Sintered shaped body composition, green shaped body and sintered shaped body

Abstract

The present invention aims to provide a composition for sintered molded bodies that can degrease an organic binder in a short time without special equipment and processes, avoid mold contamination during molding, and suppress cracking and bulging during molding and after sintering. To achieve the above objectives, the present invention provides a composition for sintered molded bodies comprising a sinterable inorganic powder and an organic binder, characterized in that the organic binder comprises at least a polyacetal resin, a polyolefin resin, and an epoxy resin, wherein the polyacetal resin has a terminal amount of 0.1 mol% or more and 0.75 mol% or less relative to the total amount of polyoxymethylene units.

Description

Technical Field

[0001] This invention relates to compositions for sintered bodies, green bodies, and sintered bodies. Background Technology

[0002] Regarding precision sintered bodies and sintered bodies with complex shapes that use sinterable inorganic powders such as metals, ceramics, and cermets as materials, it is known to use a composition for manufacturing sintered bodies containing sinterable inorganic powders and a binder. The sintered body is manufactured by heating and mixing the composition for manufacturing sintered bodies to obtain a raw material for sintered bodies; injection molding the raw material to form a green body; then debinding the green body; and finally sintering it.

[0003] Regarding the manufacture of sintered bodies using the composition for sintering body manufacturing as described above, the most important process for obtaining high-quality sintered bodies free from defects such as cracking, bulging, and deformation is the debinding process. This debinding process removes the binder from the green molded body, which is the molded body of the composition for sintering body manufacturing. Methods include heating the green molded body to decompose and vaporize the binder; or solvent treatment of the green molded body to dissolve and remove the soluble binder components, followed by heating and decomposing the remaining binder to vaporize it.

[0004] However, in the heating degreasing method described above, which degreases the green molded body by heating, when the thermal decomposition and vaporization of the binder contained in the green molded body occur intensively in a short period of time, the molded body may crack or bulge during the degreasing process. Therefore, degreasing must be carried out by heating for a long time.

[0005] Therefore, in order to suppress cracking or bulging of the molded body during the aforementioned degreasing process, techniques using depolymerizable polymers as binders are known. For example, by using polyacetal resin, which is a depolymerizable polymer, together with other resins as a binder, it is possible to improve the shape retention of the green molded body based on the rigidity of the polyacetal resin, and also to improve the shape retention of the molded body during the degreasing process performed by heating.

[0006] As such a technology, patent documents 1 and 2 disclose, for example, the following technique: by using polyacetal resin and epoxy resin as binders, the compatibility of the binder resin components is improved, homogenization is promoted, thereby improving the quality of the green body, degreased body, and sintered body, and the degreasing speed is increased. Research has also been conducted with this goal in mind.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2021-109994

[0010] Patent Document 2: Japanese Patent Application Publication No. 2021-080350 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, although Patent Document 1 describes how using a resin component containing polyacetal resin and epoxy resin as an organic binder can suppress deformation and bulging even after degreasing and calcination, it does not disclose specific methods for suppressing mold contamination (mold fouling) and improving dimensional accuracy during the manufacture of green bodies. Further improvements are expected in these aspects.

[0013] Furthermore, although Patent Document 2 describes that by including an organic compound with a melting point below 100°C and a thermoplastic resin with a Vicat softening point below 130°C as components of an organic binder, it is possible to obtain a sintered body with shortened heating degreasing and sintering time and no defects, the following problem exists: the degreasing process of this organic binder is indispensable to be carried out in superheated steam at a temperature above 100°C and below 600°C. Compared with the usual degreasing process carried out in an inactive gas atmosphere, special equipment is required, and the manufacturing process becomes complicated.

[0014] Therefore, the object of the present invention is to provide a composition, a green molded body, and a sintered molded body that can degrease organic binders in a short time without special equipment and processes, without causing mold contamination during molding, and can suppress cracking and bulging during molding and after sintering.

[0015] means for solving problems

[0016] To solve the above problems, the inventors conducted repeated and in-depth studies on compositions for sintered molded bodies containing sinterable inorganic powder and organic binders. As a result, it was found that by using polyacetal resin, polyolefin resin and epoxy resin as organic binders, and by optimizing the amount of polyacetal resin relative to the total terminal amount of all polyoxymethylene units, the compatibility of the components constituting the organic binder was improved. During molding, the resin components were less likely to adhere to the mold. Therefore, the organic binder could be degreased in a short time without special equipment and processes, and mold contamination, cracking and bulging of the molded body could be suppressed, thus completing the present invention.

[0017] This invention is based on the above insights, and its main points are as follows.

[0018] [1] A composition for sintering molded bodies, the composition comprising a sinterable inorganic powder and an organic binder, characterized in that,

[0019] The organic binder comprises at least polyacetal resin, polyolefin resin, and epoxy resin.

[0020] The polyacetal resin has a terminal amount of more than 0.1 mol% and less than 0.75 mol% relative to the total amount of all polyoxymethylene units.

[0021] [2] The composition for sintering as described in [1] above is characterized in that the amount of hemiacetal end-formaldehyde relative to all polyoxymethylene units of the polyacetal resin is 0.05 mol% or more and 0.20 mol% or less.

[0022] [3] The composition for sintered molding as described in [1] or [2] above is characterized in that the polyacetal resin has a total terminal amount of 0.31 mol% or more and 0.50 mol% or less relative to the total amount of all polyoxymethylene units.

[0023] [4] The composition for sintering as described in [2] above is characterized in that the amount of hemiacetal end-units of the polyacetal resin relative to all polyoxymethylene units is 0.14 mol% or more and 0.20 mol% or less.

[0024] [5] The composition for sintering molded body as described in any one of [1] to [4] above is characterized in that the melt flow index of the polyacetal resin is 80 g / 10 min to 200 g / 10 min.

[0025] [6] The composition for sintered molded body as described in any one of [1] to [5] above, characterized in that the organic binder contains at least one formaldehyde scavenger.

