Magna Mirrors of Am. v. 3M Co.

The defense of equitable estoppel provides a complete defense for alleged patent infringement.

Opinion (ROBERTS): Magna sued 3M alleging some of 3M's adhesives infringed its patent 5,587,236, covering an autoclave process for attaching mirrors to windshields using a structural adhesive. 3M moved for summary judgment that the patent was unenforceable because of Magna's inequitable conduct. Equitable estoppel is a defense to claims of patent infringement, the defense has three elements: 1) a misleading act communicated by the patentee, 2) reliance by the alleged infringer on that communication, and 3) the alleged infringer would be harmed if the patentee were permitted to assert a claim inconsistent with its prior conduct. To invoke estoppel, the alleged infringer must show, by a preponderance of the evidence, conduct by the patentee from which it could reasonably be inferred that the patentee had abandoned its claim. The court found that joint development work by 3M and Magna informed Magna of the nature of 3M's adhesive and that it was potentially infringing. That knowledge, combined with Magna's failure to pursue requests for payment for the potential infringement, was conduct that could reasonably support the inference that Magna has abandoned any claim against 3M. 3M's reliance, the court found, was shown by its continued sales and investment in the accused adhesive. The final element, harm to the alleged infringer, requires a showing that the alleged infringer has suffered material economic or evidentiary prejudice as a result of the delay in legal action. The court found that 3M's investment of $18 million in the continued development of the product showed material prejudice. Additionally, Magna's delay in filing suit presented evidentiary problems because it forced witnesses to rely on old memories and because relevant documents were no longer available. Because all three elements of the defense were established, the court GRANTED 3M's motion for summary judgment.