JP6980467B2 - Powder for spherical silica filler and its manufacturing method - Google Patents

Description

The present invention relates to a spheroidized powder for a spherical silica filler as a filler for the purpose of improving fluidity and filling property when blended in ceramic glass or a resin material. The present invention relates to a powder for a spherical silica filler, which is characterized in that it is used by blending it in a material such as ceramic glass, plastic or rubber, for example.

Generally, various fillers are used for the purpose of improving the physical properties and functions of ceramic glass, resin materials and the like. Keetite is one of the crystal structures of silica, and its existence under high temperature, high pressure, and high water vapor pressure has been confirmed [Non-Patent Documents 1 and 2]. In addition, the refractive index of keytite is 1.52 and the coefficient of thermal expansion is -1 ppm / K (0 ° C to 500 ° C), which are different from amorphous silica, which is one of the widely used fillers. Have. Therefore, it is expected to be used in many applications as a filler in order to control the coefficient of thermal expansion, the refractive index, etc. of ceramic glass, resin materials, and the like.

However, keytite is not common as a filler. Keetite is not a general crystalline phase such as quartz and cristobalite, and it is difficult to synthesize it at low cost, and there are few examples of its application as a filler.

In order to use it more preferably as a filler, it is necessary to improve the filling property, processability, and melt fluidity in ceramic glass and resin. Less is required. For example, in Patent Document 1, 20% by mass of keetite is filled in a synthetic resin as an inorganic filler having a small coefficient of thermal expansion, but the filling rate of keetite particles is low and the effect of reducing thermal expansion is insufficient. In addition, fillers other than keetite are also filled, and it cannot be said that the effect of reducing thermal expansion is due to keetite.

Various methods have been disclosed as methods for synthesizing keytite.

Keetite is mainly synthesized under high temperature, high pressure and high steam pressure. For example, Non-Patent Document 1 exemplifies that it is synthesized for hydrothermal crystallization under the conditions of a temperature of 380 to 585 ° C. and a pressure of 34 to 124 MPa. Further, Non-Patent Document 2 exemplifies that it is synthesized by hydrothermal treatment at a temperature of 300 ° C., a pressure of 1 to 3 kbar, and a treatment time of 50 hours or less. Such hydrothermal synthesis requires a container that can withstand high temperatures and high pressures, and it is difficult to synthesize at low cost.

Methods other than the hydrothermal synthesis method under high temperature, high pressure, and high steam pressure have also been proposed. For example, in Non-Patent Document 3, 0.5 to 7% by mass (oxide equivalent) of alkali metal carbonate (lithium carbonate) is added to a submicron spherical silica prepared by hydrolysis of a metal alkoxide in a Menou dairy pot. It is exemplified that keetite is synthesized by mixing and baking a molded product formed at 100 MPa by a rubber breath method at 700 to 800 ° C. for 6 hours. However, since keetite is obtained as a sintered body by this method, it is difficult to obtain it as spherical particles that can be mixed with ceramic glass, resin, or the like. In addition, the ratio of the keytite phase, the average circularity of the obtained particles, and the effect of filling the resin are not specified.

Special Fair 7-39146 Gazette

British Ceramic Transaction Journal 83 (5), 129 (1984) Connections to Minerology and Technology 53,25 (1975) Journal of the Ceramic Society of Japan 105 (5), 385 (1997)

An object of the present invention is to provide a powder for a spherical silica filler whose thermal expansion coefficient can be easily controlled because it has low viscosity and high fluidity when filled in ceramic glass or resin and can be filled highly. It is in.

(1) A powder for a spherical silica filler, which has an average circularity of 0.80 or more and contains 80% or more of a keetite phase.
( 2 ) The powder for spherical silica filler according to (1), which is used by blending in ceramic glass or resin .

According to the present inventor, it is possible to provide a powder for a spherical silica filler having low viscosity and high fluidity when filled in ceramic glass or a resin material. Further, since the keytite phase content is high, the effect of controlling the coefficient of thermal expansion is large when the ceramic glass or resin is filled.

FIG. 1 is a scanning electron micrograph of the powder for spherical silica filler obtained in Example 1. FIG. 2 is an X-ray diffraction pattern of the powder for spherical silica filler obtained in Example 1.

