JPH021090B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to powdered silica homogeneously dispersible in organic solvents and a method for producing the same. In this specification, "organic solvent" includes both hydrophilic organic solvents and hydrophobic organic solvents, and "uniformly dispersible in organic solvent" refers to organic solvents of 100 c.c.
When 10 g of powdered silica was added and mixed, a transparent to semi-transparent dispersion was formed, and when the dispersion was processed in a centrifuge at 3000 rpm for 5 minutes, the amount of silica precipitated was It means less than 1g. Powdered hydrophobic silica called estersil has been known as a reinforcing agent 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 the silanol groups on the surface of silica particles with a monohydric alcohol, and the following methods have conventionally been adopted for this esterification. One method is to thermally decompose silicon tetrachloride in a hydrogen flame to produce silica (polysilicic acid), and then contact this silica with alcohol vapor to esterify the silanol groups on the silica surface. . The other method is to aggregate colloidal silica particles dispersed in water and esterify the silanol groups on the silica surface by heating the aggregated particles with alcohol. However, it is impossible to homogeneously disperse conventional hydrophobic silica powders in organic solvents; for example, when mixed with toluene,
Silica precipitation occurs in a relatively short period of time. In other words, the conventional hydrophobic silica powder cannot stably maintain the dispersed state of the hydrophobic silica powder, unless the dispersion medium is a relatively high viscosity liquid. On the other hand, as a method for producing organosilica sol, as taught in U.S. Pat. In addition to the method of replacing water with a polar organic solvent by boiling, as taught in Japanese Patent Publication No. 53-799, siloxysilanol is extracted and separated from a neutralized aqueous solution of water glass with a polar organic solvent, and then the remaining A method is known in which an organosilylating agent is added to a liquid and reacted. However, since the organosilica sol obtained by the former method uses a polar organic solvent as its dispersion medium, it has insufficient compatibility with non-polar organic solvents, and has the disadvantage that its uses are limited. Furthermore, the organosol obtained by the latter method has a relatively large amount of residual water and is low in molecular weight silica, so it lacks stability. In addition, in the latter method, siloxysilanol is extracted and separated, so there is a drawback that the utilization rate of silica from the viewpoint of raw material water glass is low. The present invention proposes powdered silica that can be homogeneously dispersed in an organic solvent and a method for producing the same. It is characterized by having 1 to 100 silyl groups chemically bonded to the silica per 10 square millimeters of silica surface. The powdered silica of the present invention has the following physical properties. 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 (using 500 mμ filter) Powder according to the present invention Silica is silylated while the silica particles remain colloidal, so even if the powder itself is agglomerated, it can be easily dispersed uniformly as colloidal silica particles when added to an organic solvent. In general, colloidal particles refer to particles with a diameter of about 1 to 100 millimicrons, but in the present invention, silica particles to which silyl groups are chemically bonded have a particle size in the range of 4 to 100 millimicrons. It is preferably in the range of 5 to 30 millimicrons. According to the present invention, the silica particles are covered with silyl groups having 1 to 36 carbon atoms chemically bonded to the surface, and the number of silyl groups is 10 to 10 on the silica surface.
It is allowed to be 1 to 100 pieces per square millimicron. Here, "the silyl group is chemically bonded to the silica surface" means that the silyl group is directly bonded to the silicon atom of the silanol group (-SiOH) on the silica surface. In powdered silica in which silyl groups are chemically bonded to colloidal silica particles, strictly speaking, the number of silyl groups required to make the powdered silica homogeneously dispersible in an organic solvent is Depends on the chain length of the group. Generally speaking, powdered silica with long-chain silyl groups is more homogeneous in organic solvents than powdered silica with short-chain silyl groups, even if there are fewer chemically bonded silyl groups. It becomes possible to disperse. By the way, in powdered silica in which silyl groups are chemically bonded to colloidal silica particles, the number of silyl groups chemically bonded to make the powdered silica homogeneously dispersible in an organic solvent. The maximum number of possible silyl groups in relation to the number of carbon atoms in the silyl group is as follows.

[Table] Next, the method for producing powdered silica according to the present invention will be explained. Since the powdered silica of the present invention requires that the core silica particles have a colloidal dimension, a silica hydrosol is used as a starting material, and the silica hydrosol has a low SiO ₂ concentration.
The viscosity at 20wt% must be less than 100 centipoise. This type of silica hydrosol can be produced by dealkalizing water glass with a cation exchange resin and polymerizing the resulting silicic acid solution in an alkaline atmosphere (commonly known as the ion exchange method), or by neutralizing water glass with acid. There is a method in which the salt is washed away with water and the resulting gel is peptized in an autoclave (commonly known as the peptization method), and a silicate solution obtained by hydrolyzing ethyl silicate with acid. It can generally be produced by a method such as heating and aging. Incidentally, when powdered silica such as aloesil or white carbon is dispersed in water at a concentration of 20 wt%, it is distinguished from the silica hydrosol of the present invention in that it has an extremely high viscosity of tens of thousands of centipoids. In addition, low-polymerized silicic acid liquids made by neutralizing water glass with acid or dealkalized with cation exchange resins, and silicic acid liquids made by hydrolyzing organosilicon compounds, are also commonly called silica hydrosols. , these also have a high viscosity of tens of thousands of centipoise at a SiO ₂ concentration of 20 wt%.
