Vinyl ester resin composition and method for producing electrical appliance insulator using same

Abstract

Provided is a vinyl ester resin composition comprising a vinyl ester resin (A), a reactive diluent (B) including styrene and / or a (meth)acrylate having an alicyclic structure, an unsaturated polyester resin (C), and a metal soap (D). This vinyl ester resin composition is used in combination with a hardener (E) which initiates a redox reaction when used in combination with the metal soap (D).

Description

Vinyl ester resin composition and method for producing electrical insulation using the same

[0001] An embodiment of the present invention relates to a vinyl ester resin composition. More specifically, an embodiment of the present invention relates to a vinyl ester resin composition that can be suitably used for insulating electrical equipment such as generators, motors such as induction coils, transformers, and coils for electrical equipment such as armatures (rotors) and stators (fixed parts). Another embodiment of the present invention relates to a method for producing an electrical equipment insulator using the vinyl ester resin composition of the above embodiment.

[0002] Conventionally, in electrical equipment equipped with coils, such as rotating machines and transformers, treatments have been carried out in which the coils are impregnated with varnish for purposes such as adhesion, insulation reinforcement, vibration prevention, and rust prevention. The varnishes used in such treatments are generally called coil impregnation varnishes or impregnation varnishes (hereinafter sometimes abbreviated to varnish). The coil impregnation varnishes are broadly divided into two types: solvent-based varnishes and solventless varnishes, and an appropriate type is selected depending on the type of electrical equipment, the treatment method, etc.

[0003] The above-mentioned solvent-based varnishes are prepared, for example, by dissolving an alkyd resin in a solvent such as naphtha, and have the problem of large amounts of solvent scattering during the heat curing treatment of the varnish. On the other hand, the above-mentioned solventless varnishes are generally prepared by dissolving a resin having an unsaturated group in a reactive diluent. Since a reactive monomer is used as the reactive diluent, solventless varnishes have the advantage that large amounts of solvent scattering do not occur during the heat curing treatment, as occurs with solvent-based varnishes. In addition, in recent years, there has been an increasing demand for a switch from solvent-based varnishes to solventless varnishes due to reasons such as high workability (shorter processing time), resource conservation, and rust prevention performance.

[0004] Furthermore, in recent years, from the viewpoint of carbon neutrality, there has been a demand for a reduction in energy consumption during work, and there is a demand for the development of varnishes that consume less energy to obtain the final cured product. Typically, when using impregnating varnish, a preheating process is performed to allow the varnish to penetrate between the windings of the coil, and a thermal curing process is performed to cure the varnish. Thus, in order to insulate a coil with impregnating varnish, heating is required for each process, resulting in a large amount of energy consumption. Therefore, from the viewpoint of reducing energy consumption, there is a need for a solvent-free varnish that has excellent impregnation properties, can be cured at low temperatures in a short time, and has excellent surface drying properties.

[0005] In response to this, various studies have been conducted to realize a solventless varnish that can be cured at low temperatures in a short time. For example, Patent Document 1 discloses a room-temperature-curable unsaturated resin composition containing an unsaturated resin, a polymerizable unsaturated monomer, and a low-profile agent, wherein the unsaturated resin is an unsaturated ester derived from dicyclopentadiene, the polymerizable unsaturated monomer is styrene, the content of the polymerizable unsaturated monomer in the resin composition is 40 to 60 mass%, and the low-profile agent contains a styrene-acrylic random copolymer, and the number-average molecular weight of the copolymer is 1,000 to less than 15,000.

[0006] Japanese Patent Application Laid-Open No. 2007-84701

[0007] As described above, from the viewpoint of reducing energy consumption while maintaining the required properties of an impregnating varnish, there is a need for a solventless varnish that has excellent impregnation properties, can be cured at low temperatures in a short time, and has excellent surface drying properties. However, it is difficult to achieve fully satisfactory surface drying properties with conventional resin compositions, and further improvements are desired. Therefore, an embodiment of the present invention provides a resin composition that has excellent surface drying properties and can be suitably used for electrical insulation applications such as impregnating varnishes. Furthermore, another embodiment of the present invention provides a method for producing an electrical device insulator using the resin composition of the above embodiment.

[0008] Varnishes containing vinyl ester resins are known as an example of solventless varnishes. Varnishes containing vinyl ester resins contain a vinyl ester resin and a crosslinkable monomer, and are excellent in various mechanical, electrical, and thermal properties, while also providing a good balance in terms of workability and economy. Therefore, they are suitable for a wide range of applications, including construction materials such as fiber-reinforced plastic (FRP) laminates and linings. From this perspective, the present inventors conducted extensive research into the curing and surface drying properties of varnishes containing vinyl ester resins, leading to the completion of the present invention.

[0009] That is, the present invention includes the embodiments described below. However, the present invention is not limited to the embodiments below and includes various embodiments. <1> A vinyl ester resin composition comprising a vinyl ester resin (A), a reactive diluent (B) containing at least one of a (meth)acrylate having an alicyclic structure and styrene, an unsaturated polyester resin (C), and a metal soap (D), and used in combination with a curing agent (E) that initiates a redox reaction in combination with the metal soap (D). <2> The vinyl ester resin composition according to <1> above, further containing a curing agent (E) that initiates a redox reaction in combination with the metal soap (D). <3> The vinyl ester resin composition according to <1> or <2> above, which is a two-component composition consisting of a first component and a second component, wherein the first component comprises a vinyl ester resin (A), a reactive diluent (B) containing at least one of a (meth)acrylate having an alicyclic structure and styrene, an unsaturated polyester resin (C), and a metal soap (D), and the second component comprises a curing agent (E) that initiates a redox reaction in combination with the metal soap (D). <4> The vinyl ester resin composition according to any one of <1> to <3> above, wherein the vinyl ester resin (A) has a number-average molecular weight in the range of 1,000 to 10,000. <5> The vinyl ester resin composition according to any one of <1> to <4> above, wherein the reactive diluent (B) contains at least a (meth)acrylate having an alicyclic structure, and the (meth)acrylate having an alicyclic structure includes dicyclopentenyloxyethyl (meth)acrylate. <6> The vinyl ester resin composition according to any one of <1> to <5> above, wherein the unsaturated polyester resin (C) comprises an unsaturated polyester resin (C1) having a dicyclopentadiene structure. <7> The vinyl ester resin composition according to any one of <1> to <6> above, wherein the metal soap (D) comprises at least one selected from the group consisting of organic acid cobalt salts and organic acid manganese salts. <8> The vinyl ester resin composition according to any one of <1> to <7> above, wherein the curing agent (E) comprises a hydroperoxide.<9> The vinyl ester resin composition according to any one of <2> to <8> above, which is used for imparting insulation to a component constituting an electric device. <10> The vinyl ester resin composition according to any one of <2> to <8> above, which is used for impregnating a coil for an electric device. <11> A method for producing an electric device, comprising: applying the vinyl ester resin composition according to any one of <2> to <8> above to at least one component constituting the electric device to form a coating film; and curing the coating film to form a cured coating film. <12> A method for producing a coil for an electric device, comprising: impregnating a coil for an electric device with the vinyl ester resin composition according to any one of <2> to <8> above; and curing the vinyl ester resin composition impregnated into the coil for an electric device.

[0010] According to one embodiment of the present invention, a vinyl ester resin composition having excellent surface drying properties and suitable for use in electrical insulation applications can be provided. In addition, another embodiment of the present invention can provide a method for producing an electrical insulator that uses the resin composition of the above embodiment and that allows for reduced energy consumption.

[0011] Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit of a certain numerical range may be replaced with the upper or lower limit of another numerical range. Furthermore, the upper or lower limit of a numerical range described in this disclosure may be replaced with a value shown in an example.

[0012] In this specification, unless otherwise specified, each component may contain one or more corresponding substances. In this specification, when a resin composition contains a plurality of substances corresponding to each component, the content of each component in the resin composition means the total amount of the plurality of substances present in the resin composition, unless otherwise specified.

[0013] In this specification, "(meth)acrylic acid" means at least one of "acrylic acid" and its corresponding "methacrylic acid." The same applies to other similar expressions such as (meth)acrylate.

[0014] One embodiment of the present invention relates to a vinyl ester resin composition (hereinafter also referred to as a resin composition) that includes a vinyl ester resin (A), a reactive diluent (B) containing at least one of a (meth)acrylate having an alicyclic structure and styrene, an unsaturated polyester resin (C), and a metal soap (D), and is used in combination with a curing agent (E) that initiates a redox reaction in combination with the metal soap (D).

[0015] The components of the vinyl ester resin composition will be specifically described below. [Vinyl ester resin (A)] Vinyl ester resin (A) is a resin obtained by reacting an epoxy compound having two or more epoxy groups with an acid component containing an unsaturated dibasic acid having one or more unsaturated groups, and, if necessary, a modifying component. A ring-opening reaction between the epoxy group in the epoxy compound and the carboxyl group in the acid component forms a compound containing an unsaturated bond (vinyl bond) and an ester bond in the molecule.

[0016] The epoxy compound may be a compound known as a solid epoxy resin or a liquid epoxy resin. The acid component includes at least the unsaturated dibasic acid. Specific examples of the unsaturated dibasic acid include maleic anhydride, maleic acid, and fumaric acid. These may be used alone or in combination of two or more.

[0017] In addition to the unsaturated dibasic acids, the acidic components may include saturated acids and lower alkyl monoesters and diesters of the saturated acids. Examples of saturated acids include saturated dibasic acids such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, tetrahydrophthalic acid, hexahydrophthalic anhydride, hexahydrophthalic acid, adipic acid, and sebacic acid. Examples of lower alkyl monoesters of saturated acids include lower alkyl monoesters of terephthalic acid. Specific examples include monomethyl terephthalate. Examples of lower alkyl diesters of saturated acids include lower alkyl diesters of terephthalic acid. Specific examples include dimethyl terephthalate.

[0018] In one embodiment, the number average molecular weight (Mn) of the vinyl ester resin (A) may be 1,000 to 10,000. Mn may preferably be 1,500 to 5,000. Adjusting Mn to 1,000 or more can prevent the curability of the resin composition and the properties of the cured resin from being significantly reduced. Adjusting Mn to 10,000 or less can prevent the viscosity of the resin composition from becoming too high, resulting in a reduction in impregnation workability. Here, Mn is a value measured by gel permeation chromatography and converted using a standard polystyrene calibration curve. The same applies to the following description.

[0019] The method for producing the vinyl ester resin (A) is not particularly limited, and conventionally known synthesis methods can be applied. For example, the vinyl ester resin (A) can be obtained by carrying out a ring-opening reaction using at least an epoxy component containing an epoxy resin and an acid component containing one or more unsaturated dibasic acids. It is preferable to use 1 to 2 equivalents of the epoxy component (total amount) relative to 1 equivalent (based on the total amount of the acid component).

[0020] In the production of the vinyl ester resin (A), the reaction temperature for carrying out the synthesis reaction is preferably 100 to 130°C. For this reason, the reaction apparatus is preferably made of glass, stainless steel, or the like. The reaction apparatus is also preferably equipped with a stirrer, a reflux device for preventing the volatilization of the acid component, a heating device for increasing the temperature of the reaction system, a temperature control device for the heating device, and the like.

[0021] [Reactive Diluent (B)] The reactive diluent (B) constituting the vinyl ester resin composition of this embodiment is a compound containing at least one unsaturated group (however, the unsaturated polyester resin (C) described below is not included). The reactive diluent (B) is preferably capable of dissolving at least the vinyl ester resin (A) described above and the unsaturated polyester resin (C) described below. The reactive diluent (B) preferably contains at least one of a (meth)acrylate (B1) having an alicyclic structure and styrene (B2).

[0022] In one embodiment, from the viewpoint of easily constructing a low-odor resin composition, the reactive diluent (B) is preferably a compound having a vapor pressure of 0.1 mmHg or less at 20° C. From this viewpoint, in one embodiment, the reactive diluent (B) preferably includes at least a (meth)acrylate (B1) having an alicyclic structure.

[0023] In one embodiment, the reactive diluent (B) preferably contains a (meth)acrylate (B1) having an alicyclic structure and does not contain styrene (B2). When the (meth)acrylate (B1) having an alicyclic structure is used as the reactive diluent (B), a low-odor resin composition can be easily provided. The (meth)acrylate (B1) having an alicyclic structure refers to a compound having a structure in which the hydrogen atom of the carboxy group in (meth)acrylic acid is substituted with an organic group having an alicyclic structure.

[0024] In one embodiment, the compound may have a structure in which an alicyclic structure is directly bonded to an oxygen atom of a carboxyl group residue (-C(=O)O). In another embodiment, the compound may have a structure in which an alicyclic structure is bonded to an acid atom of a carboxyl group residue via a linking group. The linking group may be a divalent organic group, such as an alkylene group, an ether group, or a combination thereof. Specific examples of the linking group include a methylene group, an ethylene group, an ether group, an oxymethylene group, and an oxyethylene group.

[0025] The organic group having an alicyclic structure may be a single ring, may contain two or more rings, or may contain two or more fused rings. The alicyclic structure may also contain an unsaturated bond within the ring structure. The alicyclic structure may also contain a crosslinked structure. The organic group having an alicyclic structure preferably contains two or more rings. Specific examples of organic groups having an alicyclic structure include dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, and polyethylene glycol acrylate.

[0026] Specific examples of the (meth)acrylate (B1) having an alicyclic structure include dicyclopentanyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, phenol ethylene oxide-modified (meth)acrylate, and EO-modified bisphenol A dimethacrylate. Among these, dicyclopentenyloxyethyl (meth)acrylate is particularly preferred.

[0027] In one embodiment, the reactive diluent (B) may further include a compound (B3) containing at least one unsaturated group having a structure different from those of the above (B1) and (B2). From the viewpoint of obtaining a low-odor resin composition, the compound (B3) may be a (meth)acrylate other than the above (B1) having a vapor pressure of 0.1 mmHg (20°C) or less.

[0028] Examples include modified (meth)acrylates such as trimethylpropane EO-modified triacrylate and phenol ethylene oxide-modified (meth)acrylate. Also, (meth)acrylates having a hydroxyl group can be used. Examples include 2-hydroxyethyl methacrylate and (poly)caprolactone monoethoxy (meth)acrylates such as "Placcel" FA1, FA2D, FA3, FM1D, FM2D, and FM3, available from Daicel Corporation. Furthermore, unsaturated monobasic acids, which are reaction products of monofunctional (meth)acrylates having one hydroxyl group in the molecule with saturated dibasic acids, can also be used. These may be used alone or in combination of two or more.

[0029] In one embodiment, the reactive diluent (B) may be a combination of the above (B1) and (B3), or a combination of the above (B2) and (B3). The above (B3) preferably includes trimethylpropane EO-modified triacrylate.

[0030] The content of the reactive diluent (B) having one or more unsaturated groups in the molecule is preferably in the range of 50 to 400 parts by weight per 100 parts by weight of the vinyl ester resin (A). When the content of the reactive diluent (B) is 50 parts by weight or more, the viscosity of the resulting resin composition is too high, which can easily prevent problems such as thick adhesion to the transformer surface and reduced internal penetration. Furthermore, when the content of the reactive diluent (B) is adjusted to 400 parts by weight or less, the cloudiness of the resin composition can be easily prevented. Furthermore, problems such as resin deposits that have penetrated the interior flowing out during heat curing due to a varnish viscosity that is too low can be easily prevented. The content of the reactive diluent (B) refers to the total amount of the above-mentioned (B1) and (B2), and the optional (B3). In some embodiments, the content of the reactive diluent (B) per 100 parts by weight of the vinyl ester resin (A) may be 60 parts by weight or more, 70 parts by weight or more, 80 parts by weight or more, or 90 parts by weight or more. The content of the reactive diluent (B) may be 300 parts by mass or less, 250 parts by mass or less, 200 parts by mass or less, or 150 parts by mass or less. In some embodiments, the content of the reactive diluent (B) is preferably in the range of 90 to 150 parts by mass per 100 parts by mass of the vinyl ester resin (A).

[0031] [Unsaturated Polyester Resin (C)] The unsaturated polyester resin (C) may be a resin obtained by reacting at least an α,β-unsaturated dibasic acid and an alcohol component having one or more hydroxyl groups. The unsaturated polyester resin (C) may be a resin obtained by reacting an acid component containing an α,β-unsaturated dibasic acid, an alcohol component having one or more hydroxyl groups, and, if necessary, a modified component.

[0032] In the production of the unsaturated polyester resin (C), at least an unsaturated dibasic acid is used as the acid component. Examples of the unsaturated dibasic acid include maleic anhydride, maleic acid, and fumaric acid. These may be used alone or in combination of two or more.

[0033] In addition to the unsaturated dibasic acids, the acid component may further include saturated acids and monoesters and diesters of lower alkyl groups of these saturated acids. Examples of saturated acids include saturated dibasic acids such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic anhydride, tetrahydrophthalic acid, hexahydrophthalic anhydride, hexahydrophthalic acid, adipic acid, and sebacic acid. Examples of lower alkyl monoesters of saturated acids include lower alkyl monoesters of terephthalic acid. Specific examples include monomethyl terephthalate. Examples of lower alkyl diesters of saturated acids include lower alkyl diesters of terephthalic acid. Specific examples include dimethyl terephthalate. Furthermore, edible oil fatty acids such as soybean oil fatty acids, linseed oil fatty acids, and tall oil fatty acids can also be used in combination. The amount of unsaturated acid is preferably selected within the range of 50 to 90 equivalent percent of the total acid component.

[0034] On the other hand, examples of alcohol components include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,3-butanediol, neopentyl glycol, glycerin, trimethylolpropane, pentaerythritol, etc. These may be used alone or in combination of two or more. Examples of modifying components that may be used as needed include linseed oil, soybean oil, tall oil, dehydrated castor oil, coconut oil, dicyclopentadiene, cyclopentadiene, etc.

[0035] The unsaturated polyester resin (C) used in the present invention can be produced by a conventionally known method. For example, the essential components, an α,β-unsaturated dibasic acid and an alcohol having one or more hydroxyl groups, are subjected to a condensation reaction alone, or a polybasic acid component and a polyhydric alcohol component are also used in combination. The production of the unsaturated polyester resin (C) is carried out while removing the condensed water generated during the condensation reaction from the system. It is preferable to use 1 to 2 equivalents of total alcohol components per equivalent of total acid components.

[0036] The method for removing the condensed water from the system can be preferably natural distillation by passing an inert gas through the system or distillation under reduced pressure. To promote the distillation of the condensed water, a solvent such as toluene or xylene can be added to the system as an azeotropic component. The progress of the reaction can generally be determined by measuring the amount of distillate produced by the reaction, quantifying the terminal functional groups, measuring the viscosity of the reaction system, etc.

[0037] The reaction temperature for carrying out the synthesis reaction is preferably 150 to 250°C. For this reason, a reaction apparatus made of glass, stainless steel, or the like is selected. It is preferable to use a reaction apparatus equipped with a stirrer, a fractional distillation device for preventing the distillation of the alcohol component due to the azeotropy of water and the alcohol component, a heating device for increasing the temperature of the reaction system, a temperature control device for this heating device, etc.

[0038] The pressure inside the reactor can be adjusted to carry out the polycondensation reaction in the synthesis. There are no particular restrictions on the pressure inside the reactor, and the reaction can proceed without any problems even at normal pressure. When pressurized, the reaction can be promoted by increasing the boiling point of the polyhydric alcohol. It is preferable to carry out the reaction by adjusting the pressure inside the reactor to a range of normal pressure to 0.1 MPa.

[0039] The number average molecular weight (Mn) of the unsaturated polyester resin (C) may be 1,000 to 10,000. Preferably, it is 1,500 to 5,000. When Mn is adjusted to 1,000 or more, it is possible to prevent a drastic decrease in the curability of the resin composition and the properties of the cured resin. When Mn is adjusted to 10,000 or less, it is possible to prevent the viscosity from becoming too high and the impregnation workability from deteriorating. The above Mn is a value measured by gel permeation chromatography and converted using a standard polystyrene calibration curve. The same applies to the Mn described below.

[0040] In the vinyl ester resin composition of this embodiment, the unsaturated polyester resin (C) includes at least an unsaturated polyester resin (C1) having a dicyclopentadiene structure (skeleton). The use of (C1) can easily improve surface drying properties. The unsaturated polyester resin (C1) having a dicyclopentadiene structure can be produced, for example, by using an alcohol modified with dicyclopentadiene within the range of an unsaturated dibasic acid and an alcohol having one or more hydroxyl groups. In one embodiment, the unsaturated polyester resin (C1) may be a compound obtained by charging cyclopentadiene (100 parts), maleic anhydride (70 parts), diethylene glycol (100 parts), and ethylene glycol (10 parts) and conducting a condensation reaction under heating. The amounts of each component charged are not limited to those described above and can be adjusted as appropriate.

[0041] In one embodiment, the unsaturated polyester resin (C) may further include an unsaturated polyester resin (C2) having a structure different from the unsaturated polyester resin (C1) having a dicyclopentadiene structure. The unsaturated polyester resin (C2) is not particularly limited as long as it does not contain a dicyclopentadiene structure.

[0042] The content of the unsaturated polyester resin (C) is preferably in the range of 10 to 80 parts by mass per 100 parts by mass of the vinyl ester resin (A). The content of the unsaturated polyester resin (C) is more preferably in the range of 15 to 70 parts by mass, even more preferably in the range of 20 to 60 parts by mass, and particularly preferably in the range of 20 to 50 parts by mass. When the content of the unsaturated polyester resin (C) is adjusted to 10 parts by mass or more, surface drying properties can be easily improved. Furthermore, when the content of the unsaturated polyester resin (C) is adjusted to 80 parts by mass or less, deterioration in viscosity and curability, and deterioration in impregnation workability can be suppressed.

[0043] The content of the unsaturated polyester resin (C) refers to the total amount of the (C1) and the (C2) used as needed. In one embodiment, the proportion of the (C1) in the total mass of the unsaturated polyester resin (C) may be preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. In one embodiment, the proportion of the (C1) in the total mass of the (C) is preferably 100% by mass.

[0044] [Metal Soap (D)] The metal soap (D) may be a metal salt of an organic acid. Examples of the organic acid include fatty acids such as acetic acid, octylic acid, and stearic acid, and naphthenic acid. The metal in the metal salt may be Mg, Ca, Zn, Al, V, Cr, Mn, Fe, Co, Ni, Pb, Cu, and Zr. The metal soap (D) may be used alone or in combination of two or more. In one embodiment, the metal soap (D) preferably contains either an organic acid cobalt salt or an organic acid manganese salt. In one embodiment, the metal soap (D) more preferably contains at least an organic acid cobalt salt, and even more preferably contains an organic acid manganese salt. In some embodiments, cobalt octylate and / or manganese octylate can be suitably used. In some embodiments, it is preferable to use an organic acid manganese salt alone, and manganese octylate is particularly preferred.

[0045] The amount of metal soap (D) used may be 0.01 to 3.0 parts by mass per 100 parts by mass of the total amount of vinyl ester resin (A) and reactive diluent (B). The amount of metal soap (D) used is preferably 0.05 to 2.5 parts by mass, more preferably 0.07 to 2 parts by mass. If the amount used is less than 0.01 parts by mass, the redox reaction in combination with the curing agent (E), described below, tends to proceed slowly, resulting in reduced curability. Furthermore, if the amount used exceeds 3.0 parts by mass, curability is not promoted and the hue of the resulting cured coating film may become darker. In some embodiments, the amount of metal soap (D) used may be 0.08 or more, 0.09 or more, 0.1 or more, 0.4 or more, or 0.5 or more, and may be 1.6 or less, 1.5 or less, or 1.0 or less, in parts by mass.

[0046] [Curing Agent (E)] The curing agent (E) may be a compound that initiates a redox reaction in combination with the metal soap (D). Examples of the curing agent (E) include organic peroxides such as percarbonates, alkyl peresters, diacyl peroxides, and hydroperoxides. Specific examples are as follows:

[0047] Examples of percarbonates include methyl ethyl ketone peroxide, acetylacetone peroxide, cumene hydroperoxide, tert-butylperoxy 3,5,5-trimethylhexanoate, tert-butylperoxydiisopropylcarbonate, tert-butylperoxybenzoate, benzoyl peroxide, cumyl hydroperoxide, bis(4-tert-butylcyclohexyl)peroxydicarbonate, di-2-methoxyethyl peroxydicarbonate, di-3-methoxybutyl peroxydicarbonate, di-2-methylhexyl peroxydicarbonate, and di-isopropyl peroxydicarbonate.

[0048] Examples of alkyl peresters include 1,1,3,3-tetramethylbutyl peroxyneodecanoate, α-cumene peroxyneodecanoate, tert-butyl peroxyneodecanoate, tert-hexyl peroxyneodecanoate, tert-butyl peroxypivalate, tert-hexyl peroxypivalate, 1,1,3,3-tetramethylbutyl peroxydi-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxyisobutyrate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, and tert-amylperoxy 2-ethylhexanoate.

[0049] Examples of diacyl peroxides include isobutyroyl peroxide, bis-3,5,5-trimethylhexanoyl peroxide, lauroyl peroxide, etc. Examples of hydroperoxides include cumyl hydroperoxide, p-isopropylcumyl hydroperoxide, t-butyl hydroperoxide (TBH), methyl ethyl ketone hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, cyclohexane hydroperoxide, etc.

[0050] These organic peroxides may be used alone or in combination of two or more. In one embodiment, the curing agent (E) preferably contains a hydroperoxide capable of initiating a curing reaction at a temperature of 80°C or less, more preferably 60°C or less. For example, cumyl hydroperoxide can be suitably used. In some embodiments, the curing agent (E) preferably contains lauroyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane, and such a combination of curing agents is preferred in that it tends to easily increase the penetration and pot life of the resin composition.

[0051] The amount of curing agent (E) used, which initiates a redox reaction in combination with the metal soap (D), may be 0.01 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, 0.9 parts by weight or more, or 1 part by weight or more, per 1 part by weight of the metal soap (D). The amount of curing agent (E) used may be 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less, per 1 part by weight of the metal soap (D). In some embodiments, the amount of curing agent (E) used may be 0.01 to 3.0 parts by weight, preferably 0.01 to 2.0 parts by weight, more preferably 0.1 to 1.5 parts by weight, and even more preferably 0.2 to 1.0 parts by weight, per 1 part by weight of the metal soap (D). Adjusting the amount of curing agent (E) used within the above range tends to promote the redox reaction and easily obtain excellent curability. Furthermore, it tends to easily prevent the occurrence of problems such as reduced adhesive strength with the resulting cured portion.

[0052] [Polymerization Inhibitor] In one embodiment, the vinyl ester resin composition may further contain a polymerization inhibitor as needed. Specific examples of polymerization inhibitors include p-benzoquinone, hydroquinone, naphthoquinone, p-toluquinone, 2,5-diphenyl-p-benzoquinone, 2,5-diacetoxy-p-benzoquinone, p-tert-butylcatechol, 2,5-di-tert-butylhydroquinone, di-tert-butyl-p-cresol, hydroquinone monomethyl ether, and 2,6-di-tert-butyl-4-methylphenol. The amount of the polymerization inhibitor can be determined appropriately depending on the curability of the resulting vinyl ester resin composition. For example, the amount of the polymerization inhibitor (G) is preferably 0.01 to 5.0 parts by mass, more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the vinyl ester resin composition.

[0053] [Other Additives] Various additives may be added to the vinyl ester resin composition of this embodiment, as needed, taking into consideration the desired properties. The various additives may be known compounds, and commercially available products can be used. For example, it is preferable to add various additives that have an air-blocking effect on the surface of the cured product. By incorporating such additives, the surface curing (surface drying) time can be shortened. Examples of additives that can be used to shorten the surface curing time include paraffin waxes with various melting points and low-volatility agents such as BYK-S740 and BYK-S750 (manufactured by BYK Japan Co., Ltd.). The amount of waxes to be incorporated may be 0.05 to 1 part by mass, preferably 0.1 to 0.5 parts by mass, per 100 parts by mass of the vinyl ester resin composition.

[0054] The vinyl ester resin composition of the above embodiment includes the vinyl ester resin (A), a reactive diluent (B) containing at least one of a (meth)acrylate having an alicyclic structure and styrene, an unsaturated polyester resin (C), and a metal soap (D), and when used, is used in combination with a curing agent (E) that initiates a redox reaction in combination with the metal soap (D). From this perspective, in one embodiment, the vinyl ester resin composition may include the curing agent (E) in addition to the vinyl ester resin (A), the reactive diluent (B), the unsaturated polyester resin (C), and the metal soap (D).

[0055] In another embodiment, the vinyl ester resin composition may be a two-component composition consisting of a first liquid and a second liquid, wherein the first liquid contains a vinyl ester resin (A), a reactive diluent (B) containing at least one of a (meth)acrylate having an alicyclic structure and styrene, an unsaturated polyester resin (C), and a metal soap (D), and the second liquid contains a curing agent (E) that initiates a redox reaction in combination with the metal soap (D).

[0056] The vinyl ester resin composition of the present embodiment can be cured at low temperatures in a short time (for example, at 60°C or less and within 20 minutes), and also has excellent surface drying properties, so that it can be suitably used as a varnish for insulating electrical equipment such as transformers and motors.

[0057] <Method for manufacturing electrical equipment> The vinyl ester resin composition of the above embodiment can be suitably used to impart insulation to components constituting electrical equipment (insulation treatment). Known methods can be used for the insulation treatment. The vinyl ester resin composition of the present embodiment can be cured at low temperature in a short time and has excellent surface drying properties, which enables improved workability and reduced energy consumption. From this perspective, as one embodiment of the present invention, there can be provided a method for manufacturing an electrical equipment using the vinyl ester resin composition of the above embodiment. For example, there can be provided a method for manufacturing a coil for an electrical equipment, in which the coil for an electrical equipment is impregnated (insulated) using the vinyl ester resin composition.

[0058] In one embodiment, a method for producing an electric device includes applying the vinyl ester resin composition of the above embodiment to at least one component constituting an electric device to form a coating film, and curing the coating film to form a cured coating film. Another embodiment is a method for producing a coil for an electric device, including impregnating a coil for an electric device with the vinyl ester resin composition of the above embodiment, and curing the vinyl ester resin composition impregnated into the coil for an electric device.

[0059] In the above-described manufacturing method, the application (supply) of the vinyl ester resin composition to the electrical device is preferably carried out, for example, by dripping the vinyl ester resin composition onto the electrical device or by immersing the electrical device in the vinyl ester resin composition for 2 to 20 minutes. The vinyl ester resin composition applied (supplied) to the electrical device is cured by heating after removing the electrical device if the electrical device has been immersed first. Heating during curing is preferably carried out at room temperature (approximately 25°C) for 1 to 3 hours or at 60°C for 0.5 hours (preferably 1 hour). Alternatively, the electrical device, such as a coil, may be preheated to allow the resin composition to penetrate, and the resulting thermal residue may be used to cure the resin composition.

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples and various modifications are possible. In the following, "parts" means "parts by mass" unless otherwise specified.

[0061] The number average molecular weight (Mn) and acid value described below were measured as follows. (Method for measuring number average molecular weight (Mn)) By gel permeation chromatography (GPC), conversion was performed from a calibration curve using standard polystyrene. The calibration curve was approximated by a cubic equation using standard polystyrene: TSKstandard POLYSTYRENE (Types: A-2500, A-5000, F-1, F-2, F-4, F-10, F-20, F-40) [manufactured by Tosoh Corporation, trade name]. The GPC measurement conditions are shown below. (Apparatus) Pump: L-6200 type (Hitachi High-Technologies Corporation) Detector: L-3300 type RI (Hitachi High-Technologies Corporation) Column oven: L-655A-52 (Hitachi High-Technologies Corporation) Column: Guard column; TSK Guard column HHR-L + column; TSKgel G4000HHR + TSKgel G2000HHR (all product names manufactured by Tosoh Corporation) Column size: 6.0 x 40 mm (guard column), 7.8 x 300 mm (measurement conditions) Eluent: tetrahydrofuran Sample concentration: 30 mg / 5 mL Injection volume: 20 μL Flow rate: 1.00 mL / min Measurement temperature: 40°C

[0062] (Method for Measuring Acid Value) The acid value was measured by the neutralization titration method based on JIS K0070 as shown below. 1 g of the polymer to be measured was precisely weighed, and then 30 g of acetone was added to the polymer and the polymer was uniformly dissolved. Next, an appropriate amount of phenolphthalein as an indicator was added to the solution, and titration was performed using a 0.1 N KOH aqueous solution. The acid value was then calculated using the following formula: Acid value = 0.1 × Vf × 56.1 / (Wp × I / 100) In the formula, Vf represents the titration amount (mL) of the KOH aqueous solution, Wp represents the mass (g) of the measured resin solution, and I represents the proportion (mass%) of non-volatile content in the measured resin solution.

[0063] <Synthesis of Raw Materials> (Synthesis Example 1) Synthesis of Vinyl Ester Resin (A) Into a 3-liter flask equipped with a thermometer, a nitrogen inlet tube, a rectification column, and a stirrer, 100 parts (0.47 mol) of epoxy resin, 20 parts (0.55 mol) of methacrylic acid, 0.03 parts (0.07 mol) of maleic anhydride, 0.004 parts (0.01 mol) of ammonium tetrachloride, and 0.0002 parts (0.002 mol) of hydroquinone were placed, and a thermal condensation reaction was carried out for 6 hours at 110° C. In this way, a vinyl ester resin (A-1) having a weight average molecular weight of 3,000 and an acid value of 18.0 mgKOH / g was obtained.

[0064] Synthesis Example 2: Synthesis of unsaturated polyester resin (C1) having a dicyclopentadiene structure. 100 parts of dicyclopentadiene, 70 parts of maleic anhydride, 100 parts of diethylene glycol, and 10 parts of ethylene glycol were placed in a 3-liter flask equipped with a thermometer, a nitrogen inlet tube, a rectification column, and a stirrer, and heated at 210°C for 8 hours to carry out a condensation reaction. In this way, an unsaturated polyester resin (C1-1) having a weight-average molecular weight of 2,890 and an acid value of 28.5 mgKOH / g was obtained.

[0065] <I-1> Preparation of Vinyl Ester Resin Composition Example 1 Vinyl ester resin composition 1 was obtained by blending 100 parts of the vinyl ester resin (A-1) prepared in Synthesis Example 1 above with 100 parts of dicyclopentenyloxyethyl (meth)acrylate (vapor pressure at 20°C: 0.15 mHg) as the component (B1), 20 parts of trimethylpropane EO-modified triacrylate (M3130 manufactured by Kyoeisha Chemical Co., Ltd.) as the component (B3), 50 parts of the unsaturated polyester resin (C1-1) having a dicyclopentadiene structure prepared in Synthesis Example 2 above as the component (C), and 1.0 part of manganese octoate as the component (D). Separately, 2.0 parts of cobalt octoate (manufactured by DIC Corporation, Co-OCTOATE 6%) was prepared as component (D), and 3.0 parts of cumyl hydroperoxide (manufactured by NOF Corporation, Percumyl H-80) was prepared as component (E). These were added to and mixed with the previously prepared vinyl ester resin composition 1, to obtain vinyl ester resin composition 1-1.

[0066] Example 2 100 parts of the vinyl ester resin (A-1) prepared in Synthesis Example 1 above were blended with 100 parts of dicyclopentenyloxyethyl (meth)acrylate (vapor pressure at 20°C: 0.15 mHg) as component (B1), 20 parts of trimethylpropane EO-modified triacrylate (M3130 manufactured by Kyoeisha Chemical Co., Ltd.) as component (B3), 50 parts of the unsaturated polyester resin (C1-1) having a dicyclopentadiene structure prepared in Synthesis Example 2 above as component (C), and 1.0 part of manganese octoate and 0.1 part of cobalt octoate (Co-OCTOATE 6% manufactured by DIC Corporation) as component (D), to obtain a vinyl ester resin composition 2. Separately, 3.0 parts of cumyl hydroperoxide (Percumyl H-80 manufactured by NOF Corporation) was prepared as component (E). This was blended with the previously prepared vinyl ester resin composition 2 to obtain vinyl ester resin composition 2-1.

[0067] Example 3 100 parts of the vinyl ester resin (A-1) prepared in Synthesis Example 1 above were blended with 100 parts of dicyclopentenyloxyethyl (meth)acrylate (vapor pressure at 20°C: 0.15 mHg) as component (B1), 20 parts of trimethylpropane EO-modified triacrylate (M3130 manufactured by Kyoeisha Chemical Co., Ltd.) as component (B3), 50 parts of the unsaturated polyester resin (C1-1) having a dicyclopentadiene structure prepared in Synthesis Example 2 above as component (C), and 1.0 part of manganese octylate as component (D), to obtain vinyl ester resin composition 3. Separately, 3.0 parts of cumyl hydroperoxide (Percumyl H-80 manufactured by NOF Corporation) was prepared as component (E). This was blended with the previously prepared vinyl ester resin composition 3 to obtain vinyl ester resin composition 3-1.

[0068] Example 4 100 parts of the vinyl ester resin (A-1) prepared in Synthesis Example 1 above were blended with 100 parts of dicyclopentenyloxyethyl (meth)acrylate (vapor pressure at 20°C: 0.15 mHg) as component (B1), 20 parts of trimethylpropane EO-modified triacrylate (M3130 manufactured by Kyoeisha Chemical Co., Ltd.) as component (B3), 20 parts of the unsaturated polyester resin (C1-1) having a dicyclopentadiene structure prepared in Synthesis Example 2 above as component (C), and 1.0 part of manganese octoate and 0.1 part of cobalt octoate (Co-OCTOATE 6% manufactured by DIC Corporation) as component (D), to obtain a vinyl ester resin composition 4. Separately, 3.0 parts of cumyl hydroperoxide (Percumyl H-80 manufactured by NOF Corporation) was prepared as component (E). This was blended with the previously prepared vinyl ester resin composition 4 to obtain vinyl ester resin composition 4-1.

[0069] Example 5 100 parts of the vinyl ester resin (A-1) prepared in Synthesis Example 1 above were blended with 100 parts of dicyclopentenyloxyethyl (meth)acrylate (vapor pressure at 20°C: 0.15 mHg) as component (B1), 20 parts of trimethylpropane EO-modified triacrylate (M3130 manufactured by Kyoeisha Chemical Co., Ltd.) as component (B3), 50 parts of the unsaturated polyester resin (C1-1) having a dicyclopentadiene structure prepared in Synthesis Example 2 above as component (C), and 3.0 parts of manganese octoate and 0.1 parts of cobalt octoate (Co-OCTOATE 6% manufactured by DIC Corporation) as component (D), to obtain a vinyl ester resin composition 5. Separately, 3.0 parts of cumyl hydroperoxide (Percumyl H-80 manufactured by NOF Corporation) was prepared as component (E). This was blended with the previously prepared vinyl ester resin composition 5 to obtain vinyl ester resin composition 5-1.

[0070] Example 6 100 parts of the vinyl ester resin (A-1) prepared in Synthesis Example 1 above were blended with 100 parts of styrene (vapor pressure at 20°C: 0.15 mHg) as component (B2), 20 parts of trimethylpropane EO-modified triacrylate (M3130 manufactured by Kyoeisha Chemical Co., Ltd.) as component (B3), 50 parts of the unsaturated polyester resin (C1-1) having a dicyclopentadiene structure prepared in Synthesis Example 2 above as component (C), and 1.0 part of manganese octylate as component (D), to obtain vinyl ester resin composition 6. Separately, 3.0 parts of cumyl hydroperoxide (Percumyl H-80 manufactured by NOF Corporation) was prepared as component (E). This was blended with the previously prepared vinyl ester resin composition 6 to obtain vinyl ester resin composition 6-1.

[0071] Comparative Example 1 A vinyl ester resin composition 7 was prepared in the same manner as in Example 2, except that the component (C) was not used in the preparation of the vinyl ester resin composition 2 described in Example 2, and a vinyl ester resin composition 7-1 was also prepared.

[0072] Comparative Example 2 Vinyl ester resin composition 8 was prepared in the same manner as in Example 2, except that in the preparation of vinyl ester resin composition 2 described in Example 2, component (D) (metal soap) was not used and the blending amount of component (E) (curing agent) was changed to 1.5 parts, and vinyl ester resin composition 8-1 was obtained in the same manner as in Example 2.

[0073] <I-2> Various Evaluations of Vinyl Ester Resin Compositions The vinyl ester resin compositions 1-1 to 8-1 prepared in Examples 1 to 6 and Comparative Examples 1 and 2 were evaluated for gelation time, surface drying property, and pot life according to the methods described below. The evaluation results are shown in Table 1.

[0074] [1] Gel Time Using the vinyl ester resin compositions 1-1 to 8-1 prepared in the examples and comparative examples, the gel time at 60°C was measured by the test tube method in accordance with the method described in JIS C 2105.

[0075] [2] Surface Drying Property 1.5 g of each of the vinyl ester resin compositions 1-1 to 8-1 prepared in the Examples and Comparative Examples was placed in a metal dish having a diameter of 60 mm. The metal dish was then placed in a thermostatic chamber at 60°C, and the time until the stickiness of the surface disappeared was measured.

[0076] [3] Pot life 50 g of each of the vinyl ester resin compositions 1-1 to 8-1 prepared in the examples and comparative examples was placed in a 100 mL plastic cup. The plastic cup was then placed in a water bath at 25°C, and the time until gelation was measured.

[0077]

[0078] As can be seen from Table 1, the surface drying properties of the resin compositions (Examples 1 to 6) according to the present invention, which contain all of components (A) to (E), were such that the time until the surface no longer felt sticky was within 120 minutes at 60°C. Furthermore, the gelation time and pot life were also within practically acceptable ranges. On the other hand, the surface drying properties of Comparative Examples 1 and 2 remained sticky even after 120 minutes at 60°C, which was clearly inferior to the Examples. Therefore, evaluation of the gelation time and pot life time was not performed for Comparative Example 2. Comparative Example 1 is a resin composition that does not contain component (C), and Comparative Example 2 is a resin composition that does not contain component (D). This demonstrates that the present invention enables the improvement of surface drying properties by using a resin composition having a specific combination of components (A) to (E).

[0079] <II-1> Preparation of Vinyl Ester Resin Composition (Example 7) 100 parts of the vinyl ester resin (A-1) prepared in Synthesis Example 1 above were blended with 100 parts of dicyclopentenyloxyethyl (meth)acrylate (vapor pressure at 20°C: 0.15 mHg) as component (B1), 20 parts of trimethylpropane EO-modified triacrylate (M3130 manufactured by Kyoeisha Chemical Co., Ltd.) as component (B3), 20 parts of the unsaturated polyester resin (C1-1) having a dicyclopentadiene structure prepared in Synthesis Example 2 above as component (C) and 0.2 parts of manganese octylate as component (D) to obtain vinyl ester resin composition 9. Separately, 3.0 parts of cumyl hydroperoxide (Percumyl H-80 manufactured by NOF Corporation) was prepared as component (E). This was added to and mixed with the previously prepared vinyl ester resin composition 9 to obtain vinyl ester resin composition 9-1.

[0080] Example 8 According to the blending ratios shown in Table 2, a vinyl ester resin composition 10-1 was obtained in the same manner as in the preparation of vinyl ester resin composition 9-1 described in Example 8.

[0081] (Example 9) A vinyl ester resin composition 11-1 was obtained in the same manner as in the preparation of vinyl ester resin composition 9-1 described in Example 8, using the blending ratios shown in Table 2. Details of the compounds used as component (E) in place of cumyl hydroperoxide are as follows: Lauroyl peroxide: Product name "Laurox" manufactured by Kayaku Nouryon Co., Ltd. 1,1-bis(t-butylperoxy)cyclohexane: Product name "Trigonox 22-70E" manufactured by Kayaku Nouryon Co., Ltd.

[0082] (Example 10) A vinyl ester resin composition 12-1 was obtained in the same manner as in the preparation of vinyl ester resin composition 9-1 described in Example 8, using the blending ratios shown in Table 2. As the cobalt octoate, 0.05 parts of cobalt octoate (manufactured by DIC Corporation, Co-OCTOATE 6%) was used.

[0083] <II-2> Various Evaluations of Vinyl Ester Resin Compositions The vinyl ester resin compositions 9-1 to 12-1 prepared in Examples 7 to 10 were evaluated for gelation time, surface drying property, permeability, and pot life according to the methods described below. The evaluation results are shown in Table 2.

[0084] [1] Gel Time Using the vinyl ester resin compositions 9-1 to 13-1 prepared in Examples 7 to 11, the gel time was measured at 100°C and 80°C by the test tube method in accordance with the method described in JIS C 2105 (2019). From the viewpoint of practical use, the gel time at 100°C is preferably 20 minutes or less. At 80°C, the gel time is preferably 40 minutes or less.

[0085] [2] Surface Drying Property 1.5 g of each of the vinyl ester resin compositions 9-1 to 13-1 prepared in Examples 7 to 10 and Comparative Example 3 was placed in a metal dish having a diameter of 60 mm. The metal dish was then placed in a thermostatic chamber at 80°C, and the time until the surface became no longer sticky was measured by touching with a finger every 10 minutes. From the viewpoint of practical use, the surface drying time under heating conditions at 80°C is preferably 40 minutes or less.

[0086] [3] Permeability A heat-resistant tube with a diameter of 4 mm was cut to 220 mm, and an enameled wire cut to 200 mm was filled inside (hereinafter referred to as a permeability test piece). Using vinyl ester resin compositions 9-1 to 13-1 prepared in Examples 7 to 10 and Comparative Example 3, the permeability test piece was preheated to 100°C until uniformly heated, and then 0.5 g of the resin composition was poured into the test piece from above and allowed to stand horizontally. After heating at 100°C for 20 minutes, the distance the varnish had permeated was measured visually. From the perspective of practical use, the permeation distance at 100°C is preferably 130 mm or more.

[0087] [4] Pot Life Each of the vinyl ester resin compositions 9-1 to 13-1 prepared in Examples 7 to 10 and Comparative Example 3 was placed in a clean test tube with an outer diameter of 18 mm to a height of 70 mm, and the top of the test tube was sealed with aluminum foil. The test tube was placed in a thermostatic chamber set at 40°C, and the time until gelation was measured. Note that gelation was determined when the sample reached an agar-like state or a hardened state after the start of the test. From the perspective of practical use, the pot life under heating conditions at 40°C should be at least 1 hour, and preferably at least 4 hours.

[0088]

[0089] As can be seen from the results shown in Table 2, vinyl ester resin compositions 9-1 to 12-1 each achieve surface drying properties at a practical level. Although not shown in Table 2, vinyl ester resin compositions 9-1 to 12-1 were each examined for surface drying properties under drying conditions at 60°C, and it was confirmed that all of them satisfied practical levels (drying times of 120 minutes or less). Furthermore, resin compositions 9-1 to 12-1 each achieve gelation times, surface drying properties, permeability, and pot life at practical levels. In particular, it can be seen that the vinyl ester resin composition 11-1 of Example 9 tends to easily improve permeability and pot life by using lauroyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane in combination as the curing agent (E).

Claims

1. A vinyl ester resin composition comprising a vinyl ester resin (A), a reactive diluent (B) containing at least one of a (meth)acrylate having an alicyclic structure and styrene, an unsaturated polyester resin (C), and a metal soap (D), and used in combination with a curing agent (E) that initiates a redox reaction in combination with the metal soap (D).

2. The vinyl ester resin composition according to claim 1, further comprising a curing agent (E) which initiates a redox reaction in combination with said metal soap (D).

3. The vinyl ester resin composition according to claim 2, which is configured as a two-component type consisting of a first liquid and a second liquid, the first liquid containing a vinyl ester resin (A), a reactive diluent (B) containing at least one of a (meth)acrylate having an alicyclic structure and styrene, an unsaturated polyester resin (C), and a metal soap (D), and the second liquid containing a curing agent (E) that initiates a redox reaction in combination with the metal soap (D).

4. The vinyl ester resin composition according to claim 1, wherein the number average molecular weight of the vinyl ester resin (A) is in the range of 1,000 to 10,000.

5. The vinyl ester resin composition according to claim 1, wherein the reactive diluent (B) contains at least a (meth)acrylate having an alicyclic structure, and the (meth)acrylate having an alicyclic structure includes dicyclopentenyloxyethyl (meth)acrylate.

6. The vinyl ester resin composition according to claim 1, wherein the unsaturated polyester resin (C) comprises an unsaturated polyester resin (C1) having a dicyclopentadiene structure.

7. The vinyl ester resin composition according to claim 1, wherein the metal soap (D) comprises at least one selected from the group consisting of organic acid cobalt salts and organic acid manganese salts.

8. The vinyl ester resin composition according to claim 1, wherein the curing agent (E) comprises a hydroperoxide.

9. The vinyl ester resin composition according to claim 2 or 3, which is used to impart insulating properties to parts constituting electrical equipment.

10. The vinyl ester resin composition according to claim 2 or 3, which is used for impregnating coils for electrical equipment.

11. A method for producing an electrical device, comprising: applying the vinyl ester resin composition according to any one of claims 2 to 8 to at least one component constituting the electrical device to form a coating film; and curing the coating film to form a cured coating film.

12. A method for manufacturing a coil for electric equipment, comprising: impregnating a coil for electric equipment with the vinyl ester resin composition according to any one of claims 2 to 8; and curing the vinyl ester resin composition with which the coil for electric equipment has been impregnated.

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