JPH11209106A - Production of spherical particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the agglomeration and the cohesion of a raw material powder and particles after being made spherical with each other during melting and cooling by controlling the jetting rate of an inorganic powder in the tip of a burner nozzle to a specific range. SOLUTION: The jetting rate of the inorganic powder from the nozzle is controlled to 70-1200 m/sec. The agglomeration and the cohesion of the fine particles with each other are liable to be generated at the rate below the lower limit and unmelted particles are increased at a rate exceeding the upper limit. In the ratio of a combustible gas to a supporting gas, the supporting gas quality is preferably 1.04-1.4 times of a theoretical supporting gas quantity when the theoretical supporting gas quantity is defined by the quantity of the supporting gas containing the theoretical oxygen quantity necessary for the complete combustion of the combustible gas. As the inorganic powder, a siliceous powder, which is used as a filler for a resin composition since it has required characteristics such as low thermal expansion and moisture resistance as a sealing agent, is preferably used and the particle diameter is preferably 0.1-20 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an inorganic powder containing spherical particles. More specifically, the present invention relates to a method for injecting an inorganic powder into a flame to heat and spheroidize the particles constituting the powder. The present invention relates to a method for producing spherical particles which is excellent in dispersibility and filling property and is suitable as a filler for a resin composition for semiconductor encapsulation.

[0002]

2. Description of the Related Art A sealing resin composition used for sealing a semiconductor element to isolate the element from moisture and the like and to improve its reliability has a low thermal expansion as the performance of the semiconductor element becomes higher and the surface mounting method is adopted. And high strength are required. For this reason,
A filler that can be highly filled in the resin is required while maintaining the conventional high fluidity when used as a sealing resin composition, and a spheroidizing technique of the filler has been developed as a means for solving this. ing.

As a technique for spheroidizing an inorganic powder, for example, a method of producing spherical particles while oxidizing metal fine particles by throwing them into a flame, a method of depositing a metal alcoholate under specific conditions by a sol-gel method, and a method of spheroidizing, A method has been proposed or put into practice in which irregular shaped particles are gradually rounded in a pulverizer to form pseudo spherical particles.

The present invention relates to a method in which an inorganic raw material powder is thrown into a high-temperature flame and the particles in the powder are melted or softened to form a spheroid. This method basically involves changing the chemical composition of the raw material powder. In addition, a high-purity inorganic powder can be easily obtained using a high-purity raw material. Furthermore,
This method is capable of simultaneously and widely spheroidizing particles having different particle diameters, and can be said to be a method suitable for mass production.

However, the raw material powder has a maximum particle size of 2
When a powder composed of fine particles of 0 μm or less is used, particularly a powder composed of 5 μm or less, each particle is melted in a flame while the dispersion of the particles is insufficient, and the particles are mutually attached to become enlarged spherical particles. Even if the individual particles are spheroidized as desired, during the cooling process immediately after passing through the flame, the individual particles contact each other and fuse and bond to form a dumpling. There is a problem that a coarser particle size distribution can be obtained.

[0006] In order to solve such a problem of particle enlargement due to agglomeration and coalescence between particles, see, for example, JP-A-6-19.
In JP-A-9013, cooling air is introduced into the flame forming region to adjust the flame forming region, thereby controlling the time of staying in the temperature region higher than the melting point of the raw material, thereby preventing fusion and fusion between particles. A method has been proposed. Also, Japanese Patent Application Laid-Open No. 6-56
Japanese Patent Publication No. 445 discloses a method of using a thermal spray burner that can change the cross-sectional area at the time of injection of a molten raw material, defining the gas flow rate at the time of injection of the raw material, and separately producing coarse powder and fine powder. Further, JP-A-61-35145 discloses a method in which the ratio of the amount of raw material / the amount of gas is reduced, the dispersibility between particles in a flame is improved, and the phenomenon of fusion between particles is reduced. It has been disclosed.

[0007]

However, according to the above method, when a powder composed of fine particles having a particle diameter of 20 μm or less is used as a raw material, the phenomenon of particle enlargement due to aggregation and coalescence between particles cannot be sufficiently suppressed. Therefore, the problem that it is difficult to obtain an inorganic powder containing spherical particles having the same particle size or particle size distribution as the raw material has not been solved yet.

An object of the present invention is to provide a method for producing an inorganic powder in which the inorganic powder is cast into a high-temperature flame to spheroidize the particles in the powder. And prevent aggregation and coalescence during cooling,
An object of the present invention is to stably provide an inorganic powder containing spherical particles having good dispersibility and little cohesion and coalescence.

