Silica-containing resin composition and method for producing same, and molded article produced from silica-containing resin composition

Abstract

A silica-containing resin composition, characterized by containing a resin and silica particles in an amount of 5 to 300 parts by mass, with respect to 100 parts by mass of the resin, wherein the silica particles satisfy the following requirements (a) to (c): (a) the silica particles have a specific surface area, as determined through a nitrogen absorption method, of 20 to 500 m.sup.2/g; (b) the silica particles have a percent moisture absorption of 5.0 mass % or less at a relative humidity of 50%; and (c) the silica particles contain substantially no metallic impurity or halogen.

Claims

1. A silica-containing resin composition, comprising a resin and surface-treated silica particles in an amount of 5 to 300 parts by mass, with respect to 100 parts by mass of the resin, wherein (a) the silica particles have a specific surface area, as determined through a nitrogen absorption method, of 20 to 500 m.sup.2/g, (b) the silica particles have a percent moisture absorption of 5.0 mass % or less at 23° C. and a relative humidity of 50%, (c) the silica particles contain substantially no metallic impurity or halogen, (d) the silica particles have a moisture absorption amount per surface area thereof of 0.5 mg/m.sup.2 or less at 23° C. and a relative humidity of 50%, (e) the silica particles have a ratio (D2/D1) of mean particle size (D2) measured through dynamic light scattering to mean particle size (D1) measured through the BET method of 1.6 or lower, and (f) the surface-treated silica particles are produced, without firing of the silica particles, by a method that comprises: hydrolyzing a silicon alkoxide in water and an optional hydrophilic organic solvent as a reaction medium in the presence of a hydrolysis catalyst, with the temperature of the reaction medium being 60° C. or higher and the ratio by mole of water to silicon (H.sub.2O/Si) being maintained at 25 or higher, to obtain the silica particles, wherein the hydrolysis catalyst is at least one member selected from the group consisting of ammonia, primary to tertiary amines, and a quaternary ammonium; and modifying surfaces of the silica particles with hydrolysis products and/or hydrolysis condensation products of an organic silane compound in water and/or a hydrophilic organic solvent.

2. The silica-containing resin composition according to claim 1, wherein the surface-treated silica particles have undergone organophilization with the organic silane compound at ≧0.5 molecules per 1 nm.sup.2 surface thereof.

3. The silica-containing resin composition according to claim 2, wherein the organic silane compound is at least one compound selected from the group consisting of alkoxysilane, silazane, siloxane, acetoxysilane, and silylurea.

4. The silica-containing resin composition according to claim 2, wherein the surface-modified silica particles have a percent moisture absorption of 3.0 mass % or less at 23° C. and a relative humidity of 50%.

5. A molded article formed of the silica-containing resin composition according to claim 1.

6. A method for producing a silica-containing resin composition, the method comprising: forming surface-treated silica particles without firing of the silica particles; and incorporating the silica particles into a resin in an amount of 5 to 300 parts by mass, with respect to 100 parts by mass of the resin, wherein forming the surface-treated silica particles includes: hydrolyzing a silicon alkoxide in water and an optional hydrophilic organic solvent as a reaction medium in the presence of a hydrolysis catalyst, with the temperature of the reaction medium being 60° C. or higher and the ratio by mole of water to silicon (H.sub.2O/Si) being maintained at 25 or higher, to obtain the silica particles, wherein the hydrolysis catalyst is at least one member selected from the group consisting of ammonia, primary to tertiary amines, and a quaternary ammonium; and modifying surfaces of the silica particles with hydrolysis products and/or hydrolysis condensation products of an organic silane compound in water and/or a hydrophilic organic solvent; and wherein the silica particles have a moisture absorption amount per surface area thereof of 0.5 mg/m.sup.2 or less at 23° C. and a relative humidity of 50%, a specific surface area, as determined through a nitrogen absorption method, of 20 to 500 m.sup.2/g, and a ratio (D2/D1) of mean particle size (D2) measured through dynamic light scattering to mean particle size (D1) measured through the BET method of 1.6 or lower.

7. The method according to claim 6, wherein the organic silane compound is present at ≧0.5 molecules per 1 nm.sup.2 surface of the silica particles.

8. A molded article formed of the silica-containing resin composition according to claim 2.

9. A molded article formed of the silica-containing resin composition according to claim 3.

10. A molded article formed of the silica-containing resin composition according to claim 4.

11. A method for producing a silica-containing resin composition, the method comprising: forming surface-treated silica particles; and incorporating the silica particles into a resin in an amount of 5 to 300 parts by mass, with respect to 100 parts by mass of the resin, wherein forming the surface-treated silica particles consists essentially of: hydrolyzing a silicon alkoxide in water and an optional hydrophilic organic solvent as a reaction medium in the presence of a hydrolysis catalyst, with the temperature of the reaction medium being 60° C. or higher and the ratio by mole of water to silicon (H.sub.2O/Si) being maintained at 25 or higher, to obtain the silica particles, wherein the hydrolysis catalyst is at least one member selected from the group consisting of ammonia, primary to tertiary amines, and a quaternary ammonium; and modifying surfaces of the silica particles with hydrolysis products and/or hydrolysis condensation products of an organic silane compound in water and/or a hydrophilic organic solvent; and wherein the silica particles have a moisture absorption amount per surface area thereof of 0.5 mg/m.sup.2 or less at 23° C. and a relative humidity of 50%, a specific surface area, as determined through a nitrogen absorption method, of 20 to 500 m.sup.2/g, and a ratio (D2/D1) of mean particle size (D2) measured through dynamic light scattering to mean particle size (D1) measured through the BET method of 1.6 or lower.

