Cationic curable epoxy resin composition

Abstract

To provide a cationic curable type epoxy resin composition which can maintain viscosity with good workability, and has good storage stability and a low coefficient of linear expansion of a cured product, even in the case of a large blending amount of silica and high filling.SOLUTION: A cationic curable type epoxy resin composition contains an epoxy resin, silica, calcium carbonate, and a cationic polymerization initiator, wherein the epoxy resin contains an epoxy resin having a cycloalkene oxide skeleton and diglycidyl ether having an aromatic ring, and the silica contains spherical silica having an average primary particle diameter of 0.05-1.0 μm, and spherical silica having an average primary particle diameter of 1.5 or more and less than 30 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to an epoxy resin composition that cures by cationic polymerization. [Background technology]

[0002] For bonding optical components, UV-curing adhesives have traditionally been widely used due to the demands for transparency and rapid curing. UV-curing adhesives mainly consist of radical-curing acrylics and cationic-curing epoxys. However, the former suffers from problems in terms of long-term reliability, as polymerization is inhibited by oxygen in the air, and the adhesive strength decreases due to hydrolysis of the ester group. Therefore, in fields where reliability is important, epoxy-based UV-curing adhesives have become widely used.

[0003] In these epoxy adhesives, inorganic fillers such as silica are sometimes added to improve physical properties such as thixotropy and adhesive strength. For example, as adhesives for fixing optical components, adhesives consisting of an epoxy resin in which two glycidyl groups are directly linked in an aromatic ring, an alicyclic polyether skeleton epoxy resin, an alicyclic epoxy compound, a photocationic polymerization catalyst, a silane coupling agent, and silica nanoparticles have been proposed (Patent Document 1), and adhesives containing an alicyclic epoxy, an oxetane compound, a photocationic polymerization initiator, and silica (Patent Document 2).

[0004] However, increasing the amount of inorganic filler made the adhesive prone to sedimentation, and even with the addition of a dispersant to prevent this, it tended to thicken quickly. Furthermore, when inorganic fillers were heavily packed to reduce curing shrinkage and thermal expansion coefficient, the viscosity became extremely high, sometimes resulting in problems such as reduced workability and fluidity. Therefore, there was a need for an adhesive suitable for optical components that had good workability, a sufficiently low thermal expansion coefficient, and good storage stability. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-94509 [Patent Document 2] Patent No. 6709730 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The problem that the present invention aims to solve is to provide a cationic curable epoxy resin composition that maintains good viscosity for workability even when the silica content is high and the filling is high, has good storage stability, and has a low coefficient of linear expansion of the cured product. [Means for solving the problem]

[0007] To solve the above problems, the invention of claim 1 comprises an epoxy resin (A), silica (B), calcium carbonate (C), and a cationic polymerization initiator (D), wherein (A) comprises an epoxy resin (a1) having a cycloalkene oxide skeleton and a diglycidyl ether (a2) having an aromatic ring, and (B) comprises spherical silica (b1) with an average primary particle diameter of 1.5 to 30 μm and spherical silica (b2) with an average primary particle diameter of 0.05 to 1.0 μm. Furthermore, the above (D) includes a photocationic polymerization initiator (d1) and a thermal cationic polymerization initiator (d2). The present invention provides a cationic curable epoxy resin composition characterized by [a specific feature].

[0008] The invention of claim 2 is as described above. (a2) Resorcinol diglycidyl ether The present invention provides a cationic curable epoxy resin composition according to claim 1, characterized in that it is such.

[0009] The invention of claim 3 is as described above. The mixing ratio of (a2) is 5-50% by weight relative to (A). The present invention provides a cationic curable epoxy resin composition according to claim 1 or 2, characterized in that it is such.

[0010] The invention of claim 4 is, A cationic curable epoxy resin composition according to any one of claims 1 to 3, characterized in that it is an adhesive for optical components or optical devices. To provide. [Effects of the Invention]

[0012] The cation-curable epoxy resin composition of the present invention maintains a viscosity excellent in workability even when the blending amount of silica is increased and highly filled, has good storage stability, and has a low linear expansion coefficient of the cured product, so it is useful as an adhesive for optical applications.

Mode for Carrying Out the Invention

[0013] The present invention will be described in detail below.

[0014] The epoxy resin composition of the present invention is composed of an epoxy resin (A), silica (B), calcium carbonate (C), and a cationic polymerization initiator (D).

