Siloxane resin, siloxane resin composition, cured product of siloxane resin composition, and varnish

Abstract

To provide a siloxane resin that has improved mechanical strength.SOLUTION: The siloxane resin is obtained by polymerizing a component (A), a component (B), and a component (C), where: the component (A) is a silane compound represented by general formula (1), R1SiX3; the component (B) is a silane compound represented by general formula (2), R12SiX2; and the component (C) is silica. (In general formula (1), R1 is a C1-4 alkyl group or a C6-8 aryl group, and X is a halogen atom, a C1-4 alkoxy group, or a C6-8 aryloxy group. In general formula (2), R1 and X are the same as defined for general formula (1).)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a siloxane resin, a siloxane resin composition, a cured product of the siloxane resin composition, and a varnish. [Background technology]

[0002] Siloxane resins have excellent heat resistance, weather resistance, and chemical stability due to their main structure being siloxane bonds, and they also have unique interfacial properties such as water repellency and releasability due to the organic groups they contain. For these reasons, they are used in sealants, adhesives, coatings, plastics, and other applications. There are four types of unit structures of siloxane resins: M structure, D structure, T structure, and Q structure. Among them, silsesquioxanes consisting of the T structure are "-(QSiO 1.5 It is known as a high-performance resin with a structural unit represented by the formula "(Q2SiO)-(Q is a monovalent organic group)". n "It is an inorganic-organic hybrid material that combines the high heat resistance and weather resistance of inorganic materials with various properties depending on the type of organic functional group, and has attracted attention in recent years because it is possible to design materials that reflect the function of the organic functional group by selecting the appropriate group. Silsesquioxane has three higher-order structures: random structure, ladder structure, and cage structure, and different properties can be exhibited by changing these structures and the degree of polymerization as well as the type of organic functional group. Patent Document 1 reports that ladder-structured siloxane resins have high heat resistance, hydrolysis resistance, and excellent electrical insulation properties, but have such poor mechanical strength that they are difficult to form into films. It is therefore reported that the mechanical strength can be improved by incorporating both T and D structures, but the resulting mechanical strength is still insufficient. Furthermore, Patent Document 2 aims to improve the toughness of siloxane resin by adding silicone rubber, but uses an expensive platinum catalyst during curing, which poses problems in terms of production costs and metal contamination of the product. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 59-129230 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-219768 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a siloxane resin with improved mechanical strength. [Means for solving the problem]

[0005] The present inventors focused on the fact that crosslinking points remain even after curing, which is a factor in the brittleness of siloxane resins, and discovered that by subjecting silica, which is a resin additive, and a siloxane monomer to a polymerization reaction to obtain a siloxane resin, crosslinking of the siloxane resin is promoted, resulting in a siloxane resin with improved mechanical strength, which led to the completion of the present invention.

[0006] The present invention is as follows. 1. A siloxane resin obtained by polymerizing component (A), component (B), and component (C). Component (A): a silane compound represented by general formula (1) Component (B): a silane compound represented by general formula (2) Component (C): Silica [C1] R 1 SiX3····(1) (R in the formula 1 represents an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 8 carbon atoms, and X represents a halogen atom, an alkoxy group having 1 to 4 carbon atoms, or an aryloxy group having 6 to 8 carbon atoms. [Case 2] R 1 2SiX2····(2) (R in the formula1 and X are defined as in general formula (1). 2. The siloxane resin according to 1., wherein the component (B) is polymerized in an amount of 10 to 20 parts by mole per 100 parts by mole of the component (A), and the component (C) is polymerized in an amount of 1 to 20 parts by weight per 100 parts by weight of the component (A). 3. The siloxane resin according to 1., wherein component (C) is hydrophilic silica. 4. A siloxane resin composition comprising the siloxane resin according to any one of 1. to 3. above and glass fibers. 5. The siloxane resin composition according to 4, further comprising a curing accelerator. 6. A varnish comprising the siloxane resin according to any one of 1. to 3. above and an organic solvent. 7. The varnish according to 6., further comprising a curing accelerator. A cured product of the siloxane resin composition described in 8.4. 9. A cured product of the siloxane resin composition described in 5. [Effects of the Invention]

