JPH0469111B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides a novel aluminum nitride composition that can be used as a raw material for aluminum nitride powder compacts. [Prior art] Aluminum nitride sintered body has high thermal conductivity.
It is attracting attention as an electronics material.
Methods for obtaining an aluminum nitride sintered body include a method in which aluminum nitride powder is formed by dry pressing and fired, and a method in which aluminum nitride powder is wet-formed to obtain a green sheet and then fired. In the latter case, green sheets are generally produced by mixing aluminum nitride powder with an organic polymer compound, a deflocculant, an organic solvent, etc., and forming the mixture into a sheet by a doctor blade method or the like. Here, the peptizer is used to improve the dispersibility of the aluminum nitride powder in the organic solvent, and a surface active agent such as glycerin trioleate or sorbitan trioleate is usually used. [Problems to be Solved by the Invention] However, when the above-mentioned surfactants such as glycerytrioleate and sorbitan trioleate are used, the molding density of the green sheet does not increase or, in some cases, cracks occur in the green sheet. Problems have arisen, such as: If the compaction density of the green sheet is not sufficient, a dense aluminum nitride sintered body cannot be obtained, and the shrinkage rate of the green sheet upon firing increases. on the other hand,
If a crack occurs in the green sheet, the yield will deteriorate. [Means for Solving the Problems] In view of the above-mentioned problems, the present inventors have continued their research with the aim of obtaining a green sheet that has a high molding density and does not generate cracks. As a result, it was discovered that a composition of a surfactant and aluminum nitride powder having a specific hydrophilic-oleophilic balance can be used as a raw material for a green sheet that achieves the above objectives, leading to the completion of the present invention. That is, the present invention is an aluminum nitride composition comprising 100 parts by weight of aluminum nitride powder and 0.01 to 10 parts by weight of a surfactant having a hydrophilic-oleophilic balance of 4.5 to 18. As the aluminum nitride powder used in the present invention, any known aluminum nitride powder can be used without any restriction. In general, in order to obtain an aluminum nitride sintered body with excellent thermal conductivity, it is preferable that the content of oxygen and cationic impurities be low. That is, when AlN has an aluminum nitride composition, it is preferable to use aluminum nitride powder in which the content of oxygen as an impurity is 1.5% by weight or less and the content of cationic impurities is 0.3% by weight or less. Furthermore, aluminum nitride powder having an oxygen content of 0.4 to 1.3% by weight and a cationic impurity of 0.2% by weight or less is more suitable. Note that aluminum nitride in the present invention is a 1:1 compound of aluminum and nitrogen, and anything other than this is treated as an impurity. However, although the surface of the aluminum nitride powder is inevitably oxidized in the air and Al--N bonds are replaced by Al--O bonds, this Al bond is not considered as a cationic impurity. Therefore, metal aluminum that does not have Al--N or Al--O bonds is a cationic impurity. Further, it is preferable that the particles of aluminum nitride powder used in the present invention have small particle diameters. For example, the average particle diameter (centrifugal particle size distribution analyzer, for example, manufactured by Horiba)
Refers to the average particle size of aggregated particles measured with CAPA500 etc. ) is preferably 5 μm or less, more preferably 3 μm or less. Other components constituting the aluminum nitride composition of the present invention include hydrophilic-lipophilic balance (hereinafter referred to as HLB).
It is abbreviated as ) is a surfactant of 4.5 to 18. When the HLB of the surfactant is outside the above range, it is not preferable because the molding density of the obtained green sheet does not increase and cracks may occur. The HLB of the surfactant should be within the above range, but
A range of 5.0 to 15.0, more preferably a range of 6.0 to 10.0, is preferable from the viewpoint of the compaction density of the green sheet and the shrinkage rate of the sintered body obtained by further firing. Note that HLB in the present invention is a value calculated using the Davis equation described later. Specific examples of surfactants that can be suitably used in the present invention include carboxylated trioxyethylene tridecyl ether, diglycerin monooleate, diglycerin monostearate, carboxylated heptaoxyethylene tridecyl ether, Examples include tetraglycerin monooleate, hexaglycerin monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, and the like. The surfactants in the present invention may be used in combination of two or more kinds, and the HLB in that case can be calculated from the arithmetic average of the HLB of each surfactant. The mixing ratio of the aluminum nitride powder and the surfactant is 0.01 to 10 parts by weight, preferably 0.01 to 10 parts by weight of the surfactant to 100 parts by weight of the aluminum nitride powder.
It is 0.02 to 3.0 parts by weight. If the amount of the surfactant is less than the above range, the effect of the present invention cannot be obtained, and if it is too much, the density of the green sheet may not increase and cracks may occur. unfavorable to When producing green sheets using the aluminum nitride composition of the present invention, a binder is usually used. Binders that are generally used for molding ceramic powder can be used without particular limitation in the present invention, but they have been shown to be decomposed by thermogravimetric analysis (TG).
