An examiner’s interpretation of the prior art by itself is not sufficient to warrant prosecution history disclaimer or estoppel.
Background / Facts: The patent being asserted here is directed to protecting substrates – for example, manhole covers, underground tanks, pipes, and cable sleeves – from corrosion, water ingress, and mechanical stresses. The claims recite use of “a filler comprising a plurality of fractions each comprising different size particles.” Based solely on the prosecution history of the patent, the district court determined that “a filler” can contain only “one material,” remarking that “the examiner rejected the claims and requested amendments, citing … prior art indicating that polymer-based coatings with two fillers have already been patented.”
Issue(s): Whether the prosecution history requires that any given filler and its fractions be of the same material.
Holding(s): No. “[T]he prosecution history does not support the court’s adoption of its otherwise-unwarranted narrowing of the term’s meaning.” As it turns out, during prosecution, while the examiner rejected claims 55-57 of the application as obvious in light of five pieces of prior art, concluding that “[i]t would have been obvious to one having ordinary skill in the art to apply known insulating and waterproofing coatings to electrical equipment where the kind of coatings are customarily used,” the examiner also explained that dependent claim 58 would be allowable if “rewritten in independent form,” which the patentee did. “This history does not establish exclusion of dual-material fillers. Applicants never said anything that states or implies such an exclusion. … [W]hat distinguishes the claims rejected based on … [the] prior art (claims 55-57) from the claim approved if rewritten in independent form (claim 58) is not, on its face, whether the filler contains one or more ‘materials,’ which is not a term in the claims.”