JPH0581553B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an injection molding composition comprising an inorganic powder and a specific organic binder, and a sintered body made from the composition. More specifically, the present invention relates to an injection molding composition that has excellent injection moldability and binder removal properties, and can provide a sintered body with a high yield without defects such as warpage and cracks, and a sintered body made from the same.

[Problems to be solved by conventional technology/invention]

In recent years, green molded products have been obtained by mixing organic binders with ceramic powder to give it plasticity and injection molding, followed by removing the binder.
Ceramic products made by firing are beginning to be used in automobile engine parts. Its feature is that parts with complex shapes can be mass-produced industrially.

The organic binder used here is related to the uniform dispersibility of the ceramic powder, the flow characteristics of the mixability, the strength of the green compact, and the ease of removing the binder from the green compact (debinding properties). However, if the selection or amount of the organic binder component is incorrect, a good sintered body cannot be obtained. For example, if the ceramic powder is not sufficiently uniformly dispersed in the organic binder, defects such as warpage and cracks are likely to occur in the molded or sintered body, and the strength of the molded body will also be reduced. In addition, if the thermal stability of the organic binder component is poor, the injection molded product will deteriorate in the cylinder, the fluidity will not be stable, injection molding defects will occur, and sometimes the ceramic powder and organic binder may be mixed. They may even separate. Furthermore, if too much organic binder is used, a large amount of gas will be generated from inside the molded product during the binder removal process, resulting in blistering,
Unable to prevent cracks from occurring.

Examples of the organic binder used for molding the ceramic powder include ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polystyrene, atactic polypropylene (APP), polyethylene,
(Meth)acrylic resins, waxes, etc. have been proposed, but moldability (flow characteristics, molding stability,
Each binder has advantages and disadvantages in terms of various properties such as mold releasability, green molded body strength, binder removal properties, and amount of carbon remaining after sintering.

For example, when EVA is mixed with ceramic powder, it can provide a green molded product with high strength and appropriate elasticity without impairing fluidity. This tends to cause blisters and cracks on the molded product.

Like EVA, when mixed with ceramic powder or metal powder, EEA can impart high strength and appropriate elasticity to the molded product without impairing the fluidity of the mixture, but if too much is used, When the binder is removed by thermal decomposition, blisters and cracks occur in the molded product, making it difficult to remove the binder without damaging the molded product.

In addition, polystyrene and (meth)acrylic resins (e.g. polyisobutyl methacrylate)
It exhibits an excellent binder effect on ceramic powders and metal powders, imparts high strength to green molded objects, is particularly effective in preventing damage to thin parts, and provides excellent shape retention to green molded objects. In addition, it has excellent thermal decomposition properties and makes debinding easy, but if too much is used, the fluidity of the mixture with ceramic powder, metal powder, etc. will be insufficient, resulting in injection molding defects such as insufficient filling and weld lines. easy to invite.

Furthermore, it has been shown that when mixed with ceramic powder, atactic polypropylene exhibits good fluidity, is easy to injection mold, and can produce green molded bodies with sufficient strength for handling ( (Japanese Patent Publication No. 51-29170), it has the disadvantage of poor binder removal properties.

In addition, although waxes such as paraffin have superior binder removal properties compared to general polymer compounds, they have poor injection moldability because their fluidity is unstable under high pressure, and they also have a relatively low molecular weight. Therefore, the strength of the green molded body is also low.

Therefore, it is necessary to use a well-balanced combination of resins with different performance, but each resin has a different softening point in form and is not sufficiently compatible, so it is very difficult to mix them uniformly, and it is difficult to mix them uniformly for a long time. In many cases, it is necessary to mix Generally, if sufficient mixing is not achieved, the fluidity will not be stable.
It takes a lot of time to determine the molding conditions, which impairs the homogeneity of the molded body, which affects the dimensional stability of the molded body, and also causes cracks in the sintered body.

