JPH0764645B2 - Organic binder manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a method for producing an organic binder used when forming an inorganic powder such as ceramic powder or metal powder to obtain a fired body, and a method for producing the same. Related organic binder. More specifically, by mixing with an inorganic powder, the moldability during injection molding, extrusion molding, etc. is good, and the debinding property in the subsequent steps such as degreasing and firing is good, and The present invention relates to a method for producing an organic binder capable of yielding a fired product having few defects and dimensional variations with good yield, and an organic binder obtained by the production method.

[Prior Art] Conventionally, a fired body has been manufactured by firing a molded body obtained by molding an inorganic powder using an organic binder.

Examples of the organic binder used in the molding include waxes and polymer-based binders such as ethylene-vinyl acetate copolymer, polystyrene, polypropylene, polyethylene, and acrylic polymers.

However, in terms of various characteristics such as moldability (flow characteristics, molding stability, etc.), green molded body strength, debinding property, shape retention during sintering and residual carbon content, each binder has advantages and disadvantages. is there.

For example, waxes have a good debinding property, but have poor crystallinity due to high crystallinity, and have a drawback that the green molded product has low strength.

On the other hand, polymer type binders are generally excellent in moldability, but have a drawback that they are inferior in debinding property.

The moldability of each polymer binder is described in detail below.

First, polystyrene has excellent green molded body strength and is unlikely to cause jetting, but has a high melting point and thus has poor fluidity.

Next, the ethylene-vinyl acetate copolymer has high fluidity and gives elasticity to the green molded body, but defects such as blisters and cracks are likely to occur at the time of debinding.

Further, the acrylic polymer has a high green molded body strength but is inferior in releasability.

Among these, in order to meet the recent demands for small shaped articles with complicated shapes, among the polymer-based binders, an acrylic polymer with good debinding property is mainly used, and it is Studies are being made to obtain a comprehensively balanced mixed organic binder by blending.

[Problems to be Solved by the Invention] However, in such an organic binder in which a conventional polymer-based binder is mixed, the morphology and softening point of each polymer are different, and mutual solubility (compatibility) is not sufficient. Therefore, there is a drawback that it is difficult to obtain a uniform mixture.

Solubility parameters (SP value, (Cal / c.
c.) ^1/2 ), polystyrene is 9.10, polyethylene is 7.90, polypropylene is 7.50, polymethylmethacrylate is 9.25, etc. When mixed with powder, the mixture becomes inhomogeneous, the fluidity is not stable, it takes time to calculate the molding conditions, the yield is low, and defects such as warpage, cracks and sink marks occur in the obtained fired body. There are problems such as being easy to use and adversely affecting the dimensional accuracy and density of the product.

[Means for Solving the Problems] The present invention has been made in order to obtain a novel organic binder that solves the above problems. A mixture of an inorganic powder and an organic binder is molded, debindered, and fired. A method for producing an organic binder used to obtain a fired product, comprising: (a) an α-olefin polymer; (b) a (meth) acrylic acid ester monomer alone or a (meth) acrylic acid ester monomer; A method for producing an organic binder, which comprises swelling a mixture of styrene-based monomers and (c) a polymerization initiator in an aqueous medium containing a dispersant, and performing suspension polymerization, and the method for producing the same. Regarding organic binders that can be obtained.

Example In the method of the present invention, the α-olefin polymer as the component (a), the (meth) acrylic acid ester monomer alone as the component (b) or the (meth) acrylic acid ester monomer and A swollen product is prepared from a mixture of styrenic monomers, a polymerization initiator which is the component (c), and optionally a chain transfer agent used.

The α-olefin polymer is not particularly limited, and may be used as long as it is generally called an α-olefin polymer, but the melt index (MI value) is about 0.1 to 60, further 1 to 20. Those having a certain degree are preferable from the viewpoint of viscous behavior particularly when they are used after being dissolved, and from the viewpoint of fluidity during molding and strength of the green molded body.

A swelling product of the polymer can be obtained by absorbing the monomer into the α-olefin polymer to be used. In this case, the impregnation of the monomer is facilitated, and a binder having a uniform composition is obtained. Therefore, it is preferable that the particles have a narrow particle size distribution and are finely pulverized to a size of about 16 mesh pass or less. Further, the obtained swollen product has a shape close to the shape of the polymer particles used, and this is used as an organic binder. Therefore, it is preferable to use a particle shape suitable for the organic binder.

Specific examples of the α-olefin polymer include polyethylene, polypropylene and polyisobutylene.

