T 0197/86 - Comparative tests must be specific / "Photographic couplers" - #31

Citation rank: 31
No. of citations: 124

T 197/86 looks at the nature of comparative tests, that is required to prove an alleged technical effect over the prior art.

In the underlying opposition case, the patent related to a photographic cyan-dye forming coupler. Claim 1 differed from known photographic couplers by having a paracyano group on its phenyl nucleus. The patentee claimed that the paracyano group on the phenyl nucleus led to the technical effect that the absoption half bandwidths (HBW) is narrower as compared with the closest prior art (document "(d)").

The Board, when assessing inventive step, made reference to the "Spiro compounds" decision (T 181/82) which held that, where comparative tests are submitted as evidence of an unexpected effect, there must be the closest possible structural approximation in a comparable type of use to the subject-matter claimed (T 197/86, r. 4).

In the case at hand, the closest prior art was a "coupler No. 9" disclosed in document (d). The patentee provided experimental data showing a narrower absorption half width (the alleged technical effect) of an example disclosed in the patent in suit versus coupler No. 9 of document (d). The opponent-appellant argued that the this experimental data was insufficient, in that the chemical structure of the patent's example differed from coupler No. 9 not only in terms of the paracyano group on the phenyl nucleus, but had also other structural differences. The alleged technical effect could thus not be attributed to the distinguishing feature (i.e., the paracyano group on its phenyl nucleus) of the claim only.

The Board seems to have left open the question of whether they followed that argument or whether they considered that evidence sufficient (r. 6.1.1).

In any event, the patentee had provided additional experimental data comparing the absorption half width of couplers which were not disclosed in the prior art, but differing from the examples in the patent in suit in just the distinguishing paracyano group on its phenyl nucleus. These data clearly provided evidence that the observed technical effect is due to the distinguishing feature only.

In this context, the Board stated:

"6.1.2 The Respondent has, however, now strengthened the support for his claim by voluntarily providing comparisons with variants which, although not expressly belonging to the prior art, differ from the claimed tested couplers only in respect of the paracyano group. This is an extra contribution to the clarification of the issues, which went beyond the obligations imposed by T 181/82 and could be seen as giving support to a claim with broadened definitions of the ballast group, leaving the cyano group as the only characterising, i.e. distinguishing feature over the prior art.

6.1.3 On the basis of these voluntary comparisons the Board is inclined to take the Respondent's view because the advantageous effect of the para-cyano group is clearly shown. According to an earlier decision (T 35/85, 16.12.86) the onus of proof may be discharged by "submitting comparative tests with newly prepared variants of the closest state of the art, making identical the features common with the invention in order to have a variant lying closer to the invention so that the advantageous effect attributable to the distinguishing features of the invention is thereby more clearly demonstrated".  In the present case the Board has concluded that in the case where comparative tests are chosen to demonstrate an inventive step with an improved effect over a claimed area, the nature of the comparison with the closest state of the art must be such that the effect is convincingly shown to have its origin in the distinguishing feature of the invention. For this purpose it may be necessary to modify the elements of comparison so that they differ only by such a distinguishing feature (supplementing T 181/82, "Spiro Compounds", OJ EPO 1984, 401)." (emphasis added)

Since the patentee in the case at hand supplied such comparison with compounds differing from the claimed compounds only with respect to the differentiating feature of the claim, the Board was satisfied that the claimed couplers were inventive.

The patent was hence upheld.

Remark: I note that the Headnote makes a weaker statement than what is said in point 6.1.3 of the reasons ("the nature of the comparison with the closest state of the art must be such that" vs. "may be necessary to"). As I mentioned above, point 6.1.1 of the reasons may be understood as indicating that the comparison of an example from the patent in suit with the original closest example from the prior art may have already sufficed to release the patentee from its burden of proof. Nevertheless, T 197/86 is sometimes cited for holding that the comparison "must" be such that the effect is convincingly shown to have its origin in the distinguishing feature of the invention (see, e.g., T 0197/86). This may be a too strong a statement.

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Headnote:

In the case where comparative tests are chosen to demonstrate an inventive step with an improved effect over a claimed area, the nature of the comparison with the closest state of the art must be such that the effect is convincingly shown to have its origin in the distinguishing feature of the invention. For this purpose it may be necessary to modify the elements of comparison so that they differ only by such a distinguishing feature (supplementing T 181/82, "Spiro compounds", OJ EPO 1984, 401) (cf. point 6.1.3 of the Reasons).

 The full text of the decision can be found here.

Quotes from decisions citing T 197/86 can be found here.