JP2711579B2 - Liquid curable resin composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid curable resin composition, and particularly to a liquid curable resin composition having high adhesion to a substrate and suitable for forming a cured film having excellent durability. It relates to a resin composition.

[Conventional technology]

In the production of an optical fiber, a resin coating is applied immediately after hot-melt spinning of a glass fiber for protection and reinforcement. Such a coating generally comprises a primary coating layer and a secondary coating layer. Of these, the material forming the primary coating layer is conventionally a UV-curable or thermosetting resin, for example, a polyurethane-based, epoxy-based, silicone-based, Fluorine, polybutadiene and the like are used. However, the resin material used for these primary coating layers generally has poor adhesion to an optical fiber, and has a drawback in that when moisture is absorbed, the strength of the optical fiber is reduced.

To improve this disadvantage, Japanese Patent Application Laid-Open No. 59-92
No. 947 proposes to add a silane coupling agent having an amino group to a resin material forming a primary coating layer, and JP-A-63-215707 discloses a silane coupling agent having a mercapto group. Addition of agents has been proposed.

[Problems to be solved by the invention]

However, the addition of the silane coupling agent described in these publications to the resin material does not sufficiently improve the adhesion between the obtained primary coating layer and the optical fiber, and in particular, a side pressure is applied to the optical fiber coated with these resin materials. In addition, there are drawbacks such as insufficient durability of the coating, such as that the primary coating layer may be easily peeled off from the glass fiber.

Accordingly, an object of the present invention is to provide a liquid curable resin composition which has excellent adhesion to various substrates such as optical fibers, and provides a coating having excellent durability when used as a coating material.

[Means for solving the problem]

The present inventors have achieved the above-mentioned object by using a resin composition having a specific composition in which two specific silane coupling agents are used in combination, and have significantly improved adhesion and durability to a substrate such as an optical fiber. It has been found that a coated coating can be formed.

That is, the present invention solves the above-mentioned problems of the related art by (A) urethane (meth) acrylate, (B) at least one selected from monofunctional monomers and polyfunctional monomers, (C) a polymerization initiator, And (D) a liquid curable resin composition comprising a silane coupling agent represented by the following general formula (I) and a silane coupling agent represented by the following general formula (II) (hereinafter simply referred to as a composition ).

General formula (I): HS-R ¹ -Si (R ² ) ₃ -X (OR ³ ) X wherein R ¹ is a C ₁ -C ₂₀ alkylene group, and R ² is a C ₁ -C
_{5 is} an alkyl group, R ³ is a C _{1 to} C ₁₀ alkyl group and a formula: —R ⁴ OR ² (R ⁴ is a C _{1 to} C ₁₀ alkylene group, and R ² is the same as described above) And x is an integer of 1 to 3. General formula (II): [Wherein, R ⁵ is a hydrogen atom or a methyl group, and R ¹ , R ² ,
R ³ and x are as defined for general formula (I).] (A) Urethane (meth) acrylate In the present invention, urethane (meth) acrylate refers to a compound having a urethane bond and a (meth) acryloyl group. means. The urethane (meth) acrylate generally has a number average molecular weight of 1,000 to 15,000, preferably 1,000 to 10,000.

According to a typical production example, the urethane (meth) acrylate is obtained by reacting about 2 mol of a hydroxyl group-containing (meth) acrylate with about n mol of a diol (n: 1 to 30) and about (n + 1) mol of a diisocyanate. The diamine may be used as a reaction raw material, if necessary. Each reaction raw material used in the production method will be described below.

First, as the hydroxyl group-containing (meth) acrylate, for example, hydroxyalkyl (meth) acrylate such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate; polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate and the like Polyoxyalkylene mono (meth) acrylates; polyhydric alkanols such as trimethylolpropane di (meth) acrylate, trimethylolethanedi (meth) acrylate, pentaerythritol tri (meth) acrylate and dipentaerythritol penta (meth) acrylate Partial (meth) acrylates and the like can be mentioned. These may be used alone or in combination.
More than one species may be used in combination.

