Epoxy resin composition

Abstract

The present invention provides an epoxy resin composition that is provided with flexibility to combine impact resistance and mechanical strength, while maintaining epoxy resin-specific high elastic modulus, that reduces an increase in viscosity due to mixing, and that is excellent in heat resistance, storage stability, and solvent resistance. Provided is an epoxy resin composition containing: a modified polyvinyl acetal resin having a constitutional unit with an acid-modified group; a reactive diluent; and an epoxy resin, the epoxy resin composition having a sea-island phase separated structure after being cured.

Claims

1. An epoxy resin composition comprising: a modified polyvinyl acetal resin having a constitutional unit with an acid-modified group; a reactive diluent; and an epoxy resin, the epoxy resin composition having a sea-island phase separated structure after being cured, and the modified polyvinyl acetal resin containing an acetoacetal group and a butyral group at a ratio of 6:4 to 10:0, and having an acetal group content of 60 to 90 mol %.

2. The epoxy resin composition according to claim 1, wherein the sea-island phase separated structure includes island components having an average dispersion diameter of 5.0 μm or less.

3. The epoxy resin composition according to claim 1, wherein the amount of the constitutional unit with an acid-modified group in the modified polyvinyl acetal resin is 0.01 to 20.0 mol %.

4. The epoxy resin composition according to claim 1, wherein the modified polyvinyl acetal resin has an acetyl group content of 0.1 to 25 mol %.

5. The epoxy resin composition according to claim 1, wherein the amount of the modified polyvinyl acetal resin is 0.1 to 50 parts by weight relative to 100 parts by weight of the reactive diluent and the epoxy resin in total.

6. The epoxy resin composition according to claim 1, wherein the amount of the reactive diluent is 1 to 50% by weight relative to the total of the epoxy resin and the reactive diluent.

7. The epoxy resin composition according to claim 1, wherein the reactive diluent is an acyclic aliphatic compound having one to three glycidyl groups in a molecule.

8. The epoxy resin composition according to claim 1, wherein the ratio between the amount of the reactive diluent and the amount of the epoxy resin is 1:99 to 50:50.

9. A cured product obtained by curing the epoxy resin composition according to claim 1.

10. The epoxy resin composition according to claim 1, wherein the constitutional unit with an acid-modified group is at least one selected from the group consisting of a constitutional unit represented by the following formula (1-2), a constitutional unit represented by the following formula (1-3), and a constitutional unit represented by the following formula (1-4): ##STR00003## wherein in formula (1-2), R.sup.2 and R.sup.3 each independently represents a single bond or a C1-C10 alkylene group, and X.sup.2 and X.sup.3 each independently represents a hydrogen atom, a metal atom, or a methyl group; wherein in formula (1-3), R.sup.4 and R.sup.5 each independently represents a single bond or a C1-C10 alkylene group, and X.sup.4 and X.sup.5 each independently represents a hydrogen atom, a metal atom, or a methyl group; and wherein in formula (1-4), R.sup.6 and R.sup.7 each independently represents a single bond or a C1-C10 alkylene group, and X.sup.6 and X.sup.7 each independently represents a hydrogen atom, a metal atom, or a methyl group.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a scanning electron microscopic photograph of a cut surface of a cured product of an epoxy resin composition obtained in Example 1.

(2) FIG. 2 is a scanning electron microscopic photograph of a cut surface of a cured product of the epoxy resin composition obtained in Example 1.

DESCRIPTION OF EMBODIMENTS

(3) The present invention is more specifically described in the following with reference to, but not limited to, examples.

EXAMPLE 1

(4) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 75 g of acetaldehyde, and 10 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(5) The polyvinyl alcohol used had an average degree of polymerization of 1,500, a degree of saponification of 98.8 mol %, and contained 1.0 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, and X.sup.7 represents a hydrogen atom).

(6) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(7) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of the constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 1.0 mol %).

(8) Table 1 shows the acetal group content, the acetyl group content, and the hydroxyl group content measured by .sup.13C-NMR.

(9) An amount of 20 parts by weight of the obtained modified polyvinyl acetal resin, 20 parts by weight of a reactive diluent, 80 parts by weight of an epoxy resin, 3.0 parts by weight of dicyandiamide and 2.0 parts by weight of an imidazole compound as curing agents, and 20.0 parts by weight of an inorganic filler were mixed to prepare an epoxy resin composition.

