JP2018123407A - Compound for metal powder injection molding, metal powder injection molded body and sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal powder injection molded body having high dimensional accuracy and shape retention, a compound for metal powder injection molding that enables production of the metal powder injection molded body, and a sintered body having high dimensional accuracy.SOLUTION: A compound for metal powder injection molding contains metal powder and binder. The content of the binder is more than 30 vol.% and less than 38 vol.%. When dried into a pellet with a volume of 0.25 cm, the compound has, preferably, a load bearing capacity of 4 kgf or more and 6 kgf or less.SELECTED DRAWING: None

Description

  The present invention relates to a compound for metal powder injection molding, a metal powder injection molded body, and a sintered body.

  As a method for molding metal powder, a compression molding method is known in which a granulated powder containing a metal powder and an organic binder is filled in a predetermined mold and compressed to obtain a molded body having a predetermined shape. Yes. The obtained molded body becomes a sintered metal body through a degreasing process for removing the organic binder and a firing process for sintering the metal powder. Such a technique is one of the powder metallurgy techniques, and since it can manufacture a large amount of a metal sintered body having a complicated shape depending on the shape of the mold, it has been widely used in many industrial fields in recent years.

  For example, in Patent Document 1, a molding material formed by mixing a metal powder and a binder is injected into a mold to form a molded body, and then the molded body is heated to remove the binder, and then the molded body is used. A metal powder injection molding method for sintering is disclosed. And it is disclosed that the mixing ratio when preparing a compound by mixing a metal powder and a binder is 60:40.

JP 2001-152205 A

  In recent years, there has been a strong demand for a metal sintered body to be thinner and smaller, and accordingly, the molded body has been made thinner and smaller.

  However, as the molded body becomes thinner and smaller, the mechanical strength tends to decrease, so the shape retention of the molded body decreases. As a result, there is a concern that the dimensional accuracy of the metal sintered body is lowered.

  An object of the present invention is to provide a metal powder injection molded product having high dimensional accuracy and shape retention, a compound for metal powder injection molding capable of producing such metal powder injection molded product, and a sintered body having high dimensional accuracy. It is in.

The above object is achieved by the present invention described below.
The compound for metal powder injection molding of the present invention includes a metal powder and a binder,
The binder content is more than 30% by volume and less than 38% by volume.

  Thereby, a metal powder injection molding compound capable of producing a metal powder injection molded body with high dimensional accuracy and shape retention is obtained.

In the metal powder injection molding compound of the present invention, when dried into pellets having a volume of 0.25 cm ³ ,
The load resistance is preferably 4 kgf or more and 6 kgf or less.

  Thereby, the compound contributes to the realization of a molded body having sufficient fluidity and sufficient shape retention after molding. For this reason, the sintered compact with high dimensional accuracy can finally be manufactured.

  In the metal powder injection molding compound of the present invention, the binder preferably contains a hydrocarbon polymer and a wax.

  Thereby, since the shape of a molded object is easy to be maintained, finally the sintered compact with especially high dimensional accuracy is obtained.

  In the metal powder injection molding compound of the present invention, the binder preferably further contains a copolymer containing a cyclic ether group.

  Thereby, while the structure derived from the monomer containing a cyclic ether group has excellent adhesion to the metal powder, compatibility with a hydrocarbon polymer or wax can be enhanced by using a copolymer. That is, such a copolymer contributes to increasing the mutual wettability of the metal powder, the hydrocarbon resin and the wax, and thus contributes to enhancing the mutual dispersibility in the compound. As a result, such a compound becomes homogeneous, which leads to obtaining a sintered body having high mechanical properties and high dimensional accuracy.

The metal powder injection molded product of the present invention is an injection molded product of the compound for metal powder injection molding of the present invention.
Thereby, a metal powder injection-molded body with high dimensional accuracy and shape retention is obtained.

The sintered body of the present invention is a sintered product of the metal powder injection molded body of the present invention.
Thereby, a sintered compact with high dimensional accuracy is obtained.

  Hereinafter, the compound for metal powder injection molding, the metal powder injection molded body, and the sintered body of the present invention will be described in detail based on preferred embodiments.

<Compound for metal powder injection molding>
First, an embodiment of the metal powder injection molding compound of the present invention will be described.

  The compound for metal powder injection molding according to the present embodiment (hereinafter simply referred to as “compound” for short) is a molding material used for the metal powder injection molding method, and includes metal powder and a binder. Yes.

(Metal powder)
The metal powder contained in the metal powder injection molding (MIM) compound is not particularly limited and may be any kind of metal powder. The constituent material of the metal powder includes a sinterable metal material used for powder metallurgy, for example, Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Examples thereof include simple metals such as Zr, Nb, Mo, Pd, Ag, In, Sn, Ta, and W, or alloys and intermetallic compounds containing at least one of these metals.

  Further, the metal powder may be a mixed powder obtained by mixing two or more kinds of powders having different compositions. Further, the metal powder injection molding compound may contain ceramic (metal compound such as metal oxide, metal nitride, metal carbide) powder together with the metal powder.

