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.

In 2019, the Canadian Patent Act was amended to include new Section 53.1, which provides a limited exception to the general rule that the Canadian prosecution history is not evidence. Section 53.1 reads as follows:

53.1 (1) In any action or proceeding respecting a patent, a written communication, or any part of such a communication, may be admitted into evidence to rebut any representation made by the patentee in the action or proceeding as to the construction of a claim in the patent if

(a) it is prepared in respect of

(i) the prosecution of the application for the patent,

(ii) a disclaimer made in respect of the patent, or

(iii) a request for re-examination, or a re-examination proceeding, in respect of the patent; and

(b) it is between

(i) the applicant for the patent or the patentee; and

(ii) the Commissioner, an officer or employee of the Patent Office or a member of a re-examination board.

With the introduction of section 53.1, purposive claim construction now requires consideration of not only the claims and the disclosure, but also the substance behind intentional amendments to the claims issued in Canadian patents. The language of section 53.1 is limited to communications between the patentee and the Canadian Patent Office. However, in this case, the court found that the patentee specifically referred to the corresponding US patent application prosecution history and acknowledged that the amendments to the claims in the Canadian file history were made to overcome novelty and obviousness concerns raised during US prosecution. Accordingly, the Court considered the US prosecution history as part of a purposive construction of the claims of the Canadian patent. Ignoring the reference to the United States prosecution history in this case would “…emasculate the intent and effect of section 53.1.”

In circumstance where prosecution of a foreign application is made part of the prosecution history of the Canadian patent, that foreign prosecution history, where relevant to limitations made to Canadian claims, should be admissible to aid in a purposive construction of the claims of the Canadian patent. Extraordinary circumstances arise where, as in this case, the patentee acknowledges that the claims have been amended to be substantially the same as claims submitted in another jurisdiction, and the patentee admits that the amendments have limited the scope of the claims in order to make the claims novel and non-obvious. In these circumstances, the Court should be able to refer to the foreign prosecution history for the limited purpose of purposively construing the Canadian claims.

Canmar argued that the scope of the claims should not limited as TA Foods suggested, and that TA Food’s activities could potentially infringe the patent claims. According to the Court, however, the limitations introduced during prosecution specifically excluded TA Food’s activities and asking the Court for a broadened construction of the claims was not supported by the specific language of the claims, the disclosure, or the prosecution history.

In this case, the Court could construe the claims of the Canadian patent and found no infringement, based on the evidence of the process used by TA Foods. As this was the only process used by it, the Court found that TA Foods did not infringe the claims of the Canadian patent. In view thereof, there was no genuine issue for trial, and TA Food’s motion for summary judgment was granted.