The (meth) acrylic acid ester monomer is not particularly limited, but from the viewpoints of fluidity during molding, strength of the green molded body, and debinding property, an alcohol having 1 to 8 carbon atoms and (meth) acrylic acid. The esters from and are preferred. Specific examples of such a (meth) acrylic acid ester monomer include, for example, an n-alkyl (meth) acrylate whose alkyl group has 1 to 8 carbon atoms, isopropyl (meth) acrylate, isobutyl (meth) acrylate,
Examples thereof include t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-methoxyethyl (meth) acrylate and 2-ethoxyethyl (meth) acrylate. Of these, the number of carbon atoms of the alkyl group such as n-butyl (meth) acrylate is 1
.About.4 n-alkyl (meth) acrylate, isopropyl (meth) acrylate, isobutyl (meth) acrylate are preferable. These may be used alone or in combination of two or more.

Specific examples of the styrene-based monomer include styrene, α-methylstyrene, p-methylstyrene, vinylstyrene and the like.

These may be used alone or in combination of two or more.

When the (meth) acrylic acid ester monomer and the styrene-based monomer are mixed and used, the ratio of the styrene-based monomer contained in the mixture is 80% (% by weight or less). Is preferred. As the proportion of the styrene-based monomer contained in the mixture increases, the fluidity of the obtained organic binder becomes poor, and molding becomes difficult.

The usage ratio of the component (a) and the component (b) is (a)
The weight ratio of component / (b) component is preferably about 5/95 to 80/20, more preferably about 20/80 to 70/30. If the ratio is less than 5/95, the fluidity of the mixture with the inorganic powder prepared by using the obtained organic binder tends to be insufficient, and molding defects are likely to occur. On the other hand, if it exceeds 80/20, the blistering phenomenon of the molded body that occurs when debinding by heat decomposition tends to become noticeable, the strength of the molded body tends to decrease, and the binder removal and handling become difficult. Become. Furthermore, it tends to be difficult to swell the component (a) with the component (b) or to absorb the component (b) into the component (a), and it tends to be difficult to obtain a uniform suspension polymer.

Specific preferred examples of the polymerization initiator include benzoyl peroxide, lauroyl peroxide,
Examples thereof include organic peroxides such as t-butylperoxy-2-ethylhexanate and oil-soluble polymerization initiators such as azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These may be used alone or in combination of two or more.

The amount of the polymerization initiator used is preferably 0.05 to 1.5 parts, more preferably 0.1 to 0.6 parts, relative to 100 parts (b) of the component (parts by weight, hereinafter the same) from the viewpoint of adjusting the reaction rate and the molecular weight. It is more preferable that there is.

Preferred specific examples of the chain transfer agent optionally used include mercapto compounds such as n-dodecyl mercaptan and t-octyl mercaptan, or α-methylstyrene and α-methylstyrene dimer. . These may be used alone or in combination of two or more.

When a chain transfer agent is used, the amount used is (b)
From the viewpoint of controlling the molecular weight, it is preferably 0.01 to 1.0 part, more preferably 0.03 to 0.5 part, relative to 100 parts of the component.

In the production method of the present invention, a swelling product composed of the components (a) to (c) and a chain transfer agent used if necessary,
It is dispersed in an aqueous medium containing a dispersant and suspension-polymerized.

Specific examples of the dispersant include, for example, polyvinyl alcohol, hydroxyethyl cellulose, water-soluble organic polymer compounds such as polyvinylpyrrolidone, hydroxyapatite, and sparingly water-soluble fine particles such as magnesium pyrophosphate used in combination with an anionic surfactant. . The amount of these dispersants used is preferably 0.1 to 1 part, and more preferably 0.2 to 0.5 part, relative to 100 parts of water used.

As the ratio of the swollen material to the aqueous medium containing the dispersant, 120 to 30 parts of the swollen material to 100 parts of the aqueous medium is preferable from the viewpoint of stability and productivity of the dispersion suspension, 10
0 to 50 parts is more preferable.

There are no particular restrictions on the conditions for carrying out suspension polymerization,
The method usually used may be used. For example, the polymerization reaction temperature is usually in the range of 50 to 130 ° C, although an appropriate temperature is determined depending on the decomposition temperature of the polymerization initiator used.

Thus, for example, as shown in FIG. 1, an organic binder in which the component (b) is uniformly and microscopically dispersed in the component (a) is obtained. This organic binder can be suitably used for forming an inorganic powder to obtain a fired body.

It should be noted that FIG. 1 is an electron showing the internal structure of the particles of the organic binder, which was observed with a scanning electron microscope (1000 times) after etching the organic binder manufactured by the method of the present invention with a solvent. It is a micrograph.

Examples of the inorganic powder as a target of the organic binder include metal powder and ceramic powder having an average particle size of 0.1 to 50 μm, and specific examples thereof include pure iron and iron-
Nickel, iron-cobalt, iron alloys such as stainless steel, tungsten, aluminum alloys, metal powders such as copper alloys, oxide-based ceramics such as alumina, zirconia, mullite, titanate and ferrite, silicon nitride,
In addition to powders of nitride ceramics such as aluminum nitride and boron nitride, carbide ceramics such as silicon carbide, titanium carbide and tungsten carbide, intermetallic compound powders such as titanium aluminum alloys and phosphates such as apatite. Powders, etc., and powders containing metal or inorganic fibers other than metal, whiskers, etc. in the range of 1 to 50% by volume are also included.

As the metal fibers and whiskers, for example, fibers and whiskers from steel, stainless steel, aluminum, magnesium, nickel, titanium, beryllium, tungsten, molybdenum, boron, etc., and as the inorganic fibers and whiskers other than the above metals, Examples thereof include fibers and whiskers made of alumina, zirconia, silicon carbide, boron carbide, silicon nitride, boron nitride, aluminum nitride and the like.

The organic binder obtained by the method of the present invention is first sufficiently kneaded with the above inorganic powder and a kneader such as a pressure kneader to uniformly disperse the inorganic powder in the organic binder, and then a suitable shape, for example, It is roughly crushed or pelletized. Next, after a molded product having a desired shape is formed using a known molding machine, the organic binder is usually removed from the inorganic molded product, and the product is fired at an appropriate temperature and atmosphere to obtain a fired product having a desired shape. To be

Next, the production method of the present invention and the organic binder obtained by the production method will be described based on Examples.

Example 1 900 g of n-butyl methacrylate (BMA) in the reactor
And 0.3 g of n-dodecyl mercaptan were added and the temperature was raised to 75 ° C. with stirring, then 600 g of polyethylene (PE) (Showlex M-171 manufactured by Showa Denko KK) and 3.6 g of benzoyl peroxide as a polymerization initiator. And were added for swelling and dispersion. Ion-exchanged water prepared separately in advance
1840 ml and polyvinyl alcohol (PVA) 3% aqueous solution 160
A dispersant aqueous solution consisting of 10 ml and PE-BMA swelling dispersion liquid was suspended. Then, after substituting nitrogen, 80
Polymerization was carried out by reacting at 3 ° C. for 3 hours and 110 ° C. for 2 hours, cooled, taken out, washed and dried to obtain white spherical particles having a particle size of 0.3 to 1 mm.

Example 2 To the reactor of Example 5, 600 g of BMA, 500 g of styrene and 0.35 g of n-dodecyl mercaptan were added and dissolved, and then 400 g of PE (Shorex M-171) was added with stirring to 75 ° C.
The temperature is raised to swelling and dispersion, and then benzoyl peroxide 4.4 g, t-butyl peroxybenzoate 0.25 g
Was added and dissolved. To this, an aqueous dispersant solution at 80 ° C. composed of 1840 ml of ion-exchanged water and 160 ml of a 3% aqueous solution of PVA, which had been separately prepared in advance, was added and stirred to suspend. Then, the space was replaced with nitrogen, and the reaction was carried out at 80 ° C. for 5 hours and at 100 ° C. for 2 hours to complete the polymerization. After cooling, it was washed with water and dried to obtain white spherical particles having a particle size of 0.3 to 1.0 mm.

Example 3.5 600 g of BMA and 0.3 g of n-dodecyl mercaptan were added to the reactor of Example 5, and the temperature was raised to 75 ° C. with stirring, followed by polypropylene (PP) (Show Allomer manufactured by Showa Denko KK).
FD230) (900 g) and benzoyl peroxide (3.0 g) as a polymerization initiator were added, and the mixture was swollen and dispersed. 1840 ml of ion-exchanged water and 160 ml of 3% aqueous solution of PVA prepared separately in advance.
An aqueous dispersant solution consisting of and was added and stirred to suspend the PP-BAM swelling dispersion. Then, after substituting nitrogen, 80 ℃
After 4 hours and 110 ° C for 2 hours to polymerize, the mixture was cooled, taken out, washed and dried to obtain spherical particles having a particle size of 0.3 to 1 mm.

Comparative Example 1 60 parts of PE (Sholex M-171) used in Example 1 and 90 parts of polybutylmethacrylate (molecular weight 300,000) were well kneaded at 140 ° C. for 30 minutes to obtain a mixture.

Comparative Example 2 40 parts of PE (Sholex M-171) used in Example 2,
60 parts of polybutyl methacrylate (molecular weight 300,000) and 50 parts of polystyrene were well kneaded for 30 minutes at 150 ° C. using a roll to obtain a mixture.

Example 4 Scanning electron microscopes were obtained by subjecting the suspension polymers obtained in Examples 1 and 2 and the simple mixture obtained in Comparative Examples 1 and 2 to a solvent etching method (immersing in hexane for 2 minutes). The internal structure was observed by observing (1,000 times) and observing the state of the etched product.
The results are the observation photographs of FIGS. 1 and 3.
Shown in Figures and Figures 2 and 4.

As can be seen from the comparison between FIG. 1 and FIG. 2, PE was uniformly dispersed as fine particles in the PE-BMA suspension polymer (Example 1), and PE in the simple mixture (Comparative Example 1) was obtained. A significant difference is recognized from the dispersed state of.

Further, from the comparison between FIG. 3 and FIG. 4, it can be seen that the PE-BMA-styrene suspension polymer (Example 2) and the simple mixture (Comparative Example 2) have the same difference.

Next, examples in which the polymers obtained in Examples 1 to 3 and Comparative Examples 1 and 2 are used as a binder for molding an inorganic powder will be shown.

Example 5 Alumina powder having an average particle size of 0.4 μm (Sumitomo Chemical Co., Ltd.)
Made of alumina AES-11) of 100 parts,
16.0 parts of each of the suspension polymer obtained in 3 and the simple mixture obtained in Comparative Examples 1 and 2 was added with 2 parts of dibutyl phthalate as a plasticizer and mixed with a pressure kneader at 150 ° C. for 1 hour. After that, it was crushed with a table crusher to obtain a molding material.

Using this, molding temperature 130-160 ℃, injection pressure 500-110
Molding was performed under the condition of 0 kg / cm ^{2 to} obtain a rectangular parallelepiped (thickness 4 mm, width 5 mm, length 50 mm) molded body.

The obtained molded product is heated to 400 ° C at a heating rate of 5 ° C / hour.
The temperature was raised to 1620 ° C (heating rate 100 ° C / hour) to remove the binder, and the temperature was maintained for 1 hour for firing. The fired bodies were evaluated for poor appearance and bulk specific gravity.

The results are shown in Table 1.

Example 6 Partially stabilized zirconia powder having a specific surface area of 7 m ² / g produced by the same method as in Example 5 (HS manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.)
The molded product of Y-3.0) was held at 1550 ° C. (temperature rise 100 ° C./hour) for 1 hour for firing, and evaluated in the same manner as in Example 5. The results are shown in Table 1.

[Effects of the Invention] When the organic binder obtained by the method of the present invention is used, an excellent fired body (for example, warpage, cracks, sink marks, etc.) which cannot be recognized by the use of the conventional mixed organic binder does not occur, and A fired body excellent in dimensional accuracy and density can be obtained. Therefore, it can greatly contribute to the field of molding of inorganic powder.

[Brief description of drawings]

1 to 4 show the states after etching the organic binders obtained in Example 1, Comparative Example 1, Example 2 and Comparative Example 2 with a solvent, respectively, and observing the states with a scanning electron microscope (1000 ×). 2 is an electron micrograph showing an internal structure of particles of an organic binder.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kensei Uesugi 11 No. 11 Enohonmachi, Kashihara, Nishikyo-ku, Kyoto (56) References JP-A-57-185309 (JP, A) JP-A-62-235307 (JP, A) )

Claims (3)

[Claims] 1. A method for producing an organic binder used when a mixture comprising an inorganic powder and an organic binder is molded, debindered, and then fired to obtain a fired product, which comprises (a) an α-olefin polymer, A water-based medium containing a dispersant, (b) a (meth) acrylic acid ester monomer alone or a swollen product composed of a mixture of a (meth) acrylic acid ester monomer and a styrene-based monomer and (c) a polymerization initiator. A method for producing an organic binder, which comprises dispersing in an aqueous solution and polymerizing the suspension. 2. The method according to claim 1, wherein the swollen material further contains a chain transfer agent. 3. An organic binder obtained by the production method according to claim 1.