In a split decision, a panel of the US Court of Appeals for the Federal Circuit upheld a district court claim construction, finding that the claim term “100% by weight (of a layer),” considered in the context of the claim and in view of intrinsic evidence, included the possibility of less than 100% of the total components of the layer. E.I. DuPont de Nemours & Co. v. Unifrax I LLC, Case No. 17-2575 (Fed. Cir. Apr. 17, 2019) (Reyna, J) (O’Malley, J, dissenting).

DuPont owns a patent directed to laminate materials used in manufacturing airplanes. The claimed laminates have a polymeric film layer and an inorganic refractory layer, separated by an adhesive layer. The claims specify that the refractory layer comprises mineral platelets “in an amount of 100% by weight,” but also allow for “a residual moisture content of no greater than 10 percent by weight.”

DuPont sued Unifrax for infringement of the patent, and during claim construction, the parties disputed the meaning of the phrase “100% by weight.” DuPont argued that “100% by weight” means “[t]here is no carrier material such as resin, adhesive, cloth or paper in addition to the inorganic platelets. There may be some residual dispersant arising from incomplete drying of the platelet dispersion.” Unifrax argued that “100% by weight” should be given its plain meaning and that no construction was necessary. The district court adopted DuPont’s proposed construction, finding that intrinsic evidence supported a construction that “100% by weight” platelets refers to a quantity of platelets relative to the carrier material, which allows for residual dispersant in the inorganic refractory layer. Unifrax appealed.

The Federal Circuit determined that the district court’s construction was correct, finding it consistent with the plain language and intrinsic evidence. First, the Court focused on the plain language of the claim, finding that its recitation of both the 100% platelet limitation and a 10% residual moisture limitation supported a construction in which “100% by weight” is measured relative to a carrier material. To conclude otherwise would be “nonsensical” because it would allow the total percentage of components in the refractory layer to exceed 100%.

Second, the Federal Circuit found that all of the embodiments disclosed in the specification allowed for some amount of residual dispersant. The Court also relied on teachings in the parent patent, of which the asserted patent is a continuation-in-part. In particular, the patent describes one embodiment containing 100% platelets and “no carrier material such as resin, adhesive, cloth or paper,” and then states that “there may be some residual dispersant arising from incomplete drying of the platelet dispersion.” Although this language was not carried forward into the asserted patent, the Court did not identify any reason to infer that the patentee intended “100% by weight” to mean different things in the two patents. Finding that this passage from the parent patent relates to subject matter in common with the asserted patent, and that it clarifies the meaning of the 100% limitation, the Court concluded that it was appropriate to rely on the parent patent specification as intrinsic evidence.

Third, the Court rejected Unifrax’s argument that DuPont disclaimed during prosecution embodiments in which the refractory layer contains residual moisture. Citing DuPont’s arguments to the examiner, the Court found that the patentee “understood the claimed percentage as relative to carrier material in the same way that [the cited prior art reference] used the term.” As such, patentee’s amendment to overcome the reference did not constitute a disclaimer of embodiments having residual moisture in the refractory layer.

Judge O’Malley dissented, stating that “[t]here is no ambiguity in this language,” and that the plain and ordinary meaning of “100% by weight” is simply that the platelets constitute all of the refractory layer. She concluded that the specification and trial testimony indicated that the 100% by weight limitation relates to the platelet composition of the refractory layer when fully dry, which is not inconsistent with there being residual moisture acquired when the dry refractory layer is subjected to subsequent processing steps (e.g., when exposed to a solution and then dried incompletely). Judge O’Malley also argued that the majority relied too heavily on the specification of the parent patent, explaining that the patentee made a deliberate choice to omit the parent patent’s language concerning “carrier material” from the asserted patent. She stated that the “value” of the parent patent in construing the claims of the asserted patent “is limited where the two patents recite different claims based on different specifications using different words.”