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Prosecution History Estoppel: Festo I and II Revisited
September 20, 2007

I. Prosecution History Estoppel as Complete Bar to Claim of Equivalence (Festo I)

Prosecution history (otherwise known as "file wrapper") generally refers to official record that has to do with a particular patent application. There are stages in the prosecution of patent application where patent claims are required to be amended to conform to patentability requirements. Certain amendments necessarily limit the scope of a patent in such a way that a patentee is prevented from disputing later that its patent still encompasses even the claims surrendered during prosecution as unforeseen equivalents. The doctrine of prosecution history estoppel has been well in place in U.S. jurisprudence as an effective counter-balance to the doctrine of equivalents (please see related article entitled "Doctrine of Equivalents: Its Equivalence in the Philippines"). 

Prior to 2000, the controlling jurisprudence is that prosecution history estoppel constituted a flexible bar to the application of the doctrine of equivalents. This means that there was sufficient latitude for patentees who foreclosed some claims to sue for infringement by equivalents on unsurrendered claims. However, the U.S. Court of Appeals for the Federal Circuit ("Federal Circuit") in Festo v. Shoketsu Kinzoku Kogyo Kabushiki, 234 F.3d 558 (Fed. Cir. 2000) ("Festo I") made life difficult for patentees to maintain infringement suits as it constricted the application of the doctrine of equivalents to the hilt. Thus, patentees, who at a certain point during the prosecution of their patent applications, amended particular claims to obtain patentability, are automatically and completely enjoined from asserting infringement by equivalents. Festo I categorically held that prosecution history estoppel relative to an amended claim is a complete bar against the application of the doctrine of equivalents, regardless of whether the amendment pertains to prior art or not. 

In this case, Festo Corporation owns two patents for an industrial device. During the prosecution of the first patent, the patent examiner rejected the application because of certain defects in the description. Corrolarily, the application was amended to include the limitations that the device would contain a pair of "one-way sealing rings" and that its outer sleeve would be made of "magnetizable material." Similarly, the application for the second patent was also amended to comprise the sealing rings limitation. Before Festo Corporation could sell its product in the market, SMC sold a similar device that uses one two-way sealing ring and a non-magnetizable sleeve. Festo Corporation sued SMC for patent infringement under the doctrine of equivalents. When the case reached the Federal Circuit, it ruled that Festo Corporation was barred from claiming equivalents from a subject matter that it has surrendered by amendment. Further, the Federal Circuit ruled that estoppel arises from any amendment that narrows a claim to comply with the Patent Act, not only from amendments made to avoid prior art. 

II. Rebuttable Presumption of Estoppel (Festo II)

The U.S. Supreme Court in Festo v. Shoketsu Kogyo Kabushiki Co. Ltd., 535 U.S. 722, 152 L. Ed. 2d 944. 122 S. Ct. 1831 (2002) ("Festo II") affirmed that prosecution history is still an effective bar against the application of the doctrine of equivalents. Notably, however, the Supreme Court completely disregarded the Federal Court's ruling that prosecution history estoppel is a complete bar to a finding of equivalence. Instead, it created a rebuttable presumption that prosecution history estoppel bars a finding of equivalence. 

Festo II set parameters by which the presumption may be rebutted, to wit:

There are some cases, however, where the amendment cannot reasonably be viewed as surrendering a particular equivalent. The equivalent may have been unforeseeable at the time of the application; the rationale of the amendment may bear no more than a tangential relation to the equivalent in question; or there may be some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question. In those cases, the patentee can overcome the presumption that prosecution history estoppel bars a finding of equivalence.

From a patentee's vantage point, the introduction of the rebuttable presumption will somehow release them from a legal straightjacket. Such notwithstanding, prosecution history estoppel remains an equitable offset against the doctrine of equivalents. As it is, patentees will still have to bear the burden of overcoming the presumption. Festo II made this clear in this manner:

When the patentee is unable to explain the reason for amendment, estoppel not only applies but also "bar(s) the application of the doctrine of equivalents as to that element. xxx xxx.

Just as Warner-Jenkinson held that the patentee bears the burden of proving that an amendment was not made for a reason that would give rise to estoppel, we hold here that the patentee should bear the burden of showing that the amendment does not surrender the particular equivalent in question.

Under the circumstances, Festo Corporation still has to contend with the tall order of proving that its amendments on the sealing rings and sleeve of its subject device are not narrowing; if they are narrowing, Festo Corporation should point out other unsurrendered claims that may have equivalents in the infringing device.

III. Festo II: Philippine Setting

In the Philippines, patent examiners are given leverage to make preliminary rejections of patent applications (Rules 903 and 904, Rules and Regulations on Inventions). A preliminary rejection under the rules would necessitate amendments by the applicant in order to conform to requirements on patentability, form or content. 

Republic Act No. 8293, otherwise known as the Intellectual Property Code ("IP Code") prescribes requirements for patentability i.e. novelty, inventive step and industrial applicability. These requirements are common yet strong grounds for preliminary rejection of patent applications. Other grounds for preliminary rejection that may prompt patent applicants to amend their applications are those pertaining to the patent application's form and content. 

The Festo decisions on prosecution history estoppel hold utmost significance on amendments pertaining to novelty and inventive step. This is mainly because amendments in compliance with these requisites essentially involve avoidance of prior art. It is in these areas where a patent applicant necessarily surrenders claims and foreseeable equivalents that may later on estop him from claiming infringement. Overcoming the Festo II presumption, in such situations, would entail a clear showing that the surrendered claims and equivalents do not constrict the patents reach and that the alleged equivalent in the infringing device could not have been foreseen at the time of the amendment. 

Otherwise, if amendments to the patent application pertain to matters other than avoidance of prior art, the Festo II presumption may not at all be a stumbling block against an infringement suit based on equivalents. Amendments in conformity with the law's requirements as to form and content are merely cosmetic; hence not limiting vis-à-vis the scope of the patent. In addition, proving industrial applicability, in response to a preliminary rejection, would not involve avoidance of prior art. Following the Festo II parameters, amendments of such nature may be characterized as merely bearing "tangential" connection to the equivalent; hence not effective bars to a finding of equivalence.
 

IV. Conclusion

With the Philippine Supreme Court's recognition of the doctrine of equivalents in Pascual Godines v. Court of Appeals, et al. (G.R. No. 97343, September 13, 1993) and Smith Kline Beckman Corp. v. Court of Appeals, et al. (G.R. No. 126627, August 14, 2003) (please read related article entitled "Doctrine of Equivalents: Its Equivalence in the Philippines") as a means of committing patent infringement, it is expected that prosecution history estoppel and the Festo II presumption will eventually find their way in Philippine jurisprudence. That being the case, Festo II should be regarded as a welcome development for Philippine patentees.

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