Case No: HC 00 04957
Neutral Citation [2002] EWHC 1556(Ch)
IN THE HIGH COURT OF JUSTICE
CHANCERY DIVISION
PATENTS COURT

Royal Courts of Justice
Strand, London, WC2A 2LL

Date: 26 July 2002

Before :

THE HONOURABLE MR JUSTICE PUMFREY
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Between :

	SEB S.A.	Claimant	
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	(1) DE’LONGHI Spa
(2) DE’LONGHI LIMITED	Defendants	

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Henry Carr QC and Thomas Moody-Stuart (instructed by Wragge & Co) for the Claimants
Andrew Waugh QC and Andrew Lykiardopoulos (solicitor advocate) (instructed by Bristows) for the Defendants

Hearing dates : 22-25 April 2002
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Approved Judgment

I direct that pursuant to CPR PD 39A para 6.1 no official shorthand note shall be taken of this Judgment and that copies of this version as handed down may be treated as authentic.

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Mr Justice Pumfrey

Mr Justice Pumfrey: 
Introduction
1.	This is a case about deep fat fryers. The claimant is a very substantial French manufacturer of kitchen utensils, and the first defendant is an Italian company similarly engaged. The claimant sells utensils under the TEFAL, MOULINEX, KRUPS and ROWENTA marks. The second defendant is the United Kingdom subsidiary of the first defendant, and, as it is not necessary to distinguish between the defendants I shall refer to them collectively as De’Longhi. Their goods are sold under the mark DE’LONGHI.
2.	The title of the invention for which European Patent (UK) was granted is ‘Appareil de cuisson à chauffage électrique’. Despite the wide terms of the title, claim 1, the only independent claim, is to an electric fryer. The case is concerned with fryers which have plastics external housings, and SEB contend that it is the features of the claim which render such constructions possible, notwithstanding the high temperatures of the fat in the cooking vessel itself. The validity of the patent is challenged on the basis of lack of novelty or obviousness, but the defendants say that if the claim covers their various fryers as alleged, the specification does not disclose the invention clearly enough and completely enough for it to be performed by a man skilled in the art. The claimants contend that claim 9 possesses validity independently of claim 1. SEB initially relied on commercial success of deep–fat fryers according to the invention as negativing any suggestion of obviousness, but this aspect of the case was not, in the end, pursued.
3.	The patent was applied for on 11 May 1988, and claims priority from an application made on 11 May 1987. The specification is in French, and the translation was filed on 17 September 1990, in anticipation of the notice of grant appearing in the journal on 10 October 1990.
4.	Twenty–one distinct models of deep–fat fryer are alleged to infringe claims 1 and 9. The parties agreed that they can be divided into five classes, F2, F2–E9, F7, F7–E9 and FP.
The witnesses
5.	The patent in suit is to be construed through the eyes of the notional addressee of the specification, the skilled person. The teaching of the prior art, and the obviousness of the differences between the alleged invention and the prior art is to be ascertained from the perspective of the skilled person. The common general knowledge in the art, the possession of which distinguishes the skilled person from the general run of humanity is ascertained from the evidence of expert witnesses. In the present case, I had the advantage of two helpful witnesses. The patentees relied on the evidence of Mr Wassall. He had started his apprenticeship at sixteen in 1972 with Radiation–Ascot Limited, a manufacturer of electrical and gas appliances. He became concerned with quality control, and became Chief Inspector in 1978. In April 1984 he was a Quality Manager and Engineer with Moulinex Swan Holdings Limited, where he became Technical Service Manager in July 1993. He is presently Quality Manager with Winterwarm Limited. He has followed a General Course in Engineering, and holds T2 and T4 qualifications in Mechanical Engineering. He is an Associate Member of the Institute of Quality Assurance. Although directly concerned with quality assurance, Mr Wassall was part of the design team at Swan, and provided input into the design of an electric fryer at Swan in 1987. Mr Robben, who gave evidence for De’Longhi, is a Belgian citizen, who qualified as an Electromechanical Engineer at the University of Leuven (Louvain) and worked as an assistant there until 1970, when he became Chief Engineer at Ridge Tool NV, a tool manufacturer. In 1977 he became Senior Project Engineer at Klippan NV, a car seatbelt manufacturer, and in 1984 he became Director of Research and Development at Nova Electro International NV, which is a manufacturer of small electrical appliances, including deep fat fryers and waffle irons. He has been an independent consultant since 1998. He is of an inventive turn of mind, and has some familiarity with patent law.
