Any claim of an issued Canadian patent may be narrowed by filing a disclaimer. Disclaimers have been used to narrow a claim to avoid prior art and thereby prevent the claim being invalid. The patent owner may then be left with a valid claim that is still infringed by a competitor. However, disclaimers are now being carefully scrutinized by the courts. In its recent decision Hershkovitz v. Tyco Safety Systems, the Federal Court of Appeal has held that if a disclaimer does not fully comply with the Patent Act, then the claim must be invalid.

To be eligible for patent protection in Canada, an invention must be new, useful and non-obvious. A patent owner defines the scope of an invention with the claims of a patent. Patent claims are commonly analogized as legal fences which a patent owner uses to stake a claim to a particular area on the patent landscape, and which serves as a warning to keep others from venturing into the claimed territory. However, in some instances a patent owner may later discover that the claim covers more territory than it should (i.e., the area enclosed by the fences is too large). If such an error is the result of accident, mistake or inadvertence, as opposed to intent to mislead or deceive the public, the patent owner can use a disclaimer to narrow the claim.

According to the Federal Court of Appeal, in order to be valid, a disclaimer must be filed in a good faith attempt to correct a mistake and must only narrow the scope of the claims. Therefore, a disclaimer should be filed in a timely manner after a mistake has been recognized, and must introduce at least one additional “essential element” into the claims, which has the effect of narrowing the claims and shrinking the legal fence. If a disclaimer attempts to remove features of the claim or otherwise has the de facto effect of broadening the claim, it will be invalid. Interestingly, the Court held that a disclaimer must also be invalid if it introduces additional “inventive elements” into the claims, even if the scope of the claims is not actually broadened by such elements. In other words, it appears that a disclaimer will be invalid if it has the effect of shifting the legal fences across the landscape, even if the fences have not actually increased in size.

The effect of either scenario is the same, the claims that were the subject of the disclaimer will be found invalid, based solely on the patent owner’s admissions contained in the disclaimer.

While disclaiming some or all of the claims in a patent can be a tool to preserve the validity of an issued patent, patent owners must ensure that the effect of the disclaimer will be to narrow (as opposed to expand or shift) the scope of the claims, and that they can establish that the disclaimer is filed as part of a good faith effort to correct a mistake in the patent. If these conditions cannot be satisfied, a patent owner may wish to consider other possible avenues of patent amendment such as re-issue and re-examination. Accordingly, if a patent owner becomes aware of any new prior art that may impact the validity of an issued patent, they should promptly discuss the new prior art with their patent agent.