Cast molded article for electrical insulation and method for producing same

Abstract

Provided is a method for producing a cast molded article (10) for electrical insulation in which a metal component (1) is cast molded using a cast molding material (2) that contains a thermosetting resin or a thermosetting elastomer. The method includes a first primer layer formation step, a second primer layer formation step, and a cast molding step. In the first primer layer formation step, a first primer composition, which is a solution obtained by uniformly dissolving an organosilicon compound that has a reactive organic functional group in an organic solvent, is applied to the surface of a metal component to form a first primer layer (3). In the second primer layer formation step, a second primer composition, which is a solution obtained by uniformly dissolving a thermoplastic resin and a thermosetting resin in an organic solvent, is applied onto the first primer layer that has been formed on the surface of the metal component to form a second primer layer (4). In the cast molding step, the metal component which has the first primer layer and the second primer layer formed on the surface thereof is disposed inside a mold, and a cast molding material is cast molded.

Description

Cast molded product for electrical insulation and method for producing the same

[0001] The present disclosure relates to a cast molded product for electrical insulation adhered by a primer layer using a primer composition formed at the interface between a metal part and a casting material of a thermosetting resin or a thermosetting elastomer, and a method for producing the same.

[0002] Cast molded products used in gas-insulated switchgear (GIS) that uses gas as an insulating medium are exposed to the gas filling pressure and temperature changes in the use environment, i.e., temperature cycles, for a long time. In a cast molded product in which a metal part is embedded in an epoxy resin casting material, stress due to the difference in the linear expansion coefficients of the two occurs repeatedly at the interface between the metal part and the casting material in addition to the gas filling pressure, so the adhesive force at the interface decreases and the casting material may peel off. This peeled part becomes the starting point of partial discharge, and the discharge tree progresses inside the casting material, leading to insulation breakdown.

[0003] As a method for suppressing the occurrence of this peeling, it is conceivable to strengthen the adhesive force between the metal part and the epoxy resin as the casting material. Specific methods for strengthening the adhesive force include a method of forming a primer layer at the interface between the metal part and the epoxy resin, a method of increasing the surface roughness of the metal part and utilizing the anchor effect due to the curing shrinkage of the epoxy resin, or a method of forming a chromate film, which is a chemical conversion film, by the reaction between the surface of the metal part and a chromate treatment solution.

[0004] Patent Document 1 relates to a primer agent for improving the adhesion between a cast resin and a shield electrode, and discloses the combined use of coating with a primer made of an epoxy resin, which is a thermosetting resin, and 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.

[0005] JP-A-2006-115691 JP-A-4-348832

[0006] Cast electrical insulating parts used in gas-insulated switchgear (GIS), which uses gas as an insulating medium, are exposed to the gas's sealing pressure or the temperature changes of the operating environment, i.e., temperature cycles, over long periods. In cast parts with embedded metal components, stress is repeatedly generated at the interface due to the difference in the coefficients of thermal expansion between the gas and the embedded metal, in addition to the gas's sealing pressure. When a primer made of epoxy resin, a thermosetting resin as described in Patent Document 1, is applied to a cast part with embedded metal components, the high elasticity and lack of toughness can reduce the adhesion at the interface, potentially leading to delamination. This delamination can become the starting point for partial discharge, and a discharge tree may propagate into the epoxy resin, potentially leading to dielectric breakdown.

[0007] On the other hand, when the primer described in Patent Document 2 is applied to a cast product with embedded metal parts, the polyvinyl butyral resin has the effect of relieving stress generated at the interface between the metal parts and the casting material due to the flexibility of the butyral groups. However, the adhesion to the interface is greatly affected by the amount of hydroxyl groups remaining during the synthesis of the polyvinyl butyral resin. To achieve both stress relief and adhesion, the amount of butyral groups and hydroxyl groups present in the molecule are important. If the amount of butyral groups is too high and the amount of hydroxyl groups is too low, chemical adhesion cannot be obtained. Conversely, if the amount of butyral groups is too low and the amount of hydroxyl groups is too high, stress relief is small, the primer layer becomes a brittle film, and the adhesion strength at the interface between the metal parts and the epoxy resin does not improve. In addition, if the molecular weight of the polyvinyl butyral resin is high, its solubility in organic solvents decreases, and a homogeneous primer solution cannot be obtained. As a result, a coating film with a uniform thickness cannot be obtained, and variations in the adhesion strength at the interface between the metal parts and the epoxy resin occur. Furthermore, because polyvinyl butyral resin has low heat resistance, stable adhesive strength cannot be obtained in high-temperature environments of 80°C to 120°C, which are the operating environments for cast electrical insulation products, depending on the crosslinking density between resins during the curing of the primer layer. In particular, when metal parts heat up during energization, delamination is likely to occur at the interface due to stress caused by the difference in the coefficient of thermal expansion between the cast material and the metal.

[0008] This disclosure has been made in view of the above, and aims to provide a method for manufacturing an electrically insulating cast molded product that has high adhesion to a cast molding material of thermosetting resin or thermosetting elastomer without surface treatment of the metal part, and can form a primer layer that suppresses the occurrence of interfacial delamination with the metal part even when placed in a high-temperature environment of 80°C to 120°C.

[0009] To solve the above-mentioned problems and achieve the objectives, the present disclosure provides a method for manufacturing an electrically insulating cast molded product, comprising casting a metal part with a cast molding material containing a thermosetting resin or a thermosetting elastomer, and including a first primer layer formation step, a second primer layer formation step, and a casting step. In the first primer layer formation step, a first primer composition, which is a solution obtained by uniformly dissolving an organosilicon compound having a reactive organic functional group in an organic solvent, is applied to the surface of the metal part to form a first primer layer. In the second primer layer formation step, a second primer composition, which is a solution obtained by uniformly dissolving a thermoplastic resin and a thermosetting resin in an organic solvent, is applied onto the first primer layer formed on the surface of the metal part to form a second primer layer. In the casting step, the metal part with the first primer layer and the second primer layer formed on its surface is placed inside a mold, and the cast molding material is cast.

[0010] The method for manufacturing an electrically insulating cast product according to this disclosure has the effect of providing high adhesion to the cast material of thermosetting resin or thermosetting elastomer without surface treatment of the metal part, and forming a primer layer that suppresses the occurrence of interfacial delamination with the metal part even when placed in a high-temperature environment of 80°C to 120°C.

[0011] A schematic cross-sectional view showing an example of the configuration of an electrically insulating cast molded product according to Embodiment 1.

[0012] The following describes in detail, with reference to the drawings, an electrically insulating cast molded article and a method for manufacturing the same according to an embodiment of the present disclosure.