[0026] [7] The composition for sintering molded body as described in any one of [1] to [6] above is characterized in that the epoxy resin is a copolymer of an olefin and an unsaturated compound having a glycidyl group.

[0027] [8] The composition for sintered molded body as described above [7] is characterized in that, relative to the total weight of epoxy resin, the unsaturated compound having a glycidyl group in the epoxy resin is 1% to 25% by weight.

[0028] [9] The composition for sintering molded body as described in any one of [1] to [8] above, characterized in that the melt flow index of the epoxy resin is 3 g / 10 min to 400 g / 10 min.

[0029]

[10] The composition for sintered molded body as described in any one of [1] to [9] above is characterized in that it further comprises a compatibilizer.

[0030]

[11] The composition for sintering molded body as described in any one of [1] to

[10] above is 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.

[0031]

[12] A green body, characterized in that the green body is obtained by molding the sintered body described in any one of [1] to

[11] above with a composition.

[0032]

[13] A sintered molded body, characterized in that the sintered molded body is obtained by sintering the green molded body described in

[12] above.

[0033]

[14] A composition for sintering molded bodies, the composition comprising a sinterable inorganic powder and an organic binder, characterized in that,

[0034] The organic binder comprises at least polyacetal resin, polyolefin resin, and epoxy resin.

[0035] The polyacetal resin contained in the compounded sintered body composition has a semi-acetal end content of 0.14 mol% or more and 0.20 mol% or less relative to all polyoxymethylene units.

[0036] Invention Effects

[0037] 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 special equipment and processes, without causing mold contamination during molding, and can suppress cracking and bulging during molding and after sintering, as well as green molded bodies and sintered molded bodies using the composition for sintered molded bodies. Detailed Implementation

[0038] Hereinafter, a method for implementing the present invention (hereinafter referred to as "this embodiment") will be described in detail. It should be noted that this embodiment is merely an example for illustrating 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 spirit.

[0039] <Composition for Sintered Molded Body>

[0040] The composition for sintering molded articles according to this embodiment comprises sinterable inorganic powder and organic binder. In addition to the inorganic powder and organic binder, the composition for sintering molded articles according to this embodiment may also contain other additives as described below.

[0041] (Sinterable inorganic powder)

[0042] The composition for sintering in this embodiment comprises sinterable inorganic powder.

[0043] It should be noted that sinterable inorganic powders can be used alone or in combination.

[0044] 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, carbonyl metal powders, and mixtures thereof. Among these materials, metal powders and ceramic powders are particularly preferred for imparting functionality.

[0045] Examples of metal powders include, for example, powders of aluminum, magnesium, barium, calcium, cobalt, zinc, copper, nickel, iron, silicon, titanium, tungsten, and metal compounds and alloys based on these metals. Here, the metal powder can be not only a pre-made alloy, but also a mixture of the various alloy components.

[0046] Examples of ceramic powders include: oxides such as zinc oxide, aluminum oxide, and zirconium oxide; hydroxides such as hydroxyapatite; carbides such as silicon carbide; nitrides such as silicon nitride and boron nitride; halides such as fluorite; silicates such as block talc; titanates such as barium titanate and lead zirconate titanate; carbonates; phosphates; ferrites; high-temperature superconducting materials; etc.

[0047] It should be noted that the sinterable inorganic powder can be used alone or in combination with several inorganic substances such as various metals, metal alloys or ceramics.

[0048] As particularly preferred metals and metal alloys, examples include titanium alloys and stainless steel; as ceramics, examples include Al2O3 and ZrO2. For instance, Ti-6Al-4V alloy is preferred as a titanium alloy, and SUS316L is preferred as a stainless steel.

[0049] (Organic binder)

[0050] The composition for sintering in this embodiment includes an organic binder in addition to sinterable inorganic powder.

[0051] Furthermore, the organic binder needs to contain at least polyacetal resin, polyolefin resin and epoxy resin, wherein the polyacetal resin has a terminal amount of more than 0.1 mol% and less than 0.75 mol% relative to the total amount of all polyoxymethylene units.

[0052] The epoxy resin can improve the compatibility between the polyacetal resin and the polyolefin resin. Moreover, by ensuring that the total amount of polyacetal resin relative to all polyoxymethylene units is within a specific range (more than 0.31 mol% and less than 0.5 mol%), the compatibility between the resin components in the organic binder can be further improved.

[0053] The volume ratio of the organic binder in the sintered body composition of this embodiment is not particularly limited, but the volume ratio of the organic binder relative to 100% of the sintered body composition is preferably 25% to 60% by volume, more preferably 30% to 55% by volume, and particularly preferably 35% to 50% by volume.

[0054] By including the organic binder within the above-mentioned range, a sintered molding composition having a melt viscosity suitable for injection molding can be obtained, and a sintered product with good shrinkage suppression and dimensional accuracy can be obtained.

[0055] Polyacetal resin

[0056] Examples of polyacetal resins include polyacetal homopolymers, polyacetal copolymers, or mixtures thereof. From the viewpoint of thermal stability, polyacetal copolymers are preferred as the polyacetal resin.

[0057] It should be noted that the polyacetal resin can be used alone or in combination.

[0058] In addition to the commonly provided granules, the polyacetal resin can also be used in powder form. The particle size of the powder is preferably D50 = 500 μm or less, more preferably D50 = 300 μm or less.

[0059] As the polyacetal homopolymer, polymers having oxymethylene units in the main chain can be listed, and the ends of the polymer can be capped using ester or ether groups. The polyacetal homopolymer can be obtained using formaldehyde and a known molecular weight regulator as raw materials, and can utilize known... Salt-based polymerization catalysts are obtained from these raw materials using known slurry polymerization methods, such as those described in Japanese Patent Publication Nos. 47-6420 and 47-10059, with hydrocarbons or the like as solvents.

