Challenging a Patent in Japan: An Overview of Oppositions and Invalidation Trials

In Japan, the grant of a patent by the Japan Patent Office (JPO) does not signify the end of scrutiny. The Japanese patent system provides robust administrative mechanisms for third parties to challenge the validity of a granted patent. Understanding these post-grant review procedures is crucial for businesses, whether they are looking to clear a path for their own activities, defend against infringement allegations, or manage their own patent portfolio. The two primary administrative routes for such challenges are the Patent Opposition system (特許異議の申立て - Tokkyo Igi Mōshitate) and the Invalidation Trial (無効審判 - Mukō Shinpan).

This article provides a comprehensive overview of these two key procedures, outlining their purpose, grounds, procedural aspects, and strategic considerations.

I. The Patent Opposition System (特許異議の申立て - Tokkyo Igi Mōshitate) - A Public Review Window

The Patent Opposition system in Japan offers an early opportunity for any member of the public to challenge the validity of a newly granted patent. It serves as a public quality control mechanism, aiming to revoke patents that may have been erroneously granted.

A. Purpose and Historical Context

The primary purpose of the patent opposition system is to enhance the reliability and quality of granted patents by allowing for a relatively quick and low-cost review shortly after grant. It invites public scrutiny to identify patents that may not meet the statutory requirements for patentability.

Historically, Japan has had an opposition system in various forms. The current system was notably re-introduced by a 2014 amendment to the Patent Act (effective April 2015). This revived a post-grant opposition system that had been abolished in 2003 when patent challenges were consolidated into the invalidation trial system. The 2003 reform, however, did not lead to the anticipated volume of challenges through invalidation trials alone, and concerns arose about potentially invalid patents remaining in force without early review. The re-introduction of the opposition system was intended to address these concerns, providing a more accessible avenue for early challenges and contributing to the faster stabilization of patent rights.

B. Key Features of the Opposition System

1. Who Can File an Opposition? (Article 113)
   • An opposition can be filed by "any person" (何人も - nannin mo). There is no requirement for the opponent to demonstrate a specific legal or commercial interest in the patent being challenged. This open standing reflects the public interest nature of the opposition system – it's a tool for anyone to help ensure patent quality.
2. Timing – A Limited Window (Article 113)
   • The opposition must be filed within a strict six-month period from the date of publication of the patent in the official Patent Gazette (特許掲載公報 - tokkyo keisai kōhō), which occurs after the patent is granted and registration fees are paid. This relatively short window emphasizes its role as an early review mechanism.
3. Grounds for Opposition (Article 113)
   • The grounds for opposition are specifically enumerated and are generally limited to issues that should have been considered during the pre-grant examination. They are primarily related to substantive patentability requirements and certain formal defects. Common grounds include:
     • Lack of novelty (Article 29, 29-2).
     • Lack of inventive step (Article 29(2)).
     • Unpatentable subject matter (e.g., not a statutory "invention," contrary to public order or morality under Article 32, or inventions by non-natural persons where applicable under Article 25).
     • Violation of joint application requirements (Article 38) or patent granted to a non-entitled person (though for these, an invalidation trial by the rightful owner is often the more direct path to regaining rights).
     • Insufficient disclosure (lack of enablement under Article 36(4)(i), or lack of support, clarity, or conciseness of claims under Article 36(6)(i)-(iii)).
     • Addition of new matter beyond the original disclosure during prosecution (Article 17-2(3)).
     • Violation of treaty provisions.
   • It's important to note that certain grounds for invalidation, such as those relating to the true entitlement to the patent (e.g., if the patent was granted to someone who was not the true inventor and did not have the right to apply), are typically addressed through invalidation trials or court actions rather than oppositions, although some overlap exists.
4. The Opposition Procedure (Articles 114-120-8)
   • The opposition is filed with the JPO by submitting a written statement of opposition, including the grounds and supporting evidence.
   • The procedure is conducted by a panel of three (or, for complex cases, five) administrative judges (審判官 - shinpan-kan) of the JPO's trial and appeal department.
   • The nature of the proceeding is largely ex officio and primarily paper-based, meaning the JPO panel takes an active role in examining the issues based on the submissions, though the patentee is a key participant.
   • The patentee is notified of the opposition and given an opportunity to submit a written response (答弁書 - tōbensho).
   • Patentee's Right to Correct (訂正請求 - Teisei Seikyū): If the JPO panel issues a preliminary "Notice of Reasons for Revocation" (取消理由通知 - torikeshi riyū tsūchi), indicating an intent to revoke the patent, the patentee has a crucial opportunity to file a request for correction of the claims, specification, or drawings to overcome the cited grounds (Article 120-5). The allowability of such corrections is subject to strict conditions (e.g., they must not add new matter or unacceptably broaden the claims).
   • The opponent may be given a chance to submit observations on the patentee's response or proposed corrections.
   • The panel of judges then makes a decision based on all submitted materials and its own assessment.
5. Outcome and Appeals (Article 114)
   • The JPO will issue a decision (決定 - kettei) to:
     • (a) Maintain the patent as granted: If the opposition is found to be unmeritorious.
     • (b) Revoke the patent: If the grounds for opposition are found to be valid and cannot be overcome by correction. This can be a full or partial revocation (affecting specific claims).
     • (c) Maintain the patent as corrected: If the patentee successfully corrects the patent to address the grounds for revocation.
   • Appeals:
     • If the patent is revoked (in whole or in part) or maintained as corrected in a way unsatisfactory to the patentee, only the patentee can appeal this decision to the Intellectual Property (IP) High Court of Japan.
     • The opponent cannot appeal a JPO decision to maintain the patent (either as originally granted or as corrected). If the opponent is still dissatisfied, their subsequent recourse would be to file a separate Invalidation Trial.

