JPH03279209A - Black silica grain and production thereof - Google Patents

Abstract

PURPOSE:To obtain sufficiently black silica grains without elution of alkali metals by specifying the average grain diameter within a specific range and incorporating a specified amount or more of carbon substantially without containing the alkali metals therein. CONSTITUTION:Black silica grains, having an average grain diameter of 0.1-50mum and containing >=0.1wt.% carbon substantially without containing alkali metals. The aforementioned black silica grains are obtained by bringing silica grains substantially without containing the alkali metals into contact with a fluorinating agent (e.g. hydrofluoric acid or hydrosilicofluoric acid) and an organic solvent and then heating the resultant grains at >=500 deg.C temperature. The above-mentioned black silica grains assume excellent black color without causing problems in elution of the alkali metals and will not fade even by washing with an organic solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to black silica particles, particularly black silica particles useful as spacers for liquid crystal display elements.

(Prior art and problem to be solved by the invention) Silica particles are widely used as ceramic raw materials, chromatography carriers, etc. They are also used as spacers for liquid crystal display elements, but in recent years, they have been used to improve image quality. Instead of the conventional white silica, black silica particles, or in other words, silica particles that do not transmit light, have become desirable.

As a method for obtaining black silica, a method has been considered in which silica particles are impregnated with an alkali metal and an organic substance, and then heat-treated. This method involves adding an alkali metal to accelerate the sintering of silica, carbonizing the organic matter in the silica, and turning it black. Since the black silica particles obtained by this method naturally contain an alkali metal, they are disadvantageous due to alkali elution, and therefore cannot be practically used as a spacer for liquid crystal display elements.

In order to reduce the effect of alkali elution, it is possible to reduce the amount of alkali during heat treatment, but in that case,
The degree of blackness becomes dull and light shielding becomes insufficient.

(Means for Solving the Problems) The present inventors have conducted extensive research with the aim of obtaining silica particles that are free from elution of the above-mentioned alkali metals and are sufficiently black. As a result, we succeeded in achieving the above object and came to propose the present invention.

That is, the present invention provides black silica particles having an average particle diameter of 0.1 to 50 microns, substantially free of alkali metals, and containing 0.1% by weight or more of carbon.

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 they require too much time and strain for particle growth.

In the present invention, if black silica particles with high blackness are to be obtained, the average particle size is preferably 2 to 10 μm.

The black silica particles of the present invention are characterized in that they do not substantially contain alkali metals. "Substantially free of alkali metal" means that there is substantially no problem when used as a spacer for a liquid crystal display element, and usually the content is 1 oopp- or less.

The black color of the black silica particles of the present invention is due to carbon produced by carbonizing organic matter within the silica particles, but the carbon content in the silica particles of the present invention is usually 0.1% by weight.
That's all. If this content is lower, the color will naturally become lighter and light shielding will be insufficient, which is not desirable. ), it can be reduced to 4% or less.

Furthermore, although the black silica particles of the present invention contain carbon as described above, they have a high electrical resistance.For example, the volume resistivity described below is generally 10"Ω.
It is also possible to obtain black silica particles with a high electrical resistance of 1 or more, and even more than 109Ω.

Furthermore, the particle shape of the black silica particles of the present invention observed by electron microscopy is spherical with a ratio of the major axis to the minor axis of 0.8 or more, and furthermore, 0.9 or more, and also shows variations in particle diameter. The coefficient (standard deviation of particle size/average particle size) is 5% or less, further 3% or less, and the particles have excellent uniformity in particle size.

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

This is a method in which silica particles substantially free of 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 that do not substantially contain an alkali metal as a raw material are preferably used in the present invention because silica particles obtained by hydrolysis of alkyl silicate, such as ethyl silicate, are spherical and have a small coefficient of variation in particle size. However, silica particles obtained by other methods can also be used.

