When does a modified product infringe a patent?

In a ruling on Dec. 8, 2025, the Brussels Court of Appeal ruled that the displays sold by Thinkerbell for Corona and Jupiler did not infringe Pozo Negro Beheer's patent EP 3 205 240. A competitor does not infringe a product on the market if it applies a substantially different technical principle, even if it ostensibly provides the same benefit. The ruling illustrates how strictly the court tests the equivalence doctrine, and the risks a patentee runs when he sharply delineates his own invention in opposition proceedings.

The facts

Pozo Negro Beheer designs creative store displays. Holbox, a company in the same group with manufacturing plants in the Netherlands and Poland, commercializes those displays under a license and distribution agreement. Pozo Negro Beheer holds European patent EP 3 205 240 on a basic structure for displays, granted in November 2018 on the basis of a 2016 Dutch priority application.

The patented invention revolves around a specific fastening system. Swiveling folding strips on both sides are connected to the supporting surface of the tray and engage on gripping surfaces of connecting structures in the side walls. The combination of those pivoting folding strips with the other elements, according to the patent holder, provides improved stability through three mutually reinforcing interlocks.

In May 2019, Pozo Negro Beheer learned through brewer Anheuser Busch InBev that Thinkerbell was offering similar “Corona Ice Bucket Retail” displays in the French market. Further investigation revealed that the same type of display was also being used in the Belgian market, this time for Jupiler 0.0%. On July 9, 2019, Holbox wrote to AB InBev about this, stating that the displays infringed its patent.

After a descriptive seizure regarding counterfeiting and failed direct negotiations, the patent holders sued Thinkerbell on Oct. 31, 2019. The Dutch-speaking enterprise court in Brussels dismissed the infringement claim by judgment on Nov. 10, 2020. However, the first judge did rule that the summons to AB InBev was a unfair market practice . Both sides appealed.

The decision

The court affirmed the judgment on the main point - no patent infringement - and reforms it at the point of badmouthing.

No literal infringement

A literal patent infringement requires that all of the features of the patent claim be present in the allegedly infringing product. The court found that the two distinguishing features of EP 3 205 240 - the swivel side fold strips that engage the engagement surfaces of the connecting structures - were not present in the Thinkerbell displays.

In those displays, the front fold strips are correctly glued to the underside of the support surface. Because of that bonding, they are no longer pivotable. The rear fold strips do swivel, but do not engage the engagement surfaces as required by the patent. That during the production stage the folding strips were still pivotable is irrelevant: at that stage there is no basic structure in the sense of claim 1.

No infringement by equivalent

Equivalence is assessed via the function-way-result test. A replacement feature must perform substantially the same function, in substantially the same way, with substantially the same result. The three conditions are cumulative.

The court held that none of those three conditions is met. The Thinkerbell displays operate on a substantially different principle: a tab-slot connection in which a protrusion on the side wall engages a slot in the support surface - exactly the principle from US 2015/0068998, which is undisputedly state-of-the-art. The additional glued third panel with a slot strengthens the tray, but does not change the connection principle: even without the glued folding strip, the tab-slot connection would be established.

In interpreting the feature “gripping surface,” the court expressly relies on the opposition argument of Pozo Negro Beheer's patent attorney before the European Patent Office. In his January 7, 2020 response, that patent attorney had described the gripping surface as a plane behind the connecting structure, in a pocket or pocket between the outer and inner walls, on which the swivel folding strip engages behind. The court adopted that interpretation as the meaning the skilled person would give to the patent, in accordance with Art. 69 European Patent Convention (EPC). Since the Thinkerbell displays have no engagement behind the connecting structure, their design falls outside the scope of protection.

No badmouthing

The court now dismisses the malpractice claim in its entirety, reforming on this point the judgment of the first judge, who did characterize the July 9, 2019 email as badmouthing.

The fact that Holbox described the displays in that e-mail as “infringing,” rather than “potentially infringing,” does not in itself make that e-mail a prohibited act under Article VI.104 Code of Economic Law (CEL). The content of the e-mail sufficiently showed that no court decision had yet been intervened, and Holbox expressly announced that it would keep AB InBev itself out of the legal action. Under these circumstances, the court finds neither bad faith nor potential harm to Thinkerbell demonstrated.

Legal analysis and interpretation

What you say in opposition proceedings is taken into account under the doctrine of equivalence

What is most striking about this ruling is how the court uses the views of Pozo Negro Beheer's patent attorney in the opposition proceedings before the European Patent Office to delineate the scope of protection of the patent. In his January 7, 2020 answer, the patent attorney had described the operation of the swivel folding strip as an engagement in an intermediate space (“pocket”) behind the connecting structure, with the folding strip pulling the sidewall inward. This was distinctive from the tab slot solution of US 998, which the patent attorney explicitly described as less effective and less reliable.

