Assignor Estoppel Prevents Inventor Testimony on Invalidity
"Assignor estoppel is an equitable doctrine that prevents one who has assigned the rights to a patent (or patent application) from later contending that what was assigned is a nullity." Diamond Scientific Co. v. Ambico, Inc., 848 F.2d 1220, 1224 (Fed. Cir. 1988). Thus, an assignor and parties in privity with the assignor are estopped or barred from asserting invalidity defenses. Id. In this case, the district court invoked that doctrine to bar an assignor from testifying against the validity of its own patent.
Courts frequently mention four justifications for the doctrine of assignor estoppel: "(1) to prevent unfairness and injustice; (2) to prevent one [from] benefiting from his own wrong; (3) [to adopt the] analogy [of]. . . estoppel by deed in real estate; and
(4) [to adopt the] analogy to a landlord-tenant relationship." Id. (quoting Hal Cooper, Estoppel to Challenge Patent Validity: The Case of Private Good Faith vs. Public Policy, 18 Case W. Res. 1122, 1128 (1967)).
This case relies primarily on the "unfairness and injustice" justification. "[A]n assignor should not be permitted to sell something and later assert that what was sold is worthless, all to the detriment of the assignee." Diamond, 848 F.2d at 1224.
"The principle of fair dealing as between assignor and assignee of a patent whereby the assignor will not be allowed to say that what he has sold as a patent was not a patent has been part of the fabric of our law throughout the life of this nation." Id. (quoting Scott Paper Co. v. Marcalus Mfg. Co., 326 U.S. 249, 260 (Frankfurter, J., dissenting)). Thus, assignor estoppel prevents an assignor from asserting that its own patent, for which it may have received value upon assignment, is invalid and worthless. The district court properly excluded Mr. Young’s testimony on this basis.
The district court also correctly excluded Mr. Young’s testimony because Airboss did not produce his expert report before trial. Under Federal Rule of Civil Procedure (FRCP) 26(a)(2), testimony offered as expert opinion requires the offer of an expert report prior to trial. Mr. Young’s declaration contains expert opinion because he opines on claim construction and interpretation of the original application. Thus, without an expert report proffered for the record at any time, the district court correctly excluded this testimony on the basis of FRCP 26(a)(2).