6.	Both expert witnesses had relevant experience. Mr Carr QC, on behalf of the claimants, suggested that Mr Robben’s evidence does not assist in ascertaining the approach of the skilled person at the priority date. I do not accept this. There is no doubt that the experience of the two witnesses was different but both contributed to the identification of the attainments of the skilled person, who is the legal counterpart of the person or persons at Nova Electro or Swan responsible for the design of new domestic appliances. More than one set of skills is represented in the team of people who will design an appliance. There will be a design engineer and a draftsman, of course. There will also be a production person and no doubt a marketing person, since the impulse for new developments almost invariably comes from the marketing department. Obvious constraints on a design include expense, including cost of materials and cost of manufacturing, and safety, which is crucial. Mr Waugh QC identified the following matters of common general knowledge for a design team:
a)	the properties of the standard metals and plastics used in domestic appliances and the processes used for shaping them, their cost and availability;
b)	the increasing trend (at the priority date in May 1987) for plastics to be used in domestic appliances and the increased stress on aesthetic considerations in the marketing of domestic products;
c)	the greater versatility of plastics in shaping compared with metals;
d)	the requirements for plastics used in the manufacture of domestic appliances including their surface characteristics (i.e. whether glossy, resistant to staining and cleanable) their stiffness and feel, the effects of temperature on those characteristics and also on their rates of degradation and discolouration, the ease with which they can be moulded and the expense of tooling for them;
e)	the plastics suitable for use in domestic appliances and the low cost, chemical resistance and advantages in manufacture of polypropylene compared to other plastics usable for the outer covers of heated appliances and the heat resistance advantages of glass filled polybutylene terephthalate (PBT), nylon or similar polymers if direct contact with heated parts is required. Exhibit 6 to Mr Robben’s report is a useful summary of the principal materials used in domestic devices and their respective properties. In designing a deep fat fryer for mass production, I would expect the skilled man to be possessed of this information.
f)	familiarity with the range of available electrical household appliances that include heating elements, such as fryers, irons, kettles and toasters including polypropylene kettles and cool wall toasters;
g)	the range of temperatures to be expected in such devices
h)	the use of insulating gaskets to separate hot metal parts from plastics components of low temperature resistance.
To this list Mr Waugh QC added that the skilled man could be expected to understand conduction and convection. This also, it seems to me, is correct. I would add that it is clear that the skilled person has the safety of the devices which he designs very much in mind. Safety is paramount.
7.	At the priority date, deep fat fryers were well established on the market. So far as the evidence goes, they were principally double-walled fryers, the skirt of which was metal. There were relevant safety standards, but these did not necessarily extend to the temperature of the skirt if the device was not intended to be lifted when hot by placing the hand on the skirt.
8.	I shall return to this list when I come to consider the objection of obviousness. These are the areas of knowledge which the addressee of the specification brings to its consideration.
The patent in suit.
9.	Having set out the field of the invention, the patent first describes the state of the art. The draftsman refers to the container for the hot oil or fat as ‘the vessel’, and the outer container as ‘the skirt’, and I shall do the same. It observes that in most known electric fryers the vessel, which is made from a metal such as aluminium, is directly exposed to ambient air which has certain drawbacks, viz:
a)	During operation of the fryer, the vessel readily reaches a temperature of 150ºC with the result that users may burn themselves if they touch the vessel;
b)	Given that the vessel is exposed to air, there are major heat losses, affecting electricity consumption;
c)	The bare metal of the vessel ‘does not make it possible to provide the vessel with a very attractive appearance’.
10.	The specification then acknowledges two prior methods of overcoming these problems. The first is to surround the vessel with a metal skirt, an expedient which was well-known at the date. The other is to provide a plastics skirt. Since there are heat bridges between the prior plastics skirt and the vessel, the specification observes that it is necessary to make the skirt of heat resisting plastics such as polyamides and polyesters, which are comparatively expensive.
11.	There then follows a detailed acknowledgment of Spanish Utility Model 290 283 (‘Taurus’). I shall return to this document below. De’Longhi rely upon both the Taurus document and a sample of the Taurus fryer itself was produced by SEB. This fryer was the subject of experiments, to which I shall return. As will be seen, the claim of the patent is constructed around the disclosure of Taurus, and in order to follow the discussion I reproduce two more or less self-explanatory figures from that specification:

12.	The acknowledgment of Taurus is as follows:
‘[Taurus] also discloses an electric fryer comprising a metal vessel and an electrical heating resistance, which vessel is adapted to be heated to at least 150ºC and is surrounded by a skirt of plastics material such as polypropylene which does not continuously bear the temperature of the vessel wall since the skirt is spaced from the side walls and base of the vessel by a layer of air. The skirt is completely free with respect to the vessel with the exception of a connection between the top edges of the skirt and the vessel.
This connection takes the form of metal flanges [rigid with] firmly/immovably attached to a metal plate fitted on the top edge of the plastics skirt.
Openings are provided in the base of the skirt and in the metal plates located at the top of the skirt so as to allow air to circulate between the plastics skirt and the metal vessel. This air circulation makes it possible to cool the plastics skirt.
However, the air emerging from the openings in the metal plates located at the top of the skirt is at a high temperature. Given that these openings are disposed in an area which may be touched by users, the latter may receive burns.’
13.	The phrase in italics sets out my understanding of what is meant by the words ‘rigid with’ in this context. The openings through which the air emerges are the openings 13 in the figures above. The metal flanges which carry the vessel are shown at 6, and the plate let into the top part of the skirt is shown generally at 4. The specification of Taurus makes it clear that the purpose of the openings is to provide for the flow of air:
‘The support plates 4 have holes 13 along their length while the base 2 of the body 1 has more holes 14; the said base rests on feet 15. The purpose of these holes 13 and 14 is to establish air circulation by convection between the body 1 and the container 8; the air enters at the bottom and exits at the top as shown in Figure 3 [the right hand figure above] which contributes to cooling the space between the walls of the body and the oil container 8 which, when in use, reaches temperatures of about 200ºC and heats the said space by radiation.’ [Taurus translation page 3 lines 11ff.]
