JPH07144970A - Aluminum nitride green sheet - Google Patents

Abstract

PURPOSE:To obtain an aluminum nitride green sheet having toughness and excellent workability by blending a solvent and a binder composed of a specific copolymer with a powdery aluminum nitride. CONSTITUTION:This aluminum nitride green sheet contains the powdery aluminum nitride, the solvent and the binder obtained by copolymerizing one or more kinds of methacrylic ester monomer represented by the formula and an unsaturated monomer having polar groups except carboxylic acid. In the formula, R is a group containing carbon and the average carbon number of R is 1<=n<=9. For the powdery aluminum nitride as a starting material powdery, a single form may be used, however >=2 kinds of the powdery aluminum nitride may be properly mixed and used so as to acquire <=18% firing shrinkage factor of the green sheet instead of a single form to control shrinkage factor at the time of firing. If the firing shrinkage factor of the green sheet in the case of being used in single form is over 18%, the particle size distribution is hardly controllable because of excess coarse particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride green sheet.

[0002]

2. Description of the Related Art A green sheet formed by a doctor blade method is generally used as a molded body of a ceramic substrate.

In the doctor blade method, a ceramic powder and an organic binder are slurried using a solvent or the like, coated on a carrier tape with a blade to a certain thickness, and dried to solidify to produce a green sheet. Is the way. The obtained green sheet is processed as required and fired to form a ceramic substrate. When mass-producing aluminum nitride substrates using this technique, necessary factors include stabilization of dimensional accuracy and prevention of yield reduction due to cracking during molding.

The dimensional accuracy depends on how stable the density of the green sheet is. The green sheet density has a value almost determined by the raw material powder of aluminum nitride. However, conventionally, the firing shrinkage ratio has slightly changed due to other factors in the raw material slurry, such as a change in the mixing ratio of the organic solvent and a molding condition such as a drying condition.

On the other hand, the formability, strength, etc. of the green sheet vary depending on the kind of binder present in the sheet.
This is considered to be because these values change depending on the bonding state of the ceramic powder and the binder.

[0006] In the firing, sufficient degreasing is necessary in order to prevent sintering inhibition due to carbon remaining in the binder. The better the degreasing characteristics of the sheet, the lower the degreasing temperature can be, which facilitates the control of conditions in the subsequent main firing. Therefore, a binder that is easier to degrease is desired.

Polyvinyl butyral (PVB) is generally known as a binder for forming a green sheet. If you add an appropriate amount of plasticizer to PVB,
The film exhibits toughness and flexibility, and the green sheet using this as a binder is tough and has good workability.

However, the PVB-based binder has a problem that it has a poor thermal decomposability due to the structure of the polymer and that a decomposition residue remains in the air unless it is heated to a high temperature of 600 ° C. or higher.

For this reason, green sheets using an acrylic resin-based binder, which has a better thermal decomposability than PVB, have been developed. There is a possibility that cracks or damage may occur during molding or during handling in the subsequent process.

[0010]

SUMMARY OF THE INVENTION The present invention is intended to eliminate the above-mentioned drawbacks of the prior art. To the aluminum nitride powder, a solvent and a binder are added, and further plasticization is carried out if necessary. Use a homopolymer or two or more copolymers of methacrylic acid ester monomer as a binder when forming a ceramic green sheet by adding a dispersant and a dispersant to form a slurry and forming the slurry using a doctor blade method. This is a new proposal for a ceramics green sheet characterized by.

[0011]

The present invention is an aluminum nitride green sheet containing aluminum nitride powder, a solvent, and a binder, wherein the binder is a methacrylic acid ester monomer shown in Chemical formula 2 (wherein R represents carbon). An aluminum nitride which is a group containing a copolymer of one or more of R having an average carbon number of 1 ≦ n <9) and an unsaturated monomer having a polar group other than a carboxylic acid. It provides a green sheet.

[0012]

[Chemical 2]

The present invention will be described in detail below. The aluminum nitride powder, which is the raw material powder used in the present invention, can be used alone, but the shrinkage rate of the green sheet when used alone is 18% or less in order to control the shrinkage rate during firing. It is possible to use a mixture of two or more of the above-mentioned substances in an appropriate amount. If the green sheet firing shrinkage when used alone exceeds 18%,
Since there are too many coarse particles, it may be difficult to adjust the particle size distribution.

The green sheet filling rate changes depending on the binder and solvent composition and the drying conditions.
By mixing more than one kind of aluminum nitride, it is possible to control the firing shrinkage rate by the raw material powder, and thus this problem can be overcome. In this case, since the shrinkage ratio can be adjusted, it is possible to deal with a substrate having a high dimensional accuracy of shape. The average particle size of aluminum nitride powder is 1
It is desirable that the thickness is about 5 μm to 5 μm. If it exceeds this range, the filling rate is lowered and the sintering tends to be insufficient. Further, the amount of impurity oxygen is 3% or less, preferably 1.5% or less. If the amount of oxygen is large, the thermal conductivity of aluminum nitride may be reduced.

