JPH0483752A - Mixture of sinterable substance - Google Patents

Abstract

PURPOSE:To easily form a green material having complicate form and to prevent the deformation of a green material after taking out of a mold by compounding a sinterable substance with a specific polysaccharide and a water- soluble polymer at specific ratios. CONSTITUTION:The objective composition is produced by compounding 100 pts.wt. of a sinterable substance with 1.0-15.0 pts.wt. of a polysaccharide gelatinizable by cooling after dissolving in hot water and 1.0-15.0 pts.wt. of a water-soluble polymer gelatinizable by heating. The sinterable substance is metals, alloys or ceramics. Any kind of polysaccharide, e.g. carrageenan, alginic acid salt and galactomannan, can be used in the present composition. The water-soluble polymer is a substance soluble in water at about <=30 deg.C and gelatinizable at a temperature higher than a specific level. Examples of the water-soluble polymer are cellulose ethers such as methylcellulose and hydroxymethylcellulose.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a mixture of sinterable materials suitable for forming sinterable materials by injection molding.

[Prior Art] Molded bodies of sinterable materials such as metals or ceramics having complex shapes are widely molded by injection molding.

In particular, it is an effective means for manufacturing engineering parts such as electronics parts and automobile parts, which are manufactured in large quantities, and plays an important role along with dry pressing methods, slip casting methods, etc.

To obtain a metal or ceramic molded body by injection molding, a green body is created by mixing and kneading metal powder or ceramic powder with a thermoplastic resin binder, and degreasing is performed to decompose and remove the binder component by heating. A commonly used method is to sinter at a predetermined temperature.

In this method, a green body with a complex shape is degreased and sintered, but due to the characteristics of the sinterable material mixture, the green body can be injection molded without defects, regardless of its thickness, and It is necessary that the binder component be removed in a short time during degreasing, and that harmful deformations such as blisters, cracks, and cracks do not occur in the molded product.

Currently, various waxes, amorphous polypropylene, acrylic resins, styrene resins, and the like are used as binders for injection molding of sinterable substances. However, the degreasing process to remove these binders takes a long time when the thickness of the green body becomes 15 mm or more.
Moreover, cracks and cracks occur inside the molded product during degreasing, making it difficult to obtain a product with good appearance and performance.

In order to solve these problems, attempts have been made to use water, which is easily volatilized, as a binder. for example,
JP-A-61-94702, JP-A-61-101447
No. 1, US Pat. No. 4,113,480 discloses a method using a composition consisting essentially of various metal powders or ceramic powders, to which are added a component that gels on heating and water.

However, in these methods, it is necessary to heat the mold to 60 degrees Celsius or more, and when the green body is taken out from the heated mold, there is a risk that the green body will deform if the temperature drops.

Further, USP-4734237 proposes a method using a composition in which various ceramic powders and metal powders are added with water and a component that gels at a temperature of 0 to 22 degrees Celsius.

However, at temperatures above 80 degrees Celsius, which is the molding temperature, water easily evaporates and it is difficult to maintain a constant concentration of metal powder or ceramic powder. There was a problem that the injected composition was scattered around.

[Problems to be Solved by the Invention] The present invention solves these problems and provides a sintering method that allows a green body having a complicated shape to be easily molded and that does not deform even after the green body is taken out of the mold. The purpose is to provide a mixture of sexual substances.

[Means and effects for solving the problems] According to the present invention, these problems are solved by adding (B) a polysaccharide that can be gelled by heating and dissolving and then cooling to (A) 100 parts by weight of a sinterable substance.
(C) 1.0 to 15.0 parts by weight of a water-soluble polymer that can be gelled by heating. The present invention will be explained in detail below.

The sinterable substance mixture in the present invention essentially consists of the following sinterable substance, a polysaccharide that can be gelled by heating and melting and cooling, and a gelatable water-soluble polymer.

(A) Sinterable substance The melting point, decomposition temperature or sublimation temperature of the sinterable substance used in the present invention is usually 600 degrees Celsius or higher, and 10
The temperature is preferably 00 degrees or more, and particularly preferably 1400 degrees or more. If a metal or ceramic with a melting point, decomposition temperature or sublimation temperature of less than 600 degrees is used as a sinterable material, harmful deformation or blistering will occur during degreasing.