[0013] In this specification, "casting material" refers to a material that is a raw material for casting methods such as atmospheric pressure casting, vacuum casting, and pressurized gel casting, or for molding methods such as injection molding, extrusion molding, and insert molding, and which can be used to obtain cast molded products (cast products, molded products) by filling a mold with it and allowing it to solidify. Generally, casting materials used in casting methods consist of thermosetting resins such as epoxy resins and phenolic resins, curing agents, fillers, and various additives (curing accelerators, defoamers, anti-settling agents, etc.), while molding materials used in molding methods consist of thermosetting elastomers such as silicone rubber and ethylene propylene diene rubber, curing agents (crosslinking agents, vulcanizing agents), fillers, and various additives (curing accelerators, defoamers, anti-settling agents, plasticizers, etc.). These casting materials and molding materials are collectively referred to as casting materials, and the product obtained by heating and curing them in a mold, i.e., undergoing a chemical change, is called a cast molded product.

[0014] Embodiment 1. Figure 1 is a schematic cross-sectional view showing an example of the configuration of an electrically insulating cast molded product according to Embodiment 1. The electrically insulating cast molded product 10 comprises 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 Figure 1, the first primer layer 3 and the second primer layer 4 are arranged in order between the metal part 1 and the cast molding material 2, from the metal part 1 side. That is, the first primer layer 3 acts as an adhesive layer that bonds the metal part 1 and the second primer layer 4, and the second primer layer 4 acts 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 placed on the first primer layer 3 and contains a thermoplastic resin and a thermosetting resin. An example of the casting material 2 is 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. In particular, epoxy resin, phenolic resin, and silicone rubber react with the functional groups of the raw material and the functional groups of the second primer layer 4 during heating in casting, causing crosslinking, which has a great effect in chemically bonding the metal part 1 and the casting material 2. For this reason, epoxy resin, phenolic resin, or silicone rubber is preferred as the main component of the casting material 2.

[0015] The manufacturing method for the electrically insulating cast molded product 10 in Embodiment 1 is carried out in the following procedure. First, ultrasonic degreasing using a solvent is performed on the metal part 1 which has been machined into a predetermined shape. Then, if necessary, the metal part 1 is degreased with an alkaline solution, or immersed in hydrochloric acid or sulfuric acid to remove oxide film or surface impurities. Next, it 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 produced, which is a solution obtained by uniformly dissolving an organosilicon compound having multiple alkoxy groups in addition to one or more groups selected from the group consisting of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups, in an organic solvent. Here, whether or not the organosilicon compound is uniformly dissolved in the organic solvent can be confirmed by visual inspection whether or not the organic solvent is a transparent solution. In other words, if the organic solvent is opaque to the naked eye, the organosilicon compound is non-uniformly dissolved in the organic solvent, and if the organic solvent is transparent to the naked eye, the organosilicon compound is uniformly dissolved in the organic solvent. A state in which the organosilicon compound is non-uniformly dissolved in the organic solvent is a state in which the organosilicon compound has not completely dissolved in the organic solvent, and in one example, a state in which the opaque organosilicon compound that has not completely dissolved is present in a transparent organic solvent.

[0017] Next, a second primer composition is prepared by uniformly dissolving alkyl acetalized polyvinyl alcohol, a thermoplastic resin with a hydroxyl group content of 10 mol% to 50 mol%, a thermosetting resin called a phenol resin, and a thermosetting resin called a bisphenol A or bisphenol F type liquid epoxy resin, which can be miscible with these two resins at room temperature, i.e., 25°C, in an organic solvent. Here, whether or not the resin has been uniformly dissolved in the organic solvent can be confirmed by visual inspection whether or not the organic solvent is a transparent solution. In other words, if the organic solvent is opaque to the naked eye, the resin has been non-uniformly dissolved in the organic solvent, and if the organic solvent is transparent to the naked eye, the resin has been uniformly dissolved in the organic solvent. A state in which the resin has been non-uniformly dissolved in the organic solvent is a state in which the resin has not been completely dissolved in the organic solvent, and in one example, a state in which the undissolved opaque resin exists in a transparent organic solvent.

[0018] Subsequently, a first primer layer formation step is performed, in which the generated first primer composition is applied to the surface of the metal part 1 that has been cleaned by the method described above, thereby forming a first primer layer 3 on the surface of the metal part 1. In one example, the first primer composition is applied to the surface of the metal part 1 by brush, spray, dipping, etc. Alternatively, the first primer layer 3 is formed by removing the solvent in the first primer composition by air drying at room temperature or by heat treatment 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 hardens when the mold for the casting process described later is preheated, but the first primer layer 3 obtained as a result of this heat treatment may be in a semi-cured state or a fully cured state. Here, from the viewpoint of improving adhesion, the metal part 1 may be subjected to sandblasting treatment beforehand before applying the first primer composition.

[0019] Subsequently, a second primer layer formation step is performed, in which the generated second primer composition is applied onto the first primer layer 3 formed on the surface of the metal part 1 to form a 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 brush, spray, dipping, etc. Alternatively, the second primer layer 4 is formed by removing the solvent in the second primer composition by air drying at room temperature or by heat treatment 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, and 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 heat treatment may be in a semi-cured state or a fully cured state.

[0020] Next, a casting process is carried out in which a metal part 1, which has a first primer layer 3 and a second primer layer 4 formed on its surface in that order, is placed inside a mold, and a casting material 2 is cast into it. The casting material 2 is made from 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, which is the raw material for the casting material 2. The casting material 2 is cured by injecting it into the mold and heating it at a temperature in the range of 80°C to 200°C for a period of 10 minutes to 36 hours. This is because heating at a temperature below 80°C or for a period of less than 10 minutes does not allow the casting material 2 to cure sufficiently, and heating at a temperature above 200°C or for a period of more than 36 hours tends to cause the casting material 2 to deteriorate due to heat, which is undesirable. Furthermore, the main component of the casting material 2 is preferably an epoxy resin, phenolic resin, or silicone rubber, as these have a significant effect in chemically bonding the metal part 1 and the casting material 2, as they crosslink with the functional groups of the second primer layer 4 during heating in the casting process. In this way, by forming the second primer layer 4, which is a mixture of multiple thermosetting resins and thermoplastic resins with different characteristics, on the surface of the metal part 1 via the first primer layer 3, the affinity with the interface of the metal part 1 is improved during the thermosetting process of the casting material 2, ensuring strong chemical adhesion. This results in the production of the electrically insulating casting product 10 shown in Figure 1.

[0021] The details of the first primer composition and the second primer composition are described below.

[0022] The first primer composition will now be described. The first primer composition is a solution obtained by uniformly dissolving an organosilicon compound having a reactive organic functional group 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 a compound that has reactive groups capable of chemically bonding with both the metal part 1 and the second primer layer 4, strong adhesion can be obtained between 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, methacrylic 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 multiple alkoxy groups is more preferable from the viewpoint of adhesion between the second primer layer 4 and the surface of the metal part 1. Furthermore, one or more organosilicon compounds can be used. Examples of organosilicon compounds, though not particularly limited, include N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-2-(aminoethyl)-8-aminooctyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 3-glycidoxypropylmethyl Examples include dimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 8-glycidoxyoctyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, N-(trimethoxysilyl-propyl)-1H-benzotriazole-1-carbodidad, triethoxy[3-(1H-imidazole-1-yl)propyl]silane, trisu-(trimethoxysilylpropyl)isocyanurate, and tetraethoxysilane.

