JP3061285B2 - Black silica particles and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to black silica particles, particularly to black silica particles useful as spacers for liquid crystal display devices.

(Prior Art and Problems to be Solved by the Invention) Silica particles are widely used for ceramic raw materials, chromatographic carriers and the like. Although they are also used as spacers for liquid crystal display elements, in recent years, instead of conventional white silica, silica particles that are not transparent, in other words, do not transmit light, have been desired to improve image quality.

As a method for obtaining black silica, a method has been considered in which an alkali metal and an organic substance are contained in silica particles and then heat treatment is performed. In this method, sintering of silica is accelerated by including an alkali metal, and carbonization of organic substances in the silica is attempted to blacken. The black silica particles obtained by this method naturally contain alkali metals and thus have disadvantages due to alkali elution, and therefore cannot be practically used as spacers for liquid crystal display elements. In order to reduce the influence of alkali elution, it is conceivable to reduce the amount of alkali at the time of heat treatment. However, in such a case, the degree of black color becomes lighter and light shielding becomes insufficient.

(Means for Solving the Problems) The present inventors have conducted intensive studies for the purpose of obtaining sufficiently black silica particles without elution of the alkali metal described above. As a result, the above object was successfully achieved, and the present invention was proposed.

That is, the present invention has an average particle diameter of 0.1 to 50 μm,
0.1% by weight of carbon, substantially free of alkali metals
Containing more than a volume resistivity of 10 ⁷ · cm or more, JIS Z870
Black silica particles, wherein the Y value according to 1 is 10% or less.

The average particle size of the black silica particles of the present invention is 0.1 to 50 μm. Black silica particles smaller than the above range are difficult to produce, and black silica particles larger than the above range are not practical because the particle growth takes too long.

In order to obtain black silica particles having a large blackness in the present invention, the average particle size is preferably 2 to 10 μm.

The black silica particles of the present invention are characterized by being substantially free of alkali metals. The phrase "contains substantially no alkali metal" means that there is substantially no problem when used as a spacer for a liquid crystal display element, and it means that the content is usually 100 ppm or less.

The black color of the black silica particles of the present invention is expressed by carbon formed by carbonizing organic matter in the silica particles. The carbon content of the silica particles of the present invention is usually 0.1% by weight or more. If this content is low, the color becomes lighter and the light shielding is insufficient, which is not preferable. The content of carbon is generally in the range of 0.1 to 7% by weight, and preferably in the range of 0.3 to 7% by weight from the viewpoint of blackness.

The degree of blackness of the black silica particles of the present invention is JIS Z8701
When expressed in terms of the Y value (%), it can be 10% or less, preferably 6% or less, and more preferably 4% or less.

Further, the black silica particles of the present invention have high electrical resistance despite containing carbon as described above. That is, the black silica particles of the present invention have a volume resistivity described later of 10 ⁷ Ωcm or more, and more preferably 10 ⁹ Ωcm.
It is also possible to obtain black silica particles having a high electrical resistance exceeding cm.

Furthermore, the particle shape of the black silica particles of the present invention observed by an electron microscope is spherical with a ratio of the major axis to the minor axis of 0.8 or more, and more preferably 0.9 or more, and the coefficient of variation (particle size) showing the variation of the particle size. Standard deviation / average particle size) is 5
% Or less, more preferably 3% or less, and are particles having excellent uniformity in particle diameter.

The black silica particles of the present invention can be suitably produced by the following method.

This is a method in which silica particles containing substantially no alkali metal are brought into contact with a fluorinating agent and an organic solvent, and then heated at a temperature of 500 ° C. or higher.

Silica particles containing substantially no alkali metal as a raw material are preferably used in the present invention because silica particles obtained by hydrolysis of an alkyl silicate represented by ethyl silicate are spherical and have a small coefficient of variation in particle diameter. However, silica particles obtained by other methods can also be used.

