Composition for sintered molding, green molding, and sintered molding

Abstract

To provide a composition for a sintered molding which can degrease an organic binder in a short time without requiring a special facility or process, prevents die contamination during molding, and can suppress cracking and swelling during molding and after sintering.SOLUTION: A composition for a sintered molding contains sinterable inorganic powder, and an organic binder, wherein the organic binder contains at least a polyacetal resin, a polyolefin resin and an epoxy resin, and the total terminal amount of the polyacetal resin to the total polyoxymethylene units is 0.1 mol% or more and 0.75 mol% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composition for sintered molded bodies, a green molded body, and a sintered molded body. [Background technology]

[0002] Among sintered bodies made using sinterable inorganic powders such as metals, ceramics, and cermets as materials, techniques are known for producing precise sintered bodies and sintered bodies with complex shapes using a sinterable inorganic powder and a binder composition. This sintered body production composition is used to produce a green molded body by injection molding the heated and kneaded raw material for sintered molded bodies, followed by a degreasing process for the green molded body, and then sintering.

[0003] In the production of sintered bodies using the above-mentioned sintered body manufacturing compositions, the most important step in obtaining a high-quality sintered body free from defects such as cracks, blistering, and deformation is the degreasing step. This degreasing step is a process of removing the binder from the green molded body, which is a molded body of the sintered body manufacturing composition. Methods used for this include heating the green molded body to decompose and gasify the binder, or treating the green molded body with a solvent to dissolve and remove the soluble binder components in the green molded body, and then heating and gasifying the remaining binder. However, in the heat degreasing method described above, which involves heating and degreasing a green molded body, if the thermal decomposition and gasification of the binder contained in the green molded body occur rapidly and intensely, there is a risk of cracking or blistering occurring in the molded body during the degreasing process. Therefore, degreasing had to be carried out by heating for a long period of time.

[0004] Therefore, in order to suppress cracking and blistering of the molded product during the degreasing process described above, a technique is known that uses a depolymerizable polymer as a binder. For example, by using polyacetal resin, which is a depolymerizable polymer, as a binder together with other resins, the shape retention of the green molded product can be improved based on the rigidity of the polyacetal resin, and the shape retention of the molded product during the degreasing process by heating can be improved. Such technologies include, for example, those disclosed in Patent Documents 1 and 2, which involve using polyacetal resin and epoxy resin in combination as a binder to improve the compatibility and homogenization of the binder resin components, thereby enhancing the quality of green molded products, degreased products, and sintered products, and improving the degreasing speed. Research is also being conducted to achieve this. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-109994 [Patent Document 2] Japanese Patent Publication No. 2021-080350 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, while the technology described in Patent Document 1 states that deformation and swelling can be suppressed even after degreasing and firing by using a resin component containing polyacetal resin and epoxy resin as an organic binder, it does not disclose specific methods for suppressing mold contamination (mold deposits) during the production of green molded products or for improving dimensional accuracy, and further improvements in these areas were desired.

[0007] In addition, in the technology of Patent Document 2, by including an organic compound having a melting point of 100°C or lower and a thermoplastic resin having a Vicat softening point of 130°C or lower as components constituting an organic binder, it is described that the heating debinding and sintering times can be shortened and a sintered body without defects can be obtained. However, the debinding process of this organic binder must be carried out in superheated steam at 100°C or higher and 600°C or lower. Compared with the normal debinding process carried out in an inert gas atmosphere, it requires special equipment and the manufacturing process becomes complicated.

[0008] Therefore, an object of the present invention is to provide a composition for a sintered compact, a green compact, and a sintered compact that can debind an organic binder in a short time without requiring special equipment or processes, does not cause mold contamination during molding, and can suppress cracking and swelling during molding and after sintering.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above-described problems with respect to a composition for a sintered compact containing a sinterable inorganic powder and an organic binder, the present inventors used a polyacetal resin, a polyolefin resin, and an epoxy resin as the organic binder, and by optimizing the total terminal amount of the polyacetal resin with respect to all polyoxymethylene units, the compatibility of the components constituting the organic binder was enhanced, and the resin components were less likely to adhere to the mold during molding. Thus, it was found that the organic binder can be debound in a short time without requiring special equipment or processes, and mold contamination, cracking, and swelling of the compact can also be suppressed, leading to the completion of the present invention.

[0010] The present invention has been made based on the above findings, and the gist thereof is as follows. 〔1〕A composition for a sintered compact containing a sinterable inorganic powder and an organic binder, wherein the organic binder contains at least a polyacetal resin, a polyolefin resin, and an epoxy resin, A composition for sintered molded articles, characterized in that the total amount of terminals of the polyacetal resin relative to the total polyoxymethylene units is 0.1 mol% or more and 0.75 mol% or less. [2] The sintered molded body composition according to [1], characterized in that the amount of hemiformal terminals relative to the total polyoxymethylene units of the polyacetal resin is 0.05 mol% or more and 0.2 mol% or less. [3] The sintered molded article composition according to [1] or [2], characterized in that the total amount of terminals of the polyacetal resin relative to the total polyoxymethylene units is 0.31 mol% or more and 0.5 mol% or less. [4] The sintered molded body composition according to [2], characterized in that the amount of hemiformal terminals relative to the total polyoxymethylene units of the polyacetal resin is 0.14 mol% or more and 0.20 mol% or less. [5] The sintered molded body composition according to any one of [1] to [4], characterized in that the melt flow index of the polyacetal resin is 80 to 200 g / 10 min. [6] The composition for a sintered molded body according to any one of [1] to [5], characterized in that the organic binder contains at least one form-catching agent. [7] The sintered molded body composition according to any one of [1] to [6], characterized in that the epoxy resin is a copolymer of an olefin and an unsaturated compound having a glycidyl group. [8] The sintered molded body composition according to any one of [1] to [7], characterized in that the unsaturated compound having a glycidyl group in the epoxy resin is 1 to 25% by weight relative to the total weight of the epoxy resin. [9] The sintered molded body composition according to any one of [1] to [8], characterized in that the melt flow index of the epoxy resin is 3 to 400 g / 10 min.

[10] A composition for a sintered molded body according to any one of [1] to [9], characterized in that the organic binder contains a compatibilizer.

[11] A sintered molded body composition according to any one of [1] to

[10] , characterized in that the ratio of the organic binder to the total volume of the sinterable inorganic powder and the organic binder is less than 40% by volume.

[12] A green molded body characterized by being formed by molding a sintered molded body composition described in any of [1] to

[12] above.

[13] A sintered molded body characterized by being formed by sintering the green molded body described in

[12] above.