[Means to solve the problem]

In view of the above-mentioned circumstances, the present invention has been developed to provide various necessary properties such as injection moldability, strength of green molded products, and binder removal properties when producing sintered bodies such as ceramic powders and metal powders by injection molding. This was done in order to obtain a well-balanced injection molding composition with a high yield of good sintered bodies free from defects such as warpage and cracks. A molding composition, wherein the organic binder is (a) an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer, (b) a (meth)acrylic ester monomer alone or a (meth)acrylic ester. Composite acrylic resin 45-80 obtained by suspending and polymerizing a solution consisting of a monomer, a mixture of styrenic monomers, and (c) a polymerization initiator in an aqueous medium containing a dispersant.
% (weight %, the same shall apply hereinafter) and is compatible with the composite acrylic resin having a melting point of 100°C or less.
An injection molding composition comprising a binder containing at least two components of 10 to 50% and prepared such that the ratio of inorganic powder/organic binder is 0.65/0.35 to 0.25/0.75 by volume, and the injection molding composition It relates to a sintered body obtained by sintering a molded object.

〔Example〕

The injection molding composition of the present invention is prepared from an inorganic powder and an organic binder.

The above-mentioned inorganic powder is not particularly limited as long as it is an inorganic powder that has conventionally been used to form a compact with an organic binder and be used as a sintered compact, but the powder particle shape is close to spherical and the average particle size is It is preferable to have a diameter of about 0.1 to 50 μm from the viewpoint of packing density of the inorganic powder and fluidity during injection molding, and more preferably about 0.1 to 20 μm.

Examples of the inorganic powder include metal powders and ceramic powders having the above-mentioned average particle diameter, and specific examples thereof include pure iron, iron alloys such as iron-nickel, iron-cobalt, and stainless steel; Metal powders such as tungsten, aluminum alloys, and copper alloys; oxide ceramic powders such as alumina, zirconia, mullite, titanate, and ferrite; titudide ceramic powders such as silicon nitride, aluminum nitride, and boron nitride; In addition to carbide ceramic powders such as silicon carbide, titanium carbide, and tungsten carbide, intermetallic compound powders such as titanium aluminum alloys, phosphate powders such as apatite, etc.
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 made of 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, for example, alumina, zirconia, silicon carbide, boron carbide, silicon nitride, boron nitride, aluminum nitride, and the like.

The organic binder used in the present invention is an ethylene-vinyl acetate copolymer (EVA), which is component (a).
or ethylene-ethyl acrylate copolymer (EEA), (b) component (meth)acrylic ester monomer alone or a mixture of (meth)acrylic ester monomer and styrene monomer;
(c) A composite acrylic resin of 45 to 80% obtained by dispersing a solution consisting of a polymerization initiator in an aqueous medium containing a dispersant and carrying out suspension polymerization, and the aforementioned composite acrylic resin having a melting point of 100°C or less. Waxes with compatibility
Contains 10 to 50%, preferably 15 to 40%, if necessary, in addition to plasticizers such as phthalate esters, lubricants such as higher fatty acids, and mold release agent components, to improve the wettability of the inorganic powder surface. It contains 0 to 40%, preferably 0 to 25%, of a surfactant, a surface treatment agent (coupling agent), etc.

When the composite acrylic resin is mixed with inorganic powder, it imparts sufficient fluidity to the mixture, exhibits an excellent binder effect on the inorganic powder, and strongly binds the particles to each other, making it possible to form a green molded body with sufficient fluidity. It is a component that provides strength and elasticity, and also has excellent binder removal properties.

Composite acrylic resin is produced by dissolving EVA or EEA in a (meth)acrylic ester monomer alone or in a (meth)acrylic ester monomer and a styrene monomer, and dispersing this in an aqueous medium for suspension polymerization. As a result, composite acrylic resin is a kind of polymer alloy that is microscopically mixed very uniformly (see Figures 1 and 3), and is simply a blend of polymers (see Figures 1 and 3). 2 and 4), it is easier to determine the molding conditions for the mixture with inorganic powder, and a good sintered body with stable fluidity and a high yield with little variation can be obtained.

