JP808H - Powdery silica that can be homogeneously dispersed in organic solvent and its production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a powdery silica that can be homogeneously dispersed in an organic solvent, and a method for producing the same. In the present specification, "organic solvent" includes both a hydrophilic organic solvent and a hydrophobic organic solvent, and "is homogeneously dispersible in an organic solvent" means that 10 g of powdered silica is added to 100 cc of toluene. When mixed, a transparent to translucent dispersion is formed and the dispersion is centrifuged at 3000 r.
When treated with pm for 5 minutes, the amount of precipitated silica is 1 g or less. BACKGROUND ART Powdered hydrophobic silica called ester sils has been conventionally known as an enhancer for elastomers, plastics, waxes, etc., or as a thickening agent or viscosity modifier for liquid resins, paints, etc. This hydrophobic silica powder is obtained by esterifying silanol groups on the surface of silica particles with a monohydric alcohol, and the following means have been conventionally adopted for this esterification. One of them is silica (polysilicic acid) which is obtained by thermally decomposing silicon tetrachloride in a hydrogen flame.
Is produced, and the silica is then brought into contact with alcohol vapor to esterify silanol groups on the silica surface. The other is a method in which colloidal silica particles dispersed in water are aggregated, and the silanol groups on the silica surface are esterified by a treatment such as heating the aggregated particles with alcohol. However, none of the conventional hydrophobic silica powders can be homogeneously dispersed in an organic solvent, and when added to and mixed with toluene, silica precipitation occurs in a relatively short time. That is, the conventional hydrophobic silica powder is not always stable when the dispersion medium is a liquid having a relatively high viscosity, and otherwise the stable dispersion state of the hydrophobic silica powder cannot be maintained. On the other hand, as a method for producing an organosilica sol, as taught in US Pat. Nos. 2,285,446 to 2,285,449, silica hydrosol is mixed with a polar organic solvent which forms an azeotropic mixture with water, and the mixture is distilled to obtain In addition to the known method of replacing water with a polar organic solvent by boiling,
As taught in Japanese Examined Patent Publication No. 53-799, there is known a method in which siloxysilanol is extracted and separated from a neutralized aqueous solution of water glass with a polar organic solvent, and then an organosilylating agent is added to the residual liquid for reaction. There is. However, since the dispersion medium of the organosilica sol obtained by the former method is a polar organic solvent, its compatibility with a nonpolar organic solvent is insufficient and its use is limited. Further, the organosol obtained by the latter method has a relatively large amount of residual water content and is low-molecular-weight silica, so that it lacks stability. In addition, in the latter method, since siloxysilanol is extracted and separated, there is a drawback that the utilization rate of silica as viewed from the raw water glass is low. The present invention proposes a powdery silica that can be uniformly dispersed in an organic solvent and a method for producing the same, and the powdery silica of the present invention is a colloidal silica particle covered with a silyl group having 1 to 36 carbon atoms. And is characterized by having 1 to 100 silyl groups chemically bonded to silica per 10 square millimeters of silica surface. The powdery silica of the present invention has the following physical characteristics. Bulk density 0.6 to 1.0 g / ml Oil absorption 50 g / 100 ml or less Powder particle size (90%) 0.01 to 3.0 mm Toluene dispersion (concentration 10 wt%) Viscosity 10 cps or less Transparency 80% or more (use 500 mμ filter) ) In the powder silica according to the present invention, since the silica particles are silylated in the colloidal dimension as they are, even if the powder itself is agglomerated, it can be easily dispersed uniformly as colloidal silica particles by adding it to the organic solvent. . Generally, particles of colloidal dimension refer to particles having a diameter of about 1 to 100 millimicrons. In the present invention, silica particles to which a silyl group is chemically bound have a particle size of 4 to 10.
It may be in the range of 0 millimicron, and preferably in the range of 5 to 30 millimicron. According to the present invention, the silica particles have 1 to 1 carbon atoms chemically bonded to their surface.