[0007] According to the present invention, the siloxane resin of the present invention is extremely useful for industrial use because a siloxane resin material with improved mechanical strength can be obtained by curing the siloxane resin or a siloxane resin composition containing the siloxane resin. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a graph showing the results of the third measurement when dynamic viscoelasticity measurements were repeated three times under the same conditions for the glass fiber reinforced plastics using the siloxane resins obtained in Example 1, Comparative Example 1, and Comparative Example 2, and showing the change in storage modulus within the measurement temperature range. [Figure 2] 1 is a graph showing the results of the third measurement when dynamic viscoelasticity measurements were repeated three times under the same conditions for the glass fiber reinforced plastics using the siloxane resins obtained in Example 1, Comparative Example 1, and Comparative Example 2, and showing the change in loss tangent within the measurement temperature range. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in detail below. <Component (A)> Component (A) in the present invention is a silane compound represented by general formula (1). [C3] R 1 SiX3····(1) (R in the formula 1 represents an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 8 carbon atoms, and X represents a halogen atom, an alkoxy group having 1 to 4 carbon atoms, or an aryloxy group having 6 to 8 carbon atoms. R in general formula (1) 1 is preferably a methyl group, an ethyl group or a phenyl group, more preferably a methyl group or a phenyl group, and particularly preferably a methyl group. Furthermore, X in general formula (1) is preferably a chlorine atom, a bromine atom, a methoxy group, an ethoxy group or a phenoxy group, more preferably a chlorine atom, a methoxy group or a phenoxy group, and particularly preferably a chlorine atom or a methoxy group. Specific examples of the silane compound represented by the general formula (1) include trimethoxymethylsilane, triethoxymethylsilane, and trichloromethylsilane.

[0010] <Ingredient (B)> Component (B) in the present invention is a silane compound represented by general formula (2). [C4] R 1 2SiX2····(2) (R in the formula 1 and X are defined as in general formula (1). R in general formula (2) 1 and suitable examples of X are the same as those in general formula (1). Specific examples of the silane compound represented by the general formula (2) include dimethoxydimethylsilane, diethoxydimethylsilane, and dichlorodimethylsilane.

[0011] <Component (C)> As the silica of component (C) in the present invention, wet silica or dry silica can be used, and these are preferred. The silica in the present invention includes hydrophilic silica with no surface treatment, and hydrophobic silica produced by modifying the silanol group portion of hydrophilic silica with a silyl group or an organic group. Examples of organic silica, which is silica modified with an organic group, include silica modified with an organic group containing a reactive group such as a hydroxy group, a thiol group, a carboxy group, an amino group, or an epoxy group, and silica in which some of the silanol groups on the silica have been modified with organic groups that do not contain reactive groups such as an alkoxy group or an acyl group, and the remaining silanol groups remain on the silica. To improve the properties of the siloxane resin obtained by forming bonds through the reaction with component (A) and component (B), it is more preferable to use hydrophilic silica having many silanol groups on its surface. Specific examples of hydrophilic silica include Aerosil (registered trademark) 50, 130, 200, 300, and 380 (trade names, manufactured by Nippon Aerosil Co., Ltd.), and Cabosil (registered trademark) HS-5 and M-5 (trade names, manufactured by Cabot Corporation). Specific examples of hydrophobic silica include Aerosil (registered trademark) R-972, R-974, R-976, RX50, RX200, RX300 (trade names, manufactured by Nippon Aerosil Co., Ltd.), and Cabosil (registered trademark) TS-720, TS-622, and TS382 (trade names, manufactured by Cabot Corporation). There is no limit to the specific surface area of ​​silica, but it should be between 100 and 300 m 2 / g, and 150 to 250m 2 / g is more preferable, and 170 to 230m 2 / g range is more preferred.

[0012] <Polymerization reaction> In the polymerization reaction to obtain the siloxane resin of the present invention, there is no limitation on the method for mixing components (A) to (C) and the catalyst and solvent that are preferably used in addition to these. Examples of mixing methods include preparing a mixture of component (C), catalyst, and solvent, and a mixture of components (A) and (B), and then mixing them. In such cases, the entire amount of the mixture of components (A) and (B) may be mixed with the mixture of component (C), catalyst, and solvent all at once, or may be mixed in portions intermittently, or may be mixed continuously. Another example is a method in which component (A), components (B), components (C), catalyst, and solvent are mixed all at once. In order to control the heat generated by the reaction, it is preferable to prepare a mixture of component (C), a catalyst, and a solvent, and a mixture of component (A) and component (B), and then mix the mixture of component (A) and component (B) with the mixture of component (C), a catalyst, and a solvent in portions intermittently or continuously.

