Primer composition, electrically insulating cast molded product, and method for producing same

Abstract

The 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 type liquid epoxy resin that is compatible with the alkyl acetalized polyvinyl alcohol resin and the phenolic resin at room temperature, has an epoxy equivalent of 700 g / eq or less, a weight average molecular weight of 1500 or less, and a viscosity at room temperature of 35000 mPa·s or less. The primer composition is a solution in which the alkyl acetalized polyvinyl alcohol resin, the phenolic resin, and the bisphenol A or bisphenol F type liquid epoxy resin are uniformly dissolved in an organic solvent.

Description

[Technical field]

[0001] The present disclosure relates to a primer composition that has excellent adhesion between a metal part and a cast molding material of a thermosetting resin or a thermosetting elastomer, and to an electrically insulating cast molding product in which the metal part and the cast molding material are bonded together by a primer layer formed at the interface between them using the primer composition, and 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 discloses a primer agent having a base agent containing an epoxy compound having two or more epoxy groups in one molecule and a polyesteramide, and an epoxy curing 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 2014-105304 A [Patent Document 2] Japanese Patent Application Publication No. 7-14453 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology described in Patent Document 1 relates to a primer that can easily separate the metal conductor from the molded resin layer, allowing the metal conductor to be reused, but by raising the temperature to 160°C or higher, the crosslinking points with the polyesteramide are broken, reducing the adhesive strength. When casting with epoxy resin, it is easy to imagine that the temperature will rise to 160°C or higher due to internal heat generation during the curing reaction in the heating process, which may cause peeling at the interface with the metal conductor of the cast product and reduce the insulating performance.

[0007] On the other hand, in the technology described in Patent Document 2, the polyvinyl butyral resin has the effect of relieving the stress generated at the interface between the metal part and the casting 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 view of the above, and aims to obtain a primer composition that can form a primer layer that has high adhesive strength with a thermosetting resin or thermosetting elastomer cast molding material even without subjecting the metal part to a surface treatment, 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. [Means for solving the problem]

[0009] In order to solve the above problems and achieve the object, the present disclosure provides a primer composition comprising a thermoplastic resin and a thermosetting resin, and a metal part and The base resin is epoxy resin, phenolic resin, or silicone rubber.A primer layer is formed to bond the cast molding material. 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 type liquid epoxy resin that is compatible with the alkyl acetalized polyvinyl alcohol resin and the phenolic resin 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 of 35000 mPa·s or less at room temperature. The primer composition is a solution in which the alkyl acetalized polyvinyl alcohol resin, the phenolic resin, and the bisphenol A or bisphenol F type liquid epoxy resin are uniformly dissolved in an organic solvent. Effect of the Invention

[0010] The primer composition according to the present disclosure has the effect of forming a primer layer that has high adhesion to a thermosetting resin or thermosetting elastomer casting molding material 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 part is 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 A primer composition, an electrically insulating cast molded article, 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 has a metal part 1, a cast molding material 2, and a primer layer 3. As shown in FIG. 1, the primer layer 3 is disposed between the metal part 1 and the cast molding material 2. That is, the primer layer 3 serves as an adhesive layer that bonds the metal part 1 and the cast molding material 2. Examples of the cast molding material 2 are 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 material and the functional groups of the primer layer 3 during heating during cast molding to crosslink, and therefore have a large effect of 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 agent of the cast molding material 2.

[0015] The manufacturing method of the electrically insulating cast molded 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, if necessary, the metal part 1 is degreased with an alkaline solution and immersed in hydrochloric acid or sulfuric acid to remove 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 primer composition is produced by uniformly 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 of bisphenol A type or bisphenol F type, which is a thermosetting resin capable of making these two resins compatible at room temperature, i.e., 25°C. Here, whether or not the resin is uniformly dissolved 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 to the naked eye, the resin is in a state where it is non-uniformly dissolved in the organic solvent, and when the organic solvent is transparent to the naked eye, the resin is in a state where it is uniformly dissolved in the organic solvent. The state where the resin is non-uniformly dissolved 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 non-dissolved opaque resin is present in a transparent organic solvent.