It is clearly distinguished from the silica hydrosol of the present invention by gelling over time. Although the SiO ₂ concentration of the silica hydrosol as a starting material can be arbitrarily selected, it is generally preferable that the SiO ₂ concentration is 50 wt% or less. According to the invention, a silica hydrosol is first converted into an organosilica sol by solvent displacement. This solvent substitution involves mixing a mutually soluble hydrophilic organic solvent in an arbitrary ratio with the silica hydrosol.
The content is to gradually replace water, which is the dispersion medium of silica hydrosol, with an organic solvent. In this case, the hydrophilic organic solvent may be used in combination with a hydrophobic organic solvent that is mutually soluble therein. Methods for replacing the solvent include, for example, removing water by distillation, using an ultrafiltration membrane to gradually replace the solvent with an organic solvent, using a dehydrating agent such as a molecular sieve, A method of removing only water can be adopted. Incidentally, for solvents with a boiling point lower than water, such as acetone, it is advantageous to use ultrafiltration or molecular sieves. If you want to replace the solvent with alcohols with larger molecular weights such as n-butyl alcohol and n-octyl alcohol, ketones such as methyl ethyl ketone, or esters such as isobutyl acetate, these alcohols have poor compatibility with the raw material silica hydrosol. Therefore, it is preferable to replace the water with methyl alcohol or the like beforehand, and then perform the solvent replacement again. Ethers such as ethyl glycol, polyhydric alcohols such as ethylene glycol,
Alkylamides such as N,N-dimethylformamide (DMF) can be replaced with water by direct distillation. However, alcohols having 3 or less carbon atoms are undesirable because they tend to react directly with the silylating agent used in the subsequent step. In this manner, the solvent-substituted organosilica sol contains some water, although it differs depending on the method of solvent substitution. However, in the present invention, the amount of water remaining in the organosilica sol is
It should be less than 10wt%, preferably less than 5wt%. If more than 10 wt% of water is present, the rate of hydrolysis of the silylating agent in the next step will be rapid, the reaction between the silylating agents will be accelerated, and a selective reaction to the colloid surface can hardly be expected. However, if special measures are taken, such as using a very low concentration of silica sol and adding a silylating agent at a low concentration over a long period of time, a reaction on the colloid surface can be expected to some extent, but this is not practical. When the water content is less than 5 wt%, even if the silylating agent is mixed all at once with high-concentration silica, a selective reaction will occur on the colloid particle surface, and the desired product will be obtained. The organosilica sol obtained by solvent substitution is then subjected to silylation treatment, and the silica surface is modified to be lipophilic while maintaining its colloidal state through a chemical reaction between the surface silanol and the silylation agent. The silylating agents used in the present invention include methyltrichlorosilane, dimethyldichlorosilane,
Trimethylchlorosilane, ethyltrichlorosilane, diethyldichlorosilane, triethylchlorosilane, vinyltrichlorosilane, stearyltrichlorosilane, dihexyldichlorosilane,
Chlorosilanes such as diphenyldichlorosilane, triphenylchlorosilane, and n-amyltrichlorosilane; alkoxy compounds such as methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, n-amyltriethoxysilane, and benzyltrimethoxysilane; Any of silanes, silazane such as hexamethyldisilazane, and hydroxysilanes obtained by hydrolyzing these can be used. When using chlorosilanes, hydrogen chloride (hydrochloric acid) is produced as a by-product, and when using alkoxysilanes, alcohol is produced as a by-product, but in both cases, they are removed along with the solvent during the desolvation operation after the reaction. So there is no problem. In the case of hydroxysilane, it is unstable and easily polymerizes, so in practice, chlorosilane is hydrolyzed while cooling immediately before use.
It is effective to immediately use the hydroxysilane in the oil layer in the present invention. In the present invention, the maximum number of silyl groups that react on the silica surface depends on the number of carbon atoms in the silyl group, and decreases as the number of carbon atoms in the silyl group increases, as shown in Table 1 above. Therefore, in silylation treatment, calculate the required amount of silylating agent and maximum amount of silylating agent according to the number of carbon atoms in the silyl group from the specific surface area of silica and Table 1 above, and calculate the required amount. and the maximum amount of silylating agent must be used. Below this range, during the next step of powdering, unreacted surface silanol groups cause reactions between adjacent colloid particles, resulting in a powder with poor redispersibility. Further, if the amount exceeds the above range, non-volatile components will be generated due to the reaction of the excess silylating agent with each other, making it difficult to powderize. For silylation, it is sufficient to simply mix the silylating agent and organosilica sol, but in order to complete the reaction, it is preferable to heat the mixed solution. Particularly when the silylating agent has a large number of carbon atoms, it is important to complete the reaction by heating. The reaction mixture after the silylation reaction is in a state in which silylated colloidal silica particles are dispersed in an organic medium containing hydrochloric acid, alcohol, and water, which are by-produced during silylation. Therefore, the powdered silica of the present invention can be obtained by distilling off the liquid phase component from this reaction mixture. Preferably, the powdering step is carried out subsequent to the silylation step. When powdering, liquid phase distillation is preferably carried out at a temperature of 200°C or lower; at a temperature of 200°C or higher, the organic components of the silyl group may burn and a well-dispersed powder may not be obtained. Powdering at 150° C. or below and under reduced pressure if necessary is most preferred. The powdered silica obtained in this way is usually white in color and contains alcohol,
Homogeneously disperses in most organic solvents such as ketones, ethers, aromatic hydrocarbons, and aliphatic hydrocarbons. Comparative Example 1 In a three-necked flask equipped with a dropping port and a distillation port, an average particle size of 12 mμ (specific surface area of 230 m ² /SiO ₂
g) Pour 150 ml of silica hydrosol with a SiO ₂ concentration of 20%, and add the same amount of i-propyl alcohol. Then, while distilling under reduced pressure, i-
Propyl alcohol was gradually added, and water and alcohol were distilled out from the distillation port. This operation
The process was continued until an i-propyl alcohol sol with a SiO ₂ concentration of 20% and a water content of 2.0% was obtained. Next, the above i-propyl alcohol sol was added with n-
200 ml of butyl alcohol was added, and i-propyl alcohol, water, and n-butyl alcohol were distilled off under reduced pressure to obtain 150 ml of organosilica sol using n-butyl alcohol as a dispersion medium. This sol had a SiO ₂ concentration of 21.4%, a water content of 1.5%, and a viscosity of 7 centipoise. Add trimethylchlorosilane to 100g of this organosilica sol using n-butyl alcohol as a dispersion medium.
After adding 0.05 g (0.02×10 ⁻³ mol/SiO ₂ g) and stirring at 50° C. for 10 minutes, the solvent and by-products were evaporated under reduced pressure to obtain powdered silica. Comparative Example 2 An organosilica sol using n-butyl alcohol as a dispersion medium was obtained in the same manner as in Comparative Example 1. However, the amount of n-butyl alcohol when replacing the solvent should be 70ml.
limited to. The resulting sol using n-butyl alcohol as a dispersion medium had a SiO ₂ concentration of 20.3%, a water content of 20.3%, and a viscosity of 5 centipoise. A sol using this n-butyl alcohol as a dispersion medium
2.8g of trimethylchlorosilane (1.3×10 ^-3 per 100g)
mol/g of SiO ₂ ) and heated to 50 °C for 10
After stirring for a minute, the solvent and by-products were evaporated under reduced pressure to obtain powdered silica. Example 1 Into a three-necked flask equipped with a dropping port and a distillation port, particles with an average particle diameter of 12 mμ (specific surface area of 230 m ² /SiO ₂
g) Add 150 ml of silica hydrosol with a SiO ₂ concentration of 20%, and add the same amount of i-propyl alcohol. Next, i-propyl alcohol was gradually added through the dropping port while distilling under reduced pressure, and water and alcohol were distilled out from the distillation port. This operation was continued until an i-propyl alcohol sol with a SiO ₂ concentration of 20.5% and a water content of 3.0% was obtained. Next, 200 ml of n-butyl alcohol was added to the above i-propyl alcohol sol, and the i-propyl alcohol, water, and n-butyl alcohol were distilled off under reduced pressure to form an organosilica sol using 150 ml of n-butyl alcohol as a dispersion medium. Obtained. of this sol
The SiO ₂ concentration was 20.1%, the moisture was 2.0%, and the viscosity was 6 centipoise. Add trimethylchlorosilane to 100g of this organosilica sol using n-butyl alcohol as a dispersion medium.
After adding 2.8 g (1.3×10 ⁻³ mol/SiO ₂ g) and stirring at 50° C. for 10 minutes, the solvent and by-products were evaporated under reduced pressure to obtain powdered silica. Examples 2 to 7 Except that trimethylchlorosilane as the silylating agent was replaced with that shown in Table 2, and the amount of the silylating agent added and the heating temperature during the silylation treatment were changed as shown in Table 2. Various powdered silicas were obtained in exactly the same manner as in Example 1.

[Table] Orchid

Claims (1)

[Claims] 1 Consisting of colloidal silica particles covered with silyl groups having 1 to 36 carbon atoms, with 1 to 100 silyl groups chemically bonded to the silica per 10 square millimeters of the silica surface. Powdered silica that can be homogeneously dispersed in organic solvents. 2. Claim 1, wherein the colloidal silica particles are silica particles with a particle size of 5 to 30 millimicrons.
Powdered silica as described in section. 3 A silica hydrosol with a viscosity of 100 centipoise or less measured at a SiO ₂ concentration of 20 wt% is replaced with a solvent to prepare an organosilica sol with a water content of 10 wt% or less.
A method for producing powdered silica homogeneously dispersible in an organic solvent, which comprises silylating the silica surface by reacting it with an organosilylating agent, and then removing a liquid phase component from the resulting reaction mixture. 4. The method according to claim 3, wherein the water content in the organosilica sol is 5 wt% or less.