[0013] (Amount of components (A) to (C) used) Regarding the amounts of components (A) to (C) used in the polymerization reaction to obtain the siloxane resin of the present invention, component (B) is preferably used in the range of 10 to 20 parts by mole, more preferably 10 to 15 parts by mole, and even more preferably 10 to 13 parts by mole, per 100 parts by mole of component (A). Furthermore, component (C) is preferably used in the range of 1 to 20 parts by weight, more preferably 1 to 10 parts by weight, even more preferably 1 to 8 parts by weight, and especially preferably 1 to 4 parts by weight, per 100 parts by weight of component (A).

[0014] (catalyst) In the polymerization reaction to obtain the siloxane resin of the present invention, a catalyst is preferably used. The catalyst used is preferably an inorganic acid or an organic acid, more preferably an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, or acetic acid, still more preferably sulfuric acid, hydrochloric acid, nitric acid, or acetic acid, and particularly preferably hydrochloric acid. The amount of catalyst used is preferably in the range of 0.01 to 5 moles per mole of component (A), more preferably 0.01 to 1 mole, and even more preferably 0.01 to 0.2 moles.

[0015] (solvent) In the polymerization reaction to obtain the siloxane resin of the present invention, a solvent is preferably used. The solvent used is preferably a mixed solvent of an alcoholic solvent having 3 to 10 carbon atoms and water, more preferably a mixed solvent of an alcoholic solvent having 3 to 8 carbon atoms and water, even more preferably a mixed solvent of an alcoholic solvent having 3 to 6 carbon atoms and water, and particularly preferably a mixed solvent of an alcoholic solvent having 3 or 4 carbon atoms and water. Examples of alcohol solvents having 3 to 10 carbon atoms include n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, cyclohexanol, n-octanol, and n-decanol. Among these, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, and cyclohexanol are preferred, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, and t-butyl alcohol are more preferred, and isopropyl alcohol is particularly preferred. The proportion of the alcoholic solvent in the mixed solvent of the alcoholic solvent and water is preferably in the range of 30 to 90% by weight, more preferably in the range of 40 to 90% by weight, and even more preferably in the range of 50 to 80% by weight. The amount of the solvent used is preferably in the range of 2 to 10 times by weight, more preferably 2 to 6 times by weight, and even more preferably 2 to 4 times by weight, relative to the amount of component (A).

[0016] (Reaction conditions) The reaction temperature in the polymerization reaction to obtain the siloxane resin of the present invention is usually in the range of 30 to 100° C., preferably in the range of 50 to 80° C., and more preferably in the range of 70 to 80° C. The reaction pressure may be normal pressure or reduced pressure, but normal pressure is preferred. The completion of the polymerization reaction to obtain the siloxane resin of the present invention can be confirmed by analyzing the polymerization reaction solution by gel permeation chromatography (GPC) to confirm that no components (A) or (B) remain.

[0017] (Post-processing) After the polymerization reaction is completed, the siloxane resin produced may be isolated from the resulting reaction mixture by any method, including, for example, the following methods. First, it is preferable to wash the reaction mixture with water to remove the catalyst, if used, and metal impurities contained in components (A) to (C). The washing process can be carried out according to a conventional method. For example, the solvent used in the reaction can be distilled off from the resulting reaction mixture, if necessary, and an organic solvent that dissolves the resulting siloxane resin and separates from water is added to form a siloxane resin solution, followed by washing with water. If a catalyst is used, a neutralization process may be carried out before washing with water. The organic solvent can then be distilled off under reduced pressure and heating to isolate the siloxane resin of the present invention. The resulting siloxane resin is preferably dried to remove any adhering or clathrated solvent. The drying temperature is preferably in the range of 50 to 120°C, more preferably in the range of 50 to 100°C, and even more preferably in the range of 50 to 70°C.