[0015] The epoxy resin (A) used in the present invention is a main constituent resin having high transparency, excellent heat resistance and flexibility, which has an epoxy group that is ring-opened by a cationic polymerization initiator to form a crosslinked structure, and includes an epoxy resin (a1) having a cycloalkene oxide skeleton and a diglycidyl ether (a2) having an aromatic ring.

[0016] The epoxy resin (a1) having a cycloalkene oxide skeleton used in the present invention has a structure in which an epoxy group is directly arranged on an alicyclic skeleton, has good reactivity with a cationic catalyst, has good adhesiveness and curability, and is also excellent in low-temperature curability. Since it has excellent curability, the amount of uncured matter remaining in the cured product after curing can be reduced, and an increase in shrinkage stress can be suppressed even in a high-temperature and high-humidity environment. As a result, the high-temperature and high-humidity resistance can be improved. It is preferably liquid at room temperature, and in terms of reactivity, it is preferable that the epoxy group has two or more functional groups. Examples of the bifunctional or higher-functional (a1) include 3′,4′-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, 3,4,3′,4′-diepoxy bicyclohexane, ε-caprolactone-modified 3′,4′-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate), etc., and they can be used alone or in combination of two or more. Among these, 3′,4′-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, which can obtain a cured product with low viscosity and high crosslink density, is preferable.

[0017] The blending ratio of the above (a1) is preferably 40 to 90% by weight, more preferably 45 to 85% by weight, and particularly preferably 50 to 75% by weight with respect to (A). By setting it to 40% by weight or more, a sufficiently high glass transition temperature (hereinafter referred to as Tg) can be ensured, and by setting it to 90% by weight or less, sufficient photocurability can be ensured. Further, the blending ratio of (a1) with respect to the total of (a1) and (a2) is preferably 45 to 95% by weight, and more preferably 50 to 90% by weight.

[0018] The aromatic ring-containing diglycidyl ether (a2) used in the present invention is a low-viscosity, high-photocuring-sensitivity resin. Examples include resorcinol diglycidyl ether, 4-ethyl resorcinol diglycidyl ether, catechol diglycidyl ether, hydroquinone diglycidyl ether, etc., which have one aromatic ring, and bisphenol-type and biphenyl-type glycidyl ethers, which have multiple aromatic rings. These can be used individually or in combination of two or more types. Among these, it is preferable to include resorcinol diglycidyl ether, which is readily available and is a crystalline epoxy that allows for high silica filling.

[0019] The mixing ratio of (a2) is preferably 5 to 50% by weight, more preferably 8 to 45% by weight, and particularly preferably 20 to 40% by weight relative to (A). A ratio of 5% by weight or more ensures sufficient curability, and a ratio of 50% by weight or less ensures a sufficiently high Tg. Furthermore, the mixing ratio of (a2) to the total of (a1) and (a2) is preferably 5 to 55% by weight, and more preferably 10 to 40% by weight.

[0020] In addition to (a1) and (a2) above, epoxy resins (a3) ​​having a monofunctional or bifunctional linear aliphatic skeleton or a branched aliphatic skeleton may be added as reactive diluents to adjust the viscosity of the composition. Among these, diglycidyl ethers with a linear aliphatic skeleton are preferred due to their very low viscosity, and 1,4-butanediol diglycidyl ether and 1,6-hexanediol diglycidyl ether, which have a viscosity of 30 mPa·s or less at 25°C, are even more preferred.

[0021] The overall blending ratio of (A), including (a1), (a2), and (a3), is preferably 15 to 45% by weight, more preferably 20 to 40% by weight, and particularly preferably 25 to 35% by weight, based on the total amount of solids. A ratio of 15% by weight or more ensures sufficient adhesive strength and film curing properties, while a ratio of 45% by weight or less allows for a sufficiently low coefficient of linear expansion of the cured product.

[0022] The silica (B) used in the present invention is blended for the purpose of suppressing curing shrinkage, reducing the coefficient of linear thermal expansion, and improving the fluidity of the composition. (B) includes at least two types: spherical silica (b1) with an average primary particle diameter (hereinafter referred to as average particle size) of 1.5 to 30 μm, and spherical silica (b2) with an average particle size of 0.05 to 1.0 μm.

[0023] Spherical silica can be obtained by melting crushed silica in a flame at a high temperature of over 2000°C, and rapidly cooling the molten silica that has been sphericalized by surface tension. The resulting spherical silica is amorphous and has a very low coefficient of thermal expansion of 0.5 ppm / K. Therefore, even in resins with a high expansion coefficient, incorporating it can suppress curing shrinkage of the cured product and reduce the coefficient of linear thermal expansion.