  Among these, examples of the Fe-based alloy include stainless steel, low carbon steel, carbon steel, heat resistant steel, die steel, high speed tool steel, Fe—Ni alloy, Fe—Ni—Co alloy, and the like.

  Examples of the Ni-based alloy include Ni-Cr-Fe-based alloys, Ni-Cr-Mo-based alloys, Ni-Fe-based alloys, and the like.

  Examples of the Co-based alloy include a Co-Cr-based alloy, a Co-Cr-Mo-based alloy, and a Co-Al-W-based alloy.

  Examples of Ti-based alloys include alloys of Ti and metal elements such as Al, V, Nb, Zr, Ta, and Mo. Specifically, Ti-6Al-4V, Ti-6Al— 7Nb and the like.

Examples of the Al-based alloy include duralumin.
Examples of the ceramic material constituting the ceramic powder include oxides such as alumina, magnesia, beryllia, zirconia, yttria, forsterite, steatite, wollastonite, mullite, cordierite, ferrite, sialon, and cerium oxide. Examples thereof include ceramic materials, non-oxide ceramic materials such as silicon nitride, aluminum nitride, boron nitride, titanium nitride, silicon carbide, boron carbide, titanium carbide, and tungsten carbide.

  When ceramic powder is included, the amount of ceramic powder added to the metal powder is preferably 30% by volume or less, and more preferably 20% by volume or less. Thereby, weight reduction etc. of a sintered compact can be achieved, without impairing the characteristic property of a metal.

  The average particle size of the metal powder is preferably 1 μm or more and 30 μm or less, more preferably 2 μm or more and 20 μm or less, and further preferably 3 μm or more and 10 μm or less. Since the metal powder having such a particle size avoids a decrease in compressibility during molding and the shape retention of the molded body is sufficiently high, a sufficiently dense sintered body can be finally produced. Become.

  When the average particle size is less than the lower limit, the metal powder is likely to aggregate, and the metal powder may be unevenly distributed in the compound, or the shape retention of the molded body formed by molding the compound may be reduced. There is. On the other hand, when the average particle diameter exceeds the upper limit, the uniformity of the compound is lowered, the shape retention of the molded body is lowered, and the mechanical strength of the finally obtained sintered body may be lowered. There is.

  The average particle size of the metal powder is the particle size when the cumulative particle size based on mass is 50% from the small diameter side in the particle size distribution obtained by the laser diffraction method.

  Further, the average particle diameter of the metal powder is D50, and the particle diameter distribution when the accumulation of the mass-based particle size is 10% from the small diameter side in the particle size distribution obtained by the laser diffraction method for the metal powder is D10. (D90−D10) / D50 is preferably 0.5 or more and 5 or less, and more preferably 1.0 or more and 3.5 or less, when the particle size at 90% to 90% is D90. The metal powder satisfying such conditions can improve the fluidity of the compound and the shape retention of the molded body. For this reason, even when it is a case where a thin molded object and a small molded object are shape | molded, the molded object which has high shape retention property can be manufactured. As a result, a sintered body with high dimensional accuracy can be obtained.

  Such a metal powder may be produced by any method, for example, by an atomization method (water atomization method, gas atomization method, high-speed rotating water atomization method, etc.), reduction method, carbonyl method, pulverization method, or the like. What was manufactured can be used.

  Among these, it is preferable to use what was manufactured by the atomizing method for metal powder. According to the atomizing method, a metal powder having an extremely small average particle diameter as described above can be efficiently produced. In addition, a metal powder having a uniform particle size can be obtained with little variation in particle size. Therefore, by using such a metal powder, the formation of pores in the sintered body can be prevented, and the density can be improved.

  In addition, since the metal powder produced by the atomizing method has a spherical shape that is relatively close to a true sphere, the metal powder has excellent filling properties during molding and excellent dispersibility with respect to the binder. For this reason, when the compound is filled in the molding die and molded, the filling property and uniformity can be improved, and finally a sintered body with higher density and higher dimensional accuracy can be obtained.

(binder)
The binder is dispersed in the compound and binds the metal powder particles (including ceramic powder, including metal particles, ceramic particles, and ceramic particles). Moreover, this binder is substantially removed in a degreasing process after shaping | molding. Thereby, a high quality sintered compact is obtained in a baking process.

  In such a process, in order to increase the dimensional accuracy of the sintered body, it is important that the dimensional accuracy and shape retention of the molded body are high. In order to improve the dimensional accuracy and shape retention of the molded body, the compound is filled in the cavity of the mold without gaps and molded, and after the mold release, the molded body maintains the shape immediately after the mold release. Need to be.

  The inventor has intensively studied to realize a compound capable of producing such a molded article having high shape retention. And when the content rate of the binder in a compound is more than 30 volume% and less than 38 volume%, it discovered that a molded object with high shape retention property could be manufactured specifically, and came to complete this invention.

