Curable resin composition

Abstract

A liquid thermally expandable curable resin composition for use such as bonding by filling a clearance has difficulty in achieving both drying property and film forming property and also has a problem with storage stability. The problems were solved with a curable resin composition having the following composition. A curable resin composition comprises: (A) a film forming resin, (B) an epoxy resin, (C) an organic solvent, (D) thermally expandable particles, and (E) a curing agent ingredient for the (B). The (C) is selected from organic solvents having a boiling point of 100° C. or less and being liquid at normal temperature and contains a combination of (C-1) an ester-based solvent and (C-2) one or more solvents selected from ketone-based solvents, ether-based solvents, and glycol-based solvents, and a content ratio between the (C-1) and the (C-2) in a mass ratio is in a range of (C-1)/(C-2)=0.12 to 0.23.

Claims

1. A curable resin composition comprising: (A) a film forming resin, (B) an epoxy resin, (C) an organic solvent, (D) thermally expandable particles, and (E) a curing agent ingredient for the (B), wherein the (C) is selected from organic solvents having a boiling point of 100° C. or less and being liquid at normal temperature and contains a combination of (C-1) an ester-based solvent and (C-2) one or more solvents selected from ketone-based solvents, ether-based solvents, and glycol-based solvents, and a content ratio between the (C-1) and the (C-2) in a mass ratio is in a range of (C-1)/(C-2)=0.12 to 0.23.

2. The curable resin composition according to claim 1, wherein a content of the (C) is 193 to 211 parts by mass relative to 100 parts by mass of the (A).

3. The curable resin composition according to claim 1, wherein a content of the (D) is 45 to 88 parts by mass relative to 100 parts by mass of the (A).

4. The curable resin composition according to claim 1, wherein the (A) contains a phenoxy resin.

5. The curable resin composition according to claim 1, wherein the (E) contains one or more selected from imidazole derivatives and dicyandiamide.

6. The curable resin composition according to claim 1, wherein the (A) is a bisphenol A type phenoxy resin.

7. The curable resin composition according to claim 1, wherein the (B) is selected from the group consisting of a bisphenol A type epoxy resin, a cresol novolak type epoxy resin, a bisphenol F type epoxy resin, and a mixture thereof.

8. The curable resin composition according to claim 1, wherein the ester-based solvent (C-1) has a boiling point in a range of 55 to 85° C., and the solvent (C-2) has a boiling point in a range of 55 to 85° C.

9. The curable resin composition according to claim 1, wherein the (D) is a microcapsule-based thermally expandable particle having a gas barrier thermoplastic resin as a shell and enclosing a low boiling point compound in the shell, wherein the low boiling point compound is in the liquid state at normal temperature and has a boiling point of up to approximately 100° C.

10. A cured product formed by curing the curable resin composition according to claim 1.

11. A method of producing a cured product of the curable resin composition according to claim 1, comprising: obtaining a cured product of the curable resin composition by heating the curable resin composition to a temperature equal to or higher than an activation temperature of the (E) at which the (E) starts to cure the epoxy resin (B).

12. The method according to claim 11, wherein a content of the (C) is 193 to 211 parts by mass relative to 100 parts by mass of the (A).

13. The method according to claim 11, wherein a content of the (D) is 45 to 88 parts by mass relative to 100 parts by mass of the (A).

14. The method according to claim 11, wherein the (A) contains a phenoxy resin.

15. The method according to claim 11, wherein the (E) contains one or more selected from imidazole derivatives and dicyandiamide.

16. The method according to claim 11, wherein the (B) is selected from the group consisting of a bisphenol A type epoxy resin, a cresol novolak type epoxy resin, a bisphenol F type epoxy resin, and a mixture thereof.

17. The method according to claim 11, wherein the (D) is a microcapsule-based thermally expandable particle having a gas barrier thermoplastic resin as a shell and enclosing a low boiling point compound in the shell, wherein the low boiling point compound is in the liquid state at normal temperature and has a boiling point of up to approximately 100° C.

Description

EXAMPLES

(1) The characteristics of the curable resin composition of the present invention were evaluated and studied in. Examples and Comparative Examples by the following methods. The following materials were used for the constituent ingredients contained in the curable resin composition of the present invention and the curable resin compositions used for comparison (hereinafter collectively referred to simply as the “composition”). In addition, the compositions were prepared in accordance with the composition ratios listed in Tables 1 to 3. The numerical values listed in the tables are in parts by mass of the ingredients unless otherwise specified.

