JP2605542B2 - Binder for producing inorganic sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder for producing an inorganic sintered body, and more particularly to a green molded body having excellent formability and excellent shape retention, and especially under non-sintering conditions. Decomposes easily even under oxidizing atmosphere sintering conditions
The present invention relates to a binder which is scattered and does not remain as undecomposed carbide in a sintered body.

[0002]

2. Description of the Related Art The most widely practiced method for producing various sintered compacts at present is to mix an inorganic powder such as alumina, silica, zirconia, mullite, silicon carbide and silicon nitride together with an organic polymer binder. A green compact, which is fired to decompose and scatter the binder and to sinter the ceramic powder.

In this case, since sintering is usually carried out in an oxidizing gas atmosphere such as in air, the organic binder is thermally decomposed and burned off, and undecomposed and unburned carbide hardly remains inside the sintered body. In addition, since the inorganic fine powder is sintered and solidified after the binder is burned off, a dense sintered compact having almost no void defects can be obtained.

However, depending on the type of the inorganic powder or the use of the sintered compact, firing and sintering may need to be performed in a non-oxidizing atmosphere. For example, when the inorganic fine powder contains a nitride, a carbide, a metal, or the like, firing and sintering in an oxidizing atmosphere will oxidize them and lose their properties as a non-oxide sintered body. Must be sintered. In addition, we want to form a film made of non-oxide material on the surface of a molded product such as ceramics or ceramic green molded product, and then fire and sinter the ceramic green molded product while maintaining this non-oxide material film in a non-oxidized state. In such a case, it is necessary to similarly perform firing and sintering in a non-oxidizing atmosphere. However, when a normal green molded body molded using an organic polymer binder is heated in a non-oxidizing atmosphere, a part of the organic polymer binder does not decompose or scatter and easily remains as a carbide in the sintered body. In the sintering process, cracks, warpage, swelling, etc. occur in the molded body, and a large amount of carbide remains in the sintered molded body, reducing the denseness, making the sintered molded body brittle and reducing the electrical insulation Or cause various problems such as gray to black coloration.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to effectively function as a binder in the molding step of a green molded article, and to provide an excellent molding. Demonstrates the properties and shape retention properties.On the other hand, when sintering is performed in an oxidizing atmosphere as well as in a non-oxidizing atmosphere, it is easily decomposed and scattered. An object of the present invention is to provide a binder for producing an inorganic sintered body that does not remain as a carbide in a sintered compact.

[0006]

Means for Solving the Problems The constitution of the binder according to the present invention which can attain the above object comprises butyl methacrylate, cycloalkyl group-containing methacrylate, hydroxyl group-containing methacrylate and C8 or more having an alkyl side chain at the β-position. The methacrylate unit selected from the group consisting of methacrylates occupies 90% by weight or more of the whole, and is composed of a methacrylate-based polymer having an isobutyl methacrylate unit content of 70% by weight or more, and has a molecular weight of 1,000 to 1,000,000. Where the content of the polymer accounts for 90% by weight or more, and the content ratio of the polymer having a molecular weight of 150,000 or less and the polymer having a molecular weight of more than 150,000 in the molecular weight range is 1/1 to 5/1 by weight ratio. It has a gist.

The measurement of the molecular weight in the present invention was carried out by the following method. Measuring apparatus: Gel permeation chromatography "M-410" manufactured by WATERS Detector: Differential refractometer Column used: Ultra Styra Jur (diameter 7.8 mm x 300 mm) x 4 manufactured by WATERS Standard substance: polystyrene Measurement conditions ： Flow rate 1cc / min (THF) Temperature 40 ℃

