File wrapper estoppel is sometimes also referred to as prosecution history estoppel. It is a limitation of the doctrine of equivalents. The basic rationale is that when the patent applicant or patentee narrows down the protection scope of the claims by certain amendments or statements in order to meet the requirements of patentability, he cannot recapture the protection territory he surrendered during patent litigations. In other words, he cannot gain benefits on both sides. The following is a brief introduction of file wrapper estoppel practice in China.

1. Legal basis and a typical case

China Patent Law does not stipulate file wrapper estoppel.

The file wrapper estoppel principle was adopted based on the principle of good faith and fairness under civil law. In 2009, the Chinese Supreme Court issued an "Interpretation on Several Issues Concerning the Application of Law in the Trial of Patent Infringement Disputes (1)", in which Art. 6 formally introduces the concept of file wrapper estoppel. "For technical solutions surrendered by the patent applicant or patentee through amendments or observation to the claims or specification during the patent prosecution or invalidation procedures, should the right holder take them back into the claims during a patent infringement dispute, this shall not be supported by the people's courts."

A landmark case was a Supreme Court retrial case in 2009, which was a patent infringement case between two Chinese parties.

The published claims 1 and 2 are as follows:

Claim 1. A medicine for preventing and treating a calcium deficiency, characterized in that: it is a medicament made of raw materials in the following parts by weight:

soluble calcium: 4-8 parts, zinc gluconate or zinc sulfate: 0.1- 0.4 parts, and glutamine or glutamate: 0.8-1.2 parts.

Claim 2. The medicine for preventing and treating a calcium deficiency according to claim 1, characterized in that the soluble calcium is calcium gluconate, calcium chloride, calcium lactate, calcium carbonate or active calcium.

During the prosecution process, in order to overcome the objection of not being supported by the specification, the claims were amended. Soluble calcium was amended to active calcium and claim 2 was deleted, and the application was then granted. The granted claim 1 is as follows:

Claim 1. A medicine for preventing and treating a calcium deficiency, characterized in that: it is a medicament made of raw materials in the following parts by weight:

active calcium 4-8 parts, zinc gluconate or zinc sulfate 0.1- 0.4 parts, and glutamine or glutamate 0.8-1.2 parts.

The alleged infringing product uses calcium gluconate instead of active calcium. The patentee believes active calcium includes calcium gluconate or they are at least equivalent under the doctrine of equivalents.

The court of first instance held that only when the amendments or statements made in order to make the patent granting authority believe that the patent application has novelty or inventiveness should the effect of estoppel be established, but not for all the amendments or statements made during the patent application process. The patentee revised the claims according to the opinions of the patent examiners and changed the "soluble calcium" in independent claim 1 to "active calcium", which is not for the purpose of overcoming novelty or inventiveness defects, but for the purpose of making the claims be supported by the description. Therefore, the amendments shall not produce the effect of estoppel.

The court of the second instance also found that the amendments were not intended to overcome novelty and inventiveness defects and did not produce an estoppel effect. Active calcium and calcium gluconate are equivalent features, and therefore infringement was established.

The accused infringer filed a request for a retrial, arguing that the right holder had amended the claims, and active calcium was different from calcium gluconate. The amendment of the right holder abandons the technical solution based on calcium gluconate, which constitutes estoppel. Based on the principle of file wrapper estoppel, the doctrine of equivalents no longer applies. Therefore, patent infringement could not be found.

The Supreme Court found that: according to the description, active calcium and calcium gluconate were explained by different embodiments. Calcium gluconate was not of active calcium. The amendments were made to overcome the problem raised by the State Intellectual Property Office that the scope of protection of soluble calcium is too broad and is not supported by the description. Moreover, in the statements, the applicant did not state that active calcium includes calcium gluconate. Therefore, the opinion that active calcium includes calcium gluconate could not be established.

According to file wrapper estoppel, the technical solution abandoned by the patent applicant or patentee through the amendment on the claims, description or statement of opinions in the patent application or invalidation procedure cannot be recaptured during the patent infringement proceedings. Therefore, the scope of protection of the patent at issue should not include the technical solution based on "calcium gluconate". The patent was thus not infringed on.

The conditions used to establish estoppel in Article 6 are relatively general. As long as the amendments or statements in the patent application or invalidation procedure lead to the abandonment of any technical solutions, file wrapper estoppel shall apply. In other words, the Judicial Interpretation does not distinguish between the types of amendments or statements, but only sets the applicable conditions for estoppel from the perspective of the results. When judging if "abandonment of technical solutions" occurs, it is not necessary to investigate the purpose of the amendments or statements in order to satisfy the substantive patentability requirements or the formality requirements. The focus should be on whether the amendment or the statement of opinion has produced a limitation or a narrowing effect on the scope of protection of the patent.

2. Limitations to file wrapper estoppel

In order to avoid the possible abuse of file wrapper estoppel, the Supreme Court issued a further judicial interpretation in 2016 entitled "Interpretation on Several Issues Concerning the Application of Law in the Trial of Patent Infringement Disputes (2)". According to Art. 13, "where the right holder proves that the restrictive amendment or statement made by the patent applicant or the patentee to the claims, description and drawings during the patent prosecution and invalidation procedure is clearly denied, the people's court shall determine that the amendment or statement does not lead to the surrender of the technical solution." The interpretation of this may be better understood by referring to the following case.