[0024] It is preferable to add the organosilicon compound to the first primer composition in an amount of 0.01% to 10% by weight. This is because if the amount added is less than 0.01% by weight, there is no effect in increasing the adhesive strength, and if it is more than 10% by weight, the storage stability of the first primer composition deteriorates, the adhesive reproducibility is lost, and the adhesive strength decreases. It is even more preferable to add the organosilicon compound in an amount of 0.1% to 5% by weight. By using such a range, the storage stability of the first primer composition can be ensured.

[0025] To further improve the curability and adhesion to the metal part 1 of the first primer composition, the first primer composition may contain an organotitanium compound having an alkoxy group in an amount of 0.01 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the organosilicon compound. In addition, one or more organotitanium compounds can be used. This is because if the amount added is less than 0.01 parts by weight, there is no effect in improving curability and adhesion, and if it is more than 20 parts by weight, the storage stability of the first primer composition deteriorates, adhesion reproducibility is lost, and the adhesive strength decreases. Furthermore, from the viewpoint of achieving both improved curability and adhesion to the metal part 1, it is more preferable to add one or more organotitanium compounds having an alkoxy group in an amount of 0.1 parts by weight or more and 10 parts by weight or less per 100 parts by weight of the organosilicon compound. Examples of organotitanium compounds, though not particularly limited, include tetra-i-propoxytitanium, tetra-n-butoxytitanium, tetrakis(2-ethylhexyloxy)titanium, (2-propoxy)(2-ethylhexane-1,3-diolato)titanium, di-i-propoxybis(acetylacetonate)titanium, and propanedioxytitanium bis(ethylacetoacetate).

[0026] The solvent in the first primer composition can be any organic solvent that dissolves organosilicon compounds, such as methyl ethyl ketone, acetone, toluene, xylene, methanol, ethanol, isopropyl alcohol, or n-hexane. Alternatively, any single solvent or a combination of multiple solvents may be used, as long as they completely dissolve the organosilicon compound. If the first primer layer 3 has a thick coating film after drying, internal stress in the first primer layer 3 can cause cracks or delamination. This reduces the adhesion between the metal part 1 and the casting material 2. Conversely, if the film thickness is too thin, interfacial adhesion between the metal part 1 and the first primer layer 3 cannot be achieved. Therefore, the amount of organic solvent is adjusted so that the applied film thickness is between 0.01 μm and 5 μm, more preferably between 0.1 μm and 2 μm. The viscosity of the first primer composition may also be varied. Furthermore, water may be added to promote the hydrolysis of the alkoxy groups. The amount of water to be added can be between 0.01 parts by weight and 10 parts by weight per 100 parts by weight of the diluent. If the amount added 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 deteriorates. From the viewpoint of achieving both the accelerating effect and storage stability, it is more preferable to add water in the range of 0.1 parts by weight and 5 parts by weight per 100 parts by weight of the diluent. This results in a film thickness of 0.01 μm to 5 μm, more preferably 0.1 μm to 2 μm, after coating. In other words, the amount of organic solvent blended or the viscosity of the first primer composition is changed so that the film thickness formed in one coating is the desired thickness. The film thickness can also be controlled by changing the number of coatings. However, if the number of coatings is two or more, the number of coating and drying processes increases, and alignment when applying to the coated substrate film becomes more difficult, so it is preferable to form the coating film in one coating.

[0027] The first primer layer 3 formed by the first primer composition is, in one example, a layer containing 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. In another example, the first primer layer 3 may also contain an organotitanium compound having an alkoxy group.

[0028] A second primer composition will now be described. The thermosetting resin incorporated into the second primer composition has groups that can bond with the casting material 2, but by incorporating a thermoplastic resin, which is an elastic material, toughness is imparted, and the adhesion between the first primer layer 3 and the casting material 2 can be improved. Two types of thermosetting resins, epoxy resin and phenolic resin, are incorporated because the phenolic resin reacts with both the epoxy resin and the alkylacetalized polyvinyl alcohol resin, thereby curing the second primer composition. Phenolic resin and alkylacetalized polyvinyl alcohol resin are generally solid at room temperature, 25°C. In the case of a second primer composition in which these solid resins and solid epoxy resin are dissolved in an organic solvent, the blending is limited due to differences in solubility in the organic solvent, and the pot life tends to decrease due to resin precipitation during storage. Furthermore, the second primer layer 4 applied to the first primer layer 3 does not form a uniform thin film, or even if it does form a film, it is brittle, making it impossible to stably increase the adhesion between the first primer layer 3 and the casting material 2. Therefore, since the epoxy resin needs to play the role of a binder that is a key element in 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 phenolic resin at room temperature, 25°C.

[0029] The above thermosetting resin may contain both liquid epoxy resin and phenolic resin, and one or more types of each resin may be used. Furthermore, the phenolic resin is preferably included in an amount of 5 to 60 parts by weight per 100 parts by weight of the thermosetting resin, and more preferably in an amount of 10 to 50 parts by weight from the viewpoint of stably advancing the curing reaction. If the amount of phenolic resin is less than 5 parts by weight, the curing of the second primer layer 4 will be insufficient, and the adhesive strength between the metal part 1 and the casting material 2 cannot be stably increased. Also, if the amount of phenolic resin is more than 60 parts by weight, it will not be compatible with the liquid epoxy resin, and in addition, the adhesive strength at the interface of the casting material 2 cannot be improved, the second primer layer 4 will become a brittle coating, and the adhesive strength will not improve. For this reason, the amount of phenolic resin is preferably in the range of 5 to 60 parts by weight per 100 parts by weight of the thermosetting resin.

[0030] The liquid epoxy resin to be blended into the second primer composition is preferably a bisphenol A or bisphenol F type liquid epoxy resin that is compatible not only with phenol resins but also with alkyl acetalized polyvinyl alcohol resins. Preferably, the liquid epoxy resin has 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 (25°C). One or more types of liquid epoxy resins can be used. If these conditions are not met, the compatibility with the alkyl acetalized polyvinyl alcohol resin will be poor, and the second primer layer 4 will be brittle and the film quality will be poor. A more preferred liquid epoxy resin is one with 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 affinity for alkyl acetalized polyvinyl alcohol resins and mixes at the molecular level. As a result, a second primer composition in a homogeneous solution can be obtained.

