Can a Priority Document "Kill" its Children?

In a recent decision of a Technical Board of Appeal (TBA), T680/08, the European Patent Office emphasised the strict approach that they take to entitlement to priority.

The patent in question related to a method of compounding polyethylene.  A key feature of claim 1 was the requirement that the total drive specific energy (SEC) applied on the polyethylene composition be from 0.330 to 0.415 kWh/kg.  The priority document disclosed only a lower limit of 0.325 kWh/kg, the amendment to 0.330 kWh/kg being introduced through error when the patent application in question was filed.  All other features of the claims were present in the priority document.

The question arose, is claim 1 entitled to priority?

It was argued that because the claimed range (0.330 to 0.415 kWh/kg) falls within the range discussed in the priority document (0.325 to 0.415 kWh/kg) the two documents relate to the same invention as methods in which the SEC is in the range 0.325 to 0.415 kWh/kg include within their scope methods in which the SEC is in the range 0.330 to 0.415 kWh/kg.

However, the new lower limit of 0.330 kWh/kg was not specifically disclosed in the priority document, and it was necessary for the TBA to consider whether a value merely falling within the range stated in the priority document, but not specifically disclosed, was enough for the priority right to be validly claimed.  By following the rules set down in Enlarged Board of Appeal decision G 2/98 it was held that this lack of explicit disclosure resulted in a situation where the patent was entitled to priority only to the extent that the features of the claim did not relate to the lower limit of 0.330 kWh/kg.

As the priority document was a European patent application that had been published, this document became citable as prior art for novelty purposes only under Article 54(3) EPC to the extent that the priority claim was not valid (i.e. for a method carried out at an SEC value of 0.330 kWh/kg).  It was argued that the narrower range of 0.330 to 0.415 kWh/kg was a selection invention over the range disclosed in the priority document.  Under European practice a selected range may qualify as patentable subject matter if the range is (a) narrow, compared to the range disclosed in the prior art, (b) removed from the preferred part of the prior art range, and (c) ‘purposive’ (i.e. selected for technical reasons).  In this case none of these criteria was held to be fulfilled as the range 0.330 to 0.415 kWh/kg was too similar to the prior art range of 0.325 to 0.415 kWh/kg, and there was no evidence that any technical effect was associated the narrower range.  As such, the claims were held to lack novelty in view of the disclosure of the priority document.

This case is similar to a previous case, T1443/05.  In that case the priority document, a European patent application which had been published, required the presence of a particular biocide in a three-component biocide composition.  The claims of the later-filed patent disclaimed the presence of this third component.  The patent and the priority documents were found to relate to different inventions, and as the priority document included an example in which this particular biocide was absent, the claims of the patent lacked novelty in view of the disclosure of the priority document.

Both these cases show the dangers of claiming priority from an earlier application filed in the same country, and particularly of allowing the priority application to publish.  It may have been wiser in both cases to claim priority from national filings (such as a UK national filing), and to allow the priority applications to lapse without publication.  If there is a need to pursue more than one application, the filing of one or more divisional applications could be a useful alternative strategy. 

Joanna Westwood
Life Sciences & Chemistry Group