[0024] By incorporating spherical silica having two different average particle sizes, (b1) and (b2), it becomes possible to position smaller particles in the gaps between larger particles, thereby improving the packing efficiency, suppressing curing shrinkage, and significantly reducing the coefficient of linear thermal expansion. Furthermore, even with high packing, the distance between particles can be maintained, preventing contact between particles and resulting in high fluidity. In particular, when used as an adhesive to fix optical components, it is possible to improve workability along with fluidity, and to reduce displacement due to curing shrinkage.

[0025] The average particle size of (b1) is 1.5 to 30 μm, preferably 2 to 15 μm, and more preferably 3.0 to 10 μm. The average particle size of (b2) is 0.05 to 1.0 μm, preferably 0.2 to 0.9 μm, and more preferably 0.4 to 0.8 μm. By setting the particle size within this range, high packing is possible, and a sufficient reduction in the coefficient of thermal expansion and improvement in fluidity can be expected. The average particle size is the median diameter (d=50) measured by the laser diffraction / scattering method in accordance with JIS Z 8825-1.

[0026] The mixing ratio of (b1) to the sum of (b1) and (b2) is preferably 60 to 95% by weight, more preferably 65 to 90% by weight, and particularly preferably 70 to 85% by weight. A ratio of 60% by weight or more allows for sufficient fluidity and reduction of the coefficient of linear expansion, while a ratio of 95% by weight or less allows for a viscosity with good workability.

[0027] In addition to (b1) and (b2) above, fumed silica (b3) may be further included to improve thixotropy and suppress the sedimentation of filler components. The specific surface area of ​​(b3) is 50 to 300 m². 2 / g is preferred, and 80-200m 2 / g is more preferable, 100-150m 2 A value of / g is particularly preferred. Within this range, sufficient sedimentation prevention can be expected due to improved thixotropy. Since untreated silica is hydrophilic and easily absorbs moisture, surface-treated silica is preferred, and examples of surface treatment agents include dimethyldichlorosilane. The specific surface area can be measured by the BET method using gas adsorption.

[0028] The mixing ratio of (b3) is preferably 3.0% by weight or less relative to (B), more preferably 0.3 to 2.0% by weight, and particularly preferably 0.5 to 1.5%. This range ensures a sufficient anti-settlement effect.

[0029] The amount of (B) containing (b1), (b2), and (b3) is preferably 130 to 350 parts by weight, more preferably 150 to 300 parts by weight, and particularly preferably 170 to 270 parts by weight, per 100 parts by weight of (A). An amount of 130 parts or more can be expected to sufficiently reduce the coefficient of linear expansion and improve fluidity, while an amount of 350 parts or less can ensure viscosity and fluidity suitable for workability. Furthermore, the blending ratio of (B) to the total solid content is preferably 50 to 75% by weight, more preferably 55 to 70% by weight, and particularly preferably 57 to 68% by weight. By setting it within this range, a composition with a good balance of curability and fluidity can be obtained.

[0030] The calcium carbonate (C) used in the present invention is blended for the purpose of suppressing a rise in the viscosity of the composition, which becomes high due to the influence of highly filled silica, to a low level. Although the reason why the viscosity can be lowered is not clear, it is considered that one of the reasons is that it neutralizes the composition with a high acidity. Also for the same reason, it is expected to suppress thickening over time and improve the storage stability.

[0031] The average particle diameter of the above (C) is preferably 0.1 to 30 μm, more preferably 1.0 to 20 μm, and particularly preferably 3.0 to 10 μm. By setting it within this range, the effect of reducing the viscosity of the composition can be obtained, and at the same time, it is highly filled as a filler in the film together with silica, and the linear expansion rate can be sufficiently maintained at a low level.

[0032] The blending amount of the above (C), the blending ratio with respect to the total solid content is preferably 1 to 15% by weight, more preferably 2 to 10% by weight, and particularly preferably 3 to 8% by weight. Also, the blending amount with respect to 100 parts by weight of (B) is preferably 2 to 20 parts by weight, more preferably 3 to 15 parts by weight, and particularly preferably 5 to 12 parts by weight. By setting it within this range, it is possible to sufficiently suppress the rise in the viscosity of the composition and obtain a viscosity range excellent in workability.

[0033] The cationic polymerization initiator (D) used in the present invention preferably contains a photo cationic polymerization initiator (d1) and a thermal cationic polymerization initiator (d2) as starting materials for photo and thermal polymerization reactions.