Moreover, the average particle size is 0.1 to 500 microns. This average particle size varies depending on the type of sinterable substance, but in the case of metals it is usually 1 to 500 microns, preferably 1 to 300 microns, most preferably 1 to 200 microns. When using metals with an average particle size of less than 1 micron,
Crosstalk is difficult.

On the other hand, if a metal with a diameter exceeding 500 microns is used, the mechanical properties of the molded product obtained by sintering will deteriorate. In the case of ceramics, it is generally 01 to 200 microns, preferably 01 to 150 microns, particularly 0.1
~100 microns is preferred. When ceramics with an average particle size of less than 0.1 micron are used, it is difficult to uniformly disperse the ceramics when preparing the mixture.

On the other hand, if ceramics with a diameter exceeding 200 microns are used,
When a molded product of the mixture is sintered, shape retention deteriorates, the density after sintering decreases, and the mechanical strength of the sintered body decreases.

Typical examples of metals used as sinterable materials in the present invention include metals such as aluminum, iron, copper, titanium, molybdenum, zirconium, cobalt, nickel, and chromium, and metals based on these metals (at least 50% by weight). Examples include alloys such as

Powders of these metals and alloys are widely used as bearing base metals, free-cutting steel, heat-resistant materials, wear-resistant materials, etc.
It is commonly referred to as a powder metallurgy material.

Further, typical examples of ceramics include materials such as alumina, silicon carbide, silicon nitride, zirconia, cordierite, tungsten carbide, ferrite, and aluminum nitride.

In addition, this sintered material contains an appropriate amount of boron, beryllium, carbon, yttrium oxide, cerium oxide, magnesium oxide, lithium oxide, etc. as a sintering aid (in general, a large amount is added per 100 parts by weight of ceramic oxide). Tomo 20
parts by weight) may be added.

(B) A polysaccharide that can be gelled by heating and dissolving and then cooling;
The polysaccharide used in the present invention that can be gelled by heating and dissolving and then cooling is not particularly limited as long as it is a known polysaccharide that can be gelled by heating and dissolving and then cooling. , can be used in the present invention. Generally a polysaccharide extracted from algae and plants.
It includes carrageenan, alginate, galactomannan, etc., and its details are described in ``Agar Handbook J'' (written by Kaneo Hayashi and Akio Okazaki, published by Korinsha, 1972) and the Chemical Encyclopedia.

In the sinterable material mixture of the present invention, the sinterable material 1
The mixing ratio of the polysaccharide that can be gelled by heating and dissolving and cooling to 00 parts by weight is 1.0 to 15.0 parts by weight, and 1.0 to 15.0 parts by weight.
．． 0 to 1090 parts by weight is preferable, especially 1.0 to 8.0 parts by weight.
Parts by weight are preferred. If the mixing ratio of the polysaccharide that can be gelled by cooling after heating and melting is less than 1.0 parts by weight, the strength of the molded product will be weak, and cracks or chips will occur in the molded product when it is released from the mold. On the other hand, if it exceeds 15 parts by weight, not only the fluidity decreases, but also cracks occur during degreasing and sintering, and the density of the sintered body decreases.

(C) Water-soluble polymers that can be gelled by heating Water-soluble polymers that can be gelled by heating are water-soluble substances in water below about 30 degrees Celsius, but when a certain temperature is exceeded, the substance gels. Specifically, cellulose ethers are known, such as methylcellulose, hydroxymethylcellulose, hydroxypropylmethylcellulose, hydroxypropylcellulose, and hydroxyethylcellulose. The molecular weight of these thermogelatable water-soluble polymers is 2,000 to 2,000,000.
000,000 to 1,500,000 is desirable, and 2,000 to 100,000 is suitable. If the molecular weight is less than 2,000, the water retention capacity at high temperatures is poor, while if the molecular weight exceeds 2,000,000, it will be difficult to decompose during degreasing, which is not preferred.

