This is an appeal against the revocation of the opposed patent by the Opposition Division.
Claim 1 of the main request read (in English translation):
Composition obtained by drying a suspension containing, on the one hand, alumina particles A having an aspect ratio of less than 15 and, on the other hand, precipitated silica particles B dispersible in a polymer medium.
The Board found the invention to be insufficiently disclosed:
*** Translation of the French original ***
[1.1] The Board is of the opinion that the information provided in the impugned patent is not sufficient for carrying out the claimed invention.
[1.2] The only passage in the impugned patent that describes the “aspect ratio” used in claim 1 for characterising alumina particles A is paragraph  of the description. The definition provided therein consists in that “the ratio of the greatest mean dimension of particles A over the smallest mean dimensions of particles A, of less than 15”.
[1.3] [The document] does not disclose any explanation whatsoever concerning the expression “dimension”. The argument of the [opponent] that this dimension can be the length, the diameter, the circumference or another feature of the particles has not been disputed or refuted by the [patent proprietor].
[1.4] Moreover, the [patent proprietor] has not provided any argument concerning what is meant by “mean dimension”. According to the [opponent], the skilled person has to choose among several definitions, such as, for instance, the arithmetic mean or the geometric mean.
[1.5] Even the examples of the impugned patent do not provide information on the aspect ratio of the alumina particles used, nor do they mention the name of a commercial product having said features.
[1.6] The expert of the [opponent] has explained that “aspect ratio” was not an established term in the technical field of the patent before the priority date. The [patent proprietor] has not provided any evidence to the contrary.
[1.7] Moreover, none of the documents cited that have been published before the priority date of the impugned patent uses this expression. The only documents that refer to the aspect ratio are not part of the state of the art within the meaning of A 54(2). Consequently, the state of the art cited cannot be used as evidence that the term was an established term in the technical field of the patent before the priority date.
[1.8] Even if a precise definition of the “aspect ratio” had been established in the technical field of the impugned patent, no method for manufacturing alumina particles having the disclosed features was known. The Board has no evidence showing that such a method was part of the knowledge of the skilled person before the priority date of the impugned patent.
[1.9] Thus the impugned patent does not disclose how the alumina particles cited in claim 1 of the main request, which are necessary for obtaining the claimed composition, are to be produced.
[1.10] This situation differs from the cases where the features of the end product disclosed in a patent are not clearly defined. In such cases, the skilled person may have doubts whether a product or composition is covered by the wording of the claim. Very often, this lack of a precise definition corresponds to a lack of clarity (A 84).
[1.11] In the present case the situation is different, because it is one of the starting products that is insufficiently defined. Contrary to the case discussed above, where one can obtain concrete final products, it is impossible to prepare the claimed composition in the present case, because there is not enough information for selecting the starting product. This situation characterises an insufficient disclosure of the invention.
[1.12] As a consequence, the subject-matter of the main request is not disclosed in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art (A 83).
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NB: This decision was first reported by Le blog du droit européen des brevets (here).