JPH05330819A - Dry pulverizing method for alumina - Google Patents

Abstract

PURPOSE:To efficiently and safely dry-pulverize alumina without any trouble in operability by adding a prescribed amount of alumina into polyethylene glycohol or polypropyleneglycohol having a prescribed molecular weight. CONSTITUTION:A pulverization additive consisting of polyethyleneglycohol having 20-600 molecular weight or polypropyleneglycohol having 400-700 molecular weight is prepared. The pulverization additive of 0.05-0.5wt.% (per alumina) is added into alumina and is pulverized in a ball mill or a vibration mill. As a result, an alumina powder excellent in dispersibility to an aq. medium is obtained excellently in pulverization efficiency, safely and without any trouble in operability. In the case of being applied for a castable refractory use, the alumina powder has excellent fluidability and sinterability even if water amount for kneading is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry grinding method for alumina. More specifically, it has excellent crushing efficiency and safety,
The present invention relates to a dry pulverization method of alumina which has no problem in operability.

[0002]

Alumina obtained by the Bayer method is used as a raw material for ceramics such as refractories, spark plugs and IC substrates. Usually, the alumina obtained by the Bayer method constitutes an aggregate having an average particle size of about 50 μm to about 100 μm in which alumina having an average particle size of several hundred nm to several μm is aggregated. For the purpose of obtaining a sintered body with a high sintering density, these alumina should be crushed into as fine and uniform particles as possible, then dispersed in water or an organic solvent, molded by slurry casting, or granulated by spray drying. After this, it is press-molded to obtain a green compact, and the compact is fired to obtain a desired sintered compact.

Upon crushing, it is necessary to reduce the average particle size of the raw material alumina and to reduce the coarse particles in order to improve the sinterability and the mechanical strength of the molded product. Therefore, alumina is pulverized for a long time by dry pulverization using a ball mill or the like. It has been reported that oleic acid and stearic acid are effective for grinding alumina for the purpose of improving grinding efficiency. In addition, it has been reported that ethylene glycol, methyl alcohol, ethyl alcohol, etc. are effective for crushing inorganic powder such as cement and limestone (for example, Handbook of Chemical Engineering).
Page 1300 Maruzen Co., Ltd.).

Oleic acid and stearic acid as a grinding aid are excellent in the grinding effect, but because they are hydrophobic, they are poor in dispersibility when applied as a raw material for sludge casting and the like, which causes a foaming problem. Not preferable. Therefore, in such applications, the use of alcohols as a hydrophilic grinding aid is considered, but in dry grinding, a temperature rise may occur due to the friction between the grinding medium and the grinding material, so methyl alcohol or ethyl alcohol may be used. The use of such as not only complicates the operation such as sealing the crushing atmosphere with an inert gas such as nitrogen and the like, but also causes inconveniences such as increase in equipment cost and crushing cost.

On the other hand, it is possible to use flame-retardant substances from the explosion-proof surface. However, when alumina powder is used as a sintered body, these flame-retardant substances are taken in as impurities and cause defects, resulting in mechanical strength of the sintered body. May cause a decrease in

[0006]

SUMMARY OF THE INVENTION In view of such circumstances,
In the dry pulverization, the present inventors have excellent pulverization efficiency, and there is no need for improvement of special pulverization equipment or control of the pulverization atmosphere. In addition, the alumina powder after pulverization uses an aqueous solvent at the time of molding. No particular problem of dispersibility, as a result of diligent study to find out a dry pulverization method of alumina, it was found that all of the above problems can be solved by pulverizing a specific substance in the presence of a specific substance. It was

[0007]

That is, the present invention provides a method for dry pulverization of alumina, which comprises pulverizing alumina in the presence of polyethylene glycol or polypropylene glycol.

The method of the present invention will be described in more detail below. The alumina powder which is the object of the present invention is not particularly limited in its production method, but usually, the average primary particle diameter is about 0.2 μm to about 10 μm and the average secondary particle diameter is about 10 μm.
m-Applied to alumina powder of about 100 μm. Examples of such alumina include alumina powder obtained by the Bayer method.

The crusher used for dry crushing is a ball mill,
A vibration mill and the like can be mentioned. These may be either batch type or continuous type. In the pulverization, the pulverization conditions such as the type of the pulverized material and the amount of the pulverized material with respect to the pulverizing medium are used within a known range. The addition timing of polyethylene glycol or polypropylene glycol (hereinafter sometimes referred to as a grinding aid) may be a known method, for example, it may be mixed with alumina powder in advance during grinding, or alumina powder may be added to a grinding machine. After feeding, the grinding aid may be added.

One of the grinding aids applicable to the present invention is polyethylene glycol, which is also called polyethylene oxide, polyox or carbowax. Polyethylene glycols with various molecular weights are commercially available, and the flash point usually increases as the molecular weight increases, but on the other hand, the solubility in water and organic solvents decreases, and the state at room temperature changes from liquid to solid. Therefore, it becomes difficult to uniformly disperse the powder in the alumina powder. Therefore, in the application to the method of the present invention, those having a molecular weight of about 200 to about 600 are preferably used. Further, in the case of polypropylene glycol, those having a molecular weight of about 400 to about 700 are preferably used. Polyethylene glycol or polypropylene glycol having such a molecular weight range is not unique depending on the type, shape and operating conditions of the dry pulverizer used,
It can be operated without special atmosphere control until the atmospheric temperature in the crusher is about 200 ° C. In addition, by crushing in a high temperature atmosphere of about 100 ° C. to about 200 ° C.,
It has advantages that mill packing and the like are unlikely to occur and that the pulverization efficiency is excellent.

The amount of the grinding aid added to the alumina powder is in the range of 0.05% by weight to 0.5% by weight. If the addition amount is less than the above range, the effect of the auxiliary agent is small, and even if a large amount is added, an effect commensurate with the addition amount is not found and it is not economical.

The crushing time is the particle size of the raw material alumina powder to be crushed, the particle size of the desired alumina powder after crushing,
Although it is not unique depending on the shape of the crusher, the crushing conditions, etc., it may be crushed for 1 to 24 hours.

[0013]

According to the method of the present invention described in detail above, since the grinding aid to be applied has a high flash point, it is possible to safely obtain a desired average particle size without replacing the grinding atmosphere with an inert gas. It is possible to grind until it is, and because of its excellent ability to suppress reaggregation of fine particles, the grinding efficiency is also excellent, and the obtained raw material alumina powder after grinding is also excellent in dispersibility in an aqueous medium, and the reason is not clear. However, for example, in castable refractory applications, the flowability is good even if the amount of kneading water is reduced,
Its industrial value is enormous, such as obtaining alumina powder with excellent sinterability.

[0014]

EXAMPLES The method of the present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, dispersibility was measured as follows. Dispersibility: 1 g of alumina was placed in a 50 ml test tube, and 30 ml of a mixed solution of purified water or 60% of toluene and 40% of ethanol was added as a dispersion medium to the test tube, and the mixture was mixed and ultrasonically dispersed for 10 minutes. The dispersibility was examined from the sedimentation rate.

Example 1 21.5 g of alumina balls 2950 g having a diameter of 15 mm, a BET specific surface area of 4 m ² / g (average primary particle diameter of about 0.5 μm) and an average secondary particle diameter of 40 μm were obtained by a Bayer method in a 3.3 liter pot mill. 370 g of α-alumina powder was added, and 0.1% by weight of polyethylene glycol (a first-class reagent, molecular weight 400, manufactured by Wako Pure Chemical Industries, Ltd.) as a grinding aid was added to the alumina powder, and then the rotation speed was 80 rpm.
The raw material alumina was pulverized with. 6 hours from the start of crushing, 10
The pulverization degree of the raw material alumina after 24 hours was measured by the average secondary particle diameter and the coarse particle amount. The results are shown in Table 1. During the pulverization, the temperature inside the container was about 150 ° C. In the present example, the average secondary particle size was measured using SEDIGRAPH 5100 (manufactured by Micrometrics),
The amount of coarse particles was calculated by measuring the weight of what remained on the 5 μm sieve using an ultrafine powder classifier (Shodex PS model PL-1).

Example 2 A grinding test of raw material alumina was carried out in the same manner as in Example 1 except that polyethylene glycol having a molecular weight of 600 (first-class reagent manufactured by Wako Pure Chemical Industries, Ltd.) was used as the grinding aid in the method of Example 1. did. The results are shown in Table 1.

Comparative Example 1 In the method of Example 1, the grinding aid was replaced with ethylene glycol (Wako Pure Chemical Industries, Ltd., first-class reagent, flash point 111 ° C.), and the inside of the grinder was replaced with nitrogen gas to carry out grinding. A pulverization test of the raw material alumina was performed in the same manner as in Example 1 except that the above was performed. The results are shown in Table 1.

Comparative Example 2 Grinding of raw material alumina in the same manner as in Example 1 except that stearic acid (manufactured by Wako Pure Chemical Industries, Ltd., first-class reagent, flash point 196 ° C.) was used as the grinding aid in the method of Example 1. The test was conducted. The results are shown in Table 1.

Comparative Example 3 A grinding test of raw material alumina was carried out in the same manner as in Example 1 except that the grinding aid was not used in the method of Example 1. The results are shown in Table 1.

Example 3 A pulverization test of raw material alumina was carried out in the same manner as in Example 1 except that the polyethylene glycol added in the method of Example 1 was changed to 0.03% by weight with respect to the alumina powder.
The results are shown in Table 1.

Example 4 A grinding test of raw material alumina was carried out in the same manner as in Example 1 except that polypropylene glycol (Kishida Chemical Co., Ltd., molecular weight 400) was used as the grinding aid in the method of Example 1.
The results are shown in Table 1.

[0022]

[Table 1] * It is a relative evaluation with respect to the case where no grinding aid is added, and shows ⊚ extremely good, ○ good, and × bad. Also, in the table, T /
E is an abbreviation for toluene / ethanol.

Claims (4)

[Claims] 1. A dry pulverization method for alumina, which comprises pulverizing alumina in the presence of polyethylene glycol or polypropylene glycol. 2. The dry pulverization method of alumina according to claim 1, wherein the amount of polyethylene glycol or polypropylene glycol added to alumina is 0.05 wt% to 0.5 wt% with respect to alumina. 3. The molecular weight of polyethylene glycol is 20.
It is 0-600, The dry pulverization method of the alumina of Claim 1 characterized by the above-mentioned. 4. The molecular weight of polypropylene glycol is 4
The dry grinding method of alumina according to claim 1, wherein the dry grinding method is from 00 to 700.