MXPA98005375A - Process for impregnating electric coils and epoxy resin composition selected to carry out the impregnac - Google Patents

Abstract

A process for impregnating an electrical coil comprising a winding comprising two or more layers consisting of more than one turn of a meterial in the form of an electrically conductive wire with a polymer material electrically insulating the individual turns of the wire-shaped material each with the aid of a thermally curable epoxy resin composition, which composition is solid at room temperature and comprises the following constituents: (a) an epoxy resin that is solid at room temperature, selected from (a1) polyglycidyl ethers based in novolacs; (a2) diglycidyl ethers based on biphenols, and (a3) mixtures of more than one of the components (a1) and (a2), (b) an interlacing agent for component (a), (c) an accelerator suitable for the reaction of component (a) and component (b); (d) from 15 to 70 weight percent, based on the overall weight of the composition, of filler selected to parat of (d1) carb calcium onate, (d2) quartz fluorine, (d3) wollastonite whose particles have an average ratio of length to cross section that is less than 5: 1; (d4) mixtures of the components (d1), (d2) and ( d3) and (d5) mixtures of the components (d1), (d2), (d3) and (d4) with other inorganic fillers, and also (e) from 10 to 60 weight percent, based on the overall weight of the composition, of inorganic reinforcements in the form of acicular or fibrillary particles with a length of 0.05 to 2.5 mm having an average length-to-cross-sectional ratio of 5: 1 or more, the overall amount of the components (d) and (e) being of not more than 80 weight percent, based on the overall weight of the composition, inter alia eliminates the need to use sacrificial molds and reduces by a multiple the curing time required to complete the coating of the coils, reducing it to the region of some minut

Description

PROCESS FOR IMPREGNATING ELECTRIC COILS. AND COMPOSITION OF SELECTED EPOXY RESIN TO CARRY A CAPE THE IMPREGNATION The present invention relates to a process for impregnating an electric coil, comprising a winding of two or more layers each consisting of more than one turn of an electrically conductive material in wire form, with a polymer material that electrically isolates the individual turns of the wire-shaped material from each other, wherein the individual windings of the coil are wrapped with the aid of a curable epoxy resin composition and this composition is thermally cured, and particularly preferred curable compositions for carrying out the impregnation. From WO-A-96/01481 it is known to use curable epoxy resin compositions which are liquid at room temperature and comprise (a) a liquid diglycidyl ether of biphenol A, (b) an interlacing agent therefor, (c) an accelerator suitable for the reaction of the liquid diglycidyl ether (a) with the cross-linking agent (b), and (d) a filler material which, based on the components (a) and (b), comprises from 40 to 60 percent by weight of calcite and synthetic wollastonite, acicular, for impregnation and, if desired, for the coating of electric coils comprising windings which in turn comprise a multiplicity of layers, each of which consists of a large number of turns of a conductive material in the form of a thin wire, examples being the secondary windings of transformers or ignition coils. The use of liquid epoxy resin systems such as those mentioned, although it allows said windings to be sufficiently impregnated, that is to say, allows the epoxy material to penetrate between all the turns of a winding, nevertheless it still has some disadvantages. For example, liquid epoxy enzyme systems can only be formulated in the form of two packages, which in terms of what the user thinks, constitutes a non-inconsiderable increase in processing complexity. In addition, the referred liquid impregnation systems require using a sacrificial mold having the desired external contours for the finished coil. The coil to be encapsulated has to be inserted into this mold. Subsequently, it is necessary, usually after its evacuation, to fill the mold with the liquid curable epoxy resin composition and cure the composition in the mold. After curing, the mold can no longer be removed and must therefore