How Are Patent Claims Interpreted in Japanese Infringement and Revocation Proceedings?

The interpretation of patent claims stands as a cornerstone in Japanese patent litigation, whether in the context of an infringement suit or during proceedings to determine a patent's validity, such as a revocation trial (often an invalidity contention within an infringement suit). The claims define the exclusive rights granted by the patent, and thus, their construction dictates the boundaries of protection. This process is not merely a literal reading of words but a nuanced legal and technical exercise governed by statutory principles and evolving case law.

The Statutory Framework: Article 70 of the Patent Act

The Japanese Patent Act, in Article 70, provides the fundamental rules for claim interpretation. Article 70(1) states that 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 claim language.

However, Article 70(2) immediately qualifies this by stipulating that in determining the technical scope under paragraph (1), the meaning of the terms used in the patent claims shall be interpreted by also considering the description (specification) and drawings attached to the application. This means that the specification and drawings serve as essential interpretive aids, providing context and, in effect, an intrinsic dictionary for the claim terms.

A third paragraph, Article 70(3), further clarifies that the abstract (要約書 - yōyakusho) cannot be used for interpreting the technical scope of the invention.

Unifying Interpretation: Infringement vs. Validity Contexts

A significant point of discussion in Japanese patent law has been whether the approach to claim interpretation should differ between infringement litigation and proceedings concerning patent validity (e.g., an invalidity trial at the Japan Patent Office or an invalidity defense in court).

Historically, some practitioners and scholars perceived a potential divergence. In infringement, Article 70(2) clearly mandates consideration of the specification. For validity assessments, particularly in determining the "gist of the invention" (発明の要旨認定 - hatsumei no yōshi nintei) for evaluating patentability requirements like novelty and inventive step, the Supreme Court decision of March 8, 1991 (Minshu Vol. 45, No. 3, p. 123, often called the "Lipase" case or 「トリグリセリドの測定方法」事件), indicated that the gist should, in principle, be determined based on the claim language itself. Only in "exceptional circumstances," such as when the technical meaning of the claim language is not unambiguously clear or when there is an obvious clerical error in light of the specification, could the detailed description of the invention be consulted.

This "exceptional circumstances" rule could imply a narrower, more claim-centric approach in validity contexts. However, the practical and logical challenges of employing different interpretive methodologies for the same patent within the same litigation (especially after the formal introduction of the invalidity defense in infringement suits by the 2004 Patent Act amendments) have led to a strong trend towards a unified approach to claim interpretation.

Recent influential court decisions have emphasized the desirability of consistency. For instance, the Intellectual Property (IP) High Court decision of January 27, 2012 (Hanrei Jihō No. 2144, p. 51, the "Pravastatin Sodium" case or 「プラバスタチンナトリウム」事件) and the IP High Court decision of October 19, 2016 (2016 (Ne) 10047, the "Electrical Connector Assembly" case or 「電気コネクタ組立体」事件) have expressed a preference for identical claim construction in both infringement and validity assessments. This unified approach aims to prevent procedural inefficiency and ensure that a patent’s scope is not viewed differently depending on the context of the argument. In practice, this means that the specification is routinely consulted to understand claim terms in both settings.

Despite this trend towards unification, courts may still find it necessary to effectively limit the scope of a claim based on the supporting specification in certain situations. This can occur if, for example, a literal interpretation of a claim would render it technically meaningless or inoperative, or in cases involving software or system-related patents where conceptual diagrams in the specification are heavily relied upon to understand the claimed invention. The overriding principle is to ascertain the invention that was actually disclosed and enabled by the patentee.

Specific Challenges in Claim Interpretation

Several specific types of claims or interpretive scenarios present unique challenges in Japanese practice.

1. Functional Claims (機能的クレーム - kinōteki kurēmu)

Functional claims define an element of an invention by what it does rather than by its specific structure. For example, a claim might recite "a means for attaching A to B." The interpretive challenge arises when the specification discloses only one or a limited number of specific structures that perform the claimed function, yet the claim language itself is broad and functional.

The question is whether such a claim should cover all means that can perform the function, or be limited to the embodiments disclosed in the specification and their equivalents.

