Abstract:
A superconducting magnet coil is produced by winding a superconducting wire to form a coil; impregnating the coil with a curable resin composition of low viscosity which contains for example at least one epoxy resin selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F and diglycidyl ether of bisphenol AF, all having a number-average molecular weight of 350-1,000, a flexibilizer and a curing catalyst, to obtain a curable-resin composition-impregnated coil; and heating the curable-resin-composition-impregnated coil to cure the composition.

Description:
This is a divisional of application Ser. No. 08/171,780, filed Dec. 22, 1993, now U.S. Pat. No. 5,384,197, which is a continuation of application Ser. No. 07/799,964 filed Nov. 29, 1991, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a superconducting magnet coil, an insulating layer thereof and a curable resin composition used in said superconducting magnet coil. 
     (2) Description of the Prior Art 
     In a superconducting magnet coil used, by being dipped in liquid helium, in linear motor cars, superconducting electromagnetic propulsion vessels, nuclear fusion reactors, superconducting generators, MRI, pion applicators (for therapy), electron microscopes, energy storage apparatuses, etc., the superconducting wires contained in the coil cause a temperature increase incurred by frictional heat or the like when the superconducting wires are moved by an electromagnetic force or a mechanical force. As a result, the magnet may shift from a superconducting state to a state of normal conduction. This phenomenon is called a quench phenomenon. Hence, it is conducted in some cases to fill the gap between the wires of the coil with a resin such as epoxy resins or the like to fix the wires. 
     The resin such as epoxy resins or the like, used for filling the coil gap usually has a thermal shrinkage factor of 1.8-3.0% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K. Meanwhile, the superconducting wires have a thermal shrinkage factor of about 0.3-0.4% under the same condition. As Y. Iwasa et al. describe in Cryogenics Vol. 25, pp. 304-326 (1985), when a superconducting magnet coil comprising superconducting wires and a resin used for filling the gap between the wires is cooled to a liquid helium temperature, i.e. 4.2K, a residual thermal stress appears due to the difference in thermal shrinkage factor between the superconducting wires and the resin. As a result, microcracks of several microns appear in the resin, a temperature increase of several degrees is induced at the peripheries of the microcracks due to the releasing energy of the residual thermal stress of the resin, and the superconducting wires show a sharp rise in resistance. Finally, the superconducting magnet coil shifts from a superconducting state to a state of normal conduction and causes an undesirable phenomenon called &#34;quench&#34;. Further, at the liquid helium temperature (4.2K), the impregnant resin such as epoxy resins or the like gets very brittle and produces microcracks of several microns, due to an electromagnetic force or a mechanical force. The releasing energy from the microcracks gives rise to a temperature increase of several degrees at the peripheries of the microcracks. Thus, the superconducting wires show a sharp rise in resistance, the superconducting magnet coil shifts from a superconducting state to a state of normal conduction and disadvantageously causes quench. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above situation. The objects of the present invention are to provide a superconducting magnet coil which is resistant to microcrack generation of impregnant resin and causes substantially no quench during operation; an insulating layer thereof; and a curable resin composition used in said superconducting magnet coil. 
     The objects of the present invention can be achieved by using, as a resin for impregnation of superconducting magnet coil, a curable resin composition capable of giving a cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, particularly a cured product having a thermal shrinkage factor of 1.0-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
     The present invention is briefly described as follows. The first aspect of the present invention relates to a superconducting magnet coil which is impregnated with a curable resin composition capable of giving a cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, particularly a cured product having a thermal shrinkage factor of 1.0-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bendbreaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
     The second aspect of the present invention relates to a resin used for impregnation of superconducting magnet coil, that is, a curable resin composition capable of giving a cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-4.5% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, particularly a cured product having a thermal shrinkage factor of 1.0-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
     The third aspect of the present invention relates to a process for producing a superconducting magnet coil which comprises a coil of superconducting wire and a cured product of a curable resin composition with which the coil has been impregnated, which process comprises the steps of: 
     (a) winding a superconducting wire to form a coil, 
     (b) filling the gap between the superconductors of the coil with a curable resin composition having a viscosity of 0.01-10 poises at the time of filling to obtain a curable-resin-composition-impregnated coil, and 
     (c) heating the curable-resin-composition-impregnated coil to cure the composition so as to give a cured product having a thermal shrinkage factor of 1.50-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bendbreaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, particularly a cured product having a thermal shrinkage factor of 1.0-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
     The fourth aspect of the present invention relates to an insulating layer of superconducting magnet coil, which is obtained by impregnation of a coil of superconducting wire with a curable resin composition and curing of the resin composition, said resin composition being capable of giving a cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-4.5% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, particularly a cured product having a thermal shrinkage factor of 1.0-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-4.5% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
     According to the present invention, there are provided: 
     a superconducting magnet coil which comprises a coil of superconducting wire and a cured product of a curable resin composition with which the coil has been impregnated, the cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to 4.2K, a bend-breaking strain of 2.9-3.9%, preferably 3.2-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K; 
     a superconducting magnet coil which comprises a coil of superconducting wire and a cured product of a curable resin composition with which the coil has been impregnated, the cured product undergoing a thermal stress of 0-10 kg/mm 2  when cooled from the glass transition temperature to 4.2K and resisting to quench during superconducting operation; 
     a curable resin composition which gives a cured product having a thermal shrinkage factor of 1.5-0.3%, preferably 1.0-0.3% when cooled from the glass transition temperature to 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K; 
     a process for producing the superconducting magnet coil which comprises the steps of: 
     (a) winding a superconducting wire to form a coil, 
     (b) impregnating the coil with a curable resin composition having a viscosity of 0.01-10 poises at the time of filling, with, for example, a curable resin composition comprising (i) at least one epoxy resin selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F and diglycidyl ether of bisphenol AF, all having a number-average molecular weight of 350-1,000, (ii) a flexibilizer and (iii) a curing catalyst, so as to fill the gap between the superconductors of the coil with the curable resin composition to obtain a curable-resin-composition-impregnated coil, and 
     (c) heating the curable-resin-composition-impregnated coil to cure the composition to allow the cured product of the composition to have a thermal shrinkage factor of 1.5-0.3%, preferably 1.0-0.3% when cooled from the glass transition temperature to 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, 
     preferably, the step (b) including the step of covering the outer surface of the coil with a release film or a perforated film, placing the film-covered coil in a mold, and effecting vacuum impregnation, and if necessary pressure impregnation, of the coil with the curable resin composition, 
     preferably, the step (c) including the step of curing the composition under pressure, and if necessary further comprising the step of clamping the curable-resin-composition-impregnated coil before the step of curing; 
     a superconducting magnet coil which comprises: 
     (a) a coil of a composite superconductor comprising a plurality of thin superconducting wires and a stabilizer selected from the group consisting of copper and aluminum which is thermally or electrically contacted with the wires, and 
     (b) a cured product of a curable resin composition with which the coil has been impregnated, 
     the cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K; 
     a superconducting magnet coil which comprises: 
     (a) a coil of a composite superconductor comprising a plurality of thin superconducting wires and a stabilizer selected from the group consisting of copper and aluminum which is thermally or electrically contacted with the wires, and 
     (b) a cured product of a curable resin composition with which the coil has been impregnated, 
     the cured product undergoing a thermal stress of 0-10 kg/mm 2  when cooled from the glass transition temperature to 4.2K and resisting to quench during superconducting operation; 
     a process for producing the superconducting magnet coil which comprises the steps of: 
     (a) winding a composite superconductor comprising a plurality of thin superconducting wires and a stabilizer selected from the group consisting of copper and aluminum which is thermally or electrically contacted with the wires to form a coil, 
     (b) filling the gap between the composite superconductors of the coil with a curable resin composition to obtain a curable-resin-composition-impregnated coil, and 