[0034] The above (d1) is an initiator that generates cation ions by irradiation with active energy rays such as visible light, ultraviolet rays, and electron beams. For example, aromatic organic atomic cations of antimony, phosphorus, sulfur, nitrogen, iodine, and FG - , FGa - , BF4 - , PF6 - , SbF6 - , (C2F5)3PF3 -These are onium salts composed of anions such as diazonium salts, aromatic sulfonium salts, and aromatic iodonium salts, which can be used individually or in combination of two or more. Among these, aromatic triarylsulfonium salts are preferred because they have low toxicity, excellent solubility in monomers, and good photosensitivity.

[0035] The amount of component (d1) is preferably 0.1 to 5.0 parts by weight, more preferably 0.3 to 4.0 parts by weight, and particularly preferably 0.5 to 3.0 parts by weight, per 100 parts by weight of (A). Within this range, sufficient photocurability and storage stability can be ensured. Commercially available products include the CPI-100 series, 200 series, and 300 series (product names: all manufactured by Sunapro Co., Ltd.). In particular, the non-antimony CPI-310FG, which is highly sensitive to i-line (365 nm), is preferred because it does not cause discoloration of the cured product.

[0036] The aforementioned (d2) is an initiator that generates cationic ions upon heating, and examples include onium salts of nitrogen, sulfur, phosphorus, and iodine. An example of the anionic component of these onium salts is SbF6. - SbF4 - AsF6 - , B(C6F5)4 - PF4 - Examples include (c1) compounds, and in some cases they can be used as component (c1). Specifically, these include quaternary ammonium salt compounds, sulfonium salt compounds, phosphonium salt compounds, iodonium salt compounds, etc., which can be used individually or in combination of two or more. Among these, phosphorus-based aromatic sulfonium salt compounds, boron-based aromatic sulfonium salt compounds, and quaternary ammonium salt compounds are preferred due to their good low-temperature curability.

[0037] If the solubility of (d2) in (A) is low, it is preferable to dissolve (d2) in a solvent first before combining them. Examples of solvents include γ-butyrolactone, but the solvent is not particularly limited as long as it is a good solvent for solvent (d2) and has good compatibility with other components including (A), and solvents other than γ-butyrolactone may also be used. Additives such as stabilizers may also be added.

[0038] The amount of (d2) is preferably 0.1 to 3.0 parts by weight, more preferably 0.3 to 2.5 parts by weight, and particularly preferably 0.5 to 2.0 parts by weight, per 100 parts by weight of (A). Within this range, sufficient thermosetting properties and storage stability can be ensured. Examples of commercially available products include TA-100 (trade name: manufactured by Sunapro, aromatic sulfonium salt compound), CXC-1612 and CXC-1821 (both trade names: manufactured by KING INDUSTRIES, quaternary ammonium salt type compounds).

[0039] The amount of (D), which is the sum of (d1) and (d2), is preferably 0.3 to 8.0 parts by weight, more preferably 1.0 to 6.0 parts by weight, and particularly preferably 2.0 to 5.0 parts by weight, per 100 parts by weight of (A). Within this range, sufficient low-temperature curing properties and storage stability can be ensured. The mixing ratio of (d1) to (d2) is preferably (d2) / (d1) = 0.30 to 0.95, more preferably 0.50 to 0.90, and particularly preferably 0.65 to 0.85. By making the amount of (d2) less than that of (d1), the risk of (d2) cleaving due to photoacid generated from (d1) during light irradiation can be reduced, and as a result, the fixing accuracy of the optical components can be maintained.

[0040] The composition of the present invention (hereinafter referred to as "this composition") can be further enriched with a silane coupling agent (E) to improve adhesion to the adherend, suppress precipitation, and improve long-term storage. (E) has a structure in which functional groups that bond with organic and inorganic materials are combined within the molecule. Examples of functional groups that react with organic materials include vinyl groups, epoxy groups, amino groups, methacrylic groups, and mercapto groups, while hydrolyzable silyl groups react with inorganic materials.

[0041] The aforementioned (E) is preferably a type having epoxy functional groups that have good compatibility with (A), and a type having an isocyanurate skeleton is also preferred as it is highly effective in improving adhesive strength and heat resistance. A commercially available example of the former is GLYMO (product name: manufactured by Evonik Industries), and a commercially available example of the latter is KBM9659 (product name: manufactured by Shin-Etsu Chemical Co., Ltd.). The amount of silane coupling agent to be blended is preferably 0.5 to 8 parts by weight, and more preferably 1 to 5 parts by weight, per 100 parts by weight of (A).

