JP2718431B2 - Silica organosol and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a silica organosol and a method for producing the same, and more particularly, to a silica organosol that can be suitably used for producing a transparent protective film having a low refractive index and the like. And its manufacturing method.

Technical Background of the Invention Silica organosol is used as a compounding agent for a transparent protective film formed on the surface of a substrate such as glass or a plastic molded product.

Conventionally, such a silica organosol has been produced by various methods.For example, an alkoxysilane is hydrolyzed and polycondensed in a mixed solvent of water and an organic solvent such as an alcohol to form silica particles, and then the silica particles are produced. It has been produced by replacing a mixed solvent in a silica particle dispersion in which silica particles are dispersed with an organic solvent such as glycol.

Incidentally, JP-A-63-185439 discloses that a hydrolyzable organic metal oxide is hydrolyzed in a mixed solvent of alcohol and water to prepare a dispersion of hydrate fine particles, and then the dispersion is prepared. A method for producing a glycol monodispersion of inorganic oxide fine particles, which comprises subjecting an alcohol containing water to a glycol solvent and then subjecting to heat treatment.

However, in the glycol monodispersion of silica particles produced by such a method, the silica particles contained in the liquid have a high refractive index. When used for
There is a problem that a material having a low refractive index cannot always be obtained.

Object of the Invention The present invention is to solve the problems associated with the prior art as described above, a transparent protective film having a low refractive index,
It is an object of the present invention to provide a silica organosol capable of producing a plastic molded article and the like and a method for producing the same.

SUMMARY OF THE INVENTION The silica organosol according to the present invention is characterized in that silica particles obtained by hydrolysis of an alkoxysilane and having a refractive index of 1.450 or less are dispersed in an organic dispersion medium.

Such a silica organosol has a general formula R _n Si (OR ′) _4-n (wherein R and R ′ may be the same or different and have an alkyl group having 1 to 8 carbon atoms, An aryl group or a vinyl group, and n is an integer of 0 to 3) is hydrolyzed and polycondensed in a mixed solvent of water and an organic solvent to produce silica particles, The silica particle dispersion in which the silica particles are dispersed is subjected to heat treatment, and then at least a part of water in the silica particle dispersion is replaced with an organic solvent.

Hereinafter, the silica organosol according to the present invention and a method for producing the same will be described in detail.

Silica organosol according to the present invention is obtained by hydrolysis of alkoxysilane, the refractive index is 1.450 or less, preferably 1.300 to 1.450, more preferably 1.350 to 1.430.
Is dispersed in an organic dispersion medium.

The refractive index (n ₁ (25 ° C.)) of the silica particles in the silica organosol according to the present invention is defined by a value calculated by the following formula [I].

Where n ₂ : refractive index of organic dispersion medium (25 ° C.), n ₃ : refractive index of water (25 ° C.), n ₄ : refractive index of silica organosol (25 ° C.), C ₁ : weight of silica particles Fraction, C ₂ : weight fraction of organic dispersion medium, C ₃ : weight fraction of water.

Such a refractive index n ₁ is specifically can be calculated as follows.

(A) Using a refractometer, the refractive index n _{4 of the} silica organosol
And the refractive index n ₂ of the organic dispersion medium and the refractive index n _{3 of} water are measured.

(B) the concentration of silica particles in the silica organosol, and the concentration of water is measured, the weight fraction C ₁ of the silica particles, to calculate the weight fraction C ₃ weight fraction C ₂ and water in the organic dispersion medium .

C) the refractive indices n ₂ , n ₃ and
It is calculated by substituting n ₄ and the weight fractions C ₁ , C ₂ and C ₃ into the above formula [I].

The silica particles contained in the silica organosol according to the present invention may have a small average particle size of about 0.01 μm or a large particle size of 10 μm or more. Such silica particles are preferably monodispersed in an organic dispersion medium, have a sharp particle size distribution, and have a CV value defined by the following formula [II] of 0.2 or less.

CV = (D ₂ −D ₁ ) / (2D _p ) [II] In the formula, D ₂ : particle size at a cumulative weight of 84%, D ₁ : particle size at a cumulative weight of 16%, D _p : Average particle size.

Further, in the silica organosol according to the present invention, the silica particles can be present in a stable dispersion state in the silica organosol even if the silica particles are present at a high concentration of about 50% by weight in terms of SiO ₂ .

As the organic dispersion medium of the silica organosol according to the present invention, usually, monohydric or polyhydric alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, hexylene glycol, glycerin, ethylene glycol monomethyl ether, Ethers such as ethylene glycol monoethyl ether are used. Further, an organic solvent other than the above may be used depending on the use of the silica organosol.

Next, the method for producing a silica organosol according to the present invention will be described in detail.

