JPH08183610A - Production of colored spherical silica - Google Patents

Abstract

PURPOSE: To easily obtain fine colored spherical silica having a narrow particle size distribution and a very low alkali metal content by forming spherical silica gel under specified conditions and firing it under prescribed conditions. CONSTITUTION: A silicon alkoxide (e.g. methyltrimethoxysilane) contg. >=30mol% silicon alkoxide having a nonhydrolyzable org. substituent is hydrolyzed in a state practically free from an alkali metal, e.g. in an aq. ammonia soln. and the resultant spherical silica gel is fired at the thermal decomposition temp. of org. matter in the silica gel or above in a state in which oxygen is rare. An org. compd. and free carbon formed by the thermal decomposition of org. matter in the silica gel are confined in the resultant silica and color the silica. The hue of coloration can be selected in accordance with the degree of thermal decomposition and a higher degree of thermal decomposition generally gives higher blackness.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the production of black spherical silica in which very fine carbon particles are uniformly dispersed.

[0002]

2. Description of the Related Art Conventionally, there is known a method of hydrolyzing an alkyl silicate in a reaction system in which aqueous ammonia and water for hydrolysis are added to alcohol to produce spherical silica having a narrow particle size distribution of submicron or 1 micron level. Has been. Here, in order to obtain a spherical silica having a larger particle size and a narrow particle size distribution, for example, in Japanese Patent Publication No. 2805/1990, an alkali metal is present in the above hydrolysis system so that the particle size becomes uniform at 1 micron or more. It is proposed to make silica particles.

As a method for producing black spherical silica, which is particularly useful for spacers for liquid crystal display elements, etc.
In Japanese Patent Publication No. 279209-, a spherical gel particle is prepared by a sol-gel method from an alkyl silicate consisting of all hydrolyzable substituents represented by ethyl silicate by a sol-gel method in the presence of alcohol, water, ammonia and caustic soda. It has been proposed to carbonize unreacted alkyl groups and alcohol remaining in the dried gel by firing to produce black spherical silica.

[0004]

However, since silica particles made from a system in which an alkali metal is present adsorb a large amount of alkali metal inside silica, they are used for electronic material applications where alkali metal must be avoided. Can not. Therefore, Japanese Patent Publication No. 3-279209, which applies the above technique to the production of silica particles, requires a great deal of process treatment to remove the alkali metal adsorbed inside the silica particles. That is, silica gel particles are produced by a sol-gel method under the same conditions as in Japanese Examined Patent Publication No. 2-2805, or the produced particles are grown and then made into dry gel particles. However, a large amount of alkali metal is contained in the dry gel particles. Since it has been adsorbed, it needs a dealkalizing metal treatment. 1) After suspending the white particles in methanol, an aqueous nitric acid solution is added, and after stirring for a long time, the mixture is left to stand and sediment, and decanted. Further, the procedure of suspending in methanol, leaving still and decanting is repeated 3 times, and then dried.

2) The powder treated as described above is suspended again in methanol, a mixed solution of an aqueous solution of hydrogen fluoride and methanol is added to this slurry, and the mixture is stirred for a long time. Then, it is allowed to stand still, decant, and further add methanol. Repeat suspension, standing and decantation. Dry again and powder
After the dealkalizing metal treatment by such a complicated process, the particles are fired to thermally decompose the organic matter remaining in the gel particles to blacken the carbonization. That is, such a large amount of solvent is used and complicated treatment is carried out until the alkali metal is reduced to 100 ppm or less. Such a complicated treatment step is essential by using an alkali metal such as caustic soda and caustic potash during the production of the particles in order to obtain particles having a large particle size and a narrow particle size distribution.