  That is, the compound according to this embodiment includes metal powder and a binder, and the binder content is more than 30% by volume and less than 38% by volume. By setting the content of the binder in the compound within the above range, the compound is filled in the cavity of the mold without any gap, and the obtained molded body can maintain the shape immediately after the mold release. In addition, the shrinkage rate during degreasing and sintering can be suppressed. As a result, a high-quality sintered body with high dimensional accuracy is finally obtained. Since such a sintered body is the same as or close to the target shape, it contributes to omitting the secondary processing or reducing the processing amount. For this reason, cost reduction of metal parts and labor saving of production can be achieved.

  The content of the binder in the compound is preferably 32% by volume to 36% by volume, more preferably 33% by volume to 35% by volume.

  If the binder content in the compound is lower than the lower limit, the fluidity of the compound is lowered, and therefore the compound may not be completely filled in the narrow cavity. For this reason, there exists a possibility that the dimensional accuracy of a molded object may fall. In addition, problems such as cracking of the molded body and wear of the mold may occur. On the other hand, if the content of the binder in the compound exceeds the upper limit, the shape retention by the metal powder is weakened in the compound, so that the shape retention property is lowered. Further, as the amount of the binder to be removed in the degreasing step increases, the molded body may crack due to the vaporized binder.

  Moreover, the content rate of the binder in a compound can be calculated | required from the area ratio of the binder in a cross section, for example by observing the cross section of a compound.

  The constituent material of the binder contained in the compound is not particularly limited as long as it can be removed in the degreasing step or the firing step, but a material containing a hydrocarbon-based polymer and a wax is preferably used as the binder.

  Among these, the hydrocarbon-based polymer refers to a polymer compound mainly composed of carbon atoms and hydrogen atoms and having a degree of polymerization of about 50 or more (preferably 100 or more). The hydrocarbon polymer has a higher thermal decomposition temperature than wax.

  On the other hand, the wax refers to a saturated chain polymer compound mainly composed of carbon atoms and hydrogen atoms and having a polymerization degree of less than 50 (preferably 30 or less).

  By using such a hydrocarbon polymer and wax together, the initial shape retention of the molded body is maintained by the wax, while the hydrocarbon polymer is gradually decomposed over a relatively wide temperature range. Is easily established. Since the shape of the molded body is easily maintained throughout the process, a sintered body with a particularly high dimensional accuracy is finally obtained.

-Hydrocarbon polymer-
Examples of the hydrocarbon polymer include saturated hydrocarbon resins and unsaturated hydrocarbon resins. Moreover, it classify | categorizes also into chain | strand-shaped hydrocarbon resin, cyclic hydrocarbon resin, etc. according to the coupling | bonding form of a carbon atom.

  Examples of such hydrocarbon polymers include polyolefins such as polyethylene, polypropylene, polybutylene and polypentene, polyolefin copolymers such as polyethylene-polypropylene copolymer, polyethylene-polybutylene copolymer, and polystyrene. It is comprised by 1 type, or 2 or more types of these.

  Among these, it is preferable that the binder contains at least one of polyolefin resin and polystyrene resin. Since these hydrocarbon polymers have a relatively large binding force and a relatively high thermal decomposability, the shape of the molded body is easily maintained during degreasing. Therefore, these hydrocarbon-based polymers contribute to rapid degreasing and thereby improved sinterability. As a result, a sintered body with high dimensional accuracy can be obtained.

  The weight average molecular weight of the hydrocarbon polymer is preferably 10,000 or more and 100,000 or less, and more preferably 20,000 or more and 80,000 or less. By setting the weight-average molecular weight of the hydrocarbon polymer within the above range, easy and reliable degreasing can be achieved while imparting sufficient shape retention to the molded body. In addition, when the weight average molecular weight of the hydrocarbon-based polymer is below the lower limit value, there is a possibility that sufficient shape retention cannot be imparted to the molded body. When the weight average molecular weight exceeds the upper limit value, the molded body may be degreased. There is a possibility that the decomposability of the hydrocarbon-based polymer is lowered.

  The content of the hydrocarbon polymer in the binder is preferably 1% by mass or more and 98% by mass or less, more preferably 15% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 45% by mass or less. More preferably. By setting the content of the hydrocarbon-based polymer within the above range, the characteristics of the hydrocarbon-based polymer in the binder can be expressed necessary and sufficiently. In addition, when content of a hydrocarbon type polymer is less than the said lower limit, there exists a possibility that sufficient shape retention property cannot be provided to a molded object. On the other hand, when the upper limit is exceeded, components other than hydrocarbon-based polymers such as wax are relatively reduced, so that it takes a long time to degrease the molded product, or a large amount of hydrocarbon-based polymers at once. There is a risk of incurring problems such as cracking of the molded product caused by the decomposition.

  As the hydrocarbon-based polymer, those having a thermal decomposition temperature of 300 ° C. or higher and 550 ° C. or lower are preferably used, and more preferably 400 ° C. or higher and 500 ° C. or lower. Such a hydrocarbon-based polymer corresponds to a binder component that thermally decomposes in a relatively high temperature range, and therefore, when degreasing the molded body, it contributes to maintaining the shape of the molded body until the degreasing is completed. To do. As a result, a sintered body with high dimensional accuracy can be finally obtained.