The monomer that is the starting material of the binder that can be used in the present invention is a methacrylic acid ester monomer shown in Chemical formula 2 (wherein R is a group containing carbon,
The average carbon number n of R is 1 ≦ n <9). R is typically a hydrocarbon group, and specific examples of the compound of Chemical formula 2 are methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and stearyl methacrylate. These compounds are used so that the average carbon number of the alcohol residue is less than 9 in the final binder.

When the average carbon number of the alcohol residue is 9 or more, since the solubility in the solvent used is low, it is difficult to form a slurry and a strong green sheet may not be obtained.

Polymethacrylic acid ester is a binder having excellent thermal decomposability because it undergoes thermal decomposition upon depolymerization. However, when two or more monomers of methacrylic acid ester are copolymerized, they are compared to a single homopolymer. The thermal decomposability is further improved. For example, in this case, if the green sheet of AlN powder is thermally decomposed in an inert gas atmosphere, Al
The binder can be removed without impairing the characteristics of N.

When two or more monomers of the methacrylic acid ester are copolymerized in this way, the reason why the thermal decomposability is good is as follows. It is estimated that it is the starting point of.

In the present invention, the above-mentioned one or more kinds of methacrylic acid ester and a monomer having a polar group other than carboxylic acid are copolymerized. As the monomer having a polar group other than the carboxylic acid to be copolymerized, methacrylic acid 2-
Hydroxyl group-containing unsaturated monomers such as hydroxyethyl, 2-hydroxypropyl acrylate and 2-hydroxyethyl acrylate, and amide group-containing unsaturated monomers such as methacrylamide, acrylamide, N-methylol acrylamide and vinylpyrrolidone, 2- Acrylamide-2-methylpropanesulfonic acid, 2-sulfoethyl methacrylate-containing unsaturated monomer containing sulfonic acid group, methoxy polyethylene glycol monomethacrylate, polyethylene glycol monomethacrylate, unsaturated monomer containing ether group such as ethoxyethoxyethyl acrylate, methacryl Amino group-containing unsaturated monomers such as acid N, N-dimethylaminoethyl, acrylic acid N, N-dimethylaminoethyl, glycidyl methacrylate, glycidyl acrylate, etc. Epoxy group-containing unsaturated monomer, may be used as appropriate unsaturated monomer containing a polar group of methacrylamide propyl trimethyl ammonium chloride, methacryloyl ammonium salt-containing unsaturated monomers such as trimethyl ammonium chloride or the like. It is necessary to introduce a larger amount of these functional groups, probably because they have lower reactivity with the aluminum nitride powder than the carboxyl groups, but on the other hand, it becomes easy to adjust an appropriate amount. The amount introduced is 0.5 to 60 as a monomer fraction.
It can be used in an amount such that it is 10 mol%.

If the amount introduced is less than 0.5 mol%, sufficient green sheet strength may not be obtained. If it exceeds 10 mol%, the viscosity may become too high depending on the component. In particular, when the amount of the monomer having a polar group is large, the degreasing property is deteriorated due to an increase in electrostatic interaction with the particle surface or a problem in the molecular structure. In addition, the decomposition residue after degreasing increases.

Further, since the solvent solubility of the binder changes, the solubility in ketones such as methyl ethyl ketone and halogen-based organic solvents such as trichloroethylene, which are highly volatile and suitable for forming green sheets, is reduced. Therefore, molding using these solvents will not be possible.

The weight average molecular weight is preferably between 50,000 and 500,000, more preferably between 100,000 and 300,000. If the molecular weight is 50,000 or less, the green sheet cannot be provided with the required strength, and defects are likely to occur during molding and handling. On the other hand, when the molecular weight exceeds 500,000, the solubility in an organic solvent decreases, so that the viscosity of the slurry before forming the green sheet increases, and the moldability and the degreasing property may decrease.

The ratio (weight ratio) of the binder to the ceramic powder is 100% of the ceramic powder and 3 to 3 of the binder.
0 is preferable, and if the binder is less than 3, a good green sheet is not obtained, and if it exceeds 30, it is difficult to degrease the binder.

In the present invention, as a sintering aid added to the aluminum nitride powder to obtain a dense sintered body,
Y ₂ O ₃ , CaO and the like are preferable, but not limited to these as long as they promote densification. When the addition amount of the sintering aid is too large, the crystal phase other than aluminum nitride increases and the thermal conductivity decreases, so that it is preferably 10% by weight or less, particularly preferably 5% by weight or less.

