JP2009107870A - Method for manufacturing silica particle and silica particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing spherical silica particles free from a crack, a flaw and coloring (blackening). <P>SOLUTION: The method for manufacturing the silica particles includes: hydrolyzing and polycondensing an alkoxysilane having a non-hydrolyzable group to form polyorganosiloxane particles; and firing the polyorganosiloxane particles to manufacture silica particles, wherein the firing is carried out in a firing atmosphere while keeping the oxygen concentration in the firing atmosphere at 1-15%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing silica particles.

A method is known in which alkoxysilane is hydrolyzed and polycondensed to produce polyorganosiloxane particles, which are fired to produce silica particles. Since the silica particles produced by this method are fine spherical particles, they are used in various applications by taking advantage of their characteristics. For example, it is used as a filler for semiconductor resin sealing materials and as a spacer for liquid crystal display panels.
JP-A-8-183610

  Tetraalkoxysilane (all four groups of Si atoms are all hydrolyzable groups, TEOS: tetraethoxysilane, etc.) is the most common alkoxysilane used for the production of silica particles. However, TEOS has low reactivity with water, and particle growth cannot be achieved unless a high concentration basic catalyst (about pH 12) is added. Therefore, a small reaction of less than 1 μm in a single reaction (reaction by one addition of raw materials). Only particles can be obtained. Therefore, after growing the particles in the first reaction, this particle is used as a seed particle, and then the raw material is added in multiple batches and reacted repeatedly to gradually grow the particles. ing. For this reason, it takes time to grow to a desired particle size. Further, in this method, the larger the particle size, the worse the efficiency of particle growth with respect to the addition of the raw material. Therefore, it is difficult to obtain silica particles having a large particle size (for example, particles of 7 μm or more).

  Therefore, a method using an alkoxysilane having a non-hydrolyzable group such as methyltrimethoxysilane (MTMS) instead of TEOS has been proposed. Since MTMS has higher reactivity with water than TEOS, it has a feature that particle growth is easy and particles having a desired size can be obtained in a short time. However, in the conventional method using MTMS, the silica particles may be cracked or cracked by firing. In addition, the silica particles may be blackened.

  Patent Document 1 describes that colored silica particles can be obtained by firing in a dilute state of oxygen. However, this patent document does not describe a method for producing silica particles which are free from cracks and cracks and which are not colored.

  This invention makes it a subject to provide the method of manufacturing a spherical silica particle without a crack, a crack, and coloring (blackening).

  The method for producing silica particles of the present invention is a method for producing silica particles in which an alkoxysilane having a non-hydrolyzable group is hydrolyzed and polycondensed to produce polyorganosiloxane particles, which are fired to produce silica particles. Thus, firing is performed while maintaining the oxygen concentration in the firing atmosphere at 1 to 15%.

  In the present invention, the alkoxysilane having a non-hydrolyzable group is preferably methyltrimethoxysilane.

  In the present invention, firing at 400 to 1000 ° C. is preferable.

  In the present invention, firing is preferably performed while flowing a mixed gas of air and an inert gas into the atmosphere.

  The silica particles of the present invention are produced by the above method.

  The silica particles of the present invention are silica particles obtained by hydrolyzing and polycondensation reaction of alkoxysilane having a non-hydrolyzable group to produce polyorganosiloxane particles, which are obtained by firing, and are cracked. The total content of particles and cracked particles is less than 0.1% by volume, and the content of blackened particles is less than 0.01% by volume.

  When the oxygen concentration in the firing atmosphere is high, the decomposition reaction of the organic groups contained in the polyorganosiloxane particles occurs actively, and the heat of reaction causes the particle temperature to rise rapidly, causing the particles to shrink rapidly and cracks. It breaks. On the other hand, when firing in an atmosphere where the oxygen concentration is too low, decomposition of the organic group is suppressed, carbon atoms may remain in the silica particles, and the particles may be blackened.

  According to the method of the present invention, since the firing is performed in an atmosphere having a low oxygen concentration, the decomposition reaction of the organic group proceeds slowly, and a rapid increase in the particle temperature due to the reaction heat can be suppressed. In addition, since the firing is performed while maintaining the atmosphere at a predetermined oxygen concentration, the decomposition of the organic group is not suppressed. Therefore, it is possible to obtain silica particles which are free from cracks and cracks and are not blackened.

