Epoxy resin, curable resin composition, and cured object therefrom

Abstract

The present invention provides an epoxy resin and a curable resin composition from which a cured object has excellent heat resistance and tracking resistance properties. An epoxy resin represented by the following Formula (1) and having a value obtained by dividing the epoxy equivalent (g / eq.) by a softening point (°C) of 2.0 or more and less than 2.2: in Formula (1), a plurality of R’s are present independently and each represents a methyl group or a hydrogen atom, and n is an average number of repetitions, and a real number of 1 to 10. Fig. 1

Description

Epoxy resin, curable resin composition, and cured product thereof

[0001] The present invention relates to an epoxy resin having a specific structure, a curable resin composition, and a cured product thereof.

[0002] Epoxy resins have excellent electrical properties (dielectric constant, dielectric dissipation factor, insulation), mechanical properties, adhesive properties, and thermal properties (heat resistance, etc.), and are therefore widely used in the electrical and electronic fields, such as in cast products, laminates, and IC encapsulation materials, as well as in structural materials, adhesives, paints, and other fields.

[0003] In recent years, in the fields of electricity and electronics, there has been a demand for resin compositions with improved performance such as flame retardancy, moisture resistance, adhesion, and dielectric properties, as well as for further improvements in various properties such as high purity, low viscosity for high filler (inorganic or organic filler) loading, and improved reactivity for shortening molding cycles (Patent Document 1).In addition, as structural materials, lightweight materials with excellent mechanical properties are required for aerospace materials, leisure and sports equipment applications, and the like.

[0004] In the field of semiconductor encapsulation, substrates (the substrate itself or its peripheral materials) have become increasingly complex as semiconductors evolve, becoming thinner, stacked, systemized, and three-dimensional, requiring extremely high levels of heat resistance and high fluidity. In particular, the expansion of plastic packaging into automotive applications has led to increasingly stringent requirements for improved heat resistance. Specifically, rising semiconductor operating temperatures have created a demand for extremely high heat resistance. With the recent trend toward high-gap semiconductors, operating temperatures of 175°C and even 200°C or higher have become necessary. Peripheral components are required to have sufficient heat resistance (glass transition temperature (Tg), particularly the Tg in thermomechanical analysis (TMA)) to withstand these operating temperatures. Specifically, a temperature approximately 10% higher than the operating temperature is required (for example, a Tg of 220°C or higher, e.g., 225°C, is required for a 200°C operating temperature), and this demand is increasing year by year (Non-Patent Document 1).

[0005] Furthermore, in recent years, the need for high-voltage power devices has grown rapidly in response to needs for electric vehicles, etc., and tracking resistance is becoming increasingly important. Tracking resistance is also becoming increasingly important in applications such as solar power generation, wind power generation, and EVs, and in particularly demanding applications, a comparative tracking index (CTI) of over 600 is required.

[0006] Japanese Patent Application Laid-Open No. 2019-001841

[0007] Fuji Electric Technical Report 2016 vol. 89 No. 4 pp. 247-250

[0008] Generally, aromatic crosslinking units are introduced to improve the heat resistance of resin compositions. However, in this case, the aromatic main skeleton is prone to carbonization, resulting in a decrease in tracking resistance. Furthermore, when heat resistance is improved by increasing the molecular weight, the increased molecular weight leads to an increase in the thermal decomposition temperature, resulting in a decrease in tracking resistance. In other words, because heat resistance and tracking resistance are in a trade-off relationship, it is extremely difficult to achieve this tracking resistance while maintaining heat resistance. Furthermore, when a resin containing a polyfunctional aromatic compound is blended to impart properties such as flame retardancy, tracking resistance tends to deteriorate, making it difficult to achieve both high tracking resistance and flame retardancy. Generally, performance level categories (PLCs) are determined based on the CTI value. Since a smaller PLC class allows for smaller device design dimensions (creepage distances), a PLC of 3 or less is preferred, and a PLC of 1 or less is particularly preferred. The relationship between PLC and CTI is as follows: PLC1: CTI 600 or more, PLC2: CTI 400 or more but less than 600, PLC3: 250 or more but less than 400, PLC4: 100 or more but less than 175, PLC5: less than 100.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide an epoxy resin and a curable resin composition which provide a cured product having excellent heat resistance and tracking resistance.

[0010] The present inventors have conducted extensive research to solve the above problems, and as a result have completed the present invention. Specifically, the present invention relates to the following [1] to [3]. In this application, "(numerical value 1) to (numerical value 2)" indicates that the upper and lower limits are included. [1] An epoxy resin represented by the following formula (1), in which the value obtained by dividing the epoxy equivalent (g / eq.) by the softening point (°C) is 2.0 or more and less than 2.2.

[0011]

[0012] (In formula (1), multiple R's exist independently and represent a methyl group or a hydrogen atom. n is the average number of repeating units and is a real number from 1 to 10.) [2] A curable resin composition containing the epoxy resin described in the preceding item [1]. [3] The curable resin composition described in the preceding item [2], wherein the content of the inorganic filler in the total amount of the curable resin composition is 74% by weight or more and 95% by weight or less. [4] A cured product obtained by curing the curable resin composition described in the preceding item [2] or [3].

[0013] The present invention relates to an epoxy resin having a specific structure, a curable resin composition, and a cured product thereof, which have excellent heat resistance and tracking resistance. Therefore, the present invention is useful for insulating materials for electric and electronic components (e.g., highly reliable semiconductor encapsulation materials), laminates (e.g., printed wiring boards, build-up boards), various composite materials including CFRP, adhesives, paints, etc.

[0014]

[0033] Figure 1 shows a GPC chart for Synthesis Example 1.

[0034] Figure 2 shows a GPC chart for Synthesis Example 2.

[0035] Figure 3 shows a GPC chart for Synthesis Example 3.

[0036] Figure 4 shows a GPC chart for Example 1.

[0037] Figure 5 shows a GPC chart for Example 2.

[0038] Figure 6 shows a GPC chart for Example 3.

[0039] Figure 7 shows a GPC chart for Synthesis Example 1.

[0040] Figure 8 shows a GPC chart for Comparative Synthesis Example 1.

[0041] Figure 9 shows a GPC chart for Comparative Synthesis Example 2.

[0042] Figure 10 shows a GPC chart for FAE-2500.

[0043] Figure 11 shows TMA charts for Examples 4 and 5, and Comparative Examples 1 and 2.

[0044] Figure 12 shows a GPC chart for Synthesis Example 4.

[0045] Figure 13 shows a GPC chart for Example 7.

[0046] Figure 14 shows the CTI measurement results for Examples 10 to 13 and Comparative Examples 5 to 8.

[0015] The epoxy resin of the present invention is represented by the following formula (1), and the value obtained by dividing the epoxy equivalent (g / eq.) by the softening point (°C) is 2.0 or more and less than 2.2.

[0016]

[0017] (In formula (1), multiple R's exist independently and represent a methyl group or a hydrogen atom. n is the average number of repetitions and is a real number from 1 to 10.)

