Warner-Jenkinson Company, Inc. v. Hilton Davis Chemical Co.

520 U.S. 17 (1997)

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Nature of the Case

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Facts

P and D manufacture dyes. Impurities in those dyes must be removed. P holds the '746 patent, which discloses an improved purification process involving 'ultrafiltration.' The process filters impure dye through a porous membrane at certain pressures and pH levels, resulting in a high purity dye product. P added the phrase 'at a pH from approximately 6.0 to 9.0' during patent prosecution. At a minimum, this phrase was added to distinguish the Booth patent that disclosed an ultrafiltration process operating at a pH above 9.0. The parties disagree as to why the low-end pH limit of 6.0 was included as part of the claim. D developed an ultrafiltration process at a pH of 5.0. D did not learn of the '746 patent until after it had begun commercial use of its ultrafiltration process. P sued D for patent infringement. P conceded that there was no literal infringement, and relied solely on the doctrine of equivalents. The issue of equivalence was included among those sent to the jury. The jury found that the '746 patent was not invalid and that D infringed upon the patent under the doctrine of equivalents. The jury found that D had not intentionally infringed, and therefore awarded only 20% of the damages sought by P. The court entered a permanent injunction prohibiting D from practicing ultrafiltration below 500 p.s.i.g. and below 9.01 pH. The majority of the Court of Appeals held that the doctrine of equivalents continues to exist and that its touchstone is whether substantial differences exist between the accused process and the patented process. It held that the question of equivalence is for the jury to decide. One dissenter, the late Judge Nies, was able to reconcile the prohibition against enlarging the scope of claims and the doctrine of equivalents by applying the doctrine to each element of a claim, rather than to the accused product or process 'overall.' 'The 'scope' is not enlarged if courts do not go beyond the substitution of equivalent elements.' The Supreme Court granted certiorari.