[0042] In addition to the above, antioxidants, photosensitizers, tackifiers, leveling agents, defoamers, curing accelerators, colorants, thickeners, flame retardants, organic fine particles, etc. may be added as needed, to the extent that they do not impair the performance of this composition.

[0043] The viscosity of this lipid composition, as measured with an E-type viscometer at 25°C, rotor 3°×R7.7, and 1 rpm, is preferably 0.1 to 20 Pa·s, and more preferably 1 to 15 Pa·s. Furthermore, the increase in viscosity after being left at 23°C for 24 hours is preferably 1.6 times or less of the initial value, and more preferably 1.3 times or less. By keeping the increase rate below this, sufficient storage stability can be ensured.

[0044] The linear expansion coefficient of this composition, measured in a 1 mm thick sample at a heating rate of 10°C / min, is preferably α1 (linear expansion coefficient below Tg) of 30 ppm or less, and more preferably 20 ppm or less. Furthermore, α2 (linear expansion coefficient above Tg) is preferably 60 ppm or less, and more preferably 40 ppm or less. By keeping it within this range, it can be sufficiently used as an adhesive for joining optical components such as optical communication devices that require high reliability.

[0045] Any known light source can be used to cure this composition, such as low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, xenon lamps, metal halide lamps, LED lamps, and electrodeless ultraviolet lamps. The curing conditions are 50 mW / cm². 2 ~3000mW / cm 2 At this irradiation intensity, the integrated light dose is 50-6,000 mJ / cm². 2 Examples include the following. The irradiation atmosphere may be air, or an inert gas such as nitrogen or argon.

[0046] The cationic curable epoxy resin compositions of the present invention will be specifically described below with reference to examples and comparative examples, but these are merely examples and the invention is not limited to them. Unless otherwise stated, measurements were taken at room temperature of 25°C and relative humidity of 65%. [Examples]

[0047] Example 1 In a light-shielding bottle, (a1) Celoxide 2021P (product name: manufactured by Daicel Corporation, 3′,4′-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate), (a2) EX-201-IM (product name: manufactured by Nagase ChemteX Corporation, resorcinol diglycidyl ether), (a3) ​​YED216D (product name: manufactured by Mitsubishi Chemical Corporation, 1,6-hexanediol diglycidyl ether, viscosity 15 mPa·s), (b1) FB-5SDC (product name: manufactured by Denka Corporation, average particle size 5 μm, fused silica), (b2) FSP-130MC (product name: manufactured by Denka Corporation, average particle size 0.5 μm, fused silica), and (b3) TS610 (product name: manufactured by CABOT Corporation, fumed silica, dimethyldichlorosilane treated, specific surface area 130 m²). 2The following ingredients were added in the amounts shown in Table 1: (C) Cypron A (product name: manufactured by Cipro Chemical Co., Ltd., average particle size 5 μm), (d1) CPI-210S (product name: manufactured by Sunapro Co., Ltd., diphenyl[4-(phenylthio)phenyl]sulfonium tris(pentafluoroethyl)trifluorophosphate), (d2) CXC1612 (product name: manufactured by KING INDUSTRIES, quaternary ammonium salt compound), (d2) γ-butyllactone as the solvent for (d2), and (E) KBM9659 (product name: manufactured by Shin-Etsu Chemical Co., Ltd., tris-(triethoxysilylpropyl)isocyanurate) and GLYMO (product name: manufactured by Evonik Japan, 3-glycidoxypropyltrimethoxysilane). The mixture was stirred using a stirring and degassing device until homogeneous to obtain the cationic curable epoxy resin composition of Example 1. The units in the formulation table are parts by weight.

[0048] Examples 2-10 In addition to the materials used in Example 1, YL980 (product name: Mitsubishi Chemical Corporation, bisphenol A epoxy, epoxy equivalent 180-190) as (a2), and CXC1821 (product name: KING INDUSTRIES Corporation, quaternary ammonium salt type compound) and TA-100 (product name: Sunapro Corporation, aromatic sulfonium salt type compound) as (d2) were added to a light-shielding bottle in the amounts shown in Table 1, and stirred using a stirring and degassing device until homogeneous to obtain the cationic curing epoxy resin compositions of Examples 2 to 10.

[0049] Comparative Examples 1-4 In addition to the materials used in the examples, YX8000 (product name: Mitsubishi Chemical Corporation, hydrogenated bisphenol A epoxy, epoxy equivalent 205) was added as (A) in the amounts shown in Table 2, and the mixture was stirred using a stirring and degassing device until homogeneous to obtain the cationic curing epoxy resin compositions of Comparative Examples 1 to 4.

