JP5267758B2 - Method for producing hydrophobic silica powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently producing a hydrophobic silica powder excellently redispersible into an organic solvent. <P>SOLUTION: The method for producing the hydrophobic silica powder comprises the hydrophobization step of obtaining a hydrophobized colloidal silica slurry dispersion by adding 0.1 to 20 mmol, per 100 m<SP>2</SP>of the surface area of hydrophilic colloidal silica, disilazane compound represented by formula (1) (R<SP>1</SP><SB>3</SB>Si)<SB>2</SB>NH (wherein R<SP>1</SP>s are each independently selected from among 1-6C alkyl groups and a phenyl group) to a mixed solvent silica sol of a silica concentration of 5 to 50 mass% obtained by mixing a water-based silica sol containing hydrophilic colloidal silica of a specific surface area of 5.5 to 550 m<SP>2</SP>/g with a hydrophilic organic solvent in a mass ratio of 0.12 to 2.5 to the water in the water-based silica sol and aging the resultant mixture by heating to 50 to 100&deg;C. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a hydrophobic silica powder excellent in redispersibility in an organic solvent using an aqueous silica sol as a raw material.

  Conventionally, fine silica (generally referred to as fumed silica) produced by flame pyrolysis of chlorosilane has been frequently used as a silica base used for producing hydrophobic silica powder. As a hydrophobizing treatment method, a hydrophobizing treatment is performed by bringing silica powder into contact with a hydrophobizing agent such as a surfactant, silicone oil, or a gas of a silylating agent such as alkylhalogenosilane, alkylalkoxysilane, or alkyldisilazane. And a hydrophobizing treatment by contacting with a silylating agent in a hydrophilic organic solvent containing water.

  However, in any of the hydrophobization treatment methods, when the precipitated silica or fumed silica is used, the silica base itself is agglomerated, so that a hydrophobic silica powder having excellent dispersibility could not be obtained. .

  Actually, the following hydrophobizing method using precipitated silica and fumed silica is disclosed. None of the methods described the relationship between the primary particle size of the silica raw material and the aggregated particle size after the hydrophobization treatment, and a highly dispersible hydrophobic silica powder has not been obtained.

  An aqueous suspension of hydrophilic precipitated silica is mixed with a catalytic amount of acid and organsilane compound in the presence of a sufficient amount of a water-miscible organic solvent to promote the reaction between the organosilicon compound and the hydrophilic precipitated silica. A method of producing hydrophobic precipitated silica by contact (see Patent Document 1).

Silicon oxide particles having an average primary particle diameter of 5 to 50 nm, surface-treated with hexamethyldisilazane to block 40% or more of silanol groups on the particle surface, and a residual silanol group concentration of 1.5 / nm ² or less (See Patent Document 2).

Hydrophobic silica is hydrophobized with an organosilicon compound such as hexamethyldisilazane and has a bulk density of 80 to 300 g / l, OH groups per unit surface area of 0.5 / nm ² or less, and a particle diameter of 45 μm or more Hydrophobic fumed silica, characterized in that the agglomerated particles are 2000 ppm or less, and a method for producing the same (see Patent Document 3).

  A process for producing hydrophobic silica powder, characterized in that fumed silica is treated with polysiloxane and then treated with a trimethylsilylating agent. (See Patent Document 4).

  Highly-dispersed hydrophobic silica powder characterized by performing primary surface treatment with a silicone oil-based treatment agent, pulverization after the primary surface treatment, and secondary surface treatment with an alkylsilazane-based treatment agent after pulverization (See Patent Document 5).

  On the other hand, a method of hydrophobizing a silica sol with a highly dispersible silica sol as a starting material is also known. Silica sol using a hydrophilic organic solvent such as alcohol or a mixed solvent of water and hydrophilic organic solvent as a dispersion medium is reacted with a silylating agent such as alkylhalogenosilane, alkylalkoxysilane, or alkyldisiloxane, and then the solvent is removed. Thus, a hydrophobic silica powder is obtained. These methods have drawbacks such as a complicated manufacturing process of the organic solvent-dispersed silica sol and the need for solvent replacement and distillation. Furthermore, hydrophobization with alkylhalogenosilanes has the disadvantage that corrosive acids are by-produced. Of the alkylalkoxysilanes, monoalkoxysilanes are slightly less reactive, dialkoxysilanes and trialkoxysilanes tend to undergo condensation reactions, and the condensation reactions may cause cross-linking between particles, resulting in good dispersibility. It is difficult to obtain hydrophobic silica powder. In addition, it is difficult to remove the alkoxysilane self-condensate. In addition, since alkyldisiloxane needs to be reacted with a large amount of mineral acid as a catalyst, there are disadvantages that cause corrosion problems and the process of removing the catalyst acid from the hydrophobized silica is complicated. . Examples of the disclosed technology will be given below.

