Challenging Patent Validity in Japan: Patent Invalidation Trials vs. Post-Grant Oppositions for U.S. Businesses

A granted patent in Japan, while conferring significant exclusive rights, is not immune to challenges regarding its validity. Japanese patent law provides robust administrative mechanisms for third parties—and in some cases, the patentee themselves—to re-examine and potentially nullify or amend a granted patent. For U.S. businesses operating in Japan, whether as patentees defending their rights or as entities seeking to clear the path by challenging a competitor's patent, understanding these post-grant procedures is crucial. The two primary administrative routes for challenging patent validity before the Japan Patent Office (JPO) are Patent Invalidation Trials (Mukō Shinpan) and the more recently reintroduced Post-Grant Opposition system (Tokkyo Igi no Mōshitate). This article provides a comparative overview of these two distinct yet related mechanisms.

Patent Invalidation Trials (無効審判 - Mukō Shinpan) - Patent Act Article 123

The Patent Invalidation Trial is a formal, inter partes proceeding before the JPO's Trial and Appeal Board, designed to determine whether a granted patent should be invalidated.

Purpose and Effect:
The core purpose of an invalidation trial is to seek a retroactive nullification of a patent. If an invalidation trial is successful and the decision to invalidate becomes final and binding, the patent is deemed to have never existed from its grant date (Patent Act, Article 125). This erga omnes (against all parties) effect can have significant commercial consequences, impacting past infringement judgments, ongoing litigation, and licensing agreements. (Note: Post-2011 amendments to the Patent Act, such as Article 104-4, have introduced complexities regarding the effect of a subsequent patent invalidation on a prior, final infringement judgment, aiming to preserve the finality of court decisions under certain circumstances.)

Who Can Request an Invalidation Trial?
Prior to a 2014 amendment, "any person" could theoretically request an invalidation trial. However, following the reintroduction of the post-grant opposition system (discussed below), standing to request an invalidation trial was narrowed. Under the current Article 123(2), an invalidation trial can generally only be requested by an "interested party" (rigai kankeinin)—that is, a person or entity who has a legal interest that would be affected by the patent's validity (e.g., an alleged infringer, a direct competitor operating in the same field, or a party threatened with an infringement suit).
A key exception is that if the ground for invalidation is non-entitlement (e.g., the patent was granted to someone other than the true inventor or their rightful successor), only the person actually entitled to obtain the patent can request invalidation on that specific ground.

Timing of the Request:
An invalidation trial can be requested at any time during the term of the patent, and importantly, even after the patent has expired or ceased to exist (Article 123(3)). The rationale for allowing post-expiration challenges is that the patent's effects during its term (e.g., liability for past infringement damages) can still be relevant.

Grounds for Invalidation:
The grounds for seeking patent invalidation are enumerated in Article 123(1) and largely mirror the reasons for which a patent application can be refused during examination (under Article 49). Common grounds include:

• Lack of novelty or inventive step (non-obviousness).
• Inability to work the invention (lack of enablement) or insufficient disclosure.
• Claims not supported by the description.
• Unclear or indefinite claims.
• Addition of "new matter" during prosecution that went beyond the original disclosure.
• Non-entitlement (e.g., patent granted to a party not entitled to it).
• Violation of joint application requirements.
  However, certain grounds for pre-grant refusal, such as lack of unity of invention (Article 37) or failure by the applicant to disclose information on known inventions during prosecution (Article 36(4)(ii)), are not grounds for post-grant invalidation.

Procedure:
An invalidation trial is a formal adversarial proceeding conducted by a panel of three or five Administrative Patent Judges (shinpan-kan) at the JPO.

