JPH02199013A - Production of fine fused spherical silica - Google Patents

Abstract

PURPOSE:To obtain fine fused spherical silica in good yield by melting a silica raw material with a frame formed by combustion of a combustible gas and oxygen and introducing a cooling gas into a flame-forming zone. CONSTITUTION:A silica raw material is melted with a flame formed by combustion of a combustible gas and oxygen to produce fused spherical silica. In the process, a cooling gas is introduced into a frame-forming zone. The silica raw material used is preferably natural or synthetic silica of a as high a purity as possible. Purified quartzite, quartz sand, rock crystal, etc., are cited as the natural silica and silica which is a hydrolyzate of an organosilicate, such as ethyl silicate, prepared by hydrolyzing a silicon halide or neutralizing an aqueous solution of an alkali silica, etc., is cited as the synthetic silica. The above- mentioned silica raw materials are finely pulverized in a desired pulverizer, such as ball mill or jet mill. In most cases, the average particle diameter is <=10mu, preferably within the range of 2-8mu.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the addition of filler resin for semiconductor resin encapsulation, or to a method for producing fused spherical silica having a fine morphology useful as a raw material for glass or ceramics.

[Conventional technology]

Fused spherical silica has conventionally been produced by a method in which silica is dispersed in combustible gas-oxygen, melted, and spheroidized by surface tension in an air flow. Silica, which is a molten raw material, is made by pulverizing natural silica stone, fused silica, synthetic silica, etc. using a pulverizer such as a ball mill, and in order to obtain a high temperature higher than the melting point of silica (1720°C), it is mixed with flammable gas and oxygen. forms a flame due to combustion. Propane, butane, hydrogen, etc. can be used as combustible gases, but
Propane gas is mainly used due to economic efficiency.

A method for producing fused spherical silica based on this kind of flame fusion method is described in Bulletin Che+wical 5oci
ety of JapaOvol, 53 NfL 1, paragraphs 26-29.

[Problem to be solved by the invention]

Generally, such melting systems have an average particle size of at least 1
A fused spherical silica larger than 0 is obtained, and its particle size control depends primarily on the milled particle size of the raw silica. Therefore, it is very difficult to obtain a molten product with an average particle size of Ion or less using a method for producing spherical silica using flame melting.

The reason for this is that the particle size of fused spherical silica always becomes larger than that of raw silica due to fusion between particles of raw silica powder during melting, and this tendency becomes more pronounced as the flame formation area becomes larger.

The present inventors have developed a method for producing fine fused spherical silica by first subjecting raw material silica to a special pulverization treatment to make it fine and controlling the heat load during flame melting. (Japanese Patent Application No. 63-211691) However, even with this method, it is difficult to obtain fine spherical silica with a good yield.

In view of these problems, the present inventors have conducted intensive research on the production of fine fused spherical silica, and as a result, the present inventors have succeeded in producing fine crystals by adding a completely unexpected operation of preparing the flame formation region by introducing a cooling gas. The present invention has been completed based on the discovery that it is possible to manufacture the product with high yield.

(Means for Solving the Problems) That is, the method for producing fine fused spherical silica according to the present invention involves flame-melting a silica raw material by combustion with combustible gas and oxygen to produce fused spherical silica. A structural feature is that a cooling gas is introduced into the formation region.

The present invention will be explained in detail below.

First, the silica raw material that can be used in the present invention is not particularly limited, but is preferably natural or synthetic silica with the highest possible purity.

Further, these may be molten products.

Examples of natural silica include purified silica, silica sand, and crystal, and examples of synthetic silica include those produced by hydrolysis of silicon halides, hydrolysates of organosilicate such as ethyl silicate, or those produced by neutralization of aqueous alkali silicate solutions. Examples include silica.

In particular, the applicant has already successfully developed a method for producing high-purity silica obtained by neutralizing an aqueous alkali silicate solution with a mineral acid, and it can be used as an industrially advantageous raw material for silica. However, the details can be found in, for example, JP-A-61-48421, JP-A-61-48422, JP-A-61-178414, and JP-A-62-
It is described in Publication No. 12608 and the like.

These silica raw materials are finely pulverized using a desired pulverizer such as a ball mill or a jet mill, but in most cases, the average particle size is less than 1〇, preferably 2 to 8 μm.
within the range of Since it is necessary to melt such a fine silica raw material and make it spheroidized as independent particles without causing the raw material particles to fuse with each other, well-controlled flame melting must be performed.

That is, molten spheroidization is carried out using a flame caused by the combustion of an oxygen-combustible gas, often an oxygen-propane flame, but the raw silica powder is placed in a steady state in the center of the flame, which has a temperature above the melting point of the silica. This is done by dispersing and supplying the water.

A heating furnace capable of such flame melting usually has a structure in which a melting burner is installed at the top of the shaped furnace and a flame is formed downward.