It is covered with 36 silyl groups, and the number of silyl groups can be 1 to 100 per 10 square millimeters of silica surface. Here, “the silyl group is chemically bonded to the surface of silica” means that the silyl group is bonded to the silicon atom of the silanol group (—SiOH) on the surface of the silica via the oxygen atom. . In the powdery silica in which a silyl group is chemically bonded to colloidal silica particles, the number of silyl groups required to uniformly disperse the powdery silica in an organic solvent is
Strictly speaking, it depends on the chain length of the silyl group. Generally speaking, powdered silica having a long chain silyl group is more homogeneously dispersed in an organic solvent than powdered silica having a short chain silyl group, even if it has less chemically bonded silyl groups. It will be possible. By the way, in the case of powdered silica in which a silyl group is chemically bonded to colloidal silica particles, the number of silyl groups and the chemical bond required to make the powdered silica homogeneously dispersible in an organic solvent. The maximum number of possible silyl groups is shown below in relation to the carbon number of the silyl group. Next, the method for producing powdered silica according to the present invention will be described. In the powdery silica of the present invention, the silica particles as the core must be in the colloidal dimension, and thus silica hydrosol is used as a starting material. The silica hydrosol has a viscosity of 100 centipoise at a SiO ₂ concentration of 20 wt%. Must be: This type of silica hydrosol is a method in which water glass is dealkalized with a cation exchange resin and the resulting silicic acid solution is polymerized in an alkaline atmosphere (commonly called an ion exchange method). After gelling by gelling, wash the salt with water to deflocculate the gel obtained by autoclave (commonly called deflocculation method), and further remove silicic acid solution obtained by hydrolyzing ethyl silicate with acid. It can be generally produced by a method such as heat aging. By the way, it is distinguished from the silica hydrosol of the present invention in that when powdered silica such as Aerosil and white carbon is dispersed in water at a concentration of 20 wt%, the viscosity is extremely high at tens of thousands centipoise. In addition, a low-polymerization silicic acid solution obtained by neutralizing water glass with an acid or dealkalization with a cation exchange resin or a silicic acid solution obtained by simply hydrolyzing an organosilicon compound is commonly called a silica hydrosol. , These are also SiO ₂
The viscosity at a concentration of 20 wt% is as high as tens of thousands of centipoise, and gels over time, so that it is clearly distinguished from the silica hydrosol of the present invention. Although SiO ₂ concentration of the starting material serving silica hydrosol can be arbitrarily selected, typically 50 wt% of SiO ₂ concentration
The following is preferable. According to the invention, the silica hydrosol is first converted into an organosilica sol by solvent substitution. This solvent replacement involves mixing a hydrophilic organic solvent that is mutually soluble in silica hydrosol at an arbitrary ratio, and gradually replacing water, which is a dispersion medium of silica hydrosol, with the organic solvent. In this case, the hydrophilic organic solvent may be used in combination with a hydrophobic organic solvent which is mutually soluble. As a method for replacing the solvent, for example, a method of distilling off water by distillation, a method of gradually replacing the solvent from water to an organic solvent using an ultrafiltration membrane, and a dehydrating agent such as molecular sieves to remove only water Can be adopted. By the way, for a solvent having a boiling point lower than that of water such as acetone, it is advantageous to use ultrafiltration or molecular sieve. n-
Alcohols having a higher molecular weight such as butyl alcohol and n-octyl alcohol, ketones such as methyl ethyl ketone, and solvent substitution with esters such as isobutyl acetate are inferior in compatibility with the raw material silica hydrosol, It is preferable to carry out the solvent replacement of water with methyl alcohol or the like in advance, and then carry out the solvent replacement again. Ethers such as ethyl glycol, polyhydric alcohols such as ethylene glycol, and alkyl amides such as N, N-dimethylformamide (DMF) can be replaced with water by a direct distillation method. However, alcohols having 3 or less carbon atoms are not desirable because they easily react directly with the silylating agent used in the subsequent step. In this way, the solvent-substituted organosilica sol contains some water although there is a difference depending on the method of solvent substitution. However, in the present invention, the amount of water remaining in the organosilica sol is 10 wt% or less, preferably 5 wt%.