(10) The raw materials used are listed below.

(11) (Epoxy Resin)

(12) Bisphenol A-type epoxy resin (jER828, product of Mitsubishi Chemical Corporation, epoxy equivalent of 190, molecular weight of 370)

(13) (Reactive Diluent)

(14) Polypropylene glycol diglycidyl ether (EX920, product of Nagase ChemteX Corporation, epoxy equivalent of 176, molecular weight of 350)

(15) (Curing Agent)

(16) Dicyandiamide (DICY7, product of Mitsubishi Chemical Corporation)

(17) Imidazole compound (jERCURE EMI24, product of Mitsubishi Chemical Corporation)

(18) (Inorganic Filler)

(19) Calcium carbonate (Whiten P-30, product of Shiraishi Calcium Kaisha Ltd.)

EXAMPLE 2

(20) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 parts by weight of hydrochloric acid having a concentration of 35% by weight, 75 g of acetaldehyde, and 10 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(21) The polyvinyl alcohol used had an average degree of polymerization of 2,600, a degree of saponification of 98.8 mol %, and contained 1.0 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, and X.sup.7 represents a hydrogen atom).

(22) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(23) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of the constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 1.0 mol %).

(24) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

EXAMPLE 3

(25) An amount of 200 g of polyvinyl alcohol were added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 75 g of acetaldehyde, and 10 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(26) The polyvinyl alcohol used had an average degree of polymerization of 1,500, a degree of saponification of 98.8 mol %, and contained 2.0 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, X.sup.7 represents a hydrogen atom).

(27) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(28) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of the constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 2.0 mol %).

(29) Table 1 shows the acetal group content, the acetyl group content, and the hydroxyl group content measured by .sup.13C-NMR.

(30) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

EXAMPLE 4

(31) An amount of 200 parts by weight of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 75 g of acetaldehyde, and 10 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(32) The polyvinyl alcohol used had an average degree of polymerization of 1,500, a degree of saponification of 98.8 mol %, and contained 10.0 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, and X.sup.7 represents a hydrogen atom).

(33) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(34) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of the constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 10.0 mol %).

(35) Table 1 shows the acetal group content, the acetyl group content, and the hydroxyl group content measured by .sup.13C-NMR.

(36) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

EXAMPLE 5

(37) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight and 80 g of acetaldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(38) The polyvinyl alcohol used had an average degree of polymerization of 1,500, a degree of saponification of 98.8 mol %, and contained 1.0 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, X.sup.7 represents a hydrogen atom).

(39) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(40) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of a constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 1.0 mol %).

(41) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

EXAMPLES 6 TO 9

(42) Epoxy resin compositions were produced as in Example 1, except that the modified polyvinyl acetal resin obtained in Example 1 was used and that the amount of the polyvinyl acetal resin and the type and amount of the reactive diluent were changed as shown in Table 1.

(43) The reactive diluent mentioned below was used in Example 8.

(44) (Reactive Diluent)

(45) 1,6-Hexanediol diglycidyl ether (EX212, product of Nagase ChemteX Corporation, epoxy equivalent of 151, molecular weight of 300)

EXAMPLE 10

(46) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 70 g of acetaldehyde, and 8 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(47) The polyvinyl alcohol used had an average degree of polymerization of 1,500, a degree of saponification of 98.8 mol %, and contained 18.0 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, and X.sup.7 represents a hydrogen atom).

(48) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(49) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of a constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 18.0 mol %).

(50) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

EXAMPLE 11

(51) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 50 g of acetaldehyde, and 50 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(52) The polyvinyl alcohol used had an average degree of polymerization of 1,500, a degree of saponification of 98.8 mol %, and contained 1.0 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, and X.sup.7 represents a hydrogen atom).

(53) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(54) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of a constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 1.0 mol %).

(55) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

EXAMPLE 12

(56) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 75 g of acetaldehyde, and 10 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(57) The polyvinyl alcohol used had an average degree of polymerization of 320, a degree of saponification of 98.8 mol %, and contained 0.05 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, and X.sup.7 represents a hydrogen atom).

(58) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained by neutralization, washing with water, and drying by normal methods.

(59) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of a constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 0.05 mol %).