     (c) heating the curable-resin-composition-impregnated coil to cure the composition, 
     the step (a) including the step of subjecting the composite superconductor to surface treatment with a coupling agent before winding the composite superconductor; and 
     an insulating layer of superconducting magnet coil which comprises: 
     (a) a coil of a composite superconductor comprising a plurality of thin superconducting wires and a stabilizer selected from the group consisting of copper and aluminum which is thermally or electrically contacted with the wires, and 
     (b) a cured product of a curable resin composition with which the coil has been impregnated, 
     the cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a race track-shaped superconducting magnet coil. The numeral 1 is a round superconducting magnet coil. 
     FIG. 2 is a cross-sectional view of the coil of FIG. 1 when cut at an II-II&#39; line. 
     FIG. 3 is a fragmentary enlarged view of FIG. 2 of a conventional race track-shaped superconducting magnet coil. 
     FIG. 4 is a perspective view of a saddle-shaped superconducting magnet coil. 
     FIG. 5 is a cross-sectional view of the coil of FIG. 4 when cut at a V-V&#39; line. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The curable resin composition according to the present invention can also be preferably used in switches for permanent current which are required in superconducting magnet coils for linear motor cars, MRI, energy storage and nuclear fusions. 
     The superconducting wire used in the present invention has no particular restriction and can be any wire as long as it has superconductivity. There can be mentioned, for example, alloy superconductors such as Nb-Ti and the like; intermetallic compound super-conductors such as Nb 3  Sn, Nb 3  Al, V 3  Ga and the like; and oxide superconductors such as LaBaCuO, YBaCuO and the like. Ordinarily, the superconducting wire has a composite structure comprising (a) the above super-conductor and (2) a metal of normal conduction such as Cu, cupro-nickel (CuNi), CuNi-Cu, Al or the like. That is, the superconducting wire includes an ultrafine multiconductor wire obtained by embedding a large number of thin filament-like superconducting wires into a metal of normal conduction as a matrix, a straight twisted wire obtained by binding a large number of superconducting material wires into a straight bundle and twisting the bundle with the straightness being maintained, a straight wire obtained by embedding a straight superconducting material wire into a straight normal conductor, and an internal cooling type conductor having inside a passage for cooling medium. 
     The resin for impregnation of superconducting magnet coil, used in the present invention has no particular restriction and can be any resin as long as it can give a cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, particularly a cured product having a thermal shrinkage factor of 1.00-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bendbreaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
     When the cured product of the resin has a thermal shrinkage factor larger than 1.5% and a modulus larger than 1,000 kg/mm 2 , the stress applied to the superconducting magnet during the superconducting operation surpasses the strength of the cured product. As a result, the cured product generates cracks, and quench occurs due to the releasing energy of the stress. When the cured product has a thermal shrinkage factor smaller than 0.3%, the stress applied to the super-conducting magnet during the superconducting operation surpasses the strength of the cured product due to the difference in thermal shrinkage factor between the cured product and the superconductor of the magnet. As a result, the cured product generates cracks, and quench tends to occur due to the releasing energy of the stress. When the modulus is smaller than 500 kg/mm 2 , the glass transition temperature tends to be lower than room temperature and, when the superconducting magnet has been returned to room temperature, the cured product generates cracks due to the low strength; when the magnet is recooled to 4.2K and reoperated, the cracks become a nucleus of further crack generation and the superconducting magnet causes quench. When the bend-breaking strain is smaller than 2.9%, the cured product has low adhesion to the superconductor and, after the cooling or during the operation of the superconducting magnet, peeling takes place between the superconductor and the cured product. As a result, thermal conductivity between them is reduced, even slight cracking invites temperature increase, and the superconducting magnet tends to incur quench. 
     As the method for increasing the bend-breaking strain of a thermosetting resin, that is, for toughening a thermosetting resin, there are a number of methods. In the case of an epoxy resin, for example, there are (1) a method of subjecting an epoxy resin to preliminary polymerization to obtain an epoxy resin having a higher molecular weight between crosslinked sites, (2) a method of adding a flexibilizer (e.g. polyol, phenoxy resin) to an epoxy resin to increase the specific volume of the latter, (3) a method of introducing a soft molecular skeleton into an epoxy resin by using a curing agent such as elastomer-modified epoxy resins, long-chain epoxy resins, long-chain amines, acid anhydrides, mercaptans or the like, (4) a method of using an internal plasticizer such as branched epoxy resins, polyamide-amines, dodecyl succinic anhydrides or the like, (5) a method of using, in combination with an epoxy resin, a monofunctional epoxy resin to give rise to internal plasticization, (6) a method of using an epoxy resin as a main component and a curing agent in proportions deviating from the stoichiometric amounts to give rise to internal plasticization, (7) a method of adding a plasticizer (e.g. phthalic acid ester) to give rise to external plasticization, (8) a method of dispersing butadiene rubber particles, silicone rubber particles or the like in an epoxy resin to form an islands-in-a-sea structure, (9) a method of introducing, into an epoxy resin, an acrylic resin, an urethane resin, a polycaprolactone, an unsaturated polyester or the like to form an interpenetrating network structure, i.e. an IPN structure, (10) a method of adding, to an epoxy resin, a polyether having a molecular weight of 1,000-5,000 to form a microvoid structure, and so forth. Of these methods, the methods (1) and (2) are preferable in view of the low thermal shrinkage and high toughness of the improved epoxy resin. 
     Specific examples of the improved epoxy resin obtained according to the above methods, are an epoxy resin obtained by curing an epoxy resin of high molecular weight with an acid anhydride, an epoxy resin obtained by curing an epoxy resin of high molecular weight with a catalyst alone, an epoxy resin obtained by adding a flexibilizer to an epoxy resin and curing the resin with an acid anhydride, an epoxy resin obtained by adding a flexibilizer to an epoxy resin and curing the resin with a catalyst alone, and a maleimide resin obtained by adding a flexibilizer. 
     The epoxy resin usable in the present invention can be any epoxy resin as long as it has at least two epoxy groups in the molecule. Such an epoxy resin includes, for example, bifunctional epoxy resins such as diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of bisphenol AF, diglycidyl ether of bisphenol AD, diglycidyl ether of hydrogenated bisphenol A, diglycidyl ether of 2,2-(4-hydroxyphenyl)nonadecane, 4,4&#39;-bis(2,3-epoxypropyl) diphenyl ether, 3,4-epoxycyclohexylmethyl (3,4-epoxy)cyclohexanecarboxylate, 4-(1,2-epoxypropyl)-1,2-epoxycyclohexane, 2-(3,4-epoxy)cyclohexyl-5,5-spiro(3,4-epoxy)-cyclohexane-m-dioxane, 3,4-epoxy-6-methylcyclohexylmethyl-4-epoxy-6-methylcyclohexanecarboxylate, butadiene-modified epoxy resin, urethane-modified epoxy resin, thiol-modified epoxy resin, diglycidyl ether of diethylene glycol, diglycidyl ether of triethylene glycol, diglycidyl ether of polyethylene glycol, diglycidyl ether of polypropylene glycol, diglycidyl ether of 1,4-butanediol, diglycidyl ether of neopentyl glycol, diglycidyl ether of propylene oxide adduct of bisphenol A, diglycidyl ether of ethylene oxide adduct of bisppenol A, and the like; trifunctional epoxy resins such as tris[p-(2,3-epoxypropoxy)phenyl]methane, 1,1,3-tris[P-(2,3-epoxypopoxy)phenyl]butane and the like; and polyfunctional epoxy resins such as glycidylamine (e.g. tetraglycidyldiaminodiphenylmethane, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, diglycidylamine, tetraglycidyl-m-xylylenediamine, tetraglycidyl-bis-aminomethylcyclohexane), phenolic novolac type epoxy resin, cresol type epoxy resin and the like. It is also possible to use a polyfunctional epoxy resin obtained by reacting epichlorohydrin with at least two polyhydric phenols selected from (a) bis(4-hydroxyphenyl)methane, (b) bis(4-hydroxyphenyl)ethane, (c) bis(4-hydroxyphenyl)propane, (d) tris(4-hydroxyphenyl)alkane and (e) tetrakis(4-hydroxyphenyl)alkane, because the resin has a low viscosity before curing and gives easy working. Specific examples of tris(4-hydroxyphenyl)alkane are tris(4-hydroxyphenyl)methane, tris(4-hydroxyphenyl)-ethane, tris(4-hydroxyphenyl)propane, tris(4-hydroxyphenyl)butane, tris(4-hydroxyphenyl)hexane, tris(4-hydroxyphenyl)heptane, tris(4-hydroxyphenyl)-octane, tris(4-hydroxyphenyl)nonane, etc. There can also be used tris(4-hydroxyphenyl)alkane derivatives such as tris(4-hydroxydimethylphenyl)methane and the like. 
     Specific examples of tetrakis(4-hydroxyphenyl)alkane are tetrakis(4-hydroxyphenyl)methane, tetrakis(4-hydroxyphenyl)ethane, tetrakis(4-hydroxyphenyl)propane, tetrakis(4-hydroxyphenyl)butane, tetrakis(4-hydroxyphenyl)hexane, tetrakis(4-hydroxyphenyl) heptane, tetrakis(4-hydroxyphenyl)octane, tetrakis(4-hydroxyphenyl)nonane and the like. It is also possible to use tetrakis(4-hydroxyphenyl)alkane derivatives such as tetrakis(4-hydroxydimethylphenyl)methane and the like. Of these, useful are diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of bisphenol AF, diglycidyl ether of bisphenol AD, and diglycidyl ethers of higher-molecular-weight bisphenols A, F, AF and AD, because they have a low thermal shrinkage factor. Particularly preferable are diglycidyl ethers of higher-molecular-weight bisphenols A, F, AF and AD wherein the n of the repeating unit has a value of 2-18. The above polyfunctinal epoxy resins may be used in combination of two or more. If necessary, the polyfunctional epoxy resin may be mixed with a monofunctional epoxy resin such as butyl glycidyl ether, styrene oxide, phenyl glycidyl ether, allyl glycidyl ether or the like in order to obtain a lower viscosity. However, the amount of the monofunctional epoxy resin added should be small because, in general, the monofunctional epoxy resin has an effect for viscosity reduction but brings about increase in thermal shrinkage factor. 
