JPS62207770A - Aluminum nitride powder for manufacturing sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to aluminum nitride powder for producing sintered bodies. That is, the present invention relates to an aluminum nitride powder for producing a sintered body, which is suitable for producing an aluminum nitride sintered body by casting or tape forming and pressureless sintering.

Conventionally, a sintered body of aluminum nitride has been used as a highly thermally conductive ceramic. However, the raw material, aluminum nitride powder, is itself highly reactive with water, and when it comes into contact with water even at room temperature, it undergoes the following hydrolysis reaction to form aluminum hydroxide and ammonia.

AIN+3H, zO→^l (OR) s+NH3↑
・－－－－・－(1) Therefore, when using aluminum nitride powder to make a molded body of a desired shape that is an intermediate for manufacturing a sintered body, aluminum nitride powder is used as a medium in water. When the powder is made into a slurry, aluminum hydroxide (Al(OH)3), which is partially generated, is mixed into the aluminum nitride, and when a molded body made from this is sintered, the AI(OH)* becomes Al2O2 during firing. Due to this change, the amount of aluminum oxide A1.01 in the finished sintered body increases, resulting in a significant loss of properties of the sintered body such as thermal conductivity. Furthermore, when molding a molded body from a slurry, the ammonia generated increases the pH of the slurry, causing decomposition of the organic binder mixed in the slurry or a decrease in the bonding strength, which significantly reduces the strength of the molded body. It will cause damage. In this way, unless the surface of aluminum nitride powder particles is coated with a layer that prevents reaction with water, it is not possible to make a slurry using water as a medium. No tape molding was performed.

In view of the above-mentioned problems, the present invention improves the hydrolyzability disadvantage that aluminum nitride inherently has, improves its dispersibility in water, and makes it possible to create a slurry using water as a medium. The present invention aims to provide aluminum nitride powder for producing sintered bodies to which a surface modification method is applied.

When surface-modifying aluminum nitride powder particles, first the surface of the aluminum nitride powder particles is coated with a hydrophobic film, and then this is covered with a hydrophilic film to improve water resistance and water resistance. It is necessary to achieve both decentralization and decentralization.

Therefore, the following surface treatment methods can be considered.

That is, (1) Inorganic surface treatment method A, thin film treatment layer, fine particle coating layer (2) Organic surface treatment method R (B) Coupling agent layer Among these, (1) Inorganic surface treatment method is vapor phase treatment. A layer of metal or metal compounds (including metal oxides, etc.) is attached to the surface of powder by liquid phase reaction treatment. Generally, coating with an oxide layer such as Ti0g or A1zO++5if2 is performed, but this is not appropriate because it may remain as an impurity during sintering of aluminum nitride. Suitable aluminum nitrides are those that are less likely to remain, such as metal phosphates.

On the other hand, (2) organic surface treatment method covers the surface of powder particles with a coupling agent or surfactant, or attaches a monomer that forms a polymer, and then polymerizes it to create a polymer coating layer. This is a method to do so. Among these methods, surface treatment with coupling agents uses silane coupling agents, organic titanium coupling agents, chromium-based coupling agents, organic phosphoric acid-based coupling agents, etc., and dissolves them in these solvents. Powder is placed inside and heat treated. In the case of aluminum nitride, since it is desired to avoid contamination with Si, Cr, and Ti, a phosphoric acid-based coupling agent is preferable. The surface of the particles of aluminum nitride powder treated with a camping agent has R groups removed by heating during the treatment, making it water resistant.

Next, the method of coating with a polymer layer is originally carried out in order to protect the raw material powder from the atmosphere such as moisture, or to improve compatibility with a binder and the like. Examples of polymer treatment methods include: (1) polymerization of adsorbed monomers, (2) mechanochemical effects, (2) grafting reactions, (2) phase separation, etc. None of these methods contain metal elements that could become impurities, and are good methods for coating the surface of aluminum nitride powder to make it water-resistant.

Among these polymer processing methods, two methods, adsorption monomer and phase separation, are relatively easy to handle. For example, using tetraethylene glycol dimethacrylate as the adsorbed monomer,
A common method is to dissolve this in a benzene solvent, add the treated powder, volatilize the benzene, and then place it in mineral oil and heat and stir to form a polymer layer on the surface of the powder. Next, as a phase separation method, the treated powder is suspended in an organic solvent, and polyethylene glycol,
Dissolve polymers such as paraffin and polyvinyl alcohol and stir well. Next, a method is used in which this polymer is insolubilized to form a polymer treatment layer on the powder surface.

