JP3113806B2 - 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 a composition for producing a sintered compact containing a sinterable powder and a binder, the binder is a polyacetal resin (A), a modified polyolefin resin (B), and another binder (C). And the proportion of the polyacetal resin (A) in the range of 5 to 60% by volume, and the proportion of the modified polyolefin resin (B) in the range of 5 to 85% by volume based on the whole binder
Wherein the total ratio of the polyacetal resin (A) and the modified polyolefin resin (B) satisfies the range ratio of 10 to 90% by volume, respectively. You. Further, according to the present invention, there is provided the composition for producing a sintered molded article, wherein the modified polyolefin resin is a copolymer of an olefin and an unsaturated monomer having a glycidyl group. According to the present invention, the modified polyolefin resin is based on a polymer of an olefin or a copolymer of an olefin and another unsaturated monomer, and a vinyl polymer is chemically bonded to the branched or crosslinked structure. The composition for producing a sintered molded article, which is a copolymer, is provided. According to the present invention, the vinyl-based polymer is a polymer comprising one or more monomers selected from (meth) acrylic acid or an alkyl ester thereof, acrylonitrile, and styrene. A composition is provided. According to the present invention,
The composition for producing a sintered molded article, wherein the modified polyolefin resin is obtained by copolymerizing polyethylene, polypropylene or ethylene-glycidyl methacrylate copolymer with acrylonitrile styrene copolymer, polymethyl methacrylate or polystyrene. . Hereinafter, the present invention will be described in detail.

[0010] In a composition for producing a sintered compact, comprising a sinterable powder and a binder comprising a polyacetal resin (A), a modified polyolefin resin (B) and another binder (C), the composition comprises a polyacetal resin (A); When the total amount of the modified polyolefin resin (B) is less than 10% by volume in the binder, the molded article in the degreasing step by heating is easily deformed, and when it exceeds 90% by volume, the fluidity of the composition decreases. However, it is not possible to smoothly perform injection molding when molding a green molded body.

When the content of the polyacetal resin (A) to be blended as a binder is less than 5% by volume relative to the total amount of the binder, the thermal deformation temperature of the green molded body is greatly reduced, and the green molded body is deformed into a molded body in a degreasing step by heating. Is more likely 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 polyacetal resin (A) is more than 60% by volume, the amount of decomposition gas of the polyacetal resin generated in the degreasing step by heating the green molded body increases, and the molded body in the degreasing step cracks or swells. 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. If the modified polyolefin resin (B) to be blended as a binder is less than 5% by volume relative to the entire binder, the compatibility between the polyacetal resin (A) and the other binder (C) is significantly reduced,
It becomes difficult to obtain a good green molded body, which also causes cracking and swelling in the heating degreasing step. Further, when the modified polyolefin resin (B) exceeds 85% by volume, the amount of the polyacetal resin (A) is inevitably restricted, and the molding in the degreasing step accompanying the lowering of the thermal deformation temperature of the green molded body as described above. This causes deformation of the body and an increase in the amount of residual carbon after degreasing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the composition for producing a sintered molded article of the present invention, the polyacetal resin (A) constituting the binder is a polymer compound having an oxymethylene group (—CH ₂ O—) as a main constituent unit. Any copolymers, terpolymers and block copolymers containing other structural units besides polyoxymethylene homopolymer and oxymethylene 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,
Examples thereof include 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolan, and dioxepane.

The modified polyolefin resin (B) constituting the binder is an olefin polymer modified by the introduction of an aromatic group or a polar group, such as copolymerization and graft copolymerization as described below. Various polymers obtained by the above are exemplified.

(1) A copolymer of an olefin (and a monomer copolymerizable therewith) with an unsaturated compound having a glycidyl group, for example, a glycidyl ester of an α, β-unsaturated acid such as glycidyl methacrylate. Ethylene-
Glycidyl methacrylate copolymer, (2) polyethylene, polypropylene, olefin polymer such as ethylene-propylene copolymer, vinyl polymer, for example, polymethyl methacrylate, polystyrene or polystyrene-based copolymer and the like, branched. Or a copolymer chemically bonded in a cross-linked structure, (3) a copolymer of an α-olefin and an unsaturated compound, for example, a glycidyl ester of an α, β-unsaturated acid, and Other possible monomers, such as one or more monomers such as acrylonitrile, styrene, methyl methacrylate, methyl acrylate, methacrylic acid, or vinyl (co) polymers composed of these monomers, such as polymethyl methacrylate, polystyrene , Polyacrylonitrile, acrylonitrile-
Those obtained by copolymerizing a styrene copolymer or the like by graft polymerization or the like, for example, those obtained by graft-polymerizing an ethylene-glycidyl methacrylate copolymer with an acrylonitrile-styrene copolymer, polymethyl methacrylate, polystyrene, etc., (4) olefin Of olefins, copolymers of olefins, olefins and other vinyl monomers such as diene compounds, derivatives such as α, β-unsaturated acids or esters thereof, or olefins copolymerized with vinyl compounds. For an olefin polymer composed of a copolymer or the like, a hydroxyl-modified olefin polymer obtained by reacting an unsaturated compound having a hydroxyl group, (5) an olefin homopolymer, an olefin copolymer, an olefin Other vinyl monomers such as diene compounds, α, β-unsaturated acids or esters thereof Olefin-based copolymers such as copolymers mainly composed of olefins copolymerized with derivatives of the same, and unsaturated carboxylic acids or derivatives thereof, for example, maleic acid, unsaturated dicarboxylic acids such as fumaric acid or anhydrides thereof. Product, acrylic acid, or those obtained by copolymerizing an unsaturated carboxylic acid such as methacrylic acid or an ester thereof by graft polymerization or the like, (6) an olefin polymer, and an ether polymer, for example, polyethylene oxide,
(7) An olefin polymer and an epoxy group-containing monomer such as glycidyl methacrylate and glycidyl acrylate are heated in the presence of a radical initiator. And (8) an olefin polymer modified with an isocyanate group-containing monomer. As the modified polyolefin resin used in the present invention, the above (1), (2) and
Those exemplified as (3) are preferred.

In the composition for producing a sintered compact of the present invention, the polyacetal resin (A) based on the entire binder
Is 5 to 60% by volume for the above reason, preferably 10 to 50% by volume, particularly preferably 15 to 40% by volume. The proportion of the modified polyolefin resin (B) is 5 to 85% by volume, preferably 10 to 70% by volume, particularly preferably 15 to 60% by volume. The ratio of the total amount of the polyacetal resin (A) and the modified polyolefin resin (B) in 100% by volume of the total binder is 10 to 10%.
90% by volume, preferably 15-80% by volume, particularly preferably 20-70% by volume, the remainder being other binders.

The other binder (C) is specifically one or more organic substances such as thermoplastic resins, waxes, plasticizers, and lubricants.

As the thermoplastic resin, for example, acrylic resin, polyethylene, polypropylene, polystyrene,
Polyvinyl butyral and the like. Examples of waxes include paraffin wax, polyethylene wax, carbana wax, polyethylene glycol,
Beeswax, wood wax, synthetic wasks and the like. Furthermore,
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.

The composition for producing a sintered compact of the present invention, comprising a sinterable powder and a binder comprising a polyacetal resin (A), a modified polyolefin resin (B) and another binder (C), comprises a ceramic used in the present invention. , Metal, cermet, etc., and the type of sinterable powder, and the type of other binders. In 100% by volume of the composition for producing a sintered compact, the total amount of the binders is usually 20 to 60% by volume, preferably Is 25-55% by volume,
Particularly preferably, the content is 30 to 50% by volume. The compounding method and the compounding order are not particularly limited, but the polyacetal resin (A) and the modified polyolefin resin (B), which are binder components, can be mixed in advance or melt-kneaded and used. Without kneading, it can be combined with other components at once.

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.

(Examples 1 to 8 and Comparative Examples 1 to 5) <Preparation of composition for producing sintered compact> Powder of SUS316L (average particle size 10 μm) was used as a sinterable powder.
Table 1 shows the polyacetal resin (A), the modified polyolefin resin (B) shown in Table 1, and other binder components.
2 and Table 3 to prepare a composition for producing a sintered compact.

<Molding of Green Formed Body> The compounded compositions of Examples 1 to 8 and Comparative Examples 1 to 5 were kneaded by a pressure kneader at 160 ° C. for 40 minutes, and then the kneaded material was cooled and crushed to obtain a mixture. Injection molding raw material, molding temperature 140 ~
Molding was performed at 180 ° C. to obtain a green molded body having a dumbbell test piece shape shown in FIG.

<Degreasing Step> Next, each of these green compacts was heated to 120 ° C. over 2 hours, and then heated at 30 ° C. /
The temperature was raised to 320 ° C. at a rate of
It was subjected to a degreasing step under heating conditions maintained at 2 ° C. for 2 hours.

<Sintering Step> The compact having undergone the degreasing step was sintered at 1320 ° C. under sintering conditions for 2 hours to obtain a sintered compact.

<Evaluation> The following evaluation was performed in each of the above steps for obtaining a sintered compact. In each of the evaluation items, superiority was evaluated as ○ (excellent), Δ (intermediate), ×
In addition to the evaluation of (poor), what was possible was quantitatively measured. The measurement results are shown in Tables 2 and 3. (1) Moldability: The ease of molding in molding a green molded article and the properties of the obtained green molded article (particularly, the uniformity of the molded article) were relatively evaluated. (2) Deformation amount after degreasing: After holding the green molded body in the shape of a dumbbell test piece as shown in FIG. (3) Properties of sintered body: The state of occurrence of cracks and blisters 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.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

The composition for producing a sintered compact of the present invention has a polyacetal resin (A) content of 5 to 60% by volume and a modified polyolefin resin (B) content of 5 to 85% by volume, based on the total binder. The total is in the range of 10 to 90% by volume.

Therefore, according to the composition for producing a sintered compact of the present invention having the above-described structure, the effect obtained by using the polyacetal resin, which is a depolymerized polymer, as a binder, that is, the rigidity of the polyacetal resin is improved. It is excellent in the shape retention of the green molded body based on and the shape retention of the molded body in the degreasing step by heating, and also because the residue does not remain after degreasing by heating, cracks, swelling, deformation, etc. And the production efficiency can be improved since the degreasing step by heating is quicker. Also,
According to the composition for producing a sintered molded article of the present invention, since the modified polyolefin resin in the composition for producing a sintered molded article has good compatibility with many other organic components, For example, other resins, wax,
Since the affinity between the lubricant and the like and the modified polyolefin resin is good, a homogeneous sintered molded article without layer separation can be 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.

Continuation of the front page (56) References JP-A-6-158107 (JP, A) JP-A-6-212053 (JP, A) JP-A-6-240106 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) B22F 3/02 C04B 35/632 C08L 23 / 26,51 / 06,59 / 00

Claims (5)

(57) [Claims] 1. A composition for producing a sintered compact comprising a sinterable powder and a binder, wherein the binder comprises a polyacetal resin (A), a modified polyolefin resin (B) and another binder (C). The ratio of the polyacetal resin (A) to the entire binder is 5 to 60% by volume, the modified polyolefin resin (B) is 5 to 85% by volume, the polyacetal resin (A) and the modified polyolefin resin (B). The composition for producing a sintered compact is characterized in that the composition is blended so that the total of the above ranges satisfies the respective proportions of 10 to 90% by volume. 2. The composition according to claim 1, wherein the modified polyolefin resin (B) is a copolymer of an olefin and an unsaturated monomer having a glycidyl group. 3. The modified polyolefin resin (B) is based on a polymer of an olefin or a copolymer of an olefin and another unsaturated monomer, to which a vinyl polymer is chemically or chemically bonded in a branched or crosslinked structure. The composition for producing a sintered molded article according to claim 1, which is a copolymer obtained. 4. The sintered compact according to claim 3, wherein the vinyl polymer is a polymer comprising one or more monomers selected from (meth) acrylic acid or an alkyl ester thereof, acrylonitrile, and styrene. Production composition. 5. The modified polyolefin resin (B) is obtained by copolymerizing polyethylene, polypropylene or ethylene-glycidyl methacrylate copolymer with acrylonitrile styrene copolymer, polymethyl methacrylate or polystyrene. A composition for producing a sintered molded article.