     The acid anhydride used in the present invention has no particular restriction and can be any ordinary acid anhydride. Such an acid anhydride includes methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, tetrahydrophthalic anhydride, nadic anhydride, methylnadic anhydride, dodecylsuccinic anhydride, succinic anhydride, octadecylsuccinic anhydride, maleic anhydride, benzophenonetetracarboxylic anhydride, ethylene glycol bis(anhydrotrimellitate), glycerol tris(anhydrotrimellitate), etc. They can be used alone or in combination of two or more. 
     The maleimide used in the present invention can be any maleimide as long as it is an unsaturated imide containing in the molecule the group having the formula (I), ##STR1## wherein D is a bivalent group containing a carbon-carbon double bond. Such an unsaturated imide includes, for example, bifunctional maleimides such as N,N&#39;-ethylenebismaleimide, N,N&#39;-hexamethylene-bis-maleimide, N,N&#39;-dodecamethylene-bismaleimide, N,N&#39;-m-xylylenebismaleimide, N,N&#39;-p-xylylene-bismaleimide, N,N&#39;-1,3-bismethylenecyclohexane-bismaleimide. N,N&#39;-1,4-bismethylenecyclohexane-bismaleimide, N,N&#39;-2,4-tolylene-bismaleimide, N,N&#39;-2,6-tolylene-bismaleimide, N,N&#39;-3,3&#39;-diphenylmethane-bismaleimide, N,N&#39;-(3-ethyl)-3,3&#39;-diphenylmethane-bismaleimide, N,N&#39;-(3,3&#39;-dimethyl)-3,3&#39;-diphenylmethane-bismaleimide, N,N&#39;-(3,3&#39;-diethyl)-3,3&#39;-diphenylmethane-bismaleimide, N,N&#39;-(3,3&#39;-dichloro)-3,3&#39;-diphenylmethane-bismaleimide, N,N&#39;-4,4&#39;-diphenylmethane-bismaleimide, N,N&#39;-(3-ethyl)-4,4&#39;-diphenylmethane-bismaleimide, N,N&#39;-(3,3&#39;-dimethyl)-4,4&#39;-diphenylmethane-bismaleimide, N,N&#39;-(3,3&#39;-diethyl)-4,4&#39;-diphenylmethane-bismaleimide, N,N&#39;-(3,3&#39;-dichloro)-4,4&#39;-diphenylmethane-bismaleimide, N,N&#39;-3,3&#39;-diphenylsulfonebismaleimide, N,N&#39;-4,4&#39;-diphenylsulfone-bismaleimide, N,N&#39;-3,3&#39;-diphenylsulfide-bismaleimide, N,N&#39;-4,4&#39;-diphenylsulfide-bismaleimide, N,N&#39;-p-benzophenone-bismaleimide, N,N&#39;-4,4&#39;-diphenylethane-bismaleimide, N,N&#39;-4,4&#39;-diphenylether-bismaleimide, N,N&#39;-(methyleneditetrahydrophenyl)bismaleimide, N,N&#39;-tolidinebismaleimide, N,N&#39;-isophorone-bismaleimide, N,N&#39;-p-diphenyldimethylsilyl-bismaleimide, N,N&#39;-4,4&#39;-diphenylpropane-bismaleimide, N,N&#39;-naphthalene-bismaleimide, N,N&#39;-p-phenylene-bismaleimide, N,N&#39;-m-phenylene-bismaleimide, N,N&#39;-4,4&#39;-(1,1&#39;-diphenylcyclohexane)bismaleimide, N,N&#39;-3,5-(1,2,4-triazole)bismaleimide, N,N&#39;-pyridine-2,6-diyl-bismaleimide, N,N&#39;-5-methoxy-1,3-phenylene-bismaleimide, 1,2-bis(2-maleimideethoxy)ethane, 1,3-bis(3-maleimidepropoxy)propane, N,N&#39;-4,4&#39;-diphenylmethane-bisdimethylmaleimide, N,N&#39;-hexamethylene-bisdimethylmaleimide, N,N&#39;-4,4&#39;-(diphenylether)bisdimethylmaleimide, N,N&#39;-4,4&#39;-(diphenylsulfone)bisdimethylmaleimide, N,N&#39;-bismaleimide of 4,4&#39;-diaminotriphenyl phosphate, N,N&#39;-bismaleimide of 2,2&#39;-bis[4-(4-aminophenoxy)phenyl]propane, N,N&#39;-bismaleimide of 2,2&#39;-bis[4-(4-aminophenoxy)phenylmethane, N,N&#39;-bismaleimide of 2,2&#39;-bis[4-(4-aminophenoxy)phenylethane and the like; polyfunctional maleimides obtained by reacting maleic anhydride with an aniline-formalin reaction product (a polyamine compound), 3,4,4&#39;-triaminodiphenylmethane, triaminophenol or the like; monomaleimides such as phenylmaleimide, tolylmaleimide, xylylmaleimide and the like; various citraconimides; and various itaconimides. These unsaturated imides can be used by adding to an epoxy resin, or can be cured with a diallylphenol compound, an allylphenol compound or a diamine compound or with a catalyst alone. 
     The flexibilizer used in the present invention can be any flexibility-imparting agent as long as it can impart flexibility, toughness and adhesion. Such a flexibilizer includes, for example, diglycidyl ether of linoleic acid dimer, diglycidyl ether of polyethylene glycol, diglycidyl ether of polypropylene glycol, diglycinyl ether of alkylene oxide adduct of bisphenol A, urethane-modified epoxy resin, polybutadiene-modified epoxy resin, polyethylene glycol, polypropylene glycol, polyol (e.g. hydroxyl group-terminated polyester), polybutadiene, alkylene oxide adduct of bisphenol A, polythiol, urethane prepolymer, polycarboxyl compound, phenoxy resin and polycaprolactone. The flexibilizer may be a low viscosity compound such as caprolactone or the like, which is polymerized at the time of curing of the impregnant resin and thereby exhibits flexibility. Of the above flexibilizers, a polyol, a phenoxy resin or a polycaprolactone is preferable in view of the high toughness and low thermal expansion. 
     The catalyst used in the present invention has no particular restriction and can be any compound as long as it has an action of accelerating the reaction of an epoxy resin or a maleimide. Such a compound include, for example, tertiary amines such as trimethylamine, triethylamine, tetramethylbutanediamine, triethylenediamine and the like; amines such as dimethylaminoethanol, dimethylaminopentanol, tris(dimethylaminomethyl)phenol, N-methylmorpholine and the like; quaternary ammonium salts such as cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, cetyl-trimethyl-ammonium iodide, dodecyltrimethylammonium bromide, dodecyltri-methylammonium chloride, dodecyltrimethylammonium iodide, benzyldimethyltetradecylammonium chloride, benzyldimethyltetradecylammonium bromide, allyldodecyltrimethylammonium bromide, benzyldimethylstearylammonium bromide, stearyltrimethylammonium chloride, benzyldimethyltetradecylammonium acetylate and the like; imidazoles such as 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-methyl-4-ethylimidazole, 1-butylimidazole, 1-propyl-2-methylimidazole, 1-benzyl-2-methylimidazole, 1-cycanoethyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-azine-2-methylimidazole, 1-azine-2-undecylimidazole and the like; microcapsules of amines or imidazoles; metal salts between (a) an amine or imidazole and (b) zinc octanoate, cobalt or the like; 1,8-diaza-bicyclo[5.4.0]-undecene-7; N-methylpiperazine; tetramethylbutylguanidine; amine tetraphenyl borates such as triethylammonium tetraphenyl borate, 2-ethyl-4-methyltetraphenyl borate, 1,8-diazabicyclo[5.4.0]-undecene-7-tetraphenyl borate and the like; triphenylphosphine; triphenylphosphonium tetraphenyl borate; aluminum trialkylacetoacetates; aluminum trisacetylacetoacetate; aluminum alcoholates; aluminum acylates; sodium alcoholates; boron trifluoride; complexes between boron trifluoride and an amine or imidazole; diphenyliodonium salt of HAsF 6  ; aliphatic sulfonium salts; amineimides obtained by reacting an alkyl monocarboxylate with a hydrazine and a monoepoxy compound; and metal (e.g. cobalt, manganese, iron) salts of octylic acid or naphthenic acid. Of these, particularly useful are quaternary ammonium salts, metal salts between (a) an amine or imidazole and (b) zinc octanoate, cobalt or the like, amine tetraphenyl borates, complexes between boron trifluoride and an amine or imidazole, diphenyliodonium salt of HAsF 6 , aliphatic sulfonium salts, amineimides, microcapsules of amines or imidazoles, etc. because they are relatively stable at room temperature but can cause a reaction easily at elevated temperatures, that is, they are a latent curing catalyst. These curing agents are added ordinarily in an amount of 0.1-10% by weight based on the polyfunctional epoxy resin. 
     The stress which a superconducting magnet coil undergoes during operation of the superconducting magnet, includes a residual stress generated at the time of production, a thermal stress applied during cooling and an electromagnetic force applied during operation. First, description is made on the thermal stress applied to the cured resin of a superconducting magnet coil when the coil after production is cooled to a liquid helium temperature, i.e. 4.2K. 
     The thermal stress σ applied to the cured resin of a superconducting magnet coil when the coil after production is cooled to a liquid helium temperature, i.e 4.2K, can be represented by the following formula: ##EQU1## wherein α R  is a thermal expansion coefficient of the cured resin; α S  is a thermal expansion coefficient of the superconducting wire of the coil; E is a modulus of the cured resin; and T is a curing temperature of the resin used for obtaining the cured resin. Since the modulus at temperatures above the glass transition temperature Tg of the cured resin is smaller by about two figures than the modulus at the glass transition temperature Tg or below, the thermal stress applied to the cured resin of superconducting magnet coil when the coil after production is cooled to 4.2K, can be substantially represented by the following formula (1) holding for when the coil after production is cooled from the glass transition temperature of the cured resin to 4.2K: ##EQU2## 
     Now, the thermal stress a applied to the cured resin of superconducting magnet coil when the coil after production is cured to 4.2K, is roughly calculated from the above formula (1), using assumptions that the thermal shrinkage factor of the cured resin when cooled from the glass transition temperature Tg to 4.2K be 2.0%, the thermal shrinkage factor of the super-conducting wire of coil when cooled under the same condition be 0.3% and the modulus of the cured resin be 1.000 kg/mm 2  at 4.2K; the rough calculation gives a thermal stress σ of about 17 kg/mm 2 . Meanwhile, cured epoxy resins ordinarily have a strength of 17-20 kg/mm 2  at 4.2K. Accordingly, when the superconducting magnet coil after production is cooled to a liquid helium temperature, i.e. 4.2K, the thermal stress σ plus the residual stress generated at the time of coil production allow the cured resin to form microcracks of several microns; the releasing energy of the stress of the cured resin gives rise to a temperature increase of several degress at the peripheries of the microcracks; as a result, the resistance of the superconducting wire is increased rapidly and there occurs a transition from a superconducting state to a state of normal conduction, i.e. a so-called quench phenomenon. In superconducting magnet coils used in linear motor cars, MRI, etc., further an electromagnetic force of at least about 4 kg/mm 2  is repeatedly applied during operation at 4.2K. This force plus the above-mentioned thermal stress and residual stress allow the cured resin to form cracks, and the releasing energy of the stress gives rise to a quench phenomenon. 