[0060] It should be noted that the polyacetal homopolymer preferably has more than 99.8 mol% of the main chain, excluding the two ends, composed of oxymethylene units, and more preferably is a polyacetal homopolymer whose main chain, excluding the two ends, is composed only of oxymethylene units.

[0061] Examples of polyacetal copolymers include polymers having oxymethylene and oxyethylidene units in the main chain, which can be obtained, for example, by copolymerizing trioxymethylene with cyclic ethers and / or cyclic methyl acetals in the presence of a polymerization catalyst.

[0062] The trioxymethylene is a cyclic trimer of formaldehyde, which is usually obtained by reacting an aqueous solution of formaldehyde in the presence of an acidic catalyst.

[0063] The cyclic ether and / or cyclic methylal are components capable of copolymerizing with the trioxymethylene, and examples include: ethylene oxide, propylene oxide, epibutylene oxide, epichlorohydrin, epibromopropane, phenylethylene oxide, oxetane, 1,3-dioxacyclopentane, ethylene glycol formaldehyde, propylene glycol formaldehyde, diethylene glycol formaldehyde, triethylene glycol formaldehyde, 1,4-butanediol formaldehyde, 1,5-pentanediol formaldehyde, 1,6-hexanediol formaldehyde, etc. Ethylene oxide and 1,3-dioxacyclopentane are particularly preferred. These substances can be used alone or in combination of two or more.

[0064] It should be noted that there are no particular limitations on the polymerization catalyst used in the manufacture of the polyacetal copolymer, and examples include halides of boron, tin, titanium, phosphorus, arsenic, and antimony, represented by Lewis acids. Of particular preference are one or more of boron trifluoride, boron trifluoride hydrates, and coordination complexes of boron trifluoride with organic compounds containing oxygen or sulfur atoms. More specifically, examples include boron trifluoride, boron trifluoride diethyl ether complexes, and boron trifluoride di-n-butyl ether complexes. These substances may be used individually or in combination of two or more.

[0065] In addition, the deactivation of the polymerization catalyst in the manufacture of the polyacetal copolymer can be carried out by the following method: the polyacetal resin obtained by the polymerization reaction is added to an aqueous solution or organic solvent solution containing at least one of the following catalysts and deactivating agents: amines such as ammonia, triethylamine, tri-n-butylamine, or hydroxides of alkali metals or alkaline earth metals, inorganic acid salts, organic acid salts, etc., and stirred in a slurry state for a few minutes to a few hours.

[0066] The slurry after catalyst neutralization and deactivation is filtered and washed to remove unreacted monomers, catalyst neutralization and deactivation agents, and catalyst neutralization salts, and then dried.

[0067] Furthermore, as a method for deactivating the polymerization catalyst, it is also possible to use a method of deactivating the polymerization catalyst by contacting the vapor of ammonia, triethylamine, etc. with the polyacetal copolymer, or a method of deactivating it by contacting at least one of hindered amines, triphenylphosphine, and calcium hydroxide with the polyacetal resin in a mixer.

[0068] Alternatively, instead of deactivating the polymerization catalyst, the polyacetal copolymer after reducing the volatilization of the polymerization catalyst by heating it at a temperature below the melting point of the polyacetal copolymer in an inactive gas atmosphere can be subjected to the end-stabilization treatment described later.

[0069] It should be noted that the above-mentioned deactivation and volatilization reduction operations of the polymerization catalyst can be carried out as needed after the polyacetal resin obtained by the polymerization reaction is crushed.

[0070] As an end-stabilization treatment for the obtained polyacetal resin, the unstable end portions can be removed as described below. For example, a single-screw extruder or a twin-screw extruder with venting holes can be used to melt the polyacetal resin and decompose and remove the unstable end portions in the presence of aliphatic amines such as ammonia, triethylamine, and tributylamine, hydroxides of alkali metals or alkaline earth metals such as calcium hydroxide, inorganic weak acid salts, organic weak acid salts, etc., which are known to decompose the unstable end portions.

[0071] It should be noted that the polyacetal resin mentioned can also be recycled polyacetal resin. In the material recycling process, polyacetal resin obtained as follows can be used: the polyacetal resin used in the product is recycled, and if impurities such as grease are present, these impurities are removed, and then the resin is pulverized. Furthermore, not limited to material recycling, polyacetal resin used in products such as chemical recycling can also be recycled into monomers, and polyacetal resin generated from these monomers can be used.

[0072] The recycled polyacetal resin can be used alone or mixed with non-recycled polyacetal resin.

[0073] Furthermore, the polyacetal resin can be a modified polyacetal. Typically, a modified polyacetal is a block copolymer containing modified segments. Polyacetal segments can be homopolymer residues containing only oxymethylene units or copolymer residues obtained by random copolymerization of oxymethylene and oxyalkylene units. Modified segments are components not belonging to the polyacetal segment family, such as polyolefins, polyurethanes, polyesters, polyamides, polystyrene, and alkyl polyacrylates.

[0074] The preferred polyacetal segment is a polyacetal copolymer residue obtained by random copolymerization of oxymethylene and oxyalkylene units, and the preferred modified segment is a polyolefin or polyurethane.

[0075] From the viewpoint of reducing residues from organic binders during the degreasing process, the modified segment of the modified polyacetal is preferably a polyolefin. Specifically, examples include: polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyisoprene, polybutadiene, hydrogenated polybutadiene, etc.

[0076] From the same point of view, the modified segments of the modified polyacetal are more preferably polyethylene, polypropylene, or hydrogenated polybutadiene. From the viewpoint of shape retention during the degreasing process and suppression of cracking and bulging during the degreasing process, hydrogenated polybutadiene is particularly preferred.

[0077] It should be noted that 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.

