T 0639/14 02-05-2018

Reasons for the Decision

1. Amendments - Article 123(2) EPC

The main request differs from the fifth auxiliary request found allowable by the opposition division only in that the dependency of claim 13 of the main request was amended so that it was dependent solely on claim 12. This amendment overcomes the appellant's objection to the amended dependency ("according to any one of claims 1 to 12") of claim 13 of the fifth auxiliary request held allowable by the opposition division (Article 123(2) and Rule 80 EPC). The appellant has not raised any objection to the main request with respect to added subject-matter. The board is also satisfied that the amendment complies with the requirements of Article 123(2) EPC.

2. Inventive step

2.1 The remaining issue in the appeal proceedings concerns inventive step. The appellant raised inventive step attacks in view of D1 alone and of D1 in combination with D2.

2.2 Closest prior art

2.2.1 In the same way as the patent, D1 refers to processes for the polymerisation of expandable styrene polymers, generically designated as EPS (e.g. column 1, lines 10 to 11; claim 11). It is an objective of D1 to produce EPS at accelerated conversion rates. The specific organic peroxide initiators used allow to obtain EPS resins with molecular weights suitable for typical EPS applications (column 3, lines 5 to 13). D1 can therefore be considered to represent the closest prior art. This is also common ground between the parties.

2.2.2 More precisely, D1 relates to the use of peroxide-based initiators in the production of expandable polystyrene which allow an effective conversion within an acceptable period of time (column 1, lines 20 to 24). According to D1, "intermediate" temperature peroxides with a one hour half-life temperature of from 101 to 111°C enhance conversion rates (column 4, lines 56 to 59). D1 discloses various such intermediate temperature peroxides, including 1-alkoxy-1-t-alkylperoxycyclohexane, where the t-alkyl group contains 4 to 8 and the alkoxy group 1 to 8 carbon atoms (column 5, lines 32 to 39). As an example of this type of peroxide initiator, 1-methoxy-1-t-amylperoxycyclohexane (TAPMC) is mentioned (column 5, lines 46 to 47).

In order to render the polystyrene beads obtained by the polymerisation process expandable, the addition of a blowing agent is required. This agent is typically a low molecular weight alkane such as butane, 2-methylbutane, pentane and cyclohexane (column 1, lines 49 to 53). Blowing agents can be added before or at any time during the polymerisation (column 7, lines 25 to 26), but also after the polymerisation process, in a second step, following isolation of the polymer beads (column 1, lines 57 to 59).

In example 11, one of the polymerisation initiators used is TAPMC, which falls within the scope of claim 1 of the main request. In fact, TAPMC is the only peroxide initiator of claim 1 exemplified in the opposed patent (column 3, lines 24 to 26 and examples of the invention 2, 3 and 4).

The addition of a blowing agent is not mentioned in example 11 of D1. Since, however, the whole teaching of D1 is directed to the production of EPS, the appellant argued that example 11 described the first part of the polymerisation process and that the blowing agent was added in a second step, after polymerisation of the styrene monomer.

2.2.3 A first contested point was precisely what part of D1 constitutes the closest prior art. The appellant's view was that example 11 of D1 (which uses TAPMC as an initiator) was the closest prior art, whereas the respondent considered the general disclosure of D1 (directed to "intermediate" temperature peroxides) to be the appropriate starting point for the assessment of inventive step.

2.2.4 Claim 1 of the main request relates to a process wherein the blowing agent pentane is added during the polymerisation step. In light of this, the board considers that the selection of example 11 as the closest prior art is the result of an ex post facto analysis, because the disclosure of this example is described within the context of a two-step process not covered by claim 1 of the main request. Thus, the board agrees with the respondent that the skilled person would rather start from the generic disclosure of D1, which leaves various possibilities for selecting (i) the initiator (which may or may not be a 1-alkoxy-1-t-alkylperoxycyclohexane), (ii) the point in time for the addition of the blowing agent, and (iii) the type of blowing agent.

2.2.5 Nevertheless, for the sake of argument and in the appellant's favour, the board will start in the following from example 11 of D1 for the assessment of inventive step.

2.3 The objective technical problem

2.3.1 The technical problem to be solved was a matter of dispute between the parties:

- The appellant saw the technical problem in the provision of an alternative process for making EPS.

- The respondent's view was that the technical problem resides in the provision of a simple process for obtaining EPS having a high molecular weight while keeping the amount of residual styrene monomers low.

2.3.2 In this respect, the tests submitted by the respondent with letter dated 30 April 2013 and referred to in the appeal proceedings are of relevance. In these tests, the respondent carried out the same process as disclosed in example 2 of the opposed patent, except that instead of pentane (C5) as the blowing agent, hexane (C6) or butane (C4) was used. The results were as follows:

Molecular Residual

weight styrene content

Example 2 of 226000 700 ppm

opposed patent (C5)

Comparative example 173000 1650 ppm

(C6)

Comparative example 183000 1380 ppm

(C4)

It follows from these tests that if butane or hexane is added as a blowing agent during polymerisation - instead of pentane as required by claim 1 - the molecular weight of the resulting expandable polystyrene is reduced and the amount of residual styrene increased. In this context, the board notes that according to paragraph [0014] of the opposed patent, EPS preferably has a molecular weight of above 190,000 g/mol. Molecular weights above this value are achieved when pentane is used as the blowing agent, as demonstrated by the invention examples 2 to 4.

2.3.3 In view of these tests, the objective technical problem cannot be regarded as the provision of an alternative process, as asserted by the appellant, but rather as the provision of a simple process that leads to polystyrene with high molecular weight and low residual styrene content. Clearly, in view of what is stated above, the objective technical problem is solved.

2.4 The appellant's remaining counter-arguments regarding the formulation of the objective technical problem do not convince the board:

2.4.1 The appellant argued that the technical problem proposed by the respondent was not derivable from the opposed patent. In the light of paragraphs [0007] to [0009], it was evident that the presence of pentane or flame retardants caused a decrease in the molecular weight of the polystyrene. Rather than being the solution to a technical problem, the presence of pentane was the source of disadvantages regarding the molecular weight. The effects the respondent relied upon to demonstrate an inventive contribution were reported for the first time in tests which it filed in April 2013.

2.4.2 The board cannot agree.

Firstly, both the molecular weight of the expandable polystyrene and the amount of residual monomer obtained are two important results of the process of the invention. These results are consistently highlighted in invention examples 2 to 4 and in comparative examples 5 to 7 of the opposed patent, as can be seen from paragraphs [0050], [0054], [0057], [0062], [0064] and [0066].

Secondly, the skilled person would understand from paragraph [0012] that the opposed patent aims at simultaneously providing the following:

(a) accelerating the preparation of expandable polystyrene,

(b) using a blowing agent during the polymerisation, and

(c) obtaining polystyrene having a particularly high molecular weight.

In this context, it is worth noting that the blowing agent consistently used in invention examples 2 to 4 is pentane, which is the preferred blowing agent described in the opposed patent (see paragraph [0039]).

Thirdly, it is also derivable from the opposed patent that a low concentration of residual monomer is desirable (see paragraph [0003]).

In short, the board is convinced that the technical problem proposed by the respondent is straightforwardly derivable from the opposed patent. For this reason, decisions T 344/89 and T 767/02 - both relating to an unallowable reformulation of the technical problem - do not support the appellant's case. The tests filed in April 2013 simply represent additional evidence, but they do not alter the technical problem derivable from the opposed patent.

2.4.3 In its written submissions, the appellant compared the molecular weight of the polystyrene obtained in example 11 of D1 (278,000) with the polystyrene obtained in example 2 of the opposed patent (226,000). Similarly, the content of the residual monomer was lower in example 11 of D1 as compared to example 2 of the opposed patent. Therefore, the appellant concluded that the technical problem suggested by the appellant was not solved over D1.

