Defenses in patent infringement cases are not always pertinent to actual legislation, but rather actual terms or definitions of the United States patent laws. An excellent example is with the term patent history estoppel. Patent history estoppel, also known as file wrapper estoppel, a term that is unique to American patent laws. The term simply refers to a person or party that has already filed for a patent application, and then proceeds to make changes or amendments to the application or patent claims in order adhere to the requirements of the patent laws.
Once these changes are made, the owner of the patent, if approved, will no longer have rights or cause for infringement action to the original information contained in the application prior to the changes or amendments. Contingent to the United States Patent and Trademark Office conducting an examination of those claims and/or information provided in the application, the amendments may also limit the range of equivalents that the patent owner may be entitled to.
In essence, once amendments are made to the information in the original application or to the scope of claims of the patent–for example, making them more specific or narrowing the descriptions–the patent owner is then considered to have surrendered the original claims or descriptions as prescribed in the original.
The concept of patent history estoppel has been used in patent infringement cases as a defense against infringement in the sense that no prior patent for a particular product exists under the interpretation of the patent history estoppel. Technically speaking, the patent history estoppel is issued to a patent holder to stop the infringement action lawsuit against another party due to the changes made to the patent, which render them void under this provision. The issue regarding litigation involving patent history estoppel has been one of controversy, as is best exhibited by the Festo Corp. v. Shoketsu Kinzoki Kogyo Kabushi Co. Case.
The Festo Corporation filed an infringement suit claiming that Shoketsu had violated patent protection rights when the introduced into the market a device which the Festo Corporation already owned two patents for a similar device. However, the original application for those two patents were initially rejected, and changes were made in order to be considered and acceptable for patent registration. Shoketsu then used the patent history estoppel to claim that such infringement suit was invalid because the original patents for the designs for the device in question were altered from the original.
Therefore, the Festo Corporation had no rights for patent infringement action based on the original designs that were initially denied for registration in the first place. Initially, the courts ruled in favor of Festo, claiming that the changes to the original application were made with no ill intention, such as to circumvent providing information of prior art as required by patent laws.
Under such an interpretation, the patent history estoppel could not be legally applied. However, an appeal would eventually reverse the decision, claiming that the patent history estoppel would successfully bar Festo from suing for patent infringement on the basis of the patents being changed or amended, regardless if they were made to comply with the patent law requirements or avoiding the prior art statute. Patent history estoppel prohibits a patent owner from equivocating the new amendments to an application to the prior original information or claims of the patented product in question.