Description

EXAMPLES

(1) The present invention will next be described in detail by way of example, which should not be construed as limiting the invention thereto.

[Production Example 1] Silica Sol [1]

(2) To a 3-L stainless steel reactor equipped with a stirrer and a condenser, pure water (2,237 g) and 28-mass % aqueous ammonia (2.5 g) were added, and the contents of the reactor were maintained at 90° C. by means of an oil bath. Subsequently, a commercial product of tetraethyl silicate (TEOS) (261 g) was added dropwise to the reactor over 2.4 hours continuously under stirring. The water concentration of the reaction medium was maintained at 90 mass % or higher, and the ratio by mole of water to the total amount of added silicon (H.sub.2O/Si) was maintained at 97 or higher.

(3) After completion of feeding, the reaction was continuously stirred for a further 2 hours, while the temperature of the contents of the reactor was maintained at 90° C. Subsequently, the entirety of the liquid in the reactor was removed from the reactor, to thereby yield silica particles. The product was concentrated to 370 g under a reduced pressure of 26.7 to 10.7 kPa by means of a rotary evaporator, to thereby yield a silica sol having an SiO.sub.2 content of 20.2 mass %, a pH of 7.0, a viscosity, as determined by means of a B-type viscometer at 25° C. (hereinafter referred to as “B-type viscosity”), of 4.5 mPa.Math.s, and a dynamic light scattering particle size of 40 nm.

[Production Example 2] Silica Sol [2]

(4) To the same reactor as employed in Production Example 1, pure water (2,240 g) and 28-mass % aqueous ammonia (6.7 g) were added, and the contents of the reactor were maintained at 80° C. by means of an oil bath. Subsequently, a commercial product of tetramethyl silicate (TMOS) (253 g) was added dropwise to the reactor over 3 hours continuously under stirring. The water concentration of the reaction medium was maintained at 91 mass % or higher, and the ratio by mole (H.sub.2O/Si) was maintained at 72 or higher.

(5) After completion of feeding, the temperature of the contents of the reactor was maintained at 80° C. for one hour and then elevated to 90° C. The reaction was continuously stirred at 90° C. for one hour. Subsequently, the liquid in the reactor was evaporated to the outside, to thereby concentrate the contents to a liquid temperature of 99° C. Then, the entirety of the contents was recovered from the reactor, to thereby recover silica particles. The product was concentrated to 400 g by means of a rotary evaporator under a reduced pressure of 13.3 kPa, to thereby yield silica sol [2] having an SiO.sub.2 content of 25.0 mass %, a pH of 7.3, a B-type viscosity of 5.0 mPa.Math.s, and a dynamic light scattering particle size of 17 nm.

[Production Example 3] Silica Sol [3]

(6) To the same reactor as employed in Production Example 1, pure water (2,135 g), silica sol produced in Production Example 2 (42 g), and 28-mass % aqueous ammonia (27 g) were added, and the contents of the reactor were maintained at 80° C. by means of an oil bath. Subsequently, a commercial product of tetramethyl silicate (TMOS) (253 g) was added dropwise to the reactor over 5 hours continuously under stirring. The water concentration of the reaction medium was maintained at 90 mass or higher, and the ratio by mole (H.sub.2O/Si) was maintained at 71 or higher.

(7) After completion of feeding, the temperature of the contents of the reactor was maintained at 80° C. for one hour and then elevated to 90° C. The reaction was continuously stirred at 90° C. for one hour. Subsequently, similar to Production Example 1, the liquid in the reactor was evaporated to the outside, to thereby concentrate the contents to a liquid temperature of 99° C. Then, the entirety of the contents was recovered from the reactor, to thereby recover silica particles. The product was concentrated to 442 g by means of a rotary evaporator under a reduced pressure of 13.3 kPa, to thereby yield silica sol [3] having an SiO.sub.2 content of 25.0 mass %, a pH of 7.8, a B-type viscosity of 7.4 mPa.Math.s, and a dynamic light scattering particle size of 42 nm.

[Production Example 4] Silica Sol [4]

(8) To the same reactor as employed in Production Example 1, pure water (2,235 g) and 25-mass % aqueous tetramethylammonium hydroxide (12 g) were added, and the contents of the reactor were maintained at 80° C. by means of an oil bath. Subsequently, a commercial product of tetramethyl silicate (TMOS) (253 g) was added dropwise to the reactor over 3 hours continuously under stirring.

(9) After completion of feeding, the temperature of the contents of the reactor was maintained at 80° C. for one hour and then elevated to 90° C., at which stirring was continued. The reaction was cooled, to thereby recover a dispersion of grown particle. Then, to the same reactor as employed in Production Example 1, pure water (1,680 g), the dispersion of grown particle (380 g), and 25-mass % aqueous tetramethylammonium hydroxide (TMAH) (15 g) were added, and the contents of the reactor were maintained at 80° C. by means of an oil bath. Subsequently, a commercial product of tetramethyl silicate (TMOS) (425 g) was added dropwise to the reactor over 3 hours continuously under stirring. The water concentration of the reaction medium was maintained at 84 mass % or higher, and the ratio by mole (H.sub.2O/Si) was maintained at 38 or higher.

(10) After completion of feeding, the temperature of the contents of the reactor was maintained at 80° C. for one hour and then the liquid in the reactor was evaporated to the outside, to thereby concentrate the contents to a liquid temperature of 99° C. Then, the entirety of the contents was recovered from the reactor, to thereby recover silica particles. The product was concentrated to 873 g by means of a rotary evaporator under a reduced pressure of 13.3 kPa, to thereby yield silica sol [4] having an SiO.sub.2 content of 21.0 mass %, a pH of 7.0, a B-type viscosity of 6.0 mP.Math.s, and a dynamic light scattering particle size of 44 nm.