     The thermal stress a applied to the cured resin of superconducting magnet coil when the coil after production is cooled to 4.2K, is roughly calculated from the formula (1), using a thermal shrinkage factor of the cured resin of 1.5% when cooled to 4.2K and a modulus of the cured resin of 1,000 kg/mm 2  at 4.2K; the rough calculation gives a thermal stress σ of about 12 kg/mm 2 . When an electromagnetic force of about 4 kg/mm 2  is repeatedly applied to the above thermal stress during operation at 4.2K, the total stress becomes about 16 kg/mm 2 . 
     Meanwhile, cured epoxy resins ordinarily have a strength of 17-20 kg/mm 2  at 4.2K. Therefore, on calculation, this strength can withstand the thermal stress applied to the cured resin of superconducting magnet coil when cooled to 4.2K and the electromagnetic force repeatedly applied to the cured resin during operation. 
     Various impregnant resins of different thermal shrinkage factors for superconducting magnet coil were actually tested. The test indicated that when there is used, as an impregnant resin for superconducting magnet coil, a curable resin composition giving a cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, the cured resin composition of superconducting magnet coil generates no crack when cooled to a liquid helium temperature, i.e. 4.2K. The test also indicated that no quench appears even in a superconducting operation at 4.2K wherein an electromagnetic force is further applied. 
     When there is used, in particular, a thermosetting resin composition giving a cured product having a thermal shrinkage factor of 1.0-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% and a modulus of 500-1,000 kg/mm 2 , quench can be prevented with a large allowance even in a superconducting operation at 4.2K in which an electromagnetic force is applied. 
     The present invention is hereinafter described more specifically by way of Examples. However, the present invention is by no means restricted to these Examples. 
     The determination of thermal shrinkage was carried out with a thermal-mechanical analyzer (TMA) having a sample-system provided in a cryostat which can cool a sample to a very low temperature and a measurement-system containing a differential transformer with which the change of dimension of the sample detected by a detecting rod can be measured. 
     The determination of bending properties was carried out by immersing a sample in liquid helium using a conventional bend test apparatus equipped with a cryostat which can cool the sample to a very low temperature. The size of the sample is 80 mm×9 mm×5 mm. The conditions of the determination were: 
     length between supports: 60 mm 
     head speed: 2 mm/min 
     three-point bending. 
     In the Examples, the abbreviations used for polyfunctional epoxy resins, flexibilizers, curing catalysts and bismaleimides refer to the followings. 
     DER-332: diglycidyl ether of bisphenol A (epoxy equivalent: 175) 
     EP-825: diglycidyl ether of bisphenol A (epoxy equivalent: 178) 
     EP-827: diglycidyl ether of bisphenol A (epoxy equivalent: 185) 
     EP-828: diglycidyl ether of bisphenol A (epoxy equivalent: 189) 
     EP-1001: diglycidyl ether of bisphenol A (epoxy equivalent: 472) 
     EP-1002: diglycidyl ether of bisphenol A (epoxy equivalent: 636) 
     EP-1003: diglycidyl ether of bisphenol A (epoxy equivalent: 745) 
     EP-1055: diglycidyl ether of bisphenol A (epoxy equivalent: 865) 
     EP-1004AF: diglycidyl ether of bisphenol A (epoxy equivalent: 975) 
     EP-1007: diglycidyl ether of bisphenol A (epoxy equivalent: 2006) 
     EP-1009: diglycidyl ether of bisphenol A (epoxy equivalent: 2473) 
     EP-1010: diglycidyl ether of bisphenol A (epoxy equivalent: 2785) 
     EP-807: diglycidyl ether of bisphenol F (epoxy equivalent: 170) 
     PY-302-2: diglycidyl ether of bisphenol AF (epoxy equivalent: 175) 
     DGEBAD: diglycidyl ether of bisphenol AD (epoxy equivalent: 173) 
     HP-4032: 2,7-diglycidyl ether naphthalene (epoxy equivalent: 150) 
     TGADPM: tetraglycidylaminodiphenylmethane 
     TTGmAP: tetraglycidyl-m-xylylenediamine 
     TGpAP: triglycidyl-p-aminophenol 
     TGmAP: triglycidyl-m-aminophenol 
     CEL-2021: 3,4-epoxycyclohexylmethyl-(3,4-epoxy)cyclohexane carboxylate (epoxy equivalent: 138) 
     LS-108: bis-2,2&#39;-{4,4&#39;-[2-(2,3-epoxy)propoxy-3-butoxypropoxy]phenyl}propane (epoxy equivalent: 2100) 
     LS-402: bis-2,2&#39;-{4,4&#39;-[2-(2,3-epoxy)propoxy-3-butoxypropoxy]phenyl}propane (epoxy equivalent: 4600) 
     HN-5500: methylhexahydrophthalic anhydride (acid anhydride equivalent: 168) 
     HN-2200: methyltetrahydrophthalic anhydride (acid anhydride equivalent: 166) 
     iPA-Na: sodium isopropylate 
     BTPP-K: tetraphenylborate of triphenylbutylphosphine 
     2E4MZ-K: tetraphenylborate of 2-ethyl-4-methylimidazole 
     2E4MZ-CN-K: tetraphenylborate of 1-cyanoethyl-2-ethyl-4-methylimidazole 
     TEA-K: tetraphenylborate of triethylamine 
     TPP-K: tetraphenylborate of triphenylphosphine 
     TPP: triphenylphosphine 
     IOZ: salt between 2-ethyl-4-methylimidazole and zinc octanoate 
     DY063: alkyl alkoholate 
     YPH-201: an amineimide obtained by reacting an alkyl monocarboxylate with a hydrazine and a monoepoxy compound (YPH-201 manufactured by Yuka Shell Epoxy K.K.) 
     CP-66: an aliphatic sulfonium salt of a protonic acid (ADEKA OPTON CP-66 manufactured by ASAHI DENKA KOGYO K.K.) 
     PX-4BT: tetrabutylphosphonium benzotriazolate 
     BF 3  -400: boron trifluoride salt of piperazine 
     BF 3  -100: boron trifluoride salt of triethylamine 
     2E4MZ-CNS: trimellitic acid salt of 2-ethyl-4-methylimidazole 
     2E4MZ-OK: isocyanuric acid salt of 2-ethyl-4-methylimidazole 
     MC-C11Z-AZINE: microcapsule of 1-azine-2-undecylimidazole 
     2E4MZ-CN: 1-cycnoethyl-2-ethyl-4-methylimidazole 
     BDMTDAC: benzyldimethyltetradecylammonium chloride 
     BDMTDAI: benzyldimethyltetradecylammonium iodide 
     HMBMI: N,N&#39;-hexamethylene-bismaleimide 
     BMI: N,N&#39;-4,4&#39;-diphenylmethane-bismaleimide 
     DMBMI: N,N&#39;-(3,3&#39;-dimethyl)-4,4&#39;-diphepylmethanebismaleimide 
     DAPPBMI: N,N&#39;-bismaleimide of 2,2&#39;-bis[4-(4-aminophenoxy)phenyl]propane 
     PMI: N,N&#39;-polymaleimide of a reaction product (a polyamine compound) between aniline and formalin 
     DABPA: diallylbisphenol A 
     PPG: polypropylene glycol 
     KR: ε-caprolactone 
     DGEAOBA: diglycidyl ether of an alkylene oxide adduct of bisphenol A 
     PPO: phenoxy resin 
     CTBN: acrylonitrile-modified carboxyl group-terminated polybutadiene rubber 
     2PZCN: 1-cyanoethyl-2-phenylimidazole 
     LBO: lithium butoxide 
     PZ: pyridine 
     TEA: triethylamine 
     M2-100: benzylconium chloride 
     N-MM: N-methylmorpholine 
     MDI: 4,4&#39;-diphenylmethane diisocyanate, equivalent: 125 
     LMDI: a mixture of MDI, an MDI derivative whose isocyanate group has been converted to carbodiimide and an MDI derivative whose isocyanate groups have been converted to carbodiimide, which mixture is liquid at room temperature, equivalent: about 140 
     TDI: a mixture of 80% of 2,4-tolylene diisocyanate and 20% of 2,6-tolylene diisocyanate, equivalent: 87 
     KR2019: a resin obtained by condensation polymerization of methylphenylsilicone 
     Examples 1-65 and Comparative Examples 1-6 
     Each of the resin compositions shown in Tables 1-1 to 1-13 was thoroughly stirred, placed in a mold, and heat-cured under the curing conditions shown in Tables 1-1 to 1-13. Each of the resulting cured products was measured for thermal shrinkage factor when cooled from the glass transition temperature to 4.2K, and the results are shown in Tables 1-1 to 1-13. Each cured product was also measured for bending properties at 4.2K, and the bending strain and bending modulus are shown in Tables 1-1 to 1-13. All of the curable resin compositions of Examples 1-65 according to the present invention, when cured, had a thermal strinkage factor of 1.5-0.3% when cooled from the glass transition temperature to 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
     Example 66 and Comparative Example 7 
     Superconducting wires were wound to form coils of the same material and the same shape. The coils were impregnated with the curable resin compositions of Examples 1-65 and Comparative Examples 1-6, and the impregnated coils were heat-cured under given curing conditions to prepare small race track-shaped superconducting magnet coils. Switches for permanent current were also prepared by impregnation with each of the curable resin compositions of Examples 1-65 and Comparative Examples 1-6 and subsequent heat-curing under given curing conditions. FIG. 1 is a perspective view showing the superconducting magnet coils thus prepared. FIG. 2 is a cross-sectional view of the coil of FIG. 1 when cut at an II-II&#39; line. In any of the coils, a cured product 3 of an curable resin composition was filled between the conductors 2 and any unfilled portion (e.g. void) was not observed. These coils were cooled to 4.2K. As shown in FIG. 3, in each of the coils impregnated with each of the curable resin compositions of Comparative Examples 1-6, cracks were generated in the cured resin composition 3; the cracks reached even the enamel insulating layer 5 of each conductor 2, which caused even the peeling 6 of the enamel insulating layer 5. Meanwhile, in the coils impregnated with each of the curable resin compositions of Examples 1-65, neither cracking of the cured resin composition nor peeling of the enamel insulating layer was observed. 
     Example 67 and Comparative Example 8 
     Superconducting wires were wound to form coils of the same material and the same shape. The coils were impregnated with each of the curable resin compositions of examples 1-65 and Comparative Examples 1-6, and the impregnated coils were heat-cured under given curing conditions to prepare saddle-shaped superconducting magnet coils. FIG. 4 is a perpspective view showing the superconducting magnet coils thus prepared. FIG. 5 is a cross-sectional view of the coil of FIG. 4 when cut at a V-V&#39; line. These saddle-shaped superconducting magnet coils were cooled to 4.2K. In the coils impregnated with each of the curable resin compositions of Comparative Examples 1-6, cracks were generated in the cured resin composition. Meanwhile, in the coils impregnated with each of the curable resin compositions of Examples 1-65, no crack was observed. 
     