In the above, among the main monomer units constituting the methacrylate polymer, particularly preferred are n-butyl methacrylate, isobutyl methacrylate, secondary butyl methacrylate, tertiary butyl methacrylate, cyclohexyl methacrylate, 2-hydroxy A methacrylate polymer in which at least one selected from the group consisting of ethyl methacrylate, 2-hydroxypropyl methacrylate, and 2-ethylhexyl methacrylate accounts for 90% by weight or more of the total, and isobutyl methacrylate units account for 70% by weight or more of the entirety. It is the easiest and quickest to decompose and scatter in the firing and sintering process under a non-oxidizing atmosphere. The methacrylate-based polymer preferably has an acid value of 0.1 to 10 from the viewpoint of ensuring the dispersibility and moldability of the inorganic powder during the production of the green molded product, and more preferably has a number average molecular weight of 1 to 10. The use of a material having a molecular weight in the range of 10,000 to 60,000 makes it possible to further improve the moldability, the shape retention, and the dissociation and scattering during sintering.

[0009]

As described above, in the present invention, the content of a methacrylate-based polymer containing a selected methacrylate as a main monomer unit and having a specific molecular weight range is specified, and a molecular weight of 150,000 within the molecular weight range is specified. It specifies the content ratio of the low molecular weight polymer and the high molecular weight polymer as criteria, and these setting criteria are the moldability and shape retention, which are the original required properties of a green molded article binder containing inorganic powder. While securing the nature
It is determined in order to secure characteristics that allow it to be easily decomposed and scattered even during sintering in a non-oxidizing atmosphere. The reasons for setting each component will be described in detail below.

First, butyl methacrylate, cycloalkyl group-containing methacrylate, hydroxyl group-containing methacrylate and C8 or more methacrylate having an alkyl side chain at the β-position were selected as the main monomer units of the methacrylate-based polymer. The polymer containing easily depolymerizes, even when heated in a non-oxidizing atmosphere, easily depolymerizes and scatters,
This is because it is difficult for the carbide to remain in the sintered body.

[0011] As here butyl methacrylate acrylate is n-
Butyl methacrylate, isobutyl methacrylate, secondary butyl methacrylate, tertiary butyl methacrylate, and the like, these isobutyl meta acrylate is most preferred among all methacrylate monomer including methacrylate shown below. Specific examples of the cycloalkyl group-containing methacrylate include cyclohexyl methacrylate, cycloheptyl methacrylate, cyclooctyl methacrylate and the like, and among them, cyclohexyl methacrylate is particularly preferred. Specific examples of the hydroxyl group-containing methacrylate include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, glycerol monomethacrylate, trimethylolpropane monomethacrylate, polyethylene glycol monomethacrylate, and polypropylene. Glycol monomethacrylate and the like, among which particularly preferred are 2-hydroxyethyl methacrylate and 2-hydroxyethyl methacrylate
Hydroxypropyl methacrylate. Specific examples of C8 or higher methacrylate having an alkyl side chain at the β-position include 2-ethylhexyl methacrylate, isooctyl methacrylate, isodecyl methacrylate,
Isolauryl methacrylate, isostearyl methacrylate and the like are exemplified, and among these, 2-ethylhexyl methacrylate is particularly preferred.

In order to achieve the object of the present invention, at least one methacrylate selected from the group consisting of the above methacrylates is used.
The seed accounts for 90% by weight or more, more preferably 95% by weight or more of the total monomer units, and isobutyl methacrylate showing particularly excellent depolymerizability among the methacrylates is 70% by weight or more, more preferably 80% by weight of the whole. If the methacrylate-based polymer occupying the above conditions must be used, and these requirements are lacking, carbides tend to remain under heating conditions in a non-oxidizing atmosphere, and the object of the present invention cannot be achieved. Therefore, in the present invention, it is preferable that all or most of the monomer units are the above methacrylate units, and these may be homopolymers or copolymers using two or more monomers. It doesn't matter.

