EP0511428B1 - Verdichtungs-Injektionszusammensetzung zur Herstellung von Metallpulver-Sinterformkörper und daraus hergestellter Sinterformkörper - Google Patents

Verdichtungs-Injektionszusammensetzung zur Herstellung von Metallpulver-Sinterformkörper und daraus hergestellter Sinterformkörper Download PDF

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EP0511428B1
EP0511428B1 EP91107049A EP91107049A EP0511428B1 EP 0511428 B1 EP0511428 B1 EP 0511428B1 EP 91107049 A EP91107049 A EP 91107049A EP 91107049 A EP91107049 A EP 91107049A EP 0511428 B1 EP0511428 B1 EP 0511428B1
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Prior art keywords
composition
compacts
binder
weight
polymer
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French (fr)
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EP0511428A1 (de
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Norimasa Uesugi
Hirokazu Kato
Katuyoshi Saitoh
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Dai Ichi Ceramo Co Ltd
DKS Co Ltd
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Dai Ichi Kogyo Seiyaku Co Ltd
Dai Ichi Ceramo Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
    • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B22F1/103—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material containing an organic binding agent comprising a mixture of, or obtained by reaction of, two or more components other than a solvent or a lubricating agent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy

Definitions

  • the present invention relates to an injection compacting composition for preparing sintered bodies of metallic powders which comprises a metallic powder and a specific organic binder. More particularly, the present invention relates to the injection compacting composition which has a good injection compactibility and shows a high shape retainability of compacts prepared therefrom without deformation when removing the binder from the compacts, and which can provide sintered bodies having no or little defects such as warpage and cracks and having a high density in high yields, and also relates to sintered bodies prepared therefrom and a process for the preparation of the sintered bodies.
  • Sintered bodies have been prepared by compacting a mixture of an inorganic powder with an organic binder and sintering the resulting compacts.
  • ceramic products have been prepared by mixing a ceramic powder and an organic binder, imparting a plasticity to the mixture, injection-compacting the mixture to give green compacts, removing the binder from the compacts and sintering the compacts.
  • the production of sintered ceramic products by injection molding has the features that parts of complicated shape which cannot be produced by press molding, can be mass-produced industrially.
  • metal powders have a relatively large particle size
  • ceramic powders have an average particle size as fine as below 3 ⁇ m
  • metal powders used as raw materials for the production of sintered metallic materials have in general a higher specific gravity than usual ceramic powders such as alumina powder
  • metal powders are poor in wettability with binders as compared with usual ceramic powders, for example, oxide ceramic powders such as alumina
  • problems are encountered, e.g. poor injection compactibility, lack of strength of green compacts and deformation of compacts in removal of the binder. Accordingly, it has been difficult to produce good sintered metallic materials as in the case of the production of ceramic products, and at times even green compacts cannot be satisfactorily prepared.
  • Removal of the binder from compacts prepared by compacting a mixture of a metal powder and the binder by thermal decomposition has been generally conducted by embedding the compacts in a powder unreactive to the compacts, e.g. alumina or zirconia, whereby seeping out of the binder by capillary action is accelerated to shorten the time required for binder removal, and the shape retainability of compacts is raised.
  • a powder unreactive to the compacts e.g. alumina or zirconia
  • the removal of binder by such a method requires a wider space due to the use of powder medium for embedding the compacts, and also, when taking the compacts in and out from the powder medium, the surface of the compacts may be frequently scratched. Also, it is troublesome to completely remove the medium powder sticking to the surface of the compacts which have become fragile by the removal of binder, and it frequently takes time beyond expectation.
  • binders For producing sintered metallic materials by injection compacting, there are required various characteristics, e.g. a mixture of a metal powder and a binder having an excellent compactibility such as powder flowability or compacting stability, the obtained compacts having a high strength sufficient for handling, and the binder being easily removed from the compacts without causing cracking, blistering and deformation such as warpage. Accordingly, the selection of binders to be admixed with metallic powders is important.
