5.5.2 Open-ended parameter features

Recent decision T 1977/22 reviewed in detail the case law and landmark decisions about open-ended ranges, and reproducibility over the whole claimed scope.

In T 1697/12 the claims covered, through open-ended ranges, embodiments that could not be obtained with the process disclosed in the patent, but which might be obtainable with different methods still to be invented in the future (insufficiently disclosed invention). Related decisions: T 61/14 (point 5 of the Reasons, along the same lines, range not achievable over whole scope), T 2344/12 (point 1.1.2 of the Reasons, along the same lines, open ended range not sufficiently disclosed), T 517/98 (point 1.5 of the Reasons, similar, no teaching for whole range), T 615/19 (point 1.2 of the Reasons, conclusions of T 1697/12 not applicable, implicit limitation of open-ended range due to the existence of other features) and T 398/19, summarised below, in which the board rejected objections to open-ended ranges starting with "at least …" or "at most …" which the opponent had raised in relation to preparation methods that were still to be invented, invoking T 1697/12 and T 113/19 and the German Federal Court of Justice's decisions X ZR 32/17 and X ZR 34/17 in support of its arguments.

The decision in T 398/19 contains detailed reasons on the issue of a parameter defined by open-ended ranges. The opponent had objected to open-ended ranges of the kind starting with "at least …" or "at most …", alleging that they were not sufficiently disclosed. The board observed that the sole fact that certain features were expressed in terms of open-ended ranges was not enough to support an objection of insufficient disclosure, especially where, as in the case in hand, the description and the examples contained precise information on how to prepare one or more specific products having all the claimed features. Besides, it was common practice in the technical field concerned to characterise a product in terms of open-ended ranges and the claimed subject-matter often omitted parameters equally important for the claimed product's efficacy. Defining a product by all its structural parameters would clearly be impossible, and indeed often unnecessary in view of the invention's purpose. Lastly, the board observed that defining a parameter by an open-ended range by no means precluded the later invention of new methods whereby parameters having values very far from those claimed and so likewise patentable could be obtained. The board found that the requirements of Art. 83 EPC were met, endorsing the findings in T 113/19, T 1018/05 and T 624/08, and holding T 1697/12 to be inapplicable to the case in hand.

In T 2702/19 (small diameter medical devices containing visualisation means), the board found that the person skilled in the art would not be able to derive from the patent, using their common general knowledge, a limit for the values of the maximum outer diameter of the medical device below which they would immediately exclude variants as being clearly outside the scope of practical application of the claimed subject-matter. As argued by the respondent (opponent), the patent did not disclose how to carry out the invention over the whole effective claimed range of the maximum outer diameter of the medical device. The appellant (patentee) also alleged that T 2773/18 confirmed that values of a parameter not obtainable in practice could not justify an objection of insufficiency of disclosure. But the board was not convinced that the situation dealt with in T 2773/18 was comparable to the case at hand since the relevant claim in that decision did not contain an open-ended range. (Similar cases to T 2702/19 include T 2401/19 and T 953/21; oral proceedings in these cases were held consecutively).

In case T 1708/22 the board considered that the "total light transmittance" was inherently limited by the other features of claim 1. The open-ended range hence did not lead to insufficiency of disclosure.

In T 1942/21 it had to be determined whether the patent gave the skilled person adequate instructions on how to obtain high proportions of methane in the synthesis gas. The appellant (patent proprietor) argued that this was not an issue as there would not have been any reproducibility problem had a lower limit not been specified for methane. The board disagreed. Accepting this argument would imply that any restriction added to a claim by way of a non-reproducible parameter would be allowable since the broader claim without the parameter would indeed be unlikely to have reproducibility issues. However, it is established case law that when an essential feature of an invention is expressed by a parameter, it has to be determined whether the parameter is defined so as to allow the skilled person, on the basis of the disclosure as a whole and using common general knowledge, to identify (without undue burden) the technical features that lead to the claimed subject-matter. This viewpoint was also in keeping with decisions that deemed dependent claims, i.e. those with restrictions, not to be reproducible despite there being no such sufficiency objections in relation to the broader independent claim. For the case in hand, this meant that the patent had to contain adequate instructions on how to implement the now essential feature over the entire scope since this feature defined the result to be achieved, namely a methane proportion of more than 12 vol.% in the synthesis gas. Since synthesis gas containing less methane was already known, this feature was the crux of the invention. Therefore, the teaching of the patent should enable this new feature to be obtained over the whole scope claimed. Although the case in hand related to a result to be achieved from a chemical reaction rather than to a physical parameter, it was still similar to T 1697/12 cited in the case law, in which some realistic values could not be achieved by the claimed method, resulting in sufficiency being denied. Here, adding the amount of methane in the synthesis gas rendered this an essential feature (R. 43(3) EPC), leading to the question of how the claimed aim could be achieved across the whole scope claimed. The patent contained information on how to exceed the lower limit of methane (12 vol.%), yet it did not contain any information on how to achieve methane amounts of 20 to 25%, which arguably were not considered unrealistic. While it was true that the open-ended range was restricted by the method per se (reaction with water vapour), it was undisputed that this restriction did not rule out methane values in the range of 20 to 25 vol.%. The board acknowledged that there were decisions related to a physical parameter in which the open-ended range was not considered an issue. However, that was not the case here. Since the parties agreed that the claim encompassed methane levels of 20 to 25 vol.% and that the teaching of the patent was lacking in this regard, the subject-matter of claim 1 was not considered reproducible.