[0018] In the formula (1), n ​​can be calculated from the number average molecular weight determined by measurement using gel permeation chromatography (GPC, detector: UV 254 nm) or the area ratio of each separated peak. n is more preferably a real number of 1 to 5, and particularly preferably a real number of 2 to 4.

[0019] In the formula (1), n ​​= 1 is preferably less than 50 area%, more preferably less than 45 area%. The lower limit is 25 area%, and if it is less than 25 area%, the resin has poor fluidity, resulting in poor productivity when used as an encapsulant. The melt viscosity of the resin is used as an indicator of fluidity, and a viscosity of 2 Pa·s or less is preferred when measured by the cone-plate method at 150°C (ICI melt viscosity). If the viscosity is too low, air or other substances may be trapped during molding, resulting in voids, and blocking may occur during the blending (or modification) of liquid resins, etc.; therefore, a viscosity of 0.4 Pa·s or more is preferred. Considering the balance between heat resistance and thermal decomposition properties, a viscosity of 0.45 Pa·s or more is more preferred, and a viscosity of 0.5 Pa·s or more is particularly preferred.

[0020] Furthermore, the compound of formula (1) where n is less than 1 is preferably contained at a ratio of 0.5 to 10 area %, more preferably 0.5 to 5 area %, and particularly preferably 0.5 to 2.5 area %. Since the compound of n is less than 1 is a compound having a structure with less than three functionalities or an epoxy resin of tertiary butylmethylphenol, if the compound of n is less than 10 area %, not only is there a decrease in heat resistance suggested, but there are also concerns about odor during handling and adverse effects on the human body. On the other hand, if the compound of n is less than 1 is less than 0.5 area %, the network becomes too dense, and there is concern about a large weight loss due to thermal decomposition, which may have an adverse effect on thermal decomposition characteristics (and ultimately on tracking characteristics).

[0021] The epoxy resin of the present invention is typically a solid resin at room temperature, and its softening point is preferably 90°C or higher, more preferably 95°C or higher. The upper limit is 150°C. A softening point higher than 150°C is likely to result in residual solvent when the resin is removed, leading to voids during curing. Furthermore, significant production issues arise, such as increased foaming during solvent distillation. On the other hand, a softening point of 90°C or lower adversely affects heat resistance and thermal decomposition resistance. Furthermore, the epoxy equivalent is preferably 200 to 300 g / eq., more preferably 205 to 250 g / eq. An epoxy equivalent below 200 g / eq. may result in residual epichlorohydrin or a large amount of residual epoxidized impurities, potentially deteriorating properties. Furthermore, a softening point above 300 g / eq. may result in reduced heat resistance.

[0022] In the present invention, the epoxy equivalent was measured by a method according to JIS K-7236. The softening point was measured using a softening point measuring instrument FP90 manufactured by METLER TOLEDO.

[0023] The epoxy resin of the present invention preferably has a high softening point and a large number of functional groups per unit molecular weight. The softening point tends to be higher as the molecular weight increases. This means that the softening point measures the flowability of the resin when heated, and the higher the molecular weight, the less the molecules move, meaning the softening point increases. On the other hand, it is generally said that a higher softening point improves heat resistance, but an increase in the number of functional groups per unit weight is more effective in improving heat resistance, and the epoxy equivalent is a value linked to the number of functional groups.

[0024] A low softening point and a high epoxy equivalent weight suggest that there are few functional groups per molecule, whereas a high softening point and a low epoxy equivalent weight suggest that there are many functional groups per molecule. Therefore, compounds with a high softening point and a low epoxy equivalent weight are preferred.

[0025] In the present invention, the value obtained by dividing the epoxy equivalent (g / eq.) by the softening point (°C) is taken as parameter A, and it is preferable that parameter A is 2.0 or more and less than 2.2. If parameter A is less than 2.0, the epoxy equivalent is too small, which may indicate that some impurities remain, and conversely, if parameter A is 2.2 or more, this means that the epoxy equivalent is large and the softening point is low compared to the epoxy equivalent value, and both heat resistance and thermal decomposition properties cannot be achieved.

[0026] Here, thermal decomposition characteristics are said to be a parameter that affects tracking resistance characteristics, and it is thought that the lower the thermal decomposition temperature in a trunking test, the less likely it is that electrical conduction between electrodes will occur, and therefore the higher the voltage that can be withstood. Normally, the thermal decomposition temperature tends to rise as the molecular weight increases, but in the present invention, there is no significant difference in the thermal decomposition temperature even when the molecular weight is increased, and it is thought that high tracking resistance characteristics can be maintained.

[0027] The method for producing the epoxy resin of the present invention is not particularly limited, but it can be obtained, for example, by subjecting a phenolic resin represented by the following formula (2) to an addition or ring-closing reaction with epihalohydrin in the presence of a solvent and a catalyst.

[0028]

[0029] (In formula (2), multiple R's exist independently and represent a methyl group or a hydrogen atom. n is the average number of repetitions and is a real number from 1 to 10.)

[0030] In the formula (2), n can be calculated from the number average molecular weight determined by gel permeation chromatography (GPC, detector: UV 254 nm) or the area ratio of each separated peak. n is more preferably 1 to 5, and particularly preferably 1 to 3.

[0031] The hydroxyl group equivalent of the phenolic resin of formula (2) is preferably 140 to 180 g / eq., more preferably 140 to 165 g / eq. The amount of the compound where n=1 is preferably 30 to 60 area %, more preferably 40 to 60 area %. The total amount of the compounds where n=2 or more is preferably 25 to 40 area %.

[0032] Here, a method for producing the phenolic resin represented by formula (2) will be described. While there are no particular limitations on the method for producing the phenolic resin represented by formula (2), specifically, alkylphenols (3-methyl-6-t-butylphenol and 4-methyl-2-t-butylphenol) and p-hydroxybenzaldehyde are polycondensed under acidic conditions to form a novolak. It is preferable to react alkylphenols (3-methyl-6-t-butylphenol and 4-methyl-2-t-butylphenol) with p-hydroxybenzaldehyde in a ratio of 3:2 to 2:1. It is preferable that the ratio of 3-methyl-6-t-butylphenol to 4-methyl-2-t-butylphenol is 90% by weight or more of the alkylphenols, and this ratio is adjusted by the amount of alkylphenol blended during the production of the phenolic resin. Specifically, the alkylphenols serving as raw materials are charged in the desired alkylphenol introduction ratio. The hydroxyl group equivalent of the resulting phenolic resin is 140 to 170 g / eq. Preferably, the weight average molecular weight is 145 to 165 g / eq., more preferably 145 to 165 g / eq., and particularly preferably 150 to 160 g / eq.

[0033] Examples of acidic catalysts used in synthesizing the phenolic resin represented by formula (2) include hydrochloric acid, phosphoric acid, sulfuric acid, formic acid, zinc chloride, ferric chloride, aluminum chloride, p-toluenesulfonic acid, methanesulfonic acid, activated clay, and ion exchange resins. These may be used alone or in combination. The amount of catalyst used is 0.1 to 50% by weight, preferably 1 to 30% by weight, based on the phenolic hydroxyl groups used. If the amount is too high, waste increases, and if the amount is too low, the reaction proceeds slowly.