In the present invention, as long as the content of the methacrylate unit is satisfied, a small amount of another copolymerizable monomer can be copolymerized. As such a copolymerizable monomer, methyl (meth) Acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl acrylate, isobutyl acrylate, 2
(Meth) acrylate monomers such as -methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and dimethylamino (meth) acrylate; styrene, α-methylstyrene, Styrenic monomers such as β-methylstyrene, α-ethylstyrene, β-ethylstyrene, vinylstyrene, etc .; acrylic acid, methacrylic acid, maleic acid, itaconic acid, citraconic acid, maleic acid monoester (such as monoisopropyl maleate) Copolymerizable unsaturated carboxylic acids; furthermore, (meth) acrylonitrile, acrylamide, vinyl acetate,
Examples thereof include vinyl chloride and the like, and if necessary, two or more kinds can be used in combination. Among these copolymerizable monomers, the copolymerizable unsaturated carboxylic acid imparts an appropriate acid value to the methacrylate-based polymer to increase the dispersibility and dispersion stability of the inorganic powder. Therefore, it is desirable in the present invention to use a small amount of a copolymerizable unsaturated carboxylic acid in combination. Particularly preferred among the copolymerizable unsaturated carboxylic acids is methacrylic acid.

In the methacrylate-based polymer constituting the binder of the present invention, the molecular weight is an extremely important factor in addition to the above-mentioned requirements for the monomer unit, and the function as a binder (particularly, the moldability and shape retention of a green molded article) Sex)
In order to ensure that decomposition and scattering at the time of sintering are performed while effectively performing the above, the content of the polymer having a molecular weight in the range of 1,000 to 1,000,000 determined by the above method is 90% by weight or more. Preferably, it occupies 95% by weight or more, and the content ratio of a polymer having a molecular weight of 150,000 or less and a polymer having a molecular weight of more than 150,000 in the molecular weight range is 1/1 by weight.
It must be in the range of 1-5 / 1, more preferably 2 / 1-4 / 1.

If the ratio of the low molecular weight compound and the high molecular weight compound outside the above molecular weight range exceeds 10% by weight,
If there are too many low molecular weight substances, the performance as a binder will be insufficient and it will be difficult to obtain satisfactory moldability and shape retention, while if there are too many high molecular weight substances, decomposition and scattering during sintering will be difficult. It becomes worse, and the amount of carbide remaining in the sintered compact becomes so large that it cannot be ignored.

Further, even if the content of the polymer within the above-mentioned preferred molecular weight range satisfies the above requirements, the content ratio of the polymer on the low molecular weight side exceeds the above-mentioned range based on the molecular weight of 150,000. In the case of, the moldability and shape retention of the green molded body are deteriorated. On the other hand, when the content ratio of the polymer on the high molecular weight side exceeds the above range, the amount remaining as a carbide in the sintered molded body increases.

In the present invention, any object satisfying the two requirements of the above-mentioned monomer unit content and molecular weight can be achieved, but the moldability and shape retention of the green molded product and the firing temperature In order to further improve the ease of decomposition, the number average molecular weight is 10,000 to 60,000, more preferably 20,000 to 50,000, and the glass transition temperature is 30 to 60.
C., more preferably 30 to 50 C.

Further, in order to improve the dispersibility of the inorganic powder and further enhance the moldability of the green molded body, it is preferable to give an appropriate acid value to the polymer, and therefore, an appropriate amount of a copolymerizable unsaturated carboxylic acid. It is mentioned earlier that it is preferable to copolymerize However, if the acid value of the copolymer is too high, the decomposition and scattering properties during sintering tend to deteriorate, so the acid value is preferably suppressed to about 0.1 to 10. The more preferable acid value of the copolymer varies depending on the type, polarity, acidity, basicity and the like of the inorganic fine powder. Therefore, it is desirable to use an acid having an optimum acid value in accordance with these.

