At the European Patent Office, the principle of res judicata dictates that matters decided on by a Board of Appeal are binding on the Opposition Division in any subsequently resumed proceedings. In T 0308/14, a Board of Appeal had to decide on whether a finding of insufficiency by the Opposition Division violated the principle of res judicata.

T 0308/14 was the second appeal concerning EP 1 578 879, which related to an extended polyacrylic acid based binder composition.

In the first instance proceedings, the Opposition Division decided to revoke the patent on the grounds that all of the claim requests on file contained added subject matter. This decision was subsequently appealed by the proprietor.

During the appeal proceedings (T 1115/10), the issue of clarity under Article 84 EPC was also considered by the Board. The respondent (opponent) had argued that the feature of “polysaccharides having a weight average molecular weight of not more than 10,000” in Claim 1 of the second auxiliary request, which was not present in the claims as originally granted, lacked clarity, as there was no disclosure in the specification on how to determine the weight average molecular weight of the polysaccharides, and it was common general knowledge that weight average molecular weight values could vary depending on the method by which they were measured. Naturally, the appellant (proprietor) disagreed, and argued that there was no evidence that different measurement methods gave rise to different weight average molecular weight values.

In arriving at its decision, the Board acknowledged that weight average molecular weight values may depend on the measurement method applied as far as high molecular weights are concerned (eg 500,000 or higher). However, the Board stated that no proof had been provided that the same dependence exists for low-weight average molecular weights of not more than 10,000. Thus, taking into account the evidence on file, the Board sided with the appellant and held that the weight average molecular weight of not more than 10,000 was clear as there was no proof that it depended on the measurement method applied. As the second auxiliary request was also held to meet the requirements concerning added subject matter, the Board remitted the case back to the Opposition Division for further examination.

In the course of the subsequent opposition proceedings, the opponent argued that the patent lacked sufficiency due to the lack of a measurement method for the weight average molecular weight in the patent. The opponent also filed documentary evidence showing that weight average molecular weight values for polysaccharides depend on the measurement method. In the light of this evidence, the Opposition Division concluded that the claims of the previous second auxiliary request – now the main request – lacked sufficiency because the method of measurement was essential to enable the skilled person to work the invention.

The proprietor appealed the decision of the Opposition Division and argued that the sufficiency objection regarding the weight average molecular weight of the polysaccharides could not succeed since the question of whether this feature was clear had already been decided by the board in T 1115/10 and therefore constituted res judicata.

In T 0308/14, the Board noted that the Opposition Division’s decision to reject the claims as lacking sufficiency was “a decision in insufficiency arising out of ambiguity, namely the ambiguity of the weight average molecular weight of the polysaccharides in claim 1”. The Board went on to note that the binding effect of T 1115/10 does not only concern the decision on clarity as such, but extends to any finding of fact that led to this decision, eg the finding of fact that that the weight average molecular weight of not more than 10 000 in claim 1 was clear since, taking into account the evidence on file, it did not depend on the measurement method applied. Since the Opposition Division’s finding of lack of sufficiency started from the opposite assumption, the Board found that the Opposition Division had violated the principle of res judicata. As such, the Board found the requirement of sufficiency to be met.

Ultimately, the appeal was dismissed as the claims on file were found to lack an inventive step. Therefore, the decisions of the Board in T 1115/10 and T 0308/14 in respect of clarity and sufficiency had no bearing on the final outcome of the case. However, had an inventive step been acknowledged, the failure of the opponent to support its observations on clarity with documentary evidence earlier in the proceedings would have (to the detriment of the opponent) resulted in the allowance of claims that were arguably unclear and insufficient.

To conclude, it appears that the decision of the Board in T 0308/14 has implications that reach beyond the specific interrelated issues of clarity and sufficiency. Indeed, it suggests that the principle of res judicata may extend to any finding of fact made on the way to a decision of a Board of Appeal and is not just limited to the decision itself.