For the hydrolysis of the alkyl silicate, known methods can be used without any restrictions. For example, the alkyl silicate is added to a mixed solvent of water, methanol, and ammonia, and an alkali metal hydroxide is added as necessary. If particles with a large zero particle diameter are required, a method is used in which the reaction is carried out in multiple stages to further grow the produced silica particles and sequentially increase the size. When an alkali metal hydroxide is used in this reaction, up to 20% of the alkali metal is present in the silica particles produced.
Included up to. Although black silica particles can be easily obtained by heating while the alkali metal is still contained, the alkali metal remains mixed in the produced black silica particles, which is not preferable.

Therefore, in such cases, we recommend a method in which the silica particles containing alkali metals obtained by reaction are first brought into contact with an acid, usually a mineral acid such as hydrochloric acid, sulfuric acid, or nitric acid, and then washed to remove the alkali metals. By doing so, it is possible to easily obtain silica particles having an alkali metal content of 100 ppa+ or less.

The conditions for the acid treatment described above may be determined by appropriately selecting the acid concentration, acid amount, etc.; The metal content can be reduced to 1100 pp or less.

However, the lower the acid concentration and the amount of acid, the longer the acid treatment takes, so it is preferable that the acid concentration is 5% or more and the amount of acid is at least twice the equivalent amount.

The silica particles substantially free of alkali metal are contacted with a fluorinating agent and an organic solvent.

The contact with the fluorinating agent and the organic solvent may be carried out simultaneously or separately. Contact with the fluorinating agent is carried out by immersing the silica particles in a solution of the fluorinating agent in water or an organic solvent. When using a solution in which a fluorinating agent is dissolved in an organic solvent, the fluorinating agent and the liquid must be mixed together. Contact with the solvent can be carried out simultaneously. The concentration of the fluorinating agent in water or organic solvent is 0.1 to 10% by weight, and the amount of the fluorinating agent is preferably equivalent to the equivalent of silica to reduce dissolution of silica particles and sufficiently perform blackening. As the fluorinating agent, any known fluorinating agent may be employed without any restriction, but in the present invention, acids are particularly preferably used. For example, hydrofluoric acid, hydrofluorosilicic acid, hydrofluoroboric acid, etc. are preferably used. be.

The type of organic solvent affects the degree of blackening.

In order to increase the degree of blackening, alcohols are preferably used, including monohydric alcohols such as methanol, ethanol, and isopropanol; divalent alconyls such as ethylene glycol, diethylene glycol, triethylene glycol, and propylene glycol; and trihydric alcohols such as glycerin. Specific examples include alcohols and the like. Among these, dihydric alcohols are particularly suitable because they have a large degree of blackening.

When the silica particles are brought into contact with the fluorinating agent in water without using an organic solvent, the silica particles are brought into contact with the organic solvent after the contact with the fluorinating agent.

After contacting the fluorinating agent and the organic solvent, the silica particles usually contain 1 to 20% by weight of fluorine and 1 to 10% by weight of the organic solvent.
Including weight.

Black silica particles can be obtained by heating the silica particles thus obtained to temperatures above soo'c. It is preferable to increase the degree of blackness of the obtained black silica particles by rapidly increasing the temperature in the temperature range of , usually 5 to b.The heating time is not particularly limited, but is generally employed in the range of 8 to 30 hours.The black silica particles of the present invention are thus obtained.

(Effects) Since the black silica particles of the present invention do not substantially contain alkali metals, elution of alkali metals does not become a problem, and moreover, they exhibit excellent black color.

This black color does not fade by washing with an organic solvent, and as shown in the examples, the carbon in the black silica particles of the present invention has a large volume resistivity.
It is presumed that it 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 developed by carbon, the color does not fade due to light irradiation unlike black dyes.

Furthermore, black silica particles with a small coefficient of variation in particle size are
Since the particle size distribution is sharp, the present invention will be explained in more detail using Examples below. Measurement of content and elution amount, measurement of fluorine amount in silica particles, measurement of Y value as degree of blackness of silica particles, content of carbon in silica particles, and volume as electrical conductivity of silica powder. The specific resistance was measured by the method shown below.

(1) Average particle diameter and coefficient of variation The particle diameter of 100 arbitrary particles was measured using a scanning electron microscope, and calculated from the following formula.

Enter However, X is a measured value of particle diameter, and n=100.