• Historical Approach: Historically, in infringement litigation, Japanese courts tended to limit the scope of functional claims. The scope was often confined to the specific structures disclosed in the specification and equivalents that a person skilled in the art could easily implement based on the disclosed technical idea. An example of this approach can be found in the Tokyo District Court decision of December 22, 1998 (Hanrei Jihō No. 1674, p. 152, the "Magnetic Media Reader" case or 「磁気媒体リーダー」事件). Conversely, in validity assessments, such broad functional claims were sometimes interpreted literally, which could lead to findings of lack of novelty or inventive step if prior art fell within that broad literal scope.
• Modern Trend (Unified and Limited): More recently, aligning with the unified interpretation approach, the tendency is to interpret functional claims based on the technical scope actually supported and enabled by the specification in both infringement and validity contexts. The rationale is that patent protection should not extend to subject matter that the inventor did not actually invent or enable the public to practice. Therefore, if the specification only teaches specific means to achieve a function, the claim, even if functionally worded, will likely be construed to cover only those means and their close equivalents that a skilled person could derive from the disclosed technical thought.

2. Product-by-Process Claims (プロダクト・バイ・プロセス・クレーム - purodakuto bai purosesu kurēmu)

Product-by-process (PBP) claims define a product, at least in part, by reference to the manufacturing process used to create it (e.g., "Chemical X obtained by process Y"). These claims have been a significant source of legal debate and development in Japan.

The core interpretive issue is whether the process steps recited in the claim limit the scope of the product claim.

• Two Competing Theories:
  • Product Identity Theory (物同一性説 - mono dōitsusei setsu): The claim covers any product that is structurally and materially identical to the product produced by the recited process, regardless of how it was actually made. The process language is seen as merely defining the product, not limiting its scope to only products made by that specific process.
  • Process Limitation Theory (製法限定説 - seihō gentei setsu): The claim is limited to products made by the specific process recited in the claim. A product, even if identical, made by a different process would not infringe.
• Evolution of Case Law:
  • Early Divergence: For many years, Japanese court decisions were inconsistent, with some adopting the product identity theory and others the process limitation theory in both infringement and validity contexts.
  • IP High Court Grand Panel (2012): The IP High Court Grand Panel decision of January 27, 2012 (Hanrei Jihō No. 2144, p. 51, the "Pravastatin Lactone I" case or 「プラバスタチンラクトンⅠ」事件) attempted to bring clarity. It distinguished between:
    • "True" PBP claims: Where it was impossible or impractical to define the product by its structure or properties at the time of filing. For these, the court adopted the product identity theory (process non-limiting).
    • "False" (or "Impure") PBP claims: Where the product could have been defined by structure or properties, but the applicant chose to include process limitations. For these, the court adopted the process limitation theory.
      This distinction, however, proved difficult to apply consistently, as the "true" or "false" nature often had to be determined by courts long after the patent was granted, creating uncertainty.
  • Supreme Court (2015) - The Current Leading Authority: The landscape was significantly reshaped by two Supreme Court decisions on June 5, 2015 (Minshu Vol. 69, No. 4, p. 700, "Pravastatin Lactone I"; and Minshu Vol. 69, No. 4, p. 904, "Pravastatin Lactone III" or 「プラバスタチンラクトンⅢ」事件). The Supreme Court held:
    1. Interpretation: The technical scope of a PBP claim should, in principle, be determined based on the product itself, irrespective of the manufacturing process (i.e., adopting the product identity theory). The claim covers any product identical in structure and properties, regardless of the process used to make it.
    2. Validity (Clarity Requirement): However, a PBP claim will be deemed to lack clarity under Article 36(6)(ii) of the Patent Act and thus be invalid unless there were "unavoidable circumstances" (不可能又は困難であるとの事情 - fukanō matawa konnan de aru to no jijō, or more precisely, 不可能又はおよそ実際的でないという事情 - fukanō matawa oyoso jissaiteki de nai to iu jijō) that made it impossible or utterly impractical for the applicant to define the product by its structure or properties at the time of filing.
       "Unavoidable circumstances" are considered to exist if, for example, analyzing the product's structure or properties was technically impossible at the time of filing, or would have required an extremely unreasonable amount of economic expenditure or time, considering the nature of patent applications which require a degree of expediency. This exception is often relevant for certain chemical compounds or biotechnological inventions.
  • Implications of the Supreme Court's Pravastatin Decisions: This ruling shifted the focus from how PBP claims are interpreted for infringement to whether they are valid in the first place. Most PBP claims drafted without such "unavoidable circumstances" are now vulnerable to invalidity challenges based on lack of clarity. This encourages applicants to define products by structure/properties whenever feasible. For existing patents, it created a need to reassess their validity. The decisions also prompted discussions about the possibility of amending or correcting PBP claims to, for instance, change them into process claims or to define the product by structure if that becomes possible post-filing, though such amendments are subject to restrictions against adding new matter.
  • "Apparent" or "Seeming" PBP Claims (表見的PBPクレーム - hyōkenteki PBP kurēmu): A subsequent line of discussion and case law has emerged concerning claims that include some process-like or temporal language but might not be intended as true PBP claims defining an otherwise unspecifiable product. For example, a claim might describe a product by reciting steps involved in its assembly or a state achieved through a process, where such language is arguably just a way to define the final structure or characteristics of the product. Some IP High Court decisions post-Pravastatin have shown a degree of leniency towards such "apparent PBP claims," finding them clear if the process-like language effectively conveys the structure or properties of the claimed product to a person skilled in the art. However, if the process language in a product claim does not actually define the product's structure or properties (e.g., describing the method of use of a device within a claim for the device itself), the claim may still be found to lack clarity. The precise boundaries here continue to be developed by the courts.