                                           TABLE 1-1__________________________________________________________________________Thermal shrinkage factors of thermosetting resins[Effect of repeating unit (molecularweight between crosslinked sites)]           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Compara- DER332 100           1.73  2.3    650      n = 0.02tive  HN-5500        92                       BisphenolExample 1 PPG    15                       A type 2E4MZ-CN        0.9Compara- EP-825 100           1.68  2.7    670      n = 0.06tive  HN-5500        90                       BisphenolExample 2 PPG    15                       A type 2E4MZ-CN        0.95Compara- EP-828 100           1.65  2.9    690      n = 0.13tive  HN-5500        85                       BisphenolExample 3 PPG    15                       A type 2E4MZ-CN        0.93Example 1 EP-1001        100           1.23  3.0    720      n = 2.13 HN-5500        34                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.33Example 2 EP-1002        100           1.19  3.0    730      n = 3.28 HN-5500        25                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.25__________________________________________________________________________ Chemical structure of epoxy resin Curing conditions 100° C./15 h + 120° C./15 h 
    
     
                                           TABLE 1-2__________________________________________________________________________Thermal shrinkage factors of thermosetting resins[Effect of repeating unit (molecularweight between crosslinked sites)]           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example 3 EP-1003        100           1.16  3.1    730      n = 4.05 HN-5500        22                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.21Example 4 EP-1055        100           0.92  3.2    740      n = 4.89 HN-5500        19                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.18Example 5 EP-1004AF        100           0.88  3.3    740      n = 5.67 HN-5500        17                       Bisphenol PPG    15                       A type iPA-Na 0.16Example 6 EP-1007        100           0.75  3.3    740      n = 12.93 HN-5500        8                        Bisphenol PPG    15                       A type iPA-Na 0.2Example 7 EP-1002        100           0.55  3.5    720      n = 6.21 HN-5500        7                        Bisphenol PPG    15                       A type iPA-Na 0.2__________________________________________________________________________ Chemical structure of epoxy resin Curing conditions 100° C./15 h + 120° C./15 h 
    