(2) (A) Film Forming Resin

(3) jER 1256B40: This is a bisphenol A type phenoxy resin having a molecular weight of about 45,000 dissolved and diluted with methyl ethyl ketone, and is a product of Mitsubishi Chemical Corporation with a solid content of 40% by mass and an epoxy equivalent weight of 6,700 to 8,000. Note that, in the tables, only the mass of the solid content (resin ingredient) is listed for the ingredient, and methyl ethyl ketone is listed in the row of (C-2).
(B) Epoxy Resin
DER 331: a bisphenol A type epoxy resin in the liquid state at normal temperature (25° C.), an epoxy equivalent weight of 186 to 190, and a product of Dow Chemical Japan Ltd.
EPICLON N-695: a cresol novolak type epoxy resin, an epoxy equivalent weight of 209 to 219, and a product of DIC Corporation.
EPICLON EXA-830: a bisphenol F type epoxy resin in the liquid state at normal temperature, an epoxy equivalent weight of 165 to 177, and a product of DIC Corporation.
(C) Organic Solvent Having Boiling Point of 100° C. or Less
(C-1) Ester-Based Solvent
ethyl acetate: a boiling point of about 77° C. and a product of San-Ai Oil Co., Ltd.
(C-1′) Solvents Other than Above
butyl acetate: a boiling point of about 126° C. and a product of San-Ai Oil Co., Ltd.
hexane: a boiling point of about 68° C. and a product of Maruzen Petrochemical
(C-2) Combination of Solvents Selected from Ketone-Based Solvents, Ether-Based Solvents, and Glycol-Based Solvents
methyl ethyl ketone: a boiling point of about 80° C. and a product of San-Ai Oil Co., Ltd.
(D) Thermally Expandable Particle
Expancel 920 DU 40: an average particle diameter of 10 to 14 μm before expansion, an expansion start temperature of 123 to 133° C., a shell material of acrylic polymer, a microcapsule composed of isopentane expansion ingredient, and a product of Japan Fillite Co., Ltd.
(E) Curing Agent Ingredient for Above (B)
jERCURE DICY7: a finely pulverized product of dicyandiamide, a 50% particle diameter of 3 μm, a melting point of 210° C., and a product of Mitsubishi Chemical Corporation.
CUREZOL 2MAOK-PW: an isocyanuric acid adduct of imidazole compound, a decomposition temperature of 260° C., a decomposition temperature of 260° C., and a product of Shikoku Chemicals Corporation.

(4) Each of the compositions evaluated in Examples and Comparative Examples was prepared by the following procedures. Specifically, predetermined amounts of the (A), (B), and (C) were first charged into a mixing vessel, and mixed and stirred to form a uniform mixture solution. After that, predetermined amounts of (D) and (E) were sequentially charged into the mixture solution, followed by mixture and stirring to obtain a uniform composition.

(5) The compositions for evaluation prepared by the above procedures were subjected to characteristic evaluation under the following conditions for the purpose of first studying the combination of (C). Table 1 also shows the results.

(6) [Drying Property]

(7) An area of 3 cm squares on the surface of a smooth glass plate was uniformly coated using a bar coater so that the uncured film thickness of each composition was 100 μm. This was allowed to stand in a thermostatic chamber at 90° C. for 10 minutes, followed by volatilization of the volatile ingredients to form an uncured coating film. The surface of the coating film was lightly touched with a fingertip degreased and cleaned with alcohol to visually observe the presence of absence of the adhesion of the coating film to the fingertip. Evaluation was carried out such that the ones without adhesion to the fingertip was acceptable (expressed as “◯”) and the ones with adhesion were unacceptable (expressed as “×”).

(8) [Film Forming Property]

(9) Evaluation was carried out by visually observing the uniformity of the coating film when an uncured coating film was formed under the same conditions as in the drying property evaluation. Evaluation was carried out as follows. The acceptable ones (expressed as “◯”) were such that the coating film was completely uniform in the coating area and there was no failure such as cissing, crawling, or orange peel, and the unacceptable ones (expressed as “×”) were such that part of the coating film was not uniformly distributed on the glass surface due to cissing, crawling, or orange peel, or the like.

(10) [Heat Volatilization Residual Balance]

(11) Measurement was carried out on the mass of each composition before and after the formation of an uncured coating film under the same conditions as in the drying property evaluation (before and after the volatilization of the volatile ingredients by heating at 90° C.), and the heat volatilization residual balance (%) was calculated in accordance with the following formula for listing.
heat volatilization residual balance (%)=mass after volatilization/mass before volatilization×100
[Storage Stability]

(12) Each of the compositions with an elapsed time of 30 minutes or less after preparation was sealed in a transparent glass reagent bottle and allowed to stand in a thermostatic chamber at 10° C. for 2 months, which was visually observed for evaluation. The ones evaluated as acceptable (expressed as “◯”) were such that no separation, precipitate, or the like was observed in the liquid and little reduction in fluidity was observed, specifically, it took less than 2 seconds for the liquid surface to move toward the upper portion of the bottle after horizontally tilting the reagent bottle. On the other hand, the ones evaluated as unacceptable (expressed as “×”) were such that obvious separation or precipitate was observed (dispersion failure) and the fluidity of the compositions initially having fluidity was significantly reduced, specifically; it took 2 seconds or more for the liquid surface to move toward the upper portion of the bottle after horizontally tilting the reagent bottle (thickening) and both dispersion failure and thickening were observed.

