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Can Patent Claims have Partial Priorities

An Appeal Board of the EPO has announced its decision to refer one or more questions to the Enlarged Board of Appeal in a case questioning whether the claims of a divisional application are partially entitled to the priority date. The precise wording of the referred questions has yet to be announced.

The matter concerns the validity of a European divisional application with claims that are broader than the parent application. The parent application as filed represents prior art against the divisional under EPC a 54(3). However, if the claims of the divisional are entitled to partial priority there is no effect on patentability from the parent as the portion of the claim that is entitled to priority and the remaining portion of the claim with no basis in the priority document have the same effective dates as the corresponding parts of the parent application.

The partial priority issue follows from Enlarged Board of Appeal Decision G2/98 which ruled that a claim could have multiple priority dates “provided that it gives rise to the claiming of a limited number of clearly defined alternative subject matters” and to recent diverging decisions in case law by the Boards of Appeal regarding the partial priority of claims.

The background to the present case is that in opposition proceedings (T 557/13), European patent 0921183 (based on a divisional application) was revoked on the basis that the claims were not entitled to their priority date and, accordingly, the published parent application was prior art under EPC a54(3). In this case, Claim 1 of the divisional application required a cold flow improver which was an oil-soluble polar nitrogen compound with one or more amine groups (or cation). These claims were broader than the disclosure of the priority document which required the cold flow improver to be present as an amine salt or an amide. Example 1 of the divisional application was also present in the priority and parent applications and thus represented novelty-destroying prior art against the divisional application. Although the patentee argued that the claims were entitled to partial priority to overcome the novelty-destroying effect of the parent, the opposition division decided that the claims were not entitled to partial priority because the genus of compounds disclosed in the priority document was not “a limited number of clearly defined subject matters” – the test for establishing partial priority set down in G 2/98. The Board considered that it was necessary to refer relevant questions to the Enlarged Board of Appeal to resolve the diverging approaches to assessing partial priority.

This case is concerned with the situation in which a difference in priority entitlement of a parent application and a divisional derived from it results in the former destroying the novelty of the latter. It is to be hoped that the questions referred to the Enlarged Board of Appeal will be framed in such a way that they also provide a resolution of the much-debated and alarming issue of “toxic divisionals”, ie divisional applications that for similar reasons have the effect of invalidating the parent applications from which they are derived.

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