[Production Example 5] Silica Sol [5]

(11) To the same reactor as employed in Production Example 1, pure water (2,237 g) and 28-mass % aqueous ammonia (2.5 g) were added, and the contents of the reactor were maintained at 85° C. by means of an oil bath. Subsequently, a commercial product of tetraethyl silicate (TEOS) (261 g) was added dropwise to the reactor over 2 hours continuously under stirring. The water concentration of the reaction medium was maintained at 90 mass or higher, and the ratio by mole (H.sub.2O/Si) was maintained at 97 or higher.

(12) After completion of feeding, the temperature of the contents of the reactor was elevated to 90° C., and the reaction was continuously stirred at 90° C. for 2 hours. Then, the entirety of the contents was recovered from the reactor, to thereby recover silica particles. The product was concentrated to 285 g by means of a rotary evaporator under a reduced pressure of 26.7 to 10.7 kPa, to thereby yield silica sol [5] having an SiO.sub.2 content of 26.0 mass %, a pH of 6.8, a B-type viscosity of 6.3 mPa.Math.s, and a dynamic light scattering particle size of 29.5 nm.

(13) <Evaluation of Characteristics of Silica Sol Dry Powder>

(14) [Measurement of Specific Surface Area]

(15) The specific surface area of each of the silica sols of Production Examples 1 to 5 was determined through a nitrogen absorption method in the following manner. Specifically, the silica gel produced by drying the silica sol at 80° C. in a vacuum drier was pulverized with a mortar and further dried at 180° C. for 3 hours, to thereby yield dry silica powder. The specific surface area S (m.sup.2/g) of the powder was determined through a nitrogen absorption method. From the specific surface area S, the mean particle size (D1) of each of the aqueous silica sol was calculated by the following formula.
[F1] D1 (nm)=2,720/S  (1)

(16) Also, the particle size (D2) of the silica sol measured through dynamic light scattering was derived, and D2/D1 was calculated. Notably, the dynamic light scattering particle size (D2) was determined through a measurement procedure in which a silica sol was placed in a sealable container and stored therein at 50° C. for two weeks, and then diluted with 0.01-mass % aqueous ammonia.

(17) The commercial product of silica particles [6] and that of silica sol [7] were subjected to measurement of specific surface area, and the D2/D1 of silica sol [7] was calculated. Table 1 shows the results.

(18) [Moisture Absorption Property]

(19) The percent moisture absorption of each of the silica sols of Production Examples 1 to 5 was determined in the following manner. Specifically, the same 180° C.-dried powder (0.2 to 0.3 g) as employed in specific surface area determination was placed in a weighing bottle, and the weight of the sample was determined. While the cap of the bottle was opened, the bottle was allowed to stand in an atmosphere (23° C., 50% RH) for 48 hours. Then, the bottle was closed by the cap, and the weight of the bottle was measured again. Percent moisture absorption was determined by the following formula [2]. The moisture absorption amount per specific surface area was determined based on the specific surface area (via nitrogen adsorption method) by the following formula [3]. The percent moisture absorption and the moisture absorption amount per specific surface area of the commercial product of silica particles [6] and that of silica sol [7] were also determined. Table 1 shows the results.
[F2] Percent moisture absorption (mass %)=(weight increase (g)/sample amount (g))×100  (2)
[F3] Moisture absorption amount per surface area (mg/m.sup.2)=weight increase (mg)/(sample amount (g)×specific surface area (m.sup.2/g))  (3)
[Metallic Impurity and Chlorine Content of Silica Particles]

(20) The metallic impurity (Na, Fe) content and the chlorine content of each of the silica sols [1] to [5] produced in Production Examples 1 to 5 were determined in the following manner. Specifically, the metallic impurity was determined by dissolving silica sol in a platinum dish with diluted nitric acid and hydrofluoric acid, drying the solution to solid, adding diluted nitric acid to the platinum dish, and analyzing the resultant liquid through ICP emission analysis. The chloride ion was determined by diluting a silica sol and subjecting the liquid to anion chromatography. Table 1 shows the results.

(21) TABLE-US-00001 TABLE 1 Prodn. Exs. Commercial 1 2 3 4 5 product Silica sol [1] sol [2] sol [3] sol [4] sol [5] particle [6] sol [7] Si alkoxide TEOS TMOS TMOS TMOS TEOS — Hydrolysis catalyst NH.sub.3 NH.sub.3 NH.sub.3 TMAH NH.sub.3 — — Temp. 90 80 80 80 85 — — Sp. surface area 99 200 91 92 129 141 81 (m.sup.2/g) BET particle size D1 27.5 13.6 29.9 29.6 21.0 — 33.5 (nm) D2/D1 1.46 1.25 1.40 1.49 1.40 — 2.24 Percent moisture 3.2 6.0 2.0 2.5 4.3 — 8.4 absorption (%) Moisture absorption 0.32 0.30 0.22 0.28 0.33 — 1.04 amount per surface area (mg/m.sup.2) Na (ppm) <1 <1 <1 <1 <1 — <1 Fe (ppm) <1 <1 <1 <1 <1 — <1 Cl (ppm) <2 <2 <2 <2 <2 — <2 Commercial silica particles [6]: “Aerosil R711” (product of Nippon Aerosil Co., Ltd.) Commercial silica sol [7]: “Quartron PL-3” (product of Fuso Chemical Co., Ltd.)

[Production Example 6] MMA-Dispersed Silica Sol [1]

(22) To a 1-L glass container equipped with a stirrer and a condenser, silica sol [1] produced in Production Example 1 (300 g), methanol (30 g), and 28-mass % aqueous ammonia (0.1 g) were added. Then, methacryloxypropyltrimethoxysilane (“KBM-503,” product of Shin-Etsu Chemical Co., Ltd.) (6.3 g) was added to the above mixture under stirring.

(23) The sol was heated to 95° C. Subsequently, while methanol gas, separately prepared through boiling in another container, was fed into the sol in the reaction container, methanol-water mixture was distilled out, to thereby yield a methanol-dispersed silica sol (SiO.sub.2 concentration: 25.0 mass %, water content: 0.9 mass %). The methanol-dispersed sol was transferred to a 1-L round-bottom (egg-plant shape) flask, and solvent substitution was performed through distillation under reduced pressure at 20.0 to 13.3 kPa, while methyl methacrylate (hereinafter abbreviated as MMA) was added thereto, to thereby yield 200 g of an MMA-dispersed silica sol [1] (SiO.sub.2 concentration: 30.5 mass %, methanol concentration: 0.3 mass %, water content: 0.1 mass %).

[Production Example 7] MEK-Dispersed Silica sol [2]

(24) To the same reaction container as employed in Production Example 6, silica sol [2] produced in Production Example 2 (380 g) and methanol (40 g) were added. Then, tri-n-propylamine (0.2 g) and phenyltrimethoxysilane (“KBM-103,” product of Shin-Etsu Chemical Co., Ltd.) (3.1 g) were added to the above mixture under stirring. Subsequently, while methanol gas, separately prepared in the same manner as employed in Production Example 6, was fed into the sol, methanol-water mixture was distilled out, to thereby yield 446 g of a methanol-dispersed silica sol (SiO.sub.2 concentration: 21.7 mass %, water content: 0.5 mass %).

(25) To the methanol-dispersed sol (400 g), tri-n-propylamine (0.3 g) and phenyltrimethoxysilane (14.0 g) were added, and the resultant mixture was heated for 2 hours under stirring, with the liquid temperature being maintained at 60° C. Then, the entirety of the reaction mixture was transferred to a 1-L round-bottom (egg-plant shape) flask, and solvent substitution was performed through distillation under reduced pressure at 60.0 to 53.3 kPa, while methyl ethyl ketone (hereinafter abbreviated as MEK) was added thereto, to thereby yield an MEK-dispersed silica sol [2] (SiO.sub.2 concentration: 27.1 mass %, methanol concentration: 0.5 mass %, water content: 0.1 mass %).

[Production Example 8] MEK-Dispersed Silica Sol [3]

(26) To the same reaction container as employed in Production Example 6, silica sol [3] produced in Production Example 3 (400 g) and methanol (40 g) were added. Then, phenyltrimethoxysilane (“KBM-103,” product of Shin-Etsu Chemical Co., Ltd.) (1.5 g) was added to the above mixture under stirring. Subsequently, while methanol gas, separately prepared in the same manner as employed in Production Example 6, was fed into the sol, methanol-water mixture was distilled out, to thereby yield 415 g of a methanol-dispersed silica sol (SiO.sub.2 concentration: 24.3 mass %, water content: 0.2 mass %).

(27) To the methanol-dispersed sol (343 g), tri-n-propylamine (0.3 g) and phenyltrimethoxysilane (6.1 g) were added, and the resultant mixture was heated for 2 hours under stirring, with the liquid temperature being maintained at 60° C. Then, the entirety of the reaction mixture was transferred to a 1-L round-bottom (egg-plant shape) flask, and solvent substitution was performed through distillation under reduced pressure at 60.0 to 53.3 kPa, while MEK was added thereto, to thereby yield an MEK-dispersed silica sol [3] (SiO.sub.2 concentration: 24.6 mass %, methanol concentration: 0.4 mass %, water content: 0.2 mass %).

[Production Example 9] MEK-Dispersed Silica sol [4]

(28) To the same reaction container as employed in Production Example 6, silica sol [4] produced in Production Example 4 (475 g) and methanol (48 g) were added. Then, phenyltrimethoxysilane (“KBM-103,” product of Shin-Etsu Chemical Co., Ltd.) (1.5 g) was added to the above mixture under stirring. Subsequently, while methanol gas, separately prepared in the same manner as employed in Production Example 6, was fed into the sol, methanol-water mixture was distilled out, to thereby yield 485 g of a methanol-dispersed silica sol (SiO.sub.2 concentration: 20.5 mass %, water content: 0.5 mass %).

(29) To the methanol-dispersed sol (470 g), tri-n-propylamine (0.04 g) and phenyltrimethoxysilane (7.3 g) were added, and the resultant mixture was heated for 2 hours under stirring, with the liquid temperature being maintained at 60° C. Then, the entirety of the reaction mixture was transferred to a 1-L round-bottom (egg-plant shape) flask, and solvent substitution was performed through distillation under reduced pressure at 60.0 to 53.3 kPa, while MEK was added thereto, to thereby yield an MEK-dispersed silica sol [4] (SiO.sub.2 concentration: 24.7 mass %, methanol concentration: 0.2 mass %, water content: 0.1 mass %).

[Production Example 10] Hydrophobic Silica Powder [5]

(30) To a 1-L glass reactor equipped with a stirrer and a condenser, silica sol [5] produced in Production Example 5 (300 g), and isopropyl alcohol (90 g) was added thereto, to thereby prepare a mixed solvent silica sol having a silica concentration of 20.0 mass %. The mixed solvent silica sol was heated to 65° C., and hexamethyldisilazane (45 g) was added dropwise thereto. The thus-treated mixed solvent silica sol was mixed for 30 minutes and heated at 70° C. for one hour, to thereby prepare a slurry dispersion of hydrophobicized colloidal silica.

(31) Subsequently, the slurry dispersion of hydrophobicized colloidal silica was aged for 3 hours under reflux and stirring, to thereby granulate silica. The hydrophobicized colloidal silica in granule form was separated from the liquid phase by means of a Buchner funnel (with qualitative filter paper No. 131, product of ADVANTEC), and the thus-obtained cake of the hydrophobicized colloidal silica in granule form was dried under reduced pressure at 80° C.

(32) The thus-dried hydrophobicized colloidal silica in granule form was pulverized by means of a powder mill, and the powder was further dried at 150° C., to thereby yield 80 g of a hydrophobic silica powder [5]. The hydrophobic silica powder was found to have an SiO.sub.2 concentration of 96.5 mass % and a water content of 0.3 mass %.

[Production Example 11] Comparative MEK-Dispersed Silica Sol

(33) To the same reaction container as employed in Production Example 6, commercial water-dispersed silica sol [7] (tradename “Quartron PL-3,” product of Fuso Chemical Co., Ltd., SiO.sub.2 concentration: 19.5%) (530 g) and methanol (53 g) were added. Then, tri-n-propylamine (0.04 g) and phenyltrimethoxysilane (“KBM-103,” product of Shin-Etsu Chemical Co., Ltd.) (1.3 g) were added to the above mixture under stirring.

(34) Subsequently, while methanol gas, separately prepared in the same manner as employed in Production Example 6, was fed into the sol, methanol-water mixture was distilled out, to thereby yield a methanol-dispersed silica sol (SiO.sub.2 concentration: 20.6 mass %, water content: 1.5 mass %). To the methanol-dispersed sol (446 g), phenyltrimethoxysilane (5.9 g) was added, and the resultant mixture was heated for 2 hours under stirring at 60° C.

(35) Then, tri-n-propylamine (0.023 g) was added the mixture, and solvent substitution was performed through distillation under reduced pressure at 60.0 to 53.3 kPa, while MEK was added thereto, to thereby yield a comparative MEK-dispersed silica sol [6] (SiO.sub.2 concentration: 24.5 mass %, methanol concentration: 0.1 mass %, water content: 0.2 mass %).

(36) <Assessing of Characteristic of Surface-Modified Silica>

(37) [Percent Moisture Absorption]

(38) Percent moisture absorption of each of MMA-dispersed silica sol [1], MEK-dispersed silica sols [2] to [4], hydrophobic silica powder [5], and comparative MEK-dispersed silica sol [6], produced in Production Examples 6 to 11, was measured in a manner similar to that of Production Examples 1 to 5.

(39) Table 2 shows the percent moisture absorption measurements of the surface-modified silicas produced in Production Examples 6 to 11, along with the percent moisture absorption measurements of the corresponding silica sols before surface modification.

(40) TABLE-US-00002 TABLE 2 Prodn. Exs. 6 7 8 9 10 11 Surface-treated silica MMA MEK MEK MEK Silica Comp. sol [1] sol [2] sol [3] sol [4] powder [5] Ex. MEK sol [6] Raw silica sol [1] sol [2] sol [3] sol [4] sol [5] sol [7] Percent moisture 3.2 6.0 2.0 2.5 4.3 8.4 absorption (%) before surface treatment Percent moisture 1.2 1.2 1.2 1.7 1.0 6.9 absorption (%) after surface treatment Relative drop in moisture 2.7 5.0 1.7 1.5 3.6 1.2 absorption (before/after)

(41) As is clear from Table 2, MMA-dispersed silica sol [1], MEK-dispersed silica sols [2] to [4], and hydrophobic silica powder [5], produced in Production Examples 6 to 10, were found to have a percent moisture absorption of 3.0 mass % or less at a relative humidity of 50%, further 2.0 mass % or less. Such a percent moisture absorption indicates a moisture absorption property lower than that of comparative MEK-dispersed silica sol [6], produced in Production Example 11.

(42) As is also clear from Table 2, MMA-dispersed silica sol [1], MEK-dispersed silica sols [2] to [4], and hydrophobic silica powder [5], produced in Production Examples 6 to 10, were found to exhibit a greater drop in percent moisture absorption (percent moisture absorption before surface modification/percent moisture absorption after surface modification), as compared with comparative MEK-dispersed silica sol [6], produced in Production Example 11.

(43) <Production of Silica-Containing Resin Composition and Molded Article (Cured Resin Product)>

[Example 1] Silica-Containing Resin Composition [1A] and Cured Resin Product [1A]

(44) 2,2′-Azodiisobutyronitrile (product of Tokyo Chemical Industry Co., Ltd.) (0.1 parts by mass) was added to MMA-dispersed silica sol [1] produced in Production Example 6 (130 parts by mass), to thereby provide a silica-containing resin composition [1A]. The silica particle content of the silica-containing resin composition [1A] was adjusted to 43 parts by mass, with respect to 100 parts by mass of the resin.

(45) The silica-containing resin composition [1A] was heated at 95° C. for one hour under stirring. Then, the composition was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated at 60° C. for 8 hours, at 80° C. for 2 hours, and 100° C. for 2 hours so as to cure the composition, to thereby produce a cured resin product [1A] (SiO.sub.2 content: 43 parts by mass).

[Example 2] Silica-Containing Resin Composition [2A] and Cured Resin Product [2A]

(46) MMA (Kanto Chemical Co., Inc.) (100 parts by mass) was mixed with 2,2′-azodiisobutyronitrile (product of Tokyo Chemical Industry Co., Ltd.) (0.1 parts by mass), hydrophobic silica powder [5] produced in Production Example 10 (30 parts by mass), and 3-methacryloxypropyltrimethoxysilane (“KBM-503,” product of Shin-Etsu Chemical Co., Ltd.) (2.0 parts by mass), to thereby provide a silica-containing resin composition [2A]. The silica particle content of the silica-containing resin composition [2A] was adjusted to 29 parts by mass, with respect to 100 parts by mass of the resin.

(47) The silica-containing resin composition [2A] was heated at 95° C. for one hour under stirring. Then, the composition was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated at 60° C. for 8 hours, at 80° C. for 2 hours, and 100° C. for 2 hours so as to cure the composition, to thereby produce a cured resin product [2A] (SiO.sub.2 content: 29 parts by mass).

[Referential Example 1] Referential Resin Composition [1a] and Referential Cured Resin Product [1a]

(48) 2,2′-Azodiisobutyronitrile (product of Tokyo Chemical Industry Co., Ltd.) (0.1 parts by mass) was added to MMA (Kanto Chemical Co., Inc.) (100 parts by mass), to thereby provide a referential resin composition [1a]. The silica particle content of the referential resin composition [1a] was adjusted to 0 part by mass, with respect to 100 parts by mass of the resin.

(49) The referential resin composition [1a] was heated at 95° C. for one hour under stirring. Then, the composition was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated at 60° C. for 8 hours, at 80° C. for 2 hours, and 100° C. for 2 hours so as to cure the composition, to thereby produce a referential cured resin product [1a] (SiO.sub.2 content: 0 part by mass).

Comparative Example 1

(50) A commercial hydrophobic fumed silica (“AEROSIL (registered trademark) R711” methacryloxysilane-treated, product of Nippon Aerosil Co., Ltd.) was gradually added to to MMA (Kanto Chemical Co., Inc.) (100 parts by mass) under stirring. When 15 parts by mass of silica was added, the viscosity of the mixture considerably increased, making stirring difficult. As a result, silica was not able to be dispersed in MMA at high concentration.

[Example 3] Silica-Containing Resin Composition [3A] and Cured Resin Product [3A]

(51) Bisphenol F-type epoxy resin (“YL-983U,” Mitsubishi Chemical Corporation) (20 g) was mixed with MEK-dispersed silica sol [2] produced in Production Example 7 (22.2 g), and the solvent of the mixture was removed at 26.7 to 4.0 kPa, to thereby provide a silica sol containing bisphenol F-type epoxy resin as a dispersion medium (SiO.sub.2 concentration: 23 mass %, viscosity (at 23° C.): 1,500 mPa.Math.s).

(52) Separately, 4-methylcyclohexane-1,2-dicarboxylic anhydride (20 g) was mixed with MEK-dispersed silica sol [2] produced in Production Example 7, and the solvent of the mixture was removed at 26.7 to 4.0 kPa, to thereby provide a silica sol containing 4-methylcyclohexane-1,2-dicarboxylic anhydride as a dispersion medium (SiO.sub.2 concentration: 23 mass %, viscosity (at 50° C.): 680 mPa.Math.s). The bisphenol F-type epoxy resin-dispersed sol (100 parts by mass) and 4-methylcyclohexane-1,2-dicarboxylic anhydride-dispersed sol (100 parts by mass) were combined. Then, tetra-n-butylsulfonium (“PX4ET,” product of Nippon Chemical Industrial Co., Ltd.) (0.0073 parts by mass) was added there to as a curing accelerator with sufficient mixing, to thereby provide a silica-containing resin composition [3A]. The silica particle content of the silica-containing resin composition [3A] was adjusted to 30 parts by mass, with respect to 100 parts by mass of the resin.

(53) The silica-containing resin composition [3A] was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated in a drier at 80° C. for 30 minutes, at 100° C. for 2 hours, and 150° C. for 4 hours, to thereby produce a cured resin product [3A] (SiO.sub.2 content: 30 parts by mass).

[Example 4] Silica-Containing Resin Composition [4A] and Cured Resin Product [4A]

(54) Bisphenol F-type epoxy resin (“YL-983U,” Mitsubishi Chemical Corporation) (45 g) was mixed with MEK-dispersed silica sol [4] produced in Production Example 9 (81 g), and the solvent of the mixture was removed at 26.7 to 4.0 kPa, to thereby provide a silica sol containing bisphenol F-type epoxy resin as a dispersion medium (SiO.sub.2 concentration: 30.5 mass %, MEK concentration: 0.1 mass %, viscosity (at 23° C.) 1,060 mPa.Math.s).

(55) To the thus-produced bisphenol epoxy resin-dispersed sol (100 parts by mass), 4-methylcyclohexane-1,2-dicarboxylic anhydride (70 parts by mass) serving as a curing agent and tetra-n-butylsulfonium (“PX4ET,” product of Nippon Chemical Industrial Co., Ltd.) (0.0068 parts by mass) serving as a curing accelerator were added, to thereby provide a silica-containing resin composition [4A]. The silica particle content of the silica-containing resin composition [4A] was adjusted to 21 parts by mass, with respect to 100 parts by mass of the resin.

(56) The silica-containing resin composition [4A] was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated in a drier at 80° C. for 30 minutes, at 100° C. for 2 hours, and 150° C. for 4 hours, to thereby produce a cured resin product [4A] (SiO.sub.2 content: 21 parts by mass).

[Example 5] Silica-Containing Resin Composition [5A] and Cured Resin Product [5A]

(57) An alicyclic epoxy resin (“Celloxide 2021P,” product of Daicel Corporation) (24.8 g) was mixed with MEK-dispersed silica sol [3] produced in Production Example 8 (67.1 g), and the solvent of the mixture was removed at 26.7 to 4.0 kPa, to thereby provide an alicyclic epoxy resin-dispersed silica sol (SiO.sub.2 concentration: 40 mass %, MEK concentration: 0 mass %, viscosity (at 23° C.): 955 mPa.Math.s).

