Prior Art Known Before Filing IPR Petition Leads to Estoppel of Invalidity Grounds in District Court

In Oil-Dri Corp. of Am. v. Nestle Purina Petcare Co., the district court granted a renewed estoppel motion under the rationale that references relied upon to challenge the validity of an asserted patent reasonably could have been presented in a previous IPR challenging the asserted patent.[i] Under 35 U.S.C. §§315(e)(2) and 325(e)(2), a petitioner is estopped from challenging the claims of a patent-in-suit on any ground of challenge that the petitioner “raised or reasonably could have raised during” the IPR or PGR. As discussed in our previous article, in Shaw Industries Group, Inc. v. Automated Creel Systems, Inc., the Federal Circuit held that estoppel did not apply to grounds of challenge presented in an IPR petition but denied institution by the PTAB.[ii] In Shaw, the issue of what constitutes prior art references that a petitioner “reasonably could have raised” was not before the court. Since Shaw, district courts have examined the reach of estoppel under §§315(e) and 325(e) by grappling with what constitutes prior art that “reasonably could have [been] raised” in a post-grant proceeding at the PTAB.

In Oil-Dri, the prior art references at issue before the district court included the “Akiyama,” “Shinohara,” and “Banschick” references. The Akiyama and Shinohara references were Japanese publications, while the Banschik reference was a U.S. patent application. Purina filed an IPR petition two weeks after Oil-Dri’s complaint. The petition cited “Hughes” and “Pattengill,” which are both U.S. patents, in grounds challenging the patent-in-suit. The PTAB instituted the IPR on the grounds that certain claims were obvious over Hughes and Pattengill, and later issued a final written decision concluding that Purina failed to show by a preponderance of the evidence that any of the claims in question were unpatentable.[iii]

Oil-Dri filed a renewed estoppel motion alleging that because Purina was aware of the prior art cited in the district court proceeding at the time the IPR petition was filed, it is estopped under § 315(e)(2) from asserting invalidity in district court based on the prior art references.[iv] The court appointed an independent expert to determine whether the Akiyama, Shinohara, and Banschick references could reasonably have been discovered by a “skilled searcher conducting a diligent search.”[v] The expert concluded that neither the Shinohara nor Banschick references would have been located by a skilled patent searcher focused on the claim language of the patent-in-suit.[vi] The court, however, relied on Purina’s admission in response to Oil Dri’s Third Set of Request for Admissions that it knew of the Akiyama, Shinohara, and Banschick references prior to filing the IPR petition. Purina argued that while Akiyama and Shinohara were known, these references were not relevant to the IPR proceeding because they were not directed to features recited in the patent-in-suit.[vii] The court was not persuaded and found Purina’s argument inconsistent with its position in the final invalidity contentions presented to the court. Also, because Purina’s argument focused on the interpretation of elements recited in the claims, the court viewed the argument as a request for it to adopt the claim construction of the PTAB during the IPR proceeding.[viii] Furthermore, the court held that denying Oil-Dri’s renewed motion for estoppel would run counter to the purpose of IPR proceedings and the AIA as a vehicle for promoting efficient dispute resolution in patent disputes.[ix]

Oil-Dri exemplifies how district courts are willing to apply estoppel to preclude consideration of invalidity arguments that could have been raised in related IPRs. The decision shows the importance of conducting a thorough search and review of prior art when drafting a petition. Practitioners should take appropriate measures to ensure that the closest prior art and strongest challenges are presented to the PTAB. As exemplified in Oil-Dri, failure to follow this approach can preclude an alleged infringer from relying on prior art it was aware of from being relied upon in an invalidity challenge in subsequent litigation.


[i] Case No. 1:15-cv-01067, ECF No. 224. p. 4 (N.D. Ill. Jan. 16, 2018) (St. Eve)).

[ii] 817 F.3d 1293, 1300 (Fed. Cir. 2016).

[iii] see Oil-Dri. at p. 2.

[iv] Id.

[v] Id. at p. 3.

[vi] Id.

[vii] Id. Purina argued that Akiyama and Shinohara were not directed to “particulates of swelling and non-swelling clays” as recited in the claims of the patent-in-suit.

[viii] Id. at pp. 3-4.

[ix] Id. at p. 4

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