Examples of the diol used in the production method include polyether diols obtained by ring-opening (co) polymerizing one or more alkylene oxides such as ethylene oxide, propylene oxide, and tetrahydrofuran;
Ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1,
6-hexanediol, neopentyl glycol, 1,4-
Dihydric alcohols such as cyclohexanedimethanol, bisphenol A and bisphenol F; alkylene oxide adducts of dihydric alcohols obtained by adding the alkylene oxide to the dihydric alcohol; alkylene oxide addition of the dihydric alcohol or dihydric alcohol Polyester diol obtained by reacting a product with a polybasic acid such as isophthalic acid, terephthalic acid, maleic acid, adipic acid, sebacic acid; and reacting caprolactone with the dihydric alcohol or an alkylene oxide adduct of the dihydric alcohol. Polycaprolactone diol obtained;
And a polycarbonate diol obtained by reacting phosgene with a dihydric alcohol such as bisphenol A, halogenated bisphenol A, bisphenol F, propylene glycol, tetramethylene glycol, pentamethylene glycol, and hexamethylene glycol; A chain carbitol-modified polyol may be mentioned. Among these diols, polypropylene glycol, polytetramethylene glycol, a ring-opening copolymer of tetrahydrofuran and propylene oxide, an adduct obtained by adding an alkylene oxide to bisphenol A or bisphenol F, polycarbonate diol, polycaprolactone diol, and the like. preferable.

As the diol, commercially available products may be used. For example, PTMG1000 (Mitsubishi Kasei Kogyo Co., Ltd.), PTMG2000 (same as above),
PTMG3000 (same), PPTG2000 (Hodogaya Chemical Industry Co., Ltd.), PPTG3000 (same), PPTG4000 (same), PTGL2000
(Same as above), DA300F (Nippon Oil & Fats Co., Ltd.), DA400 (same as above), DB4
00 (same), DB900 (same), DN-980 (Nippon Polyurethane Co., Ltd.), DN-987 (same), DN-982 (same), DN-983
And PC-8000 (US PPC), EXCENOL2020 (Asahi Orin Co., Ltd.), EXCENOL3020 (same as above), and Placcel (Daicel).

These diols may be used alone or in combination of two or more.

Further, as the diisocyanate used in the production method, for example, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,3-xylene diisocyanate, 1,4-xylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene Diisocyanate, p-phenylene diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4 '
-Diphenylmethane diisocyanate, 3,3'-dimethylphenylene diisocyanate, 4,4'-biphenylene diisocyanate, hexamethylene diisocyanate,
Examples include isophorone diisocyanate, trimethylhexamethylene diisocyanate, hydrogenated diphenylmethane diisoyanate, and the like. Among these diisocyanates, preferred are 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, isophorone diisocyanate and the like. These diisocyanates may be used alone or in combination of two or more.

Examples of the diamine appropriately used in the above production method as needed include, for example, a diamine containing a hetero atom such as ethylenediamine, tetramethylenediamine, hexamethylenediamine, paraphenylenediamine, and 4,4′-diaminodiphenylmethane, and Jeffamine D-230 ( Texaco Chemical), Jeffamine D-400 (same as above), and polyether diamines such as Jeffamine D-2000 (same as above). The use amount of these diamines is usually 50% by weight or less of the use amount of the diol.

As a more specific embodiment of the method for producing the urethane (meth) acrylate, for example, (1) a diisocyanate and a diol are reacted to produce a polyurethane having an isocyanate group at a terminal, and a hydroxyl group-containing (meth) is added thereto.
(2) First, a hydroxyl group-containing (meth) acrylate and a diisocyanate are reacted at such a ratio that an isocyanate group partially remains, and then a diol is added to the isocyanate group of the obtained reaction product. And (3) a method in which a predetermined amount of (meth) acrylate, diisocyanate and diol containing a hydroxyl group are mixed, and these three kinds of raw materials are reacted at the same time.

A urethane-forming catalyst is used in the urethane bond forming reaction in these methods, and examples thereof include copper naphthenate, cobalt naphthenate, zinc naphthenate, zinc laurate, dibutyltin laurate, and triethylamine.
The catalyst is used at about 0.01 to 1 part by weight per 100 parts by weight of total reactants. The reaction is usually performed at about 30 to 80 ° C.

In the above urethane (meth) acrylate production method, the molecular weight of the target urethane (meth) acrylate can be adjusted by appropriately selecting the diol to be used and changing the addition amounts of the diol and the diisocyanate. .