(60) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

EXAMPLE 13

(61) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 75 g of acetaldehyde, and 10 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(62) The polyvinyl alcohol used had an average degree of polymerization of 1,500 and a degree of saponification of 98.8 mol %, and contained 23.0 mol % of a constitutional unit with a carboxyl group represented by the formula (1-4) (in the formula (1-4), R.sup.6 represents a single bond, X.sup.6 represents a hydrogen atom, R.sup.7 represents a methylene group, and X.sup.7 represents a hydrogen atom).

(63) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(64) The obtained modified polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to confirm the presence of a constitutional unit with a carboxyl group represented by the formula (1-4) (amount: 23.0 mol %).

(65) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

EXAMPLES 14 AND 15

(66) Epoxy resin compositions were produced as in Example 1, except that the modified polyvinyl acetal resin obtained in Example 1 was used and that the amount of the polyvinyl acetal resin and the type and amount of the reactive diluent were changed as shown in Table 1.

COMPARATIVE EXAMPLE 1

(67) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 75 g of acetaldehyde, and 10 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(68) The polyvinyl alcohol used had an average degree of polymerization of 1,500 and a degree of saponification of 98.8 mol %.

(69) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(70) The obtained polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to fail to identify the presence of a constitutional unit with an acid-modified group.

(71) Table 1 shows the acetal group content, the acetyl group content, and the hydroxyl group content measured by .sup.13C-NMR.

(72) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

COMPARATIVE EXAMPLE 2

(73) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight and 150 g of acetaldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(74) The polyvinyl alcohol used had an average degree of polymerization of 1,500 and a degree of saponification of 98.8 mol %.

(75) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(76) The obtained polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to fail to identify the presence of a constitutional unit with an acid-modified group.

(77) Table 1 shows the acetal group content, the acetyl group content, and the hydroxyl group content measured by .sup.13C-NMR.

(78) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

COMPARATIVE EXAMPLE 3

(79) An amount of 200 g of polyvinyl alcohol was added to 1,800 g of pure water, and stirred at 90° C. for about two hours to be dissolved. The solution was cooled to 40° C., and to the solution were added 150 g of hydrochloric acid having a concentration of 35% by weight, 25 g of acetaldehyde, and 80 g of butyraldehyde. The acetalization reaction was carried out to precipitate a reaction product by maintaining the solution temperature at 40° C.

(80) The polyvinyl alcohol used had an average degree of polymerization of 1,500 and a degree of saponification of 98.8 mol %.

(81) Then, the reaction solution was held to maintain the temperature at 40° C. for three hours, thereby completing the reaction. A modified polyvinyl acetal resin powder was obtained through neutralization, washing with water, and drying by normal methods.

(82) The obtained polyvinyl acetal resin was dissolved in DMSO-D.sub.6 (dimethylsulfoxide), and analyzed by .sup.13C-NMR (nuclear magnetic resonance spectrum) to fail to identify the presence of of a constitutional unit with an acid-modified group.

(83) Table 1 shows the acetal group content, the acetyl group content, and the hydroxyl group content measured by .sup.13C-NMR.

(84) An epoxy resin composition was produced as in Example 1, except that the obtained modified polyvinyl acetal resin was used.

COMPARATIVE EXAMPLES 4 TO 6

(85) Epoxy resin compositions were produced as in Example 1, except that the modified polyvinyl acetal resin obtained in Comparative Example 1 was used and that the amount of the polyvinyl acetal resin and the type and amount of the reactive diluent were changed as shown in Table 1.

(86) The reactive diluent mentioned below was used in Comparative Example 5.

(87) (Reactive Diluent)

(88) Polyglycerol polyglycidyl ether (EX521, product of Nagase ChemteX Corporation, epoxy equivalent of 183, molecular weight of 900)

(89) <Evaluation>

(90) The following evaluation was performed on the epoxy resin compositions obtained in the examples and comparative examples. Table 1 shows the results.

(91) (Measurement of Viscosity and Thixotropic Index (TI))

(92) Using a cone-plate viscometer Gemini (product of Bohlin Instruments Ltd.), the viscosity of the epoxy resin composition was measured at 25° C. The TI was obtained by dividing the viscosity at a shear rate of 1/s by the viscosity at a shear rate of 10/s.

(93) (Confirmation of the Presence or Absence of Sea-Island Phase Separated Structure)

(94) The epoxy resin composition was heated at 160° C. for one hour to be cured, thereby preparing a cured product.