14.	The object of the invention is stated to be the provision of an inexpensive fryer which simultaneously provides users with effective protection against possible burns and prevents external heat losses. The consistory clause which follows echoes claim 1, which I set out here subdivided into features which were referred to by number at the trial:
‘[1]	An electric fryer
comprising
[2]	a metal vessel and an electrical hearing element,
[3]	the vessel readily reaching a temperature of 150ºC and
[4]	surrounded by a plastics skirt which does not continuously withstand the temperature of the vessel wall
[5]	which skirt is spaced from the side wall and base of the vessel by a layer of air and
[6]	is completely free with respect to the vessel except for a connection between the top edge of the skirt and the top edge of the vessel
characterised
[7]	in that the skirt completely surrounds the side wall and the base of the vessel and
[8]	in that the connection is made by means of a ring which connects the top edge of the skirt to the top edge of the vessel and closes the air filled space between the skirt and the vessel,
[9]	the layer of air being thick enough to limit the skirt temperature to a value compatible with the thermal characteristic of the plastics material of the skirt,
[10]	the ring being of a thermally insulating material which is continuously resistant to the temperature of the top edge of the vessel which rests freely on this ring.’
15.	Claim 9 adds no feature to this claim save that the skirt and lid be made of polypropylene.
16.	It will be observed that the ‘precharacterising’ part of claim 1 reads directly onto Taurus, the material of whose body is said to be preferably polypropylene. The characterising portion of the claim defines the features which are alleged to constitute invention over this disclosure. The advantages conferred by this combination of features are said (page 3 lines 21-39) to be
i)	The skirt is unlikely to be heated to an excessive temperature, given that the ring, which is of heat resistant material, is the only part in contact with the vessel;
ii)	Since only the ring is of high quality material, the remainder of the skirt can be made from a low quality plastics material which does not withstand a temperature of more than 80ºC;
iii)	Because of the large layer of air between the vessel and the plastics skirt, there are very reduced external heat losses, which makes the appliance economical to use;
iv)	Users who touch the plastics skirt run no risk of being burnt, and the appliance can be handled at any time;
v)	The plastics skirt can be moulded into any shape which may be desired, so making the appliance aesthetically attractive.
17.	Other preferred features relating to the lid are then described. The preferred embodiment is described by reference to the figures. I reproduce Figure 2 which shows the interrelationship of skirt 3, vessel 1 and ring 5 in the preferred embodiment:

18.	The description of the preferred embodiment does not need to be considered in detail. It is followed by further remarks about the merits of the invention (page 6 lines 1–27):
‘The outer plastics skirt 3 separated from the oil vessel 1 makes it possible to insulate the latter and prevent any risk of burns on the part of the user. At the same time the air space 4 which surrounds the vessel 1 substantially limits external heat losses which allows a reduction in electricity consumption.
Given that the skirt 3 is practically free with respect to the vessel 1, i.e. no heat bridge is created between this vessel and the skirt, the latter can be made from plastics material of an inexpensive, widely available quality which does not withstand high temperatures; this means that the fryer can be produced at low cost.
The merit of the present invention lies in particular in that this ring of simple design provides an effective solution to the problem raised. This ring performs all the following functions:
–	it defines the spacing between the vessel 1 and the outer plastics skirt 3,
–	it is designed to support and centre the vessel 1 within the skirt 3,
–	it completely shuts off the air space between the vessel 1 and the skirt 3,
–	it allows the vessel 1 to expand freely with respect to the skirt 3,
–	it allows the transmission of heat between the vessel 1 and the skirt 3 to be limited.’
Construction
19.	The main issue arises in respect of feature 8 of the claim set out above. In each of the De’Longhi fryers alleged to infringe the claim, there is a ring of more heat-resistant material and a skirt of less heat-resistant material. The edges of the vessel are spaced from the ring by spacing elements of various designs, which leave a gap (albeit a rather small gap) through which air must be capable of flowing to some extent. This raises the question of what the claim means when in says that the ring ‘closes the air-filled space between the skirt and the vessel.’ ‘Close’ is a word with a considerable penumbra of meaning. It can mean anything from a hermetic joint to a general closure as may be achieved by closing a door. The meaning of the word necessarily must be ascertained in its context, giving it a purposive construction which will satisfy the requirements of the protocol on the interpretation of Article 69 of the European Patent Convention, which requires that the meaning placed on the claim be sufficient to give fair protection to the patentee and simultaneously a reasonable degree of certainty for third parties. I will return to the customary approach to this question, which is to apply the principles of construction set out by Hoffmann J in Improver Corporation v Remington [1990] FSR 181 as explained by the Court of Appeal in Wheatley v Drillsafe [2001] RPC 7 after considering the function of this word in its context.