[0078] Furthermore, in the composition for sintered molding of this embodiment, the amount of the polyacetal resin relative to the total amount of polyoxymethylene units should be 0.1 mol% or more. It is believed that the higher the amount of the polyacetal resin relative to the total amount of polyoxymethylene units, the more interaction points it has with other resins (polyolefin resins, epoxy resins, etc.), and particularly by adjusting it to 0.31 mol% or more, excellent compatibility can be achieved. From the same viewpoint, the amount of the polyacetal resin relative to the total amount of polyoxymethylene units is preferably 0.1 mol% or more, and more preferably 0.31 mol% or more.

[0079] When the total terminal amount of the polyacetal resin relative to all polyoxymethylene units is 0.1 mol% or more, it tends to exhibit excellent compatibility with epoxy resins and polyolefin resins. Higher compatibility among the resins facilitates homogenization and reduces uneven distribution of resin components, thus helping to reduce appearance defects such as cracking and bulging in the sintered body and improve dimensional accuracy. Furthermore, when the compatibility of the resins is excellent, resin components are less likely to adhere to the mold during molding, reducing mold contamination. Although the following is speculative, it is believed that epoxy resin has strong adhesive strength to metal, and when there is significant uneven distribution of epoxy resin, it is prone to adherence to the mold. However, by improving the compatibility between the resin components, the individual adhesive strength of the epoxy resin can be mitigated, suppressing adhesion to the mold.

[0080] It should be noted that, from the viewpoint of thermal stability, the amount of the polyacetal resin relative to the total amount of polyoxymethylene units should be less than 0.75 mol%, and from the same viewpoint, it is preferably less than 0.5 mol%.

[0081] Here, the total terminal amount of the polyacetal resin relative to all polyoxymethylene units can be determined using an NMR instrument.

[0082] For example, when the measurement is performed at an observation frequency of 900 MHz, a cumulative number of 128 times, and a measurement temperature of 25 °C, the total amount (mol%) of the acetyl end, formyl end, methoxy end, and hemiacetal end of the main chain -OCH2- structure can be calculated as the total amount of the end units relative to all polyoxymethylene units.

[0083] The amount of hemiacetal terminus of the polyacetal resin processed into raw materials, etc., relative to all polyoxymethylene units can be separated and measured by, for example, through the following operation steps.

[0084] First, the sample is subjected to cryogenic pulverization. Then, HFIP (hexafluoroisopropanol) is added to the pulverized sample to extract polyacetal resin and other substances.

[0085] To further remove oligomer components such as polyolefins, the obtained HFIP solution was concentrated, chloroform and methanol were added, and a reprecipitation process was carried out. After filtration, the solution was air-dried and then dried overnight at 50°C using a vacuum dryer to obtain solid polyacetal resin.

[0086] The polyacetal resin solid substance obtained was determined by the above-described method.

[0087] It should be noted that the total amount of terminal components relative to all polyoxymethylene units in the polyacetal resin can be controlled by adjusting the amount of molecular weight regulators (such as methyl acetal, methanol, formic acid, methyl formate, etc.) added during the polymerization of the polyacetal resin.

[0088] Furthermore, the total amount of terminal components of the polyacetal resin relative to all polyoxymethylene units can be controlled by mixing resins with different total terminal components or by using a polyacetal resin with a branched structure. In this case, recycled polyacetal resins or other polyacetal resins whose molecular chains have been broken down through heat and time changes can also be used.

[0089] In the sintered molding composition of this embodiment, the amount of the polyacetal resin relative to the total amount of polyoxymethylene units is specified. Examples of the types of terminals include acetyl terminals, formyl terminals, methoxy terminals, and hemiacetal terminals.

[0090] Furthermore, in the composition for sintered molded articles according to this embodiment, the amount of hemiacetal terminals relative to all polyoxymethylene units is preferably 0.05 mol% or more and 0.2 mol% or less, more preferably 0.14 mol% or more and 0.2 mol% or less. Among the terminals present in all polyoxymethylene units, the hemiacetal terminals have particularly strong interactions with other resin components, which can further improve compatibility.

[0091] The amount of hemiacetal terminus of the polyacetal resin relative to all polyoxymethylene units can be determined by the same method as the total terminus mentioned above.

[0092] It should be noted that when the molecular chain of the polyacetal resin is cut, the end of the cut portion is a hemiacetal end. Therefore, as a method to adjust the hemiacetal end, it is simple to mix polyacetal resin that has undergone thermal decomposition, recycled polyacetal resin, or other polyacetal resin that has changed over time.

[0093] Here, the amount of hemiacetal end-caps of the polyacetal resin relative to all polyoxymethylene units can be controlled by using a branched polyacetal resin and by compounding resins with different amounts of hemiacetal end-caps.

[0094] Polyolefin resin

[0095] In addition to the aforementioned polyacetal resin, the organic binder also contains polyolefin resin.

[0096] Here, the polyolefin resin is a homopolymer or copolymer having structural units derived from olefins having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms.

[0097] Specifically, examples of the polyolefin resin include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyisoprene, and polybutadiene. Polyethylene, polypropylene, and mixtures thereof are preferred, and from the viewpoint of shape retention during the degreasing process and suppression of cracking and blistering during the degreasing process, polyethylene or polypropylene is more preferred. Examples of polyethylene that can be appropriately used in commercially available polyethylene products include: Suntec HD series (manufactured by Asahi Kasei Corporation), Suntec LD series (manufactured by Asahi Kasei Corporation), Suntec EVA series (manufactured by Asahi Kasei Corporation), NEO-ZEX, ULTZEX, and Evolue (all manufactured by Prime Polymer Co., Ltd.). Examples of polypropylene include: Sumitomo Noblen (manufactured by Sumitomo Chemical Co., Ltd.), Novatec PP (manufactured by Nippon Polypropylene Co., Ltd.), SunAllomer PM series (manufactured by SunAllomer Corporation), and Prime Polypro (manufactured by Prime Polymer Co., Ltd.).