  Hereinafter, the manufacturing method of the silica particle of this invention is explained in full detail.

The method of the present invention first includes a step of preparing polyorganosiloxane particles by hydrolyzing and polycondensing an alkoxysilane having a non-hydrolyzable group. This process can be further subdivided. A suitable example is introduced below. However, the method of the present invention is not limited to the following steps.
(1) A preparation step of preparing a reaction solution by adding a mixed solution of an alkoxysilane having a non-hydrolyzable group and an alcohol to an aqueous solvent,
(2) A precipitation / growth step in which aqueous ammonia is added to the reaction solution to precipitate and grow polyorganosiloxane particles;
(3) an aging step of aging polyorganosiloxane particles by adding aqueous ammonia to the reaction solution;
(4) a recovery step of recovering polyorganosiloxane particles from the reaction solution;
Thus, polyorganosiloxane particles are obtained.

  First, the preparation process will be described.

  The preparation step is a step of preparing a reaction solution by adding a mixed solution of alkoxysilane and alcohol to an aqueous solvent.

  As the aqueous solvent, it is preferable to use a mixed solvent of water and alcohol. The reason why the alcohol is added to the water here is to improve the mixing property between the alkoxysilane such as MTMS and the aqueous solvent and to grow particles having a uniform diameter.

  As the alcohol, lower alcohols such as methanol, ethanol, propanol and butanol can be used. Among these, it is particularly preferable to use n-butanol. The reason is that when alcohols other than n-butanol are used, particles having a large diameter (for example, 5 μm or more) tend to hardly grow. This is because butanol has a larger molecular size than methanol, ethanol, and propanol, and this point is thought to contribute to the growth of large particles. In addition, alcohol having a molecular size larger than that of butanol (having many carbon atoms) has very poor solubility in water, resulting in poor mixing of alkoxysilane (MTMS, etc.) and water. It is thought that it will vary. The addition ratio of n-butanol is preferably about 3 to 7% by mass with respect to water. If the n-butanol concentration is lower than this, the mixing property with the alkoxysilane is deteriorated, and the diameters of the growing particles are likely to vary. If the n-butanol concentration is higher than this, the solubility of n-butanol in water exceeds 7.7%, so that n-butanol and water cannot be completely mixed, and the homogeneity of the aqueous solvent And the diameter of particles growing in the reaction solution varies.

  The mixed solution contains an alkoxysilane having a non-hydrolyzable group and an alcohol.

  The reason why alkoxysilane having non-hydrolyzable groups is used is that polyorganosiloxane particles by hydrolysis and polycondensation reaction under the condition of low basic catalyst concentration (about pH 9) because of the high reactivity of this material with water This is because it is possible to advance the growth. Therefore, polyorganosiloxane particles having a large diameter can be obtained by a single reaction (a reaction by adding a raw material once). If this type of alkoxysilane is used, silica particles having a diameter of about 15 μm can be obtained.

  The alkoxysilane having a non-hydrolyzable group is represented by the following formula.

R1nSi (OR2) 4-n (wherein n is an integer of 1 to 3)
In the above formula, R1 represents an organic group having 1 to 10 carbon atoms selected from a substituted or unsubstituted hydrocarbon group. Among these, the unsubstituted hydrocarbon includes an alkyl group (chain alkyl group or cyclic alkyl group), an alkenyl group, an aralkyl group, an aryl group, and the like, and the substituted hydrocarbon includes a part of hydrocarbon hydrogen atoms. Or all of them are non-hydrocarbon groups or groups substituted with atoms other than hydrogen, specifically, chloroalkyl groups, γ-methacryloxypropyl groups, γ-glycidoxypropyl groups, aminopropyl groups, 3,4- Examples thereof include an epoxycyclohexylethyl group, a γ-mercaptropropyl group, a trifluoropropyl group, and a fluorocarbon group.

