JP2006096599A - Method of producing spherical molten silica powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a spherical molten silica powder stuck with silica fume, by which the melting rate is made high and the sticking amount of the silica fume can be easily adjusted. <P>SOLUTION: The method for producing the spherical molten silica powder stuck with silica fume is characterized by spraying an aqueous slurry containing a silicon dioxide powdery raw material in a concentration of 20-80 mass% into a flame formed in a furnace while dispersing the slurry with a gas having a projection speed of at least 50 m/s or higher. In this case, it is preferable to adopt at least one embodiment selected from the embodiments that the concentration of the silicon dioxide powdery raw material in the aqueous slurry is 50-70 mass% and the gas having a projection speed of at least 50 m/s forms a swirl stream in the furnace. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing spherical fused silica powder.

  Conventionally, as a resin composition for semiconductor encapsulation (hereinafter, also referred to as “sealing material”), for example, inorganic particles that are melt-processed in a resin such as an epoxy resin, particularly those filled with fused silica powder are used. ing. If the particles constituting the fused silica powder are spherical, the resin can be highly filled, and the fluidity at the time of sealing, mold wear resistance, etc. are excellent, so the spherical fused silica powder is preferred. It is used.

  Spherical fused silica powder is produced, for example, through a process in which a silicon dioxide powder raw material (for example, silica powder) is entrained with a carrier gas such as air in a flame in a flame formed in a melting zone in a furnace and injected from a burner. The The injected silicon dioxide powder raw material is subjected to melting and spheroidizing treatment to become spherical fused silica powder, cooled and solidified while passing through a cooling zone continuous with the melting zone, and collected by a collection system. In the collection system, a collector such as a gravity settling chamber, a cyclone, a bag filter or the like is installed as appropriate so that powder of a desired particle size can be obtained stepwise.

On the particle surface of the spherical fused silica powder produced in this way, fine particles of 1 μm or less called silica fume, which is generated when the SiO ₂ component of the silicon dioxide powder raw material once becomes SiO vapor and is oxidized and deposited, are attached. . When the amount of silica fume adhering to the particle surface is an appropriate amount, it is preferable because it exhibits a roller action in the gaps between the silica particles and improves the fluidity of the sealing material. This increases the flow rate and inhibits fluidity, and also causes the particles to aggregate due to the adhesion of silica fume.

Since it is usually difficult to adjust the amount of silica fume attached, it has been proposed to remove the silica fume component by wet mixing with an auxiliary agent (Patent Document 1). However, since this method requires a drying step and a crushing step, the steps are complicated. In addition, since most of the silica fume is removed, the above-mentioned roller action of the corner cannot be used. Silica fume, on the other hand, pays attention to the fact that the SiO ₂ component of the silicon dioxide powder raw material once forms SiO vapor, which is oxidized and deposited. In order to reduce the temperature of the combustion flame and prevent the generation of SiO vapor, silicon dioxide is used. It has been proposed (Patent Document 2) that a powder raw material is supplied into a frame with an inert gas. However, in this method, since the recovered powder contains a large amount of unmelted particles, there is a risk that the electrical insulating property, the low thermal expansion coefficient, etc. of the sealing material may deteriorate.
JP 2000-007319 A JP 2003-261328 A

  In view of the above, an object of the present invention is to provide a method for producing a spherical fused silica powder having a silica fume attached, which has a high melting rate and can easily adjust the amount of silica fume deposited. The object of the present invention can be achieved by covering a silicon dioxide powder raw material with water molecules and spraying it into a flame.

  That is, the present invention sprays water slurry having a silicon dioxide powder raw material concentration of 20 to 80% by mass into a flame formed in the furnace while dispersing it in a gas having a protrusion speed of at least 50 m / s. It is a manufacturing method of the spherical fused silica powder to which the silica fume adhered was characterized. In this case, the concentration of the silicon dioxide powder in the water slurry was selected to be 50 to 70% by mass, and the gas having a protrusion speed of at least 50 m / s formed a swirling airflow in the furnace. It is preferred to have at least one embodiment.

  Furthermore, the average particle diameter of the spherical fused silica powder is 1.5 times or less of the average particle diameter of the silicon dioxide powder raw material, and the specific surface area is 5 times or less of the theoretical value calculated from the average particle diameter of the spherical silica powder, and 1 μm or less. Silicon slurry powder of water slurry so that spherical fused silica powder having a particle content of 5% by mass or less (excluding 0), that is, silica fume adhesion amount of 5% by mass or less (excluding 0) is obtained. It is preferable to adjust the concentration of the raw material and the gas protruding speed.

