JP2000191320A - Production of alumina powder or sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain alumina powder having good binder removing ability and giving a high density sintered body by pulverizing alumina having a specified average primary particle diameter and a specified specific surface area with an air stream pulverizer. SOLUTION: Alumina having 0.5-5 μm average primary particle diameter, <=2 m2/g BET specific surface area and <=9,500 cm2/g Blain specific surface area is pulverized with an air stream pulverizer. The average particle diameter of secondary particles formed by the aggregation of primary particles is about 30-100 μm. The alumina is obtained, e.g. by firing aluminum hydroxide (gibbsite) obtained by the Bayer process in a rotary kiln, a tunnel kiln or the like. The air stream pulverizer is, e.g. an air stream impact pulverizer, an air stream collision pulverizer, a counter air stream pulverizer or the like. The air stream impact pulverizer is preferably used because the occurrence of fine particles is suppressed. The pressure of pulverization air is usually about >=5 kg/cm2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing alumina powder for a sintered body. In detail, a compact obtained by mixing and molding an alumina powder and an organic binder has an organic residue remaining in the sintered body after sintering even in a sintering atmosphere such as H ₂ / H ₂ O. The present invention relates to a method for producing alumina powder for a sintered body, which has a small amount of inspection, that is, has a good binder removal property and can obtain a high-density molded body.

[0002]

2. Description of the Related Art Conventionally, alumina powder has excellent physical properties such as heat resistance, corrosion resistance, abrasion resistance, electric insulation, and mechanical strength, so that it can be used for IC substrates, light-transmitting tubes, bearings, cutting tools, and the like. It is used as a raw material for sintered bodies or as a filler for floppy (registered trademark) disks, magnetic tapes and the like.

[0003] Among them, a raw material of a sintered body, in particular, an organic substance such as an IC substrate is mixed as a binder, and sintering is performed using H ₂ / H ₂ O.
The raw material alumina powder used in a non-oxidizing atmosphere such as that described above must have not only a small amount of coarse particles that hinder sintering but also a good binder removal property.

[0004] Normally, in the case of an IC substrate or the like, an unsintered formed body (sometimes referred to as a green sheet) obtained by molding alumina powder is used as a substrate, and wiring is printed on the substrate. Sinter. When the substrate is sintered in an oxidizing atmosphere like a white substrate, the high melting point metal such as tungsten and molybdenum used as a wiring material is oxidized, and the substrate is subjected to an oxygen partial pressure such as H ₂ / H ₂ O. Sintering under a non-oxidizing atmosphere where

However, when sintering the substrate, the organic binder used for molding the alumina powder under a non-oxidizing atmosphere is compared with the case where the organic binder is sintered under an oxidizing atmosphere.
It is known that, unless the temperature is higher, it does not decompose and is hardly discharged out of the system as a gas. As a result, when sintering a substrate obtained from alumina powder having a poor binder removal property during sintering in a non-oxidizing atmosphere, pores remain inside the sintering substrate and high-density firing is performed. Substrates that were aggregates could not be obtained.

Conventionally, as an alumina powder which has excellent binder removal properties and can be a high-density sintered body, a powder having a uniform particle size distribution, a small number of extremely large coarse particles, and a small number of significant fine particles is preferred. Thus, as the alumina powder, from a commercial point of view, usually, alumina obtained by the Bayer method is pulverized by a pulverizer such as a ball mill or a vibration mill, or a powder obtained by pulverizing aggregated particles is used. In the case of using the alumina powder obtained by the pulverizer, there is a problem that a high-density sintered body cannot be obtained due to poor generation of binder due to generation of many fine particles.

On the other hand, even with an alumina powder obtained by a method using a ball mill or the like, it is possible to remove fine particles to some extent by using a classifier, but it is possible to obtain an alumina powder having a satisfactory level of classification accuracy. No powder could be obtained.

[0008]

In view of such circumstances,
The present inventors have conducted intensive studies to obtain an alumina powder having a good binder removal property and a high-density sintered body by a simple method.As a result, surprisingly, the specific average primary particle diameter and the specific surface area were increased. It has been found that when the alumina having the above properties is treated with a specific pulverizer, an alumina powder satisfying the above object can be obtained, and the present invention has been completed.