[0034] The reaction may be carried out using an organic solvent as needed, or may be carried out without a solvent. However, since the reaction can be more efficiently carried out by azeotropically dehydrating the water purified during the reaction, it is preferable to use a solvent that can form an azeotrope with water. In the present invention, it is particularly preferable to use a hydrocarbon organic solvent such as toluene or xylene. Thereafter, steps such as water washing and neutralization are carried out, and the resin can be extracted after the solvent has been drained, or the resin can be extracted by techniques such as reprecipitation or recrystallization. Since the softening point of the phenolic resin represented by formula (2) is very high, it is preferable to extract it by techniques such as reprecipitation or recrystallization. For example, a technique such as replacing the solvent with a poor solvent can be applied to precipitate the resin.

[0035] The phenolic resin represented by formula (2) is a crystal or resin solid, and the proportion of n=1 in GPC is preferably less than 60%. It is particularly 55 area % or less, and even more preferably 50 area % or less. The total amount of residual raw material monomers is preferably 5 area % or less, and each peak is preferably less than 1.5 area %. The amount of this monomer affects the amount of residual low molecular weight epoxy resin, which in turn affects heat resistance, etc.

[0036] Next, a method for producing the epoxy resin of the present invention will be described. As mentioned above, the method for producing the epoxy resin of the present invention is not particularly limited, but it can be obtained, for example, by subjecting the phenolic resin represented by formula (2) above to an addition or ring-closing reaction with epihalohydrin in the presence of a solvent and a catalyst. The amount of epihalohydrin used is usually 1.0 to 20.0 mol, preferably 1.5 to 10.0 mol, per mol of phenolic hydroxyl groups in the phenolic resin.

[0037] Examples of alkali metal hydroxides that can be used in the epoxidation reaction include sodium hydroxide and potassium hydroxide. The alkali metal hydroxide may be a solid or an aqueous solution. When an aqueous solution is used, the alkali metal hydroxide may be continuously added to the reaction system while continuously distilling water and epihalohydrin under reduced pressure or normal pressure, followed by liquid separation to remove water and continuously returning the epihalohydrin to the reaction system. The amount of alkali metal hydroxide used is typically 0.9 to 2.5 moles, preferably 0.95 to 1.5 moles, per mole of phenolic hydroxyl groups in the phenolic resin. If the amount of alkali metal hydroxide used is too small, the reaction will not proceed sufficiently. On the other hand, excessive use of more than 2.5 moles of alkali metal hydroxide per mole of phenolic hydroxyl groups in the phenolic resin will result in the production of unnecessary waste by-products.

[0038] To accelerate the reaction, a quaternary ammonium salt such as tetramethylammonium chloride, tetramethylammonium bromide, or trimethylbenzylammonium chloride may be added as a catalyst. The amount of quaternary ammonium salt used is typically 0.1 to 15 g, and preferably 0.2 to 10 g, per mole of phenolic hydroxyl groups in the phenolic resin. If the amount used is too small, a sufficient reaction acceleration effect cannot be obtained, while if the amount used is too large, the amount of quaternary ammonium salt remaining in the epoxy resin increases, which may cause a deterioration in electrical reliability.

[0039] During the epoxidation reaction, it is preferable to add an alcohol such as methanol, ethanol, or isopropyl alcohol, or an aprotic polar solvent such as dimethyl sulfone, dimethyl sulfoxide, tetrahydrofuran, or dioxane to the reaction. When an alcohol is used, the amount used is usually 2 to 50 wt %, preferably 4 to 20 wt %, based on the amount of epihalohydrin used. When an aprotic polar solvent is used, the amount used is usually 5 to 100 wt %, preferably 10 to 80 wt %, based on the amount of epihalohydrin used. The reaction temperature is usually 30 to 90°C, preferably 35 to 80°C. The reaction time is usually 0.5 to 100 hours, preferably 1 to 30 hours. After completion of the reaction, the epihalohydrin and the solvent are removed from the reaction product by heating under reduced pressure, either after washing with water or without washing with water. Furthermore, to obtain an epoxy resin with even less hydrolyzable halogen, the recovered epoxy resin can be dissolved in a solvent such as toluene or methyl isobutyl ketone, and an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is added to carry out the reaction, ensuring ring closure. In this case, the amount of alkali metal hydroxide used is typically 0.01 to 0.3 mol, preferably 0.05 to 0.2 mol, per mol of phenolic hydroxyl groups in the phenolic resin used for glycidylation. The reaction temperature is typically 50 to 120°C, and the reaction time is typically 0.5 to 24 hours. After completion of the reaction, the resulting salt is removed by filtration, washing with water, or the like, and the solvent is then distilled off under heating and reduced pressure to obtain the epoxy resin of the present invention.

[0040] The curable resin composition of the present invention will now be described. The epoxy resin used in the curable resin composition of the present invention may be the epoxy resin represented by formula (1) alone, or may be used in combination with other epoxy resins. When used in combination, the proportion of the epoxy resin represented by formula (1) in the total epoxy resin is preferably 10 to 98% by weight, more preferably 30 to 95% by weight, and even more preferably 60 to 95% by weight. By adding the epoxy resin represented by formula (1) in an amount of 10% or more, an improved elastic modulus and low water absorption can be achieved.

[0041] Specific examples of other epoxy resins that can be used in combination with the epoxy resin represented by formula (1) include polycondensates of bisphenols (bisphenol A, bisphenol F, bisphenol S, biphenol, bisphenol AD, etc.) or phenols (phenol, alkyl-substituted phenol, aromatic-substituted phenol, naphthol, alkyl-substituted naphthol, dihydroxybenzene, alkyl-substituted dihydroxybenzene, dihydroxynaphthalene, etc.) with various aldehydes (formaldehyde, acetaldehyde, alkylaldehyde, benzaldehyde, alkyl-substituted benzaldehyde, hydroxybenzaldehyde, naphthaldehyde, glutaraldehyde, phthalaldehyde, crotonaldehyde, cinnamaldehyde, etc.); polycondensates of the phenols with various diene compounds (dicyclopentadiene, terpenes, vinylcyclohexene, norbornadiene, vinylnorbornene, tetrahydroindene, divinylbenzene, divinylbiphenyl, diisopropyl ether, methyl methyl ether, methyl ethyl ... Examples of epoxy resins include polymers of the phenols and ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, benzophenone, etc.); polycondensates of the phenols and aromatic dimethanols (benzenedimethanol, biphenyldimethanol, etc.); polycondensates of the phenols and aromatic dichloromethyls (α,α'-dichloroxylene, bischloromethylbiphenyl, etc.); polycondensates of the phenols and aromatic bisalkoxymethyls (bismethoxymethylbenzene, bismethoxymethylbiphenyl, bisphenoxymethylbiphenyl, etc.); and glycidyl ether epoxy resins, alicyclic epoxy resins, glycidylamine epoxy resins, and glycidyl ester epoxy resins obtained by glycidylating polycondensates of the bisphenols and various aldehydes or alcohols, but are not limited to these, so long as they are commonly used epoxy resins. These may be used alone or in combination of two or more.