The powder for spherical silica filler of the present invention has an average circularity of 0.80 or more, preferably 0.85 or more, and more preferably 0.90 or more. When the average circularity is less than 0.80, the rolling resistance of the particles when mixed with glass or resin increases, and the fluidity decreases. Further, the powder for spherical silica filler of the present invention contains 80% by mass or more of the keetite phase. If the content of the keytite phase is less than 80% by mass, the effect of reducing the coefficient of thermal expansion is insufficient.

The average particle size of the powder for spherical silica filler of the present invention is not particularly specified, but is preferably 0.05 μm to 100 μm, particularly preferably 0.2 μm to 50 μm in consideration of being used as a filler.

The spherical amorphous silica particles which are the raw materials of the present invention have an average circularity of 0.80 or more, preferably 0.85 or more, and more preferably 0.90 or more. When the average circularity of the spherical amorphous silica particles is less than 0.80, the average circularity of the obtained spherical keytite is less than 0.80, the rolling resistance of the particles when mixed with the resin is increased, and the fluidity is increased. Decreases.

As a method for producing a powder for a spherical silica filler of the present invention, a heat crystallization method is used.

The heat crystallization method is a method of heating raw material powder at a high temperature to crystallize it. Any heating device may be used as long as a high temperature can be obtained, and for example, an electric furnace, a rotary kiln, a pusher furnace, a roller herskilln, and the like are used.

The temperature for heating the raw material spherical amorphous silica particles is preferably 650 to 725 ° C. If the heating temperature is less than 650 ° C., crystallization takes time, crystallization is insufficient, the ratio of the keytite phase is low, and the effect of reducing thermal expansion is insufficient. If the heating temperature exceeds 725 ° C., a crystal phase other than keetite, for example, quartz or the like is formed, so that the effect of reducing thermal expansion is insufficient. The heating time is preferably 3 to 20 hours. If the heating time is less than 3 hours, the crystallization into keetite becomes insufficient, and the effect of reducing thermal expansion becomes insufficient. Further, if the heating time exceeds 20 hours, it is not economical and quartz or the like, which is a crystal phase other than keetite, is produced, so that the effect of reducing thermal expansion is insufficient.

The agglomerates of silica containing the keetite phase obtained by the heat crystallization method are crushed into a powder. The crushing method is not particularly specified, but an agate mortar, a ball mill, a vibration mill, a jet mill, a wet jet mill, or the like is used. The crushing may be carried out by a dry method, or may be mixed with a liquid such as water or alcohol and crushed by a wet method. The added lithium compound can be removed by washing with water or alcohols before or after crushing. By drying after washing, a powdery spherical keetite can be obtained. The drying method is not particularly specified, but examples thereof include heat drying, vacuum drying, freeze drying, and supercritical carbon dioxide drying.

The method for mixing the lithium compound and the spherical amorphous silica as a raw material is not particularly specified, and examples thereof include agate mortars, ball mills, crushers such as vibration mills, and various mixers. At the time of mixing, the lithium compound and the raw material spherical amorphous silica may be mixed as a powder, or alcohols such as water, methanol, ethanol and isopropyl alcohol, and ketones such as acetone and methyl ethyl ketone may be mixed. It may be mixed with an organic solvent. Of these, it is particularly preferable to dissolve the lithium compound in water or an organic solvent and wet-mix it with spherical amorphous silica as a raw material because it is easy to uniformly mix.

The amount of the lithium compound added is preferably 0.01% by mass to 10% by mass in terms of lithium oxide. If it is less than 0.01% by mass, the crystallization rate to keytite is slow, crystallization takes a long time, and crystallization is insufficient, so that the effect of controlling the physical properties of ceramic glass or resin, for example, heat. The effect of reducing the expansion rate becomes insufficient. If it exceeds 10% by mass, the obtained keetite particles are easily fused, and spherical particles having a high average circularity cannot be obtained, so that it becomes difficult to fill ceramic glass, a resin material, or the like. Further, since quartz or the like which is a crystal phase other than keetite is also produced, the effect of controlling the physical properties of the ceramic glass or the resin, for example, the effect of reducing the coefficient of thermal expansion is insufficient.

