T 0956/98 20-10-2000

I. The appellant contests the decision of the opposition division to revoke European patent No. 0 412 442. The reason given for the revocation was that the subject-matter of claim 1 of the main request and claim 1 of the auxiliary request then on file did not involve an inventive step, having regard to the prior art cited by the opponent.

II. In reply to the summons to attend oral proceedings, the appellant filed with the letter dated 12 September 2000 new claims 1 and 2 in replacement of the claims considered in the decision under appeal, and new pages 2, 2a, 2b, 3 and 4 of the description in replacement of pages 2, 3 and 4 of the patent specification. With the letter dated 11 October 2000 the appellant filed a further set of claims 1 and 2 in respect of an auxiliary request.

III. In the oral proceedings held on 20 October 2000 the appellant filed an amended page 2 of the description for the main request and for the auxiliary request.

IV. Claim 1 of the main request is worded as follows:

"A superconductive conductor (8) comprising

at least three longitudinal superconducting wires (3) extending parallel to each other;

a longitudinal supporting member (9) having a symmetrical cross-section, for supporting said superconducting wires (3) which are arranged parallel to said supporting member and which partially or entirely cover the periphery thereof, such that the superconducting wires (3) are symmetrically arranged when viewed in cross-section, and

each superconductive wire (3) comprises a superconductive member (4) and a stabilizing member (5) enclosing said superconductive member (4),

characterized in that

said superconducting wires (3) are tape-shaped wires,

said superconductive members (4) are oxide superconductors,

each superconductive wire (3) is extending linearly in the longitudinal direction of said supporting member (9),

wherein said supporting member (9) is a hollow tube of polygonal cross-section, and said superconducting wires (3) are arranged on the outer periphery of said hollow tube,

the surfaces of said tape-shaped superconducting wires (3) are disposed to face radially from the center of the polygonal cross section so that each of said tape-shaped superconducting wires (3) is disposed completely on a side of the polygonal cross section, and

said tape-shaped superconducting wires (3) are disposed adjoining to one another, the width dimension of each of said tape-shaped superconducting wires (3) being approximately equal to the side dimension of each side of the polygonal cross-section."

Claim 1 of the auxiliary request differs from claim 1 of the main request in that the superconductive conductor (8) comprises "at least five longitudinal superconducting wires" and in that the polygonal cross-section of the hollow tube is specified as "having at least five sides".

Claim 2 is dependent on claim 1 of each request.

V. The following documents cited in support of the opposition have been taken into consideration in the appeal procedure:

D1: DE-A-2 035 654,

D2: Takeshi HIKATA et al., "Ag-Sheathed Bi-Pb-Sr-Ca-Cu-O Superconducting Wires with High Critical Current Density", Japanese Journal of Applied Physics, Vol. 28, No. 1, January 1989; pages L82 to L84,

D4: DE-A-2 749 052,

D10: DE-B-1 952 148,

D11: DE-A-2 029 076,

D12: DE-A-2 136 019.

VI. With the statement of grounds of appeal the appellant patent proprietor submitted a sheet of explanatory Figures A, B, C and D, and referred to the following documents:

Document A: KEN-ICHI SATO et al., "Electromagnetic Properties and Structures of BiPbSrCaCuO Superconducting Wires", Advances in Superconductivity II, Proceedings of the 2nd International Symposium on Superconductivity (ISS '89), 14-17 November 1989, Tsukuba, Springer-Verlag Tokyo 1990,

Document B: Munetsugu Ueyama et al., "Transport Properties of Silver-sheathed Bi(2223) Superconducting Wires and Coils for High-Field", Proceedings of the 9th US-Japan Workshop on HIGH-FIELD SUPERCONDUCTING MATERIALS, WIRES AND CONDUCTORS and STANDARD PROCEDURES FOR HIGH-FIELD SUPERCONDUCTING WIRES TESTING, 13-15 March 1995, Holiday Inn Kyoto, K. Osamura et al. Editors.

VII. With the letter dated 11 September 2000 the respondent opponent cited the following additional documents:

D13: G.A. Whitlow et al. "SILVER ENCASED HIGH TEMPERATURE SUPERCONDUCTOR RIBBONS PRODUCED BY ROLLING", IEEE TRANSACTIONS ON MAGNETICS, VOL. 25. NO. 2, MARCH 1989, pages 2317 to 2319.

D14: M. MIMURA et al. :"Improvement of the critical current density in the silver sheathed Bi-Pb-Sr-Ca-Cu-O superconducting tape", Applied Physics Letters, 54 (16), 17 April 1989, pages 1582 to 1584.

