JPH0465348A - Binder for molding ceramics - Google Patents

Abstract

PURPOSE:To improve adhesive strength to ceramic particulate matter and the physical properties of a coating film by using a specified PVA-based polymer as a principal component. CONSTITUTION:Vinyl ester such as vinyl acetate is copolymerized with other ethylenic monomer copolymerizable with the vinyl ester at <=60 deg.C as required and the resulting polymer is saponified to obtain a PVA-based polymer having 50-100mol% degree of saponification and >=4,000 average degree of polymn. This polymer is blended with a peptizer such as NaOH, a lubricant such as paraffin wax and an org. binder or plasticizer as required to obtain a binder for molding ceramics. This binder is dissolved in water to prepare an aq. soln., 100pts. wt. ceramic powder such as alumina powder is mixed with 0.1-20 pts.wt. (expressed in terms of solid matter) of the aq. soln. and this mixture is molded.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a water-soluble binder for molding ceramics.

B. Prior Art Conventionally, ceramic green molded bodies have been manufactured using various methods, such as press molding, slurry casting, sort molding, extrusion molding, and injection molding.

Among these molding methods, in various molding methods such as press molding using water as a medium, polyvinyl alcohol (
The PVA (hereinafter abbreviated as "PVA") type polymer is water-soluble and has excellent binding power to inorganic materials, and the strength of the resulting green molded product is high9, making it suitable for processing such as cutting and sintering. Because it is easy to handle, it is often used.

However, when PVC is used as a binder, after molding, during the drying process, the ingredients in the molded object migrate to the surface of the molded object. There were some drawbacks such as uneven strength or raw carbon.

In addition, for molded products that require a relatively large amount of binder,
The porosity of the molded product after sintering increases, making it impossible to obtain a molded product with high density.

Problems to be Solved by the Invention The present invention is a binder for ceramic molding that can be used in an aqueous system as a binder for ceramic molding, has extremely high binder strength, provides large green molding strength with a small amount, and has very little binder migration phenomenon. It is intended to provide a binder.

D. Means for Solving the Problems In order to solve the above problems, the present inventors have made a keen study and have developed a ceramic molded body binder made of a polyvinyl alcohol polymer with an average degree of polymerization of 4000 or more. ) and reached the completion of non-invention.

In the past, PVA has been widely proposed as a binder for ceramic molding and is already well known, and the average degree of polymerization of the present invention is 4.
The idea of using P to A with a very high molecular weight of 000 or more as a binder for molding ceramics is that it is well known. This is because ultra-high molecular weight P''VA is difficult to produce industrially, and PVA, which is difficult to handle due to the high viscosity of water and S liquid, can be used industrially as a binder for ceramic molding. It is presumed that this is because it was unthinkable to use it.

The major feature of the binder for ceramic molding of the present invention, which uses PVA with an average degree of polymerization of 4000 or more, is that it has a high adhesive strength with ceramic powder and the green molding strength of ceramics is much greater than that of conventional commercially available PVA.
It has high toughness and impact strength, and has excellent post-processability for drilling, drilling, etc. Furthermore, the so-called movement phenomenon L) is also a feature of dog-like ζ. This is because the degree of polymerization is extremely high, which dramatically improves the physical properties of the film.
It is thought that no movement was observed when adhering to the surface of the ceramic powder, probably due to the molecular movement of PVA, which was extremely small compared to conventional PVA.

In addition, by using PVA with an average polymerization degree of 4000 or more, the performance as a binder for ceramic molding is equivalent to or higher than when using conventional commercially available PVA, even when treated at a lower temperature. There is no difficulty in handling the resulting material; however, in an aqueous solution of PVA with an average degree of polymerization of 4000 or more, the so-called no air nonning phenomenon, in which the solution viscosity decreases at high shear, is observed, and the workability of forming ceramics is affected. It won't be a big problem.

The PVA used in the present invention has an average polymerization degree of 4000 or more,
Preferably it is 7000 or more. The PVA of the present invention is produced by hydrolyzing polyvinyl ester or by alcohol treatment.

As the vinyl ester, vinyl formate, vinyl acetate, vinyl brobionate, vinyl persate, vinyl pivalate, etc. can be used. Here, the average degree of polymerization of PVA is calculated from the following formula by re-acetating the PVA-based polymer and measuring polyvinyl acetate in acetonate at 30°C. This is what I would like to express once again.

p = CCrr Ix 1000/ 7.94)""
If the 2-average degree of polymerization is less than 4,000, the above-mentioned undercut effect as a binder for ceramic molding of the present invention will not be exhibited.