[0031] Examples of phenolic resins include novolac-type and resol-type synthetic resins made from phenols such as phenol or cresol and aldehydes as raw materials. They may be liquid or solid as long as they are compatible with the liquid epoxy resin mentioned above, and one or more types of phenolic resins can be used. The second primer layer 4 hardens due to heating during the casting of the casting material 2, so it is not necessary to complete the hardening immediately after application of 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 setting it in the mold is poor, the second primer layer 4 may be hardened in advance. For example, if a resorcinol-modified phenolic resin or resorcinol resin that hardens at room temperature is used, the second primer composition can be hardened at room temperature, eliminating the need for heating, and improving workability as the tackiness of the surface of the metal part 1 with the first primer layer 3 and the second primer layer 4 is improved when setting it in the mold. Furthermore, to increase the curing speed, curing accelerators such as amine-based, phosphorus-based, imidazole-based, and organometallic compounds such as organotitanium and organozirconium may be added as curing accelerators 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 curing accelerator added is preferably in the range of 0.01 parts by weight or more and 30 parts by weight or less per 100 parts by weight of phenolic resin. This is because if the amount of curing accelerator added is less than 0.01 parts by weight, there is no reaction-accelerating effect, i.e., no curing acceleration, and if it exceeds 30 parts by weight, the storage stability deteriorates. A more preferable amount of curing accelerator added is in the range of 1 part by weight or more and 20 parts by weight or less per 100 parts by weight of phenolic resin. By using such an amount, both curing acceleration and storage stability can be achieved.

[0032] The alkylacetalized polyvinyl alcohol resin used as a thermoplastic resin is obtained by partially saponifying polyvinyl acetate to obtain polyvinyl alcohol, and then reacting it with an aldehyde such as formaldehyde, acetaldehyde, propionaldehyde, or butyraldehyde using an acid catalyst to acetalize it. The chemical structure of the alkylacetalized polyvinyl alcohol resin is shown in the following formula (1).

[0033]

[0034] The molecular structure of the alkylacetalized polyvinyl alcohol resin is represented by equation (1), and it has three functional groups: an acetyl group, a hydroxyl group, and an acetal group. In equation (1), l, x, and y are natural numbers, and n is an integer greater than or equal to 0. By using an alkylacetalized polyvinyl alcohol resin with a high molecular weight and a high hydroxyl group content that can react with hydroxyl groups present in the structure of the casting material 2 through dehydration condensation, it is possible to achieve a stronger bond by using an alkylacetalized polyvinyl alcohol resin that has excellent elasticity and plasticity effective for adhesion to the first primer layer 3 and by bonding with the casting material 2 through a chemical reaction. The adhesive strength is greatly influenced by the hydroxyl group content of the alkylacetalized polyvinyl alcohol resin, with a hydroxyl group content of 10 mol% to 60 mol% being preferred, and one type or two or more types of alkylacetalized polyvinyl alcohol resins with different hydroxyl group content can be used. If the hydroxyl group content is less than 10 mol%, the reactivity of the alkylacetalized polyvinyl alcohol resin with the thermosetting resin decreases, and the effect of improving adhesion to the metal part 1 cannot be obtained. Furthermore, if the hydroxyl group content exceeds 60 mol%, in addition to the storage stability of the second primer composition decreasing, the toughness is poor, resulting in a brittle second primer layer 4, and no improvement in adhesive strength can be obtained. For this reason, the hydroxyl group content of the alkylacetalized polyvinyl alcohol resin is preferably 10 mol% or more and 60 mol or less. A more preferable hydroxyl group content is 15 mol% or more and 55 mol or less. By setting the hydroxyl group content in this manner, it is possible to achieve both reactivity with the thermosetting resin and storage stability.

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

[0036] Furthermore, in order to increase the toughness of the second primer layer 4, the thermoplastic resin is preferably an alkylacetalized polyvinyl alcohol resin having a polymerization average molecular weight of 1000 or more and an acetalization degree of 30 mol% to 90 mol%, and one or more alkylacetalized polyvinyl alcohol resins can be used. This is because if 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 if the acetalization degree exceeds 90 mol%, it is not compatible with the liquid epoxy resin. Moreover, it is more preferable that the thermoplastic resin has a polymerization average molecular weight of 10000 to 150000 and an acetalization degree of 45 mol% to 85 mol. 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 casting material 2 and the first primer layer 3.

[0037] Formalized polyvinyl alcohol resin, i.e., polyvinyl formal resin where n=0 in equation (1), has high mechanical strength, easy reproducibility of cured films, and excellent chemical resistance such as water resistance. Furthermore, acetacetalized polyvinyl alcohol resin, i.e., polyvinyl acetacetal resin where n=1 in equation (1), has high heat resistance, is highly flexible, hydrophilic, and water-resistant. In addition, butyralized polyvinyl alcohol resin, i.e., polyvinyl butyral resin where n=3 in equation (1), is tough and highly flexible.

[0038] Since the electrically insulating cast molded product 10 is exposed to high temperatures of up to 80°C to 120°C in its operating environment, it is important that the second primer layer 4 possesses both toughness and heat resistance, and the adhesive strength changes depending on the selection of thermoplastic resin. When comparing the properties of polyvinyl formal resin, polyvinyl acetal resin, and polyvinyl butyral resin, the following trends are observed.

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

[0040] Therefore, by combining a resin with high mechanical strength and heat resistance with a resin with high toughness and flexibility, stable adhesive strength can be obtained from room temperature to high temperatures. Accordingly, it is preferable to use a mixed resin in which a butyralized polyvinyl alcohol resin with n=3 in formula (1), which has high toughness and flexibility, is added to at least one of a formalized polyvinyl alcohol resin with n=0 in formula (1) and an acetacetalized polyvinyl alcohol resin with n=1 in formula (1), which have high mechanical strength and heat resistance. In the case of a mixed resin containing a formalized polyvinyl alcohol resin with n=0 in formula (1), an effect of improving adhesive strength can be obtained, but the effect of the formal group tends to result in a hard second primer layer 4, and the effect of improving adhesive strength is limited compared to the acetacetalized polyvinyl alcohol resin with n=1 in formula (1). Therefore, 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 acetacetalized polyvinyl alcohol resin where n=1 in equation (1).

[0041] The alkyl acetalized polyvinyl alcohol resin having two or more groups selected from the above formal group, acetoacetal group and butyral group can have the characteristics attributed to each group, and thus can be suitably used. 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 simultaneously enhanced, and the adhesiveness between the casting 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 adhesiveness between the metal part 1 and the casting 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 the formula (2), l, m, x, and y are natural numbers. The acetal group of the formula (1) has a molecular structure in which the acetoacetal group and the butyral group are substituted.

[0042]

[0043] For the thermoplastic resin used in the second primer composition according to Embodiment 1, one type of alkyl acetalized polyvinyl alcohol resin having the molecular structure of the above-described formula (2) with high compatibility with the liquid epoxy resin, or two or more types of alkyl acetalized polyvinyl alcohol resins having the molecular structures of the above-described formula (1) or (2) with different acetalization raw materials can be used. In particular, the alkyl acetalized polyvinyl alcohol resin having an acetoacetal group can be more preferably used from the viewpoint of achieving both flexibility and heat resistance. Further, since the alkyl acetalized polyvinyl alcohol resin containing a butyral group has high flexibility, it can be more preferably used.

[0044] In other words, it is more preferable that the thermoplastic resin used in the second primer composition according to Embodiment 1 contains both butyral groups and acetacetal groups. There are two main types of such thermoplastic resins: (a) when the thermoplastic resin is a mixed resin of a resin having butyral groups and a resin having acetacetal groups; (b) when the thermoplastic resin is a resin having both butyral groups and acetacetal groups.

