T 0069/83 (Thermoplastic moulding compositions) of 5.4.1984

European Case Law Identifier: ECLI:EP:BA:1984:T006983.19840405
Date of decision: 05 April 1984
Case number: T 0069/83
Application number: 78101145.7
IPC class: -
Language of proceedings: DE
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Documentation of the appeal procedure can be found in the Register
Bibliographic information is available in: DE | EN | FR
Versions: OJ
Title of application: -
Applicant name: Bayer
Opponent name: -
Board: 3.3.01
Headnote: I. The mere fact that the disadvantage resulting from the omission of a component of a mixture recognised in the art as advantageous is accepted does not mean that a prejudice has been overcome.
II. Where, because of an essential part of the technical problem being addressed, the state of the art obliges a skilled person to adopt a certain solution, that solution is not automatically rendered inventive by the fact that it also unexpectedly solves part of the problem.
Relevant legal provisions:
European Patent Convention 1973 Art 56
European Patent Convention 1973 Art 52
Keywords: Closest state of the art
Inventive step - omission of a component of a mixture
Obvious effect
Prejudice (denied)


Cited decisions:
Citing decisions:
T 0021/89
T 0146/89
T 0541/89
T 0713/90
T 0920/90
T 0412/93
T 0431/93
T 0703/93
T 0663/94
T 0681/94
T 0848/94
T 0317/95
T 0741/95
T 0777/95
T 0422/97
T 0956/98
T 0164/00
T 0184/00
T 0660/00
T 0866/01
T 1013/02
T 0881/05
T 0030/10
T 2043/12
T 1311/13

Summary of Facts and Submissions

I. European patent 0 001 624 was granted on 15 July 1981 on the basis of a single patent claim in response to European patent application 78 101 145.7 filed on 14 October 1978 claiming the priority of the earlier German application of 26 October 1977. The claim reads as follows:

"Thermoplastic moulding compositions composed of:

A 25 to 95% by weight of a graft polymer of 70 to 30% by weight of a mixture of 95 to 50% by weight of styrene and 5 to 50% by weight of acrylonitrile on 30 to 70% by weight of an EPDM rubber, and

B 5 to 75% by weight of a terpolymer of acrylonitrile, maleic acid anhydride and styrene, characterised in that the terpolymer contains 10 to 30% by weight of acrylonitrile 7.5 to 15% by weight of maleic acid anhydride and 82.5 to 55% by weight of styrene in copolymerised form, the indicated percentages adding up to 100."

The following abbreviations will be used throughout the Decision:

AN=acrylonitrile; S=styrene; MA=maleic acid anhydride; SAN=styrene/acrylonitrile resin; SAN-MA=styrene/acrylonitrile/maleic acid anhydride resin; ABS=graft polymer of styrene and acrylonitrile on polybutadiene; AES=graft polymer of styrene and acrylonitrile on EPDM rubber.

II. The opponents filed opposition against the European patent on 23 January and 3 April 1982 respectively, requesting that it be revoked on the grounds of lack of novelty and inventive step. The opposition was supported by a new state of the art, viz. (1) DE-A-1 949 487 (2) DE-A-1 965 283 (3) GB-A-1 375 508. After the period allowed for opposition had expired a further citation was added, namely (4) "EPDM elastomers in rubber modified plastics" in: Rubber Chemistry and Technology, September 1971, Volume 44 (4), pages 1130-1146.

