In a recent decision, the Supreme Court ruled that the prosecution history of a parent patent may be taken into consideration when interpreting the scope of the claims of its divisional patent (Supreme Court Case No. 2023 Hu 11340 rendered on July 17, 2025).

▶Background of the Case

Claim 1 of the subject divisional patent, entitled “Self-cleaning Water Purifier,” recites an element: a “cleaning unit connected to a storage tank to clean the storage tank using water filtered by a filtration unit, and having a cleaning means.”  However, there is no structural/technical definition or limitation of the “cleaning means” in the claim.

In contrast, however, during the prosecution of the parent application, in order to overcome the grounds for rejection, the patentee submitted a statement that the “cleaning means” recited in the claims of the parent application did not include a “cleaning means by generating a sterilizing material through an electrolysis method.”  The patentee further limited the “cleaning means” of claim 1 thereof to “cleaning means comprising a filter including a cleaning or sterilizing material therein, or a cleaning sterilant dosing system.”  

After the claim amendment described above, the patentee filed a divisional application, which subsequently matured into the subject divisional patent.

The Petitioner filed a negative scope confirmation petition with the Intellectual Property Trial and Appeal Board (“Board”), seeking a declaratory judgement that the Petitioner’s product did not fall within the scope of claim 1 and its dependent claim 10 of the subject divisional patent.

The description of the Petitioner’s product showed that it “includes an electrode sterilizer that generates electrolyzed water by electrolyzing filtered water,” and that “the electrode sterilizer does not include any cleaning or sterilizing material.”

▶Lower Decisions

The Board did not make a judgment on whether the prosecution history of the parent application affects its divisional; but determined that the claim scope of the “cleaning means” included a “cleaning or sterilizing material.”  The Board, therefore, ruled that the Petitioner’s product did not fall within the scope of claims 1 and 10 of the subject divisional patent.

The IP High Court, however, was of the view that since claim 1 of the subject divisional patent differed from that of the parent patent and the claims of the subject divisional patent were not limited in the same manner as the parent patent, the “cleaning means” was not limited to a “filter including a cleaning or sterilizing material therein, or a cleaning sterilant dosing system.”  Accordingly, the IP High Court determined that the Petitioner’s product fell within the scope of claims 1 and 10 of the subject divisional patent.

▶Supreme Court Decision

Reversing the decision of the IP High Court, the Supreme Court determined that the Petitioner’s product does not fall within the scope of claims 1 and 10 of the subject divisional patent.

The Court stated that, in a situation where a claim contains a functional expression and the specific technical feature thereof cannot be ascertained from the description of the claim, the scope thereof may be limited by considering a totality of relevant factors including the technical idea presented in the patent specification and the intent of the applicant shown during the patent prosecution.

In this regard, the Court determined that the prosecution history of the parent patent could be considered when interpreting the claims of the subject divisional patent, taking into account the following factors: (i) during the prosecution of the parent application, the patentee submitted a statement that the “cleaning means” of claim 1 of the parent application did not include a “cleaning means by generating a sterilizing material through an electrolysis method” to overcome a rejection; (ii) the applicant for both the parent application and the subject divisional patent was the same; (iii) the subject divisional patent is an invention within the scope of the matters described in the specification or drawings originally attached to the parent application; and (iv) the patentee filed the subject divisional application after submitting the claim amendment during the examination proceedings of the parent application.

Taking these factors into account, the Court found that the patentee had consciously excluded the “cleaning means by generating a sterilizing material through an electrolysis method” from the “cleaning means” of the subject divisional patent.  Further, the Court determined that the “cleaning means” of the subject divisional patent should be construed as a “means for cleaning the storage tank by including a cleaning or sterilizing material therein and diluting such material in water filtered by the filtration unit to supply same to the storage tank.”  Thus, the Court concluded that the “cleaning means” of the subject divisional patent differs from the corresponding element of the Petitioner’s product, and the latter does not fall within the scope of claims 1 and 10 of the subject divisional patent.

▶Implications

This decision has made it clear that the prosecution history of a parent patent may be taken into consideration when interpreting the claims of its divisional patent, especially with regard to matters consciously excluded during the prosecution of the parent patent.