Furthermore, in this urethane (meth) acrylate production method, a polyol other than difunctional to diol, a polyamine other than difunctional to diamine, and a polyisocyanate other than difunctional to diisocyanate can be obtained. They can be used together to the extent that urethane (meth) acrylate does not gel. Polyols,
The combined amount of the polyamine or polyisocyanate is usually 5 to 30 parts by weight with respect to 100 parts by weight of the diol, diamine or diisocyanate. Here, as the polyol other than difunctional, for example, an addition product of glycerin and propylene oxide, glycerin,
Pentanetriol, butanetriol, tri (hydroxypolyoxypropyl) polysiloxane, polycaprolactonetriol, polycaprolactone titraol, liquid polybutadiene having more than two hydroxyl groups in one molecule or hydrogenated product of this compound, etc. be able to. Examples of non-bifunctional polyamines include, for example, diethylenetriamine, triaminopropane, and polyoxypropyleneamine. Examples of polyisocyanates other than bifunctional include polymethylene polyphenyl isocyanate, triphenylmethane triisocyanate, and the like.

(B) Monofunctional monomer and polyfunctional monomer Examples of the monofunctional monomer include hydroxyethyl acrylate, hydroxypropyl acrylate, tetrahydrofurfuryl acrylate, butoxyethyl acrylate, ethyldiethylene glycol acrylate,
Ethylhexyl acrylate, cyclohexyl acrylate, phenoxyethyl acrylate, dicyclopentadiene acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, methyltriethylene diglycol acrylate, isobornyl acrylate, isobornyl methacrylate, N-vinylpyrrolidone, N-vinylcaprolactam, Diacetone acrylamide, isobutoxymethyl acrylamide,
N, N-dimethylacrylamide, t-octylacrylamide, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, acryloylmorpholine,
Examples thereof include dicyclopentenyl acrylate and dicyclopentenyl methacrylate.

Examples of polyfunctional monomers include, for example, trimethylolpropane triacrylate, pentaerythritol triacrylate, ethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, neopentyl glycol diacrylate, Trimethylolpropane trioxyethyl acrylate, tricyclodecane dimethanol diacrylate, tricyclodecane dimethanol dimethacrylate, dicyclopentadiene diacrylate, dicyclopentane diacrylate, dicyclopentadiene dimethacrylate, and the like can be given.

Among these monofunctional monomers and polyfunctional monomers, preferred are 2-ethylhexyl acrylate, cyclohexyl acrylate, phenoxyethyl acrylate, isobornyl acrylate, N-vinylpyrrolidone, N-vinyl cabrolactam, dicyclopentenyl acrylate, tricyclopentenyl acrylate, and tricyclopentenyl acrylate. Cyclodecane dimethanol diacrylate, trimethylol propane triacrylate and the like.

One of these monofunctional monomers and polyfunctional monomers may be used alone or in combination of two or more, or both may be used alone or in combination of two or more.

(C) Polymerization initiator Examples of the polymerization initiator include dimethoxyphenylacetophenone, acetophenone, benzophenone, xanthone, fluorenone, benzaldehyde, fluorene,
Anthraquinone, triphenylamine, carbazole,
Methyl acetophenone, chlorobenzophenone, dimethoxybenzophenone, diaminobenzophenone, Michler's ketone, benzoin propyl ether, acetophenone diethyl ketal, benzoin ethyl ether, hydroxycyclohexyl phenyl ketone, benzyl dimethyl ketal, (isopropylphenyl) hydroxymethylpropan-1-one, hydroxymethylphenyl Examples thereof include polymerization initiators such as propan-1-one, trimethylbenzoyldiphenylphosphine oxide, and thioxanthone compounds. These polymerization initiators include 1
A single species or a combination of two or more species can be used.

If necessary, a sensitizer (polymerization accelerator) such as an amine compound can be used in combination with the polymerization initiator as long as the effects of the present invention are not impaired.

(D) Silane coupling agent In the general formula (I), the alkylene group of R ¹ is
Methylene group, ethylene group, propylene group, tetramethylene group, hexamethylene group, octamethylene group, decamethylene group, dodecamethylene group, a pentadecamethylene group, a octadecamethylene group, the alkyl group of R ^2, a methyl group , Ethyl group, propyl group. Pentyl group, the alkyl group of R ^3, the same alkyl group and a hexyl group and R ^2, Akuchiru group, a decyl group, the alkylene group of R ^4, a methylene group, an ethylene group, a propylene group, tetramethylene Examples include a methylene group, a hexamethylene group, and an octamethylene group.

Specific examples of the silane coupling agent represented by the general formula (I) include γ-mercaptomethyltrimethoxysilane, γ-mercaptoethyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptobutyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane and the like can be mentioned. Among them, preferred are γ-mercaptopropyltrimethoxysilane and the like.

Specific examples of the silane coupling agent represented by the general formula (II) include γ-methacrylmethyltrimethoxysilane, γ-methacrylethyltrimethoxysilane, γ-methacrylpropyltrimethoxysilane, γ-methacrylbutyltrimethoxysilane, γ-acrylpropyltrimethoxysilane, γ-methacrylpropyltrimethoxysilane, γ-methacrylpropylmethyldimethoxysilane and the like can be mentioned. Among these, preferred are γ-methacrylpropyltrimethoxysilane and the like.

The composition of the present invention includes the general formula (I) and the general formula (I
A silane coupling agent other than the silane coupling agent of I) can be used alone or in combination of two or more as necessary. Such other silane coupling agents, for example, KA1003, KBC1003, KBE100
3, KBM1003, KBM303, KBM404, KBE402, KBM603, KBM60
2. There may be mentioned those commercially available under trade names such as KBM903, KBE573 and KBM703 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

Mixing ratio A preferable mixing ratio of each component in the composition of the present invention is as follows.
85% by weight, particularly preferably 40 to 80% by weight, (B)
At least one component selected from monofunctional monomers and polyfunctional monomers is 10 to 70% by weight, particularly preferably 15 to 70% by weight.
60% by weight, the polymerization initiator of the component (C) is 1 to 5% by weight, preferably 1.5 to 4% by weight, and the silane represented by the general formulas (I) and (II) of the component (D) is The coupling agents are each 0.1 to 10% by weight, particularly preferably 0.1 to 2% by weight, respectively.

Further, the amount of the silane coupling agent other than the silane coupling agents of the general formulas (I) and (II) when used in combination is preferably 0.1 to 10% by weight, particularly 0.1 to 2% by weight of the composition. .

Other Components In addition to the above-mentioned components, various additives such as a coloring agent, an antioxidant, a storage stabilizer, and a leveling agent can be added to the composition of the present invention as needed. The amount of each of these additives is usually about 10% by weight or less in the composition.

In preparing the composition of the present invention, the required components may be blended in a predetermined ratio, and the mixing method is not particularly limited.

Properties and uses The viscosity of the composition of the present invention is usually 1000 to 25 ° C.
It is 20000 cP, preferably 2000 to 10000 cP.

The composition may be used with various radiations, such as X-rays, electron beams,
It is cured by ultraviolet rays, visible light, etc., and usually shows a Young's modulus of 0.01 to 100 kg / mm ² at 23 ° C. after curing.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples.
The present invention is not limited to these examples.

Synthesis Example 1 A reaction vessel equipped with a stirrer was charged with 261 g of 2,4-toluene diisocyanate, 1 g of dibutyltin dilaurate, and 1 g of a polymerization inhibitor 2,6-di-t-butyl-4-methylphenol. While controlling the temperature of the mixture to 20 ° C. or lower, 116 g of 2-hydroxyethyl acrylate was added. After the addition, the reaction was further continued at 10 to 20 ° C. for 1 hour, and then polyether diol, a copolymer of tetrahydrofuran and 3-methyltetrahydrofuran (manufactured by Hodogaya Chemical Co., Ltd .: PTGL-2000, number average molecular weight 2000; below) 2,000 g of polyether (1)) was added thereto while maintaining the temperature of the reaction mixture in the reaction vessel at 40-50 ° C.
Next, after continuing the reaction at 40 to 50 ° C. for 3 hours, the reaction was terminated, and a polymer having a number average molecular weight of about 4800 was obtained. Hereinafter, this polymer is referred to as polymer (A).

Synthesis Example 2 Synthesis Example 1 was the same as Synthesis Example 1 except that the polyether diol was replaced by 2000 g of polytetramethylene glycol having a number average molecular weight of 2000 (Mitsubishi Kasei Kogyo Co., Ltd., PTHG2000; hereinafter, referred to as polyether (2)). In the same manner as in the above, a polymer having a number average molecular weight of about 4800 was obtained. Hereinafter, this polymer is referred to as a polymer (B).

Synthesis Example 3 In Synthesis Example 1, 3000 g of the polyether diol was replaced with polypropylene glycol (EXENOL3020 manufactured by Asahi Glass Co., Ltd., number average molecular weight 3000; hereinafter referred to as polyether (3)).
A polymer having a number average molecular weight of about 6800 was obtained in the same manner as in Synthesis Example 1 except for changing the above. Hereinafter, this polymer is referred to as polymer (C).

Synthesis Example 4 In the same manner as in Synthesis Example 1 except that the polyether diol was changed to a mixture of 1000 g of the polyether (1) and 1500 g of the polyether (3), a weight average molecular weight of about 5800 was used. A coalescence was obtained. Hereinafter, this polymer is referred to as a polymer (D).

Synthesis Example 5 In Synthesis Example 1, the number average was calculated in the same manner as in Synthesis Example 1 except that the diisocyanate was changed to 333 g of isophorone diisocyanate and the polyether diol was changed to a mixture of 1000 g of polyether (2) and 1500 g of polyether (3). A polymer having a molecular weight of about 5800 was obtained. Hereinafter, this polymer is referred to as a polymer (E).

Examples 1 to 10 and Comparative Examples 1 to 3 According to the formulation shown in Table 1, compositions of Examples and Comparative Examples were obtained. These compositions were tested for Young's modulus, curing rate, adhesion, adhesion after wet heat treatment, and ironing resistance by the methods described below. Table 1 shows the results.

After applying the Young's modulus composition on a glass plate to a thickness of 0.2 mm, the composition was irradiated with ultraviolet rays using a metal halide lamp and cured so that the total irradiation energy amount was 1 J / cm ² . The resulting cured film was cut into strips having a width of 6 mm, and a test length of 25 mm was applied at −40 ° C. by a tensile test method based on JIS K6911.
And the Young's modulus of the cured film at 23 ° C. was measured.

After the curing rate composition was coated to a thickness of 0.04mm on a glass plate, with two conditions total irradiation energy amount is 10 mJ / cm ² and 500 mJ / cm ^2, irradiating ultraviolet radiation using a metal halide lamp The sample was cured and prepared.

Each of the obtained two cured sample samples was subjected to extraction treatment using methyl ethyl ketone as a solvent for 12 hours using a Soxhlet extractor, and then vacuum dried at 50 ° C. for 8 hours. The gel fraction was measured from the change in weight before and after the treatment. Then, the ratio of the gel fraction when the total irradiation energy amount is 10 mJ / cm ² and when the total irradiation energy amount is 500 mJ / cm ² (the gel fraction in the case of 10 mJ / cm ² )
/ 500 mJ / cm ² ) was used as an index of the curing rate.

Adhesion (a) After coating the composition on a quartz plate so that the thickness after curing becomes 0.2 mm, apply ultraviolet rays to the quartz plate using a metal halide lamp so that the total irradiation energy becomes 1 J / cm ^2. Irradiation to obtain a cured film.

(B) The cured film on the quartz plate was left on the quartz plate in the form of a tape having a width of 1 cm, and one end of the cured film was pulled in a direction perpendicular to the quartz plate to be peeled off, and the force required for peeling was measured. The same measurement was performed three times, and the average value was evaluated as the adhesion of the cured film to the quartz plate.

Adhesion after wet heat treatment (a) A cured film was obtained by the same method as in the adhesion (a) and used as a sample.

(B) The above sample was stored under the conditions of 60 ° C. × 95% RH for 7 days.

(C) After conditioning this at 23 ° C x 50% for one day, leave the cured film on the quartz plate in a tape shape with a width of 1 cm on the quartz plate, and attach one end of the cured film to the quartz plate. And pulled in the vertical direction to peel, and the force required for peeling was measured. The same test was performed three times, and the average value was evaluated as the adhesion after the wet heat treatment.

