Case Comment

Imperial Oil v.


citation(s): F.C.A.

copyright 1997 Donald M. Cameron, Aird & Berlis




The Decision

It is important to set out the numerical parameters exactly, rather than paraphrase even to the limited extent the trial judge did: 

        (a) a Mn value of 1300 to about 5000;

(b) an Mw/Mn value of about 1.5 to about 4;

(c) a succination ratio of at least 1.5 to 4.

If, as said in Beecham, it is unnecessary to have recourse to the disclosure to construe a claim where its words are plain and unambiguous, it is likewise unnecessary to have recourse to parol evidence, however expert. It follows, for example, that, while recourse to the disclosure and experts is necessary to understand what a succination ratio is and how it is tot be calculated, there can be no question that the claims in issue do not assert a monopoly over compositions having a succination ratio of 1.25%; the plain and unambiguous meaning of "at least 1.3" cannot include 1.25. It is likewise as to the lower limit of the first parameter, where the Mn value of 1300 is unqualified.


What may still be asked, however, is whether a composition with a succination ratio of 1.25 infringes because that is but a minor or immaterial variant of the invention, or to put it another way, because the "pith and marrow" of the invention has been taken. As was said in Lightning Fastener Co., Ltd. v. Colonial Fastener Co. Ltd., [1932] Ex. C.R. 89 at p.98; reversed [1933] 3 D.L.R. 791, [1933] S.C.R. 363; reversed [1934] 3 D.L.R. 737, 51 R.P.C. 349 (P.C.):

... the question is not whether the substantial part of the machine or method has been taken from the specification, but the very different one, whether what is done by the alleged infringer takes from the patentee the substance of his invention.

That the principle remains alive and well and applicable in the present circumstances was confirmed by the House of Lords in Beecham Group v. Bristol Laboratories, [1978] R.P.C. 153 at p. 200, per Lord Diplock, a pharmaceutical case.

The increasing particularity with which the claims are drafted and multiplied may have reduced the scope and application of the doctrine of pith and marrow, but I am unable to accept the argument advanced by Bristol that this has made the doctrine obsolete...Directed as it is against colourable evasion of a patent it is not in my view confined to mechanical inventions or to claims for new combinations of integers, but in appropriate cases, though they may be rare, is applicable to claims for new products.

At one point in this judgment the trial judge said (at p.44):

The defendant raised the issue of "minor variant". I considered the argument the defendant presented, but could not accept this assertion because then I would gave to accept that the succination ratio is not part of the invitation. I find quite the contrary, for the patent's very pith and narrow would be offended if the minor variant argument were applied here.

At an earlier point, had said (at p. 33):

On a purposive construction of the patent, it is my belief that strict compliance with the words "at least 1.3" were not essential to the invention. I have concluded that unreacted PIB is to be excluded in calculating the succination ratio.

Imperial argues that the first is a finding that a succination ratio of at least 1.3 is of the very pith and marrow, while the second dismisses it as not essential.

Imperial also suggested that the references to "defendant", i.e. Imperial, in the first must have been a slip and that it should have said "plaintiff", i.e., Lubrizol. Imperial is mistaken in this. The trial judge was clearly dealing with its argument that, a succination ratio of at least 1.3 being an essential element, "it is not colourable evasion to go outside an essential element (transcript, vol. XXVII, p.p. 71-2).


To find conflict between the two statements requires that each be taken out of its context. As tot he first, his appreciation of "minor variant" and "pith and marrow" is much to be preferred to that urged on him by Imperial which, in my view, was an inversion of the law. However strictly one construes a claim, the pith and marrow doctrine precludes its colourable evasion. In the second, the choice of words may have been less than precise but the trial judge was simply saying that the exclusions of unreacted PIB from the calculation of the succination ratio was not precluded by strict adherence to "at least 1.3".

This was the only attack on the finding of infringement as it is related to the products in Columns A, B and C of the schedule as well as those in Columns D, E and F. It is without merit.


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