Lubrizol Corp v Esso Petroleum Co Ltd (No.5)
Lubrizol (L) sued Esso Petroleum (E) for infringement of its patent relating to lubricating oil. E denied infringement, alleging that the patent was invalid, and counterclaimed for its revocation. The grounds for invalidity were that the claim was ambiguous and was not fairly based, that the invention was obvious in light of two prior US patents, and that the invention had either been prior used or alternatively secretly used. Judgment was first given in favour of E and then L appealed.
The appeal was dismissed. It was held that although claim 1 was not ambiguous, was fairly based and would have been infringed, it was invalid for obviousness and prior use. As regards interpretation of patent claims it was observed that patent specifications, like other documents, had to be construed purposively. That meant that not only must the language of the claim be construed so as to ascertain the intention of the patentee as expressed, but also so as to take into account the purpose of the various parts of the specification. Patent specifications were intended to be read by persons skilled in the relevant art, but their construction was for the court. Thus the court must adopt the mantle of the notional skilled addressee and determine, from the language used, what the notional skilled addressee would understand to be the ambit of the claim.
The specification supported L’s interpretation. It was held that earlier the judge came to the wrong conclusion in relation to a particular procedure concerning the effect of “RI divergence”. The judge found that the scope of the claim was not sufficiently and clearly defined in accordance with the Patents Act 1949 s.32. The judge had approached the issue incorrectly by not asking what the specification was teaching. To answer the question it was necessary to adopt the mantle of the notional skilled addressee. Instead, the judge relied on the evidence of witnesses who were not necessarily equivalent to the notional skilled addressee. E could not establish that the claim was ambiguous.
The products alleged to have infringed fell within claim 1. The allegation of invalidity based on fair basis had no substance as the patent, when fairly read, described as the invention the product which was claimed.
However, claim 1 was eventually held to be invalid for obviousness because an example given in two prior US patents led to a product within claim 1 being produced.
  R.P.C. 727; (1998) 21(8) I.P.D. 21081