     
                                           TABLE 1-3__________________________________________________________________________Thermal shrinkage factors of thermosetting resins[Effect of repeating unit (molecularweight between crosslinked sites)]           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example 8 EP-1010        100           0.35  3.5    720      n = 18.42 HN-5500        6                        Bisphenol PPG    15                       A type iPA-Na 0.2Example 9 DER-332        50 1.15  3.0    705      n = 0.02 EP-1003        213                      n = 4.05 HN-5500        85                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.1Example DER-332        50 1.10  3.1    710      n = 0.0210    EP-1055        301                      n = 4.89 HN-5500        85                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.1Example DER-332        50 1.00  3.1    710      n = 0.0211    EP-1004AF        279                      n = 5.67 HN-5500        85                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.1__________________________________________________________________________ Chemical structure of epoxy resin Curing conditions 100° C./15 h + 120° C./15 h 
    
     
                                           TABLE 1-4__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example DER-332        50 0.95  3.1    710      n = 0.0212    EP-1009        707                      n = 16.21 HN-5500        85                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.1Example DER-332        50 0.90  3.2    710      n = 0.0213    EP-1010        757                      n = 18.42 HN-5500        85                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.1Example XB-4122        100           1.39  2.9    720      n = 0.214    HN-5500        46 2E4MZ-CN        0.1Example LS-108 100           1.35  2.9    720      n = 515    HN-5500        8 2E4MZ-CN        0.1Example LS-402 100           1.15  2.9    720      n = 1016    HN-5500        4 2E4MZ-CN        0.1__________________________________________________________________________ Curing conditions 100° C./15 h + 120° C./15 h 
    