(95) The obtained cured product was cut with a cryo-microtome (product of Leica microsystems: UC7) into a test sample having a thickness of 70 nm. Specifically, a small piece obtained by trimming of the cured product was dyed in a 2% osmic acid aqueous solution at 60° C. for 12 hours, and then washed. Then, the temperature of the small piece of the cured product was set to −20° C., and cut with a cryo-microtome in a direction perpendicular to the thickness direction at a central portion in the thickness direction, and further cut to have a thickness of 70 nm. Thus, a test sample was prepared. The cut surface of the obtained test sample was observed using an electron microscope to confirm the presence or absence of the structure including: a continuous phase formed of a polymerized product of the reactive diluent and the epoxy resin; and a dispersion phase formed of the polyvinyl acetal resin dispersed in the continuous phase. Thus, the presence or absence of a sea-island phase separated structure was determined.

(96) FIG. 1 and FIG. 2 each show a scanning electron microscopic photograph of a cut surface of a cured product of the epoxy resin composition obtained in Example 1.

(97) (Measurement of Average Dispersion Diameter of Island Components)

(98) The cut surface of the cured product obtained in (Confirmation of the presence or absence of sea-island phase separated structure) was observed using a transmission electron microscope. The Feret's diameters of 200 island components (dispersion phase) were measured and the average was calculated, thereby obtaining the average dispersion diameter.

(99) (Measurement of Flattening of Island Components)

(100) The cut surface of the cured product obtained in (Confirmation of the presence or absence of sea-island phase separated structure) was observed using a transmission electron microscope. The proportion of the minor axis to the major axis of 200 island components (dispersion phase) were measured and the average was calculated, thereby obtaining the flattening.

(101) (Confirmation of the Number of Island Components)

(102) The cut surface of the cured product obtained in (Confirmation of the presence or absence of sea-island phase separated structure) was observed using a transmission electron microscope. The number of the island components per 10 μm×10 μm was confirmed.

(103) (Measurement of tan δ Change Rate)

(104) Using a dynamic viscoelastometer (product of IT Measurement Co., Ltd., DVA-200), tan δ of the cured product obtained in (Confirmation of the presence or absence of sea-island phase separated structure) was measured.

(105) The epoxy resin compositions obtained in the examples and comparative examples were also prepared without adding a polyvinyl acetal resin. Each obtained resin composition was heated at 160° C. for one hour to prepare a cured product. The tan δ of the obtained cured product (no PVB added) was similarly measured, and the tan δ change rate (%) was obtained from the following formula.
tan δ change rate=(tan δ of cured product/tan δ of cured product (no PVB added))×100.
(Impact Resistance)

(106) The obtained resin composition was poured into a mold and heated at 160° C. for one hour, thereby preparing a resin cured product. The obtained resin cured product was subjected to a Charpy impact test by a method in conformity with JIS K 7111 using a digital impact tester DG-UB type (product of Toyo Seiki Seisakusho, Ltd.). Based on the measured Charpy impact value (kJ/m.sup.2) upon breakage of the resin cured product, the impact resistance was evaluated.

(107) (Elongation at Break, Elastic Modulus)

(108) The obtained epoxy resin composition was poured into a release-treated specimen mold made of Teflon (®) and heated at 160° C. for one hour to prepare a specimen having a shape of Type 1 dumbbell (JIS K 7161).

(109) The elongation at break (%) and the elastic modulus (MPa) of the obtained specimen were measured using an AUTOGRAPH (AGS-J, product of Shimadzu Corporation) at a tension speed of 5 mm/min by a method in conformity with JIS K 7161.

(110) (T-Peel Strength)

(111) By a method in conformity with JIS K 6854-3, two SPCC steel plates were bonded to each other with the obtained resin composition applied thereto, and the obtained specimen was heated at 160° C. for one hour so that the resin composition was cured. The T-peel strength (N/25 mm) was measured under the conditions of a peel angle of 180 degrees and a peel rate of 200 mm/min.