[0045] In case (a), the thermoplastic resin is a mixture of at least one of two types: a thermoplastic resin having a butyral group and a thermoplastic resin having an acetacetal group. 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 acetacetal group in formula (1), a mixed resin of a thermoplastic resin having both a butyral group and an acetacetal group in formula (2) and a thermoplastic resin having only an acetacetal 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 acetacetal group in formula (2).

[0046] In Embodiment 1, the thermoplastic resin is an alkylacetalized polyvinyl alcohol resin. Therefore, the thermoplastic resin having a butyral group is an alkylacetalized polyvinyl alcohol resin having a butyral group, i.e., a butyralized polyvinyl alcohol resin. Similarly, the thermoplastic resin having an acetacetal group is an alkylacetalized polyvinyl alcohol resin having an acetacetal group, i.e., an acetacetalized polyvinyl alcohol resin. For this reason, the alkylacetalized polyvinyl alcohol resin in case (a) can also be said to be a mixed resin obtained by mixing two or more resins selected from the group consisting of polyvinyl butyral resin, polyvinyl acetacetal resin, and alkylacetalized polyvinyl alcohol resin having an acetacetal group and a butyral group.

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

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

[0049] When an alkyl acetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group is used as the thermoplastic resin, the sum of the acetoacetalization degree and the butyralization degree in this resin is the acetoacetalization degree. When the thermoplastic resin is the mixed resin in case (a) above, the total sum of the acetoacetalization degrees of the respective thermoplastic resins is the acetoacetalization degree of the mixed resin.

[0050] By coexisting an acetoacetal group and a butyral group in the thermoplastic resin in this way, the heat resistance, flexibility, and toughness of the second primer layer 4 can be enhanced, and even in a high-temperature environment in the range of 80°C or higher and 120°C or lower in the usage environment of the electrical insulation cast molded product 10, a stable adhesive strength between the cast molding material 2 and the first primer layer 3 can be obtained. 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] The effect of improving interfacial adhesion varies depending on the type and amount of reactive groups present on the surfaces of the casting material 2 and the first primer layer 3. However, there is no clear difference in the blending ratio of thermosetting resin to thermoplastic resin depending on the type and amount of these reactive groups, and it is preferable that the thermoplastic resin is included in an amount of 5 parts by weight or more and 200 parts by weight or less per 100 parts by weight of thermosetting resin. This is because if the amount of thermoplastic resin is less than 5 parts by weight, the affinity with the surfaces of the casting material 2 and the first primer layer 3 will be low and adhesion will not be possible, and if the amount of thermoplastic resin exceeds 200 parts by weight, it will not be compatible with the liquid epoxy resin and the adhesion strength of the interface of the casting material 2 cannot be improved. In particular, it is more preferable that the amount of thermoplastic resin be 10 parts by weight or more and 150 parts by weight or less. By setting it within this range, stable adhesive strength can be obtained. Furthermore, by using rubber particles or organosilicon compounds having reactive organic functional groups as adhesion aids, as described later, the effect of improving adhesion between the casting 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 is made less stressed, the toughness of the adhesive interface is increased, and the adhesion between the casting material 2 and the first primer layer 3 can be improved. The rubber particles are micro-sized or nano-sized fine particles of rubber. 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 an amount of 0.1 parts by weight or more and 40 parts by weight or less per 100 parts by weight of the total amount of thermosetting resin and thermoplastic resin. This is because if the amount of rubber particles is less than 0.1 parts by weight, the amount added is too small to make the coating film less stressed and to improve the adhesion. Also, if the amount of rubber particles exceeds 40 parts by weight, a homogeneous second primer layer 4 will not be formed, resulting in poor adhesion reproducibility and reduced adhesion. Furthermore, it is more preferable that the amount of rubber particles added is in the range of 1 part by weight or more and 30 parts by weight or less per 100 parts by weight of the total amount of thermosetting resin and thermoplastic resin. By using such an amount of additive, the storage stability of the second primer composition can be obtained while ensuring that the adhesive strength of the second primer composition is above the desired value. The rubber particles may be core-shell type rubber particles having a graft layer on the outside. The average particle size of the primary rubber particles is in the range of 0.01 μm to 10 μm. If the average particle size of the primary rubber particles is smaller than 0.01 μm, aggregation is likely to occur. Also, if the average particle size of the primary rubber particles is larger than 10 μm, the rubber particles tend to settle, and the second primer layer 4 becomes thicker, making it impossible to form a homogeneous second primer layer 4, resulting in a loss of adhesive reproducibility and a decrease in adhesive strength. For this reason, it is preferable that the average particle size of the primary rubber particles is in the range of 0.01 μm to 10 μm. It is even more preferable that the average particle size of the primary rubber particles is 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, ensuring dispersion stability in the state 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 their primary particle state. 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. For example, whether or not 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 raw material of the first primer composition, as an adhesion aid, the second primer composition can chemically bond with the surface of the casting material 2 and the first primer layer 3, thereby further improving adhesion. 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 its affinity, resulting in an extremely high effect in improving adhesion to this interface. It is preferable to add the organosilicon compound as an adhesion aid in an amount of 0.01 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the total amount of thermosetting resin and thermoplastic resin. This is because if the amount added is less than 0.01 parts by weight, there is no effect in improving adhesion, and if it is more than 5 parts by weight, the storage stability of the second primer composition deteriorates, adhesion reproducibility is lost, and adhesion decreases. Furthermore, it is more preferable to add the organosilicon compound in an amount of 0.1 parts by weight or more and 2 parts by weight or less per 100 parts by weight of the total amount of thermosetting resin and thermoplastic resin. By setting the range in this manner, 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, methacrylic 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 multiple alkoxy groups is more preferable from the viewpoint of adhesion to the surface of the first primer layer 3 and the casting material 2. Furthermore, one or more organosilicon compounds can be used as adhesion enhancers. Examples of organosilicon compounds, though not particularly limited, include N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-2-(aminoethyl)-8-aminooctyltrimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, and 3-glycidoxypropylmethyl Examples include dimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 8-glycidoxyoctyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, N-(trimethoxysilyl-propyl)-1H-benzotriazole-1-carbodidad, triethoxy[3-(1H-imidazole-1-yl)propyl]silane, trisu-(trimethoxysilylpropyl)isocyanurate, and tetraethoxysilane.