The polymerization method for obtaining the methacrylate polymer is not limited at all, but the most common one is suspension polymerization in the presence of a radical polymerization initiator such as peroxide, hydroperoxide and azobisisobutyronitrile.
Normal polymerization methods such as solution polymerization and emulsion polymerization are adopted, and usually 5
In this method, the reaction is carried out at 0 to 150 ° C. for several minutes to several hours. In this case, if necessary, a chain transfer agent can be further added during the polymerization reaction. The greatest feature of the present invention is that the weight ratio of a relatively low molecular weight compound having a molecular weight of 150,000 or less and a relatively high molecular weight compound having a molecular weight of more than 150,000 is specified based on the molecular weight of 150,000 as described above. A methacrylic polymer having a similar molecular weight can be produced as a single polymerization reaction product by properly controlling polymerization conditions and the like, and in some cases, a relatively low molecular weight polymer and a high molecular weight polymer may be produced. It is also possible to satisfy the above-mentioned molecular weight constitution by preparing them separately and mixing them in an appropriate ratio.

The kind of the inorganic powder used in combination with the binder composed of the methacrylic polymer is not limited at all, and oxides such as alumina, titania, silica, magnesia and zirconia, mullite, cordierite, zircon, titanic acid Of course, it can be used as a binder for one or more oxide-based ceramic powders such as barium, zircon, lead titanate, and aluminum titanate that can be fired and sintered in an oxidizing atmosphere. However, the characteristics of the binder of the present invention are most effectively exhibited when inorganic powders such as aluminum nitride, silicon nitride, boron nitride, etc., which cause oxidative deterioration when fired and sintered in an oxidizing atmosphere. Nitride; carbide such as silicon carbide, tungsten carbide, boron carbide; or stainless steel, stellite 1, such as a metal such as titanium aluminum alloy
More than one kind of powder. Depending on the type of sintering raw material, even if a small amount of oxygen is present in the firing / sintering atmosphere, there is no substantial adverse effect. The sintering atmosphere may contain a small amount of oxygen, moisture, or the like.

The method for producing an inorganic sintered compact using the binder of the present invention is not particularly special, and may be carried out in accordance with a conventional method. The binder of the present invention and an appropriate dispersion medium (preferably an organic solvent such as acetone, methyl ethyl ketone, methanol, ethanol, isopropyl alcohol, butanol, ethyl acetate, toluene, and xylene, alone or in a mixture) are uniformly kneaded.
The amount of the binder used may be appropriately determined, but the moldability, the shape retention of the green molded body, or the decomposition and
The most common type is inorganic powder 100 in consideration of scattering properties and the like.
It is in the range of 5 to 40 parts by weight based on parts by weight. At this time, if necessary, a dispersant (eg, a polyhydric alcohol ester such as glycerin or sorbitan, or an amine-based dispersant), a plasticizer (eg, polyethylene glycol, dibutyl phthalate, or dioctyl phthalate) for imparting plasticity to the green molded article, or It is also possible to mix an appropriate amount of a sintering aid (glass powder, clay, talc, magnesia, calcia, yttria, ceria, etc.).

Next, defoaming is performed if necessary, and then molded into an arbitrary shape to obtain a green molded body. This molding method is not limited at all, and conventional molding methods such as press molding, injection molding, extrusion molding, doctor blade method, etc. Any method known from can be employed. Next, this green molded body is subjected to heat treatment to volatilize and remove the dispersion medium, decompose, disperse, and sinter the binder. When the heat treatment temperature is increased to the sintering temperature at a stretch, cracks and void defects occur in the molded body. Because it ’s easier to do
Preferably, the temperature is gradually increased stepwise or continuously, and sintering is performed after volatilization of the dispersion medium and dispersion / scattering of the binder are completed in a relatively low temperature range.

[0023]

The present invention is configured as described above, and has the property of easily decomposing and scattering without being carbonized even when heated in a non-oxidizing atmosphere, while retaining various functions as a binder. Therefore, even when a sintered compact made of an inorganic powder that is particularly susceptible to oxidation is obtained, there is no risk of remaining as a carbide in the sintered body to deteriorate the appearance or lowering the sintered density. In addition, depending on the application, it is necessary to impart various properties such as insulating properties, conductivity, and magnetic properties to the sintered compact, and these required properties may be significantly impaired by the remaining carbides. Such a problem can be avoided when used. Further, since the binder of the present invention easily decomposes and burns off even under the sintering and sintering conditions in an oxidizing atmosphere, it can be used without any trouble as a binder for inorganic powders in which sintering and sintering are performed in an oxidizing atmosphere.