(112) (Initial Viscosity)

(113) The viscosity (Pa.Math.s) of the obtained epoxy resin composition was measured using a cone-plate viscometer Gemini (product of Bohlin Instruments Ltd.) at 25° C. and at a shear rate of 20 s.sup.−1, and evaluated based on the following criteria. ∘∘ (Excellent): viscosity of not less than 2.0 Pa.Math.s but less than 3.0 Pa.Math.s ∘ (Good): viscosity of not less than 3.0 Pa.Math.s but less than 5.0 Pa.Math.s Δ (Fair): viscosity of not less than 5.0 Pa.Math.s but less than 7.0 Pa.Math.s × (Poor): viscosity of not less than 7.0 Pa.Math.s
(Storage Stability)

(114) The obtained epoxy resin composition was left to stand in an oven at 40° C. The viscosity right after the preparation and after standing for 30 days were measured using a cone-plate viscometer Gemini (product of Bohlin Instruments Ltd.). The change rate (%) of the viscosity was determined and evaluated based on the following criteria. ∘∘ (Good): viscosity change rate of less than 5% Δ (Fair): viscosity change rate of not less than 5% but less than 30% Δ (Poor): viscosity change rate of not less than 30%
(Heat Resistance)

(115) By a method in conformity with JIS K 6854-3, two SPCC steel plates were bonded to each other with the obtained resin composition applied thereto, and the obtained specimen was heated at 160° C. for one hour so that the resin composition was cured. Thus, a T-peel strength specimen was prepared. Then, the specimen was left to stand in an oven at 80°. The T-peel strength (N/25 mm) of the specimen was measured right after the preparation and after standing for 30 days under the conditions of a peel angle of 180 degrees and a peel rate of 200 mm/min, and evaluated based on the following criteria. ∘∘ (Good): T-peel strength change rate of less than 10% Δ (Fair): T-peel strength change rate of not less than 10% but less than 20% × (Poor): T-peel strength change rate of not less than 20%
(Solvent Resistance)

(116) The obtained resin composition was applied to an aluminum sheet to prepare a sheet having a thickness of 50 μm. The obtained sheet was immersed in an ethanol/toluene solvent mixture (weight ratio 1:1) for 24 hours. The weight change rate between before and after the immersion [(weight after immersion/weight before immersion)×100] (%) was calculated, and evaluated based on the following criteria. ∘∘ (Excellent): weight change rate of not less than 95% ∘ (Good): weight change rate of not less than 85% but less than 95% Δ (Fair): weight change rate of not less than 75% but less than 85% × (Poor): weight change rate of less than 75%