For hydrolysis of the alkyl silicate, a known method is employed without any limitation. For example, there is a method in which an alkyl silicate is added to a mixed solvent of water-methanol-ammonia and a mixed solvent to which an alkali metal hydroxide is added, if necessary, to carry out hydrolysis. When particles having a large particle size are required, a method is employed in which the reaction is carried out in several stages, and the generated silica particles are further grown and sequentially enlarged. When alkali metal hydroxide is used in this reaction, the silica particles formed contain up to 20% of alkali metal.
Up to and including. Black silica particles can be easily obtained by heating while containing the alkali metal, but this is not preferred because the alkali metal remains mixed in the produced black silica particles.

Therefore, in such a case, the silica particles containing the alkali metal obtained by the reaction are first treated with an acid, usually hydrochloric acid.
A method of contacting with a mineral acid such as sulfuric acid or nitric acid, followed by washing to remove alkali metals may be employed. By doing so, silica particles having an alkali metal content of 100 ppm or less can be easily obtained.

The conditions of the above-mentioned acid treatment may be appropriately selected from the concentration of the acid, the amount of the acid, and the like. Can be reduced to 100 ppm or less.

However, the lower the acid concentration and the amount of acid, the longer the acid treatment time. Therefore, the acid concentration is preferably 5% or more, and the amount of the acid is preferably at least twice the equivalent.

Silica particles substantially free of alkali metal are brought into contact with a fluorinating agent and an organic solvent. The contact with the fluorinating agent and the organic solvent may be performed simultaneously or separately. The contact with the fluorinating agent is performed by immersing the silica particles in a solution of the fluorinating agent dissolved in water or an organic solvent. When a solution in which a fluorinating agent is dissolved in an organic solvent is used, contact with the fluorinating agent and the organic solvent can be performed simultaneously. The concentration of the fluorinating agent in water or an organic solvent is 0.1 to 10% by weight, and the amount of the fluorinating agent is preferably equivalent to silica to reduce the dissolution of silica particles and to sufficiently perform blackening. As the fluorinating agent, a known fluorinating agent may be used without any limitation. In the present invention, an acid is particularly preferably used. For example, hydrofluoric acid, hydrofluoric acid, borofluoric acid, and the like are preferable.

The type of organic solvent affects the degree of blackening. Alcohols are preferably used to increase the degree of blackening, and monohydric alcohols such as methanol, ethanol, and isopropanol; dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol; trihydric alcohols such as glycerin And the like can be specifically mentioned. Of these, dihydric alcohols are particularly preferred because of the large degree of blackening.

When the contact between the silica particles and the fluorinating agent is performed in water without using an organic solvent, the contact between the silica particles and the organic solvent is performed after the contact with the fluorinating agent.

The silica particles after being brought into contact with the fluorinating agent and the organic solvent usually contain 1 to 20% by weight of fluorine and 1 to 10% by weight of the organic solvent.

By heating the silica particles thus obtained to 500 ° C. or higher, black silica particles can be obtained. If the heating temperature is too high, the silica particles may be sintered to each other. Therefore, the heating temperature is preferably set to 1350 ° C. or less. When the temperature is raised to 500 ° C. or more for heating, by rapidly raising the temperature in a temperature range of at least 200 to 400 ° C., the degree of blackness of the obtained black silica particles can be increased. Preferred. In this case, the rate of temperature rise is preferably 5 ° C./min or more, and is usually adopted from the range of 5 to 50 ° C./min.

The heating time is not particularly limited, but is generally selected from the range of 1 to 30 hours. Thus, the black silica particles of the present invention are obtained.

(Effect) Since the black silica particles of the present invention do not substantially contain an alkali metal, elution of the alkali metal does not cause a problem, and the black silica particles exhibit excellent black color. This black color does not fade by washing with an organic solvent, and has a large volume resistivity as shown in the examples. Therefore, it is presumed that the carbon in the black silica particles of the present invention is not present on the surface of the silica particles, but is incorporated inside the silica particles.

Further, since the black color of the black silica particles of the present invention is expressed by carbon, the black color does not fade due to light irradiation unlike black dyes.

Further, black silica particles having a small coefficient of variation in particle diameter are optimal as spacers for liquid crystal display elements because of their sharp distribution of particle diameter.

(Examples) The present invention will be described in more detail with reference to the following examples. However, in the following examples, measurement of the average particle diameter and the coefficient of variation of the silica particles, the content of the alkali metal and the elution amount Measurement, measurement of the amount of fluorine in the silica particles, measurement of the Y value as the degree of blackness of the silica particles, the content of carbon in the silica particles, further, measurement of the volume resistivity as the electrical conductivity of the silica powder, The following procedure was used.

(1) Average Particle Diameter and Coefficient of Variation The particle diameter of 100 arbitrary particles was measured using a scanning electron microscope, and calculated by the following equation.

Here, x _i is a measured value of the particle diameter and n = 100.

(2) Alkali metal content Perchloric acid and hydrofluoric acid were added to the sample, evaporated to dryness, dissolved by heating, and measured using an atomic absorption spectrometer.

(3) Elution amount of alkali metal 1.0 g of a sample and 100 g of distilled water were placed in an autoclave made of Teflon, heated at 90 ° C. for 5 hours, and then alkali metal in the supernatant was measured with an atomic absorption spectrometer. .

(4) Fluorine content The sample was fixed to the cell with a double-sided tape and measured with a fluorescent X-ray analyzer.

(5) Degree of black (Y value) SM color computer (SM-4, Suga Test Machine Co., Ltd.)
Was measured using the XYZ system defined in JIS Z8701 as an index of the degree of black.

The measurement was performed by a 45 ° reflection method using a powder cell.

(6) Carbon content After crushing the sample in an agate mortar, it was measured using a carbon analyzer.

(7) Volume resistivity of silica powder After drying the sample at 120 ° C for 10 hours, the sample was dried at room temperature (20 ° C).
It was measured under a humidity of 50% and a pressure of 5 kg / cm ² .

(8) Light Shielding Property (Photo Y Value) After arranging black silica particles in a layer on a glass plate so that the particles are in contact with each other, a polarizing microscope (50
(0x), and a photograph was taken while exposing from behind the glass plate, and the blackness of the obtained photograph was measured in the same manner as in (5) above.

 The equipment and conditions used are as follows.

・ Polarizing microscope: OLYMPUS BHA (without polarizing plate and filter) ・ Automatic exposure system: AD system PM10 (with dedicated camera) Film characteristics correction 4 Sample distribution correction 1 ・ Film: Fuji FP400B (ISO400) ・ Exposure correction: Measurement in the field of view One black silica particle having a carbon amount of 3% by weight or more was put in the circle, and the light amount of the light source was adjusted so that the exposure time was 2.46 seconds by the automatic photometry of the AD system.

・ Exposure time: 10 seconds ・ Development time: 30 seconds ± 2 seconds (25 ° C.) Example 1 In a glass reactor (internal volume 5) with a stirrer, methanol, aqueous ammonia (25% by weight) and 5N-NaOH aqueous solution were added. , 1600 ml, 350 ml and 8 ml, respectively, were charged and mixed well to obtain a reaction solution.

Next, a raw material solution was prepared by dissolving 205 g of tetraethyl silicate [Si (OC ₂ H ₅ ) ₄ , manufactured by Nippon Colcoat Chemical Co., Ltd., trade name: ethyl silicate 28] in 1 part of methanol.

In addition, methanol, ammonia water (25% by weight) and
5N-NaOH aqueous solution, 700ml, 200ml and 100ml respectively
To prepare an alkali solution for addition.

While maintaining the temperature of the reaction solution at 20 ° C., the raw material solution was added dropwise to the reaction solution at a rate of 1 ml / min using a metering pump. About 2 hours after the start of the addition, the sodium ion concentration
After that, the reaction was stopped until the sodium ion concentration in the reaction solution was 5 mmol /, the water concentration was 7.0 to 8.5 mol /, and the ammonia concentration was 2.5 to 3.0 mol /. The above-mentioned alkali solution for addition was appropriately added dropwise.

Approximately 30 hours after the start of the reaction, the particle size of the silica particles in the reaction solution became 3.0 μm, the addition of the raw material solution and the alkali solution for addition was stopped, the reaction solution was allowed to stand, the particles were settled, and the supernatant was separated did. Furthermore, redispersed in methanol,
A decantation process was performed.

50 g of the silica particles obtained as described above was redispersed in a mixed solution of 1600 ml of methanol and 400 ml of aqueous ammonia (25% by weight) to obtain a slurry after the reaction.

In addition, methanol 800ml, ammonia water (25% by weight)
An ammonia solution for addition was prepared by mixing 00 ml with 10 ml of 5N-NaOH aqueous solution. The raw material solution used had the same composition as the above-mentioned raw material solution.

Next, the ammonia solution for addition was added to the reaction solution slurry at a rate of 2 ml / min, and after about 30 minutes, the raw material solution was added at 1 ml / min.
Minutes were added in parallel with the addition ammonia solution. The addition of the ammonia solution for addition is continued until the reaction is stopped, the sodium ion concentration is 3.5 mmol /, the water concentration is 7.
The concentration was kept constant at 5 to 8.5 mol / and the ammonia concentration at 2.5 to 3.0 mol /.

About 48 hours after the start of the addition of the raw material solution, the particle size of the silica particles grew to 4.6 μm.

Further, the above operation was repeated twice using the obtained particles having a particle diameter of 4.6 μm as seed particles, and the particle diameter was 6.2 μm.
m. After that, the reaction solution is allowed to stand, the particles are settled,
The supernatant was separated. Further, it was redispersed in methanol, the decantation treatment was repeated three times, and methanol was removed by an evaporator, followed by drying under reduced pressure at 120 ° C. to obtain white silica particles (A).

The obtained white silica particles (A) have an average particle size of 6.20 μm.
m, the coefficient of variation in particle size was 0.9%, and the sodium content was 5.2% by weight.

Next, 50 g of the above white silica particles (A) were added to methanol 5
After the solution was put into 00 ml and made into a slurry, 100 ml of an aqueous nitric acid solution (61% by weight) was added, and stirring was continued at room temperature for 16 hours.
Thereafter, the particles were settled and decanted, and washed with methanol. After performing the washing operation three times,
After drying under reduced pressure for a period of time, white silica particles (B) were obtained.

The sodium content of the obtained white silica particles (B) was 12 ppm.

After slurrying 10 g of the above-mentioned white silica particles (B) with 50 ml of methanol, a mixed solution of 2.3 ml of a hydrofluoric acid aqueous solution (50% by weight) and 100 ml of methanol is added to this slurry at room temperature for about 1 hour. And stirring was continued for 10 hours. Thereafter, it was washed with methanol and dried at 120 ° C. under reduced pressure to obtain white silica particles (C).

The sodium content of the white silica particles (C) is 12ppm
By X-ray fluorescence analysis, the amount of fluorine was 7.7% by weight.

Next, 5 g of the above-mentioned white silica particles (C) were put into a porcelain crucible and heated at a rate of 10 ° C./min in an air atmosphere.
Heat treatment was performed for an hour to obtain black silica particles.

The obtained black silica particles were perfectly spherical, had an average particle diameter of 5.60 μm, and a coefficient of variation of the particle diameter of 0.9%. In addition, no sodium was eluted and no fluorine was detected by fluorescent X-ray analysis, and the Y value of the color computer was 0.77%. Also, the carbon content in the black silica particles,
1.06 wt%, the volume resistivity is 1.0 × 10 at 5 kg / cm ² pressure
^It exceeded ⁹ Ω · cm.

The obtained black silica particles were prepared from methanol and chlorofluorocarbon.
No discoloration occurred when dispersed in 113.

Example 2 By changing the synthesis conditions of the white silica particles (A) in Example 1, the average particle diameter of the white silica particles (A) was 2.47 μm,
5.63 μm, 9.25 μm and 18.00 μm. Further, the amount of the aqueous nitric acid solution added in Example 1 and the type of the mineral acid were changed.

Except as described above, the reaction was performed under the same conditions as in Example 1 to obtain completely spherical black silica particles. The results are shown in Table 1.

The obtained black silica particles were prepared from methanol and chlorofluorocarbon.
No discoloration occurred when dispersed in 113.

Example 3 White silica particles (C) were prepared using the white silica particles (B) of Example 1 and Example 2 while changing the addition amount of the hydrofluoric acid aqueous solution. Further, black silica particles were prepared by changing the heating conditions of the obtained white silica particles (C).

Except as described above, the same conditions as in Examples 1 and 2 were carried out to obtain completely spherical black silica particles.
The results are shown in Table 2.

The obtained black silica particles were prepared from methanol and chlorofluorocarbon.
No discoloration occurred when dispersed in 113.

Example 4 White silica particles (C) were prepared using the white silica particles (B) of Example 1 and Example 2 and changing the organic solvent during the fluorination treatment.

Except as described above, the same conditions as in Examples 1 and 2 were carried out to obtain completely spherical black silica particles.
The results are shown in Table 3.

The obtained black silica particles were prepared from methanol and chlorofluorocarbon.
No discoloration occurred when dispersed in 113.

Comparative Example 1 The white silica particles (A) and white silica particles (B) of Example 1 were subjected to heat treatment under different heat treatment conditions. The results are shown in Table 4.

Example 5 10 g of the white silica particles (B) obtained in Example 1 were slurried with 50 ml of methanol, and 5 ml of an aqueous solution of hydrofluoric acid (40% by weight) was added to the slurry. 100m
l of the mixed solution was added, and stirring was continued for 10 hours. Thereafter, the resultant was decanted and dried at 120 ° C. under reduced pressure to obtain white silica particles (C).

The sodium content of the white silica particles (C) is 12ppm
The amount of fluorine determined by fluorescent X-ray analysis was 7.6% by weight.

Next, 5 g of the above-mentioned white silica particles (C) were put into a porcelain crucible, and the temperature was increased at 30 ° C./min in an air atmosphere.
A minute heat treatment was performed to obtain black silica particles.

The resulting black silica particles are perfectly spherical and have an average particle size of
6.0 μm and the coefficient of variation of the particle size was 0.9%. No sodium was eluted and no fluorine was detected by X-ray fluorescence analysis, and the Y value of the color computer was 0.62%. The carbon content in the black silica particles is 5.0
Weight%, 5kg / cm ² Volume resistivity under pressure 1.0 × 10 ⁹ Ω ・
cm.

The obtained black silica particles are made of methanol and chlorofluorocarbon.
No discoloration occurred when dispersed in 113.

Example 6 White silica particles of Example 2 having various average particle diameters (A)
, The amount of the aqueous nitric acid solution of Example 5 and the type of mineral acid were changed.

Except as described above, the reaction was carried out under exactly the same conditions as in Example 5 to obtain completely spherical black silica particles. Table 5 shows the results.

The obtained black silica particles are made of methanol and chlorofluorocarbon.
No discoloration occurred when dispersed in 113.

Example 7 White silica particles (C) were prepared using the white silica particles (B) of Example 5 and Example 6 while changing the amount of the aqueous hydrofluoric acid solution added. Further, black silica particles were prepared by changing the heating conditions of the obtained white silica particles (C).

Except as described above, the reaction was carried out under exactly the same conditions as in Examples 5 and 6, to obtain completely spherical black silica particles.
The results are shown in Table 6.

The obtained black silica particles are made of methanol and chlorofluorocarbon.
No discoloration occurred when dispersed in 113.

Example 8 White silica particles (C) were prepared using the white silica particles (B) of Example 5 and Example 6 while changing the organic solvent at the time of the fluorine treatment.

Except as described above, the reaction was carried out under exactly the same conditions as in Examples 5 and 6, to obtain completely spherical black silica particles.
The results are shown in Table 7.

The obtained black silica particles are made of methanol and chlorofluorocarbon.
No discoloration occurred when dispersed in 113.

Example 9 The procedure of Example 5 was repeated except that the aqueous solution of borofluoric acid was used in place of the aqueous solution of hydrofluoric acid and the amount shown in Table 8 was used, and heating was performed under the conditions shown in Table 8. Similarly, black silica particles were obtained. Table 8 shows the physical properties of the obtained black silica particles.

Example 10 No. 1 of Examples 1 and 2, No. 6 of Example, No. 5, Example 5, No. 6 of Example 6, No. 6 of Example 7, No. 1 and No. of Example 9 A liquid crystal display device was prepared by the following method using the black silica particles of Example 2 as a spacer.

250 mg of each black silica particle is dispersed in 900 ml of 1,1,2-trichloro-1--2,2-trifluoroethane + 100 ml of ethanol.
l) Disperse the particles in 1 and use a spacer sprayer to apply black silica particles to a polished glass substrate (160 m) for a liquid crystal display cell.
m × 230 mm) so as to have a spray density of 25 pieces / mm ² . In addition, the above-mentioned glass substrate was provided with a transparent electrode pattern of ITO (indium tin oxide), and after applying a polyimide alignment film, rubbing was used.

The same black silica particles and a sealing epoxy resin (1.5 g of black silica particles + epoxy Using a 100 g of the base resin), seal printing was performed by a screen printing machine.

Next, after laminating the above pair of glass substrates, 0.
Heating was performed at 150 ° C. for 1 hour under a pressure of 8 kg / cm ² to cure the seal portion, thereby forming an empty cell for liquid crystal display.

The empty cells prepared using the black silica particles of Examples 1, 5, 6, 7 and 9 were filled with SBE (Super Twisted Birefringence Effect) liquid crystal (manufactured by Merck) in No. 2 of Example 2. In the empty cell using the black silica particles of 1, an SmC ^* (chiral smectic C) liquid crystal (ferroelectric liquid crystal, manufactured by Merck)
The empty cell using the black silica particles of No. 6 of Example 3 has TN
A (twisted nematic) liquid crystal (manufactured by Merck) was injected using a liquid crystal injection device to prepare a liquid crystal display cell.

The cell thickness of the prepared liquid crystal display cell and the variation of the cell thickness were measured at 50 arbitrary points. Further, the cell was lit and displayed, and the contrast and the life of the cell were examined.
The results are shown in Table 9.

Comparative Example 2 Using the silica particles obtained in No. 1 and No. 3 of Comparative Example 1 as spacers, empty cells for liquid crystal display were respectively formed. The method of creating an empty cell was the same as in Example 10. An SBE liquid crystal was injected into the empty cell to create a liquid crystal display cell.

Table 9 shows cell thickness data and display performance of the prepared liquid crystal display cell.

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01B 33/12-33/193 G02F 1/1339 500 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. An average particle diameter of 0.1 to 50 μm, containing substantially no alkali metal, containing 0.1% by weight or more of carbon, having a volume resistivity of 10 ⁷ Ω · cm or more, and a Y value according to JIS Z8701. Is not more than 10%. 2. The method according to claim 1, wherein the silica particles substantially free of an alkali metal are brought into contact with a fluorinating agent and an organic solvent, and then heated at a temperature of 500 ° C. or more. The method for producing black silica particles according to the above. 3. A spacer for a liquid crystal display device comprising the black silica particles according to claim 1.