[Means for Solving the Problems]

The present invention has been made in view of the above circumstances, and relates to a method for producing an inorganic powder containing spherical particles by charging a fine inorganic powder into a flame. Focusing attention on the particle size and the relationship between them, as a result of an experiment on their influence on the spheroidization process, the combustion gas was discharged at the tip of the burner nozzle at 70 to 12 mm.
When blowing at a high speed of 00 m / sec, the inorganic powder is preferably 300 to 12 with respect to silica fine powder of 5 μm or less.
When blowing at an ultra-high speed of 00 m / sec, there is little agglomeration and coalescence of the particles inside, and spheroidization is achieved,
As a result, the present inventors have found that inorganic powder containing spherical fine particles can be easily produced, and have reached the present invention. Also,
The inventors have found that the above effects can be more preferably obtained when supplying a predetermined range of the supporting gas amount larger than the stoichiometric combustion ratio, and have reached the present invention.

That is, the present invention relates to a method of carrying an inorganic powder on a combustible gas and / or a supporting gas and injecting it into a flame to heat and sphericalize the inorganic powder. 70-120 powder injection speed
This is a method for producing spherical particles, which is characterized by being performed at 0 m / sec. Further, the method is a method for producing spherical particles in which the inorganic raw material powder is a silica-based powder and has an average particle diameter of 0.1 to 20 μm.

Further, a method of supporting a combustible gas and / or a supporting gas with a siliceous powder having an average particle diameter of 0.1 to 5 μm and injecting it into a flame to heat and spheroidize the siliceous powder. Wherein the injection speed of the siliceous powder at the tip of the burner nozzle is 300 to 1200 m / sec. 1.04 ~ of quantity
This is a method for producing the spherical particles, which is 1.4 times.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, when an inorganic powder containing a large amount of fine particles is used as a raw material, the ratio of the raw material powder / gas amount is increased and the mixture is injected into a flame and heated and melted. In the cooling step, the particles repeatedly collide with each other, and the rate of aggregation and coalescence increases. Therefore, as the particle size of the raw material powder becomes closer to the fine powder side, the ratio of the raw material powder amount / gas amount has to be reduced. However, according to the present invention, since the gas velocity at the burner nozzle outlet is high, for example, even if a fine powder having an average particle diameter of 0.1 to 20 μm and having high cohesiveness is used as a raw material, ,
It is possible to easily obtain a powder composed of spherical particles having no average coalescence and having an average particle diameter comparable to that of the raw material.

The injection speed of the inorganic powder from the nozzle is equivalent to that of the carrier gas, and the injection speed of the inorganic powder can be known by knowing the speed of the carrier gas. At this time, when Qm = the amount of heat required for melting calculated from the specific heat and heat of fusion of the inorganic powder, Qt = the theoretical heat of combustion of combustible gas, the heat ratio P = Qm / Qt is 0.01 to 0.2.
It is preferable to set the inorganic powder concentration such that

The velocity of the carrier gas at the nozzle outlet is 70 m /
When the time is less than sec, aggregation and coalescence of the fine particles tend to occur, and when it exceeds 1200 m / sec, unmelted particles increase. A suitable range is 300 to 1000 m / sec, and particularly preferably 400 m / sec or more when using a siliceous fine powder raw material of 5 μm or less. The most desirable method is to inject a combustible gas and a supporting gas at the same speed or as a mixed gas from a burner and to put them into the formed flame.

Here, the gas velocity V is defined as S (m ² ), which is the nozzle opening area of the gas carrying the raw material inorganic powder at the nozzle tip of the burner for forming a flame.
Standard condition of gas carrying inorganic powder (0 ° C, 1 at
When the gas flow rate converted to m) is Qg (Nm ³ / sec), the flow rate is defined by the value calculated by the following equation (1). V = Qg / S (m / sec) (1)

As a method for supporting the inorganic powder on the carrier gas, for example, a known method such as supplying the inorganic powder cut from a table feeder to a burner together with the carrier gas may be used. The inorganic powder can be carried on one or both of a combustible gas and a supporting gas. Regarding the method of carrying on either one, according to the results of the study by the present inventors, the reason is not clear, but it is preferable to carry on a supporting gas, and it is easy to achieve the object of the present invention. .