  • binders As the organic binder used in compacting ceramic powders, there have been known, for instance, waxes and polymers such as ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polystyrene, polyethylene, and acrylic and methacrylic polymers. These binders are also applicable to the production of sintered metallic materials. However, these known binders have both merits and demerits and are not always satisfactory in required characteristics such as compactibility (e.g.
  • ethylene-vinyl acetate copolymer is superior in powder flowability and can provide green compacts having a high strength and an adequate elasticity without impairing the flowability when mixed with a metal powder.
  • EVA ethylene-vinyl acetate copolymer
  • the ethylene-ethyl acrylate copolymer can also provide a high strength and an adequate elasticity to compacts without impairing the flowability when mixed with metallic powders.
  • EVA ethylene-ethyl acrylate copolymer
  • polystyrene, and acrylic and methacrylic polymers have an excellent binding effect on metallic powders and impart a high strength to green compacts.
  • they are effective for preventing damages of thin portions, thus imparting an excellent shape retainability to green compacts.
  • They are also superior in thermal decomposability and are easy to be removed from the compacts.
  • mixtures with metallic powders are insufficient in flowability, and are easy to invite poor results in injection molding such as shortage of filling and weld line.
  • binders In order to obtain a binder having satisfactory properties, it is desirable to use these binders in combination by combining two or more of binders having different characteristics in a good balance.
  • a difficulty is encountered in obtaining a homogeneous mixture by mixing such known binders, or a long time is required for the mixing, because they differ from each other in form and softening point and also because the solubility or compatibility is not satisfactory.
  • the mixing of two or more binders is not so sufficient as to provide a homogeneous mixture, it takes a longer time to determine the compacting conditions since the flowability of the mixture is not stabilized.
  • the use of nonuniform binder mixture may cause cracking of sintered bodies in addition to influence on dimensional stability of compacts.
  • US-A-4 000 110 discloses an injection molding composition comprising a ceramic material and a binder.
  • the binder comprises atactic polypropylene and a thermal plastic resin such as ethylene vinyl acetate copolymer, polystyrene or polymethacrylate.
  • the binder comprises a dispersed copolymer of ethylene and vinylacetate or ethyl acrylate and (meth)acrylic ester monomer in styrene monomer.
  • EP-A-0 296 552 discloses an injection molding composition comprising a metal powder and a binder, which binder comprises polymers such as atactic polypropylene and mixtures of ethylene vinylacetate copolymer and an acrylic resin and an auxiliary binder agent such a adamantane.
  • a still another object of the present invention is to provide a process for preparing a sintered metallic body wherein the removal of binder from compacts is conducted without using a powder medium.
  • an injection compacting composition suitable for preparing sintered bodies of metal powders which comprises a metal powder and an organic binder, said organic binder comprising a composite acrylic polymer and an atactic polypropylene, and said composite acrylic polymer being a suspension polymerization product prepared by dissolving (a) a polymer selected from the group consisting of an ethylene-vinyl acetate copolymer and an ethylene-ethyl acrylate copolymer in (b) an acrylic or methacrylic acid ester monomer or a mixture of an acrylic or methacrylic acid ester monomer and a styrene compound monomer, dispersing the resulting solution in an aqueous medium in the presence of a dispersing agent, and subjecting the resulting dispersion to a suspension polymerization.
  • Sintered metallic materials can be easily prepared from the injection compacting composition, for example, by injection-compacting the composition, heating the resulting compact at a rate of 3° to 300°C/hour to a temperature of 450° to 600°C, thereby removing binder from the compact, and sintering the compact.
  • the metal powders used with the specific organic binder for preparing the injection compacting composition of the present invention are not particularly limited so long as they are metal powders which have been used for the purposes of sintered bodies.
  • metal powders having a spherical particle form or a form near sphere and having an average particle size of about 1 to about 50 ⁇ m, especially about 1 to about 12 ⁇ m, are preferred.
  • the average particle size is less than 1 ⁇ m, the specific surface area of the powder increases relatively.
  • the powder having a large specific surface area is hard to provide a compacting composition having a flowability adequate for injection compacting even if the amount of binder used is increased.