III. The Opposition Division rejected the opposition by a decision of 4 November 1982, stating that not only was the subject-matter of the patent novel but that it also represented an inventive selection from the state of the art as described in (1). This selection involved both chosing EPDM rubber from all rubbers having a glass transition temperature below -30°C as the backbone, and choosing certain terpolymers from a group that included such terpolymers in substantially greater quantity ratios, MA-S copolymers, and mixtures of both groups with SAN copolymers. Moreover, according to the invention the proportion of graft polymer could be almost double that known in the art. The operation of selection, therefore, was by no means simply a matter of choosing the only class of rubber covered by the claim of (1) not mentioned in that document. Comparative tests showed that the combination of choices resulted in an enhanced workability of the moulding compositions of the invention as temperature rose, whereas in the case of similar polybutadiene-based products workability deteriorated (description page 4, lines 36 ff). The mere fact that EPDM rubber was chosen as the backbone for component A resulted, it was maintained, in a reversal of the temperature-dependence in the spiral flow test as compared with the state of the art with polybutadiene as the backbone used. This result was unexpected. The second opponent might deny the validity of this comparative test because Example 25 of (1) should, as the nearest state of the art, have been taken into account for comparison purposes. However, the onus was on the opponents to demonstrate by their own tests that such a comparison would have carried greater conviction. Moreover, it was stated in (1) that although the moulding compositions there described could, like those of the present patent, be made of a two-component mixture of graft polymer and terpolymer, the presence of a third component, namely an SAN copolymer, was particularly advantageous (cf. page 3, paragraph 3, lines 4-8). In the circumstances, therefore, even an expert would have been disinclined to choose the combination claimed by the patent proprietor. The remaining citations were even less related to the invention. The second opponent appealed against this decision on 30 December 1982, at the same time paying the appropriate fee. Grounds for the appeal filed on 28 February 1983 were essentially as follows: It was known from (1) that a mixture of an SAN-MA terpolymer and an SAN graft polymer on a rubber had a higher Vicat temperature than the graft polymer on its own. Furthermore, (3) taught that graft copolymers on EPDM rubber showed improved resistance to oxidation and light radiation. It had therefore been obvious to combine a graft polymer on EPDM with a terpolymer as described in (1). Moreover, the obvious subject-matter of the application could not be rendered patentable by an additional effect. It was hence requested that the patent be revoked.

IV. The proprietor of the patent contested the opponent's argument and requested that the appeal be rejected.

V. In a communication to the various parties the Board of Appeal sought to determine the technical problem which formed the basis of the disputed patent and which was important for assessing inventive step. In this connection it referred mainly to (3) and indicated that the moulding compositions there described only differed from those of the disputed patent in the fact that the SAN copolymer had been replaced by an SAN-MA terpolymer, which according to the specification resulted in apparently equally good flow properties and toughness and a heat resistance that was at least 12°C higher. Accordingly, the problem could be considered to have been to improve this particular property. However, a question that had to be asked was whether the solution proposed to this problem was not obvious in view of (1), according to which the high heat resistance was obviously attributable to the SAN-MA component (cf. Example 25 and page 5, lines 1-4). As far as the general remarks in the specification regarding high weather resistance, heat resistance, toughness and ease of workability were concerned, it was as yet impossible to say whether an improvement had been achieved over the moulding compositions covered by citation (3). Referring to the comparative test, the Board made the point that so far the practical significance of the effect achieved had not been explained in such a way as to assist with a definition of the problem.

VI. In his response the patent proprietor put forward the view that the decision as to whether (1) or (3) was the closest state of the art and hence relevant in determining the problem to be solved was a matter for the Board of Appeal. Broadly speaking, the disputed patent related to a mixture of SAN-MA and AES, citation (3) to a mixture of SAN and AES, and citation (1) to a mixture of SAN-MA and ABS. In fact, the similarities and differences had to be considered more closely. The composition of the various products, for instance, needed to be taken into account and it had to be borne in mind that of 27 examples in (1) SAN-MA occurred in only one, and then in combination with a graft product which was not an ABS but a graft polymer having an acrylate rubber backbone. If (1) were to be regarded as the closest state of the art, then the unexpected effect had to be seen as the improvement in workability as temperature rose. If (3) were to be considered the closest state of the art, then the unexpected effect was the substantial increase in heat resistance without detriment to other essential properties. Years of experience had shown that an improvement in one property of polymer products of the type under discussion could only be achieved at the cost of a deterioration in other properties. Thus, an improvement in dimensional stability under heat normally went hand in hand with lessened workability, while an improvement in toughness brought reduced surface quality. The effect, therefore, should not be seen as lying solely in the improved dimensional stability under heat but also in the fact that this improvement did not result in a deterioration in other properties. This was certainly not the case of (1), where although it was stated (page 2, paragraph 2) that the products described showed increased dimensional stability under heat, mechanical properties were referred to merely as acceptable and not as good or exceptional.