When the inorganic powder is carried on both a combustible gas and a supportive gas, the gas velocity must satisfy the above-described predetermined range for each gas. On the other hand, when the velocity of the gas is lower than the predetermined velocity range, the possibility that the particles come into contact with each other increases, so that even if spheroidization is possible, agglomeration and coalescence are induced, and the average particle of the powder obtained The diameter becomes large. On the other hand, when the speed of one of the gases is higher than the predetermined speed range, spheroidization is insufficient and crushed particles are undesirably included in the product in a large amount.

As for the ratio between the amount of combustible gas and the amount of combustible gas, the theoretical amount of combustible gas including the theoretical amount of oxygen necessary for complete combustion of the combustible gas is defined as the theoretical amount of combustible gas Qs. It is preferable to set the amount of the supporting gas Qs to 1.04 to 1.4 times. More preferably, the amount of the supporting gas is 1.1 to 1.3 times. When the amount of the supporting gas is 1.00 or more of Qs,
If the ratio is less than 04 times, the flame temperature is high and the temperature rise of the inorganic powder is too easy, so that it takes a long time to cool down after jumping out of the flame, causing a change in particle size due to aggregation and coalescence. On the other hand, when it exceeds 1.4 times the stoichiometric amount Qs, the flame temperature is also lowered, the melting becomes insufficient, and a large amount of crushed particles is contained.

As the flammable gas used in the present invention, any one of hydrocarbon gases such as acetylene, propane and butane, or a mixed gas of these gases can be used. Of these, propane, butane, or a mixed gas thereof, which has a relatively low calorific value, is preferable for heating and melting and spheroidizing fine powder having an average particle diameter of 20 μm or less.

If the supporting gas is a gas containing oxygen,
Any gas can be used. In general,
Although it is inexpensive and most preferable to use 99% or more of pure oxygen, air or an inert gas such as argon is used as a component other than oxygen in the combustion supporting gas for the purpose of reducing the calorific value of the gas. It can also be added.

The inorganic powder of the present invention can be spheroidized as long as it is a substance which is heated and melt-softened, such as silica stone or alumina, and can be used as the inorganic powder. Even if the material has no melting point such as silicon nitride, or even if the crystal such as BN is an amorphous material, the particle surface of the material is coated with ultrafine silica and / or alumina, By spraying this into a flame, the surface of the particles of the substance is smoothed and spheroidized, and by further covering the surface with a dense oxide, a spherical product having high thermal conductivity can be obtained. In addition, for example,
By using an inorganic powder in which silica and titania are mixed as a raw material, it is possible to react in a flame and at the same time to spheroidize. As described above, as the inorganic powder of the present invention, it is only necessary that the inorganic powder be spheroidized by the heat history in the flame, and only the one that melts and softens, the reaction from the mixed raw material, the coating method, etc. There is no restriction.

Among the inorganic powders, as a filler for a resin composition for encapsulating a semiconductor, it can meet the characteristics required as a sealing material such as low thermal expansion and moisture resistance.
Siliceous powders are preferred. As the siliceous powder, it is preferable to use crystalline so-called silica stone from the viewpoint of cost, but it may be amorphous or a mixture of crystalline and amorphous.

As for the particle diameter of the raw material silica, the average particle diameter is preferably 0.1 to 20 μm. In general, silica used as a raw material is often obtained by pulverizing massive silica, and thus the particles constituting the powder are angular, and especially the fine particles have remarkable cohesiveness. According to this, if the average particle size is in a specific range, the object of the present invention can be stably achieved. The reason is that when the average particle diameter is smaller than 0.1 μm, the silica fine powder has remarkable agglomeration characteristics, so that even when the silica fine powder is melted and spheroidized under specific gas conditions, the particle dispersion is sometimes unsatisfactory. This is because the product may be melted sufficiently and increase the particle size of the product, and if the average particle size is larger than 20 μm, the product tends to contain many crushed particles without sufficient spheroidization.

In the present invention, it is necessary to obtain a high-speed gas, but this can be achieved by a known method such as using a pore orifice and a ring nozzle. For this purpose, the gas pressure at the inlet of the burner section is set to 0.05 to 2 MPa. Also,
Since a high-speed gas containing an inorganic powder flows at the tip of the burner, wear and abrasion are severe. Therefore, the burner tip can be manufactured more stably for a long time by using a member having high heat resistance and wear resistance such as ceramics.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

The configuration of the equipment used for spheroidization will be described with reference to FIG. The equipment includes a vertical furnace body of a water-cooled jacket type provided with a spheroidizing burner 1 and an outside air suction port 3 for cooling the high-temperature exhaust gas of the flame 2 and a bag filter 9 for collecting generated spherical particles from the exhaust gas. And a blower 10. The furnace body is made horizontal and blows out the flame in the horizontal direction. There is no limitation on the method of rotating the furnace body into a so-called horizontal furnace or inclined furnace to make it spherical. The generated spherical particles sucked by the blower together with the combustion exhaust gas from the burner and the dilution air from the suction port provided near the burner pass through the connection portion 8 and are collected by the bag filter.

