Earlier this year, Stephan Schultes and Magnus Johnston took an in-depth look at the way the European Patent Office (EPO) examines claims to inventions defined in terms of parameters. They noted that while chemical and materials related inventions often lend themselves to parametric definitions in terms of physical structures and experimentally measurable properties, such definitions can lead to problems with clarity and sufficiency. In some cases, EPO examiners can consider the use of parameters to be an attempt to disguise a lack of novelty.
A recent decision (T 0555/18) by a Technical Board of Appeal at the EPO considered how inventive step is to be assessed when the only distinguishing feature of the claim is an unusual parameter.
In this case, the claim related to a multilayer, heat-shrinkable film defined inter alia in terms of a Fourier-transform infrared (FTIR) spectroscopic transmission absorbance ratio to be measured upon conditioning at a specified temperature and humidity for a specified length of time. The patent explained that an absorbance ratio of 1.65 or lower indicated a high polyamide content, which conferred high strength, and a low degree of crystallinity, which conferred high transparency.
The opponent as appellant argued that the FTIR transmission absorbance ratio was an unusual parameter not commonly used in the field, and the Board agreed.
According to the EPO’s Guidelines for Examination, there are two types of unusual parameter:
(i) The unusual parameter measures a property of the product/process for which another generally recognised parameter is used in the field of the invention.
(ii) The unusual parameter measures a property of the product/process that was not measured before in the field of the invention.
Parameters which fall into class (i) are considered to be prima facie objectionable on grounds of lack of clarity, because no meaningful comparison can be made with the prior art, if no straightforward conversion from the unusual parameter to a parameter generally recognised in the art is possible, or if a non-accessible apparatus for measuring the unusual parameter must be used.
Parameters which fall into class (ii) are allowable if it is evident from the application that the skilled person would face no difficulty in carrying out the presented tests and would thereby be able to establish the exact meaning of the parameter and make a meaningful comparison with the prior art. However, the onus of proof that an unusual parameter is a genuine distinctive feature vis-à-vis the prior art lies with the applicant.
In T 0555/18, the Board considered that the FTIR transmission absorbance ratio was the only distinguishing feature over prior art document D3 and had to determine (a) whether a difference in this parameter really led to improved optical properties and (b) whether working in the claimed range would not be obvious based on a combination of disclosures within D3, as the patent proprietor had argued.
With regard to question (a), the Board was not convinced by the proprietor’s arguments and concluded that the stated technical effect was not achieved. The objective technical problem was therefore merely the provision of an alternative film to the one known from D3.
With regard to question (b), the Board noted that, when the only distinguishing feature is a range of an unusual parameter, the assessment of obviousness might be clouded by the fact that such parameters are by definition rarely described in the relevant prior art. This means that indirect comparisons between the claimed parameter and estimates based on more common parameters in the prior art could lead to uncertain conclusions. This opened the question of who should bear the burden of proof as to whether or not the resulting estimates are sufficient to render the invention obvious.
The Board then determined that the case law on unusual parameters in the context of novelty had to be followed when assessing inventive step, meaning that, in cases of doubt, the burden of proof had to lie with the patent proprietor. The Board considered this approach to be justified because it would be unequitable for a party to benefit from the uncertainties created by its decision to define the invention in terms of an unusual parameter.
In the present case, the Board found that this burden of proof had not been discharged by the proprietor because no evidence had been provided to demonstrate that a film which would result from combining the relevant disclosures in D3 would have an FTIR ratio falling outside the claimed range. The claim was therefore found to lack an inventive step.
This decision highlights the difficulties which may be encountered when defining inventions in terms of unusual parameters. As noted in our previous article, extreme care must be taken when drafting applications of this nature, and the burden on the proprietor to provide evidence substantiating the invention continues even after grant.