[14] A composition for a sintered molded body comprising a sinterable inorganic powder and an organic binder, The organic binder comprises at least a polyacetal resin, a polyolefin resin, and an epoxy resin. A sintered molded body composition characterized in that the amount of hemiformal terminals relative to the total polyoxymethylene units of the polyacetal resin contained in the kneaded sintered molded body composition is 0.14 mol% or more and 0.20 mol% or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a composition for sintered molded bodies that can degrease organic binders in a short time without requiring special equipment or processes, prevent mold contamination during molding, and suppress cracking and blistering during molding and after sintering, as well as green molded bodies and sintered molded bodies using the sintered molded body composition. [Modes for carrying out the invention]

[0012] The following describes in detail an embodiment for carrying out the present invention (hereinafter referred to as "this embodiment"). This embodiment is an example for explaining the present invention, and the present invention is not limited to this embodiment. That is, the present invention can be modified in various ways without departing from its essence.

[0013] <Composition for sintered molded bodies> The sintered molded body composition of this embodiment comprises a sinterable inorganic powder and an organic binder. In addition to the inorganic powder and the organic binder, the sintered molded body composition of this embodiment may also contain other additives as described later.

[0014] (Sinterable inorganic powder) The sintered molded body composition of this embodiment contains sinterable inorganic powder. Furthermore, the sinterable inorganic powder may be used individually or in combination with multiple other types.

[0015] In this embodiment, the sinterable inorganic powder can be selected from all known suitable sinterable inorganic powders. For example, it can be selected from metal powders, alloy powders, metal carbonyl powders, and mixtures thereof. Among these, it is particularly preferable to use metal powders or ceramic powders in order to impart functionality.

[0016] Examples of the metal powder include aluminum, magnesium, barium, calcium, cobalt, zinc, copper, nickel, iron, silicon, titanium, tungsten, and powders of metal compounds and metal alloys based on these. Here, the metal powder can be a mixture of individual alloy components, not just already completed alloys.

[0017] Examples of the aforementioned ceramic powders include oxides such as zinc oxide, aluminum oxide, and zirconia; hydroxides such as hydroxyapatite; carbides such as silicon carbide; nitrides such as silicon nitride and boron nitride; halides such as fluorite; silicates such as stearite; titanates such as barium titanate and lead zirconate titanate; carbonates; phosphates; ferrites; high-temperature superconducting materials; and the like.

[0018] Furthermore, the sinterable inorganic powder may be used alone, or it is also possible to use a combination of several inorganic substances, such as various metals, metal alloys, or ceramics. Particularly preferred metals and alloys include titanium alloys and stainless steel, while preferred ceramics include Al2O3 and ZrO2. For example, titanium-6 aluminum-4 vanadium alloy can be suitably used as a titanium alloy, and SUS316L can be suitably used as a stainless steel.

[0019] (Organic binder) The sintered molded body composition of this embodiment includes an organic binder in addition to a sinterable inorganic powder. Furthermore, the organic binder must contain at least a polyacetal resin, a polyolefin resin, and an epoxy resin, and the total amount of the polyacetal resin relative to the total polyoxymethylene units must be 0.1 mol% or more and 0.75 mol% or less. The epoxy resin can enhance the compatibility between the polyacetal resin and the polyolefin resin. In addition, by having the total amount of terminal components relative to the total polyoxymethylene units of the polyacetal resin be within a specific range (0.31 mol% or more and 0.5 mol% or less), the compatibility between the resin components in the organic binder can be further improved.

[0020] The volume ratio of the organic binder in the sintered molded body composition of this embodiment is not particularly limited, but is preferably 25 to 60% by volume, more preferably 30 to 55% by volume, and particularly preferably 35 to 50% by volume, based on 100% by volume of the sintered molded body composition. By including the organic binder within the range described above, a sintered molded body composition having a melt viscosity suitable for injection molding can be obtained, and a sintered product with reduced shrinkage and good dimensional accuracy can be obtained.

[0021] • Polyacetal resin Examples of the polyacetal resin include polyacetal homopolymers, polyacetal copolymers, or mixtures thereof. Among these, polyacetal copolymers are preferred as the polyacetal resin from the viewpoint of thermal stability. The polyacetal resin may be used individually or in combination of multiple types. Furthermore, the polyacetal may be used in powder form in addition to the pellets that are usually provided. The particle size of the powder is preferably D50 = 500 μm or less, and more preferably D50 = 300 μm or less.

[0022] Examples of the polyacetal homopolymer include polymers having oxymethylene units in their main chain, and both ends of the polymer can be encapsulated with ester groups or ether groups. The polyacetal homopolymer can be obtained from formaldehyde and known molecular weight modifiers as raw materials, and from these raw materials, it can be obtained from known slurry methods using known onium salt-based polymerization catalysts and hydrocarbons as solvents, for example, by polymerization methods described in Japanese Patent Publication No. 47-6420 and Japanese Patent Publication No. 47-10059. Furthermore, it is preferable that the polyacetal homopolymer is composed of oxymethylene units for 99.8 mol% or more of the main chain excluding both ends, and more preferably that the main chain excluding both ends is composed solely of oxymethylene units.

[0023] Examples of the polyacetal copolymer include polymers having oxymethylene units and oxyethylene units in their main chains, which can be obtained, for example, by copolymerizing trioxane with a cyclic ether and / or cyclic formal in the presence of a polymerization catalyst. The aforementioned trioxane is a cyclic trimer of formaldehyde, and is generally obtained by reacting it with an aqueous solution of formalin in the presence of an acidic catalyst. The cyclic ether and / or cyclic formal is a component copolymerizable with the trioxane, and examples include ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxatan, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, and 1,6-hexanediol formal. Ethylene oxide and 1,3-dioxolane are particularly preferred. These may be used individually or in combination of two or more.

[0024] The polymerization catalyst used in the production of the polyacetal copolymer is not particularly limited, but examples include boric acid (represented by Lewis acids), tin, titanium, phosphorus, arsenic, and antimonides. Among these, it is particularly preferable to use one or more of the following: boron trifluoride, boron trifluoride-based hydrates, and coordination complex compounds of organic compounds containing an oxygen atom or a sulfur atom with boron trifluoride. More specifically, for example, boron trifluoride, boron trifluoride diethyl etherate, and boron trifluoride-di-n-butyl etherate can be given as preferred examples. These may be used individually or in combination of two or more.

[0025] Furthermore, the deactivation of the polymerization catalyst in the production of the polyacetal copolymer can be carried out by adding the polyacetal resin obtained by the polymerization reaction to an aqueous solution containing at least one catalyst neutralizing deactivator such as ammonia, triethylamine, tri-n-butylamine, or hydroxides, inorganic salts, or organic salts of alkali metals or alkaline earth metals, or to an organic solvent, and stirring the slurry for several minutes to several hours. After catalyst neutralization and deactivation, the slurry is filtered and washed to remove unreacted monomers, catalyst neutralization deactivators, and catalyst neutralization salts, and then dried.

[0026] Furthermore, methods for deactivating the polymerization catalyst include contacting the polyacetal copolymer with a vapor such as ammonia or triethylamine, or contacting the polyacetal resin with at least one of the following in a mixer to deactivate the catalyst.

[0027] Furthermore, without deactivating the polymerization catalyst, the polyacetal copolymer can be heated in an inert gas atmosphere at a temperature below its melting point, thereby reducing the volatilization of the polymerization catalyst, and the end-stabilization treatment described later can be performed using the polyacetal copolymer.

