T 0015/20 28-09-2022

Main request

1. Admittance of documents

1.1 D16 and D17 are documents submitted by the appellant with their statement of grounds of appeal. They are both extracts providing generic definitions for chain transfer agents which should mirror the understanding of the skilled person according to their common general knowledge.

1.2 D16 represents indeed the common general knowledge relating to the distinguishing feature over the closest prior art as identified in the contested decision (section 4.6.1). The respondent declared at the oral proceedings before the Board that they did not oppose its admittance into the proceedings. On this basis the Board finds it appropriate to exercise its discretion according to Article 12(4) RPBA 2020 by admitting document D16 into the proceedings.

1.3 With regard to D17, it is not apparent and was also not shown by the appellant how that document, which was published on 18 November 2009, i.e. over three years after the priority date of the patent in suit (17 May 2006), could represent the common general knowledge of the skilled person and be relevant to the discussion of inventive step over D1 as closest prior art. On this basis the Board finds it appropriate to exercise its discretion according to Article 12(4) RPBA 2020 by not admitting document D17 into the proceedings.

2. Inventive step

2.1 The decision of the opposition division on inventive step is based on D1 as the closest prior art. The parties in appeal also considered that D1 and in particular the process disclosed in examples 14a and 14b (referred to as example 14a/b thereafter) represented the closest prior art. The Board does not see any reason to depart from that view.

2.2 The opposition division established (section 4.6.1 of their decision) that the sole difference between claim 1 of the main request and the closest prior art was the presence, in the ethylene polymerization process, of 0.015 to 2 mol% percent hydrogen based on ethylene as a chain transfer agent.

2.3 Relying on documents D7 (page 4 of the letter of 26 August 2022) and D11-D13 (page 4 of the statement of grounds of appeal) the appellant however contended in appeal that hydrogen was produced in significant amounts during the polymerization reaction of example 14a/b of D1. The Board however does not follow the appellant for the following reasons.

2.3.1 The process of example 14a/b of D1 is a solution copolymerization of ethylene and 1-octene in the presence of a catalyst ((p-Et3Si-phenyl)2C(2,7-**(t)Bu2Flu)(Cp)HfMe2: catalyst A) based on Hafmium (pages 25 and 26 with reference to page 18, lines 15-21 for the catalyst). The production of hydrogen in the course of that process is neither explicitly disclosed nor directly derivable from the information contained in D1. The Board also finds that none of D7 and D11-D13 establish that the process of example 14a/b of D1 is accompanied by the production of hydrogen.

2.3.2 In particular, D7 is an academic publication exploring the high-temperature copolymerization of ethylene/alpha-olefin in the presence of Zirconocene catalysts (Abstract). The process cited by the appellant in D7 is a polymerization using Ph2C(Cp)(Flu)ZrCl2 as a catalyst and is reported in Table VII on page 4646. For that polymerization, D7 proposes a mechanistic pathway involving the release of hydrogen (Scheme 1) but the representation in Scheme 1 relies on a Zirconocene catalyst being used. There is no teaching in D7 from which it could be deduced that the release of hydrogen referred to in Scheme 1 of D7 would also take place when using a Hafnocene catalyst as in example 14a/b of D1.

2.3.3 D11-D13 pertain to polymerization processes of ethylene in the presence of metallocene catalysts. As for D7, D11 shows a polymerization based on a Zirconocene catalyst (Scheme 1, page 8535). In that regard, D11 is not more relevant to D1 than D7 discussed above. D12 discloses the release of hydrogen in the copolymerization of ethylene using metallocene catalysts. D12 however uses specifically a gas phase polymerization and not a solution polymerization as in D1. In that regard D12 cannot be directly relevant to D1. D13 pertains to solution polymerization using metallocene catalysts but it is not apparent how the passage on page 4, lines 6-10 cited by the appellant could be relevant to D1 as it merely mentions the generation of hydrogen when using single site catalysts but it cannot be deduced therefrom that hydrogen would also be produced in the presence of a Hafnocene as used in example 14a/b of D1.

2.3.4 Since none of D7 and D11-D13 are relevant to D1, the Board does not see any reason to deviate from the conclusion of the opposition division on the distinguishing feature over the process of example 14a/b of D1.

2.4 At the oral proceedings before the Board the respondent formulated the problem solved with respect to D1, example 14a/b as the provision of a process with an improved control of the final molecular weight and at the same time maintaining other advantages such as high temperatures, low densities and low melt index.

2.4.1 According to the established case law, an unexpected effect (advantageous effect or feature) demonstrated in a comparative test can be taken as an indication of inventive step but the nature of the comparison with the closest state of the art must be such that the alleged advantage or effect is convincingly shown to have its origin in the distinguishing feature of the invention compared with the closest state of the art (Case Law of the Boards of Appeal, 10th Edition 2022, I.D.4.3.2).

2.4.2 In the present case, the examples of the patent in suit do not disclose a process in which hydrogen was not used as a chain transfer agent. In view of this, the examples of the patent in suit do not offer a valid comparison with the process according to example 14a/b of D1. The respondent further contended that the experimental report D15 would establish the presence of an effect over the closest prior art. Section "1. Continuous Polymerization Data" of D15 which discloses several runs for the polymerization of ethylene and 1-octene (runs 1-5, 7 and 8) was found to be relevant by the respondent. These runs however do not establish the presence of an effect that could unambiguously be attributed to the use of 0.015 to 2 mol percent hydrogen as a chain transfer agent during polymerization. In particular, the polymerizations in runs 1 and 2 were carried out in the absence of hydrogen and runs 3-5, for which hydrogen was used during polymerization, are such that they lead to a polymer having a melt index (Table 4: run 3: 3.39 dg/min, run 4: 5.65 dg/min, run 5: 8.41 dg/min) that is outside the range limiting claim 1 (below 2.0). These runs are thus not according to claim 1 of the main request. Runs 7 and 8 in tables 7 and 8 of D15 were conducted in the presence of hydrogen and are according to claim 1 as they lead to a polymer having a melt index below 2.0 (Table 8: run 7: 0.72 dg/min, rung 8: 1.45 dg/min) but these runs also lack relevance because for these runs different polymerization conditions were used (Table 7: Catalyst A-10 with scavenger MMAO-3A and 1-octene feed of 0.70 kg/hr) than in runs 1-5 (Table 1: Catalyst A with scavenger TOA and 1-octene feed of 0.45kg/hr). In view of these differences, it is impossible to establish whether any effect seen in runs 7 and 8 is attributable to the distinguishing feature over D1, namely the use of hydrogen in an amount of 0.015 to 2 mol percent.

2.5 Under these circumstances, the problem that can be defined in view of the lack of evidence of an effect over D1 is, in agreement with the appellant, the provision of an alternative process conducted at high temperature to reach high molecular weight with high catalyst efficiency.

2.6 The appellant held that it was obvious in view of the prior art to use hydrogen as chain transfer agent, in particular when a regulation of the molecular weight of the polymer was needed. Specifically, example 14a/b of D1 already indicated that hydrogen could optionally be used and the hydrogen amount defined in claim 1 of the main request was a conventional one. Furthermore, the appellant mentioned at the oral proceedings before the Board that D12 (page 13, Table 1) and D7 (page 4646, Table VII), which disclosed similar processes to that of D1 and the patent in suit, established that the hydrogen amount defined in claim 1 of the main request was already commonly used in the prior art.

2.7 The question of obviousness in the present case however is not whether hydrogen in the specific amount of claim 1 could have been used in the process of example 14a/b of D1. It was in particular not disputed that the use of hydrogen as chain transfer agent in a high temperature polymerization process of ethylene was known in the art or even that the hydrogen amount defined in claim 1 of the main request (0.015 to 2 mol percent based on ethylene) was already known to the skilled person. Indeed the skilled person could have used hydrogen as a common measure in the polymerization process of example 14a/b of D1 as is in fact already suggested on page 25, line 13 of that document.

2.8 The decisive question is, however, whether the skilled person starting from the process of example 14a/b of D1 and adding hydrogen in the specific amount would have been able to arrive at a process according to claim 1 of the main request, in particular obtaining a polymer as defined therein. In this respect, the opposition division had decided that this was not the case.

2.8.1 The polymers according to example 14a/b of D1 have properties that are according to claim 1 of the main request. Claim 1 of the main request defines the polyethylenes obtained as having a density between 0.885 and 0.950 g/cm**(3) (also corresponding to kg/m**(3)), a molecular weight distribution Mw/Mn<3.0 and a melt index I2<2.0. In example 14a/b of D1 the copolymers of ethylene and 1-octene have densities of 0.903 kg/m**(3) (example 14a) and 0.909 kg/m**(3) (example 14b), a molecular weight distribution of 2.3 (example 14a) and 2.2 (example 14b) and melt indexes of 0.84 dg/min (example 14a) and 0.96 dg/min (example 14b). Properties within the defined ranges should, however, also be maintained after the introduction of hydrogen in order to arrive at a process according to claim 1.

2.8.2 Since the purpose of a chain transfer agent is mainly to influence the molecular weight of a polymer and its use is in particular known to lead to an increase of its melt index, the question is whether the use of a 0.015-2 mol percent of hydrogen (based on ethylene) as a chain transfer agent in the polymerization process of example 14a/b of D1 would still lead to a polymer with a melt index below 2.0 as required in claim 1 of the main request.

2.8.3 In that regard, the decision of the opposition division concluded (section 4.6.4) that the addition of hydrogen would have resulted in an increase of melt index above the maximum value of 2.0 defined in claim 1 of the present main request. In particular, D15 showed that using hydrogen in the process of example 14a/b of D1, even in an amount that was at the lower end of the range defined in claim 1 of the main request, resulted in an increase of the melt index of the polymer produced such that the melt index of the polymer was outside the range defined in that claim. The communication of the Board sent in preparation of the oral proceedings underlined that that point of the decision was also key to the question of obviousness in appeal (sections 3 and 7.8 of the Board's communication).

2.9 The appellant however did not provide in appeal sufficient reasons to overturn that conclusion. With regard to D15, the argument of the appellant was essentially that the experimental report D15 lacked relevance because it did not represent a faithful reproduction of the process of example 14a/b of D1. D15 and in particular runs 2 and 3 thereof, however, concern polymerization processes of ethylene and 1-octene that were conducted under comparable conditions, differing only in the presence of 0.016 mol percent of hydrogen in run 3. The comparison of runs 2 and 3 establishes that the copolymer of run 3 obtained in the presence of hydrogen has a melt index (3.39 dg/min) that is significantly higher than that of the copolymer obtained without hydrogen (0.85 dg/min). The melt index of the copolymer obtained in the presence of 0.016 mol percent of hydrogen is clearly well outside the range defined in claim 1 of the main request (below 2.0). The Board therefore finds that run 3 in D15, even though it is not a perfectly accurate reproduction of the polymerization described in example 14a/b of D1 with addition of hydrogen, offers reasonable evidence that addition of even minimal amounts of hydrogen can affect the melt index of the copolymer to such an extent that it is well outside the range defined in claim 1 of the main request. The appellant did not submit counter-evidence in reply to D15. While the onus of proof of showing lack of inventive step starting from the closest prior art was on them, they did not discharge it with regard to the preparation of a copolymer having the properties defined in claim 1 of the main request starting from the polymerization process of example 14a/b of D1 and adding 0.015-2 mol percent hydrogen based on ethylene. It has thus not been established by the appellant that the polyethylene polymers according to claim 1 of the main request could have been obtained starting from the process of example 14a/b of D1. The Board therefore sees no reason to overturn the decision of the opposition division on inventive step of claim 1 of the main request.

2.10 In view of that the Board can only conclude that claim 1 of the main request meets the requirements of Article 56 EPC.

3. As the only objection maintained in appeal does not succeed, the Board does not need to decide on any other issue and the appeal is to be dismissed.