JPH04240110A - Production of celled silica particles - Google Patents

Abstract

PURPOSE:To control particle diameters and particle diameter distribution of spherical silica gel with good packing property and non-agglomerate by specifying agitation power required and retention time in a suspension process in obtaining powder silica by the wet method. CONSTITUTION:When mixed liquid of ester silicate and water is made to be suspended in an organic liquid non compatible with it in the presence of a disperse stabilizer, ester silicate is hydrolyzed to produce gelled silica particles. In this method, the suspension process is performed with >=0.1A/m<3> agitation required and <=10min retension time. Particle diameters and particle diameter distribution are controlled within very small particle diameters, especially within the range of <=20mum particle diameters to obtain silica gel particle which have high purity and sphericity without agglomerate and consequently have good packing property, and silica gel particles formed by sintering the former. Since agitation is insufficient to form uniform emulsion at <0.1A/m<3> agitation power required and the gelation of liquid drops suspended starts at >10min retention time, part of the gel particles are crushed or agglomerated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to spherical silica gel particles that are free from agglomeration, have good dispersibility, and are highly pure, as well as a method for obtaining silica particles. The silica gel particles and silica particles obtained by the present invention are used as fillers and catalyst carriers in various fields such as ceramic raw materials and fillers for resin sealing of semiconductor elements such as ICs and LSIs.

0002

[Prior Art] One use of silica particles is IC, L
There are fillers for plastic encapsulation of semiconductor devices such as SI. This is because in highly integrated semiconductor devices, the heat-molded encapsulant contracts when cooled, causing harmful effects if stress is applied to the device, so silica with a small coefficient of thermal expansion is mixed into the encapsulant. This is because the coefficient of thermal expansion of the entire sealing material is lowered. Conventionally, silica particles made by crushing and classifying natural silica stone have been mainly used, but when the degree of accumulation becomes high, the sealing material, especially the radiation from the silica particles, can destroy the memory and cause malfunctions, so uranium There is a demand for fillers that contain less radioactive impurities such as thorium. Furthermore, high-quality natural silica stone is becoming scarce, and in order to meet the increasing demand and provide a stable supply of high-quality fillers, it is desired to develop a method for producing high-purity synthetic silica particles.

Conventionally, methods for synthesizing high-purity silica particles include a dry method in which high-purity silicon halide is decomposed with an oxygen/hydrogen flame, and a method using silicate ester and water as described in JP-A-58-176136. A wet method in which a mixed solution of is dispersed and suspended in a liquid that is incompatible with the solution, a silicic acid ester is hydrolyzed and polymerized to synthesize a granular gel, and this is further calcined to obtain granular silica. There is. However, the silica particles obtained by the dry method have an average particle size of 0.1
Since it is as fine as micrometers or less, it has poor filling properties into the encapsulant resin as it is, and there is a problem that steps such as granulation and firing are required. In addition, in the wet method, in the process of gelling suspended particles of a mixed solution of silicate ester and water dispersed or suspended in a liquid, the suspended particles are subject to the progress of the hydrolysis and polymerization reaction of the silicate ester. In order to pass through a viscous state,
During this process, particles coalesce due to adhesion, and aggregated gel particles are inevitably generated. The agglomerated gel particles maintain their shape even after firing, and since the particles have a distorted shape, they have poor filling properties into a matrix such as a resin, and are therefore unsuitable as a filler.

Therefore, in order to solve these problems, the present inventors first carried out suspension polymerization of a mixed solution of silicate ester and water in a solvent liquid that is incompatible with the mixed solution. It was discovered that if a specific ethyl cellulose is present in the liquid, it is possible to prevent the suspended particles from coalescing due to adhesion, and it is possible to obtain spherical silica gel particles with no agglomeration, and has filed a patent application (Japanese Patent Application Laid-Open No. 1999-1-1992). 69
508 Publication).

[0005]

[Problems to be Solved by the Invention] However, even in this method, spherical particles can be produced by suspension polymerizing a mixed solution of silicate ester and water in a solvent liquid that is incompatible with the solution. Small particle size, especially 20μm
It was very difficult to control the particle size and particle size distribution in the following particle size range. Therefore, as a result of further studies, the present inventors found that suspension polymerization of a mixed solution of silicate ester and water was carried out in a solvent liquid that was incompatible with the mixed solution and in the presence of a specific organic polymer. The present invention was achieved by discovering that if suspension polymerization is not carried out under specific conditions, it is possible to prevent the suspended particles from coalescing due to adhesion and to obtain spherical silica gel particles with no agglomeration. That is,
An object of the present invention is to provide a method for producing spherical silica gel particles having no agglomeration and therefore having good filler properties and high purity, with highly controlled particle size and particle size distribution.