At the time of heat crystallization, a lithium compound is added as an auxiliary agent for promoting crystallization to keytite. The lithium compound is not particularly specified as long as it contains a lithium element, but inorganic salts such as lithium oxide, lithium hydroxide, lithium carbonate, lithium chloride, lithium nitrate and lithium sulfate, lithium acetate, lithium oxalate and citric acid. Examples thereof include organic acid salts such as lithium, metallic soaps such as lithium octylate and lithium stearate, and organic lithiums such as methyl lithium, butyl lithium and phenyl lithium. Among them, lithium hydroxide or lithium oxide is particularly preferable because it can be uniformly mixed by wet mixing while being dissolved in water or an organic solvent, and impurities are less likely to remain after heating.

The spherical amorphous silica as the raw material powder is not particularly specified as long as it is obtained by a wet synthesis method such as a sol-gel method or a water glass method. The synthetic conditions of the sol-gel method are not particularly specified, but commonly used solvents such as alcohols such as methanol, ethanol, methoxyethanol and ethoxyethanol are used. As the silica source, alkoxysilanes such as tetraethoxysilane and tetramethoxysilane are used. As the catalyst, a basic catalyst such as ammonia, methylamine, sodium hydroxide and lithium hydroxide, and an acidic catalyst such as acetic acid, hydrochloric acid and sulfuric acid are used. Water is also added to hydrolyze the alkoxysilane. The particle size of the spherical amorphous silica can be adjusted by adjusting the amount of alkoxysilanes to be added. The spherical amorphous particles having a small particle size can be adjusted by reducing the amount of alkoxysilane added, and the spherical amorphous particles having a large particle size can be adjusted by increasing the amount of alkoxysilane added. In order to obtain a large particle shape, the alkoxysilane is not added all at once, but is added gradually or in several batches to obtain spherical particles. When a large amount of alkoxysilane is added at one time, aggregated particles are generated, which makes it difficult to obtain spherical particles. Ammonia is suitable as the catalyst, and the pH of the solution is preferably 8 to 12. The amount of water added is preferably 1 to 30% by mass. Spherical amorphous silica can also be obtained by adding an acid such as hydrochloric acid or sulfuric acid to an aqueous solution of water glass (sodium silicate), but spherical amorphous silica obtained by the sol-gel method having a small residual amount of impurities is preferable. ..

The spherical amorphous silica obtained by the wet method is dried to obtain a powder. The drying method is not particularly specified, but examples thereof include heat drying, vacuum drying, freeze drying, and supercritical carbon dioxide drying. In addition, by concentrating before drying, it can be dried efficiently. Filtration and centrifugation are examples of dry concentration methods. In order to suppress the aggregation of spherical amorphous silica, it is preferable to concentrate by filtration or the like, and then wash and remove the residual catalyst and alkoxysilanes with ethanol or the like and dry them.

Since the powder for spherical silica filler obtained in the present invention has a high average circularity, it has extremely good fluidity, exhibits extremely good moldability when filled in a resin, and can increase the filling rate. The obtained spherical particles can be further increased in filling rate by classifying the obtained spherical particles so as to obtain a desired average particle diameter or by performing surface treatment, if necessary. As the surface treatment agent, a silane coupling agent is generally used, but a titanate coupling agent or an aluminate-based coupling agent can also be used.

The powder for spherical silica filler of the present invention is used, for example, by blending it in glass. Examples of the type of glass include PbO-B ₂ O _3- ZnO system, PbO-B ₂ O _3- Bi ₂ O ₃ system, PbO-V ₂ O _5- TeO ₂ system, SiO _2- ZnO-R ₂ O. It has a composition of a system (R ₂ O is an alkali metal oxide), a SiO _2- B ₂ O _3- R ₂ O system, a SiO _2- B ₂ O _3- RO system (RO is an alkaline earth metal oxide), and the like. Glass is mentioned.