A silylating agent is added to and reacted with an organosilica sol having a water content of 10% by mass or less, and then the solvent is distilled off so that a silyl group having 1 to 36 carbon atoms is 1 to 100/10 nm on the surface of colloidal silica particles. It is described that a silica powder that is ^two- bonded and can be uniformly dispersed in an organic solvent is obtained (see Patent Document 6).

  Hydrophilic colloidal silica with an average particle diameter larger than 4 nm is added to a mixed solvent of concentrated hydrochloric acid, isopropanol, and hexamethyldisiloxane for hydrophobic treatment, and then the hydrophobic colloidal silica is extracted with a hydrophobic organic solvent and heated to reflux. Thereafter, a silane compound is added, and the mixture is heated to reflux to perform a hydrophobic treatment (see Patent Document 7).

  By hydrolyzing the tetraalkoxysilane compound together with a basic substance, an aqueous dispersion of hydrophilic silica fine particles is prepared and alcohol is removed. Next, the silica fine particles are hydrophobized with an alkyltrialkoxysilane compound, the solvent is replaced with a ketone solvent, the reactive groups remaining on the surface of the silica fine particles are triorganosilylated with a silazane compound or a trialkylalkoxysilane compound, and finally the solvent is removed. Distilled under reduced pressure to obtain surface-treated silica (see Patent Document 8).

After adding 5 mol% or more of a trimethylsilylating agent to methanol-dispersed silica obtained by hydrolyzing alkyl silicate in methanol and reacting with 1 mol of silica contained, the excess trimethylsilylating agent and dispersion solvent It is described that a silica powder excellent in dispersibility can be obtained by distilling off the water. For example, 20 mol% of methoxytrimethylsilane is added to 1 mol of silica contained in methanol-dispersed silica obtained by hydrolyzing tetramethoxysilane in methanol in the presence of aqueous ammonia, and excess silylating agent is added. After the recovery, it is dried to obtain a hydrophobized silica powder (see Patent Document 9).
JP 2000-327321 A Japanese Patent Application Laid-Open No. 07-286095 JP 2000-256008 A JP 2002-256170 A JP 2004-168559 A JP 58-145614 A JP 2000-080201 A JP 2000-042426 A Japanese Patent Laid-Open No. 03-187913

  The present invention provides a method for efficiently producing a hydrophobic silica powder excellent in redispersibility in an organic solvent.

In the method for producing the hydrophobic silica powder of the present invention, a hydrophilic organic solvent is contained in an aqueous silica sol containing hydrophilic colloidal silica having a specific surface area of 5.5 to 550 m ² / g. To a mixed solvent silica sol having a silica concentration of 5 to 50% by mass obtained by mixing at 0.12 to 2.5, the formula (1)
(R ¹ ₃ Si) ₂ NH (1)
(In the formula, each R ¹ is an independently selected alkyl group having 1 to 6 carbon atoms or a phenyl group.)
The disilazane compound represented by the formula (1) is added in an amount of 0.1 to 20 mmol per 100 m ² of the surface area of hydrophilic colloidal silica, and is heated and matured at a temperature of 50 to 100 ° C. to form a hydrophobized colloidal silica slurry. Including a hydrophobizing step of obtaining a dispersion.

  The preferable aspect is shown below.

  Subsequent to the hydrophobizing treatment step, the obtained hydrophobized colloidal silica slurry dispersion is aged by heating at 50 to 100 ° C. with stirring to be hydrophobized in the dispersion. Including the step of granulating colloidal silica into granules.

Especially this invention relates to the manufacturing method of hydrophobic silica powder including the following (A), (B), (C) and (D) process.
(A): An aqueous silica sol containing hydrophilic colloidal silica having a specific surface area of 5.5 to 550 m ² / g is mixed with a hydrophilic organic solvent at a mass ratio of 0.12 to 2.5 with respect to the water of the aqueous silica sol. A mixed solvent silica sol having a silica concentration of 5 to 50% by mass obtained by mixing is mixed with the formula (1).
(R ¹ ₃ Si) ₂ NH (1)
(In the formula, each R ¹ is an independently selected alkyl group having 1 to 6 carbon atoms or a phenyl group.)
The disilazane compound represented by the formula (1) is added in an amount of 0.1 to 20 mmol per 100 m ² of the surface area of hydrophilic colloidal silica and heated at a temperature of 50 to 70 ° C. for aging to make a hydrophobized colloidal silica slurry. A hydrophobizing step for obtaining a dispersion;
(B): The slurry-like dispersion obtained in the step (A) is aged by heating at 50 to 100 ° C. with stirring and at a temperature higher than the temperature in the hydrophobization treatment step. A step of granulating the hydrophobized colloidal silica into granules,
(C): a step of separating the hydrophobized colloidal silica granulated in the step (B) and the liquid phase in the dispersion, and (D): obtained in the step (C) Drying the granular hydrophobized colloidal silica cake.

  Use hexamethyldisilazane as the disilazane compound represented by the above formula (1).

