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File Wrapper Estoppel: Federal Court applies new section 53.1 of the Patent Act

September 27, 2019


Canmar Foods Ltd. v. TA Foods Ltd. (2019 FC 1233) represents the Federal Court’s (“Court”) first opportunity to interpret the scope of new section 53.1 of the Patent Act (“Act”). Section 53.1 allows a party to a patent proceeding to admit a patent’s prosecution history as evidence to rebut a patentee’s representations concerning the construction of claims within the patent.


Canmar Foods Ltd.’s (“Canmar”) and TA Foods Ltd.’s (“TA Foods”) are competitors in the manufacture and supply of roasted flax seed products.

Canmar is the owner of Canadian Letters Patent No. 2,582,376 (the “376 Patent”) which includes claims for methods of roasting flax seed by heating the seed in a stream of air and transferring the seed to an insulated roasting chamber.

Conversely, TA Foods roasts the oil seed using a micronizer, which subjects the seed to infrared radiation as it travels along a steel plate under a series of heated tiles.

Canmar brought a patent infringement action against TA Foods, alleging that its roasting process infringed the claims of the 376 Patent.

The Federal Court’s Decision

The central issue in the case concerned the scope of admissibility under s. 53.1 of the Act.

TA Foods sought an order granting summary judgment based on non-infringement of the 376 Patent. The essence of TA Foods’ argument was that its roasting process fell outside of the claims of the 376 Patent, as it did not heat flax seed in a stream of air, nor did it maintain the seed in an insulated roasting chamber. Additionally, TA Foods maintained that in applying a purposive construction to the claims of the 376 Patent, the Court must consider representations made during prosecution of the 376 Patent, including representations made to the U.S. Patent Office for the corresponding U.S. patent application.

The Court noted that, prior to the enactment of s. 53.1, prosecution histories in Canadian or foreign patent applications were not admissible with respect to construing terms in Canadian patents. However, s. 53.1 established an exception to that general rule by allowing written communications made between the patentee and the Patent Office to be admitted into evidence to rebut representations by the patentee during the course of subsequent litigation.

The Court concluded that, with the introduction of s. 53.1, purposive construction of patent claims in Canada now includes three prongs:

  1. the claims themselves;

  2. the disclosure; and

  3. the prosecution history in Canada, when used to rebut a representation made by the patentee as to the construction of a claim in the patent.

The Court held that s. 53.1 is specific to admitting Canadian prosecution histories to rebut positions taken on claim construction. However, the Court found that Canmar had specifically referred to its U.S. prosecution history in communications with the Canadian patent office, and had acknowledged that amendments to claims in the Canadian file history were made to overcome novelty and obviousness concerns raised in the U.S. application.

The Court emphasized that purposive construction in light of s. 53.1 requires consideration of not only the claims and the disclosure, but also the substance behind amendments to the claims issued in Canadian patents. With that in mind, ignoring the reference to the U.S. prosecution history would “emasculate the intent and effect of section 53.1”. Therefore, the Court held that an interpretation of s. 53.1 that allows for the consideration of foreign prosecution histories in “extraordinary circumstances” is consistent with the realities of patent prosecution in Canada, as the prosecution of patents in Canada often follows the prosecution of corresponding patent applications in other jurisdictions.

The Court found that “extraordinary circumstances” would arise where 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 such situations, the Court considered it appropriate to refer to the foreign prosecution history for the limited purpose of purposively construing the Canadian claims.

Taking into account the Canadian prosecution history of the Canmar patent, including the points at which Canmar referred to the U.S. prosecution history, the Court found that the two essential elements of Canmar’s claim were (a) heating the seed in a stream of air and (b) roasting the seed in an insulated roasting chamber. The Court found that those two elements were not included in TA Foods’ roasting process, and therefore TA Foods had not infringed on Canmar’s patent.

Accordingly, the Court granted TA Foods’ motion for summary judgment.


Canmar Foods Ltd. v. TA Foods Ltd. provided the Federal Court with a meaningful opportunity to establish the scope of admissibility under s. 53.1. The Court’s reasons for the decision provide a window into the circumstances when courts will admit Canadian and foreign prosecution histories as evidence to rebut the representations made by a patentee during the course of subsequent litigation.


Authors: Jordan Scopa, Jaclyn Tilak and Duncan Lurie


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