  • the metal powder are, for instance, pure iron, an iron alloy such as iron-nickel alloy, iron-cobalt alloy or stainless steel, tungsten, an aluminum alloy, copper or a copper alloy, and the like.
  • the metal powders used in the present invention are not limited to these exemplified powders.
  • the organic binder used in the present invention comprises at least two components, namely the composite acrylic polymer and an atactic polypropylene.
  • the above mixed organic binder may also contain additives, e.g. a plasticizer such as a phthalic acid ester for imparting a plasticity to the organic binder, waxes for improving the flowability, a lubricant or mold releasing agent such as a higher fatty acid, a surface active agent for improving the wettability of the surface of metal powders, and a surface treating agent (coupling agent).
  • the composite acrylic polymer, atactic polypropylene and optionally additives may be previously admixed to form the organic binder and be added to the metal powder, or they may be individually added to the metal powder.
  • the composite acrylic polymer has an excellent uniform structure as compared with a polymer blend. It is superior in the flowability of the compacting composition and the removability from green compacts, and has an excellent effect of binding metal particles. It is used for the purpose of imparting a sufficient flowability to the obtained composition and imparting sufficient strength and elasticity to the green compacts obtained from the composition.
  • the composite acrylic polymer is prepared by dissolving the polymer component (a), i.e. an ethylene-vinyl acetate copolymer and/or an ethylene-ethyl acrylate copolymer, and a polymerization initiator in the monomer component (b), i.e. an acrylic or methacrylic acid ester alone or a mixture of an acrylic or methacrylic acid ester and styrene, dispersing the resulting solution in an aqueous medium containing a dispersing agent, and subjecting the resulting dispersion to a suspension polymerization.
  • a chain transfer agent may be used as occasion demands, and it is added to the above-mentioned solution.
  • the composite acrylic polymer is prepared by previously dissolving EVA and/or EEA in the monomer component and then dispersing the resulting solution in an aqueous medium followed by suspension polymerization, it is in the state like a sort of a polymer alloy wherein the polymer formed from the monomer component (b) is very uniformly dispersed in the polymer component (a), as observed in Figs. 1 and 3 which are microphotographs of composite acrylic polymer particles prepared according to the present invention and etched with a solvent to reveal the inner structure of the particles.
  • the composite acrylic polymer has the advantages that the conditions for compacting the composition can be determined more easily as compared with the use of a mere blend of the polymers (cf. Figs. 2 and 4) and the flowability of the composition is stabilized and, therefore, good sintered bodies can be obtained in high yields with a little scatter.
  • the ethylene-vinyl acetate copolymers (EVA) used in the present invention are not particularly limited, and any of commercially available ethylele-vinyl acetate copolymers can be used.
  • Copolymers of ethylene and vinyl acetate in a ratio of 85/15 to 50/50 by weight, especially 80/20 to 60/40 by weight, are particularly preferred, since if the ratio is more than 85/15 by weight, it becomes hard to dissolve in the monomer component (b), and since if the ratio is less than 50/50 by weight, such copolymers are available with difficulty and also there is a tendency to lower the strength of green compacts.
  • the ethylene-vinyl acetate copolymers are those having a melt index of about 10 to about 500.
  • the copolymers are those having a melt index of about 20 to about 400.
  • the ethylene-ethyl acrylate copolymers (EEA) used in the present invention are not particularly limited, and any of commercially available ethylene-ethyl acrylate copolymers can be used.
  • Copolymers of ethylene and ethyl acrylate in a ratio of 85/15 to 50/50 by weight, especially 80/20 to 60/40 by weight, are preferred, since if the ratio is more than 85/15 by weight, it becomes hard to dissolve in the monomer component (b), and since if the ratio is less than 50/50 by weight such copolymers are available with difficulty and also there is a tendency to lower the strength of green compacts.
  • the ethylene-ethyl acrylate copolymers are those having a melt index of about 10 to about 2,000. From the viewpoints of the powder flowability and the strength of green compacts, it is more preferable that the copolymers are those having a melt index of about 100 to about 1,500.
  • the acrylic and methacrylic acid esters used as the monomer component (b) are not particularly limited, but from the viewpoints of powder flowability in compacting, strength of green compacts and binder removability, esters of acrylic or methacrylic acid with an alcohol having 1 to 8 carbon atoms are preferred.