The ethylene-vinyl acetate copolymer (EVA)
There are no particular limitations on the copolymer, and any copolymer generally called ethylene-vinyl acetate copolymer may be used; however, if the weight ratio of ethylene/vinyl acetate is 85/15,
~50/50 copolymer is preferred, and
Preferably, the ratio is 80/20 to 60/40. The ratio is
When it exceeds 85/15, it becomes difficult to dissolve the ethylene-vinyl acetate copolymer in the (meth)acrylic ester monomer or the mixture of the (meth)acrylic ester monomer and styrene monomer,
When the ratio is less than 50/50, it is difficult to obtain an ethylene-vinyl acetate copolymer, and the strength of the green molded product also tends to decrease.

In addition, the melt index (MI value) of the ethylene-vinyl acetate copolymer is preferably about 10 to 500, especially from the viewpoint of viscosity when used after being dissolved, and also from the viewpoint of fluidity during molding. From the viewpoint of the strength of the green molded product, it is more preferable that the number is about 20 to 400.

The above-mentioned ethylene-ethyl acrylate copolymer (EEA) is not particularly limited, and any commonly called ethylene-ethyl acrylate copolymer can be used, but if the weight ratio of ethylene-ethyl acrylate is 85/ It is preferably a 15-50/50 copolymer, more preferably an 80/20-60/40 copolymer. When the ratio exceeds 85/15, the ethylene-ethyl acrylate copolymer is converted into a (meth)acrylate monomer or a (meth)acrylate monomer.
Difficult to dissolve in mixtures of acrylate monomers and styrenic monomers, resulting in 50/50
If it is less than that, it is difficult to obtain the ethylene-ethyl acrylate copolymer, and the strength of the green molded product tends to be low.

In addition, the melt index (MI value) of the ethylene-ethyl acrylate copolymer is 10
~2000 is preferable from the viewpoint of viscosity, especially when used after being dissolved, and 100 from the viewpoint of fluidity during molding, strength of green molded product, etc.
A value of about 1,500 to 1,500 is more preferable.

The (meth)acrylic acid ester monomer is not particularly limited, but from the viewpoints of fluidity during molding, strength of green molded products, binder removal properties, etc., alcohols having 1 to 8 carbon atoms and (meth)acrylic are preferred. Preferably, it is an ester from an acid. Specific examples of such (meth)acrylic acid ester monomers include n-
Alkyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2
-Ethylhexyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and the like. Among these, n-butyl (meth)
The number of carbon atoms in the alkyl group such as acrylate is 1 or more
Preferred are n-alkyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, and t-butyl (meth)acrylate. These may be used alone,
Two or more types may be used in combination.

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

When the styrene monomer (meth)acrylate and the styrene monomer are used as a mixture, the proportion of the styrene monomer in the mixture is preferably 80% or less. As the proportion of the styrene monomer in the mixture increases, the fluidity of the resulting organic binder tends to deteriorate and molding becomes difficult.

In addition, other monomers such as (meth)acrylic acid, vinyl acetate,
A small amount of a monomer such as vinyl chloride may also be used in combination.

The ratio of component (a) to component (b) is preferably about 5/95 to 80/20 (component (a)/component (b) by weight, and 20/80 to 70/30). It is more preferable that it be about a certain degree. When 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. 80/20 again
If the temperature exceeds 100%, 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.

Preferred specific examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, lauroyl peroxide, and t-butylperoxy-2-ethylhexanate, azobisisobutyronitrile, and azobisdimethylvaleronitrile. Examples include oil-soluble polymerization initiators such as azo compounds such as. 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, based on 100 parts (by weight, the same applies hereinafter) of component (b), from the viewpoint of controlling the reaction rate and molecular weight. It is even more preferable to have one.

During the polymerization, a chain transfer agent may be used to adjust the molecular weight, if necessary. Preferred specific examples of such chain transfer agents include n-dodecylmercaptan and t-octylmercaptan. Examples include mercapto compounds and α-methylstyrene duplexes. These may be used alone or in combination of two or more.

When using a chain transfer agent, the amount used is preferably 0.01 to 1.0 parts, and 0.03 to 0.5 parts, based on 100 parts of component (b), from the viewpoint of controlling the molecular weight.
It is more preferable that it is part.