(13) TABLE-US-00001 TABLE 1 Compar- Compar- Compar- Exam- ative ative ative Ingredient ple 1 Example 1 Example 2 Example 3 (A) jER 1256B40 20 20 20 20 (B) DER 331 28 28 28 28 N-695 40 40 40 40 EXA-830 12 12 12 12 (C) (C-1) Ethyl Acetate 6.0 (C-1′) Hexane 6.0 Butyl Acetate 6.0 (C-2) Methyl Ethyl 34.5 34.5 34.5 40.5 Ketone (D) 920 DU 40 12.0 12.0 12.0 12.0 (E) DICY7 6.8 6.8 6.8 6.8 2MAOK-PW 1.2 1.2 1.2 1.2 Total 160.5 160.5 160.5 160.5 (C-1)/(C-2) 0.174 0.174 0.174 0 Charac- Drying ∘ ∘ x ∘ teristic Property Eval- Film Forming ∘ ∘ ∘ ∘ uation Property Heat Volatil- 78 78 78 78 ization Residual Balance (%) Storage ∘ x ∘ x Stability

(14) The results of Table 1 show that no problem arose in all of the characteristics, drying property, film forming property, and storage stability, only in the case of the combination of (C-1) ethyl acetate being an ester-based solvent having a boiling point of 100° C. or less and (C-2) MEK being a ketone-based solvent having a boiling point of 100° C. or less as the (C). On one hand, Comparative Example 1 using hexane being an aliphatic hydrocarbon-based solvent (non-ester-based solvent) having a boiling point of 100° C. or less as the (C-1) was continued to result in poor stability during storage due to the inability to homogeneously disperse the composition. On the other hand, Comparative Example 2 using butyl acetate being an ester-based solvent having a boiling point of 100° C. or more as the (C-1) was confirmed to lead to poor evaluation results of drying property due to insufficient volatility. Moreover, Comparative Example 3 not containing the (C-1) and only using the solvent (C-2) was also confirmed to result in poor storage stability.

(15) Next, the combination of (C-1) and (C-2) was fixed to ethyl acetate and MEK to carry out evaluation for the study of the range of each content ratio. In addition to the above four items, the evaluation item was also carried out on the viscosity measured under the following conditions. Table 2 also shows the evaluation results.

(16) [Viscosity]

(17) Each of the compositions was weighed and taken in an amount of 0.4 ml and added dropwise to the center portion of the sample cup of a cone plate type rotational viscometer to carry out measurement under the following measurement conditions. As the measurement results, the viscosity values (Pa.Math.s in accordance with JIS-K-7117-2 or JIS-Z-8803) were listed. measurement temperature: 25° C. cone plate: 3° R14 rotational speed: 10 rpm measurement time: 1 minute

(18) It is desirable that a suitable viscosity range in the curable resin composition of the present invention is preferably less than 20 Pa.Math.s and more suitably less than 18 Pa.Math.s from the viewpoint of handling property as a liquid composition, for example easiness of forming a homogeneous and smooth coating film and securing easiness of coating with a dispenser.

(19) TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Comparative Ingredient Example 4 Example 5 Example 2 Example 1 Example 3 Example 6 Example 7 (A) jER 1256B40 20 20 20 20 20 20 20 (B) DER 331 28 28 28 28 28 28 28 N-695 40 40 40 40 40 40 40 EXA-830 12 12 12 12 12 12 12 (C) (C-1) Ethyl Acetate 2.0 4.0 4.5 6.0 7.0 8.0 10.0 (C-2) Methyl Ethyl Ketone 34.5 34.5 34.5 34.5 34.5 34.5 34.5 (D) 920 DU 40 12.0 12.0 12.0 12.0 12.0 12.0 12.0 (E) DICY7 6.8 6.8 6.8 6.8 6.8 6.8 6.8 2MAOK-PW 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Total 156.5 158.5 159.0 160.5 161.5 162.5 164.5 (C-1)/(C-2) 0.058 0.116 0.130 0.174 0.203 0.232 0.290 Mass of (C) Relative to 100 182.5 192.5 195.0 202.5 207.5 212.5 222.5 Part by Mass of (A) Characteristic Viscosity [Pa .Math. s] 24 18 13 10 8 7 5 Evaluation Drying Property ∘ ∘ ∘ ∘ ∘ ∘ ∘ Film Forming Property x ∘ ∘ ∘ ∘ x x Heat Volatilization 81.0 79.5 79.0 78.0 78.0 76.5 75.0 Residual Balance (%) Storage Stability x x ∘ ∘ ∘ ∘ ∘