2.4.4 This argument is not convincing. Although the same peroxide initiator is used in both example 11 of D1 and example 2 of the opposed patent, these examples are not comparable, since no blowing agent, let alone pentane, is present during the polymerisation in example 11 of D1.

2.5 Obviousness

2.5.1 It remains to be decided whether, in view of the available prior art, it would have been obvious for the skilled person to solve the objective technical problem as defined above by the means claimed.

2.5.2 There is no indication in D1 itself that pentane should be used as the blowing agent in order to solve the objective technical problem. More precisely, starting from example 11 of D1 (which already discloses the initiator TAPMC), the skilled person may have chosen to add the blowing agent during the polymerisation process in order to simplify the manufacturing process, in line with the disclosure of D1, column 1, line 55 to 57. But the skilled person had no indication from the teaching of D1 to specifically select pentane as the blowing agent with the expectation to improve the molecular weight and the residual monomer content of the obtained EPC. There is no teaching whatsoever in D1 in this direction. In fact, according to D1, all blowing agents are interchangeable, so that there is no reason to choose a specific blowing agent instead of another with the aim of improving the molecular weight of the expandable polystyrene.

2.5.3 As regards the combination of D1 with D2, the latter is a textbook which discloses pentane as a blowing agent for styrene polymerisation. The appellant argued that D2 demonstrated that pentane was the most commonly used blowing agent. Therefore, the skilled person would also use pentane in the process of example 11 of D1 during the styrene polymerisation. However, this alone does not compel the skilled person to use pentane as the blowing agent. Such an approach appears to be tainted by hindsight. On the contrary, what needs to be decided at this juncture is whether the skilled person had any indication to use pentane and not other blowing agents equally suggested in D1 for solving the objective technical problem.

On this point, however, D2 contains no indication that pentane would optimise the molecular weight and residual monomer content in the EPS production. There is simply no pointer for the solution in D2 either.

To be complete, D3 (page 2, left column, last paragraph) confirms that many blowing agents (including e.g. heptane) are known in the art, but there is no teaching that one of the blowing agents, and in particular pentane, would improve the molecular weight and residual monomer content in the EPS production.

2.5.4 The board notes that precisely this issue was a point in the opposition division's reasoning (see reasons for the decision, point 5.2):

"Neither D2 nor D3, however, give any incentive to use pentane for improving the Mw build up of the polystyrene or for obtaining low residual monomer contents.

The Opponent has not submitted any evidence or literature that said technical effects were expectable from the prior art or general knowledge."

In the appeal proceedings too, the appellant has not provided any evidence demonstrating the (improved) influence of pentane on the molecular weight and/or residual monomer content in the production of EPS. Thus, the board sees no reason for reversing the appealed decision.

2.5.5 Also, the board cannot accept the appellant's argument that no "synergy" or "link" has been demonstrated for the combination of the features of claim 1. On the contrary, the respondent's experiments show that pentane has a technical effect. Whether or not there is also a synergistic effect between the initiator and the pentane is therefore not relevant in the present case.

2.5.6 Finally, the appellant argued that any effect associated with the selection of pentane was a bonus effect, because the skilled person would have selected pentane in view of D2 anyway as the blowing agent. This argument is not convincing. As already explained above, the advantageous effect could not be expected from the teaching of the prior art documents. Furthermore, there is no lack of alternatives that would place the skilled person into the notorious "one-way-street" situation: both the closest prior art D1 and D3 suggest various equally suited blowing agents.

2.5.7 Thus, the subject-matter of claim 1 involves an inventive step, Article 56 EPC. The same applies to claims 2 to 13 which are all dependent on claim 1.

3. Description

The description was adapted during the oral proceedings before the opposition division. In the board's view, the so amended description was correctly adapted. The parties agreed that no further modification was necessary.