[0098] Furthermore, from the viewpoint of compatibility with sinterable inorganic powders and injection molding properties, the melt flow index of the polyolefin resin is preferably 40 g / 10 min or higher.

[0099] Here, the melt flow index of the polyolefin resin can be determined at 190°C and 2.16 kg.

[0100] · Epoxy resin

[0101] The organic binder includes epoxy resin in addition to the aforementioned polyacetal resin and polyolefin resin. By including the epoxy resin, the compatibility with the polyacetal resin and the polyolefin resin can be improved, while the interaction (adhesiveness) with the metal powder is enhanced, thereby improving the dispersibility and sintering density of the metal powder.

[0102] The epoxy resin refers to a resin composed of an aggregate of various epoxy compounds, wherein each epoxy compound is a compound having an epoxy group in its molecule. Here, the molecular structures of the various epoxy compounds constituting the epoxy resin may be the same or different.

[0103] Furthermore, from the viewpoint of compatibility with sinterable inorganic powders and injection molding properties, the melt flow index of the epoxy resin is preferably 40 g / 10 min or higher.

[0104] Here, the melt flow index of the epoxy resin can be determined with reference to ASTM-D-1238-57T at 190°C and 2.16 kg.

[0105] There are no particular restrictions on the type of epoxy resin used here. Bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenolic varnish type epoxy resin, aliphatic epoxy resin, and epoxy resins with glycidyl groups described later can be used.

[0106] Preferably, the epoxy resin is a copolymer of glycidyl ester of unsaturated acid and olefin, and particularly preferably ethylene-glycidyl methacrylate copolymer (EGMA).

[0107] Here, the unsaturated acid glycidyl ester is a compound represented by general formula (1), having an ester structure formed by an unsaturated acid and an alcohol compound having a glycidyl group. Specific compounds may be exemplified by: glycidyl acrylate, glycidyl methacrylate, glycidyl ethyl acrylate, glycidyl itaconic acid, etc. Among these, glycidyl methacrylate is preferred.

[0108]

[0109] (In the formula, R represents an alkenyl group with 2 to 18 carbon atoms, and X represents a carbonyl group.)

[0110] In addition, as optional components, unsaturated acids and / or their derivatives, besides the glycidyl esters mentioned above, may include 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 compounds may include: unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, citraconic acid, and mesoconic acid; unsaturated carboxylic 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.

[0111] Furthermore, α-olefins with 2 to 10 carbon atoms can be listed as copolymers of the glycidyl ester of the unsaturated acid, among which ethylene, propylene, and 1-butene are particularly preferred. In addition, there are no particular limitations on the copolymerization method of the glycidyl ester of the unsaturated acid and the olefin, and conventionally known methods can be used.

[0112] Furthermore, among the copolymers of the glycidyl ester of the unsaturated acid and the olefin, ethylene-glycidyl methacrylate copolymer (EGMA) is preferred. EGMA can be commercially available products; preferred examples include Celloxide manufactured by Daicel Chemical Co., Ltd., and Bondfast manufactured by Sumitomo Chemical Co., Ltd.

[0113] Furthermore, the EGMA can also be synthesized by various methods. For example, it can be manufactured by bulk polymerization, emulsion polymerization, solution polymerization, etc., using a free radical initiator. It should be noted that, regarding representative polymerization methods, those described in Japanese Patent Publication No. 46-45085 and Japanese Patent Application Publication No. 61-127709, etc., can be used in the presence of a free radical-generating polymerization initiator at a pressure of 500 kg / cm². 2 Manufactured under the above conditions at temperatures of 40°C to 300°C. Alternatively, the following methods can be used: a method of melt graft copolymerization in an extruder by mixing an unsaturated epoxy compound and a free radical generator in a resin containing at least one monomer selected from ethylene and olefinic unsaturated compounds other than ethylene; or a method of copolymerizing the unsaturated epoxy compound and the olefinic unsaturated compound in the presence of a free radical generator in an inert medium such as water or an organic solvent.

[0114] The unsaturated glycidyl ester unit in the copolymer of the unsaturated acid glycidyl ester and the olefin is 1% to 25% by weight, preferably 3% to 20% by weight, and more preferably 13% to 20% by weight. With an unsaturated acid glycidyl ester unit content of 1% or more, the interaction with other resin components and metal powders is strengthened, and the dispersibility is improved. Furthermore, with an unsaturated acid glycidyl ester unit content of 25% or less, excellent thermal stability is achieved during compounding and injection molding.

[0115] The content of the unsaturated acid glycidyl ester can be determined by measuring the infrared absorption spectrum of a compressed sheet of the copolymer of the unsaturated acid glycidyl ester and an olefin. This can be determined by correcting the absorbance of the characteristic absorption of the infrared absorption spectrum using the thickness of the sheet used in the measurement, and then determining the content of the unsaturated compound containing the glycidyl group using a calibration curve method based on the obtained corrected absorbance.

[0116] It should be noted that the characteristic absorption peak often appears at 910 cm⁻¹. -1 It is near the location, so it can be used as an indicator.

[0117] Furthermore, when using EGMA as the epoxy resin, the melt flow index of EGMA is preferably 3 g / 10 min or more and 400 g / 10 min or less, more preferably 10 g / 10 min or more and less than 400 g / 10 min, and even more preferably 50 g / 10 min or more and less than 400 g / 10 min. With a melt flow index within the above range, EGMA tends to suppress separation from other resins during injection molding and shorten degreasing time.

[0118] Here, the melt flow index of the EGMA can be determined with reference to ASTM-D-1238 at 190°C and 2.16 kg.

[0119] Formaldehyde scavenger

[0120] In addition to the aforementioned polyacetal resin, polyolefin resin, and epoxy resin, the organic binder preferably also contains a formaldehyde scavenger.

[0121] The formaldehyde scavenger refers to a substance that, when producing molded bodies using the polyacetal resin, has the function of capturing residual formaldehyde, formic acid produced by its modification, and other products that adversely affect productivity and appearance, or inhibiting their effects.