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

(3) Amount of alkali metal eluted: Put 1.0 g of the sample and 100 g of distilled water into a Teflon autoclave, heat treat at 90°C for 5 hours, and then measure the alkali metal in the supernatant using an atomic absorption spectrometer. did.

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

(5) Degree of blackness (Y value) XYZ specified by JIS Z 8701 using a 3M color computer (SM-4, manufactured by Suga Test Instruments)
The Y value of the system was measured and used as an index of the degree of blackness.

Note that the measurement was performed using a powder cell using a 45° reflection method.

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

(7) Volume resistivity sample of silica powder was dried for 12 inches at 0°C for 10 hours, then at room temperature (20°C).
℃), humidity 50%, and 5 kg/:ffl pressure.

Deep prayer →→ (8) Light shielding property (photo Y value) After arranging black silica particles in a layer on a glass plate so that each particle is in contact with each other, a polarizing microscope equipped with an exposure device (50
A photograph was taken while exposing the glass plate from the rear using a magnifying glass (0x), and the degree of 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 device: AD system PMIO (with dedicated camera) Film characteristic correction 4 Sample distribution correction Film: Fuji FP400B (ISO400) ・Exposure correction: Measurement circle within the field of view Insert one black silica particle with a carbon content of 3% or more by weight, and use the automatic photometry of the AD system! The light intensity of the light source was adjusted so that the light time was 2.46 seconds.

・Exposure time: 10 seconds ・Development time: 30 seconds ± 2 seconds (25°C) and 5N-NaO
H aqueous solution at 1600mf each! .

350m4! and 81Ill were prepared and mixed well to prepare a reaction solution.

Next, Methanol II! A raw material solution was prepared by dissolving 205 g of tetraethyl silicate (Si(OCzHs) 4, manufactured by Nihon Colcoat Chemical Co., Ltd., trade name: ethyl silicate 28).

In addition, methanol, ammonia water (25% by weight) and 5N-NaOH aqueous solution were each added at 700 mj! , 20
An alkaline solution for addition was prepared by mixing 0a+f and 100IIIN.

While keeping the temperature of the reaction solution at 20°C, the above raw material solution was added to 1o+4! using a metering pump. It was added neatly to the reaction solution at a rate of 1/min. After about 2 hours after the addition started, the sodium ion concentration decreased to 5 mmol/~l, and from then on, the sodium ion concentration in the reaction solution decreased to 5 mmol/j! , the concentration of water is 7.0-8.5 mol/l, and the concentration of ammonia is 2.5-3. Omol, / 7! The above alkaline solution for addition was added as appropriate until the reaction was stopped at a constant value of .

Approximately 30 hours after the start of the reaction, the particle size of the silica particles in the reaction solution reached 3.0 μm, and the addition of the raw material solution and the alkaline solution for addition was stopped, the reaction solution was allowed to stand, and the particles were allowed to settle.
The supernatant was separated. Furthermore, it was redispersed in methanol and subjected to a decantation treatment.

50 g of the silica particles obtained as above were mixed with 1600 mj of methanol! and ammonia water (25% by weight)4
It was redispersed in a mixed solution of 0.00all to prepare a post-reaction slurry.

Also, methanol 800mj! , 200 all of ammonia water (25% by weight) and 10 moj of 5N-NaOH aqueous solution! An ammonia solution for addition was prepared. The raw material solution used had the same composition as the raw material solution described above.

Next, the ammonia solution for addition was added into the reaction slurry at a rate of 2 trrl 1 minute, and after about 30 minutes, the raw material solution was added at a rate of 111117 minutes in parallel with the ammonia solution for addition. . Addition of the ammonia solution for addition is continued until the reaction is stopped, and the sodium ion concentration is 3.5.
m+++ol/l, water concentration 7.5~B, 5rno
l/l, ammonia concentration is 2.5-3.0 mo I!
/! It was made to be constant.

The particle size of the silica particles grew to 4.6 μm in about 48 hours after starting addition of the raw material solution.