20.	When one encounters a word of degree the problem is to ascertain its function in the claim, so as to obtain a handle on its meaning. A classic case is the phrase ‘thin and flexible’ in Cleveland Graphite v Glacier Metal (1950) 67 RPC 149, and there are many similar cases. Words of degree are often introduced to draw a distinction from what has gone before, whether that is acknowledged in the specification or is to be ascertained from the practice in the trade. In Cleveland Graphite the words were used to distinguish the invention from the self-supporting, rigid bearing liners of the prior art. The thin and flexible liner of the invention was not self-supporting, and derived its support from the bearing housing. The way to describe the difference from what had gone before was by direct comparison with it. That, in my view, is plainly the manner in which the word ‘closes’ is being used here. Another example is the used of the word ‘fixed’ in Taylor v Ishida [2001] EWCA Civ 1092, (unreported). In paragraph 24 of the his judgment, with which Hale and Jonathan Parker LJJ agreed, Aldous LJ said
‘The specification draws attention to the complex and intermittent operation of the prior art machines. The invention is having a continuous rotary machine with a stripper and sealer on the same arm. In that way the whole operation required … is carried out by rotary movement of arms about axes. Those axes are fixed in the sense that the movement is not that of the type described in Zwight and the other prior art machines referred to. However they do have movement to enable the jaws, which rotate, to strip and seal. Such a construction gives effect to what I perceive to have been the obvious intention of the patentee. No skilled person reading the specification would give the word “fixed” its acontextual meaning. Such a person would realise that the advantage described was the machine with continuous rotary stripping and sealing and for that to be achieved some movement [of the axes] was required. The extent would depend upon the design of the actual machine. The actual extent of movement that falls within the ambit of the claim is that which the notional skilled person would realise would obviously have no material effect upon the way the invention worked taken at the level of generality of claim 1. Such a construction gives fair protection to the patentee and reasonable certainty to the public.’
21.	One of the stated disadvantages of the Taurus construction is that the air emerging from the slots 13 is at a high temperature and may burn the users. The invention of the patent is to be distinguished from this because hot air is no longer to emerge in such a way as to heat the skirt or otherwise imperil the users. In my judgment, it is in this sense that the word ‘closes’ is to be understood. Such an interpretation is consistent with the passage from page 6 quoted above which observes that the ring ‘completely shuts off the air space between the vessel 1 and the skirt 3’. I do not think that the use of the word ‘completely’ here qualifies the meaning of ‘closes’ in the claim. Indeed, it is difficult to see how it could do so. Construed strictly, it would require the space to be sealed, but that is not possible and is not described. I conclude that the purpose of the word is practically to exclude convective cooling with the associate risk of the escape of hot air where the user may put his or her hand. The air in a device according to claim 1 is to act as an insulating layer.
22.	Mr Waugh QC on behalf of the defendants submitted that this was not the whole story. He said that the skilled reader would appreciate that the requirement for complete closure relates not only to the passage of air but also to the ingress of unwanted material, particularly oil. This is no doubt correct, but it does not have any impact on the function of the word ‘closes’ in its context in the specification. The specification is not concerned with the ingress of oil into the space between the skirt and the vessel. No doubt such ingress is undesirable, but that fact has nothing to do with the manner in which the claim seeks to define the invention. The same is true of the fact that the layer of air insulates the vessel from the skirt whether it is stationary or moving. What Taurus is concerned with (among other things) is heating the space between the skirt and the vessel by radiation, and it is therefore concerned to cool the skirt by convection, and to avoid contact between hot air and the skirt. 
23.	Having now expressed my view of the meaning of ‘closes’ in its context, I can return to the Improver questions. These questions are designed to provide a methodical approach to ascertaining the scope of the words of a claim in their context. As Mance LJ, speaking for the majority in Wheatley v Drillsafe [2001] RPC 7 observes, 
‘These passages in Lord Diplock’s speech in [Catnic v Hill & Smith Ltd [1982] RPC 183, 242] underline the fact that, in this context as elsewhere in the law, the issue of construction is ultimately a unitary one. The various matters arising … which were reformulated by Hoffman J in Improver as the three Improver questions, aim simply to assist in arrival at the proper purposive and contextual interpretation. They assist, in particular, to decide “whether a feature embodied in an alleged infringement which fell outside the primary, literal or acontextual meaning of a descriptive word or phrase in the claim (“a variant”) was nevertheless within its language as properly interpreted (Improver, per Hoffmann J at p. 189). “In the end, therefore”, as Hoffman J went on to say
“The question is always whether the infringement is covered by the language of the claim. This, I think, is what Lord Diplock meant in Catnic when he said that there was no dichotomy between ‘textual infringement’ and infringement of the ‘pith and marrow’ of the patent and why I respectfully think that Fox LJ put the question with great precision in Anchor Building Products Ltd v Redland Roof Tiles Ltd (November 23, 1988, unrep) when he said the question was whether the absence of a feature mentioned in the claim was ‘an immaterial variant which a person skilled in the trade would have regarded as being within the ambit of the language’ (my emphasis). It is worth noticing that Lord Diplock’s first two questions, although they cannot sensibly be answered without reference to the patent, do not primarily involve questions of construction: whether the variant would make a material difference to the way the invention worked and whether this would have been obvious to the skilled reader are questions of fact. The answers are used to provide the factual background against which the specification must be construed. It is the third question which raises the question of construction and Lord Diplock’s formulation makes it clear that on this question the answers to the first two questions are not conclusive. Even a purposive construction of the language of the patent may lead to the conclusion that although the variant made no material difference and this would have been obvious at the time, the patentee for some reason was confining his claim to the primary meaning and excluding the variant. If this were not the case, there would be no point in asking the third question at all.”’
24.	To ascertain the proper scope to attribute to a word like ‘vertical’ in Catnic itself, or ‘opaque’ in 3M v Plastus Creativ [1997] RPC 737 is, to use Robert Walker LJ’s phrase in Cartonneries de Thulin SA v CTP White Knight Ltd [2001] RPC 6 at paragraph 22, to answer the simple questions, how vertical? or how opaque? In this case, the question is, how tightly closed? and in my judgment the answer is to be found in the specification by considering the purpose of the closing.