The method for producing PVA with an average degree of polymerization of 4000 or more is difficult to produce by conventional polymerization in a methanol solution at 60°C, and it is necessary to carry out the polymerization at a low polymerization rate and rate in a state close to a block of vinyl acetate. In addition, P with an average degree of polymerization of 7000 or more
VA needs to be polymerized at a low temperature of 20 to 50°C. Furthermore, PVA with an average degree of polymerization of 10,000 or more is -30 to 5℃.
Polymerization method using bulk, @ turbidity, emulsion, etc. Proposal 8
However, the polymerization rate is fast and the emulsion polymerization method, which can polymerize to a high polymerization rate, is particularly important (Japanese Patent Application Laid-Open No. 63-3
No. 7106).

The 1-dipolyvinyl acetate obtained by these polymerization methods is obtained by distilling off unreacted monomers and then saponifying it by a known method.

The degree of nanohydration is usually preferably in the range of 50 to 100 mol%,
More preferably, it is 60 to 90 mol%.

Further, it may be copolymerized with other ethylenic monomers that are copolymerizable with vinyl acetate, as long as the gist of the present invention is not impaired. For example, these monomers include α-olefinos, carphonic acid-containing monomers, norogeno-impregnated monomers, unsaturated esters, vinyl ethers, sulfonic acid-containing monomers,
Examples include amide group-containing monomers, quaternary ammonium salt-containing monomers, nlyl group-containing monomers, hydroxyl group-containing monomers, and acetyl group-containing monomers. In particular, from the viewpoint of water solubility, it is preferable to copolymerize a small amount of ionic monomer.

The present invention is characterized by using a PVA-based polymer having an average degree of polymerization of 4000 or more as a binder for molding ceramics, but a deflocculant, a lubricant, etc. may be used in combination. As the deflocculant, commonly used deflocculants can be used. For example, inorganic deflocculants include sodium phosphate, caustic soda, sodium citrate, etc., and organic deflocculants include amines, pyrinone, piperidine, metal salts or ammonium salts of polyacrylic acid, styrene or isobutylene/anhydride. Murray〉
'There are gold salts of copolymers of acids (ll, ammonium salts,
Examples include polyquine ethylene nonylphenyl ether. On the other hand, lubricants that are commonly used include natural waxes such as beeswax and Japanese wax, paraffin wax, microcrystalline wax, synthetic waxes such as low-molecular polyethylene and its derivatives, fatty acids such as stearic acid and lauric acid, and stearin. Metal salts of fatty acids such as magnenium acid and carnoum stearate; fatty acid amides such as oleic acid amide and stearic acid amide;
Examples include polyethylene glycol, which may also be in the form of an aqueous dispersion.

Further, other organic binders or plasticizers may be used in combination with the PVA-based polymer of the present invention within a range that does not impair the effects of the present invention. As the organic binder, water-soluble polymers and water-based emulsions of hydrophobic polymers, which are usually used in ceramic molding, can be used in combination.

As the plasticizer, any commonly used plasticizer may be used. For example, polyhydric alcohols M such as ethylene alcohol, propylene glycol, chryselino, mannitol, and turhite, derivatives thereof, and esters such as noethyl phthalate can be used.

Ceramic powders to which the highly polymerized ltm PVA-based polymer of the present invention can be applied include powders of metal or non-metal oxides that can be used in the production of ceramics. Further, these powders may have a single composition, or may be used singly or in the form of a compound.

The constituent elements of the metal oxide or non-oxide may be cations or anions, double elements, or composed of multiple elements, and additives may be added to improve the properties of the oxide or non-oxide. Systems containing the following can be used in the present invention.

Specifically, lithium, potassium, helium, machinium, boron, aluminum, silicon, calcium, copper,
Zinc, cadmium, gallium, barium, rank 2F,
Oxides, carbides, nitrogen compounds, borides, and sulfides of actinides, titanium, turconium, manganese, iron, cobalt, nickel, etc. are discovered.

Among these ceramic powders, it is particularly suitable for use as oxide powder or metal oxide powder for producing electronic materials, magnetic materials, optical materials, high-temperature materials, and the like.

The PVA polymer of the present invention having an average degree of polymerization of 4,000 or more has a solid content of 01 to 20 parts by weight per 100 parts by weight of ceramic powder.
It can be used in an amount of 5 to 10 parts by weight, preferably fl.

Further, the PVA-based polymer of the present invention is usually handled as an aqueous solution, but it can also be handled as a powder that is added to a ceramic slurry.

The PVA-based polymer of the present invention is suitably used in various molding methods for lamix using water as a medium, such as molding, notebook molding, and extrusion molding.

E. Examples Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited in any way by these Examples. Note that 1 part 1 or ``%-'' in the implementation ρj
・Unless otherwise specified, each represents 1 part by weight and 1% by weight.

Example 1 Bulk polymerization of vinyl acetate was carried out at a polymerization temperature of 1111L'6D'C.
1. Polymerization was carried out at a polymerization rate of 5%/hr and a polymerization rate of 22 to 25%, and after distilling off unreacted vinyl acetate, a saponification reaction was carried out using a methanol solution of sodium hydroxide, resulting in a polymerization degree of 425° and a saponification degree of 725 mol%. PVA was obtained.

100 parts of alumina (998% purity), 50 parts of water, ammonium salt of isophthylene-maleic anhydride copolymer 02
After dispersing in a hole mill for 90 hours using 1 part as a deflocculant, 2 parts of the above PVA aqueous solution as a binder was added as a solid content and mixed uniformly. Granule #i (particle size 100±20 μ) was prepared from this slurry, width 20 II 1 m, length 10
0mm, thickness], flmm rectangular parallelepiped was pressurized with a mold (10
00kg/am') and molded. Evaluation results first
Shown in the table.

Example 2 Bulk copolymerization of vinyl acetate and sodium allylsulfonate was carried out using a bottom point azo polymerization initiator at a polymerization temperature of 35° C.
Polymerization was carried out at a rate of 3%/min and a polymerization rate of 14 to 16%, and the resulting polyvinyl acetate was saponified, resulting in a modification rate of tetrium allylsulfonate of 04 mol% and an average degree of polymerization of 7.
060, PVA with a saponification degree of 617 mol% was obtained.

One molded product was obtained in the same manner as in Example 1 except that the above PVA was used instead of the PVA in Example 1. Evaluation results first
Shown in the table.

Example 3 Vinyl acetate was emulsion polymerized in a water-methanol solvent at -20°C. Using hydrogen peroxide-rongalitto ferric salt as a polymerization initiator, the polymerization rate was 12%/h.
The resulting emulsion was transferred to a large excess of methanol and dissolved, and unreacted monomers were distilled off to perform saponification. Obtained r: p
VA has an average degree of polymerization of 18,300 and a degree of saponification of 828 mol%.

A molded article was obtained in the same manner as in Example 1 except that the above PvA was used instead of PVA in Example 1. Evaluation results first
Shown in the table.

Comparative Example 1 A molded article was obtained in the same manner as in Example 1 except that PVA having a degree of polymerization of 1750 and a degree of saponification of 72.0 mol % was used instead of the PVA of Example 1. The evaluation results are shown in Table 1.

Comparative Example 2 A molded article was obtained in the same manner as in Example 1 except that polyvinyl acetate emulsion was used instead of PVA in Example 1.

The evaluation results are shown in Table 1.

Table 1 1) The strength of the molded product was determined by a three-point bending test (Subano length 5cm, head speed 0.1mm/m1n), and the energy (toughness) required for the molded product to break was determined from the area of the SS curve. The value of Comparative Example 1 was assumed to be 10, and the relative value was determined for each value.

2) For workability, drilling was performed using a trill and the difficulty level was evaluated.

○: Easy to process.

△ It is difficult to process.

E Effects of the Invention The present invention uses an ultra-high polymerization degree PVA polymer with an average degree of polymerization of 4,000 or more, preferably 7,000 or more as a binder for ceramic molding, so that the adhesive strength with ceramic powder and the physical properties of the film are extremely improved. Because of this, the clean molding strength of ceramics is much higher than that of conventional commercially available P~rA, and furthermore, the toughness and impact strength are high, making it difficult to perform post-processing such as drilling and hole drilling. Furthermore, this r-coat provides physical properties equal to or higher than that of conventional binders with a smaller amount of added binder than conventional binders.
A high-density molded product with low porosity can be obtained.

Another major feature is that since PVA is a polymer, there is no so-called binder movement phenomenon during the drying process or handling. The binder of the present invention is P V
Since it is made of A-based polymer, it can be used in aqueous solution and has good stability against spoilage and solution.

Patent applicant RiRashi Co., Ltd.

Claims (2)

[Claims] (1) A ceramic molding binder comprising a polyvinyl alcohol polymer having an average degree of polymerization of 4,000 or more. (2) The binder for ceramic molding according to claim 1, which has an average degree of polymerization of 7,000 or more.