In the present invention, a plasticizer may be used in combination so as to obtain the desired green sheet characteristics. As the plasticizer, dioctyl phthalate, dibutyl phthalate, butylbenzyl phthalate, and other commonly used plasticizers can be used.

Examples of the solvent used in the present invention include ketone solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone, aromatic solvents such as benzene, toluene and xylene, chloroform, 1,1,1-trichloroethane and trichloroethylene. Halogen solvent, R-113, R
-225, R-141b and other freon-based solvents can be used alone or as a mixture. You may slightly mix alcohol solvents, such as methanol and ethanol. Also, various surfactants can be used as a dispersant for the ceramic powder.

The aluminum nitride powder and the sintering aid to which an organic binder has been added are wet mixed in a ball mill using an organic solvent, and a slurry is formed by a doctor blade method to obtain a green sheet. In addition,
The molding method is not limited to sheet molding by the doctor blade method, powder pressing method, extrusion molding method,
The effects of the present invention can be similarly obtained by any of the injection molding methods.

The green sheet produced by the method described above is degreased in air or a non-oxidizing atmosphere. Degreasing is performed in the air or in an inert atmosphere within a temperature range in which the organic binder is sufficiently decomposed. Specifically, 350
C.-600.degree. C. is desirable. After degreasing, stored in a firing sheath to prevent carbon from entering the firing furnace, in an inert atmosphere,
Firing is performed at 1500 ° C. to 2000 ° C. to obtain a dense sintered body having no pores.

[0029]

【Example】

1. Molding of green sheet Aluminum nitride powder A and powder B having different particle size distributions were mixed at a weight ratio of 60:40, and a sintering aid was mixed at a predetermined ratio with respect to 100 parts by weight of the starting material.
10 parts by weight of a binder produced by copolymerizing the composition as shown in the above, 60 parts by weight of toluene, 1 part by weight of oleic acid and 4 parts by weight of dimethyl phthalate were added, and the mixture was mixed with a ball mill to obtain 10 parts by weight.
The mixture was mixed for a time to form a slurry. Next, this slurry was formed into a thickness of 0.8 mm by a doctor blade machine and dried at 60 to 80 ° C. for 2 hours to obtain a green sheet.

2. Evaluation of Strength of Green Sheet The green sheet was pulled by a tensile tester and its cutting strength was compared with that when polyvinyl butyral was used as a binder.

3. Evaluation of Degreasing Property The degreasing property was evaluated by measuring the thermal decomposition temperature of the binder. The thermal decomposition temperature in Table 1 is measured by TG-DTA of the binder alone.

The results obtained as described above are also shown in Table 1. In Table 1, the composition indicates the molar ratio of the methacrylic acid ester monomer. Here, MMA is methyl methacrylate, iBMA is isobutyl methacrylate, OMA
Is octyl methacrylate. The molar average carbon number is the molar average carbon number of the portion corresponding to R in Chemical formula 1. The polar group monomer is a type of unsaturated monomer copolymerized with the methacrylic acid ester monomer. The introduced amount of the functional group is the amount of the polar group monomer and is represented by mol% of the polar group with respect to the total amount of the binder. The unit of thermal decomposition temperature in N ₂ is ° C.

[0033]

[Table 1]

The sheet strength ratio indicates the relative strength when the strength when polyvinyl butyral is used as the binder is 100, but when this value is 50 or less, the moldability and handleability are poor. , Can not be used.

Regarding degreasing property, it can be understood that degreasing can be performed at a lower temperature by using a copolymer of methacrylic acid ester. In particular, in this case
Degreasing time tends to be short.

[0036]

EFFECTS OF THE INVENTION By molding a ceramic green sheet according to the present invention, a tough green sheet having good workability can be obtained. In the present invention, an acrylic resin having a good thermal decomposability is used as the binder, so that the thermal decomposability is good, and a very good thermal decomposability is exhibited even in a nitrogen gas atmosphere.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication C04B 35/58 104 Z (72) Inventor Shiro Otaki 1 Kamiterashita, Katahira-cho, Koriyama-shi, Fukushima Prefecture West Koriyama Second Industrial Park Asahi Glass Koriyama Electric Co., Ltd.Koriyama Factory (72) Inventor Keiichi Kawakami 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Central Research Laboratory, Asahi Glass Co., Ltd.

Claims (1)

[Claims] 1. An aluminum nitride green sheet containing aluminum nitride powder, a solvent, and a binder, wherein the binder is a methacrylic acid ester monomer shown in Chemical formula 1 (wherein R is a group containing carbon, and R is an average of R). An aluminum nitride green sheet, characterized by comprising one or more carbon atoms having 1 ≦ n <9) and an unsaturated monomer having a polar group other than carboxylic acid copolymerized. [Chemical 1]