(58) To the thus-produced alicyclic epoxy resin-dispersed sol (100 parts by mass), 4-methylcyclohexane-1,2-dicarboxylic anhydride (72 parts by mass) serving as a curing agent and tetra-n-butylsulfonium (“PX4ET,” product of Nippon Chemical Industrial Co., Ltd.) (0.0060 parts by mass) serving as a curing accelerator were added, to thereby provide a silica-containing resin composition [5A]. The silica particle content of the silica-containing resin composition [5A] was adjusted to 30 parts by mass, with respect to 100 parts by mass of the resin.

(59) The silica-containing resin composition [5A] was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated in a drier at 80° C. for 30 minutes, at 100° C. for 2 hours, and 150° C. for 4 hours, to thereby produce a cured resin product [5A] (SiO.sub.2 content: 20 parts by mass).

[Example 6] Silica-Containing Resin Composition [6A] and Cured Resin Product [6A]

(60) An alicyclic epoxy resin (“Celloxide 2021P,” product of Daicel Corporation) (45 g) was mixed with MEK-dispersed silica sol [4] produced in Production Example 9 (80 g), and the solvent of the mixture was removed at 26.7 to 4.0 kPa, to thereby provide an alicyclic epoxy resin-dispersed silica sol (SiO.sub.2 concentration: 30.4 mass %, MEK concentration: 0.2 mass %, viscosity (at 23° C.): 600 mPa.Math.s).

(61) To the thus-produced alicyclic epoxy resin-dispersed sol (100 parts by mass), 4-methylcyclohexane-1,2-dicarboxylic anhydride (83 parts by mass) serving as a curing agent and tetra-n-butylsulfonium (“PX4ET,” product of Nippon Chemical Industrial Co., Ltd.) (0.0068 parts by mass) serving as a curing accelerator were added, to thereby provide a silica-containing resin composition [6A]. The silica particle content of the silica-containing resin composition [6A] was adjusted to 30 parts by mass, with respect to 100 parts by mass of the resin.

(62) The silica-containing resin composition [6A] was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated in a drier at 80° C. for 30 minutes, at 100° C. for 2 hours, and 150° C. for 4 hours, to thereby produce a cured resin product [6A] (SiO.sub.2 content: 20 parts by mass).

[Referential Example 2] Referential Resin Composition [2a] and Referential Cured Resin Product [2a]

(63) A bisphenol F-type epoxy resin-dispersed sol (100 parts by mass) was mixed with 4-methylcyclohexane-1,2-dicarboxylic anhydride (100 parts by mass), and tetra-n-butylsulfonium (“PX4ET,” product of Nippon Chemical Industrial Co., Ltd.) (0.0068 parts by mass) serving as a curing accelerator was added to the mixture, to thereby provide a referential resin composition [2a]. The silica particle content of the referential resin composition [2a] was adjusted to 0 part by mass, with respect to 100 parts by mass of the resin.

(64) The referential resin composition [2a] was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated in a drier at 80° C. for 30 minutes, at 100° C. for 2 hours, and 150° C. for 4 hours, to thereby produce a referential cured resin product [2a] (SiO.sub.2 content: 0 part by mass).

[Referential Example 3] Referential Resin Composition [3a] and Referential Cured Resin Product [3a]

(65) An alicyclic epoxy resin-dispersed sol (100 parts by mass) was mixed with 4-methylcyclohexane-1,2-dicarboxylic anhydride (120 parts by mass), and tetra-n-butylsulfonium (“PX4ET,” product of Nippon Chemical Industrial Co., Ltd.) (0.0068 parts by mass) serving as a curing accelerator was added to the mixture, to thereby provide a referential resin composition [3a]. The silica particle content of the referential resin composition [3a] was adjusted to 0 part by mass, with respect to 100 parts by mass of the resin.

(66) The referential resin composition [3a] was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated in a drier at 80° C. for 30 minutes, at 100° C. for 2 hours, and 150° C. for 4 hours, to thereby produce a referential cured resin product [3a] (SiO.sub.2 content: 0 part by mass).

[Comparative Example 2] Comparative Silica-Containing Resin Composition [2B] and Comparative Cured Resin Product [2B]

(67) Bisphenol F-type epoxy resin (“YL-983U,” Mitsubishi Chemical Corporation) (45 g) was mixed with comparative MEK-dispersed silica sol [6] produced in Production Example 11 (80 g), and the solvent of the mixture was removed at 26.7 to 4.0 kPa, to thereby provide a silica sol containing bisphenol F-type epoxy resin as a dispersion medium (SiO.sub.2 concentration: 30.5 mass %, MEK concentration: 0.1 mass %, viscosity (at 50° C.): 1,450 mPa.Math.s).

(68) To the thus-produced bisphenol epoxy resin-dispersed sol (100 parts by mass), 4-methylcyclohexane-1,2-dicarboxylic anhydride (70 parts by mass) serving as a curing agent and tetra-n-butylsulfonium (“PX4ET,” product of Nippon Chemical Industrial Co., Ltd.) (0.0068 parts by mass) serving as a curing accelerator were added, to thereby provide a comparative silica-containing resin composition [2B]. The silica particle content of the comparative silica-containing resin composition [2B] was adjusted to 21 parts by mass, with respect to 100 parts by mass of the resin.

(69) The comparative silica-containing resin composition [2B] was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated in a drier at 80° C. for 30 minutes, at 100° C. for 2 hours, and 150° C. for 4 hours, to thereby produce a comparative cured resin product [2B] (SiO.sub.2 content: 21 parts by mass).