     
                                           TABLE 1-5__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example PY-302-2        95 1.23  3.0    69017    EP-1007        50 HN-5500        92 PPG    15 iPA-Na 0.2Example DGEBAD 94 1.28  2.9    67018    EP-1007        50 HN-5500        92 PPG    15 iPA-Na 0.2Example TGADPM 80 1.25  2.9    69019    EP-1075        50 HN-5500        92 PPG    15 iPA-Na 0.2Example TTGmAP 80 1.23  3.0    70020    EP-1007        50 HN-5500        92 PPG    15 iPA-Na 0.2__________________________________________________________________________ Curing conditions 100° C./15 h + 120° C./15 h 
    
     
                                           TABLE 1-6__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example TGpAP  80 1.15  3.0    70021    EP-1007        50 HN-5500        92 PPG    15 iPA-Na 0.2Example TGmAP  80 1.20  2.9    73022    EP-1007        50 HN-5500        92 PPG    15 iPA-NA 0.2Example CEL-2021        76 1.20  3.2    74023    EP-1055        50 HN-5500        92 PPG    15 iPA-Na 0.2Example CEL-2021        76 1.10  3.3    74024    EP-1004AF        100 HN-2200        91 PPG    15 iPA-Na 0.16__________________________________________________________________________ Curing conditions 100° C./15 h + 120° C./15 h 
    
     
                                           TABLE 1-7__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example EP-807 100           1.28  3.0    73525    PPG    10 BF.sub.3 -400        10Example EP-807 100           1.18  3.2    72026    PPG    15 BF.sub.3 -400        10Example EP-807 100           1.09  3.2    72027    PPG    20 BF.sub.3 -400        10Example EP-807 100           1.28  3.1    72528    PPG    10 BF.sub.3 -100        10Example EP-807 100           1.25  2.9    74029    PPG    10 CP-66  3Example EP-807 100           1.20  3.1    73230    PPG    10 PX-4BT 5Example EP-807 100           1.10  3.3    72031    PPG    10 YPH-201        5__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 1-8__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example EP-807 100           1.15  3.1    70532    PPG    10 IOZ    5Example EP-807 100           1.10  3.2    70033    PPG    15 TPP    5Example EP-807 100           1.05  3.2    72034    PPG    20 TPP-K  8Example EP-807 100           1.20  3.1    70035    PPG    10 TEA-K  8Example EP-807 100           1.20  3.1    69836    PPG    10 2ED4MZ-K        5Example EP-807 100           1.15  3.2    70037    PPG    10 BTPP-K 5Example EP-807 100           1.10  3.2    70038    PPG    10 iPA-Na 1.0__________________________________________________________________________ Curing conditions 90° C./15h + 120° C./15 h 
    
     
                                           TABLE 1-9__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example EP-807 100           1.20  2.9    71039    PPG    10 2E4MZ- 5 CN-KExample EP-807 100           1.20  3.0    72040    PPG    15 2E4MZ-CNS        5Example EP-807 100           1.05  3.2    72041    PPG    20 2E4MZ-OK        8Example EP-807 100           1.20  2.9    72042    PPG    10 2E4MZ-CN        2Example EP-807 100           1.20  2.9    72043    PPG    10 MC-C11Z-        5 AZINEExample EP-807 100           1.95  3.2    70044    PPG    10 BDMTDAC        10Example EP-807 100           0.96  3.2    70045    PPG    10 BDMTDAI        10__________________________________________________________________________ Curing conditions 90° C./15h + 130° C./15 h 
    
     
                                           TABLE 1-10__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example PY-302-2        100           1.20  3.2    73544    PPG    10 BF.sub.3 -400        10Example PY-302-2        100           1.16  3.3    72045    PPG    15 BF.sub.3 -400        10Example PY-302-2        100           1.09  3.3    71546    PPG    20 BF.sub.3 -400        10Example EP-807 100           1.00  3.3    71047    PPO    10 BF.sub.3 -400        10Example EP-807 100           1.15  3.1    72048    DGEAOBA        10 BF.sub.3 -400        10Example EP-807 100           1.20  3.1    73249    KR     10 BF.sub.3 -400        10Example EP-807 100           1.30  2.9    75050    CTBN   10 BF.sub.3 -400        10__________________________________________________________________________ Curing conditions 90° C./15h + 120° C./15 h 
    
     
                                           TABLE 1-11__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example EP-807 100           0.85  3.3    71552    DABPA  20 DBMTDAC        5Example EP-807 100           0.90  3.4    71053    DABPA  15 BDMTDAI        5Example BMI    50 0.80  3.2    72054    DABPA  50 KR     10 TPP-K  8Example BMI    50 0.75  3.1    73055    DABPA  50 PPG    10 TEA-K  8Example DAPPBMI        100           0.75  3.1    71056    DABPA  50 PPG    10 TEA-K  5Example DAPPBMI        100           1.70  2.9    74557    DABPA  20 PPG    10 TEA-K  5__________________________________________________________________________ Curing conditions 90° C./15h + 120° C./15 h 
    
     
                                           TABLE 1-12__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example DAPPBMI        100           0.90  3.2    73058    DABPA  5 PPG    10 BDMTDAC        5Example DAPPBMI        100           1.0   2.9    75059    DABPA  0 DR     10 2E4MZ-OK        5Example DMBMI  100           0.90  3.1    73060    DABPA  50 KR     15 2E4MZ-OK        5Example PMI    100           0.90  3.1    72061    DABPA  50 KR     20 2E4MZ-OK        5Example HMBMI  100           0.82  3.2    72062    DABPA  50 KR     20 2E4MZ-OK        5Example DAPPBMI        100           1.20  2.9    73063    HMBMI  100 2E4MZ-OK        5__________________________________________________________________________ Curing conditions 100° C./15h + 180° C./15 h 
    
     
                                           TABLE 1-13__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Compara EP-1002        100           1.23  2.3    720tive  HN-5500        25Example PPG    04     2E4MZ-CN        0.25Compara- EP-1007        100           1.98  2.4    770tifve HN-5500        8Example PPG    05     iPA-Na 0.2Compara- EP-807 100           1.20  2.2    790tive  PPG    5Example 6 iPA-Na 1.0Example DER-332        100           1.00  3.2    74064    HN-5500        92 PPG    15 DAPPBMI        50 2E4MZ-CN        0.33Example DER-332        100           0.98  3.2    76065    HN-5500        92 DAPPBMI        50 DABPA  20 PPG    15 2E4MZ-CN        0.5__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     EXAMPLES 68-115 
     Each of the resin composition shown in Tables 2-1 to 2-11 was thoroughly stirred, placed in a mold, and heat-cured under the curing conditions shown in Tables 2-1 to 2-11. Each of the resulting cured products was measured for thermal shrinkage factor when cooled from the glass transition temperature to 4.2K, and the results are shown in Tables 2-1 to 2-11. Each cured product was also measured for bending properties at 4.2K, and the bending strain and bending modulus are shown in Tables 2-1 to 2-11. All of the curable resin compositions of Examples 68-115 according to the present invention, when cured, had a thermal shrinkage factor of 1.8-0.3% when cooled from the glass transition temperature to 4.2K, a bend-breaking strain of 3.5-4.5% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K. 
     
