to 75 millimicrons.”

Nothing turns on the degree of crystallinity or the range of polymers covered. They encompass the majority of the standard polymers which would be used for PPTC manufacture at the priority date. The feature relied on to distinguish the claim from the prior art is the restriction to the use of carbon black having a particle size of 20 to 75 millimicrons. Bourns have not shown that any piece of prior art actually describes a PPTC composition meeting all the parameters of this claim and the claims it is dependent on which employs a carbon black within this particular range. 

Professor Runt explains the need for small particles in PTC compositions as follows;

“Chapter 4 of Norman is devoted to the nature of carbon black.  It examines the varying properties of carbon blacks made in different ways.  It explains that both the structure and the particle size of the carbon black are important in determining the conductivity of composites.  In particular it can be seen that the resistivity of a particular carbon black decreases with increasing surface area.  It notes that the diameters of carbon black particles used to make rubbers conductive lie in the range 10-300 millimicrons.  Smuckler and Finnerty confirm this.  They explain that an increase in the structure and porosity increases the conductivity of the carbon black.” 
and
“As noted above, Cabot explains in outline the relationship between the nature of the carbon black and the conductivity of polymer loaded with it.  This is also discussed on pages 172-4 of Smuckler and Finnerty.  This relationship can be used to predict which carbon blacks will have the highest conductivity at particular loadings in a particular polymer.  It can be seen from these materials that the greater the structure and porosity of the carbon black, the higher its conductivity.  Equally, the smaller the particle size the greater the conductivity.  Thus, to have a highly conductive carbon black one is looking for small particle size coupled with high structure and porosity.”

None of this was disputed. Again it was not suggested that this claim could be viewed as covering some sort of selection invention. It covers part of the wider range of particle sizes referred to in claim 1. Raychem does not claim to have invented carbon blacks exhibiting these smaller particle sizes. It is not suggested that they were anything other than available to those in the art at the priority date. That art shows that PPTC compositions using carbon black within the size limits of claim 1 of this patent but outside the precise limits of claim 9 had been proposed and produced very good results.  None of it teaches away from trying even smaller carbon black particles. In the light of Professor Runt’s evidence, I have come to the conclusion that it would have been obvious at the priority date to try using carbon black particles within the limits set by claim 9 with the expectation that some such compositions would exhibit useful PTC characteristics, including low resistivity below the transition temperature. This claim also is obvious.
The Circuit Protection Patent (No. 2,038,550)
This is a patent in which the claims are of great complexity. It is concerned with what are known as circuit protection devices. As the patent acknowledges, the use of PTC devices in such circuits had been proposed before the priority date. That this concept was known is also admitted in Raychem’s Answer.

There are really two types of circuit protection of relevance to the issues here. In one, the circuit is sensitive to an unacceptable increase in current, caused for example by a short circuit, and is closed down. The simplest form of this sort of circuit protection is the wire fuse referred to earlier in this judgment. When the current is too high the fuse introduces a very high resistance into the circuit (represented by the air-gap created by the burning or melting of the fuse wire) to stop current flow. The second consists of circuits designed to protect an electrical apparatus from overheating. If a heat sensitive switch is introduced into the electric supply  to the apparatus, it can be tripped by passing its switching temperature to reduce  or stop current flow. During normal operation, i.e. when not faced with high current or temperature, both types of device should add very little resistance to the circuit being protected. The majority of the energy in the electric current should be used in operating the rest of the circuit. 

One of the basic texts in this field is US Patent No. 3,243,753, referred to as Kohler 1. When Professor Runt was an undergraduate in the mid 1970’s it was one of the documents referred to and discussed in the part of his course concerned with the electrical properties of polymers. It describes PPTC devices and how they can be used in overload protection circuits, that is to say as fuses. It also recommends their use in overheat protection circuits. The use of ceramic PTC devices for both types of circuit protection is also described in a piece of prior art described as Saburi. With that background, I can turn to the claims of the patent in suit. The first to be asserted as having independent validity is claim 3. However this is dependent on and incorporates claim 1 and therefore the latter must be considered first. For ease of comprehension, I have set it out below split into sections.

Claim 1:

A:		An electrical circuit which comprises 
(1) a source of electrical power;
(2) a circuit protection device comprising at least two electrodes and a PTC element composed of a PTC composition having a switching temperature Ts; and
(3) other circuit elements which are connected in series with said PTC element and which have an impedance Rl ohms;	

B:		said electrical circuit having a normal operating condition in which 
(A) a current in flows through said PTC element over an area of equivalent diameter d with an average path length t such that d/t is at least 2;	

C:		(B) said device is at a temperature Tdn at which the device has a resistance Rdn  which is
	(a) less than 1 ohm; and
	(b) less than 0.5 x Rl  ohm,
and at which said PTC composition has a resistivity of less than 10 ohm. cm.;	

D:		(C) said device is in contact with a medium which is at a temperature Tn and  
(D) there is a stable equilibrium between the rate at which the device generates heat by I2R heating and the rate at which heat is lost from the device;	

E:		and said device having an electrical power/temperature relationship and being capable of losing heat to said medium at a rate such that
(a)	if (i) said medium is heated slowly from Tn while maintaining Rl  and the voltage of the source of electrical power substantially constant, or (ii) elements of the circuit are changed so that the current flowing through said device increases slowly from in while maintaining Tn substantially constant, then the temperature of the device increases slowly until a critical operating condition is reached in which the equilibrium between the rate at which the device generates heat by I2R  heating and the rate at which heat is lost from the device is unstable, and the device is at a temperature Td trip and has a resistance Rd trip , the rate at which the resistance of the device changes with temperature,
dRd trip
_____
dTd trip
 
is positive, and either (i) the medium is at a temperature Tcrit or (ii) the current is at a value icrit ; and
(b) if either (i) said medium is then heated just above Tcrit while maintaining Rl  and the voltage of the source of electrical power substantially constant or (ii) elements of the circuit are further changed so that the current flowing through the device increases to 2 X icrit  while maintaining Tn  substantially constant, then the rate at which the device generates heat by I2R  heating exceeds the rate at which heat can be lost from the device and thus causes the temperature and the resistance of the device to rise rapidly and the circuit current to fall	

F:		until a high temperature stable operating condition is reached in which the rate at which the device generates heat by I2R heating is equal to the rate at which heat is lost from the device; and the device is at a temperature Td latch and has a resistance Rd latch which is such that the ratio of the power in the circuit in the normal operating condition to the power in the circuit in the high temperature stable operating condition, the Switching Ratio, is at least 8.	

The effect of all of this is as follows. The PTC device, which is short and flat (B), is fitted in series in the circuit (A). It is made of a PTC material which, at the normal operating temperatures, exhibits low resistivity and the resistance of the device at that temperature is lower than the resistance of the rest of the circuit (C), i.e. at that temperature most of the electrical power is consumed by the other components in the circuit. Also at that temperature the device is stable, i.e. it loses as much heat to the surrounding environment as it generates (D). If the temperature of the environment rises or the current through the circuit rises a point is reached at which the amount of heat lost from the device is not as great as the heat generated internally so that the device heats up and it reaches a point where its resistance rises rapidly (because it is made of PTC material), thereby causing the current in the circuit to fall (E). The circuit finds a new high temperature equilibrium point at which the power in the circuit is much less than it was in normal operation (F).

The numerical limits set in this claim are very wide. For example the resistance of the device during normal operation can be up to half the resistance of the other components in the circuit; “said device ... has a resistance ... which is ... less than 0.5 x Rl ohm”. In other words it includes, for example, cases in which in normal operation, almost one third of the power in the circuit is consumed by the PTC fuse. This is far less demanding than might be expected of a normal fuse. This is consistent with the teaching in the specification:

“... Rdn is less that 0.5 x Rl ohm ... Rdn is preferably less than 0.1 x Rl ohm, particularly less than 0.04 x Rl, especially less than 0.001 x Rl. ”

It will be appreciated that with these numerical limits, claim 1 covers a very wide range of circuit protection devices.

There is one point of construction on this claim on which the parties differed and in relation to which there was a considerable amount of cross-examination.. The issue is as to what the claim means when it refers to a “high temperature stable operating condition” being reached. To understand this point it is necessary to distinguish between equilibrium conditions and a phenomenon called “latching”. 

When the input into a system is matched by the output from it, the system can be said to be in equilibrium. If a one bar electric heater is turned on in a room, the room will reach an equilibrium temperature when the rate at which heat supplied to it by the heater is matched by the rate at which heat is lost from it, e.g. by draughts and conduction through the wall. If the ability of the room to lose heat is reduced, for example by double glazing the windows, a new equilibrium temperature will be reached. In this example the rate at which heat is added to the room from the heater is the same, but the room has to be hotter before the rate of heat loss matches it. If the system is changed, whether by altering the insulation of the room or by altering the rate at which heat is added to it, a new equilibrium is established at which input = output. A temperature equilibrium will also be achieved by a component in an electrical circuit. As the current passes through the component it will generate heat by I2R heating. The component will reach a temperature which is determined by the amount of heat generated by I2R heating and the rate at which the heat can escape to the environment. This latter rate is affected by the difference between the temperature of the component and the environment round it - the larger the difference the greater the rate of heat loss. If everything stays the same but the device is insulated, a new equilibrium will be achieved at a higher temperature. On the other hand if everything stays the same except that the current (I) or resistance (R) is increased, the heat generated in the component will rise and the equilibrium temperature achieved will go up unless there is a compensating increase in the rate at which heat is lost from it. This concept applies to all components in an electrical circuit. It applies to PTC devices. During normal operation, the resistance in the device is low so the heat generated by I2R heating is low. Absent insulation, the temperature of the device will not rise a lot. When the device passes its switching temperature its resistivity shoots up. Once again the temperature of the device will be determined by the amount of heat generated in it by I2R heating at its new higher resistance and the amount of heat it loses to the environment. At some point these two will match and the device will be at a new, high temperature equilibrium. While nothing changes, the equilibrium temperature will be maintained. The system is in balance.

There is another known concept, called “latching”, which is referred to in the patent. It can be explained as follows. When a system reaches an equilibrium, it may tend to stick in that position. This type of behaviour is exhibited, for example, in domestic room thermostats. A thermostat may be set to operate at, say, 19oC. When the room temperature reaches that figure, the thermostat switches and turns the room heating off. However as the temperature falls the thermostat does not switch on again immediately it passes through 19oC. It may not do so until the room temperature reaches, say, 18oC. Effectively it sticks in the off position. This type of behaviour can be, but is not always, exhibited by PTC devices. Once a PTC device has gone past its switching temperature and reaches a new high temperature equilibrium, because of the interrelationship between the characteristics of the PTC device and its environment, a drop in temperature of the environment will not always result in the resistivity of the device falling as quickly as it rose. It may latch and, if it does, it will stay at its high temperature level for longer than might otherwise be expected. This in turn will mean that it stays at its high resistance level for longer than might otherwise be expected. The extent of this latching will depend on the characteristics of the PTC device and of the environment in which it is used. It may be only a minor effect or it may be significant.

According to Raychem, when the claim refers to a high temperature stable operating condition it is referring to this type of sticking or latching. On the other hand, Mr. Silverleaf argued that this is not what the claim means at all. Whatever Raychem may have meant to say, the claim only requires that the device reaches a new high temperature equilibrium. It is not concerned with whether the circuit sticks in that state. 

Although he was tendered as an expert witness, Dr. Whitney put forward Raychem’s view of the meaning of the claim. Since his explanation is particularly clear, it is convenient to explain the point by reference to what he said. Dr. Whitney was cross-examined about the disclosure in Kohler 1. Mr. Silverleaf suggested that Kohler described a device which exhibited a “high temperature stable operating condition” as required by the claim. A passage in the transcript of this cross-examination illustrates the nature of the difference between the parties on the issue of latching;

Q.  ...  Pick [Kohler] up at line 34, column 6: "Thus, while normal current flow would not cause heating to the temperature above which there is a rapid increase in resistivity, the increase in current due to the short circuiting gives a sudden increase in heat generation and greatly increase the resistivity of the fuse to such a high value that the present composition itself will thus become the current limiting device, thereby limiting the final equilibrium current to a final fraction of its initial safe value."  Is that not latching?      
A.  Not in my definition. 
Q.  What is the difference between that and latching?       
A.  Latching, to me, means a device or a circuit which goes to its temperature, high resistance state, and then stays there when the conditions are changed. 
Q.  That is a high temperature equilibrium.       
A.  It is a high temperature equilibrium, but it is also latched there.  It cannot return to its previous state and, therefore, it is latched in that high temperature.  There is nothing here that says that this has latched.       
Q.  Let us read slightly higher in the column.  Pick it up at line 20:  "During the course of normal use the temperature of the overall circuit may rise to, for example, 200 degrees F. However, the resistance of the PTC device will only increase to about 0.10 ohm.  Heat dissipation in the composition will be about 0.1 watt.  However, when the load element is short circuited, there is initially a very substantial increase in  current passing through the circuit and due to the I2R  voltage factor the fuse of the present invention is heated to a temperature within the critical range  this causes the resistance of the fuse element to increase to the order of  1,000 ohms at 300 degrees or 50,000 ohms or greater at 350 degrees.  Thus a new equilibrium point is reached where heat dissipation due to I2R equals thermal losses." There is an equilibrium condition in which the I2R  heating is at the same rate as the thermal losses.  That is a high temperature latched state, is it not?   
A.  It is a high temperature, but it is not latched.       
Q.  Can you explain, so that his Lordship can understand, the difference between that state and that state described as latched in the 550 patent? 
A.  The difference, as I understand it, is that in this example and Kohler, the PTC device is in a circuit.  It is presumed that, originally, there is a load resistance.  Then it is short-circuited.  Short-circuited means that there is essentially no resistance in the circuit.  It is just the power source, which is 100 volts, 120 volts, and the PTC device.  It will heat itself up to some equilibrium point. However, if that current is then reduced, it will come back down and will return down the RT curve.  It is not latched in that position at that state.

He also said;

“I will admit that Kohler says his device is at a high temperature equilibrium state, but I do not agree that it is latched.”

I think that Dr. Whitney was accurate when he described what an equilibrium was; 

“An equilibrium is one where the power generated  in the device equals the power dissipated by the device.”

I shall refer to this as the “Whitney definition of equilibrium”. 

As Mr. Longhurst said, latching was known in the art. I accept Dr. Whitney’s explanation of what it means, as exemplified in the passage set out above. It is also explained in the following passage from his cross-examination;

“[Equilibrium]  can be achieved at a lot of points with these curves and load  lines.  Latching is what I believe the patent calls a stable equilibrium.  It means it is going to stay more or less in that position.  It means that the device in that circuit is going to switch from one state, which is more or less stable, to another state, which is more or less stable, and then stay there even if some of the other parameters are changed.  It does stay in that high temperature, stable equilibrium state.”

Dr. Whitney’s view, which was Raychem’s view and was supported by Mr. Floyd, was that the claim required latching in this sense. Mr. Silverleaf says that the claim is not limited to PTC devices which latch. It covers any device which reaches a high temperature equilibrium. All PTC devices are capable of doing that and Kohler expressly describes his compositions as doing so. In my view, Mr. Silverleaf’s construction is correct. The words used in claim 1 are:

“... thus causes the temperature and the resistance of the device to rise rapidly and the circuit current to fall until a high temperature stable operating condition is reached in which the rate at which the device generates heat by I2R heating is equal to the rate at which heat is lost from the device ... ” (my emphasis)

When the resistance of the PTC device rises, this causes it to generate more heat internally. A new higher temperature point will be reached at which the heat loss from the device equals the heat generated by it. The words used in the claims say nothing about how quickly or slowly the resistance of the device will fall as its temperature falls (e.g. by a fall in the temperature of the surrounding environment). It is concerned only with the equilibrium position. The words in the claim which have been italicised above are, in effect, the same as Dr. Whitney’s definition of equilibrium. When the claim refers to a “high temperature stable operating condition” it makes clear, in the words which I have italicised above, that what it is talking about is an equilibrium temperature. Dr. Whitney gave the following evidence which, once again, accurately reflected Raychem’s argument as to the meaning of the claim;

Q. ... You are saying that something which reaches a high temperature, stable operating condition, whether it is a short circuit, but which returns to its normal condition when the short circuit is removed, is outside of the claims of this patent.      
A.  Yes, I do.

However the claim only requires that the device reaches a high temperature, stable operating condition. There is no legitimate basis upon which to construe it so as to exclude such devices which behave in a particular manner after the short circuit is removed.

Although it is true that the body of the specification describes circumstances where the PTC device can be made to latch, I can see no reason why claim 1 should be read as if it was limited to circuits where such latching is employed. In this regard, it should be borne in mind that a PTC device will work effectively in a protection circuit even if it does not latch. The only difference being whether, on a reduction of the temperature in the surrounding environment or the current through the circuit, the device switches quickly or slowly from high to low resistivity. This claim has been drafted elaborately and with apparent care. It is reasonable to assume that the claim would have been limited to that expressly, had that been the inventor’s intention. There is nothing in it or in the body of the specification which suggest that the inventor intended to exclude from protection those circuit protection devices which worked perfectly well but do not latch.

Furthermore, even if Raychem’s construction had been correct, Mr. Longhurst’s evidence was not only that latching was well known, it was also known specifically in relation to ceramic PTC devices. His evidence was that whether a component latched or not in the particular situation was a normal consideration to be taken into account by a circuit designer.

Notwithstanding the complexity of the language used, this claim covers little more than a circuit containing a short flat PTC device which at normal operating temperatures is highly conductive but which responds to increased temperature (either caused by an increase in the temperature of its environment or by internal heating as a result of increased current flows, for example due to a short circuit) to switch to a high resistance state so as to cut down the current in the circuit. 

As Professor Runt explained, and was not disputed, a man in the art would expect to use a short flat PTC device. That shape ensures a short current path, and therefore low resistance at normal operating temperatures, and rapid heat transfer. The achievement of a high resistance, high temperature equilibrium point is inevitable when the temperature of the environment or the current through the device rises. It is what happens when the PTC device switches. That higher temperature equilibrium point will be maintained until the temperature of the environment or the current through the circuit changes. It was not suggested that any of the numerical limits in the claim were of particular significance. They clearly encompass all or the overwhelming majority of useful protection circuits. 

Although Raychem does not now assert independent validity of claim 1, it does for claim 3 which it described as the claim of primary importance. Claim 3 is dependent on claim 2, so both of them should be considered. They are in the following terms;

Claim 2:
“A circuit according to claim 1 wherein said PTC element is composed of a conductive polymer.”

Claim 3:
“A circuit according to claim 2 wherein said conductive polymer has been obtained by a process which comprises dispersing a conductive carbon black in a polymer.”

The advantage of claim 3 to Raychem is that it avoids anticipation by the prior art. Kohler 2 does not disclose a thin device, Meyer and Isogai do not disclose  circuit protection devices as such or devices in a circuit. Saburi is a ceramic device not a PPTC. Kohler 1 is avoided because his devices are made from PTC compositions where the carbon black is distributed throughout the monomer from which the polymer is subsequently made. Thus, it is said, the PTC material is not “obtained by a process which comprises dispersing a conductive carbon black in the polymer”.

Although Kohler 1 teaches as its preferred embodiments the in situ polymerisation of the polymer round the carbon black, most of the prior art PPTC compositions consist of carbon black dispersed in prior-made polymer. The claim covers nothing more than a PTC device in an obvious shape made of good PTC material and employed in a circuit which performs to protect against overheating or overloading in an obviously desirable manner. It too fails for obviousness.  Mr. Floyd accepted that claims 3 and 23 should be treated together. claim 23 is also bad for obviousness. 

The only other claims said to have independent validity are 28 and 34 which are as follows;

Claim 28:
“A device according to any one of claims 21 to 27 wherein said source of power has a voltage of 100 volts and Rdn  is at most 0.01 times the resistance of said resistor.”

Claim 34:
“A device according to any one of claims 21 to 33 which, after said circuit has been subjected to an ageing treatment which consists of operating the circuit for 10 hours in said high temperature stable operating condition, switching the current off, and causing the device and the medium to cool to 0oC , has an electrical power/temperature relationship such that the circuit has normal, critical and high temperature stable operating conditions as defined, and, when the aged circuit has been brought to the critical operating condition solely by increasing the temperature of the medium, the medium has a temperature Tcrit/10  which is between 5 and 35oC .”

The reference in claim 28 to Rdn being no more than 0.01 times the resistance of the resistor means nothing more than that, in normal use, the PTC device has a very low resistance compared with the total resistance of the other components in the circuit. As explained above, this is how fuses normally work and is clearly an obvious requirement of such a device. The figure of 0.01 is quite arbitrary. Similarly the requirement that the source of power is at 100 volts is arbitrary. This claim adds nothing of technical or inventive significance to the claims it is dependent on and it too fails for obviousness.

Claim 34, as Mr. Floyd agreed, is directed at PTC devices which are stable after a burn in period. The precise numerical limits of the claim are arbitrary. The inventive concept, if any, is making a device which is stable. For much the same reasons as applied to claim 7 of the Composition Patent, this too is a claim for mere obvious desiderata. It too is invalid. 
The Oxygen Barrier Patent (No. 2,038,549)
Raychem eventually only asserted independent validity for one claim, no. 5. This, and the other claims it is dependent on are as follows;

Claim 1:
“An electrical device which comprises
(1) a PTC element which is composed of a composition which exhibits PTC behaviour with a switch temperature Ts and which comprises a macromolecular polymer and conductive particles dispersed therein; and
(2) at least two electrodes which can be connected to a source of electrical power and which, when so connected, cause current to flow through said PTC element;
(3) an oxygen barrier which, when the device is in air at standard temperature and pressure, restricts access of air to the PTC element so that the rate at which the PTC element absorbs oxygen is less than 10-6 cc/sec/gram.”

Claim 3:
“A device according to claim 1 or 2 characterised in that it exhibits a change in resistance, at at least one temperature between (Ts -110)oC and Ts, of -50% to +200%, after having been subjected to an ageing treatment which comprises passing current through the device for 250 hours, the current being such that I2R heating of the device maintains said PTC element at a temperature between Ts and (Ts + 50)oC ”

Claim 5:
“A device according to claim 3 or 4 characterised in that it exhibits a change in resistance, at at least one temperature between Ts - 110)oC  and Ts of -50% to + 200%, after having been subjected to an ageing treatment which comprises passing current through the device for 250 hours, the current being such that I2R  heating of  the device maintains said PTC element at a temperature between Ts and (Ts + 50)oC ”

Raychem came down to claim 5 because Bourns were unable to prove anticipation of it. Having avoided anticipation, Raychem said that this claim was not obvious either. Once again it is necessary to identify the allegedly inventive concept involved. Neither party suggested that anything turned on the arbitrary numerical parameters in claims 3 or 5 or the ageing criteria in claim 5. The inventive concept, if there is one, consists of the idea of using an oxygen barrier to protect the PTC device from the adverse effects of oxygen.

That PPTC compositions are adversely affected by oxygen was established by Dr. Meyer. The document referred to as Meyer 1I deals with this subject extensively. Professor Runt’s evidence was;

“It has been very well known since before the 1950s that polyolefins are susceptible to oxidation.  Chain scission may occur and oxygen is incorporated into the chemical structure.  Ultimately the material loses mechanical integrity.  It has therefore been the practice for a long time to incorporate anti-oxidants in such materials in commercial use to inhibit this.  It clearly follows that the PTC properties of a polyolefin such as polyethylene, loaded with carbon black will deteriorate as the polymer oxidises.  To avoid this one must incorporate a sufficient amount of antioxidant and/or encapsulate the polymer.”
and
“The invention is very simple.  As acknowledged in the specification it is well known that PTC materials degrade in use through oxidation.  The invention is to inhibit this by coating the device with an oxygen impermeable barrier.  This is intrinsically obvious.  It describes a self-evident method for countering a well-known problem.  Furthermore, any practical device has to be encapsulated so that the reference to the reduction in oxygen permeation resulting from this is little more than an ancillary benefit of doing this.  Electrical components such as resistors, capacitors, transistors and the like were all encapsulated in a variety of materials long before the priority date of this patent.”

Kohler 2 also describes encapsulation of PTC devices. Professor Runt explained;

“Encapsulation of PTC devices was not new at the priority date of this patent.  Kohler 2 describes typical encapsulants at column 4 line 73 to column 5 line 6.  These include epoxy resins which are specifically referenced as suitable in the patent at page 2 line 12.  These are generally stiff polymer glasses which have very low oxygen permeability.  His reasons for encapsulation include protecting the device from deterioration effects from exposure to the atmosphere.  These are primarily the effects of oxidation so that Kohler is encapsulating for precisely the purpose described and claimed in the patent.  Kohler is, accordingly, a complete disclosure of the invention that is the subject of claim 1.”

None of this evidence was effectively challenged. Dr. Whitney gave evidence on this issue under cross examination. His response to simple direct questions illustrated his partiality. Some flavour of this can be detected in the transcript which starts at page 294. Watching him in the witness box it was apparent that he was trying hard to tailor his answers so as not to inflict damage on his employer’s case. Even he, in the end, seemed to accept that encapsulation would be something which a man in the art would try;

“Q.  So it is clear from Meyer 2 that you need, for a practical polymer PTC device, to ensure that it does not oxidize in use.  That is correct, is it not? 
A.  Again, if I can equivocate and say that you cannot prevent it. You can minimise the oxidization.
Q.  You can reduce it to the minimum possible.
A.  Given the device in the circumstance and the application involved, yes.
Q.  There are really only two things you can do to achieve that objective: the first is to put anti-oxidant into the material and the second is to encapsulate it in a oxygen impermeable, or as near impermeable as possible, barrier.  Yes?
A.  Again, given a particular polymer in a given structure, those are two of the methods you might use.  However, polymer stability varies from polymer to polymer.  There might be other stabilizers that you can use for the formulation. We have been through all this.  Any oxidants and good encapsulants are two of the methods, but not the only ones. 
Q.  Not the only methods, but anti-oxidants and encapsulation are two extremely obvious things to do.
A.  They are well known.
Q.  And therefore extremely obvious.
A.  They are approaches that one would use.”

I accept Mr. Silverleaf’s submission that this patent is intrinsically obvious given the facts that encapsulation with epoxy resin and metals and the usefulness of protecting PTC devices from oxidative degradation were known. 
The Battery Protection Patent (No. 2,042,789)
This patent is concerned with protecting batteries against problems which might be caused by excessive current output, as when they are short circuited, and excessive current input, which can occur during the charging of rechargeable batteries. Originally Raychem asserted independent validity for numerous claims. At the trial it came down to asserting validity in only claims 1 and 2. As mentioned above, on the final day of the trial, Raychem abandoned claim 1 of this patent. That only left claim 2 for consideration as independently valid. However because it is dependent on, and therefore incorporates all the features of, claim 1 and because Raychem did not accept that claim 1 itself was obvious, both claims need to be considered. However, before doing so it is useful to have in mind some basic battery technology which would have been well known to a man in the art at the priority date. 

A battery which is of the use-once variety is called a primary cell. A rechargeable battery is called a secondary cell. When any battery is short circuited, the current it delivers will rise very significantly. This has at least two effects. First, the electricity generating capacity of the battery will be depleted rapidly. It will soon go “flat”. Secondly the increased current flowing through it will mean that much greater heat will be generated by I2R heating inside the battery. The battery will get warmer. Depending on the thermal characteristics of the battery and its packaging, the size of the current flowing and the internal resistance of the battery, the heat generated may exceed the ability of the battery and its packaging to lose heat. The battery will then get hotter until it reaches a point at which heat generation and loss are again in balance.  In most applications there is no commercial need to protect against these adverse effects of unwanted short circuiting. As Mr. Longhurst pointed out, even today an ordinary “AA” primary cell does not contain a short circuit protection component. 

In the case of secondary cells, the overall behaviour of the cell changes as it approaches its fully recharged state. At that point the charging current causes the production of highly reactive molecules inside the cell such as oxygen. These molecules react with other components in the cell and give out heat. If the rate of charging is kept low, the reactive oxygen may be able to diffuse out of the cell without too much of it reacting and in any event a low rate of charging means that the temperature of the cell will not rise a lot. However if an attempt is made to quick charge the cell by applying a high charging current to it, as the cell nears its fully charged state, it will generate ever larger amounts of oxygen and heat. It will rapidly overheat and may burst. Therefore, for many applications secondary cell charging is carried out over an extended period, for example over night. If a rapid charge is required, what is needed is a charging circuit which will either cut out completely once sufficient charging has been achieved and before the temperature rise becomes too damaging to the fabric of the cell, or will step down to a lower “trickle-charge” to complete the topping up of the cell. 

Against that general background, I can turn to claims 1 and 2 which are as follows;

Claim 1:
“A battery comprising one or more cells and at least one PTC electrical device which is in thermal contact with at least one cell of said battery, wherein said PTC electrical device
	(i) is connected in series with the cell or cells of the battery so that when the battery is being charged and/or discharged, current flows through a PTC element which forms part of the device; and
	(ii) has an electrical power/temperature relationship and is capable is dissipating heat at a rate such that it has a low resistance when the cell or cells are at normal operating temperatures and relatively high resistance when the cell or cells are at excessively high temperatures.”

Claim 2:
“A battery according to claim 1 wherein the cell or cells are secondary cells, and the PTC electrical device (i) is connected in series with the cell or cells when the battery is being charged and (ii) has an electrical power/temperature relationship and is capable of dissipating heat at a rate such that, if the battery, after having been discharged, is recharged in a charging circuit which is initially in a rapid-charging condition in which (a) a rapid-charging current, Ir, is passed through the cell or cells and (b) the device has a low resistance and a low temperature such that there is a stable equilibrium between the rate at which heat is lost from the device , then after the cell or cells have reached a certain state of charge and the cell or cells and the device have reached elevated temperatures, the rate at which the device generates heat by I2R heating exceeds the rate at which heat is dissipated from the device and thus causes the temperature and the resistance of the device to rise rapidly, and in consequence the charging circuit thereafter reaches a trickle charging  condition in which (a) there is a relatively low trickle-charging current, It, through the cell or cells  and (b) there is a stable equilibrium between the rate at which the device generates heat by I2R heating and the rate at which heat is dissipated from the device.”

