In a recent ruling, the Supreme People’s Court of China has reinforced a crucial principle in patent litigation: a patent owner cannot narrow the scope of a patent to maintain its validity during invalidation proceedings, and later broaden it to claim infringement.
This principle—known in patent law as file wrapper estoppel—has significant implications for how patents are enforced and interpreted in China.
What Is File Wrapper Estoppel?
File wrapper estoppel, also called prosecution history estoppel, prevents a patent holder from asserting that a product infringes a patent if they previously narrowed their claims during examination or invalidation proceedings to obtain or preserve the patent.
In other words, if a patentee has made specific arguments to limit their patent’s scope in front of the patent office, they cannot take the opposite position in court just to win an infringement case.
This doctrine ensures legal consistency to prevent patent holders from being inconsistent and benefiting from “both sides”, and protects third parties who rely on the patentee’s earlier statements.
Case Summary
The dispute involved a utility model patent for a device called a “mobile number plate holder” used in cars. The patent was held by a Shenzhen-based company, which claimed that a Dongguan-based company had infringed its rights by producing a similar product.
In the first-instance trial, the Shenzhen company won partial relief: the court found the competitor’s product to fall within the scope of the patent. However, both parties appealed.
During the appeal, it came to light that the patentee had argued during invalidation proceedings that the core function of the invention—maintaining a flip-plate’s position—depended solely on gravity, and not on additional features like springs or magnets.
However, in the infringement lawsuit, the same patent holder tried to claim that a product using a spring-based support structure also infringed the patent.
Supreme Court’s Reasoning
The Court made three key findings:
Patent Scope Must Match Contribution
As a utility model with a relatively low level of inventiveness, the patent could not be interpreted too broadly. The protection granted must align with the invention’s technical contribution.
Prior Arguments Limit Later Claims
The patentee’s prior statements before the CNIPA (during two invalidation proceedings) explicitly excluded the use of spring-loaded or friction-based structures from the invention’s scope. These statements formed part of the official patent file, which must be considered during infringement assessment.
No Infringement
Since the allegedly infringing product relied on a spring mechanism to achieve stability—unlike the gravity-only mechanism described and defended in the invalidation phase—the court ruled no infringement occurred. The earlier statements were binding, and the Shenzhen company could not reverse its position.
The Supreme Court overturned the lower court’s ruling and dismissed the lawsuit in its entirety.
Why This Decision Matters
This ruling is a significant clarification of how Chinese courts are applying principles of estoppel and consistency in patent enforcement, especially in utility model cases where inventiveness is often limited.
Ensures Fairness in Litigation
Patent owners cannot switch positions opportunistically to gain advantage during enforcement. The ruling protects businesses from being unfairly targeted with overbroad infringement claims.
Promotes Integrity in Patent Practice
It sends a clear message to right holders: the statements you make during prosecution or invalidation will follow you—and must be consistent with your enforcement strategy.
Aligns Patent Scope with Technical Contribution
Especially for utility models or lower-tier patents, the courts are unlikely to support overly expansive interpretations.
Conclusion
This case illustrates how file wrapper estoppel is being actively used by Chinese courts to prevent abuse of patent rights and ensure procedural integrity. For patent holders, it is a reminder to strategically manage arguments made during invalidation, as these may define the boundaries of future enforcement.
For businesses defending against infringement claims, this case shows that prior prosecution history can be a powerful tool—especially when used to counter overly aggressive litigation strategies.