JP2007126357A - Manufacturing method of spherical inorganic ultra-fine powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily manufacturing a spherical inorganic ultra-fine powder having 0.01-3 μm of a mean particle diameter. <P>SOLUTION: The manufacturing method of the spherical inorganic ultra-fine powder having 0.01-3 μm of a mean particle diameter comprises spraying a slurry including an inorganic raw powder excluding a metallic silicon powder into the flames of an elevated temperature and making a spherical shape, wherein the slurry has 1.35 kg/L or less of a liquid specific gravity and includes an inorganic raw powder having 5 μm or less of a mean first particle diameter and methanol having one mass% or less of moisture, and is sprayed so that the liquid droplets have 5.0-14.3 μm of a mean diameter and the liquid droplets having 50 μm or more is 5 mass% or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for producing a spherical inorganic ultrafine powder having an average particle size of 0.01 to 3 μm. Specifically, when used as a resin or rubber filler alone or mixed with other powders, the average particle size of 0.01 to 3 μm has the effect of increasing the strength of the molded body or decreasing the viscosity. The present invention relates to a method for producing a spherical inorganic powder.

Conventionally, in a method in which a slurry containing an inorganic raw material powder is sprayed onto a high-temperature flame to form a spheroid, water or a flammable liquid is used as a raw material powder medium. However, since the size of droplets when spraying into the flame differs depending on the type of medium, the particle size of the obtained spherical inorganic powder varies greatly. In the case of using water, since the surface tension of the medium is large, the droplets are also large, and it is difficult to increase the particle diameter of the spherical inorganic powder even if it is easy.

On the other hand, a method for producing ultrafine powder of spherical alumina using a flammable liquid is described (Patent Document 1). The medium used here only states that the spray combustion process is not limited as long as it can generate a combustion temperature to the extent that the raw material in the dispersion is melted. It has not been. Therefore, when using kerosene or the like described in the examples, the droplet diameter becomes large, and since the evaporation is slow, the obtained spherical inorganic powder has a smaller particle size than that in the aqueous medium. Even so, I was not satisfied.
Japanese Patent Laid-Open No. 11-147711

An object of the present invention is to provide a method for producing a spherical inorganic ultrafine powder having an average particle size of 0.01 to 3 μm.

The present invention relates to a method in which a slurry containing an inorganic raw material powder (excluding metal silicon powder) is sprayed onto a high-temperature flame to form a spheroid, and the slurry comprises an inorganic raw material powder having an average primary particle size of 5 μm or less and moisture 1 A liquid specific gravity of 1.35 kg / L or less consisting of methanol of not more than mass%, and spraying this with droplets having an average diameter of 5.0 to 14.3 μm and droplets of 50 μm or more being 5 mass% or less. This is a method for producing a spherical inorganic ultrafine powder having an average particle size of 0.01 to 3 μm.

According to the present invention, it is possible to easily produce a spherical inorganic ultrafine powder having an average particle size of 0.01 to 3 μm, which is suitably used in fillers such as various resins and other applications.

In the present invention, in order to obtain an ultrafine spherical inorganic powder having an average particle size of 0.01 to 3 μm, an inorganic raw material powder (excluding metal silicon powder) in a methanol medium (hereinafter simply referred to as “inorganic raw material powder”). Also used was a method of dispersing and spraying on a high-temperature flame. Thereby, since the dispersibility of the raw material powder is better than the conventional method of pneumatically transporting dry powder and can be quantitatively supplied to the high-temperature flame, it is possible to produce a spherical inorganic powder of ultrafine powder.

There are two types of mechanisms by which inorganic raw material powders are spheroidized in a flame. One is that the medium evaporates quickly and the particles in the droplets are divided into individual spheroids, and the other is that the inorganic raw material powder contained in the droplets becomes one particle (liquid Intradrop adhesion). Therefore, in order to obtain ultrafine spherical particles having an average particle size of 0.01 to 3 μm, it is necessary to reduce the adhesion within the droplets and to reduce the droplets.

In the present invention, the reason why methanol having a water content of 1% by mass or less is used as a medium is that methanol has a small surface tension, so that the droplet diameter during spraying can be made minute. For example, when water having a large surface tension is used, the collected spherical inorganic powder results in a larger particle size than the target particle size. The second reason is that since the boiling point is low, the ratio of coalescence in the droplets is suppressed, and it is possible to obtain ultrafine powder spherical particles. The availability of highly pure methanol is also an important reason for selection. Kerosene, which has a surface tension value close to that of methanol, is slow to evaporate, so that the ratio of coalescence in the droplets increases and the spherical inorganic powder becomes larger, and there is a concern that sulfur components may be mixed.