  According to the present invention, the melting rate is, for example, 99% or more, and the fused amount of silica fume on the surface of the fused silica particles is adjusted within a range of 5% by mass or less (not including 0), and the spherical melting with silica fume adhered thereto Silica powder can be produced. Furthermore, mass production of spherical fused silica powder having such characteristics becomes possible. The reason why such an effect could be achieved is that the transfer of heat to the silicon dioxide particles in the melting zone is mild by making the silicon dioxide powder raw material into a water slurry, that is, by covering the silicon dioxide particles with water molecules. In addition, the fine silicon dioxide particles confined in the water droplets are spheroidized as particles having a size corresponding to the diameter of the water droplets, and the water slurry is a high-speed gas having a protrusion speed of at least 50 m / s. It is related to the fact that the SiO vapor corresponding to the speed of the high-speed gas could be generated by dispersing in the above, that is, the amount of silica fume adhered to the surface of the fused silica particles could be adjusted. I believe.

The silicon dioxide powder raw material used in the present invention was obtained by a sol-gel method from, for example, silica powder, particularly silica powder obtained by pulverizing natural high-purity silica, silica gel synthesized by a wet reaction of alkali silicate and mineral acid, and alkoxysilane. For example, a crushed gel. Among these, natural high-purity quartzite pulverized powder having a SiO ₂ purity of 99.5% by mass or more is preferable from the viewpoint of production cost and ease of adjusting the particle size of the raw material powder. The particle size of the silicon dioxide powder raw material can be freely changed according to the desired product particle size. In general, the average particle diameter may be, for example, 100 μm or less, and the powder may contain a large amount of fine powder of 1 μm or less in which the powders easily aggregate. For example, propane, butane, propylene, acetylene, hydrogen or the like is used as the fuel gas for forming the flame, and air, oxygen or the like is used as the auxiliary combustion gas.

  A feature of the present invention is that when a silicon dioxide powder raw material is injected into a flame, a water slurry having a concentration of the silicon dioxide powder raw material of 20 to 80% by mass is sprayed, and the protrusion speed of the water slurry is at least 50 m / s. It is spraying while being dispersed with the above gas.

  If the silicon dioxide powder raw material concentration in the water slurry is remarkably smaller than 20% by mass, the viscosity of the water slurry decreases and droplet formation at the time of dispersion becomes easy, but the amount of heat required for water evaporation increases, and silicon dioxide There is a risk that the amount of heat required to melt the powder will be insufficient. On the other hand, if the silicon dioxide powder concentration is significantly higher than 80% by mass, the water slurry viscosity increases, so that not only another means is required for spraying with good dispersibility in the flame, but also particle size control is easy. There is a risk of disappearing. The silicon dioxide powder raw material concentration of a particularly preferable water slurry is 50 to 70% by mass.

  Japanese Patent Application Laid-Open No. 2000-247626 describes that a mixed powder obtained by mixing a metal powder with a silica powder raw material is sprayed as a water slurry. This prior art is a method in which silica powder is gasified to SiO by using metal silicon powder as a reducing agent to produce ultrafine silica powder (silica fume) of 1 μm or less, and the total amount of recovered powder exceeds 1 μm or less. The present invention is different from the present invention in that a spherical fused silica powder in which a small amount of silica fume adheres to the surface of fused silica particles is produced, whereas the purpose is to obtain finely divided silica powder. Therefore, it is desirable that the water slurry used in the present invention does not contain metal silicon powder.

  The water slurry can be adjusted by a batch method in which a predetermined amount of water and silicon dioxide powder are put into a container and slurried with a stirrer, or a continuous method in which the slurry is continuously adjusted with a line mixer. In order to improve the dispersibility of the silicon dioxide powder raw material in the water slurry, a dispersant containing a small amount of, for example, polycarboxylic acid, polyacrylic acid or a salt of those acids, specifically, trade name manufactured by Kao Corporation It is preferable to use 1 type (s) or 2 or more types selected from "Poise 532A", Nippon Oil & Fats Co., Ltd. trade names "AKM-0531", "HKM-50A", and "AKM-3011-60".

  In the present invention, the water slurry is dispersed in a gas having a protruding speed of at least 50 m / s, preferably 100 to 300 m / s, and sprayed into the flame. That is, the protrusion speed of the water slurry is determined by the gas speed that gives dispersion when the slurry is sprayed into the flame. If the gas projection speed is significantly lower than less than 50 m / s, the water slurry droplets cannot be sufficiently dispersed, so that they are supplied into the flame in a state close to the water flow, and contain many unmelted particles. There is a fear. As the gas to be dispersed, an auxiliary combustion gas such as air or oxygen, or an inert gas such as nitrogen or argon is preferably used, but a flammable gas such as propane or hydrogen can also be used.

  As a means for conveying the water slurry to the injection port, a general-purpose pump such as a tube pump, a diaphragm pump, or a vortex pump can be used. For spraying the water slurry, for example, a spray sprayer such as a two-fluid nozzle is used. At that time, in order to make the droplets of the slurry fine, a high-pressure gas is used, and the water slurry is sprayed into the flame accompanying the gas.

