Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd.

Brief Fact Summary. Festo Corporation (Plaintiff), which was the holder of two patents relating to magnetic rodless cylinders, sued Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd. (Kabushiki) (Defendant), a competitor, for infringement. The federal district court held for Plaintiff, and Defendant appealed. The court of appeals affirmed. On grant of writ of certiorari, the United States Supreme Court vacated and remanded. On remand, the court of appeals initially affirmed in part, vacated in part, and remanded, but on rehearing en banc reversed. The United States Supreme Court granted certiorari.

Synopsis of Rule of Law. Narrowing a claim to obtain a patent does not cause the patentee to surrender all equivalents to the amended claim element.

Facts.Festo Corporation (Plaintiff) owned two patents for an industrial device. When the patent examiner rejected the initial application for the first patent because of defects in description, the application was amended to add the new limitations that the device would contain a pair of one-way sealing rings and that its outer sleeve would be made of a magnetizable material. The second patent was also amended during a reexamination proceeding to add the sealing rings limitation. After Festo (Plaintiff) began selling its device, Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd. (Defendant) entered the market with a similar device that uses one two-way sealing ring and a nonmagnetizable sleeve. Plaintiff filed suit, claiming that Defendant’s device was so similar that it infringed Plaintiff’s patents under the doctrine of equivalents. The district court ruled for Plaintiff, rejecting Defendant’s argument that the prosecution history estopped Plaintiff from saying that Defendant’s device was equivalent. The en banc federal circuit, reversing, held that prosecution history estoppel applied, noting that estoppel arises from any amendment that narrows a claim to comply with the Patent Act, not only from amendments made to avoid the prior art, as the district court had originally held. The federal circuit also held that, when estoppel applies, it bars any claim of equivalence for the element that was amended. Plaintiff appealed.

Issue.

Does narrowing a claim to obtain a patent cause the patentee to surrender all equivalents to the amended claim element?

Held. (Kennedy, J.) No. Prosecution history estoppel may apply to any claim amendment made to satisfy the requirements of the Patent Act, not just to amendments made to avoid the prior art, but estoppel need not bar suit against every equivalent to the amended claim element. A patent holder’s temporary monopoly is a property right, and the scope of the patent is not limited to its literal terms but instead embraces all equivalents to the claims described. As in this case, whether the amendment of a patent claim in response to an examiner objection bars a subsequent infringement claim based on the doctrine of equivalents requires an examination of the nature of the subject matter surrendered by the narrowing amendment. In addition, prosecution history estoppel requires that claims of patent be interpreted in light of the proceedings in the patent office during the application process. The circuit court erred in holding that when estoppel applies, it bars any claim of equivalence for the element that was amended. To the contrary, (1) prosecution history estoppel may apply to any claim amendment made to satisfy the requirements of the Patent Act; (2) amendment is not an absolute bar to a claim of infringement under the doctrine of equivalents; and (3) the patentee is burdened with proving that amendment did not surrender the particular equivalent in question. Vacated and remanded.

Discussion. The Supreme Court noted that estoppel arises from any amendment that narrows a claim to comply with the Patent Act, not only from amendments made to avoid the prior art, as the district court had originally held.