  • Examples of the (meth)acrylic acid ester are, for instance, n-alkyl (meth)acrylates having a C 1 to C 8 alkyl group, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)-acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, and the like.
  • n-alkyl (meth)acrylates having a C 1 to C 4 alkyl group, isopropyl (meth)acrylate and isobutyl (meth)acrylate are particularly preferred.
  • the (meth)acrylic acid esters may be used alone or in admixture thereof.
  • the (meth)acrylic acid esters can be used in admixture with a styrene compound.
  • styrene compound are, for instance, styrene, ⁇ -methylstyrene, p-methylstyrene and vinyl styrene.
  • the content of the styrene compound in a mixture of the (meth)acrylic acid ester and the styrene compound is not more than 80 % by weight.
  • the flowability of the obtained binder decreases with increasing the amount of styrene compound, thus the use of the styrene compound in a higher proportion tends to lower the compactibility.
  • monomers e.g. acrylic acid, methacrylic acid, vinyl acetate and vinyl chloride, may be used in a small amount as the component (b) so long as the desired properties of the obtained polymer used as the binder are not substantially impaired.
  • the polymer component (a) and the monomer component (b) are used in an (a)/(b) ratio of about 5/95 to about 80/20 by weight, preferably about 20/80 to about 70/30 by weight.
  • the powder flowability in compacting is apt to be insufficient. Insufficient flowability is easy to cause bad compacting.
  • blistering may occur when the binder is removed by thermal decomposition, thus resulting in lowering of the strength of sintered body, and also the binder removal and the handling become difficult.
  • an oil-soluble polymerization initiator so that the polymerization proceeds in oil droplets dispersed in the aqueous medium, thus polymer particles wherein the polymer component (a) and the polymer formed from the monomer component (b) are uniformly blended, are produced.
  • the polymerization initiator are, for instance, an organic peroxide such as benzoyl peroxide, lauroyl peroxide or t-butyl-peroxy-2-ethylhexanate, an azo compound such as azoisobutylonitrile or azobisdimethylvaleronitrile, and other oil-soluble polymerization initiators.
  • the initiators may be used alone or in admixture thereof.
  • the amount of the initiator is from 0.05 to 1.5 parts by weight, preferably 0.1 to 0.6 part by weight, per 100 parts by weight of the monomer component (b).
  • chain transfer agent which may be used in the polymerization in order to control the molecular weight are, for instance, a mercaptan such as dodecylmercaptan or t-octylmercaptan, ⁇ -methylstyrene, and a dimer of ⁇ -methylstyrene.
  • the chain transfer agents may be used alone or in admixture thereof.
  • the amount of the chain transfer agent is from 0.01 to 1.0 part by weight, preferably 0.03 to 0.5 part by weight, per 100 parts by weight of the monomer component (b).
  • the polymer component (a) is completely dissolved in the monomer component (b) so that the reaction proceeds uniformly, thus producing a polymer having a uniform composition.
  • the manner of the dissolution is not particularly restricted. When a polymerization initiator is dissolved, the dissolution should be conducted at a temperature lower than the decomposition temperature of the initiator. The solution is dispersed in an aqueous medium in the presence of a dispersing agent, and the resulting suspension is subjected to a suspension polymerization.
  • dispersing agents can be used in the present invention.
  • Representative examples of the dispersing agent are, for instance, a water-soluble organic high molecular weight compound such as polyvinyl alcohol, hydroxyethyl cellulose or polyvinylpyrrolidone, and a combination of an anionic surface active agent and a fine powder of a slightly water-soluble inorganic compound such as hydroxyapatite or magnesium pyrophosphate.
  • the dispersing agent is used in an amount of 0.1 to 1 part by weight, preferably 0.2 to 0.5 part by weight, per 100 parts by weight of the aqueous medium.
  • the solution of the polymer component (a) and the initiator in the monomer component (b), which may further contain a chain transfer agent, is dispersed in an aqueous medium, e.g. water, in an amount of 30 to 120 parts by weight, preferably 50 to 100 parts by weight, per 100 parts by weight of the aqueous medium.
  • an aqueous medium e.g. water
  • the conditions and the like for the suspension polymerization are not particularly limited, thus the suspension polymerization can be conducted in a usual manner.
  • the polymerization temperature is determined according to the decomposition temperature of the polymerization initiator used.
  • the polymerization is usually carried out at a temperature of 50° to 130°C for 2 to 10 hours.
  • the thus obtained product of the suspension polymerization is a composite polymer wherein the polymer formed from the monomer component (b) is uniformly dispersed in the polymer component (a), as observed in Figs. 1 and 3 which are microphotographs of polymer particles prepared according to the present invention and etched with a solvent to reveal the inner structure of the particles.