In the present invention, the characteristics of the mixed organic binder are expressed as a mere collection of the characteristics of each organic binder, and the purpose of the present invention is to improve the fact that the characteristics of the mixed organic binder are not expressed as one. It is preferable that component (b) is polymerized in a state where component (a) is sufficiently dissolved to form a polymer that is homogeneous with component (a) as a base. therefore,
It is preferable to use an oil-soluble polymerization initiator so that component (b) is not only uniform with component (a), but also uniformly polymerized as a whole.

There are no particular limitations on the method of preparing a solution from component (a), component (b), component (c) and, if necessary, a chain transfer agent. It may be prepared by any method.

The prepared solution is dispersed in an aqueous medium containing a dispersant and subjected to suspension polymerization.

Specific examples of the dispersant include polyvinyl alcohol, hydroxyethyl cellulose,
Examples include those using a water-soluble organic polymer compound such as polyvinylpyrrolidone, or poorly water-soluble fine particles such as hydroxyapatite or magnesium pyrophosphate in combination with an anionic surfactant. The amount of these dispersants used is based on 100 parts of water used.
The amount is preferably 0.1 to 1 part, more preferably 0.2 to 0.5 part.

(a) to (c) above for the aqueous medium containing the dispersant
The ratio of the solution consisting of the components and, if necessary, a chain transfer agent used, is preferably 30 to 120 parts of the solution to 100 parts of the aqueous medium from the viewpoint of stability and productivity of the dispersion suspension. More preferably 50 to 100 parts.

There are no particular limitations on the conditions for carrying out suspension polymerization, and 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, but is usually in the range of 50 to 130°C.

In this way, for example, as shown in Figure 1, (a)
A composite acrylic resin used for an organic binder in which component (b) is uniformly microdispersed can be obtained. This composite acrylic resin can be suitably used for molding inorganic powder to obtain a sintered body.

In addition, Figure 1 shows the internal structure of the composite acrylic resin particles, which was obtained by observing the state of the composite acrylic resin used in the composition of the present invention after etching with a solvent using a scanning electron microscope (5000x magnification). This is an electron micrograph.

The wax is a component that facilitates kneading of the inorganic powder and composite acrylic resin, uniformly disperses the inorganic powder in the composite acrylic resin, imparts plasticity to the mixture, and improves fluidity. By using it in combination with the composite acrylic resin, it is possible to reduce the amount of organic binder used.

If the melting point of the wax exceeds 100°C, the melting point of the organic binder will be high, and fluidity will be insufficient, making it difficult to reduce the amount of organic binder used. On the other hand, oils with a melting point below room temperature tend to cause molding defects in terms of molded product strength and mold releasability, and in the case of waxes that are not compatible with composite acrylic resins, inorganic powders are mixed with organic binders. It becomes difficult to uniformly disperse the particles, and the above-mentioned effects cannot be obtained in either case.

The proportion of the wax in the organic binder is 10 to 50%, preferably 15 to 35%, as described above, but if the amount of wax used is less than 10%, the above effect may not be sufficient. If it is used in excess of 50%, the lack of strength, which is a major drawback of wax, will become noticeable, and the green molded product will crack or break when released from the mold, making it virtually the same as normal wax. It is no longer possible to obtain a green molded product that has enough strength to withstand handling.

Both synthetic and natural waxes can be used, and specific examples include paraffin wax, microcrystalline wax, polyethylene wax, beeswax, carnauba wax, and montan wax.

The injection molding composition of the present invention is prepared such that the ratio of the inorganic powder to the organic binder whose essential components are a composite acrylic resin and wax is 0.65/0.35 to 0.25/0.75 by volume. It is a composition. In addition, the volume ratio referred to in this specification is when W _p is the weight of the inorganic powder, d _p is the true specific gravity of the inorganic powder, W _B is the weight of the organic binder, and d _B is the true specific gravity of the organic binder. It is expressed by the following formula.

Volume ratio = W _p /d _p /W _p /d _p +W _B /d _B /W _B /d _B /W _p /
d _p + W _B / d _B If the above ratio exceeds 0.65/0.35,
The fluidity of the mixture as an injection molding material is insufficient, making it difficult to mold into the desired shape.On the other hand, if it is less than 0.25/0.75, the density of the molded product will not increase and shrinkage during firing will increase. Not only does the dimensional accuracy deteriorate, but when the binder is removed by thermal decomposition, a large amount of gas is generated, which significantly increases the occurrence of defects such as cracks and blisters in the molded product.

