JPH03131604A - Production of organic binder - Google Patents

Abstract

PURPOSE:To obtain an organic binder giving a baked material free from warpage, crack, etc., by dispersing a swollen material consisting of an alpha-olefin polymer, a (meth)acrylic ester monomer, etc., and a polymerization initiator in an aqueous medium containing a dispersing agent and carrying out suspension polymerization of the monomer. CONSTITUTION:The objective organic binder is produced by dispersing a swollen material consisting of (A) an alpha-olefin polymer (e.g. PE or PP), (B) a (meth) acrylic ester monomer [preferably n-alkyl (meth)acrylate, etc., having 1-8C alkyl group] or its mixture with a styrene monomer and (C) a polymerization initiator (preferably benzoyl peroxide, etc.) in an aqueous medium containing a dispersing agent and carrying out suspension polymerization of the monomers. A baked material can be produced from the organic binder by forming a mixture of inorganic powder and the organic binder, removing the binder from the formed article and baking the product.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing an organic binder used when molding inorganic powder such as ceramic powder or metal powder to obtain a fired body. More specifically, by mixing it with inorganic powder, it has good moldability during injection molding and extrusion molding, and has good binder removal properties in subsequent processes such as degreasing and firing. The present invention relates to a method for producing an organic binder that can produce fired products with a high yield and less defects and dimensional variations.

[Prior Art] A fired body has conventionally been produced 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 binders such as ethylene-vinyl acetate copolymer, polystyrene, polypropylene, polyethylene, and acrylic polymers.

However, each binder has its advantages and disadvantages in terms of moldability (flow characteristics, molding stability, etc.), green compact strength, debinding properties, shape retention during sintering, and timekeeping performance such as residual carbon content. be.

For example, waxes have good debinding properties, but have the drawbacks of poor moldability due to high crystallinity and low strength of green molded products.

On the other hand, polymeric binders generally have excellent moldability, but have the disadvantage of poor debinding properties.

The moldability of each polymeric binder is detailed below.

First, polystyrene has excellent green molded body strength and is less likely to cause jetting, but has poor fluidity due to its high melting point.

Next, the ethylene-vinyl acetate copolymer has high fluidity and imparts elasticity to the green molded article, but it tends to cause defects such as blisters and cracks when the binder is removed.

Furthermore, although acrylic polymers have high green molded body strength, they have poor mold releasability.

Under these circumstances, in order to meet the recent demand for being suitable for small molded products with complex shapes, among polymer binders, acrylic polymers with good debinding properties are mainly used, and in addition to this, acrylic polymers with good debinding properties are used. Studies have been conducted to create a comprehensively balanced mixed organic binder through blending.

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

For example, solubility parameters (SP value, CCa1/c
, c, ) ”), polystyrene is 9.10
, polyethylene is 7.90, polypropylene is 7.5
0, polymethyl methacrylate has a molecular weight of 9.25, etc., and in the case of an organic binder mixed with these, the binders are not uniformly compatible with each other, so when mixed with an inorganic powder, the mixture becomes non-uniform and the fluidity becomes unstable. There are problems such as it takes time to determine the molding conditions, the yield is low, the resulting fired product is prone to defects such as warping, cracks, and whiskers, and it has a negative effect on the dimensional accuracy and density of the product.

[Means for Solving the Problems] The present invention was made to obtain a novel organic binder that solves the above problems, and involves molding a mixture of an inorganic powder and an a-organic binder, removing the binder, and sintering the mixture. (ωα-olefin polymer, <b) (meth)acrylic acid ester monomer alone or (meth)acrylic acid ester monomer alone or (meth)acrylic acid ester monomer and (c) a polymerization initiator, which is dispersed in an aqueous medium containing a dispersant and subjected to suspension polymerization.

[Example] In the method of the present invention, (α-olefin polymer as the ω component, (meth)acrylic ester monomer alone or (meth)acrylic ester monomer and styrene-based component as the (b) component) A swollen product is prepared from a mixture of monomers, a polymerization initiator as component (c), and a chain transfer agent used if necessary.

