d) Unusual parameters 

In T 131/03 the board pointed out that, once the opponent had established a strong presumption that unusual parameters as those used to define the claimed subject-matter were inherently disclosed in the prior art, the patent proprietor could not merely claim the benefit of the doubt. It was incumbent upon the patentee to establish the extent to which the parameters used in the definition of its invention actually distinguished the claimed subject-matter from the prior art (followed by T 2732/16). See also T 1452/16 (unusual parameters – alleged prior use – public availability of a product): as to the possibility for the patent proprietor to obtain samples and test them, the board stated that when testing samples manufactured after the priority date the legitimate question could arise of whether the results obtained were representative of the ratios present in the samples of the prior art. However, by using a parameter which had not been used in the prior art, the burden was on the patentee to prove that the prior art did not fall within the terms of the claim.

In T 1666/16, the appellant (opponent), relying on T 131/03 and T 740/01, argued that since the angle of repose (PVDF resin powder) was an unusual parameter in the context of PVDF resins, it would be legitimate to reverse the burden of proof and require the patent proprietor, who had chosen to rely on an unusual parameter as the sole distinguishing feature over the powder disclosed in example 4 of D1, to demonstrate that this parameter was not fulfilled by that powder in D1. The board decided that T 131/03 and T 740/01 were based on the same rationale, namely that when it had been established that there was a strong presumption that claimed subject-matter defined by an unusual parameter was inherently disclosed in the prior art, the patent proprietor could not merely claim the benefit of the doubt and had to demonstrate that the chosen parameter-based definition distinguished the claimed subject-matter from the prior art. In T 1666/16, however, the appellant had not failed to show that the unusual parameter was inherently disclosed in the prior art and there was therefore no justification for reversing the burden of proof.