Next, surface treatment using a surfactant utilizes the hydrophobic group and hydrophilic group that the surfactant has. Among surfactants, anionic ones are easy to use as surface modifiers for polar powders. Aluminum nitride powder has an active surface, so A1.0! It is covered with a thin film of AI (OR) 3. Therefore, it is considered that the aluminum nitride powder appears to be an upper polar powder. When polar powder is treated in a surfactant with an organic solvent as the solvent,
The side in contact with the powder surface becomes a hydrophilic group, and the surface of the treated powder is covered with the hydrophobic groups of the surfactant facing outward. Therefore, aluminum nitride powder subjected to this treatment becomes water resistant. In other words, the surface of the powder particles is made hydrophobic so as not to react with water.

However, when using only this type of treatment, when trying to make a slurry using water as a medium and cast aluminum nitride, the surface of the treated powder does not get wet with water, so it is difficult to wet it with water. Dispersibility deteriorates significantly. Therefore,
New surface modification is required to improve dispersibility in water. This is precisely the feature of the present invention.

The above-mentioned treatment to make the surface of the aluminum nitride powder hydrophobic and water resistant is the first treatment, and the aluminum nitride powder that has undergone water resistance treatment is further treated with hydrophilic properties to improve its dispersibility in water. The second process is to perform the process of changing the In order to carry out this secondary treatment, it is effective to use the above-mentioned surfactant. When aluminum nitride powder that has undergone the first running water treatment is treated in a surfactant using water as a medium, hydrophobic groups are adsorbed on the powder surface, and the surface of the treated powder becomes hydrophilic to the surfactant. It will be covered with the base facing outward. Therefore, the aluminum nitride powder that has undergone this second hydrophilic treatment is not eroded by water, has good wettability to water, and is well dispersed in water, making it easy to make a good slurry using water as a medium. can be made to

As described above, the aluminum nitride powder for producing sintered bodies of the present invention is produced by coating the surface of the aluminum nitride raw material powder with an inorganic or organic surface treatment agent as the first surface treatment, and then reacting with water. After suppressing the properties, as a second surface treatment, this first-treated powder is treated in a surfactant using water as a medium to improve its dispersibility in water. Of course, if only the first treatment was performed, the dispersibility in water would be extremely poor, and a slurry that could be cast or tape-molded using a doctor blade would not be obtained.

Therefore, even if the first surface treatment is known, it is recommended to perform a second surface treatment to further improve the dispersibility in water when manufacturing sintered bodies. The application to aluminum nitride powder can be said to be completely new and innovative.

Using the surface-modified aluminum nitride powder of the present invention, cast molding or tape molding with a doctor blade is performed in this way, and the resulting molded body is sintered under atmospheric pressure in nitrogen gas. In this case, a good sintered body can be obtained.

This is because surface modification treatment suppresses the reactivity between aluminum nitride powder and water, so even when slurry for casting molding is prepared using water as a medium,
Because it does not cause the reaction that generates ammonia of formula 11, it remains in aluminum nitride as A11as after sintering, which deteriorates thermal conductivity and other properties.
) This is due to the fact that 3 is hardly included. In addition, since the aluminum nitride powder after surface modification treatment has excellent dispersibility in water, the compact obtained from the slurry prepared using this powder has a high density, and the density of the sintered compact inevitably decreases. It gets expensive. Therefore, various good properties can be obtained.

〔Example〕

Da Chong Charcoal - Commercially available aluminum nitride powder (average particle size 1.7 μm) 50
g in 100+++1 ethanol and stir well.

Next, in this, a phosphate ester monomer (i.e.
Add 2 ml of anionic surfactant) and mix thoroughly with a stirrer. This is placed in a dryer at a temperature of 70°C to volatilize the ethanol.

The powder after such treatment is a water-resistant aluminum nitride powder in which the surface of the aluminum nitride powder particles is covered with the above-mentioned phosphate ester monomer oriented with the hydrophobic groups on the outside. (This treatment is the first surface treatment.) Next, the aluminum nitride powder that has undergone this surface treatment is
Add 4 ml of the above phosphate monomer to 100+ sl of an aqueous solution, and stir and mix thoroughly using a stirrer. Take it out and put it in a dryer at 100℃ to dry it.
After that, it is powdered. The surface of the obtained powder is covered with a phosphoric acid ester monomer with the hydrophilic groups on the outside. (This treatment is, so to speak, a secondary surface treatment.) Using the aluminum nitride powder obtained in this example and the untreated aluminum nitride powder Comparative Example 1, a slurry (aluminum nitride Table 1 shows the results of comparing the pH changes over time of the preparations (concentration 70%).

Table-1 = pH change of aluminum nitride powder slurry-
As is clear from 1, when the untreated aluminum nitride powder (Comparative Example 1) is made into a slurry using water as a medium, the reaction of formula (1) proceeds rapidly and the pH rapidly increases. After 5 hours, the reaction of this slurry was completed, water disappeared, and a mixture of AIN and AI (OR) 3 was formed into a dry solid state. On the other hand, in Example 1, there was almost no change in pH, and the pH only increased slightly after 5 hours.

Next, we will calculate the average particle size when the surface-treated aluminum nitride powder obtained in Example 1 is dispersed in an aqueous medium, the relative density of the molded body when a slurry is made and cast molding is performed, and this molded body. The relative density of the sintered body when sintered under pressure and its thermal conductivity were investigated. Table 2 shows the results obtained.
are shown respectively.

The slurry concentration was 70%, and the binder was 5% of a waxy ester John type binder.

Also, as a sintering aid, 'It's' is 3% to AIN.
Added. In addition, sintering was performed at 600°C in 1 atm of Nt gas.
After performing a binder removal treatment for 2 hours, the treatment was performed at 1800° C. for 2 hours in the same atmosphere of N2 gas at 1 atmosphere.

A small Tammann furnace was used as the sintering furnace. For thermal conductivity, the thermal diffusivity and specific heat are determined using a laser flash method thermal constant measuring device (TC-3000 model (product name) manufactured by Shinku Riko Co., Ltd.), and these values are calculated using toluene as a medium. The density was calculated using the Archimedean method, and

Note that Comparative Example 1 is the result of using the same material as used in Table 1 (i.e., no surface modification treatment was performed at all), and Comparative Example 2 is the result of using the same material as that used in Table 1 (i.e., no surface modification treatment was performed at all). The results are shown using a sample that was subjected to surface treatment without any secondary surface treatment. In both cases, except for this difference in surface treatment, the aluminum nitride raw material powder, slurry concentration, binder, sintering aid, and sintering conditions were the same as the samples of Example 1.

Table-2 As is clear from Table-2, the surface treatment AI of this example product
N powder has water resistance and excellent dispersibility in water, and hardly aggregates as a slurry, so the average particle size is as fine as 2.5 μ-, which is not much different from the raw material powder. On the other hand, the untreated AIN powder of Comparative Example 1 reacts with water, has poor dispersibility, and causes agglomeration of the slurry, so the average particle size is 7.
．． It is large at 2 μm. Furthermore, although Comparative Example 2 has water resistance, the average particle size is 12 μm due to poor dispersibility in water.
m, which is very large. Due to this difference in dispersibility and the difference in reactivity with water, the relative density of the cast compact and the relative density of the sintered compact when using Comparative Examples 1 and 2 are both those of Example 1. In addition, the thermal conductivity is the lowest in Comparative Example 1 due to the low density and the increase in Ah03 due to the generation of Al(OH)3.
Comparative Example 2 also has a low value.

Man 11-1 Commercially available AIN powder 5 with the same average particle size of 1.7 μm as in Example 1
0g in 100ml of ethanol and stir well.

Next, 5 g of stearic acid was added to the mixture and thoroughly stirred and mixed using a stirrer. This is taken out and placed in a dryer at 70°C to volatilize the ethanol. The powder that has undergone such treatment becomes AIN powder that hardly gets wet with water and has water resistance.

The above-mentioned so-called primary surface treatment powder is placed in 100 ml of an aqueous solution containing 5 g of sodium oleate, and thoroughly stirred and mixed using a stirrer. This is taken out, placed in a dryer at 100°C, dried, and then powdered. The AIN powder subjected to this secondary surface treatment has excellent water resistance and good dispersibility in water. The surface treatment AI thus obtained
Slurry was made in the same manner as in Example 1 using N powder.

When we measured the pH change over time5
After some time, the pH remained the same as the initial value, 7. In addition, when the average particle size and relative density were similarly measured, the average particle size was 2.8 μm.
It shows good dispersibility, and the relative density of the cast molded product is 56%.
, the relative density of the sintered body is 98%, and the thermal conductivity is 85/l1
It was l-.

50 g of commercially available ^IN powder with a main average particle size of 1.7 μm is placed in 100 ml of toluene and stirred well. Next, 5 g of liquid paraffin was added into the mixture and thoroughly stirred and mixed. This is taken out and placed in a dryer at 80°C to volatilize the toluene, and then pulverized. The AIN powder after grinding is water resistant.

The above primary surface-treated powder is placed in 100 ml of an aqueous solution containing 5 g of sodium stearate, and thoroughly stirred and mixed using a stirrer.

This is taken out, placed in a dryer at 100°C, dried, and then ground. AIN that underwent this secondary surface treatment
The powder had excellent water resistance and good dispersibility in water. Using the obtained surface-treated AIN powder and making it into a slurry in the same manner as in Example 1, the pH change over time was measured, and the pi was 7.2 after 5 hours, with only a slight change from the initial value of 7.0. Met. In addition, when the average particle size and relative density were similarly measured, the average particle size was 2.5 μm, showing good dispersibility, the relative density of the cast molded body was 56%, the relative density of the sintered body was 98%, and the thermal conductivity was 2.5 μm. was 85 W/m·K.

5 g of an organic phosphoric acid coupling agent was added to 100 ml of ethanol in which 1 ml of acetic acid had been dissolved, and dissolved with stirring. After heating this solution to 90° C., 50 g of commercially available AIN powder having an average particle size of 1.7 μm was added, and the mixture was sufficiently stirred and mixed. This A
The slurry in which IN powder is dispersed is filtered and dried in a dryer at 70°C. Next, the temperature of the dryer was raised to 150° C., and heat treatment was performed for 1 hour. AIN obtained by this process
The powder is water resistant.

The AIN powder that has been subjected to the primary surface treatment is placed in 100 ml of an aqueous solution in which phosphate ester monomer 4+al is dissolved, and thoroughly stirred and mixed using a stirrer. This was taken out and placed in a dryer at 100°C to dry it.

Next, using the surface-treated AIN powder obtained as a slurry and measuring the pH change over time in the same manner as in Example 1, the pt+ after 5 hours was 7, the same as the initial value, and no change was observed. do not have. In addition, when the average particle size and relative density were similarly measured, the average particle size was 2.5 μm, indicating good dispersibility, and the relative density of the cast molded body was 57%, the relative density of the sintered body was 98%, and the thermal conductivity was 2.5 μm. The rate was 90 W/m-.

As is clear from the examples above, the aluminum nitride powder of the present invention has water resistance and excellent dispersibility in water, so it is extremely easy to make a slurry using water as a medium. As a result, good cast molded bodies and tape molded bodies can be obtained, and the industrially suitable value thereof is high.

Patent Applicant: Furukawa Electric Co., Ltd. Procedural Amendment Written by December 4, 1986 Commissioner of the Patent Office Kuro 1) Akio Yu 1, Indication of the case 1986 Patent Application No. 47414 2, Name of the invention Sintered body Aluminum nitride powder for production 3, relationship with the case of the person making the amendment Patent applicant (529) Furukawa Electric Co., Ltd. 4, agent 5, subject of amendment The scope of claims in column 1 of ``Description'', lines 4 to 8 of page 1 of the specification is corrected as follows.

2. Claim 1: An aluminum nitride powder for producing a sintered body, characterized in that the particle surface of the aluminum nitride powder is sequentially coated with a hydrophobic coating and a hydrophilic coating. 2. rAhOJ on page 2, line 1θ of the specification is r (Ali
as) Correct to J.

3.Page 6, line 9, “Surface treatment by -・-・” was changed to “
Corrected to ``Surface treatment by...''.

4. On page 7, line 1, "water resistance" is corrected to "hydrophobic."

5. On page 12, lines 11-12, "wax-shaped" is corrected to "wax-based."

6. On page 18, line 5, ``industrial suitability'' is corrected to ``industrial''.

Claims (1)

[Claims] 1. An aluminum nitride powder for producing a sintered body, characterized in that the particle surface of the aluminum nitride powder is coated with a hydrophobic coating and a hydrophilic coating in sequence.