Legal background: Use claims and functional effects 

The Enlarged Board of Appeal (EBA) decisions in G 2/88 and G 6/88 established that the new use of a known substance could be patented based on a new technical effect. In many cases, the newly discovered use is qualitatively distinct from what was known before and the line between the prior and new use is clear. However, the new use may also be very similar to a previously known use, wherein the technical effect is the achievement of a better effect. The question for the Board of Appeal in T 2387/22 was the legal test for the validity of a use claim based on and claiming a relative improvement as a functional effect. 

Functional features of use claims

The case in T 2387/22 concerned European patent EP 3325559, owned by Sun Chemical Corporation. The granted patent claimed a VMP (Vacuum Metallised Pigment) pigment slurry, comprising pigments, solvents, and specific dispersing additives. The patent was opposed by Schlenk Metallic Pigments GmbH and Eckart GmbH. 

On appeal, the Main Request was found to lack inventive step. The Board of Appeal found that the claimed product differed from the closest prior art only in the choice of solvent. As the closest prior art was considered to teach that the claimed solvents were preferred alternatives, the Board of Appeal considered the solution to be an obvious one to the problem of providing an alternative VMP slurry. 

The Board of Appeal then turned to the Auxiliary Requests, which sought to define the invention as the use of the VMP pigment in a flexographic ink formulation for providing certain technical effects, including "fewer print defects, higher hiding and stronger colour and allowing a lower volume anilox". The Patentee, citing G 2/88, argued that the effects were functional features that limited the claim's scope and rendered it novel and inventive. 

In response, the Opponent argued that the functional features of the claims were defined by relative terms and diffusely defined concepts, and thus failed to meet the clarity requirements of Article 84 EPC. It was impossible, the Opponent submitted, to objectively determine if a particular use specified by the claims met the requirement of "providing fewer printing defects" or "higher hiding," as no reference point or measurement method was provided. By contrast, the Patentee submitted that it was not necessary to define any further specifics regarding the functional feature. Pointing to the case in G 2/88 the Patentee argued that the claims at issue in G 2/88 were allowed without further specifying how the functional feature in question ("friction reduction") was to be identified or measured. The Patentee noted that despite the broad and relative nature of the claimed effect, no clarity objection was raised in that foundational case (r.3.4).

Broad and relative or objectively verifiable?

The Board of Appeal was convinced by the Opponent's argument and found the claims to be unclear. The Board of Appeal first observed that "there is no basis - be it in the case law or in the EPC - for concluding that the limiting functional features of a use claim are exempt from the clarity requirement under Article 84 EPC or somehow exposed to lower standards in this respect" (3.5.1, emphasis added). Importantly, however, the Board of Appeal was also at pains to emphasise that "irrespective of whether a claim is directed to a use or to any other category of subject-matter" the mere breadth of protection does not in itself imply a lack of clarity. The decisive consideration is whether the feature(s) in question give(s) rise, or could plausibly give rise, to legal uncertainty when assessing whether a particular subject-matter falls within or outside the scope of protection conferred by the claim."

In particular, for use claims where the invention concerns a use claim directed to a known entity for a clearly distinct technical purpose or effect, the Board of Appeal confirmed that the purpose or effect may be defined in correspondingly broad and relative terms without necessarily infringing the clarity requirement "provided that the definition of the effect enables a clear distinction between the scope of protection and the prior art, thereby eliminating the risk of legal uncertainty or at least confining such risk to speculative theoretical scenarios". 

However, the Board of Appeal also found that, by contrast, where "a claimed invention is defined by the use of a known entity to achieve a known technical effect or purpose, and the alleged technical contribution of the invention resides in a relative improvement or enhancement of that effect or purpose, the requirement of clarity under Article 84 EPC generally demands that the feature defining such relative improvement or enhancement be expressed in objectively verifiable terms, thereby ensuring legal certainty regarding the scope of protection."

In other words, the novelty of a use claim can be based on technical effects that constitute relative improvements of effects of the prior art, but the features defining these relative improvements must be expressed "in objectively verifiable terms". The Board of Appeal considered that this test was not satisfied in the present case. None of the requests were thus found allowable and the Board of Appeal set aside the decision of the Opposition Division and revoked the patent. 

Of course, clarity is not usually permissible as a ground of opposition. A clarity objection was permitted in this case because the relevant features constituted post-grant amendments. However, it seems likely to this Kat that, had clarity not been a possible objection, the claims may well have been found insufficient for very similar reasons. 

Final thoughts

T 2387/22 arguably puts limits on the use of functional claim language for use claims based on a relative improvement compared to a prior art use, namely these effects should not be over broadly defined. The decision also contrasts with the recent decision in T 2130/22, which also related to the validity of functional features, albeit under the heading of sufficiency as opposed to clarity. In T 2130/22, the Board of Appeal found that the patent for a pharmaceutical formulation did provide clear guidance on how to achieve the claimed functional feature of "storage stable for at least one year" (albeit considered under sufficiency as opposed to clarity) (IPKat). The clear guidance from both of these decisions is thus that functional features relied on in a claim need to be adequately explained and defined for the skilled person. 

Therefore, whilst functional features can provide impressively broad scope for an invention, they can also run the risk of invalidity if they are not expressed in sufficiently clear and objectively verifiable terms. Unclear and insufficiently disclosed functional features may similarly be challenging to enforce. Patentees must therefore be careful that their claims do not fall short of providing legal certainty. 

Source: https://ipkitten.blogspot.com/2025/09/walking-line-between-broad-scope-and.html