[0017] The primer composition thus produced is then applied to the surface of the metal part 1 cleaned by the above method, and dried by air drying or heat treatment to form a primer layer 3 on the surface of the metal part 1. Then, a cast molding material 2 is cast onto the metal part 1 on which the primer layer 3 has been formed, to produce an electrically insulating cast molded product 10 as shown in FIG.

[0018] The thermosetting resin blended in the primer composition has a group capable of bonding with the cast molding material 2, so it has high adhesive strength, but is poor in elasticity and plasticity, so it is difficult to adhere to the metal part 1. Therefore, by blending a thermoplastic resin, which is an elastic substance, it is possible to improve the adhesive strength with both the cast molding material 2 and the metal part 1. The reason why two types of thermosetting resins, epoxy resin and phenolic resin, are blended is that the phenolic resin reacts with both the epoxy resin and the alkyl acetalized polyvinyl alcohol resin, and can harden the primer composition. Phenol resins and alkyl acetalized polyvinyl alcohol resins are generally solid at room temperature of 25°C. In the case of a 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, so that the pot life tends to be reduced. In addition, the primer layer 3 applied to the metal part 1 does not become a uniform thin film, or even if it can be made into a film, it is brittle, and the adhesive strength between the metal part 1 and the cast molding material 2 cannot be stably increased. Therefore, since the epoxy resin must act as a binder, which is the main element in forming a uniform, tough coating film from the primer composition, it is necessary to select a liquid epoxy resin that is compatible with the phenolic resin at room temperature, that is, 25°C.

[0019] 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 primer layer 3 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 primer layer 3 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.

[0020] The liquid epoxy resin to be blended in the 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 (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 primer layer 3 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 primer composition in the form of a homogeneous solution can be obtained.

[0021] 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 primer layer 3 is cured by heating during the casting of the casting material 2, it is not necessary to complete the curing immediately after applying the primer composition. However, if the surface of the metal part 1 to which the primer composition is applied has tackiness and the workability when placing it in a mold is poor, the primer layer 3 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 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 when placed in a mold is improved, improving the workability. In addition, in order to increase the curing speed, an organometallic compound-based curing accelerator such as an amine-based, phosphorus-based, imidazole-based, or organotitanium-organozirconium-based curing accelerator 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 to 100 parts by weight of 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 acceleration effect, i.e., curing acceleration, and when it exceeds 30 parts by weight, 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 to 100 parts by weight of phenolic resin. By adding such an amount, both curing acceleration and storage stability can be achieved.

[0022] 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).

[0023] [ka]

[0024] 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 content of hydroxyl groups capable of undergoing a dehydration condensation reaction with the hydroxyl groups present in the structure of the casting molding material 2, the resin has excellent elasticity and plasticity that are effective for adhesion to metals, 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 with 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. Furthermore, if the hydroxyl group content exceeds 60 mol%, not only does the storage stability of the primer composition decrease, but the toughness is poor, resulting in a brittle primer layer 3, and no improvement in adhesive strength can be achieved. 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. A more preferred 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 thermosetting resins and storage stability.

[0025] 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 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.

[0026] In order to increase the toughness of the primer layer 3, 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 the primer layer 3 becomes brittle when the polymerization average molecular weight is less than 1000 or the acetalization degree is less than 30 mol%, and is not compatible with the liquid epoxy resin when the acetalization degree exceeds 90 mol%. 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 is possible to make it compatible with the liquid epoxy resin at a high concentration, and to increase the toughness of the primer layer 3. This improves the affinity with the metal part 1.

[0027] 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.

[0028] 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 primer layer 3 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.

[0029] 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

[0030] 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. 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 primer layer 3 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 primer layer 3, it is more preferable to use a mixed resin containing an acetoacetalized polyvinyl alcohol resin having n=1 in formula (1).

[0031] 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 combine 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 primer layer 3 can be simultaneously increased, and 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.

[0032] [ka]

[0033] The thermoplastic resin used in the 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.

[0034] In other words, it is more preferable that a butyral group and an acetoacetal group are present in the thermoplastic resin used in the 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

[0035] 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).

[0036] 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.

[0037] 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.

[0038] 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).

[0039] 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.

[0040] By having acetoacetal groups and butyral groups coexist in the thermoplastic resin in this way, the heat resistance, flexibility and toughness of the primer layer 3 can be increased, and stable adhesive strength can be obtained between the metal part 1 and the cast molding material 2 even in high temperature environments in the range of 80°C or higher and 120°C or lower in the environment in which the electrically insulating cast molding product 10 is used.

