JP3081779B2 - Composition for manufacturing sintered compact - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forming raw material used for producing a sintered compact.

[0002]

2. Description of the Related Art Particularly precise sintered compacts and sintered compacts of complex shapes utilizing sinterable powders such as ceramics, metals, cermets, etc. are required to produce sintered compacts containing a sinterable powder and a binder. A green molded body is formed by injection molding of a molding material obtained by heating and kneading the composition for molding, and then the green molded body is subjected to a degreasing step, followed by sintering.

[0003] In forming a sintered compact by the above-described method, the most important step for obtaining a good quality compact without defects such as cracks, swelling and deformation is a degreasing step.
This degreasing step is a step of removing the binder from the green molded body made of the injection molded body, and a method of heating and decomposing the binder by heating the green molded body to gasify the green molded body, or treating the green molded body with a solvent. In this method, a soluble binder component in a green molded body is eluted and removed, and then the remaining binder is thermally decomposed and gasified. By the way, in the thermal degreasing method of heating and degreasing the green molded body, when the thermal decomposition and gasification of the binder in the green molded body are concentrated in a short time, cracks and blisters are formed in the molded body during the degreasing step. Because of what may occur, degreasing must be performed by prolonged heating. In particular, when a powder for sintering having a small particle size, that is, a powder having a large specific surface area, is used, a binder is blended so that the heating fluidity of the forming raw material when forming a green compact is stabilized. It is necessary to increase the amount, and it is necessary to devise a heating step at the time of degreasing in multiple stages. In addition, even if there is no risk of cracking or swelling during the degreasing process by heating, in the case of a green compact using a metal powder or a spherical powder having a high specific gravity, it is molded during the degreasing process by heating. Deformation often occurs in the body, which also necessitates a slower rate of heating during degreasing. For this reason, a method of adding a sublimable substance to the binder has been considered,
In the case where the sublimable substance is added, since the sublimable substance evaporates at the time of kneading the molding raw material of the green molded body and at the time of injection molding of the green molded body, the sprue / runner portion at the time of molding the green molded body is used. Reproduction becomes difficult.

On the other hand, in a degreasing method comprising eluting and removing a binder in the green molded article by treating the green molded article with a solvent, and then thermally decomposing and gasifying the remaining binder, a green treatment is carried out by the solvent treatment. The solvent-soluble binder in the molded body is removed, and the voids thus formed become passages, so that the thermal decomposition and gasification of the remaining binder by heating are smoothly performed. For this reason, cracking, swelling, deformation, and the like in the degreasing step of the green molded body can be avoided. However, currently used binders contain a large amount of liquid raw materials such as mineral oils, fatty acid-based oils, and natural oils, and these oil components often ooze out of green molded articles, In the stored green molded body, the oozing of the oil component is more severe, and the oil component oozing on the surface of the green molded body causes cracks and swelling during degreasing by solvent treatment.

[0005] A method in which a plasticizer or a lubricant in a binder is eluted with boiling water is also conceivable. However, it is possible to maintain the stability of the molding raw material of the green molded body, and to improve the heating fluidity during injection molding of the molding raw material. In terms of maintaining and maintaining the strength of the green molded body, the amount of the plasticizer or lubricant cannot be increased. Furthermore, a method has been proposed in which a water-soluble resin in a green molded body is extracted by water treatment using a binder made of a water-soluble resin (Japanese Patent Publication No. 2-10110).
However, this method cannot be applied to a method using a ceramic powder or a metal powder having a property of reacting or corroding with water.

Further, by using a polyacetal resin, which is a depolymerized polymer, alone or together with another polymer as a binder, the shape retention of a green molded article based on the rigidity of the polyacetal resin, and a degreasing step by heating It is already known that the molded article has an excellent shape retention property, and that no residue remains after degreasing by heating, and that the degreasing step by heating is faster, so that the production efficiency can be improved. (For example, JP-A-4-247802 and JP-A-5-98306). However, on the other hand, when the polyacetal resin is used as a binder, the polyacetal resin is chemically stable and has poor compatibility with many other organic components. In addition, there is a problem that a homogeneous sintered molded article cannot be obtained because of poor affinity with wax, lubricant and the like and easy separation of layers in the components. In particular, in order to increase the above-mentioned effect of using a polyacetal resin as a binder, that is, to enhance the shape retention of a green molded body, and the shape retention of a molded body in a degreasing step by heating, and to enhance the heat degreasing efficiency, It is necessary to increase the blending ratio of the polyacetal resin in the binder, and the above-mentioned drawbacks due to insufficient affinity of the polyacetal resin for other resins, waxes, lubricants, and the like are further increased.