[0042] Curing agents that can be used in the curable resin composition of the present invention include amine-based curing agents, acid anhydride-based curing agents, amide-based curing agents, phenol-based curing agents, etc. Specific examples of curing agents that can be used include o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 2,2'-diaminodiphenylsulfone, diethyltoluenediamine, dimethylthiotoluenediamine, diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-4,4'-diaminodiphenylmethane, ... , 4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, 4,4'-diamino-3,3',5,5'-tetramethyldiphenylmethane, 4,4'-diamino-3,3',5,5'-tetraethyldiphenylmethane, 4,4'-diamino-3,3',5,5'-tetraisopropyldiphenylmethane, 4,4'-methylenebis(N-methylaniline), bis(aminophenyl)fluorene, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 2,2'-bis [4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]sulfone, 1,3'-bis(4-aminophenoxy)benzene, 1,4'-bis(4-aminophenoxy)benzene, 1,4'-bis(4-aminophenoxy)biphenyl, 4,4'-(1,3-phenylenediisopropylidene)bisaniline, 4,4'-(1,4-phenylenediisopropylidene)bisaniline, naphthalenediamine, benzidine, dimethylbenzidine, WO 2017 / 170551 Examples of suitable amines include aromatic amine compounds such as the aromatic amine compounds described in Synthesis Examples 1 and 2, and aliphatic amines such as 1,3-bis(aminomethyl)cyclohexane, isophoronediamine, 4,4′-methylenebis(cyclohexylamine), norbornanediamine, ethylenediamine, propanediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, dimer diamine, and triethylenetetramine, but are not limited thereto, and can be suitably used depending on the properties desired to be imparted to the composition.In order to ensure a pot life, it is preferable to use an aromatic amine, and in order to impart quick-curing properties, it is preferable to use an aliphatic amine. By using an amine compound containing a bifunctional component as a main component as a curing agent, a highly linear network can be constructed during the curing reaction, and particularly excellent toughness can be exhibited.Further, amide compounds such as polyamide resins synthesized from dicyandiamide, a dimer of linolenic acid, and ethylenediamine; acid anhydride compounds such as phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride; bisphenols (bisphenol A, bisphenol F, bisphenol S, biphenol, bisphenol AD, etc.) or phenols (phenol polycondensates of phenols and various diene compounds (e.g., alkyl substituted phenols, aromatic substituted phenols, naphthol, alkyl substituted naphthols, dihydroxybenzenes, alkyl substituted dihydroxybenzenes, dihydroxynaphthalenes, etc.) with various aldehydes (e.g., formaldehyde, acetaldehyde, alkyl aldehydes, benzaldehyde, alkyl substituted benzaldehydes, hydroxybenzaldehyde, naphthaldehyde, glutaraldehyde, phthalaldehyde, crotonaldehyde, cinnamaldehyde, etc.); dicyclopentadiene, terpenes, vinylcyclohexene, norbornadiene, vinylnorbornene, tetrahydroindene, divinylbenzene, divinylbiphenyl, disopropenylbiphenyl, butadiene, isoprene, etc.), or polycondensates of the above phenols with ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, benzophenone, etc.), or polycondensates of the above phenols with aromatic dimethanols (benzenedimethanol, biphenyldimethanol, etc.), or Examples of the phenolic compounds include, but are not limited to, polycondensates of phenols and aromatic dichloromethyls (α,α'-dichloroxylene, bischloromethylbiphenyl, etc.), polycondensates of the phenols and aromatic bisalkoxymethyls (bismethoxymethylbenzene, bismethoxymethylbiphenyl, bisphenoxymethylbiphenyl, etc.), polycondensates of the bisphenols and various aldehydes, and modified products thereof; imidazole, trifluoroborane-amine complexes, guanidine derivatives, and the like.

[0043] In the curable resin composition of the present invention, the amount of the curing agent used is preferably 0.5 to 1.5 equivalents, and particularly preferably 0.6 to 1.2 equivalents, per equivalent of the epoxy group of the epoxy resin. By using an amount of 0.5 to 1.5 equivalents, good cured physical properties can be obtained.

[0044] When the curing reaction is carried out using the above curing agent, a curing accelerator may be used in combination. Examples of usable curing accelerators include imidazoles such as 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, and 2-ethyl-4-methylimidazole; tertiary amines such as 2-(dimethylaminomethyl)phenol, triethylenediamine, triethanolamine, and 1,8-diazabicyclo(5,4,0)undecene-7; organic phosphines such as triphenylphosphine, diphenylphosphine, and tributylphosphine; metal compounds such as tin octoate; tetra-substituted phosphonium tetra-substituted borates such as tetraphenylphosphonium tetraphenylborate and tetraphenylphosphonium ethyltriphenylborate; tetraphenylboron salts such as 2-ethyl-4-methylimidazole tetraphenylborate and N-methylmorpholine tetraphenylborate; and carboxylic acid compounds such as benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthoic acid, and salicylic acid. From the viewpoint of accelerating the curing reaction between the amine compound and the epoxy resin, a carboxylic acid compound such as salicylic acid is preferred. The curing accelerator is used in an amount of 0.01 to 15 parts by weight per 100 parts by weight of the epoxy resin, as required.

[0045] Furthermore, inorganic fillers can be added to the curable resin composition of the present invention as needed. Examples of inorganic fillers include, but are not limited to, powders such as crystalline silica, fused silica, alumina, zircon, calcium silicate, calcium carbonate, silicon carbide, silicon nitride, boron nitride, zirconia, fosterite, steatite, spinel, titania, and talc, as well as spherical beads thereof. These fillers may be used alone or in combination of two or more. The amount of inorganic filler used varies depending on the application. For example, when used as a semiconductor sealant, it is preferable to use the filler in a proportion of 20% by weight or more of the curable resin composition in terms of the heat resistance, moisture resistance, mechanical properties, and flame retardancy of the cured product of the curable resin composition, more preferably 30% by weight or more. In particular, it is even more preferable to use the filler in a proportion of 70 to 95% by weight to improve the linear expansion coefficient with the lead frame. In the present invention, the content of the inorganic filler is important, particularly in improving tracking resistance. When taking tracking resistance into consideration, the content of the inorganic filler in the total amount of the curable resin composition of the present invention is preferably 74% by weight or more and 95% by weight or less, and particularly preferably 78% by weight or more and 95% by weight or less. In the case of the epoxy resin structure of the present invention, it has been confirmed that tracking resistance is greatly improved when the content is 74% by weight or more, and when it is less than 74% by weight, for example, less than 70% by weight, the tracking performance becomes less advantageous compared to other epoxy resins.

