JP2000272970A - Binder for molding ceramics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molded product excellent in moldability, processability, strength, etc., with a small amount of a binder added by including a polyvinyl alcohol-based polymer having a specific value or below of cloud point within a specified concentration range of an aqueous solution as a principal component. SOLUTION: A polyvinyl alcohol-based polymer used as a binder exhibits <=90 deg.C cloud point within the concentration range of 0.1-10% aqueous solution and is obtained by suitably selecting the degree of saponification, the degree of polymerization and the content of a <=4C α-olefin or a vinyl ether unit. The binder is preferably added in an amount of 0.1-20 pts.wt. based on 100 pts.wt. of a ceramics powder. An aqueous kneaded material comprising a ceramics powder, water and the binder is dried so as to provide a granular shape having a suitable grain diameter and the resultant granules are then preferably press molded. The resultant molded product (an intermediate product) can be baked to thereby afford a molded product with slight or no cracking or blister.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic molding binder.

[0002]

2. Description of the Related Art In recent years, ceramics have been used in a wide range of applications such as electronic materials, magnetic materials, optical materials, and high-temperature materials, taking advantage of their characteristics. From these various uses, improvements in various aspects such as physical properties and shapes are demanded. For example, a denser and more uniform product is desired in terms of thermal, electrical, and mechanical properties. In the fields of mechanical parts, electric parts, and the like, products with more complicated shapes and larger products are desired. In order to fulfill these demands, various studies have been made from the viewpoint of the raw ceramic powder and the molding method.

[0003] Conventionally, thermal, electrical,
As a method for improving various mechanical and optical properties, a method of increasing the purity of a raw material powder or a method of using a powder having a fine particle size has been proposed. When using these methods,
From the viewpoint of molding, a decrease in the amount of a plastic substance derived from raw material impurities or an increase in the particle surface area is required, and a larger amount of an organic binder is required.

[0004] Considering the size or complexity of the product from the molding aspect, it is necessary that the molded product (unfired product; intermediate product) be a product having higher strength at the time of handling or processing. In such a case, the prior art employs a method of increasing the amount of the organic binder to be added. However, increasing the amount of the organic binder added to the raw material powder has the following problems. Problems Occurring During Firing When firing a molded product, a debinding operation is first performed. However, since the calorific value and the amount of decomposition gas increase, there is a possibility that cracks and blisters due to explosion or the like may occur. Problem of Incorporation of Impurities, etc. Addition of a large amount of an organic binder may cause the incorporation of impurities or an increase in carbonization residue after firing of a molded product, and in such a case, lowers product purity. Various binders have been studied to solve these problems. However, with a small addition amount, a molded product (unsintered product; intermediate product) having excellent moldability, processability and strength can be obtained. The number of binders that give a molded product (fired product; final product) that is cracked by firing the product and does not have blisters is small. For example, JP-B-63-44709 discloses an example using a vinyl alcohol-based polymer having a specific hydrophobic group and a hydrophilic group. With a low addition amount, the miscibility is good and the performance such as strength is improved as compared with the conventional binder, but it is still difficult to say that the performance is still satisfactory.

[0005]

SUMMARY OF THE INVENTION The present invention relates to
By providing a ceramic binder that gives a molded product (intermediate product) having excellent moldability, workability, strength, and the like with a low addition amount, and by firing the molded product It is an object of the present invention to provide a molded product (final product) having no or few cracks and blisters.

[0006]

Means for Solving the Problems The above objects are attained by 0.1 to
This is attained by providing a binder for ceramics molding mainly containing a vinyl alcohol-based polymer having a cloud point of 90 ° C. or less in a 10% aqueous solution concentration range.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The PVA used in the present invention is 0.1%.
The cloud point is 90 ° C. or less in the aqueous solution concentration range of 10% to 10%. PVA having such a cloud point has a degree of saponification,
It can be obtained by appropriately selecting the degree of polymerization, or by appropriately selecting the degree of saponification, the degree of polymerization, and the content of α-olefin or vinyl ether units having 4 or less carbon atoms.
For example, as the degree of saponification is lower, the degree of polymerization is higher, and the content of α-olefin or vinyl ether units having 4 or less carbon atoms is higher, the cloud point tends to decrease. You can choose. Here, that the cloud point is 90 ° C. or lower in the 0.1 to 10% aqueous solution concentration range means that the cloud point is 90 ° C. or lower at any concentration in this concentration range. In the present invention, the preferred cloud point is 80 ° C. or less, more preferably 70 ° C.
It is as follows. The lower limit of the cloud point is preferably 30 ° C. or higher, more preferably 35 ° C. or higher. Further, those having a cloud point within the above range at an aqueous solution concentration of 4% are more preferable. Among such PVAs, PVA containing an α-olefin or vinyl ether unit having 4 or less carbon atoms is preferred in terms of moldability, workability, and strength of ceramic molded articles, and in terms of strength of molded articles after firing. Is preferably used.

[0008] PVA containing an α-olefin or vinyl ether unit having 4 or less carbon atoms has an α-olefin having 4 or less carbon atoms.
Examples of the olefin or vinyl ether monomer include α- such as ethylene, propylene, isobutene, and 1-butene.
Examples include vinyl ethers such as olefins, ethyl vinyl ether, and methyl vinyl ether, with ethylene being the best. The content of α-olefin or vinyl ether monomer units having 4 or less carbon atoms cannot be unconditionally specified because the cloud point of the PVA aqueous solution varies depending on the type of monomer unit, saponification degree and viscosity average polymerization degree. In order to maintain the property, it is usually 20 mol% or less, preferably 1 mol% or less.
It is at most 5 mol%, more preferably at most 10 mol%. The lower limit is preferably at least 0.1 mol%, more preferably at least 0.5 mol%.

The degree of saponification of the PVA used in the present invention is determined by the type and content of α-olefin or vinyl ether monomer units having 4 or less carbon atoms and the viscosity average degree of polymerization.
Because the cloud point of the aqueous solution is different, it cannot be specified unconditionally, but from the viewpoint of the moldability at the time of obtaining the molded product, the strength of the obtained molded product, the workability, and the cracking of the molded product after firing, the suppression of blisters Is usually 50 mol% or more, preferably 70 mol% or more, and more preferably 85 mol% or more.

The viscosity-average degree of polymerization of PVA used in the present invention (hereinafter abbreviated as “degree of polymerization”) is α-C 4 or less.
The type and content of the olefin or vinyl ether unit, the cloud point of the PVA aqueous solution differs depending on the degree of saponification, but cannot be specified unconditionally, but the moldability when obtaining a molded product, the strength of the obtained molded product, the workability, and In light of suppression of cracking and blistering of the molded article after firing, 100 to 5000 is preferable, 200 to 3000 is more preferable, and 300 to 2 is preferable.
000 is particularly preferred.

The method for producing PVA used in the present invention is a vinyl ester polymer obtained by polymerizing a vinyl ester, or a copolymer obtained by copolymerizing a vinyl ester with α-olefin or vinyl ether having 4 or less carbon atoms. A known method such as a method of saponifying the vinyl ester polymer in an alcohol or dimethyl sulfoxide solution. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and the like. Of these, vinyl acetate is preferred.

The PVA polymer used in the present invention may be a copolymer of a copolymerizable ethylenically unsaturated monomer as long as the effects of the present invention are not impaired. Examples of the ethylenically unsaturated monomer include unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, fumaric acid, (anhydrous) maleic acid, (anhydrous) itaconic acid and salts thereof, and mono- or mono- or mono-C 1 -C acids. Dialkyl esters; acrylamide such as acrylamide, N-alkylacrylamide having 1 to 18 carbon atoms, N, N-dimethylacrylamide, 2-acrylamidopropanesulfonic acid or a salt thereof, acrylamidopropyldimethylamine or an acid salt thereof or a quaternary salt thereof Methacrylamide,
N-alkyl methacrylamide having 1 to 18 carbon atoms, N,
Methacrylamides such as N-dimethylmethacrylamide, 2-methacrylamidopropanesulfonic acid or a salt thereof, methacrylamidopropyldimethylamine or an acid salt or a quaternary salt thereof; N-vinylpyrrolidone, N-vinylformamide, N-vinyl N-vinylamides such as acetamide; vinyl cyanides such as acrylonitrile and methacrylonitrile;
Vinyl ethers such as alkyl vinyl ether, hydroxyalkyl vinyl ether and alkoxyalkyl vinyl ether; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and vinyl bromide; vinyl silanes such as trimethoxy vinyl silane; allyl acetate , Allyl chloride, allyl alcohol,
Examples include dimethylallyl alcohol, trimethyl- (3-acrylamido-3-dimethylpropyl) -ammonium chloride, acrylamido-2-methylpropanesulfonic acid and the like. Further, the PVA-based polymer used for the ceramic molding binder of the present invention is thiolacetic acid,
A terminal modified product obtained by copolymerizing a vinyl ester-based monomer such as vinyl acetate with a hydroxyalkyl group-containing olefin in the presence of a thiol compound such as mercaptopropionic acid and saponifying it may be used.

As a method for polymerizing a vinyl ester and a method for copolymerizing a vinyl ester with α-olefin or vinyl ether having 4 or less carbon atoms, known methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization are known. Method. Above all, a bulk polymerization method or a solution polymerization method in which polymerization is carried out without a solvent or in a solvent such as an alcohol is usually employed, and when a polymer having a high degree of polymerization is obtained, an emulsion polymerization method is employed. Examples of the alcohol used as a solvent during the solution polymerization include lower alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol. Examples of the initiator used for the copolymerization include, for example, α, α′-
Azobisisobutyronitrile, 2,2'-azobis (2,4-dimethyl-valeronitrile), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), benzoyl peroxide, n- Known initiators such as azo initiators such as propyl peroxycarbonate and peroxide initiators are exemplified. The polymerization temperature is not particularly limited, but is preferably in the range of -30 to 150 ° C.

The obtained vinyl ester polymer is saponified by a known method. For example, it is saponified in a state of being dissolved in alcohol, and in some cases, hydroalcoholic. Examples of the alcohol used for the saponification reaction include lower alcohols such as methyl alcohol and ethyl alcohol, and methyl alcohol is particularly preferably used. 40% by weight of alcohol used in the saponification reaction
If it is below, a solvent such as acetone, methyl acetate, ethyl acetate, benzene, etc. may be contained. As a catalyst used for the saponification reaction, an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide, an alkali catalyst such as sodium methylate, or an acid catalyst such as a mineral acid is used. The temperature of the saponification reaction is not particularly limited, but is preferably in the range of 20 to 60 ° C. When a gel-like product precipitates as the saponification reaction proceeds, the product is pulverized at that time, washed, and dried to obtain PVA used in the present invention.

In the present invention, a peptizer, a lubricant and the like can be used in combination with PVA having a cloud point of 90 ° C. or less in an aqueous solution concentration range of 0.1 to 10%. A commonly used peptizer can be used. For example, inorganic deflocculants such as sodium phosphate, caustic soda and sodium citrate, and organic deflocculants such as amines, pyridine, piperidine, metal or ammonium salts of polyacrylic acid, and copolymerization of styrene or isobutene with maleic anhydride. Metal salt or ammonium salt of the product, polyoxyethylene nonylphenol ether and the like. On the other hand, glycols, polyethylene glycol, glycerin, triol and the like are used as plasticizers. Lubricants that are usually used include, for example, natural waxes such as beeswax and wood wax, paraffin wax, microcrystalline wax, synthetic waxes such as low molecular weight polyethylene and derivatives thereof, fatty acids such as stearic acid and lauric acid, magnesium stearate, and stearic acid. Examples thereof include metal salts of fatty acids such as calcium phosphate, fatty acid amides such as maleic imide and stearic acid amide, and polyethylene glycol. These may be in the form of an aqueous dispersion.

Further, other binders can be used in combination with the PVA used in the present invention as long as the effects of the present invention are not impaired. For example, various starches and their derivatives, various sugars and their derivatives, rubbers, soluble proteins, cellulose derivatives, and synthetic polymers such as PV
A, polyvinylpyrrolidone, polyacrylamide, isobutene-maleic anhydride copolymer or acrylic acid, methacrylic acid and their ester homopolymers or copolymers, ethylene as an aqueous dispersion, olefins such as propylene, butadiene, isoprene and the like An aqueous dispersion of a polymer comprising one or more monomers such as diolefins, vinyl esters such as vinyl acetate, vinyl ethers such as lauryl vinyl ether, acrylic acid, methacrylic acid and their esters, and styrene can be used in combination. it can.

The ceramic powder to which the PVA used in the present invention is applicable includes metal or non-metal oxide or non-oxide powder that can be used in the production of ceramics. The composition of these powders may be a single composition or a single compound or a mixture of compounds. In addition, the constituent element of the metal oxide or non-oxide may be composed of a single element or a plurality of elements together with the cation or anion, and further includes an additive added to improve the properties of the oxide or non-oxide. Systems can also be used in the present invention. Specifically, Li,
K, Mg, B, Al, Si, Cu, Ca, Br, Ba, Zn, Cd, Ga, In,
Lanthanoid, actinoid, Ti, Zr, Hf, Bi, V, N
b, Ta, W, Mn, Fe, Co, Ni, and other oxides, carbides, nitrides, borides, sulfides, and the like. Also, when classifying a specific oxide powder containing a reverting metal element usually called a superoxide from the crystal structure, those having a perovskite structure include NaNbO ₃ , SrZrO ₃ , PbZrO ₃ , Sr
TiO ₃ , BaZrO ₃ , PbTiO ₃ , BaTiO _{3 and the} like having a spinel structure include MgAl ₂ O ₄ , ZnAl ₂ O ₄ , CoAl ₂ O ₄ , NiAl ₂
O _4, MgFe ₂ O ₄ and the like, as taking ilmenite type _{structure, MgTiO 3, MnTiO 3, FeTiO} 3 etc., as to take a garnet-type _{structure, GdGa 5 O 12, Y 6} Fe 5 O 12 And the like.

Among these ceramic powders, PVA used in the present invention is preferably used for oxide powders, especially metal oxide powders for producing electronic materials, magnetic materials, optical materials, high-temperature materials and the like. . P used in the present invention
VA is effective irrespective of the particle size and shape of the ceramic powder, but since the problem of granulation becomes more important as the particle size of the powder becomes smaller, powder having an average particle size of 20 μ or less is particularly preferable. Exerts excellent effects.

Examples of the molding method of the molded article (intermediate product) of the present invention include molding methods having an aqueous kneaded product as a molding step, such as press molding, extrusion molding, tape molding, and plasma casting. The water-based kneaded material mentioned here consists of raw material powder, water and a binder.
It is a system to which a plasticizer, a lubricant, etc. are added. If necessary, an organic solvent may be present in a range that does not cause a problem in dissolving PVA.

Among the molding methods, the best is a press molding method in which the aqueous kneaded product is dried into granules having an appropriate particle size, supplied to an appropriate mold material, and molded by pressing. The amount of PVA used in the present invention varies depending on the type of ceramic powder, the molding method, the shape of the molded product, the shape of the molded product, and the like.
It is 1 to 20 parts by weight, preferably 0.2 to 15 parts by weight, more preferably 0.2 to 10 parts by weight.

Molded product (intermediate product) obtained by the above method
Is fired to obtain a molded article without cracks or blisters. The firing conditions at that time are, for example,
Using an electric furnace or the like, take 3 to 5 hours from room temperature.
After heating to 00 ° C. to 500 ° C. to thermally decompose organic substances such as a binder, the temperature is increased at a rate of 10 to 50 ° C./min.
By heating to 0 to 1500 ° C. and heating at the same temperature for 2 to 24 hours, a ceramic molded body is obtained. In addition, the PVA-based polymer used in the present invention can also be suitably used as a precursor which can be converted into a metal or non-metal oxide or non-oxide by firing after obtaining a molded product.
Examples of the precursor include a metal or nonmetal alcoholate, a hydroxide sol obtained by hydrolysis thereof, a silica sol obtained from water glass, a basic metal chloride salt, sulfuric acid, nitric acid, and formic acid. And metal salts such as acetic acid.

[0022]

The present invention will be described below in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In the examples and comparative examples, “parts” and “%” mean on a weight basis unless otherwise specified.

Polymers 1 to 12 Polymers shown in Table 1 were obtained. The contents of vinyl ester units, vinyl alcohol units and other monomer units in PVA were determined by 500 MHz ¹ H-NMR. Deuterated DMSO was used as a solvent for the PVA-based polymer at the time of ¹ H-NMR measurement. The degree of polymerization of the PVA-based polymer and the cloud point of the aqueous solution were measured by the following methods.