  In said formula, R2 is a C1-C10 organic group chosen from a hydrogen atom or an alkyl group, an alkoxyalkyl group, and an acyl group. Specific examples of such organosilicon compounds include methyltrimethoxysilane (MTMS), methyltriethoxysilane, methyltriisopropoxysilane, methyltris (methoxyethoxy) silane, ethyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane. Methoxysilane, γ-chloropropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, methyltriacetoxysilane, phenyltriacetoxysilane, etc. (in the above formula, n = 1 organosilicon compound), dimethoxydimethylsilane, diethoxy- 3-glycidoxypropylmethylsilane, dimethoxydiphenylsilane, diacetoxydimethylsilane, diphenylsilanediol, etc. (organosilicon compound of n = 2 in the above formula), trimethylmethoxysilane, trimethyl And ruethoxysilane, acetoxytrimethylsilane, trimethylsilanol and the like (organosilicon compound wherein n = 3 in the above formula).

  Among these, methyltrimethoxysilane (MTMS) and vinyltrimethoxysilane are preferable, and methyltrimethoxysilane is particularly preferable. The reason for this is that, after obtaining polyorganosiloxane particles, in the step of silicidation by firing, those with less organic components are preferred because of their small particle shrinkage and efficiency during silicification by removing organic components. is there.

  The amount of alcohol mixed with alkoxysilane is preferably about 1 to 5% by mass with respect to the reaction solution after addition of the mixture. If the alcohol concentration is lower than this, the miscibility with the aqueous solvent is deteriorated, and the diameters of the growing particles tend to vary. If the alcohol concentration is higher than this, the concentration of alkoxysilane and water in the reaction solution becomes relatively thin, and the growth rate of the polyorganosiloxane particles becomes slow, or the polyorganosiloxane particles are difficult to grow. Such a problem is likely to occur.

  As the alcohol, lower alcohols having excellent solubility in water, such as methanol, ethanol, and propanol, can be used, but ethanol and propanol are particularly preferable because methanol has a safety problem.

  The reason why an alcohol is added to an alkoxysilane having a non-hydrolyzable group in advance to prepare a mixed solution is that if the alcohol is added to the alkoxysilane, the solubility of the mixed solution in an aqueous solvent is improved and the mixed solution is shortened. This is because the alkoxysilane is uniformly mixed in the aqueous solvent. When the alkoxysilane is uniformly present in the aqueous solvent, the polyorganosiloxane particles are easily grown uniformly, and silica particles having a small variation in particle size distribution can be produced.

  Next, the precipitation / growth process will be described.

  This step is a step of growing polyorganosiloxane particles by adding ammonia water as a basic catalyst to the reaction solution to hydrolyze and polycondense alkoxysilane. The polyorganosiloxane particles obtained in this step have a substantially spherical shape.

  As the basic catalyst, amines and the like can be considered in addition to ammonia, but ammonia is selected in the present invention because of its low toxicity, easy removal and low cost.

  If the ammonia concentration of the ammonia water to be added is too high, the ammonia concentration in the region where the ammonia water is added becomes very high before the ammonia water is uniformly mixed with the whole reaction solution. The reaction with water is promoted, the growth speed of the polyorganosiloxane particles in the reaction solution is not uniform, and the diameter of the resulting silica particles varies. On the other hand, when the ammonia concentration of the ammonia water to be added is too thin, it is necessary to increase the amount of ammonia water added, which is disadvantageous in terms of workability. Considering the above points, the ammonia concentration of the ammonia water to be added is preferably about 0.1 to 0.5% by mass.

  It is preferable that the ammonia concentration of the reaction liquid after adding ammonia water is 0.0015 to 0.015 mass%. By adjusting this concentration, the diameter of the silica particles obtained can be adjusted. If the ammonia concentration in the reaction solution is too high, the resulting silica particles grow only below 1 μm. Therefore, it becomes impossible to produce particles having a diameter of 2 to 10 μm suitable as a spacer for a seal portion of a liquid crystal display panel. On the other hand, when the ammonia concentration is too low, the rate of hydrolysis and polycondensation reaction of alkoxysilane is slowed, and the variation in the diameter of silica particles becomes large.

  Next, the aging process will be described.