  The production method of the present invention is effective for aqueous silica sols having various particle sizes. By using an aqueous silica sol having a high dispersibility in the silica base, a hydrophobic silica powder having a high redispersibility with respect to various organic solvents can be obtained even after the hydrophobization treatment. By mixing, the contact between the disilazane compound and the hydrophilic colloidal silica is promoted, and since the slurry-like, preferably the granular hydrophobized colloidal silica and the liquid phase are separated after the hydrophobization treatment, Hydrophobic silica powder can be produced by a simple hydrophobization treatment process with a simple apparatus by the production method of the present invention, such as being able to take out the hydrophobized silica by a simple method such as filtration.

  The hydrophobic silica powder obtained in the present invention is useful as an external additive for toner such as electrophotography, an internal additive for resin, a hard coat agent, a water repellent, a flame retardant and the like.

The aqueous silica sol used in the present invention is an aqueous silica sol having a silica concentration of 5 to 55% by mass containing hydrophilic colloidal silica having a specific surface area of 5.5 to 550 m ² / g, preferably 5.5 to 300 m ² / g. However, an aqueous silica sol having a silica concentration of 10 to 55% by mass is preferable. The aqueous silica sol can be produced by a known method using, for example, water glass as a raw material.

The particle size of the hydrophilic colloidal silica is calculated from the specific surface area S (m ² / g) determined by the nitrogen adsorption method (BET method) by the formula D (nm) = 2720 / S. Therefore, the BET method particle diameter of hydrophilic colloidal silica is 5 nm or more, preferably 9 nm or more. It is difficult to achieve a high concentration with an aqueous silica sol having a BET particle diameter of less than 5 nm for hydrophilic colloidal silica, and the surface treatment requires a large amount of silylating agent per unit mass of the colloidal silica.

  The aqueous silica sol to be used is preferably an aqueous silica sol containing no free alkali metal ions. When an alkaline aqueous silica sol containing liberated alkali metal ions is used as a raw material, the reactivity between the silylating agent and the silanol group on the surface of the hydrophilic colloidal silica is reduced, the reaction rate of the silylating agent is reduced, and hydrophobic silica is used. It adversely affects the hydrophobicity of the powder. An aqueous silica sol containing no free alkali metal ions can be obtained, for example, by removing Na ions released from an alkaline aqueous silica sol containing Na ions by a method such as cation exchange. Examples of the aqueous silica sol obtained include acidic aqueous silica sol. An aqueous silica sol stabilized with ammonia, amine, or the like can also be used as a raw material.

The hydrophobizing agent used in the present invention is a disilazane compound, specifically, hexamethyldisilazane, di-n-butyltetramethyldisilazane, divinyltetramethyldisilazane, diphenyltetramethyldisilazane, tetraphenyldimethyldisilazane. It is preferably at least one compound selected from the group consisting of silazanes, and hexamethyldisilazane is particularly preferred. The disilazane compound is added to the mixed solvent silica sol obtained by mixing the hydrophilic organic solvent with the aqueous silica sol in an amount of 0.1 to 20 mmol, preferably 0.5 to 10 mmol, per 100 m ² of the surface area of the hydrophilic colloidal silica. Even if an excess of the disilazane compound is used, it is not consumed in the hydrophobization reaction, and it is economically inefficient. Further, when the disilazane compound is insufficient, the hydrophobicity becomes insufficient.

  The form after the hydrophobization treatment of the present invention is a slurry dispersion of hydrophobized colloidal silica or a granulated product of hydrophobized colloidal silica, and it is necessary to make the phase separated from the liquid phase. It is. Slurry means a state in which fine particles formed by agglomeration of colloidal silica are dispersed in a mixed solvent and can be separated by filtration with commercially available filter paper or the like. The granular form means a state in which the hydrophobized colloidal silica is granulated to 0.1 mm or more in the slurry dispersion. In order to obtain a slurry-like dispersion or granular product of hydrophobized colloidal silica, the mass ratio of the hydrophilic organic solvent of the mixed solvent silica sol to water is important.

The mixed solvent silica sol of the present invention requires the presence of a sufficient amount of the hydrophilic organic solvent to promote contact between the disilazane compound and the hydrophilic colloidal silica. The mixed solvent silica sol is preferably prepared by mixing a hydrophilic organic solvent having a mass ratio of 0.12 to 2.5 with respect to the water of the aqueous silica sol to be used. When the mass ratio is less than 0.12, the solubility of the disilazane compound in the mixed solvent is low, the contact between the disilazane compound and the hydrophilic colloidal silica is insufficient, or the colloidal silica and the mixed solvent that have been hydrophobized. In this case, the colloidal silica that has been subjected to the hydrophobization treatment may precipitate in the form of a lump as the hydrophobization reaction proceeds, making it difficult to manufacture. And when the mass ratio is larger than 2.5, when the colloidal silica hydrophobized cannot be obtained in the form of a slurry dispersion while being dispersed in the mixed solvent in a sol form, and cannot be separated by filtration, In some cases, it becomes unstable during the hydrophobization treatment process and thickens in a gel form. In the latter case, it cannot be produced substantially.
As the hydrophilic organic solvent, for example, alcohols having a boiling point of 100 ° C. or less such as methanol, ethanol, 1-propanol, isopropanol, tert-butanol and the like having no compatibility limit with water are preferable, and miscible with water and a silazane compound. Isopropanol is most preferred from the standpoint of the properties and ease of removal in the drying step. In addition, the mass ratio of the appropriate hydrophilic organic solvent and water in the mixed solvent silica sol differs depending on the type of the hydrophilic organic solvent, and the better the miscibility of the hydrophilic organic solvent with water and the disilazane compound, the better the mixed solvent silica sol has. The mass ratio of the hydrophilic organic solvent to water becomes small.

  In the mixed solvent silica sol, the silica concentration is preferably 5 to 50% by mass. When the silica concentration in the mixed solvent silica sol is lower than 5% by mass, the production efficiency of the hydrophobic silica powder is lowered, and the contact efficiency between the hydrophilic colloidal silica and the disilazane compound is lowered, so that the surface area of the hydrophilic colloidal silica is decreased. This is not preferable because the required amount of per-disilazan compound increases. On the other hand, when the silica concentration exceeds 50% by mass, the mixed solvent silica sol is remarkably thickened in the hydrophobizing treatment step, so that stirring becomes difficult and it becomes difficult to perform a uniform hydrophobizing treatment.

  In order to obtain a slurry dispersion of hydrophobized colloidal silica, the silica concentration in the mixed solvent silica sol and the mass ratio of the hydrophilic organic solvent to water are determined by the BET particle size and hydrophilicity of the hydrophilic colloidal silica. Depends on the type of organic solvent. In order to prepare a mixed solvent silica sol having an appropriate composition, the smaller the BET particle diameter of the hydrophilic colloidal silica, the larger the mass of the hydrophilic organic solvent added relative to the mass of the hydrophilic colloidal silica. There is a tendency.

  In the method of the present invention, the temperature of the mixed solvent silica sol at the time of addition of the disilazane compound is not particularly limited. It is preferable to adjust to ℃-70 ℃. When the temperature exceeds 70 ° C., the reaction is intense, and foaming may occur due to ammonia generated during the reaction of the disilazane compound. Further, after adding the disilazane compound, the mixed solvent silica sol is heated at a temperature of 50 ° C. to 100 ° C. and aged for 0.5 hour or longer, so that the mixed solvent silica sol becomes hydrophobic until it becomes a slurry dispersion of hydrophobized colloidal silica. It is good to promote the chemical reaction. If the aging time is less than 0.5 hour, the hydrophobization treatment may be insufficient. By making it into a slurry state, separation of the hydrophobized colloidal silica from the liquid phase becomes easy, and the hydrophobized colloidal silica can be easily taken out by a simple method such as filtration.

  Further, following the hydrophobization treatment step, the obtained hydrophobized colloidal silica slurry dispersion is aged by heating at 50 to 100 ° C. with stirring, thereby hydrophobizing the dispersion. Colloidal silica is preferably granulated into granules of 0.1 mm or more. By granulating into granules by stirring operation, the workability of the separation step from the liquid phase performed after the hydrophobization treatment is remarkably improved. The temperature of the liquid phase in the granulation step can be carried out at the same temperature as in the hydrophobization treatment step, but granulation can be promoted by setting the temperature higher than that in the hydrophobization treatment step. The size of the granules and the particle size distribution are not particularly limited, but the average size is preferably 5 mm or less. If it is larger than 5 mm, the stirring resistance may increase during granulation, or it may be difficult to remove from the reactor after granulation.

  After the hydrophobization treatment, the separation method from the liquid phase is not particularly limited, but the slurry-like or granulated hydrophobization colloidal silica and the liquid phase can be separated by a known method. Examples thereof include filtration by filtration, centrifugation, and liquid phase distillation.

  The drying method of the slurry-like or granulated hydrophobized colloidal silica cake obtained in the separation step is not particularly limited, but may be a known method such as hot air drying, microwave drying, infrared drying, ultrasonic drying, vacuum drying, etc. Can be dried. Although a drying temperature is not specifically limited, Preferably it is 200 degrees C or less. When the temperature is higher than 200 ° C., the primary particles are likely to be bonded to each other by condensation of silanol groups remaining on the surface of the hydrophobized colloidal silica. This bond is not easily dissociated by dry pulverization, and as a result, the redispersibility of the hydrophobic silica powder in an organic solvent is deteriorated. The separation step and the drying step can also be performed as a series of steps using an apparatus such as a filter dryer. The hydrophobic silica thus obtained is homogeneously dispersed in most organic solvents such as alcohols, ketones, ethers, aromatic hydrocarbons and aliphatic hydrocarbons.

  Further, the drying time can be shortened by performing the pulverization in the middle of the drying step.