[0009]

That is, according to the present invention, the average primary particle diameter is 0.5 μm to 5 μm, the BET specific surface area is 2 m ² / g or less, and the Blaine specific surface area is 95 μm or less.
It is an object of the present invention to provide a method for producing alumina powder for a sintered body, characterized in that alumina having a flow rate of not more than 00 cm ² / g is pulverized using an airflow pulverizer.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The raw material alumina (hereinafter, simply referred to as alumina) used in the present invention has an average primary particle diameter of 0.5 μm to 5 μm, preferably 1 μm to 4 μm, and more preferably 1.2 μm.
It is to 3.2, BET specific surface area of 2m ² / g or less, preferably 0.4m ² /g~1.8m ² / g, the Blaine specific surface area of 9500cm ² / g or less, preferably 50
00cm ² / g~9500cm ² / g may be in the range of, about the size of the secondary particles in which primary particles are formed by aggregation is usually an average secondary particle size of about 30μm~ about 10
0 μm. If the average primary particle diameter of the alumina is out of the above range or if the specific surface area is out of the above range, even if pulverized using an air-flow type pulverizer, alumina powder from which a high-density sintered body can be obtained is obtained. I can't get it. Also, the particle size distribution of the alumina powder after pulverization,
Due to the particle size distribution of the primary particles that make up the alumina, the alumina is usually rosin-Rammler (Rosi
n-Rammler) slope (n-value) represented by a diagram
It is recommended to use those having a sharp primary particle size distribution of about 2.5 or more in the range of 20% to 90% of the cumulative weight.

The method for producing alumina used in the present invention includes, for example, a method in which aluminum hydroxide (gibbsite) obtained by the Bayer method is calcined in a rotary kiln, tunnel kiln, or the like.

In the present invention, it is essential that alumina having the above-mentioned physical properties is pulverized by a pneumatic pulverizer.

Examples of the air-flow type pulverizer used in the present invention include an air-flow impact type pulverizer (a device for crushing particles by colliding particles by air flow) and an air-flow collision plate type pulverizer (particles are caused to collide with a collision plate by air flow). Crusher) or a counter-current crusher. It is recommended to use an airflow impact crusher because it can reduce the generation of fine particles, and it is recommended to use an airflow crusher of a model that incorporates a classification function because it can reduce the remaining amount of coarse particles. In particular, it is recommended to use an airflow impact type pulverizer of a type in which particles collide and pulverize, and coarse particles are recycled by a classification function.

The pulverizing conditions are different depending on the type of the air-flow type pulverizer and are not unique. However, usually, the conditions should be selected so that the aggregated particles of alumina are pulverized and become close to the primary particle diameter. The setting of such conditions depends on the model of the airflow crusher to be used,
Once the alumina to be pulverized is determined, it can be set by preliminary experiments. As a specific example of the crushing conditions, the crushing air pressure is about 5
kg / cm ² or more, preferably about 6 kg / cm ² to about 8 k
g / cm ² . In addition, when the alumina powder is flowing at a high speed as generally used as an abrasive, a certain amount of abrasion occurs on the inner surface of the crusher, so that a portion susceptible to abrasion, for example, a portion such as a nozzle, has abrasion resistance. It is desirable to use a material having high properties, such as alumina and silicon carbide.

In carrying out the production method of the present invention, aluminum hydroxide obtained by the Bayer method is usually calcined in a rotary kiln and has an average secondary particle diameter of about 30 μm.
m to about 100 μm, and the average primary particle diameter is about 0.5 μm.
Alumina having a BET specific surface area of about 2 m ² / g or less and a Blaine specific surface area of 9500 cm ² / g or less is milled using a pneumatic mill at a pulverizing air pressure of 5 kg / cm ² or more. Then, the alumina powder discharged from the pulverizer may be collected and collected by a cyclone and / or a bag filter.

