became a substitute for electrical initiating methods and for conventional detonation cord. Shock tubes consist of
plastic tubes with an outside diameter of approximately 3 millimetres, the inside wall of which is coated with a fine
layer of explosive dust. A detonator is attached to the tube by a process known as crimping. The tube operates by
the propagation of a shock wave the initiation of which at one end of the tube causes the
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progressive detonation of the explosive agent (it being selfpropagating) which, at the far end, initiates the main or
intended explosion by means of the detonator.
Page 456 of [1998] 4 All SA 453 (A)
All the shock tubes dealt with in evidence used a make or grade of Surlyn a plastic tubing, provided by a firm Du
Pont. It seems that Surlyns were well known and readily available in a range of grades. Explosive powders were
also readily available in the market.
The trial had some unusual features. Not only had Nobel and EB America, for the reasons already given, insight
into the technical developments of the other but the plaintiff itself also seems to have had some relationship and
communication on a technical level with EB America (though this too was not investigated). EB, however, was the
manufacturer of the tubes sold locally which were alleged to infringe the patent. What had a large influence on the
proceedings was the fact that prior to the South African litigation there had been litigation (on the counterpart
American patent) between Nobel, a company known as Ireco and EB America. As is usually the case with American
litigation depositions (an adverse party procedure related to discovery which allows parties to take evidence on
oath of the other party's officers) were taken from a number of persons including one of the inventors, Mr Hans
Lundborg. Both the plaintiff and the defendants made extensive use in crossexamination of the American
depositions and of documents discovered in the course of taking such depositions. As far as the defendants are
concerned it must have been the fact that Lundborg's deposition was available to them that led them to apply
before the trial in South Africa commenced to take his evidence on commission in Stockholm. In the application for
such leave it was stated that the witness would be able to support the counterclaim for revocation of the patent by
reason of his knowledge of, inter alia, the details of the development of the patented shock tube; details of the
problems encountered with the prior art products which the patentee sought to overcome; the commercial success
of the patented product, and tests conducted on the patented product and the prior art. When Lundborg's evidence
was led not all these promises were fulfilled. It is reasonably clear that the defendants had not had access to
Lundborg for the purposes of consultation before deciding to lead his evidence. An expert summary relating to his
evidence was filed but this he himself had not seen at the time of giving evidence. It was presumably prepared by
defendants on the basis of his deposition. Since Lundborg is one of the inventors of the patent and an exemployee
of Nobel the procedure would seem to have been a slightly ambitious attempt by defendants to advance their case.
It was, in the end result, not entirely unhelpful to their cause.
The onus of proof on the issue of infringement was on the plaintiff and on the issue of invalidity on the
defendants. The plaintiff led the evidence of only one witness, Dr Viljoen a well qualified scientist in the plaintiff's
employ, but only since January 1992. The defendants thereafter called a number of witnesses (who will be identified
later) in support of their contention that the patent was invalid.
At trial three grounds of invalidity were relied on. In the pleadings additional grounds had been advanced but
these were not pursued. The objections with which the defendants persisted were a contention that
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the patent was not patentable in terms of section 25 of the Act as it was not new in the light of the use or sale
before the priority date of two products known as HD Nonel (novelty); a contention that the patent did not involve
an inventive step (obviousness), and a contention that the claims were, in terms of section 61(1)(f)(i), not clear
(ambiguity). The last of these was so faintly urged in this Court that it can be disregarded. McArthur J, as has been
stated, found against
Page 457 of [1998] 4 All SA 453 (A)
the defendants on all the grounds for revocation and on the issue of infringement.
I turn then to the specification. The general introduction I have given above in relation to shock tubes is also set
out, in a broad sense, in the specification. It must be said, however, that the specification is a very terse document
and, as I will show, in a material sense uninformative. In terms of section 32 of the Act a specification must be
framed in what is now a conventional manner and the present specification broadly takes this form. (To the extent
that it would seem not to do so no issue was made thereof in the pleadings and such shortcomings are now
irrelevant.) There is a brief discussion in the specification of the prior art as it has been explained. The plastic
material produced by Du Pont (a grade of Surlyn) is identified in the specification as a suitable material for the
plastic tube. The document then proceeds to discuss the problems said to have been encountered with the prior art
products. The object of the invention and a brief consistory clause follow. It will be of assistance if I quote the
specification. It reads:
"It has been found that explosive in powder form which is applied on the inner surface of the plastic tube does not adhere
sufficiently firmly to this surface, the explosive powder often becoming dislodged from the inner surface during transport or
storage. During handling the powder may form blockages in the tube or fall down into said detonator. If a shock wave
encounters such a blockage it will terminate at this point. If the explosive powder falls down into the detonator, this may be