(1) Viscosity average degree of polymerization Degree of polymerization of vinyl alcohol polymer (viscosity average degree of polymerization)
When the degree of saponification is less than 99.5 mol%, PVA saponified to a degree of saponification of 99.5 mol% or more is re-acetylated in acetic anhydride and pyridine. Measured intrinsic viscosity [η] (g / d
It is represented by the viscosity average degree of polymerization (P) obtained from l) by the following equation. P = ([η] × 10 ³ /7.94) ^{(1 / 0.62)}

(2) Aqueous Solution Cloud Point A 4% aqueous solution of PVA is prepared.
° C / min. The solution was heated to 90 ° C. at the heating rate, and the temperature at which the aqueous solution became cloudy during the heating was visually observed.

[0026]

[Table 1]

Comparative Polymers 1 to 6 Comparative polymers shown in Table 2 were obtained.

[0028]

[Table 2]

Example 1 100 parts of alumina (purity: 99.8%), 50 parts of water, and 0.3 part of a peptizer of ammonium polyacrylate were put into a ball mill and pulverized for 90 hours. Two parts by solid content were added and uniformly mixed with the powder. This slurry was granulated by spray drying to obtain granules (particle diameter: 100 ± 20 μ). This granule is 20mm wide, 100mm long, 10mm thick
Is pressed with a mold (1.2 ton / cm ² and 1.0 t)
on / cm ² ). Table 3 shows the evaluation results.

Examples 2 to 12 A molded product was obtained in the same manner as in Example 1 except that Polymers 2 to 10 were used instead of the binder of Example 1. Table 3 shows the evaluation results.

Comparative Examples 1 to 6 A molded product was obtained in the same manner as in Example 1 except that Comparative Polymers 1 to 6 were used instead of the binder of Example 1. Table 3 shows the evaluation results.

The evaluation method of the molded product is shown below. (1) Moldability The mold releasability was determined from the state of adhesion to the mold when the ceramic molded product obtained by press molding was removed from the mold. ：: No adhesion Δ: Almost no adhesion ×: Strong adhesion The homogeneity was determined by observing the surface of the ceramic molded body obtained by press molding with a microscope and observing the appearance. ：: Granules were sufficiently crushed and homogeneous △: Granules were slightly crushed and slightly uneven, ×: Granules were largely crushed (2) Workability The workability was evaluated by drilling holes with a drill. . ：: easy processing △: difficult processing ×: very difficult processing

(3) Molded product strength (toughness) The molded product strength was measured by a three-point bending test, and the energy (toughness) required for breaking the molded product was determined from the area of the SS curve. It was determined by a relative value when the value was set to 1.0.

Molded product (intermediate product) after firing (molded product) (final product) Using a molded product molded at a pressure of 1.0 ton / cm ² , in an electric furnace, from room temperature to 300 ° C. for 6 hours Then, the mixture was heated to 1200 ° C. at a rate of 10 ° C./min and heated at the same temperature for 2 hours. After cooling to room temperature, the fired compact was observed. ：: good without cracks and blisters Δ: Cracks and blisters were partially observed. ×: Swelling and cracking were recognized as a whole and were poor.

[0035]

[Table 3]

[0036]

According to the present invention, when PVA having a cloud point of 90 ° C. or less in a 0.1 to 10% aqueous solution range is used as a main component as a binder, various molding methods, particularly press molding,
By using a small amount, a molded product (intermediate product) having excellent moldability and processability and excellent strength can be obtained, and when the molded product is fired, a molded product having no or few cracks and blisters (final product) Product) can be obtained.

Claims (6)

[Claims] 1. A ceramic molding binder comprising a vinyl alcohol-based polymer having a cloud point of 90 ° C. or less in a 0.1 to 10% aqueous solution concentration as a main component. 2. The ceramic molding binder according to claim 1, wherein the vinyl alcohol-based polymer contains an α-olefin or vinyl ether unit having 4 or less carbon atoms. 3. The binder according to claim 1 or 2,
A ceramic molding composition containing 0.1 to 20 parts by weight based on 100 parts by weight of ceramic powder. 4. A ceramic molded product obtained by converting the composition according to claim 3 into an aqueous kneaded product, drying, granulating, and then molding. 5. A ceramic molded article obtained by molding the composition according to claim 3 and then firing the composition. 6. A ceramic molded product obtained by converting the composition according to claim 3 into an aqueous kneaded product, drying, granulating, molding and firing.