However, such a heating furnace is connected to a molten powder recovery facility, and the system inside the furnace is operated under negative pressure using a blower, etc., and the flame melting of the silica converts the raw silica, which is carried by a carrier gas, into oxygen and combustible gas. The particles are dispersed in the flame-forming region downwardly generated by the combustion of the particles, and are spheroidized by surface tension.

The present invention is characterized in that, in a method for producing spherical silica based on such a flame melting method, a cooling gas is introduced into a flame forming region.

Here, the flame formation region refers to the region where flame is generated by combustion of oxygen and combustible gas discharged from the melting burner, and this region is at a high temperature higher than the melting point of silica. Therefore, this area can be easily understood by thinking of a candle flame, for example, and its size (diameter and length)
varies depending on the structure and operating conditions of the melting burner.

When a cooling gas is introduced into such a flame-forming region, the flame-forming region is substantially extinguished by contact with the gas. That is,
The cooling gas acts to cut the flame formation area, so by setting the location and method to introduce it,
Optionally, the flame formation hI range can be adjusted.

The method of introducing cooling gas into the flame formation area is to blow cooling gas in a ring shape from a melting burner installed at the top of the furnace in a direction perpendicular (horizontal) to the flame that is formed downward, or, Since the furnace is operated under negative pressure, a cooling gas introduction hole is provided in a part of the furnace, and the cooling gas is introduced into the flame formation area through this hole. However, there is no need to be limited to these methods; the key is to introduce cooling gas to the flame formation area. Any method may be used as long as it is a means of ff. Therefore, the amount of cooling gas introduced, the flow rate, the introduction position with respect to the flame formation region, the angle, etc. should be set appropriately according to the particle size characteristics of the target product. good.

Generally, as the amount of cooling gas increases and the introduction position approaches the burner, the product particle size becomes finer.

Note that there are no particular restrictions on the cooling gas, or in the case of cooling gas, purified air is used.

In addition, in the present invention, in addition to silica, other glass powders, metal oxides such as alumina and titania, inorganic powders such as various spinel-type oxides, metal silicates, and aluminosilicate are used as raw materials to form fine spherical particles. It becomes possible to manufacture

[For production]

In the method for producing fused spherical silica by flame melting, the flame formation region can be adjusted by introducing a cooling gas into the flame formation region. This means controlling the residence time of silica in the flame, in other words, the residence time in the temperature range above the melting point of silica,
By doing so, it is possible to prevent the growth of particles due to fusion and fusion between particles, so that fine molten spherical particles can be produced with a high yield.

(Examples) Hereinafter, the present invention will be described in more detail by giving Examples and Comparative Examples.

Example 1 (1) Preparation of raw material silica Table 1 shows the preparation method, physical properties, etc. of the raw material silica used in this example.

Table 1 (2) Flame melting test A closed cylindrical heating furnace with a diameter of 800 m and a length of 3000 sm is used. This furnace has a melting burner facing downward at the top of the furnace, and is connected to a cyclone and bag filter for product recovery. The product is collected by introducing clean air for cooling into the connection, and after collection, it is released into the atmosphere using a blower.

In such a heating furnace, propane gas: 36Nrrf/
11 and combustion tAM element: 12ONrd/H1 A flame was formed under the melting conditions of 50 mH and 0 differential pressure in the furnace, and the raw material silica of Table 1 was charged into the flame formation region, respectively.
150kg/H, carrier gas (Ox): 6
Distributed charge and flame melt under the condition of ON I/f(.

During this flame melting, the middle part of the furnace (600mm from the top of the tower
) Clean air for cooling is supplied by the compressor through the ring-shaped cooling air introduction hole at the position of 565N td / H.
and the flame formation region (
A length of about 900 mm) was introduced and melted.

All of the silica recovered by the cyclone was fine fused spherical silica, and the evaluation results are shown in Table 2.

Table 2 Table 3 Example 2 In Example 1, the cooling air introduction hole was installed 200 meters from the top of the tower.
The silica was melted using the same operations and conditions as in Example 1, except that a ring was provided at two positions, 600 m (top) and 600 m (bottom), and a predetermined amount of cooling air was introduced from each introduction hole. As a result, the results shown in Table 3 were obtained.

Comparative Example Spherical silica was produced by melting each raw material silica under the flame melting conditions of Example 1 without introducing cooling air into the flame formation region, and the results shown in Table 4 were obtained.

These are necessary for preparing the particle size structure shown in Table 4, and can also be effectively used as additives for ceramics, glass materials, and resins.

Patent applicant: Nippon Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. Fine melting characterized by introducing a cooling gas into a flame forming region when producing fused spherical silica by flame melting a silica raw material by combustion of combustible gas and oxygen. Method for producing spherical silica. 2. The method for producing fine fused spherical silica according to claim 1, wherein the fused spherical silica has an average particle diameter in the range of 2 to 10 μm.