  In some two-fluid nozzles, a gas injected with water slurry forms a swirling flow in a furnace. In the present invention, a swirl airflow pattern is formed from the point that the droplets of the slurry are atomized, and further, such a swirl airflow pattern is formed without applying a large load to the transport to the injection port. Use is preferred. An example of a commercial product of a two-flow nozzle that forms a swirling flow is a trade name “BNH500S-IS” manufactured by Atmax Co., Ltd.

  The apparatus used in the present invention comprises a furnace in which a two-fluid nozzle is installed and a collection system for spherical fused silica powder. The furnace is composed of a melting zone where a flame is formed and a silicon dioxide powder raw material is melted and spheroidized, and a cooling zone where the spherical fused silica powder is cooled and solidified naturally or forcibly. In the cooling zone, the spherical fused silica powder is cooled to a temperature of, for example, 1000 ° C. or less so that the operation of the collection system is facilitated. When forced cooling is not performed, the length of the cooling zone is designed so that the spherical fused silica powder stays for the time to reach that temperature. In order to produce fine spherical fused silica powder having an average particle size of 10 μm or less by the production method of the present invention, the spherical fused silica particles formed in the melting zone are coalesced so that the particles are not deformed or coarsened. It is preferable to perform forced cooling promptly. The forced cooling is desirably performed by supplying a cooling gas such as air from the vicinity of the connection portion between the melting zone and the cooling zone, which also has an advantage that the spherical fused silica particles can be transported by gas to the collection system.

  In the present invention, each particle of the silicon dioxide powder raw material is covered with water molecules and sprayed, so that heat transfer to the silicon dioxide particles in the melting zone becomes mild. As a result, the particles that are melted collide with each other and the size of the particles becomes extremely small, so that the average particle size of the spherical fused silica powder is 1.5 times or less than the average particle size of the silicon dioxide powder raw material, The specific surface area can be reduced to 5 times or less of the theoretical value calculated from the average particle diameter of the spherical silica powder. Moreover, since the amount of SiO vapor can be generated in accordance with the velocity of the water slurry by setting the gas slurry protruding speed to 50 m / s or more as the gas protruding speed, The amount of silica fume adhering to the surface can be freely controlled within a range of 5% by mass or less (excluding 0).

  Spherical fused silica powder was produced using a vertical furnace in which a two-fluid nozzle was installed at the top of the furnace and an apparatus in which the lower part was directly connected to a collection system. The water slurry is pumped from the center of the two-fluid nozzle and sprayed into the flame. Combustion gas and auxiliary combustion gas are injected from its surroundings to form a flame. Control of the amount of combustion gas and auxiliary gas Adjusts the flame length and flame temperature. The spherical fused silica powder produced in the furnace is sucked by a blower, guided to a collection system, and collected by a bag filter.

Example 1
100 parts by mass of pulverized silica stone powder (average particle size: 12 μm, SiO ₂ purity: 99.9% by mass) and 100 parts by mass of ion-exchanged water are mixed with a stirring mixer to form an aqueous slurry (silicon dioxide powder raw material concentration: 50% by mass). Was prepared. This slurry was sprayed at 30 L / hr in a flame (temperature about 1900 ° C.) from a two-fluid nozzle (“BNH500S-IS” manufactured by Atmax Co., Ltd.) by pump conveyance. For spraying, a gas (oxygen) of 24 Nm ³ / hr was used in a two-fluid nozzle, and the protrusion speed was 150 m / s. It has been separately confirmed that this gas forms a swirling airflow in the furnace. Incidentally, the burner, LPG as fuel gas: 10 Nm ³ / hr, oxygen as combustion support gas: inject 40 Nm ³ / hr to form a flame.

  The spherical fused silica powder collected by the bag filter partially adhered to the furnace body, but the recovery rate was 95% by mass. The obtained spherical fused silica powder was measured for the following physical properties. The results are shown in Table 1.

Examples 2 to 7, Comparative Examples 1 and 2
Spherical fused silica powder was produced in the same manner as in Example 1 except that the concentration of the silicon dioxide powder raw material in the water slurry, the amount of water slurry feed, and the gas projection speed were variously changed.

Comparative Example 3
The same conditions as in Example 1 except that a water slurry mixed with metal silicon powder was used, that is, a water slurry of 50 mass% water, 45 mass% silicon dioxide powder, and 5 mass% metal silicon powder was used. To produce spherical fused silica powder.

Comparative Example 4
A spherical fused silica powder was produced according to Example 1 except that the pulverized silica powder was supplied as a powder instead of being sprayed with a water slurry. The pulverized silica powder was transported 21.4 kg / h of the pulverized silica powder to the injection port with a table feeder and sprayed from a feed tube having an inner diameter of 21 mm at the center of the burner using 20 Nm ³ / h oxygen gas.