  • the composite polymer prepared according to the present invention is useful as a binder for the preparation of sintered bodies of metal powders, and has the advantages as mentioned above.
  • the composite acrylic polymer is used in combination with an atactic polypropylene, in order to improve the shape retainability of compacts in the step of removing the binder from the compacts by thermal decomposition. Accordingly, the deformation of the compacts in the binder removing step can be remarkably decreased by the combination use of the composite acrylic polymer and atactic polypropylene.
  • the proportion of the composite acrylic polymer in the organic binder used in the present invention is usually from 20 to 80 % by weight, preferably 35 to 65 % by weight, based on the weight of the organic binder.
  • the proportion of the composite acrylic polymer is less than 20 % by weight, the strength of compacts prepared from the composition of the invention is insufficient, and accordingly a difficulty is encountered in taking out the compact from a mold. It is also difficult to handle the compact.
  • the proportion is more than 80 % by weight, mixing of a metal powder and the binder requires a long time due to lack of the wettability. Also, there is a tendency to be lacking in flowability of the obtained composition.
  • atactic polypropylene (APP) polymers can be used in the present invention.
  • Atactic polypropylene having a softening point of at most 110°C is preferable from the viewpoint of the flowability of the mixture of a metal powder and the binder.
  • the proportion of the atactic polypropylene in the organic binder used in the present invention is usually from 8 to 50 % by weight, preferably from 12 to 35 % by weight, based on the weight of the organic binder.
  • the proportion of the atactic polypropylene is less than 8 % by weight, the desired effects mentioned above are not sufficiently exhibited.
  • the proportion is more than 50 % by weight, the fatal defect of the atactic polypropylene, namely poor mold releasing property, markedly appears and, therefore, green compacts are released from a mold with difficulty, thus decreasing the compacting efficiency. Also, there is a tendency to decrease the strength of compacts.
  • the organic binder may contain waxes or other additives such as a plasticizer, a lubricant, a surfactant, etc., as occasion demands.
  • a plasticizer such as paraffin waxes, microcrystalline wax, carnauba wax, montan wax, and the like.
  • the plasticizer are, for instance, a phthalate such as dibutyl phthalate or octyl phthalate, a phosphate, a fatty acid ester, and the like.
  • the lubricant are, for instance, a higher fatty acid, a higher fatty acid amide, a higher fatty acid ester, a higher fatty acid salt.
  • Additives which have been usually used for injection compacting of ceramic powders can be used without any restriction.
  • the total content of these optional components in the organic binder is preferably at most 50 % by weight from the viewpoints of the strength of compacts and the shape retainability of compacts in removal of the binder.
  • the ratio of the metal powder to the organic binder which contains the composite acrylic polymer and the atactic polypropylene as the essential components is preferably from 100/4 to 100/15 by weight.
  • the weight ratio is more than 100/4, the injection compacting composition is lacking in flowability, thus formation into a desired shape is apt to be difficult.
  • the weight ratio is less than 100/15, the density of the obtained compacts is low and, therefore, the sintered compacts are poor in dimensional accuracy due to large shrinkage in sintering and also defects such as cracks and blister are produced in the compacts due to generation of a gas in removal of the binder by thermal decomposition.
  • the preparation of sintered metallic materials from the injection compacting composition of the present invention is conducted usually according to the following method, but is not limited thereto.
  • a metal powder is kneaded sufficiently with the organic binder under heating by a kneader such as a pressure kneader to disperse uniformly the metal powder into the organic binder.
  • the resulting mixture is formed into an appropriate shape such as pellets or pulverized coarse particles to provide an injection compacting composition.
  • the composition is then injection-compacted into a desired shape using a known injection molding machine as used for usual plastic molding by a known method.
  • the organic binder is then removed from the obtained compacts by thermal decomposition or other methods, and the sintering is carried out in an appropriate atmosphere at an appropriate temperature to give sintered bodies having a desired shape.
  • the removal of the binder is carried out by placing the compacts in a non-oxidizing atmosphere, e.g. a reducing atmosphere such as hydrogen gas or an inert gas atmosphere such as helium, argon or nitrogen gas, and heating at a temperature elevation rate of 3° to 300°C/hour to a temperature of 450° to 600°C.
