Burden of proof for inventive step based on an unusual parameter (T 0555/18)

The recent decision T 0555/18 from the EPO Boards of Appeal considered the burden of proof for unusual parameters relied on for inventive step. The patent in question (EP2117839) related to shrink wrap for use in food packaging. On appeal, the Opponent argued that the patent lacked inventive step. The only distinguishing feature between the prior art and the claimed invention was found to be the specified range of an unusual parameter that was not commonly used in the field of shrink wrap. The question before the Board of Appeal thus became whether the unusual parameter could be relied on for inventive step. 

Legal background: Unusual Parameters 

Shrink wrap
"Unusual parameters" are those which are not commonly used in the technical field of an invention (F-IV, 4.11.1). When specified in a patent claim, unusual parameters can only confer novelty on the invention when the parameter can be easily measured or converted to a normal parameter. In other words, it must be straightforward for a skilled person to assess whether the parameter corresponds to a true distinguishing feature of the invention from the prior art. Furthermore, the burden of proof is placed on the Patentee to show that an unusual parameter relied on for novelty does actually distinguish the claimed subject-matter from the prior art (Case Law of the Boards of Appeal, III-G, 5.2.2(d)T 0131/03T 2732/16). 

Case background

In T 0555/18, the Patentee submitted that the claimed invention solved the problem of providing a shrink wrap film that was sufficiently strong without compromising on transparency. The granted claims specified shrink wrap films having a "FTIR Transmission Absorbance Ratio" (FTIT ratio) of 1.65 or lower. The patent explained in the description that a low FTIT ratio value implied a film with a large polyamide content (i.e. high strength) and a low degree of crystallinity (i.e. transparency). 

The Board of Appeal considered the FTIT ratio to be an unusual parameter not commonly used in the field (r. 1.5.5). The specified FTIT ratio range was also found to be the only distinguishing feature between the claimed film and the films disclosed in the closet prior art (r. 1.3). The question became whether it would have been obvious for a skilled person to make films having FTIT ratios falling within the claimed range. 

Reliance on an unusual parameter for inventive step

The Board of Appeal noted that the very unusualness of an unusual parameter might cloud the issue of obviousness. A rare parameter might appear to confer distinctiveness on an invention that is, in fact, inherently lacking. Furthermore, substituting a more common parameter to indirectly compare the invention to the prior art might itself lead to uncertain conclusions. In such cases, the Board of Appeal thought it appropriate to follow the case law on unusual parameters in the context of novelty (T 0131/03T 2732/16). In other words, the burden of proof should lie with the Patentee to demonstrate that obvious solutions in view of the prior art would not implicitly fall under the scope of the unusual parametrical range specified by the claim (r. 1.6.1). 

In the case in question, the Board of Appeal found that the obvious solutions that would suggest themselves to the skilled person in view of the prior art would necessarily result in films having the FTIT ratios falling within the scope of the claimed invention. The burden of proof was then placed on the Patentee to demonstrate that this would not be the case. The fact there was no definitive proof either way as to whether the obvious solutions would fall under the scope of the claims appeared to the Board of Appeal "to be an attempt by the proprietor to benefit from the uncertainties caused by its decision to draft the invention in terms of an unusual parameter, which is precisely what the board intends to avoid by shifting the burden of proof to the proprietor or by giving the opponent the benefit of the doubt."

In the absence of proof establishing that the obvious solutions in view of the prior art would not fall under the scope of the claim, the claims were found to lack inventive step.

Final Thoughts

The decision of the Boards of Appeal in this case flows naturally from the requirement in Europe that the technical effects of a claimed invention and that of the closet prior art to be directly compared. The decision in T 0555/18 is a caution against defining an invention by unusual parameters that make it difficult to compare the technical effect of the invention with that of the prior art. When including any parameter in a patent application, it is therefore critical for the skilled person to be able to straightforwardly measure that parameter, both when practising the invention and for prior art disclosures. 

Burden of proof for inventive step based on an unusual parameter (T 0555/18) Burden of proof for inventive step based on an unusual parameter (T 0555/18) Reviewed by Rose Hughes on Saturday, November 19, 2022 Rating: 5


  1. Rose, thanks for flagging up this case, which made me smile. The EPO's problem-solution approach tells us that only one sort of inventiveness "counts" for patentability, namely that which solves a technical problem in a technical way. But its very ubiquitousness has consequences for patent drafting.

    Patent drafters know what is needed, to get the EPO to issue them with a patent. Working with their inventors, they are getting ever more inventive, in devising a technical problem which the subject matter for which they crave exclusive rights plausibly solves. Unfortunately for their clients though, this sort of inventive activity, and this sort of drafting style, doesn't succeed if the EPO Examiners see through it straightaway.

  2. This looks like a reasonable approach to take. One classic example of a patent office which got it wrong was the Russian beer bottle patent, where the shape of the bottle was defined using mathematical formulae which were not in the prior art. Once granted, the patentee sought to enforce the patent against conventional bottles.

  3. I’m puzzled. An “obvious solution” falling within the claimed scope? What is that? Why was the claim then novel?

  4. I can't help wondering whether the "closet prior art" [sic] was disclosed to the public.

  5. Dear Max Drei,

    The inventiveness of some inventors and patent drafters does not stop at inventing a “favourable” technical problems, but goes as far as to come up with new terminology in order to hide the fact that what is apparently “invented” is actually lacking novelty and inventive step.

    In the present case the effect obtained by the claimed shrinkable films, easier to orient in the solid state (cf. § 11), was not in the claim.

    According to G 1/03 or T 2001/12, the objection was thus lack of inventive step. Should the effect have been claimed, then the objection should have been lack of sufficiency.

    The question then is: is it not possible to reproduce the invention? I would say yes.

    The decision leaves me somehow puzzled. On the other hand, in T 59/08 relating to polymer composition of pipes, the board considered that there exists a trade-off between sufficiency and inventive step. If the requirement of sufficiency is less stringent, this could lead to more stringent requirements for inventive step.

  6. Good comments, Curious. They motivate me to have another read of the Decision, looking critically at the reasoning deployed to establish the OTP (the trivial one, of finding an alternative).

  7. If the values of the unusual parameter that the skilled person would have necessarily contemplated were those falling within the claimed scope, then the claim was simply lacking novelty. The inventiveness of some patent drafters can only be equated with the inventiveness of argumentation shown currently in many boards’ decisions.

    1. Not really, the example taken as closest prior art did not disclose any shrink value, so to arrive at something which was likely to anticipate the unusual parameter there was a need to combine the specific teachings of that example with the highest values of the ranges presented as preferred. That is why the decision is taken on obviousness and not on novelty.

    2. An unusual parameter is per definition not anticipated in the prior art. The proposition that one would need to engage in an intellectual exercise “to arrive at something which was likely to anticipate the unusual parameter” is therefore abstruse, because nodoby would ever arrive at the unusual parameter, except its creative inventor. This is just disguised lack of novelty.

  8. Here is a further decision placing the burden of proof of novelty on the patentee when the prior art document does not provide an explicit disclosure of the parameters recited in the claim.


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