[0041] There is a difference in the effect of improving adhesion between metals such as aluminum that have reactive groups such as hydroxyl groups on the surface and metals such as copper and gold that do not have such reactive groups. However, there is no clear difference in the compounding ratio of the thermosetting resin and the thermoplastic resin when these metals are used as the metal part 1, and it is preferable that the thermoplastic resin is contained in a range of 5 parts by weight to 200 parts by weight per 100 parts by weight of the thermosetting resin. This is because if the thermoplastic resin is less than 5 parts by weight, it has low affinity with the metal surface and cannot be bonded, and if the thermoplastic resin is more than 200 parts by weight, it is not compatible with the liquid epoxy resin and the adhesive strength of 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 to 150 parts by weight. By setting it in such a range, a stable adhesive strength can be obtained. In addition to metals that have reactive groups, even metals that do not have reactive groups can have an improved adhesion improvement effect by using rubber particles or an organosilicon compound having a reactive organic functional group, which will be described later, as an adhesion assistant.

[0042] By adding rubber particles as an adhesion aid, the coating film of the 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 metal part 1 can be improved. The rubber particles are micro- 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 primer layer 3 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 adding such an amount, the adhesive strength of the primer composition can be made greater than the desired value, while the storage stability of the 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, the primer layer 3 becomes thick, and a homogeneous primer layer 3 cannot be formed, and the adhesion reproducibility is lost and the adhesive strength is reduced. 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 setting the average particle size of the primary particles of the rubber particles in such a range, the rubber particles can be dispersed stably in the primer composition without aggregation in the primary particle state.

[0043] 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.

[0044] By adding an organosilicon compound having a reactive organic functional group as an adhesion aid, the cast molding material 2 and the surface of the metal part 1 are chemically bonded to each other, and the adhesive strength can be further improved. 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 to 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 primer composition is deteriorated, the adhesive reproducibility is lost, and the adhesive strength is reduced. It is more preferable to add an organosilicon compound in a range of 0.1 parts by weight to 2 parts by weight to 100 parts by weight of the total amount of the thermosetting resin and the thermoplastic resin. By setting the amount in this range, the storage stability of the primer composition can be ensured.

[0045] 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 cast molding material 2 and the surface of the metal part 1. In addition, one or more organosilicon compounds can be used as the adhesion assistant. Examples of organosilicon compounds include, but are not limited to, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, N-(trimethoxysilyl-propyl)-1H-benzotriazole-1-carbodiamide, triethoxy[3-(1H-imidazol-1-yl)propyl]silane, tetraethoxysilane, and the like.

[0046] The solvent of the 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, and ethanol. 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 primer layer 3 after drying is thick, the adhesive strength between the cast molding material 2 and the metal part 1 decreases due to the internal stress of the primer layer 3. 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 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 primer composition is changed so that the film thickness formed by one application is the desired thickness. The film thickness can also be controlled by changing the number of applications. However, when the number of coatings is two or more, the number of coating and drying steps increases, and alignment is required when coating the coated base film, so it is preferable to form a coating film in one coating. The primer composition is applied by brushing, spraying, dipping, etc., and then dried by air drying or heat treatment at a temperature of 50°C to 150°C to remove the solvent. This forms the primer layer 3. In this heat treatment for removing the solvent, the coating film may be in a semi-cured state or a completely cured state.

[0047] As described above, the primer composition according to the first embodiment 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 can make the alkyl acetalized polyvinyl alcohol resin and the phenolic resin compatible at room temperature. The 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. The thermoplastic resin is an elastic material, and therefore can increase the adhesive strength with the metal part 1. The thermosetting resin also has a group that can bond with the cast molding material 2, and therefore has high adhesive strength. By blending two types of thermosetting resins, an epoxy resin and a phenolic resin, the phenolic resin reacts with both the epoxy resin and the alkyl acetalized polyvinyl alcohol resin, and the primer composition can be cured. Furthermore, by using 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 types of thermosetting resins and a thermoplastic resin and blending a plurality of resins with different characteristics, the affinity with the interface of the metal part 1 can be improved regardless of the metal type during the thermosetting process of the cast molding material 2, and strong chemical adhesion can be expressed. In other words, even without performing surface treatment such as increasing the surface roughness of the metal part 1 or forming a chromate film, the adhesion with the thermosetting resin or thermosetting elastomer, which is the cast molding material 2, is high, and when placed in a high temperature environment of 80 ° C. or more and 120 ° C. or less, for example, even when the metal part 1 heats up during current application, the primer layer 3 that suppresses the occurrence of interface peeling can be formed on the surface of the metal part 1.