[0028] Furthermore, the deactivation and volatilization reduction operations of the polymerization catalyst described above can be performed after pulverizing the polyacetal resin obtained by the polymerization reaction, if necessary.

[0029] The resulting polyacetal resin can be stabilized by decomposing and removing the unstable end portions as follows. For example, using a vented single-screw extruder or a vented twin-screw extruder, the polyacetal resin can be melted and the unstable end portions removed by decomposing and removing them in the presence of a known basic substance capable of decomposing unstable end portions, such as ammonia, fatty acid amines such as triethylamine and tributylamine, hydroxides of alkali metals or alkaline earth metals represented by calcium hydroxide, inorganic weak acid salts, or organic weak acid salts, as a notching agent.

[0030] Furthermore, recycled polyacetal resin can also be used. In the material recycling process, polyacetal resin used in products is recovered, and after removing any impurities such as grease, the crushed polyacetal resin can be used. In addition to material recycling, polyacetal resin used in products may also be recycled back into monomers through chemical recycling, and polyacetal resin produced from those monomers may be used. The recycled polyacetal resin may be used alone or mixed with non-recycled polyacetal resin.

[0031] Furthermore, the polyacetal resin may be a modified polyacetal. Generally, a modified polyacetal is a block copolymer having a modified segment in the polyacetal. The polyacetal segment may be a homopolymer residue consisting only of oxymethylene units, or a copolymer residue in which oxymethylene units and oxyalkylene units are randomly copolymerized. The modified segment is a component that does not correspond to the polyacetal segment, and examples include polyolefins, polyurethanes, polyesters, polyamides, polystyrenes, and alkyl polyacrylates.

[0032] The polyacetal segment is preferably a polyacetal copolymer residue in which oxymethylene units and oxyalkylene units are randomly copolymerized, and the modified segment is preferably a polyolefin or polyurethane.

[0033] The modified segment of the modified polyacetal is preferably a polyolefin from the viewpoint of reducing residue derived from the organic binder in the degreasing process. Specifically, examples include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyisoprene, polybutadiene, hydrogenated polybutadiene, and the like. From a similar viewpoint, the modified segment of the modified polyacetal is more preferably polyethylene, polypropylene, or hydrogenated polybutadiene, and is particularly preferably hydrogenated polybutadiene from the viewpoint of shape retention in the degreasing process and suppression of cracking and blistering in the degreasing process. The modified polyacetal resin can be used alone, or two or more modified polyacetal resins can be used together, or it can be mixed with unmodified polyacetal resin.

[0034] Furthermore, in the sintered molded body composition of this embodiment, the total amount of terminals of the polyacetal resin relative to the total polyoxymethylene units must be 0.1 mol% or more. It is believed that the higher the total amount of terminals relative to the total polyoxymethylene units, the more interaction points there will be with other resins (polyolefin resin, epoxy resin, etc.), and in particular, by setting it to 0.31 mol% or more, excellent compatibility can be achieved. From a similar viewpoint, the total amount of terminals of the polyacetal resin relative to the total polyoxymethylene units is preferably 0.1 mol% or more, and more preferably 0.31 mol% or more. When the total end-level content of the polyacetal resin relative to the total polyoxymethylene units is 0.1 mol% or more, the compatibility between the epoxy resin and the polyolefin resin tends to be excellent. Higher compatibility between each resin makes homogenization easier and reduces the uneven distribution of resin components, thereby reducing surface defects such as cracks and blistering in the sintered body and contributing to improved dimensional accuracy. Furthermore, excellent compatibility between each resin makes it less likely for resin components to adhere to the mold during molding, which can also reduce mold contamination. This is speculation, but epoxy resin has strong adhesive properties to metal, and if there is an uneven distribution of epoxy resin, it is more likely to adhere to the mold. However, by increasing the compatibility between the resin components, it is thought that the adhesive strength of the epoxy resin alone can be mitigated, thereby suppressing adhesion to the mold.

[0035] Furthermore, from the viewpoint of thermal stability, the total amount of terminals relative to the total polyoxymethylene units in the polyacetal resin must be 0.75 mol% or less, and from the same viewpoint, it is preferable that it be 0.5 mol% or less.

[0036] Here, the total amount of end-tickets relative to the total polyoxymethylene units in the polyacetal resin can be measured using an NMR measuring instrument. For example, when measurements are taken at an observation frequency of 900 MHz, with 128 cumulative measurements and a measurement temperature of 25°C, the total amount (mol%) of acetyl, formyl, methoxy, and hemiformal terminals relative to the main chain -OCH2- structure can be calculated as the total terminal amount relative to the total polyoxymethylene units.

[0037] The amount of hemiformal at the end of the polyacetal resin processed into feedstock, etc., relative to the total polyoxymethylene units, can be measured by separating only the polyacetal resin using, for example, the following procedure. First, the sample is freeze-dried and then HFIP (hexafluoroisopropanol) is added to the resulting pulverized sample to extract polyacetal resin and other materials. Furthermore, in order to remove oligomer components such as polyolefins, the obtained HFIP solution is concentrated, chloroform and methanol are added, and the solution is reprecipitated. After filtration, it is air-dried and then dried overnight in a vacuum dryer at 50°C to obtain a polyacetal resin solid. The obtained polyacetal resin solid is measured using the measurement method described above.

[0038] Furthermore, the total amount of terminal components relative to the total polyoxymethylene units in the polyacetal resin can be controlled by adjusting the amount of molecular weight modifier (e.g., methylal, methanol, formic acid, methyl formate, etc.) added during the polymerization of the polyacetal resin. Furthermore, the control of the total end-chain amount relative to the total polyoxymethylene units in the polyacetal resin can also be adjusted by kneading resins with different total end-chain amounts or by using polyacetal resins having a branched structure. In this case, recycled polyacetal resins, such as those in which the molecular chains have been cleaved due to thermal and aging changes, can also be used.

[0039] In the sintered molded body composition of this embodiment, the total amount of terminals relative to the total polyoxymethylene units of the polyacetal resin is specified, and examples of terminal types include acetyl terminals, formyl terminals, methoxy terminals, hemiformal terminals, and the like. Furthermore, in the sintered molded body composition of this embodiment, the amount of hemiformal terminals relative to the total polyoxymethylene units is preferably 0.05 mol% or more and 0.2 mol% or less, and more preferably 0.14 mol% or more and 0.2 mol% or less. Among the terminals present in the total polyoxymethylene units, the hemiformal terminals have particularly strong interactions with other resin components, which can further enhance compatibility.

[0040] The amount of hemiformal at the end of the polyacetal resin relative to the total polyoxymethylene units can be measured using the same measurement method as described above for the amount at the front end.

[0041] Furthermore, when the molecular chains of the polyacetal resin are cleaved, the ends of the cleaved sections become hemiformal ends. Therefore, a simple way to adjust the hemiformal ends is to mix in thermally decomposed polyacetal resin or recycled polyacetal resin that has undergone changes over time. Here, the amount of hemiformal terminals relative to the total polyoxymethylene units of the polyacetal resin can be controlled by using a polyacetal resin having a branched structure or by kneading resins with different amounts of hemiformal terminals.

[0042] • Polyolefin resin The aforementioned organic binder further comprises a polyolefin resin in addition to the polyacetal resin described above. Here, the polyolefin resin is a homopolymer or copolymer having structural units derived from alkenes having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms.

[0043] Specifically, the polyolefin resins mentioned above include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyisoprene, and polybutadiene. Preferably, polyethylene, polypropylene, and mixtures thereof are used, and polyethylene or polypropylene is more preferable from the viewpoint of shape retention in the degreasing process and suppression of cracking and blistering in the degreasing process. Suitable commercially available polyethylenes include, for example, the Suntec HD series (manufactured by Asahi Kasei), Suntec LD series (manufactured by Asahi Kasei), Suntec EVA series (manufactured by Asahi Kasei), Neozex, Ultzex, and Evolu (all manufactured by Prime Polymer), and suitable polypropylenes include Sumitomo Noblen (manufactured by Sumitomo Chemical), Novatec PP (manufactured by Nippon Polypropylene), Sun Allomer PM series (manufactured by Sun Allomer Co., Ltd.), and Prime Polypro (manufactured by Prime Polymer).

[0044] Furthermore, from the viewpoint of kneadability with sinterable inorganic powder and injection moldability, the polyolefin resin preferably has a melt flow index of 40 g / 10 min or more. Here, the melt flow index of the polyolefin resin can be measured under the conditions of 190°C and 2.16 kg.

[0045] Epoxy resin The organic binder further comprises an epoxy resin in addition to the polyacetal resin and polyolefin resin described above. The inclusion of the epoxy resin enhances compatibility with the polyacetal resin and polyolefin resin, while simultaneously increasing interaction (adhesion) with the metal powder, thereby improving the dispersibility and sintering density of the metal powder. The epoxy resin refers to a resin composed of an aggregate of multiple epoxy compounds, where the epoxy compound refers to a compound having an epoxy group in its molecule. Here, the multiple epoxy compounds constituting the epoxy resin may have the same or different molecular structures.

[0046] Furthermore, from the viewpoint of kneadability with sinterable inorganic powder and injection moldability, the epoxy resin preferably has a melt flow index of 40 g / 10 min or more. Here, the melt flow index of the polyolefin resin can be measured under the conditions of 190°C and 2.16 kg, referring to ASTM-D-1238-57T.

[0047] Here, the type of epoxy resin is not particularly limited, but bisphenol A type epoxy, bisphenol F type epoxy, novolac type epoxy, aliphatic type epoxy, and epoxy resins containing glycidyl, as described later, can be used. Suitable epoxy resins include copolymers of glycidyl esters of unsaturated acids and olefins, and particularly preferred are ethylene-glycidyl methacrylate copolymers (EGMA).

[0048] Here, the saturated glycidyl ester is defined by general formula (1): [ka] (In the formula, R represents an alkenyl group having 2 to 18 carbon atoms, and X represents a carbonyloxy group.) The compound is represented by [formula] and has a structure formed by esterification of an unsaturated acid and an alcohol compound having a glucidyl group. Specific examples of such compounds include glycidyl acrylate, glycidyl methacrylate, glycidyl ethacrylate, and glycidyl itaconic acid. Among these, glycidyl methacrylate is preferably used.

[0049] In addition, as optional components, unsaturated acids and / or derivatives thereof include, in addition to the glycidyl esters mentioned above, unsaturated compounds having one or more carboxylic acid groups, unsaturated compounds having one or more carboxylic anhydride groups, and esters of compounds having carboxylic acid groups with alkyl alcohols. Specific examples of compounds include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, citraconic acid, and mesaconic acid; unsaturated carboxylic acid anhydrides such as maleic anhydride; vinyl esters of saturated carboxylic acids such as vinyl acetate, vinyl propionate, and vinyl butyrate; and alkyl esters of unsaturated carboxylic acids such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate. Among these, vinyl acetate, methyl acrylate, ethyl acrylate, and methyl methacrylate are preferred.

[0050] Furthermore, examples of olefins copolymerized with the glycidyl ester of the unsaturated acid include α-olefins having 2 to 10 carbon atoms, among which ethylene, propylene, and 1-butene are particularly preferred. The copolymerization method for the glycidyl ester of the unsaturated acid and the olefin is not particularly limited and can be carried out by conventionally known methods.

[0051] Furthermore, among copolymers of the glycidyl ester of the unsaturated acid and the olefin, ethylene-glycidyl methacrylate copolymer (EGMA) is preferred. Commercially available EGMA can be used, and preferred examples include Celoxide manufactured by Daicel Chemical Corporation and Bondfast manufactured by Sumitomo Chemical Corporation.

[0052] Furthermore, EGMA can be synthesized by various methods. For example, it can be produced by bulk polymerization, emulsion polymerization, or solution polymerization using a free radical initiator. Typical polymerization methods include those described in Japanese Patent Publication No. 46-45085 and Japanese Patent Publication No. 61-127709, which involve producing EGMA under conditions of a pressure of 500 kg / cm2 or higher and a temperature of 40-300°C in the presence of a free radical-generating polymerization initiator. Other methods include mixing an unsaturated epoxy compound and a radical generator with a resin consisting of at least one monomer selected from ethylene and other olefinic unsaturated compounds, and melt-graft copolymerizing them in an extruder, or copolymerizing an unsaturated epoxy compound and an olefinic unsaturated compound in an inert medium such as water or an organic solvent in the presence of a radical generator.

[0053] The copolymer of the unsaturated glycidyl ester and the olefin resin contains 1 to 25% by weight, preferably 3 to 20% by weight, and more preferably 13 to 20% by weight, of unsaturated glycidyl ester units. Having 1% or more unsaturated glycidyl ester units strengthens the interaction with other resin components and metal powders, resulting in improved dispersibility. Furthermore, having 25% or less unsaturated glycidyl ester units provides excellent thermal stability during kneading and injection molding.

[0054] The content of the unsaturated acid glycidyl ester can be determined by measuring the infrared absorption spectrum of a press sheet of the ethylene polymer having the epoxy group. The content of the unsaturated compound having the glycidyl group can be determined by correcting the absorbance of the characteristic absorption in the infrared absorption spectrum by the thickness of the sheet used for measurement, and then determining the content of the unsaturated compound having the glycidyl group based on the corrected absorbance obtained using a calibration curve method. The peak of characteristic absorption is at 910 cm. -1 Since they often appear in the vicinity of [location], this can be used as an indicator.

[0055] Furthermore, when EGMA is used as the epoxy resin, the melt flow index of EGMA is preferably 3 g / 10 min to 400 g / 10 min, more preferably 10 g / 10 min to less than 400 g / 10 min, and even more preferably 50 g / 10 min to less than 400 g / 10 min. Having the melt flow index of EGMA within the above range tends to suppress separation from other resins during injection molding and shorten the degreasing time. Here, the melt flow index of the EGMA can be measured under the conditions of 190°C and 2.16 kg, referring to ASTM-D-1238.