[0056] The solvent in the second primer composition can be any organic solvent that dissolves thermosetting resins and thermoplastic resins, such as methyl ethyl ketone, acetone, toluene, xylene, methanol, ethanol, and isopropyl alcohol. Alternatively, any single solvent or a combination of multiple solvents may be used, as long as they completely dissolve the resin. If the film thickness of the second primer layer 4 after drying is too thick, the internal stress in this layer reduces the adhesion between the casting material 2 and the metal part 1. Therefore, the amount of organic solvent is adjusted so that the film thickness after application is between 0.01 μm and 20 μm, more preferably between 0.1 μm and 5 μm. The viscosity of the second primer composition may also be changed. This ensures that the film thickness after application is between 0.01 μm and 20 μm, more preferably between 0.1 μm and 5 μm. In other words, the amount of organic solvent is adjusted or the viscosity of the second primer composition is changed so that the film thickness formed in a single application is the desired thickness. The film thickness can also be controlled by changing the number of applications. However, if the coating is applied two or more times, the number of coating and drying steps increases, and alignment is required when applying the coating onto the already coated substrate. Therefore, it is preferable to form the coating in a single application.

[0057] The second primer layer 4 formed by the second primer composition is, in one example, a layer comprising an alkylacetalized polyvinyl alcohol, which is a thermoplastic resin; a phenol resin, which is a thermosetting resin; and a bisphenol A or bisphenol F type epoxy resin, which is a thermosetting resin. The alkylacetalized 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 alkylacetalized polyvinyl alcohol resin is a polyvinyl acetal resin. In another example, the alkylacetalized polyvinyl alcohol resin is an alkylacetalized polyvinyl alcohol resin having both an acetal group and a butyral group. In yet another example, the alkylacetalized polyvinyl alcohol resin is a mixed resin obtained by mixing two or more resins selected from the group consisting of polyvinyl butyral resin, polyvinyl acetal resin, and alkylacetalized polyvinyl alcohol resin having both an acetal group and a butyral group. The second primer layer 4 may also contain rubber particles or organosilicon compounds. The organosilicon compound contained in the second primer layer 4 has, in addition to multiple 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.

[0058] The electrically insulating cast molded product 10 obtained according to Embodiment 1 as described above has excellent adhesion between the metal part 1 and the cast molding material 2. Examples of applications for such electrically insulating cast molded product 10 include insulating spacers, insulating rods, insulating bushings, insulating support tubes, solid insulating busbars, etc., used in gas-insulated equipment such as gas-insulated buses (GIB), gas-insulated switchgear, and gas circuit breakers (GCB) that use SF6 gas, dry air, etc. as insulating media, as well as various substation equipment such as transformers.

[0059] As described above, the method for manufacturing an electrically insulating cast molded product 10 according to Embodiment 1 is a method for manufacturing an electrically insulating cast molded product 10 by casting a metal part 1 with a cast molding material 2 made of a thermosetting resin or thermosetting elastomer, and includes a first primer layer formation step, a second primer layer formation step, and a casting step. In the first primer layer formation step, a first primer composition, which is a solution obtained by uniformly dissolving an organosilicon compound having a reactive organic functional group 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 formation step, a second primer composition, which is a solution obtained by uniformly dissolving a thermoplastic resin and a thermosetting resin in an organic solvent, is applied on the first primer layer 3 formed on the surface of the metal part 1 to form a second primer layer 4. In the casting step, the metal part 1 with 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. Examples of casting methods include atmospheric pressure casting, vacuum casting, and pressurized gel casting, as well as molding methods such as injection molding, extrusion molding, insert molding, and injection molding. By pre-laminating a first primer layer 3 and a second primer layer 4 of different compositions onto the surface of the metal part 1, the affinity of the casting material 2 with the interface of the metal part 1 is improved during the thermosetting process of the casting material 2, ensuring strong chemical adhesion and thus suppressing the peeling of the casting material 2 from the metal part 1 at the interface. As a result, an electrically insulating casting product 10 that does not cause electric field concentration can be obtained.

[0060] Furthermore, the first primer composition was prepared as a solution obtained by uniformly dissolving 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, in an organic solvent. The first primer layer 3 formed from the first primer composition has reactive groups that can chemically bond with the metal part 1 and the second primer layer 4, thus providing the effect of obtaining strong adhesion 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 an amount of 0.01% to 10% by weight per 100 parts by weight of the organosilicon compound. This 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 comprises a thermoplastic resin and a thermosetting resin. The thermoplastic resin is an alkylacetalized polyvinyl alcohol resin having a hydroxyl group content of 10 mol% to 50 mol%. The thermosetting resin comprises a phenol resin and a bisphenol A or bisphenol F type liquid epoxy resin that can make the alkylacetalized polyvinyl alcohol resin and the phenol resin miscible at room temperature, having an epoxy equivalent of 700 g / eq or less, a polymerization average molecular weight of 1500 or less, and a viscosity at room temperature of 35000 mPa·s or less. The second primer composition is a solution obtained by uniformly dissolving the alkylacetalized polyvinyl alcohol resin, the phenol resin, and the bisphenol A or bisphenol F type liquid epoxy resin in an organic solvent. Since the thermoplastic resin is an elastic material, it can increase the adhesion between the casting material 2 and the first primer layer 3. Furthermore, the thermosetting resin has groups that can bond with the casting material 2, thus providing high adhesion. Furthermore, by blending two types of thermosetting resins, epoxy resin and phenolic resin, the phenolic resin reacts with both the epoxy resin and the alkylacetalized polyvinyl alcohol resin, allowing the second primer composition to cure. Additionally, by using a bisphenol A or bisphenol F type liquid epoxy resin, the alkylacetalized polyvinyl alcohol resin and the phenolic resin can be made compatible at room temperature. In this way, by combining two types of thermosetting resins and a thermoplastic resin, and blending multiple resins with different characteristics, the affinity between the interface of the casting material 2 and the first primer layer 3 can be improved during the thermosetting process of the casting material 2. As a result, strong chemical adhesion to the metal part 1 can be achieved. In other words, by forming the second primer layer 4 on the first primer layer 3, the adhesion to the casting material 2, which is a thermosetting resin or thermosetting elastomer, can be enhanced without the need for surface treatments such as increasing the surface roughness of the metal part 1 or forming a chromate film.Furthermore, since the first primer layer 3, whose constituent material is an organosilicon compound, also has heat resistance exceeding 120°C, it has the effect of forming a two-layer primer layer on the surface of the metal part 1 that suppresses the occurrence of interfacial delamination, even when placed in a high-temperature environment between 80°C and 120°C, for example, when the metal part 1 generates heat while energized.

[0063] Furthermore, the second primer composition has an acetalization degree of 30 mol% to 90 mol% 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 compatible with the liquid epoxy resin at a high concentration, resulting in a homogeneous second primer composition. As a result, the toughness of the second primer layer 4 can be increased, improving its affinity with the metal part 1. In addition, because the second primer composition is homogeneous, a coating film with a uniform thickness can be obtained, suppressing variations in adhesive strength at the interface between the casting material 2 and the first primer layer 3, and consequently achieving uniform adhesion to the metal part 1.