[0046] The curable resin composition of the present invention can be blended with a release agent to improve release from the mold during molding. Any of the conventionally known release agents can be used, including ester waxes such as carnauba wax and montan wax, fatty acids such as stearic acid and palmitic acid and their metal salts, and polyolefin waxes such as oxidized polyethylene and non-oxidized polyethylene. These may be used alone or in combination. The blending amount of these release agents is preferably 0.5 to 3 wt % of the total organic components. If the amount is less than this, release from the mold is poor, and if the amount is too high, adhesion to a lead frame or the like is poor.

[0047] The curable resin composition of the present invention can contain a coupling agent to enhance the adhesion between the inorganic filler and the resin component. Any conventionally known coupling agent can be used, including, for example, various alkoxysilane compounds such as vinylalkoxysilane, epoxyalkoxysilane, styrylalkoxysilane, methacryloxyalkoxysilane, acryloxyalkoxysilane, aminoalkoxysilane, mercaptoalkoxysilane, and isocyanatoalkoxysilane, alkoxytitanium compounds, and aluminum chelates. These can be used alone or in combination of two or more. The coupling agent can be added by first treating the surface of the inorganic filler with the coupling agent and then kneading it with the resin, or by mixing the coupling agent with the resin and then kneading the inorganic filler.

[0048] Furthermore, known additives can be blended into the curable resin composition of the present invention as needed. Specific examples of usable additives include polybutadiene and its modified products, modified acrylonitrile copolymers, polyphenylene ether, polystyrene, polyethylene, polyimide, fluororesin, maleimide compounds, cyanate ester compounds, silicone gel, silicone oil, and colorants such as carbon black, phthalocyanine blue, and phthalocyanine green.

[0049] The curable resin composition of the present invention can be obtained by uniformly mixing the above-mentioned components. The curable resin composition of the present invention can be easily cured by the same method as conventionally known methods. For example, the curable resin composition of the present invention can be obtained by thoroughly mixing an epoxy resin and a curing agent, and optionally a curing accelerator, inorganic filler, mold release agent, silane coupling agent, and additives, using an extruder, kneader, roll, or the like, until uniform, and then molding the composition by melt casting, transfer molding, injection molding, compression molding, or the like, and further heating at 80 to 200°C for 2 to 10 hours to obtain a cured product.

[0050] The curable resin composition of the present invention may also contain a solvent, if necessary. The solvent-containing curable resin composition (epoxy resin varnish) is impregnated into a fibrous material (substrate) such as glass fiber, carbon fiber, polyester fiber, polyamide fiber, alumina fiber, or paper, and the resulting prepreg is heat-dried and hot-press molded to produce a cured product of the curable resin composition of the present invention. The solvent content of this curable resin composition is typically about 10 to 70 wt %, preferably about 15 to 70 wt %, in terms of internal weight. Examples of the solvent include amide solvents such as γ-butyrolactones, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethylimidazolidinone; sulfones such as tetramethylene sulfone; ether solvents such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether monoacetate, and propylene glycol monobutyl ether, preferably mono- or di-lower (1 to 3 carbon atoms) alkyl ethers of lower (1 to 3 carbon atoms) alkylene glycols; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, preferably in which the two alkyl groups may be the same or different; di-lower (1 to 3 carbon atoms) alkyl ketones; and aromatic solvents such as toluene and xylene. These may be used alone or in combination.

[0051] Alternatively, a sheet-like adhesive can be obtained by applying the epoxy resin varnish onto a release film, removing the solvent under heating, and then B-staging the varnish. This sheet-like adhesive can be used as an interlayer insulating layer in a multilayer substrate or the like.

[0052] The cured product obtained by the present invention can be used in various applications, including general applications in which thermosetting resins such as epoxy resins are used, such as adhesives, paints, coating agents, molding materials (including sheets, films, FRP, etc.), insulating materials (including printed circuit boards, electric wire coatings, etc.), sealants, and additives for other resins, etc.

[0053] Examples of adhesives include adhesives for civil engineering, construction, automobiles, general office use, and medical use, as well as adhesives for electronic materials. Among these, adhesives for electronic materials include interlayer adhesives for multilayer substrates such as build-up substrates, die bonding agents, semiconductor adhesives such as underfills, underfills for reinforcing BGAs, and mounting adhesives such as anisotropic conductive films (ACFs) and anisotropic conductive pastes (ACPs).

[0054] Examples of the sealant include potting, dipping, and transfer mold sealing for capacitors, transistors, diodes, light-emitting diodes, ICs, and LSIs; potting sealing for COB, COF, TAB, and the like for ICs and LSIs; underfill for flip chips; and sealing (including reinforcing underfill) when mounting IC packages such as QFP, BGA, and CSP.

[0055] The present invention will now be described in more detail with reference to examples, in which parts are by weight unless otherwise specified, but the present invention is not limited to these examples.

[0056] Epoxy equivalent: Measured according to a method in accordance with JIS K-7236. Softening point: Measured using a METLER TOLEDO softening point measuring instrument FP90. Hydroxyl equivalent: Acetylation of a sample was carried out using acetic anhydride in a pyridine solution, and after acetylation was completed, the remaining acid anhydride was decomposed with water. The amount of free acetic acid was measured by titrating this using a 0.5N KOH ethanol solution using a potentiometric titrator, and the hydroxyl equivalent was calculated from the results.

[0057] GPC (gel permeation chromatography) (Measurement condition 1) Apparatus: Waters e2695 Column: SHODEX GPC KF-401HQ, KF-402HQ, KF-403HQ, KF-404HQ (total of 4 columns) Flow rate: 0.3 ml / min Column temperature: 40°C Solvent used: THF (tetrahydrofuran) Detector: UV 254 nm (Measurement condition 2) Apparatus: Tosoh Corporation HLC-8220GPC Column: Tosoh Corporation TSK gel G3000HXL 1 column, TSK gel G2000HXL 2 columns (total of 3 columns) Flow rate: 1.065 ml / min Column temperature: 40°C Solvent used: THF (tetrahydrofuran) Detector: UV 254 nm (Measurement condition 3) Apparatus: Tosoh Corporation HLC-8420GPC Column: Tosoh Corporation TSK gel G3000HXL 1 column, TSK gel G2000HXL 2 columns (total 3 columns) Flow rate: 1.065 ml / min Column temperature: 40°C Solvent used: THF (tetrahydrofuran) Detector: UV 254 nm Standard polystyrene (Tosoh Corporation) PStQuick C, PStQuick D (when measuring molecular weight, correction was performed by adding styrene as an internal standard)

[0058] [Synthesis Example 1] While purging with nitrogen into a flask equipped with a thermometer, condenser, fractionating column, and stirrer, 137.2 parts of 3-methyl-6-t-butylphenol, 0.16 parts of 4-methyl-2-t-butylphenol, 60 parts of p-hydroxybenzaldehyde, 142 parts of toluene, and 1.4 parts of p-toluenesulfonic acid were added and reacted at 110 to 115°C for 8 hours. After completion of the reaction, 25% aqueous NaOH was added, and the toluene was distilled off by azeotropic dehydration. Then, 75% sulfuric acid was added, the pH was adjusted to 5 to 7, and the precipitated resin powder was filtered and dried at 60°C to obtain 186 parts of phenolic resin (P1). The resulting phenolic resin (PI) was powdery, had a softening point of 150°C or higher, a hydroxyl equivalent of 155 g / eq., and n = 1 by GPC was 48.8 area%. The GPC chart (measurement condition 1) is shown in Figure 1.