Claim 1 covers a battery in which a PTC switch is connected in series with the cell. It switches from its low resistance to high resistance state when the switching temperature is passed. It does not require that this switching temperature is achieved either entirely or primarily by heating caused by excessive charging or discharging of the battery. Therefore it covers any battery employing a PTC device in series as a thermal switch. Within this broad scope are included batteries in which the switching temperature is achieved by heating either caused by short circuiting or excessive high current charging. 

As mentioned in relation to the Circuit Protection Patent, the concept of using a suitable PTC device to guard a circuit against excessive current flow is obvious. It is equally obvious to employ it to protect a battery from the known adverse effects caused by a high current flow associated with a short circuit. Similarly, one of the basic attractions of PTC compositions is that their change to high resistance on reaching a particular temperature makes them suitable for use in over-temperature protection circuits. The patent itself acknowledges that when a battery is discharged or when a secondary battery is being recharged and is approaching a fully charged state it generates heat internally. It also acknowledges that it is known for batteries to contain a thermal fuse or a thermostat to prevent current being drawn from them when they are excessively hot or to prevent excessive currents being drawn from them. 

I have come to the conclusion that, even absent specific pieces of prior art, it would have been obvious on the basis of common general knowledge to use PTC devices in series to cut the current from or to a cell in the case of either excessive discharge or excessive charging. Mr. Longhurst’s evidence was that this would have been obvious to him. He pointed to the fact that his own employer, Duracell, had used a simple thermal fuse, incorporating a bimetallic strip, to protect some of its batteries. This was not a piece of pleaded prior art but was used to illustrate what Mr. Longhurst was putting forward as a common sense and obvious use of a thermal fuse. 

Bourn’s case also relied on the disclosure in a patent specification called “Ono” after the name of its inventor. Bourns said that Ono demonstrated that there was nothing inventive in claim 1 of the Battery Patent. Ono is concerned with batteries and, in particular, secondary cells. He points to the fact that such cells can easily be damaged by high temperature and he notes that this can be caused by abrupt, i.e. intense, charging or discharging of the cell. He therefore employs a thermistor in series with the battery. When the battery overheats the thermistor switches. Mr. Longhurst’s evidence in relation to this disclosure was;

“The Ono publication (mid 1970s) is a simple example of a thermistor, of the PTC sort, used in series for battery protection (in either charging or discharging). The publication clearly sets out the principle; it leaves many engineering details open. The feature specifically described by the publication is a signal flag, showing when the fault had occurred.”

In my view there is nothing in the features of claim 1 which is inventive. The fact that, even now, there is little commercial call for batteries containing this type of protection does not detract from the obviousness of the claim. I can therefore turn to the claim Raychem does rely on, claim 2 which I have set out above.

This claim again is complex but its inventive concept is simple. It covers secondary cells in which a PTC device is connected in series with the charging circuit. The battery can be rapid charged. When the battery is in a low-charged condition, the heat generated internally is matched by the heat loss from the cell. However a point will be reached as the cell gets nearer full charge at which its temperature will rise. The heat generated by chemical reaction and I2R heating will exceed the rate at which it is being lost to the surrounding environment. As the temperature rises, the PTC device passes its switching temperature and its resistance rises rapidly. The charging circuit then trickle charges while a stable equilibrium at a higher temperature is maintained. 

The detailed design of a cell and circuit to achieve this two phase charging may be tricky and Mr. Longhurst admitted as much. Indeed, as Mr. Longhurst said, he was not aware of any battery made in accordance with this patent which has been put on the market. He said that in practice any battery which fell within the claim would be likely to be inefficient in operation. But the patent is concerned with the principle of how a two phase charging circuit could be made rather than how to do it in practice. The difficulty in turning this idea into practice, which the patent does not help to solve, does not alter the simplicity of the idea which is covered by claim 2. As Mr. Longhurst said, two phase charging was well known at the priority date as was the rise in temperature which signified the need to change from the first to the second phase. In the first phase a high current is used, in the second a low current. Using thermistors to control charging was known. Once PTC devices able to change from low resistivity (high current passing) to high resistivity (low current passing) were known it was obvious to try to use these temperature dependent characteristics to control secondary cell charging. To this extent claim 2 contains nothing inventive. However two features of the claim do merit special consideration. 

First, it might be said that if a PTC device is considered as a temperature activated switch, then it does not appear to be well suited to the second phase of charging. A switch, in normal parlance, goes from completely on to completely off.  However, it is apparent and has been for a long time that a PTC device is not a simple switch in this sense. Its resistance changes from low to high, and its current passing capacity changes from high to low i.e. from it goes from “on” to “less-on”. The extent of that change is dependent on the height of the PTC effect. Therefore it might be said to be particularly suited to passing high and then low currents. But if a PTC device is and was considered as a simple on/off switch could it still be used in a two phase charging circuit and would it be obvious to do so?