3. Consideration of Prosecution History (出願経過の参酌 - shutsugan keika no sanshaku)

The prosecution history of a patent (the record of proceedings between the applicant and the JPO, including office actions, applicant's arguments, and amendments) can play a significant role in claim interpretation.

• Prosecution History Estoppel (File Wrapper Estoppel): This is a well-established doctrine, particularly relevant to the doctrine of equivalents (as one of its limiting factors). If an applicant narrows their claims or makes arguments to distinguish their invention from prior art to secure the patent, they may be estopped from later asserting a scope of protection that effectively recaptures the subject matter they surrendered.
• Literal Claim Interpretation: Beyond its role in limiting equivalents, the prosecution history can also inform the literal interpretation of claim terms. If, during prosecution, the patentee explicitly defined a term in a particular way or emphasized a specific feature to overcome a rejection based on prior art, they are generally bound by those representations. Courts may reject a patentee's attempt in litigation to argue for a broader interpretation that contradicts statements made to the JPO. For instance, if a patentee stressed a difference from a prior art device to obtain the patent, they cannot later argue that their claim covers that very prior art device or something structurally and functionally indistinct from it.

Practical Aspects of Understanding Specifications for Claim Construction

While claim construction is a legal determination, it is deeply rooted in the technical disclosure. For those involved in patent matters, effectively reading and understanding the patent specification is key to anticipating how claims might be interpreted.

• Initial Approach: Often, the claims themselves, being dense and technical, can be difficult to grasp in isolation. Reading the "Background Art" (【背景技術】- haikei gijutsu) and "Problem to be Solved by the Invention" (【発明が解決しようとする課題】- hatsumei ga kaiketsu shiyō to suru kadai) sections of the specification first can provide valuable context about the prior art's shortcomings and the invention's purpose, making the claims more understandable.
• Ascertaining Technical Meaning: For those without a deep background in the specific technology, consulting introductory technical literature can be helpful. Crucially, one must check if the applicant has provided any special definitions for terms used in the claims within the specification itself (applicant as lexicographer). The JPO practice allows applicants to define terms in a way that may differ from their ordinary meaning, as long as this is clearly done in the specification.
• Identifying the Invention's Core: A key analytical step is to compare the invention with the prior art to identify its "essential part" (本質的部分 - honshitsuteki bubun) – often understood as the core technical problem addressed and the fundamental principle of its solution. Then, one assesses whether the accused product or process utilizes this essential part. This aligns with the idea that patent law aims to reward and protect the actual technical contribution disclosed, not merely clever claim drafting. If the specification clearly discloses a general solving principle, minor infelicities in claim drafting might be overcome through purposive construction or the doctrine of equivalents. Conversely, if the specification does not support a broad reading or if the accused product operates on a different technical principle, claim scope will likely be constrained.

Conclusion

Claim interpretation in Japanese patent law is a multifaceted discipline that forms the bedrock of both infringement and validity determinations. It requires a careful reading of the claim language, viewed through the lens of the specification and drawings, and informed by the understanding of a person skilled in the art. The trend towards a unified interpretive approach seeks consistency, but specific challenges posed by functional claims and, notably, product-by-process claims continue to shape the legal landscape, with the Supreme Court's Pravastatin decisions fundamentally altering the analysis for the latter. Furthermore, the prosecution history can provide critical insights into the intended meaning and scope of the claims. Ultimately, a precise and well-reasoned claim construction is indispensable for resolving patent disputes in Japan.