Further, the mixing ratio of the water-soluble polymer that gels by heating with respect to 100 parts by weight of the sinterable material is 0.5 to 15 parts by weight, preferably 0.5 to 10.0 parts by weight, and especially 0.5 to 15 parts by weight. ~8.0 parts by weight is preferred. If the mixing ratio of the water-soluble polymer is less than 0.5 parts by weight, it is difficult to prevent the mixture from scattering from the nozzle during injection molding, and if the mixing ratio of the water-soluble polymer exceeds 15.0 parts by weight. This not only reduces fluidity but also causes weld marks on the molded product and microcracks on the surface.

The sinterable substance mixture of the present invention basically consists of the above-mentioned sinterable substance, a polysaccharide that can be gelled by heating and melting and then cooling, and a water-soluble polymer substance that can be gelled by heating, and is sufficiently homogeneous. It can be treated as a mixture of mixed forms.

When used, an appropriate amount of water is mixed with this to give it appropriate fluidity, and the mixture is used as a raw material for injection molding.

Further, the mixing ratio of water is 5.0 to 50.0 parts by weight, and 5.0 to 45.0 parts by weight based on 100 parts by weight of the sinterable material.
Parts by weight are preferred, particularly preferably 5.0 to 40.0 parts by weight.

If the mixing ratio of water is less than 5.0 parts by weight, not only will the fluidity decrease, but also it will be difficult to uniformly disperse the sinterable material. On the other hand, if the amount exceeds 50.0 parts by weight, the strength of the molded product will be low, resulting in deformation, chipping, and cracking when released from the mold.

The sinterable substance mixture of the present invention is mixed and mixed to become a raw material for injection molding, but during mixing and mixing, dispersants such as polyacrylates, alginates, polycarboxylic acid type surfactants, polyvinyl alcohol, polyethylene Plasticizers such as glycols, polybrobylene glycols, glycerin and sorbitan esters can be added. At this time, the amount of processing aids such as dispersants and plasticizers added is 100% of the sinterable material.
It is preferably at most 30 parts by weight, particularly preferably 20 parts by weight or less.

When using the sinterable material mixture of the present invention, water is added to the mixture of the above sinterable material, a polysaccharide that can be gelled by heating and melting and cooling, and a water-soluble polymer that can be gelled by heating. They may be mixed uniformly within the mixing ratio range.

In producing the mixture, all of the mixed components may be mixed at the same time, or some of the mixed components may be mixed in advance and the remaining mixed components may be mixed into the resulting mixture. It can also be produced by tri-blending using a mixer such as a Henschel mixer or a super mixer, which are commonly used in the field, or by leaving the tri-blending mixture for several days and then using a Banbury mixer or kneader. A homogeneous mixture can be obtained by applying shear force and kneading using a mixer such as a roll mill or a screw extruder. In this case, the mixture is generally kneaded and then formed into pellets, which are then subjected to injection molding as described later.

The sinterable substance mixture thus obtained is shaped into molded bodies having various shapes by injection molding, which is commonly practiced in the field of synthetic resins. The molding temperature is higher than the dissolution temperature in water of the polysaccharide that can be gelled by cooling after heating and dissolving, but it is necessary to carry out the molding in a temperature range of 100 degrees Celsius or lower, which is the boiling temperature of water. For these reasons, injection molding may be carried out at a temperature of the mixture in the range of 80 to 100 degrees Celsius. Moreover, the mold temperature may be in the range of 10 to 40°C. The thickness of the molded body obtained is generally 0.5 to 200 mm. The thickness of this molded body is 20
If it exceeds 0 mm, blisters or cracks are likely to occur on the surface of the molded product.

The temperature of the obtained molded product is increased, and the molded product is essentially degreased until the polysaccharide and water-soluble polymer that can be gelled by heating and dissolving and cooling are completely eliminated. At this time, the maximum temperature for degreasing is usually 200 degrees Celsius or higher.

The molded body thus degreased is sintered. When the sinterable material is an oxide, it is sintered at a temperature in the range of 500 to 1,700 degrees Celsius, although it varies depending on the type. On the other hand 1,
For non-oxide systems, the temperature is 1500 degrees Celsius in an inert gas atmosphere.
It is sintered at a temperature ranging from ~2500 degrees Celsius, again depending on the type.