Reasons for the Decision

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

2. The first question which has to be decided is which of the two patent documents (1) and (3) is more closely related to the subject-matter of the disputed patent. Citation (3) relates to thermoplastic moulding compositions in the form of a mixture of AES (component A) and SAN-MA (component B), proportions both within and between the individual components being kept within the limits defined in more detail in the claim. The mixtures are notable particularly for their high weather resistance, dimensional stability under heat, toughness and ease of workability (see page 3, lines 37-38). The Examining Division regarded this subject-matter as involving a selection from (1) and hence the latter as the most closely related citation. Broadly speaking, it concerns mixtures of ABS and SAN-MA which differ from those described in the claim of the disputed patent in that ABS has been replaced by AES, hence in the graft polymer component. If on the other hand citation (3) - which, in general terms, describes mixtures of AES and SAN - is taken as the basis for comparison, the difference between the mixtures it describes and those of the disputed patent lies in the fact that SAN has been replaced by SAN-MA and hence in the copolymer component. At first glance, therefore, the decision as to whether to take (1) or (3) as the basis of reference in considering the patent subject-matter would appear arbitrary. A more detailed consideration of the ratio of the two components within the mixture does not give any further assistance here because the moulding compositions described in (3) and those claimed in the disputed patent may each contain either of the two constituents as the main component (see (3) claims 1, 12 and 16 in conjunction with page 3, lines 57-72 and 106-108). The citation (1) similarly fails to specify a main component, particularly nearer the borderline (50:50). Nor does a comparison of the compositions of the various individual components help (cf. the claim of the disputed patent with that of (1), as also (3), claims 1 and 12 and Tables 1 and 2). In cases where a consideration of composition in conjunction with the general field of application (thermoplastic moulding compositions) does not help in determining the closest art, the particular properties of the mixtures which it is aimed to enhance may provide a key. As initially mentioned, the purpose of the mixtures claimed is good weather resistance, a high degree of toughness and ease of workability. Given these requirements, mixtures based on ABS graft polymers, as also those described in (1) must be eliminated from the outset on the grounds of insufficient weather resistance, whereas AES graft polymer based mixtures - which are also very tough - are suitable (see (3), page 1, lines 37-44, page 2, lines 1-9 and the disputed European patent specification page 2, lines 3-7). Inadequate weather resistance is inherent in the ABS system and cannot be influenced, as can dimensional stability under heat and workability, by varying the copolymer component (see (1), page 3, paragraph 3, and page 5, paragraph 1) but only by the addition of anti-aging agents and ultraviolet stabilisers; this means that in terms of composition the concept underlying citation (1) is less closely related to the patent subject-matter while citation (3) is closer. Citation (3) must therefore be taken as the starting point for determining the technical purpose of the patent concerned.

3. Citation (3), as has already been said, describes AES graft polymers (see Claim 1 in conjunction with Claim 16, page 3, lines 57-72 in conjunction with page 2, lines 77-119) and thermoplastic mixtures of such polymers with SAN (see claim 16, page 3, lines 57-72 in conjunction with page 2, lines 116-119) which are highly weather-resistant (see page 1), lines 37-50) and possess good mechanical and physical properties, especially that of high notch impact strength (see page 2, lines 1-6, page 3, lines 51-56 and Examples 1-21). In order to ascertain the technical problem addressed by the disputed patent it has to be asked what by comparison is achieved by the mixtures the patent describes. The patent proprietor claims improved dimensional stability under heat in combination with otherwise good properties such as toughness and flow. Table 1 of the European patent specification in question, in which AES-SAN-MA (Examples 1-5) and AES-SAN (Example 6) are considered in terms of impact resistance (an), notch impact strength (ak), dimensional stability under heat (Vicat) and flow properties (MFI) shows the compounds of Examples 1-5 as offering a marked improvement in dimensional stability under heat (11-16°C for Vicat B). No similar improvement is noticeable in terms of notch impact strength, since values fluctuate more or less markedly upwards and downwards from the value for the substance of comparison (Example 6) according to the temperature. In terms of flow properties the mixtures of the patent (Examples 1-5) are inferior to the AES-SAN mixtures. The technical problem by comparison with (3), therefore, was to propose AES graft polymer-based thermoplastic moulding compositions which whilst also weather-resistant display improved dimensional stability under heat in conjunction with comparable toughness (impact resistance), and accepted reduced properties of flow, i.e. workability (see letter from the patent proprietor of 14 September 1983, page 2, paragraph 2). The mixtures of AES graft polymers and SAN-MA terpolymers more closely defined in the patent claim were devised in order to solve this problem.