[0059] [Synthesis Example 2] While purging with nitrogen into a flask equipped with a thermometer, condenser, fractionating column, and stirrer, 153.1 parts of 3-methyl-6-t-butylphenol, 0.17 parts of 4-methyl-2-t-butylphenol, 60 parts of p-hydroxybenzaldehyde, 142 parts of toluene, and 0.6 parts of p-toluenesulfonic acid were added and reacted at 100 to 105 °C for 6 hours. After completion of the reaction, 25% aqueous NaOH was added, and the toluene was distilled off by azeotropic dehydration. Then, 75% sulfuric acid was added, the pH was adjusted to 5 to 7, and the precipitated resin powder was filtered and dried at 60 °C to obtain 198 parts of phenolic resin (P2). The obtained phenolic resin (P2) was powdery, had a softening point of 150 °C or higher, a hydroxyl equivalent of 144 g / eq., and n = 1 by GPC was 51.7 area %. The GPC chart (measurement condition 1) is shown in Figure 2.

[0060] [Synthesis Example 3] While purging with nitrogen into a flask equipped with a thermometer, condenser, fractionating column, and stirrer, 137.2 parts of 3-methyl-6-t-butylphenol, 0.16 parts of 4-methyl-2-t-butylphenol, 60 parts of p-hydroxybenzaldehyde, 142 parts of toluene, and 1.4 parts of p-toluenesulfonic acid were added and reacted at 110-115°C for 8 hours. After completion of the reaction, 25% NaOH water was added, and the toluene was distilled off by azeotropic dehydration. Then, 75% sulfuric acid was added, the pH was adjusted to 5-7, and the precipitated resin powder was filtered and dried at 60°C to obtain 180 parts of phenolic resin (P3). The obtained phenolic resin (P3) was powdery, had a softening point of 150°C or higher, a hydroxyl equivalent of 153 g / eq., and n = 1 by GPC was 47.6 area%. The GPC chart (measurement condition 1) is shown in Figure 3.

[0061] Example 1: While purging with nitrogen into a flask equipped with a thermometer, a condenser, a fractionating column, and a stirrer, 310 parts of the phenolic resin (P1) obtained in Synthesis Example 1, 973 parts of epichlorohydrin, 274 parts of dimethyl sulfoxide, and 15 parts of water were added, and the internal temperature was raised to 45°C. 16 parts of sodium hydroxide were added in portions over 1.5 hours, and the mixture was allowed to react at 45°C for 2 hours and at 70°C for 1 hour. Unreacted epichlorohydrin and the solvent were distilled off under heating and reduced pressure. 1040 parts of MIBK were added, and the organic layer was washed once with 440 parts of water. The organic layer was returned to the reaction vessel, and 20 parts of a 30 wt% aqueous sodium hydroxide solution was added and the mixture was allowed to react at 70°C for 2 hours. After cooling, the organic layer was washed four times with 130 parts of water, and the solvent was distilled off under heating and reduced pressure, yielding 170 parts of epoxy resin (E1) as a solid resin. The epoxy equivalent was 214 g / eq. The ICI viscosity (150°C) was 0.57 Pa s, the softening point was 100°C, and the parameter A was 2.14. The average repeating unit n estimated by GPC (detector UV 254 nm) was 2.4, with n=1 accounting for 42.3 area % and n=less than 1 accounting for 1.57 area %. The GPC chart (measurement condition 2) is shown in Figure 4.

[0062] [Example 2] While purging with nitrogen into a flask equipped with a thermometer, a condenser, a fractionating column, and a stirrer, 310 parts of the phenolic resin (P1) obtained in Synthesis Example 1, 584 parts of epichlorohydrin, 274 parts of dimethyl sulfoxide, and 15 parts of water were added, and the internal temperature was raised to 45°C. 16 parts of sodium hydroxide were added in portions over 1.5 hours, and the mixture was allowed to react at 45°C for 2 hours and at 70°C for 1 hour. Unreacted epichlorohydrin and the solvent were distilled off under heating and reduced pressure. 1,040 parts of MIBK were added, and the organic layer was washed once with 440 parts of water. The organic layer was returned to the reaction vessel, and 20 parts of a 30 wt% aqueous sodium hydroxide solution was added and the mixture was allowed to react at 70°C for 2 hours. After cooling, the organic layer was washed four times with 130 parts of water, and the solvent was distilled off under heating and reduced pressure, yielding 141 parts of epoxy resin (E2) as a solid resin. The epoxy equivalent was 225 g / eq. The ICI viscosity (150°C) was 1.92 Pa s, the softening point was 110°C, and the parameter A was 2.05. The average repeating unit n estimated by GPC (detector UV 254 nm) was 2.9, with n=1 accounting for 31.1 area % and n=less than 1 accounting for 1.28 area %. The GPC chart (measurement condition 2) is shown in Figure 5.

[0063] [Example 3] While purging with nitrogen into a flask equipped with a thermometer, a condenser, a fractionating column, and a stirrer, 310 parts of the phenolic resin (P3) obtained in Synthesis Example 3, 778 parts of epichlorohydrin, 274 parts of dimethyl sulfoxide, and 15 parts of water were added, and the internal temperature was raised to 45°C. 16 parts of sodium hydroxide were added in portions over 1.5 hours, and the mixture was allowed to react at 45°C for 2 hours and at 70°C for 1 hour. Unreacted epichlorohydrin and the solvent were distilled off under heating and reduced pressure. 1,040 parts of MIBK were added, and the organic layer was washed once with 440 parts of water. The organic layer was returned to the reaction vessel, and 20 parts of a 30 wt% aqueous sodium hydroxide solution was added and the mixture was allowed to react at 70°C for 2 hours. After cooling, the organic layer was washed four times with 130 parts of water, and the solvent was distilled off under heating and reduced pressure, yielding 303 parts of epoxy resin (E3) as a solid resin. The epoxy equivalent was 216 g / eq. The total chlorine was 440 ppm (based on ISO 21627-3), the inorganic chlorine ion concentration was 0.3 ppm, the ICI viscosity (150°C) was 0.64 Pa s, the softening point was 100°C, and the parameter A was 2.16. The Mn estimated by GPC (detector UV 254 nm) was 1059, the Mw was 2001 (polystyrene equivalent), n=1 was 39.5 area %, and n=less than 1 was 1.95 area %. The GPC chart (measurement condition 3) is shown in Figure 6.

