IPR includes an estoppel provision, similar to that provided by the inter partes reexamination statute. The estoppel provision prohibits an IPR requester from asserting any ground of invalidity, which the requester raised or reasonably could have raised during the IPR, in a subsequent civil action, or ITC proceeding. The timing of IPR estoppel differs from inter partes reexamination estoppel, but the scope of the invalidity arguments prohibited by both estoppel provisions is likely similar.

Estoppel from an inter partes reexamination takes effect after a claim subject to reexamination has been finally determined as valid and patentable. The Federal Circuit interpreted finally determined to mean after all appeal rights, including appeals to the Federal Circuit, have been exhausted. See Bettcher Indus, Inc. v. Bunzl USA, Inc., 661 F.3d 629, 648 (Fed. Cir. 2011). In contrast, the IPR statute makes clear that IPR estoppel attaches once the Patent Trial and Appeal Board (PTAB) issues a final written decision—in other words, before the Federal Circuit has decided any appeals from the PTAB decision. See 35 U.S.C. § 315(b).

Estoppel applies to any invalidity argument that a requester raised or could have raised during an inter partesreexamination (35 U.S.C. § 315(c) (Pre-AIA)) and to any argument that a petition raised or “reasonably” could have raised in an IPR proceeding. 35 U.S.C. § 315(e). The reexamination statute also explicitly states that estoppel does not attach to invalidity arguments based on “newly discovered” prior art unavailable to the requester or the USPTO at the time of the reexamination. 35 U.S.C. § 315(c) (Pre-AIA). The IPR statute does not include such language. But given that IPR estoppel applies to arguments that the petitioner “reasonably” could have raised, the USPTO and courts may interpret the IPR statute, like inter partesreexamination estoppel, to mean that IPR estoppel does not apply to “newly discovered” prior art unavailable to the requester during an IPR proceeding. Indeed during congressional debate on the Patent Reform Act of 2011, Senator Kyl commented on the modifier “reasonably,” stating that it “softens the could-have-raised estoppel” and “ensures that could-have-raised estoppel extends only to that prior art which a skilled searcher conducting a diligent search reasonably could have been expected to discover” as opposed to requiring “a scorched-earth search around the world.” 157 Cong. Rec. S1375 (daily ed. Mar. 8, 2011) (statement of Sen. Kyl).