Paint-spray, proof and prior disclosure

Wagner International AG & Others v Earlex Ltd [2012] EWHC 984 (Pat) is a decision of Mr Justice Floyd on 18 April in the Patents Court, England and Wales. Though not a major ruling, enriched by profound pronouncements of legal principle, it is nonetheless instructive for the tidy and efficient manner in which the trial judge marshalled the evidence -- and as a reminder of how easily a claimant patent owner can sow at least some of the seeds of its own defeat in court through disclosure of its own prior art in an exhibition. Wagner's patent was for a paint spray gun with venting passages in the air cap which relieved the problem of back pressure to the air source. Earlex made a spray gun which, according to Wagner, infringed. Earlex denied infringement and counterclaimed invalidity.

After comparing Earlex's products with the patent as claimed, the judge dismissed the infringement claim.  He then turned to the patent itself.

In the first place, Wagner's patent was invalid for added matter since the content of the specification of the granted patent extended beyond that disclosed in the application for the patent as filed. As if that wasn't enough, there was a problem of prior disclosure too. It appeared that at least one prototype of Wagner's paint sprayer with the venting passages in the air cap, as described in the patent, featured at their exhibition stand at the Home Center Show 1991 in Chicago, which the public could not only see but even try for themselves. The holes in the air cap would have been visible to anyone who looked at the gun with interest and there was evidence that it would be possible from an examination of the device to estimate the holes' diameters and their relative positioning on the air cap. Having installed the venting holes, the skilled person would undoubtedly have been able to make adjustments by a simple process of trial and error to avoid interference of the venting air with the paint spray, and would thereby be working the invention. The skilled person would be interested in the function of the holes, which represented a departure from the standard air cap, and would be able to establish their function without the exercise of inventiveness. Accordingly, the invention as described in the patent was obvious in the light of the disclosure at the show.

This conclusion is a neat blend of objectively provable fact, plausible hypothesis and projection of the characteristics of the person skilled in the art. Since the burden in civil proceedings is only on the balance of probabilities, inferences such as that drawn by the judge in this case are more than plausible: they are constitutive of fact.