Must be less than or equal to%. The presence of water in excess of 10 wt% accelerates the hydrolysis rate of the silylating agent in the next step, promotes the reaction between the silylating agents, and the selective reaction on the surface of the colloid can hardly be expected. However, if the silica sol is made to have a very low concentration and the silylating agent is added at a low concentration over a long period of time, it is possible to expect a reaction to the colloid surface to some extent, but this is not practical. When the water content is 5 wt% or less, even if the silylating agent is mixed with high-concentration silica all at once, a selective reaction occurs on the surface of the colloidal particles and the intended product can be obtained. The organosilica sol obtained by the solvent substitution is then subjected to a silylation treatment, and the silica surface is modified to be lipophilic while maintaining the colloidal state by the chemical reaction between the surface silanol and the silylating agent. As the silylating agent used in the present invention, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, ethyltrichlorosilane, diethyldichlorosilane, triethylchlorosilane, vinyltrichlorosilane, stearyltrichlorosilane, dihexyldichlorosilane, Chlorosilanes such as diphenyldichlorosilane, triphenylchlorosilane, n-amyltrichlorosilane, etc., alkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, n-amyltriethoxysilane and benzyltrimethoxysilane. It is possible to use any of these, silazanes such as hexamethyldisilazane, and hydroxysilanes obtained by hydrolyzing these. When chlorosilanes are used, hydrogen chloride (hydrochloric acid) is by-produced by the reaction, and when alkoxysilanes are used, alcohol is by-produced, but in both cases, it is removed together with the solvent during the desolvation operation after the reaction. There is no.
In the case of hydroxysilane, it is unstable and easily polymerized,
Practically, it is effective that the chlorosilane is hydrolyzed while being cooled immediately before use and the hydroxysilane in the oil layer is quickly used in the present invention. In the present invention, the maximum number of silyl groups that react with the silica surface depends on the carbon number of the silyl group, and as shown in Table 1 above, it decreases as the carbon number of the silyl group increases.
Therefore, in the silylation treatment, the required amount of silylating agent and the maximum amount of silylating agent are calculated from the specific surface area of silica and Table 1 described above according to the number of carbon atoms of the silyl group, and the required amount is calculated. An amount of silylating agent that falls within the maximum amount must be used. Below this range, when powdering in the next step,
Reaction between adjacent colloidal particles occurs due to unreacted surface silanol groups, and only powder having poor redispersibility is obtained. On the other hand, if the amount exceeds the above range, a non-volatile component is produced by the reaction between the surplus silylating agents, which makes powdering difficult. For the silylation, it is sufficient to mix the silylating agent and the organosilica sol, but it is preferable to heat the mixed solution in order to complete the reaction. Especially when the number of carbon atoms in the silylating agent is large, it is important to complete the reaction by heating. The reaction mixture after completion of the silylation reaction is in a state where the silylated colloidal silica particles are dispersed in an organic medium containing hydrochloric acid, alcohol and water which are by-produced during the silylation. Therefore, the powdery silica of the present invention can be obtained by distilling the liquid phase component from this reaction mixture. The powdering step is preferably performed subsequent to the silylation step. At the time of pulverization, liquid phase distillation at 200 ° C. or lower is preferable, and at 200 ° C. or higher, the organic component of the silyl group may be burned, and a powder having good dispersion may not be obtained. 150
The most preferable is pulverization under reduced pressure at a temperature of not higher than 0 ° C.
The powdery silica thus obtained usually has a white color, and includes alcohols, ketones, ethers, aromatic hydrocarbons,
Disperses homogeneously in most organic solvents such as aliphatic hydrocarbons. Comparative Example 1 An average particle diameter of 12 mμ (specific surface area 230 m ² / SiO ₂ g) was added to a three-necked flask equipped with a dropping port and a distillation port.