Further, a method of using a polyacetal resin as a binder and adopting a degreasing method of decomposing the polyacetal resin in the green molded article with an acidic catalyst is considered, whereby a method of greatly shortening the degreasing time can be considered.
This method uses a strong acid such as nitric acid for the degreasing catalyst,
There is a disadvantage that the sinterable powder may be deteriorated by oxidation or the like, and the types of sinterable powder that can be used are greatly limited.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to make it possible to complete the degreasing step of the green molded body by heating for a short time, and to provide the molded article during the degreasing step with defects such as cracks, swelling and deformation. It is an object of the present invention to provide a composition for producing a sintered molded article which can obtain a homogeneous sintered molded article having no dimensional accuracy, high dimensional accuracy, and no layer separation.

[0009]

The above object is achieved by a composition for producing a sintered compact according to the present invention having the following constitution. That is, according to the present invention, in the composition for producing a sintered compact containing a sinterable powder and a binder, the polyolefin-based polymer-modified polyacetal resin is compounded in a proportion of 10 to 95% by volume of the whole binder. A composition for producing a sintered compact is provided.
According to the present invention, the ratio of the polyacetal skeleton to the polyolefin-based polymer skeleton in the polyolefin-based polymer-modified polyacetal resin is 10 to 95% by weight: 90.
To 5% by weight (total 100% by weight of both). Hereinafter, the present invention will be described in detail.

A binder comprising a sinterable powder, a polyolefin polymer-modified polyacetal resin (hereinafter, also simply referred to as “modified polyacetal resin”) and a binder other than the modified polyacetal resin (hereinafter, referred to as “other binders”) If the ratio of the modified polyacetal resin is less than 10% by volume of the binder in the composition for producing a sintered molded article, the molded article in the degreasing step by heating tends to be deformed, and 95% by volume.
If the ratio exceeds the above range, the fluidity of the composition will decrease, and it will be impossible to smoothly perform injection molding when molding a green molded body.

When the ratio of the polyacetal skeleton in the modified polyacetal resin blended as a binder is less than 10% by weight, the thermal deformation temperature of the green molded body is greatly reduced, and the green molded body is deformed in the degreasing step by heating. It is easy to occur. In addition, the amount of carbon remaining after degreasing of the green compact increases, and a sintered compact of good quality cannot be obtained. Further, when the proportion of the polyacetal skeleton exceeds 95% by weight, the amount of decomposition gas of the polyacetal resin generated in the degreasing step by heating the green molded body increases, and cracks and blisters occur in the molded body in the degreasing step. It will be easier. Further, since the compatibility with other binders is greatly reduced, the strength of the green molded body is reduced and the green molded body becomes brittle.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the composition for producing a sintered molded article of the present invention, the polyacetal resin constituting the base of the polyolefin-based polymer-modified polyacetal resin, which is an essential binder component, is an oxymethylene group (—CH ₂
Any polymer compound having O-) as a main structural unit may be used, and any of a polyoxymethylene homopolymer, a copolymer containing other structural units in addition to oxymethylene, a terpolymer, and a block copolymer can be used. The molecule may have not only a linear shape but also a branched or crosslinked structure. Examples of the comonomer serving as the other structural unit include ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolan, and dioxepane. Is done.

The polyolefin polymer used for modifying the polyacetal resin is a homopolymer of α-olefin such as ethylene, propylene, butene, hexene, octene, nonene, decene, dodecene, or a mixture of two or more of these. Random, block, or graft copolymers, or conjugates thereof, such as non-conjugated dienes such as 1,4-hexadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 2,5-norbonadiene, butadiene, isoprene, and piperylene; Diene components, α, β-unsaturated acids such as acrylic acid and methacrylic acid or derivatives thereof such as esters, acrylonitrile, styrene,
A random or block comprising at least one of comonomer components such as aromatic vinyl compounds such as α-methylstyrene, or vinyl esters such as vinyl acetate, vinyl ethers such as vinyl methyl ether, and derivatives of these vinyl compounds. Or a graft copolymer. Depending on the method for modifying the polyacetal resin, these polyolefin polymers can be modified in advance with an acid anhydride or modified with a polyfunctional compound such as a polyfunctional isocyanate compound or a polyfunctional epoxy compound. The above-mentioned monomer component may be used in the form of a monomer or an oligomer thereof, and the polymerization and the modification of the polyacetal resin may be carried out in the step of producing the modified polyacetal resin. The method for producing the polyolefin-based polymer-modified polyacetal resin used in the present invention is not particularly limited, and examples thereof include the following method.

(1) Formaldehyde or trioxane is homopolymerized in the presence of a polyolefin polymer having a functional group such as a hydroxyl group, a carboxyl group, an acid anhydride group, an amino group or an epoxy group, or formaldehyde or trioxane is cyclically polymerized. A method of copolymerizing an ether or a cyclic formal, (2) a method of melting and heating a polyacetal resin and a polyolefin polymer together with a polyfunctional compound such as a polyisocyanate compound in the presence or absence of a catalyst, (3 A) a method in which a polyacetal resin or a polyolefin-based polymer is reacted with a polyfunctional compound in advance, and this and the other resin component are melt-heated in the presence or absence of a catalyst. the above
In the methods (2) and (3), it is preferable to use a hydroxyl-rich polyacetal resin as the polyacetal resin. As the polyolefin polymer, it is preferable to use a polyolefin polymer modified with an acid anhydride, or a polyolefin polymer having an active hydrogen species such as a hydroxyl group, a carboxyl group, or an amino group. Depending on the method for producing these polyolefin-based modified polyacetal resins, an unreacted polyacetal resin and / or an unreacted polyolefin-based polymer coexist with the modified polyacetal resin as a reaction product, and are substantially compatible or uniformly dispersed. In the form of a modified composition. In such a case, the whole composition can be handled as the modified polyacetal resin used in the present invention.

In the composition for producing a sintered compact of the present invention, the ratio of the polyacetal skeleton in the modified polyacetal resin is preferably from 10 to 95% by weight, particularly preferably from 20 to 80% by weight. All binders 100
The ratio of the modified polyacetal resin in the volume% is 10 to 95.
% By volume, preferably 15 to 80% by volume, particularly preferably 20 to 70% by volume, and the remainder is other binders.

The other binder is specifically one or more organic substances such as a thermoplastic resin, a wax, a plasticizer, and a lubricant.

As the thermoplastic resin, for example, acrylic resin, polyethylene, polypropylene, polystyrene,
Examples include an ethylene-vinyl acetate copolymer and polyvinyl butyral. Examples of the waxes include, for example, paraffin wax, polyethylene wax, carbana wax, polyethylene glycol, beeswax, wood wax, synthetic wasks, and the like. Further, examples of the plasticizer include phthalic acid compounds such as dioctyl phthalate, dibutyl phthalate, and diethyl phthalate. Furthermore, examples of the lubricant include fatty acid esters such as stearic acid esters and derivatives thereof.

[0018] The composition for producing a sintered compact of the present invention containing a sinterable powder, a modified polyacetal resin binder and other binders is characterized in that the type of the sinterable powder such as ceramics, metal and cermet to be used is determined. Although it depends on the type of the other binder, the total amount of the binder is usually 20 to 60% by volume, preferably 25 to 55% by volume in 100% by volume of the composition for producing a sintered compact.
Particularly preferably, the content is 30 to 50% by volume. The blending method and the blending order are not particularly limited, but they are usually blended together.

The composition for producing a sintered compact of the present invention is a raw material for molding a green compact which is a preform of the sintered compact by injection molding. After molding a green molded body by injection molding a molding raw material obtained by heating and kneading the material, the green molded body is subjected to a degreasing step by heating, and the molded body after the degreasing is further sintered to obtain an object. To obtain a sintered compact.

[0020]

EXAMPLES Hereinafter, more specific components of the composition for producing a sintered compact according to the present invention having the above-described structure will be described based on Examples, but the present invention is not limited thereto.

Example 1 <Preparation of Modified Polyacetal Resin> 99 parts by weight of a polyacetal resin and 1 part by weight of isophorone diisocyanate were used.
After melt-kneading at 190 ° C. in the presence of zinc stearate to obtain an isocyanate-modified polyacetal resin,
To this, 20 parts by weight of maleic anhydride-modified polyethylene was added and further melt-kneaded at 190 ° C. to obtain a polyethylene-modified polyacetal resin.

<Production and Evaluation of Sintered Molded Product> SUS316L (average particle size: 10 μm) powder as a sinterable powder, and the above-mentioned modified polyacetal resin / low density polyethylene / paraffin wax = 40 /
Using a 10/50 (vol%) mixture, SUS316L
A mixture of 60% by volume of powder and 40% by volume of the binder is kneaded with a pressure kneader at 160 ° C. for 40 minutes, and the kneaded material is cooled and crushed to obtain a composition for producing a sintered compact ( Injection molding raw material) was prepared. Next, using this injection molding material, a molding temperature of 140
Injection molding was performed at ~ 180 ° C to obtain a green molded body having a dumbbell test piece shape shown in Fig. 1. The moldability was extremely good. After holding the green molded body as shown in FIG. 2 and increasing the temperature to 120 ° C. over 2 hours, the temperature was increased to 320 ° C. at a rate of 30 ° C./hour, and further to 320 ° C. for 2 hours. Degreasing was performed by maintaining heating conditions. When the amount of deformation at the center of the dumbbell test piece after degreasing was measured, the deformation was only 0.2%.
mm. After degreasing, the resultant was further sintered in air at 1320 ° C. for 2 hours to obtain a sintered compact. The sintered compact obtained here had good appearance without cracking or swelling, and the amount of carbon remaining in the sintered compact was 80 p.
pm, which was a range without any problem.

(Comparative Example 1) A sintered compact was produced in the same manner as in Example 1 except that the unmodified polyacetal resin was used instead of the modified polyacetal resin in Example 1, but the moldability was extremely poor. However, it was not possible to obtain a green molded body that could withstand subsequent heat degreasing and sintering.

(Comparative Example 2) The modified polyacetal resin in Example 1 was reduced to 5% by volume (in all binders), and the low-density polyethylene was increased by an amount corresponding to this. Manufacture and evaluation of the compact were performed. In this case, the moldability was good, but the amount of deformation after degreasing was as large as 3.8 mm, and the amount of carbon remaining in the sintered compact was as large as 1100 ppm.

(Example 2) <Preparation of modified polyacetal resin> Trioxane (20 parts by weight) and ethylene-vinyl acetate copolymer (50 parts by weight) were dissolved in benzene, and then dioxolane (2 parts by weight) was added. A graft copolymerization reaction was carried out at 60 ° C. for 15 hours using the catalyst as a catalyst.
By drying, a prepolymer for producing a modified polyacetal resin was obtained. 6.5 parts by weight of this prepolymer, 92 parts by weight of trioxane, and 1.5 parts by weight of dioxolane were subjected to a graft copolymerization reaction at 60 ° C. for 15 minutes using boron trifluoride ethyl ether as a catalyst. Then, a modified polyacetal resin having an ethylene-vinyl acetate copolymer content of 12% by weight was obtained by removing the unstable portion by heating.

<Production and evaluation of sintered compact> A sintered compact was produced using this modified polyacetal resin in the same manner as in Example 1, and the same good results as in Example 1 were obtained. The amount of deformation after degreasing was 0.3 mm, and the amount of carbon remaining in the sintered compact was 90 ppm, all of which were good.

[0027]

The composition for producing a sintered molded article of the present invention comprises a resin binder composed of a polyolefin-based polymer-modified polyacetal resin in an amount of 10 to 95% by volume of the total binder.
Is blended in the ratio of

Therefore, according to the composition for producing a sintered compact of the present invention having the above structure, the effect obtained by using a modified polyacetal resin having a polyacetal skeleton, which is a depolymerization type polymer, as a binder, that is, a polyacetal resin Excellent in shape retention of the green molded body based on the rigidity provided and in shape retention of the molded body in the degreasing step by heating, and also because the residue does not remain after degreasing by heating, the molded body in the degreasing step is cracked. No defects such as swelling, deformation and the like are generated, and the degreasing step by heating is faster, so that the production efficiency can be improved. Further, according to the composition for producing a sintered molded article of the present invention, the polyolefin polymer skeleton constituting the modified polyacetal resin in the composition for producing a sintered molded article has a favorable property with respect to many other organic components. Since it has compatibility, it has good affinity between the polyolefin-based polymer skeleton and other thermoplastic resins, waxes, lubricants, etc. constituting the binder, so that homogeneous sintering without layer separation is possible. A form is obtained.

[Brief description of the drawings]

FIG. 1 shows the shape of a dumbbell test piece formed from a green molded body.

FIG. 2 shows a measurement position of a deformation amount after degreasing of a green molded body having a dumbbell test piece shape.

Claims (2)

(57) [Claims] 1. A composition for producing a sintered compact containing a sinterable powder and a binder, wherein a polyolefin-based polymer-modified polyacetal resin is contained in all the binders.
A composition for producing a sintered molded product, wherein the composition is blended at a ratio of up to 95% by volume. 2. The ratio of the polyacetal skeleton and the polyolefin-based polymer skeleton in the polyolefin-based polymer-modified polyacetal resin is in the range of 10 to 95% by weight: 90 to 5% by weight (total 100% by weight of both). The composition for producing a sintered compact according to claim 1.