Claim Construction in Japanese Patent Litigation: What Approaches Do Courts Take?

Determining the scope of a patented invention is the cornerstone of any patent infringement analysis. In Japan, this process, known as determining the "technical scope of a patented invention" (tokkyo hatsumei no gijutsu-teki han'i), is governed by specific statutory provisions and a rich body of case law. For companies, including U.S. entities, involved in patent litigation in Japan, or those drafting patents with an eye towards Japanese enforcement, understanding how Japanese courts construe patent claims is paramount. This article delves into the principles and methodologies applied in Japanese claim construction.

The Statutory Foundation: Article 70 of the Patent Act

The primary legal basis for claim construction in Japan is Article 70 of the Patent Act. Its key provisions are:

• Article 70(1): "The technical scope of a patented invention shall be determined based on the statements in the patent claims attached to the application." This establishes the primacy of the patent claims (特許請求の範囲 - tokkyo seikyū no han'i). The claims are not merely a starting point but the definitive basis for ascertaining the invention's scope.
• Article 70(2): "In the case of the preceding paragraph, the meaning of terms used in the patent claims shall be interpreted by also considering the statements in the description (明細書 - meisaisho) and the drawings (図面 - zumen) attached to the application." This crucial paragraph, added by amendment in 1994, clarifies that while claims are paramount, the intrinsic evidence of the specification (which includes the detailed description of the invention) and any accompanying drawings must be consulted to understand the meaning of the terms used within those claims.
• Article 70(3): "In the cases of the preceding two paragraphs, the statements in the abstract (要約書 - yōyakusho) shall not be considered." The abstract serves a different purpose (primarily for technical information searching) and is explicitly excluded as a basis for claim construction.

The overall objective of these provisions is to define the patented invention clearly, not only to inform the public of the patentee's exclusive rights but also to provide a reliable basis for third parties to assess freedom to operate and to innovate around the patented technology.

Key Interpretative Resources and Principles

Japanese courts employ a methodical approach to claim construction, relying on several key sources of information:

1. The Patent Claims: The Definitive Text

As per Article 70(1), the literal wording of the patent claims is the most important element. Courts generally give terms their ordinary meaning as understood by a person skilled in the art (当業者 - tōgyōsha) at the time of the patent application, unless the specification or prosecution history provides a clear and specific alternative definition. The claims are intended to particularly point out and distinctly claim the subject matter which the applicant regards as their invention (as required by patent drafting rules under Article 36(5) of the Patent Act). Expanding the interpretation of claim language significantly beyond its ordinary meaning or clear definitions provided in the specification is generally disfavored, as it would undermine the public notice function of the claims.

2. The Specification (Description and Drawings): Illuminating Claim Terms

Article 70(2) mandates that the description and drawings be used to interpret the meaning of terms within the claims. The detailed description of the invention (発明の詳細な説明 - hatsumei no shōsai na setsumei) provides context, explains the invention's background, problem to be solved, technical solution, and specific embodiments or examples. This intrinsic evidence is vital for understanding what the patentee meant by the terms they chose in the claims.

However, there's a critical balance:

• The specification cannot be used to import limitations into the claims that are not already present in the claim language itself, merely because those limitations appear in the description or embodiments.
• Conversely, the specification cannot be used to expand the scope of the claims beyond what the claim language reasonably covers to encompass subject matter that is only disclosed in the description but not actually claimed.

The invention as claimed must also be supported by the disclosure in the detailed description (Patent Act, Article 36(6)(i) – often referred to as the "support requirement"). If a claim is broader than the invention described and enabled in the specification, it may be vulnerable to an invalidity challenge.

3. The Prosecution History (File Wrapper Estoppel - Kinhangen)

The prosecution history (出願経過 - shutsugan keika), which includes amendments to the claims or specification, arguments made by the applicant, and statements made to the Japan Patent Office (JPO) examiner to overcome rejections (e.g., for lack of novelty or inventive step), plays a significant role in claim construction. This history is publicly accessible through resources like the J-PlatPat database.

Japanese courts consider the prosecution history to understand the patentee's own representations about the scope of their invention. If an applicant, during prosecution, narrowed their claims or made arguments that disclaimed certain subject matter to secure the patent, they may be "estopped" (this principle is known as kinhangen, akin to prosecution history estoppel or file wrapper estoppel in U.S. practice) from later asserting a claim scope that is inconsistent with those earlier representations. This can lead to a more limited interpretation of the claim terms than their ordinary meaning might otherwise suggest. The prosecution history is thus a powerful tool for preventing patentees from "recapturing" subject matter they previously surrendered.

4. Prior Art (Publicly Known Technology - 公知技術 Kōchi Gijutsu)

While not explicitly mentioned in Article 70 as an interpretative tool, the state of the art at the time of the patent application is an essential backdrop against which claims are construed. An invention, to be patentable, must be novel and involve an inventive step over this prior art. Courts may consider prior art to better understand the technical field, the problem the invention aimed to solve, and the meaning that a person skilled in the art would have attributed to the claim terms in light of what was already known.

Historically, if a literal interpretation of a claim would cause it to read on known prior art (thus rendering the patent invalid for lack of novelty), courts sometimes adopted a narrowing construction to "save" the patent by implicitly excluding the prior art. This was often referred to as the "exclusion of prior art" (kōchi gijutsu no jogai) principle.

The Impact of the Kilby Doctrine and Patent Act Article 104-3

The approach to claims that appear to cover invalidating prior art or are otherwise clearly invalid has been significantly influenced by the Supreme Court's decision in Fujitsu Ltd. v. Texas Instruments Inc. (April 11, 2000, commonly known as the Kilby case) and the subsequent enactment of Article 104-3 of the Patent Act in 2004.

The Kilby decision established that if a patent is "clearly invalid" (e.g., for lack of novelty or inventive step), asserting rights under that patent (such as seeking an injunction or damages) constitutes an abuse of rights and is impermissible, even within an infringement lawsuit where the court itself cannot formally invalidate the patent (invalidation being primarily the JPO's jurisdiction through invalidation trials).

Building on this, Patent Act Article 104-3 provides a direct defense in infringement litigation: "Where it is found that the patent concerned should be invalidated by a patent invalidation trial, the patentee or exclusive licensee may not enforce his/her rights against the adverse party."

The introduction of this "invalidity defense" (often called the "Article 104-3 defense" or "Kilby defense") has profound implications for claim construction. It has reduced the pressure on courts to adopt strained or artificially narrow claim interpretations solely to avoid finding a patent invalid within the confines of an infringement suit. If a claim, when given its proper construction based on its language, the specification, and the prosecution history, clearly covers prior art or is otherwise fatally flawed, the defendant can now more directly argue unenforceability under Article 104-3, rather than forcing the court into complex claim construction gymnastics to preserve validity. The issue can be confronted more directly as one of validity affecting enforceability.

Special Considerations in Claim Construction

Certain types of claim language present unique interpretative challenges:

Functional Claims (機能的クレーム - Kinō-teki Kurēmu)

Japanese patent law permits claims where an element is defined, at least in part, by the function it performs rather than by its specific structure or material (functional claiming). This became more common after the 1994 Patent Act amendments relaxed some of the strictures on claim drafting.

However, the interpretation of functional claims is carefully managed to prevent them from becoming overly broad and covering subject matter not adequately disclosed or enabled by the patentee. The general approach of Japanese courts is to interpret a functional claim element as covering the corresponding structure, material, or acts described in the specification that perform the claimed function, and equivalents thereof. A decision by the Tokyo District Court on December 22, 1998 (the "Magnetic Medium Reader case") indicated that the scope of such claims should be limited to the structures disclosed in the description and those that a person skilled in the art could implement based on that disclosure. This approach bears resemblance to the interpretation of means-plus-function claims under 35 U.S.C. § 112(f) in the United States.

If a functional claim is so broad that it is not supported by the specification across its entire scope, it risks being found invalid for lack of support (Article 36(6)(i)) or lack of enablement, which can then be raised as an Article 104-3 defense.

Product-by-Process Claims (プロダクト・バイ・プロセス・クレーム - Purodakuto-bai-Purosesu Kurēmu)

These are claims directed to a product (物 - mono) but where the product is defined, at least partially, by the process used to make it. Such claims are often used in fields like chemistry or biotechnology where a product's structure may be complex or difficult to define directly by its properties alone.

The central interpretative issue has been whether the claim scope is limited to products made only by the recited process (a process-limited interpretation, 製法限定説 - seihō gentei setsu), or whether it covers the product itself, regardless of the method of manufacture, provided the product is identical to that produced by the recited process (a product identity interpretation, 物同一性説 - mono dōitsusei setsu).

This was a contentious area until the Supreme Court of Japan issued landmark decisions in the Pravastatin Sodium cases on June 5, 2015. The Court distinguished between:

1. "True" product-by-process claims: Where it was impossible or utterly impractical to define the product by its structure or characteristics at the time of filing. For these claims, the Supreme Court held that their technical scope (for infringement purposes) covers a product that is identical in structure and properties to that made by the recited process, even if produced by a different method (i.e., the product identity theory applies).
2. "Untrue" product-by-process claims: Where the product could have been defined by its structure or characteristics at the time of filing, but the applicant chose to include process limitations. The Supreme Court ruled that such "untrue" product-by-process claims generally lack clarity as required by Article 36(6)(ii) of the Patent Act and are therefore invalid. This effectively means that if a product can be defined by its structure, claiming it by its process is improper from a validity standpoint.

These decisions significantly clarified the landscape for product-by-process claims, emphasizing that the "product identity" approach to infringement scope is reserved for situations where defining the product by its process was a genuine necessity. For other situations, including process limitations in a product claim primarily creates a validity problem due to lack of clarity.

Overly Broad Claims (広すぎるクレーム - Hirosugiru Kurēmu)

Claims that are significantly broader than the invention disclosed and enabled in the specification may violate the support requirement (Article 36(6)(i)) or the clarity requirement (Article 36(6)(ii)). While courts historically might have attempted to construe such claims narrowly by limiting them to the disclosed embodiments, the more modern approach, especially with the availability of the Article 104-3 defense, is to address such overbreadth as an invalidity issue that renders the patent unenforceable.

The Lipase Case and its Context

The Supreme Court's judgment on March 8, 1991 (often called the Lipase case) is sometimes discussed in the context of claim construction. This case primarily concerned the determination of the "gist of the invention" (hatsumei no yōshi) for assessing patentability requirements (like novelty and inventive step) during examination. The Court held that the gist should be determined from the claims, and the specification should generally not be consulted to narrow or interpret clear claim language unless the claims were ambiguous or contained obvious errors.

The subsequent addition of Article 70(2) in 1994 (mandating consideration of the specification for interpreting claim terms) was partly to ensure that for post-grant infringement analysis, the specification would indeed be fully considered to understand claim terminology, distinguishing this from the stricter approach to defining the "gist" during examination as outlined in Lipase. The current understanding is that while Lipase set a standard for examination, Article 70(2) governs claim construction in infringement litigation, allowing for a contextual interpretation of claim terms based on the specification.

Conclusion

Claim construction in Japanese patent litigation is a claim-centric process, fundamentally guided by Article 70 of the Patent Act. While the patent claims themselves are paramount, their terms are interpreted in light of the detailed description of the invention and drawings, as well as the prosecution history. The advent of the invalidity defense under Article 104-3 has significantly influenced this area, allowing courts to address clear validity issues more directly rather than relying on strained claim constructions to avoid them. Special claim formats like functional claims and product-by-process claims have their own interpretative nuances, with recent Supreme Court guidance on product-by-process claims bringing much-needed clarity. For any entity involved with Japanese patents, a deep appreciation of these claim construction principles is indispensable for accurately assessing patent scope and navigating infringement disputes.