The powder for spherical silica filler of the present invention is used, for example, by blending it in a resin. Examples of the type of resin include polyamide resins such as epoxy resin, silicone resin, phenol resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyimide, polyamideimide and polyetherimide, polybutylene terephthalate and polyethylene terephthalate. Polyester, polyphenylene sulfide, total aromatic polyester, polysulfone, liquid crystal polymer, polyether sulfone, polycarbonate, maleimide modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber, styrene) resin, AES (acrylonitrile, ethylene, propylene, diene rubber-styrene) ) Resin and the like can be mentioned.

The ratio of the powder for spherical silica filler in the glass or resin is appropriately selected according to the physical properties such as the target coefficient of thermal expansion. For example, the amount of the resin used is appropriately selected in the range of preferably 1 to 100 parts by mass, more preferably 10 to 50 parts by mass with respect to 100 parts by mass of the keytite phase-containing spherical silica.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the Examples.

[Example 1]
(Synthesis of spherical amorphous silica)
Tetraethoxysilane: 21 g was added to a mixed solution of ethanol: 528 g, water: 48 g, and ammonia water (28% by mass): 122 g, and the mixture was reacted at room temperature for 3 hours with stirring. Centrifugal sedimentation and ethanol washing were repeated 3 times and then dried. The formation of spherical particles was confirmed with a scanning electron microscope, and it was confirmed that they were amorphous by powder X-ray diffraction. The average circularity was 0.97 and the average particle size was 0.4 μm.

(Synthesis of powder for spherical silica filler)
To 1 g of spherical amorphous silica, 14.1 mg of lithium hydroxide dissolved in 10 g of ethanol (5.0 mg as lithium oxide) was added, and the mixture was mixed in an agate mortar for 1 hour. The mixture was heated at 675 ° C. for 5 hours in an electric furnace, cooled, and then crushed in an agate mortar. The formation of spherical particles was confirmed with a scanning electron microscope (see FIG. 1). It was confirmed by powder X-ray diffraction that keytite was generated (see FIG. 2). The average circularity was 0.91 and the average particle size was 0.3 μm.

The characteristics of the particle compositions prepared in Examples and Comparative Examples were evaluated by the following methods.

[Identification and quantification of keytite phase]
The identification and quantification of the keytite phase was performed by powder X-ray diffraction measurement and Rietveld method. The equipment used was RINT-Ultima IV manufactured by Rigaku Co., Ltd., the X-ray source was CuKα, the tube voltage was 40 kV, the tube current was 40 mA, the scan speed was 5.0 ° / min, and the 2θ scan range was 10 ° to 80 °. For the quantitative analysis, Rietveld method software (integrated powder X-ray software PDXL manufactured by Rigaku Co., Ltd.) was used. As for the content of the keetite phase, 50% by mass of NIST standard sample α-alumina for X-ray diffraction was added to each sample as an internal standard substance, and the content of the keetite phase was measured. The results are shown in Tables 1 and 2.

[Average circularity]
After fixing the sample to the sample table with carbon tape, osmium coating was applied, and an image with a magnification of 100,000 times and a resolution of 2048 x 1356 pixels taken with a scanning electron microscope "JSM-7001F SHL" manufactured by JEOL Ltd. was captured in a personal computer. .. Using the image analysis device "MacView Ver.4" manufactured by Mountech Co., Ltd., the particles are recognized using a simple capture tool, and the projected area (S) of the particles and the projected peripheral length (L) of the particles are calculated. , The circularity was measured from the formula (1). When the photographed particles have a shape in which a plurality of primary particles are aggregated to form secondary particles, the secondary particles are regarded as a single particle, and the projected area (S) is the area and peripheral length of the entire secondary particles. (L) is the length measured along the interface of the secondary particles. The circularity of 100 particles having an arbitrary projected area equivalent circle diameter of 50 nm or more obtained in this manner was determined, and the average value thereof was taken as the average circularity.
Circularity = 4πS / L ² (1)

[density]
5 g of the powder obtained in Example 1 was placed in a sample cell for measurement, and measured by a gas substitution method using a dry densitometer (“Accupic II 1340” manufactured by Shimadzu Corporation).