C. Strategic Value of the Opposition System

• Early Challenge: Provides a mechanism to challenge a potentially weak patent shortly after grant.
• Lower Cost/Complexity (Potentially): Generally considered less burdensome and less expensive than a full inter partes invalidation trial.
• Public Interest Tool: Allows anyone to contribute to patent quality control.
• For Patentees: While a challenge, a successful defense in an opposition (or a successful correction) can lead to a stronger, more stable patent right earlier in its life.

II. The Invalidation Trial (無効審判 - Mukō Shinpan) - A More Formal Challenge

The Invalidation Trial is a more formal, inter partes administrative proceeding before the JPO that can be initiated to retroactively invalidate a granted patent.

A. Purpose and Nature

The primary purpose of an invalidation trial is to eliminate patents that should not have been granted or that have other fatal flaws. It serves as a crucial check on patent validity throughout the entire term of a patent and even after its expiration. Unlike the largely ex officio nature of the opposition, an invalidation trial is a contentious proceeding between the party requesting invalidation (the requester/challenger) and the patentee.

B. Key Features of the Invalidation Trial

1. Who Can Request an Invalidation Trial? (Standing - Article 123(2))
   • Generally, an invalidation trial can be requested only by an "interested party" (利害関係人 - rigai kankeinin). An interested party is defined as a person whose rights or legal interests are, or are likely to be, directly affected by the existence of the patent. This typically includes:
     • Competitors operating in the same technical field.
     • Parties who have been accused of infringing the patent or have received warning letters.
     • Parties legitimately seeking to use the patented technology (e.g., needing a license or freedom to operate).
   • Exception for Entitlement Issues: If the ground for invalidation is that the patent was granted to someone not entitled to it (e.g., not the true inventor or their successor, or in violation of joint application requirements by co-inventors), then only the person who is truly entitled to the patent (or their share) can request invalidation on these specific grounds.
   • The "interested party" requirement for most grounds marks a key difference from the "any person" standing in oppositions, reflecting the invalidation trial's role in resolving specific disputes. This standing requirement was clarified and generally narrowed in the 2014 amendments that reintroduced the opposition system.
2. Timing – Broad Availability (Article 123(3))
   • An invalidation trial can be requested at any time during the patent's term.
   • Crucially, it can also be requested even after the patent has expired or been otherwise extinguished (e.g., through non-payment of annuities). This is because a patent, even an expired one, could still form the basis for claims of past infringement damages. Invalidating it retroactively can thus have significant legal consequences for past liabilities.
3. Grounds for Invalidation (Article 123(1))
   • The grounds for invalidation are generally broader and more comprehensive than those for opposition. They include:
     • Most grounds for which an application could have been rejected pre-grant (e.g., lack of novelty, inventive step, industrial applicability, insufficient disclosure (enablement, support, clarity), unpatentable subject matter, added new matter).
     • The patent having been granted to a person not entitled to it (e.g., not the inventor or their legitimate successor).
     • The patent having been granted in violation of joint application requirements (Article 38).
     • The patent having been granted in violation of a treaty.
     • The patent having become non-compliant with certain provisions after grant (e.g., the patentee ceasing to be entitled to hold a patent under Article 25, or the patent becoming contrary to a treaty post-grant).
     • The patent having been improperly amended (corrected) through a post-grant correction trial or during a previous opposition/invalidation trial (e.g., the correction added new matter or unallowably broadened the claims).
4. The Invalidation Trial Procedure (Articles 123-134ter, 135-168)
   • The trial is initiated by filing a detailed request for invalidation with the JPO, specifying the patent, the claims targeted, the grounds for invalidation, and supporting evidence.
   • It is an inter partes proceeding conducted by a panel of three (or five) administrative judges.
   • The patentee receives a copy of the request and must file a written response (答弁書 - tōbensho) within a specified period.
   • Patentee's Right to Request Correction (訂正請求 - Teisei Seikyū or 訂正の請求 - teisei no seikyū): This is a very important defensive measure for the patentee. During the invalidation trial, the patentee has prescribed opportunities to file a request to correct the specification, claims, or drawings to address the alleged grounds of invalidity (Article 134-2).
     • Allowable corrections are typically limited to: (a) restriction (narrowing) of the scope of claims; (b) correction of errors in the description or drawings; (c) clarification of ambiguous statements.
     • Corrections must not add new matter or substantially enlarge or alter the scope of the claims as granted.
     • The allowability of the requested correction is itself examined by the JPO panel as part of the trial. If a correction is allowed, the validity of the patent is then assessed based on the corrected claims/specification.
   • The proceedings may involve several rounds of written submissions.
   • Oral hearings (口頭審理 - kōtō shinri) are often held to allow the parties to present their arguments directly to the judges and for the examination of evidence, including witness testimony if necessary.
   • The JPO panel will actively examine the case, but the burden of proving invalidity generally rests with the requester.
5. Outcome and Appeals (Articles 125, 167, 178)
   • The JPO Trial Board issues a formal trial decision (審決 - shinketsu). This decision will either:
     • (a) Invalidate the patent: In whole or in part (i.e., for specific claims), if grounds for invalidation are found.
     • (b) Maintain the patent: If no grounds for invalidation are established. If the patentee successfully corrected the patent during the trial, the decision will be to maintain the patent as corrected.
   • Retroactive Effect: A final decision to invalidate a patent has retroactive effect, meaning the patent is treated as having been void ab initio (from the beginning) (Article 125).
   • Appeals: Either party (the requester or the patentee) who is dissatisfied with the JPO's trial decision can appeal to the Intellectual Property High Court of Japan within a specified period (typically 30 days from service of the trial decision).
   • Res Judicata (一事不再理効 - Ichiji Fusaikō): Once an invalidation trial decision becomes final and binding (e.g., after appeals are exhausted or the appeal period expires), it has a res judicata effect. This generally prevents the same parties (and their privies) from re-litigating the same invalidity grounds based on the same facts and evidence (Article 167). However, this effect does not typically bind unrelated third parties from filing their own invalidation trial on the same or different grounds.