150 ml of silica hydrosol having a SiO ₂ concentration of 20% is added, and the same amount of i-propyl alcohol is further added. Then, while distilling under reduced pressure, i-propyl alcohol was gradually added from the dropping port, and water and alcohol were distilled from the distillation outlet. This operation is performed with a SiO ₂ concentration of 20% and a water content of 2.0.
Continued until a% i-propyl alcohol sol was obtained. Next, 200 ml of n-butyl alcohol was added to the above i-propyl alcohol sol, and i-propyl alcohol was added under reduced pressure.
Water and n-butyl alcohol were distilled off to obtain an organosilica sol having 150 ml of n-butyl alcohol as a dispersion medium. The sol had a SiO ₂ concentration of 21.4% and a water content of 1.5.
%, The viscosity was 7 centipoise. 0.05 g of trimethylchlorosilane was added to 100 g of organosilica sol containing n-butyl alcohol as a dispersion medium.
(0.02 × 10 ⁻³ mol / SiO ₂ g) was added, the mixture was heated and stirred at 50 ° C. for 10 minutes, and then the solvent and byproducts were evaporated under reduced pressure to obtain powdery silica. Comparative Example 2 By the same method as in Comparative Example 1, an organosilica sol containing n-butyl alcohol as a dispersion medium was obtained. However, when replacing the solvent
The amount of n-butyl alcohol was limited to 70 ml. The obtained sol using n-butyl alcohol as a dispersion medium is Si
The O ₂ concentration was 20.3%, the water content was 20.3%, and the viscosity was 5 centipoise. To 100 g of the sol having n-butyl alcohol as a dispersion medium, 2.8 g (1.3 × 10 ⁻³ mol / SiO ₂ g) of trimethylchlorosilane was added, and the mixture was stirred at 50 ° C. for 10 minutes by heating and then under reduced pressure. The solvent and by-products were evaporated with to obtain powdery silica. Example 1 An average particle diameter of 12 mμ (specific surface area 230 m ² / SiO ₂ g),
150 ml of silica hydrosol having a SiO ₂ concentration of 20% is added, and the same amount of i-propyl alcohol is added. Then, while distilling under reduced pressure, i-propyl alcohol was gradually added from the dropping port, and water and alcohol were distilled from the distillation outlet. This operation is performed with a SiO ₂ concentration of 20.5.
%, Water content 3.0% until i-propyl alcohol sol was obtained. Next, 200 ml of n-butyl alcohol was added to the above i-propyl alcohol sol, and i-propyl alcohol was added under reduced pressure.
Water and n-butyl alcohol were distilled off to obtain an organosilica sol having 150 ml of n-butyl alcohol as a dispersion medium. The sol had a SiO ₂ concentration of 20.1% and a water content of 2.0.
%, The viscosity was 6 centipoise. To 100 g of this organo-silica sol having n-butyl alcohol as a dispersion medium, 2.8 g of trimethylchlorosilane (1.
3 × 10 ⁻³ mol / SiO ₂ g) was added and heated to 5
After stirring at 0 ° C. for 10 minutes, the solvent and by-products were evaporated under reduced pressure to give powdery silica. Examples 2 to 7 Except that trimethylchlorosilane as the silylating agent was replaced with that shown in Table 2 and the addition amount of the silylating agent and the heating temperature during the silylation treatment were changed as shown in Table 2. Various powdery silicas were obtained in exactly the same manner as in Example 1. Example 8 A powdery silica was obtained under the same conditions as in Example 1, except that the amount of n-butyl alcohol added was reduced to 143 ml when the solvent was replaced with i-propyl alcohol. The n-butyl alcohol sol before adding the silylating agent is S
The iO ₂ concentration was 20.2%, the water content was 4.3%, and the viscosity was 5 centipoise. Example 9 50 g of water cooled to 15 ° C. in 7 g of trimethylchlorosilane
After mixing g and stirring well, it stood and the layers were separated. After removing the lower aqueous layer, 50 g of cold water was mixed again and well stirred, and then the mixture was allowed to stand and the layers were separated. After repeating this operation 5 times in total, 5.7 g of a hydrolyzate of trimethylchlorosilane (trimethylhydroxysilane) was obtained. 100 g of n-butyl alcohol sol (SiO ₂ concentration 30.1%, water content 0.47%) obtained in the same manner as in Example 1.