[0006]

Therefore, the present inventors have developed a simple method without such complicated processing steps, which has a small alkali metal content, a large particle size and a narrow particle size distribution, and is colored. An intensive study was conducted on a method capable of producing spherical silica. As a result, caustic soda was added to the catalyst during particle production.
Alkali metal such as potassium hydroxide is not used at all, a volatile alkaline catalyst is used, and a silicon alkoxide having a non-hydrolyzable alkyl group or phenyl group is used as a raw material, and water containing the above alkaline catalyst is used. If the interfacial reaction is carried out in a heterogeneous system, spherical silica having a large particle size of more than 1 micron and having a uniform particle size containing no alkali metal can be produced. The present invention has been found to contain a large amount of alkyl groups or phenyl groups in the particles, and by thermally decomposing this organic group, free carbon is precipitated in the silica particles to obtain colored silica. did. That is, the gist of the present invention is a spherical silica gel obtained by hydrolyzing a silicon alkoxide containing at least 30 mol% or more of a silicon alkoxide having a non-hydrolyzable organic substituent in a state in which an alkali metal is substantially absent. ,
It is a colored spherical silica obtained by firing in a state where oxygen is diluted at a temperature higher than the thermal decomposition temperature of organic substances in silica gel.

[Raw Material] The silicon alkoxide usable in the present invention may be any silicon alkoxide having two or more alkoxy groups directly bonded to a silicon atom. Specifically, for example, the general formula

[0008]

Embedded image SiR _n (OR ′) _4-n

However, R is CH ₃ , C ₂ H ₅ , C
Alkyl groups such as ₃ H ₇ , C ₄ H ₉ , CH ₂ ═CH, C ₆ H _{5 and the} like, phenyl group R ′ is a C ₁ -C ₄ alkyl group, n is a silicon alkoxide represented by 0, 1 or 2. Among these, 1 type (s) or 2 or more types can be used. here,
In the present invention, at least 50 mol% or more of the above-mentioned silicon alkoxides are those having a non-hydrolyzable organic substituent, that is, one or two or more having n = 1 or 2 in the above general formula. N = 0 in the above general formula
An alkoxide such as Si (OCH ₃ ) ₄ , Si
(OC ₂ H ₅ ) ₄ etc. 4 functional type decomposable alkoxide 7
It may be added in the range of 0 mol% or less, but 50 mol% or less is preferable in order to obtain sufficient coloring. Over 70 mol% 4
When the functional type-separating alkoxide is added, the organic component remaining in the obtained silica is reduced, and as a result, the organic component remaining in the silica particles after firing and / or the residual carbon amount is reduced, resulting in a sufficient blackness. Can't get Besides, it may be appropriately selected within the above range according to the required color tone and blackness.

[Method of forming a sphere] The above general formula

[0011]

Embedded image SiR _n (OR ′) _4-n

1 of the silicon alkoxides represented by
In the case of using various types, spherical silica gel can be obtained by directly performing hydrolysis according to a known method. Further, in the case of using a mixture of two or more kinds of silicon alkoxides of the above general formula, it is necessary to combine those having a similar hydrolysis rate. If the hydrolysis rates are significantly different, particles having a uniform composition cannot be obtained. That is, the alkoxide having a high hydrolysis rate forms particles first, and then the slow alkoxide forms particles. In such a case, the same result as mixing individual particles is obtained, which is not desirable for obtaining uniform particles.

In the present invention, these silicon alkoxides are hydrolyzed in the substantially absence of alkali hydroxide. As a specific method of hydrolysis, for example, a reaction vessel equipped with a stirrer is added with a silicon alkoxide containing a non-hydrolyzable organic substituent in the presence of an alkaline catalyst such as an aqueous ammonia solution to separate into an aqueous phase and an oil phase. Charge in the state. As the catalyst that can be used in this case,
In addition to ammonia, monomethylamine, monoethylamine, ethanolamine, dimethylamine, diethylamine, diethanolamine, propylamine, dipropylamine, dipropanolamine, propanolamine, etc., ammonia or amine-based catalysts, the resulting sillin particles have a uniform shape. Therefore, the particle size distribution is narrow and impurities can be prevented from remaining, which is desirable. Then, while stirring the two-layer solution at an appropriate speed, the hydrolysis and condensation reaction between the alkoxide and the alkaline aqueous solution is gradually performed at the interface.

As the reaction proceeds, spherical particles are produced and migrate to the alkaline aqueous solution side. The stirring speed at this time determines the size of the generated particles. If the stirring speed is remarkably high, the contact area of the interface remarkably increases, and as a result, the reaction abruptly occurs, the particles are likely to be in an agglomerated state, and spherical particles may not be obtained in some cases.

The relationship between the stirring speed and the particle size is also related to the shape of the stirrer, which cannot be said to be unequivocal, but within a certain range, the particles tend to be larger when the stirring speed is higher. still,
At the time of hydrolysis, a solvent such as alcohol that dissolves in water is not substantially present, and by carrying out in a two-phase mixed state, it is possible to obtain silica gel particles having a large particle size and a narrow particle size distribution, and thus colored spherical silica. .

[Removal of Particles] The particles are removed from the liquid after the reaction by a commonly used method such as centrifugation or filtration. The wet gel taken out is preferably dried in advance at 100 to 200 ° C. in a dryer or the like to prevent strong aggregation and sintering in the firing process, which is desirable. When the dried gel (dry gel) is agglomerated, it is advisable to loosen the agglomerates of the particles with a disintegrator such as a jet mill to give a white powder. The gel thus obtained is one in which organic substances derived from the alkoxy group, the alkyl group, the phenyl group, etc. of the raw material alkoxide are contained inside.

[Firing] Firing was produced as an organic substance in these silica gels, that is, an alkyl group which is a non-hydrolyzable organic substituent derived from the raw material silicon alkoxide, a phenyl group, an unhydrolyzed alkyl group, and a by-product of hydrolysis. In order to thermally decompose organic substances such as alcohols and leave them in the state of carbon in the particles, oxygen is diluted at a temperature higher than the temperature at which these organic substances burn.

The term "diluted oxygen" as used herein means that an organic substance in silica gel or a substance produced by decomposing the organic substance in the silica is not oxidized by oxygen in the gas phase at a temperature above the decomposition temperature of the organic substance. Refers to the oxygen concentration. The upper limit of the oxygen concentration is generally 5 vol, although it depends on the raw materials used and the susceptibility to oxidation of thermal decomposition products.
%, Preferably about 1 vol%.

The temperature at which the organic substance thermally decomposes varies depending on the type of the organic substance, but in most cases, the thermal decomposition starts in air at about 300 ° C and ends at about 600 ° C. However, the thermal decomposition in the state where oxygen is lean starts at about 500 ° C and ends at about 900 ° C. For this reason, the temperature range in which oxygen must be maintained in a lean state is the temperature at which thermal decomposition starts in air, but is not limited, but in general, pores existing in silica above 300 ° C. It is until the organic compound and free carbon generated by thermal decomposition of the organic substance in the collapsed silica gel are confined in the silica. The temperature at which the pores existing in silica are closed depends on the pore diameter and the holding time. By such a firing step, the organic compound and free carbon produced by the thermal decomposition of the organic matter in the silica gel are confined in the silica, and the silica is colored. It is also possible to select the hue of coloring depending on the degree of thermal decomposition. That is, the higher the degree of thermal decomposition, the higher the blackness in general.

As a method for keeping oxygen in a lean state,
Before firing, the inside of the container is replaced with an inert gas such as nitrogen gas, and then the container is covered. Alternatively, an inert gas such as nitrogen gas is circulated in the container during firing or in the firing furnace. As a simple method, it is also effective to fill the container with a large amount of dry gel or to reduce the void ratio in the container with the lid. In particular, this object is achieved only by setting the packing rate of particles having a particle size of 2 microns or more to 50% or more and closing the lid.

[0021] This means that as the firing temperature rises, the air inside expands out of the vessel, resulting in a decrease in the oxygen content. The oxygen remaining in the container reacts with the organic matter on the surface of the dry gel at 300 ° C. or higher and oxygen is consumed, the oxygen concentration in the container is reduced, and the gas generated by oxidizing the organic matter on the surface is further oxygen in the container. Pushes out. As a result, the gas phase portion in the container becomes lean in oxygen.

According to the differential thermal analysis, the thermal decomposition in a lean oxygen state starts at about 500 ° C., and the amount of generated gas reaches a maximum at 700 ° C. to 800 ° C. Rapid gas generation causes problems such as blowing out powder from the container. For this reason,
It is desirable to maintain the temperature near 600 ° C. at which thermal decomposition occurs in a state where oxygen is diluted, to sufficiently decompose organic substances, remove generated gas, and then raise the temperature to perform stable firing.

The heating rate is not particularly limited, but for example, 100 ° C./h to 300 ° C./h is practical. This is because if it is too slow, it will take a long time, and if it is too fast, it will burden the device. Further, the temperature holding time in a state where oxygen is diluted has a relationship with the amount of firing, but it is usually about 1 hour or more until the carbon is confined, that is, specifically.

The dried gel generally starts to shrink at 600 ° C. or higher, and the pores present in the dried gel gradually begin to collapse. The speed at which the pores collapse is dependent on the pore size and temperature. The pores collapse faster as the temperature increases.
At 800 ° C or higher, the speed becomes much faster. The size of the pores depends on the conditions for producing the particles, but is generally several tens of angstroms.

If the calcination is stopped at around 600 ° C., spherical silica containing fine carbon in the particles and having a large specific surface area with pores remaining can be obtained. When the calcination temperature is raised to about 800 ° C., the pores are almost eliminated and the specific surface area almost agrees with the theoretical value. The color of silica changes depending on the temperature when firing. For example, at 600 ° C to 800 ° C, it is brown and 800 ° C
At ~ 1000 ° C, it changes to brown to blackish brown, and at 1000 ° C or higher, it becomes black.

It is considered that the color changes depending on the decomposition state of the organic matter contained in the dry gel, that is, the degree of carbonization. Thus, the firing conditions may be selected according to the desired coloring. When the temperature is heated above 1400 ° C,
Since a part of the particle surface is sintered and becomes an agglomerated state, it is generally preferable to perform firing at a temperature of 1400 ° C. or lower.

The colored spherical silica thus obtained can have a desired particle size depending on the stirring conditions during the production of silica gel particles, and those having a particle size of 1 μm or less and particles having a particle size of more than 1 μm can be used depending on the purpose. Obtainable. In addition, it does not substantially contain an alkali metal, and the total is 100 ppm or less, 50
It is possible to easily obtain one having a content of ppm or less and 1 ppm or less.

[Use] The colored spherical silica of the present invention thus obtained is used for electronic materials containing substantially no alkali metal, for example, for keeping a constant gap between substrate glasses of a liquid crystal display device. It is preferably used for spacers and the like. In addition, carbon black is generally used in liquid encapsulating materials that require hiding properties, but when carbon black is added, the thixotropy of the liquid encapsulating material is affected by the large specific surface area. Therefore, there are some which do not have satisfactory physical properties.

In such a case, when the colored spherical silica of the present invention is used, since the coloring component is in the silica, it is not affected by the specific surface area at all, and the hiding property by the coloring component, the specific surface area of silica and the performance of the filler are Can be expressed simultaneously.
Further, in the field of electronic materials, high temperature treatment is required during the treatment step, and in applications requiring concealability, carbon black will be lost by oxidation during high temperature treatment, but if the colored spherical silica of the present invention is used, Even in an oxygen atmosphere, carbon in the particles does not disappear by oxidation, which is preferable.

[0030]

EXAMPLES The present invention will be described below with reference to examples. Parts and% are parts by weight and% by weight, unless otherwise specified. [Example 1] 4000 parts of an aqueous ammonia solution (consisting of 3 parts of 28% ammonia water and 3997 parts of water) was placed in a four-necked flask equipped with a thermometer, a reflux condenser and a stirrer, and 100 r.
Stirred at pm for 10 minutes to make uniform aqueous ammonia. 700 parts of methyltrimethoxysilane was added rapidly with stirring at 5 rpm so that it would not mix with the aqueous phase.

The upper layer is a methyltrimethoxysilane layer, and the lower layer is an ammo water layer. Then 30
The stirrer was rotated with rpm to carry out hydrolysis and condensation reaction at the interface between methyltrimethoxysilane and aqueous ammonia while maintaining the two-layer state. As the reaction progresses,
The reaction product floated in the lower aqueous phase and became cloudy. The upper oil phase disappeared. In order to complete the reaction, the temperature was raised from room temperature to 60 ° C., stirred for 3 hours, and then cooled to room temperature.

The reaction product was filtered with a vacuum filter. The cake was dried by placing it in an electric dryer at 200 ° C. Since the obtained dried product was agglomerated, it was crushed using a jet mill crusher to obtain a white powder. When the particles were observed with a scanning electron microscope, they were found to have an average particle diameter of 4.5 μm and had a uniform particle diameter.

70% of the dried gel powder was filled in a quartz container, a quartz lid was placed on the container, and the container was placed in an electric furnace. The electric furnace is 1
It was heated to 600 ° C. at a rate of 00 ° C./hour and kept at this temperature for 4 hours. Then, it was again heated to 1000 ° C. at a rate of 100 ° C./hour. After holding at 1000 ° C. for 1 hour, the heater was turned off and naturally cooled.

When the inside of the quartz container taken out from the electric furnace was observed, black particles were entirely observed and no aggregation due to firing was found. When the particles were observed with a scanning electron microscope, they had an average particle diameter of 3.5 μm and had a uniform particle diameter, and no appearance of sintering of the particles was found. An electron micrograph of the obtained particles is shown in FIG. When carbon analysis was performed on the black particles by LECO (manufactured by Japan Analyst), the carbon content was 10%.

When X-ray diffraction analysis was performed, a gentle pattern was drawn on the whole and it was amorphous. After decomposing and removing the silica from the spherical silica with an aqueous solution of hydrogen fluoride, the alkali metal was analyzed by an atomic absorption method. As a result, as shown in Table 1, the content of the alkali metal was extremely low. Also,
When this decomposed solution was analyzed by the ICP method, as shown in Table 2, the levels of other metals were similarly low.

[0036]

[Table 1]

[0037]

[Table 2]

Example 2 Basically the same operation as in Example 1 was carried out, the concentration of ammonia water and the stirring speed were changed, and 6.5 μm dry gel particles were prepared.
Firing at 0 ° C. for 1 hour gave 5.5 micron black spherical silica. When the contained alkali metal was measured by the same method as in Example 1, it was as shown in Table 3.

[0039]

[Table 3]

Example 3 The same procedure as in Example 1 was repeated except that the starting materials were charged and the reaction was carried out at a reduced stirring speed to give a dry gel of 2 microns. This was fired at 800 ° C. for 1 hour in a lean oxygen state. The powder after firing was brown. When this powder was fired again at 1200 ° C. for 1 hour, black spherical silica having an average particle diameter of 1.5 μ was obtained. An electron micrograph of the obtained black spherical silica is shown in FIG.

[Example 4] 680 parts of water, 990 parts of phenyltrimethoxysilane and 0.2 part of acetic acid were added to a reactor equipped with a thermometer, a condenser and a stirrer to cause a hydrolysis reaction to obtain a transparent liquid. It was This was further stirred for 4 hours and then filtered to obtain a hydrolyzed liquid. Water 20 in another reactor
Add 00 parts and 100 parts of 28% ammonia water, and set the temperature to 2
The temperature was 5 ° C. When the hydrolysis solution was added thereto for 180 minutes, particles were produced and the solution became cloudy. This was centrifuged and the particles were taken out and dried at 200 ° C. When the particles were observed with a scanning electron microscope, they were spherical and had an average particle diameter of 0.1 micron. When fired in a state where oxygen was diluted in the same manner as in Example 1, black spherical silica was obtained.

[0042]

EFFECTS OF THE INVENTION According to the present invention, black spherical silica having an extremely low content of alkali metal can be easily obtained, which is suitable for applications such as electronic materials and liquid sealing materials.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle structure of the colored spherical silica obtained in Example 1.

FIG. 2 is an electron micrograph showing the particle structure of the colored spherical silica obtained in Example 3.

Claims (3)

[Claims] 1. A spherical silica gel obtained by hydrolyzing a silicon alkoxide containing at least 30 mol% of a silicon alkoxide having a non-hydrolyzable organic substituent in the absence of an alkali metal, in a silica gel. The colored spherical silica obtained by firing in a state where oxygen is diluted above the thermal decomposition temperature of the organic substance. 2. The colored spherical silica according to claim 1, which has an alkali metal content of less than 100 ppm. 3. A spherical silica gel is prepared by hydrolyzing a silicon alkoxide containing at least 70 mol% of a silicon alkoxide having a non-hydrolyzable organic substituent in the absence of an alkali metal to form a spherical silica gel. A method for producing colored spherical silica, which comprises producing black spherical silica by firing in a state where oxygen is diluted at a temperature equal to or higher than the temperature at which the organic substances therein decompose.