Further, the methanol used in the present invention must have a moisture content of 1% by mass or less. Methanol with a water content of more than 1% by mass does not significantly increase the surface tension, but the evaporation in the flame occurs unevenly, making it difficult to produce a spherical inorganic ultrafine powder having an average particle size of 0.01 to 3 μm. Become.

Examples of the material of the spherical inorganic powder targeted by the present invention include silica, alumina, mullite, and the like that can be softened and spheroidized by a flame. Of these, fused silica or alumina is preferable as the filler for the resin or rubber. As this inorganic raw material powder (however, excluding metal silicon powder), any material can be used as long as the material is obtained at a high temperature, for example, fused silica powder, fused silica powder, crystalline silica powder, etc. Examples of the alumina include alumina powder, aluminum hydroxide powder, and metal aluminum.

In the present invention, in order to obtain the ultrafine powder of the spherical inorganic powder, the average primary particle diameter of the inorganic raw material powder must be 5 μm or less. More preferably, it is 1 μm or less. When the diameter is larger than 5 μm, the droplet diameter becomes large, and a spherical inorganic powder having an average particle diameter of 0.01 to 3 μm cannot be obtained.

Nonionic surfactants, cationic surfactants, anionic surfactants, polymer surfactants, etc. in order to improve the dispersibility even when the average primary particle size of the inorganic raw material powder is 5 μm or less Various surfactants can be used. As the surface treatment method of inorganic raw material powder with surfactant, spray method using fluid nozzle by dry method, stirring method with shear force, ball mill, mixer etc. and similar method by wet method, ultrasonic homogenizer etc. are adopted be able to. However, since the slurry is sprayed and melted in a flame, the wet method in which the liquid specific gravity is adjusted in advance is the most efficient.

The liquid specific gravity of the slurry needs to be adjusted to 1.35 kg / L or less, preferably 0.80 to 1.35 kg / L. If it is greater than 1.35 kg / L, the concentration of the inorganic raw material powder increases, so that the particles of the spherical inorganic powder generated by the coalescence in the droplets become large, and blockage in the supply line, etc. This may cause difficulty in quantitative supply of slurry.

The inorganic raw material powder in the slurry, except for the metal silicon powder. ) Is preferably 10 to 50% by mass. A slurry larger than 50% by mass has a liquid specific gravity of more than 1.35 kg / L in most inorganic powders, and the powder tends to clog in the supply line, and if it is less than 10% by mass, the productivity is lowered.

In the method of the present invention, the slurry prepared as described above is sprayed into droplets, and the droplets are burned.

In the present invention, these droplets are required to have an average diameter of 5.0 to 14.3 μm. When the particle size is larger than 14.3 μm, the spherical inorganic powder obtained by coalescence in the droplets becomes larger. When the particle size is smaller than 5.0 μm, not only is it non-productive, but also the inorganic raw material larger than the droplet diameter. When the powder is sprayed on the high temperature flame, the powder is separated from the high temperature range of the flame and is not spheroidized.

In addition, the droplets must have a ratio of 50 μm or more and 5% by mass or less. When it is larger than 5% by mass, the evaporation of the droplets is slowed, the ratio of coalescence in the droplets is increased, and the particle size of the spherical inorganic powder is increased. In addition, the average diameter of a droplet and the ratio of 50 micrometers or more can be measured using the apparatus of "LDSA-1400A" by Tohnichi Computer.

The average diameter of the droplets and the ratio of 50 μm or more can be adjusted by one or more factors selected from the spraying method, the slurry spraying amount, the dispersed gas amount and the flow rate thereof. Specifically, it can be performed by using a two-fluid nozzle or the like that can produce finer droplets, reducing the slurry spray amount relative to the amount of dispersed gas, and further increasing the flow rate of the dispersed gas.

As the spraying method, a spray sprayer such as a liquid injection type or a liquid film type two-fluid nozzle, an ultrasonic sprayer, a rotating disk sprayer, etc. can be used, but droplets can be miniaturized, handled, and mass-produced. From the point of view, a two-fluid nozzle is preferred.

As the dispersed gas for spraying the slurry from the nozzle discharge port, a nonflammable gas such as carbon dioxide gas or nitrogen gas, an auxiliary combustion gas such as air or oxygen, or a flammable gas such as propane gas may be used alone or in combination.

For example, when the two-fluid nozzle is used, the flow rate of the dispersed gas is preferably 100 m / second or more during discharge. If it is less than 100 m / sec, the spraying action as a nozzle does not occur. Further, the amount of the dispersed gas is preferably 100 times or more of the slurry spray amount. If it is less than 100 times, it becomes difficult to obtain a target droplet diameter, and no spray action occurs.