[0050] [Table 1]

[0051] [Table 2]

[0052] Evaluation items and evaluation methods

[0053] Preparation of a linear thermal expansion coefficient test specimen The epoxy resin composition obtained above was cast to a size of 5 mm x 5 mm x 1 mm thickness after curing, and then treated with a Heraeus LH6 / LC-6B ultraviolet irradiation device (electrodeless) at a D-bulb output of 100 mW / cm². 2 , cumulative light intensity 6000 mJ / cm 2 After irradiation and photocuring under these conditions, the material was further cured by heat curing at 130°C for 2 hours.

[0054] Linear expansion coefficient: Using a ThermoPlus2 TMA8310 thermomechanical analyzer manufactured by Rigaku Denki Co., Ltd., the above-mentioned test specimen measuring 5 mm × 5 mm × 1 mm in thickness was measured under a heating rate of 10 °C / min. The temperature at which the slope of the temperature / expansion coefficient graph changed was defined as the thermal expansion coefficient, with α1 defined as the temperature before the glass transition and α2 as the temperature after the glass transition.

[0055] Viscosity: Measured using a Toki Sangyo E-type viscometer RE-215R at a cone angle of 3°R7.7, a temperature of 25±1℃, and a rotation speed of 10 rpm. Values ​​between 0.1 and 20 Pa·S were marked with ○, and values ​​outside this range were marked with ×.

[0056] Storage life: Viscosity increase rate was measured after leaving the product at 23°C for 24 hours. A value of 1.6 times or less compared to the initial value is marked with a circle (○). A value greater than 1.6 times was marked with an "X".

[0057] Glass transition temperature: A resin composition was poured into a 5mm × 40mm × t0.5mm silicone mold, a release film was placed on top, and cured with a FusionD bulb at 100mW / cm2 and 6000mJ / cm2. The test specimen removed from the mold was heat-treated in a 130°C constant temperature bath for 2 hours to obtain the sample. The obtained sample was subjected to a tensile test using a TA Instruments Q800 dynamic viscoelasticity analyzer from room temperature to 200°C at a heating rate of 3°C / min and a frequency of 1Hz to determine the storage modulus and loss modulus. The temperature at the maximum point of the obtained TanΔ was defined as the glass transition temperature, with values ​​of 150°C or higher being marked with ○ and values ​​of less than 150°C being marked with ×.

[0058] Curability: Using a differential scanning calorimeter, the total heat generated by the resin before curing (A) and the total heat generated by the resin after curing (B) were measured when each epoxy resin composition was held at 100°C for 3 hours. The response rate was calculated as (AB) / A × 100, with a response rate of over 95% being marked with ◎, 90-95% with ○, and less than 90% with ×.

[0059] Evaluation results The evaluation results are shown in Tables 3 and 4.

[0060] [Table 3]

[0061] [Table 4]

[0062] The epoxy resin compositions used in the examples showed good results in all evaluations, including coefficient of linear expansion, viscosity, storage properties, glass transition temperature, and curability.

[0063] On the other hand, Comparative Example 1, which did not contain (B), had poor compatibility and separated; Comparative Example 2, which did not contain (b2), and Comparative Example 3, which did not contain (C), had high viscosity; and Comparative Example 4, which did not contain (a1), had a low Tg. In all cases, none of these were suitable for the present invention.

Claims

1. A cationic curable epoxy resin composition comprising an epoxy resin (A), silica (B), calcium carbonate (C), and a cationic polymerization initiator (D), wherein (A) comprises an epoxy resin having a cycloalkene oxide skeleton (a1) and a diglycidyl ether having an aromatic ring (a2), (B) comprises spherical silica (b1) with an average primary particle diameter of 1.5 to 30 μm and spherical silica (b2) with an average primary particle diameter of 0.05 to 1.0 μm, and (D) comprises a photocationic polymerization initiator (d1) and a thermal cationic polymerization initiator (d2).

2. The cationic curable epoxy resin composition according to claim 1, characterized in that (a2) is resorcinol diglycidyl ether.

3. The cationic curable epoxy resin composition according to claim 1 or 2, characterized in that the blending ratio of (a2) is 5 to 50% by weight relative to (A).

4. A cationic curable epoxy resin composition according to any one of claims 1 to 3, characterized in that it is an adhesive for optical components or optical devices.

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