JP2001106581A - Composition for manufacturing sintered molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for manufacturing a sintered molding which improves the affinity between composition components, improves the brittleness of a green molding for manufacturing the sintered molding and is capable of yielding the homogeneous sintered molding which does not give rise to a defect in the sintered molding. SOLUTION: The composition consists of respective components; sinterable inorganic powder, more particularly the inorganic powder of <=1 micron in average grain size, a binder and a lubricant, in which the lubricant component has a melt viscosity of <=100 mPa.s at 120 deg.C and is incorporated into the composition at 10 to 30 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a composition for producing a sintered compact. More specifically, it is a composition for producing a sintered compact using a specific amount of a sinterable inorganic powder, a binder and a specific lubricant, and more specifically, improves the wettability of the binder and the lubricant to the powder. The present invention also relates to a composition for producing a sintered compact, which has improved brittleness of the green compact and defects of the sintered compact as much as possible. In particular, the present invention relates to a composition for producing a sintered compact, which has been conventionally regarded as difficult, and which enables the sintering of a fine powder having an average particle diameter of 1 μm or less.

[0002]

2. Description of the Related Art Conventionally manufactured sintered compacts use inorganic powders of ceramics, metals, cermets and the like which can be sintered and have a relatively large average particle size of about 10 μm. For precision sintering moldings and sintering moldings of complex shapes, the sintering molding composition containing a sinterable powder and a binder is heated and kneaded. After molding a green molded body by using a means, a method of subjecting the green molded body to a degreasing step and subsequently sintering the green molded body has been adopted. The binder referred to herein is a polyolefin-based polymer-modified polyacetal, a polyacetal resin, a modified polyolefin resin, and other thermoplastic resins (such as acrylic resin, polyethylene, polypropylene, polystyrene, and polyvinyl butyral).
Is a concept including a so-called lubricant used for molding a synthetic resin such as a resin or a resin mixture, a plasticizer such as dioctyl phthalate, a wax such as paraffin wax, and a stearic acid ester.

A sinterable powder and a binder are mixed, the binder is degreased after pressure molding, and the sintering of the powder is performed to form a sintered compact having good quality without defects such as cracks, swelling and deformation. The most important step for obtaining a molded article is a degreasing step. This degreasing step is a step of removing the binder from a green body obtained by using a molding raw material comprising a sinterable powder and a binder, most typically an injection molded body, A method in which the binder is thermally decomposed and gasified and removed by heating the green molded body, or a solvent-soluble component in the binder constituting the green molded body is eluted and removed by treating the green molded body with a solvent. For example, a method in which a residual binder is thermally decomposed and gasified is used.

In the thermal degreasing method of heating and degreasing the green compact, if the thermal decomposition and gasification of the binder in the green compact occur in a short period of time, the compact during the degreasing process will crack. Because of the presence of swelling and blistering, degreasing must be performed by heating for a long time. In particular, when the particle size of the powder to be sintered is small, that is, when the powder for sintering having a large specific surface area is used,
The amount of the binder must be increased so that the heating fluidity of the molding raw material when the green molded body is molded is stabilized, and a long heating step is required in the degreasing. 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. In many cases, the body is deformed, and in this case also, it is necessary to reduce the heating rate during degreasing.
For this reason, a method of adding a sublimable substance to the binder has been considered.However, the one added with the sublimable substance is used 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. Since the sublimable substance evaporates, it is difficult to regenerate the sprue / runner portion at the time of molding the green molded body.

On the other hand, by subjecting the green molded body to a solvent treatment, a part of the binder in the green molded body is eluted,
After the removal, in a degreasing method comprising a method of gasifying the remaining binder by heat decomposition, the solvent-soluble binder in the green molded body is removed by solvent treatment,
The voids created by this process become passages, and the thermal decomposition and gasification of the remaining binder by heating are performed smoothly. For this reason, cracking, swelling, deformation, and the like in the degreasing step of the green molded body may be able to be avoided. However, the use of a solvent causes deterioration of the working environment, and there are many problems such as extra equipment and labor required for safety and health measures.

Further, a method has been proposed in which a water-soluble resin in a green molded body is extracted by water treatment using a binder using 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.

[0007] The polyacetal resin, which is a depolymerized polymer, is used alone or together with another polymer as a binder to maintain the shape of a green molded article based on the rigidity of the polyacetal resin and to form the green accommodating resin in a degreasing step by heating. It is already known that it has excellent body shape retention properties, and that no residue remains after degreasing by heating, and that the degreasing step by heating is fast, so that the production efficiency can be improved. JP-A-2-145704, JP-A-4-247802, JP-A-5-983
No. 06 publication). For example, Japanese Patent Application Laid-Open No. 2-145704 describes, as a general description, that waxes can be used in a composition of metal powder and polyacetal, and that the metal powder has an average particle size of 0.01 to 50 μm. Is described.

On the other hand, in the case where the polyacetal resin is used as one component of the binder, the polyacetal resin is chemically stable but has poor compatibility with many other organic compound components. There is a problem that the affinity with the other components constituting the binder is low, and the binder is easily separated at a place where a shear force is applied, such as during injection molding, so that a homogeneous sintered compact may not be obtained. In particular, the above-mentioned effect of using a polyacetal resin as a binder, that is, improving the brittleness of the green molded body, improving the shape retention of the green molded body itself, and enhancing the shape retention of the molded body in the degreasing step by heating. In addition, in order to increase the heat degreasing efficiency, it is necessary to increase the blending ratio of the polyacetal resin in the entire binder, but the above-mentioned disadvantages due to insufficient affinity of the polyacetal resin for other components of the binder are further increased. The problem of being done increases.

Furthermore, 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 reducing the degreasing time is 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.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the affinity between the components of a composition, to improve the brittleness of a green compact for producing a sintered compact, and to reduce defects in the sintered compact. An object of the present invention is to provide a composition for producing a sintered compact which can obtain a homogeneous sintered compact which does not occur. It is particularly useful in a composition containing an inorganic powder having an average particle size of 1 μm or less.

[0011]

As a result of extensive studies on the above-mentioned problems, the present inventors have found that the above-mentioned composition can be achieved by the composition for producing a sintered compact of the present invention. The first invention is a composition comprising components of a sinterable inorganic powder, a binder and a lubricant, wherein the lubricant component comprises 1 component.
The present invention relates to a composition for producing a sintered compact, which has a melt viscosity at 20 ° C. of 100 mPa · s or less and is contained in the composition in an amount of 10 to 30% by volume. The second invention relates to the composition for producing a sintered compact according to the first invention, wherein the lubricant is a wax. In the third invention, the melting point of the wax is 40.
The present invention relates to the composition for producing a sintered compact according to the second invention, which has a temperature of from to 120 ° C. The fourth invention relates to the composition for producing a sintered compact according to the second or third invention, wherein the wax is an amide-based, ester-based or urethane-based modified wax. According to a fifth aspect of the present invention, there is provided the sintered compact according to any one of the first to fourth aspects, wherein the binder is mainly composed of a polyacetal resin and a modified polyolefin resin, and is contained in the composition in an amount of 10 to 30% by volume. Composition. A sixth invention is a modified polyolefin resin,
The present invention relates to the composition for producing a sintered compact according to the fifth aspect of the present invention, wherein the modifying component is a resin constituting at least a part of at least one of a main chain component and a side chain component of the polyolefin. A seventh aspect of the present invention is the composition for producing a sintered molded article according to the fifth aspect, wherein the modified polyolefin resin is a resin obtained by adding a modifying component to at least one of a main chain and a side chain of a polyolefin in a branched manner. About things. The eighth invention relates to the composition for producing a sintered compact according to the sixth or seventh invention, wherein the modifying component is a component having an aromatic group or a polar group. In a ninth aspect, the inorganic powder is at least one selected from metals and ceramics,
The present invention relates to the composition for producing a sintered compact according to any one of the first to eighth inventions, wherein the composition comprises 80% by volume. A tenth invention relates to the composition for producing a sintered compact according to any one of the first to ninth inventions, wherein the inorganic powder has an average particle size of 1 μm or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the contents of the present invention will be described in detail. The sinterable inorganic powder according to the present invention refers to an inorganic powder capable of producing a solid having a certain degree of strength when baked when the powder is heated to a temperature below a melting point or a temperature at which a liquid phase is partially generated. It is a body, and usually a metal powder and / or a ceramic powder is used. Specifically, as the metal powder, Fe, Ni, Co, Cr, C
u and the like are used.
Oxides such as ₂ O ₃ , BeO, ZrO ₂ , ThO ₂ , Ti
Carbides such as C, ZrC, B ₄ C, WC, CrB, ZrB
Boride such as _2, TiN, ZrN, VN, nitrides such as NbN and the like. Examples of these combinations include Al ₂ O ₃ —Fe, TiC—Ni, and TiC—Co.
System, B ₄ C-Fe system, and the like.

The particle size of the metal powder is not particularly limited. However, when the binder and the lubricant according to the present invention are used, the particle size is reduced to a small particle size, for example, a conventionally used average particle size of about 10 μm. It can be suitably used for submicron particles having an extremely small average particle diameter of about 1 μm or less, in comparison with the present invention. Incidentally, a powder having a small particle size improves the strength of the sintered body since no crystal growth of the powder itself can be seen, and the use of the powder having a small particle size results in the physical strength and density of the sintered body. The average particle diameter is more preferably 5 μm or less, and particularly preferably 1 μm or less. The amount of the inorganic powder in the composition for producing a sintered compact according to the present invention is not particularly limited, but is preferably from 40 to 80% by volume. The concept of the binder according to the present invention includes conventional waxes,
It does not include a lubricant and refers to a thermoplastic resin or a resin mixture thereof. The concept of the lubricant does not include a fatty acid ester such as a conventional stearic acid ester and refers to waxes.

In the composition for producing a sintered molded article according to the present invention, an ordinary thermoplastic resin can be suitably used as a binder, but it is particularly preferable to use a polyacetal resin and a modified polyolefin resin as main components in combination. The polyacetal resin may be a high molecular compound having an oxymethylene group (—CH ₂ O—) as a main structural unit. Therefore, a polyoxymethylene homopolymer, a copolymer containing other structural units in addition to oxymethylene, or a terpolymer may be used. Either a polymer or a block copolymer can be used. 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.

When a polyacetal resin is used as the binder component according to the present invention, the content of the comonomer used as the other structural unit is not particularly limited as long as the properties of the polyacetal resin are not impaired.
It is preferably at most 70 mol% of all monomers,
It is more preferably at most 50 mol%. If it exceeds 70 mol%, the rigidity tends to be low, and problems such as deformation tend to occur. The molecular weight and fluidity of the polyacetal resin are not particularly limited, but the melt index (hereinafter, referred to as MI) is preferably 20 g / min or more, and 2
5 to 50 are particularly preferred.

As the modified polyolefin resin (B),
Examples of the olefin polymer modified by introduction of an aromatic group or a polar group include various polymers obtained by, for example, copolymerization and graft copolymerization as described below. (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, for example, ethylene-glycidyl Methacrylate copolymer, (2) polyethylene, polypropylene, olefin polymers such as ethylene-propylene copolymer, vinyl polymers, for example, polymethyl methacrylate, polystyrene or polystyrene-based copolymers, etc., branched or (3) copolymerizable with a copolymer of an α-olefin and an unsaturated compound such as a glycidyl ester of an α, β-unsaturated acid. Other monomers such as acrylonitrile, styrene, methyl methacrylate, methyl acrylate, methacrylic acid And the like, or a vinyl (co) polymer composed of these monomers, for example, polymethyl methacrylate, polystyrene,
Polyacrylonitrile, acrylonitrile-styrene copolymer or the like copolymerized by graft polymerization or the like, for example, ethylene-glycidyl methacrylate copolymer acrylonitrile-styrene copolymer, polymethyl methacrylate, polystyrene, etc. graft polymerized ,
(4) olefin homopolymer, olefin copolymer,
Olefins and other vinyl monomers such as diene compounds, derivatives such as α, β-unsaturated acids or esters thereof,
Or, for an olefin-based polymer composed of a copolymer mainly composed of an olefin copolymerized with a vinyl compound or the like, a hydroxyl-modified olefin polymer obtained by reacting an unsaturated compound having a hydroxyl group, (5) Copolymers mainly composed of olefin homopolymers, olefin copolymers, olefins obtained by copolymerizing olefins with other vinyl monomers such as diene compounds, α, β-unsaturated acids or derivatives thereof, and the like. To an olefin-based polymer consisting of an unsaturated carboxylic acid or a derivative thereof, for example, maleic acid, an unsaturated dicarboxylic acid such as fumaric acid or an anhydride thereof, acrylic acid, or an unsaturated carboxylic acid such as methacrylic acid. Those obtained by copolymerizing those esters by graft polymerization or the like, (6) an olefin polymer,
Ether polymers, such as polyethylene oxide, polypropylene oxide and the like, a copolymer obtained by chemically bonding in a branched or cross-linked structure, (7) an olefin polymer and an epoxy group-containing monomer such as glycidyl methacrylate, glycidyl acrylate, etc. And an epoxy-modified olefin polymer obtained by heating in the presence of a radical initiator, and (8) an olefin polymer modified with an isocyanate group-containing monomer.

When the binder according to the present invention comprises a polyacetal resin and a modified polyolefin resin, the total amount thereof is preferably from 10 to 30% by volume in the composition for producing a sintered compact. If the total of both is less than 10% by volume, the molded body is likely to be deformed in the degreasing step by heating, and if it exceeds 30% by volume, the fluidity of the above composition is reduced, and the green molded body is molded. Injection molding cannot be performed smoothly.

The essential function of the lubricant, which is a component of the composition for producing a sintered compact according to the present invention, is that the green material is molded from a mold after molding by a method such as injection molding of a compounded composition of a sintering powder and a binder. It is in the separability of the molded body, that is, in imparting and improving the easy-removability, but in the case of the present invention in particular, in order to improve the wettability between the sintering powder and the binder,
Waxes are most preferably used.

Examples of the wax used herein include amide waxes (specifically, for example, fatty acid amide waxes) which are modified waxes having polar groups introduced therein, and ester waxes (specifically, for example, alkyl esters, Acrylic acid esters, methacrylic acid esters, etc.), urethane-based waxes (specifically, for example, long-chain paraffins are air-oxidized to secondary alcohols, and tolylene diisocyanate (TDI) modified urethane-bonded waxes) and carbana Wax, beeswax, wood wax, synthetic wasks and the like.

Examples of the type of the lubricant include the various types described above, and those usable in the present invention include:
It is required to have melting characteristics such that the melt viscosity at 0 ° C. is 100 mPa · s or less. If the melt viscosity of the lubricant such as wax exceeds 100 mPa · s at 120 ° C., since the lubricant component hardly flows out at the time of degreasing, a gap is hardly generated between the binders, and the decomposition gas of the binder cannot be easily removed. As a result, defects such as swelling and cracks are generated in the degreased body.

The amount of the lubricant such as wax in the composition for producing a sintered compact according to the present invention is required to be 10 to 30% by volume. When the amount is less than 10% by volume, the fluidity of the composition is remarkably lowered, and injection molding for obtaining a green molded body cannot be performed smoothly. On the other hand, when the amount exceeds 30% by volume, the rigidity of the green molded body becomes insufficient. In addition, the shape of the compact cannot be maintained during sintering.

Further, it is preferable that the melting point of the lubricant, especially the wax, is 40 to 120 ° C. When the temperature is lower than 40 ° C., the green molded body tends to become brittle,
If the temperature exceeds ℃, care must be taken that the degreasing temperature must be increased, the degreasing time needs to be increased, and significant deformation may occur during degreasing.

[0023]

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 5 and Comparative Examples 1 and 2) <Preparation of Composition for Manufacturing Sintered Molded Product> ZrO ₂ powder having a particle size of 0.3 μm was used as a sinterable powder, and polyacetal was used as a binder. Resin (Polyplastics Co., Ltd.)
A mixture of DURACON ^™ M270 and M450) and a modified polyolefin wax (methacrylic acid-modified polyethylene, MI = 500 g / 10 min) was prepared, and the waxes were used as lubricants in the proportions shown in Table 1. A composition for producing a sintered compact was prepared. For Examples 1 to 4 and Comparative Examples 1 and 2, M270 was used for the polyacetal resin, and for Example 5, M450 was also used.

<Molding of Green Formed Body> The compounded compositions of Examples 1 to 5 and Comparative Example 1 were kneaded with a pressure kneader at 160 ° C. for 60 minutes, and the kneaded material was cooled.
The injection molding raw material obtained by crushing is molded at a molding temperature of 180-20.
Injection molding was performed at 0 ° C. to obtain a green molded body.

<Degreasing Step> Next, each of these green compacts was heated to 220 ° C. over 2 hours, and then heated at 30 ° C. /
The temperature was raised to 340 ° C. at a rate of 300 ° C.
To a degreasing step under heating conditions maintained for 2 hours.

<Sintering Step> The compact having undergone the degreasing step was sintered at 1350 ° C. under sintering conditions for 2 hours to obtain a sintered compact.

<Evaluation> The following characteristics were evaluated in each of the above steps for obtaining a sintered compact. In each evaluation item, superiority is indicated by ○ (excellent), △ (middle),
X (poor) was evaluated. The measurement results are shown in Table 1. (1) Formability: The ease of forming the green molded body and the uniformity of the obtained green molded body were relatively evaluated. (2) Green body properties: The toughness of the green body was relatively evaluated. (3) Sintering property: The sintering density was relatively compared. (4) Properties of sintered body: The state of occurrence of cracks and swelling after sintering was observed, and relative evaluation was made.

[0029]

[Table 1]

[0030]

The composition for producing a sintered compact according to the present invention is characterized in that a lubricant such as wax is provided with a specific upper limit value for the melt viscosity at 120 ° C. so that the compatibility between the sintering powder, the binder and the lubricant is improved. , The brittleness of the green compact can be improved, the occurrence of defects in the compact during the degreasing step can be reduced, and a high-quality sintered compact can be obtained in a short time. Further, conventionally, when a fine powder having an average particle size of 1 μm or less is used, it has been difficult to produce a high-quality sintered compact having good dimensional accuracy and no defect in appearance such as phase separation. Is also available.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) C08L 59/00 C08L 101/00 91/06 C04B 35/00 D 101/00 108 F term (reference) 4G030 AA06 AA11 AA17 AA36 AA45 AA46 AA53 AA54 GA11 GA14 GA15 PA11 PA21 4J002 AA00W AE03X AE05X BB00W BB07W BB20W BB21W BN03W BN05W BN06W BN11W BN13W CB00W CD19W CD20W DA0916 016 016 016

Claims (10)

[Claims] 1. A composition comprising components of a sinterable inorganic powder, a binder and a lubricant, wherein the lubricant component comprises 120
A composition for producing a sintered molded article having a melt viscosity at 100C of 100 mPa-s or less and containing 10 to 30% by volume of the composition. 2. The composition according to claim 1, wherein the lubricant is a wax. 3. The composition according to claim 2, wherein the wax has a melting point of 40 to 120 ° C. 4. The composition according to claim 2, wherein the wax is an amide-based, ester-based or urethane-based modified wax. 5. The composition according to claim 1, wherein the binder is mainly composed of a polyacetal resin and a modified polyolefin resin.
The composition for producing a sintered compact according to any one of claims 1 to 4, which is contained at 0% by volume. 6. The composition for producing a sintered molded article according to claim 5, wherein the modified polyolefin resin is a resin in which the modifying component constitutes at least one of the main chain component and the side chain component of the polyolefin. 7. The composition for producing a sintered molded article according to claim 5, wherein the modified polyolefin resin is a resin obtained by adding a modifying component to at least one of a main chain and a side chain of a polyolefin in a branched manner. 8. The composition for producing a sintered compact according to claim 6, wherein the modifying component is a component having an aromatic group or a polar group. 9. The composition for producing a sintered compact according to claim 1, wherein the inorganic powder is at least one selected from metals and ceramics, and is contained in the composition in an amount of 40 to 80% by volume. object. 10. The composition for producing a sintered compact according to claim 1, wherein the inorganic powder has an average particle size of 1 μm or less.