JPH0637323B2 - Manufacturing method of organic binder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for producing an organic binder used when forming an inorganic powder such as ceramic powder or metal powder to obtain a fired product, and an organic compound obtained by the method. Regarding the 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 firing is good, and there are no defects or defects. The present invention relates to a method for producing an organic binder capable of yielding a fired product with little dimensional variation and the like, and an organic binder obtained by the 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 for 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 following describes the moldability of each polymer binder.

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 imparts elasticity to the green molded body, but defects such as blisters and cracks are likely to occur during 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 compact molded products with complex shapes, among the polymer-based binders, the release properties of green molded products are slightly inferior, but acrylic polymers with good debinding properties. It has been studied to obtain a well-balanced mixed organic binder by blending it with other polymers such as polystyrene, ethylene-vinyl acetate copolymer, and polyethylene.

[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.

For example, the solubility parameter (SP value, (Cal / (c.
c) Looking at ^1/2 ), polystyrene is 9.10, ethylene-
Vinyl acetate copolymer (weight ratio ethylene / vinyl acetate =
70/30) is 8.49, polymethylmethacrylate is 9.25, etc. Since organic binders mixed with each other do not mix the binders uniformly, the mixture becomes non-uniform when mixed with inorganic powder, resulting in poor fluidity. It is not stable, it takes time to determine the molding conditions, the yield is low, and defects such as warpage, cracks and sinks are likely to occur in the obtained fired body, and it has an adverse effect on the dimensional accuracy and density of the product. There is.

[Means for Solving the Problems] The present invention has been made in order to obtain a novel organic binder that solves the above-mentioned problems, and a binder made of an inorganic powder and an organic binder is molded, then debindered, and fired. A method for producing an organic binder used for obtaining a fired product, comprising: (a) ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer; (b) (meth) acrylic acid ester monomer alone or (meth ) A solution of a mixture of an acrylic acid ester monomer and a styrene monomer and (c) a polymerization initiator is dispersed in an aqueous medium containing a dispersant to carry out suspension polymerization. The present invention relates to a production method and an organic binder obtained by the production method.

Examples In the method of the present invention, the ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer as the component (a), the (meth) acrylic acid ester monomer alone as the component (b) or A solution is prepared from a mixture of a (meth) acrylic acid ester monomer and a styrenic monomer, a polymerization initiator which is the component (c), and a chain transfer agent used if necessary.

The ethylene-vinyl acetate copolymer (hereinafter, also referred to as EVA) is not particularly limited, and any one generally called an ethylene-vinyl acetate copolymer can be used,
The ethylene / vinyl acetate is preferably a copolymer having a weight ratio of 85/15 to 50/50, more preferably 80/20 to 60/40. When the ratio exceeds 85/15, it is difficult to dissolve the ethylene-vinyl acetate copolymer in the (meth) acrylic acid ester monomer or the mixture of the (meth) acrylic acid ester monomer and the styrene monomer. Becomes, 50
If it is less than / 50, it is difficult to obtain an ethylene-vinyl acetate copolymer, and the green molded body strength tends to be lowered.

Further, the melt index (MI value) of the ethylene-vinyl acetate copolymer is preferably about 10 to 500 from the viewpoint of viscosity when it is used by being dissolved, and also has fluidity during molding and green molding. 20 from the point of strength of the body
More preferably about 400.

The ethylene-ethyl acrylate copolymer (hereinafter, EE
(Also referred to as A) is not particularly limited, and generally ethylene-
What is called an ethyl acrylate copolymer may be used, but it is preferable that ethylene / ethyl acrylate is a copolymer having a weight ratio of 85/15 to 50/50.
More preferably, it is a copolymer of / 20 to 60/40. When the ratio exceeds 85/15, it becomes difficult to dissolve the ethylene-ethyl acrylate copolymer in the (meth) acrylic acid ester monomer or the mixture of the (meth) acrylic acid ester monomer and the styrene monomer. When it is less than 50/50, it is difficult to obtain an ethylene-ethyl acrylate copolymer, and the green molded body strength tends to be lowered.

Further, the melt index (MI value) of the ethylene-ethyl acrylate copolymer is preferably about 10 to 2000 from the viewpoint of the viscosity when it is used by being dissolved, and the fluidity at the time of molding and green molding. From the standpoint of strength of the body, those of about 100 to 1500 are more preferable.

When EVA is used as the component (a), the fluidity at the time of molding and the strength of the green molded product are excellent, and when EEA is used, an organic binder excellent in debinding is obtained.

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 alkyl group having 1 to 8 carbon atoms.
n-alkyl (meth) acrylate, 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, n-alkyl (meth) acrylates having an alkyl group having 1 to 4 carbon atoms such as n-butyl (meth) acrylate, isopropyl (meth) acrylate, and isobutyl (meth) acrylate are particularly 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.

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 styrenic monomer contained in the mixture increases, the fluidity of the obtained organic binder becomes poor, and molding tends to be difficult.

The ratio of the components (a) and (b) used is (a) component / (b)
The weight ratio of the components 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. Also
If it exceeds 80/20, the blistering phenomenon of the molded product that occurs when debinding by heat decomposition tends to become noticeable, the strength of the molded product tends to decrease, and the binder removal and handling tend to become difficult. .

Specific preferred examples of the polymerization initiator include benzoyl peroxide, lauroyl peroxide,
Examples thereof include organic peroxides such as t-butylperoxy and -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 to be used is preferably 0.05 to 1.5 parts, and 0.1 to 0.6 parts, per 100 parts of the component (b) (parts by weight, the same applies hereinafter) in view of adjustment of reaction rate and molecular weight. It is more preferable that there is.

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

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

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 0.1 to 1 with respect to 100 parts of water used.
It is preferably 0.1 part, and more preferably 0.2 to 0.5 part.

The ratio of the solution comprising the components (a) to (c) and optionally the chain transfer agent to the aqueous medium containing the dispersant is 30 to 120 parts of the solution dispersed in 100 parts of the aqueous medium. From the viewpoint of stability and productivity of the suspension, 50 to 100 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.

In this way, for example, as shown in FIG. 1, an organic binder in which the component (b) is uniformly 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 is to be noted that FIG. 1 is an electron showing the internal structure of the particles of the organic binder, which is observed with a scanning electron microscope (5000 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 to be used as the organic binder include metal powder and ceramic powder having an average particle size of 0.1 to 50 μm. Specific examples thereof include pure iron, iron-nickel, iron-cobalt, and stainless steel. Metal powders such as iron alloys, tungsten, aluminum alloys and copper alloys, oxide-based ceramic powders such as alumina, zirconia, mullite, titanate and ferrite, silicon nitride, aluminum nitride, nitrides such as boron nitride In addition to ceramics powder, carbide-based ceramics powder such as silicon carbide, titanium carbide, tungsten carbide, etc., intermetallic compound powder such as titanium aluminum alloy, phosphate powder such as apatite, etc. Examples include powders containing metal or inorganic fibers other than metal, and whiskers. .

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.

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

Example 1 600 g of n-butyl methacrylate (BMA) and 0.3 g of n-dodecyl mercaptan were added to the reactor of Example 5 with stirring.
After heating to 5 ℃, EVA (Ultrasen 722, Tosoh
900 g) and benzoyl peroxide 2.4 g as a polymerization initiator were added and dissolved. An EVA-BMA solution was suspended by adding an aqueous dispersant solution containing 1840 ml of ion-exchanged water and 160 ml of a 3% aqueous solution of polyvinyl alcohol (PVA) prepared separately in advance. Then, after substituting with nitrogen, reaction was carried out at 80 ° C. for 3 hours and at 100 ° C. for 2 hours to polymerize, followed by cooling, taking out, washing and drying.

The obtained polymer was spherical particles having a particle size in the range of 0.3 to 1 mm, and the intrinsic viscosity [η] at 30 ° C in a toluene solution was 0.85.

Example 2 To the reactor of Example 5, 700 g of BMA, 500 g of styrene and 0.35 g of n-dodecyl mercaptan were added and dissolved, and then 300 g of EVA (Ultrasen 722, manufactured by Tosoh Corporation) was added with stirring to 75 ° C. The temperature was raised to dissolve, and 4.8 g of benzoyl peroxide and 0.25 g of t-butylperoxybenzoate were added and dissolved. Ion-exchanged water prepared separately in advance
An aqueous dispersant solution at 80 ° C consisting of 1840 ml and 160 ml of a 3% aqueous solution of PVA 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 110 ° C. for 2 hours to complete the polymerization. Then, it was cooled, washed with water, and dried to obtain white spherical particles having a particle size of 0.3 to 1.0 mm. The toluene solution of these polymer particles and the specific year [η] at 30 ° C was 0.70.

Example 3 In the reactor of 5 750 g of BMA and n-dodecyl mercaptan
0.3 g was added and the temperature was raised to 75 ° C with stirring, then EEA
(NUC-6070, manufactured by Nippon Unicar Co., Ltd.) and 750 g of benzoyl peroxide as a polymerization initiator were added and dissolved. 1840 ml of ion-exchanged water and PVA prepared separately in advance
An aqueous solution of a dispersant consisting of 160 ml of a 3% aqueous solution of was added and stirred to suspend the EVA-BMA solution. Then, after substituting with nitrogen, the reaction was carried out at 80 ° C. for 4 hours and at 100 ° C. for 2 hours to polymerize and cool. After that, take out, wash and dry the particles
Spherical particles in the range 0.3-1 mm were obtained. Toluene solution of polymer particles obtained, specific year [η] at 30 ℃ is 0.7
Was eight.

Comparative Example 1 EVA 90 parts used in Example 1 (Ultrasen 722, Tosoh
Co., Ltd.) and polybutylmethacrylate (molecular weight 30
10,000) 60 parts well kneaded for 30 minutes at 140 ℃ using a roll,
A mixture was obtained.

Comparative Example 2 30 parts of EVA used in Example 2 (Ultrasen 722, Tosoh
Co., Ltd.), polybutylmethacrylate (molecular weight 300,000) 70
Parts and 50 parts of polystyrene were well kneaded for 30 minutes at 150 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). (5000 times), and the internal structure was observed by 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, the EVA-BMA suspension polymer (Example 1) had fine particles uniformly dispersed, and the dispersion state in the simple mixture (Comparative Example 1) was Shows a marked difference.

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

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 5 100 parts of an alumina powder having an average particle size of 0.4 μm (alumina AES-11 manufactured by Sumitomo Chemical Co., Ltd.) was added to the suspension polymer obtained in Examples 1, 2, and 3, Comparative Example 1, 18.0 parts of each of the simple mixtures obtained in 2 were added, 2 parts of dibutyl phthalate was added as a plasticizer, and the mixture was mixed with a pressure kneader at 150 ° C. for 1 hour, and then pulverized with a table pulverizer to obtain a molding material.

Using this, molding temperature 130-160 ℃, injection pressure 500-
Was molded under the conditions of 1100 kg / cm ^2, a rectangular parallelepiped (thickness 5 mm, width 20m
m, length 20 mm) was obtained. At this time, the moldability was observed.

Next, the molded body obtained is heated to 400 ° C. at a temperature rising rate of 5 ° C./hr to remove the binder, and then, at 1620 ° C. (temperature rising rate
The temperature was raised to 100 ° C./hr), 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 prepared by the same method as in Example 5 (HS7- manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.)
The molded body of (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]

FIGS. 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, and observing the states with a scanning electron microscope (5000 times). 2 is an electron micrograph showing an internal structure of particles of an organic binder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norimasa Uesugi 11 Kashihara Enohonmachi, Nishikyo-ku, Kyoto City, Kyoto Prefecture

Claims (3)

[Claims] 1. A method for producing an organic binder which is used when a mixture of an inorganic powder and an organic binder is molded, then debindered and fired to obtain a fired product, which comprises (a) an ethylene-vinyl acetate copolymer or A solution comprising an ethylene-ethyl acrylate copolymer, (b) a (meth) acrylic acid ester monomer alone or a mixture of a (meth) acrylic acid ester monomer and a styrene-based monomer, and (c) a polymerization initiator is added. A method for producing an organic binder, which comprises dispersing in an aqueous medium containing a dispersant and carrying out suspension polymerization. 2. The method according to claim 1, wherein the solution further contains a chain transfer agent. 3. An organic binder obtained by the method according to claim 1.