In a case when an accused product (or process) satisfies all elements defined in a claim of a patent, the accused product literally infringes the patent. As in the US and Japan, even when an accused product does not fall within the literal scope of the claim but is equivalent to the claimed invention, patent infringement under the doctrine of equivalents has been acknowledged by many precedents in Korea. As an accused product often involves a modified element different from a patented invention, it is important to understand the principle of the doctrine of equivalents.
According to the decisions of the Korean courts, an accused product that includes a modified element as compared with a patented invention may still be recognised as infringing the patent under the doctrine of equivalents when the following requirements are met:
- the technical idea or principle to solve a problem is identical between the patented invention and the accused product;
- the accused product with the modified element accomplishes substantially the same function and effect as the patented invention; and
- the modification of an element in the patented invention to the corresponding element in the accused product is obvious to a person skilled in the art.
Regarding requirement (i), in the past, the accused product was considered to have the same technical idea or principle to solve a problem as the patented invention when the modified element of the accused product was a non-essential part of the patented invention and the accused product thus had the characteristic constitution of the patented invention.
In Supreme Court Case No 2012Hu1132 (July 24 2014), the Supreme Court ruled that whether two inventions adopt the same technical idea or principle to solve a problem should be determined by comparing the "essence or core of the technical idea" based on the disclosures of the specification and known technologies as of the filing date, rather than by extracting a part of the constitution recited in the claim.
In this case, the patented invention relates to a cutter for dried seaweed which has cutting blades laid out in a grid pattern. When seaweed is placed on top of the cutting blades and pressed downward, the cut seaweed is automatically stored in a container by sliding down an incline of a grid-patterned box attached to the bottom of the cutting blades.
The accused product, on the other hand, has cutting blades moving downward from above the seaweed, unlike the cutting blades of the patented cutter fixed below the seaweed. The seaweed cut by the cutting blades in the accused product also automatically slides down an incline of a grid-patterned box and then is stored in a container.
The Supreme Court decided that although the patented invention and the accused product use different cutting blades, the two inventions adopt the same core of the technical idea that the incline of the grid-patterned box leads seaweed to automatically move to a container after being cut, concluding that the accused product falls within the scope of the patent. This case is of significance in that the possibility of falling under the doctrine of equivalents has been increased by applying requirement (i) flexibly.
The doctrine of equivalents may not apply if the accused product was already known or could have been easily conceived from the prior art by a person skilled in the art at the time of filing the patent, or if the accused product was intentionally excluded from the scope of the claim during the prosecution of the patent (see for example Supreme Court Case No 97Hu2200 rendered on July 28 2000).
Whether a specific element was intentionally excluded from the scope of a claim (so-called prosecution history estoppel or file wrapper estoppel) is determined based on the prosecution history of the patent at issue, including the examiner's office action, the applicant's response and amendment, etc, in addition to the patent specification (see for example Korean Supreme Court Case No 2001Hu171 dated September 6 2002).
For example, if a broadly defined constitution is restricted to a particular element so as to cover only a specific embodiment of an invention in response to the examiner's rejection for lack of an inventive step, elements other than that specified may be considered to be excluded from the protection scope of the claim. In contrast, when a claim amendment is made to resolve clarity issues, whether the deleted element(s) may be deemed to be intentionally excluded by the applicant may be determined in consideration of special circumstances of individual cases.
The Japanese Supreme Court recently affirmed infringement of a process patent under the doctrine of equivalents (Chugai Pharmaceutical Co Ltd v Takata Seiyaku Co, Ltd et al, 2017(Ju)1242, Mach 24, 2017). Also, the United Kingdom Supreme Court provided an expanded interpretation on patent infringement under the doctrine of equivalents in July (Actavis UK Limited and others v Eli Lilly and Company,  UKSC 48, July 12 2017). The Korean courts seem to take a similar position to the current worldwide trend of applying the doctrine of equivalents in an expanded way.
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