[0048] In addition, the degree of acetalization of the alkyl acetalized polyvinyl alcohol resin is set to 30 mol% or more and 90 mol% or less, and the weight average molecular weight is set to 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 primer composition can be obtained. As a result, the toughness of the primer layer 3 can be increased, and the affinity with the metal part 1 is improved. In addition, since the primer composition is homogeneous, a coating film with a uniform thickness can be obtained, and the occurrence of variations in adhesive strength at the interface between the metal part 1 and the cast molding material 2 can be suppressed, and a uniform adhesive strength can be obtained.

[0049] Embodiment 2 As shown in FIG. 1, the cast-molded product for electrical insulation 10 according to the second embodiment is a cast-molded product for electrical insulation 10 obtained by casting a metal part 1 with a cast-molding material 2 containing a thermosetting resin such as an epoxy resin or a phenol resin, or a thermosetting elastomer such as silicone rubber, ethylene propylene rubber, ethylene propylene diene rubber, or urethane rubber, and is characterized in that the cast-molded product for electrical insulation 10 includes a primer layer 3 disposed in contact with the surface of the metal part 1 that is in contact with the cast-molding material 2. That is, the cast-molded product for electrical insulation 10 includes a primer layer 3 between the metal part 1 and the cast-molding material 2. The primer layer 3 is formed by a primer composition. The cast-molded product for electrical insulation 10 can be manufactured using the primer composition described in the first embodiment. The configuration and manufacturing method of the cast-molded product for electrical insulation 10 according to the second embodiment will be described with reference to FIG. 1.

[0050] As shown in FIG. 1, an electrically insulating cast molded product 10 comprises a metal part 1, a cast molding material 2, and a primer layer 3, with the metal part 1 and the cast molding material 2 being bonded via the primer layer 3.

[0051] In the manufacturing method of the cast-molded product 10 for electrical insulation according to the second embodiment, first, the primer composition described in the first embodiment is applied to the surface of the metal part 1 to form the primer layer 3. In one example, the primer composition is applied to the surface of the metal part 1 by brushing, spraying, dipping, or the like. The primer layer 3 is formed by removing the solvent in the primer composition by air drying at room temperature or by heating at a temperature in the range of 50°C to 150°C. The thickness of the primer layer 3 is preferably 0.01 μm to 20 μm, more preferably 0.1 μm to 5 μm. The primer layer 3 formed on the surface of the metal part 1 is cured when the mold for the subsequent cast molding process is preheated, and the 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 primer composition is applied.

[0052] Next, the metal part 1 with the primer layer 3 formed on its surface is placed inside the mold, and the cast molding process is performed to cast the cast molding material 2. The raw material of the cast molding material 2, a thermosetting resin such as epoxy resin or phenol 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 phenol resin, or a silicone rubber, which has a large effect of chemically bonding the metal part 1 and the cast molding material 2, because the functional group of the raw material reacts with the functional group of the primer layer 3 during heating during cast molding to crosslink. In this way, by forming a primer layer 3 containing a combination of multiple thermosetting and thermoplastic resins with different characteristics on the surface of the metal part 1 in advance, the affinity of the cast molding material 2 with the interface of the metal part 1 is improved during the thermal curing process, and strong chemical adhesion is ensured.

[0053] The cast-molded product 10 for electrical insulation according to the second embodiment obtained in this manner 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 Bus (GIB), gas-insulated switchgear, and Gas Circuit Breaker (GCB) that use SF6 gas, dry air, or the like as an insulating medium, and in various substation equipment such as transformers.