The production of sintered parts such as ceramics and metals using the injection molding composition according to the present invention is usually carried out as follows, but the method is not limited to this method.

First, an inorganic powder such as ceramic powder or metal powder and an organic binder are sufficiently heated and kneaded using a kneader such as a pressure kneader to uniformly disperse the inorganic powder in the organic binder. Grind or pelletize and use as injection molding material.

This material is then injection molded into a molded article of the desired shape using known equipment and methods commonly used in plastic molding.

Thereafter, the organic binder is removed from the molded body by a method such as thermal decomposition, and the molded body is fired at an appropriate temperature and atmosphere to obtain an inorganic sintered body in a desired shape.

Next, the present invention will be explained based on examples.

Production Example 1 600 g of n-butyl methacrylate (BMA) and n-dodecyl mercaptan were placed in the 5 reactor.
After adding 0.3g and raising the temperature to 75℃ while stirring,
900g of EVA (Ultracene 722, manufactured by Tosoh Corporation) and 2.4g of benzoyl peroxide as a polymerization initiator
was added and dissolved. To this was added an aqueous decomposing agent solution prepared separately in advance, consisting of 1840 ml of ion-exchanged water and 160 ml of a 3% aqueous solution of polyvinyl alcohol (PVA), and the mixture was stirred to suspend the EVA-BMA solution. Then, after nitrogen substitution, polymerization was carried out by reacting at 80℃ for 3 hours and at 100℃ for 2 hours,
It was cooled, taken out, washed and dried.

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

Production Example 2 After adding and dissolving 700 g of BMA, 500 g of styrene, and 0.35 g of n-dodecyl mercaptan in the reactor of 5, EVA (Ultracene) was added while stirring.
722 (manufactured by Tosoh Co., Ltd.) was added, the temperature was raised to 75°C to dissolve, and then 4.8 g of benzoyl peroxide was added.
g, and 0.25 g of t-butyl peroxybenzoate were added and dissolved. Add to this 1,840 ml of ion-exchanged water and 160 ml of 3% PVA aqueous solution, which were prepared separately in advance.
Add and stir an 80℃ dispersant aqueous solution consisting of
Suspended. After the space was replaced with nitrogen, the reaction was carried out at 80°C for 5 hours and at 110°C for 2 hours to complete the polymerization. Thereafter, it was cooled, washed with water, and dried to obtain white spherical particles with a particle size in the range of 0.3 to 1.0 mm. A toluene solution of this polymer particle at 30℃
The intrinsic viscosity [η] was 0.70. The obtained polymer is called composite acrylic resin B.

Comparative Production Example 1 The EVA (Ultracene 722, manufactured by Tosoh Corporation) used in Production Example 1, polybutyl methacrylate (molecular weight
300,000) were well kneaded for 30 minutes at 140℃ using a roll so that they had almost the same composition and intrinsic viscosity [η],
A mixture (mixed acrylic resin A) was obtained.

Comparative Production Example 2 The EVA (Ultracene 722, manufactured by Tosoh Corporation) used in Production Example 2, polybutyl methacrylate (molecular weight
300,000) and polystyrene with approximately the same composition and intrinsic viscosity [η] at 150℃ using a roll.
The mixture was thoroughly kneaded for 30 minutes to obtain a mixture (mixed acrylic resin B).

Reference Example 1 The suspension polymers obtained in Production Examples 1 and 2 and the simple mixture products obtained in Comparative Production Examples 1 and 2 were processed by a solvent etching method (immersion in hexane for 2 minutes) and then scanned using a scanning electron microscope. Microscope (5000x)
The internal structure was observed by observing the state of the etched material. The results are shown in FIGS. 1 and 3, and FIGS. 2 and 4, which are observation photographs, respectively.

As can be seen from the comparison between Figures 1 and 2,
In the EVA-BMA suspension polymer (Production Example 1), fine particles are uniformly dispersed, which is significantly different from the dispersion state in the simple mixture product (Comparative Production Example 1).