  • a non-oxidizing atmosphere e.g. a reducing atmosphere such as hydrogen gas or an inert gas atmosphere such as helium, argon or nitrogen gas
  • the temperature may be elevated at a constant rate or stepwise.
  • the temperature elevation rate varies depending on the shape of compacts, the thickness of compacts, and other factors, and is suitably selected from the above range. It is general to conduct the binder removing treatment under such conditions that the treatment is completed in the shortest time, but when the temperature elevation rate is more than 300°C/hour, defects such as blister or cracks are produced in the compacts and it is difficult to carry out the treatment satisfactorily. On the other hand, when the temperature elevation rate is less than 3°C/hour, the treatment requires a too long time and is not practical. If the maximum temperature of the heating is lower than 450°C, the treatment may result in insufficient removal of binder when the compacts is thick. If the compacts are heated to over 600°C, deformation of the compacts may occur.
  • the organic binder containing the composite acrylic polymer and atactic polypropylene as the essential components has the advantages that the removal of the binder from compacts can be achieved by directly placing the compacts on a suitable plate such as an alumina plate and heating them with a simple temperature elevation pattern, without adopting a general method wherein the compacts are embedded in a powder such as alumina and heated, or other special methods for removing binder, and that even if the treated compacts are subsequently sintered, good sintered bodies having no defects are obtained.
  • the organic binder according to the present invention has an excellent shape retention property and, therefore, it is effective particularly for compacts having a complicated shape, for example, compacts having a projecting long portion like a pin which require a very high shape retainability.
  • the removal of the binder from compacts may be carried out according to a conventional manner, for example, by embedding the compacts in a powder medium such as alumina powder and heating them.
  • a 5 liter reactor was charged with 700 g of n-butyl methacrylate (BMA), 500 g of styrene and 0.35 g of n-dodecylmercaptan.
  • BMA n-butyl methacrylate
  • EVA ethylene-vinyl acetate copolymer
  • the temperature was elevated to 75°C and the EVA was dissolved in the monomer mixture, and 4.8 g of benzoyl peroxide and 0.25 g of t-butylperoxybenzoate were further dissolved therein.
  • a 5 liter reactor was charged with 600 g of n-butyl methacrylate (BMA) and 0.3 g of n-dodecylmercaptan, and the temperature was elevated to 75°C with stirring.
  • BMA n-butyl methacrylate
  • EVA ethylene-vinyl acetate copolymer
  • Ultracen trade mark "Ultracen” 722 made by Tosoh Corporation
  • aqueous solution of a dispersing agent prepared from 1,840 ml of deionized water and 160 ml of 3 % aqueous solution of polyvinyl alcohol was added to the reactor and stirred to suspend the EVA-BMA solution in the aqueous solution. After replacing the polymerization system with nitrogen gas, the polymerization was carried out at 80°C for 3 hours and then at 100°C for 2 hours. After cooling the reaction mixture, the produced polymer was taken out of the reactor, washed with water and dried.
  • the produced polymer was in the form of spherical particles, the particle size of which fell within the range of 0.3 to 1 mm, and had an intrinsic viscosity [ ⁇ ] of 0.85 (toluene solution at 30°C).
  • composite acrylic polymer (B) The thus obtained polymer is hereinafter referred to as "composite acrylic polymer (B)".
  • an organic binder having the composition shown in Table 1 was added to 100 parts of the metal powder. They were kneaded by a Laboplasto Mill (made by Toyo Seiki Kabushiki Kaisha) at a temperature of 140° ⁇ 10°C for 30 minutes.
  • the obtained mixture was ground to particles having a particle size of 3 to 5 mm, and formed into bobbin-shaped compacts shown in Fig. 5 by an injection molding machine (vertical plunger type injection molding machine made by Yamashiro Seiki Kabushiki Kaisha) at an injection temperature of 120° to 170°C at an injection pressure of 500 to 700 kg/cm 2 .
  • the compacts were directly placed on an alumina plate without embedding in a powder such as alumina, and were heated in a nitrogen atmosphere at a rate of 10°C/hour from room temperature to 500°C to remove the binder from the compacts.
  • the compacts were subsequently sintered under the conditions shown in Table 2 to give sintered metallic materials.
  • the metal powder composition containing the specific organic binder according to the present invention provides, by injection molding, compacts which can withstand a thermal treatment to remove the binder with a high shape retention and without causing defects such as cracks and deformation, thus provides sintered metallic materials having no defects and a high theoretical density percentage.

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  • Powder Metallurgy (AREA)

Claims (8)

  1. Eine durch Spritzgießen verdichtbare Zusammensetzung, aus der gesinterte Formkörper aus metallischem Pulver hergestellt werden können und die ein metallisches Pulver und ein organisches Bindemittel umfaßt, wobei das organische Bindemittel ein zusammengesetztes Acrylpolymeres und ein ataktisches Polypropylen enthält und das zusammengesetzte Acrylpolymere ein Suspensionspolymerisationsprodukt ist, das hergestellt wurde, indem man
    a) ein Polymeres, ausgewählt aus der Gruppe bestehend aus einem Ethylenvinylacetatcopolymeren und einem Ethylenethylacrylatcopolymeren in
    b) einem Acryl- oder Methacrylsäureestermonomer oder einer Mischung aus einem Acryl- oder Methacrylsäureestermonomer und einer monomeren Styrolverbindung löst, die resultierende Lösung in einem wäßrigen Medium in Gegenwart eines Dispersionsmittels dispergiert und die resultierende Dispersion einer Suspensionspolymerisation unterwirft.
  2. Zusammensetzung nach Anspruch 1, worin das Gewichtsverhältnis des metallischen Pulvers zu dem organischen Bindemittel von 100:4 bis 100:15 beträgt.
  3. Zusammensetzung nach Anspruch 1, worin das organische Bindemittel 20-80 Gew.-% des zusammengesetzten Acrylpolymeren und 8-50 Gew.-% des ataktischen Polypropylens enthält.
  4. Zusammensetzung nach Anspruch 1, worin das organische Bindemittel maximal 50 Gew.-% eines weiteren Additivs ausgewählt aus der Gruppe bestehend aus einem Wachs, einem Weichmacher und einem Gleitmittel enthält.
  5. Zusammensetzung nach Anspruch 1, worin die Lösung der Komponente a) in der Komponente b) einen öllöslichen Polymerisationsstarter enthält.
  6. Zusammensetzung nach Anspruch 1, worin die Lösung der Komponente a) in der Komponente b) ein Kettenübertragungsmittel enthält.
  7. Zusammensetzung nach Anspruch 1, worin die Polymerkomponente a) und die Monomerkomponente b) in einem Gewichtsverhältnis a):b) von 5:95 bis 80:20 verwendet werden.
  8. Ein Verfahren zur Herstellung eines gesinterten Formkörpers aus einem metallischen Pulver, indem man die Zusammensetzung nach Anspruch 1 durch Spritzgießen verdichtet, den erhaltenen verdichteten Formkörper in einer nichtoxidierenden Atmosphäre mit einer Temperatursteigerung von 3-300°C/h auf eine Temperatur von 450-600°C zum Entfernen des Bindemittels erhitzt und den Formkörper sintert.
EP91107049A 1989-11-28 1991-05-01 Verdichtungs-Injektionszusammensetzung zur Herstellung von Metallpulver-Sinterformkörper und daraus hergestellter Sinterformkörper Expired - Lifetime EP0511428B1 (de)