[0064] Furthermore, the electrically insulating cast molded product 10 according to Embodiment 1 is an electrically insulating cast molded product 10 in which a metal part 1 is cast using a cast molding material 2 containing a thermosetting resin or thermosetting elastomer, and comprises a first primer layer 3 disposed between the surface of the metal part 1 and the cast molding material 2 and containing an organosilicon compound having a reactive organic functional group, and a second primer layer 4 disposed on the first primer layer 3 and containing a thermoplastic resin and a thermosetting resin, wherein the first primer layer 3 adheres the metal part 1 and the second primer layer 4, and the second primer layer 4 adheres 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 provide high adhesion to the cast molding material 2 of a thermosetting resin or thermosetting elastomer without requiring surface treatment of the metal part 1, and suppress the occurrence of interfacial delamination with the metal part 1 even when placed in a high-temperature environment of 80°C to 120°C.

[0065] The configurations shown in the above embodiments are merely examples of the content, and can be combined with other known technologies. It is also possible to omit or modify parts of the configuration without departing from the gist of the invention.

[0066] The details of the electrically insulating cast molded article 10 using the first primer composition and the second primer composition of this disclosure will be described below with reference to examples and comparative examples, but the combinations of these primer compositions and laminations are not limited to these.

[0067] Table 1 shows the ratios of raw materials for 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 were blended in the proportions shown in Table 1 to prepare the first primer composition and the second primer composition. For the solvent diluent, isopropyl alcohol was used for the first primer composition, and at least one of methyl ethyl ketone and acetone was used for the second primer composition. These first primer compositions were applied to the adhesive interface with the metal part 1, and the diluent was evaporated to produce the first primer layer 3. The second primer composition was then applied to the surface of the first primer layer 3, and the diluent was evaporated to produce the second primer layer 4.

[0068]

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

[0070] <Organosilicon compounds (a)> (a-1) N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (a-2) N-(trimethoxysilyl-propyl)-1H-benzotriazole-1-carbodidad (a-3) 3-mercaptopropylmethyldimethoxysilane (a-4) 3-isocyanatetopropyltriethoxysilane

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

[0072] <Diluent (c)> (c-1) Isopropyl alcohol (c-2) Ethanol (c-3) Purified 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)> Epoxy resin (A) is an example of a thermosetting resin. (A-1) Bisphenol A type epoxy resin: epoxy equivalent 189 g / eq, average polymerization molecular weight 372, viscosity at 25°C 10500 mPa·s (A-2) Bisphenol F type epoxy resin: epoxy equivalent 165 g / eq, average polymerization molecular weight 280, viscosity at 25°C 1200 mPa·s (A-3) Bisphenol A type epoxy resin: epoxy equivalent 450 g / eq, average polymerization molecular weight 900, viscosity at 25°C 24000 mPa·s (A-4) Bisphenol F type epoxy resin: epoxy equivalent 2550 g / eq, average polymerization molecular weight 1700, solid

[0075] <Phenolic Resins (B)> Phenolic resins (B) are examples of thermosetting resins. (B-1) Phenol novolac resin: Polymer average molecular weight 4700 (B-2) Phenol-modified resorcinol resin: Polymer average molecular weight 2500 (B-3) Cresol novolac resin: Polymer average molecular weight 12000

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

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

[0078] <Rubber Particles (E)> (E-1) Butadiene-based rubber: Average particle size 130 nm (E-2) Polystyrene-based 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 formulation described in Embodiment 1. On the other hand, the primer composition according to Comparative Example 1-6 is not suitable in terms of the type of raw materials, formulation, etc., and is not compatible with the first or second primer composition according to Embodiment 1.

[0082] Specifically, in the first primer composition of Comparative Example 1, the amount of organosilicon compound is more than 10% by weight and the amount of organotitanium compound is more than 20% by weight, and thus the conditions for the first primer composition according to Embodiment 1 are not met. In the first primer composition of Comparative Example 2, the amount of organosilicon compound is less than 0.01% by weight and the amount of organotitanium compound is less than 0.01% by weight, and thus the conditions for the first primer composition according to Embodiment 1 are not met.

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

[0084] The adhesive strength between the metal part 1 coated with the first and second primer compositions according to Examples 1-7 and Comparative Examples 1-6 and the casting material 2 is evaluated. In the examples and comparative examples, two types of casting materials 2 are used: epoxy resin and silicone rubber. Table 2 shows the adhesion between the metal part coated with the first and second primer compositions and the casting material in the examples and comparative examples.

[0085]

[0086] Adhesion strength is evaluated by preparing adhesive test specimens and using a tensile testing machine. A 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 metal pieces. Subsequently, the metal pieces coated with the first and second primer compositions are set in a casting mold, and 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 adhesive test specimens. Tensile tests are performed at temperatures of 25°C, 80°C, 100°C, and 120°C under conditions of a tensile speed of 1 mm / min. The resulting adhesive strength is evaluated by comparing it with the adhesion strength of a test specimen with only the second primer layer 4 (without the first primer layer 3) and a test specimen without the first and second primer layers 3, i.e., an unprimed test specimen, which are judged based on these criteria. In Table 2, adhesive test specimens that exhibit an adhesive strength at least 1.1 times higher than that of the untreated specimen and at least twice the adhesive strength of the specimen with only the second primer layer 4 are marked with a double circle. Adhesive test specimens that exhibit an adhesive strength at least 1.1 times higher than that of the untreated specimen and less than twice the adhesive strength of the specimen with only the second primer layer 4 are marked with a single circle. Furthermore, adhesive test specimens that exhibit an adhesive strength less than 1.1 times that of the untreated specimen, or less than 1.1 times the adhesive strength of the specimen with only the second primer layer 4, are marked with an "X".

[0087] First, the evaluation results of the examples will be explained with reference to Tables 1 and 2. As shown in Tables 1 and 2, in Examples 1-7, by forming two types of first primer layers 3 and second primer layers 4, each consisting of the first and second primer compositions, it was confirmed that the adhesive strength in the range of 25°C to 120°C was at least 1.1 times higher than in the case of no primer treatment, regardless of whether the casting material 2 was epoxy resin or silicone rubber, or whether the metal part 1 was aluminum or copper. Furthermore, it was confirmed that this had the effect of further improving adhesion compared to the case of only the second primer layer 4.

[0088] In Examples 2 and 3, acetacetalized polyvinyl alcohol resin is used alone as the alkylacetalized polyvinyl alcohol resin in the second primer composition. As a result, the adhesive strength is more than twice as high in a wider temperature range compared to the case of using only the second primer layer 4, compared to the case of using only the butyralized polyvinyl alcohol resin in Example 4.

[0089] Furthermore, in Examples 6-7, a mixed resin was used for the alkylacetalized polyvinyl alcohol resin in the second primer composition, while in Example 5, a single alkylacetalized polyvinyl alcohol resin having both acetal groups and butyral groups was used. In Examples 5-7, due to the inclusion of both acetal groups and butyral groups in the thermoplastic resin, the adhesive strength in the range of 25°C to 120°C was more than double that of the case with only the second primer layer 4. Significant differences in adhesive strength were observed between Examples 3 and 6, and between Examples 4 and 7, simply due to differences in the constituent raw materials of the alkylacetalized polyvinyl alcohol resin. Thus, in an electrically insulating cast molded product 10 in which a cast molding material 2 and a metal part 1 with the first primer layer 3 formed on its surface are joined via a second primer layer 4 combining a resin having acetal groups and butyral groups, strong chemical adhesion to the interface of the metal part 1 is ensured even at high operating temperatures, suppressing delamination at the interface. As a result, an electrically insulating cast molded 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. Due to the high amounts of these compounds, storage stability is poor, adhesion reproducibility is poor, the first primer layer 3 is prone to peeling due to internal stress, and adhesive strength cannot be obtained. As a result, the adhesive strength is lower than that of the case with only the second primer layer 4.