Example 8
A spherical fused silica powder was produced under the same conditions as in Example 1 except that a gas that does not form a swirling flow in the furnace was used as the two-fluid nozzle.

(1) Average sphericity A particle image photographed with a scanning electron microscope “FE-SEM, model JSM-6301F” manufactured by JEOL Ltd. was subjected to image analysis and measured. That is, the projected area (A) and the perimeter (PM) of the particle are measured from the photograph. When the area of a perfect circle corresponding to the perimeter (PM) is (B), the roundness of the particle can be displayed as A / B. Therefore, assuming a perfect circle having the same circumference as the sample particle (PM), PM = 2πr and B = πr ² , so that B = π × (PM / 2π) ² , and each particle Can be calculated as sphericity = A / B = A × 4π / (PM) ² . The sphericity of 200 arbitrary particles thus obtained was determined, and the average value was taken as the average sphericity of the powder. The average sphericity is preferably 0.80 or more.

(2) Melting rate Using a powder X-ray diffractometer “Model Mini Flex” manufactured by RIGAKU, X-ray diffraction analysis of the sample was performed in the range of 2θ of CuKα ray of 26 ° to 27.5 °. In the case of crystalline silica, a main peak exists at 26.7 °, but in fused silica it does not exist at this position. When fused silica and crystalline silica are mixed, the peak height of 26.7 ° changes depending on the ratio thereof. Therefore, from the ratio of the X-ray intensity of the sample to the X-ray intensity of the crystalline silica standard sample, the mixed ratio of crystalline silica (X-ray intensity of the measured substance / X-ray intensity of the crystalline silica) is calculated, and the formula, melting rate (%) = (Mixing ratio of 1-crystalline silica) × 100 The melting rate was determined.

(3) Average particle diameter It measured using the "model LS-230" (laser diffraction light scattering method) particle size distribution measuring machine by a Beckman Coulter company. A sample was prepared by using water as a solvent and dispersing the output of 200 W for 1 minute using a homogenizer. The concentration of PIDS (Polarization Intensity Differential Scattering) was adjusted to 45 to 55%, the refractive index of water was 1.33, and the refractive indexes of silicon dioxide powder and fused silica powder were 1.50.

(4) Adhesion amount of silica fume In the cumulative weight distribution in the particle size distribution analyzer, the cumulative weight value of 1 μm or less was defined as the adhesion amount of silica fume. In the particle size distribution measuring instrument “Model LS-230” used in the present invention, since there is no boundary in measurement at 1 μm, the value was determined to be 0.953 μm or less. The adhesion amount of silica fume is preferably 5% by mass or less (excluding 0).

(5) Specific surface area BET method specific surface area was measured using a measuring machine “4-SORB U2” manufactured by Yuasa Ionics.

  From Table 1, it can be seen that Examples 1 to 7 of the present invention have spherical fused silica powders with excellent melting rate and low specific surface area to which silica fume adheres, as compared with Comparative Examples 1 to 4. In particular, if the concentration of the silicon dioxide powder raw material in the water slurry, the amount of water slurry feed and the gas projection speed are selected, the average particle size of the spherical fused silica powder is 1.5 times or less than the average particle size of the silicon dioxide powder raw material. A spherical fused silica powder having a surface area of 5 times or less the theoretical value calculated from the average particle diameter of the spherical silica powder and a silica fume adhesion amount of 5 mass% or less (not including 0) was obtained. Further, in Examples 1, 4, and 6, particle enlargement was also suppressed as compared with Comparative Examples 1 and 2. Example 8 was slightly inferior in average sphericity and average particle size as compared to Example 1.

  The spherical fused silica powder produced by the present invention can be used, for example, as a sealing material filler.

Claims (4)

  A water slurry having a silicon dioxide powder raw material concentration of 20 to 80% by mass is sprayed into a flame formed in a furnace while being dispersed in a gas having a protrusion speed of at least 50 m / s or more. A method for producing spherical fused silica powder with silica fume attached.   2. The production method according to claim 1, wherein the concentration of the silicon dioxide powder in the water slurry is 50 to 70% by mass.   The method according to claim 1 or 2, wherein the gas having a protrusion speed of at least 50 m / s forms a swirling airflow in the furnace.   Containing particles having an average particle diameter of spherical fused silica powder of 1.5 times or less of the average particle diameter of silicon dioxide powder raw material and a specific surface area of 5 times or less of the theoretical value calculated from the average particle diameter of spherical silica powder and 1 μm or less 4. The method according to claim 3, wherein the concentration of the silicon dioxide powder raw material in the water slurry and the gas protrusion speed are adjusted so that a powder having a rate of 5% by mass or less (not including 0) is obtained.