4. This teaching is indisputably not derivable from the reference state of the art and is therefore novel. This makes it necessary to consider whether the teaching involves an inventive step. As already mentioned, the subject-matter of the disputed patent differs from the thermoplastic mixtures described in (3) mainly in the fact that the SAN copolymer has been replaced by the SAN-MA terpolymer giving rise to the question of whether (1) provided a suggestion as to the approach to be adopted. According to the proposal contained in this specification, the disadvantage of the low dimensional stability under heat of thermoplastic mixtures of SAN copolymers on the one hand and graft polymers of rubber with S and AN on the other (see page 1, paragraph 1) is overcome by the addition of an S-MA copolymer or SAN-MA terpolymer (embodiment in which the components A, B and C of the patent claim are present in the mixture) or by replacing SAN copolymers by a terpolymer of the above-mentioned type (mixture of components A and C as claimed in the patent claim). The paragraph beginning on page 4 and ending on page 5 confirms the compatibility of the three components which results in the high dimensional stability under heat of the S-MA component (a) - which according to the claim may also be SAN-MA - the good properties of the SAN component (b) and the toughness of the graft polymer component (c) being maintained. The good properties of the optional component (b) are, moreover, seen not only in a better resistance to solvent but in an improvement in the properties of workability with which we are concerned here (see page 3, lines 18-22). From this it may be concluded that every component makes its own particular contribution to the useful properties of the mixture without influencing one another unfavourably. This contradicts the unsubstantiated contention of the patent proprietor that it has been known for years that an improvement in a property of the polymer products here involved is only obtained at the expense of other properties. A person skilled in the art who, starting from thermoplastic compositions as described in (3), was mainly concerned with improving dimensional stability under heat should, relying on the information contained in (1), expect from the cumulative properties of the constituent components that the SAN-MA terpolymer responsible for dimensional stability under heat would produce this effect in the case of similar AES-based mixtures as well. It is not intended in saying this to disregard the specific structural characteristics of the AES graft polymers as compared with ABS graft polymers (see the European patent specification, page 1, paragraph 1) which are responsible for the improved weather resistance of the AES system. However, each of the two graft polymer systems mentioned imparts the necessary toughness to the thermoplastic moulding compositions described in (1) and (3), so that the systems could be seen as interchangeable in this regard without any fear that this and other properties might be impaired when the SAN copolymer was replaced by the SAN-MA terpolymer in the thermoplastic compositions of (3). A skilled person who, faced with the problem of improving the dimensional stability under heat of thermoplastic materials described in (3) without impairing their toughness, followed the teaching of (1) and suggested replacing SAN by SAN-MA, would, however, have been aware that the absence of the SAN component resulting from this exchange would lead to lessened flow properties, since the presence of this component improves the workability of the ABS graft polymer/SAN-MA mixture (see page 3, lines 18-22). The reduction in the flow properties of such thermoplastic materials is in fact observable (see the European patent specification Table 1, column MFI, Example 6 as compared with Examples 1-5) and accepted, so that in evolving the compositions as described in the disputed patent the patent proprietor has only taught what was to be expected given the state of the art. The omission of a component regarded in the present state of the art as advantageous (component B in (1)) thus suggests conscious acceptance of a disadvantage, not the overcoming of a prejudice as thought by the Examining Division. When the patent proprietor claims that the similarities and differences should be looked at much more closely, especially since of the 27 Examples of moulding compositions described in (1) the SAN-MA combination occurs only in one (Example 25) and then in combination with a graft polymer having an acrylate rubber backbone (see Example 25 in conjunction with page 5, last line and page 6, paragraph 3), he is concentrating inadmissibly on the examples in this specification. Apart from the fact that only 14 of these examples (Examples 14-27) represent the mixtures claimed, according to the case law of the Boards of Appeal all previously disclosed embodiments which might have offered a suggestion as to how to solve the problem to a skilled practitioner must be considered when assessing inventive step, regardless of whether they have been particularly emphasised (see T 24/81 "Metal refining", in Official Journal of the European Patent Office 4/1983, page 133, especially Headnote

II). As stated, this requirement applies both to the SAN-MA terpolymer as the only alternative to the S-MA copolymer (see patent claim and page 2, 4th and 5th lines from below) as also to the acrylate rubber based graft polymer (see page 6, paragraph 4).