  The dried hydrophobized silica can be pulverized with a powder mill or the like to obtain powdered hydrophobic silica. The pulverization method is not particularly limited, and a dry pulverization apparatus such as a jet mill, a vibration mill, a ball mill, or an attritor can be used.

In each Example and Comparative Example, the hydrophobization treatment step and the granulation step were performed under the following stirring conditions.
Example 1
1 liter glass reaction vessel with an inner diameter of 85 mm
Faudler wing (diameter 70mm), 250 rotations per minute Liquid temperature of granulation process: 74 ° C
Examples 2 and 4
2 liter glass reaction vessel with an inner diameter of 130 mm
Faudler wing (diameter 100mm), 250 rotations per minute Liquid temperature of granulation process: 75 ° C
Examples 3 and 5
2 liter glass reaction vessel with an inner diameter of 130 mm
Faudler wing (diameter 100mm), 150 revolutions per minute Liquid temperature of granulation process: 76 ° C
Comparative Examples 1, 3, 5
1 liter glass reaction vessel with an inner diameter of 85 mm
Faudler wing (diameter 70 mm), 200 revolutions per minute Comparative Examples 2 and 4
1 liter glass reaction vessel with an inner diameter of 85 mm
Faudler wing (70mm diameter), 500 revolutions per minute

Example 1
Commercially available acidic aqueous silica sol (trade name: Snowtex (registered trademark) -O, manufactured by Nissan Chemical Industries, Ltd.), silica concentration 20 mass%, pH 3.0, BET method particle size 12 nm) with a rotary evaporator, silica concentration 33 % To obtain a concentrated acidic aqueous silica sol. Subsequently, 450 g of the concentrated acidic aqueous silica sol, 75 g of pure water, and 225 g of isopropanol (IPA) were added to a 1 liter glass reaction vessel equipped with a stirrer, a dropping funnel, a condenser, and a thermometer. A mixed solvent silica sol having 0% by mass, an IPA concentration of 30.0% by mass, and a water content of 50% by mass was prepared. This mixed solvent silica sol was heated to 65 ° C., and 75 g of hexamethyldisilazane (1.4 mmol per 100 m ² of surface area of hydrophilic colloidal silica) was added dropwise. The mixed solvent silica sol was mixed for 30 minutes and then heated to 70 ° C. and aged for 1 hour to obtain a slurry dispersion of hydrophobized colloidal silica. Next, this hydrophobized colloidal silica slurry dispersion was granulated into granules by aging under reflux for 3 hours with stirring. The granular hydrophobized colloidal silica and the liquid phase were separated by filtration with a Buchner funnel (Qualitative filter paper No. 131 manufactured by ADVANTEC), and the obtained hydrophobized colloidal silica cake was dried at 120 ° C. . Next, the dried granular hydrophobized colloidal silica was pulverized by a powder mill and further dried at 150 ° C. to obtain 150 g of hydrophobic silica powder. The obtained hydrophobic silica powder was re-dispersed in the form of a sol in methyl ethyl ketone.

  In addition, this hydrophobic silica powder is the same as other organic solvents such as methanol, ethanol, isopropanol, methyl isobutyl ketone, ethyl acetate, toluene, methyl methacrylate monomer, polydimethylsiloxane, n-hexane, tetrahydroxyfuran and methyl ethyl ketone. Re-dispersed in a sol form.

Example 2
In a 2 liter glass reaction vessel equipped with a stirrer, dropping funnel, condenser, and thermometer, acidic aqueous silica sol (silica concentration 31.5 mass%, pH 2.5, BET particle size 80 nm) 1200 g, pure water 75 g Then, 350 g of isopropanol (IPA) was added to prepare a mixed solvent silica sol having a silica concentration of 23.3 mass%, an IPA concentration of 21.5 mass%, and a water content of 55.2 mass%. This mixed solvent silica sol was heated to 65 ° C., and 80 g of hexamethyldisilazane (3.9 mmol per 100 m ² of surface area of hydrophilic colloidal silica) was added dropwise. The mixed solvent silica sol was mixed for 30 minutes and then heated to 70 ° C. and aged for 1 hour to obtain a slurry dispersion of hydrophobized colloidal silica. Next, this hydrophobized colloidal silica slurry dispersion was granulated into granules by aging under reflux for 3 hours with stirring. The granular hydrophobized colloidal silica and the liquid phase were separated by filtration with a Buchner funnel (Qualitative filter paper No. 131 manufactured by ADVANTEC), and the obtained hydrophobized colloidal silica cake was dried at 120 ° C. . Next, the dried granular hydrophobized colloidal silica was pulverized by a powder mill and further dried at 200 ° C. to obtain 380 g of hydrophobic silica powder. The obtained hydrophobic silica powder was re-dispersed in the form of a sol in methyl ethyl ketone.

