The PTAB recently confirmed that the doctrine of assignor estoppel does not apply to IPR proceedings. Esselte Corp. v. Sanford L.P., IPR2015-00771, Paper 13 (Aug. 28, 2015). Assignor estoppel is an equitable doctrine that generally prohibits an assignor of a patent, or one in privity with him, from later challenging the validity of the assigned patent in an infringement suit filed by the assignee. The doctrine prevents the intrinsic unfairness of allowing an assignor “to sell something and later to assert that what was sold is worthless.”

In prior decisions, the Board had held that assignor estoppel is inapplicable to IPR proceedings, under the rationale that 35 U.S.C. § 311 makes IPRs “widely available to ‘a person who is not the owner of a patent.’”

In Esselte Corporation, the Petitioner sold the Patent Owner, then a subsidiary of the Petitioner, to another entity. The sale transferred the challenged patent. Later, the Patent Owner sued the Petitioner for infringement of the patent, and in response the Petitioner filed an IPR petition challenging the validity of the patent.

The Patent Owner argued that the IPR petition was barred by assignor estoppel. Acknowledging the Board’s prior decisions declining to recognize assignor estoppel in IPRs under § 311, the Patent Owner argued that assignor estoppel could also be recognized under 35 U.S.C. §§ 314(a) and 316(a)(2).

The Board rejected both arguments, using its prior rationale that “Congress has demonstrated that it will provide expressly for the application of equitable defenses when it so desires.” Because the Patent Owner could not point to any regulations it contended pertain to recognizing and applying assignor estoppel to IPR proceedings, the Board rejected the Patent Owner’s contentions pertaining to assignor estoppel.

The Board’s decision echoes the USPTO’s decisions in inter partes reexaminations under the pre-AIA versions of § 311. See, e.g., Decision Dismissing Pet. to Vacate at 6–7, In re Harvey, Control No. 95/000,155 (Mar. 8, 2007) (declining to apply assignor estoppel). Unless the Federal Circuits speaks to the contrary, it appears that challenges to IPRs based on assignor estoppel will continue to fail.