25.	In this connection, it should be remembered that Catnic is also concerned with another possibility. This is the case in which the variant cannot be encompassed by the words of the claim on any sensible meaning. In the passage immediately preceding the much-cited passage, Lord Diplock mentioned the case of the hayrake, C van der Lely NV v Bamfords [1963] RPC 61. There, the problematic word was ‘hindmost’ in the phrase ‘one or more of the rake wheels situated hindmost in the direction of motion…is…dismountable’. In the alleged infringement, the dismountable wheels were foremost in the direction of motion. The House of Lords, by a majority, found infringement. Robert Walker LJ’s question, how hindmost? received the answer, it does not matter—what matters is dismountability. Lord Diplock explains that ‘the word “hindmost” as descriptive of the rake wheels to be dismounted could not as a matter of linguistics mean “foremost”: but this did not exhaust the question of construction of the specification that was determinative of whether there had been infringement of the claim or not.’ 
26.	In the present case, Mr Waugh QC on behalf of De’Longhi submits that the guidance provided by the passages on pages 2, 3 and 6 of the specification that I have quoted above indicates that the claim should be construed to require that the space between the vessel and the skirt be completely shut off when the vessel rests upon the ring. He says that the ring should ‘as nearly as possible’ close off the air space between the two components. 
‘Accordingly, although fat fryers are not precision objects and the Defendants accept that the claim should not be construed to require an absolute or hermetic seal, nevertheless it is clear that the ring should be such that it serves to shut off the space and eliminate airflows between the gaps between the vessel and the skirt. In this way hot air is prevented from emerging from the opening at the top of the skirt. This construction is … the only construction which is consistent with the stated aims of the patent and the avoidance of the prior art.’
27.	All that this proposed construction does is to introduce new words having the potential themselves to start further debate. Does ‘eliminate’ mean eliminate entirely, or merely eliminate for all practical purposes? The purpose of construing the claim is to identify the questions which need to be answered to decide the issue of infringement, and it is no good merely to multiply questions without providing a workable test for infringement. How closed? closed enough practically to prevent convection between the skirt and the vessel and the consequent escape of hot air, with the associated risk of burning.
28.	In coming to this view, I have rejected a submission of Mr Waugh’s based on the decision of the Court of Appeal in Société Technique de Pulverisation STEP v Emson Europe Ltd [1993] RPC 513. In this case, Hoffmann LJ observed that 
‘The well known principle that patent claims are given a purposive construction does not mean that an integer can be treated as struck out if it does not appear to make any difference to the inventive concept. It may have some other purpose buried in the prior art and  even if this is not discernible, the patentee may have had some reason of his own for introducing it.’
29.	This passage is an introduction to an examination of the purpose of the disputed feature and cannot be divorced from the construction of the words ‘conduit means’ which follows. The alleged infringement did not contain conduit means, as those words were construed, at all. In other words, something lacking anything which could fairly be described as a conduit means was not within the ambit of the language.
Infringement
30.	Samples of each of the alleged infringements were made available to me, together with photographs. There is no doubt that all the features of the claim other than feature 8 are present. The ring in the alleged infringements is not simple, but has spacers and other features moulded into it. The various features of the rings are well described by Mr Waugh QC, as follows.
·	F2	The ring has 8 vertical spacers of approximately 3mm in height around its circumference which support and raise the metal vessel and decrease the heat conduction between the vessel and the ring.  The fryer also has air vents on each side of its base.
·	F2-E9	The spacers are increased to 3.5mm (thereby producing a larger gap between the vessel and the ring).  The fryer also has air vents on each side of its base. 
·	F7 	The F7 fryers are larger in capacity than the F2s and the design of the ring is different to the F2 and F2-E9 series and includes both spacers above the ring as well as “feet” between the base of the ring and the skirt.  The eight spacers are 1mm high. As in all fryers there is a slot in the lower front of the skirt through which air can enter.
·	F7-E9 	Corner gaps have been introduced by means of indentations in the top of the skirt below the ring.  The skirt has been cut down slightly and the rim of the skirt pulled back at the corners. The spacers remain at 1mm high.  The fryer also has vents introduced to its base. 
·	FP	The spacing elements have been placed on the underside of the vessel collar at regular intervals.  These spacers are 0.8mm high.  The fryer has vents in its base and skirt.  There is a screw between the ring and the vessel.
31.	The various gaps were measured by the parties and by Mr Wassall,.
Fryer	Measured by Dall’Acqua (in re-amended Product Description)
	Mr Wassall’s Measurements
	Zabattini’s  Measurements
[average (and range)]	
F2	1.1 (0.75)		0.49  (0.15 - 1.15)  	
F2-E9	2.3 (2.5)		2.28  (1.65 - 2.75)	
F7	2.5 (2.5)		2.14  (1.5 - 2.6)	
F7- E9	2.5 (2.5)	2.28/2.36
	2.00  (0.9-3.3)
1.56  (0.3 - 1.95)  	
FP	1.5 (1.5)		1.76 (0.5-2.6)	
32.	The parties also performed experiments. I found these experiments unhelpful. In particular the infrared photographs of the Taurus and the alleged infringements, which might have been very useful, are marred by the fact that in each case the range of colours used was freshly standardised against the range of temperatures. This means that in some of the Taurus photographs green denotes a temperature of about 40ºC, while in others about 55ºC. In certain of the photographs of the alleged infringements, it represents a temperature of about 61ºC or so. This means the photographs are difficult to compare. I do think, however, that they do establish that if there is a problem with the Taurus it is caused by the flow of air, since the actual skirt temperature is comparable with, or lower than, the alleged infringements. The technique used did not allow hot air which was not glowing to be clearly seen, as the photographs of a candle flame made clear. Anyone putting their finger into the space immediately above the part of the flame which can be seen on the photographs would soon be burnt.