Example 3
In a 2 liter glass reaction vessel equipped with a stirrer, dropping funnel, condenser, thermometer, commercially available alkaline aqueous silica sol (product name: MP-2040, manufactured by Nissan Chemical Industries, Ltd.), silica concentration 40% by mass , PH 9.4, BET particle size 120 nm) obtained by cation exchange, 1430 g of acidic aqueous silica sol (silica concentration 35 mass%, pH 2.0), 270 g of pure water, 300 g of isopropanol (IPA) were added, and the silica concentration A mixed solvent silica sol having 25.0% by mass, IPA concentration of 15.0% by mass and water content of 60.0% by mass was prepared. This mixed solvent silica sol was heated to 65 ° C., and 86 g of hexamethyldisilazane (5.0 mmol per 100 m ² of surface area of hydrophilic colloidal silica) was added dropwise. The mixed solvent silica sol was mixed for 15 minutes, then heated to 70 ° C. and aged for 30 minutes to obtain a slurry dispersion of hydrophobized colloidal silica. Next, this hydrophobized colloidal silica slurry dispersion was granulated into granules by aging under reflux for 3 hours with stirring. The granular hydrophobized colloidal silica and the liquid phase were separated by filtration with a Buchner funnel (Qualitative filter paper No. 131 manufactured by ADVANTEC), and the obtained hydrophobized colloidal silica cake was dried at 120 ° C. . Next, the dried granular hydrophobized colloidal silica was pulverized by a powder mill and further dried at 200 ° C. to obtain 500 g of hydrophobic silica powder. The obtained hydrophobic silica powder was re-dispersed in the form of a sol in methyl ethyl ketone.

Example 4
In Example 2, the same operation was performed except that the granular hydrophobized colloidal silica dried at 120 ° C. was dried at 200 ° C. without being pulverized by a powder mill. The obtained hydrophobic silica powder was re-dispersed in the form of a sol in methyl ethyl ketone.

Example 5
In Example 3, the same operation was performed except that the granular hydrophobized colloidal silica dried at 120 ° C. was dried at 200 ° C. without being pulverized by a powder mill. The obtained hydrophobic silica powder was re-dispersed in the form of a sol in methyl ethyl ketone.

Comparative Example 1
In a 1 liter glass reaction vessel equipped with a stirrer, a dropping funnel, a condenser, and a thermometer, 150 g of acidic aqueous silica sol (silica concentration 31.5 mass%, pH 2.5, BET particle size 80 nm), 270 g of pure water Then, 30 g of isopropanol (IPA) was added to prepare a mixed solvent silica sol having a silica concentration of 10.5% by mass, an IPA concentration of 6.7% by mass, and a water content of 82.8% by mass. This mixed solvent silica sol was heated to 65 ° C., and 10 g of hexamethyldisilazane (3.9 mmol per 100 m ² of surface area of hydrophilic colloidal silica) was added dropwise. The added hexamethyldisilazane immediately floated on the surface layer without being mixed with the mixed solvent silica sol. Even if the mixed solvent silica sol was mixed for 30 minutes and then heated to 70 ° C. and aged for 1 hour, a slurry dispersion of hydrophobized colloidal silica could not be obtained. Further, even when the mixture was aged for 3 hours under stirring in a reflux state, a slurry dispersion of hydrophobized colloidal silica could not be obtained.

  Since the state after the hydrophobization treatment remained in a sol state and could not be separated by a filter paper (ADVANTEC qualitative filter paper No. 131) using a Buchner funnel, the sol-like product was transferred to a metal vat, Dry at 120 ° C. Since the obtained sol-like product did not separate the liquid phase, the drying efficiency was remarkably poor, and it took a long time to dry. The dried hydrophobized colloidal silica was pulverized by a powder mill and dried at 200 ° C. to obtain 48 g of hydrophobic silica powder. Part of the obtained hydrophobic silica powder was redispersed in methyl ethyl ketone, but a precipitate that did not redisperse was also produced.

Comparative Example 2
Commercially available acidic aqueous silica sol (trade name: Snowtex (registered trademark) -O, manufactured by Nissan Chemical Industries, Ltd.), silica concentration 20 mass%, pH 3.0, BET method particle size 12 nm) with a rotary evaporator, silica concentration 33 Concentrated to% mass. Subsequently, 200 g of concentrated acidic aqueous silica sol and 400 g of isopropanol (IPA) were added to a 1 liter glass reaction vessel equipped with a stirrer, a dropping funnel, a condenser, and a thermometer, and a silica concentration of 11.0% by mass, IPA A mixed solvent silica sol having a concentration of 66.7% by mass and a water content of 22.3% by mass was prepared. This mixed solvent silica sol was heated to 65 ° C., and 34 g of hexamethyldisilazane (1.4 mmol per 100 m ² of surface area of hydrophilic colloidal silica) was added dropwise. The mixed solvent silica sol was mixed for 30 minutes and then heated to 70 ° C. and aged for 1 hour. However, a slurry dispersion of hydrophobized colloidal silica could not be obtained in the sol state. Further, although the mixture was aged for 3 hours under stirring in a reflux state, a thickened gel was formed, and a slurry dispersion of hydrophobized colloidal silica could not be obtained. Since the product was a gel-like hydrophobized silica and could not be filtered off with a filter paper (Qualitative filter paper No. 131 from ADVANTEC) using a Buchner funnel, the product was transferred to a metal vat. It put into the dryer of ℃. The product still contained the liquid phase, the drying efficiency was extremely poor, and drying took a long time. The dried hydrophobized silica was pulverized by a powder mill and further dried at 150 ° C. to obtain 69 g of hydrophobic silica powder. Part of the obtained hydrophobic silica powder was redispersed in methyl ethyl ketone, but a precipitate that did not redisperse was also produced.