The issued claim 1 of the patent is as follows:

Claim 1. A shark fin antenna, characterized in that it has an antenna casing, a radio receiving antenna is arranged on the inner upper part of the antenna casing, one end of the radio receiving antenna is provided with an antenna signal output end, and the antenna signal output end is connected with the signal input end of the antenna amplifier through the antenna connecting element, connect, or directly match with the coaxial cable (feature a), the bottom of the antenna housing is equipped with a mounting base plate; the radio receiving antenna is mounted on the inner upper part of the antenna housing by injection molding or fixed clips (feature b); on the inner side of the antenna housing the upper part is provided with a radio receiving antenna, the radio receiving antenna adopts a helical spring antenna or a metal antenna, which increases the effective length of the antenna to receive radio signals and realizes 360-degree omnidirectional signal reception; the radio receiving antenna is an AM/FM shared antenna (feature c).

During the patent prosecution procedure, the examiner pointed out in both the first and second office actions that features a and b are the distinguishing features of claim 1 compared to reference 1, which involves the signal output connection method and the installation method of the upper part of the inner side of the antenna housing. Although the signal output connection method and installation method adopted in the reference document are different from those in claim 1, features a and b belong to common knowledge or conventional technical means in the field. Therefore, claim 1 does not have inventiveness. The patentee then added feature c in reply to the second office action. Subsequently, the claim was granted.

In the patent invalidation procedure brought by the alleged infringer, the patentee still believes that features a and b are different from the prior art. In the invalidation decision, the State Intellectual Property Office determined that the patent has inventiveness. The relevant reason is that in the prior art, the AM antenna and FM antenna are separately designed, which is a different teaching away from those of the patent, in which the "radio receiving antenna is shared by AM/FM." That is to say, the State Intellectual Property Office believes that claim 1 has inventiveness because of feature c. In the invalidation decision, although the State Intellectual Property Office believed that features a and b were the distinguishing features of claim 1 compared to reference 1, they did not make specific comments on the contribution of features a and b to the inventiveness.

During the patent infringement proceedings, the accused infringer believed that the technical solution of the accused infringing product is different from the patent involved. The signal output connection method and installation method adopted are the technical solutions in the prior art, which are the solutions abandoned by the patentee during the prosecution and invalidation procedure. According to file wrapper estoppel, the technical solution of the accused infringing product can no longer be included in the protection scope of the patent at issue under the doctrine of equivalents.

The court of the second instance, in this case, held that since the State Intellectual Property Office did not comment on the contribution of features a and b to the inventiveness during the patent invalidation procedure, the "clearly deny" condition was not met. According to file wrapper estoppel, the technical solution that the patentee has abandoned in the invalidation procedure can no longer be included in the scope of protection of the patent as an equivalent infringement during the infringement proceedings. Therefore, the alleged infringement is not established. In its ruling, the Supreme People's Court pointed out that: "due to the continuity of the identification of technical features in the patent application and invalidation process, whether the statement made by the right holder is 'clearly denied', an objective and comprehensive judgment should be made on the examination of the technical features of the patent application and invalidation procedures, especially focusing on whether the restrictive statement is finally recognized by the referee, and whether it leads to the patent application to be granted or the patent right to be maintained. During the procedure, the Patent Examination Department of the State Intellectual Property Office did not approve the statements regarding technical features a and b, and held a clear negative opinion. Moreover, the patent in question was not granted based on the limitations on features a and b. During the invalidation procedure, although the Reexamination Board also believed that features a and b count as distinguishing features, it did not overturn the comments on features a and b made during the prosecution procedure and maintained the validity of the patent based on the inventiveness of feature c. It cannot be concluded that the Reexamination Board held that features a and b do not belong to common knowledge and conventional methods. The second-instance court of this case departed from the specific examination facts that the patent in question was granted, and ignored the fact that the patentee's statements had been 'clearly denied' in the substantive examination procedure, and then ... draws the erroneous conclusion regarding the application of file wrapper estoppel".

3. How to avoid file wrapper estoppel for a patent applicant or patentee

From the above interpretation and case analysis, any amendments or statements made in the patent prosecution and invalidation procedures may lead to possible file wrapper estoppel. The exception of file wrapper estoppel normally has very strict requirements, i.e. the amendments or statements should be clearly denied by the authorities. In connection to this, the patent applicant or patentee should be very cautious when making amendments to or statements on the claims, description and accompanying drawings. It may not be a good idea to distinguish each and every one of the technical features in the claims from those of the prior art in order for the patent application to be granted, especially in the case where some of the features in the claims are amended. In order to overcome the inventiveness objection raised by the examiner, the patent applicants should focus more on the substantive improvements made in light of the prior art and make amendments or arguments regarding same. In some cases, a telephone interview may be a good choice to convince the examiner and is unlikely to lead to file wrapper estoppel.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.