Issue 250 | November 5, 2004
Insituform Technologies v. CAT Contracting

The Federal Circuit recently handed down a decision that for the first time addressed whether, in a Doctrine of Equivalents analysis, a narrowing amendment made during prosecution bore no more than a “tangential relation to the equivalent” in question and, therefore, did not create a prosecution history estoppel. Insituform Technologies, Inc., v. CAT Contracting, Inc., 2004 U.S. App. LEXIS 20694 (Fed. Cir. Oct. 4, 2004). Since the Supreme Court first announced this standard (Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 525 U.S. 722, 62 USPQ2d 1705 (2002)), practitioners have awaited the Federal Circuit’s implementation to determine the nature of this estoppel exemption.

The patent in Insituform was directed to a method of impregnating the interior of a flexible tube with a resin. The method involved inserting a bolus of resin into one end of the tube and drawing the tube through rollers to force the resin into the inner lining of the tube. The prior art taught such a method in which a vacuum was drawn within the tube on the side of the resin opposite the rollers by a large vacuum compressor attached to the far end of the tube. Because the tube could be quite long, large compressors were necessary to draw an adequate vacuum. Under the patented method, the vacuum was drawn by a single vacuum cup through a hole in the tube near the resin bolus. As the tube was pulled through the rollers and the cup approached the resin, the cup would be removed, the hole sealed, and the cup moved to a location further from the rollers where another hole would be made from which to draw a vacuum. This process resulted in application of a discontinuous vacuum as the cup was repeatedly removed and reapplied. Because the cup was relatively close to the resin bolus, one could use a much smaller vacuum compressor than had been employed in the prior art.

The accused infringing method worked in a similar manner, except it drew a vacuum using multiple cups situated along the tube near the resin bolus. As the lead cup approached the resin it was removed and placed behind the trailing cup. This resulted in a continuous vacuum while the lead cup was moved due to the presence of the other cups pulling a vacuum.

The applicants initially submitted claims without any limitations as to the number of cups but amended the claims during prosecution to recite a single cup in view of the prior art teaching of a method employing a single compressor at the end of the tube. At issue in this case was whether the amendment limiting the claim to a single vacuum cup was tangential to the equivalent in question, i.e., the method employing multiple cups. The court held that it was.

The court found that during prosecution the applicant had stated that the advantage of the method of the claims as amended was that it obviated the need for a large vacuum compressor as taught in the prior art. The court noted that the applicant never stated that the problem of the prior art could not be solved using more than one vacuum source or a continuous vacuum. The court found that there was no evidence in the prosecution history of any relationship between the narrowing amendment and the multiple cup process.

Until now, the nature of narrowing amendments that may be considered to be tangential to the equivalent in question was uncertain. Now the court has made clear that such amendments can be made for prior art purposes. In view of this, one would presume that under the proper factual circumstances narrowing amendments made for 35 U.S.C. § 112 purposes might also be considered tangential to the equivalent in question. It will be well worth watching as the case law develops on this subject.

To discuss these topics further, please feel free to contact the author, Michael S. Greenfield, a partner at the law firm of McDonnell Boehnen Hulbert & Berghoff.

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