Historically, file wrappers - the back and forth with the Patent Office in a patent application file - were irrelevant and inadmissible in Canadian patent construction. This allowed the Court to focus when construing a patent on the actual language of the claims in the issued patent, while avoiding "opening the pandora's box of file wrapper estoppel"1. This bar to file wrapper estoppel in Canadian claim construction distinguished Canada from the United States, where prosecution history estoppel was intended "to hold the inventor to the representations made during the application process... by amending, the inventor is deemed to concede the patent does not extend as far as the original claim"2.
Canada Introduces File Wrapper Estoppel
In late 2018, the Canadian Federal government amended the Patent Act to add section 53.1, which allows written communications between the patentee and Patent Office during patent prosecution to be admitted into evidence to rebut representations made by the patentee in litigation regarding claim construction.
On September 25, 2019, the Federal Court applied section 53.1 to for the first time in Canada3. In Canmar Foods Ltd v TA Foods Ltd, the patentee Canmar Foods brought a patent infringement action against TA Foods for alleged infringement of Canmar Foods' patent, which claimed a method for roasting oil seed.
TA Foods argued that its roasting process differed from the patented method because it did not heat its flax seeds in a "stream of air" or maintain the seeds in an "insulated roasting chamber or tower". TA Foods submitted because these two elements were added intentionally during the Canadian patent prosecution, they became essential elements of the claims. TA Foods claimed the American prosecution history was incorporated into the Canadian prosecution history by reference, because Canmar Foods acknowledged in correspondence to the Patent Office that the amendments in the U.S. had overcome novelty and obviousness rejections.
Specifically, during Canadian prosecution, Canmar Foods had acknowledged that the amended claims "correspond substantially to those submitted during prosecution of a related United States application"4. Canmar Foods continued, explaining the newly submitted claims were "much narrower in scope than the previously examined claims in view of the introduction of significant limitations derived from the description and previous dependent claims" and "encompass[ed] both novel and non-obvious...