33.	De’Longhi’s experiment designed to show some convection by the injection of smoke into the skirt did demonstrate that there was some flow of air. I was shown video recordings of this experiment, and I can record that the flow of smoke was slow. Mr Wassall said that the smoke was not drawn in. By this I understood him to mean that the rate of flow of the smoke was comparable with its natural tendency to disperse. The flow appeared to be practically negligible.
34.	The gaps are small. The experts readily accepted that there was no risk of burning from the small quantity of hot air escaping from below the ring. It is clear that the products are variable, and that the gaps vary in each case. Perhaps the real point is that the airflow, which is small, emerges from underneath the turned over rim of the vessel itself, and that in any event this must be a hot region. In contrast, in the Taurus device, the air emerges in the side of the skirt, through slots cut a substantial metal plate where hands might naturally be placed.
35.	The experiments relating to power consumption were inconclusive. They were intended to show the steady state temperatures of the vessel, and the upper and lower skirt with and without the ventilation louvers in the base of the machine open. The results are difficult to interpret and compare because the differences are slight, and the ambient temperature was different for different runs. The best the experiments can be taken to show is a slight reduction in temperature, probably caused by the airflow.
36.	I conclude that all the De’Longhi fryers infringe claim 1. They are all made of polypropylene, and they therefore all infringe claim 9 as well.
Validity
37.	There is no question of any anticipation. The alleged invention is new. Mr Waugh QC contended that it was obvious in the light of the skilled person’s common general knowledge, or, in the alternative, in the light of the disclosure of a rice boiler in Japanese Patent Application no 52-132964. I shall now return to the question of the common general knowledge of the skilled man.
38.	In Beloit v Valmet [1997] RPC 489 at 494, Aldous LJ said this: 
‘It has never been easy to differentiate between common general knowledge and that which is known by some. It has become particularly difficult with the modern ability to circulate and retrieve information. Employees of some companies, with the use of libraries and patent departments, will become aware of information soon after it is published in a whole variety of documents; whereas others, without such advantages, may never do so until that information is accepted generally and put into practice. The notional skilled addressee is the ordinary man who may not have the advantages that some employees of large companies may have. The information in a patent specification is addressed to such a man and must contain sufficient details for him to understand and to apply the invention. It will only lack an inventive step if it is obvious to such a man. 
It follows that evidence that a fact is known or event well-known to a witness does not establish that that fact forms part of the common general knowledge. Neither does it follow that it will form part of the common general knowledge if it is recorded in a document.’
39.	Where an item of prior art is not specifically relied on to support an allegation of obviousness, it is essential that all material which cannot fairly be described as common general knowledge are excluded. Mr Robben’s evidence did not make this easy. He regarded a number of catalogues and other fryers (including one referred to as the Grossag and, indeed, the Taurus) as commonly known. I do not think the evidence supports this. Even with an instruction in 1987 to go and design a deep fat fryer, I am far from confident that these fryers would have become known to the skilled man. I think, however, that Mr Waugh did establish the scope of the common general knowledge fairly in his cross-examination of Mr Wassall in the following passage:
‘[Mr Waugh] …We have to look at the prior art, Mr. Wassall, with common general knowledge in mind.  Those things are the generally known.  You have been very helpful this morning on that.  Just to recap matters that we need to look at prior art in the light of so that you know what we have in mind.  As part of the basic knowledge in 1987, basic design of these electric fryers, for example with a metal skirt were known, both unskirted and skirted? A.  Yes. 
Q.  The metal skirt would serve to support the vessel generally known? A.  Yes. 
Q.  The concept of the vessel resting on the outer skirt to be supported, sitting on the skirt was generally known? A.  Yes. 
Q.  The use of an air filled gap between the vessel and the skirt to insulate was generally known? A.  Yes. 
Q.  The use of plastic outer casings in fryers, not fryers, in other domestic appliance was generally known? A.  Yes. 
Q.  Even if you were not aware for example of Taurus, Grossag or Fri-Fri, the chances are you would have known of at least the concept of using plastic on outer -- as the outer casing? A.  As I explained in my report we investigated. 
Q.  Fryers? A.  Yes. 
Q.  One of the commonly used and preferred plastics at this time was polypropylene? A.  I would not say commonly used at this time. 
Q.  But known to be used? A.  Known to be used but not necessarily commonly used. 
Q.  We have seen the polypropylene kettle and the like.  We have been over that.  In terms of manufacture and for aesthetic reasons, plastics are preferred over metal? A.  Yes. 
Q.  Knowledge of the properties of plastics, you have seen as a general section Mr. Robben's report, a designer would be generally familiar with the properties of these plastics? A.  Maybe generally familiar, but if not he would seek expert advice. 