The alumina powder for a sintered body obtained by the present invention generally has an average secondary particle diameter of 0.5 μm to 5 μm, preferably 1 μm to 4 μm, and has a coarse particle of +15 μm of about 2 μm.
%, Preferably 0.5% or less, more preferably 0.1% or less, and rosin-ramlar (Rosin-
The slope (n value) represented by a Rammler diagram is
It has a sharp particle size distribution of 2.5 or more in the range of 20% to 90% of the cumulative weight. In addition, the alumina powder for a sintered body is used as a raw material for a sintered body such as an IC substrate.
It can be used as a raw material for a sintered body such as a light transmitting tube, a bearing and a cutting tool, a filler for a floppy disk and a magnetic tape, an abrasive or a refractory.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. The physical properties of alumina and alumina powder were measured by the following methods.

Measurement of Physical Properties of Alumina Average Primary Particle Diameter (μm): The primary particle diameter of each of 100 alumina particles was measured from a micrograph, and the average particle diameter was determined. Average secondary particle diameter (μm): Measured by a sieving method. BET specific surface area (m ² / g): Measured by a BET specific surface area measuring device QS-9 (manufactured by Yuasa-Kantachrome). Blaine specific surface area (cm ² / g): Measured by a constant-pressure pneumatic measurement method using a brane specific surface area measuring device SS-100 (manufactured by Shimadzu Corporation).

Measurement of Physical Properties of Alumina Powder Average secondary particle diameter (μm): The particle size distribution of the alumina powder was measured by a Sedigraph 5000-ET (manufactured by Shimadzu-Micromeritex Co., Ltd.), and the 50% diameter was determined as the average secondary particle diameter. And +15 μm amount (% by weight): The particle size distribution of the alumina powder was measured by Sedigraph 5000-ET (manufactured by Shimadzu-Micromeritex Co., Ltd.), and the +15 μm amount was determined. n value (-): The particle size distribution of the alumina powder was measured by Sedigraph 5000-ET (manufactured by Shimadzu-Micromeritex Co., Ltd.), and rosin-Rammer (Rosin-Ramm) was measured.
The results of the particle size distribution were plotted on a ler) diagram. When the accumulated weight is in the range of 20% by weight to 90% by weight, ta
nθ was obtained and set as an n value.

Example 1 Aluminum hydroxide obtained by the Bayer method was calcined in a rotary kiln and had an average secondary particle diameter of 45 μm, an average primary particle diameter of 3.5 μm, and a BET specific surface area of 0.5 μm. 56 m ² / g and a Blaine specific surface area of 49
50 cm ² / g of alumina was fed in an amount of 30 kg
/ Hr, pulverization using a pneumatic impact pulverizer (trade name: PJM-280SP type, manufactured by Nippon Pneumatic) under the conditions of pulverization air pressure of 6 kg / cm ² , and alumina powder discharged from the pulverizer is subjected to cyclone. Collected and collected. Table 1 shows the physical properties of the obtained alumina powder.

Next, 96 parts by weight of the alumina powder was added with S
4 parts by weight of a flux component of iO ₂ / MgO / CaO composition was added, 5.3 parts by weight of polyvinyl butyral (trade name: B-76, manufactured by Mitsubishi Monsanto Co., Ltd.) as a binder and dibutyl phthalate (Wako Reagents Co., Ltd.) as a plasticizer After adding 2.6 parts by weight and dry-mixing for 6 hours, 63.5 parts by weight of a solvent of a tricrene-perchrene-butanol composition and 1 part by weight of a dispersant were added, and further 2 parts by weight were added.
The mixture was wet mixed for 0 hr. Degas the obtained slurry,
After adjusting the viscosity to about 2000 cps, a green sheet was obtained by a doctor blade molding method.

The obtained green sheet was subjected to H ₂ / H ₂ O
(Molar ratio: 7) 900 in the atmosphere at a heating rate of 200 ° C./hr
The temperature was raised to 0 ° C., and the mixture was sintered for 1 hour. The weight loss ratio before and after sintering was measured. The results are shown in Table 2.

