T 0483/88 10-08-1990

Reasons for the Decision

1. The appeal complies with Articles 106 to 108 and Rule 64 EPC and is, therefore, admissible.

2. The Appellant has filed fresh claims several times during opposition proceedings, again together with the appeal grounds, and once more on 10 July 1990. This is, in principle, an undesirable practice, and the Board has therefore considered whether the latest set of claims should be admitted at all. It has in this case decided to do so, because the said set differs from the preceding one only in the omission of Claim 7, a claim which the Board would anyway not have admitted because it had no counterpart in the granted claims (cf. T 295/87 of 6 December 1988, "Polyetherketones/ICI", to be published). In these circumstances, the latest set of claims served to render the claims in the appeal clearly allowable and was therefore to be admitted (cf. T 153/85, "Alternative Claims/AMOCO", OJ EPO 1988,1).

3. The claims before the Board meet the requirements of Article 123(2) and (3) EPC.

Claim 1 differs from the granted Claim 1 essentially in that the relative proportions of the SAN resin and the nitrile rubber in the compositions claimed are amended, that the rubber particles are defined by their number average particle size and that the compositions are designated as elastoplastic. These amendments, in particular the numerical data inserted, find support in Claims 2 and 7 as originally filed and as granted. Dependent Claims 2 to 5 and process Claim 6, correspond to Claims 3 and 8 to 11 of the originally filed documents and of the published patent specification.

4. Citation (9) was - without appropriate justification - mentioned for the first time by the Respondent with his Statement of Grounds of Appeal and is, therefore, regarded as not submitted in due time within the meaning of Article 114(2) EPC. Having checked the relevance of (9), the Board considers it not relevant in the sense of influencing the outcome of this case and decides, in exercising its discretion conferred to it by Article 114 EPC, to disregard it.

5. The patent in suit is concerned with thermoplastic compositions comprising blends of thermoplastic styrene-acrylonitrile (SAN) resin and nitrile rubber exhibiting improved processing characteristics and physical properties and with a process for the production of such compositions.

The blends contain sufficient thermoplastic SAN resin to impart thermoplasticity and sufficient gelled nitrile rubber to impart rubberlike properties such as high extensibility and toughness. They are processable to products which form continuous sheets. The sheets can be reprocessed by melting and shaping.

6. The sole substantive issue to be decided in this appeal is the question of novelty of the subject-matter of the patent in suit vis-à-vis document (1).

6.1. The thermoplastic compositions of instant Claim 1 can be briefly characterised by the following features:

the blends comprise 25 to 40 p.b.w. of SAN resin and 75 to 60 p.b.w. of nitrile rubber; the rubber component is cured with a rubber curative and has a toluene insoluble gel content of at least 85%; the rubber particles have a number average particle size of 50 "m or less and are dispersed in a matrix of SAN resin; the compositions are elastoplastic, i.e. they exhibit rubber-like elasticity yet are processable as a thermoplastic.

6.2. Document (1), on the other hand, describes composite thermoplastic homogeneous mixtures of a normally inelastic resinous thermoplastic SAN copolymer and a normally elastic rubbery butadiene-acrylonitrile copolymer, said thermoplastic resin comprising from 25 to 90% b.w. and said rubbery copolymer correspondingly comprising from 75 to 10% b.w. of the rubber-resin mixture (cf. Claim 3).

6.2.1. The rubbery copolymer of (1) is defined by its MEK-insoluble gel content, gel swelling index and Mooney viscosity. The MEK-insoluble gel content for the rubbery copolymer in the unvulcanised state should be from 40 to 100% b.w., with optimum results being achieved when the gel content ranges from 50 to 75%. If one of the three critical parameters specified for the rubbery copolymer falls outside the ranges indicated, the processing characteristics and the physical properties of the resulting blends with thermoplastic resins are impaired in one or more respects (column 3, paragraphs 2 and 4).

6.2.2. When determining the gel content of the rubber component by means of MEK or toluene it has to be observed that the two solvents exhibit entirely different solvent action upon the material in question. In the given example, a butadiene-acrylonitrile rubbery copolymer which was ground on the mill at 300°F (149°C) at the time when the toluene-insoluble gel level has reached 50% and 66% respectively, the MEK-insoluble level was only about 24% and 40% respectively (cf. column 2, paragraph 2). From these data it can be gathered that the toluene-insoluble gel level in general is higher than the MEK-gel level.

6.2.3. A closer study of the worked examples in (1) reveals that throughout 70/30 or 65/35 resin-rubber mixtures were investigated.

In Example 1, a commercial grade of an untreated and a hot-milled rubbery copolymer - the latter having a MEK-insoluble gel content of 65% - were compounded with sulphur and vulcanised for various times (30', 60' and 120' at 287°F) to determine the differences in physical properties of the untreated elastomer and the vulcanisate.

In Example 2, the aforementioned (unvulcanised) products were processed with SAN resin by banding the resin on a mill (at 300 to 320°F), then adding the rubber and blending thoroughly (10 to 12 minutes total milling time). The hot-milled rubber-resin mixtures exhibited improved physical properties over the untreated product. Further, it is mentioned that samples of rubber-resin mixtures prepared from the treated and the untreated rubber and containing a vulcanising system after vulcanisation in the conventional manner showed similar improvements in properties.

Rubbery copolymers, which were directly made by emulsion polymerisation, may contain a cross-linking monomer which is capable of joining molecule groups to form a cross-linked or gel structure. The cross-linking agent should be used in such a manner as to yield a product which is still rubber-like and can be handled by the usual rubber techniques. The amount of such cross-linking agent should, in general, range from 0.75 to 2% b.w. based on the weight of the other monomers present (cf. column 3, last paragraph, column 4, paragraph 1, column 11, lines 1-4). If the cross-linking agent, such as divinyl benzene, is added at the start of the emulsion polymerisation, the product obtained usually has from about 90 to 100% MEK-insoluble gel (cf. column 11, lines 18-23). Run G of Example 11, with a MEK-insoluble gel content of the hot-milled rubbery polymer of 89% and containing 1% divinyl benzene, was smooth in processing and gave, when blended with a resinous copolymer, satisfactory mixtures.

6.2.4. Specific mixtures containing from 25 up to 50% bw. of hard resin are disclosed in column 6, paragraph 5 of (1). These mixtures, after vulcanisation in the conventional manner, result in tough, flexible, leather-like materials. It is preferred to add vulcanising agents, such as sulphur, to the mixture and to vulcanise the resulting blends. The vulcanising agent should be used in such an amount as would vulcanise the rubbery copolymer to a soft vulcanised state if such rubbery copolymer were cured alone. Generally, from 0.5 to 5 parts of sulphur based on each 100 parts of total resin-rubber mix are employed.

6.3. When the claimed and the known systems are compared, it becomes evident that (1) does not expressly disclose at the places indicated SAN resin-nitrile rubber compositions having all the features specified in present Claim 1 of the patent in suit:

The claimed compositions are distinguished, in any case, from the known ones, referred to in Claim 3 of (1), in that they comprise a rubbery ingredient which is cured to the extent that its toluene-insoluble gel content is of at least 85% and which is present in the form of small dispersed particles (cf. section 6.2).

The compositions defined in the worked examples of (1) lie outside the scope of present Claim 1 and are, therefore, of minor relevance in deciding the issue of novelty; apart from this, in the samples with cured rubber copolymers, neither the gel content of the said rubber nor the particle size when blended with resin is reported (cf. section 6.2.3).

The statements in column 6, paragraph 5 of (1) imply that the balance to "the mixtures containing from 25 up to 50% by weight of the hard resin" would be 75 to 50% b.w. of rubber, which means that feed stock and amount of the claimed mixtures are in fact embraced by the known areas (cf. section 6.2.3). The resin-rubber mix is compounded with a vulcansing system and vulcanised in the conventional manner, i.e. under static conditions.

No further details are disclosed in (1), and in particular no instruction is available stating or implying that cross- linking of the rubbery copolymer has to be carried out to a point where it is 85% or more insoluble in toluene (or correspondingly in MEK) and that a dispersion of microsized, cross-linked rubber particles (having a number average particle size of 50 "m and less) has to be produced within the matrix of SAN resin, thus avoiding formation of thermoset, not reworkable material.

It is therefore at least questionable that the very general teaching of (1) - even if the additional information from the text of the description and the Examples quoted under sections 6.2.1 to 6.2.4 are taken into accout - would inevitably lead to the very specific compositions of present Claim 1 as alleged by the Respondent.

7. In a situation like this, where the parties make divergent submissions concerning the appearance of the claimed and known compositions, and the Board is in no position to establish the facts of its own motion, the burden of proof lies with the Respondent, who is the former Opponent. In the absence of any evidence, the Respondent's allegation that the blends of Claim 1 of the patent in suit are the same as those known from the prior art can only be held to be an unproven statement (cf. T 219/83, "Zeolites/BASF", OJ EPO 1986, 211).

8. For these reasons, document (1) is deemed not to be prejudicial as to novelty and the subject-matter of amended Claim 1 of the patent in suit is considered novel within the meaning of Article 54 EPC. The same applies mutatis mutandis to dependent Claims 2 to 5 and to process Claim 6. As a consequence, the decision of the Opposition Division can no longer be maintained.

9. The other requirements for patentability, in particular inventive step, have not yet been examined by the Opposition Division. The Board, therefore, deems it appropriate to remit the case to the first instance for further prosecution (Article 111(1) EPC).