[Examples and comparative examples] Hereinafter, the present invention will be explained in more detail with reference to Examples.

In addition, in the examples and comparative examples, the melt viscosity was measured using a Koka type flow tester at 90 degrees Celsius and a load of 30 kg.
Measured under the following conditions.

Degreasing is done using an electronic furnace (inner volume 2000cc) at 4 degrees Celsius.
The temperature was raised to 00 degrees. In addition, sintering was performed at 1000 degrees or 16 degrees at 90 degrees/hour under atmospheric pressure using the same electronic furnace as above.
The temperature was raised to 00 degrees.

The types and physical properties of the sinterable substances, polysaccharides that can be gelled by heating and melting and cooling, and water-soluble polymers that can be gelled by heating, used in Examples and Comparative Examples are shown below.

[(A) Sinterable substance] Alumina with an average particle size of 0.4 microns and ferrite with an average particle size of 1.5 microns were used as sinterable substances.

[(B) Polysaccharide that can be gelled by cooling after heating and dissolving]

Galactomannan extracted from red algae was used as a polysaccharide that can be gelled by heating and dissolving and then cooling.

[(C) Water-soluble polymer that gels when heated] Hydroxypropyl methylcellulose (hereinafter referred to as rHPMC), which has a molecular weight of 6000, is a water-soluble polymer that gels when heated.
It's called J. ) and methylcellulose with a molecular weight of 10,000 (
Hereinafter referred to as rMCJ. ) was used.

[(D) Plasticizer] Polyethylene glycol having a molecular weight of 3000 was used as a plasticizer.

(Examples 1 to 4, Comparative Examples 1 to 5) Sinterable substances whose types and mixing ratios are shown in Table 1, polysaccharides that can be gelled by cooling after heating and melting, and polysaccharides that can be gelled by heating The water-soluble polymer, plasticizer, and water were each triblended for 2 minutes using a Henschel mixer. After each of the obtained mixtures was left to stand for 15 hours, pellets were produced while kneading at a temperature of 50 degrees Celsius using a vented twin-screw extruder (diameter 35 mm). Each pellet was molded into a cylinder (diameter 25 m) using an injection molding machine (mold clamping pressure 100 tons) at a mold temperature of 20 degrees Celsius.
A green molded body having a length of 150 mm and a length of 150 mm was prepared. Each of the obtained cylinders was degreased using a degreasing furnace under the above conditions. The degreased products thus obtained were sintered under the conditions described above (sintering temperatures are shown in Table 2) to produce sintered products. Table 2 shows the appearance of each of the green bodies, molded bodies and sintered bodies after degreasing, the rate of degreasing of the green bodies, and the viscosity of the sinterable substance mixture thus obtained.

(The following is a blank space) [Effects of the Invention] The sinterable substance mixture of the present invention exhibits the following effects including the characteristics of the green body and the degreased body and the method for producing them.

(1) Due to good fluidity and water retention during molding, it is easy to shape even molded products with complex shapes.

(2) Since it can be molded at a mold temperature of 10 to 40°C, it is easy to handle without worrying about burns.

(3) Since the viscosity of the mixture does not decrease significantly even at temperatures of 80°C or higher, it has excellent flow stability and moldability during injection molding.

(4) Since the green body has excellent shape retention, the molded body does not suffer from deformation, cracks, chips, etc., even when the product is released from the mold or when it is left standing after being released from the mold.

(5) There is no deformation during degreasing, and it is possible to increase the temperature increase rate during degreasing, and as a result, the degreasing time can be shortened.

(6) Degreasing is easy during degreasing, and deformation due to degreasing can be significantly reduced.

In order for the sinterable substance mixture of the present invention to exhibit the above-mentioned effects, the sintered body formed into various shapes can be used in fields such as machine parts, electronic equipment parts, home appliance parts, and automobile parts. used for.

Claims (1)

[Claims] 1.0 to 15.0 parts by weight of a polysaccharide that can be gelled by heating and melting and cooling, and 1.0 to 15.0 parts by weight of a water-soluble polymer that can be gelled by heating, per 100 parts by weight of the sinterable substance. A sinterable material mixture consisting of: