Electrically insulating cast molding and its manufacturing method

Abstract

A manufacturing method for an electrically insulating cast-molded product (10) by cast-molding a metal part (1) with a cast-molding material (2) containing a thermosetting resin or a thermosetting elastomer includes a first primer layer forming step, a second primer layer forming step, and a cast-molding step. In the first primer layer forming step, a first primer composition, which is a solution in which an organosilicon compound having a reactive organic functional group is uniformly dissolved in an organic solvent, is applied to the surface of the metal part to form a first primer layer (3). In the second primer layer forming step, a second primer composition, which is a solution in which a thermoplastic resin and a thermosetting resin are uniformly dissolved in an organic solvent, is applied to the first primer layer formed on the surface of the metal part to form a second primer layer (4). In the cast-molding step, the metal part on which the first primer layer and the second primer layer are formed on the surface is placed inside a mold, and the cast-molding material is cast-molded.

Description

[Technical field]

[0001] The present disclosure relates to an electrically insulating cast-molded product in which a metal part and a cast-molded material of a thermosetting resin or a thermosetting elastomer are bonded to each other via a primer layer formed at the interface between the metal part and the cast-molded material using a primer composition, and to a method for producing the same. [Background technology]

[0002] Castings for electrical insulation used in Gas Insulated Switchgear (GIS), which uses gas as an insulating medium, are exposed to the gas pressure and temperature changes in the operating environment, i.e., temperature cycles, for long periods of time. In castings in which metal parts are embedded in epoxy resin casting material, the gas pressure and the difference in linear expansion coefficient between the two repeatedly occur at the interface between the metal parts and the casting material, which reduces the adhesive strength at the interface and can cause the casting material to peel off. This peeled part becomes the starting point of partial discharge, and a discharge tree progresses into the casting material, leading to insulation breakdown.

[0003] One method to prevent this peeling is to strengthen the adhesive force between the metal part and the epoxy resin, which is the casting material. Typical specific methods for strengthening the adhesive force include forming a primer layer on the interface between the metal part and the epoxy resin, increasing the surface roughness of the metal part to utilize the anchor effect caused by the cure shrinkage of the epoxy resin, and forming a chromate film, which is a chemical conversion film, by reacting the surface of the metal part with a chromate treatment liquid.

[0004] Patent Document 1 relates to a primer agent that improves the adhesion between a casting resin and a shield electrode, and discloses the combined use of a primer coating made of an epoxy resin, which is a thermosetting resin, and a coating with a coupling agent. Patent Document 2 discloses a primer agent obtained by diluting a mixture of a bisphenol-type epoxy resin, a polyvinyl butyral resin, and a phenol resin with acetone and alcohol. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-115691 A [Patent Document 2] Japanese Patent Application Publication No. 4-348832 Summary of the Invention [Problem to be solved by the invention]

[0006] Castings for electrical insulation used in gas-insulated switchgears (GIS) that use gas as an insulating medium are exposed to changes in the pressure of the gas or the temperature of the environment in which they are used, i.e., temperature cycles, for a long period of time. In castings with embedded metal parts, stresses occur repeatedly at the interface due to the difference in linear expansion coefficient between the two, in addition to the pressure of the gas. When a primer agent made of epoxy resin, which is a thermosetting resin described in Patent Document 1, is applied to a casting with embedded metal parts, the adhesion at the interface decreases and peeling may occur due to its high elasticity and lack of toughness. This peeling portion becomes the starting point of partial discharge, and a discharge tree may progress into the epoxy resin, leading to insulation breakdown.

[0007] On the other hand, when the primer agent described in Patent Document 2 is applied to a cast product in which a metal part is embedded, the polyvinyl butyral resin has the effect of relieving the stress generated at the interface between the metal part and the cast material due to the flexibility of the butyral group, but the adhesion to the interface is greatly affected by the amount of hydroxyl groups remaining during the synthesis of the polyvinyl butyral resin. In order to achieve both stress relaxation and adhesion, the amount of butyral groups and the amount of hydroxyl groups present in the molecule are important, and if the amount of butyral groups is large and the amount of hydroxyl groups is too small, chemical adhesion cannot be obtained. Conversely, if the amount of butyral groups is small and the amount of hydroxyl groups is large, stress relaxation is small, the primer layer becomes a brittle film, and the adhesion at the interface between the metal part and the epoxy resin is not improved. In addition, if the molecular weight of the polyvinyl butyral resin is high, its solubility in organic solvents decreases, and a homogeneous primer solution is not obtained, so a coating film with a uniform thickness cannot be obtained, and the adhesion at the interface between the metal part and the epoxy resin varies. Furthermore, since polyvinyl butyral resin has low heat resistance, depending on the crosslink density between the resins when the primer layer hardens, stable adhesive strength cannot be obtained in the high-temperature environment of 80°C to 120°C in which the cast electrical insulating product is used. In particular, when the metal part generates heat while current is flowing, the stress caused by the difference in linear expansion coefficient with the cast material makes it easy for peeling to occur at the interface.

[0008] The present disclosure has been made in consideration of the above, and aims to provide a method for producing a cast molding for electrical insulation, which is capable of forming a primer layer that has high adhesion to a cast molding material of a thermosetting resin or a thermosetting elastomer even without subjecting the metal part to a surface treatment, and that suppresses the occurrence of interfacial peeling with the metal part even when the metal part is placed in a high-temperature environment of 80°C or higher and 120°C or lower. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems and achieve the object, the manufacturing method of the cast-molded product for electrical insulation according to the present disclosure is a manufacturing method of the cast-molded product for electrical insulation by cast-molding a metal part with a cast-molding material containing a thermosetting resin or a thermosetting elastomer, and includes a first primer layer forming step, a second primer layer forming step, and a cast-molding step. In the first primer layer forming step, a first primer composition, which is a solution in which an organosilicon compound having a reactive organic functional group is uniformly dissolved in an organic solvent, is applied to the surface of the metal part to form a first primer layer. In the second primer layer forming step, a second primer composition, which is a solution in which a thermoplastic resin and a thermosetting resin are uniformly dissolved in an organic solvent, is applied to the first primer layer formed on the surface of the metal part to form a second primer layer. In the cast-molding step, the metal part on which the first primer layer and the second primer layer are formed on the surface is placed inside a mold, and the cast-molding material is cast-molded. Effect of the Invention

[0010] The manufacturing method for electrically insulating cast molded products according to the present disclosure has the advantage of being able to form a primer layer that has high adhesion to a thermosetting resin or thermosetting elastomer cast molding material even without surface treatment of the metal part, and that suppresses the occurrence of interfacial peeling with the metal part even when placed in a high-temperature environment of 80°C or higher and 120°C or lower. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic example of a configuration of an electrically insulating cast molded product according to a first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrically insulating cast molded product and a method for producing the same according to embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0013] In this specification, the term "cast molding material" refers to a material that is a raw material for casting methods such as normal pressure casting, vacuum casting, and pressure gelation casting, or molding methods such as injection molding, extrusion molding, and insert molding, and is a material that can be filled into a mold and solidified to obtain a cast molded product (cast product, molded product). Casting materials generally used in casting methods are composed of thermosetting resins such as epoxy resins and phenolic resins, hardeners, fillers, and various additives (hardening accelerators, defoamers, anti-settling agents, etc.), while molding materials used in molding methods are composed of thermosetting elastomers such as silicone rubber and ethylene propylene diene rubber, hardeners (crosslinking agents, vulcanizing agents), fillers, and various additives (hardening accelerators, defoamers, anti-settling agents, plasticizers, etc.). These casting materials and molding materials are collectively referred to as cast molding materials, and the products obtained by heating and hardening, i.e., chemically changing, in a mold are called cast molding products.

[0014] Embodiment 1 FIG. 1 is a cross-sectional view showing a schematic example of the configuration of the cast-molded product for electrical insulation according to the first embodiment. The cast-molded product for electrical insulation 10 includes a metal part 1, a cast molding material 2, a first primer layer 3, and a second primer layer 4, and the metal part 1 and the cast molding material 2 are joined via the first primer layer 3 and the second primer layer 4. As shown in FIG. 1, the first primer layer 3 and the second primer layer 4 are arranged in order from the metal part 1 side between the metal part 1 and the cast molding material 2. That is, the first primer layer 3 serves as an adhesive layer that bonds the metal part 1 and the second primer layer 4, and the second primer layer 4 serves as an adhesive layer that bonds the first primer layer 3 and the cast molding material 2. The first primer layer 3 contains an organosilicon compound having a reactive organic functional group. The second primer layer 4 is arranged on the first primer layer 3 and contains a thermoplastic resin and a thermosetting resin. Examples of the cast molding material 2 include thermosetting resins such as epoxy resins and phenolic resins, and thermosetting elastomers such as silicone rubber, ethylene propylene rubber, ethylene propylene diene rubber, and urethane rubber. In particular, epoxy resins, phenolic resins, and silicone rubbers react with the functional groups of the raw materials and the functional groups of the second primer layer 4 when heated during cast molding to form crosslinks, and therefore are highly effective in chemically bonding the metal part 1 and the cast molding material 2. For this reason, epoxy resins, phenolic resins, or silicone rubbers are preferred as the main agents of the cast molding material 2.

[0015] The manufacturing method of the electrically insulating cast product 10 in the first embodiment is as follows. First, the metal part 1 machined into a predetermined shape is ultrasonically degreased using a solvent. Then, as necessary, the metal part 1 is degreased with an alkaline solution, and immersed in hydrochloric acid or sulfuric acid to remove oxide film or surface impurities. Next, the metal part 1 is washed with water to remove any liquid adhering to the metal part 1 during the machining process.

[0016] Next, a first primer composition is prepared, which is a solution in which an organosilicon compound having one or more groups selected from the group consisting of an amino group, an epoxy group, a mercapto group, a benzotriazole group, an imidazole group, and a hydroxyl group in addition to a plurality of alkoxy groups is uniformly dissolved in an organic solvent. Here, whether or not the organosilicon compound is uniformly dissolved in an organic solvent can be confirmed by visually checking whether or not the organic solvent is a transparent solution. That is, when the organic solvent is opaque to the naked eye, the organosilicon compound is in a state in which it is non-uniformly dissolved in the organic solvent, and when the organic solvent is transparent to the naked eye, the organosilicon compound is in a state in which it is uniformly dissolved in the organic solvent. The state in which the organosilicon compound is non-uniformly dissolved in the organic solvent is a state in which the organosilicon compound is not completely dissolved in the organic solvent, and in one example, a state in which the non-completely dissolved opaque organosilicon compound is present in a transparent organic solvent.

[0017] Next, a second primer composition is prepared by dissolving in an organic solvent an alkyl acetalized polyvinyl alcohol, which is a thermoplastic resin having a hydroxyl group content of 10 mol% or more and 50 mol% or less, a phenolic resin, which is a thermosetting resin, and a liquid epoxy resin, which is a bisphenol A type or bisphenol F type, which is a thermosetting resin that can make these two resins compatible at room temperature, i.e., 25°C. Here, whether or not the resin is dissolved uniformly in the organic solvent can be confirmed by visually checking whether or not the organic solvent is a transparent solution. In other words, when the organic solvent is opaque when visually observed, the resin is in a state where it is dissolved in an uneven manner in the organic solvent, and when the organic solvent is transparent when visually observed, the resin is in a state where it is dissolved in an even manner in the organic solvent. The state where the resin is dissolved in an uneven manner in the organic solvent is a state where the resin is not completely dissolved in the organic solvent, and in one example, a state where the opaque resin that is not completely dissolved is present in the transparent organic solvent.

[0018] Thereafter, the first primer composition thus produced is applied to the surface of the metal part 1 cleaned by the above method, and a first primer layer 3 is formed on the surface of the metal part 1 in a first primer layer forming step. In one example, the first primer composition is applied to the surface of the metal part 1 by brushing, spraying, dipping, or the like. The first primer layer 3 is formed by removing the solvent in the first primer composition by air drying at room temperature or by heating at a temperature in the range of 50°C to 150°C. The film thickness of the first primer layer 3 is preferably 0.01 μm to 20 μm, and more preferably 0.1 μm to 5 μm. The first primer layer 3 formed on the surface of the metal part 1 is cured when the mold for the cast molding step described later is preheated, and the first primer layer 3 obtained as a result of this heating process may be in a semi-cured state or a completely cured state. Here, from the viewpoint of improving adhesion, the metal part 1 may be sandblasted in advance before the application of the first primer composition.

[0019] Thereafter, the second primer layer forming step is carried out in which the second primer composition thus produced is applied onto the first primer layer 3 formed on the surface of the metal part 1 to form the second primer layer 4. In one example, the second primer composition is applied onto the first primer layer 3 formed on the surface of the metal part 1 by brushing, spraying, dipping, or the like. The second primer layer 4 is formed by removing the solvent in the second primer composition by air drying at room temperature or by heating at a temperature in the range of 50°C to 150°C. The film thickness of the second primer layer 4 is preferably 0.01 μm to 20 μm, more preferably 0.1 μm to 5 μm. The second primer layer 4 formed on the first primer layer 3 on the surface of the metal part 1 hardens when the mold for the subsequent casting process is preheated, but the second primer layer 4 obtained as a result of this heating process may be in a semi-cured state or a completely cured state.

[0020] Next, the metal part 1 having the first primer layer 3 and the second primer layer 4 formed on the surface in this order is placed inside a mold, and a cast molding process is performed in which the cast molding material 2 is cast. The raw material of the cast molding material 2, a thermosetting resin such as epoxy resin or phenolic resin, or a thermosetting elastomer such as silicone rubber, ethylene propylene rubber, ethylene propylene diene rubber, or urethane rubber, is injected into the mold and heated at a temperature in the range of 80°C to 200°C for a period of 10 minutes to 36 hours, thereby hardening the cast molding material 2. This is because the cast molding material 2 does not harden sufficiently when heated at a temperature below 80°C or for a period of less than 10 minutes, and the cast molding material 2 tends to deteriorate due to heat when heated at a temperature above 200°C or for a period of more than 36 hours, which is not preferable. The main agent of the cast molding material 2 is preferably an epoxy resin, a phenolic resin, or a silicone rubber, which is effective in chemically bonding the metal part 1 and the cast molding material 2, since the functional groups of the raw material react with the functional groups of the second primer layer 4 to crosslink when heated during cast molding. In this way, by forming the second primer layer 4, which is a mixture of a plurality of thermosetting resins and thermoplastic resins with different characteristics, on the surface of the metal part 1 through the first primer layer 3 in advance, the affinity with the interface of the metal part 1 is improved during the heat curing process of the cast molding material 2, and strong chemical adhesion is ensured. In this way, the cast molding product 10 for electrical insulation shown in FIG. 1 is manufactured.

[0021] The first primer composition and the second primer composition will be described in detail below.

[0022] The first primer composition will be described. The first primer composition is a solution in which an organosilicon compound having a reactive organic functional group is uniformly dissolved in an organic solvent. This organosilicon compound has one or more groups selected from the group consisting of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups, in addition to multiple alkoxy groups, and by selecting one having a reactive group capable of chemically bonding with both the metal part 1 and the second primer layer 4, strong adhesive strength can be obtained between each of them.

[0023] The organic functional group is preferably one or more groups selected from the group consisting of alkoxy groups, acrylic groups, amino groups, isocyanate groups, isocyanurate groups, imidazole groups, ureido groups, epoxy groups, vinyl groups, benzotriazole groups, mercapto groups, methacryl groups, and hydroxyl groups. In particular, an organosilicon compound having one or more groups selected from the group consisting of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups in addition to a plurality of alkoxy groups is more preferred from the viewpoint of adhesion between the second primer layer 4 and the surface of the metal part 1. Also, one or more types of organosilicon compounds can be used. Examples of the organic silicon compounds include, but are not limited to, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-2-(aminoethyl)-8-aminooctyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyl ... dimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 8-glycidoxyoctyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, N-(trimethoxysilylpropyl)-1H-benzotriazole-1-carbodiamide, triethoxy[3-(1H-imidazol-1-yl)propyl]silane, tris-(trimethoxysilylpropyl)isocyanurate, tetraethoxysilane, and the like.

[0024] The organosilicon compound is preferably added to the first primer composition in a range of 0.01% by weight to 10% by weight. This is because if the amount added is less than 0.01% by weight, there is no effect of increasing adhesive strength, and if the amount added is more than 10% by weight, the storage stability of the first primer composition is deteriorated, adhesion reproducibility is lost, and adhesive strength is reduced. It is more preferable to add the organosilicon compound in a range of 0.1% by weight to 5% by weight. By setting the amount in this range, the storage stability of the first primer composition can be ensured.

[0025] In order to further improve the curability of the first primer composition and the adhesion to the metal part 1, the first primer composition can contain an organotitanium compound having an alkoxy group in a range of 0.01 parts by weight to 20 parts by weight to 100 parts by weight of the organosilicon compound. In addition, one or more organotitanium compounds can be used. This is because, when the amount added is less than 0.01 parts by weight, there is no effect of enhancing the curability and adhesion, and when it is more than 20 parts by weight, the storage stability of the first primer composition is deteriorated, the adhesion reproducibility is lost, and the adhesive strength is reduced. In addition, from the viewpoint of achieving both the curability and the effect of improving the adhesion to the metal part 1, it is more preferable to add an organotitanium compound having one or more alkoxy groups in a range of 0.1 parts by weight to 10 parts by weight to 100 parts by weight of the organosilicon compound. Examples of organic titanium compounds include, but are not limited to, tetra-i-propoxytitanium, tetra-n-butoxytitanium, tetrakis(2-ethylhexyloxy)titanium, (2-propoxy)(2-ethylhexane-1,3-diolato)titanium, di-i-propoxy bis(acetylacetonato)titanium, and propanedioxytitanium bis(ethylacetoacetate).

[0026] The solvent of the first primer composition may be any organic solvent that dissolves the organosilicon compound, such as methyl ethyl ketone, acetone, toluene, xylene, methanol, ethanol, isopropyl alcohol, and n-hexane. In addition, as long as the organosilicon compound can be completely dissolved, one type of solvent may be used, or a combination of multiple types of solvents may be used. If the coating film of the first primer layer 3 is thick after drying, the coating film may crack or peel due to the internal stress of the first primer layer 3. As a result, the adhesive strength between the metal part 1 and the cast molding material 2 decreases. On the other hand, if the coating film is thin, the interfacial adhesive strength between the metal part 1 and the first primer layer 3 cannot be obtained. For this reason, the amount of the organic solvent is adjusted so that the coating film thickness when applied is in the range of 0.01 μm to 5 μm, more preferably 0.1 μm to 2 μm. The viscosity of the first primer composition may be changed. Furthermore, water may be added to promote hydrolysis of the alkoxy group. The amount of water to be added can be in the range of 0.01 to 10 parts by weight relative to 100 parts by weight of diluent. If the amount is less than 0.01 parts by weight, the accelerating effect is low, and if it is more than 10 parts by weight, the storage stability of the first primer composition is poor. From the viewpoint of achieving both the accelerating effect and the storage stability, it is more preferable to add water in the range of 0.1 to 5 parts by weight relative to 100 parts by weight of diluent. This makes the film thickness when applied 0.01 μm to 5 μm, more preferably 0.1 μm to 2 μm. In other words, the amount of organic solvent is adjusted or the viscosity of the first primer composition is changed so that the thickness of the film formed by one application is the desired thickness. The film thickness can also be controlled by changing the number of applications. However, if the number of applications is two or more, the number of application and drying processes increases, and it is also time-consuming to align the film when applied on the applied base film, so it is preferable to form the coating film by one application.

[0027] The first primer layer 3 thus formed by the first primer composition is, in one example, a layer containing an organosilicon compound having, in addition to a plurality of alkoxy groups, one or more groups selected from the group consisting of an amino group, an epoxy group, a mercapto group, a benzotriazole group, an imidazole group, and a hydroxyl group. In one example, the first primer layer 3 may also contain an organotitanium compound having an alkoxy group.

[0028] The second primer composition will be described. The thermosetting resin blended in the second primer composition has a group capable of bonding with the cast molding material 2, but by blending a thermoplastic resin, which is an elastic substance, toughness is imparted, and the adhesion between both the first primer layer 3 and the cast molding material 2 can be improved. The reason why two types of thermosetting resins, an epoxy resin and a phenolic resin, are blended as the thermosetting resin is that the phenolic resin reacts with both the epoxy resin and the alkyl acetalized polyvinyl alcohol resin, and can harden the second primer composition. The phenolic resin and the alkyl acetalized polyvinyl alcohol resin are generally solid at room temperature of 25°C. In the case of the second primer composition in which these solid resins and solid epoxy resins are dissolved in an organic solvent, the blending is limited due to the difference in solubility in the organic solvent, and the resin precipitates during storage, which tends to reduce the pot life. In addition, the second primer layer 4 applied to the first primer layer 3 does not become a uniform thin film, or even if it can be formed, it is brittle, and it is not possible to stably increase the adhesive strength between the first primer layer 3 and the cast molding material 2. Therefore, since the epoxy resin must play the role of a binder, which is the main element for forming a uniform and tough coating film of the second primer composition, it is necessary to select a liquid epoxy resin that is compatible with the phenolic resin at room temperature of 25°C.

[0029] The thermosetting resin may contain both liquid epoxy resin and phenolic resin, and one or more of each resin may be used. The phenolic resin is preferably contained in a range of 5 parts by weight to 60 parts by weight relative to 100 parts by weight of the thermosetting resin, and more preferably in a range of 10 parts by weight to 50 parts by weight from the viewpoint of stably proceeding with the curing reaction. When the amount of the phenolic resin is less than 5 parts by weight, the curing of the second primer layer 4 becomes insufficient, and the adhesive strength between the metal part 1 and the cast molding material 2 cannot be stably increased. When the amount of the phenolic resin is more than 60 parts by weight, the phenolic resin is not compatible with the liquid epoxy resin, and in addition to being unable to improve the adhesive strength at the interface of the cast molding material 2, the second primer layer 4 becomes a brittle coating film, and the adhesive strength is not improved. For this reason, the amount of the phenolic resin is preferably in a range of 5 parts by weight to 60 parts by weight relative to 100 parts by weight of the thermosetting resin.

[0030] The liquid epoxy resin to be blended in the second primer composition is preferably a bisphenol A or bisphenol F type liquid epoxy resin that can be compatible with not only phenol resins but also alkyl acetalized polyvinyl alcohol resins, and is preferably a liquid resin having an epoxy equivalent of 700 g / eq or less, a polymerization average molecular weight of 1500 or less, and a viscosity of 35000 mPa·s or less at room temperature of 25°C. One or more liquid epoxy resins can be used. If these conditions are not satisfied, the compatibility with the alkyl acetalized polyvinyl alcohol resin is poor, and the second primer layer 4 becomes brittle and the film quality is poor. A more preferred liquid epoxy resin is a liquid resin having an epoxy equivalent of 500 g / eq or less, a polymerization average molecular weight of 1000 or less, and a viscosity of 25000 mPa·s or less at 25°C. By using such a liquid epoxy resin, it is possible to blend a liquid epoxy resin that has an affinity for alkyl acetalized polyvinyl alcohol resins and is mixed with them at the molecular level. As a result, a second primer composition in the form of a homogeneous solution can be obtained.

[0031] The phenolic resin may be a novolac type or a resol type, which is a synthetic resin made of phenols such as phenol or cresol and aldehydes as raw materials. As long as it is compatible with the liquid epoxy resin, it may be liquid or solid, and one or more types of phenolic resins may be used. Since the second primer layer 4 is cured by heating during the casting of the casting material 2, it is not necessary to complete the curing immediately after applying the second primer composition. However, if the second primer layer 4 applied to the outermost surface of the metal part 1 is sticky and the workability when placing it in a mold is poor, the second primer layer 4 may be cured in advance. In one example, if a resorcinol-modified phenolic resin or a resorcinol resin that cures at room temperature is used, the second primer composition can be cured at room temperature, so there is no need to heat it, and the tackiness of the surface of the metal part 1 on which the first primer layer 3 and the second primer layer 4 are formed is improved when placing it in a mold, improving the workability. In addition, in order to increase the curing speed, an organometallic compound curing accelerator such as an amine, phosphorus, imidazole, or organic titanium / organic zirconium may be added as a curing accelerator for the phenolic resin. The curing accelerator is not particularly limited, but at least one material selected from the group consisting of hexamethylenetetramine, triphenylphosphine, N-methylpiperazine, 2-ethyl-4-methylimidazole, and tetra-n-butoxytitanium can be used. The amount of the curing accelerator added is preferably in the range of 0.01 parts by weight to 30 parts by weight with respect to 100 parts by weight of the phenolic resin. This is because when the amount of the curing accelerator added is less than 0.01 parts by weight, there is no reaction promotion effect, i.e., curing promotion, and when it exceeds 30 parts by weight, the storage stability is deteriorated. A more preferable amount of the curing accelerator added is in the range of 1 part by weight to 20 parts by weight with respect to 100 parts by weight of the phenolic resin. By adding such an amount, both the curing promotion effect and the storage stability can be achieved.

[0032] The alkyl acetalized polyvinyl alcohol resin used as the thermoplastic resin is obtained by acetalization of polyvinyl alcohol obtained by partially saponifying polyvinyl acetate with an aldehyde such as formaldehyde, acetaldehyde, propionaldehyde, or butylaldehyde using an acid catalyst. The chemical structure of alkyl acetalized polyvinyl alcohol resin is shown in the following formula (1).

[0033] [ka]

[0034] The molecular structure of the alkyl acetalized polyvinyl alcohol resin is represented by formula (1), and has three functional groups, namely, an acetyl group, a hydroxyl group, and an acetal group. In formula (1), l, x, and y are natural numbers, and n is an integer of 0 or more. By using an alkyl acetalized polyvinyl alcohol resin having a high molecular weight and a high hydroxyl group content capable of undergoing a dehydration condensation reaction with the hydroxyl group present in the structure of the casting molding material 2, the resin has excellent elasticity and plasticity effective for adhesion to the first primer layer 3, and is bonded to the casting molding material 2 by chemical reaction, so that stronger adhesion can be achieved. The adhesive strength is greatly influenced by the hydroxyl group content of the alkyl acetalized polyvinyl alcohol resin, and a hydroxyl group content of 10 mol% to 60 mol% is preferable, and one type or two or more types of alkyl acetalized polyvinyl alcohol resins having different hydroxyl group contents can be used. If the hydroxyl group content is less than 10 mol%, the reactivity of the alkyl acetalized polyvinyl alcohol resin with the thermosetting resin decreases, and the effect of improving the adhesion to the metal part 1 cannot be obtained. If the hydroxyl group content is more than 60 mol%, in addition to the storage stability of the second primer composition decreasing, the toughness is poor, and the second primer layer 4 becomes brittle, and the improvement of the adhesive strength cannot be obtained. For this reason, the hydroxyl group content of the alkyl acetalized polyvinyl alcohol resin is preferably 10 mol% or more and 60 mol% or less. More preferably, the hydroxyl group content is 15 mol% or more and 55 mol% or less. By setting the hydroxyl group content in this range, it is possible to achieve both reactivity with the thermosetting resin and storage stability.

[0035] The chemical structural formula of the alkyl acetalized polyvinyl alcohol resin of the first embodiment is shown as formula (1), and an acetal group, a hydroxyl group, and an acetyl group are bonded to the ethylene chain of the main chain. The acetalization degree can be expressed as a value expressed as a percentage, which is a mole fraction obtained by dividing the amount of ethylene groups bonded to acetal groups by the total amount of ethylene groups in the main chain. In one example, the acetalization degree can be calculated as follows. First, the acetylation degree and the hydroxyl group content are measured by a method conforming to Japanese Industrial Standards (JIS) K6728, and the mole fraction is calculated from the measurement results obtained. Next, the acetalization degree is calculated by subtracting the acetylation degree and the hydroxyl group content from 100 mol%. Here, when the acetal group is a formal group, the acetalization degree is also called the formalization degree, when the acetal group is an acetoacetal group, the acetalization degree is also called the acetoacetalization degree, and when the acetal group is a butyral group, the acetalization degree is also called the butyralization degree. In order to improve the adhesion and toughness of the second primer composition, in addition to the molecular weight of the alkylacetalized polyvinyl alcohol resin, the acetalization degree and the amount of hydroxyl groups are important.

[0036] In order to increase the toughness of the second primer layer 4, the thermoplastic resin is preferably an alkyl acetalized polyvinyl alcohol resin having a polymerization average molecular weight of 1000 or more and an acetalization degree of 30 mol% or more and 90 mol% or less, and one or more alkyl acetalized polyvinyl alcohol resins can be used. This is because when the polymerization average molecular weight is less than 1000 or the acetalization degree is less than 30 mol%, the second primer layer 4 becomes brittle, and when the acetalization degree exceeds 90 mol%, the thermoplastic resin is not compatible with the liquid epoxy resin. In addition, it is more preferable that the thermoplastic resin has a polymerization average molecular weight of 10000 or more and 150000 or less and an acetalization degree of 45 mol% or more and 85 mol% or less. By using such a thermoplastic resin, it can be compatible with the liquid epoxy resin at a high concentration, and the toughness of the second primer layer 4 can be increased. This improves the affinity between the cast molding material 2 and the first primer layer 3.

[0037] Formalized polyvinyl alcohol resin acetalized with formaldehyde, i.e., polyvinyl formal resin where n = 0 in formula (1), has high mechanical strength, is easy to reproduce the cured film, and excels in chemical resistance such as water resistance. Also, acetoacetalized polyvinyl alcohol resin acetalized with acetaldehyde, i.e., polyvinyl acetoacetal resin where n = 1 in formula (1), has high heat resistance, is highly flexible, hydrophilic, and water resistant. Furthermore, butyralized polyvinyl alcohol resin acetalized with butylaldehyde, i.e., polyvinyl butyral resin where n = 3 in formula (1), is tough and has excellent flexibility.

[0038] Since the electrical insulating cast molded product 10 is exposed to a high temperature environment of 80°C or more and 120°C or less during use, it is important that the second primer layer 4 has both toughness and heat resistance, and the adhesive strength changes depending on the thermoplastic resin selected. Comparing the characteristics of polyvinyl formal resin, polyvinyl acetoacetal resin, and polyvinyl butyral resin, the following trends are observed.

[0039] Mechanical strength and heat resistance Polyvinyl formal resin > Polyvinyl acetoacetal resin > Polyvinyl butyral resin -Toughness and flexibility Polyvinyl formal resin < Polyvinyl acetoacetal resin < Polyvinyl butyral resin

[0040] Therefore, by combining a resin having high mechanical strength and heat resistance with a resin having high toughness and flexibility, a stable adhesive strength can be obtained from room temperature to high temperature. Therefore, it is preferable to use a mixed resin in which at least one of a formalized polyvinyl alcohol resin having n=0 in formula (1) and an acetoacetalized polyvinyl alcohol resin having n=1 in formula (1) is added to a butyralized polyvinyl alcohol resin having high toughness and flexibility, and which has high mechanical strength and heat resistance, and which has n=3 in formula (1). In the case of a mixed resin containing a formalized polyvinyl alcohol resin having n=0 in formula (1), the adhesive strength can be improved, but the second primer layer 4 tends to be hard due to the effect of the formal group, and the adhesive strength improvement effect is limited compared to an acetoacetalized polyvinyl alcohol resin having n=1 in formula (1). For this reason, in order to more efficiently improve the heat resistance, flexibility and toughness of the second primer layer 4, it is more preferable to use a mixed resin containing an acetoacetalized polyvinyl alcohol resin in which n = 1 in formula (1).

[0041] The alkyl acetalized polyvinyl alcohol resin having two or more groups selected from the above-mentioned formal group, acetoacetal group, and butyral group can be preferably used because it can have the features due to each group. In particular, by using an alkyl acetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group, the heat resistance, flexibility, and toughness of the second primer layer 4 can be increased at the same time, and the adhesion between the cast molding material 2 and the first primer layer 3 can be further improved even in a high temperature environment. As a result, by forming two types of primer layers, the adhesion between the metal part 1 and the cast molding material 2 can be further improved even in a high temperature environment. The chemical structural formula of the alkyl acetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group is shown in the following formula (2). In formula (2), l, m, x, and y are natural numbers. It has a molecular structure in which the acetal group in formula (1) is replaced with an acetoacetal group and a butyral group.

[0042] [ka]

[0043] The thermoplastic resin used in the second primer composition according to the first embodiment can be one type of alkyl acetalized polyvinyl alcohol resin having the molecular structure of the above-described formula (2) that is highly compatible with liquid epoxy resin, or a mixed resin of two or more types of alkyl acetalized polyvinyl alcohol resins having the molecular structure of the above-described formula (1) or formula (2) that are different in acetalization raw material. In particular, alkyl acetalized polyvinyl alcohol resins having acetoacetal groups can be more preferably used from the viewpoint of achieving both flexibility and heat resistance. In addition, alkyl acetalized polyvinyl alcohol resins containing butyral groups can be more preferably used because they have high flexibility.

[0044] In other words, it is more preferable that a butyral group and an acetoacetal group are present in the thermoplastic resin used in the second primer composition according to embodiment 1. The form of such a thermoplastic resin can be roughly categorized into the following two types. (a) When the thermoplastic resin is a mixed resin of a resin having a butyral group and a resin having an acetoacetal group (b) When the thermoplastic resin is a resin having both butyral and acetoacetal groups

[0045] The thermoplastic resin in the case of (a) is a mixture of at least one of two types of thermoplastic resins, a butyral group-containing thermoplastic resin and an acetoacetal group-containing thermoplastic resin. Examples of this include a mixed resin of a thermoplastic resin having only a butyral group in formula (1) and a thermoplastic resin having only an acetoacetal group in formula (1), a mixed resin of a thermoplastic resin having both a butyral group and an acetoacetal group in formula (2) and a thermoplastic resin having only an acetoacetal group in formula (1), and a mixed resin of a thermoplastic resin having only a butyral group in formula (1) and a thermoplastic resin having both a butyral group and an acetoacetal group in formula (2).

[0046] In the first embodiment, the thermoplastic resin is an alkyl acetalized polyvinyl alcohol resin, so the thermoplastic resin having a butyral group is an alkyl acetalized polyvinyl alcohol resin having a butyral group, i.e., a butyralized polyvinyl alcohol resin. Similarly, the thermoplastic resin having an acetoacetal group is an alkyl acetalized polyvinyl alcohol resin having an acetoacetal group, i.e., an acetoacetalized polyvinyl alcohol resin. Therefore, the alkyl acetalized polyvinyl alcohol resin in the case of (a) can be said to be a mixed resin obtained by mixing two or more resins selected from the group consisting of polyvinyl butyral resin, polyvinyl acetoacetal resin, and alkyl acetalized polyvinyl alcohol resin having an acetoacetal group and a butyral group.

[0047] In one example, a mixed resin obtained by adding an alkylacetalized polyvinyl alcohol resin having an acetoacetal group where n = 1 in formula (1) to a butyralized polyvinyl alcohol resin where n = 3 in formula (1) or an alkylacetalized polyvinyl alcohol resin having a butyral group and an acetoacetal group as shown in formula (2) can be used as a thermoplastic resin.

[0048] The thermoplastic resin in the case of (b) is a compound containing at least one thermoplastic resin containing both a butyral group and an acetoacetal group. In one example, the thermoplastic resin may be an alkylacetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group as shown in formula (2).

[0049] When an alkylacetalized polyvinyl alcohol resin having both acetoacetal and butyral groups is used as the thermoplastic resin, the sum of the acetoacetalization degree and the butyralization degree in this resin is the acetalization degree. When the thermoplastic resin is a mixed resin as in the above (a), the sum of the acetalization degrees of each thermoplastic resin is the acetalization degree of the mixed resin.

[0050] By having the acetoacetal group and the butyral group coexist in the thermoplastic resin in this way, the heat resistance, flexibility, and toughness of the second primer layer 4 can be increased, and a stable adhesive strength can be obtained between the cast molding material 2 and the first primer layer 3 even in a high-temperature environment of 80° C. or higher and 120° C. or lower in the use environment of the electrically insulating cast molded product 10. As a result, by forming two types of primer layers, the adhesiveness between the metal part 1 and the cast molding material 2 can be further improved even in a high-temperature environment.

[0051] Depending on the type and amount of reactive groups present on the surfaces of the cast molding material 2 and the first primer layer 3, there is a difference in the effect of improving the adhesion at the interface. However, depending on the type and amount of these reactive groups, there is no clear difference in the compounding ratio of the thermosetting resin and the thermoplastic resin, and it is preferable that the thermoplastic resin is contained in a range of 5 parts by weight or more and 200 parts by weight or less with respect to 100 parts by weight of the thermosetting resin. This is because, when the thermoplastic resin is less than 5 parts by weight, it has low affinity with the surfaces of the cast molding material 2 and the first primer layer 3 and cannot be bonded, and when the thermoplastic resin is more than 200 parts by weight, it is not compatible with the liquid epoxy resin and the adhesive strength at the interface of the cast molding material 2 cannot be improved. In particular, it is more preferable that the thermoplastic resin is 10 parts by weight or more and 150 parts by weight or less. By setting it in such a range, a stable adhesive strength can be obtained. In addition, by using rubber particles or an organosilicon compound having a reactive organic functional group, which will be described later, as an adhesion assistant, the adhesion improvement effect between the cast molding material 2 and the first primer layer 3 can be enhanced.

[0052] By adding rubber particles as an adhesion aid, the coating film of the second primer composition can be made stress-reducing, the toughness of the adhesive interface can be increased, and the adhesive strength between the cast molding material 2 and the first primer layer 3 can be improved. The rubber particles are micro-sized or nano-sized rubber particles. It is preferable to add rubber particles consisting of at least one of butadiene resin, acrylic resin, and polystyrene resin as an adhesion aid in a range of 0.1 parts by weight to 40 parts by weight to 100 parts by weight of the total amount of the thermosetting resin and the thermoplastic resin. This is because if the rubber particles are less than 0.1 parts by weight, the amount added is small, and the coating film cannot be made stress-reducing, and the adhesive strength cannot be improved. In addition, if the rubber particles are more than 40 parts by weight, a homogeneous second primer layer 4 is not formed, there is no adhesion reproducibility, and the adhesive strength is reduced. In addition, it is more preferable that the amount of rubber particles added is in the range of 1 part by weight to 30 parts by weight to 100 parts by weight of the total amount of the thermosetting resin and the thermoplastic resin. By using such an amount, the adhesive strength of the second primer composition can be increased to a desired value or more while the storage stability of the second primer composition can be obtained. The rubber particles may be core-shell type rubber particles having a graft layer on the outside. The average particle size of the primary particles of the rubber particles is in the range of 0.01 μm to 10 μm. If the average particle size of the primary particles of the rubber particles is smaller than 0.01 μm, the rubber particles are likely to aggregate. If the average particle size of the primary particles of the rubber particles is larger than 10 μm, the rubber particles are likely to settle and the second primer layer 4 becomes thick, making it impossible to form a homogeneous second primer layer 4, resulting in loss of adhesion reproducibility and a decrease in adhesive strength. For this reason, the average particle size of the primary particles of the rubber particles is preferably in the range of 0.01 μm to 10 μm. Moreover, the average particle size of the primary particles of the rubber particles is more preferably in the range of 0.03 μm to 2 μm. By using such a range, the rubber particles can be dispersed in the second primer composition without agglomerating and can be ensured in the form of primary particles.

[0053] When adding rubber particles to an organic solvent, it is necessary that the rubber particles are uniformly dispersed in the transparent organic solvent in the form of primary particles. On the other hand, if the rubber particles aggregate and settle in the organic solvent, it cannot be said that the rubber particles are uniformly dispersed in the organic solvent. In one example, whether the rubber particles are uniformly dispersed in the organic solvent can be determined by visual inspection.

[0054] By adding an organosilicon compound having a reactive organic functional group, which is a constituent material of the first primer composition, as an adhesion aid, the second primer composition can chemically bond with the surfaces of the cast molding material 2 and the first primer layer 3, and can further improve the adhesive strength. In particular, since the first primer layer 3 is mainly composed of an organosilicon compound, adding an organosilicon compound to the second primer composition improves the affinity, and the effect of improving the adhesive strength at this interface is extremely high. It is preferable to add an organosilicon compound as an adhesion aid in a range of 0.01 parts by weight to 5 parts by weight based on 100 parts by weight of the total amount of the thermosetting resin and the thermoplastic resin. This is because if the amount added is less than 0.01 parts by weight, there is no effect of increasing the adhesive strength, and if it is more than 5 parts by weight, the storage stability of the second primer composition is deteriorated, the adhesive reproducibility is lost, and the adhesive strength is reduced. It is also more preferable to add an organosilicon compound in a range of 0.1 parts by weight to 2 parts by weight based on 100 parts by weight of the total amount of the thermosetting resin and the thermoplastic resin. By setting the content within such a range, the storage stability of the second primer composition can be ensured.

[0055] The organic functional group is preferably one or more groups selected from the group consisting of alkoxy groups, acrylic groups, amino groups, isocyanate groups, isocyanurate groups, imidazole groups, ureido groups, epoxy groups, vinyl groups, benzotriazole groups, mercapto groups, methacryl groups, and hydroxyl groups. In particular, an organosilicon compound having one or more groups selected from the group consisting of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups in addition to a plurality of alkoxy groups is more preferred from the viewpoint of adhesion to the surfaces of the first primer layer 3 and the cast molding material 2. In addition, one or more organosilicon compounds can be used as the adhesion assistant. Examples of the organic silicon compounds include, but are not limited to, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-2-(aminoethyl)-8-aminooctyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyl ... dimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 8-glycidoxyoctyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, N-(trimethoxysilylpropyl)-1H-benzotriazole-1-carbodiamide, triethoxy[3-(1H-imidazol-1-yl)propyl]silane, tris-(trimethoxysilylpropyl)isocyanurate, tetraethoxysilane, and the like.

[0056] The solvent of the second primer composition may be any organic solvent that dissolves the thermosetting resin and the thermoplastic resin, and examples of the solvent include methyl ethyl ketone, acetone, toluene, xylene, methanol, ethanol, and isopropyl alcohol. In addition, as long as the resin can be completely dissolved, one type of solvent may be used, or a combination of multiple types of solvents may be used. If the thickness of the coating film of the second primer layer 4 after drying is thick, the adhesive strength between the cast molding material 2 and the metal part 1 will decrease due to the internal stress of the second primer layer 4. For this reason, the amount of the organic solvent is adjusted so that the film thickness when applied is in the range of 0.01 μm to 20 μm, more preferably 0.1 μm to 5 μm. The viscosity of the second primer composition may also be changed. This allows the film thickness when applied to be 0.01 μm to 20 μm, more preferably 0.1 μm to 5 μm. In other words, the amount of the organic solvent is adjusted or the viscosity of the second primer composition is changed so that the thickness of the film formed by one application is the desired thickness. The film thickness can also be controlled by changing the number of applications. However, when the coating is performed two or more times, the number of coating and drying steps increases, and it is also time-consuming to align the coating onto the coated base film, so it is preferable to form the coating film in a single coating.

[0057] The second primer layer 4 formed by the second primer composition is, in one example, a layer containing an alkyl acetalized polyvinyl alcohol, which is a thermoplastic resin, a phenolic resin, which is a thermosetting resin, and a bisphenol A-type or bisphenol F-type epoxy resin, which is a thermosetting resin. The alkyl acetalized polyvinyl alcohol resin, which is a thermoplastic resin, has three functional groups, an acetyl group, a hydroxyl group, and an acetal group. In one example, the alkyl acetalized polyvinyl alcohol resin is a polyvinyl acetoacetal resin. In another example, the alkyl acetalized polyvinyl alcohol resin is an alkyl acetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group. In yet another example, the alkyl acetalized polyvinyl alcohol resin is a mixed resin obtained by mixing two or more resins selected from the group consisting of polyvinyl butyral resin, polyvinyl acetoacetal resin, and alkyl acetalized polyvinyl alcohol resin having an acetoacetal group and a butyral group. The second primer layer 4 may also contain rubber particles or an organosilicon compound. The organosilicon compound contained in the second primer layer 4 has, in addition to a plurality of alkoxy groups, one or more groups selected from the group consisting of an amino group, an epoxy group, a mercapto group, a benzotriazole group, an imidazole group, and a hydroxyl group.

[0058] The cast-molded product 10 for electrical insulation according to the first embodiment obtained as described above has excellent adhesive strength between the metal part 1 and the cast molding material 2. Examples of applications of such cast-molded product 10 for electrical insulation include insulating spacers, insulating rods, insulating bushings, insulating support tubes, solid-insulated busbars, etc., used in gas-insulated equipment such as gas-insulated busbar devices (GIBs), gas-insulated switchgears, and gas circuit breakers (GCBs) that use SF6 gas, dry air, or the like as an insulating medium, and in various types of substation equipment such as transformers.

[0059] As described above, the manufacturing method of the cast-molded product 10 for electrical insulation according to the first embodiment is a manufacturing method of the cast-molded product 10 for electrical insulation, which comprises cast-molding the metal part 1 with the cast-molding material 2 made of a thermosetting resin or a thermosetting elastomer, and includes a first primer layer forming step, a second primer layer forming step, and a cast-molding step. In the first primer layer forming step, a first primer composition, which is a solution in which an organosilicon compound having a reactive organic functional group is uniformly dissolved in an organic solvent, is applied to the surface of the metal part 1 to form a first primer layer 3. In the second primer layer forming step, a second primer composition, which is a solution in which a thermoplastic resin and a thermosetting resin are uniformly dissolved in an organic solvent, is applied to the first primer layer 3 formed on the surface of the metal part 1 to form a second primer layer 4. In the cast-molding step, the metal part 1 having the first primer layer 3 and the second primer layer 4 formed on its surface is placed inside a mold, and the cast-molding material 2 is cast-molded. Examples of cast molding include casting methods such as normal pressure casting, vacuum casting, and pressure gelling casting, and molding methods such as injection molding, extrusion molding, insert molding, and injection molding. By pre-laminating the first primer layer 3 and the second primer layer 4 of different compositions on the surface of the metal part 1 in this way, the affinity with the interface of the metal part 1 is improved during the thermal curing process of the cast molding material 2, and strong chemical adhesion is ensured, thereby suppressing peeling of the cast molding material 2 from the metal part 1 at the interface. As a result, an electrically insulating cast molding product 10 that does not cause electric field concentration can be obtained.

[0060] The first primer composition is a solution obtained by uniformly dissolving an organosilicon compound having one or more groups selected from the group consisting of amino, epoxy, mercapto, benzotriazole, imidazole, and hydroxyl groups in addition to a plurality of alkoxy groups in an organic solvent. The first primer layer 3 formed from the first primer composition has reactive groups capable of chemically bonding with the metal part 1 and the second primer layer 4, and therefore has the effect of providing strong adhesive strength between the metal part 1 and the second primer layer 4.

[0061] Furthermore, the first primer composition contains an organotitanium compound having an alkoxy group in a range of 0.01% by weight to 10% by weight based on 100 parts by weight of the organosilicon compound, which has the effect of further improving the curability of the first primer composition and its adhesion to the metal part 1.

[0062] The second primer composition includes a thermoplastic resin and a thermosetting resin. The thermoplastic resin is an alkyl acetalized polyvinyl alcohol resin having a hydroxyl group content of 10 mol% or more and 50 mol% or less. The thermosetting resin includes a phenolic resin and a bisphenol A or bisphenol F liquid epoxy resin having an epoxy equivalent of 700 g / eq or less, a weight average molecular weight of 1500 or less, and a viscosity of 35000 mPa·s or less at room temperature, which is capable of making the alkyl acetalized polyvinyl alcohol resin and the phenolic resin compatible at room temperature. The second primer composition is a solution in which the alkyl acetalized polyvinyl alcohol resin, the phenolic resin, and the bisphenol A or bisphenol F liquid epoxy resin are uniformly dissolved in an organic solvent. Since the thermoplastic resin is an elastic material, it can increase the adhesive strength between the cast molding material 2 and the first primer layer 3. In addition, the thermosetting resin has a group that can bond with the cast molding material 2, so that the adhesive strength is high. And, by blending two kinds of thermosetting resins, epoxy resin and phenolic resin, the phenolic resin reacts with both the epoxy resin and the alkyl acetalized polyvinyl alcohol resin, and the second primer composition can be cured. Furthermore, by making it a liquid epoxy resin of bisphenol A type or bisphenol F type, the alkyl acetalized polyvinyl alcohol resin and the phenolic resin can be made compatible at room temperature. In this way, by combining two kinds of thermosetting resin and thermoplastic resin and blending multiple resins with different characteristics, the affinity between the cast molding material 2 and the interface of the first primer layer 3 can be improved during the thermal curing process of the cast molding material 2. As a result, it is possible to develop a strong chemical adhesive force with the metal part 1. In other words, by forming the second primer layer 4 on the first primer layer 3, the adhesive force with the thermosetting resin or thermosetting elastomer, which is the cast molding material 2, can be increased without performing surface treatment such as increasing the surface roughness of the metal part 1 or forming a chromate film.In addition, the first primer layer 3, whose constituent raw material is an organosilicon compound, also has heat resistance of over 120°C. Therefore, when placed in a high-temperature environment of 80°C or higher and 120°C or lower, for example when the metal part 1 generates heat while current is flowing through it, a two-layer primer layer that suppresses the occurrence of interfacial peeling can be formed on the surface of the metal part 1.

[0063] In addition, the second primer composition has an acetalization degree of 30 mol% or more and 90 mol% or less of the alkyl acetalized polyvinyl alcohol resin, and a polymerization average molecular weight of 1000 or more. This allows the alkyl acetalized polyvinyl alcohol resin to be dissolved in the liquid epoxy resin at a high concentration, and a homogeneous second primer composition can be obtained. As a result, the toughness of the second primer layer 4 can be increased, and the affinity with the metal part 1 can be improved. In addition, since the second primer composition is homogeneous, a coating film with a uniform thickness can be obtained, and the occurrence of variation in adhesion at the interface between the cast molding material 2 and the first primer layer 3 can be suppressed, and as a result, a uniform adhesion to the metal part 1 can be obtained.

[0064] Furthermore, the cast-molded product for electrical insulation 10 according to the first embodiment is a cast-molded product for electrical insulation 10 obtained by cast-molding a metal part 1 with a cast-molding material 2 containing a thermosetting resin or a thermosetting elastomer, and is provided with: a first primer layer 3 that is disposed between the surface of the metal part 1 and the cast-molding material 2 and contains an organosilicon compound having a reactive organic functional group; and a second primer layer 4 that is disposed on the first primer layer 3 and contains a thermoplastic resin and a thermosetting resin, wherein the first primer layer 3 bonds between the metal part 1 and the second primer layer 4, and the second primer layer 4 bonds between the first primer layer 3 and the cast-molding material 2. This results in an electrically insulating cast molded product 10 having a first primer layer 3 and a second primer layer 4 that have high adhesion to the cast molding material 2 of thermosetting resin or thermosetting elastomer even without surface treatment of the metal part 1, and that suppresses the occurrence of interfacial peeling with the metal part 1 even when placed in a high-temperature environment of 80°C or higher and 120°C or lower.

[0065] The configurations shown in the above embodiments are merely examples of the contents, and may be combined with other known technologies. Parts of the configurations may be omitted or modified without departing from the spirit of the invention. EXAMPLES

[0066] Below, the details of the electrically insulating cast molded article 10 using the first primer composition and the second primer composition of the present disclosure are explained using examples and comparative examples, but the combinations of these primer compositions and laminations are not limited to these.

[0067] Table 1 is a table showing the ratio of the raw materials of the first primer composition and the second primer composition in the examples and comparative examples. In Examples 1 to 7 and Comparative Examples 1 to 6, the following materials are mixed in the ratios shown in Table 1 to prepare the first primer composition and the second primer composition. As the diluent, which is a solvent, isopropyl alcohol is used in the first primer composition, and at least one of methyl ethyl ketone and acetone is used in the second primer composition. These first primer compositions are applied to the adhesive interface with the metal part 1, the diluent is volatilized and dried to prepare the first primer layer 3, and the second primer composition is applied to the surface of the first primer layer 3, and the diluent is volatilized and dried to prepare the second primer layer 4.

[0068] [Table 1]

[0069] An example of the constituent materials of the first primer composition used in the examples and comparative examples is shown below.

[0070] <Organosilicon compound (a)> (a-1) N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (a-2) N-(trimethoxysilyl-propyl)-1H-benzotriazole-1-carbodiamide (a-3) 3-Mercaptopropylmethyldimethoxysilane (a-4) 3-Isocyanatepropyltriethoxysilane

[0071] <Organotitanium Compound (b)> (b-1) Tetra-n-butoxytitanium (b-2) Tetrakis(2-ethylhexyloxy)titanium

[0072] <Diluent (c)> (c-1) Isopropyl alcohol (c-2) Ethanol (c-3) Pure water

[0073] An example of the constituent materials of the second primer composition used in the examples and comparative examples is shown below.

[0074] <Epoxy resin (A)> The epoxy resin (A) is an example of a thermosetting resin. (A-1) Bisphenol A type epoxy resin: epoxy equivalent 189 g / eq, weight average molecular weight 372, viscosity at 25°C 10,500 mPa s (A-2) Bisphenol F type epoxy resin: epoxy equivalent 165g / eq, weight average molecular weight 280, viscosity at 25℃ 1200mPa s (A-3) Bisphenol A type epoxy resin: epoxy equivalent 450g / eq, weight average molecular weight 900, viscosity at 25℃ 24000mPa s (A-4) Bisphenol F type epoxy resin: epoxy equivalent 2550g / eq, weight average molecular weight 1700, solid

[0075] <Phenol resin (B)> The phenolic resin (B) is an example of a thermosetting resin. (B-1) Phenol novolac resin: Weight average molecular weight 4700 (B-2) Phenol-modified resorcinol resin: Weight average molecular weight 2500 (B-3) Cresol novolac resin: Weight average molecular weight 12,000

[0076] <Alkyl acetalized polyvinyl alcohol resin (C)> The alkyl acetalized polyvinyl alcohol resin (C) is an example of a thermoplastic resin. (C-1) Formalized polyvinyl alcohol resin (polyvinyl formal resin in formula (1) where n = 0): polymerization average molecular weight 1020, hydroxyl group content 32 mol%, acetalization degree 65 mol% (C-2) Acetoacetalized polyvinyl alcohol resin (polyvinyl acetoacetal resin in formula (1) where n = 1): polymerization average molecular weight 110,000, hydroxyl group content 57 mol%, acetalization degree 33 mol% (C-3) Acetoacetalized polyvinyl alcohol resin (polyvinyl acetoacetal resin in which n = 1 in formula (1)): polymerization average molecular weight 29,000, hydroxyl group content 16 mol%, acetalization degree 82 mol% (C-4) Butyralized polyvinyl alcohol resin (polyvinyl butyral resin in which n = 3 in formula (1)): polymerization average molecular weight 57,000, hydroxyl group content 46 mol%, acetalization degree 46 mol% (C-5) Alkylacetalized polyvinyl alcohol resin having both acetoacetal and butyral groups (formula (2)): polymerization average molecular weight 140,000, hydroxyl group content 25 mol%, acetalization degree 73 mol% (acetoacetalization degree 43 mol%, butyralization degree 30 mol%) (C-6) Butyralized polyvinyl alcohol resin (polyvinyl butyral resin in which n = 3 in formula (1)): polymerization average molecular weight 220,000, hydroxyl group content 62 mol%, acetalization degree 27 mol% (C-7) Butyralized polyvinyl alcohol resin (polyvinyl butyral resin in which n = 3 in formula (1)): polymerization average molecular weight 960, hydroxyl group content 6 mol%, acetalization degree 93 mol%

[0077] <Curing accelerator (D)> (D-1) Hexamethylenetetramine (D-2) N-Methylpiperazine

[0078] <Rubber particles (E)> (E-1) Butadiene rubber: average particle size 130 nm (E-2) Polystyrene rubber: average particle size 480 nm

[0079] <Organosilicon Compounds (F)> (F-1) 3-Aminopropyltrimethoxysilane (F-2) 3-Mercaptopropyltrimethoxysilane

[0080] <Diluent (G)> (G-1) Acetone (G-2) Methyl ethyl ketone

[0081] The first and second primer compositions according to Examples 1-7 were prepared according to the raw materials and blending described in Embodiment 1. On the other hand, the primer composition according to Comparative Example 1-6 does not conform to the first or second primer composition according to Embodiment 1 because the raw material types, blending, etc. are not appropriate.

[0082] Specifically, the first primer composition of Comparative Example 1 contains more than 10% by weight of the organosilicon compound and more than 20% by weight of the organotitanium compound, which does not meet the conditions of the first primer composition of Embodiment 1. The first primer composition of Comparative Example 2 contains less than 0.01% by weight of the organosilicon compound and less than 0.01% by weight of the organotitanium compound, which are low, which does not meet the conditions of the first primer composition of Embodiment 1.

[0083] In Comparative Example 3-6, the first primer composition satisfies the conditions of the first primer composition according to the first embodiment, but the second primer composition does not satisfy the conditions of the second primer composition according to the first embodiment. In the second primer composition of Comparative Example 3, the material (A-4) of the epoxy resin (A) has an epoxy equivalent of more than 700 g / eq, a weight average molecular weight of more than 1500, and is solid at room temperature, and does not satisfy the conditions of the epoxy resin of the second primer composition according to the first embodiment. In the second primer composition of Comparative Example 4, the alkyl acetalized polyvinyl alcohol resin (C) is not blended. In the second primer composition of Comparative Example 5, the material (C-6) of the alkyl acetalized polyvinyl alcohol resin (C) has a hydroxyl group content of more than 60 mol% and an acetalization degree of less than 30 mol%, and does not satisfy the conditions of the alkyl acetalized polyvinyl alcohol resin of the second primer composition according to the first embodiment. In the second primer composition of Comparative Example 6, the material (C-7) of the alkyl acetalized polyvinyl alcohol resin (C) has a weight average molecular weight of less than 1000, a hydroxyl group content of less than 10 mol%, and a degree of acetalization of more than 90 mol%, and does not satisfy the conditions of the alkyl acetalized polyvinyl alcohol resin of the second primer composition of Embodiment 1.

[0084] The adhesive strength between the metal part 1 coated with the first and second primer compositions of Examples 1-7 and Comparative Examples 1-6 and the cast molding material 2 is evaluated. In the Examples and Comparative Examples, two types of materials, epoxy resin and silicone rubber, are used as the cast molding material 2. Table 2 shows the adhesiveness between the metal part coated with the first primer composition and the second primer composition of the Examples and Comparative Examples and the cast molding material.

[0085] [Table 2]

[0086] The adhesive strength is evaluated by preparing an adhesive test piece and using a tensile tester. The primer composition is applied with a brush to the adhesive interface of a metal piece whose surface has been degreased with acetone, and dried at 130°C for 5 minutes. Aluminum and copper are used as the metal pieces. Then, the metal pieces to which the first and second primer compositions have been applied are set in a casting mold, and the epoxy resin or silicone resin, which is the casting material 2, is injected into the casting mold and cured at 150°C for 12 hours to prepare an adhesive test piece. The tensile test is performed at temperatures of 25°C, 80°C, 100°C, and 120°C at a tensile speed of 1 mm / min. The adhesive strength obtained as a result is evaluated by comparing it with the adhesive strength of a test piece having only the second primer layer 4 without the first primer layer 3, and a test piece having neither the first primer layer 3 nor the second primer layer 4, i.e., an unprimed test piece, as a judgment standard. In Table 2, adhesion test pieces whose adhesive strength is 1.1 times or more higher than that of the unprimed case and is 2 times or more higher than the judgment criterion, which is the adhesive strength of the test piece with only the second primer layer 4, are marked with a double circle. Also, adhesion test pieces whose adhesive strength is 1.1 times or more higher than that of the unprimed case and is less than 2 times higher than that of the test piece with only the second primer layer 4 are marked with a circle. Furthermore, adhesion test pieces whose adhesive strength is less than 1.1 times that of the unprimed case or less than 1.1 times higher than the judgment criterion, which is the adhesive strength of the test piece with only the second primer layer 4, are marked with a cross.

[0087] First, the evaluation results of the examples will be described with reference to Tables 1 and 2. As shown in Tables 1 and 2, in Examples 1-7, by forming two types of the first primer layer 3 and the second primer layer 4, both of which are made of the first and second primer compositions, the adhesive strength in the range of 25°C to 120°C is 1.1 times or more higher than that of the unprimed case, regardless of whether the cast molding material 2 is epoxy resin or silicone rubber, or whether the metal part 1 is aluminum or copper, and it is confirmed that there is an effect of further increasing the adhesiveness compared to the case of only the second primer layer 4.

[0088] In Examples 2 and 3, the second primer composition contains only an acetoacetalized polyvinyl alcohol resin as the alkyl acetalized polyvinyl alcohol resin, and therefore, compared to Example 4, which contains only a butyralized polyvinyl alcohol resin, there are many temperature ranges in which the adhesive strength is improved by more than twice that of the second primer layer 4 alone.

[0089] In addition, in Examples 6-7, a mixed resin is used for the alkyl acetalized polyvinyl alcohol resin in the second primer composition, and in Example 5, a single resin of an alkyl acetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group is used. In these Examples 5-7, due to the inclusion of both an acetoacetal group and a butyral group in the thermoplastic resin, all of the adhesive strengths in the range of 25°C to 120°C are improved to more than twice that of the case of only the second primer layer 4. Between Examples 3 and 6, and between Examples 4 and 7, there is a significant difference in adhesive strength, simply because the constituent raw materials of the alkyl acetalized polyvinyl alcohol resin are different. In this way, in the electrically insulating cast molded product 10 in which the cast molding material 2 and the metal part 1 on whose surface the first primer layer 3 are formed are joined via the second primer layer 4 in which a resin having an acetoacetal group and a butyral group is combined, a strong chemical adhesive force with the interface of the metal part 1 is ensured and peeling at the interface is suppressed even when the temperature of the operating environment is high. As a result, an electrically insulating cast product 10 that does not cause electric field concentration can be obtained.

[0090] In Comparative Example 1, the first primer composition contains more than 10% by weight of an organosilicon compound and more than 20% by weight of an organotitanium compound. Because the amounts are so high, the storage stability is poor, there is no adhesion reproducibility, the first primer layer 3 is easily peeled off due to internal stress, and no adhesive strength is obtained. As a result, the adhesive strength is lower than when only the second primer layer 4 is used.

[0091] In Comparative Example 2, the first primer composition contains less than 0.01% by weight of an organosilicon compound and less than 0.01% by weight of an organotitanium compound. Because the amounts are so small, the first primer layer 3 does not have the effect of increasing the adhesive strength, and the adhesive strength is equal to or less than that of the case where only the second primer layer 4 is used.

[0092] In Comparative Example 3, the second primer composition uses a solid bisphenol F type epoxy resin having an epoxy equivalent of more than 700 g / eq and a weight average molecular weight of more than 1500, i.e., material (A-4). For this reason, compatibility with alkyl acetalized polyvinyl alcohol resin is low, and there are few epoxy groups in the molecule, so the effect of chemically bonding the epoxy resin or silicone rubber cast molding material 2 to the metal part 1 is small. As a result, the adhesive strength is equal to or less than that of the unprimed case.

[0093] In Comparative Example 4, the second primer composition does not contain an alkyl acetalized polyvinyl alcohol resin, so the cast molding material 2 cannot be chemically bonded to the metal part 1. As a result, the adhesive strength is equal to or less than that of the unprimed case.

[0094] In Comparative Example 5, the second primer composition uses a butyralized polyvinyl alcohol resin having a high hydroxyl content of 62 mol% and a low acetalization degree of 27 mol%, i.e., material (C-6). Therefore, in Comparative Example 5, the second primer layer 4 has low toughness and is brittle, and no improvement in adhesive strength is obtained. As a result, the adhesive strength is equal to or less than that of the unprimed material.

[0095] In Comparative Example 6, the second primer composition uses a butyralized polyvinyl alcohol resin having a low weight average molecular weight of 960, a low hydroxyl content of 6 mol%, and a high degree of acetalization of 93 mol%, that is, material (C-7). As a result, the second primer layer 4 is brittle and has a reduced reactivity with the thermosetting resin, so that the effect of improving the adhesion to the metal part 1 is not obtained. As a result, the adhesive strength is equal to or less than that of an unprimed part. [Explanation of symbols]

[0096] 1 metal part, 2 cast molding material, 3 first primer layer, 4 second primer layer, 10 cast molding product for electrical insulation.

Claims

1. A method for producing an electrically insulating cast-molded product by cast-molding a metal part with a cast molding material containing a thermosetting resin or a thermosetting elastomer, comprising the steps of: a first primer layer forming step of applying a first primer composition, which is a solution in which an organosilicon compound having a reactive organic functional group is uniformly dissolved in an organic solvent, to the surface of the metal part to form a first primer layer; a second primer layer forming step of applying a second primer composition, which is a solution in which a thermoplastic resin and a thermosetting resin are uniformly dissolved in an organic solvent, onto the first primer layer formed on the surface of the metal component to form a second primer layer; a casting step of placing the metal part having the first primer layer and the second primer layer formed on the surface thereof inside a mold and casting the cast molding material; A method for producing an electrically insulating cast molded product, comprising:

2. 2. The method for producing an electrically insulating cast molding according to claim 1, characterized in that the organosilicon compound has, in addition to a plurality of alkoxy groups, one or more groups selected from the group consisting of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups.

3. 2. The method for producing an electrically insulating cast molding according to claim 1, wherein the first primer composition contains an organotitanium compound having an alkoxy group in an amount of 0.01 to 20 parts by weight per 100 parts by weight of the organosilicon compound.

4. The second primer composition includes the thermoplastic resin and the thermosetting resin, the thermoplastic resin is an alkyl acetalized polyvinyl alcohol resin having a hydroxyl group content of 10 mol % or more and 50 mol % or less, the thermosetting resin comprises a phenolic resin, and a bisphenol A type or bisphenol F type liquid epoxy resin which is capable of making the alkyl acetalized polyvinyl alcohol resin and the phenolic resin compatible at room temperature, has an epoxy equivalent of 700 g / eq or less, a weight average molecular weight of 1500 or less, and has a viscosity at room temperature of 35000 mPa s or less, 2. The method for producing an electrically insulating cast molding according to claim 1, characterized in that the alkylacetalized polyvinyl alcohol resin, the phenolic resin, and the bisphenol A type or bisphenol F type liquid epoxy resin are uniformly dissolved in an organic solvent to produce a solution.

5. 5. The method for producing an electrically insulating cast molding according to claim 4, wherein the alkyl acetalized polyvinyl alcohol resin has a degree of acetalization of 30 mol % or more and 90 mol % or less and a weight average molecular weight of 1,000 or more.

6. 5. The method for producing an electrical insulating cast molding according to claim 4, wherein the alkyl acetalized polyvinyl alcohol resin is a polyvinyl acetoacetal resin.

7. 5. The method for producing an electrically insulating cast molding according to claim 4, wherein the alkylacetalized polyvinyl alcohol resin is an alkylacetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group.

8. 5. The method for producing an electrically insulating cast molding according to claim 4, characterized in that the alkyl acetalized polyvinyl alcohol resin is a mixed resin obtained by mixing two or more resins selected from the group consisting of polyvinyl butyral resin, polyvinyl acetoacetal resin, and alkyl acetalized polyvinyl alcohol resin having an acetoacetal group and a butyral group.

9. 2. The method for producing an electrically insulating cast molded product according to claim 1, wherein the thermoplastic resin is contained in an amount ranging from 5 parts by weight to 200 parts by weight based on 100 parts by weight of the thermosetting resin.

10. The second primer composition further comprises an organosilicon compound having, in addition to a plurality of alkoxy groups, one or more groups selected from the group consisting of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups; 2. The method for producing an electrically insulating cast molded product according to claim 1, wherein the organosilicon compound of the second primer composition is added in an amount of 0.01 to 5 parts by weight per 100 parts by weight of the total amount of the thermosetting resin and the thermoplastic resin.

11. 11. The method for producing an electrically insulating cast molding product according to claim 1, wherein the base material of the cast molding material is an epoxy resin, a phenolic resin or a silicone rubber.

12. A cast-molded product for electrical insulation, which is obtained by casting a metal part with a cast molding material containing a thermosetting resin or a thermosetting elastomer, a first primer layer disposed between the surface of the metal part and the cast molding material, the first primer layer including an organosilicon compound having a reactive organic functional group; a second primer layer disposed on the first primer layer and including a thermoplastic resin and a thermosetting resin; Equipped with the first primer layer provides adhesion between the metal component and the second primer layer; 2. An electrically insulating cast-molded product, comprising: a first primer layer and a second primer layer that adheres to the first primer layer and the cast-molding material.

13. 13. The electrically insulating cast article according to claim 12, characterized in that the organosilicon compound has, in addition to a plurality of alkoxy groups, one or more groups selected from the group consisting of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups.

14. 13. The electrically insulating cast article according to claim 12, wherein the first primer layer further contains an organotitanium compound having an alkoxy group.

15. the thermoplastic resin comprises an alkyl acetalized polyvinyl alcohol resin; 13. The electrically insulating cast molded product according to claim 12, wherein the thermosetting resin contains a phenolic resin and a bisphenol A or bisphenol F epoxy resin.

16. 16. The electrically insulating cast molded article according to claim 15, wherein the alkyl acetalized polyvinyl alcohol resin is a polyvinyl acetoacetal resin.

17. 16. The electrically insulating cast molded article according to claim 15, wherein the alkyl acetalized polyvinyl alcohol resin is an alkyl acetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group.

18. 16. The electrically insulating cast molded product according to claim 15, characterized in that the alkyl acetalized polyvinyl alcohol resin is a mixed resin obtained by mixing two or more resins selected from the group consisting of polyvinyl butyral resin, polyvinyl acetoacetal resin, and alkyl acetalized polyvinyl alcohol resin having an acetoacetal group and a butyral group.

19. 13. The electrically insulating cast article according to claim 12, characterized in that the second primer layer further comprises an organosilicon compound having, in addition to a plurality of alkoxy groups, one or more groups selected from the group consisting of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups.

20. 20. The electrically insulating cast molded product according to claim 12, wherein the base material of the cast molding material is an epoxy resin, a phenolic resin or a silicone rubber.