• It is an inter partes proceeding, with the requester (petitioner) and the patentee (respondent) as the main parties. Third parties with a direct legal interest may be allowed to intervene.
• While written submissions are central, oral hearings are, in principle, part of the process (Article 145(1)), reflecting a shift towards more court-like procedures.
• Patentee's Opportunity to Correct (Request for Correction - 訂正請求 Teisei Seikyū): A crucial feature of invalidation trials is the patentee's ability to file a "Request for Correction" (Article 134-2) during the trial to amend the description, claims, or drawings. This allows the patentee to attempt to overcome the cited grounds of invalidity, typically by narrowing the scope of the claims, correcting errors, or clarifying ambiguities. The allowable scope of such corrections is strictly limited (e.g., no addition of new matter, no substantial broadening or change of the claimed invention, and the corrected claims must generally be independently patentable).

Decision (Shinketsu) and Appeal:
The panel of Administrative Patent Judges will issue a trial decision (shinketsu), either upholding the patent, invalidating it in whole, or invalidating some claims while upholding others. The losing party can appeal this JPO decision to the Intellectual Property (IP) High Court in Tokyo.

Res Judicata (Article 167):
A final and binding decision in an invalidation trial has a res judicata effect. Prior to a 2011 amendment, this effect was erga omnes regarding the same facts and evidence. However, the 2011 amendment limited the res judicata effect of an invalidation trial decision primarily to the parties and interveners involved in that specific trial. This means that, in principle, a different interested party could potentially initiate a new invalidation trial even on the same grounds and evidence, although practical considerations and judicial efficiency might still play a role in how such subsequent challenges are viewed.

Post-Grant Oppositions (特許異議の申立て - Tokkyo Igi no Mōshitate) - Patent Act Article 113

The Post-Grant Opposition system was reintroduced into Japanese patent law by a 2014 amendment (effective April 1, 2015), having been abolished in 2003. It provides an earlier, simpler, and more broadly accessible mechanism for reviewing the validity of recently granted patents.

Purpose and Nature:
The primary aim of the opposition system is to serve as a public quality control mechanism, allowing for the early identification and revocation (or correction) of erroneously granted patents. It is intended to be a more streamlined, less adversarial process than an invalidation trial, with a stronger element of ex officio (by the JPO's own motion) examination once an opposition is filed. It is seen as a procedure for the public good, rather than purely a means for resolving disputes between specific parties. If a patent is revoked through an opposition, the revocation has retroactive effect, meaning the patent is deemed to have never existed (Article 114(3)).

Who Can File an Opposition?
A key feature of the opposition system is its accessibility: any person (nanibito mo) can file an opposition (Article 113). Unlike an invalidation trial, the opponent does not need to demonstrate a specific legal interest or standing. This allows a broader range of parties, including public interest groups or individuals, to challenge a patent's validity.

Timing of Filing:
The window for filing a post-grant opposition is very specific and relatively short: it must be filed within six months from the date of publication of the granted patent in the official Patent Gazette (Article 113, main proviso). This strict deadline emphasizes the system's role as an early review mechanism.

Grounds for Opposition:
The grounds for opposition are listed in Article 113 and largely overlap with the substantive grounds for invalidation (and pre-grant refusal), such as lack of novelty, inventive step, insufficient disclosure (enablement/support), lack of clarity, or addition of new matter. However, certain grounds available in invalidation trials, notably those relating to non-entitlement (e.g., the patent being granted to the wrong inventor or applicant, per Article 123(1)(vi)) or breaches of joint application requirements (Article 123(1)(ii)), are not available as grounds for a post-grant opposition. Such issues must be addressed through an invalidation trial by an appropriate party.

Procedure:

• The opposition is examined by a panel of three or five Administrative Patent Judges at the JPO (Article 114(1)).
• The proceedings are conducted primarily on the basis of written submissions (書面審理 - shomen shinri) (Article 118(1)).
• Once an opposition is filed and the patentee is notified, the JPO largely takes control of the examination. The opponent's active role is somewhat limited after the initial filing, though they do get an opportunity to comment on the patentee's response and any proposed corrections.
• An opponent generally cannot withdraw the opposition after the patentee has been notified by the JPO and the process is underway (Article 120-4).
• Patentee's Opportunity to Correct (Request for Correction - 訂正請求 Teisei Seikyū): Similar to invalidation trials, the patentee is given an opportunity to respond to the opposition and may file a Request for Correction of the description, claims, or drawings to address the grounds raised (Article 120-5). The allowable scope of corrections is subject to the same strict limitations as in invalidation trials (e.g., narrowing, no new matter). The opponent is then given a chance to submit an opinion on the patentee's response and/or proposed correction (Article 120-5(5)).
• Intervention in opposition proceedings is limited to parties wishing to assist the patentee (Article 119).