(117) TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Polyvinyl acetal Average degree of polymerization 1500 2600 1500 1500 resin Total acetal group content (mol %) 73.6 73.6 71.5 65 Acetoacetal group content (mol %) 66.2 66.2 64.7 58.5 Butyral group content (mol %) 7.4 7.4 6.8 6.5 Acetoacetal group content:Butyral 9:1 9:1 9:1 9:1 group content Acetyl group content (mol %) 1.2 1.2 1.2 1.2 Hydroxyl group content (mol %) 24.2 24.2 25.3 23.8 Amount of constitutional unit 1.0 1.0 2.0 10.0 with acid-modified group (mol %) Type of acid-modified group Carboxylic Carboxylic Carboxylic Carboxylic acid acid acid acid Amount (parts by weight) 20 20 20 20 Epoxy resin Bisphenol A-type epoxy resin 80 80 80 80 (parts by weight) Reactive diluent Polypropylene glycol diglycidyl 20 20 20 20 (parts by weight) ether 1,6-hexanediol diglycidyl ether — — — — Polyglycerol polyglycidyl ether — — — — Acid-modified group number/epoxy group numbner 0.013 0.013 0.026 0.120 Curing agent Dicyandiamide 3.0 3.0 3.0 3.0 (parts by weight) Imidazole compound 2.0 2.0 2.0 2.0 Inorganic filler Calsium carbonate 20.0 20.0 20.0 20.0 (parts by weight) Viscosity (Pa .Math. s) Shear rate 1/s 285.4 312.6 386.6 372.5 Shear rate 10/s 52.1 60.2 82.5 118.2 T I 5.5 5.2 4.7 3.2 Presence or absence of sea-island phase separation structure Present Present Present Present Average dispersion diameter of island components (μm) 0.45 0.28 0.32 0.21 Flattening of island components 0.125 0.139 0.143 0.13 Number of island components per unit area (pcs/10 μm × 10 μm) 892 842 810 825 tanδ change rate (%) 5.1 5.6 4.1 3.8 Evaluation Impact resistance (kJ/m.sup.2) 3.1 3.8 4.0 5.1 Elongation at break (%) 7.9 8.2 9.0 12.5 Elastic modulus (MPa) 3125 3120 3140 3150 T-peel strength (N/25 mm) 46.7 48.2 51.7 58.5 Initial viscosity (Pa .Math. s) ∘ ∘∘ ∘ ∘ Storage stability ∘∘ ∘∘ ∘∘ ∘∘ Heat resistance ∘∘ ∘∘ ∘∘ ∘∘ Solvent resistance ∘∘ ∘∘ ∘∘ ∘∘ Example 5 Example 6 Example 7 Example 8 Polyvinyl acetal Average degree of polymerization 1500 1500 1500 1500 resin Total acetal group content (mol %) 73.6 73.6 73.6 73.6 Acetoacetal group content (mol %) 73.6 66.2 66.2 66.2 Butyral group content (mol %) 0 7.4 7.4 7.4 Acetoacetal group content:Butyral 10:0 9:1 9:1 9:1 group content Acetyl group content (mol %) 1.2 1.2 1.2 1.2 Hydroxyl group content (mol %) 24.2 24.2 24.2 24.2 Amount of constitutional unit 1.0 1.0 1.0 1.0 with acid-modified group (mol %) Type of acid-modified group Carboxylic Carboxylic Carboxylic Carboxylic acid acid acid acid Amount (parts by weight) 20 10 30 20 Epoxy resin Bisphenol A-type epoxy resin 80 80 80 80 (parts by weight) Reactive diluent Polypropylene glycol diglycidyl 20 20 20 — (parts by weight) ether 1,6-hexanediol diglycidyl ether — — — 20 Polyglycerol polyglycidyl ether — — — — Acid-modified group number/epoxy group numbner 0.014 0.007 0.020 0.013 Curing agent Dicyandiamide 3.0 3.0 3.0 3.0 (parts by weight) Imidazole compound 2.0 2.0 2.0 2.0 Inorganic filler Calsium carbonate 20.0 20.0 20.0 20.0 (parts by weight) Viscosity (Pa .Math. s) Shear rate 1/s 263.5 217.6 386.5 359.9 Shear rate 10/s 40.9 72.4 56.2 51.2 T I 6.4 3.0 6.9 7.0 Presence or absence of sea-island phase separation structure Present Present Present Present Average dispersion diameter of island components (μm) 0.2 0.42 0.5 2.8 Flattening of island components 0.121 0.133 0.142 0.138 Number of island components per unit area (pcs/10 μm × 10 μm) 901 848 827 859 tanδ change rate (%) 2.7 3.7 9.2 15.2 Evaluation Impact resistance (kJ/m.sup.2) 3.3 2.6 4.1 2.9 Elongation at break (%) 7.8 6.1 11.1 9.0 Elastic modulus (MPa) 3210 3130 3160 3130 T-peel strength (N/25 mm) 45.2 40.1 49.9 44.4 Initial viscosity (Pa .Math. s) ∘∘ ∘∘ ∘ ∘∘ Storage stability ∘∘ ∘∘ Δ ∘∘ Heat