C. Strategic Importance of the Invalidation Trial

• Key Defensive Tool: For companies accused of patent infringement, an invalidation trial is a primary means to challenge the validity of the asserted patent directly at the JPO.
• Proactive Clearance: Businesses can use invalidation trials proactively to "clear the path" by attempting to invalidate problematic patents owned by competitors before launching a new product or service.
• Leverage in Negotiations: The filing (or threat of filing) of an invalidation trial can provide significant leverage in licensing negotiations or settlement discussions.
• Complexity and Cost: Invalidation trials are generally more complex, time-consuming, and costly than oppositions due to their inter partes nature and the potential for extensive evidence and oral hearings.

III. Comparing Oppositions and Invalidation Trials: Key Differences and Strategic Choices

While both systems aim to review patent validity, they differ significantly:

Strategic Choices for Challengers:

• If a patent is newly granted and the grounds for challenge fall within those available for opposition, the opposition system offers a quicker and potentially less expensive first line of attack.
• If the 6-month opposition window has passed, or if the grounds for challenge are broader (e.g., related to entitlement, or complex issues requiring more extensive evidence and argument), an invalidation trial is the appropriate route.
• It is possible for an opposition and an invalidation trial concerning the same patent to proceed in parallel, though the JPO may stay one proceeding pending the outcome of the other to avoid duplication of effort.
• A party unsuccessful in an opposition (if the patent is maintained) can subsequently file an invalidation trial, potentially with new evidence or arguments.

IV. Relationship with Court Litigation (Infringement Proceedings)

It's important to understand how these JPO procedures interact with patent infringement lawsuits in Japanese courts:

• Invalidity as a Defense in Court (Article 104-3): In a patent infringement lawsuit, the defendant can raise the invalidity of the patent as a defense. If the court finds that the patent has grounds for invalidation that are "clear," it can refuse to enforce the patent rights against that defendant in that specific case.
• JPO's Exclusive Power to Invalidate Per Se: However, a court in an infringement action cannot itself formally invalidate or revoke a patent on the JPO register. Only the JPO, through an opposition decision or an invalidation trial decision, has the power to invalidate a patent with erga omnes (against the world) and retroactive effect.
• Concurrent Proceedings: It is common for infringement litigation in court and an invalidation trial at the JPO concerning the same patent to run concurrently. The outcomes can influence each other, leading to complex strategic considerations for both parties.

Conclusion

Japan provides two significant administrative pathways for challenging the validity of granted patents: the Patent Opposition system for early public review, and the Invalidation Trial for more formal, inter partes contests. The revived opposition system offers a relatively streamlined and accessible route for anyone to question a patent's validity shortly after grant on specific grounds. The invalidation trial remains a powerful tool for interested parties to seek retroactive nullification of a patent at any time based on a broader range of grounds.

For businesses, understanding the distinctions between these procedures—including standing requirements, timing, available grounds, procedural intensity, and appeal routes—is essential for effectively asserting their own rights, defending against claims, and navigating the competitive landscape in Japan. Strategic use of these mechanisms can be pivotal in managing patent-related risks and opportunities.