[0122] By including a formaldehyde scavenger in the organic binder, the composition containing the polyacetal resin of this embodiment can not only improve the appearance and texture of the molded article through the formaldehyde scavenging function, but also eliminate reaction sites by preferentially interacting the formaldehyde scavenger with the metal powder, thereby preventing the depolymerization of the polyacetal resin. This can improve the appearance and texture of the moldable material beyond expectations, maintain productivity, and improve quality.

[0123] Examples of formaldehyde scavenging agents include nitrogen-containing compounds, metal salts of inorganic acids, metal oxides, and metal salts of organic acids. Preferably, the formaldehyde scavenging agent is a compound that is as free of acid as possible and / or does not readily produce acid as an impurity.

[0124] It should be noted that the formaldehyde scavenger can be used alone or in combination with two or more.

[0125] Examples of nitrogen-containing compounds include: polyamide resins, amide compounds, amino-substituted triazine compounds, adducts of amino-substituted triazine compounds with formaldehyde, condensates of amino-substituted triazine compounds with formaldehyde, urea, urea derivatives, hydrazine derivatives, imidazole compounds, and imide compounds.

[0126] Examples of the polyamide resin include nylon 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12, and nylon 12. Additionally, the polyamide resin may be copolymers of nylon 6 / 6-6 / 6-10 or nylon 6 / 6-12. Furthermore, examples of the polyamide resin include homopolymers of acrylamide and its derivatives, copolymers of acrylamide and its derivatives with other vinyl monomers, and, for example, poly-β-alanine copolymers obtained by polymerizing acrylamide and its derivatives with other vinyl monomers in the presence of metal alkoxides.

[0127] Examples of such amide compounds include polycarboxylic acid amides such as isophthalimide and o-aminobenzamide.

[0128] Examples of amino-substituted triazine compounds include: 2,4-diaminotriazine, 2,4,6-triaminotriazine, N-butylmelamine, N-phenylmelamine, N,N'-diphenylmelamine, N,N'-diallylmelamine, phenylguanidine (2,4-diamino-6-phenyltriazine), methylguanidine (2,4-diamino-6-methyltriazine), 2,4-diamino-6-butyltriazine, etc.

[0129] Examples of amino-substituted triazine compounds that are adducts of formaldehyde include N-hydroxymethyl melamine, N,N'-dihydroxymethyl melamine, and N,N',N”-trihydroxymethyl melamine.

[0130] Specific examples of the condensation products of the amino-substituted triazine compounds and formaldehyde include, for example, melamine-formaldehyde condensates.

[0131] Examples of urea derivatives include: N-substituted ureas, urea condensates, ethylidene ureas, hydantoin compounds, and ureoyl compounds. Specific examples of N-substituted ureas include: methylureas substituted with alkyl groups, alkylidene diureas, and aryl-substituted ureas. Specific examples of urea condensates include: urea-formaldehyde condensates. Specific examples of hydantoin compounds include: hydantoin, 5,5-dimethylhydantoin, and 5,5-diphenylhydantoin. Specific examples of ureoyl compounds include: allantoin.

[0132] Examples of hydrazine derivatives include, for example, acylhydrazine compounds. Specific examples of acylhydrazine compounds include dicarboxylic acid diacylhydrazines, and more specifically, malonic acid diacylhydrazine, succinic acid diacylhydrazine, glutaric acid diacylhydrazine, adipic acid diacylhydrazine, heptaic acid diacylhydrazine, octanoic acid diacylhydrazine, azelaic acid diacylhydrazine, sebacate diacylhydrazine, dodecanoic acid diacylhydrazine, isophthalic acid diacylhydrazine, phthalic acid diacylhydrazine, 2,6-naphthalenedicarboxylic acid diacylhydrazine, etc.

[0133] Examples of the imidazole compounds mentioned above include imidazole, 1-methylimidazolium, 2-methylimidazolium, 1,2-dimethylimidazolium, etc.

[0134] In addition, examples of such imide compounds include succinimide, glutarimide, and phthalimide.

[0135] It should be noted that, in addition to the above-mentioned formaldehyde scavengers, metal salts of inorganic acids, metal oxides, and metal salts of organic acids can also be listed. Examples include hydroxides of sodium, potassium, magnesium, calcium, or barium, carbonates, phosphates, silicates, borates, carboxylates, and layered double hydroxides of the aforementioned metals.

[0136] The carboxylic acid salt is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, which may be substituted with a hydroxyl group. Specific examples of the saturated or unsaturated aliphatic carboxylic acid salt include: calcium dimyristicate, calcium distearate, calcium distearate, calcium (myristic acid-palmitic acid) phosphate, calcium (myristic acid-stearic acid) phosphate, calcium (palmitic acid-stearic acid) phosphate, etc., with calcium distearate and calcium distearate being preferred.

[0137] Examples of layered double hydroxides include hydrotalcites represented by formula (4).

[0138] [(M 2+ ) 1-x (M 3+ ) x (OH)2] x+ [(A n- ) x / n ·mH2O] x- ……(4)

[0139] (In equation (4), M) 2+ M is a divalent metal. 3+ A is a trivalent metal. n- This represents an anion with an n-valence (n is an integer greater than or equal to 1), where x is in the range 0 < x ≤ 0.33, and m represents a positive number.

[0140] In equation (4), as M 2+ Examples can be listed as follows: Mg 2+ Mn 2+ Fe 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+ etc., as M 3+ Examples can be listed as follows: Al 3+ Fe 3+ Cr 3+ Co 3+ In 3+ etc., as A n- Examples can be listed for OH - F - Cl - ,Br - NO3- CO3 2- SO4 2- Fe(CN)6 3- CH3COO - Oxalate ions, salicylate ions, etc. As A n- Examples, preferably OH - CO3 2- .

[0141] As specific examples of hydrotalcites, those made of Mg can be listed as follows: 0.75 Al 0.25 (OH)2(CO3) 0.125 ·0.5H2O represents natural hydrotalcite, composed of Mg 4.5 Al2(OH) 13 CO3·3.5H2O, Mg 4.3 Al2(OH) 12.6 Synthetic hydrotalcite, etc., represented by CO3.

[0142] (Flowability enhancer)

[0143] The composition for sintering molded articles according to this embodiment preferably includes a flowability improver in addition to the aforementioned sinterable inorganic powder and organic binder. By including the flowability improver, the flowability of the composition for sintering molded articles can be further improved.

[0144] The aforementioned flowability-improving agents are compounds other than the aforementioned polyacetal resins, polyolefin resins, and epoxy resins, such as waxes. It should be noted that, for convenience, in this specification, substances with melting points below 100°C are referred to as "waxes," and substances with melting points above 100°C are referred to as "resins" to distinguish them.

[0145] Examples of waxes include: paraffin wax, polyethylene wax, polypropylene wax, carnauba wax, polyethylene glycol, polytetramethylene glycol, polytetraethylene glycol, polyisobutylene, microcrystalline wax, lignite wax, beeswax, wood wax, synthetic wax, poly-1,3-dioxacyclopentane, poly-1,3-dioxacycloheptane, etc. Among these, from the viewpoint of superior flowability of the composition for sintered bodies in injection molding, paraffin wax, polyethylene glycol, and polytetramethylene glycol are preferred.

[0146] • Compatibilizer

[0147] The composition for sintering molded bodies in this embodiment preferably includes a compatibilizer in addition to the aforementioned sinterable inorganic powder, organic binder, and flowability improver. By including the compatibilizer, the quality of the composition for sintering molded bodies can be further improved.

[0148] The compatibilizer has properties different from the aforementioned resins and waxes, and has the effect of further improving the compatibility of the metal with the resins and waxes, for example, by acting like a surfactant.

[0149] Examples of compatibilizers include: Sannix, Sanflex, Tafmer DF&A, Tafmer XM, Tafmer BL, Tafmer M, Tafmer PN, and Maricom.

[0150] It should be noted that there are no particular limitations on the manufacturing method of the composition for sintering the molded body of this embodiment, and it can be manufactured by known methods. For example, it can be manufactured by mixing the above-mentioned sinterable inorganic powder, organic binder and other optional components, for example using a Henschel mixer, rotary drum, V-type mixer, etc., and then melt-mixing in a semi-molten state using a single-screw extruder or twin-screw extruder, heated roller, kneader, Banbury mixer or other mixing mill, and can be obtained in the form of products in various forms such as filaments and granules.

[0151] When using a pressure kneader for mixing, the mixing temperature is preferably set to 160℃~210℃, more preferably 170℃~190℃. Additionally, the blade rotation speed is preferably 10rpm~50rpm, more preferably 15rpm~40rpm. The mixing time is preferably 45 minutes or more and 2 hours or less. By performing mixing within the above conditions, the compatibility of the resins can be improved, and organic bonding caused by thermal decomposition can be suppressed.

[0152] <Green body>

[0153] The green body of this embodiment is a green body obtained by using the sintering body composition of this embodiment as raw material.

[0154] The resulting green body was free from mold contamination and also suppressed cracking and bulging.

[0155] The green body of this embodiment can be obtained by using a screw-type and piston-type injection molding machine to form a composition for sintering.

[0156] In the injection molding process, the barrel temperature is preferably set to 160°C to 210°C, and more preferably to 170°C to 190°C. Setting the temperature above 160°C improves the fluidity of the resin, while setting it below 200°C reduces mold contamination caused by resin decomposition.

[0157] Furthermore, the mold temperature is preferably 30°C to 90°C, and more preferably 50°C to 70°C. By setting the mold temperature to 30°C or higher, the dimensional stability during molding is improved, and by setting the mold temperature to 90°C or lower, the appearance defects of the green body caused by waxes with melting points below 100°C can be suppressed.

[0158] <Sintered Molded Body>

[0159] The sintered molded body of this embodiment is obtained by sintering the green molded body of this embodiment as described above.

[0160] The resulting sintered body was free from mold contamination and also suppressed cracking and bulging.

[0161] By placing the green body in a closed degreasing / sintering furnace and degreasing and sintering under desired conditions, degreased and sintered bodies can be produced.

[0162] In the case of degreasing by heating, degreasing is carried out by raising the temperature from room temperature to approximately 500°C to approximately 600°C under a nitrogen or argon atmosphere. Before heating, a flowability enhancer can be added to the solvent.

[0163] Next, the temperature is raised to the sintering temperature of the sinterable inorganic powder, thereby obtaining a sintered molded body.

[0164] In the case of degreasing using acid, degreasing is carried out by passing nitric acid gas through a nitrogen atmosphere and raising the temperature from room temperature to 110℃~120℃.

[0165] Next, the temperature is raised to the sintering temperature of the sinterable inorganic powder, thereby obtaining a sintered molded body.

[0166] Example

[0167] The present invention will be described below with specific embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0168] (Composition of each sample)

[0169] The components contained in each sample of the Examples and Comparative Examples are shown below.

[0170] (A) Polyacetal resin

[0171] (A-1) Polyacetal resin

[0172] A twin-shaft paddle-type continuous polymerization reactor (manufactured by Kurimoto Iron Works Co., Ltd., diameter 2B, L / D = 14.8) with a jacket capable of transmitting a heat medium was adjusted to a temperature of 80°C. A catalyst mixture obtained by diluting a boron trifluoride-di-n-butyl ether complex used as a polymerization catalyst to 0.26% by mass using cyclohexane was continuously fed into the polymerization reactor at a rate of 69 g / h, trioxymethylene at a rate of 3500 g / h, 1,3-dioxane at a rate of 121 g / h, and methylal as a molecular weight regulator at a rate of 5.41 g / h, and polymerization was carried out.

