KR100434648B1 - Composition for producing sintered compact - Google Patents

Abstract

It is possible to complete the degreasing process of the green compacted body by heating for a short time and to obtain a homogeneous sintered compacted body which does not cause defects such as cracks, expansion and deformation in the compacted body during the degreasing process, Which is a composition for producing a sintered compact.

The composition for producing a sintered compact according to the present invention is a composition for producing a sintered compact containing a sinterable powder and a binder, wherein the binder is composed of a polyacetal resin (A), a modified polyolefin resin (B) and other binder component (C) (A) is in a range of 5 to 60% by volume, the modified polyolefin resin (B) is in a range of 5 to 85% by volume, the ratio of the polyacetal resin (A) and the modified polyolefin resin (B) is in the range of 10 to 90% by volume.

Description

Composition for producing sintered compact

Precise sintered compacts or sintered compacts having complicated shapes are generally manufactured by the following method using sinterable powder. That is, first, the sinterable powder and the binder are heated and kneaded and then cooled to form the molding material into particles. Subsequently, this is injection-molded to prepare a green compact, and the green compact is sintered in accordance with the degreasing process.

Among them, the degreasing process is performed for the purpose of removing the binder in the green compact. In addition, it is the most important process for producing a sintered formed article having good quality without defects such as cracking, expansion, deformation and the like.

The degreasing process includes a heating degreasing method in which a green compact is heated to decompose and gasify it by heating the green compact, a method in which the green compact is subjected to a solvent treatment to dissolve and remove the soluble binder component, and then the remaining binder is heated and decomposed to be gasified and removed .

However, in the heating degreasing method, if the decomposition gas of the binder is diverged from the surface of the green compact, or the binder is exuded to vaporize, the thermal decomposition and gasification of the binder in the green compact are concentrated in a short time, The gas generated by the heat decomposition in the central portion can not smoothly move to the surface, and pressure is applied to the inside of the formed body, so that cracks and expansion may occur in the formed body. Therefore, rapid heating must be avoided, and degreasing must be carried out by heating for a long time under a temperature condition in which such a problem does not occur.

Particularly, when the sinterable powder contained in the composition for producing a sintered compact has a small particle size and a large surface area, it is necessary to increase the blending amount of the binder so that the heating fluidity of the molding material at the time of producing the green compact is stabilized . Therefore, in the degreasing step in the case of using such a three-dimensional composition for producing a sintered formed article, it is necessary to devise a multistage heating step in order to remove a binder contained in a large amount.

Even if the sinterable powder contained in the sintered compact forming composition is a metal powder or a spherical powder having a high specific gravity, even if it is not likely to cause cracking or expansion during the degreasing step by heating, There are many cases where deformation occurs. Therefore, even in such a case, it is necessary to slow down the heating rate at the time of degreasing.

Therefore, in order to facilitate the removal of the binder, there is a method of adding a sublimable substance to the binder. However, the addition of the sublimable material means that the sublimable material sublimates during kneading of the molding material at the time of manufacturing the green molding or during injection molding of the green molding, and a sprue & runner It is difficult to regenerate the negative portion.

On the other hand, in the method of dissolving and removing the binder component soluble in the solvent by solvent treatment of the green compact, and heating and decomposing the remaining binder component to remove it by gasification, voids are generated in the green compact by the solvent treatment, So that the thermal decomposition of the remaining binder and the gasification are smoothly performed. Thus, cracking, expansion, deformation, and the like of the green compact in the degreasing step can be avoided.

However, since currently used binders contain a large amount of liquid raw materials such as mineral oil, fatty acid oil, and natural oil, these oil components often seep out from the inside of the green compact. Particularly, the long-term preservation of the green molded body causes the oil component to penetrate more strongly. Therefore, cracking or expansion may occur during degreasing by solvent treatment due to the oil component permeating the surface of the green compact.

Further, there is a method of eluting a plasticizer or a lubricant in a binder by boiling water. However, there is a limit to increase the blending amount of the plasticizer and the lubricant in terms of maintaining the stability of the molding material for the green molding, maintaining the heating fluidity during injection molding of the molding material, and maintaining the strength of the green molding.

Further, there is a method of extracting the binder by water treatment using a binder composed of a water-soluble resin (Japanese Patent Publication No. 210101/1990). However, this method can not be applied to ceramics powders or metal powders having a property of reacting with water or corroding.

Further, there is a method of using a polyacetal resin, which is a depolymerization type polymer, alone or in combination with another polymer as a binder (JP-A-4-247802 and JP-A-5-98306). This is because the stiffness of the polyacetal resin is used to enhance the shape retaining property of the green molded body and the shape retaining property in the heated degreasing step and at the same time, by using the depolymerization characteristic, Thereby accelerating the heating degreasing process to increase the production efficiency.

However, the polyacetal resin is chemically stable and has poor compatibility with many other organic components, for example, other resins constituting the binder, wax, lubricant and the like. Therefore, when a polyacetal resin is simply used as a binder component, a homogeneous sintered compact can not be obtained which easily separates from other binder components. Particularly, in order to improve the shape retention of the green compact, the shape retention of the formed body in the degreasing process by heating, and the heating degreasing efficiency, it is necessary to increase the blending ratio of the polyacetal resin in the entire binder, Or the lack of affinity of the polyacetal resin with respect to the lubricant or the like, the above-mentioned drawbacks are further exacerbated.

There is also a method in which a polyacetal resin is used as a binder and the polyacetal resin in the green compact is decomposed and degreased with an acidic catalyst to greatly shorten the degreasing time. However, since this method uses a strong acid such as nitric acid for the degreasing catalyst, the sinterable powder may be altered by oxidation or the like, and the kind of sinterable powder that can be used is greatly restricted.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a method for producing a green molded article by performing a degreasing step of a green molded body by heating for a short period of time and forming a molded article which does not cause cracking, And to provide a composition for producing a sintered compact capable of obtaining a sintered compact.

That is, the present invention relates to a composition for producing a sintered compact containing a sinterable powder and a binder, wherein the binder is composed of a polyacetal resin (A), a modified polyolefin resin (B) and other binder component (C) (A) in the range of 5 to 60% by volume, the modified polyolefin resin (B) in the range of 5 to 85% by volume, the total of the polyacetal resin (A) and the modified polyolefin resin (B) Is in the range of 10 to 90% by volume, based on the total weight of the sintered body. The present invention also provides a composition for producing the sintered compact, wherein the modified polyolefin resin (B) is a copolymer of an olefin and an unsaturated monomer having a glycidyl group. The modified polyolefin resin (B) is a copolymer obtained by polymerizing an olefin or a copolymer of an olefin and another unsaturated monomer as a base, and then subjecting the vinyl-based polymer to branching or crosslinking structural chemical bonding, To provide a composition. The present invention also provides a composition for producing the sintered compact, wherein the vinyl polymer is a polymer composed of one or more monomers selected from (meth) acrylic acid or its alkyl ester, acrylonitrile, and styrene. The modified polyolefin resin (B) is obtained by copolymerizing an acrylonitrile-styrene copolymer, polymethyl methacrylate or polystyrene with a polyethylene, polypropylene or ethylene-glycidyl methacrylate copolymer, And to provide a composition for manufacture. The present invention also provides a composition for producing the sintered compact, characterized in that the other binder component (C) is at least polyethylene or paraffin wax. In addition, the present invention provides a composition for producing a sintered compact, characterized in that the content of the binder in 100% by volume of the composition for producing a sintered compact is 20 to 60% by volume. Hereinafter, the present invention will be described in detail.

BEST MODE FOR CARRYING OUT THE INVENTION

The composition for producing a sintered compact according to the present invention comprises a sinterable powder and a binder. Examples of the sinterable powder that can be used in the composition for producing a sintered compact according to the present invention include ceramics, metal, and cermet.

The binder used in the composition for producing sintered compact of the present invention is composed of a polyacetal resin (A), a modified polyolefin resin (B) and other binder component (C). The polyacetal resin (A) is preferably contained in the binder in an amount of 5 to 60% by volume, preferably 10 to 50% by volume, more preferably 15 to 40% by volume.

When the content of the polyacetal resin (A) in the binder is less than 5% by volume, the heat distortion temperature of the green compact significantly decreases, and the molded body in the degreasing step due to heating tends to be deformed. Further, the amount of carbon remaining after degreasing the green compact increases, and it becomes impossible to obtain a sintered compact having a good quality. On the other hand, when the polyacetal resin (A) exceeds 60% by volume in the binder, the amount of decomposition gas of the polyacetal resin is increased in the degreasing process by heating the green compact, and cracks and expansion occur in the degreasing process It gets easier. In addition, the compatibility with other binder component (C) is greatly lowered, so that the strength of the green molded article is lowered and may be weakened.

As the polyacetal resin (A) constituting the binder used in the present invention, any polymeric compound having an oxymethylene group (-CH ₂ O-) as its main constituent unit may be used, and other structural units other than polyoxymethylene homopolymer and oxymethylene , A terpolymer, and a block copolymer, each of which may be used. The molecule may be not only linear but also branched or crosslinked. Examples of the comonomer to be the other constituent unit include ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, Soran, dioxepan, and the like.

The binder used in the composition for producing a sintered compact of the present invention preferably contains 5 to 85% by volume, more preferably 10 to 70% by volume, particularly 15 to 60% by weight of the modified polyolefin resin (B) in the binder. When the ratio in the binder is less than 5% by volume, the compatibility of the polyacetal resin (A) with the other binder component (C) remarkably decreases, so that it becomes difficult to obtain a good green compact, Cracks or swelling may occur. When the amount of the modified polyolefin resin (B) exceeds 85% by volume in the binder, the amount of the polyacetal resin (A) is inevitably limited. As a result, It may cause deformation and an increase in the amount of residual carbon after degreasing.

The content of the polyacetal resin (A) and the modified polyolefin resin (B) in the binder is preferably 10 to 90% by volume, more preferably 15 to 80% by volume, particularly 20 to 70% by volume desirable. And the other is the other binder component (C). When the total content is less than 10% by volume in the binder, the molded article is liable to be deformed during the heating step by heating. When the content exceeds 90% by volume, the fluidity of the composition is lowered, Can not be performed smoothly.

The modified polyolefin resin (B) is an olefin polymer modified by introduction of an aromatic group or a polar group, and examples thereof include various polymers obtained by copolymerization or graft copolymerization as described below.

(1) a copolymer of an olefin (and a copolymerizable monomer thereof) with an unsaturated compound having a glycidyl group, for example, a glycidyl ester of an?,? - unsaturated acid such as glycidyl methacrylate, For example, an ethylene-glycidyl methacrylate copolymer,

(2) A vinyl polymer such as a copolymer mainly composed of polymethyl methacrylate, polystyrene or polystyrene is added to an olefin polymer such as polyethylene, polypropylene or ethylene-propylene copolymer in a branched or crosslinked structure, , ≪ / RTI &

(3) a copolymer of an alpha -olefin and an unsaturated compound, for example, a glycidyl ester of an alpha, beta -unsaturated acid, with other monomers copolymerizable with the polymer, such as acrylonitrile, styrene, (Co) polymers composed of one or more monomers such as methyl acrylate, methyl methacrylate, methyl methacrylate and methacrylate, or monomers thereof, such as polymethyl methacrylate, polystyrene, polyacrylonitrile, acrylonitrile -Styrene copolymer or the like by graft polymerization or the like, for example, by graft polymerization of an acrylonitrile-styrene copolymer, polymethyl methacrylate, polystyrene or the like to an ethylene-glycidyl methacrylate copolymer However,

(4) olefin copolymers, copolymers of olefins, olefins and other vinyl-based monomers, such as olefin copolymerized with a diene compound, a derivative such as an?,? - unsaturated acid or ester thereof, or a vinyl compound A hydroxyl group-modified olefin polymer obtained by reacting an olefinic polymer composed of a copolymer or the like with an unsaturated compound having a hydroxyl group,

(5) Copolymers mainly composed of olefins obtained by copolymerizing olefin homopolymers, olefin copolymers, olefins and other vinyl monomers such as diene compounds,?,? - unsaturated acids or esters thereof, Unsaturated carboxylic acids or their derivatives such as unsaturated dicarboxylic acids such as maleic acid and fumaric acid or their anhydrides, unsaturated carboxylic acids such as acrylic acid or methacrylic acid or their esters are graft polymerized Or the like,

(6) Copolymers in which an olefin polymer and an ether polymer such as polyethylene oxide, polypropylene oxide and the like are branched or crosslinked structurally and chemically bonded,

(7) An epoxy-modified olefin-based polymer obtained by heating an olefin-based polymer and an epoxy group-containing monomer such as glycidyl methacrylate in the presence of a radical initiator,

(8) an olefin-based polymer modified with an isocyanate group-containing monomer.

The modified polyolefin resin used in the present invention is particularly preferably those exemplified as the above-mentioned (1), (2) and (3).

The binder used in the composition for producing a sintered compact according to the present invention is preferably a thermoplastic resin other than the polyacetal resin (A) and the modified polyolefin resin (B), a wax, a plasticizer or a lubricant as the other binder component (C) Organic materials can be used.

Examples of the thermoplastic resin include acrylic resin, polyethylene, polypropylene, polystyrene, polyvinyl butyral, and the like.

Examples of waxes include paraffin wax, polyethylene wax, calbana wax, polyethylene glycol, beeswax, wood wax, synthetic wax, and the like.

Examples of the plasticizer include phthalic acid compounds such as dioctyl phthalate, dibutyl phthalate and diethyl phthalate.

Examples of lubricants include fatty acid esters such as stearic acid esters and derivatives thereof.

Preferable examples of the other binder component (C) include waxes such as thermoplastic resins other than the polyacetal resin (A) and the modified polyolefin resin (B), paraffin wax, polyethylene wax and polyethylene glycol. Particularly preferred are polyethylene, Wax, and polyethylene glycol. In the present invention, the above components may be used singly or in combination of two or more kinds. In this case, at least one of them is preferably polyethylene or paraffin wax.

The composition for preparing a sintered compact according to the present invention preferably contains 20 to 60% by volume, preferably 25 to 55% by volume, particularly 30 to 50% by volume of the binder in 100% by volume of the composition for producing a sintered compact. The blending ratio of each component constituting the binder can be appropriately selected depending on the kind of sinterable powder such as ceramics, metal, and cermet to be used.

In the preparation of the composition for producing a sintered compact according to the present invention, there is no particular limitation on the order of compounding each constituent component. For example, the polyacetal resin (A) and the modified polyolefin resin (B) as the binder component may be mixed in advance or may be melt-kneaded. Alternatively, the binder component may be mixed and kneaded in advance Maybe.

The composition for producing a sintered compact according to the present invention is a molding material for injection molding a green compact as a preform of a sintered compact. The composition for producing a sintered compact is heated and kneaded and cooled to form particles, which are used as a molding material for a green compact. The green compact is injection-molded by injection molding the material for molding, and then the green compact is degreased by heating or the like, and then the degreased compact is sintered to obtain the intended sintered compact.

By using the composition for producing a sintered compact of the present invention, it is possible to produce a precise sintered compact such as a clock part, an industrial machine part, a medical appliance, an automobile part, or the like, or a sintered compact having a complicated shape.

The present invention relates to a composition for producing a sintered compact.

FIG. 1 is a view showing a dumbbell specimen shape in which a green compact is molded, and FIG. 2 is a view showing a measurement position of deformation amount after degreasing of a green compact having a dumbbell specimen shape.

Hereinafter, the composition for producing a sintered formed article of the present invention will be described with reference to examples, but the present invention is not limited thereto.

(Examples 1 to 8 and Comparative Examples 1 to 5)

≪ Preparation of composition for producing sintered compact &

SUS316L having an average particle diameter of 10 mu m was used as sinterable powder, and the polyacetal resin (A) as the binder component, the modified polyolefin resin (B) as shown in Table-1 and the other binder component (C) -3, thereby preparing a composition for producing a sintered compact.

≪ Production of green compacts &

The compounding compositions of Examples 1 to 8 and Comparative Examples 1 to 5 were kneaded at 160 DEG C for 40 minutes by a pressurized kneader and then the kneaded material was cooled and crushed to obtain a molding material which was molded at a temperature of 140 to 180 DEG C To obtain a green compact having a dumb-bell specimen shape as shown in Fig.

<Tingji process>

Each green compact was heated to 120 DEG C over 2 hours, then heated to 320 DEG C at a temperature elevation rate of 30 DEG C / hour, and then subjected to a tempering process under a heating condition of holding at 320 DEG C for 2 hours.

<Sintering Process>

The formed body after completion of the tempering process was sintered at 1320 占 폚 for 2 hours under sintering conditions to obtain a sintered compact.

<Evaluation>

The following items were observed in each step. In all items, the superiority was evaluated by ○ (right), Δ (middle), × (heat), and quantitative measurement was made as much as possible. The results are shown in Tables 2 and 3.

(1) Molded article: The ease of molding in the production of the green molded article and the properties of the obtained green molded article (in particular, the uniformity of the molded article) were relatively evaluated.

(2) Deformation amount after degreasing: The amount of deformation of the central portion of the dumbbell specimen after heating and degreasing was maintained by holding the green compact of the dumbbell specimen shape as shown in Fig.

(3) Characteristics of sintered body: The occurrence of cracking and expansion after sintering was observed and evaluated.

(4) Residual carbon in the sintered product: The amount of carbon remaining in the sintered product after sintering was measured.

The composition for producing a sintered compact according to the present invention uses a polyacetal resin which is a depolymerized polymer as a binder. The green compact formed from the composition for producing a sintered compact according to the present invention is excellent in shape retentivity based on the rigidity of the polyacetal resin and excellent in shape retention in the degreasing step by heating and has a degreasing process Can be shortened. On top of that, the composition for producing a sintered compact of the present invention contains a modified polyolefin resin as a binder, which exhibits good compatibility with other binder components, so that a homogeneous sintered compact without layer separation can be obtained. That is, when the composition for producing a sintered compact of the present invention is used, it is possible to complete the degreasing process of the green compact by heating for a short period of time, without causing defects such as cracking, expansion and deformation in the degreasing process, , A homogeneous sintered compact without layer separation can be obtained.

Claims (6)

A composition for producing a sintered compact containing a sinterable powder and a binder, wherein the binder is composed of a polyacetal resin (A), a modified polyolefin resin (B) and other binder component (C) The binder component (C) is at least polyethylene or paraffin wax, (A) in the range of 5 to 60% by volume, the modified polyolefin resin (B) in the range of 5 to 85% by volume, the ratio of the polyacetal resin (A) and the modified polyolefin resin B) is in the range of 10 to 90% by volume. The composition for producing a sintered compact according to claim 1, wherein the modified polyolefin resin (B) is a copolymer of an olefin and an unsaturated monomer having a glycidyl group. The polyolefin resin composition according to claim 1, wherein the modified polyolefin resin (B) is a copolymer of an olefin polymer or an olefin with an unsaturated monomer other than the olefin polymer, and the vinyl polymer is branched or cross- Wherein the copolymer is chemically bonded structurally. The sintered compact according to claim 3, wherein the vinyl-based polymer is a polymer comprising one or more monomers selected from (meth) acrylic acid or its alkyl ester, acrylonitrile, and styrene. The thermoplastic resin composition according to claim 3, wherein the modified polyolefin resin (B) is a copolymer obtained by copolymerizing an acrylonitrile-styrene copolymer, polymethyl methacrylate or polystyrene with polyethylene, polypropylene or ethylene-glycidyl methacrylate copolymer By weight. The sintered compact forming composition according to any one of claims 1 to 5, wherein the binder content in 100% by volume of the composition for producing a sintered compact is 20 to 60% by volume.

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