[Comparative Example 3] Comparative Silica-Containing Resin Composition [3B] and Comparative Cured Resin Product [3B]

(70) An alicyclic epoxy resin (“Celloxide 2021P,” product of Daicel Corporation) (46 g) was mixed with comparative MEK-dispersed silica sol [6] produced in Production Example 11 (81 g), and the solvent of the mixture was removed at 26.7 to 4.0 kPa, to thereby provide a silica sol containing an aliphatic epoxy resin as a dispersion medium (SiO.sub.2 concentration: 40 mass %, MEK concentration: 0 mass %, viscosity (at 23° C.): 955 mPa.Math.s).

(71) To the thus-produced alicyclic epoxy resin-dispersed sol (100 parts by mass), 4-methylcyclohexane-1,2-dicarboxylic anhydride (83 parts by mass) serving as a curing agent and tetra-n-butylsulfonium (“PX4ET,” product of Nippon Chemical Industrial Co., Ltd.) (0.0068 parts by mass) serving as a curing accelerator were added, to thereby provide a comparative silica-containing resin composition [3B]. The silica particle content of the comparative silica-containing resin composition [3B] was adjusted to 19 parts by mass, with respect to 100 parts by mass of the resin.

(72) The comparative silica-containing resin composition [3B] was cast into a mold having dimensions of 4.5 cm (length)×2.5 cm (width)×3 mm (thickness) and heated in a drier at 80° C. for 30 minutes, at 100° C. for 2 hours, and 150° C. for 4 hours, to thereby produce a comparative cured resin product [3B] (5102 content: 19 parts by mass).

(73) <Assessing of Characteristic of Cured Resin Product>

(74) [Transmittance]

(75) Transmittance of each of cured resin products [1A] to [6A] produced in Examples 1 to 6, referential cured resin products [1a] to [3a], and comparative cured resin products [2B] and [3B] was measured at 550 nm by means of a spectrophotometer. Transmittance of the sample of Comparative Example 1 was not measurable.

(76) [Percent Water Absorption]

(77) Percent water absorption of each of cured resin products [1A] to [6A] produced in Examples 1 to 6, referential cured resin products [1a] to [3a], and comparative cured resin products [2B] and [3B] was measured in the following manner. Specifically, a cured resin product sample was allowed to stand in a drier oven at 50° C. for 24 hours, and the mass of the dried sample (mass (A)) was measured. Then, the sample was boiled at 100° C. under reflux for 3 hours, and the mass of the boiled sample (mass (B)) was measured. From masses (A) and (B), percent water absorption was calculated by the following formula [4]. Percent water absorption of the sample of Comparative Example 1 was not measurable.

(78) [F4]
Percent water absorption (mass %)=[(mass B−mass A)/mass A]×100  (4)
[Coefficient of Thermal Linear Expansion (CTE)]

(79) Coefficient of thermal linear expansion of each of cured resin products [3A] to [6A] produced in Examples 3 to 6, referential cured resin products [1a] to [3a], and comparative cured resin products [2B] and [3B] was measured. The measurement was performed according to JIS K-6911. Specifically, a test piece was obtained from each cured product, and the thickness thereof was measured. In the thermal mechanical analysis (TMA), a load of 0.05 N was applied, and temperature was elevated at 1° C./minute. A change in length in a temperature range of 30 to 80° C. is denoted by ΔL1, and the initial length of the test piece is denoted by L. Linear thermal expansion coefficient al was calculated by the following formula [5].

(80) [F5]
Linear thermal expansion coefficient α.sub.1 (ppm/° C.)=(ΔL1/L)×[1/(80-30)]  (5)

(81) Table 3 shows the measurement results of cured resin products [1A] to [6A] produced in Examples 1 to 6, referential cured resin products [1a] to [3a], and comparative cured resin products [2B] and [3B].

(82) As is clear from Table 3, in Examples 1 to 6, a considerable drop in moisture resistance or transparency can be prevented, whereby a cured resin product containing high-purity silica at high concentration can be produced, as compared with Comparative Examples 2 and 3.

(83) As is also clear from Table 3, in Examples 1 to 6, a considerable drop in moisture resistance or transparency can be prevented, whereby a silica-containing resin composition which enables provision of a cured resin product containing high-purity silica at high concentration can be produced, as compared with Comparative Examples 2 and 3.

(84) TABLE-US-00003 TABLE 3 Ref. Comp. Ref. Comp. Ref. Comp. Ex. 1 Ex. 2 Ex. 1 Ex. 1 Ex. 3 Ex. 4 Ex. 2 Ex. 2 Ex. 5 Ex. 6 Ex. 3 Ex. 3 Silica MMA Silica — Comp. MEK MEK — Comp. MEK MEK — Comp. sol [1] powder Ex. MEK sol [2] sol [4] Ex. MEK sol [3] sol [4] Ex. MEK [5] sol [6] sol [6] sol [6] Resin compn. [1A] [2A] [1a] — [3A] [4A] [2a] [2B] [5A] [6A] [3a] [3B] Type of resin PMMA PMMA PMMA alicy- aro- aro- aro- aro- alicy- alicy- alicy- alicy- clic matic matic matic matic clic clic clic clic EP EP EP EP EP EP EP EP EP Cured resin [1A] [2A] [1a] — [3A] [4A] [2a] [2B] [5A] [6A] [3a] [3B] SiO.sub.2 content of 43 29 0 not 30 21 0 21 30 20 0 19 cured resin (resin mea- compn.) surable (parts by mass) Transmittance of 82 84 86 75 59 87 4 76 78 85 19 cured product (%) Percent water 0.67 0.72 0.84 0.64 0.52 0.48 0.71 0.62 0.86 0.98 1.08 absorption of cured product (%) Linear expansion — — — — 59 64 74 65 55 60 71 61 coeff. of cured product (ppm/° C.)