W.L. Gore & Associates v. Garlock, Inc.

Gore (plaintiff) patented both a Teflon-tape-stretching process and the resulting product, having discovered that high-speed stretching (contrary to conventional wisdom favoring slow stretching) was surprisingly effective. Garlock (defendant), sued for infringement, argued the patents were invalid because Budd, having licensed a similar stretching machine from inventor Cropper before Gore's filing date, had already secretly used the same process — under strict confidentiality agreements with Cropper and its own employees — to make similar tape, which it then sold publicly more than a year before Gore's filing. The district court held the patents invalidated by this prior use.

Whether, where a person uses a secret process to manufacture a product, and a later inventor seeks to protect the same process through a patent application, that secret prior use anticipates the later-filed patent claims.