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples, and may be appropriately modified in accordance with the above and following points. Everything that is performed is included in the technical scope of the present invention.

Examples 1 to 11 and Comparative Examples 1 to 6 A separable flask equipped with a stirrer, a thermometer, a nitrogen inlet tube, a monomer dropping funnel and a polymerization initiator dropping funnel was charged with 120 parts by weight of toluene as a solvent. Nitrogen is blown from a nitrogen inlet tube to replace the inside of the flask with nitrogen. Also, 100 parts by weight of the monomers shown in Table 1 are charged into the monomer dropping funnel, and a solution obtained by dissolving 1.8 parts by weight of azobisisobutyronitrile in 30 parts by weight of toluene is charged into the polymerization initiator dropping funnel. . Then add flask to 60
C., the monomer and the polymerization initiator were added dropwise over 2 hours while stirring at the same temperature, and stirring was continued for another 2 hours at the same temperature. Then, the internal temperature was raised to 80 ° C. and further 2 hours. After heating and stirring, the mixture was cooled and cooled to obtain a methacrylate polymer.

The molecular weight distribution of each of the obtained polymers was measured by the above-described method, and the content of those having a molecular weight of 1,000 to 1,000,000, the molecular weight (1000 to 150,000) / (150,000 to 100,000)
Weight), the number average molecular weight, the glass transition temperature (Tg) and the acid value were determined, and the results are shown in Table 1. Further, a predetermined amount of each copolymer was placed in a platinum crucible, the temperature was raised to 600 ° C. in a nitrogen stream, and the amount of residual carbon when the temperature was maintained for 2 hours was measured.
The thermal decomposability of each of the obtained polymers was measured with a thermobalance (measurement conditions: heated to 600 ° C. at a rate of 3 ° C./min in a nitrogen stream of 4 liters / minute), and each thermal decomposition curve was obtained. I asked. FIG. 1 shows the thermal decomposition curves of Example 1 and Comparative Examples 2 and 3 as representative examples of the results.

The meanings of the symbols in Table 1 are as follows. i-BMA: isobutyl methacrylate MAA : methacrylic acid AA: acrylate n-BMA: n-butyl methacrylate sec-BMA: secondary butyl methacrylate t-BMA: tertiary butyl methacrylate CHMA: cyclohexyl methacrylate 2-HEMA: 2- Hydroxyethyl methacrylate 2-HPMA: 2-hydroxypropyl methacrylate 2-EHMA: 2-ethylhexyl methacrylate EA: ethyl acrylate

[0028]

[Table 1]

Test Example 1 100 parts by weight of a mixed powder of 45% by weight of aluminum oxide fine powder having an average particle diameter of 15 μm and 55% by weight of borosilicate glass powder having an average particle diameter of 20 μm, and the methacrylate copolymer obtained in Example 1 15 parts by weight as a binder, 3 parts by weight of dioctyl phthalate as a plasticizer, and a mixed solvent of toluene / methyl ethyl ketone (1/1) 50 as a solvent.
After mixing parts by weight to form a slurry, an alumina / glass green sheet having a thickness of 0.3 mm was obtained by a doctor blade method.

The green sheet is placed in a nitrogen stream at 600 ° C.
After heating for 2 hours to remove the binder, the mixture was held at 900 ° C. for 1 hour and fired and sintered. The residual carbon content of the obtained sintered sheet was extremely small at 30 ppm, and the flexural strength was 180 ppm.
It was very good at 0 kg / cm ² . The green sheet was heated in air at 500 ° C. for 1 hour to remove the binder, and then fired and sintered at 900 ° C. for 1 hour. The residual carbon content of the obtained sintered sheet was 10 ppm or less.
Flexural strength was 1800 kg / cm ² .