The green sheet obtained by the same method was heated in a H ₂ / H ₂ O (molar ratio 7) atmosphere at a heating rate of 200 ° C.
The temperature was raised to 1600 ° C. at / hr, and sintered for 2 hours. The sintered density of the obtained sintered body was measured. Table 2 shows the results.

Examples 2-5 Aluminum hydroxide obtained by the Bayer method was calcined in a rotary kiln, and the average secondary particle diameter shown in Table 1 was obtained.
Alumina having an average primary particle size, a BET specific surface area, and a Blaine specific surface area was pulverized using the same pulverizer as in Example 1, and the alumina powder discharged from the pulverizer was collected and collected by a cyclone. The powder properties of the obtained alumina powder were examined in the same manner as in Example 1. The result is
It is shown in the table. Further, the reduction ratio before and after sintering of the green sheet and the sintered density of the sintered body were examined in the same manner as in Example 1.
The results are shown in Table 2.

Example 6 Aluminum hydroxide obtained by the Bayer method was calcined in a rotary kiln and had an average secondary particle diameter of 45 μm, an average primary particle diameter of 3.5 μm, and a BET specific surface area of 0.5 μm. 53 m ² / g and a Blaine specific surface area of 51 m ² / g.
Alumina of 50 cm ² / g was fed in an amount of 10 kg.
/ Hr, pulverization using a gas impingement plate type pulverizer (trade name: IDS-2, manufactured by Nippon Pneumatic) under the conditions of pulverization air pressure of 6 kg / cm ² , and alumina powder discharged from the pulverizer is cyclone. And collected. Table 1 shows the physical properties of the obtained alumina powder. Further, the reduction ratio before and after sintering of the green sheet and the sintered density of the sintered body were examined in the same manner as in Example 1. The results are shown in Table 2.

Comparative Examples 1-2 The average secondary particle diameter shown in Table 1 was obtained by calcining aluminum hydroxide obtained by the Bayer method in a rotary kiln.
Alumina having an average primary particle size, a BET specific surface area, and a Blaine specific surface area was prepared by mixing a ball / alumina ratio of 9 and a pulverization time of 1
Pulverization was performed using a ball mill (internal volume 110 L) under the condition of 0 hr. Table 1 shows the physical properties of the obtained alumina powder. Further, the reduction ratio before and after sintering of the green sheet and the sintered density of the sintered body were examined in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 3 Aluminum hydroxide obtained by the Bayer method was calcined in a rotary kiln, and the average secondary particle diameter was 45 μm, the average primary particle diameter was 0.8 μm, and the BET specific surface area was 3. 02 m ² / g, and the Blaine specific surface area is 11
Alumina of 400 cm ² / g was fed at a feed rate of 30 k
g / hr, pulverizing air pressure 6 kg / cm ² , using a jet mill (trade name: PJM-280SP, manufactured by Nippon Pneumatic), and collecting the alumina powder discharged from the pulverizer with a cyclone. , Collected. Table 1 shows the physical properties of the obtained alumina powder. Further, the reduction ratio before and after sintering of the green sheet and the sintered density of the sintered body were examined in the same manner as in Example 1. The results are shown in Table 2.

[0028]

As described above in detail, the present invention provides a method for easily providing alumina powder for a sintered body having a good binder removal property even in a non-oxidizing atmosphere and obtaining a high-density sintered body. Yes, its industrial value is great.

[0029]

[Table 1]

[0030]

[Table 2]

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toru Ogawa 5-1, Sokai-cho, Niihama-shi, Ehime Sumitomo Chemical Co., Ltd. F-term (reference) 4D067 CA02 CA05 GA07 4G030 AA36 BA12 BA15 BA19 BA25 BA33 CA04 GA03 4G076 AA02 BA46 BE20 BH01 CA05 CA26 CA28

Claims (1)

[Claims] An alumina having an average primary particle size of 0.5 μm to 5 μm, a BET specific surface area of 2 m ² / g or less, and a Blaine specific surface area of 9500 cm ² / g or less, using a pneumatic mill. A method for producing alumina powder for a sintered body, characterized by pulverizing.