The α-olefin polymer is not particularly limited and may be used as long as it is generally called an α-olefin polymer, but one with a melt index (1 value) of 0.1
~BO, more preferably 1 to 20, is preferred from the viewpoint of viscosity behavior, particularly when used after being dissolved, and is also preferred from the viewpoint of fluidity during molding and strength of the green molded product.

By absorbing a monomer into the α-olefin polymer used, the swollen product of the polymer can be changed. It is preferable that the particle size distribution is narrow and that it is finely ground to about 16 mesh size or less. Furthermore, the resulting swollen product has a shape close to that of the polymer particles used and is used as a binder, so it is preferable to use a particle shape suitable for use as an organic binder.

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

There are no particular limitations on the (meth)acrylic acid ester monomer, but from the viewpoints of fluidity during molding, strength of the green molded product, and binder removal properties, alcohols having 1 to 8 carbon atoms and (
Preferably, it is an ester from meth)acrylic acid. Specific examples of such (meth)acrylic acid ester monomers include n, where the alkyl group has 1 to 8 carbon atoms;
-Alkyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t
-Butyl (meth)acrylate, 2-ethylhexyl (
Examples include meth)acrylate, 2-methoxyethyl(meth)acrylate, and 2-ethoxyethyl(meth)acrylate. Among these, n-butyl (
The number of carbon atoms in the alkyl group is 1 or more, such as meth)acrylate.
Preferred are n-alkyl (meth)acrylate, isopropyl (meth)acrylate, and isobutyl (meth)acrylate. These may be used alone, and 21'1
The above may be used in combination.

Specific examples of the styrene 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 above-mentioned (meth)acrylic acid ester monomer and styrene monomer are mixed and used, the proportion of the styrene monomer in the mixture is 80% or less (weight 6, the same applies hereinafter). It is preferable to have one. As the proportion of the styrene monomer in the mixture increases, the fluidity of the resulting organic binder decreases and molding becomes difficult.

(As for the ratio of the ω component to the city component, it is preferable that the weight ratio of the (ω component/mountain) component is about 5795 to 80/20, and 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 using the organic binder obtained tends to be insufficient, and molding defects are likely to occur.

In addition, if it exceeds 80/20, the blistering phenomenon of the molded product that occurs when removing the binder by thermal decomposition tends to become noticeable, the strength of the molded product tends to decrease, and it becomes difficult to remove the binder and handle it. Become. moreover(
a) Pile of components) Swelling caused by the components (↓) It tends to be difficult to absorb the components into the components, making it difficult to form a homogeneous suspended polymer.

Preferred specific examples of the polymerization initiator include benzoyl peroxide, lauroyl peroxide,
Examples 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 to be used is preferably 0.05 to 1.5 parts, and 0.05 to 1.5 parts, based on 100 parts (parts by weight, same hereinafter) of the component 1), from the viewpoint of controlling the reaction rate and molecular weight.
Part 1 to O1B is more preferable.

Preferred specific examples of the optional chain transfer agent include mercapto compounds such as n-dodecyl mercaptan and t-octyl mercaptan, α-methylstyrene, α-methylstyrene dimer, and the like. can give.

These may be used alone or in combination of 2tli or more.

When using a chain transfer agent, the amount to be used is o, ot-, based on 100 parts of component 1), from the viewpoint of controlling the molecular weight.
It is preferably i and o parts, and more preferably 0.03 to 0.5 parts.

In the production method of the present invention, a swollen product consisting of components (v to (c)) and a chain transfer agent used if necessary is dispersed in an aqueous medium containing a dispersant and subjected to suspension polymerization.

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

The ratio of the swollen product to the aqueous medium containing the dispersant is 120 to 30 parts of the swollen product to 100 parts of the aqueous medium.
parts is preferable from the viewpoint of stability and productivity of the dispersion suspension, and ioo to 50 parts is more preferable.

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

In this way, for example, as shown in FIG. 1, component (a) is replaced with an organic binder in which component +b> is uniformly microdispersed. This organic binder can be suitably used for molding inorganic powder to obtain a fired product.

In addition, FIG. 1 shows the state of the organic binder produced by the method of the present invention etched with a solvent and then observed with a scanning electron microscope (100 times magnification) to clearly visualize the internal structure of the particles of the organic binder. This is an electron micrograph.

Examples of inorganic powders to be used as the organic binder include metal powders and ceramic powders with an average particle size of 0.1 to 50 um, and specific examples thereof include pure iron, pure iron,
Iron alloys such as iron-nickel, iron-cobalt, and stainless steel, metal powders such as tungsten, aluminum alloys, and copper alloys, oxide ceramics such as alumina, zirconia, mullite, titanate, and ferrite, silicon nitride, and ferrite. In addition to powders such as didide ceramics such as aluminum oxide and boron fluoride, carbide ceramics such as silicon carbide, titanium carbide, and tungsten carbide, intermetallic compound powders such as titanium-aluminum alloys, and phosphates such as apatite. Further examples include powders containing metal or non-metallic inorganic fibers, whiskers, etc. in a range of 1 to 50% by volume.

Examples of the metal fibers and whiskers include fibers and whiskers from steel, stainless steel, aluminum, magnesium, nickel, titanium, beryllium, tungsten, molybdenum, boron, etc., and inorganic fibers and whiskers other than the metals mentioned above. Examples include fibers and whiskers from 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 heat-kneaded with the inorganic powder in a kneader such as a pressure kneader to uniformly disperse the inorganic powder in the organic binder, and then shaped into an appropriate shape. For example, coarsely ground or Beret I.
to be shaped.

Next, after the molded body is formed into a desired shape using a known molding machine, the organic binder is usually removed from the inorganic molded body, and the fired body is changed into the desired shape by being fired at an appropriate temperature and atmosphere. .

Next, the manufacturing method of the present invention will be explained based on Examples.

Example 1 In a 5 g reactor, n-butyl methacrylate (HMA) 9
After adding 0.0g and 0.3g of n-dodecyl mercaptan and raising the temperature to 75°C with stirring, polyethylene (
PE) (Shorex M-171 manufactured by Showa Denko)
600 g and 3.6 g of penzoyl peroxide as a polymerization initiator were added to swell and disperse. An aqueous dispersant solution consisting of 1,840 ml of ion-exchanged water and 160 ml of a 3% aqueous solution of polyvinyl alcohol (PVA) prepared separately in advance was added to this and stirred to suspend the PE-BMA swelling dispersion. Then, after nitrogen substitution, 3
After polymerization by reacting at 110 DEG C. for 2 hours, the mixture was cooled and taken out, washed and dried to obtain white spherical particles having a particle size in the range of 0.3 to 1 square centimeter.

Example 2 8DOg of BMA, 500g of styrene and 0.35g of n-dodecyl mercaptan were added and dissolved in a 5g reactor, and after stirring, PE (Shorex Ka-17
1) Add 400g of benzoyl peroxide, heat to 75°C, swell and disperse, and add 4.4g of benzoyl peroxide.

0.25 g of t-butyl peroxybenzoate was added and dissolved. Ion-exchanged water 184 which was prepared separately in advance
0 ml and 160 ml of a 3% aqueous solution of PVA.
An aqueous dispersant solution at ℃ was added and stirred to suspend the mixture. Then, after replacing the space with nitrogen, it was heated at 80°C for 5 hours at 100°C.
The reaction was carried out at ℃ for 2 hours to complete the polymerization. Thereafter, it was cooled, washed with water, and dried to obtain white spherical particles having a particle size in the range of 0.3 to 1.0 + u.

Example 3 800 g of BMA and 0.3 g of n-dodecylmercaptan were added to a 5 g reactor, and the temperature was raised to 75°C with stirring, and then polymerized with 900 g of polypropylene (PP) (Showaromer FD 230 manufactured by Showa Denko ■). Add 3.0 g of benzoyl peroxide as an initiator,
Swelled and dispersed. An aqueous dispersant solution consisting of 1840 ml of ion-exchanged water and 1 Hml of a 3% aqueous solution of PVA, prepared separately in advance, was added to this and stirred to suspend the PP-BM^ swollen dispersion. Next, after nitrogen substitution, the reaction was carried out at 80°C for 4 hours and at 110°C for 2 hours to polymerize, cooled, taken out, washed and dried to obtain spherical particles with a particle size in the range of 0.3 to 1. I got it.