(20) The results of Table 2 show that the handling property as a liquid composition also deteriorates because Comparative Example 5 in which (C-1)/(C-2) is less than the lower limit, 0.12, of the range of the present invention is poor in storage stability; moreover Comparative Example 4 with a smaller value thereof is also poor in film forming property, and the value of viscosity increases as that value decreases. On the other hand, Comparative Examples 6 and 7 exceeding the upper limit value, 0.23, of the present invention was confirmed to be poor in film forming property. Therefore, the content ratio of (C) was confirmed to be particularly preferably in the range specified in the present invention. Note that the heat volatilization residual balance (%) when in that range was a value which exceeded 76.5 and was less than 79.

(21) Next, the combination and the content of (C) were fixed to carry out evaluation for the study of a suitable range of the content of (D). In addition to the drying property, film forming property, storage stability, and viscosity described above, the evaluation item was also carried out on the foaming magnification measured under the following conditions. Table 3 also shows the evaluation results.

(22) [Foaming Magnification]

(23) An uncured coating film was formed under the same conditions as in the drying property evaluation, and the film thickness of the coating film at that time was measured with a film thickness meter (Digimatic Micrometer, a product of Mitsutoyo Corporation) (average value of three or more measurement sites). After that, the test piece was allowed to stand for 30 minutes in a thermostatic chamber at 150° C. to promote the expansion of (D) and the curing reaction of (B), and the test piece was taken from the thermostatic chamber, allowed to stand in a room at normal temperature (20° C.) for 30 minutes, and returned to normal temperature (20° C.). The film thickness of the coating film at that time was measured in the same manner as described above, and the foaming magnification (%) was calculated in accordance with the following formula for listing.
foaming magnification (%)=film thickness after heating/film thickness before heating×100

(24) Usually, a foaming magnification suitable for filling adhesion between the members with clearance is desirably 150% or more and more desirably 200% or more, and a particularly preferable foaming magnification in consideration of the mechanical strength and the like of the cured product is in a range of 300 to 700%.

(25) TABLE-US-00003 TABLE 3 Ingredient Example 4 Example 5 Example 1 Example 6 Example 7 Example 8 Example 9 (A) jER 1256B40 20 20 20 20 20 20 20 (B) DER 331 28 28 28 28 28 28 28 N-695 40 40 40 40 40 40 40 EXA-830 12 12 12 12 12 12 12 (C) (C-1) Ethyl Acetate 6.0 6.0 6.0 6.0 6.0 6.0 6.0 (C-2) Methyl Ethyl Ketone 34.5 34.5 34.5 34.5 34.5 34.5 34.5 (D) 920 DU 40 8.0 10.0 12.0 14.0 16.0 17.5 18.0 (E) DICY7 6.8 6.8 6.8 6.8 6.8 6.8 6.8 2MAOK-PW 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Total 156.5 158.5 160.5 162.5 164.5 166.0 166.5 (c-1)/(c-2) 0.174 0.174 0.174 0.174 0.174 0.174 0.174 Mass of (D) Relative to 100 40 50 60 70 80 88 90 Parts by Mass of (A) Characteristic Viscosity [Pa .Math. s] 7 8 10 11 12 16 19 Evaluation Drying Property ∘ ∘ ∘ ∘ ∘ ∘ ∘ Film Forming Property ∘ ∘ ∘ ∘ ∘ ∘ ∘ Storage Stability ∘ ∘ ∘ ∘ ∘ ∘ ∘ Foaming Magnification 150% 300% 400% 500% 650% 700% 800%

(26) The results of Examples 1 and 4 to 9 show that the foaming magnification also increases in proportion to the increase in the content of (D) and at the same time that the viscosity also increases, reducing the handling property as a liquid composition.

INDUSTRIAL APPLICABILITY

(27) Since the curable resin composition by the present invention is excellent in drying property and film forming property while being a liquid thermally expandable adhesive having fluidity, highly reliable adhesion is possible, and moreover, storage stability is also excellent. In addition, by forming a coating film from which volatile ingredients have volatilized after coating on the adherends in advance, it is possible to provide an extremely useful adhesive which does not cause problems such as dripping at the time of attachment.