resistance ∘∘ ∘∘ ∘∘ ∘∘ Solvent resistance ∘∘ ∘∘ ∘∘ ∘∘ Example 9 Example 10 Example 11 Example 12 Polyvinyl acetal Average degree of polymerization 1500 1500 1500 320 resin Total acetal group content (mol %) 73.6 56.6 73.6 74.05 Acetoacetal group content (mol %) 66.2 50.9 44.2 66.75 Butyral group content (mol %) 7.4 5.7 29.4 7.3 Acetoacetal group content:Butyral 9:1 9:1 6:4 9:1 group content Acetyl group content (mol %) 1.2 1.2 1.2 1.2 Hydroxyl group content (mol %) 24.2 24.2 24.2 24.7 Amount of constitutional unit 1.0 18.0 1.0 0.05 with acid-modified group (mol %) Type of acid-modified group Carboxylic Carboxylic Carboxylic Carboxylic acid acid acid acid Amount (parts by weight) 20 20 20 20 Epoxy resin Bisphenol A-type epoxy resin 70 80 80 80 (parts by weight) Reactive diluent Polypropylene glycol diglycidyl 30 20 20 20 (parts by weight) ether 1,6-hexanediol diglycidyl ether — — — — Polyglycerol polyglycidyl ether — — — — Acid-modified group number/epoxy group numbner 0.013 0.197 0.013 0.001 Curing agent Dicyandiamide 3.0 3.0 3.0 3.0 (parts by weight) Imidazole compound 2.0 2.0 2.0 2.0 Inorganic filler Calsium carbonate 20.0 20.0 20.0 20.0 (parts by weight) Viscosity (Pa .Math. s) Shear rate 1/s 321.2 425.3 495.6 192.5 Shear rate 10/s 102.5 165.5 73.6 43.6 T I 3.1 2.6 6.7 4.4 Presence or absence of sea-island phase separation structure Present Present Present Present Average dispersion diameter of island components (μm) 2.6 0.18 4.7 3.4 Flattening of island components 0.34 0.31 0.384 0.225 Number of island components per unit area (pcs/10 μm × 10 μm) 442 466 410 966 tanδ change rate (%) 21.2 1.7 24.6 17.6 Evaluation Impact resistance (kJ/m.sup.2) 3.5 2.7 2.3 2.2 Elongation at break (%) 9.5 7.5 7.0 5.4 Elastic modulus (MPa) 2980 3120 3050 2880 T-peel strength (N/25 mm) 48.5 64.3 43.2 28.2 Initial viscosity (Pa .Math. s) ∘∘ ∘ Δ ∘∘ Storage stability ∘∘ Δ Δ ∘∘ Heat resistance ∘∘ Δ Δ ∘ Solvent resistance ∘∘ ∘∘ ∘ ∘ Example 13 Example 14 Example 15 Polyvinyl acetal Average degree of polymerization 1500 1500 1500 resin Total acetal group content (mol %) 49.6 73.6 73.6 Acetoacetal group content (mol %) 44.7 66.2 66.2 Butyral group content (mol %) 4.9 7.4 7.4 Acetoacetal group content:Butyral 9:1 9:1 9:1 group content Acetyl group content (mol %) 1.2 1.2 1.2 Hydroxyl group content (mol %) 26.2 24.2 24.2 Amount of constitutional unit 23.0 1.0 1.0 with acid-modified group (mol %) Type of acid-modified group Carboxylic Carboxylic Carboxylic acid acid acid Amount (parts by weight) 20 20 20 Epoxy resin Bisphenol A-type epoxy resin 80 55 95 (parts by weight) Reactive diluent Polypropylene glycol diglycidyl 20 45 5 (parts by weight) ether 1,6-hexanediol diglycidyl ether — — — Polyglycerol polyglycidyl ether — — — Acid-modified group number/epoxy group numbner 0.241 0.013 0.014 Curing agent Dicyandiamide 3.0 3.0 3.0 (parts by weight) Imidazole compound 2.0 2.0 2.0 Inorganic filler Calsium carbonate 20.0 20.0 20.0 (parts by weight) Viscosity (Pa .Math. s) Shear rate 1/s 454.5 168.5 542.1 Shear rate 10/s 215.8 17.2 245.6 T I 2.1 9.8 2.2 Presence or absence of sea-island phase separation structure Present Present Present Average dispersion diameter of island components (μm) 0.13 4.8 0.18 Flattening of island components 0.41 0.47 0.123 Number of island components per unit area (pcs/10 μm × 10 μm) 218 222 982 tanδ change rate (%) 1.4 40.7 4.9 Evaluation Impact resistance (kJ/m.sup.2) 2.3 3.1 2.0 Elongation at break (%) 7.0 7.4 4.7 Elastic modulus (MPa) 3350 2590 3450 T-peel strength (N/25 mm) 68.0 36.7 32.1 Initial viscosity (Pa .Math. s) x ∘ x Storage stability Δ Δ ∘∘ Heat resistance ∘∘ Δ ∘∘ Solvent resistance ∘∘ Δ ∘∘ Compar- Compar- Compar- ative ative ative Example 1 Example 2 Example 3 Polyvinyl