JPH0377831B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a powder binder for molded articles made of ceramic particle powder. Ceramic sintered bodies are excellent in terms of heat resistance, hardness, insulation, etc., and are of great importance in various fields as heat-resistant materials, superhard materials, insulating materials, shielding materials, and structural materials. Ceramic sintered bodies are usually made by bonding powdered ceramic particles using a polymer as a binder.
It is obtained by sintering the obtained composite body.
Binders for this powder include hydrophobic binders typified by polyvinyl butyral, starch, molasses,
Water-soluble binders such as casein, methylcellulose, carboxymethylcellulose, and polyvinyl alcohol have been used. However, none of these binders can be said to have satisfactory performance. For example, when using a hydrophobic binder such as polyvinyl butyral, it is necessary to dissolve it in an organic solvent, which makes the process complicated, and there are safety concerns against explosions and fires. There is a problem in that there are significant restrictions in terms of measures to be taken, sanitary measures for treatment against absorption of solvent vapor, and measures for facilities such as solvent recovery equipment. Further, when using the above-mentioned water-soluble binder, since it is dissolved in water and used, there is no problem when using an organic solvent, but a problem arises in its performance as a binder. For example, when starch or molasses is used, the resulting molded product does not have sufficient strength and is likely to collapse or crack. Furthermore, when using methylcellulose, carboxymethylcellulose, polyvinyl alcohol, etc., the adhesiveness required for molding cannot be obtained;
In addition, since the dry film itself is hard, the obtained molded product becomes brittle and is prone to chipping and cracking. For this reason, it is necessary to use a plasticizer to impart flexibility to the molded product, but the use of a plasticizer is accompanied by a decrease in tackiness as a binder and brings about various disadvantages. Of the above-mentioned binders, natural or semi-synthetic ones are biodegradable, so when they are stored in the form of an aqueous solution or present in a molded product containing water, molecular cleavage occurs. This causes deterioration and rot, resulting in a decline in its performance as a binder, which impedes its practical use. Under these circumstances, there is a strong demand for a binder that is water-soluble, has excellent bonding strength between powders, and provides molded products with excellent flexibility. Taking this situation into consideration, the present inventors investigated various water-soluble binders suitable for manufacturing molded products made of ceramic particle powder, and found that by using a water-soluble modified diene polymer as a binder, It was discovered that a molded article exhibiting excellent bonding strength to the ceramic particle powder and having sufficient flexibility could be obtained, and the present invention was completed. That is, according to the present invention, the molecular weight is from 5000 to
Add maleic anhydride or its derivative to the monomer unit of the diene polymer of 100,000
The modified diene polymer obtained by adding 5 to 50 mol per 100 mol per 100 ml and then reacting with a basic compound provides excellent bonding strength to the ceramic particle powder and prevents chipping, cracking, etc. It gives a molded product with no flexibility. The water-soluble modified diene polymer used in the present invention can be obtained by subjecting the diene polymer to an addition reaction with maleic anhydride or a derivative thereof, and then reacting it with a basic compound. Examples of diene polymers that can be used as a base for water-soluble modified diene polymers include polybutadiene, polyisoprene, polypentadiene, butadiene-isoprene copolymer, butadiene-styrene copolymer, isoprene-styrene copolymer, and butadiene-styrene copolymer. Examples include acrylonitrile copolymer, isoprene-acrylonitrile copolymer, and the like. Among these polymers, polybutadiene, polyisoprene, and butadiene-isoprene copolymers are preferably used because they have sufficient binding strength when used as a binder and provide flexible molded products.