  This step is a step of curing and stabilizing the grown polyorganosiloxane particles. The polyorganosiloxane particles obtained in the precipitation / growth process have a very soft surface as they are, and when the particles are naturally settled to collect the particles or are precipitated by a centrifuge, the particles are pressed against each other. As a result, the particles are easily crushed and the spherical shape cannot be maintained. Therefore, in the present invention, ammonia water is added again to increase the concentration of the basic catalyst in the reaction solution, to cure the polyorganosiloxane particles, and to stabilize the shape.

  As the basic catalyst, amines and the like can be considered. However, ammonia is selected in the present invention because it is less toxic, easy to remove, and inexpensive.

  If the ammonia concentration to be added is too high, the ammonia concentration in the region where the ammonia water is added becomes very high before the ammonia water is uniformly mixed with the whole reaction solution. Will be promoted. On the other hand, when the ammonia concentration of the ammonia water to be added is too low, it is necessary to increase the ammonia water addition ratio, which is disadvantageous in terms of workability. Considering the above points, the ammonia concentration of the ammonia water to be added is preferably approximately 1 to 5% by mass.

  The ammonia concentration of the reaction solution after addition of aqueous ammonia is preferably 0.05 to 0.2% by mass. If the ammonia concentration in the reaction solution is too high, the polyorganosiloxane particles will aggregate immediately after the addition of aqueous ammonia. On the other hand, if the ammonia concentration is too thin, the polyorganosiloxane particles cannot be sufficiently cured and the particles are easily crushed.

  The timing of adding the ammonia water, that is, the method for determining the growth stop of the polyorganosiloxane particles can be performed, for example, as follows. First, a sample of the reaction solution during the growth of polyorganosiloxane particles is collected and observed with a microscope. Next, the microscopic image is image-processed, and the diameter of the polyorganosiloxane particles is measured. This operation is repeated every 10 minutes, and when there is no change in the diameter of the polyorganosiloxane particles, it is determined that the growth is stopped, and ammonia water for curing may be added.

  The time until the particle growth stops depends on the ammonia concentration of the reaction solution, and is about 30 minutes (when the ammonia concentration is high) to 70 minutes (when the ammonia concentration is low).

  In the aging step, stirring is preferably performed after the addition of aqueous ammonia. This is to quickly mix the reaction solution and aqueous ammonia. The stirring time is preferably a short time, preferably 1 to 15 minutes, particularly 5 to 10 minutes. When ammonia water is added, the surface of the polyorganosiloxane particles becomes sticky, and the particles easily aggregate. If stirring is continued for a long time in this state, the particles collide with each other in the reaction solution to form huge aggregates, making it difficult to obtain monodispersed silica particles. Therefore, the stirring is quickly stopped to ripen the polyorganosiloxane particles while preventing the aggregation by preventing the reaction solution from flowing. When ripening proceeds in this state, the adhesiveness of the polyorganosiloxane particle surface will eventually disappear, and the precipitated particles will not aggregate.

  After completion of the stirring, the reaction solution is allowed to stand as it is, and polyorganosiloxane particles are aged. The aging time is preferably 8 to 24 hours, particularly 12 to 16 hours. The polyorganosiloxane particles that have been aged have a stabilized surface, and can be recovered without scratches, chips, or aggregation.

  Next, the recovery process will be described.

  The recovery step is a step of recovering and drying polyorganosiloxane particles from the reaction solution. In order to recover the polyorganosiloxane particles, for example, after the polyorganosiloxane particles are naturally settled and precipitated, or after the particles are precipitated by a centrifuge, the supernatant of the reaction solution is removed, and then placed in a container. A method of drying the remaining polyorganosiloxane particles can be employed.

  The method of the present invention includes a step of firing the obtained polyorganosiloxane particles while maintaining the oxygen concentration in the atmosphere at 1 to 10%.

  This firing step will be described below.