Also, from the comparison between Figures 3 and 4, EVA-
It can be seen that similar differences are observed between the BMA-styrene suspension polymer (Production Example 2) and the simple mixture product (Comparative Example 2).

Example 1 Alumina powder (AES-11, manufactured by Sumitomo Chemical Co., Ltd.)
Add 12.35 parts of composite acrylic resin A, 4.75 parts of microcrystalline wax (melting point 84°C), and 1.90 parts of stearic acid to 100 parts, and heat at 140°C in a pressure kneader.
The mixture was thoroughly kneaded for 60 minutes and cut into pellets of 2 to 4 mm to prepare a ceramic composition for injection molding with a volume ratio of alumina powder/organic binder of 0.59/0.41. Using this, the molding temperature is 120 to 160.
℃, injection pressure 500-1300Kg/ ^cm2 , height 50mm,
Bolts specified in JISB-1176 with a maximum wall thickness of 5 mm are formed and heated from 20 to 140°C at a heating rate of 30°C/h, from 140 to 140°C.
Desorption was achieved by embedding it in alumina powder and heating it under the following conditions: 350°C at a heating rate of 4°C/h, 350-450°C at a heating rate of 10°C/h, and 450-600°C at a heating rate of 30°C/h. Binder and then put in a firing furnace at 1620℃
A good sintered body without any defects was obtained by holding it for 1 hour after reaching the temperature and sintering it.

Example 2 100 parts of partially stabilized zirconia (HSY-3.0, manufactured by Daiichi Kigenso Kogyo Co., Ltd., specific surface area 6 m ² /g), 10.4 parts of composite acrylic resin A, and paraffin wax (melting point 58°C) 4.0 parts, add 1.6 parts of stearic acid, 140 parts
The mixture was thoroughly kneaded for 60 minutes at a temperature of 2.0 to 4.0 mm and cut into pellets of 2 to 4 mm to prepare a ceramic composition for injection molding having a volume ratio of partially stabilized zirconia/organic binder of 0.51/0.49. Using this, a bolt was formed in the same manner as in Example 1, and after removing the binder, it was placed in a firing furnace and held for 2 hours after reaching 1500°C to sinter it. A sintered body was obtained.

Example 3 9.5 parts of composite acrylic resin B, 5.0 parts of paraffin wax (melting point 58°C), and 1.3 parts of dibutyl phthalate were added to 100 parts of the same partially stabilized zirconia as in Example 2, and thoroughly kneaded at 150°C for 60 minutes. 2~4mm
A ceramic composition for injection molding with a volume ratio of partially stabilized zirconia/organic binder of 0.51/0.49 was prepared by cutting the mixture into pellets. Using this, a bolt was formed in the same manner as in Example 1, and after removing the binder, it was held at 1500°C for 2 hours and sintered, and a good sintered body with no warping or cracks was obtained. .

Example 4 Stainless steel powder with an average particle size of 8.9 μm,
(SUS304L, manufactured by Mitsubishi Steel Corporation) 100 parts, composite acrylic resin B 6.6 parts, paraffin wax (melting point
Add 1.8 parts of dibutyl phthalate (69℃) and 2.6 parts of dibutyl phthalate.
Thoroughly knead at 150°C for 60 minutes to form stainless steel powder/
A metal composition for injection molding with an organic binder in a volume ratio of 0.53/0.47 was prepared. Example 1 using this
A bolt was formed in the same manner. The obtained molded product was buried in alumina powder, and the temperature was raised from room temperature to 120°C at a rate of 3°C/h in a _N2 atmosphere.
After 120℃, the temperature was raised to 450℃ at a rate of 6℃/h, held at the same temperature for 2 hours to remove the organic binder, and then placed in a vacuum sintering furnace and held for 1 hour after reaching 1350℃ for sintering. As a result, a good sintered body with a sintered density of 98% and no cracks was obtained.

Examples 5 and 6 An organic binder was prepared by uniformly mixing in advance 70 parts of composite acrylic resin A, 20 parts of paraffin wax (melting point 47°C), and 10 parts of stearic acid.