Among these, isoprene-based polymers such as polyisoprene and butadiene-isoprene copolymers are preferred from the viewpoint of ease of reaction when adding maleic anhydride or its derivatives. These diene polymers may be used alone or in combination of two or more. If the molecular weight of the diene polymer is too small, the binding force will not be sufficient when used as a binder, and a molded product with sufficient strength will not be obtained.On the other hand, if the molecular weight is too large, maleic anhydride or When adding the derivative, problems such as the viscosity of the reaction system becoming too high and the difficulty in dissolving in water occur, so it is necessary that the molecular weight be in the range of 5,000 to 100,000, and especially in the range of 10,000 to 50,000. It is desirable that the molecular weight be in the low molecular weight range. In addition, the molecular weight here means the viscosity average molecular weight (Mv), and in the case of the isoprene-based polymer most preferably used in the present invention, the intrinsic viscosity ([η ]), find [η]=1.21×
10 ^-4 Mv ^0.77 . In the diene polymer, if the amount of vinyl bonds is high, flexibility cannot be imparted to the obtained molded product, so the amount of vinyl bonds is preferably 40% or less, particularly 25% or less. In addition, when the above-mentioned diene-based polymer is a copolymer, its form can be a block copolymer, as long as the above conditions are satisfied.
There is no problem whether it is a random copolymer or a graft copolymer. Here, the amount of vinyl bonds is measured by infrared absorption spectrum. Such diene polymers are produced, for example, by anionic polymerization, Ziegler polymerization, etc. using an alkali metal such as lithium metal or a lithium compound as a catalyst. It can also be produced by depolymerizing natural rubber or synthetic rubber. Maleic anhydride or a derivative thereof is added to the diene polymer, and the derivatives of maleic anhydride include maleic acid, maleic esters such as monoalkyl maleate (methyl, ethyl, propyl) and dialkyl maleate, Examples include monoalkyl maleate (methyl, ethyl, propyl)amide, dialkyl maleate, maleimide, and the like. Among these, maleic anhydride is used because of its ease of reaction and the fact that it can be reacted with alcohols or amines after addition, resulting in esterification or amidation, which is essentially the same as adding a maleic acid derivative from the beginning. Most preferably used. The addition of maleic anhydride or a derivative thereof to a diene polymer can be carried out, for example, by adding maleic anhydride or a derivative thereof to a diene polymer or
Various known methods including a method in which maleic anhydride or its derivative is added to a diene polymer solution dissolved in a hydrocarbon solvent and heated in the presence or absence of a radical generator such as a peroxide, etc. It is done in a method. The amount of maleic anhydride or its derivative added to the diene polymer is one of the important factors in the present invention in order to make the diene polymer water-soluble, and if the amount added is too small, it may be a basic compound. When treated and dissolved in water, it becomes extremely difficult to dissolve in water.On the other hand, if the amount added is too large, the viscosity of the reaction system increases significantly during the addition reaction. When dissolved in water, the viscosity of the aqueous solution becomes too high, and a molded product with high flexibility cannot be obtained. Therefore, the addition amount is 5 per 100 monomer units of the diene polymer.
It is required that the amount is from 10 to 30 mol, preferably from 10 to 30 mol. The diene polymer is made into a water-soluble modified diene polymer by adding maleic anhydride or a derivative thereof, and then reacting a basic compound with a group based on the added maleic anhydride or a derivative thereof. It is used in the following situations. As the basic compound, ammonia and organic amines such as trimethylamine and triethylamine are used alone or in combination of two or more. For the reaction between a diene polymer to which maleic anhydride or its derivative has been added and a basic compound, the basic compound is dissolved in water, and the diene polymer to which maleic anhydride or its derivative has been added is added to this. Alternatively, a method may be adopted in which a diene polymer to which maleic anhydride or a derivative thereof is added is reacted with a basic compound in bulk, in a molten state, or in a state dissolved in an organic solvent. Incidentally, maleic anhydride or a derivative-added diene polymer thereof which has been reacted with a basic compound in advance can be easily made into an aqueous solution by adding water. The amount of the basic compound used in this reaction is preferably in the range of 0.5 to 1 equivalent relative to the carboxyl group derived from maleic anhydride or its derivative. The binder for powder