Test Example 2 An alumina / glass green sheet was obtained in the same manner as in Test Example 1 except that 12 parts by weight of the methacrylate polymer obtained in Example 8 was used as a binder. This green sheet was debindered, baked and sintered in a nitrogen stream in the same manner as in Test Example 1 to obtain a sintered sheet. The obtained sintered sheet had a residual carbon content of 40 ppm and a bending strength of 2 ppm.
000 kg / cm ² .

[0032]

Comparative Test Example 1 Except that 16 parts by weight of the methacrylate polymer obtained in Comparative Example 2 was used as a binder, an alumina / glass green sheet was formed and degassed in a nitrogen stream in the same manner as in Test Example 1. The sintered sheet was obtained by firing and sintering with the binder. The residual carbon content of the sintered sheet is 450 ppm
And the sheet has a gray color and a bending strength of 110
It was 0 kg / cm ² .

Test Example 3 The methacrylate copolymer obtained in Example 7 was mixed with 100 parts by weight of a mixed powder of 97% by weight of aluminum nitride powder having an average particle diameter of 9 μm and 3% by weight of yttrium oxide powder as a sintering aid. A slurry was prepared by mixing 5 parts by weight of a binder and 40 parts by weight of methyl ethyl ketone as a solvent.

The resulting slurry was Drying was prepared block molded body (green body) by press-forming a dry powder into a cylindrical shape with a diameter of 10mm height × 10mm. The green body was heated at 600 ° C. for 2 hours in a nitrogen atmosphere to remove the binder, and then heated to 1800 ° C. and held for 6 hours to fire and sinter to obtain an aluminum nitride sintered compact.
The relative density of this sintered compact is 99.2% and the volume resistance is 9 × 1
It was 0 ¹⁴ Ω · cm.

Comparative Test Example 2 An aluminum nitride sintered compact was obtained in the same manner as in Test Example 3 except that 5 parts by weight of the methacrylate polymer obtained in Comparative Example 4 was used as a binder. The sintered compact had a relative density of 97.8%, turned grayish black, and had a volume resistance of 4 × 10 ¹² Ω · cm.

[Brief description of the drawings]

FIG. 1 is a view showing a thermal decomposition curve of a methacrylate polymer obtained in an example.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yoshinori Ogino 5-8 Nishiburi-cho, Suita-shi, Osaka Nippon Shokubai Suita Works Co., Ltd. (56) References JP-A-2-267157 (JP, A) JP-A-2-9745 (JP, A) JP-A-1-201063 (JP, A) JP-A-62-230664 (JP, A)

Claims (3)

(57) [Claims] 1. A methacrylate unit selected from the group consisting of butyl methacrylate, cycloalkyl group-containing methacrylate, hydroxyl group-containing methacrylate and C8 or more methacrylate having an alkyl side chain at the β-position accounts for 90% by weight or more of the whole. A methacrylate-based polymer having an isobutyl methacrylate unit content of 70% by weight or more, and having a molecular weight of 1,000 to 1
The content of the polymer having a molecular weight of 100,000 occupies 90% by weight or more, and the content ratio of the polymer having a molecular weight of 150,000 or less and the polymer having a molecular weight of more than 150,000 in the molecular weight range is 1% by weight.
/ 1 to 5/1. A binder for producing an inorganic sintered body. 2. A methacrylate group comprising n-butyl methacrylate, isobutyl methacrylate, secondary butyl methacrylate, tertiary butyl methacrylate, cyclohexyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and 2-ethylhexyl methacrylate. The binder according to claim 1, which is at least one member selected from the group consisting of: 3. The binder according to claim 1, wherein the methacrylate polymer has a number average molecular weight of 10,000 to 60,000 and an acid value of 0.1 to 10.