[0056] • Holmecatcher Furthermore, it is preferable that the organic binder further contains a form-catching agent in addition to the polyacetal resin, polyolefin resin, and epoxy resin described above. The aforementioned form-catching agent has the function of capturing or suppressing residual formaldehyde and formic acid produced when it is modified, which have adverse effects on productivity and appearance when producing molded articles using the polyacetal resin. Because the organic binder contains a formaldehyde catcher, the composition containing polyacetal resin in this embodiment not only improves the appearance and texture of the molded article due to its formaldehyde capture function, but also prevents the depolymerization of the polyacetal resin by having the formaldehyde catcher preferentially interact with the metal powder and eliminate reaction sites. This allows for an improvement in the appearance and texture of the molded article beyond expectations, while maintaining productivity and enhancing quality.

[0057] Examples of the form-catching agent include nitrogen-containing compounds, metal salts of inorganic acids, metal oxides, and metal salts of organic acids. Among these, the form-catching agent is preferably a compound that contains as little or no acid as an impurity and / or is unlikely to generate acid. Furthermore, while one type of formaldehyde catcher may be used alone, two or more types may be used in combination.

[0058] Examples of the nitrogen-containing compounds include polyamide resins, amide compounds, amino-substituted triazine compounds, adducts of amino-substituted triazine compounds and formaldehyde, condensates of amino-substituted triazine compounds and formaldehyde, urea, urea derivatives, hydrazine derivatives, imidazole compounds, imide compounds, and the like.

[0059] Examples of the polyamide resin include nylon 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12, and nylon 12. The polyamide resin may also be a copolymer of nylon 6 / 6-6 / 6-10, nylon 6 / 6-12, etc. Furthermore, the polyamide resin may include acrylamide and its derivatives, a copolymer of acrylamide and its derivatives with other vinyl monomers, and may be a poly-β-alanine copolymer obtained by polymerizing acrylamide and its derivatives with other vinyl monomers in the presence of a metal alcoholate.

[0060] Examples of the amide compounds include polycarboxylic acid amides such as isophthalic acid diamide and anthranilamide.

[0061] Examples of the amino-substituted triazine compounds include 2,4-diamino-sym-triazine, 2,4,6-triamino-sym-triazine, N-butylmelamine, N-phenylmelamine, N,N-diphenylmelamine, N,N-diallylmelamine, benzoguanamine (2,4-diamino-6-phenyl-sym-triazine), acetoguanamine (2,4-diamino-6-methyl-sym-triazine), and 2,4-diamino-6-butyl-sym-triazine.

[0062] Examples of adducts of the amino-substituted triazine compound with formaldehyde include N-methylolmelamine, N,N'-dimethylolmelamine, and N,N',N''-trimethylolmelamine.

[0063] Specific examples of condensates of the amino-substituted triazine compound and formaldehyde include, for example, melamine-formaldehyde condensates.

[0064] Examples of urea derivatives include N-substituted ureas, urea condensates, ethylene urea, hydantoin compounds, and ureido compounds. Specific examples of N-substituted ureas include methylurea, alkylenebisurea, and aryl-substituted ureas, all of which are substituted with substituents such as alkyl groups. Specific examples of urea condensates include condensates of urea and formaldehyde. Specific examples of hydantoin compounds include hydantoin, 5,5-dimethylhydantoin, and 5,5-diphenylhydantoin. Specific examples of ureido compounds include allantoin.

[0065] Examples of the hydrazine derivatives include hydrazide compounds. Specific examples of hydrazide compounds include dicarboxylic acid dihydrazides, and more specifically, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, superiric acid dihydrazide, azelaic acid dihydrazide, sebatic acid dihydrazide, dodecanediic acid dihydrazide, isophthalic acid dihydrazide, phthalic acid dihydrazide, and 2,6-naphthalenedicarbodide dihydrazide.

[0066] Examples of the imidazole compound include imidazole, 1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole. Examples of the aforementioned imide compounds include succinimide, glutarimide, and phthalimide.

[0067] Other formaldehyde scavengers besides those mentioned above include metal salts of inorganic acids, metal oxides, and metal salts of organic acids. For example, hydroxides of sodium, potassium, magnesium, calcium, or barium, carbonates, phosphates, silicates, borates, carboxylates of the above metals, and layered double hydroxides are examples.

[0068] As the carboxylic acid of the carboxylate, it is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, and these carboxylic acids may be substituted with a hydroxyl group. Specific examples of the saturated or unsaturated aliphatic carboxylate include calcium dimyristate, calcium dipalmitate, calcium distearate, calcium (myristate-palmitate), calcium (myristate-stearate), calcium (palmitate-stearate), etc., and preferably calcium dipalmitate and calcium distearate.

[0069] Examples of the layered double hydroxide include hydrotalcite compounds represented by the following formula (4). [(M 2+ ) 1-x (M 3+ ) x (OH)2] x+ [(A n- ) x / n ·mH2O] x- ···(4) (In the formula (4), M 2+ is a divalent metal, M 3+ is a trivalent metal, A n- is an anion of n valence (n is an integer of 1 or more), and x is in the range of 0 < x ≤ 0.33, and m represents a positive number.) In the formula (4), examples of M 2+ include Mg 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ etc., and examples of M 3+ include Al 3+ , Fe 3+ , Cr 3+ , Co 3+ , In 3+ etc., and examples of A n- include OH - , F - , Cl - , Br​​- NO3 - CO3 2- SO4 2- Fe(CN)6 3- CH3COO - Examples include oxalate ions and salicylate ions. n- Examples include OH - CO3 2- It is preferable. A specific example of hydrotalcite is Mg 0.75 Al 0.25 (OH)2(CO3) 0.125 • Natural hydrotalcite, represented as 0.5H2O, Mg 4.5 Al2(OH) 13 CO3·3.5H2O, Mg 4.3 Al2(OH) 12.6 Examples include synthetic hydrotalcite represented by CO3, etc.

[0070] (Fluid-improving agent) The sintered molded body composition of this embodiment preferably further includes a fluidity imparting agent in addition to the sinterable inorganic powder and organic binder described above. By including the fluidity imparting agent, the fluidity of the sintered molded body composition can be further improved.

[0071] The above-mentioned fluidity imparters are compounds other than the polyacetal resins, polyolefin resins, and epoxy resins mentioned above, and include, for example, waxes. For convenience, in this specification, compounds with a melting point of 100°C or less are referred to as "waxes," and those with a melting point exceeding 100°C are referred to as "resins." Examples of the aforementioned waxes include paraffin wax, polyethylene wax, polypropylene wax, carnauba wax, polyethylene glycol, polytetramethylene glycol, polytetraethylene glycol, polyisobutylene, microcrystalline wax, montan wax, beeswax, wood wax, synthetic wax, poly-1,3-dioxolane, and poly-1,3-dioxepane. Among these, paraffin wax, polyethylene glycol, and polytetramethylene glycol are preferred from the viewpoint of providing even better fluidity for compositions used in injection-molded sintered articles.