                                           TABLE 2-1__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example DER332 100           1.49  3.5    650      n = 0.0268    HN-5500        92                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.9Example EP-825 100           1.45  3.6    670      n = 0.0669    HN-5500        90                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.95Example EP-828 100           1.46  3.6    690      n = 0.1370    HN-5500        85                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.93Example EP-1001        100           1.48  3.6    720      n = 2.1371    HN-5500        34                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.33Example EP-1002        100           1.19  3.7    730      n = 3.2872    HN-5500        25                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.25__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-2__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example EP-1003        100           1.16  3.7    730      n = 4.0573    HN-5500        22                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.21Example EP-1055        100           0.92  3.8    740      n = 4.8974    HN-5500        19                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.18Example EP-1004AF        100           0.88  3.7    740      n = 5.6775    HN-5500        17                       Bisphenol PPG    10                       A type iPA-Na 0.16Example EP-1007        100           0.75  3.6    740      n = 12.9376    HN-5500        8                        Bisphenol PPG    10                       A type iPA-Na 0.2Example EP-1009        100           0.55  3.6    720      n = 16.2177    HN-5500        7                        Bisphenol PPG    10                       A type iPA-Na 0.2__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-3__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example EP-1010        100           0.55  3.6    720      n = 18.4278    HN-5500        6                        Bisphenol PPG    10                       A type iPA-Na 0.2Example DER-332        50 1.15  3.6    705      n = 0.0279    EP-1003        213                      n = 4.05 HN-5500        85                       Bisphenol PPG    15                       A type 2E4MZ-CN        0.1Example DER-332        50 1.10  3.6    710      n = 0.0280    EP-1055        301                      n = 4.89 HN-5500        85                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.1Example DER-332        50 1.00  3.7    710      n = 0.0281    EP-1004AF        279                      n = 5.67 HN-5500        85                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.1__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-4__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example DER-332        50 0.95  3.7    710      n = 0.0282    EP-1009        707                      n = 16.21 HN-5500        85                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.1Example DER-332        50 0.90  3.6    710      n = 0.0283    EP-1010        757                      n = 18.42 HN-5500        85                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.1Example LS-108 100           1.35  3.7    720      n = 584    HN-5500        8 2E4MZ-CN        0.1 PPG    10Example LS-402 100           1.15  3.9    720      n = 1085    HN-5500        4 2E4MZ-CN        0.1 PPG    10__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-5__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example PY-302-2        95 1.23  3.6    69086    EP-1007        50 HN-5500        92 PPG    10 iPA-Na 0.2Example DGEBAD 94 1.28  3.9    67087    EP-1007        50 HN-5500        92 PPG    10 iPA-Na 0.2Example TGADPM 80 1.25  3.8    69088    EP-1007        50 HN-5500        92 PPG    10 iPA-Na 0.2Example TTGmAP 80 1.23  3.9    70089    EP-1007        50 HN-5500        92 PPG    10 iPA-Na 0.2__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-6__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example TGpAP  80 1.15  3.6    70090    EP-1007        50 HN-5500        92 PPG    10 iPA-Na 0.2Example TGmAP  80 1.20  3.8    73091    EP-1007        50 HN-5500        92 PPG    10 iPA-Na 0.2Example CEL-2021        76 1.20  3.9    74092    EP-1055        50 HN-5500        92 PPG    15 iPA-Na 0.2Example CEL-2021        76 1.10  3.8    74093    EP-1004AF        100 HN-2200        91 PPG    15 iPA-Na 0.16__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-7__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example PY302.2        100           1.40  3.8    650      n = 0.0294    HN-5500        94                       Bisphenol PPG    10                       A type 2E4MZ-CN        0.9Example PY302.2        100           1.48  3.6    670      n = 0.0695    HN-5500        94                       Bisphenol PPG    10                       A type DY063  0.1Example PY302.2        100           1.35  3.6    690      n = 0.1396    HN-5500        94                       Bisphenol PPG    15                       A type DY063  0.1Example DER-332        100           1.48  3.6    720      n = 2.1397    HN-5500        94                       Bisphenol PPG    10                       A type DY063  0.1Example DER-332        100           1.31  3.6    720      n = 2.1398    HN-5500        94                       Bisphenol PPG    15                       A type DY063  0.1__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-8__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example HP4032 100           1.50  3.8    650      n = 0.0299    HN-5500        112                      Bisphenol PPG    10                       A type 2E4MZ-CN        0.9Example HP4032 100           1.45  3.6    670      n = 0.06100   HN-5500        112                      Bisphenol PPG    10                       A type DY063  0.1Example HP4032 100           1.41  3.6    690      n = 0.13101   HN-5500        112                      Bisphenol PPG    15                       A type DY063  0.1Example DER-332        100           1.38  3.6    720      n = 2.13102   HN-5500        94                       Bisphenol PPG    10                       A type TPP    0.1Example DER-332        100           1.28  3.6    720      n = 2.13103   HN-5500        94                       Bisphenol PPG    10                       A type BTPP-K 0.1__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-9__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example DER-332        100           1.38  3.8    650      n = 0.02104   HN-5500        94                       Bisphenol CTBN   10                       A type 2E4MZ-CN        0.9Example HP4032 100           1.48  3.7    670      n = 0.06105   HN-5500        112                      Bisphenol CTBN   10                       A type DY063  0.1Example DER-332        100           1.45  3.6    690      n = 0.13106   HN-5500        94                       Bisphenol CTBN   10                       A type DY063  0.1Example DY302, 2        100           1.28  3.6    720      n = 2.13107   HN-5500        94                       Bisphenol CTBN   10                       A type DY063  0.1Example DER-332        100           1.35  3.7    720      n = 2.13108   HN-5500        94                       Bisphenol CTBN   10                       A type BTPP-K 0.1__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-10__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example DER-332        100           1.38  3.7    650      n = 0.02109   HN-5500        94                       Bisphenol CTBN   10                       A type TEA-K  0.9Example DER-332        100           1.28  3.6    670      n = 0.06110   HN-5500        94                       Bisphenol PPG    10                       A type BF3-400        5Example DER-332        100           1.17  3.6    690      n = 0.13111   HN-5500        94                       Bisphenol PPG    10                       A type IOZ    0.9Example PY302, 2        100           1.38  3.7    720      n = 2.13112   HN-5500        94                       Bisphenol PPG    10                       A type 2E4MZ-K        0.1Example DER-332        100           1.48  3.6    720      n = 2.13113   HN-2200        94                       Bisphenol PPG    10                       A type DY063  0.1__________________________________________________________________________ Curing conditions 100° C./15h + 120° C./15 h 
    
     
                                           TABLE 2-11__________________________________________________________________________Thermal shrinkage factors of thermosetting resins           Thermal                 Bending                        Bending modulus           shrinkage                 strain (Kg/mm.sup.2Resin composition           factor (%)                 (% at 4.2 K)                        at 4.2 K)                                 Remarks__________________________________________________________________________Example PY302, 2        100           1.28  3.6    735114   PPG    20 BF.sub.3 -400        10Example DER-332        100           1.18  3.6    720115   PPG    20 BF.sub.3 -400        10__________________________________________________________________________ Curing conditions 90° C./15h + 120° C./15 h 
    
     As described above, in a superconducting magnet coil impregnated with a curable resin composition giving a cured product having a thermal shrinkage factor of 1.5-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bend-breaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, particularly a cured product having a thermal shrinkage factor of 1.00-0.3% when cooled from the glass transition temperature to a liquid helium temperature, i.e. 4.2K, a bendbreaking strain of 2.9-3.9% at 4.2K and a modulus of 500-1,000 kg/mm 2  at 4.2K, no microcrack is generated in the cured product when the superconducting magnet coil after production is cooled to a liquid helium temperature, i.e. 4.2K. Such a superconducting magnet coil causes substantially no quench even during its operation in which an electromagnetic force is applied.