acetal Average degree of polymerization 1500 1500 1500 resin Total acetal group content (mol %) 74.6 74.6 74.6 Acetoacetal group content (mol %) 67.1 74.6 22.4 Butyral group content (mol %) 7.5 0 52.2 Acetoacetal group content:Butyral 9:1 0:10 3:7 group content Acetyl group content (mol %) 1.2 1.2 1.2 Hydroxyl group content (mol %) 24.2 24.2 24.2 Amount of constitutional unit 0.0 0.0 0.0 with acid-modified group (mol %) Type of acid-modified group — — — Amount (parts by weight) 20 20 20 Epoxy resin Bisphenol A-type epoxy resin 80 80 80 (parts by weight) Reactive diluent Polypropylene glycol 20 20 20 (parts by weight) diglycidyl ether 1,6-hexanediol diglycidyl ether — — — Polyglycerol polyglycidyl ether — — — Acid-modified group number/epoxy group numbner — — — Curing agent Dicyandiamide 3.0 3.0 3.0 (parts by weight) Imidazole compound 2.0 2.0 2.0 Inorganic filler Calsium carbonate 20.0 20.0 20.0 (parts by weight) Viscosity (Pa .Math. s) Shear rate 1/s 214.3 724.8 695.4 Shear rate 10/s 38.5 452.2 385.7 T I 5.6 1.6 1.8 Presence or absence of sea-island phase separation structure Absent Absent Absent (bicontin- (compati- (bicontin- uous) bilized) uous) Average dispersion diameter of island components (μm) — — — Flattening of island components — — — Number of island components per unit area (pcs/10 μm × 10 μm) — — — tanδ change rate (%) 27.5 38.7 32.2 Evaluation Impact resistance (kJ/m.sup.2) 1.3 1.5 1.2 Elongation at break (%) 4.3 2.7 3.5 Elastic modulus (MPa) 2675 2250 2450 T-peel strength (N/25 mm) 34.1 30.2 31.8 Initial viscosity (Pa .Math. s) ∘ x x Storage stability Δ x x Heat resistance x x x Solvent resistance x x x Compar- Compar- Compar- ative ative ative Example 4 Example 5 Example 6 Polyvinyl acetal Average degree of polymerization 1500 1500 1500 resin Total acetal group content (mol %) 74.6 74.6 74.6 Acetoacetal group content (mol %) 67.1 67.1 67.1 Butyral group content (mol %) 7.5 7.5 7.5 Acetoacetal group content:Butyral 9:1 9:1 9:1 group content Acetyl group content (mol %) 1.2 1.2 1.2 Hydroxyl group content (mol %) 24.2 24.2 24.2 Amount of constitutional unit 0.0 0.0 0.0 with acid-modified group (mol %) Type of acid-modified group — — — Amount (parts by weight) 60 20 20 Epoxy resin Bisphenol A-type epoxy resin 80 80 40 (parts by weight) Reactive diluent Polypropylene glycol diglycidyl ether 20 — 60 (parts by weight) 1,6-hexanediol diglycidyl ether — — — Polyglycerol polyglycidyl ether — 20 — Acid-modified group number/epoxy group numbner — — — Curing agent Dicyandiamide 3.0 3.0 3.0 (parts by weight) Imidazole compound 2.0 2.0 2.0 Inorganic filler Calsium carbonate 20.0 20.0 20.0 (parts by weight) Viscosity (Pa .Math. s) Shear rate 1/s 788.9 782.2 112.2 Shear rate 10/s 552.8 453.6 9.5 T I 1.4 1.7 11.8 Presence or absence of sea-island phase separation structure Absent Absent Absent (bicontin- (bleeded) (compati- uous bilized Average dispersion diameter of island components (μm) — — — Flattening of island components — — — Number of island components per unit area (pcs/10 μm × 10 μm) — — — tanδ change rate (%) 45.6 — 52.5 Evaluation Impact resistance (kJ/m.sup.2) 1.8 1.1 1.7 Elongation at break (%) 5.1 2.1 4.6 Elastic modulus (MPa) 2120 2790 1850 T-peel strength (N/25 mm) 35.5 29.0 27.5 Initial viscosity (Pa .Math. s) x Δ ∘ Storage stability x Δ x Heat resistance x x x Solvent resistance x x x

INDUSTRIAL APPLICABILITY

(118) The present invention can provide an epoxy resin composition that is provided with flexibility to combine impact resistance and mechanical strength, while maintaining epoxy resin-specific high elastic modulus, that reduces an increase in viscosity due to mixing, and that is excellent in heat resistance, storage stability, and solvent resistance.