[0054] As described above, the manufacturing method of the cast-molded product 10 for electrical insulation according to the second embodiment is a manufacturing method of the cast-molded product 10 for electrical insulation in which the metal part 1 is cast-molded with the cast-molding material 2 made of a thermosetting resin or a thermosetting elastomer, and includes a coating step of applying a primer composition to the surface of the metal part 1 to form a primer layer 3, and a casting step of placing the metal part 1 with the primer layer 3 formed on its surface inside a mold and casting the cast-molding material 2 by a casting method such as normal pressure casting, vacuum casting, or pressure gelling casting, or a molding method such as injection molding, extrusion molding, insert molding, or injection molding. By forming the primer layer 3 on the surface of the metal part 1 in advance 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, it is possible to obtain a cast-molded product 10 for electrical insulation that does not cause electric field concentration.

[0055] 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

[0056] Hereinafter, the primer composition of the present disclosure will be described in detail with reference to examples and comparative examples, but the primer composition of the present disclosure is not limited to these.

[0057] Table 1 shows the ratio of the raw materials of the primer composition in the examples and comparative examples, and the adhesiveness of the prepared primer composition. In Examples 1 to 8 and Comparative Examples 1 to 4, the following materials are mixed in the ratio shown in Table 1 to prepare the primer composition. At least one of methyl ethyl ketone and acetone is used as the diluent, which is a solvent. These primer compositions are applied to the adhesive interface with the metal part 1, and the diluent is evaporated and dried to prepare the primer layer 3.

[0058] [Table 1]

[0059] <Epoxy resin (A)> The epoxy resin (A) is an example of a thermosetting resin. (1-1) Bisphenol A type epoxy resin: epoxy equivalent 190 g / eq, weight average molecular weight 370, viscosity at 25°C 10,000 mPa s (1-2) Bisphenol F type epoxy resin: epoxy equivalent 160g / eq, weight average molecular weight 250, viscosity at 25℃ 1000mPa s (1-3) Bisphenol A type epoxy resin: epoxy equivalent 480g / eq, weight average molecular weight 950, viscosity at 25℃ 25000mPa s (1-4) Bisphenol F type epoxy resin: epoxy equivalent 2530g / eq, weight average molecular weight 1650, solid

[0060] <Phenol resin (B)> Bisphenol resin (B) is an example of a thermosetting resin. (2-1) Phenol novolac resin: Weight average molecular weight 5000 (2-2) Phenol-modified resorcinol resin: Weight average molecular weight 2000 (2-3) Cresol novolac resin: Weight average molecular weight 12,000

[0061] <Alkyl acetalized polyvinyl alcohol resin (C)> The alkyl acetalized polyvinyl alcohol resin (C) is an example of a thermoplastic resin. (3-1) Formalized polyvinyl alcohol resin (polyvinyl formal resin in formula (1) where n = 0): polymerization average molecular weight 1050, hydroxyl group content 30 mol%, acetalization degree 67 mol% (3-2) Acetoacetalized polyvinyl alcohol resin (polyvinyl acetoacetal resin in formula (1) where n = 1): polymerization average molecular weight 100,000, hydroxyl group content 55 mol%, acetalization degree 35 mol% (3-3) Acetoacetalized polyvinyl alcohol resin (polyvinyl acetoacetal resin obtained by formula (1) where n=1): polymerization average molecular weight 27,000, hydroxyl group content 15 mol%, acetalization degree 83 mol% (3-4) Butyralized polyvinyl alcohol resin (polyvinyl butyral resin in which n = 3 in formula (1)): polymerization average molecular weight 56,000, hydroxyl group content 45 mol%, acetalization degree 45 mol% (3-5) Alkylacetalized polyvinyl alcohol resin having both acetoacetal and butyral groups (formula (2)): polymerization average molecular weight 130,000, hydroxyl group content 26 mol%, acetalization degree 75 mol% (acetoacetalization degree 45 mol%, butyralization degree 30 mol%) (3-6) Butyralized polyvinyl alcohol resin (polyvinyl butyral resin in which n = 3 in formula (1)): polymerization average molecular weight 210,000, hydroxyl group content 63 mol%, acetalization degree 25 mol% (3-7) Butyralized polyvinyl alcohol resin (polyvinyl butyral resin in which n = 3 in formula (1)): polymerization average molecular weight 950, hydroxyl group content 7 mol%, acetalization degree 92 mol%