[0072] • Compatibilizer The sintered molded body composition of this embodiment preferably further contains a compatibilizer in addition to the sinterable inorganic powder, organic binder, and fluidity imparting agent described above. Including the compatibilizer can further improve the quality of the sintered molded body composition.

[0073] The aforementioned compatibilizer has properties different from those of the resins and waxes mentioned above, and for example, it has the effect of further increasing the compatibility between metals and resins and waxes through an effect similar to that of a surfactant. Examples of the aforementioned compatibilizers include Sannix (Sanyo Chemical), Sunflex (Sanyo Chemical), Tuffmer DF&A (Mitsui Chemicals), Tuffmer XM (Mitsui Chemicals), Tuffmer BL (Mitsui Chemicals), Tuffmer M (Mitsui Chemicals), Tuffmer PN (Mitsui Chemicals), and Maricon (Osaka Gas Chemical).

[0074] The method for manufacturing the sintered molded body composition of this embodiment is not particularly limited and can be manufactured by known methods. For example, the sinterable inorganic powder described above, an organic binder, and other optional components can be mixed using, for example, a Henschel mixer, a tumbler, a V-shaped blender, etc., and then melt-kneaded in a semi-molten state using a kneader such as a single-screw extruder or a twin-screw extruder, a heated roll, a kneader, or a Banbury mixer, and the product can be obtained in various forms such as strands or pellets. When kneading using a pressurized kneader, the kneading temperature is preferably set to 160°C to 210°C, and more preferably to 170°C to 190°C. The blade rotation speed is preferably 10 rpm to 50 rpm, and more preferably to 15 rpm to 40 rpm. The kneading time is preferably 45 minutes to 2 hours. By kneading within the above conditions, it is possible to improve the compatibility of the resins and suppress the organic binder phenomenon caused by thermal decomposition.

[0075] <Green molded product> The green molded body of this embodiment is made using the sintered molded body composition of this embodiment described above as a raw material. The resulting green molded product is free from mold contamination and exhibits suppressed cracking and blistering.

[0076] The green molded body of this embodiment is obtained by using a sintered molded body composition with a screw-type and piston-type injection molding machine. In the injection molding process described above, the cylinder temperature is preferably set to 160-210°C, and more preferably to 170-190°C. Setting the temperature above 160°C improves the fluidity of the resin, while setting it below 200°C reduces mold contamination due to resin decomposition. Furthermore, the mold temperature is preferably 30 to 90°C, and more preferably 50 to 70°C. Setting the mold temperature to 30°C or higher improves dimensional stability during molding, while setting it to 90°C or lower suppresses appearance defects in green molded products caused by waxes with melting points of 100°C or lower.

[0077] <Sintered molded body> The sintered molded body of this embodiment is obtained by sintering the green molded body of this embodiment described above. The resulting sintered molded body is free from mold contamination, and cracking and blistering are also suppressed.

[0078] The green molded body is placed in a sealed degreasing and sintering furnace and degreased and sintered under desired conditions to obtain a degreased body and a sintered body. In the case of degreasing by heating, degreasing is achieved by raising the temperature from room temperature to approximately 500-600°C under a nitrogen or argon atmosphere. A fluidity enhancer may be dissolved into the solvent before heating. Next, a sintered molded body can be obtained by raising the temperature to the sintering temperature of the sinterable inorganic powder.

[0079] In the acid degreasing method, degreasing is achieved by circulating nitric acid gas under a nitrogen atmosphere and raising the temperature from room temperature to 110-120°C. Next, a sintered molded body can be obtained by raising the temperature to the sintering temperature of the sinterable inorganic powder. [Examples]

[0080] The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0081] (Components of each sample) The components contained in each sample of the examples and comparative examples are shown below.

[0082] (A) Polyacetal resin (A-1) Polyacetal resin A jacketed twin-screw paddle type continuous polymerization reactor (manufactured by Kurimoto Iron Works Co., Ltd., diameter 2B, L / D=14.8) capable of passing a heat transfer medium was adjusted to a temperature of 80°C. A catalyst preparation solution of boron trifluoride-di-n-butyl etherate diluted to 0.26% by mass with cyclohexane (69 g / hr), along with 3500 g / hr of trioxane, 121 g / hr of 1,3-dioxolane, and 5.41 g / hr of methylal as a molecular weight modifier were continuously supplied to the polymerization reactor to carry out polymerization. The material discharged from the polymerization reactor was placed in a 0.5% by mass triethylamine aqueous solution to deactivate the polymerization catalyst, and then filtered, washed, and dried. Next, the material was supplied to a twin-screw extruder with a vent (L / D=40) set to 200°C. A 0.8% by mass aqueous triethylamine solution was added to the end stabilization zone to a concentration of 20 ppm in terms of nitrogen. The material was stabilized under reduced pressure at 90 kPa while degassing, and then pelletized in a pelletizer. After that, it was dried at 100°C for 2 hours to obtain polyacetal resin (A-1). The obtained polyacetal resin (A-1) had a melting point of 164°C and a melt flow index of 10 g / 10 min. (A-2) Polyacetal resin The polyacetal resin of (A-2) was produced in the same manner as the polyacetal resin of (A-1), except that the flow rate of methylal as a molecular weight modifier was set to 5.72 g / hr. The obtained (A-2) polyacetal resin had a melting point of 164°C and a melt flow index of 20 g / 10 min. (A-3) Polyacetal resin The polyacetal resin (A-3) was produced in the same manner as the polyacetal resin (A-1) production method, except that the flow rate of methylal as a molecular weight modifier was set to 7.1 g / hr. The obtained (A-3) polyacetal resin had a melting point of 164°C and a melt flow index of 71 g / 10 min. (A-4) Polyacetal resin The polyacetal resin (A-4) was produced in the same manner as the polyacetal resin (A-1) production method, except that the flow rate of methylal as a molecular weight modifier was set to 7.62 g / hr. The obtained (A-4) polyacetal resin had a melting point of 164°C and a melt flow index of 81 g / 10 min. (A-5) Polyacetal resin The polyacetal resin (A-5) was produced in the same manner as the polyacetal resin (A-1) production method, except that the flow rate of methylal as a molecular weight modifier was set to 9.4 g / hr. The obtained (A-5) polyacetal resin had a melting point of 164°C and a melt flow index of 121 g / 10 min. (A-6) Polyacetal resin The polyacetal resin (A-6) was produced in the same manner as the polyacetal resin (A-1) production method, except that the flow rate of methylal as a molecular weight modifier was set to 10.6 g / hr. The obtained (A-6) polyacetal resin had a melting point of 164°C and a melt flow index of 200 g / 10 min.

