T 0579/94 18-08-1998

1. The appeal is admissible.

2. Admissibility of amendments

2.1. Main request

According to the decisions of the Enlarged Board of Appeal, G 0009/92 and G 0004/93 (OJ EPO 1994, 875), if the opponent is the sole appellant against an interlocutory decision maintaining a patent in amended form, as in the present case, the patent proprietor is primarily restricted during the appeal to defending the patent in the form in which it was maintained by the Opposition Division in its interlocutory decision. Amendments proposed by the patent proprietor as a party to the proceedings as of right under Article 107, second sentence, EPC, may be rejected as inadmissible by the Board if they are neither appropriate nor necessary, which is the case if the amendments do not arise from the appeal, pursuant to Article 101(2) EPC, and Rules 58(2) and 66(1) EPC (Reasons for the decision, point 15).

2.1.1. In this connection, the set of claims corresponding to the main request contains an additional independent claim (Claim 2) which was not present in the version underlying the decision under appeal, and in which the limitation of the pretreatment of the carboxylic anhydride by heating it in the presence of a diepoxide to an apparent dissolution of the carboxylic acid anhydride in the diepoxide, has been omitted. The scope of this set of claims is thus broader than that of the set of claims underlying the decision under appeal. Consequently, the new set of claims, if admitted by the Board, would result in a contravention of the principle of "Reformatio in Peius" set out in the decision of the Enlarged Board referred to above.

2.1.2. The argument of the Respondent at the oral proceedings, that the new independent claim had been introduced in response to an objection, under Article 123(2) EPC, to a dependent claim of the set of claims underlying the decision under appeal, whilst certainly providing an explanation of why the amendment was made, does not, in the Board's view, justify a departure from the principles referred to above, particularly since this was not the only possible way of meeting the official objection.

2.1.3. Consequently, the main request was refused.

2.2. Auxiliary request

Claim 1 corresponds to Claim 1 underlying the decision under appeal, apart from (i) the insertion of appropriate punctuation marks (commas) at the ends of lines and (ii) the amendment, following the specific objection of the Board (communication dated 29 May 1998, "preliminary observations", point 1) of the phrase "heating .... to a temperature ranging from 60 to 150 C" to "heating .... at a temperature ranging from 60 to 150 C". This amendment finds a basis in the documents of the application as filed (page 7, lines 13 to 16) as well as in the patent as granted (page 4, lines 38 to 40).

Claims 2 to 9 and 10 to 13 correspond to Claims 2 to 9 and 11 to 14 respectively underlying the decision under appeal.

No objection has been raised under Article 123(2) or 123(3) EPC against these claims and the Board sees no reason to take a different view. Consequently, no objection under Article 123 EPC arises in respect of the claims of this request.

The text of the description, which is made up of pages 2, 2a, 2b, 3, 4, 5, 6 and 7 filed during the oral proceedings corresponds to that underlying the decision under appeal except for necessary amendments consequential upon the amendment of the claims. No objection was raised, or, in the Board's view arises, in respect of this description, which is therefore regarded as clearly allowable.

3. The patent in suit; the technical problem

The patent in suit is concerned with compositions suitable for use as adhesives and sealants, and relates in particular to a one-package stable curable composition comprising:

(a) a polydiene;

(b) a polyepoxide having at least two 1,2 epoxy groups; and

(c) a carboxylic acid anhydride (Claim 1).

Such a composition is, however, known from E1, which was generally agreed to represent the closest state of the art.

3.1. According to E1, there is disclosed a curable epoxy resin adhesive and sealant composition comprising an epoxy resin and vulcanised rubber particles, wherein the rubber particles have been vulcanised by a vulcanising system (e.g. sulphur and zinc; column 4, lines 23 and 29 to 30; Examples 12 and 13) with the epoxy resin remaining uncured at the time of vulcanisation (Claim 1; column 2, lines 53 to 60).