Further, as the hydrocarbon polymer, those having a melting point of 100 ° C. or higher and 400 ° C. or lower are preferably used, and those having a melting point of 200 ° C. or higher and 300 ° C. or lower are more preferably used.
In addition, these thermal decomposition temperatures and melting points are measured by a differential thermothermal gravimetric simultaneous measurement device (TG / DTA) or the like.

-Wax-
The wax contains a relatively large amount of crystalline polymer, and its weight average molecular weight is smaller than that of the resin, preferably 5000 or more, more preferably 10,000 or less. Accordingly, the wax melts and decomposes at a lower temperature than the hydrocarbon polymer when the molded body is degreased, and forms a flow path when released from the molded body. Thereafter, when the molded body is heated at a higher temperature, the hydrocarbon-based polymer starts to be decomposed, and the decomposition product is discharged to the outside of the molded body through the flow path. If the hydrocarbon polymer is removed through the flow path in this way, it is possible to prevent the decomposition product of the hydrocarbon polymer from being efficiently discharged to the outside and the molded body from being damaged. Thereby, the shape of a molded object can be maintained more reliably even in the process of degreasing, and finally a sintered body with high dimensional accuracy can be obtained.

Examples of the wax include natural wax and synthetic wax.
Of these, natural waxes include, for example, plant waxes such as candelilla wax, carnauba wax, rice wax, wax wax, jojoba oil, animal waxes such as beeswax, lanolin, and whale wax, montan wax, ozokerite. And mineral wax such as ceresin, paraffin wax, microcrystalline wax, petroleum wax such as petrolatum, and the like, and one or more of them can be used in combination.

  Synthetic waxes include synthetic hydrocarbons such as polyethylene wax, modified waxes such as montan wax derivatives, paraffin wax derivatives and microcrystalline wax derivatives, hydrogenated waxes such as hardened castor oil and hardened castor oil derivatives, and 12-hydroxy. Examples include fatty acids such as stearic acid, acid amides such as stearic acid amide, esters such as phthalic anhydride imide, and one or more of these can be used in combination.

  In this embodiment, in particular, petroleum-based wax or a modified product thereof is preferably used, paraffin wax, microcrystalline wax or derivatives thereof are more preferably used, and paraffin wax is more preferably used. Since these waxes are excellent in compatibility with hydrocarbon-based polymers, it is possible to prepare homogeneous binder compositions and compounds. For this reason, it contributes to manufacture of the sintered compact finally excellent in a mechanical characteristic and dimensional accuracy.

  The weight average molecular weight of the wax is preferably 100 or more and 2000 or less, and more preferably 200 or more and 1000 or less. By setting the weight average molecular weight of the wax within the above range, when the molded product is degreased, the wax can be more reliably melted at a lower temperature than the hydrocarbon polymer. It is possible to more reliably form a flow path for the decomposition product to be discharged. In addition, when the weight average molecular weight of the wax is less than the lower limit, there is a risk that the shape retention of the molded body is lowered. On the other hand, when the value exceeds the upper limit, the temperature range where the wax melts and the temperature range where the hydrocarbon polymer melts are close to each other, which may cause cracks in the molded body.

  Further, the content of the wax in the binder is preferably 1% by mass to 70% by mass, more preferably 10% by mass to 50% by mass, and more preferably 15% by mass to 40% by mass. Is more preferable. By setting the content of the wax within the above range, the properties of the wax can be expressed sufficiently and sufficiently in the binder. If the wax content is lower than the lower limit, a sufficient amount of flow paths cannot be formed in the molded body, and cracking or the like may occur when the molded body is degreased. On the other hand, when the value exceeds the upper limit, the proportion of the hydrocarbon-based polymer is relatively lowered, so that the shape retention of the molded product may be lowered.

  As the wax, those having a melting point of 30 ° C. or higher and 200 ° C. or lower are preferably used, and those having a melting point of 50 ° C. or higher and 150 ° C. or lower are more preferably used.

  The hydrocarbon polymer and the wax have been described above. From another viewpoint, the binder preferably includes both a crystalline resin such as wax and an amorphous resin such as polystyrene. Thereby, the initial shape retention of the molded body is maintained by the crystalline resin, while the amorphous resin is gradually decomposed and released to the outside over a relatively wide temperature range. As a result, a sintered body with a particularly high dimensional accuracy is finally obtained.

  The mixing ratio of the crystalline resin and the non-crystalline resin is not particularly limited, but it is preferable to increase the non-crystalline resin rather than the crystalline resin. Specifically, with respect to 100 parts by mass of the crystalline resin, It is preferable that the non-crystalline resin is 101 parts by mass or more and 300 parts by mass or less. Thereby, the shape retention of a molded object can be improved more and a dimensional accuracy can be improved further finally. That is, when the mixing ratio of the amorphous resin is lower than the lower limit, depending on the particle size of the metal powder, the binder component, and the like, the shape retention of the molded body when the temperature changes may be slightly lowered. On the other hand, when the mixing ratio of the amorphous resin exceeds the upper limit, the initial shape retention of the molded body may be slightly lowered depending on the particle size of the metal powder, the binder component, and the like.

-Cyclic ether group-containing copolymer-
Moreover, the cyclic ether group containing copolymer may be added to the binder as needed. This cyclic ether group-containing copolymer is a copolymer obtained by copolymerizing a monomer containing a cyclic ether group and a monomer copolymerizable with this monomer. By adding such a copolymer, the structure derived from a monomer containing a cyclic ether group has excellent adhesion to the metal powder. On the other hand, by using a copolymer, compatibility with hydrocarbon polymers and waxes is improved. Can be increased. That is, such a copolymer contributes to increasing the mutual wettability of the metal powder, the hydrocarbon resin and the wax, and thus contributes to enhancing the mutual dispersibility in the compound. As a result, such a compound becomes homogeneous, which leads to obtaining a sintered body having high mechanical properties and high dimensional accuracy.

  Examples of the cyclic ether group include an epoxy group and an oxetanyl group. These ring-open by the heat | fever provided to the compound, and couple | bond with the hydroxyl group of the metal powder surface. As a result, the metal powder and the copolymer exhibit high adhesion, and the dispersibility of the metal powder in the compound becomes better. Moreover, an epoxy group is particularly preferable among the cyclic ether groups from the viewpoint of easy bonding with the metal powder surface.

  Examples of the monomer containing a cyclic ether group include glycidyl esters such as glycidyl acrylate and glycidyl methacrylate, glycidyl ethers such as vinyl glycidyl ether and allyl glycidyl ether, oxetane esters such as oxetane acrylate and oxetane methacrylate. Of these, one or two or more of these can be used in combination.

  On the other hand, examples of monomers copolymerizable with such monomers include (meth) acrylate monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate, and ethylene. Olefin monomers such as propylene, isobutylene and butadiene, vinyl acetate monomers, and the like, and one or more of them can be used in combination. Note that a notation such as (meth) acrylic acid indicates either acrylic acid or methacrylic acid.

  Of these, ethylene monomer and vinyl acetate monomer are preferably used. Ethylene and vinyl acetate have particularly excellent compatibility with hydrocarbon polymers and waxes. For this reason, by using both an ethylene monomer and a vinyl acetate monomer, the polymer is interposed between the metal powder, the hydrocarbon polymer and the wax, and has a function of particularly enhancing their wettability. It becomes.

  In addition, as a preferable combination of the monomer containing a cyclic ether group as described above and a monomer copolymerizable with the monomer, for example, glycidyl (meth) acrylate (GMA), vinyl acetate (VA), glycidyl (meth) acrylate And ethylene, glycidyl (meth) acrylate, vinyl acetate, ethylene (E), glycidyl (meth) acrylate, vinyl acetate, methyl acrylate (MA), and the like.

  Further, the content of the monomer containing a cyclic ether group in the cyclic ether group-containing copolymer is not particularly limited, but is preferably about 0.1% by mass to 50% by mass, and preferably about 1% by mass to 30% by mass. It is more preferable that Thereby, since the adhesiveness between the cyclic ether group-containing copolymer and the metal powder can be obtained with certainty, the above-described effects when using the copolymer are more reliably exhibited.

  The weight average molecular weight of the cyclic ether group-containing copolymer is preferably 10,000 or more and 400,000 or less, more preferably 30,000 or more and 300,000 or less. By making the weight average molecular weight of the cyclic ether group-containing copolymer within the above-mentioned range, while preventing the thermal decomposability of the cyclic ether group-containing copolymer from being remarkably lowered, the fluidity of the compound and the shape retention of the molded product are improved. It can be compatible.

  Moreover, the arrangement | sequence of the monomer in a cyclic ether group containing copolymer is not specifically limited, Any arrangement | sequences, such as random copolymerization, alternating copolymerization, block copolymerization, and graft copolymerization, may be sufficient.

  Further, the content of the cyclic ether group-containing copolymer in the compound is preferably about 10% or more and 100% or less, more preferably about 15% or more and 80% or less of the content of the wax by mass ratio, More preferably, it is about 20% or more and 50% or less. By setting the content of the cyclic ether group-containing copolymer within the above range, the mutual wettability between the metal powder, the hydrocarbon polymer and the wax can be particularly enhanced. As a result, it contributes to particularly enhancing the dispersibility of the metal powder and binder in the compound.

  As the cyclic ether group-containing copolymer, those having a melting point of 30 ° C. or higher and 150 ° C. or lower are preferably used, and those having a melting point of 50 ° C. or higher and 100 ° C. or lower are more preferably used.

-Other ingredients-
Moreover, the binder may contain the other component. The content of other components in the binder is preferably 10% by mass or less, for example.

  Examples of other components include acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyethylene terephthalate, and polybutylene terephthalate, polyethers, and copolymers thereof. Various resins, alcohols, higher fatty acids, fatty acid metals, higher fatty acid esters, higher fatty acid amides, nonionic surfactants, silicone-based lubricants, etc., and one or a mixture of two or more of these Used.

  Among these, examples of alcohols include polyhydric alcohols, polyglycols, polyglycerols, and the like, and cetyl alcohol, stearyl alcohol, oleyl alcohol, mannitol, and the like are particularly preferably used.

  Examples of higher fatty acids include stearic acid, oleic acid, linoleic acid and the like, and saturated fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid are particularly preferably used.

  Examples of the fatty acid metal include lauric acid, stearic acid, succinic acid, stearyl lactic acid, lactic acid, phthalic acid, benzoic acid, hydroxystearic acid, ricinoleic acid, naphthenic acid, oleic acid, palmitic acid, and erucic acid. Examples include compounds of higher fatty acids and metals such as Li, Na, Mg, Ca, Sr, Ba, Zn, Cd, Al, Sn, Pb, and Cd. In particular, magnesium stearate, calcium stearate, sodium stearate Zinc stearate, calcium oleate, zinc oleate, magnesium oleate and the like are preferably used.

  Examples of the nonionic surfactant include Electro Stripper (registered trademark) TS-2, Electro Stripper (registered trademark) TS-3 (both manufactured by Kao Corporation), and the like.

  Examples of the silicone-based lubricant include dimethylpolysiloxane and modified products thereof, carboxyl-modified silicone, α-methylstyrene-modified silicone, α-olefin-modified silicone, polyether-modified silicone, fluorine-modified silicone, hydrophilic specially-modified silicone, and olefin polysiloxane. Examples include ether-modified silicone, epoxy-modified silicone, amino-modified silicone, amide-modified silicone, and alcohol-modified silicone.

(Characteristics of compound)
The compound according to the present embodiment as described above has a relatively high load resistance. Hereinafter, a method for measuring the load resistance will be described.

First, the compound is dried and pulverized to become pellets having a volume of 0.25 cm ³ (preferably 5 mm square pellets). You may make it shape | mold before drying as needed.

  Next, a circular flat compression jig of a digital force gauge is pressed against the obtained pellet. The diameter of the pressure contact surface of this jig is 40 mm. Then, the load (withstand load) when the pellets are bent is measured.

  Subsequently, the same load-bearing measurement is sequentially performed on five or more pellets, and an average value is calculated. The load resistance is evaluated with this average value.

When the compound according to this embodiment is dried into a pellet having a volume of 0.25 cm ³ (preferably a 5 mm square pellet), the load resistance is 4 kgf (39.2 N) or more and 6 kgf (58.8 N) or less. Is preferably 4.2 kgf or more and 5.5 kgf or less, and more preferably 4.3 kgf or more and 5 kgf or less. Such a compound achieves necessary and sufficient fluidity and contributes to the realization of a molded body having sufficient shape retention after molding. For this reason, the sintered compact with high dimensional accuracy can finally be manufactured.

  That is, when the load resistance of the pellet is lower than the lower limit, depending on the shape of the molded body, the shape retention after molding may be insufficient, and the dimensional accuracy of the sintered body may be reduced. On the other hand, if the load resistance of the pellet exceeds the upper limit, the fluidity of the compound may be lowered depending on the shape of the molded body when the compound is softened for injection molding. Thereby, it cannot shape | mold to the target shape and there exists a possibility that the dimensional accuracy of a sintered compact may fall.

  In addition to the metal powder and the binder, various additives such as a solvent (dispersion medium), a rust inhibitor, an antioxidant, a surfactant, and an antifoaming agent may be added to the compound. The addition amount of these additives is preferably about 5% by mass or less, more preferably about 3% by mass or less of the compound.

<Production method of compound>
Next, an example of a method for manufacturing a compound will be described.
The compound is manufactured by kneading metal powder and a binder.

  For the kneading, for example, various kneaders such as a pressure or double-arm kneader kneader, a roll kneader, a Banbury (registered trademark) kneader, a uniaxial or biaxial extruder can be used.

  The kneading conditions vary depending on various conditions such as the particle diameter of the metal powder to be used and the mixing ratio of the metal powder and the binder composition. For example, the kneading temperature is 50 ° C. or more and 200 ° C. or less, and the kneading time is 15 It can be set to about 210 minutes or more.

<Method for producing sintered body>
Next, an example of a method for producing a sintered body using a compound will be described.

  The method for manufacturing a sintered body includes a molding step for molding a compound into a desired shape, a degreasing step for degreasing the obtained molded body, and a firing step for firing the obtained degreased body. Hereinafter, each process will be described sequentially.

(Molding process)
First, molding is performed using the compound as described above. Thereby, the molded object of a desired shape and a dimension is manufactured.

  Prior to molding, the compound may be pelletized as necessary. The pelletizing process is a process of pulverizing the compound using a pulverizer such as Pelletizer (registered trademark). The pellets thus obtained have an average particle size of about 1 mm to 10 mm.

  Next, the obtained pellets are put into an injection molding machine and injected into a mold to be molded. Thereby, the molded object to which the shape of the mold was transferred is obtained. Since the compound as described above can achieve both fluidity and shape retention after molding, the obtained molded body has a target shape and is less deformed.

  It should be noted that the shape and size of the molded body to be manufactured is determined in consideration of the shrinkage due to subsequent degreasing and sintering.

  The molded body thus obtained (the embodiment of the metal powder injection molded body of the present invention) uses the compound as described above (the embodiment of the compound for metal powder injection molding of the present invention). High accuracy and shape retention. For this reason, it is finally possible to produce a sintered body with high dimensional accuracy and mechanical strength.

  In addition, you may make it perform post-processing, such as machining and a laser processing, with respect to the obtained molded object as needed.

(Degreasing process)
Next, degreasing treatment (debinding treatment) is performed on the obtained molded body. Thereby, the binder contained in the molded body is removed (degreasing) to obtain a degreased body.

This degreasing treatment is not particularly limited, but in a non-oxidizing atmosphere, for example, in a vacuum or under reduced pressure (for example, 1 × 10 ⁻⁶ Torr or more and 1 × 10 ⁻¹ Torr or less (1.33 × 10 ⁻⁴ Pa or more and 13. 3 Pa or less)) or by performing heat treatment in a gas such as nitrogen gas or argon gas.

  The treatment temperature in the degreasing step is not particularly limited, but is preferably 100 ° C. or higher and 750 ° C. or lower, and more preferably 150 ° C. or higher and 700 ° C. or lower.

  Moreover, it is preferable that the processing time in a degreasing process is 0.5 hour or more and 20 hours or less, and it is more preferable that it is 1 hour or more and 10 hours or less.

  Further, degreasing by such heat treatment may be performed in a plurality of stages for various purposes (for example, for shortening the degreasing time). In this case, for example, a method in which the first half is degreased at a low temperature and the second half at a high temperature, a method in which low temperature and high temperature are repeated, and the like can be mentioned.

  In addition, after the degreasing treatment as described above, the obtained degreased body may be subjected to various post-processings for the purpose of, for example, deburring or forming a microstructure such as a groove.

  Note that the binder may not be completely removed from the molded body in the degreasing process, and for example, a part of the binder may remain at the time when the degreasing process is completed.

(Baking process)
Next, the degreased body that has been subjected to the degreasing treatment is fired. Thereby, a degreased body is sintered and a sintered body is obtained. That is, this sintered body is a sintered product of a metal powder injection molded body. Since the sintered body thus obtained (embodiment of the sintered body of the present invention) uses the above-mentioned formed body (embodiment of the metal powder injection molded body of the present invention), dimensional accuracy is obtained. In addition, the mechanical strength is high.

The firing conditions are not particularly limited, but in a non-oxidizing atmosphere, for example, in a vacuum or under reduced pressure (for example, 1 × 10 ⁻⁶ Torr to 1 × 10 ⁻² Torr (1.33 × 10 ⁻⁴ Pa to 133 Pa) ), Or by performing heat treatment in an inert gas such as nitrogen gas or argon gas. Thereby, it can prevent that metal powder will oxidize.

  The firing process may be performed in two steps or more. Thereby, the efficiency of sintering can be improved and firing can be performed in a shorter firing time.

  Moreover, you may make it perform a baking process continuously with the above-mentioned degreasing process. Thereby, a degreasing process can serve as a pre-sintering process, can preheat a degreased body, and can sinter a degreased body more certainly.

  Although a calcination temperature is suitably set according to the kind of metal powder, it is preferable that it is 1000 to 1400 degreeC, and it is more preferable that it is 1050 to 1350 degreeC. By using the compound as described above, a sufficiently high density sintered body can be obtained even at a relatively low firing temperature.

  The firing time is preferably 0.5 hours or more and 20 hours or less, more preferably 1 hour or more and 15 hours or less.

  Moreover, such a baking process may be performed in a plurality of steps (stages) for various purposes (for example, for the purpose of shortening the baking time, etc.). In this case, for example, a method in which the first half is fired at a low temperature and the second half is fired at a high temperature, a method in which a low temperature and a high temperature are repeated, and the like can be mentioned.

  Further, after the firing step as described above, the obtained sintered body is subjected to machining, electric discharge machining, laser machining, etching, etc. for the purpose of deburring, forming a microstructure such as a groove, etc. You may give it.

  Note that the obtained sintered body may be subjected to HIP processing (hot isostatic pressing) or the like, if necessary. Thereby, further densification of a sintered compact can be achieved.

  The sintered body obtained as described above may be used for any purpose. Examples of its use include various structural parts.

  As mentioned above, although this invention was demonstrated based on suitable embodiment, this invention is not limited to these. For example, the metal powder injection molded body may be formed by using two or more types of compounds.

Next, specific examples of the present invention will be described.
1. Production of sintered body (Example 1)
First, an austenitic stainless steel powder (SUS316L) having an average particle diameter of 4 μm manufactured by a water atomization method was prepared as a metal powder.

  Next, a binder having the composition shown in Table 1 and stainless steel powder were mixed and kneaded in a pressure kneader (kneader) at 100 ° C. for 60 minutes. This gave a compound. This kneading was performed in a nitrogen atmosphere. Table 1 shows the mixing ratio of the binder composition and the stainless steel powder.

  Next, the obtained compound was pulverized by a pelletizer (registered trademark) to obtain pellets having an average particle diameter of 5 mm.

Next, the obtained pellets were molded by an injection molding machine under molding conditions of material temperature: 130 ° C. and injection pressure: 10.8 MPa (110 kgf / cm ² ). This obtained the molded object. The shape of the compact was a cylindrical shape having a diameter of 0.5 cm and a height of 0.5 cm.

  Next, the molded body was subjected to a degreasing process under a degreasing condition of temperature: 500 ° C., time: 1 hour, atmosphere: nitrogen gas (atmospheric pressure). This obtained the defatted body.

  Next, the degreased body was subjected to a firing treatment under firing conditions of temperature: 1270 ° C., time: 3 hours, atmosphere: nitrogen gas (atmospheric pressure). This obtained the sintered compact.

(Examples 2 to 16 and Comparative Examples 1 to 4)
Granulated powder was obtained in the same manner as in Example 1 except that the metal powder and binder were changed as shown in Tables 1 and 2.

Abbreviations in Tables 1 and 2 indicate the following.
E-GMA-VA: ethylene-glycidyl methacrylate-vinyl acetate copolymer E-GMA-MA: ethylene-glycidyl methacrylate-methyl acrylate copolymer

2. Evaluation of Compound A compression jig of a digital force gauge was pressed against the pellets obtained in each Example and each Comparative Example, and the load when the pellets were bent was measured. In addition, this measurement was performed sequentially about five pellets, the average value was computed, and the average value was made into the load resistance of a compound.
The measurement results are shown in Tables 1 and 2.

3. Evaluation of Molded Body 3.1 Evaluation of Poor Filling First, in each example and each comparative example, 10 molded bodies were produced.

  Subsequently, the external appearance of each molded object was observed visually. Then, the filling failure was evaluated in light of the following evaluation criteria.

<Evaluation criteria for filling defects>
A: The number of defective fillings is 0. ○: The number of defective fillings is one. Δ: The number of defective fillings is two or three. X: The number of defective fillings is four or more. Is

3.2 Evaluation of Deformation First, the dimensions of the molded body immediately after molding were measured.

Subsequently, the compact was allowed to stand for 24 hours.
Subsequently, the dimension of each molded object after stationary was measured. And the shift | offset | difference (deformation amount) from the dimension immediately after shaping | molding was evaluated in light of the following evaluation criteria.

<Evaluation criteria for deformation amount>
◎: Deformation amount is relatively very small ○: Deformation amount is relatively small △: Deformation amount is relatively large ×: Deformation amount is relatively very large

4). Evaluation of Sintered Body First, the dimensions of the sintered body obtained in each Example and each Comparative Example were measured.

  Next, the deviation of the measured dimension from the design value was calculated. Then, the deviation from the design value (dimensional accuracy) was evaluated in light of the following evaluation criteria.

<Evaluation criteria for dimensional accuracy>
◎: Dimensional accuracy is relatively high ○: Dimensional accuracy is relatively high △: Dimensional accuracy is relatively low ×: Dimensional accuracy is relatively low

  As is apparent from Tables 1 and 2, it was confirmed that the molded bodies obtained in each Example had poor filling and a small amount of deformation. From this, it was confirmed that according to the present invention, a metal powder injection-molded article with high dimensional accuracy and shape retention can be obtained. It has also been found that such a molded body can realize a sintered body with high dimensional accuracy.

  Although not described in each table, the same as in Examples 1 to 16 and Comparative Examples 1 to 4 except that a mixed powder in which 10% by volume of stainless steel powder was replaced with alumina powder having an average particle diameter of 6 μm was used. And evaluated.

  As a result, the evaluation result which shows the tendency similar to Examples 1-16 and Comparative Examples 1-4 was obtained.

Claims (6)

Metal powder and a binder,
A compound for metal powder injection molding, wherein the binder content is more than 30% by volume and less than 38% by volume. When dried into pellets with a volume of 0.25 cm ³
The compound for metal powder injection molding according to claim 1, wherein the load resistance is 4 kgf or more and 6 kgf or less.   The metal powder injection molding compound according to claim 1, wherein the binder includes a hydrocarbon polymer and a wax.   The compound for metal powder injection molding according to claim 3, wherein the binder further comprises a copolymer containing a cyclic ether group.   5. A metal powder injection molded body, which is an injection molded body of the metal powder injection molding compound according to any one of claims 1 to 4.   A sintered body, which is a sintered product of the metal powder injection-molded body according to claim 5.