Furthermore, when the above operation was repeated twice using the obtained particles with a particle size of 4.6 μm as seed particles, the particle size was 6.2 μm.
- became. After that, the reaction solution is allowed to stand still, the particles are allowed to settle,
The supernatant was separated. Furthermore, it was redispersed in methanol, the decantation treatment was repeated three times, the methanol was removed with an evaporator, and the mixture was dried under reduced pressure at 120° C. to obtain white silica particles (A).

The obtained white silica particles (A) have an average particle diameter of 6.20
μm, particle size variation coefficient 0.9%, sodium content 5
．． It was 2% by weight.

Next, 50 g of the above white silica particles (A) were put into methanol 500111 to form a slurry, and then 100 o+1 of a nitric acid aqueous solution (61% by weight) was added, and stirring was continued for 16 hours at room temperature. Thereafter, the particles were sedimented and decanted, and washed with methanol. After performing the washing operation three times, it was dried under reduced pressure at 120° C. for 10 hours to obtain white silica particles (B).

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

The above white silica particles (B) Log in methanol 50m
After slurrying in step 1, 2.3 mj! of hydrofluoric acid aqueous solution (50% by weight) was added to the slurry. , methanol 10
0mj! A mixed solution of was added over about 1 hour at room temperature, and stirring was continued for 10 hours. Thereafter, it was washed with methanol and dried under reduced pressure at 120°C to obtain white silica particles (C).

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

Next, 5 g of the above white silica particles (C) were placed in a porcelain crucible, heated at a rate of 10°C/min in an air atmosphere, and heated to 600°C.
A heat treatment was performed at ℃ for 10 hours to obtain black silica particles.

Further, no sodium elution and no fluorine were observed by fluorescent X-ray analysis, and the Y value by color computer was 0.77%. Further, the carbon content in the black silica particles is 1.06% by weight, and the volume resistivity under a pressure of 5 kg/Ci is 1.06% by weight. The value exceeded OX 10”Ω.

The obtained black silica particles were mixed with methanol and Freon-1.
Even when dispersed in No. 13, the color did not fade.

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

Except for the above, the black silica particles obtained under the same conditions as in Example 1 did not discolor even when dispersed in methanol and Freon-113.

Example 3 Using the white silica particles (B) of Examples 1 and 2, white silica particles (C) were prepared by changing the amount of the hydrofluoric acid aqueous solution added. Further, black silica particles were prepared by changing the heat treatment conditions of the obtained white silica particles (C).

Other than the above, the black silica particles obtained in Examples 1 and 2 did not discolor even when dispersed in methanol and Freon-113.

Example 4 Using the white silica particles (B) of Examples 1 and 2, white silica particles (C) were prepared by changing the organic solvent used during the fluorination treatment.

Other than the above, the black silica particles obtained in Examples 1 and 2 did not discolor even when dispersed in methanol and Freon-113.

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

Example 5 After slurrying the white silica particles CB) 101 obtained in Example 1 with methanol 50-, in this slurry,
A mixed solution of hydrogen fluorosilicide water solution (401 Kametsu) 5- and methanol 100- was added, and stirring was continued for 10 hours.

Thereafter, it was decanted and dried under reduced pressure at 120°C to obtain white silica particles (C).

The sodium content of the white silica particles (C) is 12-,
Fluorescent X! ! The amount of fluoride smoke determined by analysis was 7.6% by weight.

Next, 5 g of the above white silica particles (C) were placed in a magnetic crucible, and the temperature was raised at 30°C/min in an air atmosphere to 900°C.
A heat treatment was performed for 30 minutes to obtain black silica particles.

The obtained black silica particles were perfectly spherical and had an average particle diameter of 6.
．． For 0p snow, the coefficient of variation of particle size was 09≦. In addition, fluorine was not found in sodium elution and fluorescent X-ray analysis, and the Y value determined by a color computer was 0.62%.
Met. In addition, the carbon content in the black silica particles is 5.0% by weight, and the volume resistivity under 5V pressure is 1.0.
It was more than X10'Ω/country.

The obtained black silica particles were mixed with methanol and Freon-1.
Even when dispersed in No. 13, the color did not fade.

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

Except for the above, the process was carried out under the same conditions as in Example 5.
Completely spherical black silica particles were obtained. The results are shown in Table 5.

The obtained black silica particles were mixed with methanol and Freon-1.
Even when dispersed in No. 13, the color did not fade.

Implementation 7 Using the white silica particles CB) of Example 5 and Example eli6, white silica particles (C) were prepared by changing the amount of the hydrogen 7tsilicate aqueous solution added. Further, black silica particles were prepared by changing the heat treatment conditions of the obtained white silica particles (C).

Except for the above, the same conditions as in Example 5 and Example 6 were used to obtain completely spherical black silica particles. The results are shown in Table 6.

The obtained black silica particles were mixed with methanol and Freon-1.
Even when dispersed in No. 13, the color did not fade.

Example 8 Using the white silica particles CB) of Examples 5 and 6, white silica particles (C) were prepared by changing the organic solvent used during the fluorination treatment.

Except for the above, the same conditions as in Example 5 and Example 6 were used to obtain completely spherical black silica particles. The results are shown in Table 7.

The obtained black silica particles were mixed with methanol and Freon-1.
Even when dispersed in No. 13, the color did not fade.

Example 9 In Example 5, instead of the silicate hydrofolic acid aqueous solution,
Using an aqueous solution of hydrogen fluoride in the amount shown in Table 8,
Black silica particles were obtained in exactly the same manner as in Example 5, except that the heating was performed under the conditions shown in Table 8. Table 8 shows the physical properties of the obtained black silica particles.

Implementation @lO Implementation @1. 46° Example 5 of A1 Example of Example 2. A liquid crystal display device was produced by the following method using the AI of Example 6, the AI of Example 7 and the black silica particles of A2 as spacers.

Disperse 250 μl of each black silica particle in a dispersion liquid (1°1.2-trichloro-1-2,2-)lifluoroethane 900 μl ethanol 100 WLt), and use a spacer scatterer to disperse the black silica particles. on a polished glass substrate for liquid crystal display cells (160m x 230cm) at a scattering density of 2.
It was distributed at a rate of 5/-. The glass substrate used above had an ITO (indium tin compound) transparent electrode pattern and was subjected to a rubbing treatment after coating with a polyimide alignment film.

In addition, on the glass substrate paired with the glass substrate on which the black silica particles were sprinkled, an ink for soles (black silica particles 1.5 I Seal printing was performed using a screen printing machine using epoxy resin 100II).

Next, after overlapping the above pair of glass substrates, α8
To! ,! The sealed portion was cured by heating at 150° C. for 1 hour under a pressure of 150° C. to prepare an empty cell for a liquid crystal display.

In the empty cells created using the black silica particles of Examples 1.5, 6.7, and 9, 5BE (super twist birefringence effect type) liquid crystal (manufactured by Merck & Co., Ltd.) was added to the black silica particles of A1 of Example 2. SmC” (chiral smectic C) liquid crystal (ferroelectric! crystal, manufactured by Merck & Co., Ltd.) was used for the empty cell using SmC”, and TN (twisted liquid crystal) was used for the empty cell using black silica particles in the experiment Nematic type) liquid crystal (Merck & Co., Ltd.)
) were respectively injected using a liquid crystal injection device to create a liquid crystal display cell.

The cell thickness and variations in cell thickness of the produced liquid crystal display cell were measured at 50 arbitrary points. In addition, the contrast and life of the cell were inspected by lighting the cell.

The results are shown in Table 9.

Comparative Example 2 Using the silica particles obtained in AI and Mu3 of Comparative Example 1 as spacers, empty cells for liquid crystal display were prepared. The empty cells were created using the same method as in Example 10. SBE liquid crystal was injected into the empty cell to create a liquid crystal display cell.

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

Claims (3)

[Claims] (1) Black silica particles having an average particle diameter of 0.1 to 50 μm, substantially free of alkali metals, and containing 0.1% by weight or more of carbon. (2) Claim No. 1, characterized in that silica particles substantially free of alkali metals are brought into contact with a fluorinating agent and an organic solvent, and then heated at a temperature of 500°C or higher.
) The method for producing black silica particles as described in item 2. (3) A spacer for a liquid crystal display element comprising black silica particles according to claim (1).