[0083] (B) Polyolefin resin (B-1) Polypropylene: Sumitomo Chemical Co., Ltd. Sumitomo Noblen UH501E1 (B-2) Polyethylene: Suntech™ LDPE M6555, manufactured by Asahi Kasei Corporation

[0084] (C) Epoxy resin (C-1) Aliphatic epoxy: Celloxide 2021P, manufactured by Daicel Chemical Corporation. (C-2) EGMA: Bond First CG5001, manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 19% by weight, Melt flow index 380g / 10min (C-3) EGMA: Bond First BF-30C, manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 19% by weight, Melt flow index 30g / 10min (C-4)EGMA: Bond First BF-E, manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 12% by weight, Melt flow index 3g / 10min (C-5) EGMA: Bond First BF-2C, manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 6% by weight, Melt flow index 3g / 10min (C-6) EGMA: Bond First BF-7B, manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 12% by weight, Melt flow index 7g / 10min (C-7)EGMA: Bond First BF-7M, manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 6% by weight, Melt flow index 7g / 10min

[0085] (D) Fluidity-improving agent Paraffin wax: Manufactured by Nippon Seiro Co., Ltd. Paraffin wax-145

[0086] (E) Formaldehyde catcher Dihydrazide sebacate: Manufactured by Finechem Japan Co., Ltd.

[0087] (F) Compatibilizer (F-1) Toughmer PN-2070, manufactured by Mitsui Chemicals, Inc. (F-2) Sanyo Chemical Industries Sannix GL-30000 (F-2) Toughmer XM-7070S, manufactured by Mitsui Chemicals, Inc.

[0088] (Meltflow Index) The melt flow indices for (A) polyacetal resin, (B) polyolefin resin, and (C) epoxy resin were measured using a MELT INDEXER manufactured by Toyo Seiki under conditions of 190°C and 2160g, referring to ASTM-D-1238.

[0089] (Total end-point amount relative to total polyoxymethylene units) Examples 1-19, Comparative Examples 1-5 (A) For the total amount of terminals relative to the total polyoxymethylene units of the polyacetal resin, measurements were taken using a Burker AVANCE III 900MHz + 5mm TCI CryoProbe at an observation frequency of 900MHz, with 128 cumulative measurements and a measurement temperature of 25°C. The total amount (mol%) of acetyl, formyl, methoxy, and hemiformal terminals relative to the main chain -OCH2- structure was calculated. The sample to be measured was dissolved in a 0.4 wt% TFA-Na / HFIP-d2 solution to a sample concentration of 0.03 wt%, heated and shaken at 40°C for 2 hours, and then, without filtration, was adjusted to a liquid height of 40 mm in a 5 mm diameter NMR sample tube (Wilmad 535-PP-7, 7 inches in length) to prepare the sample for measurement. The total end-capacity of the obtained polyacetal resin relative to the total polyoxymethylene units was adjusted by mixing (A-1), (A-2), (A-3), (A-4), (A-5), and (A-6) in a pressurized kneader at 190°C for 20 minutes to obtain the total end-capacity shown in Tables 1 and 2.

[0090] • Example 20 For Example 20 only, SUS316L (average particle size 10 μm) was used as the sinterable inorganic powder. After mixing it with each of the materials (A) to (F) in the proportions shown in Table 2, the mixture was kneaded in a pressurized kneader at a temperature of 175°C and a blade rotation speed of 30 rpm for 1 hour to prepare each sample of the sintered molded body composition. Subsequently, the obtained sintered molded body composition was subjected to freeze-pulverization, and then HFIP (hexafluoroisopropanol) was added to the resulting pulverized sample to extract polyacetal resin and the like. Furthermore, in order to remove oligomer components such as polyolefins, the obtained HFIP solution was concentrated, chloroform and methanol were added, and the solution was reprecipitated. After filtering, it was air-dried and then dried overnight in a vacuum dryer at 50°C to obtain the polyacetal resin solid, which was used as the measurement sample. The total amount of end-terminants in this polyacetal resin solid was measured using a Burker AVANCE III 900MHz + 5mm TCI CryoProbe at an observation frequency of 900MHz, with 128 cumulative measurements and a measurement temperature of 25°C. The total amount (mol%) of acetyl, formyl, methoxy, and hemiformal end-terminants relative to the main chain -OCH2- structure was calculated.

[0091] (Hemiformal end-level relative to total polyoxymethylene units) Examples 1-19, Comparative Examples 1-5 (A) The amount of hemiformal terminals relative to the total polyoxymethylene units of the polyacetal resin was measured using a Burker AVANCE III 900MHz + 5mm TCI CryoProbe at an observation frequency of 900MHz, with 128 cumulative measurements and a measurement temperature of 25°C, and the amount of hemiformal terminals (mol%) relative to the main chain -OCH2- structure was calculated. The sample to be measured was dissolved in a 0.4 wt% TFA-Na / HFIP-d2 solution to a sample concentration of 0.03 wt%, heated and shaken at 40°C for 2 hours, and then, without filtration, was adjusted to a liquid height of 40 mm in a 5 mm diameter NMR sample tube (Wilmad 535-PP-7, 7 inches in length) to prepare the sample for measurement. The total amount of end-tips relative to the total polyoxymethylene units in the obtained polyacetal resin was adjusted to the hemiformal end-tips shown in Tables 1 and 2 by mixing (A-1), (A-2), (A-3), (A-4), (A-5), and (A-6) in a pressurized kneader at 190°C for 20 minutes.

[0092] • Example 20 For Example 20 only, SUS316L (average particle size 10 μm) was used as the sinterable inorganic powder. After mixing it with each of the materials (A) to (F) in the proportions shown in Table 2, the mixture was kneaded in a pressurized kneader at a temperature of 175°C and a blade rotation speed of 30 rpm for 1 hour to prepare each sample of the sintered molded body composition. Subsequently, the obtained sintered molded body composition was subjected to freeze-pulverization, and then HFIP (hexafluoroisopropanol) was added to the resulting pulverized sample to extract polyacetal resin and the like. Furthermore, in order to remove oligomer components such as polyolefins, the obtained HFIP solution was concentrated, chloroform and methanol were added, and the solution was reprecipitated. After filtering, it was air-dried and then dried overnight in a vacuum dryer at 50°C to obtain the polyacetal resin solid, which was used as the measurement sample. The total amount of hemiformal end products in this polyacetal resin solid was measured using a Burker AVANCE III 900MHz + 5mm TCI CryoProbe at an observation frequency of 900MHz, with 128 integration cycles and a measurement temperature of 25°C. The amount of hemiformal end products relative to the main chain -OCH2- structure (mol%) was then calculated.

[0093] [Examples 1-20, Comparative Examples 1-5] As the sinterable inorganic powder, SUS316L (average particle size 10 μm) was used. After mixing it with each material according to the blending ratios shown in Tables 1 and 2, the mixture was kneaded in a pressurized kneader at a temperature of 175°C and a blade rotation speed of 30 rpm for 1 hour to prepare samples of the sintered molded body composition. Subsequently, each sample of the sintered molded body composition obtained was cooled and crushed to produce injection molding raw materials. These raw materials were then molded using an injection molding machine (Fanuc ROBOSHOT α-50iA) at a molding temperature of 175-190°C to produce multiple green molded body test specimens. Each of these green molded body test specimens measured 10 mm in width, 60 mm in length, and 3 mm in thickness.

