Milcor Steel Co. v. George A. Fuller Co.

Background

A patent owner who held a patent issued to Holdsworth sued for infringement of two claims covering a metal partition wall. The specifications describe parts like a ceiling member with a perforated flange, a base member with recesses, upstanding channel supports, and metal lathing. After the defendants answered, the patent owner filed disclaimers in the patent office that purported to narrow the two claims by making those features essential. The district court found the disclaimers added new elements and entered summary judgment for the defendants, and the court of appeals affirmed.

Reasoning

The Court looked only to the original claims to see what the patent covered. The original claims did not require the specific ceiling flange or the base recesses, but the disclaimers inserted those features into the claimed combinations. The Court explained that the disclaimer statute does not allow a patentee to add a new element that changes the identity of a claimed combination. Substantial changes must be made through the reissue process and the patent office, not by post-issue disclaimers. Because the disclaimers changed the combination, they were unauthorized and invalidated the claims.

Real world impact

The decision means patent owners cannot use a simple disclaimer to transform a combination patent after issuance. Owners seeking substantive alterations must pursue reissue and accept the reissue’s effective date and patent-office review. The ruling favors certainty for others who might otherwise face retroactive surprises about what a patent actually claims.