Claims 1 and 10 of a self-cleaning water purifier
In its decision of 17 July 2025, the Korean Supreme Court considered whether a purifier using electrolysed water fell within corrected claims 1 and 10 of a self-cleaning-purifier patent. The Board had found it outside the claimed scope in negative scope-confirmation proceedings. The Patent Court, in decision 2022허4918 of 12 October 2023, instead found equivalence. The Supreme Court reversed and remanded.
Reading the functional expression in context
The claims referred to ‘cleaning means’ without spelling out its detailed technical structure. Claim language ordinarily defines protection and should not be arbitrarily narrowed or expanded by the description. Where a purely literal reading of a functional expression is plainly unreasonable in light of the specification, however, contextual limitation can be justified. The description disclosed a substance already held inside the cleaning means, diluted with filtered water and supplied to the tank. It did not disclose generating a disinfecting substance by electrolysis.
The parent application’s prosecution history
The parent was filed on 3 February 2009, followed by a divisional on 28 October 2010 and the further divisional at issue on 4 April 2011. In an opinion of 7 March 2011, the applicant distinguished electrolysis by arguing that its pre-contained cleaning or disinfecting substance shortened cleaning time and avoided separate power. The parent claims were narrowed to cleaning means with a filter or dosing system containing that substance. Given the common applicant, the disclosed subject matter and the sequence of the applications and statements, the court treated electrolysis as deliberately excluded. This was a contextual assessment, not an automatic rule binding every divisional to every parent statement.
Equivalence requires more than a shared objective
The inquiry includes the principle of solving the technical problem, substantially the same operation and effect, and whether the modification would be readily conceivable to the skilled person. Earlier technology already included automatic disinfection using filtered water and bypassing some filters to preserve their service life. The patent’s contribution therefore could not be defined at the broad level of ‘self-cleaning with partly filtered water’. Diluting a pre-contained substance and generating disinfecting water electrochemically did not share the relevant problem-solving principle in this case.
Outcome and drafting lessons
The compared invention was outside the scope of claim 1 and dependent claim 10. The Supreme Court’s order was reversal and remand, not an award of damages or invalidation of the entire patent. Applicants should support intended implementations in the description and assess the later effect of arguments distinguishing prior art, including across related applications. Product clearance likewise requires a claim-by-claim comparison informed by the specification, prosecution history and prior art—not the functional label alone.