Assignor estoppel
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The doctrine of assignor estoppel is an equitable estoppel barring a patent's seller (assignor) from attacking the patent's validity if he/she is found to have infringed that patent later.
The exclusive right of a patent is negotiable. Even though the inventor's name remains unchanged, the inventor is allowed to sell the exclusive right to another party (assignee). Not unlike the selling of a car, the inventor is barred from using that patent afterwards if the contract says so.
[edit] Example
For example, if Tom sold his U.S. patent rights to Jerry, and was sued by Jerry over infringement of that patent later, Tom is not allowed to challenge the patent's validity because he was the inventor.
- "Doctrine of assignor estoppel prevents unfairness and injustice of permitting party to sell patent rights and later assert that what he sold is worthless." Mentor Graphics Corp. v. Quickturn Design Systems, Inc., 150 F.3d 1374 C.A.Fed.Or.,1998
This doctrine extends to those in "privity" with the assignor. If Tom becomes another company's largest shareholder, and that company is sued by Jerry over patent infringement, that company could very likely be barred from raising patent validity as a defense even if Tom was not personally involved in the infringing process.
[edit] Case law
- Westinghouse Elec. & Mfg. Co. v. Formica Insulation Co., 266 U.S. 342, 45 S.Ct. 117 (1924).
- Diamond Scientific Co. v. Ambico, Inc., 848 F.2d 1220 (Fed. Cir. 1988), in some circumstances, equity may outweigh the estoppel doctrine.
