Executive Intellectual Property Bulletin

Prosecution History Estoppel Elkay Mfg. Co. V. Ebco Mfg. Co., 52 U.S.P.Q.2d 1109 (Fed. Cir. 1999)

Are estoppels in the prosecution history of one patent applicable to another patent where both patents are derived from one parent application? Yes. The Federal Circuit held that the prosecution history of one patent can be used to limit the scope of another patent to prevent the operation of the doctrine of literal infringement and the doctrine of equivalents, given that: estoppels exist in the prosecution history of one patent, the claim at issue is similar to the claim in the other patent, and the patent holder admitted that a claim in one patent is based on a claim in the other patent.

Facts: Ebco Manufacturing Co. and Ebtech Corp. (collectively, Ebco) appealed a District Court decision for Elkay Manufacturing Co. (hereinafter, Elkay) that Ebco's accused device infringed Elkay's United States Patent Nos. 5,222,531 (hereinafter, the '531 patent) and 5,289,855 (hereinafter, the '855 patent). Both patents derived from the same parent application. The technology at issue concerns means to permit a jug of bottled water to be inserted into a water cooler with the cap still on. Ebco's accused devices comprise two concentric tubes that allow water to flow down the inner tube and air to flow up through the annular region formed by the two tubes. The subject matter of Elkay's patents focuses on the limitation "an upstanding feed tube" to dispense water and admit air into a water container.

The District Court interpreted the article "an" to not limit Elkay's invention to one tube and concluded that Ebco's accused devices infringed both patents. The Federal Circuit reversed.

Holding: The Federal Circuit agreed that the article "an" did not limit Elkay's invention to one tube. However, the Court held that Elkay gave up patent coverage of the two-tube configuration in view of the arguments and failure to respond to a statement made by the Examiner during the prosecution of the '531 patent. The Federal Circuit further held that the prosecution history of the '531 patent applies with equal force against the '855 patent.

During the prosecution of the '531 patent, the Examiner cited a reference against claim 1 that discloses a beer-dispensing device with two separate feed tubes, one for pressured air and the other for beer. Elkay responded to this by arguing, without substantive amendment, that the invention focuses on "a flow path ... for delivering liquid ... and for admitting air." The Federal Circuit reasoned that such argument necessarily relinquished patent coverage for the two-tube configuration even with no amendment to the claim language.

Additionally, the Examiner, in his reason for allowance, indicated that the invention of the '531 patent describes a single feed tube with a single flow path for both liquid and air. This, according to the Examiner, is distinguishable over the cited reference because in that reference two separate feed tubes are disclosed. Elkay did not respond to this statement. Such silence, according to the Federal Circuit, is additional evidence that Elkay disavowed patent coverage for the two-tube configuration.

After concluding that Ebco's accused devices do not infringe the limited scope of the '531 patent, the Federal Circuit scrutinized the '855 patent. The Federal Circuit noted that claim 1 of the '855 patent is similar to claim 1 of the '531 patent, that the written description of both patents is identical, and that Elkay admitted that claim 1 of the '855 patent is patterned after a combination of claims that include claim 1 of the '531 patent. Consequently, the Federal Circuit held that Elkay's relinquishment of the two-tube configuration during the prosecution of the '531 patent applies to limit claim 1 of the '855 patent.

Therefore, the Court found no literal infringement in the '531 patent because Elkay's inventions are limited to a single feed tube with a single flow for both water and air. The Court also found no infringement under the doctrine of equivalents because the prosecution history of the '531 patent limits Elkay's invention to a single feed tube. No infringement was found by the Court under the doctrine of equivalents of the '855 patent due to estoppels generated during the prosecution of the '531 patent given the formal relationship between the '531 and '855 patents, and Elkay's admission that the claim of one patent was patterned after a claim in the other patent.

Implications: This case raises two major concerns. First, given that failure to respond, argument, and claim amendment may generate prosecution history estoppel, it may be difficult for the applicant to avoid hindsight reconstruction of the limits on patent scope. Second, because estoppel in the prosecution history of one patent may limit the scope of another patent, an applicant that has a family of patent applications deriving from one parent is advised to carefully consider the impact of the prosecution of each application on the other members of the family.

For more information on this and other intellectual property topics or for assistance in your patent prosecution needs, please contact any of the attorneys at Schwegman, Lundberg & Woessner, P.A. Written by D.C. Peter Chu, registered patent attorney.