JP2007197316A - Method for preparing silica dispersion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a silica dispersion which contains silica of high concentration and in which silica hardly agglomerates or precipitates. <P>SOLUTION: The method for preparing the silica dispersion by dispersing a silica fine particle in a dispersion medium comprises the steps of: using gas-phase method silica (fumed silica) having 3-15 nm average primary particle size as the silica fine particle; adding the fumed silica to the dispersion medium, which is prepared by adding a cationic polymer having ≤50,000 average molecular weight to water, and mixing them to prepare silica slurry; and dispersing the prepared silica slurry by a dispersing machine. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a silica dispersion. Specifically, the present invention relates to a method for producing a silica dispersion having a high concentration and high stability over time.

  Silica dispersions are used for polishing semiconductor wafers typified by silicon or for polishing insulating layers in IC manufacturing processes, hard coating agents for plastics such as eyeglass lenses, inkjet recording materials, and OHP. It is used as a coating agent, an antiblocking agent for various films, an adhesion aid such as glass fiber, and a stabilizer such as emulsion and wax.

  Examples of such silica dispersions include vapor phase silica (fumed silica) made by burning silicon tetrachloride as a raw material in an oxyhydrogen flame, precipitated silica and gel silica made by neutralizing sodium silicate. So-called wet silica, or sol-gel silica prepared by hydrolyzing silicon alkoxide in an alkaline or acidic water-containing organic solvent is excellent, and silica dispersions using such silica are attracting attention. Yes. These silica dispersions are prepared by dispersing the silica fine particles in a dispersion medium (water, an organic solvent or a mixture thereof) by a dispersing machine such as a high-pressure homogenizer or a ball mill.

  However, these dispersions have a problem that aggregation and sedimentation occur during storage. In particular, the above problem became significant in a dispersion medium mainly composed of water and having a silica concentration of 15% by mass or more. Furthermore, the above problem was likely to occur in the case of ultrafine silica, that is, fine silica having an average primary particle size of 50 nm or less.

  In addition, a high-concentration silica dispersion is very advantageous in terms of cost in consideration of physical distribution. Therefore, a method for stably producing a high concentration silica dispersion is desired.

  Accordingly, an object of the present invention is to provide a method for producing a silica dispersion having a high concentration and hardly causing aggregation and sedimentation.

The above object of the present invention has been achieved by the following invention.
In the method for producing a silica dispersion in which silica fine particles are dispersed in a dispersion medium, the silica fine particles are gas phase method silica having an average primary particle size of 3 to 15 nm, and mainly composed of water and a cationic polymer having an average molecular weight of 50,000 or less. A method for producing a silica dispersion, comprising: adding and mixing silica fine particles to a dispersion medium to which silica is added to produce a silica slurry, and then dispersing the silica slurry with a disperser.

According to the present invention, a silica dispersion that is stable over time can be obtained. In particular, a high-concentration dispersion with a silica concentration of 15% by mass tends to cause aggregation and sedimentation over time, and is suitable for such a high-concentration dispersion. Among the cationic polymers, a cationic polymer having a structural unit of a water-soluble polydiallylamine derivative having an average molecular weight of 2000 to 50,000 is particularly useful for preparing an extremely stable silica dispersion. Furthermore, the present invention is effective for a dispersion of vapor phase silica having an average primary particle size of 3 to 15 nm and a specific surface area by a BET method of 200 m ² / g or more.

Hereinafter, the present invention will be described in detail.
Synthetic silica is classified into a wet method and a gas phase method. In general, silica fine particles often refer to wet process silica. Wet silicas include (1) silica sol obtained through metathesis with sodium silicate acid and ion exchange resin layer, or (2) colloidal silica obtained by heating and aging this silica sol, and (3) gelation of silica sol. In addition, by changing the production conditions, silica gel in which primary particles of several μm to 10 μm become three-dimensional secondary particles having siloxane bonds, and (4) silica sol, sodium silicate, sodium aluminate, etc. There are synthetic silicic acid compounds mainly composed of silicic acid, such as those obtained by heating to form a silicic acid.

