To infinity and beyond! The sufficiency requirements for open-ended ranges (T 1977/22)

The recent Board of Appeal decision in T 1977/22 related to the patentability of claims defining subject matter with open-ended parameter ranges. The question before the Board of Appeal was whether a claimed open range, and its numerically infinite scope, could ever be said to be sufficiently disclosed (Article 83 EPC). The Board of Appeal rejected the argument that all open-ended ranges are inherently insufficient. Instead, the Board of Appeal suggested criteria for assessing whether an open-ended range is sufficiently disclosed, based on an assessment of whether there is sufficient practical guidance enabling a skilled person to work within the range without undue burden. 

Legal Background: Open-ended ranges

According to Article 83 EPC, European patents should "disclose the invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art." For numerical ranges, this requirement is typically interpreted as meaning that the skilled person must be able to reproduce the invention across the entire claimed range (IPKat: Plausibility demystified - a review of EPO case law before G 2/21). This test is applied to all types of invention, including those in the mechanical field (IPKat). 

Unlimited Kats

The sufficiency test for ranges raises an important question for claims specifying an open-ended range for a particular parameter. An open-ended range specifies only one boundary, thereby potentially extending infinitely in one direction. Can such ranges ever satisfy the requirement of reproducibility across the entire scope, given that an infinite range would by definition include parameter values that would not be achievable by a skilled person?

The case at issue in T 1977/22 related to Rhodia Operations' patent EP 3086872, which was opposed by Neo Chemicals & Oxides (Europe) Ltd. The patent related to a thermally stable inorganic composite oxide material comprising specific amounts of metal oxides. The invention proposed to solve the problem of thermal aging in catalytic converters, where traditional materials lose their specific surface area and catalytic efficiency when exposed to high temperatures during operation. By creating a composite oxide that maintained an exceptionally high surface area even after severe calcination conditions, the invention aimed to provide improved catalysts with superior durability.

Claim 1 as granted (and on appeal) specified an inorganic composite oxide material comprising specified amounts of particular metal oxides. Crucially, the claim specified that the material exhibited a surface area defined by one of three open-ranges: >150 m²/g after calcining at 900°C for 2 hours; >85 m²/g after calcining at 1000°C for 4 hours; or >40 m²/g after calcining at 1100°C for 5 hours. In other words, there was no upper limit to the indicated surface areas specified by the claims. The Opposition Division had revoked the patent for insufficiency in view of the specified open ranges (Article 83 EPC). 

Open-ended ranges and the "reproducibility over the whole scope" standard

The Opponent argued that the claimed invention was insufficiently disclosed because it was impossible to reproduce the invention across the entire scope of the open-ended ranges. Since the specific surface area defined by each of the three open ranges could theoretically extend to infinity, the Opponent submitted that the claim inevitably included non-working embodiments that could not possibly be achieved. The Patentee argued in response that the patent provided detailed teachings in the examples that would enable a skilled person to manufacture the claimed material through routine trial and error experimentation. The Patentee also pointed out that the Opponent had not attempted to rework any examples or identified specific information gaps that would prevent reproduction. Instead, the Opponent had merely made general allegations about irreproducible embodiments without providing evidence.

Criteria for sufficient disclosure of open-ended range

The Board of Appeal rejected both extreme interpretations of the case law on open ranges. For the Board of Appeal, a literal interpretation requiring enablement of every conceivable value in the upward direction would impose an impossible burden on applicants and patentees. On the other hand, simply disclosing in the specification a few isolated examples falling within the claimed range could not always be said to be providing a sufficient disclosure. Instead, the Board of Appeal proposed that, in order to satisfy the sufficiency requirement for open ranges, the patent should provide "teachings demonstrating that, by operating within the scope of specific (essential) structural and/or process features, the skilled person would be in a position to achieve multiple variants of the invention without undue effort i.e. embodiments with different parametric values falling within the open-ended range." (r.4.13)

Applying this general principle, the Board of Appeal identified two distinct situations that may arise with respect to claims comprising parameters defined by an open range. First, there would be cases where the defined parameter was not restricted by any structural or process features. For the Board of Appeal, such claims would generally not be enabled unless the range was directly or indirectly limited by closing the range or by defining interrelated parameters imposing an upper boundary (r.4.6.7(a)). 