Priority Applications (1)

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DE1991622228 DE69122228T2 (de) 1991-05-01 1991-05-01 Verdichtungs-Injektionszusammensetzung zur Herstellung von Metallpulver-Sinterformkörper und daraus hergestellter Sinterformkörper

Applications Claiming Priority (1)

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JP1308175A JPH0711010B2 (ja) 1989-11-28 1989-11-28 金属粉末射出成形用組成物、それからの金属焼結部材および該焼結部材の製法

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EP0511428A1 EP0511428A1 (de) 1992-11-04
EP0511428B1 true EP0511428B1 (de) 1996-09-18

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US5942566A (en) * 1997-07-03 1999-08-24 Advanced Ceramics Research, Inc. Ceramic feedstock composition for the manufacture of prototype elements
US8316541B2 (en) 2007-06-29 2012-11-27 Pratt & Whitney Canada Corp. Combustor heat shield with integrated louver and method of manufacturing the same

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JP3924671B2 (ja) * 1999-04-19 2007-06-06 第一工業製薬株式会社 金属粉末射出成形用組成物

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EP0296552B1 (de) * 1987-06-25 1993-05-26 Idemitsu Petrochemical Co. Ltd. Metallbinder und Zusammensetzung für die Guss-Formung
JPH0647682B2 (ja) * 1987-09-10 1994-06-22 株式会社トーキン 金属焼結体の製造方法
JPH01212705A (ja) * 1988-02-18 1989-08-25 Seiko Epson Corp 磁性材料の製造方法
JPH02194104A (ja) * 1988-10-11 1990-07-31 Nippon Tungsten Co Ltd 金属粉末成形焼結用バインダーと同バインダーを使用した焼結体の製造法

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5942566A (en) * 1997-07-03 1999-08-24 Advanced Ceramics Research, Inc. Ceramic feedstock composition for the manufacture of prototype elements
US8316541B2 (en) 2007-06-29 2012-11-27 Pratt & Whitney Canada Corp. Combustor heat shield with integrated louver and method of manufacturing the same
US8904800B2 (en) 2007-06-29 2014-12-09 Pratt & Whitney Canada Corp. Combustor heat shield with integrated louver and method of manufacturing the same

Also Published As

Publication number Publication date
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EP0511428A1 (de) 1992-11-04
JPH03170602A (ja) 1991-07-24

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