The cured rubber may be a polydiene rubber which preferably has a functional group capable of bonding with the epoxy resin, and should be incompatible with the epoxy resin (column 3, lines 31 to 65). An acid anhydride may be present as curing agent for the epoxy resin (column 6, lines 17 to 24).

3.2. According to a typical example, a composition comprising:

Epoxy resin (Epikote 1001) ................100g

Liquid rubber (Hycar CBTN 1300 X 8).........10 g

Vulcanizing agent: sulphur powder............1 g

zinc oxide ..................................0.4 g

stearic acid ................................0.2 g

Vulcanization accelerator (2 components).....1.0 g

is formed by adding the liquid rubber having been treated with the vulcanising ingredients to the liquid epoxy resin at 150 C with vigorous stirring with a homomixer (2 000 to 10 000 rpm) and allowing to react for 30 min., the resulting particle size of the vulcanised rubber being 0.5 to 2µm (Example 12 in conjunction with Example 1).

A heat-curable one-pack type adhesive can be prepared by mixing the above composition 50:50 with the following ingredients (column 10, lines 14 to 55; "Experiments", Table 1, Example 12):

Epoxy resin (Epikote 828)......................50 pbw

Dicyandiamide...................................5 pbw

Curezole 2P4MHZ

2-phenyl-4-methyl-5-hydroxymethylimidazole).....4 pbw

anhydrous silicic acid..........................3 pbw

Al powder......................................80 pbw

On coating steel panels according to JIS G3141, curing at 150 C for 30 min. and subjecting to a T-peel test, a T-peel strength of 8.0 x 103 N/m is obtained.

Such compositions, whilst showing good flexibility and mechanical strength when cured (col. 2, lines 20 to 22), have not been shown to be capable of meeting the diversity and disparity of adhesive/sealant requirements associated with automobile manufacture, and in particular to have a wide latitude of cure temperatures with the ability to cure both at relatively low and relatively high temperatures and adhesion to differing substrates, together with storage stability.

3.3. Compared with this state of the art, the technical problem objectively arising may be seen as the search for a single "all-round" curable composition having a wide latitude of curing temperatures, capable of achieving comparable physical properties at both extremes, and displaying excellent adhesion to substrates, especially metals, whilst being storage stable (patent in suit, page 2, lines 10 to 20).

3.4. The solution proposed according to Claim 1 of the patent in suit is:

(i) to provide the rubber ingredient in unvulcanised form, for simultaneous vulcanisation with the epoxy resin on curing, using a sulphur and zinc containing vulcanising system for both rubber and epoxy;

(ii) the rubber being a non-functional polydiene; and

(iii) adding, as a further ingredient promoting adhesion to metal, a carboxylic acid anhydride which has been pretreated by heating in the presence of a diepoxide for at least five minutes at a temperature ranging from 60 to 150 C to an apparent dissolution of the anhydride, whereby the latter remains essentially unreacted with the diepoxide.

3.5. It can be seen from the description that the compositions according to the patent in suit are stated to be capable of being cured within a range of from 104 to 288 C for a time of about 10 to about 60 minutes, in particular by baking at a temperature between 163 and 204 C for from 15 to 30 min., whilst achieving comparable physical properties at both extremes, as well as having outstanding adhesion to a variety of substrates, especially metals, and particularly oily metal. They are also stated to have a package stability for prolonged periods of up to three months (page 5, lines 37 to 50). It can furthermore be seen from the illustrative Example, that a composition according to the patent in suit achieves a Lap Shear Strength of between 1.9 and 2.8 newtons/mm2 at curing temperatures between 110 C and 205 C, a T-peel strength (ASTM D1876) of 2.6 kilonewtons/m, an elongation of 180% and a tensile strength of 3.5 newtons/mm2 (Example 1, pages 6, 7).

In this connection, whilst the T-peel values achieved according to the patent in suit are numerically smaller than those quoted in E1, the measurement standard is different in each case (JIS vs ASTM). Consequently it cannot be concluded that the values obtained according to the patent in suit are worse than those according to E1.

3.5.1. The argument of the Appellant concerning the variation of the Lap Shear Strength, which showed an almost 50% increase at a higher curing temperature (section IV.(c)iii), above), is irrelevant, since there is no indication in E1 of the extent of variation of Lap Shear Strength at different curing temperatures. In any case, such an argument does not demonstrate that the minimum such strength achieved is below the useful threshold (page 2, lines 12 to 15). The onus of proof was, however, on the Appellant, to show that the variation in strength was less acceptable than that of the closest state of the art, in the context of the relevant use. This onus has not been discharged. Consequently, it must be assumed that the curing behaviour at the various curing temperatures provides an adequate alternative.

3.5.2. The argument of the Appellant concerning storage stability is no longer applicable (section IV.(c)i), above), since the offending example, which related to a different composition, has been deleted. For the rest, no evidence of deficient shelf stability has been filed, although the onus was on the Appellant to show this. Consequently, there is no basis for doubting the statements in the patent in suit.

3.5.3. Finally, the allegation of the Appellant, that the presence of the pretreated carboxylic acid anhydride did not promote adhesion to metal (section IV.(c)ii), above), was based on a comparison with a composition exemplified in another document (EP-A-309 904). Whilst this document is admittedly from the same Applicant, and even has the same filing date as the patent in suit, the exemplified composition referred to (Example 1) is not otherwise identical with that of the patent in suit. Consequently, there is no convincing basis for doubting the statement in the patent in suit that this component does indeed contribute to promoting the adhesion of the composition to metal (page 4, lines 19 to 20).

3.5.4. In the light of the above, the Board finds it plausible that the claimed measures provide an effective solution of the stated problem.

4. Novelty

It was explicitly admitted by the Appellant at the oral proceedings before the Board, that none of the cited documents disclosed feature iii) of the solution of the technical problem (section 3.4, above). Nor does the Board see any reason to take a different view. Consequently, the claimed subject-matter is held to be novel.

5. Inventive step

In order to assess the question of inventive step, it is necessary to pose the question whether the measures (i), (ii) and (iii) forming, in combination, the solution of the relevant technical problem, would suggest themselves to the skilled person, starting from E1, and searching for an alternative, storage stable "all-round" sealant adhesive suitable for use in automobile production.

5.1. It is an essential requirement of the adhesives of E1, that the rubber is vulcanised before the epoxy resin is cured. This "designed in" incompatibility between the rubber component and the epoxy resin has profound implications for the nature and extent of any "modifications" which might be considered by the skilled person.

5.1.1. Firstly, there is no suggestion in E1 that curing could be carried out at widely varying temperatures. On the contrary, whilst a relatively restricted range of 130 to 170 C is disclosed for the rubber vulcanisation (column 5, lines 22 to 28), curing of the epoxy component according to the examples is carried out only at 150 C. The fact that, according to E1, there are two different curing steps would, in the Board's view, in any case stand in the way of developing a modification with a single, but widely variable curing temperature.

5.1.2. Furthermore, whatever modifications the skilled person might contemplate making in the composition according to E1, the one feature he would not, in the normal course of development work, consider altering, is the obligatory incompatibility of the epoxy and rubber, and in particular the pre-vulcanisation of the latter. This is because the consequence(s) of changing a feature so essential to and definitive of the compositions according to E1 could not, even in principle, be remotely predicted. Consequently, there is no hint in E1 to carry out step (i) of the solution of the stated problem.

5.1.3. Quite apart from the above, the preferred liquid rubber component according to E1 has a functional group capable of bonding with the epoxy resin at one or both terminals and/or intermediate of the chain of the polymer or copolymer (column 3, lines 51 to 61). Consequently, there is no incentive for the skilled person to choose a less preferred non-functional polydiene in accordance with step ii) of the solution of the stated problem.

5.1.4. Finally, E1 discloses a carboxylic anhydride only in terms of being a curing agent for the epoxy resin component. It would therefore be expected by the skilled person to be consumed during the curing reaction. In particular, there is no mention of the presence of such an anhydride as an adhesion promoting agent, let alone of it being dissolved in an epoxy resin by heating. Consequently, there is no hint arising from E1 to carry out step (iii) of the solution of the stated problem.

5.1.5. In summary, the disclosure of E1 gives no hint to any of the measures forming the solution of the technical problem.

5.2. According to E3 (page 16-16, "Natural and Synthetic Rubbers"), which is an exerpt from a standard work on epoxy resins, "Natural and most synthetic rubbers, such as styrene-butadiene and acrylonitrile-butadiene polymers, contain no groups normally reactive with the epoxy groups directly but they do contain reactive unsaturation. The unsaturation may be epoxidised with peracids..., or the unsaturated material may be used in blend with an epoxy resin. During the process of vulcanisation by sulfur, thiol groups may be developed which are capable of reacting with at least some types of epoxy groups, thus introducing the epoxies into the cured network... . Typical is the coreaction of gum nitrile stocks with DGEBA (mol. wt. 900), giving properties as indicated in Tables 16-19 and 16-20. With SBR polymers compatibility toward DGEBA resins is enhanced through the addition of an alkylaniline... ."

In the above quotation, DGEBA stands for diglycidyl ether of bisphenol A, and SBR for styrene-butadiene rubber.

5.2.1. Whilst the relevant entries in Tables 16-19 and 16-20 admittedly show extremely high values of tensile strength and elongation of the products of "Gum nitrile rubber stock" and DGEBA, cured with a zinc and sulphur containing curing agent, there is no indication of adhesive strength. Consequently, the skilled person seeking an alternative adhesive would not regard the teaching of E3 as relevant to the solution of the technical problem.

5.2.2. Even if the skilled person were nevertheless to attempt to make use of the teaching of E3 in this respect, the "gum nitrile rubber stock" used in Table 16-19 does not correspond to the required non-functional polydiene. Furthermore, it is implicit in the reference, in the next sentence, to SBR polymers (which could be non-functional), that the principal result of introduction of epoxies into the cured network is to improve "compatibility" toward DGEBA resins. This is, however, diametrically opposed to the teaching of E1 which, as stated above, requires incompatibility with the epoxy resin as a pre-requisite of the polydiene component. Consequently, the skilled person would have no incentive to combine the disclosures of E1 and E3.

5.2.3. Finally, if the skilled person were nevertheless not only closely to consider the teaching of E3, in spite of its apparent non-relevance (section 5.2.1, above), and furthermore to utilise its teaching to modify the essential teaching of E1, in spite of the lack of combinability (section 5.2.2, above), the result would still not correspond to the solution of the stated problem, because there is no suggestion in either document, or elsewhere, to carry out step (iii) of the solution.

5.2.4. The argument of the Appellant, that it belonged to the basic general knowledge of the skilled person to carry out the anhydride pre-treatment step, was unsupported by any documentary reference, or indeed any other evidence. Even if this deficiency were overlooked, however, there was still no reason why the skilled person should associate such a step with providing enhanced adhesion to metal (cf. section 3.5.3, above).

5.2.5. Consequently, the solution of the stated problem does not arise in an obvious way from a consideration of the disclosures of E3 and E1 in combination.

5.3. In other words, the subject-matter of Claim 1 involves an inventive step in the sense of Article 56 EPC. This conclusion is equally valid for the subject-matter of independent Claim 13, since this requires, as an essential feature, the application of the composition according to Claim 1. By the same token, the subject-matter of Claims 2 to 12, which are directly or indirectly dependent upon Claim 1, also involves an inventive step. Consequently, the auxiliary request is allowable.