  Firing is performed while maintaining an atmosphere having an oxygen concentration of 1 to 15%, preferably 1 to 10%, more preferably 1 to 7%, and still more preferably 1 to 3%. When firing in an atmosphere having a high oxygen concentration (for example, in the air), the organic group decomposition reaction occurs actively, and the particle temperature may increase rapidly (for example, up to about 700 ° C.) due to the reaction heat. When the particle temperature rises rapidly, the particles shrink rapidly and cracks or cracks. Therefore, it is important to fire in an atmosphere having a low oxygen concentration. When firing in an atmosphere having a low oxygen concentration, the decomposition reaction of the organic group proceeds slowly, and it becomes easy to suppress a rapid increase in particle temperature. The lower the oxygen concentration, the fewer cracks and cracks are generated. However, when firing in an atmosphere where the oxygen concentration is too low or oxygen is not present at all, decomposition of the organic group is suppressed, carbon atoms may remain in the silica particles, and the particles may be blackened. Therefore, it is necessary to keep the oxygen concentration in the atmosphere at a predetermined concentration so that the firing atmosphere does not become deficient in oxygen.

  In order to maintain the oxygen concentration, for example, a gas adjusted to a predetermined oxygen concentration may be continuously supplied into the firing atmosphere. As a method of adjusting the oxygen concentration, for example, a method of reducing the oxygen concentration by mixing air and an inert gas (nitrogen, helium, argon, etc.) can be employed. If an inert gas is mixed with air, the oxygen concentration can be easily adjusted to a value below air. As the inert gas, it is preferable to use inexpensive nitrogen.

  The firing temperature is preferably 400 to 1000 ° C., particularly 450 to 900 ° C., and the firing time is preferably 6 to 20 hours, particularly 8 to 14 hours. If the firing temperature is too low, sufficient strength (compressive strength) may not be obtained. On the other hand, if the firing temperature is too high, the silica particles become too hard, which is not preferable because they may damage the thin film on the liquid crystal substrate when used as a spacer for a liquid crystal display. When the firing time is too short, the shrinkage of the particles according to the firing temperature is not completed, and the progress of the shrinkage of the particles varies depending on the firing position, and the diameter of the silica particles after firing may vary. Therefore, it is necessary to maintain the firing temperature at least until the silica particles at the position where the heat transfer is slowest contract completely. Moreover, since a lead time becomes long when baking time is too long, it is unpreferable.

  In this way, silica particles can be obtained. The obtained silica particles have an average particle size of about 2.0 to 10.0 μm and a CV value of about 0.5 to 1.5%. Further, it contains almost no cracked particles, cracked particles, and blackened particles. Preferably, the total of cracked particles and cracked particles is less than 5% by volume of the total particles, 0.5% Less than volume%, especially less than 0.1 volume%, and blackened particles are less than 0.3 volume%, less than 0.02 volume%, especially less than 0.01 volume% of the total particles.

“Cracked particles” mean particles that can be confirmed to have lines (cracks) in the diameter direction of the particles when observed with a microscope (see FIG. 1). “Cracked particles” means particles that appear hemispherical when observed under a microscope (see FIG. 2). “Blackened particles” mean particles that do not transmit light and appear as black spheres when observed under a microscope. (See Figure 3)
Moreover, the measuring method of an average particle diameter and a CV value is the value calculated | required using the following method (image sharing method). First, a microscope image of the dried silica particles is captured with a CCD camera, and the diameter of the silica particles is measured by image processing. Specifically, the particle image is divided into two upper and lower images on the monitor, and the coordinates A where the lower end of the upper image and the upper end of the lower image are in contact are recorded. Next, the upper and lower images are turned upside down, and the coordinates B where the lower end of the upper image and the upper end of the lower image contact again are recorded. AB is a value representing the diameter of the silica particles on the monitor, and this value (AB) is corrected to the actual size to calculate the diameter of the target silica particles (see FIG. 4). The diameter of particles is measured, and the average particle diameter and standard deviation are calculated. Furthermore, CV value is calculated | required from the following formula.

  CV value = standard deviation value / average particle size × 100 (%)

Hereinafter, the present invention will be described in detail based on examples.
(Preparation process)
First, as an aqueous solvent, a solution obtained by uniformly mixing 34373.8 g of pure water and 1865.2 g of n-butanol was prepared. Moreover, what mixed MTMS1418.0 and ethanol 736.7g uniformly was prepared as a mixed solution.