[0018] <Siloxane resin composition> One embodiment of the siloxane resin composition of the present invention comprises the siloxane resin of the present invention and glass fibers. The glass fiber used in the siloxane resin composition of the present invention is not particularly limited, and various known glass fibers can be used. The shape of the glass fiber is also not particularly limited, and like existing glass fibers, it can be chopped strands, yarn, roving, mat, cloth, milled fiber, etc., and any shape can be selected taking into consideration ease of handling and production efficiency in the production process of the siloxane resin composition or its cured product, etc. The thickness of the glass fiber is not particularly limited, but can be, for example, 3 to 25 μm, and can be set arbitrarily, as in the above embodiment. Furthermore, the minimum length of the glass fiber is not particularly limited, but can be, for example, 0.75 mm or more, and preferably 1.0 mm or more. The glass fiber is preferably in a fibrous or sheet-like form, and the siloxane resin composition of the present invention preferably contains a fibrous glass fiber and the siloxane resin of the present invention, or a sheet-like glass cloth and the siloxane resin of the present invention. The content ratio of the siloxane resin and the glass fiber in the siloxane resin composition of the present invention is not particularly limited, but it is preferable that the glass fiber is contained in an amount of 500 to 600 parts by weight per 100 parts by weight of the siloxane resin, and the fiber volume content (Vf) is in the range of 30 to 50%. The siloxane resin composition of the present invention can be obtained by mixing the siloxane resin of the present invention with glass fibers, and one method for this mixing is to impregnate the glass fibers with an organic solvent solution (varnish) of the siloxane resin of the present invention. After the glass fibers have been impregnated with the varnish, the organic solvent can be removed and the fibers can be subjected to the process for obtaining a cured product described below.

[0019] <Varnish> The siloxane resin of the present invention can be mixed with an organic solvent to form a solution (varnish). The organic solvent used for the varnish is not particularly limited as long as it can dissolve the siloxane resin of the present invention, and examples thereof include ketone solvents such as acetone and methyl ethyl ketone. There are no restrictions on the amount of organic solvent used in the varnish, and it may be determined to be a concentration that makes the varnish easy to handle depending on the application. However, it is preferably in the range of 30 to 100 parts by weight, more preferably 30 to 90 parts by weight, and even more preferably 30 to 80 parts by weight, per 100 parts by weight of the siloxane resin.

[0020] <Curing accelerator> The siloxane resin composition of the present invention and the varnish of the present invention may contain a curing accelerator to accelerate the curing reaction for obtaining the cured product described below. That is, another embodiment of the siloxane resin composition of the present invention is a siloxane resin composition containing the siloxane resin of the present invention, glass fiber, and a cure accelerator. As the curing accelerator, it is preferable to use tetraalkylammonium difluorotriarylsilicate and carboxylic acid in combination. Examples of tetraalkylammonium difluorotriarylsilicate compounds may be those that have no substituents on the benzene ring, or those that have substituents (e.g., alkyl groups having 1 to 6 carbon atoms, alkenyl groups, alkanoyl groups, alkoxy groups, nitro groups, etc.). Furthermore, at least one of the three benzene rings may have 1 to 3 substituents. Examples of alkyl groups associated with the ammonium group include alkyl groups having 1 to 6 carbon atoms. A specific example of these suitable tetraalkylammonium difluorotriaryl silicates is tetrabutylammonium difluorotriphenylsilicate (TBAT). Preferred examples of carboxylic acids include aliphatic monocarboxylic acids having 1 to 11 carbon atoms (excluding the carbon atom in the carboxy group), such as acetic acid, propionic acid, butyric acid, valeric acid, and hexanoic acid; hydroxyl group-containing carboxylic acids such as lactic acid; aliphatic dicarboxylic acids having 0 to 11 carbon atoms (excluding the carbon atom in the carboxy group), such as oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid; alicyclic carboxylic acids such as 1,2-cyclohexanedicarboxylic acid; aromatic monocarboxylic acids such as benzoic acid; and aromatic dicarboxylic acids such as phthalic acid and isophthalic acid. Of these, acetic acid, lactic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, oxalic acid, malonic acid, succinic acid, adipic acid, glutaric acid, 1,2-cyclohexanedicarboxylic acid, and benzoic acid are more preferred. The amount of the curing accelerator used is not particularly limited, but it is preferable that the tetraalkylammonium difluorotriaryl silicate is used in the range of 0.001 to 0.03 parts by weight and the carboxylic acid is used in the range of 0.0005 to 0.015 parts by weight relative to 100 parts by weight of the siloxane resin.

[0021] The cured product of the siloxane resin composition of the present invention can be obtained by curing the above-described siloxane resin composition. The cured product of the present invention can be produced, for example, by heating the siloxane resin composition in an oven or a hot press molding machine at a temperature in the range of 100 to 250°C. The pressure during heating is not particularly limited, but is preferably in the range of 3 to 5 MPa using a hydraulic test press, and the temperature is preferably in the range of 150 to 200°C. In order to efficiently remove the organic solvent contained in the siloxane resin composition after heat curing, and low molecular weight condensates formed by the condensation reaction of the silane compound, etc., it is preferable to dry the composition at 150 to 200°C under reduced pressure. [Example]

[0022] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The analysis method is as follows. <Analysis method> 1. Gel Permeation Chromatography (GPC) Device: HLC-8320 / Tosoh Corporation Detector: Differential refractometer (RI) [Measurement conditions] Flow rate: 1mL / min Eluent: tetrahydrofuran Temperature: 40℃ Wavelength: 254nm Sampling pitch: 100 msec Measurement sample: 10 mg of siloxane resin diluted 30 times with tetrahydrofuran Injection volume: 10μL [Column] (from upstream) Guard Column HXL-L + G4000HXL + G3000HXL + G2000HXL x 2 (7.8 mm ID x 30 cm, Tosoh Corporation) [Molecular weight calculation method] The molecular weight was calculated as a standard polystyrene equivalent using a calibration curve of a third-order approximation curve using the following polystyrene standard sample. The measurement conditions were the same as above except that the injection volume was changed to 10 μL. (Polystyrene standard sample) ·TSKgel Standard Polystyrene A-500:Nominal Mol.Wt. 5.9×10 2 Mw / Mn 1.19 (0005203 / Tosoh Corporation) ·TSKgel Standard Polystyrene A-2500:Nominal Mol.Wt. 2.63×10 3 Mw / Mn 1.05 (0005205 / Tosoh Corporation) ·TSKgel Standard Polystyrene A-5000:Nomi nal Mol.Wt. 5.06×10 3 Mw / Mn 1.02 (0005206 / Tosoh Corporation) ·TSKgel Standard Polystyrene F-1:Nominal Mol.Wt. 1.02×10 4 Mw / Mn 1.02 (0005207 / Tosoh Corporation) ·TSKgel Standard Polystyrene F-2:Nominal Mol.Wt. 1.74×10 4 Mw / Mn 1.01 (0005208 / Tosoh (Co., Ltd.) ·TSKgel Standard Polystyrene F-4:Nominal Mol.Wt. 3.79×10 4 Mw / Mn 1.01 (0005209 / Tosoh Corporation) 2. Dynamic Mechanical Analysis (DMA) Equipment: DMA850 / TA Instruments Japan Co., Ltd. Measurement conditions: 3-point bending Measurement temperature: 30~310℃ Measurement frequency: 1.0(Hz) Sample dimensions: (60mm x 15mm x 2mm) Heating rate: 1.0℃ / min 3. High-temperature three-point bending test Measurement equipment: Universal material measuring device 100kN Shimadzu Autograph / Shimadzu Corporation Distance between supports: 40 mm Test speed: 5mm / min Sample dimensions: (60mm x 15mm x 2mm)

[0023] Example 1 A four-neck flask equipped with a stirrer was charged with 103.2 g of purified water, 356.8 g of isopropyl alcohol (IPA), and 5.1 g of untreated fumed silica (Sigma-Aldrich Japan, LLC, dry type), followed by 2.3 g of 37% HCl catalyst. After the liquid temperature in the flask was raised to 30°C, a mixture of 200.6 g of trimethoxymethylsilane and 22.3 g of dimethoxydimethylsilane was added dropwise over 30 minutes using a dropping funnel while stirring the liquid in the flask. During this process, heat generation was observed. After the addition was completed, the liquid temperature was raised to 70°C and stirred for an additional 12 hours. After confirming the completion of the reaction by GPC, the liquid temperature in the flask was lowered to 25°C. After the reaction was completed, toluene (1.3 times by weight) and purified water (1.0 times by weight) were added to the flask relative to the added IPA. The mixture was stirred for 30 minutes, then the stirring was stopped and the mixture was allowed to stand for 30 minutes. The two liquid layers were then separated, and the aqueous layer was removed from the flask. Then, pure water was added again in an amount 1.0 times the weight of the IPA, and the mixture was stirred, allowed to stand, and the aqueous layer was removed. This water-washing process was repeated twice. The remaining oil layer was distilled at 70°C under reduced pressure to remove the solvent, yielding 106.8 g (66.1% yield) of siloxane resin containing fumed silica as a solid. The molecular weight of the resulting siloxane resin was analyzed by GPC, and the weight average molecular weight (Mw) was 28,500 and the number average molecular weight was 5,400. Methyl ethyl ketone (MEK) was added in an amount of 0.2 times by weight to the obtained siloxane resin to dissolve the siloxane resin. Acetone was added in an amount of 0.3 times by weight, tetrabutylammonium difluorotriphenyl silicate in an amount of 0.008 times by weight, and malonic acid in an amount of 0.004 times by weight to the amount of the MEK solution, and the mixture was stirred to disperse the resin. Thereafter, each of the 12 glass cloths was immersed in the prepared dispersion liquid, and after allowing it to fully penetrate, it was dried for 20 hours in a well-ventilated place away from direct sunlight. Twelve sheets of the dried glass cloth were then stacked and heat-pressed for 6 hours at 150°C and 4 MPa using a heat press (MP-2FH, manufactured by Toyo Seiki Co., Ltd.) and then dried for 6 hours at 200°C under vacuum using a vacuum dryer to produce a siloxane resin glass fiber reinforced plastic (GFRP).

[0024] <Comparative Example 1> A four-neck flask equipped with a stirrer was charged with 103.2 g of purified water and 356.8 g of isopropyl alcohol (IPA), followed by 2.3 g of 37% HCl as a catalyst. After the temperature of the liquid in the flask was raised to 30°C, a mixture of 200.6 g of trimethoxymethylsilane and 22.3 g of dimethoxydimethylsilane was added dropwise over 30 minutes using a dropping funnel while stirring the liquid in the flask. Heat generation was observed during this process. After the dropwise addition was completed, the liquid temperature was raised to 70°C and stirred for an additional 12 hours. After confirming the completion of the reaction by GPC, the liquid temperature in the flask was lowered to 25°C. After the reaction was complete, toluene (1.3 times by weight relative to the IPA) and pure water (1.0 times by weight relative to the IPA) were added to the flask, stirred for 30 minutes, then stopped and allowed to stand for 30 minutes. The two liquid layers were separated, and the aqueous layer was removed from the flask. Pure water (1.0 times by weight relative to the IPA) was then added again, and this washing process of stirring, standing, and removing the aqueous layer was repeated twice. The remaining oil layer was distilled under reduced pressure at 70°C to remove the solvent, yielding 106.8 g (92.1% yield) of siloxane resin containing no fumed silica as a solid. The molecular weight of the resulting siloxane resin was analyzed by GPC, and the weight average molecular weight (Mw) was 12,000 and the number average molecular weight was 2,800. Methyl ethyl ketone (MEK) was added in an amount of 0.2 times by weight of the obtained siloxane resin to dissolve the siloxane resin. Acetone was added in an amount of 0.3 times by weight, tetrabutylammonium difluorotriphenyl silicate in an amount of 0.008 times by weight, and malonic acid in an amount of 0.004 times by weight relative to the amount of the MEK solution, and the mixture was stirred to disperse the resin. Thereafter, each of the 12 glass cloths was immersed in the prepared dispersion liquid, and after allowing it to fully penetrate, it was dried for 20 hours in a well-ventilated place away from direct sunlight. The 12 dried glass cloths were then heat-pressed together at 150°C and 4 MPa for 6 hours in a heat press, and then dried under vacuum at 200°C for 6 hours in a vacuum dryer to produce a siloxane resin glass fiber reinforced plastic (GFRP).

[0025] <Comparative Example 2> A siloxane resin was obtained in the same manner as in Comparative Example 1. Methyl ethyl ketone (MEK) was added in an amount of 0.2 times by weight of the obtained siloxane resin to dissolve the siloxane resin. To the MEK solution, 5.1 g of fumed silica (Sigma-Aldrich Japan, LLC, dry type) was added, and acetone, tetrabutylammonium difluorotriphenyl silicate, and malonic acid were added in amounts of 1.2 times by weight, 0.008 times by weight, and 0.004 times by weight, relative to the amount of the MEK solution, and the mixture was stirred to disperse. In this case, the dispersibility of the fumed silica was very poor, and until it became dispersible enough to be easily handled, four times the amount of acetone needed to be used compared to Example 1. In other words, it was revealed that by using the siloxane resin of Example 1, which is an example of the present invention, a varnish containing it had excellent handleability even when a small amount of solvent was used. Thereafter, each of the 12 glass cloths was immersed in the prepared dispersion liquid, and after allowing it to fully penetrate, it was dried for 20 hours in a well-ventilated place away from direct sunlight. The 12 dried glass cloths were then heat-pressed together at 150°C and 4 MPa for 6 hours in a heat press, and then dried under vacuum at 200°C for 6 hours in a vacuum dryer to produce a siloxane resin glass fiber reinforced plastic (GFRP).

[0026] (High temperature three-point bending test) Table 1 shows the silica content of the GFRPs produced in Example 1 and Comparative Examples 1 and 2, the fiber volume content (Vf) of the glass fiber in the GFRP, and the results of the high-temperature three-point bending test (maximum bending stress). [Table 1]

[0027] The results of Example 1 and Comparative Example 1 revealed that the GFRP made using the siloxane resin of Example 1, which was obtained by adding silica during polymerization of the siloxane resin, had a higher bending strength (1.34 times higher) and superior mechanical properties than the GFRP made using the siloxane resin of Comparative Example 1, which did not contain silica. The results of Example 1 and Comparative Example 2 reveal that the GFRP obtained using the siloxane resin of Example 1 has a higher bending strength (1.08 times higher) and superior mechanical properties than the GFRP obtained using the siloxane resin of Comparative Example 2, despite having a 10% lower fiber volume fraction (Vf) of the glass fibers.

[0028] (Dynamic viscoelasticity measurement) The dynamic viscoelasticity measurement was repeated three times using the above-described method for the GFRPs produced in Example 1 and Comparative Examples 1 and 2. The storage modulus and loss tangent of the third measurement results for Example 1 and Comparative Examples 1 and 2 are shown in Figure 1 and Figure 2, respectively.

[0029] The GFRP produced in Example 1, which is an embodiment of the present invention, was heated to the high temperature range of 310°C, and the results of measuring the storage modulus and loss tangent up to the upper measurement temperature limit of 310°C revealed that no change indicating the glass transition temperature (Tg) was observed even in the third measurement when the dynamic viscoelasticity measurement was repeated three times under the above analysis conditions.

Claims

1. A siloxane resin obtained by polymerizing component (A), component (B), and component (C). Component (A): a silane compound represented by general formula (1) Component (B): a silane compound represented by general formula (2) Component (C): Silica [Chemical formula 1] R １ SiX ３ ・・・・(1) (R in the formula １ represents an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 8 carbon atoms, and X represents a halogen atom, an alkoxy group having 1 to 4 carbon atoms, or an aryloxy group having 6 to 8 carbon atoms. [Case 2] R １ ２ SiX ２ ・・・・(2) (R in the formula １ and X are defined as in general formula (1).

2. 2. The siloxane resin according to claim 1, wherein component (B) is polymerized in a range of 10 to 20 parts by mole per 100 parts by mole of component (A), and component (C) is polymerized in a range of 1 to 20 parts by weight per 100 parts by weight of component (A).

3. 2. The siloxane resin of claim 1, wherein component (C) is a hydrophilic silica.

4. A siloxane resin composition comprising the siloxane resin according to any one of claims 1 to 3 and glass fibers.

5. The siloxane resin composition according to claim 4, further comprising a curing accelerator.

6. A varnish comprising the siloxane resin according to any one of claims 1 to 3 and an organic solvent.

7. The varnish according to claim 6, further comprising a curing accelerator.

8. A cured product of the siloxane resin composition according to claim 4.

9. A cured product of the siloxane resin composition according to claim 5.

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