The above hydrolyzate of trimethylchlorosilane was mixed with the above, heated at 80 ° C. for 10 minutes with stirring, and then the solvent and by-products were evaporated under reduced pressure to obtain powdery silica. Example 10 In the same manner as in Example 1, 100 g of organosilica sol having n-butyl alcohol as a dispersion medium was obtained. S of this sol
The iO ₂ concentration is 20.2%, the water content is 2.0%, and the viscosity is 6.
It was 1 centipoise. 4.0 g (1.0 × 10 ⁻³ mol / SiO ₂₎ of n-propyltriethoxysilane was added to this sol.
g) was mixed and heated with stirring at 80 ° C. for 30 minutes, and then the solvent and by-products were evaporated under reduced pressure to obtain powdery silica. Example 11 An average particle diameter of 12 mμ (specific surface area 230 m ² / SiO ₂ g) was added to a one-necked three-necked flask equipped with a dropping port and a distillation port.
150 ml of silica hydrosol having a SiO ₂ concentration of 20% was added, 150 ml of ethylene glycol monoethyl ether (cellosolve) was added thereto, and water and a part of ethylene glycol monoethyl ether were distilled off under reduced pressure distillation.
160 ml of organosilica sol having ethylene glycol monoethyl ether as a dispersion medium was obtained. SiO of this sol
_{The 2} concentration was 20.1%, the water content was 2.1%, and the viscosity was 24 centipoise. To 100 g of this organosilica sol, 2.8 g of trimethylchlorosilane (1.3 × 10 ⁻³ mol / S
iO ₂ g) was added, and the mixture was heated under stirring at 50 ° C. for 10 minutes, and then the solvent and by-products were evaporated under reduced pressure to obtain powdery silica. The properties of each powder obtained in Comparative Examples 1 and 2 and Examples 1 to 11 and the dispersibility in various organic solvents are summarized in Table 3. In Table 3, "precipitation amount" means the amount of precipitation when a dispersion obtained by dispersing 10 g of powder in 100 cc of toluene was centrifuged at 3000 rpm. "Dispersibility" is powder 1
The dispersibility when 0 g was mixed with 100 cc of various organic solvents was evaluated according to the following criteria. Good (precipitation amount less than 1.0g) (precipitation amount 1.0g or more) x precipitation, separation

Claims (1)

1. A powdery silica particle comprising colloidal silica particles covered with a silyl group having 1 to 36 carbon atoms, wherein the surface of silica is 10 square millimeters. Each 1 to 100 silyl groups are chemically bonded to silica, and when 10 g of the above powdery silica particles are added to 100 cc of toluene and mixed, a transparent or translucent dispersion liquid is obtained, and this dispersion liquid is put into a centrifuge. When the silica particles are treated at 3000 rpm for 5 minutes, the precipitation amount of the silica particles is 1 g or less, and the silica particles can be uniformly dispersed in an organic solvent. 2. A colloidal silica particle having a particle size of 5 to 30.
The powdered silica of claim 1 which is a millimicron silica particle. 3. An organosilica sol having a water content of 10% by weight or less is prepared by solvent substitution of silica hydrosol having a viscosity of 100 centipoise or less measured at a SiO ₂ concentration of 20% by weight. A method for producing powdery silica which can be homogeneously dispersed in an organic solvent, which comprises reacting with an organosilylating agent of No. 36 to silylate the surface of silica, and then removing liquid phase components from the obtained reaction mixture. 4. The amount of water in the organosilica sol is 5% by weight.
A method according to claim 3 wherein: