In a landmark decision on 2 July 2025, it was clarified that a product placed on the market is generally part of the prior art, even if the material composition could not be analyzed or reproduced by persons skilled in the art without unreasonable effort.

Case constellation

The underlying case concerned an encapsulation substrate for a solar cell, which was sold under the trade name ENGAGE 8400. The material composition of ENGAGE 8400 was initially kept secret. The product could not be analyzed through reverse engineering.

After the market launch of ENGAGE 8400, Mitsui Chemicals filed a patent application for the material composition. The European Patent Office initially granted the patent to Mitsui Chemicals. Borealis GmbH then filed an opposition. Borealis referred to the commercially available product and argued that it was novelty-destroying compared to the subsequent patent application, regardless of how difficult it was to analyze or reproduce.

The case went all the way to the Enlarged Board of Appeal of the European Patent Office. The Enlarged Board of Appeal now followed the opinion of Borealis GmbH. The opposition proceedings will now continue with the proviso that the commercially available ENGAGE 8400 constitutes full prior art under Art. 54(2) EPC for the patented material composition.

Commentary

The case has a significant impact on our practice regarding the patenting of new materials, coatings, polymers and specialty chemicals.

We frequently advise clients on issues relating to market introduction and patentability of product compositions. It is often a question of disclosing just enough so that the invention can be reworked by persons skilled in the art with reasonable effort (within the meaning of Art. 83 EPC), but at the same time a certain part remains in the company as know-how.

The present decision now makes it clear that a decision made once is irreversible: Once the product is on the market, it cannot still be subsequently secured by patent protection.

In our view, the EPO’s decision makes sense, because otherwise patent protection could be extended almost at will, even though the product is already on the market.

At the end of the day, every new development has to be weighed up against whether to obtain monopoly rights in return for disclosure or whether to follow the path of secrecy. If the material composition is kept secret, there is a risk that no injunction can be demanded if reverse engineering is successful. However, reverse engineering is not the only way in which the composition of a material can become known to other parties; nowadays, data leaks, poaching of employees by competitors and the like also come to mind.

September 8, 2025
Thorsten Brüntjen
Patent Attorney