Saint-Gobain Performance Plastics Corp., HCM Div. v. Truseal USA, Inc.

In Saint-Gobain Performance Plastics Corp., HCM Div. v. Truseal USA, Inc., 2005 WL 22937 (D.N.J.), the District of New Jersey signaled the continued vitality of the equitable doctrine of “assignor estoppel” in the face of recognized exceptions. Simply stated, the doctrine holds that an assignor of a patent is, as against an assignee, estopped to deny the validity of the patent. The logic behind the doctrine is that the assignor should be estopped from defending patent infringement claims by proving that what he assigned was worthless.

This logic was tested against a line of cases, dealing primarily with licensee estoppel, that reasoned that it is as much in the public’s interest that competition should not be repressed by worthless patents, as it is that the patentee of a valuable invention should be protected in his monopoly. However, the doctrine of assignor estoppel was found to remain intact, along with its considerable conditions and exceptions.

For example, the doctrine is one of equity and not law, therefore its application, unlike estoppel by deed, is not automatic and depends upon the balance of equities between the parties. Furthermore, the assignor, while estopped from challenging the validity of the patent, may still defend against an infringement claim by arguing for narrow claim construction or on the basis that the subject of the assignment is obviously old in the art and plainly belongs to the public.

In this manner, the doctrine has evolved to combat the unfairness and injustice that would be suffered by an assignee if the assignor were permitted to raise the defense of patent invalidity, while remaining maleable to the dictates of the public good and sensitive to the facts presented in each individual set of circumstances.