remain permanently around the coil, like a sacrificial mold. A further important disadvantage of the liquid epoxy resin compositions mentioned above is their extremely long curing time, which in general amounts to several hours and which, for the mass production of coils, necessitates the use of huge curing ovens. . The object of the present invention is inter alia to avoid the aforementioned disadvantages associated with the impregnation of coils, especially ignition coils, printing transformers and high voltage transformers. It has now been discovered that said coils can be impregnated even at room temperature, i.e., at a temperature of about 15 to 25 ° C, using curable, solid epoxy resin compositions, preferably reinforced with fiber, having the specific composition defined later. A particular surprise in this context is that said compositions are also capable of penetrating sufficiently the secondary windings of normal ignition coils and transformers even if they comprise relatively large amounts of a reinforcing material consisting of inorganic fibers with a length of up to approximately 2.5 mm. The use of these solid epoxy resin compositions eliminates the need to use a housing (sometimes referred to as "lost housing" and reduces by a multiple the cure time required to complete the coil coating., reducing it to the region of a few minutes, usually no more than 15 minutes. Therefore, the present invention provides in its broadest sense a process for impregnating an electrical coil comprising a winding comprising two or more layers consisting of more than one turn of a material in the form of electrically conductive wire with a material of polymer that electrically isolates the individual turns of the wire-shaped material from one another with the aid of a thermally curable epoxy resin composition, which composition is solid at room temperature and comprises the following constituents: (a) an epoxy resin that is solid at room temperature, selected from (a 1) polyglycite ethers based on novolacs; (a2) glycidic ethers based on biphenols, and (a3) mixtures of more than one of the components (a1) and (a2); (b) an interlacing agent for component (a); (c) an accelerator suitable for the reaction of the component (a) and component (b); (d) from 15 to 70 weight percent, based on the overall weight of the composition, of filler selected from (d 1) calcium carbonate, (d 2) fluorine from quartz, (d 3) wollastonite whose particles have an average ratio of length to cross section that is less than 5: 1; (d4) mixtures of the components (d 1), (d 2) and (d 3) and (d 5) mixtures of the components (d 1), (d 2), (d 3) and (d 4) with other inorganic fillers. By impregnation it is meant in this application a treatment of the electrical coil whereby the individual turns of at least one coil winding are developed with the aid of the curable epoxy resin composition and the composition is thermally cured. However, this treatment may comprise the total encapsulation of parts of the coil or the entire coil, including the coil former, with the curable epoxy resin composition. In addition, the composition employed in the process of the invention preferably comprises: (e) from 10 to 60 weight percent, based on the overall weight of the composition, of inorganic reinforcements in the form of acicular or fibrillary particles with a length of 0.05 to 2.5 mm that have an average ratio of length to cross section of 5: 1 or more, the overall amount of the components (d) and (e) being no more than 80 percent by weight, based on the overall weight of the composition.

It is preferred to use specially selected compositions wherein the reinforcement (e) consists of needle-like or fibrillar particles having a length of 0.15 to 2.5 mm. The present invention also provides these compositions. With particular reference, the reinforcement (e) comprises a glass fiber material, especially crushed or ground glass fibers having a length of 0.05 to 2.5 mm and a diameter preferably of 10 to 30 μm, which are available in several shapes and commercially. A reinforcing material which has proved to be particularly suitable, for example, comprises glass fibers with a length of 0.05 mm, in particular from 0.15 mm to 2 mm, in particular of 1 mm; for example, approximately 0.2 to 0.25 mm.