VIII. The appellant argued essentially as follows:

D1 described a superconductive conductor according to the pre-characterizing part of claim 1 of the main request. Document A (Figure 7) and document B (Figure 2) showed that the critical current density in oxide superconductors greatly decreased under the influence of a magnetic field applied in a direction perpendicular to the plane of a tape-shaped wire as compared with the decrease of critical current density produced by a magnetic field applied in a direction parallel to the plane of the tape-shaped wire. The detrimental influence of this field anisotropy in oxide high-temperature superconductive materials did not occur in the low-temperature superconductive materials mentioned in documents D1, D4, D10, D11 and D12, so the skilled person seeking to eliminate or reduce this influence in oxide superconductors would not look for a solution in the field of conventional low-temperature superconductors.

The arrangement specified in claim 1 was efficient in that it minimized the spacing between adjacent tape-shaped wires and provided for the width dimension of each of the tape-shaped wires to be approximately equal to the side dimension of each side of the polygonal cross-section of the supporting member, as depicted for example in Figure D of the sheet submitted with the statement of grounds of appeal. This arrangement insured a substantial cancellation of the vertical components of the magnetic field produced by current flowing in the conductor and resulted in a higher value of the critical current density.

The field anisotropy problem did not arise in the low-temperature tape-shaped metal superconductors disclosed in D4 and D10. In D4 (see in particular Figure 5) the superconductors were accommodated in recesses and were not disposed adjoining to one another as specified in claim 1. In D10, although the superconductors were disposed adjoining to one another, their width was not equal to the side dimension of each side of the rectangular cross-section. Even if it was admitted that a person skilled in the art might by chance arrange tape-shaped oxide superconductors in one of the geometrical arrangements of the tape-shaped metal superconductors wires disclosed in D4 or D10, he could not have expected to obtain the field anisotropy compensation effects obtained by the present invention. This conclusion also applied when considering the arrangements which could be obtained from various combinations of the teachings of other documents such as D11 which dealt with low-temperature metal superconductors.

IX. The respondent's arguments can be summarised as follows:

The problem underlying the alleged invention should first be correctly defined. It was known from the prior art disclosed in D2, for example, that a problem might be seen in the fact that the component of the magnetic field perpendicular to the plane of a tape-shaped oxide superconductive wire heavily reduced the value of the critical current density in this wire. It was known to the skilled person that a current flowing through a conductor produced a magnetic field, including the vertical field component referred to by the appellant as being responsible for the decrease of the value of the critical current density in a tape-shaped oxide superconductive conductor. It was obvious that the effect of this component should be eliminated or reduced.

It was known that the strength of the magnetic field produced by an electric current flowing through a wire decreased with increasing distance from the wire. According to the appellant, the desired reduction of the net vertical magnetic field component was obtained by adjoining the tape-shaped wires to one another on the sides of the polygonal support member. However, the only material with superconductive properties was the oxide enclosed in the stabilizing metal matrix, not the metal matrix itself. Since claim 1 did not define the spacing between neighbouring oxide superconductive zones or of the value of the angle formed by the adjoining extremities of the tape-shaped wires, the geometry of the arrangement according to claim 1 did not differ from that known from D10, which described a superconductive conductor comprising tape-shaped superconductive metal wires disposed on the sides of a hollow supporting member having a polygonal cross-section (see claim 5 of D10) in such a manner that the wires adjoined to one another and the width of each wire was approximately equal to the side dimension of each side of the supporting member. D10 had to be considered as the document representing the prior art closest to the invention.

D10 was relevant to the claimed superconductive conductor because it concerned the problem of cooling which was a problem common to all types of superconductor. Superconductive conductors using tape-shaped oxide superconductive materials were known from the prior art disclosed in D2. Once they became available, it was obvious to try them instead of the low-temperature superconductors in D10. This was a mere analogous substitution, cf Guidelines for examination in the European Patent Office, Part C, Chapter IV-Annex, 1.1 (iv). Since efficient cooling was important in high-temperature oxide superconductive devices as well as in low-temperature metal devices, the skilled person would have tried arranging the tape-shaped oxide superconductive materials in the same or a similar manner as that taught by D10 for superconductive conductors with metal tape-shaped wires, in the expectation of obtaining efficient cooling.

X. The appellant requested that the decision under appeal be set aside and the patent be maintained as amended

- with claims 1 and 2 and pages 2a, 2b, 3 and 4 of the description filed with the letter dated 12. September 2000, page 2 of the description submitted during the oral proceedings before the Board and the drawings of the patent specification (main request), or

- with claims 1 and 2 filed with the letter dated 11. October 2000, description and drawings as per main request (auxiliary request).

XI. The respondent requested that the appeal be dismissed.