[0006]

[Means for Solving the Problems] The object of the present invention is to suspend a mixture of a silicate ester and water in an organic liquid that is substantially incompatible with the mixture in the presence of a dispersion stabilizer, In a method for producing gel-like silica particles by hydrolyzing a silicate ester, the suspension step is performed using a stirring power of 0.1 kW/m.
This can be achieved by carrying out the reaction under conditions of 3 or more and a residence time of 10 minutes or less. The present invention will be explained in detail below.

Typical examples of the silicic acid ester used in the present invention include lower alkyl esters of orthosilicic acid such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, and condensates thereof. In addition, alkoxyalkylsilanes such as trimethoxymethylsilane, dimethoxydimethylsilane, triethoxydiethylsilane, diethoxydiethylsilane, and condensates thereof may be used.

[0008] The organic liquid used as the dispersion medium may be any organic liquid as long as it is substantially incompatible with the mixed solution of silicate ester and water and can dissolve the cellulose ester and cellulose ether described below. Usually hydrocarbons or halogenated aromatic hydrocarbons are used. The hydrocarbons are preferably aromatic hydrocarbons, alicyclic hydrocarbons, or aliphatic hydrocarbons having 6 to 10 carbon atoms. Chlorinated benzene is preferred as the halogenated aromatic hydrocarbon. Particularly suitable organic solvents are benzene, toluene,
These include xylene, cyclohexane, methylcyclohexane, cyclooctane, decalin, n-hexane, n-heptane, n-octane, n-decane, chlorobenzene, dichlorobenzene, cymene, and cumene.

The cellulose ester or ether used in the present invention acts as a dispersion stabilizer, and is an oil-soluble cellulose such as cellulose acetate butyrate, ethyl cellulose, or ethyl hydroxyethyl cellulose, which is insoluble in water and soluble in the organic solvent. Mention may be made of esters or cellulose ethers. In the method of the present invention, a dispersion stabilizer is first dissolved in the organic liquid and used as a dispersion medium. The amount of the dispersion stabilizer added is in the range of 0.05 to 10% by weight, preferably 0.2 to 5% by weight, based on the total amount of the dispersion medium. The amount of dispersion stabilizer added is 0.05
If it is less than 10% by weight, the agglomeration prevention effect is insufficient.
If it exceeds % by weight, a portion tends to remain undissolved, which is inefficient.

Separately, a raw material solution is prepared by mixing silicate ester and water. The blending ratio of silicate ester and water at this time is not particularly limited, but it is preferably blended in a range of 1 to 10 times the theoretical amount of water required for complete hydrolysis and polymerization of the silicate ester. For example, the theoretical amount of water for 1 mole of silicate tetraalkyl ester is 2 moles. If the amount of water added to the silicate ester is less than 1 times the theoretical amount of water required for complete hydrolysis and polymerization of the silicate ester, the silicate ester will not be sufficiently hydrolyzed and polymerized, resulting in a low yield of silica. decreases. Conversely, if the amount of water added to the silicate ester is more than 10 times the theoretical amount of water required for complete hydrolysis and polymerization of the silicate ester, the strength of the gel formed will be low and particles will form during the drying and baking process. is easily destroyed. In addition, even if the amount of water to silicate ester is within the above range, mixing silicate ester and water may not mix uniformly and cause two-phase separation, but continue stirring the mixed solution or add alcohol. By doing so, a homogeneous solution can be obtained. If the mixed solution is continued to be stirred, the hydrolysis reaction of the silicate ester proceeds and alcohol is produced. The alcohol is a common solvent with the silicate ester and water, each forming a homogeneous solution. That is, since the mixed solution of silicate ester and water becomes a homogeneous solution by the production of alcohol or the addition of alcohol, this homogeneous solution is used as the raw material solution.

[0011] A catalyst may also be added in order to shorten the time required for the preparation of the raw material solution and the subsequent suspension step. As the catalyst, acidic catalysts such as hydrochloric acid, nitric acid, sulfuric acid, acetic acid, and oxalic acid, and basic catalysts such as ammonia, amine, and caustic alkali can be used, but hydrochloric acid or ammonium is usually used most commonly. Next, the raw material solution prepared as described above and the dispersion medium in which the dispersion stabilizer was dissolved were heated at 0.1 kW.
/m3 or more preferably 0.2 to 2000kW/m3
The mixture is mixed and stirred with the required stirring power to form an emulsion in which the raw material solution is dispersed as suspended droplets. The residence time in this suspension step is 10 minutes or less, preferably 0.1 to 5 minutes. In the method of the present invention, it is not preferable that the power required for stirring in the suspension step is less than 0.1 kW/m3 because stirring will not be performed sufficiently and the raw material solution and dispersion medium will separate and a uniform emulsion will not be obtained. Further, if the residence time in the suspension step is longer than 10 minutes, gelation of the suspension droplets will begin, which is not preferable, as some gel particles will be crushed or aggregated.

In the method of the present invention, any method may be used as long as the suspension step can be carried out under the above conditions, but when the present invention is carried out industrially, it is particularly advantageous to use a continuous mixing and dispersing device. Continuous mixing and dispersing devices are, for example, pipeline mixers for mixing and emulsion polymerization, which mix and emulsify the dispersion medium and dispersoid finely and homogeneously using strong shearing force generated in homogeneous minute gaps. A type container is used. After the suspension step is completed, the suspension droplets are subsequently gelled to produce spherical gel particles. Gelation is usually carried out by maintaining the temperature at a temperature above the melting point of the dispersion medium, preferably above 30° C. and below the boiling point of the dispersion medium. At this time, gentle stirring may be performed if necessary, and
It is also possible to maintain the temperature above the boiling point of the dispersion medium under pressurized conditions.

The generated gel particles can be separated from the reaction solution by decantation or filtration, and the dispersion stabilizer attached to the particle surface can be dissolved and washed with an organic solvent, followed by drying, or directly heated at 300 to 400°C. Silica gel particles are obtained by heating to a certain degree to burn and decompose the dispersion stabilizer. The silica gel particles are obtained as spherical particles without agglomeration, and can be used as catalyst carriers as they are, but are usually fired at a temperature of about 1000° C. to form silica glass. Even when fired, no aggregation occurs and spherical silica particles can be obtained.

[0014] In the method of the present invention, a silicate ester that can be easily purified by distillation or the like is used as a raw material, and furthermore, silica particles can be directly obtained by synthesizing silica gel particles and then firing them. There is no need for processes such as pulverization that can easily introduce impurities, and therefore highly pure silica particles can be easily obtained.

[0015]

EXAMPLES The present invention will be explained in detail with reference to Examples. The required stirring power and the residence time in the suspension step as used in the present invention were determined as follows.

(1) Power required for stirring per unit volume The power required for stirring can be determined from the following equation.

p=Np ・ρ/gc ・n3 ・d5 p: Required power for stirring [kg・m/sec] Np: Constant determined by the shape of the stirring blade ρ: Density of liquid [kg/m3] gc
:Gravity conversion factor [kg・m/kg・sec 2]n
: Stirring speed [1/sec2]d
: Blade length of stirring blade [m] The required power for stirring per unit volume is obtained by dividing p obtained from the above formula by the internal volume of the stirrer v.

P=p/v/101.972P: Required stirring power per unit volume [kW/m3]p: Required stirring power [kg・m/sec]v: Stirrer internal volume [m3] However, 1kW=101. 972kg・m/sec (2
) Residence time in the suspension process T=v/m v: Internal volume of the stirrer [m3] m: Flow rate at which the liquid to be stirred is fed into the stirrer [m3]
/min] Note that the residence time in the suspension step in batch-type stirring as shown in Comparative Example 1 below refers to the time during which stirring is continued. In addition, the particle size distribution of the manufactured silica particles shows that the cumulative weight from the minimum particle size is 75% in the cumulative weight curve diagram against particle size.
The particle size at the point is divided by the particle size at the point where the cumulative weight from the minimum particle size is 25% (d75/d25). In other words, the smaller d75/d25 is, the more uniform the particle diameters are.

Comparative Example 1 In a reaction vessel with an internal volume of 0.6 m3 equipped with an anchor-type stirring blade,
As a dispersion stabilizer, 0.7 kg of ethyl cellulose containing 49% of ethoxy groups based on the total weight and 24 kg of cyclohexane were used as dispersion stabilizers.
3 kg was added thereto and heated and stirred (27 rpm) at 60° C. for 1 hour to prepare a solution in which ethyl cellulose was sufficiently dissolved and used as a dispersion medium. Next, 12.5 kg of tetramethoxysilane and 7.5 kg of distilled water were stirred at 40° C. for 75 minutes to obtain a raw material solution in which tetramethoxysilane and distilled water were uniformly dissolved. The raw material solution was added to the dispersion medium with stirring at 27 rpm, and the stirring was continued at 60° C. for 2 hours to effect gelation by hydrolysis and polymerization of tetramethoxysilane to obtain a gel particle-dispersed slurry. Next, the gel particles were separated by decantation, washed with acetone, and dried at 200° C. for 24 hours to obtain powdered silica gel. Further, the silica gel was fired in air at 1000° C. for 2 hours to obtain powdered silica. Table 1 shows the shape, agglomeration state, average particle size, and particle size distribution of the silica.

Examples 1 to 4, Comparative Examples 2 to 3 As a dispersion stabilizer, 97 g of ethylcellulose containing 49% of ethoxy groups based on the total weight was added to 23.19 kg of p-cymene (p-isopropyltoluene) at 60°C. The mixture was heated for 15 minutes to sufficiently dissolve the ethyl cellulose and use it as a dispersion medium. Separately, 4.26 kg of tetramethoxysilane and 2.02 kg of distilled water were stirred at 40° C. for 75 minutes to obtain a raw material solution in which tetramethoxysilane and distilled water were uniformly dissolved. Next, the dispersion medium was introduced into a pipeline homo mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) so that the volume ratio of the dispersion medium to the raw material solution 1 was 4.5. By mixing under certain conditions, an emulsion in which the raw material solution was dispersed as suspended droplets was obtained. The obtained emulsion is
Further, by heating at 60° C. for 30 minutes, tetramethoxysilane was gelled by hydrolysis and polymerization to obtain a gel particle dispersion slurry. Next, the gel particles were separated by decantation, washed with acetone, and then dried at 200° C. for 24 hours to obtain powdered silica gel. Further, the silica gel was fired in air at 1000° C. for 2 hours to obtain powdered silica. Table 1 shows the shape, agglomeration state, average particle size, and particle size distribution of the silica.

Examples 5 to 7 97 g of ethylcellulose containing 49% of ethoxy groups based on the total weight as a dispersion stabilizer was added to 23.19 kg of p-cymene (p-isopropyltoluene), and the mixture was heated at 60°C for 15 minutes.
The mixture was heated for 1 minute to fully dissolve the ethyl cellulose and use it as a dispersion medium. Separately, 3.30 kg of condensate obtained by partially hydrolyzing tetramethoxysilane (SiO2 content 51% by weight)
and 1.27 kg of distilled water and 1.12 kg of methanol at 40
The mixture was stirred at ℃ for 20 minutes to obtain a raw material solution in which the tetramethoxysilane condensate, distilled water, and methanol were uniformly dissolved. Next, the dispersion medium was introduced into a pipeline homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) so that the volume ratio of the dispersion medium to the raw material solution 1 was 4.3. By mixing under the condition of 60 hours, an emulsion in which the raw material solution is dispersed as suspended droplets is obtained.
A gel particle dispersion slurry was obtained by heating at ℃ for 30 minutes. Spherical gel particles with no agglomeration were produced in the gel particle dispersion slurry. Next, the gel particles were separated by decantation, washed with acetone, and then heated at 200°C.
After drying for 24 hours, a spherical silica gel with no agglomeration was obtained. Furthermore, the silica gel particles were calcined in air at 1000° C. for 2 hours to obtain silica particles. The silica particles had no agglomeration and were perfectly spherical. The average particle size is shown in Table 1.

Examples 8 and 9 As a dispersion stabilizer, 63 g of ethyl cellulose containing 49% of ethoxy groups based on the total weight was mixed with 21.0 g of cyclohexane.
The procedure was the same as in Examples 1 to 4 except that the dispersion medium was a solution in which 7 kg of ethyl cellulose was sufficiently dissolved by heating at 60° C. for 1 hour. The results are shown in Table 1.

[0023]

[Table 1]

[0024]

Effects of the Invention: The silica gel particles obtained by the present invention and the silica particles obtained by firing the silica gel particles have high purity, have no agglomeration, are perfectly spherical, and therefore have good filling properties, and can be used for high-purity ICs. It can be used as a filler for sealants, a raw material for high-purity ceramics, a catalyst carrier, etc., and has great industrial value.

Claims (2)

[Claims] Claim 1: A mixture of a silicate ester and water is suspended in an organic liquid that is substantially incompatible with the mixture in the presence of a dispersion stabilizer, and the silicate is hydrolyzed to form a gel. In the method for producing shaped silica particles, the suspension step comprises:
Required stirring power: 0.1kW/m3 or more and residence time: 10
A method for producing gel-like silica particles characterized by carrying out under conditions of less than 10 minutes. 2. The method according to claim 1, wherein a mixed solution of a silicate ester and water, an organic liquid that is substantially incompatible with the mixed solution, and a dispersion stabilizer are continuously supplied to a continuous mixing and dispersing device. Continuous production method of gel-like silica particles, characterized by carrying out a suspension step