Comparative Example 3
In a 1 liter glass reaction vessel equipped with a stirrer, a dropping funnel, a condenser, and a thermometer, 333 g of acidic aqueous silica sol (silica concentration 31.5 mass%, pH 2.5, BET particle size 80 nm), 87 g of pure water Then, 30 g of isopropanol (IPA) was added to prepare a mixed solvent silica sol having a silica concentration of 23.3 mass%, an IPA concentration of 5.0 mass%, and water of 71.7 mass%. This mixed solvent silica sol was heated to 65 ° C., and 22.5 g of hexamethyldisilazane (3.9 mmol per 100 m ² of surface area of hydrophilic colloidal silica) was added dropwise. The added hexamethyldisilazane immediately floated on the surface layer without being mixed with the mixed solvent silica sol. The mixed solvent silica sol was mixed for 30 minutes and then heated to 70 ° C. and aged for 1 hour to obtain a slurry dispersion of hydrophobized colloidal silica. Further, the mixture was ripened under stirring in a reflux state, but a large amount of a hydrophobized colloidal silica bulk product was formed during the ripening, and the stirring resistance increased.

Comparative Example 4
Commercially available acidic aqueous silica sol (trade name: Snowtex (registered trademark) -O, manufactured by Nissan Chemical Industries, Ltd., silica concentration 20% by mass, pH 3.0, BET particle size 12 nm) was added with a rotary evaporator and isopropanol was added. Water and alcohol were distilled off under reduced pressure. This operation was continued until an isopropanol-dispersed silica sol having a silica concentration of 33% by mass and a water content of 5.7% by mass was obtained. Subsequently, 364 g of the isopropanol-dispersed silica sol, 177 g of isopropanol (IPA), and 59 g of pure water were added to a 1 liter glass reaction vessel equipped with a stirrer, a dropping funnel, a condenser, and a thermometer, and a silica concentration of 20.0 was added. A mixed solvent silica sol having a mass%, an IPA concentration of 66.7 mass%, and a water content of 13.3% by mass was prepared. This mixed solvent silica sol was heated to 65 ° C., and 62 g of hexamethyldisilazane (1.4 mmol per 100 m ² of surface area of hydrophilic colloidal silica) was added dropwise. When heating and mixing were continued, the viscosity increased significantly and the contents could not be stirred, so the production was stopped.

Comparative Example 5
In a 1 liter glass reaction vessel equipped with a stirrer, dropping funnel, condenser, thermometer, commercially available precipitated silica powder (trade name: Zeosil (registered trademark) 1165MP, manufactured by Rhodia, silica concentration 90% by mass, ratio 100 g of surface area of 165 m ² / g, laser diffraction type dispersed particle diameter 273 μm), 135 g of isopropanol (IPA) and 215 g of pure water were added, silica concentration was 20.0 mass%, IPA concentration was 30.0 mass%, and water content was 50.0. A slurry dispersion of mass% precipitated silica was prepared. This slurry dispersion of precipitated silica was heated to 65 ° C., and 45 g of hexamethyldisilazane (1.9 mmol per 100 m ² of surface area of hydrophilic precipitated silica) was added dropwise. The slurry dispersion was mixed for 30 minutes, then heated to 70 ° C. and aged for 1 hour. Further, the mixture was aged for 3 hours under stirring in a reflux state to obtain a slurry dispersion of hydrophobized precipitating silica. Using a Buchner funnel, the slurry-like hydrophobized precipitated silica was separated from the liquid phase with a filter paper (Qualitative filter paper No. 131 manufactured by ADVANTEC), and the resulting hydrophobized precipitated silica cake was dried at 120 ° C. . Next, the dried hydrophobized precipitating silica cake was pulverized by a powder mill and further dried at 200 ° C. to obtain 98 g of hydrophobic silica powder. The obtained hydrophobic silica powder was only wetted with methyl ethyl ketone, and was not redispersed in a sol form.

Evaluation [Analytical Method of Hydrophobic Silica Powder]
(1) Carbon content in hydrophobic silica powder The carbon content in the obtained hydrophobic silica powder was measured using a CHNS / O analyzer (PE2400 series II manufactured by PerkinElmer). The number of trimethylsilyl groups per unit surface area of hydrophobic silica powder (number / nm ² ) was calculated by the following calculation formula (α).

