Traditionally, statements made during prosecution of Canadian patent applications or corresponding foreign patent applications (the “file wrapper”) were not admissible for construing terms in the claims of Canadian patents (so-called “file wrapper estoppel”).  The Supreme Court of Canada even went so far as to refer to file wrapper estoppel as a “pandora’s box”.  In the immortal words of Bob Dylan, however, times they are a changing.  Recent legislative changes to the Canadian Patent Act, and more recently the decision of the Federal Court of Canada in Canmar Foods Ltd. v. TA Foods Ltd. appears to have changed that.

In view of the the legislative changes and the Canmar decision, patent applicants in Canada should be more circumspect as to what material makes its way into the Canadian prosecution file. As with many things in life, sometimes the less said the better!

In Canmar, the parties were competitors in the manufacture and supply of flax seed products, particularly roasted flax seed products. The plaintiff/patentee, Canmar Foods Ltd. (“Canmar”), owned a Canadian patent directed to methods for roasting oil seeds and the products produced by these methods. Canmar became aware of the defendant’s roasted flax seed products and, when talks broke down, Canmar commenced infringement proceedings.

In a motion for summary judgment. the defendant, TA Foods Ltd. (“TA Foods”), argued that its activities fell outside the scope of the claims of the Canadian patent, when properly construed.  TA Foods took the position that in addition to applying a purposive construction to the claims based on a reading of the claims and the specification as a whole, the Court must also take into account representations made during prosecution (e.g. the file wrapper) of the Canadian patent.  TA Foods, relying on both the Canadian and U.S. prosecution histories, argued that limitations added to overcome prior art cited in the U.S. case, which were incorporated into the Canadian patent, argued against infringement.