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Claim construction and noninfringement finding affirmed; prosecution history estoppel bars DOE
September 12, 2007

In a decision today, the Federal Circuit affirmed a district court's grant of summary judgment of noninfringement of a patent relating to a "gutter guard" designed to keep debris out of gutters. The court found the district court's claim construction correct, as it properly considered dictionary definitions when the specification provided no additional guidance on the meaning of the term "weld."

Additionally, because the patentee both criticized prior art gutter guards that used adhesives and amended the patent's claims to require a "weld" to the exclusion of other modes of attachment, the district court's holding that infringement under the doctrine of equivalents was barred by prosecution history estoppel was also affirmed.

L.B. Plastics sued Amerimax for infringing a patent on gutter guards and a method of making gutter guards. Each of the claims require, in one form or another, a "continuous heat weld defining an uninterrupted longitudinal weld line" to attach a mesh screen to the main gutter guard body, as depicted in this figure:

Gutter guard figure

In the specification of the patent, methods of attaching the mesh to the guard other than by a "weld" were stated to be inferior:

Unlike some prior art gutter guards which have a relatively fine-mesh metal layer overlying a perforated polymer guard panel, the gutter guard of the present invention includes a coated mesh layer and perforated guard panel formed of like polymer materials, such as PVC. This novel construction facilitates an effective and secure attachment of the composite by ultrasonic or heat welding along the entire length of the gutter guard. The attachment means used in other prior art gutter guards incorporating multiple layers is generally less effective, and more costly, time consuming, and labor intensive.

During prosecution, L.B. amended the claim to add the "weld" limitation in response to a prior art rejection, and the application was allowed after this amendment was made.

The district court construed the "weld" limitation to require melting the plastics to allow them to flow together. Amerimax's product did not use a heat weld, but instead affixed the mesh to the guard using hot glue, and as a result, the district court granted summary judgment of no literal infringement. The court also granted summary judgment of no infringement under the doctrine of equivalents because L.B. had amended its claims to add the "weld" limitation despite being aware of other methods of attachment, and thus prosecution history estoppel barred application of the doctrine of equivalents. L.B. appealed the district court's claim construction and the summary judgment of noninfringement.

The Federal Circuit affirmed in all respects. With regard to claim construction, the court held that the district court properly utilized dictionary definitions of "weld" when there was no further information in the specification from which the meaning could be ascertained, and that the court's construction that "welding" required melting of the plastics was correct. Based on this, the finding of no literal infringement was also affirmed.

Turning to the doctrine of equivalents, the Federal Circuit noted that under its precedent, "when a specification excludes certain prior art alternatives from the literal scope of the claims and criticizes those prior art alternatives, the patentee cannot then use the doctrine of equivalents to capture those alternatives." This doctrine applied here based on the statement in the specification quoted above noting the inadequacy of prior art means of attachment. This, combined with the fact that "the patentee elected to distinguish prior art attachment means and to limit its claim to continuous welded attachments," led the court to conclude that "a person of ordinary skill in the field of the invention reading the specification would clearly conclude that the inventor thought that adhesive attachments generally were undesirable." As a result, the finding of no infringement under the doctrine of equivalents was also affirmed.

To read the full decision in L.B. Plastics, Inc. v. Amerimax Home Prods., Inc., click here.

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