[0062] <Curing accelerator> (4-1) Hexamethylenetetramine (4-2)N-Methylpiperazine

[0063] <Rubber particles> (5-1) Butadiene rubber: average particle size 150 nm (5-2) Polystyrene rubber: average particle size 500 nm

[0064] <Organosilicon compounds> (6-1) N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (6-2) 3-Mercaptopropyltrimethoxysilane

[0065] <Diluent> (7-1) Methyl ethyl ketone (7-2) Acetone

[0066] The primer composition according to Example 1-8 is prepared according to the raw materials and the blending described in the first embodiment. On the other hand, the primer composition according to Comparative Example 1-4 does not conform to the primer composition according to the first embodiment because the type and blending of the raw materials are not appropriate. Specifically, in the primer composition according to Comparative Example 1, the material (1-4) 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 meet the conditions of the epoxy resin of the primer composition according to the first embodiment. In the primer composition according to Comparative Example 2, the alkyl acetalized polyvinyl alcohol resin (C) is not blended. In the primer composition according to Comparative Example 3, the material (3-6) 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 meet the conditions of the alkyl acetalized polyvinyl alcohol resin of the primer composition according to the first embodiment. In the primer composition of Comparative Example 4, the material (3-7) 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 for the alkyl acetalized polyvinyl alcohol resin of the primer composition of Embodiment 1.

[0067] The adhesive strength between the metal part 1 coated with the primer composition according to Examples 1-8 and Comparative Examples 1-4 and the cast molding material 2 is evaluated. In the examples and comparative examples, two types of cast molding material 2 are used: epoxy resin and silicone rubber.

[0068] The adhesive strength is evaluated by preparing an adhesive test piece and using a tensile tester. The primer composition is applied to the adhesive interface of a metal piece whose surface has been degreased with acetone using a brush, and the adhesive interface is dried at 130°C for 5 minutes. Aluminum and copper are used as the metal pieces. The metal pieces to which the primer composition has been applied are then 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 thickness of the primer layer 3 in each adhesive test piece is about 1 μm. 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 judgment standard, which is the adhesive strength of a test piece that is not treated with a primer and does not have a primer layer 3 formed. In Table 1, adhesion test specimens having an adhesion strength of at least twice the adhesive strength of the unprimed test specimen are marked with a double circle, adhesion test specimens having an adhesive strength of 1.5 times or more but less than 2 times are marked with a circle, adhesion test specimens having an adhesive strength of 1.1 times or more but less than 1.5 times are marked with a triangle, and adhesion test specimens having an adhesive strength less than 1.1 times are marked with a cross.

[0069] First, the evaluation results of the examples will be described with reference to Table 1. As shown in Table 1, in Examples 1 to 8, it is confirmed that the adhesive strength of each primer composition in the range of 25°C to 120°C is 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.

[0070] In the primer compositions of Examples 2 and 3, which contain only an acetoacetalized polyvinyl alcohol resin as the alkyl acetalized polyvinyl alcohol resin, there are many temperature ranges in which the adhesive strength is more than twice as high as that of the untreated case, compared to the case of Example 1, in which only a formalized polyvinyl alcohol resin is used, or the case of Example 4, in which only a butyralized polyvinyl alcohol resin is used.

[0071] In addition, in Examples 6-8, a mixed resin is used for the alkyl acetalized polyvinyl alcohol resin, and in Example 5, a single resin is used for the alkyl acetalized polyvinyl alcohol resin. In these Examples 5-8, due to the inclusion of both acetoacetal and butyral groups 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 where the primer is not treated. 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 cast-molded product 10 for electrical insulation in which the cast molding material 2 and the metal part 1 are bonded through the primer layer 3 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 environmental temperature is high. As a result, it is possible to obtain a cast-molded product 10 for electrical insulation that does not cause electric field concentration.

[0072] The primer composition of Comparative Example 1, which contains 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 (1-4), has low compatibility with alkyl acetalized polyvinyl alcohol resins and has few epoxy groups in the molecule, so that it is less effective at chemically bonding the epoxy resin or silicone rubber cast molding material 2 to the metal part 1. As a result, the adhesive strength of the primer composition of Comparative Example 1 is equal to or less than that of an unprimed product.

