In T 1719/21 (Technical Board of Appeal 3.3.03, 16 October 2025), the Board addressed whether a non-reproducible but commercially available product could be used as closest prior art in the problem–solution approach for the assessment of inventive step. The decision is relevant because it applies the Enlarged Board’s guidance in G 1/23 to the selection of a realistic starting point for inventive step analysis.
Background and relation with G 1/23
The appeal was against a decision of the Opposition Division maintaining European patent EP 2 833 415 in amended form. The patent concerns an encapsulating material for solar cells comprising an ethylene/α-olefin copolymer with a low fluorine content.
In the appeal, the Opponent inter alia pursued an inventive step attack under Article 56 EPC, starting from Example 3 of D4, in which the non-reproducible commercial polymer ENGAGE® 8400 was used.
In G 1/23, the Enlarged Board recently decided that non-reproducibility of a commercially available product does not exclude such product from the state of the art within the meaning of Article 54(2) EPC. The referring decision that lead to G 1/23 concerned the same commercial polymer as the present case, and also the same parties were involved.
Non-reproducible commercial product is a realistic starting point for inventive step
A central issue in T 1719/21 was whether the encapsulating material of Example 3 of D4, which includes the non-reproducible commercial product ENGAGE® 8400, could serve as the closest prior art in the problem-solution approach. In G 1/23, the Enlarged Board indicated that whether or not a non-reproducible but commercially available product could represent the closest prior art depends on the circumstances of the case.
The Proprietor argued that in the present case, it would be unrealistic to use ENGAGE® 8400 as closest prior art and modifying its synthesis conditions. According to the Proprietor, it would require an undue amount of experimental work to establish the original synthesis conditions of ENGAGE® 8400, before being able to make the necessary modifications. Instead, they argued that the skilled person would choose related polymers with known synthesis conditions and details as a starting point.
The Board disagreed and held that it cannot be derived from G 1/23 that a non-reproducible but commercially available product should be excluded as closest prior art when modification of the non-reproducible product is necessary. In the Board’s view, the assessment of which modifications are needed takes place in the steps of the problem-solution approach after selecting the starting point, and should not be a consideration in the selection of the starting point itself.
Therefore, the Board concluded that Example 3 of D4 constituted a realistic or promising starting point, even if the skilled person did not know how to reproduce ENGAGE® 8400.
Outcome of the appeal
The Board came to the conclusion that the claims of Auxiliary Request 2 were inventive in view of ENGAGE® 8400 as starting point. Therefore, the case was remitted to the Opposition Division with the order to maintain the patent on the basis of Auxiliary Request 2.
