Can a Defendant in a Patent-Infringement Action Who Previously Assigned His Rights to the Patented Invention, or Who Is in Privity with Such an Assignor, Raise a Defense of Patent Invalidity?

The Court will consider whether it is appropriate under the Patent Act to limit the application of assignor estoppel to its equitable core and apply assignor estoppel only where the assignor sells patent rights for valuable consideration in an arm's length transaction, then either contests the validity of a claim materially identical to a claim issued or pending at the time of the assignment, or otherwise contradicts preassignment representations about the patent's validity. Under such an equitable core limitation, assignor estoppel would not be an assertable defense to invalidity where the claim asserted to be invalid is broader than or otherwise different from the patent rights that were assigned. Although the Patent Act authorizes parties to raise invalidity defenses in any infringement action (35 U.S.C. 282(b) et seq.), courts, including the Supreme Court, have long recognized the doctrine of “assignor estoppel” in which a defendant in a patent-infringement suit is “estopped to attack the utility, novelty or validity of a patented invention which he has assigned. . .as against any one claiming the right under his assignment.” The Court will now review the appropriate contours of the doctrine of assignor estoppel to ensure that the doctrine is not applied over broadly and reflexively to circumstances where there is no inconsistency between an assignor’s prior representations and its current challenge to a patent’s validity. [ABSTRACT FROM AUTHOR]