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Posted in: Court Decision | Intellectual Property

Oct 9, 2019

Unwrapping File Wrapper Estoppel: Federal Court Considers Admissibility of Prosecution History Under New Section 53.1

By L.E. Trent Horne

A recent decision of the Federal Court in Canmar Foods Ltd. v. TA Foods Ltd. has provided the first interpretation of section 53.1 of the Patent Act, which permits reference to a patent’s prosecution history to assist in claim construction.


The plaintiff, Canmar Foods Ltd., owned a patent directed to a method for roasting oil seed. The only independent claim required (among other things) that the seed be heated “in a stream of air”. Canmar sued a competitor, TA Foods Ltd., for infringement. One of TA’s defences was that it heated the seed by infrared radiation and therefore could not infringe. TA successfully brought a motion for summary judgment shortly after the close of pleadings. The Court’s conclusion that the “stream of air” was an essential element of the claims was founded on the file history, particularly amendments to the claims that were made during prosecution in both Canada and the United States.

File Wrapper Estoppel New to Canada

For many years, Canadian courts considered the file wrapper (i.e. correspondence between the patentee and the patent office during prosecution) to be irrelevant for the purposes of claim construction. This was one of the significant differences between patent litigation in Canada and the United States.

In December 2018, the Canadian Patent Act was amended to add section 53.1, which allows for statements made during prosecution to be admitted into evidence to rebut any representation made by the patentee as to the construction of a claim.

File Wrappers Foreign and Domestic

In the Canmar case, the defendant argued that because the patentee amended its claims in the Canadian patent application to substantially mirror the claims that were amended in the United States to overcome patentability objections, the prosecution history of both the Canadian and the U.S. application should be considered.

The Court found that while section 53.1 makes no reference to prosecution histories from other jurisdictions, the presence of extraordinary circumstances would permit reliance on foreign file histories. Here, extraordinary circumstances were found to exist because the patentee acknowledged that the claims had been amended to be substantially the same as the claims submitted in the United States, and the patentee admitted that the amendments to the claims limited their scope in order to make them novel and non-obvious.

Ultimately, the judge in the Canmar case did not rely on the Canadian or U.S. file history to determine what the certain claim terms meant, but did rely on the file history to determine if certain claim terms were essential. In particular, since the “stream of air” limitation was added to overcome prior art objections, it was found to be clear evidence of an express intention that the element was essential. Since the defendant’s method did not use a stream of air to heat the seed, the action was dismissed.

Looking Ahead

In addition to being the first case to consider the recent amendments to the Patent Act, the Canmar case is also significant because it was resolved by way of summary judgment, and without expert evidence. The Federal Court has been historically reticent to resolve contested patent matters in a summary way. This may signal an increased willingness to determine patent cases without experts or live witnesses.