[0094] [evaluation] The following evaluations (1) to (6) were performed. The evaluation results are shown in Tables 1 and 2. (1) Appearance of the green molded body Ten green molded test specimens were randomly selected from each prepared sample and evaluated by observing their appearance according to the following criteria. ○ (Good): No cracks or chips observed. × (Defective): Cracks, chips, etc. are visible.

[0095] (2) Mold contamination For the preparation of green molded test specimens for each sample, 500 shots were performed, and the amount of dirt adhering to the mold was visually observed at the end of 10, 100, and 500 shots. Regarding mold contamination, any abnormalities on the mold surface, such as white or iridescent stains relative to the mold's color, or solid particles adhering to the surface, were defined as contamination and evaluated according to the following criteria. ◎: No contamination on the mold up to 500 shots. 〇: No contamination on the mold by 100 shots. ×: The mold is dirty by the 10th shot.

[0096] (3) Appearance of the degreased body The green molded test specimens of each prepared sample were degreased by heating. The green molded test specimens of each prepared sample were supported at two points 50 mm apart and placed in a degreasing furnace. (3-1) As the first condition, the degreasing furnace was purged with nitrogen gas and heated to 150°C at a rate of 50°C / hr. Subsequently, the temperature was increased from 150°C to 200°C at a rate of 30°C / hr and held for 1 hour, then increased from 200°C to 400°C at a rate of 30°C / hr, and finally increased from 400°C to 600°C at a rate of 120°C / hr, after which the furnace was cooled to obtain each sample of the degreased material. (Total degreasing process: approximately 15 hours) Ten degreased samples were visually inspected and evaluated according to the following criteria. ○ (Excellent): No external abnormalities such as cracks or blisters are observed. × (Defective): Cracks or blistering are visible. (3-2) Furthermore, for each sample of degreased material that showed no external abnormalities such as cracks or blistering under the first condition, the second condition was applied by supporting the green molded body at two points with a 50 mm gap between them and setting it in the degreasing furnace. The furnace was then purged with nitrogen gas and heated to 150°C at a rate of 50°C / hr. Subsequently, the temperature was increased from 150 to 200°C at a rate of 30°C / hr and held for 1 hour, then increased from 200 to 300°C at a rate of 50°C / hr, then increased from 300 to 400°C at a rate of 100°C / hr, and finally increased from 400 to 600°C at a rate of 120°C / hr, after which the material was cooled in the furnace to obtain each sample of degreased material. (Total degreasing process: approximately 12 hours) Ten degreased samples were visually inspected and evaluated according to the following criteria. ○ (Excellent): No external abnormalities such as cracks or blisters are observed. × (Defective): Cracks or blistering are visible. Note that if an item is marked with a circle (Excellent) in the second condition, it is also marked with a circle (Excellent) in the first condition, and therefore its description has been omitted.

[0097] (4) Appearance of the sintered body Each degreased sample was sintered under an argon atmosphere by gradually increasing the temperature from room temperature at 200°C / hr and holding it at a maximum temperature of 1350°C for 2 hours to obtain each sintered sample. For each sample, 10 sintered bodies were visually observed and evaluated according to the following criteria. ○ (Excellent): No external abnormalities such as cracks or blisters are observed. × (Defective): Cracks or blistering are visible.

[0098] (5) Density of the sintered body For each sample, 10 sintered bodies were measured in accordance with JIS Z 8807 using an electronic hydrometer (Alpha-Mirage Co., Ltd.) at a water temperature of 25°C to determine their density (g / cm³). 3 ) Measured.

[0099] (6) Dimensional accuracy of sintered body For each sintered body sample, the diameter of 30 pieces was measured using a micrometer. The measured values ​​were then evaluated based on the "ordinary tolerance for width" specified in JIS B 0411, according to the following evaluation criteria. ◎: The grade is high-precision (tolerance ±0.05 mm or less) ○: Grade is intermediate (tolerance greater than ±0.05 mm and less than or equal to ±0.1 mm) △: Low grade (tolerance greater than ±0.1mm and less than or equal to ±0.2mm) ×: Not acceptable.

[0100] [Table 1] [Table 2]

[0101] The results in Tables 1 and 2 show that Examples 1-20 exhibited well-balanced and excellent results in all evaluation items. On the other hand, Comparative Examples 1-5 showed inferior results compared to the examples in at least one evaluation item. In particular, mold contamination and dimensional accuracy of the sintered body were both inferior to those of the examples. [Industrial applicability]

[0102] According to the present invention, it is possible to provide a composition for sintered molded bodies that can degrease organic binders in a short time without requiring special equipment or processes, prevent mold contamination during molding, and suppress cracking and blistering during molding and after sintering, as well as green molded bodies and sintered molded bodies using the sintered molded body composition.

Claims

1. A composition for a sintered compact comprising a sinterable inorganic powder and an organic binder, the organic binder contains at least a polyacetal resin, a polyolefin resin, and an epoxy resin; A composition for sintered compacts, characterized in that the amount of hemiformal terminals relative to all polyoxymethylene units in the polyacetal resin contained in the composition for sintered compacts after kneading is 0.14 mol % or more and 0.20 mol % or less.

2. 2. The composition for sintered compacts according to claim 1, wherein the amount of hemiformal terminal groups in the polyacetal resin relative to the total polyoxymethylene units is 0.05 mol % or more and 0.20 mol % or less.

3. 3. The composition for sintered compacts according to claim 1, wherein the total amount of terminal units of the polyacetal resin relative to the total amount of polyoxymethylene units is 0.31 mol % or more and 0.50 mol % or less.

4. 3. The composition for sintered compacts according to claim 2, wherein the amount of hemiformal terminal groups in the polyacetal resin relative to the total polyoxymethylene units is 0.14 mol % or more and 0.20 mol % or less.

5. 3. The composition for sintered compacts according to claim 1, wherein the polyacetal resin has a melt flow index of 80 to 200 g / 10 min.

6. 3. The composition for sintered compacts according to claim 1, wherein the organic binder contains at least one form catcher agent.

7. 3. The composition for sintered compacts according to claim 1, wherein the epoxy resin is a copolymer of an olefin and an unsaturated compound having a glycidyl group.

8. 3. The composition for sintered compacts according to claim 1, wherein the unsaturated compound having a glycidyl group in the epoxy resin is in an amount of 1 to 25% by weight based on the total weight of the epoxy resin.

9. 3. The composition for sintered compacts according to claim 1, wherein the epoxy resin has a melt flow index of 3 to 400 g / 10 min.

10. The composition for sintered compacts according to claim 1 or 2, further comprising a compatibilizer.

11. 3. The composition for sintered compacts according to claim 1, wherein the ratio of the organic binder to the total volume of the sinterable inorganic powder and the organic binder is less than 40% by volume.

12. A green compact obtained by molding the composition for sintered compacts according to claim 1 or 2.

13. A sintered compact obtained by sintering the green compact according to claim 12.