5. The comparative test referred to in the present European patent specification also played a role in proceedings before the Examining Division because the results of the spiral flow test were regarded as unexpected and as justifying the inventive choice from (1). The result shows that the type of graft polymer in the mixture with the SAN-MA terpolymer influences the workability of the mixture differently at temperatures above 220°C and rising, doing so favourably when AES is used and unfavourably when ABS is used. According to information from the patent proprietor, the result is that the thermoplastic materials described in the disputed patent fill the injection mould more completely and rapidly and can thus be moulded more quickly than those of (1). To be relevant to the assessment of inventive step a comparative test must be based on the closest state of the art. As mentioned in point 2 above, the thermoplastic materials of (1) do not meet this requirement because a skilled person would not have tried to use such materials on an ABS base to achieve the desired improvement because of their inadequate weather resistance. But even if the comparative test is disregarded it remains a fact that the workability of the compositions described in the disputed patent improves at temperatures above 220°C and rising. The question of whether this effect is - as the patent proprietor states in the specification - only to be observed in the combination claimed need not be pursued here, since even if unexpected it would still suggest itself to a person skilled in the art acting routinely and not inventively because of the obviousness for other reasons of just these materials and thus cannot be used as an argument for inventive step.

6. It must be conceded that the ranges given in the claim of the disputed patent for the three components in each case of the AES graft polymer and of the SAN-MA terpolymer are narrower than in either (3),(see claims 1 and 12, page 3 lines 7-10 and Examples 1-21) or (1) (see the claim and page 2, lines 4/5 from below). The same is true of the proportion of the graft polymer in the thermoplastic moulding composition claimed here as compared with that of (3) (see page 3, lines 105-109 and Examples 20 and 21). These are largely minor and in no case important limitations viv-à-vis the known art. It is neither recognisable nor substantiated that this is where the actual invention lies. Such changes have no inventive status because they fall within the routine activity of a person skilled in the art.

7. The result arrived at if (1) is taken as the closest state of the art instead of (3), and if the technical problem addressed by the present patent is taken as that of improving weather resistance without detriment to dimensional stability under heat and toughness, does not lead to a more favourable outcome for the patent proprietor. Here the intention of improving weather resistance has already led a person skilled in the art to change from the ABS to the AES system for the graft polymer backbone as taught in (3). Since both graft polymers impart a high degree of toughness to the thermoplastic materials there was no reason for thinking that the change might be to the detriment of this property. In addition, the presence of the SAN-MA terpolymers pointed to maintenance of an equally good dimensional stability under heat. To turn now to the flow properties of such materials: it was to be expected that omission of a SAN component as described in (1) that favourably influenced workability would lead to a corresponding decrease in this property. That this is so is confirmed in practice (see Table 1, column headed "MFI at 220°C" in the disputed patent). The comparative spiral flow test (page 4 of the specification) shows at 220°C very similar values for ABS/SAN-MA mixtures (flow lenght 30 cm) and AES/SAN-MA mixtures (flow length 32 cm). Only at higher temperatures does the length of flow of the moulding compositions described in the disputed patent increase to any marked degree whereas length of flow of the material described in (1) gradually decreases. Even if this effect (i.e. that moulding compositions offer better and more rapid workability at higher temperatures) is included in the statement of the problem and it is conceded that the state of the art did not provide a solution, a lack of knowledge on the part of the person skilled in the art nevertheless made experimentation necessary. The most obvious possibility was the experiment with the AES/SAN-MA mixture, because thermoplastic moulding compositions of this kind looked likely to solve the other parts of the problem already referred to. Accordingly the solution to this particular aspect of the problem was bound to be obvious to a person of the art acting routinely. In summary, therefore, it may be said that (1) provided the initial impulse for solving the problem in relation to (3) in the manner proposed by the disputed patent, which must therefore be regarded as obvious and lacking in inventiveness.


For these reasons, it is decided that:

1. The decision of the Opposition Division of the European Patent Office of 4 November 1982 is set aside.

2. European patent No. 0 001 624 is revoked.

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