How either type of switch can be used to pass two different levels of current can be explained by reference to a simple hydraulic equivalent. Imagine that it is desired to supply water from a mains supply to a device which needs to be filled with water but which has a small leak. It is desired to fill the device fast until it is nearly full and then to turn down to a trickle feed. If the pipe from the mains to the device contains a tap which changes from fully open to fully closed, then a simple hydraulic circuit like the following would achieve the two phase filling;

Bypass

Tap

Mains supply

Consuming
Device

Water flow

	
During the fast filling phase water can pass through the tap and the bypass. During the slow filling phase, the water can only pass through the bypass which has a restricted bore. On the other hand if the tap could be fully opened but never fully closed, then a simple hydraulic circuit like the following would be possible; 

Water flow

Tap

Consuming
Device

Mains supply

	
In this case, because the tap never completely stops flow of water, the change from full flow to trickle may be achieved just by operation of the tap. Of course, with a tap like this, if in the closed position it passes some but not enough water a bypass could be used to supplement the flow so as to bring it up to the desired trickle level. The change from full flow to trickle flow can therefore be achieved whether the tap goes from “full on” to “full off” or from “full on” to “partially off”. The plumbing and concepts involved are simple. 

The same principles can be applied to an electrical circuit. It is illustrated in the following part of Figure 1 of the patent;

R2 (Shunt)	

Current 
Flow

	
RC (PTC device)	

The specification describes how the PTC device (Rc) has a very low resistance at room temperature but a much higher resistance in the high resistance state. It says that it is preferable that, in the high resistance state, it passes sufficient current to allow trickle charging at the desired level. However, if the resistance of the PTC device in its high resistant state is so high that it will allow insufficient current to pass to maintain trickle charging at the desired level, the shunt resistor (R2) can be put into the circuit (as illustrated above) to allow sufficient current to pass. 

Mr. Silverleaf argued that, even if the claim had been limited to circuits using  such  a shunt resistor, it was clearly the sort of arrangement which would have occurred to a skilled man in the art. It is  simple to understand and simple to design. He said that this view is supported by the fact that a number of designers had in fact arrived at the same type of circuits. In this respect he relied on the battery charging circuits shown in an Eveready manual, in a textbook on small batteries written by T.R. Crompton and a General Electric handbook. Even without these references, I accept Mr. Silverleaf’s argument that the use of a bypass or shunt resistor in the charging circuit would have been obvious at the priority date.

The second point concerns the last feature in claim 2, namely the requirement for a stable temperature equilibrium. Mr. Longhurst treated this as if it was a requirement for latching. For the reasons I have given above in relation to the similar provision in claim 1 of the Circuit Protection Patent, I do not think that the claim has this limiting effect. In any event Mr. Longhurst’s evidence, which was not seriously challenged, was that at the priority date latching was a known desirable feature for circuits like this. It adds nothing but a known desideratum to the claim. 

In the event I have come to the conclusion that all of the claims relied upon by Raychem in all four patents are invalid.
Commercial Success
In coming to this conclusion, I have not paid particular regard to the commercial exploitation of the patented compositions and devices. Raychem pleaded commercial success in support of its argument of inventiveness in relation to all the patents except for the Battery Protection Patent. In practice the commercial performance of products or processes covered by a patent rarely is a reliable indicator of non-obviousness. Even when there has been commercial success usually it is difficult to demonstrate that it is attributable to inventiveness rather than some other commercial consideration, such as improved marketing. The result is that, adding a plea of commercial success normally only adds time and expense to the proceedings and serves no useful purpose.

The evidence in support of the plea here was given by a Mr. Chiang. He said;

“I believe that as a result of the inventions of the composition, device and/or oxygen barrier patents ... Raychem has achieved a significant and rapidly growing commercial success through the manufacture and sale of polymer PTC circuit protection devices...”

That he cannot identify which of the three patents is allegedly responsible for the claimed commercial success is confirmed when he says;

“It is not possible for me  to attribute the successes to any individual invention covered by the patents.”

It is not surprising that Mr. Silverleaf chose not to cross-examine him. Mr. Chiang made an unsupported assertion that Raychem’s sales of products falling within the patents enabled it to “fill a need”. But Mr. Floyd accepted that there was at the priority date no large established market waiting for the arrival of PTC devices falling within the claims. In any event Mr. Chiang’s assertion was met by Bourns who put in evidence, which Raychem chose not to challenge, that the increase in sales of Raychem’s PPTC devices was not due to their inventive merit but to a growth in the market for third party products, like cellular telephones, in which they could be used. The growth in sales of Raychem’s products matched closely the growth in those other markets. Mr. Floyd went as far as to accept that this was not a “thumping great case of commercial success”. However, Mr. Silverleaf pointed to the fact that for the best part of 10 years after the priority date no substantial sales of products falling within the patents were made. For 4 years there were no sales at all. As he put it, either it took Raychem 10 years to get from their patents to a commercial device, or it took them 10 years to find a market for it. In this case, on the facts, the argument of commercial success is hopeless.

DATED: 12/6/97