18 parts of the organic binder per 100 parts of silicon titanide (SN-ESP, manufactured by Ube Industries, Ltd., particle size 0.1 to 0.6 μm) containing 5% each of Y ₂ O ₅ and Al ₂ O ₃ , 10% in total. , 12 parts of the above organic binder were added to 100 parts of Mn-Zn soft ferrite (manufactured by Toda Kogyo Co., Ltd., average particle size of about 1.5 μm), and kneaded, molded, and removed the binder in the same manner as in Example 1. I did it. In addition, silicon titanide/organic binder, Mn
- The volume ratios of Zn-based soft ferrite/organic binder were 0.63/0.37 and 0.62/0.38, respectively.

Then, they were each sintered using conventional sintering techniques to obtain good sintered bodies with no warpage or cracks.

Examples 7 and 8 An organic binder was prepared by uniformly mixing in advance 45 parts of composite acrylic resin B, 40 parts of paraffin wax (melting point 69°C), and 15 parts of dioctyl phthalate.

Tungsten carbide (average grain size 1.0μm)
Add 7 parts of the organic binder to 100 parts and 9 parts of the organic binder to 100 parts of carbonyl iron powder (particle size 2 to 5 μm), and knead, mold, and remove the binder in the same manner as in Example 4. Summer. The volume ratios of tungsten carbide/organic binder and carbonyl iron powder/organic binder were 0.50/0.50 and 0.58/0.42, respectively.

They were then sintered using conventional sintering techniques to obtain good sintered bodies with no defects and a sintered density of 98%.

Comparative Example 1 Mixed acrylic resin A was mixed with composite acrylic resin A
A bolt was molded, binder removed, and sintered in the same manner as in Example 1, except that the bolt was used in place of Example 1, but molding defects such as sprue breaking occurred during the injection molding stage, and The yield is about
It fell by 12%.

Comparative Example 2 Mixed acrylic resin B was mixed with composite acrylic resin B
A bolt was molded in the same manner as in Example 3, and the binder was removed and sintered, except that the bolt was used in place of .However, molding defects such as cracks occurred during injection molding. Cracks also occurred when the binder was removed from a molded product with a good appearance. The final product yield was about 22% lower than in Example 3.

Comparative Example 3 Injection molding was performed in the same manner as in Example 1, except that 14 parts of paraffin wax (melting point 58°C), 2 parts of EVA, and 1 part of dibutyl phthalate were used for 100 parts of the same alumina powder as in Example 1. Since the strength of the molded product was extremely low, it was damaged during demolding, and a good molded product could not be obtained.

Comparative Example 4 Example 1 except that only composite acrylic resin A was blended with the alumina powder used in Example 1 at the same volume ratio (0.59/0.41) as the amount of organic binder used in Example 1. Although the mixture was kneaded and injection molded in the same manner as above, a satisfactory green molded product could not be obtained due to insufficient fluidity.

[Effects of the Invention] By using the injection molding composition of the present invention, it is possible to produce a good sintered body having a desired shape and without warping or cracking with a high yield by injection molding, unlike conventional methods. can.

[Brief explanation of the drawing]

Figures 1 to 4 show the states of the acrylic resins obtained in Production Example 1, Comparative Production Example 1, Production Example 2, and Comparative Production Example 2 after being etched with a solvent using a scanning electron microscope (5000x magnification). This is an electron micrograph taken to show the internal structure of acrylic resin particles.

Claims (1)

[Scope of Claims] 1. An injection molding composition comprising an inorganic powder and an organic binder, wherein the organic binder is (a) an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer, (b) ( A solution consisting of a meth)acrylic ester monomer alone or a mixture of a (meth)acrylic ester monomer and a styrene monomer, and (c) a polymerization initiator is dispersed in an aqueous medium containing a dispersant. Suspension polymerized composite acrylic resin 45-80
% by weight and 10 to 50% by weight of wax that is compatible with the composite acrylic resin having a melting point of 100°C or lower, and the ratio of inorganic powder/organic binder is 0.65/by volume.
An injection molding composition prepared to have a ratio of 0.35 to 0.25/0.75. 2. A sintered body obtained by sintering a molded product of the injection molding composition according to claim 1.