Next, 15 minutes after the preparation of the mixed solution, the mixed solution was added to an aqueous solvent to prepare a reaction solution. Stirring (100 rpm) was continued after the mixed solution was added.
(Deposition / growth process)
First, 825.6 g of 0.3% aqueous ammonia was prepared, and this was added to the reaction solution 5 minutes after the addition of the mixed solution. As a result, MTMS and water were hydrolyzed and polycondensed to deposit and grow polyorganosiloxane particles. Stirring (100 rpm) was continued after addition of 0.3% aqueous ammonia.
(Aging process)
First, 621.5 g of 3.1% ammonia water was prepared. Next, after confirming that the growth of the polyorganosiloxane particles in the reaction solution had stopped, the prepared 3.1% aqueous ammonia was added. Stirring was stopped after 5 minutes, and the reaction vessel was immediately left in a thermostat kept at 60 ° C. and held for 16 hours. As a result, the polyorganosiloxane particles were aged and allowed to settle naturally.

The timing of adding ammonia water was determined by the following method. First, a sample of a reaction solution during the growth of polyorganosiloxane particles was collected with a dropper, dropped onto a preparation and covered with a cover glass, and observed with a microscope. Next, a microscopic image was captured with a CCD camera, and the diameter of the polyorganosiloxane particles was measured by image processing. This operation was repeated every 10 minutes, and when the change in the diameter of the polyorganosiloxane particles disappeared, it was determined that the growth was stopped. In this example, it was 90 minutes after the addition of 0.3% aqueous ammonia.
(Recovery process)
The reaction vessel in which the polyorganosiloxane particles were precipitated was taken out from the thermostat and the supernatant was removed. Subsequently, the reaction container was left still in a thermostat kept at 60 ° C. and held for 12 hours to dry the polyorganosiloxane particles.

The polyorganosiloxane particles thus produced and recovered were 587 g, the average particle size was 8.993 μm, the standard deviation was 0.067 μm, and the CV value was 0.75%.
(Baking process)
Next, the recovered polyorganosiloxane particles were placed on a baking dish, placed in an electric furnace, and baked at 450 ° C. for 12 hours while continuously supplying the gas shown in Table 1.

  As a result, 475 g of silica particles were obtained. About the obtained sample, the average particle diameter, the standard deviation, the CV value, the ratio of cracked particles, cracked particles, and blackened particles were evaluated. The results are shown in Table 1. Examples 4 and 5 show comparative examples.

  The average particle size, standard deviation, and CV value were calculated from the values obtained by the image sharing method described above. The ratio of cracked particles, cracked particles, and blackened particles was determined by observing 1000 particles with a microscope.

  The silica particles obtained by the method of the present invention are suitable as a spacer for a seal part of a liquid crystal display panel, but other than this, for example, used as a spacer for a display part of a liquid crystal display panel, a filler for a semiconductor resin sealing material, etc. Is possible.

It is a microscope picture of the silica particle which cracked. It is a microscope picture of the broken silica particle. It is a microscope picture of the blackened silica particle. It is explanatory drawing of an image sharing method.

Claims (6)

  A method for producing silica particles in which an alkoxysilane having a non-hydrolyzable group is hydrolyzed and polycondensed to produce polyorganosiloxane particles, which are fired to produce silica particles, wherein the oxygen concentration in the firing atmosphere is reduced. A method for producing silica particles, characterized by firing while maintaining 1 to 15%.   The method for producing silica particles according to claim 1, wherein the alkoxysilane having a non-hydrolyzable group is methyltrimethoxysilane.   Baking at 400-1000 degreeC, The manufacturing method of the silica particle of Claim 1 or 2 characterized by the above-mentioned.   The method for producing silica particles according to any one of claims 1 to 3, wherein firing is performed while flowing a mixed gas of air and an inert gas into the atmosphere.   Silica particles produced by the method according to claim 1.   Silica particles obtained by hydrolyzing and polycondensating alkoxysilanes having non-hydrolyzable groups to produce polyorganosiloxane particles, which are then fired, and containing cracked particles and cracked particles Silica particles, characterized in that the total amount of is less than 5% by volume and the content of blackened particles is less than 0.3% by volume.