In order to completely melt and spheroidize the particles in the droplets, a high-temperature flame is formed in the slurry spray area using a combustible gas and an auxiliary combustion gas. This is the same as the normal spheroidizing method of inorganic raw material powder, and it is not necessary to specifically limit in the present invention, but if the amount of flammable gas is excessive than the melting and spheronizing of particles, Be careful as particles may coalesce. Hydrogen, natural gas, acetylene gas, propane gas, butane, or the like is used as the combustible gas, and air, oxygen, or the like is used as the auxiliary combustion gas.

An example of the production apparatus of the present invention is based on a spheroidizing furnace and a collecting apparatus connected to the furnace. The spherical inorganic ultrafine powder produced in the spheronization furnace is pneumatically transported by a blower or the like and collected by a collecting device. It is preferable that the spheroidizing furnace main body and the transportation piping are water cooled by a water cooling jacket method. As the collecting device, a cyclone, gravity sedimentation, louver, bag filter, or the like is used. The collection temperature is determined by the amount of heat generated by the amount of methanol or combustible gas and the suction amount of the blower, and the adjustment is performed by the amount of cooling water, the amount of outside air provided in the line, or the like.

The spherical inorganic powder of the present invention means that the sphericity is 0.80 or more. The sphericity can be measured using a scanning electron microscope (“JXA-8600M type” manufactured by JEOL Ltd.) and an image analysis device (manufactured by Nippon Avionics Co., Ltd.). That is, the projected area (A) and the perimeter (PM) of the particles are measured from the SEM photograph of the powder. When the area of a perfect circle corresponding to the perimeter (PM) is (B), the sphericity of the particle is expressed as A / B. Therefore, assuming a perfect circle having the same circumference as that of the sample particle (PM), PM = 2πr and B = πr ² , so that B = π × (PM / 2π) ² . The sphericity can be calculated as sphericity = A / B = A × 4π / (PM) ² . Therefore, in the present invention, 100 arbitrary particles are measured, and the average value thereof is used as the sphericity of the powder.

Since there is a powder that does not spheroidize completely in part of the coalescence within the droplets, the coalescence within the droplets is reduced as much as possible in order to achieve a sphericity of 0.80 or more, and the raw material from the flame formed during spraying Care must be taken not to let the powder leave.

According to the production method of the present invention, a spherical inorganic powder having a target particle diameter can be obtained, but it is also possible to narrow the particle size width with a classifier such as a cyclone or an elbow jet.

Examples 1-5 Reference Example 1 Comparative Examples 1-5
Spherical inorganic powder is produced using a device that has three burners connected to a combustible gas (propane gas) supply pipe, auxiliary combustion gas (oxygen gas) supply pipe, and inorganic raw material powder supply pipe at the top of the spheroidizing furnace. did. Various raw material slurries shown in Table 1 from the center of each burner were spheroidized by jetting with a two-fluid nozzle using air as a dispersion gas. The powder discharged from the spheronization furnace was sucked from the lower part by a blower and guided to a collecting device, and spherical inorganic powder was collected by a bag filter.

In Examples 1 to 4 and Reference Example 1, air was used as the slurry Nos. A to E and the dispersed gas, and the air amount was injected 1000 times the amount of the slurry. In Example 5, slurry number A was used, and the amount of air was 10000 times as much as the amount of slurry. In Comparative Examples 1 to 4, slurry numbers F to I were used, and the amount of air was 1000 times the amount of slurry. In Comparative Example 5, slurry number A was used, and the amount of air was 10 times the amount of slurry.

Table 2 shows the size of the droplets obtained under these conditions and the characteristics of the collected product from the bag filter. In Examples 1 to 5 and Reference Example 1, spherical inorganic powder having a target particle size was produced, but in Comparative Examples 1 to 5, the inorganic powder was larger than the target particle size.

The spherical inorganic ultrafine powder produced by the present invention can be used as a filler for reinforcing rubber and resin.

Claims (1)

In the method of atomizing a slurry containing an inorganic raw material powder (excluding metal silicon powder) onto a high-temperature flame, the slurry comprises an inorganic raw material powder having an average primary particle size of 5 μm or less and a water content of 1% by mass or less. A liquid specific gravity consisting of methanol of 1.35 kg / L or less, characterized in that the droplets having an average diameter of 5.0 to 14.3 μm and droplets of 50 μm or more are sprayed as 5% by mass or less, A method for producing a spherical inorganic ultrafine powder having an average particle size of 0.01 to 3 μm.