  A: Trimethylsilyl group content (% by mass) = carbon amount (% by mass) × (73.19 / 36.03).

B: Trimethylsilyl group (g) per 1 g of hydrophobic silica powder = 6.02 × 10 ²³ × (A / 73.19) × 10 ⁻² .

C: Surface area per 1 g of hydrophobic silica powder (nm ² ) = specific surface area of hydrophobic silica powder (m ² / g) × 10 ¹⁸ × solid content (mass%) × 10 ⁻²

Number of trimethylsilyl groups per unit surface area of the hydrophobic silica powder (number / nm ² ) = B / C (α).
Here, the solid content is a baking residue obtained by baking the obtained hydrophobic silica powder at 800 ° C.
(2) Dispersed particle size of hydrophobic silica powder The obtained hydrophobic silica powder was dispersed in methyl ethyl ketone, and the dispersed particle size was measured by a dynamic light scattering method (submicron particle analyzer model N4, manufactured by Beckman Coulter, Inc.). did.
(3) Degree of hydrophobicity: 0.20 g (0.20 ± 0.01 g) of a silica powder sample was weighed and added to 50 ml of pure water in a 100 cc glass beaker so that the silica powder floated on the liquid surface. . While stirring with a magnetic stirrer, methanol is injected into the liquid using a burette so that the sample does not directly touch the sample, and the end point is when no silica powder sample is observed on the liquid surface. The amount of methanol used was X ml, and the degree of hydrophobicity was determined according to the following formula.
Hydrophobicity (%) = X / (50 + X) × 100
The evaluation results are shown in Table 1.

(4) Evaluation of organic solvent dispersibility was performed as follows.
In a 20 cc glass bottle, 1 g of the obtained hydrophobic silica powder is added to 9 g of methyl ethyl ketone, mixed for 30 minutes with a magnetic stirrer, and then dispersed for 30 seconds with a commercially available ultrasonic cleaner. Was prepared. Next, the obtained dispersion was appropriately diluted with methyl ethyl ketone, and the dispersed particle size was measured by a dynamic light scattering method (submicron particle analyzer model N4, manufactured by Beckman Coulter, Inc.).
In Comparative Examples 1 and 2, since the sedimentation component was present in the dispersion, the supernatant was appropriately diluted and measured. Further, since Comparative Example 5 was not dispersed in a sol form and could not be measured by the dynamic light scattering method, the dispersed particle size was measured with a laser diffraction particle size distribution measuring device (SALD-7000, manufactured by Shimadzu Corporation). The dispersion particle diameter of the hydrophobic silica powder was compared with the dispersion particle diameter of the aqueous silica sol used as the raw material, and the organic solvent dispersibility was evaluated.

  As described above, the production method of the present invention makes it possible to produce a hydrophobic silica powder by a simple hydrophobization process using a simple apparatus. The hydrophobic silica powder obtained in the present invention is useful as an external additive for toner such as electrophotography, an internal additive for resin, a hard coat agent, a water repellent, a flame retardant and the like.

The present invention provides a method for efficiently producing a hydrophobic silica powder excellent in redispersibility in an organic solvent. The hydrophobic silica powder obtained in the present invention is useful as an external additive for toner such as electrophotography, an internal additive for resin, a hard coat agent, a water repellent, a flame retardant and the like.

Claims (2)

Following (A), (B), (C) and (D) the preparation of hydrophobicity silica powder comprising the step.
(A): An aqueous silica sol containing hydrophilic colloidal silica having a specific surface area of 5.5 to 550 m ² / g is mixed with a hydrophilic organic solvent at a mass ratio of 0.12 to 2.5 with respect to the water of the aqueous silica sol. In a mixed solvent silica sol having a silica concentration of 5 to 50% by mass obtained by mixing,
Formula (1)
(R ¹ ₃ Si) ₂ NH (1)
(In the formula, each R ¹ is an independently selected alkyl group having 1 to 6 carbon atoms or a phenyl group.)
The disilazane compound represented by the formula (1) is added in an amount of 0.1 to 20 mmol per 100 m ² of the surface area of hydrophilic colloidal silica and heated at a temperature of 50 to 70 ° C. for aging to make a hydrophobized colloidal silica slurry. A hydrophobizing step for obtaining a dispersion;
(B): The slurry-like dispersion obtained in the step (A) is aged by heating at 50 to 100 ° C. with stirring and at a temperature higher than the temperature in the hydrophobic treatment step. A step of granulating the hydrophobized colloidal silica in a liquid,
(C): a step of separating the hydrophobized colloidal silica granulated in step (B) and the liquid phase in the dispersion, and (D): obtained in step (C). Drying the resulting hydrophobized colloidal silica cake. The process according to claim 1 , wherein the disilazane compound represented by the formula (1) is hexamethyldisilazane.