[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. Due to the low amounts, the first primer layer 3 does not enhance the adhesive strength, and the adhesive strength is equal to or less than that of the case with only the second primer layer 4.

[0092] In Comparative Example 3, the second primer composition uses a solid bisphenol F type epoxy resin, i.e., material (A-4), with an epoxy equivalent of more than 700 g / eq and a polymerization average molecular weight of more than 1500. Therefore, it has low compatibility with alkylacetalized polyvinyl alcohol resin, and also has a low number of epoxy groups in its molecule, resulting in a small chemical bonding effect between the epoxy resin or silicone rubber casting material 2 and the metal part 1. As a result, the adhesive strength is equal to or less than that of the untreated surface.

[0093] In Comparative Example 4, since the second primer composition does not contain alkylacetalized polyvinyl alcohol resin, the casting material 2 and the metal part 1 cannot be chemically bonded. As a result, the adhesive strength is equal to or less than that of the untreated case.

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

[0095] In Comparative Example 6, the second primer composition uses a butyralized polyvinyl alcohol resin, i.e., material (C-7), which has a low average polymerization molecular weight of 960, a low hydroxyl group content of 6 mol%, and a high degree of acetalization of 93 mol%. As a result, the second primer layer 4 is brittle, and its reactivity with the thermosetting resin is reduced, so the effect of improving adhesion to the metal part 1 cannot be obtained. Consequently, the adhesive strength is equal to or less than the adhesive strength of the untreated surface.

[0096] 1. Metal part, 2. Casting material, 3. First primer layer, 4. Second primer layer, 10. Casting product for electrical insulation.

Claims

1. A method for manufacturing an electrically insulating cast molded product, comprising: a first primer layer formation step of applying a first primer composition, which is a solution obtained by uniformly dissolving an organosilicon compound having a reactive organic functional group in an organic solvent, to the surface of the metal part to form a first primer layer; a second primer layer formation step of applying a second primer composition, which is a solution obtained by uniformly dissolving a thermoplastic resin and a thermosetting resin in an organic solvent, onto the first primer layer formed on the surface of the metal part to form a second primer layer; and a casting step of placing the metal part, on which the first primer layer and the second primer layer have been formed on its surface, inside a mold and casting the cast material.

2. The method for producing an electrically insulating cast article 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. The method for producing an electrically insulating cast article according to claim 1 or 2, characterized in that the first primer composition contains an organotitanium compound having an alkoxy group in an amount of 0.01 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the organosilicon compound.

4. The method for producing an electrically insulating cast article according to any one of claims 1 to 3, wherein the second primer composition comprises the thermoplastic resin and the thermosetting resin, wherein the thermoplastic resin is an alkylacetalized polyvinyl alcohol resin having a hydroxyl group content of 10 mol% to 50 mol%, and the thermosetting resin comprises a phenol resin and a bisphenol A or bisphenol F type liquid epoxy resin having an epoxy equivalent of 700 g / eq or less, a polymerization average molecular weight of 1500 or less, and a viscosity at room temperature of 35000 mPa·s or less, which can make the alkylacetalized polyvinyl alcohol resin and the phenol resin miscible at room temperature, and wherein the alkylacetalized polyvinyl alcohol resin, the phenol resin and the bisphenol A or bisphenol F type liquid epoxy resin are uniformly dissolved in an organic solvent.

5. The method for producing an electrically insulating cast article according to claim 4, characterized in that the degree of acetalization of the alkyl acetalized polyvinyl alcohol resin is 30 mol% or more and 90 mol% or less, and the average polymerization molecular weight is 1000 or more.

6. The method for producing an electrically insulating cast article according to claim 4 or 5, characterized in that the alkylacetalized polyvinyl alcohol resin is a polyvinyl acetal resin.

7. The method for producing an electrically insulating cast article according to claim 4 or 5, characterized in that the alkylacetalized polyvinyl alcohol resin is an alkylacetalized polyvinyl alcohol resin having both an acetal group and a butyral group.

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

9. The method for manufacturing an electrically insulating cast molded article according to any one of claims 1 to 8, characterized in that the thermoplastic resin is included in an amount of 5 parts by weight or more and 200 parts by weight or less per 100 parts by weight of the thermosetting resin.

10. The method for producing an electrically insulating cast article according to any one of claims 1 to 9, wherein the second primer composition further comprises 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, and the organosilicon compound of the second primer composition is added in an amount of 0.01 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the total amount of the thermosetting resin and the thermoplastic resin.

11. A method for manufacturing an electrically insulating cast molded article according to any one of claims 1 to 10, characterized in that the main component of the casting material is an epoxy resin, a phenolic resin, or a silicone rubber.

12. An electrically insulating cast molded article comprising a metal part being cast using a casting material containing a thermosetting resin or thermosetting elastomer, the cast molded article comprising: a first primer layer disposed between the surface of the metal part and the casting material and containing an organosilicon compound having a reactive organic functional group; and a second primer layer disposed on the first primer layer and containing a thermoplastic resin and a thermosetting resin, wherein the first primer layer adheres the metal part and the second primer layer, and the second primer layer adheres the first primer layer and the casting material.

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. The first primer layer further comprises an organotitanium compound having an alkoxy group, as described in claim 12 or 13, for use in electrically insulating cast articles.

15. The electrically insulating cast article according to any one of claims 12 to 14, characterized in that the thermoplastic resin comprises an alkylacetalized polyvinyl alcohol resin, and the thermosetting resin comprises a phenol resin and a bisphenol A type or bisphenol F type epoxy resin.

16. The electrically insulating cast article according to claim 15, characterized in that the alkylacetalized polyvinyl alcohol resin is a polyvinyl acetal resin.

17. The electrically insulating cast article according to claim 15, characterized in that the alkylacetalized polyvinyl alcohol resin is an alkylacetalized polyvinyl alcohol resin having both an acetal group and a butyral group.

18. The electrically insulating cast article according to claim 15, characterized in that the alkylacetalized polyvinyl alcohol resin is a mixed resin obtained by mixing two or more resins selected from the group consisting of polyvinyl butyral resin, polyvinyl acetal resin, and alkylacetalized polyvinyl alcohol resin having acetal groups and butyral groups.

19. The second primer layer further comprises 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, as described in any one of claims 12 to 18 for electrically insulating cast articles.

20. The casting article for electrical insulation according to any one of claims 12 to 19, characterized in that the main component of the casting material is epoxy resin, phenolic resin, or silicone rubber.

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