The novolac-based polydiglycidyl ethers which are used in the process of the invention and in the compositions of the invention as the component (a1) are in particular: (a1.1) polydiglycidyl ethers based on epoxy-phenol novolacs , (a.1.2) polydiglycidyl ethers based on epoxy-cresol novolacs, or (a.1.3) mixtures of epoxy novolacs of type (a.1.1) and / or (a.1.2). Component (a2) preferably comprises diglycidyl ethers based on biphenol A. These can, for example, be pre-extended (advanced) resins which can be obtained by reacting diglycidyl ether of biphenol A with a stoichiometric deficit of substances having two. functional groups that are reactive with epoxide groups, in particular by reacting 1.1 to 2 moles of diglycidyl ether of biphenol A with 1 mole of biphenol A. The crosslinking agent (b) is judiciously selected from: (b1) dicyandiamide, (b2) polycarboxylic anhydrides and (b3) mixtures of more than one of the components (b1) and / or one or more poiiphenols. If an organic carboxylic anhydride is used as the crosslinking agent, it is preferably an aromatic or cycloaliphatic polycarboxylic anhydride, in particular a corresponding dicarboxylic anhydride, such as phthalic anhydride, hexahydrophthalic anhydride or methyltetrahydrophthalic anhydride. Particular preference is given to carboxylic anhydrides which are solid at room temperature. If the crosslinking agent includes a certain proportion of polyphenols, this may be advantageous in terms of the processing of the impregnation compositions. However, since the presence of relatively large amounts of polyphenols can prevent the penetration of the curable composition into the winding and thus reduce the impregnation depth, the upper limit of the proportion of polyphenol in the interlacing agent is guided by the depth of impregnation required. Preferred polyphenols are: phenol novolacs, cresol novolacs and / or mixtures of novolacs of said types. The interlacing agent (b) is used in the commonly used amounts; for example, in amounts of up to 50 weight percent, preferably up to 25 weight percent, based on the epoxy resin. Dicyandiamide is used with particular reference in an amount of 0.16 to 0.5 moles per epoxide equivalent of the composition, and in particular it is added in amounts so that in the compositions of the invention there are from 0.25 to 0.36 moles of dicyandiamide per equivalent of epoxide .

When dicyandiamide is employed as an interlacing agent, the latency of the epoxy resin compositions of the invention is particularly good, which means that they can be stored, for example, without problems at room temperature (around 15 to 25 ° C). As for the accelerators (d) it is possible to use all the common substances that the expert knows to accelerate the reaction of epoxy resins with dicyandiamide or with polyphenols or, respectively, with organic anhydrides. Examples of accelerators for the reaction with dicyandiamide are alkali metal alcoholates, tertiary amines, especially hexamethylenetetramine, phosphines, such as triphenylphosphine, quaternary ammonium compounds, substituted ureas, such as N- (4-chlorophenyl) -N, N'- dimethylurea or N- (3-chloro-4-methylphenyl) -N, N'-dimethylurea, Mannich bases, such as 2,4,6-tri (dimethylaminomethyl) phenol or 2,4,6-tri (diethylaminomethyl) phenol , imidazole or imidazole detives, such as 2-phenylimidazole, 2-ethylimidazole, 2-methylimidazole or benzimidazole, and complexes of BCI3 and BF3 with tertiary amines such as trimethylamine, octyldimethylamine, triethylamine, piperidine, pyridine or hexamethylethylenetetramine. Preference is given to imidazoles, especially 2-ethylimidazole. Examples of accelerators for the reaction with polyphenols are tertiary amines, such as benzyldimethylamine, imidazoles, such as imidazole, 2-phenylimidazole, 2-ethylimidazole, 2-methylimidazole or benzimidazole, or quaternary ammonium compounds. Examples of accelerators for the reaction with carboxylic anhydrides are tertiary amines and their salts, such as N-benzyldimethylamine or triethanolamine, Mannich bases, such as those already mentioned above, imidazole and imidazole detives, quaternary ammonium salts, such as benzyltrimethylammonium, phosphonium salts, such as tetraphenylphosphonium bromide, and alkali metal alkoxides. The amount of accelerator is preferably from 1 to 30 parts by weight per 100 parts by weight of catalyst, with particular reference from 3 to 20 parts by weight and, in particular, from 5 to 12 parts by weight. The particle size distribution of the filler forming the component (d) of the compositions described is preferably 0.1 to 200 μm, in particular 0.2 to 60 μm. The calcium carbonate used as filler is preferably calcium carbonate anhydride in essence and finely divided. Examples of inorganic fillers other than calcium carbonate, quartz fluorine and wollastonite are kaolin, dolomite, barium sulfate, talc, mica, aluminum or aluminum oxide trihydrate. Where mixtures of calcium carbonate, quartz fluorine and / or wollastonite are used with other fillers, the compositions preferably comprise at least 20 and, in particular, at least 30 weight percent calcium carbonate, fluorine quartz and / or wollastonite. The other fillers may be present, for example, in an amount of up to 40, preferably in an amount of up to 30, weight percent. With particular preference, wollastonite is the only filler present in the compositions employed according to the invention. In some cases it is also favorable, for the compositions used according to the invention, to comprise a hardener as an additional component (f). The