Comparative Example 1 PR (Shorex M-171) 6 used in Example 1
0 parts and polybutyl methacrylate (molecular weight 300,000)
90 parts were thoroughly kneaded using a roll at 140°C for 30 minutes to obtain a mixture.

Comparative Example 2 PE (Shorext 171) 4 used in Example 2
0 parts, polybutyl methacrylate (molecular Ei 1.3 million)
60 parts of polystyrene and 50 parts of polystyrene were mixed into 15 parts using a roll.
The mixture was thoroughly kneaded for 30 minutes at 0'C to obtain a mixture.

Example 4 The suspension polymers obtained in Examples 1 and 2 and the simple mixtures obtained in Comparative Examples 1 and 2 were treated by a solvent etching method (immersion in hexane for 2 minutes) and then subjected to scanning electron microscopy. 1! (1000 times magnification), and the internal structure was observed by observing the state of the etched material.

The results are shown in Figures 1 and 3, which are observation photographs.
and FIGS. 2 and 4.

As can be seen from the comparison between Figures 1 and 2, PE-HM
In the A suspension polymer (Example 1), PE is uniformly dispersed as fine particles, and in the simple mixture product (Comparative Example 1), PE is uniformly dispersed.
A remarkable difference from the dispersion state of E is recognized.

Furthermore, from the comparison between Figures 3 and 4, it is clear that the PE-HMA-styrene suspension polymer (Example 2) and the simple mixture product (Comparative Example 2)
), it can be seen that a similar difference is observed.

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

Example 5 The suspension polymer obtained in Example 1.2.3 and Comparative Example 1 were added to 100 parts of alumina powder with an average particle size of 0.4 mol (Alumina ABS-11 manufactured by Sumitomo Chemical Oki). Using 18.0 parts of each of the simple mixtures obtained in step 2, 2 parts of dibutyl phthalate was added as a plasticizer, and the mixture was mixed in a pressure kneader.
After mixing at 150° C. for 1 hour, the mixture was pulverized using a tabletop pulverizer to obtain a molding material.

Using this, the molding temperature was 130 to 160°C and the injection pressure was 5.
The molded product was molded under the conditions of 00 to 1100 kg/c to obtain a rectangular parallelepiped molded product (thickness 4 mm, width 5++n, length 50 a+m).

Next, the obtained molded body was heated to 400°C at a heating rate of 5°C/hour.
After removing the binder by raising the temperature to 1820℃ (
The temperature was raised to a temperature increase rate of 100"C/hour) and held for 1 hour for firing. These fired bodies were evaluated for poor appearance and bulk specific gravity.

The results are shown in Table 1.

Example 6 Partially stabilized zirconia powder (H8 manufactured by Kigenso Kagaku Kogyo ■) with a specific surface area of F/g produced in the same manner as in Example 5.
Y-3,0) molded body at 1550"c (temperature increase: 100°C
/hour) for 1 hour and baked, and evaluated in the same manner as in Example 5. The results are shown in Table 1.

[Margins below] [Effects of the invention] By using the organic binder obtained by the method of the present invention, excellent fired products (for example, no warpage, cracks, sink marks, etc.) that are not observed when using conventional mixed organic binders can be obtained. , and the fired product has excellent dimensional accuracy and density). Therefore, it can greatly contribute to the field of inorganic powder molding.

[Brief explanation of the drawing]

Figures 1 to 4 show the state of the binder obtained in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 after etching with a solvent using a scanning electron microscope (1000x magnification).
This is an electron micrograph showing the internal structure of organic binder particles. Figure 2 Figure 2

Claims (1)

[Scope of Claims] 1. A method for producing an organic binder used in forming a mixture of an inorganic powder and an organic binder, removing the binder, and firing it to obtain a fired product, comprising: (a) an α-olefin polymer; (b) (meth)acrylic acid ester monomer alone or (
A swollen product consisting of a mixture of meth)acrylic acid ester monomers and styrene monomers and (c) a polymerization initiator is dispersed in an aqueous medium containing a dispersant and subjected to suspension polymerization. Binder manufacturing method. 2. Claim 1, wherein the swollen product further contains a chain transfer agent.
Manufacturing method described.