  The silica fine particles used in the present invention are vapor phase silica. Vapor phase silica (fumed silica) is also called a dry method as opposed to a wet method, and is generally made by a flame hydrolysis method. Specifically, a method of making silicon tetrachloride by burning with hydrogen and oxygen is generally known, but silanes such as methyltrichlorosilane and trichlorosilane can be used alone or silicon tetrachloride instead of silicon tetrachloride. Can be used in a mixed state. Vapor phase silica is commercially available as Aerosil from Nippon Aerosil Co., Ltd., and QS type from Tokuyama Co., Ltd., and can be obtained.

The dispersion using the cationic polymer of the present invention is particularly effective when vapor phase silica is used. Among them, it is particularly suitable for a dispersion of vapor phase method silica having an average primary particle size of 3 to 15 nm and a specific surface area by the BET method of 200 m ² / g or more, and further 250 to 500 m ² / g.

  The BET method referred to in the present invention is one of powder surface area measurement methods by vapor phase adsorption, and is a method for determining the total surface area, that is, the specific surface area of a 1 g sample from the adsorption isotherm. Usually, nitrogen gas is often used as the adsorbed gas, and the most frequently used method is to measure the amount of adsorption from the change in pressure or volume of the gas to be adsorbed. The most prominent expression for expressing the isotherm of multimolecular adsorption is the Brunauer, Emmett, and Teller formula, called the BET formula, which is widely used for determining the surface area. The adsorption amount is obtained based on the BET equation, and the surface area is obtained by multiplying the area occupied by one adsorbed molecule on the surface.

  Examples of the cationic polymer used in the present invention include polymers having a primary to tertiary amino group, a quaternary ammonium base, or a phosphonium base. Among them, a water-soluble polymer is preferable, and a polymer having an average molecular weight of 50,000 or less is particularly preferable.

  Among the above cationic polymers, cationic polymers having a structural unit of a polydiallylamine derivative are particularly preferable, and a cationic polymer having a structure represented by the following general formula (1), (2), (3) or (4) as a structural unit. It is. These derivatives are obtained by radical cyclopolymerization of diallylamine compounds. Charol DC902P (Daiichi Kogyo Seiyaku Co., Ltd.), Jetfix 110 (Satoda Chemical Industries), Unisense CP-101 to 103 (Senka), PAS-H (Nittobo) Is commercially available.

In the general formulas (1), (2), (3) and (4), R ₁ and R ₂ each represents a hydrogen atom, an alkyl group such as a methyl group or an ethyl group, or a substituted alkyl group such as a hydroxyethyl group. Y represents a radical polymerizable monomer (for example, sulfonyl, acrylamide and derivatives thereof, acrylic ester, methacrylic ester, etc.). In the general formulas (3) and (4), n / m = 9/1 to 2/8 (mass ratio), and l = 5 to 10,000. X represents an anion.

Specific examples of the polydiallylamine derivative represented by the general formula (3) or (4) include those having a SO ₂ group as a repeating unit described in JP-A-60-83882, JP-A-1-9776. Examples thereof include copolymers with acrylamide described in the publication. The average molecular weight of the cationic polymer of the polydiallylamine derivative used in the present invention is more preferably about 2,000 to 50,000.

  The amount of the cationic polymer used is preferably 1 to 10% by mass with respect to the silica fine particles.

  Even if the silica dispersion of the present invention has a high concentration, that is, a silica concentration of 15% by mass or more, and further 18% by mass or more, the dispersion stability is maintained over a long period of time.

  The dispersion medium used in the silica dispersion of the present invention is mainly composed of water, but may contain a small amount of an organic solvent (a low-boiling solvent such as lower alcohol or ethyl acetate). In that case, the organic solvent is preferably 20% by mass or less, more preferably 10% by mass or less, based on the total dispersion medium.

  Next, the manufacturing method of the silica dispersion liquid of this invention is demonstrated. Usually, the silica dispersion is prepared by adding silica fine particles to a dispersion medium such as water and mixing (preliminary mixing) to prepare a silica slurry, and the silica slurry is dispersed by a disperser such as a high-pressure homogenizer or a ball mill. For the dispersion using a high-pressure homogenizer, for example, the method described in JP-A-10-310416 can be used. Moreover, the frequency | count of processing the said silica slurry with a high pressure homogenizer is chosen from the range of 1 to several dozen times.

  The cationic polymer is preferably added to the dispersion medium before adding the silica fine particles. As a result, a more stable dispersion can be obtained.

  In the present invention, the liquid temperature when premixing is preferably 20 ° C. or less. In particular, 15 ° C. or less is preferable. Thereby, a high concentration silica slurry can be stably produced. In this case, the dispersion medium before adding the silica fine particles may be kept at a temperature of 20 ° C. or lower, or may be cooled to 20 ° C. or lower during the premixing. Moreover, it is preferable to inject | pour into a disperser in the state whose temperature of a silica slurry is 20 degrees C or less, Furthermore, 15 degrees C or less. This provides a more stable dispersion.

  The preliminary mixing can be performed by ordinary propeller stirring, turbine stirring, homomixer stirring, ultrasonic stirring, or the like.

  By the method for producing a dispersion liquid of the present invention, a high-concentration dispersion liquid having a silica concentration of 15% by mass can be produced stably. It is particularly suitable for a high concentration of 18% by mass or more.

  Further, in order to make the silica concentration in the dispersion higher, a method of adding silica fine particles stepwise can be employed.

  The silica dispersion of the present invention can be applied to various uses as described above, and is particularly suitable for use as silica fine particles constituting the ink receiving layer of an ink jet recording sheet.

  A silica dispersion was prepared as follows. In addition, a part represents a mass part.

Example 1
<Dispersion formulation>
Water 430 parts Modified ethanol 22 parts Polydiallylamine derivative cationic polymer 3 parts (Dimethyldiallylammonium chloride homopolymer, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Charol DC902P, average molecular weight 9000)
100 parts of fumed silica (average primary particle diameter 7 nm, specific surface area by the BET method: 300m ² / g)

  A cationic polymer was added to water and denatured ethanol as a dispersion medium, and then vapor phase silica was added and premixed to prepare a silica slurry. Next, this silica slurry was treated once with a high-pressure homogenizer to prepare a silica dispersion having a silica concentration of about 18% by mass.

Example 2
A silica dispersion was prepared in the same manner except that a cationic polymer of the following chemical formula 5 (average molecular weight 10,000) was used instead of the cationic polymer of the polydiallylamine derivative in the dispersion formulation of Example 1.

Comparative Example 1
A silica dispersion was prepared in the same manner except that the cationic polymer was removed from the dispersion formulation of Example 1 above.

  The dispersions of Examples 1 and 2 and Comparative Example 1 were stored over time, and the aggregation state and the sedimentation state were observed. As a result, Example 1 did not cause aggregation / sedimentation even in 2 months, Example 2 showed slight aggregation / sedation in 1 month, and Comparative Example 1 caused aggregation / sedimentation in 6 days.

Claims (3)

  In the method for producing a silica dispersion in which silica fine particles are dispersed in a dispersion medium, the silica fine particles are gas phase method silica having an average primary particle size of 3 to 15 nm, and mainly composed of water and a cationic polymer having an average molecular weight of 50,000 or less. A method for producing a silica dispersion, comprising: adding and mixing silica fine particles to a dispersion medium to which silica is added to produce a silica slurry, and then dispersing the silica slurry with a disperser.   The method for producing a silica dispersion according to claim 1, wherein the silica concentration of the silica dispersion is 18% by mass or more.   The method for producing a silica dispersion according to claim 1 or 2, wherein the cationic polymer is a cationic polymer having a structural unit of a polydiallylamine derivative.