First Step In the method for producing a silica organosol according to the present invention, first, a general formula R _n Si (OR ′) _4-n (where R and R ′ may be the same or different, Represents an alkyl group, an aryl group or a vinyl group having 1 to 8 carbon atoms, and n is 0 to 3
Are hydrolyzed and polycondensed in a mixed solvent of water and an organic solvent to produce silica particles.

As such an alkoxysilane, specifically,
Tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraoctylsilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, methyltriisopropoxysilane, dimethyldimethoxysilane, methyltributoxysilane Octyltriethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane and the like.

In the present invention, these alkoxysilanes may be used alone or in combination of two or more.

As the organic solvent to be mixed with water, alcohols are preferably used, and particularly preferably, lower alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol are used. Also, a mixed solvent of these lower alcohols can be preferably used.

In the present invention, an organic solvent other than alcohol can be mixed with a mixed solvent of water and alcohol. In such a case, an organic solvent having good compatibility with water and alcohol and good compatibility with the above-mentioned alkoxysilane is used.

Examples of such an organic solvent include glycols such as ethylene glycol, ethers such as ethylene glycol monoethyl ether, esters such as ethyl acetate, and ketones such as methyl ethyl ketone.

When the alkoxysilane is hydrolyzed and polycondensed in a mixed solvent of water and an organic solvent, the hydrolysis reaction and the polycondensation reaction of the alkoxysilane can be promoted by coexisting an alkali catalyst in the reaction system. it can.

As such an alkali catalyst, a compound exhibiting alkalinity in an aqueous solution, such as ammonia, an amine, an alkali metal hydroxide, a quaternary ammonium compound, or an amine coupling agent, is used. It is used in such an amount that

In order to produce silica particles by hydrolyzing and polycondensing alkoxysilane in a mixed solvent of water and an organic solvent, specifically, for example, while stirring a water-alcohol mixed solvent, an alkoxysilane is added to the mixed solvent. May be added and the reaction may be performed in the presence or absence of an alkali catalyst such as aqueous ammonia.

At this time, water is used in such an amount as to be 2 to 50 mol, preferably 5 to 25 mol, per 1 mol of the Si-OR group constituting the alkoxysilane.

The hydrolysis and polycondensation reaction of the alkoxysilane is carried out at a temperature not higher than the boiling point of the solvent used, preferably 5 to 5
The reaction is carried out at a temperature lower by about 10 ° C., but when using a heat-resistant and pressure-resistant container such as an autoclave, the temperature can be further increased.

When the alkoxysilane is hydrolyzed under the above conditions, the polycondensation of the alkoxysilane proceeds three-dimensionally to generate and grow silica particles.

Furthermore, metal oxides such as silica are used as seed particles.
The seed particles are previously dispersed in a mixed solvent of water and an organic solvent, and when the hydrolysis and polycondensation reaction of the alkoxysilane is performed in the dispersion, silica grows with the seed particles as nuclei and relatively large particles are formed. Silica particles having a diameter can be produced. Further, such a method for producing silica particles is described in, for example, Japanese Patent Application Laid-Open No. 62-275005 and Japanese Patent Application No. 1-310023 filed by the present applicant prior to the present invention.

By performing the above, a dispersion liquid of silica particles having a silica particle concentration of usually ₂ to 20% by weight in terms of SiO ₂ is obtained.

Second Step Next, the silica particles in which the silica particles thus obtained are dispersed are subjected to a heat treatment to ripen the silica particles in the dispersion. By this aging operation, hydrolysis of the alkoxysilane remaining in the silica particle dispersion with the silica particles as a nucleus and a polycondensation reaction proceed, and simultaneously hydrolysis and polycondensation of the alkoxide residue remaining in the silica particles, almost It grows into spherical silica particles of almost constant size with no remaining alkoxide residues.

This ripening is usually performed at 50 to 200 ° C., preferably at a temperature of the boiling point of the low boiling solvent contained in the dispersion ± 10 ° C.

This step can be performed under any pressure from reduced pressure to increased pressure.

The appropriate heating and holding time of the silica particle dispersion varies greatly depending on the heating temperature, but is usually 0.5 to 2 hours, preferably 1 to 10 hours. Generally, the higher the heating temperature, the shorter the heating holding time.

By performing the aging step of the silica particles as described above in the presence of polyhydric alcohols such as ethylene glycol and propylene glycol, the aging of the silica particles is further promoted. Therefore, when polyhydric alcohols are not used as the organic solvent, the polyhydric alcohols may be added to the reaction system comprising the mixed solvent of alkoxysilane and water and the organic solvent before the aging step of the silica particles. preferable.

Such polyhydric alcohols are preferably present in the reaction system in an amount of 10 mol or less, particularly 1.0 to 10 mol, per 1 mol of the alkoxysilane.