(1) Preparation of Raw Materials Raw Material Silica A to C High-purity natural silica was dry-pulverized and then classified to obtain siliceous powder raw materials A to C having the characteristics shown in Table 1. Raw material silica D High-purity natural silica was wet-pulverized with a stirring mill, and then dried and classified to obtain a siliceous powder raw material D having the characteristics shown in Table 1. Raw Material Silica E As the siliceous powder raw material E, Aerosil OX-50 manufactured by Nippon Aerosil Co., Ltd. was used. (2) Melting conditions The siliceous powder raw material shown in Table 1 was subjected to a carrier gas to prepare
Under various melting conditions shown in FIG. 4, a melt spheroidizing operation was attempted by throwing into propane gas-oxygen flame. On this occasion,
High-purity oxygen gas was used as a carrier gas. The powder concentration P was set such that the feed amount of siliceous powder (kg / hr) / the amount of propane gas (Nm ³ / hr) was 3.0 under any melting conditions. The molten product was collected, and its average particle size and melting rate were measured. The results are shown in Tables 2, 3, and 4.

(3) Average particle size (D50) This is an average particle size obtained from a weight particle size distribution curve obtained from a laser diffraction type particle size analyzer. The measuring device used was a model “LS230” manufactured by Coulter. However, the size of Aerosil as the raw material E shown in Table 1 is the size determined by SEM observation. When the fine particles are coalesced between the fine particles or around the coarse powder, the average particle diameter obtained after melting increases. Can be evaluated. (4) Melting rate The measurement was performed by X-ray diffraction, the crystalline content in the product was quantified based on the obtained peak area, and the residue was regarded as an amorphous component, which was defined as the melting rate. The melting rate value is a property of knowing the degree of melting when using a crystalline raw material, but a high melting rate is also a substitute property of the degree of spheroidization indicating that the particles are well melted and the sphericity is also good. .

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

According to the constitution of the present invention, the coagulation and coalescence of the fine powder raw material can be reduced, and the fine powder having a high melting ratio, that is, high sphericity can be efficiently produced. Since it contains fine spherical particles, it can be easily and highly filled into a resin composition, so that a cured product of the obtained resin composition can achieve low thermal expansion and high strength, and semiconductor encapsulation. Inorganic powder containing spherical particles suitable for a resin composition for use can be provided inexpensively, in large quantities, and stably. Therefore, high filling of the resin composition for semiconductor encapsulation contributes to high fluidization.

[Brief description of the drawings]

FIG. 1 is a schematic view of a spherical particle manufacturing apparatus.

[Description of Signs] 1 spheroidized burner 2 flame 3 cooling gas (air inlet) 4. Cooling jacket outer pipe 5 Cooling jacket inner pipe 6. 6. Cooling water inlet Cooling water outlet 8 Exhaust communication port 9 Bag filter 10 Exhaust suction blower 11 Gas control valve 12 Gas outlet 13 Molten powder extraction device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08K 7/18 C08K 7/18 C08L 101/00 C08L 101/00

Claims (4)

[Claims] In a method of carrying an inorganic powder on a flammable gas and / or a supporting gas and injecting it into a flame to heat and spheroidize the inorganic powder, the inorganic powder is injected at the tip of a burner nozzle. A method for producing spherical particles, wherein the speed is 70 to 1200 m / sec. 2. The method for producing spherical particles according to claim 1, wherein the inorganic raw material powder is a siliceous powder and has an average particle diameter of 0.1 to 20 μm. 3. A method in which a flammable gas and / or a supporting gas carry silica-based powder having an average particle size of 0.1 to 5 μm,
In the method of heating and spheroidizing the siliceous powder by injecting it into a flame, the injection speed of the siliceous powder at the tip of the burner nozzle is set to 300 to 1200 m / sec. Production method. 4. The spherical particles according to claim 1, wherein the amount of the supporting gas relative to the amount of the combustible gas is 1.04 to 1.4 times the theoretical combustion amount. Manufacturing method.