Preferably, it occurs in a temperature range of 1400°C or less. More preferably, a binder is selected in which the decomposition residue of the binder is 5% by weight or less based on the binder. More specific examples of binders preferably used in the present invention include polyvinyl butyral, polymethyl methacrylate, cellulose acetate butyrate, nitrocellulose, polyacrylic acid ester, polyvinyl alcohol, methylcellulose, hydroxymethylcellulose, and Oxygen-containing organic polymers such as polyethylene oxide; Other hydrocarbon synthetic resins such as petroleum resin, polyethylene, polypropylene, and polystyrene; Polyvinyl chloride; Acrylic resins and their emulsions; Organic polymers such as wax and their emulsions. are used singly or in combination of two or more. The molecular weight of the organic polymer used as a binder is not particularly limited, but is generally between 3000 and
1,000,000, preferably 5,000 to 300,000, is more suitable because the above-mentioned molded article, such as a green sheet, is flexible and tough and easy to handle during various processing. In particular, oxygen-containing organic polymers are preferred among the organic polymers, and further,
Polyvinyl butyral with a molecular weight of 30,000 to 100,000 is most preferred. The amount of binder used varies depending on the type of binder and the type of solvent described below, and also depends on the use of the aluminum nitride composition, such as the thickness, strength, and processability of the aluminum nitride green sheet, as well as the sintering of the green sheet. Although it cannot be definitively determined as it varies depending on the physical properties required for the aluminum nitride sintered body obtained by
Parts by weight may be selected, preferably from 2.0 to 15 parts by weight. Further, when processing the aluminum nitride composition of the present invention into a specific molded product, it is preferable to use a plasticizer for the purpose of imparting flexibility to the processed product. The plasticizer is not particularly limited, and any plasticizer known to be used for the above purpose in molding general ceramic powder can be used. Typical examples that are particularly preferably used include polyethylene glycol and its derivatives; phthalate esters such as dimethyl phthalate, dibutyl phthalate, butylbenzyl phthalate and dioctyl phthalate; stearic acid such as butyl stearate. These include esters; tricresol phosphate; tri-N-butyl phosphate; glycerin, and the like. The amount of these plasticizers added depends on the type of binder,
It varies depending on the properties of aluminum nitride, the type of solvent, the amount used, etc., and cannot be absolutely limited, but it is generally selected as appropriate from the range of 15 parts by weight or less, preferably from 0.4 to 15 parts by weight, based on 100 parts by weight of aluminum nitride. and use it. The usage mode of the aluminum nitride composition of the present invention will be explained below. When used, it is generally preferable to use it in the form of a dispersion in a solvent. Typical examples of suitable solvents include, for example, setones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; alcohols such as ethanol, propanol and butanol; benzene, toluene and xylene; It is preferable to use one or a mixture of two or more of aromatic hydrocarbons; or halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene, and bromochloromethane. The amount of the solvent to be used is also not particularly limited, but it is preferably selected in the range of 20 to 200 parts by weight per 100 parts by weight of the aluminum nitride powder. The conditions for mixing the components, binder, solvent, etc. of the aluminum nitride composition of the present invention are not particularly limited, and the mixing may be carried out at room temperature and pressure. It is preferable to choose one that has been During this mixing,
It is a preferred embodiment to add a known sintering aid. The mixture is generally used in the form of a viscous paint-like slurry called slurry so that it can be easily handled during molding. The slurry obtained as described above is formed into a sheet using a sheet forming machine such as a doctor blade method. Next, the sheet-like molded product is dried by scattering the solvent at a temperature between room temperature and the boiling point of the solvent, thereby forming a so-called aluminum nitride green sheet. Although the aluminum nitride green sheet described above can be used as it is to produce a sintered body by a known method, it is generally used in a gas atmosphere of an oxygen-containing gas, such as air, or an inert gas, such as nitriding gas or helium gas. the above-mentioned surfactant,
The temperature at which binders, plasticizers, etc. are decomposed, generally
For example, it is preferable to carry out the thermal decomposition treatment at a temperature of 300 to 1400°C, preferably 500 to 1000°C. Although it has been explained above that the aluminum nitride composition of the present invention is formed into a green sheet, the aluminum nitride composition of the present invention can be used by forming it into any shape other than a sheet shape such as a green sheet. I can do it. For example, the slurry described above can be granulated into granules by a spray dryer method. The granules are formed into a plate-like shape or the like using a press molding machine, and are fired by a known method to form an aluminum nitride sintered body. [Effects] The green sheet made from the aluminum nitride composition of the present invention has a high molding density and does not generate cracks. An aluminum nitride sintered body obtained by sintering such a green sheet with a high compaction density by a known method becomes a high-density sintered body. Further, since the shrinkage rate due to sintering is small, there is an advantage that the difference in shrinkage rate with metal can be reduced in a simultaneous firing method in which a high melting point metal paste is printed on the surface and fired. Further, the granules obtained using the aluminum nitride composition of the present invention as a raw material have no depressions on the surface, are close to perfect spheres, and have a high density. Therefore, a compact of aluminum nitride powder obtained by press-molding the above-mentioned granules has the advantage of high density and low shrinkage due to sintering. Therefore, the aluminum nitride sintered body obtained according to the present invention is an extremely useful material industrially as a heat dissipating substrate for electronic equipment, an electronic circuit board, a heat dissipating material, and an insulating material. EXAMPLES In order to explain the present invention more specifically, examples will be described below, but the present invention is not limited to these examples. In addition, measurements of various physical properties in the following Examples and Comparative Examples were performed by the following methods. (1) Specific surface area: Determined by the BET method using N ₂ adsorption.
(Using "Flowsorb 2300" manufactured by Shimadzu Corporation) (2) Average agglomerated particle size of AIl powder: Determined by centrifugal sedimentation method. (Using "CAPA500" manufactured by Horiba, Ltd.) (3) Amount of impurities in AlN powder Amount of cationic impurities: The powder was melted in an alkali, neutralized with acid, and quantified by ICP emission spectrometry of the solution. (Using "ICPS-1000" manufactured by Shimadzu Corporation) Amount of impurity carbon: Powder was burned in an oxygen stream and determined from the amount of CO and CO ₂ gas generated.
(Using ``EMIA-110'' manufactured by Horiba, Ltd.) Impurity oxygen content: Determined from the amount of CO gas generated by high-temperature pyrolysis of powder in a graphite crucible. (Manufactured by Horiba, Ltd.)
(Using "EMGA2800") (4) Sheet molded body density (dg): Calculate the green density from the dimensions and weight of the green sheet, and from this value
The density of the sheet compact made only of AlN powder was calculated. dg = compact green density × (AlN weight in slurry) / (slurry weight) -
(Weight of organic solvent) (5) Density of AlN sintered body (d _s ): Determined by Archimedes method. (Manufactured by Toyo Seiki Co., Ltd.) “High precision hydrometer D-
(6) Shrinkage rate during sintering: Determined by measuring dimensions before and after sintering. Shrinkage rate = (1 - sintered body size / molded body size before sintering) x
100 (7) HLB of surfactant: Calculated using the Davis equation shown by the following equation. HLB=7×Σ(Number of bases of hydrophilic group) +Σ(Number of bases of lipophilic group) However, the number of bases of hydrophilic group and the number of bases of lipophilic group are values determined by the number of species of the group, for example,
"Basic Chemistry Selection 22 Colloid Chemistry" by Katsuichi Ikeda
This is the value shown on page 195. (8) Light bulk density, heavy bulk density, and angle of repose: Measured using "A, B, D powder property measuring device" manufactured by Tsutsui Rikagaku Kikai Co., Ltd. Example 1 To 100 parts by weight of the aluminum nitride powder shown in Table 1, 3.0 parts by weight of calcium oxide and 2.0 parts by weight of various surfactants shown in Table 2 were added to 120 parts by weight of a toluene-ethanol mixed solvent (mixed weight ratio, A slurry was prepared by mixing in toluene/ethanol = 60/40). As for the above mixing procedure, a nylon ball with an iron core is placed in a nylon pot with an internal volume of 2, and then aluminum nitride powder, surfactant,
After adding the mixed solvent and thoroughly mixing in a ball mill, a white slurry was obtained. The viscosity of the resulting slurry was measured at 20°C using a B-type viscometer. To this slurry, 8.0 parts by weight of polyvinyl butyral with a molecular weight of 30,000 to 34,000 and 6.0 parts of dibutyl phthalate are added.
Parts by weight were added and remixed. The white paste-like slurry thus obtained was desolvated and the viscosity was reduced.
After adjusting to 1,000 cps to 3,000 cps, sheet forming was performed using the doctor blade method, and the mixture was heated at room temperature for 2 hours.
A sheet molded body (green sheet) having a width of about 10 cm and a thickness of 0.8 mm was prepared by drying at 60° C. for 5 hours, and its density was measured. The obtained green sheet was punched out using a 34 mm square mold, fired in air at 600°C for 5 hours, then placed in a carbon crucible whose inner surface was coated with boron nitride, and heated at 1800°C in a nitrogen atmosphere for 10 hours. Baked,
A sintered body was obtained. The apparent density of the obtained sintered body was measured by the Archimedes method, and the shrinkage rate was determined from the dimensional difference between the molded body and the sintered body. The results are shown in Table 2.

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[Table] Example 2 Aluminum nitride powder A100 used in Example 1
3 parts by weight of calcium oxide and 0 to 12.0 parts by weight of carboxylated heptaoxyethylene tridecyl ether as a surfactant in 80 parts by weight of a mixed solvent (toluene/ethanol = 60/40) as in Example 1. A white slurry was obtained.
The viscosity of the obtained slurry was measured at 20°C. Next, slurry preparation and sheet molding were performed in the same manner as in Example 1, and this molded body was further fired in the same manner as in Example 1 to obtain a sintered body, which was then subjected to various evaluations. The results are shown in Table 3.

[Table] Example 3 Aluminum nitride powder A100 used in Example 1
3 parts by weight of calcium oxide, 3.0 parts by weight of hexaglycerin monooleate as a surfactant, 2.0 parts by weight of polyvinyl butyral having a molecular weight of 30,000 to 34,000, and 1.0 parts by weight of dibutyl phthalate were added in a toluene solvent in the same manner as in Example 1. Mix by method,
A white slurry was obtained. The slurry thus obtained was granulated by a spray dryer method to produce granular aluminum nitride powder with an average particle size of 80 μm and nearly perfect spheres. Table 4 shows the properties of the obtained granules, and FIG. 1 shows an electron micrograph (magnification: 8 times) showing the morphology of the granules. A 1 inch square, 1 mm thick press molded body (density 1.79 g/cm ³ ) was prepared using the obtained granules, and this was fired in the same manner as in Example 1 in air and nitrogen. The density of the obtained sintered body was 3.26 g/cm ³ and the shrinkage rate was 18.1%.

[Table] Comparative Example Granular aluminum nitride powder was obtained in the same manner as in Example 3, except that sorbitan tristearate was used in place of hexaglycerol monooleate. The properties of the obtained granules are shown in Table 4, and an electron micrograph (magnification: 8x) showing the morphology of the granules is shown in FIG. Furthermore, after forming a press molded body (density 1.53 g/cm ² ) using these granules in the same manner as in Example 3, an aluminum nitride sintered body was obtained, and the density was 3.24 g/cm ³ . , the shrinkage rate was 22.2%.

[Brief explanation of the drawing]

Figures 1 and 2 are electron micrographs showing the particle structure of granular aluminum nitride powder obtained in Example 3 and Comparative Example, respectively (all magnifications are 8.
times).

Claims (1)

[Claims] 1. An aluminum nitride composition comprising 100 parts by weight of aluminum nitride powder and 0.01 to 10 parts by weight of a surfactant having a hydrophilic-oleophilic balance of 4.5 to 18.