In contrast, there would also be cases in which the claimed subject matter defined by an open-ended range was further restricted by structural and/or process features. For the Board of Appeal, such claims may be sufficiently disclosed if the teachings indicate that the skilled person could achieve different parametric values within the claimed range by making trivial adjustments within the scope of these features (r.4.6.7(b)).

Application to the case at hand

In applying its proposed criteria to the patent in question, the Board of Appeal noted that the specification provided detailed disclosure of how to manufacture the claimed material. The examples in the patent pertained to two distinct composite oxides with components and concentrations falling within the scope of claim 1, including the specified open-ended ranges (r. 6.6.6). The evidence provided in the patent indicated that the components and concentrations of the metal oxides were the essential parameters for adjusting and enhancing the specific surface area (r. 6.6.7). 

Therefore, for the Board of Appeal, the claims defined not only the open-ended range parameters but also the essential structural features (the metal oxide components and their amounts) required to achieve those parameters (r.6.6.9). Based on this analysis, the Board of Appeal concluded that the open-ended ranges were enabled by the teachings in the patent, and the invention was reproducible over the whole scope of the claim, and that the requirements of Article 83 EPC were therefore met. The decision under appeal was therefore set aside, and the case was remitted to the Opposition Division for consideration of novelty and inventive step. 

Consistency with existing case law (and no referral to the EBA)

Both parties had requested a referral to the Enlarged Board of Appeal (EBA) on the question of the correct approach to the sufficiency of open ranges. However, in its decision, the Board of Appeal took pains to demonstrate that its approach was consistent with previous decisions concerning open-ended ranges, and concluded that there was also no divergence in the case. The Board of Appeal particularly argued that the differing outcomes in previous cases were primarily due to case-specific factors rather than fundamental divergences in legal principles. The Board of Appeal was thus of the view that the previous decision on the issue could be reconciled with its own approach. 

In cases where open-ended ranges were found reproducible (such as T 487/89, T 624/08, T 2213/08, and T 398/19), the Board of Appeal argued that the claims in question were defined by structural and/or process features that enabled adjustment of the parameter. In cases where open-ended ranges were found irreproducible (such as T 1008/02, T 1942/21, and T 2344/12), the Board of Appeal argued that this was because the claims in question did not define features shown to enable achievement of high parametric values. In T 1008/02, for example, the claim defined a product (a superabsorbent material) in terms of an open-ended range for liquid absorbing capacity without specifying any structural or process features that would enable achieving this property. The Board of Appeal concluded that there was therefore no justification for a referral to the EBA.

Importantly, the case law on the novelty and inventive step of selection inventions also applies to open ranges (IPKat). As the Board of Appeal confirmed in this decision, claims specifying selected higher parameter values falling within an open range will be novel, and potentially inventive, in view of the prior disclosure of the open range (r.4.12.3). 

Final thoughts

The decision in T 1977/22 provides some useful guidance for the assessment of open-range sufficiency. In this Kat's view, the approach taken by the Board of Appeal in this case is pragmatic and thankfully avoids setting unrealistic standards that would effectively prevent the use of open-ended ranges altogether, and the consequent enforced introduction of entirely arbitrary limits. 

On the other hand, including an open range in a claim is a risky strategy that should be avoided if it is not strictly necessary for capturing the full scope of the invention.  As the Board of Appeal pointed out in this case, whilst the criteria for open range sufficiency "avoids setting unrealistic goals [...] the burden is higher than [for] a closed range", i.e. which may be satisfied by the provision of one example of a working embodiment within the claimed range. The Board of Appeal also noted that, whilst the approach taken by Boards of Appeal have been consistent on the fundamental principles of the disclosure required for open ranges, some Boards of Appeal have required a slightly higher standard than others (r. 4.10). For example, some Boards of Appeal have required the specification to enable the skilled person to work the invention outside of the range embodied by the examples. Consequently, whilst the use of open range parameters will provide a broader scope of protection, they will also open you up to a higher disclosure standard. The strategic approach is therefore to establish what claim scope is necessary for commercially relevant protection and to limit the claims accordingly. In most cases, the commercially relevant scope (even one that protects against design-around) is likely definable using a closed range. 

Further reading

• Gold Standard test for novelty reigns supreme, even for subranges (T 1688/20) (Jan 2023)
• Plausibility demystified - a review of EPO case law before G 2/21 (Feb 2023)
• Chocolate teapots and nuclear bombs: Whole range sufficiency of mechanical inventions (T 0149/21) (July 2023)