Ironing resistance A quartz rod was heated to 2000 ° C using an optical fiber drawing device, a drawing speed of 60 m / min was used to produce a quartz fiber with an outer diameter of 125 μm, and the composition was applied to the quartz fiber immediately after production. Ultraviolet rays were irradiated by a 3kW ultraviolet lamp to cure. The composition for a secondary coating prepared as described below was further applied onto the quartz fiber thus primarily coated, and cured by irradiating ultraviolet rays in the same manner as described above. The optical fiber thus obtained had an outer diameter of 200 μm after the primary coating and an outer diameter of 250 μm after the secondary coating.

The optical fiber thus manufactured was cut into a length of 30 cm, and a load of 200 g was applied thereto.
It reciprocated between 00 cm. Optical microscope (magnification 100
X) and the presence or absence of separation between the coating layer and the fiber was examined. The results were expressed as the number of times of ironing until peeling occurred.

(Composition for secondary coating) In a reaction vessel equipped with a stirrer, 145 g of 2,4-toluene diisocyanate, 0.5 g of dibutyltin dilaurate, and a polymerization inhibitor 2,6-di-t-butyl-4-methylphenol
0.2 g, and then 127 g of 2-hydroxyethyl acrylate while controlling the temperature of these mixtures to 20 ° C. or less.
Was added. After the addition, the reaction was further continued for 1 hour at 10 to 20 ° C., and then 70 g of ethylene oxide adduct of bisphenol A having a number average molecular weight of 400 (DA400, manufactured by NOF Corporation).
And a mixture of 225 g of polyether (2) were added while maintaining the temperature of the reaction mixture in the reaction vessel at 40 to 50 ° C.
Next, after continuing the reaction at 40 to 50 ° C. for 3 hours, the reaction was terminated to obtain a polymer.

Next, 567 g of the polymer thus obtained was mixed with 89 g of vinylpyrrolidone, 77 g of isobornyl acrylate, 162 g of tricyclodecane dimethanol diacrylate, 70 g of trimethylolpropane triacrylate, and 29 g of 1-hydroxycyclohexyl phenyl ketone. The composition for the next coating was prepared.

[Effect of the Invention] Since the liquid curable resin composition of the present invention has excellent adhesion to a substrate, when it is used as a material constituting a primary coating layer of an optical fiber, excellent adhesion to the optical fiber can be obtained, resulting in durability of the optical fiber. The properties are significantly improved. In addition, the resulting coating has the basic characteristics required of an optical fiber coating material, so that this liquid curable resin composition is extremely excellent as an optical fiber coating material. Further, due to its excellent adhesion to a substrate, it is also suitable as a coating material for a substrate made of various materials such as 2P resin or topcoat for optical discs and paper, wood, plastic metal, etc., for example.

Continued on the front page (72) Inventor Katsutoshi Igarashi 2-11-24 Tsukiji, Chuo-ku, Tokyo Japan Synthetic Rubber Co., Ltd. (72) Inventor Timothy Bishop 60102 Algonquin, Riverwood Drive, Illinois, USA 1720 Riverwood Drive 1720

Claims (1)

(57) [Claims] (A) urethane (meth) acrylate, (B) at least one selected from monofunctional monomers and polyfunctional monomers, (C) a polymerization initiator, and (D) a compound represented by the following general formula (I): A liquid curable resin composition comprising the silane coupling agent represented by the general formula (II) and the silane coupling agent represented by the general formula (II). General formula (I): HS-R ¹ -Si (R ² ) ₃ -X (OR ³ ) X wherein R ¹ is a C ₁ -C ₂₀ alkylene group, and R ² is a C ₁ -C
_{5 is} an alkyl group, R ³ is a C _{1 to} C ₁₀ alkyl group and a formula: —R ⁴ OR ² (R ⁴ is a C _{1 to} C ₁₀ alkylene group, and R ² is the same as described above) And x is an integer of 1 to 3. General formula (II): [Wherein, R ⁵ is a hydrogen atom or a methyl group, and R ¹ , R
² , R ³ and x are as defined for general formula (I)]