The court now uses precisely this line of argument to determine that the Thinkerbell design does not fall within the scope of protection: the tab slot with a reinforcing third panel works differently and, according to the court, does not demonstrably produce the same beneficial synergistic result. What was used in opposition as a trump card to uphold the patent becomes the source of a limited scope of protection in infringement proceedings.

This comes close to what is called “prosecution history estoppel” in U.S. law. Belgian and European patent law have no formal estoppel doctrine, but Article 69 EPC and its protocol do require that the claims be reasonably construed in light of what the patentee himself understands by the invention. This ruling confirms that the opposition file provides material that national courts do not simply ignore.

Categorical infringement allegations before judgment: not automatic badmouthing

The second point of interpretation concerns the badmouthing claim. The first judge had judged that Holbox’s communication to AB InBev — in which the Thinkerbell displays were unreservedly labelled as “infringing” — constituted an unfair market practice. The court revises that assessment in an interesting way.

The court does not deny that the e-mail was “unnecessary”; appellants could have written to Thinkerbell directly. But unnecessary is not the same as wrongful. What is decisive is that the e-mail framed an ongoing communication from several months earlier, made it sufficiently clear that legal action had yet to be taken, and kept AB InBev itself out of legal action. Under these circumstances, the court finds no bad faith present and no harm demonstrated.

This is a nuance that lowers the threshold for bad faith in IP cases in practice. Those wishing to enforce their intellectual rights do not have to submit every citation to a judge before delivering it to a third party. However, caution remains necessary: the stronger the allegation, the more direct the buyer's commercial relationship with the challenged competitor, and the less clear that a court ruling has yet to follow, the greater the risk that a court does assume fault.

Specifically, what does this mean?

For patent holders seeking to address infringement.
This ruling underscores that the equivalents doctrine is not a safety net for weak claims. The scope of protection is measured tightly by the technical effect as described in the patent - and by what the patentee himself has presented as characteristic in the opposition or examination proceedings. Those who make sharp delimitations during grant or opposition to escape an anteriority buy stronger validity, but at the same time sacrifice some of the breadth of their protection. An internal audit of previously taken positions in opposition and examination proceedings deserves consideration before any new infringement claim.

For companies looking to design around a patent.
A focused design-around remains a legitimate strategy, even in commercially sensitive sectors. What is crucial is that the alternative design not only looks different, but works substantially differently - and that this is documented. The Thinkerbell displays pass the equivalency test because they reuse a previously known tab slot principle (from US 998), supported by a reinforcing panel that does not change the connection principle per se. For those considering a design-around, a thorough analysis of the prior art as well as the opposability of the opposing patent often provide the best defense.

Frequently asked questions (FAQ)

What is the difference between literal patent infringement and infringement by equivalents?
For literal infringement, all technical features from the patent claim must be present in the alleged counterfeit product. For infringement by equivalent, at least one feature is missing, but is replaced by another feature that performs substantially the same function, in substantially the same way, with substantially the same result. That function-way-result test serves to assess equivalence, and all three conditions must be cumulatively satisfied.

May I warn a competitor's customer that their product may infringe my patent?
In principle, yes, but tone and timing are crucial. The Brussels Court of Appeal accepts that a patentee may write directly to a customer to obtain information about the supplier, even when the infringement case has not yet been decided by a judge. However, the communication must sufficiently show that the judgment is not yet final, and the customer must not be put in an untenable commercial position. Anyone spreading categorical infringement allegations without these precautions does risk a conviction for badmouthing under art. VI.104 CEL.

Are patent attorney's fees part of court costs?
No. The court confirms, in line with established cassation case law, that the fees of a patent attorney do not constitute legal costs within the meaning of article 1018 of the Judicial Code. However, those costs can, if necessary, be part of the damages in a non-contractual liability claim, but that requires a separate proof of fault, damage and causation.

Conclusion

This ruling makes it clear that the Brussels Court of Appeal applies the equivalence doctrine strictly and technically. A bonded, non-swiveling folding strip that is part of a tab slot joint is not an equivalent to a swiveling folding strip that engages behind a gripping surface - even if, at first glance, both solutions appear to aim for the same result. What the patentee has claimed as distinctive in the opposition proceedings may significantly reduce its scope of protection in a subsequent infringement proceeding.

The ruling also confirms that a notice to a purchaser about suspected patent infringement does not automatically constitute bad faith, as long as the communication is sufficiently carefully worded and does not put the purchaser in an untenable commercial position.