Third Step After aging the silica particles in a mixed solvent of water and an organic solvent in this way, at least part of the water in the silica particle dispersion is replaced with an organic solvent, whereby the silica organo-organic compound according to the present invention is obtained. A sol is obtained.

As the organic solvent to be substituted, an organic solvent as described above depending on the use of the silica organosol is used.

For example, when obtaining a silica organosol containing ethanol as a dispersion medium from a silica particle dispersion containing water-ethanol as a dispersion medium, ethanol is added to the dispersion, followed by heating to distill off water. When replacing this dispersion with ethylene glycol, ethylene glycol is added and heated to distill off water and ethanol.

 Also, replacement by ultrafiltration can be employed.

The concentration of the dispersion medium containing water before solvent replacement remaining in the silica organosol thus produced can take various values depending on the method of the solvent replacement, and the use of the silica organosol, It can be up to about 1% by weight.

Effect of the Invention According to the method for producing a silica organosol according to the present invention, a silica organosol in which silica particles having a lower refractive index are dispersed than conventional silica organosol is produced.

And the silica organosol according to the present invention obtained by such a production method and the like, since the refractive index of the silica particles dispersed in the organic dispersion medium is as low as 1.450 or less, it was produced using this silica organosol. Transparent protective film,
Plastic molded articles have a lower refractive index than conventional ones.

As described above, according to the present invention, a silica organosol in which silica particles having a low refractive index are dispersed can be produced. The reason is presumed as follows.

That is, according to the present invention, since the silica particle dispersion in which the silica particles are dispersed in the mixed solvent of water and the organic solvent is subjected to the heat treatment, the alkoxide residue remaining in the silica particles is hydrolyzed by water. It is considered that a silica organosol in which silica particles having a low refractive index are dispersed is obtained by decomposition and polycondensation.

Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist.

[Example] Example 1 3930 g of ethanol, 710 g of 28% ammonia water and 5 pure water
190 g of the mixed solution was maintained at 35 ° C., and 180 g of tetraethoxysilane was added to the mixed solution while stirring the mixed solution. After the addition, stirring was continued for another 2 hours, and then 500 g of 28% aqueous ammonia was added to the mixed solution to adjust the pH.
By adjusting to 12.5, a silica particle dispersion in which silica particles were dispersed in a water-ethanol mixed solution was obtained.

Next, the obtained silica particle dispersion liquid was placed in a glass container with a reflux condenser, set at a predetermined temperature, and then depressurized until the dispersion medium reached a pressure at which the dispersion medium boiled, and heated and held under the conditions shown in Table 1. To ripen the silica particles.

Thereafter, the silica particle dispersion liquid obtained by aging the silica particles in this manner was solvent-substituted using a rotary evaporator under the same organic solvent and temperature conditions as shown in Table 1 to obtain Example 1.
Was obtained. The amount of the mixed solvent containing water before the solvent replacement remaining in the silica organosol after the solvent replacement was 1% by weight or less.

Example 2 A silica particle dispersion was obtained in the same manner as in Example 1, except that 74 g of methyltriethoxysilane and 90 g of tetraethoxysilane were used instead of 180 g of tetraethoxysilane.

Next, the obtained silica particle dispersion was placed in an autoclave and set at the temperature shown in Table 1, and then the vapor pressure of the solvent at this temperature was kept as it was, and heated and kept under the conditions shown in Table 1.

Thereafter, Example 1 was repeated except for the organic solvent and temperature shown in Table 1.
Water and ethanol in the silica particle dispersion were solvent-substituted in the same manner as in Example 1 to obtain a silica organosol of Example 2. The amount of the mixed solvent containing water before the solvent replacement remaining in the silica organosol after the solvent replacement was 1% by weight or less.

Example 3 A silica particle dispersion was obtained in the same manner as in Example 1, except that 100 g of ethanol was replaced with ethylene glycol.

Next, the obtained silica particle dispersion was placed in an autoclave and set at the temperature shown in Table 1, and then the vapor pressure of the solvent at this temperature was kept as it was, and heated and kept under the conditions shown in Table 1.

Thereafter, Example 1 was repeated except for the organic solvent and temperature shown in Table 1.
Water and ethanol in the silica particle dispersion were solvent-substituted in the same manner as in Example 1 to obtain a silica organosol of Example 3. The amount of the mixed solvent containing water before the solvent replacement remaining in the silica organosol after the solvent replacement was 1% by weight or less.

Example 4 A silica particle dispersion was obtained in the same manner as in Example 1, except that 1500 g of the 3,930 g of ethanol in Example 1 was replaced with polypropylene glycol having a molecular weight of 3,000.

Next, the obtained silica particle dispersion liquid was placed in a glass container with a reflux condenser, set at a predetermined temperature, and then depressurized until the dispersion medium reached a pressure at which the dispersion medium boiled, and heated and maintained under the conditions shown in Table 1. .