[Average particle size]
The measurement was performed using a "laser diffraction type particle size distribution measuring device LS 13 320" manufactured by Beckman Coulter. As a sample, 50 cc of pure water and 0.1 g of the powder obtained in Example 1 were added to a glass beaker, and the sample was dispersed with an ultrasonic homogenizer (“SFX250” manufactured by BRANSON) for 1 minute. The dispersion liquid of the powder for spherical silica filler that had been subjected to the dispersion treatment was added drop by drop to the laser diffraction type particle size distribution measuring device with a dropper, and the measurement was performed 30 seconds after the predetermined amount was added. The particle size distribution was calculated from the data of the light intensity distribution of the diffracted / scattered light by the particles detected by the sensor in the laser diffraction type particle size distribution measuring device. The average particle size was obtained by multiplying the measured particle size value by the relative particle amount (difference%) and dividing by the total relative particle amount (100%). The% here is a volume%.

[viscosity]
Mix with bisphenol A type liquid epoxy resin (“JER828” manufactured by Mitsubishi Chemical Corporation) so that the powder obtained in Example 1 accounts for 50% by volume of the whole, and use a planetary stirrer (Shinky Co., Ltd. “Awatori Rentaro”). AR-250 ”, rotation speed 2000 rpm) was kneaded to prepare a resin composition. The viscosity of the obtained resin composition was measured under the following conditions using a rheometer (“MCR-300” manufactured by Nippon Sibel Hegner).
Plate shape: Circular flat plate 25 mmφ
Sample thickness: 1 mm
Temperature: 25 ± 1 ° C
Shear rate: 1s ^-1

[Coefficient of thermal expansion]
After mixing with low melting point glass (“TNS062” manufactured by Asahi Glass Co., Ltd., coefficient of thermal expansion: 13 ppm / K) so that the powder obtained in Example 1 accounts for 50% by volume of the whole, TMA ( The coefficient of thermal expansion was evaluated with "DIL402C" manufactured by Bruker. The temperature rise condition was 5 ° C./min, the measurement temperature was −10 ° C. to 280 ° C., and the atmosphere was a helium atmosphere. From the obtained results, the coefficient of thermal expansion of 0 ° C. to 100 ° C. was calculated.

Example 2-5, Comparative Example 1-6
The spherical amorphous silica obtained in Example 1 was treated in the same manner as in Example 1 except that it was treated at the heating temperature and heating time shown in Tables 1 and 2.

Example 6
The spherical amorphous silica obtained in Example 1 was mixed with 1 g of spherical amorphous silica with 12.3 mg of lithium carbonate (5.0 mg as lithium oxide) for 1 hour in an agate mortar. The procedure was the same as in Example 1.

Comparative Example 7
The spherical amorphous silica obtained in Example 1 was designated as Comparative Example 7, and evaluation was performed in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 8
Tetraethoxysilane: 21 g was added to a mixed solution of water: 48 g and ammonia water (28% by mass): 122 g, and the mixture was reacted at room temperature for 1 day without stirring. After repeating centrifugal sedimentation and ethanol washing three times, the obtained aggregates are wet-crushed in a mortar and atomized using a high-pressure homogenizer manufactured by Sugino Machine Limited (wet atomizer "Starburst Mini"). The obtained dispersion solution was centrifuged and dried to obtain a powder. The formation of crushed particles was confirmed with a scanning electron microscope, and it was confirmed that they were amorphous by powder X-ray diffraction. The average circularity was 0.78 and the average particle size was 0.5 μm. The obtained amorphous silica was heat-treated and evaluated in the same manner as in Example 1. The results are shown in Table 2.

The resin composition containing the powder for spherical silica filler of the present invention has a lower viscosity than the resin composition containing powder for spherical silica filler having a small average circularity, resulting in high filling. rice field. Further, the glass composition containing the spherical silica filler of the present invention has a result that the coefficient of thermal expansion can be suppressed to be lower than that of the glass composition containing the powder for spherical silica filler having a small keytite content.

The powder for spherical silica filler of the present invention has low viscosity and high fluidity when filled in ceramic glass or resin, can be highly filled, and has a high coefficient of thermal expansion due to its high keytite phase content. It can be used as a filler that is easy to control.

Claims (2)

A powder for a spherical silica filler having an average circularity of 0.80 or more and containing 80% by mass or more of a keetite phase. The powder for a spherical silica filler according to claim 1, wherein the powder is used by blending it in ceramic glass or a resin .

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