Decision (Revocation or Maintenance) and Appeal:
The panel of Administrative Patent Judges will issue a decision either to revoke the patent (取消決定 - torikeshi kettei) in whole or in part, or to maintain the patent (特許維持決定 - tokkyo iji kettei) (Article 114(2), (4)).

• Appeal by Patentee: If the patent is revoked, only the patentee can appeal this decision to the IP High Court (Article 178(1)).
• No Appeal by Opponent: If the patent is maintained, the opponent cannot appeal this decision (Article 114(5)). If the opponent remains dissatisfied, their recourse is to file a separate invalidation trial, provided they meet the "interested party" requirement for such a trial.

No Res Judicata Against Opponent for Maintenance Decision:
A decision to maintain a patent in an opposition proceeding does not create a res judicata effect that would bar the opponent (or any other party) from subsequently initiating an invalidation trial, even based on the same grounds or evidence.

Absence of "Middle Party Rights":
Unlike invalidation trials where under certain circumstances a party who was working an invention covered by a subsequently invalidated patent might acquire "middle party rights" (Chūyō-ken - Article 80) to continue working, there is no equivalent provision for such rights arising from a patent revocation in an opposition proceeding.

Recent statistics indicate a significant uptake of the opposition system since its reintroduction, with the number of oppositions filed in 2016 being nearly ten times that of invalidation trials, suggesting it is being actively utilized as a tool for reviewing patent validity.

Comparing Invalidation Trials and Post-Grant Oppositions: Key Differences

Strategic Considerations for U.S. Businesses

The dual system for challenging patent validity in Japan offers strategic choices:

• For Parties Seeking to Challenge a Competitor's Patent:
  • Post-Grant Opposition: This is an attractive option if the challenge can be mounted within the strict six-month window. It requires no demonstration of legal interest, can be less costly initially, and provides a relatively quick JPO review. It is well-suited for clear-cut cases of invalidity based on readily available prior art. The main drawback is that if the patent is maintained, the opponent cannot appeal and must then consider initiating a separate, more involved invalidation trial.
  • Patent Invalidation Trial: This is the route for challenges after the six-month opposition window has closed, or if the challenger is not the opponent from an earlier unsuccessful opposition, or if the grounds for challenge are those not available in an opposition (e.g., non-entitlement). It is also the necessary forum if a full inter partes adversarial proceeding with more extensive evidence and argument is desired. It requires the challenger to have standing as an "interested party."
• For Patentees Defending Their Patents:
  • In both opposition and invalidation trial proceedings, the patentee has the crucial opportunity to file a Request for Correction to amend the claims or specification to overcome the asserted grounds of invalidity. This is a vital defensive tool that can salvage patent rights, albeit often in a narrowed form.
  • The defensive strategy will differ. Oppositions, being more ex officio post-filing, require a strong initial response and effective use of the correction mechanism. Invalidation trials are more akin to litigation, requiring ongoing engagement with the petitioner's arguments and evidence.

Conclusion

Japan provides two distinct and significant administrative pathways for challenging the validity of granted patents: the early-window, publicly accessible Post-Grant Opposition system, and the more formal, inter partes Patent Invalidation Trial available to interested parties throughout a patent's life and beyond. Each system has its own unique characteristics, procedural nuances, and strategic implications. For U.S. businesses and other stakeholders involved with the Japanese patent system, a clear understanding of these mechanisms is essential for effectively protecting their own innovations, challenging questionable patents held by others, and navigating the competitive intellectual property landscape in Japan.