Thereafter, Example 1 was repeated except for the organic solvent and temperature shown in Table 1.
The water and ethanol in the silica particle dispersion were solvent-substituted in the same manner as in the above, to obtain a silica organosol of Example 4. The amount of the mixed solvent containing water before the solvent replacement remaining in the silica organosol after the solvent replacement was 1% by weight or less.

Example 5 A silica particle dispersion was obtained in the same manner as in Example 1 except that 100 g of 3930 g of ethanol was changed to methyl cellosolve.

Next, the obtained silica particle dispersion was placed in an autoclave and set at the temperature shown in Table 1, and then the vapor pressure of the solvent at this temperature was kept as it was, and heated and kept under the conditions shown in Table 1.

Thereafter, Example 1 was repeated except for the organic solvent and temperature shown in Table 1.
Water and ethanol in the silica particle dispersion were solvent-substituted in the same manner as in Example 1 to obtain a silica organosol of Example 5. The amount of the mixed solvent containing water before the solvent replacement remaining in the silica organosol after the solvent replacement was 1% by weight or less.

Comparative Examples 1 and 2 Silica organosols of Comparative Examples 1 and 2 were produced in the same manner as in Examples 1 and 2 except that the silica particles were not aged.

The refractive index, average particle diameter, CV value and surface area of each of the silica organosols of Examples 1 to 5 and Comparative Examples 1 and 2 obtained as described above were measured.

 The measuring method of each physical property value is as follows.

A. Refractive index 25 ℃ of each silica organosol by Atsube refractometer
Was measured, and the refractive index of the silica particles was calculated according to the formula [I] (see page 5).

B. Average particle size The average particle size of the silica particles in each silica organosol was measured by a light transmission type particle size measuring device (CAPA-700 manufactured by Horiba, Ltd.).

C.CV value Particle size D ₂ at a total weight of 84%,
And the particle diameter D ₁ at a cumulative weight of 16% is obtained, and the above average particle diameter is obtained.
And a D _p, was calculated CV value of the silica particles according to the above [II] formula (see page 6).

D. Surface area Remove the organic solvent in the silica organosol by drying each silica organosol, then 400
The silica particles obtained by calcining at
The surface area was determined by the T method.

 Table 1 shows the above measurement results.

From the results in Table 1, when the silica organosols of Examples 1 and 2 were compared with the silica organosols of Comparative Examples 1 and 2 in which the silica particles were not aged, the average particle size of the silica particles contained in each of them and the CV Although there is no difference in the value and the surface area, the refractive index of the silica particles contained in the silica organosols of Comparative Examples 1 and 2 exceeds 1.450, whereas the refractive index of the silica particles contained in the silica organosols of Examples 1 and 2 is It can be seen that the refractive index of each of the silica particles is less than 1.450.

Continuing on the front page (72) Inventor Yoshinori Tanaka 13-2 Kitaminato-machi, Wakamatsu-ku, Kitakyushu-shi, Fukuoka Takuya Chemical Industry Co., Ltd.Wakamatsu Plant (72) Inventor Hiroyasu Nishida 13-Kitaminato-cho, Wakamatsu-ku, Fukuoka Prefecture 2 Inside the Wakamatsu Plant of Catalyst & Chemical Co., Ltd. (72) Toshiharu Hirai 13-2 Kitaminato-cho, Wakamatsu-ku, Kitakyushu-shi, Fukuoka Prefecture Inside of the Wakamatsu Plant of Catalyst & Chemical Co., Ltd. (72) Kenji Kitazaki Wakamatsu-ku, Kitakyushu-shi 13-2 Kitaminato Town Inside the Wakamatsu Plant of Catalyst Chemicals Co., Ltd. (72) Inventor Naoyuki Enomoto 13-2 Kitaminato Town of Wakamatsu-ku, Kitakyushu-shi, Fukuoka Prefecture Inside the Wakamatsu Plant of Catalyst Chemicals Co., Ltd. (56) References JP 52 −15078 (JP, A)

Claims (2)

(57) [Claims] 1. A silica organosol comprising silica particles obtained by hydrolysis of an alkoxysilane and having a refractive index of 1.450 or less, dispersed in an organic dispersion medium. 2. A compound of the general formula R _n Si (OR ') _{4-n wherein} R, R'
May be the same or different and have 1 to 8 carbon atoms
Represents an alkyl group, an aryl group or a vinyl group,
Is an integer of 0 to 3) is hydrolyzed and polycondensed in a mixed solvent of water and an organic solvent to form silica particles, and silica obtained is dispersed in silica. Heat treatment of the particle dispersion, then the refractive index characterized by replacing at least part of the water in the silica particle dispersion with an organic solvent is 1.450
A method for producing a silica organosol comprising the following silica particles dispersed in an organic dispersion medium.