CASELAW - reviews of EPO Boards of Appeal decisions

T 2341/17 - Is disclosing the method for determining an essential parameter of the invention necessary for meeting the requirements of Art 83?

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The whole discussion in the case turned around the question whether there was a lack of definition of the essential parameter d90 (particle size distribution of 90% of the particles) as the skilled person did not know whether the parameter d90 referred to 90% of the particles by volume, by number, by weight or by surface area.

The OD’s decision

In its decision the OD was of the opinion that the requirements of Art 83 were fulfilled. The opponent had not provided any substantial evidence that the different methods of measurement existing for either of the parameters might lead to results which differ to such an extent that there are serious doubts that the person skilled in the art could not determine if a known composition falls within the scope of the claims.

The OD pointed out in its decision that the only distinguishing feature between the present invention and the disclosure of D3 is the value of the d90 parameter. It added that it “therefore appears to [sic] reasonable to deduce that the observed improvements are due to the distinguishing feature, which is thus to be associated with a technical effect.”

The appeal procedure

Contrary to the OD, the board accepted the opponent’s/appellant’s objection under Art 83 and considered that the invention was not sufficiently disclosed in the patent to the extent that different definitions of the parameter d90 were possible thus leading to different particle size distributions.

The proprietor/respondent requested that the objection under Art 83 regarding the parameter d90 raised by the opponent/appellant in appeal not be admitted into the proceedings as being late.

The board held that it was undisputed between the parties that an objection under Art 83 regarding the parameter d90 had been raised by the opponent in the OP before the OD.

For the board, the objection under Art 83 regarding the parameter d90 formed thus part of the decision under appeal.

Proof of common general knowledge

According to the proprietor late filed documents D16 (an affidavit) to D20 (“A guidebook to particle size analysis”, Copyright 2010) demonstrated that it was most common to express the parameter d90 on a volume basis and to use laser diffraction for measuring the particle size distribution.

The opponent requested not to admit these documents in application of Article 13(2) RPBA20 as they were filed only three weeks before the date of the OP, and none of the documents appeared to belong to the state of the art.

In the present case, the board was satisfied that the filing of these documents, though at a late stage in the appeal proceedings, does not imply an amendment of the proprietor’s appeal case but constitutes a further corroboration of the existing arguments on the common understanding in the art for expressing particle size distribution parameters.

It was thus to be decided that these documents, although possibly post-published, are suitable, were in view of their nature and content, proving the common general knowledge at the priority date of the patent.

Some documents D17, D18 and D19 disclosed technical properties of specific commercial products. These documents indicate parameter definitions that the manufacturers of these products chose to describe technical properties of their products. However, these documents are not suitable for demonstrating the skilled person’s common general knowledge at the priority date.

In contrast in documents D16 and D20 , definitions and measurement methods for particle size distributions are discussed in general terms. These documents reflect the skilled person’s basic understanding of the parameter d90 and the corresponding measurement methods that existed before the priority date of the patent. They also confirm that there are significant differences between particle size distribution parameters obtained on a volume versus a number basis. They were thus admitted in the proceedings.

According to the opponent, it was not disclosed in the patent whether the parameter d90 referred to a number-, volume- or weight-based distribution parameter.

The board held that significantly different results are obtained when determining the value of the parameter d90 for the same powder depending on which of these definitions is applied.

While there is thus no explicit indication in the patent, the proprietor was of the opinion that the skilled person would have understood that the parameter d90 in the context of the patent was volume based and that it was to be measured by laser diffraction.

For the board, this allegation, however, was not convincing and was furthermore not supported by the evidence provided by the proprietor.

The affidavit D16 assumed that the skilled person would have only considered laser diffraction as the method for assessing the value of the parameter d90 in the context of the patent. This assumption was not considered persuasive.

According to D20 different measurement methods are available to the skilled person. There is however no indication in document D20 that would allow the conclusion that the only standard method for measuring the parameter d90 was laser diffraction or that the skilled person being confronted with the parameter d90 in the patent implicitly understood this parameter to be measured by laser diffraction and nothing else.

Lack of sufficiency

The board noted that the patent as a whole does not disclose a single way of how the invention is to be carried out. In the context of “Example 1”, a value of d90 of 94 µm is mentioned, the description of “Example 1” does not indicate how the parameter d90 is defined, i.e. which of the various possible definitions indicated above to apply.

The board concluded that, even when taking into account the common general knowledge, the skilled person lacked a definition of the parameter d90 in the patent.

The invention as defined in claim 1 of the MR (as granted) therefore did not meet the requirements of Art 83 in view of the lack of definition of the parameter d90.

The same applied to AR I to III.

The patent was thus revoked.

Case law discussed in the decision

T 45/10

The “average-particle size” is neither clear without further definition, nor sufficiently disclosed without defined determination method.

T 1772/09

Addresses the question whether a lack of definition of a particle size parameter cited in a claim (average particle size and mean particle size, respectively) can give rise to a violation of Art 83. Answer positive. Lack of sufficiency.

T 2341/17

Explicit definition of d90 as referring to the volume distribution. No lack of sufficiency.

T 1372/16

The patent made an explicit reference to a series of instruments to be used for analysing the particle size. No lack of sufficiency.

Referral to the EBA

The proprietor/respondent requested to refer the following questions of law concerning the interpretation of Art 83 to the Enlarged Board of Appeal under
Art 112(1,a) EPC:

“1. Is disclosing the method for determining an essential parameter of the invention necessary for meeting the requirements of Art 83?

2. Should the lack of mentioning a method for the determination of such a parameter, in particular in cases where more than one method is available, automatically lead to a refusal under Art 83?

3. If the answer to question 2 is no, what are the criteria for meeting the requirements of Art 83 under these circumstances?”

The board did not dispute that the question of whether the absence of a measuring method for a parameter results in a violation of Art 83 or Art 84 may be relevant to a number of cases beyond the current one. Nevertheless, even in such a case, the criteria to be considered by the board is whether such a fundamental point of law is relevant for the appeal in question or whether a decision may be reached regardless of the answer to the referred question.

For the board, the question of definition of the parameter d90 is essentially separate from the question of choosing a specific measurement method, a clarification of whether disclosing a measurement method for a parameter in the patent is a necessary condition for meeting the requirements of Art 83 is not relevant for deciding the underlying appeal.

The request for a referral was thus rejected.


In spite of the objections to a referral raised by the board, it could have been useful to refer a question to the EBA on the applicability of Art 83 in the absence of a measurement method of an essential parameter. Further to the present case, the same situation applied in T 2161/17 or T 1188/15.

Other boards consider the absence of a measurement method in opposition appeal procedure as a clarity problem and under G 3/14 do not go further. See for instance T 1260/16 or T 719/14.

The general question as to whether the absence of a measurement method is a problem under Art n83 or 84 will be the subject of a future blog.


Art 83

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