[0064] Comparative Synthesis Example 1: While purging with nitrogen into a flask equipped with a thermometer, a condenser, a fractionating column, and a stirrer, 288 parts of the phenolic resin (P2) obtained in Synthesis Example 2, 584 parts of epichlorohydrin, 274 parts of dimethyl sulfoxide, and 15 parts of water were added, and the internal temperature was raised to 45°C. 16 parts of sodium hydroxide were added in portions over 1.5 hours, and the mixture was allowed to react at 45°C for 2 hours and at 70°C for 1 hour. Unreacted epichlorohydrin and solvent were distilled off under heating and reduced pressure. 1,040 parts of MIBK were added, and the organic layer was washed once with 440 parts of water. The organic layer was returned to the reaction vessel, and 20 parts of a 30 wt% aqueous sodium hydroxide solution was added and the mixture was allowed to react at 70°C for 2 hours. After cooling, the organic layer was washed four times with 130 parts of water, and the solvent was distilled off under heating and reduced pressure, yielding 165 parts of epoxy resin (E4) as a solid resin. The epoxy equivalent was 223 g / eq. The ICI viscosity (150°C) was 0.60 Pa s, the softening point was 99.7°C, and the parameter A was 2.24. The average repeating unit n calculated by GPC was 2.4, with n = 1 accounting for 43.9 area % and n = less than 1 accounting for 1.9 area %. The GPC chart (measurement condition 2) is shown in Figure 7.

[0065] Comparative Synthesis Example 2: While purging with nitrogen into a flask equipped with a thermometer, a condenser, a fractionating column, and a stirrer, 288 parts of the phenolic resin (P2) obtained in Synthesis Example 2, 487 parts of epichlorohydrin, 274 parts of dimethyl sulfoxide, and 15 parts of water were added, and the internal temperature was raised to 45°C. 16 parts of sodium hydroxide were added in portions over 1.5 hours, and the mixture was allowed to react at 45°C for 2 hours and at 70°C for 1 hour. Unreacted epichlorohydrin and solvent were distilled off under heating and reduced pressure. 1,040 parts of MIBK were added, and the organic layer was washed once with 440 parts of water. The organic layer was returned to the reaction vessel, and 20 parts of a 30 wt% aqueous sodium hydroxide solution was added and the mixture was allowed to react at 70°C for 2 hours. After cooling, the organic layer was washed four times with 130 parts of water, and the solvent was distilled off under heating and reduced pressure, yielding 161 parts of epoxy resin (E5) as a solid resin. The epoxy equivalent was 224 g / eq. The ICI viscosity (150°C) was 0.66 Pa s, the softening point was 100.9°C, and the parameter A was 2.22. The average repeating unit n calculated by GPC was 2.3, with n = 1 accounting for 43 area % and n = less than 1 accounting for 2.1 area %. The GPC chart (measurement condition 2) is shown in Figure 8.

[0066] [Examples 4 and 5, Comparative Examples 1 and 2] FAE-2500 (manufactured by Nippon Kayaku Co., Ltd.; analytical results will be described later) was used as the epoxy resins E1, E2, E4, and E6 obtained in the Examples and Synthesis Examples. Trisphenolmethane type phenolic resin (KAYAHARD KTG-105, manufactured by Nippon Kayaku Co., Ltd.) was used as the curing agent. Triphenylphosphine was used as the catalyst. The trisphenolmethane type phenolic resin was blended in an equivalent amount relative to the epoxy resin, and 1 phr of triphenylphosphine relative to the epoxy resin. The mixture was uniformly mixed and kneaded using a mixing roll, and after demolding, cured at 160°C for 2 hours and then at 180°C for 6 hours to obtain test specimens for evaluation.

[0067] The epoxy equivalent of FAE-2500 was 213 g / eq., the ICI viscosity (150°C) was 0.30 Pa s, the softening point was 93.5°C, and the parameter A was 2.28. The GPC chart (measurement condition 2) is shown in Figure 9.

[0068] The evaluation specimen was measured under the following conditions, and the results are shown in Table 1. The TMA chart is shown in FIG.

[0069] <Dynamic Viscoelasticity Measurement (DMA)> The glass transition temperature (the temperature at which tan δ is at its maximum value) and the value of tan δ at that time were measured using a dynamic viscoelasticity tester. Dynamic viscoelasticity measuring device: DMA-2980 manufactured by TA-instruments Heating rate: 2°C / min

[0070] <Thermo-mechanical property measurement (TMA)> The glass transition temperature (Tg) and coefficient of change of linear expansion (CTE) were evaluated using a thermo-mechanical property measurement device.

[0071] <Thermogravimetric Differential Thermal Analysis (TG-DTA)> The thermal decomposition temperature and the amount of residual carbon at 500°C were measured using TG-DTA. Measurement sample: Powder (passed through a 100 μm mesh, on a 75 μm mesh) 5 to 10 mg used. Measurement conditions: Heating rate 10°C / min, Air flow 200 ml

[0072]

[0073] [Example 6, Comparative Example 3] Epoxy resin (E1), epoxy resin (E6, FAE-2500 (manufactured by Nippon Kayaku)), Zylok-type phenolic resin (MEHC-7800SS manufactured by Meiwa Kasei) as a curing agent, triphenylphosphine (TPP, manufactured by Tokyo Chemical Industry Co., Ltd.) as a catalyst, silica gel (fused silica MSR-2212, manufactured by Tatsumori) as an inorganic filler, carnauba wax (manufactured by Cerarica Noda) as a mold release agent, and a silane coupling agent (trade name: KBM-303 manufactured by Shin-Etsu Chemical Co., Ltd.) as an additive were used, and they were uniformly mixed and kneaded using a mixing roll to obtain a curable resin composition. This curable resin composition was pulverized and then tableted using a tablet machine. The tableted curable resin composition was transfer molded (175°C for 60 to 150 minutes), demolded, and cured under conditions of 160°C x 2 hours + 180°C x 6 hours to obtain a test specimen for evaluation. The test specimen was used to perform the following evaluations. The measurement results are shown in Table 2.

[0074] <Tracking resistance test> Compliance standards: IEC Pub. 60112-2003 (4th edition) and JIS-C2134-2007 Test voltage: 400V to 600V Test solution: 0.1% aqueous solution of ammonium chloride Number of drops: 50 drops If the test piece broke after less than 50 drops, it was judged as NG. Temperature and humidity in the test room: 21°C to 23°C, 40 to 45% RH Test equipment: YST-112 model tracking resistance tester manufactured by Yamayo Testing Instruments Co., Ltd. Test sample shape: 50mm diameter, 3mm thickness One measurement per piece

[0075]

[0076] The results in Table 1 confirm that the epoxy resin of the present invention has high heat resistance as well as dimensional stability (low linear expansion). The results in Table 2 also confirm that the epoxy resin of the present invention has high tracking resistance.