Q.  Certainly be at his elbow to find out what they were? A.  More from expert advice I would say. 
Q.  Or indeed looking at the brochures of the manufacturers, Hoechst, BASF? A.  Yes. 
Q.  Again the use of insulating rings and spacing elements in various appliance we have been over that, irons, coffee makers and toasters again generally known? A.  Generally known, yes.’
40.	Obviously this evidence of what was generally known is most important. It establishes that without any particular design in mind the skilled addressee setting out to design a fryer in 1987 would bring to that exercise the knowledge that the skirt can be made of metal, and the vessel can rest on the skirt, through (if need be) an insulating ring.
41.	The only statutory question is whether the invention was obvious at the priority date. It is nonetheless often helpful to follow the well-trodden path marked out by Oliver LJ in Windsurfing International v Tabur Marine [1985] RPC 59 to answer what it essentially a question of fact. Oliver LJ said this:
‘There are, we think, four steps which require to be taken in answering the jury question. The first is to identify the inventive concept embodied in the patent in suit. Thereafter, the court has to assume the mantle of the normally skilled but unimaginative addressee in the art at the priority date and to impute to him what was, at that date, common general knowledge in the art in question. The third step is to identify what, if any, differences exist between the matter [forming part of the state of the art] and the alleged invention. Finally, the court has to ask itself whether, viewed without any knowledge of the alleged invention, those differences constitute steps which would have been obvious to the skilled man or whether they require any degree of invention.’
42.	Rolled up in the words ‘viewed without any knowledge of the alleged invention’ is a warning of the great danger of viewing this question with hindsight, a danger particularly acute where the subject matter of the invention is a quotidian article of kitchen equipment and the inventive step may be modest. The cases are full of warnings against the employment of hindsight: see Technograph v Mills & Rockley [1972] RPC 346, and the celebrated warning in British Westinghouse v Braulik (1910) 27 RPC 209 at 230, repeated by Lord Diplock in Technograph:
‘I confess that I view with suspicion arguments to the effect that a new combination, bringing with it new and important consequences in the shape of practical machines, is not an invention, because, when it has once been established, it is easy to show how it might be arrived at by starting from something known, and taking a series of apparently easy steps. This ex post facto analysis of invention is unfair to the inventors, and in my opinion it is not countenanced by English Patent Law.’
43.	To the same effect is what Lord Herschell said in Siddell v Vickers (1890) 7 RPC 292 at 304. When reading this passage, it is worth remembering that the invention was to turn huge white-hot castings using a sort of giant bicycle chain passing over a combined wheel and ratchet. The prior art was the wheel and chain, without the ratchet. The inability to control rotation conferred by the ratchet had meant that the workmen, who used handspikes, had from time to time been killed:
‘Forgings [the defendants] say, had long rested in an endless chain, the idea of turning such forgings by turning the wheel over which the chain passed was not a new one, and a ratchet working in teeth was a well-known device for causing a wheel to rotate to the desired extent. All this I think cannot be denied. But the result is an apparatus of extremely simple character, which possesses the advantage of being easily moved from place to place, and applied wherever wanted. And the question remains, whether this mode of dealing with forgings which require to be gradually turned was so obvious that it would at once occur to anyone acquainted with the subject, and desirous of accomplishing the end, or whether it required some invention to devise it. There is no doubt about the law applicable to such a question, though it is often difficult to apply it to the circumstances of a particular case, and its application is perhaps most difficult when the alleged invention consists of a new apparatus combining known elements. If the apparatus be valuable by reason of its simplicity, there is a danger of being misled by that very simplicity into the belief that no invention was needed to produce it. But experience has shown that not a few inventions, some of which have revolutionised the industries of this country, have been of so simple a character that when once they were made known it was difficult to understand how the idea had been so long in presenting itself, or not to believe that they must have been obvious to everyone.’
44.	All I would add is that this is also true of inventions that are in truth obvious, even if meritorious. This is a warning to have regard to all the evidence.
45.	The inventive concept is normally what is defined in claim 1. To abstract anything wider than this runs the risk of being unfair to the inventor, since to generalise the invention runs the risk of ignoring features in the claim which may of themselves been inventive. Thus, in the Windsurfing case itself, the inventive concept was the ‘free sail concept’, i.e. an unstayed, freely pivoting mast. The prior art was a square rig, and the claim called for a Bermuda rig, with wishbone booms. The question the Court of Appeal asked was, whether it was obvious to substitute the Bermuda rig for the square (or kite) rig disclosed.
46.	When obviousness in the light of the common general knowledge is concerned, the risk of failing to look at the problem through the eyes of the skilled person are perhaps diminished. There is no clearly defined starting point in the sense of a single publication. What was established to be common general knowledge, however, was the general idea of a double walled fryer, both walls of metal, with the features identified in the transcript passage I have quoted above. Mr Waugh came at the claim in two ways: first, it was obvious to the skilled person merely to substitute as cheap a plastics skirt as possible in a construction in which a metal wall would be held away from the vessel by an insulating ring: or alternatively, it was obvious to substitute a non-resistant plastics material and an insulating ring for a metal wall. Undoubtedly one of the possibilities is that the skirt will be wholly closed, and perhaps this is the only real possibility from the point of view of safety. Once this is done, a device falling within the claim necessarily results.
47.	Mr Wassall accepted that by the 1980’s there was a strong emphasis on the use of plastics where possible, and that there was a general trend to enclose heated appliances in plastics casings, driven in part by safety considerations. It is always safer to touch hot plastic than metal at the same temperature, as the former is a poor conductor and heat arrives at the point of touch more slowly than it does with a good conductor.