[0073] Comparative Example 2 does not contain an alkyl acetalized polyvinyl alcohol resin, and therefore cannot chemically bond the cast molding material 2 to the metal part 1. As a result, the adhesive strength of the primer composition of Comparative Example 2 is equal to or less than that of an unprimed part.

[0074] In Comparative Example 3, a butyralized polyvinyl alcohol resin having a high hydroxyl content of 63 mol% and a low acetalization degree of 25 mol%, i.e., material (3-6), is used. Therefore, in Comparative Example 3, the primer layer 3 has low toughness and is brittle, and no improvement in adhesive strength is obtained. As a result, the adhesive strength of the primer composition in Comparative Example 3 is equal to or lower than that of an unprimed substrate.

[0075] In Comparative Example 4, a butyralized polyvinyl alcohol resin having a low weight average molecular weight of 950, a low hydroxyl content of 7 mol%, and a high degree of acetalization of 92 mol%, i.e., material (3-7), is used. For this reason, the primer layer 3 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 of the primer composition in Comparative Example 4 is equal to or less than that of an unprimed part. [Explanation of symbols]

[0076] 1 Metal part, 2 Cast molding material, 3 Primer layer, 10 Cast molding product for electrical insulation.

Claims

1. A primer composition comprising a thermoplastic resin and a thermosetting resin, the primer composition forming a primer layer for bonding a metal part to a cast molding material whose main component is an epoxy resin, a phenolic resin, or a silicone rubber, the primer composition comprising: 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, A primer composition comprising the alkyl acetalized polyvinyl alcohol resin, the phenol resin, and the bisphenol A type or bisphenol F type liquid epoxy resin uniformly dissolved in an organic solvent.

2. 2. The primer composition according to claim 1, 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.

3. 2. The primer composition according to claim 1, wherein the alkyl acetalized polyvinyl alcohol resin is a polyvinyl acetoacetal resin.

4. 2. The primer composition according to claim 1, wherein the alkyl acetalized polyvinyl alcohol resin is an alkyl acetalized polyvinyl alcohol resin having both an acetoacetal group and a butyral group.

5. 2. The primer composition according to claim 1, wherein the alkyl acetalized polyvinyl alcohol resin is a mixed resin comprising two or more resins selected from the group consisting of polyvinyl butyral resins, polyvinyl acetoacetal resins, and alkyl acetalized polyvinyl alcohol resins having an acetoacetal group and a butyral group.

6. The rubber particles further include rubber particles made of at least one of a butadiene-based resin, an acrylic-based resin, and a polystyrene-based resin, 2. The primer composition according to claim 1, wherein the rubber particles are added in an amount of 0.1 to 40 parts by weight based on 100 parts by weight of the total amount of the thermosetting resin and the thermoplastic resin.

7. further comprising a cure accelerator comprising at least one material selected from the group consisting of hexamethylenetetramine, triphenylphosphine, N-methylpiperazine, 2-ethyl-4-methylimidazole, and tetra-n-butoxytitanium; The primer composition according to claim 1, wherein the curing accelerator is added in an amount of 0.01 parts by weight to 30 parts by weight based on 100 parts by weight of the phenolic resin.

8. 2. The primer composition according to claim 1, wherein the thermoplastic resin is contained in an amount of 5 parts by weight to 200 parts by weight based on 100 parts by weight of the thermosetting resin.

9. further comprising an organosilicon compound having, in addition to a plurality of alkoxy groups, one or more groups selected from the group of amino groups, epoxy groups, mercapto groups, benzotriazole groups, imidazole groups, and hydroxyl groups; 2. The primer composition according to claim 1, wherein the organosilicon compound is added 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 the thermosetting resin and the thermoplastic resin.

10. 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, 10. An electrically insulating cast-molded product comprising a primer layer formed between a surface of the metal part and the cast-molding material by the primer composition according to claim 1.

11. A method for producing a cast-molded product for electrical insulation, comprising the steps of: casting a metal part with a cast molding material whose main component is an epoxy resin, a phenolic resin, or a silicone rubber, A coating step of coating the primer composition according to any one of claims 1 to 9 on a surface of the metal part to form a primer layer; a casting step of placing the metal part having the primer layer formed on the surface thereof inside a mold and casting the casting material; A method for producing an electrically insulating cast molded product, comprising:

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