hardener in this case is preferably used in amounts of 0.5 to 5, preferably on the scale of about one to two, percent by weight, based on the overall composition. The hardener (f) is preferably selected from: (f 1) epoxy resins modified with polysiloxane and (f2) block copolymers based on polydimethylsiloxanes and caprolactone or on polycaprolactones. Hardeners of this kind are known to the expert and can be obtained in various forms and commercially. If a hardener of the type (f 1) is used, in particular it is diglycidyl ether modified with polysiloxane based on biphenol A. The compositions used according to the invention for impregnating electrical coils may further comprise a mold release agent as an additional component. (g), examples being Hoechst OP-Wachs® (wax partially hydrolyzed), Hoechst-Wachs KSL® (wax mount), carnauba wax, calcium stearate or similar mold releasing agents, or mixtures of one or more of said substances The curable compositions employed according to the invention may further comprise normal additives, examples being adhesion promoters for fillers and reinforcing materials, such as, in particular, silane adhesion promoters, pigments, such as carbon black, or flexibilizers. In a specific embodiment of the process of the invention, a curable composition is used which comprises the following constituents as components (a), (b) and (c): (a2) one or more diglycidyl ethers based on biphenols; (b2) one or more polycarboxylic anhydrides; (c) an accelerator suitable for the reaction of component (a2) and component (b2). In a particularly preferred embodiment of the process of the invention, the composition used to coat coils comprises the following constituents as components (a), (b) and (c): (a) an epoxy resin that is solid at room temperature, selected at starting from (a1) polydiglycidyl ethers based on novolacs; (a2) diglycidyl ethers based on biphenols, and preferably (a3) mixtures of more than one of the components (a 1) and (a2); (b) an interlacing agent selected from (b1) dicyandiamide and (b4) mixtures of dicyandiamide and polyphenols (b2); and (c) an accelerator suitable for the reaction of component (a) and component (b1) or (b4), for example hexamethylenetetramine. The latter mode of the process produces impregnation compositions having a particularly high Tg usually above 150 ° C (determined by the torsional vibration test of ISO 6721, heating rate 2 ° C / min). In the case of specific preferred variants of the last embodiment of the coating composition used according to the invention, component (a) is a polydiglycidyl ether based on a cresol novolac and / or the crosslinking agent (b) is dicyandiamide alone or a mixture of dicyandiamide and polyphenols wherein the polyphenols are, in particular, phenol novolacs, cresol novolacs or mixtures of these novolacs. The curable compositions used in accordance with the invention can be prepared and homogenized, for example, in a normal manner with the aid of known mixing apparatuses, such as a ball mill, co-grinder, roll mill or extruder, with or without the fusion of the compositions followed, if required, by cominution of the molten material. The appropriate combinations of the aforementioned homogenization techniques can of course also be employed. It is also possible, for example, to dissolve and / or suspend the components of the curable compositions in a suitable solvent and then evaporate the solvent to leave the homogenized composition in solid form. For impregnation of the coil, this coil is inserted into a mold immediately or after preliminary heating. Then, the curable composition is introduced into the coil-containing mold and thermally cured therein under pressure, preferably at a very low cavity pressure of, for example, no more than 100 MPa for a period of, for example, up to a maximum of 10 minutes, preferably less than about 5 minutes, preferably at temperatures in the range of 140 to 250 ° C, in particular 160 to 200 ° C and, most preferably, in the region of approximately 180 ° C. The time pressure profile in the course of filling, and the maximum pressure, depends on the coil to be impregnated. The parameters referred to can be easily determined experimentally by the experts. Before introducing the curable composition, the mold is preferably evacuated and the curable composition is introduced into the evacuated mold containing coil. This is the case in particular for the camera windings that are common today. The impregnation process of the invention is suitable, for example, for impregnating coil windings having a winding density of up to 1000 turns per mm2., preferably up to 500 rounds per mm2, it being possible, for example, to use wire with diameters of up to 20 μm, preferably up to 50 μm, for the windings. The thickness of the overall windings in this case can be, for example, up to 7.5 mm, preferably up to 5 mm. Such windings are found, for example, in ignition coils, printing transformers and high voltage transformers. In the case of the impregnation process of the invention, it is preferred to operate in accordance with the principle of a normal compression molding, transfer molding or injection molding process. If an injection molding process is employed, it is preferred, because of the comparatively low melt viscosities of the curable compositions employed according to the invention, to use a cylinder assembly with a lockable injection nozzle, so that the Nozzle can be closed when, for example, the mold is opened. Also, it may be advantageous in this case to use a screw having a non-retention valve.

EXAMPLES Figure 1 shows a diagram of the pressing tool with which the test coils are impregnated in the subsequent examples. Figure 2 is a longitudinal section through the coil former used in the examples, and their dimensions.

GENERAL PROCEDURE TO PREPARE POSITIONS OF IMPREGNATION Glass fibers and / or fillers are mixed with a silane adhesion promoter and ground for 30 minutes with a ball mill. If a hardener is used, it is subsequently ground in the required amount with the filler for 20 minutes, also in a ball mill. Finally, all the components of the curable composition, with the exception of glass fibers, are milled for approximately 4.25 minutes in a ball mill. The glass fibers are then added, and grinding continues for 45 minutes. The impregnation compositions specified in the examples are prepared by using the additives, reinforcing materials and fillers characterized below: The performance properties of the impregnation compositions are determined in each example unless otherwise specified with the help of the measurement methods indicated below: Tg: Torsional vibration test in accordance with ISO 6721 Bending stress: ISO 178 Bending module: ISO 178 Impact effort: ISO 179/1 Linear thermal expansion coefficient a: DI N 53752 (temperature scale 20 - 80 ° C) Impregnation, determination of the impregnation depth. Impregnation quality evaluation: In all the examples, the test coil is impregnated in accordance with the principle of transfer molding, by using the test apparatus shown in diagram in figure 1. This apparatus comprises two parts (1) and (6) that can be separated from each other. The first part (1) has an injection compartment (2) to receive a tablet (1 1) consisting of the impregnation composition of the invention, the transfer piston (3), the cavity (4) and a hole ( 5) to accommodate a temperature sensor. The second part (6) comprises a core (7) for mounting the coil (10) to be impregnated, a device (8) for removing the finished impregnated coil from the core (7) and a connection (9) for evacuating the cavity (4). A coil (10) that has been heated before to approximately 1 10 ° C and has the dimensions indicated in figure 2, and that in all its chambers has a winding comprising copper wire with a diameter of 94 μm with a density of winding of approximately 100 turns per mm2, the thickness of the winding that rises from the top to the bottom of the chamber of about 3.5 to about 5.5 mm, is introduced into the cavity (4) of the impregnation tool (1, 6), which is heated to 180 ° C. The granulated impregnation composition is compressed into a tablet while it is cold and then heated to about 70 ° C when using a high frequency preheating device. The tablet (11) heated before this way is introduced into the injection compartment (2), and a vacuum of about 35 mbars is applied to the cavity. Subsequently, the impregnation composition is transferred in the cavity (4) over a period of about 15 seconds with the help of the piston (3) (injection pressure between 80 and 150 bar). The subsequent healing time is 5 minutes. The coated and impregnated coil is removed from the mold. The coil, which has been extracted, is sewn in the longitudinal direction and polished. A microscope is used to measure the impregnation depth achieved in each case, and the impregnation quality is visually evaluated. In this evaluation, the impregnation is classified as "good" if more than 95 percent of the space between the wire turns of a winding has been filled with the impregnation composition.

Resistance to rupture: In order to determine the resistance to rupture, a specimen is produced by coating a rectangular metal plate with sharp edges measuring 60 mm in length, 30 mm in width and 4 mm in thickness with the respective impregnation composition, leaving an area of approximately 8 mm by 8 mm free in each of the four corners of the metal plate, and the composition is cured at 170 ° C to 180 ° C. The thickness of the coating is approximately 3 mm in the long side direction and the wide side of the metal plate, and approximately 2 mm perpendicular to it. After demolding, the specimen is subjected to the sequence of treatment steps indicated in the table below, and, after each treatment step, it is investigated whether there is rupture in the coating composition. The classification in terms of rupture corresponds to the last treatment step after which the specimen still does not show rupture. Example 1: 1 kilogram of an impregnation composition is produced and examined in accordance with the general procedure described above; Its composition is as follows: The impregnation composition has the following properties: Example 2: 1 kilogram of an additional impregnation composition is produced according to the general procedure described above; Its composition is as follows: The impregnation composition has the following properties: Example 3: 1 kilogram of an impregnation composition is produced according to the general procedure described above; Its composition is as follows: The impregnation composition has the following properties: A complete impregnation of good quality is also achieved with the impregnation compositions referred to in the previous examples if the impregnation is carried out not of the test winding (Test) impregnated in the examples but of, for example, the windings A, B and C established in the table below: Example 4: 1 kilogram of an impregnation composition is produced and examined in accordance with the general procedure described above; Its composition is as follows: The impregnation composition has the following properties:

Claims (3)

1. CLAIMS 1 - . 1 - A process for impregnating an electric coil comprising a winding comprising two or more layers consisting of more than one turn of an electrically conductive material in the form of a wire with a polymer material that electrically island the individual turns of the material in wire form together with the aid of a thermally curable epoxy resin composition, which composition is solid at room temperature and comprises the following constituents: (a) an epoxy resin that is solid at room temperature, selected from (a) 1) polyglycidyl ethers based on novolacs; (a2) diglycidyl ethers based on biphenols, and (a3) mixtures of more than one of the components (a 1) and (a2); (b) an interlacing agent for component (a); (c) an accelerator suitable for the reaction of component (a) and component (b); (d) from 15 to 70 weight percent, based on the overall weight of the composition, of filler selected from (d1) calcium carbonate, (d2) fluorine from quartz, (d3) wollastonite whose particles have a average ratio of length to cross section that is less than 5: 1; (d4) mixtures of the components (d 1), (d 2) and (d 3) and (d 5) mixtures of the components (d 1), (d 2), (d 3) and (d 4) with other inorganic fillers. 2 - A process according to claim 1, wherein the composition further comprises: (e) from 10 to 60 weight percent, based on the overall weight of the composition, of inorganic reinforcements in the form of needle-like particles or fibrillar with a length of
2. 0. 05 to 2.5 mm having an average ratio of length to cross section of 5: 1 or more, the overall amount of components (d) and (e) being no more than 80 weight percent, based on weight global composition
3. 3. - A process according to claim 2, wherein the reinforcement (e) consists of acicular or fibrillar particles with a length of 0.15 to 2.5 mm. 4 - A process according to any of claims 1 and 3, wherein the reinforcement (e) is a fiberglass material. 5. A process according to any of claims 1 to 4, wherein component (a1) is selected from: (a 1 1) polydiglycide ethers based on epoxy-phenol novolacs, (a .1) .2) polydiglycidyl ethers based on epoxy-cresol novolacs, or (a.1.3) mixtures of epoxy novolacs of type (a.1.1) and / or (a.1.2). 6 - A process according to any of claims 1 to 5, wherein the component (a2) is a diglycidyl ether based on biphenol A. 7 - A process according to any of claims 1 to 6, wherein the crosslinking agent (b) is selected from: (b1) dicyandiamide, (b2) polycarboxylic anhydrides and (b3) mixtures of more than one of the components (b1) and / or one or more polyphenols. 8 - A process according to claim 7, wherein the polyphenols are selected from: phenol novolacs, cresol novolacs and mixtures of said novolacs. 9 - A process according to any of claims 1 to 8, wherein the filler is wollastonite. 10. A process according to claim 9, wherein the composition further comprises (f) a hardener. 1 - A process according to claim 10, wherein the hardener (f) is selected from: (f1) epoxy resins modified with polysiloxane and (f2) block copolymers based on polydimethylsiloxanes and caprolactone or on polycaprolactones . 12 - A process according to claim 1, wherein the hardener (f 1) is a diglycidyl ether modified with polysiloxane based on biphenol A. 13 - A process according to any of claims 1 to 4 or 6 to 12, wherein the composition comprises the following constituents as components (a), (b) and (c): (a2) one or more diglycidyl ethers with base in biphenols; (b2) one or more polycarboxylic anhydrides; (c) an accelerator suitable for the reaction of component (a2) and component (b2). 14 - A process according to any of claims 1 to 5 or 7 to 12, wherein the composition comprises the following constituents as components (a), (b) and (c): (a) an epoxy resin that is solid at room temperature, selected from (a 1) polydiglycidyl ethers based on novolacs; (a2) diglycidyl ethers based on biphenols, and preferably (a3) mixtures of more than one of the components (a 1) and (a2); (b) an interlacing agent selected from (b1) dicyandiamide and (b4) mixtures of dicyandiamide and polyphenols (b2); and (c) an accelerator suitable for the reaction of component (a) and component (b1) or (b4), preferably hexamethylenetetramine. 15 - A process according to claim 14, wherein the component (a) is a polyglycidyl ether based on a cresol novolac. 16 - A process according to claim 14 or claim 15, wherein the interlacing agent (b) is dicyandiamide. 17. A process according to claim 14 or claim 15, wherein the interlacing agent (b) is a mixture of dicyandiamide and polyphenols and the polyphenols are selected from phenol novolacs, cresol novolacs and mixtures of said novolacs . 18. A process according to any of claims 1 to 17, wherein the composition further comprises (g) a mold releasing agent. 19. A process according to any of claims 1 to 18, wherein the coil is introduced into a mold and then the curable composition is introduced into the mold containing coil and thermally cured therein under pressure 20 - A process according to claim 19, wherein the mold is evacuated before introducing the curable composition and the curable composition is introduced into the evacuated mold containing coil. 21 - A process according to any of claims 1 to 20, according to the principle of the process of compression molding, transfer molding or injection molding. 22. An injection molding process according to claim 21, wherein a cylinder assembly is used whose injection nozzle can be closed. 23. An injection molding process according to any of claims 20 and 21, wherein a screw having a non-retention valve is used. 24. A curable epoxy resin composition, in particular for use in a process according to any of claims 2 to 23, which is solid at room temperature and comprises the following constituents: (a) an epoxy resin that is solid to room temperature, selected from (a1) polyglycidyl ethers based on novolacs; (a2) diglycidyl ethers based on biphenols, and (a3) mixtures of more than one of the components (a 1) and (a2); (b) an interlacing agent for component (a); (c) an accelerator suitable for the reaction of the component (a) and component (b); (d) from 15 to 70 weight percent, based on the overall weight of the composition, of filler selected from (d 1) calcium carbonate, (d 2) fluorine from quartz, (d 3) wollastonite whose particles have an average ratio of length to cross section that is less than 5: 1; (d4) mixtures of the components (d1), (d2) and (d3) and (d5) mixtures of the components (d1), (d2), (d3) and (d4) with other inorganic fillers; and also (e) from 10 to 60 weight percent, based on the overall weight of the composition, of inorganic reinforcements in the form of needle-like or fibrillary particles with a length of 0.05 to 2.5 mm having an average length ratio. at a cross section of 5: 1 or more, the overall amount of the components (d) and (e) being no more than 80 weight percent, based on the overall weight of the composition. 25. A composition according to claim 24, wherein the reinforcement (e) is a fiberglass material. 26 -. 26 - A composition according to any of claims 24 and 25, wherein the component (a 1) is selected from: (a 1.1) polydiglycidyl ethers based on epoxy-phenol novolacs, (a.1) .2) polydiglycidyl ethers based on epoxy-cresol novolacs, or (a .1 .3) mixtures of epoxy novolacs of type (a.1 .1) and / or (a .1 .2). 27 - A composition according to any of claims 24 to 25, wherein component (a2) is a diglycidyl ether based on biphenol A. 28 - A composition according to any of claims 24 to 27, wherein the interlacing agent (b) is selected from: (b1) dicyandiamide, (b2) polycarboxylic anhydrides and (b3) mixtures of more than one of the components (b1) and / or one or more polyphenols. 29. A composition according to claim 28, wherein the polyphenols are selected from: phenol novolacs, cresol novolacs and mixtures of said novolacs. 30 -. 30 - A composition according to any of claims 25 to 29, wherein the composition further comprises (f) a hardener. 31 - A composition according to claim 30, wherein the hardener (f) is selected from: (f 1) epoxy resins modified with polysiloxane and (f2) block copolymers based on polydimethylsiloxanes and caprolactone or on polycaprolactones. 32 - A composition according to claim 31, wherein the hardener (f1) is a diglycidyl ether modified with polysiloxane based on biphenol A. A composition according to any of claims 24 to 31, further comprising ( g) a mold releasing agent. 34 - A composition according to any of claims 24 and 25 or 27 to 33, wherein the composition comprises the following constituents as components (a), (b) and (c): (a2) one or more diglycidyl ethers with base in biphenols; (b2) one or more polycarboxylic anhydrides; (c) an accelerator suitable for the reaction of component (a2) and component (b2). 35 -. A composition according to any of claims 24 to 26 or 28 to 33, wherein the composition comprises the following constituents as components (a), (b) and (c): (a) an epoxy resin that is solid at room temperature, selected from (a 1) polydiglycidyl ethers based on novolacs; (a2) diglycidyl ethers based on biphenols, and preferably (a3) mixtures of more than one of the components (a 1) and (a2); (b) an interlacing agent selected from (b1) dicyandiamide and (b4) mixtures of dicyandiamide and polyphenols (b2); and (c) a suitable accelerator for the reaction of the component (a) and component (b1) or (b4), preferably hexamethylenetetramine. 36.- A composition according to claim 35, wherein component (a) is a polyglycidyl ether based on a cresol novolac. 37.- A composition according to claim 35 and 36, wherein the interlacing agent (b) is dicyandiamide. 38 - A composition according to claim 35 and 36, wherein the interlacing agent (b) is a mixture of dicyandiamide and polyphenols and the polyphenols are selected from phenol novolacs, cresol novolacs and mixtures of said novolacs. SUMMARY A process for impregnating an electric coil comprising a winding comprising two or more layers consisting of more than one turn of a material in the form of electrically conductive wire with a polymer material that electrically islanded the individual turns of the material in wire form together with the aid of a thermally curable epoxy resin composition, which composition is solid at room temperature and comprises the following constituents: (a) an epoxy resin that is solid at room temperature, selected from (a) ) polyglycidyl ethers based on novolacs; (a2) diglycidyl ethers based on biphenols, and (a3) mixtures of more than one of the components (a1) and (a2); (b) an interlacing agent for component (a); (c) an accelerator suitable for the reaction of component (a) and component (b); (d) from 15 to 70 weight percent, based on the overall weight of the composition, of filler selected from (d1) calcium carbonate, (d2) fluorine from quartz, (d3) wollastonite whose particles have a average ratio of length to cross section that is less than 5: 1; (d4) mixtures of the components (d1), (d2) and (d3) and (d5) mixtures of the components (d1), (d2), (d3) and (d4) with other inorganic fillers; and also (e) from 10 to 60 weight percent, based on the overall weight of the composition, of inorganic reinforcements in the form of needle-like or fibrillary particles with a length of 0.05 to 2.5 mm having an average length ratio. at a cross section of 5: 1 or more, the overall amount of components (d) and (e) being no more than 80 weight percent, based on the overall weight of the composition, inter alia eliminates the need for use sacrificial molds and reduce by a multiple the healing time required to complete the coating of the coils, reducing it to the region of a few minutes.