 Contraindications to obviousness
48.	It follows, I think, that if I am to find invention in claim 1, it must be on the basis that there was a sufficiently strong prejudice against the use of plastics in such a high-temperature application that their use would not be obvious to the skilled man. This view cannot be supported on the evidence. Many manufacturers did indeed produce fryers during the period of interest (and after it) which did not fall within the claim, and even now metal-skirted fryers command a market. 
49.	Then there is the secondary evidence of what was going on in the market at the date. Mr Carr QC referred to the Grossag, the Fri-Fri, the Taurus and the Kenwood/Nova fryers, for the last of which which Mr Robben’s team was responsible. The Grossag had a plastics skirt, but it was a resistant plastic, nylon. Fri-Fri on the other hand had a polypropylene skirt and no insulating ring. Although the vessel rested on the skirt, it was sufficiently deep that the skirt was not harmed. Taurus used convection cooling, and I have described it in detail. 
50.	The Kenwood is of some interest. Its appearance was determined by the well-known British designers Pentagram. The specification required a wall temperature of no more than 50ºC above ambient, and this was achieved by using metal shielding between the vessel and the skirt at the sides of the fryer and a double plastics skirt at the front. After the priority date, Nova produced a fryer for itself on the same constructional principles.
51.	Finally, I should refer to Mr Wassall’s own design. In 1987, Swan was importing a fryer from Belgium which consisted of a diecast aluminium vessel completely exposed at the sides. In 1987, there was an attempt to design the new fryer.
‘2.7	The high temperature of the metal outer skirt was a real safety concern. In 1987 when designing our new fryer to replace the [Belgian fryer] we were very keen to reduce the temperature of the outer skirt to levels that were safe to touch. We considered manufacturing the outer wall from a plastic with low thermal conductivity (to reduce the wall temperature) and a high melting point (to allow it to withstand the heat generated by the vessel). We considered manufacturing the outer body of the fryer from Nylon 66. Such a fryer would have had a cool wall but would have been prohibitively expensive to build. Other suitable plastics were similarly expensive both as a raw material and to mould. The cheaper plastics, such as polypropylene, could not withstand the temperature of the vessel and the temperature inside the skirt.’
52.	In answer to questions from me, he explained that the first thought had been to use plastics. These either melted (acetal) or were too expensive (nylon 66). So they ultimately used a metal skirt, made up like a biscuit tin. This evidence is strong confirmation that the use of plastics material for the skirt is per se obvious. So the only question is whether the use of an insulating ring to protect it is obvious. There is no doubt that such insulating rings are used in kettles and in electric irons.
53.	In this respect, the disagreement between Mr Wassall and Mr Robben comes down to the former’s belief that knowledge of techniques such as insulating rings and gaskets, or of materials such as more or less heat-resisting plastics, would be more compartmentalised among designers working in a particular field than the latter considered right. I must say that I am surprised by the suggestion that it was not obvious to use the insulating ring in Mr Wassall’s fryer, but one was not used or considered. I prefer Mr Robben’s evidence on this point. My reason is that his approach seems to me to be more consonant with what I would expect in a modern designer. I think that the notional skilled man would have considered an insulating ring, and that this would have given success.
54.	Finally I should mention the plea of commercial success. The invention of the patent in suit has never displaced other methods of making fryers. There are still fryers that have metal skirts, and there is a market for much more complex constructions as well. SEB are a huge and very successful manufacturer of kitchen appliances, and their fryer according to the patent was extensively promoted. It became clear at an early stage that it was never going to be possible to establish a sufficient degree of long-felt want, nor to show that the commercial success enjoyed by the claimant’s fryer was attributable to the invention, and in the end Mr Carr QC did not persist in the plea. In this I think he was quite correct. The evidence did suggest that the public put particular store on cool walls, but did not show that cool walls were achievable only using the invention. That is not to say that the alleged invention does not have some technical merit. It plainly does, but that is not of itself sufficient to indicate invention.
55.	In the result, I think that the invention of claim 1 is obvious. Claim 9 adds nothing to it: the invention is obvious because the skilled man wants to use plastics like polypropylene for the skirt.
The Toshiba rice boiler
56.	Because of the different temperature at which this device operates, the retention of the ring and of the plastics skirt if it were used to inspire the design of a fat fryer depends upon almost precisely the same considerations that I have considered when considering the obviousness of the invention in the light of the common general knowledge alone. In effect, the argument is the same. If the invention is not obvious in the light of the common general knowledge, it is not obvious in the light of the Toshiba disclosure, and I do not need to consider it further.
Insufficiency
57.	The plea of insufficiency was employed to point up what Mr Waugh contended was the weakness of the construction I have placed on the claim. The objection is that if the defendants’ fryers infringe, there is no adequate description of the ring, and its function that would enable the skilled man to produce a fryer within the claim. This is not, in my view, a properly formulated objection of invalidity, and it is merely argumentative. The skilled man would have on the evidence no difficulty in constructing a fryer in which the air flow was sufficiently low that the user’s hands were not at risk, and I reject this objection.
Conclusions.
58.	Claims 1 and 9 of the patent in suit are invalid for obviousness over the common general knowledge in the art, but, had they been valid, would have been infringed by all of the alleged infringements. I will hear counsel on the form of order.