[0077] [Synthesis Example 4] While purging with nitrogen into a flask equipped with a thermometer, condenser, fractionating column, and stirrer, 130.3 parts of 3-methyl-6-t-butylphenol, 0.2 parts of 4-methyl-2-t-butylphenol, 60 parts of p-hydroxybenzaldehyde, 142 parts of toluene, and 1.4 parts of p-toluenesulfonic acid were added and reacted at 110-115°C for 8 hours. After completion of the reaction, 25% NaOH water was added, and the toluene was distilled off by azeotropic dehydration. Then, 75% sulfuric acid was added, the pH was adjusted to 5-7, and the precipitated resin powder was filtered and dried at 60°C to obtain 186 parts of phenolic resin (P4). The obtained phenolic resin (P4) was powdery, had a softening point of 200°C or higher, a hydroxyl equivalent of 160 g / eq., and n = 1 by GPC was 37.0 area%. The GPC chart (measurement condition 1) is shown in Figure 11.

[0078] [Example 7] While purging with nitrogen into a flask equipped with a thermometer, a condenser, a fractionating column, and a stirrer, 320 parts of the phenolic resin (P4) obtained in Synthesis Example 4, 973 parts of epichlorohydrin, 274 parts of dimethyl sulfoxide, and 15 parts of water were added, and the internal temperature was raised to 45°C. 16 parts of sodium hydroxide were added in portions over 1.5 hours, and the mixture was allowed to react at 45°C for 2 hours and at 70°C for 1 hour. Unreacted epichlorohydrin and solvent were distilled off under heating and reduced pressure. 1,040 parts of MIBK were added, and the organic layer was washed once with 440 parts of water. The organic layer was returned to the reaction vessel, and 20 parts of a 30 wt% aqueous sodium hydroxide solution was added and the mixture was allowed to react at 70°C for 2 hours. After cooling, the organic layer was washed four times with 130 parts of water, and the solvent was distilled off under heating and reduced pressure, yielding 107 parts of epoxy resin (E7) as a solid resin. The epoxy equivalent was 220 g / eq. The ICI viscosity (150°C) was 0.8 Pa s or more, the softening point was 108.5°C, and the parameter A was 2.03. The average repeating unit n estimated by GPC (detector UV 254 nm) was 3.4, with n = 1 accounting for 24.9 area % and n = less than 1 accounting for 2.91 area %. The GPC chart (measurement condition 3) is shown in Figure 12. Furthermore, the peak with a retention time of 35.619 minutes accounted for 1.75% of the total, and the other peaks accounted for 1.5 area % or less.

[0079] Examples 8 and 9 Epoxy resins E3 and E7 obtained in the above Examples, trisphenolmethane phenolic resin (KAYAHARD KTG-105, manufactured by Nippon Kayaku Co., Ltd., hydroxyl equivalent: 102 g / eq.) as a curing agent, biphenylaralkyl phenolic resin (KAYAHARD GPH-65, manufactured by Nippon Kayaku Co., Ltd., curing agent, hydroxyl equivalent: 200 g / eq.) as a catalyst, triphenylphosphine (TPP, manufactured by Tokyo Chemical Industry Co., Ltd.) as a catalyst, silica gel (fused silica MSR-2212, manufactured by Tatsumori Co., Ltd.) as an inorganic filler, carnauba wax (manufactured by Cerarica Noda Co., Ltd.) as a mold release agent, and a silane coupling agent (trade name: KBM-303, manufactured by Shin-Etsu Chemical Co., Ltd.) as an additive were used in the proportions (parts by weight) shown in Table 3. The mixture was uniformly mixed and kneaded using a mixing roll, and after demolding, cured at 160°C for 2 hours and then at 180°C for 6 hours to obtain a test piece for evaluation. The test piece was used to carry out a tracking resistance test, and the measurement results are shown in Table 3.

[0080]

[0081] [Example 9, Comparative Example 4] The epoxy resin E1 obtained in the above example, biphenylaralkyl epoxy resin (manufactured by Nippon Kayaku, NC-3000), Zylok-type phenolic resin (manufactured by Meiwa Kasei, MEHC-7800SS) as a curing agent, triphenylphosphine (TPP, manufactured by Tokyo Chemical Industry Co., Ltd.) as a catalyst, silica gel (fused silica MSR-2212, manufactured by Tatsumori) as an inorganic filler, carnauba wax (manufactured by Cerarica Noda) as a mold release agent, and a silane coupling agent (trade name: KBM-303, manufactured by Shin-Etsu Chemical Co., Ltd.) as an additive were uniformly mixed and kneaded using a mixing roll to obtain a curable resin composition. This curable resin composition was pulverized and then tableted using a tablet machine. The tableted curable resin composition was transfer molded (175°C, 60-15 minutes), and then further demolded and cured under conditions of 160°C x 2 hours + 180°C x 6 hours to obtain a test specimen for evaluation. A tracking resistance test was performed using this test specimen. The measurement results are shown in Table 4.

[0082]

[0083] [Examples 10-13, Comparative Examples 5-8] The epoxy resin E1 obtained in the above examples, biphenylaralkyl epoxy resin (manufactured by Nippon Kayaku, NC-3000), Zylok phenolic resin (manufactured by Meiwa Kasei, MEHC-7800SS) as a curing agent, biphenylaralkyl phenolic resin (manufactured by Nippon Kayaku, KAYAHARD GPH-65), triphenylphosphine (TPP, manufactured by Tokyo Chemical Industry Co., Ltd.) as a catalyst, silica gel (fused silica MSR-2212, manufactured by Tatsumori) as an inorganic filler, carnauba wax (manufactured by Cerarica Noda) as a mold release agent, and a silane coupling agent (trade name: KBM-303, manufactured by Shin-Etsu Chemical Co., Ltd.) as an additive were uniformly mixed and kneaded using a mixing roll to obtain a curable resin composition. This curable resin composition was then pulverized and tableted using a tablet machine. The tableted curable resin composition was transfer molded (175°C for 60-15 minutes), and then demolded and cured under conditions of 160°C for 2 hours and 180°C for 6 hours to obtain a test specimen for evaluation. A tracking resistance test was performed using this test specimen. In particular, CTI was measured using a measurement method in accordance with IEC-Pub. 60112-2003 (4th edition). The measurement results are shown in Table 5 and Figure 13.

[0084]

[0085] From the above results, it was confirmed that the cured product using the epoxy resin of the present invention maintains a relatively high CTI, and that the rate of increase in CTI is higher than that of other compositions, particularly when the inorganic filler content is 74 wt % or more, more preferably 78 wt % or more.

[0086] The epoxy resin of the present invention is useful for automotive materials, particularly for peripheral materials for power devices, and is particularly effective in applications requiring heat resistance and a high comparative tracking index (CTI).

Claims

1. An epoxy resin represented by the following formula (1), wherein the value obtained by dividing the epoxy equivalent (g / eq.) by the softening point (°C) is 2.0 or more and less than 2.

2. (In formula (1), a plurality of Rs independently represent a methyl group or a hydrogen atom. n is the average value of the repeating number and is a real number from 1 to 10.) 2. A curable resin composition containing the epoxy resin according to claim 1.

3. The curable resin composition according to claim 2, wherein the content of the inorganic filler in the total amount of the curable resin composition is 74% by weight or more and 95% by weight or less.

4. A cured product obtained by curing the curable resin composition according to claim 2 or 3.