made of the modified diene polymer of the present invention is usually used as it is or in the form of an aqueous solution when the powder is used in the form of an aqueous dispersion. Ceramic molded products include natural ceramics such as silica sand, silica stone, pyrolite, montmorillonite, selinite, kaolinite, column dam, pottery stone, feldspar, and magnesite, alumina, magnesia, zirconia, spinel, silicon carbide, and boron carbide. , particles of ceramics such as artificial ceramics such as silicon nitride, boron nitride, and graphite, or ceramic particles dispersed in water, and a binder made of the modified diene polymer of the present invention or an aqueous solution thereof, in a ball mill, etc. The composition is mixed in a conventional manner using a mixer, and the resulting molding composition is molded in a conventional manner. Examples of the molding method include slurry casting, doctor blade method, extrusion method, injection molding method, and pressure molding method. In such a molding method, the composition may be used as it is, but the composition may also be granulated and then subjected to molding. Alternatively, a method may be adopted in which the material is formed into a sheet or film and then punched into a desired shape. In the production of ceramic sintered bodies, in order to obtain a high-quality product, the quality of the powder molding stage plays an important role, and in order to produce the desired characteristics at a high yield, It goes without saying that it is necessary to make a shrinkable molded product that has a uniform structure. In such molding, the concentration of the modified diene polymer used in the aqueous solution can be determined arbitrarily, but considering the workability when dissolving the modified diene polymer or the workability when making a molded article, 5
Preferably, it is in the range of ~50% by weight. The amount of modified diene polymer used in ceramic particles is determined by the type of ceramic particles, molding method, shape of the molded product, and plasticity of the molded product, but is generally 0.05 to 25 parts by weight per 100 parts by weight of ceramic powder. Parts by weight, preferably in the range of 0.2 to 20 parts by weight. In addition, when manufacturing a molded product made of ceramic particle powder using the powder binder of the present invention, a dispersant, lubricant, surfactant, mold release agent, etc. may be added as necessary. May be added. Further, there is no problem in adding a plasticizer such as dioctyl phthalate or polyethylene glycol to the extent that the purpose of the present invention is not impaired. It is also possible to use conventionally used binders such as carboxymethyl cellulose and polyvinyl alcohol. EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 and Comparative Example 1 Molecular weight 29000 obtained by polymerizing isoprene monomer using n-butyllithium as a catalyst
By adding 25 parts by weight of maleic anhydride to 100 parts by weight of low molecular weight polyisoprene and heating at 180°C, maleic anhydride converts into isoprene monomer units.
A modified low molecular weight polyisoprene with 16 moles added per 100 was produced. The modified low molecular weight polyisoprene was added to 300 parts by weight of water containing 8 parts by weight of ammonia to prepare an aqueous solution of water-soluble polyisoprene. Zirconium silicate (content: 88% or more, 3 to 100 meshes) was used as a powder, and 10 parts by weight of the water-soluble polyisoprene described above was added as a binder to 100 parts by weight of the powder to prepare a blend. Also,
A formulation was made in the same manner except that polyvinyl alcohol was used as the binder. Next, using these blends, a rectangular parallelepiped of 50 mm x 25 mm x 17 mm was press-molded to produce a molded product. The bending strength of the obtained molded product was measured at a span width of 18 mm. Furthermore, the compressive strength of the molded product was measured after drying it at 200°C for 2 hours. In addition, a rectangular parallelepiped test piece measuring 100 mm x 20 mm x 2 mm was press-molded from the above-mentioned mixture, and its flexibility was evaluated by a bending test. The flexibility was evaluated based on the radius of curvature when cracks appeared in the molded product. These results are shown in Table 1, and when water-soluble polyisoprene is used, it shows sufficient bonding strength,
It can be seen that the molded product obtained has sufficient strength and at the same time exhibits sufficient flexibility.

[Table] Comparative example of isoprene Polyvinyl 4.18 35.8 21.0
alcohol

Claims (1)

[Claims] 1 Powder binder for molded articles manufactured from ceramic particle powder, with a molecular weight of 5000 to 5000
Add maleic anhydride or its derivative to the monomer unit of the diene polymer of 100,000
A binder for powder consisting of a modified diene polymer obtained by adding 5 to 50 moles per 100 mol and then reacting with a basic compound.