Canadian Patent Act amendments introduce file wrapper estoppel

New amendments to the Canadian Patent Act deem a patent’s Canadian prosecution history (the so-called file wrapper) material in litigation where claim construction is at issue. Specifically, the file wrapper can now be admitted into evidence to rebut a patentee’s representations about patent claim construction.

The practical impact of these amendments is that a patentee has to be even more careful about making representations regarding the construction of patent claims during Canadian prosecution. Such representations may now return to haunt the patentee in the form of permissible rebuttal to any claim construction positions advanced in litigation.

This poses a great challenge and burden on patentees. Many Canadian patents are prosecuted on a budget, without an eye to eventual litigation, often by non-lawyers.

The amendments overrule the long-affirmed precedent set by the Supreme Court of Canada (Free World Trust v Électro Santé, 2000 SCC 66) that, as the patent’s function is to give notice to the public of what is protected, evidence from outside the patent should not be material to claim construction: “To allow such extrinsic evidence for the purpose of defining the monopoly would undermine the public notice function of the claims, and increase uncertainty as well as fuelling the already overheated engines of patent litigation” (at para. 66).

The new language of section 53.1(1) of the Act provides:

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.

The amendment came into force upon royal assent on December 13, 2018, and applies in respect of any proceeding that has not been finally disposed of before that date.

This new provision may be heralded as a welcome change for some. For example, in Pollard Banknote v BABN Technologies, 2016 FC 883 at paras 238-39, Justice Locke was not impressed when the patentee (SG) took a position at trial supposedly inconsistent with the file wrapper:

I would expect that SG’s argument would never have made it to a trial in the US where the principle of file wrapper estoppel applies. There, SG would likely not have been allowed to argue a claim construction that attempts to recapture ground conceded during prosecution of the patent application to avoid prior art.

This case highlights a potential risk in taking a simpler approach to claim construction by ignoring extrinsic evidence, such as the prosecution history of the patent in suit.

In the United States, there is a long history of file wrapper estoppel. With this concept being newly introduced in Canada, foreign file wrapper jurisprudence may influence how Canadian courts grapple with these new amendments to Canada’s Patent Act.

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