[0173] The material discharged from the polymerization reactor is added to a 0.5% by mass triethylamine aqueous solution to deactivate the polymerization catalyst, followed by filtration, washing, and drying.

[0174] Next, a 0.8% by mass triethylamine aqueous solution was added to the end stabilization zone in a vented twin-screw extruder (L / D = 40) set to 200°C. Stabilization was carried out simultaneously with degassing under reduced pressure at 90 kPa, and the mixture was granulated using a granulator. Then, it was dried at 100°C for 2 hours to obtain polyacetal resin (A-1).

[0175] The obtained (A-1) polyacetal resin has a melting point of 164℃ and a melt flow index of 10 g / 10 min.

[0176] (A-2) Polyacetal resin

[0177] Except that the flow rate of methyl acetal, used as a molecular weight regulator, was adjusted to 5.72 g / h, (A-2) polyacetal resin was manufactured in the same manner as (A-1) polyacetal resin. The resulting (A-2) polyacetal resin had a melting point of 164°C and a melt flow index of 20 g / 10 min.

[0178] (A-3) Polyacetal resin

[0179] Except that the flow rate of methyl acetal, which serves as a molecular weight regulator, was adjusted to 7.1 g / h, (A-3) polyacetal resin was manufactured using the same method as (A-1) polyacetal resin. The resulting (A-3) polyacetal resin had a melting point of 164°C and a melt flow index of 71 g / 10 min.

[0180] (A-4) Polyacetal resin

[0181] Except that the flow rate of methyl acetal, which serves as a molecular weight regulator, was adjusted to 7.62 g / h, (A-4) polyacetal resin was manufactured using the same method as (A-1) polyacetal resin. The resulting (A-4) polyacetal resin had a melting point of 164°C and a melt flow index of 81 g / 10 min.

[0182] (A-5) Polyacetal resin

[0183] Except that the flow rate of methyl acetal, which serves as a molecular weight regulator, was adjusted to 9.4 g / h, (A-5) polyacetal resin was manufactured using the same method as (A-1) polyacetal resin. The resulting (A-5) polyacetal resin had a melting point of 164°C and a melt flow index of 121 g / 10 min.

[0184] (A-6) Polyacetal resin

[0185] Except that the flow rate of methyl acetal, which serves as a molecular weight regulator, was adjusted to 10.6 g / h, (A-6) polyacetal resin was manufactured using the same method as (A-1) polyacetal resin. The resulting (A-6) polyacetal resin had a melting point of 164°C and a melt flow index of 200 g / 10 min.

[0186] (B) Polyolefin resin

[0187] (B-1) Polypropylene: Manufactured by Sumitomo Chemical Co., Ltd., Sumitomo Noblen UH501E1

[0188] (B-2) Polyethylene: Manufactured by Asahi Kasei Corporation, Suntec™ LDPE M6555

[0189] (C) Epoxy resin

[0190] (C-1) Aliphatic epoxy resin: manufactured by Celesl Chemical Co., Ltd., Celloxide 2021P

[0191] (C-2)EGMA: Manufactured by Sumitomo Chemical Co., Ltd., Bondfast CG5001

[0192] The GMA ratio is 19% by weight, and the melt flow index is 380 g / 10 min.

[0193] (C-3)EGMA: Manufactured by Sumitomo Chemical Co., Ltd., Bondfast BF-30C

[0194] The GMA ratio is 19% by weight, and the melt flow index is 30 g / 10 min.

[0195] (C-4)EGMA: Manufactured by Sumitomo Chemical Co., Ltd., Bondfast BF-E

[0196] The GMA ratio is 12% by weight, and the melt flow index is 3 g / 10 min.

[0197] (C-5)EGMA: Manufactured by Sumitomo Chemical Co., Ltd., Bondfast BF-2C

[0198] The GMA ratio is 6% by weight, and the melt flow index is 3 g / 10 min.

[0199] (C-6)EGMA: Manufactured by Sumitomo Chemical Co., Ltd., Bondfast BF-7B

[0200] The GMA ratio is 12% by weight, and the melt flow index is 7 g / 10 min.

[0201] (C-7)EGMA: Manufactured by Sumitomo Chemical Co., Ltd., Bondfast BF-7M

[0202] The GMA ratio is 6% by weight, and the melt flow index is 7 g / 10 min.

[0203] (D) Flowability enhancer

[0204] Paraffin wax: Manufactured by Nippon Seiwa Co., Ltd., Paraffin wax-145

[0205] (E) Formaldehyde scavenger

[0206] Sebacate dihydrazide: manufactured by Japan Finechem Co., Ltd.

[0207] (F) Compatibilizer

[0208] (F-1) Made by Mitsui Chemicals Co., Ltd., Tafmer PN-2070

[0209] (F-2) Sannyx GL-30000 manufactured by Sanyo Chemical Co., Ltd.

[0210] (F-2) Manufactured by Mitsui Chemicals, Ltd., Tafmer XM-7070S

[0211] (Mel flow index)

[0212] It should be noted that the melt flow index of (A) polyacetal resin, (B) polyolefin resin, and (C) epoxy resin was measured using MELT INDEXER manufactured by Toyo Seiki Co., Ltd. at 190°C and 2160g, in accordance with ASTM-D-1238.

[0213] (Relative to the total number of terminal units of all polyoxymethylene units)

[0214] • Examples 1-19, Comparative Examples 1-5

[0215] Regarding (A), the total amount of polyoxymethylene units relative to the total terminal amount of polyacetal resin was measured using an AVANCEⅢ 900MHz + 5mm TCI CryoProbe manufactured by Burker, under the conditions of observation frequency of 900MHz, cumulative number of times of 128, and measurement temperature of 25°C, and the total amount (mol%) of acetyl, formyl, methoxy, and hemiacetal terminals relative to the main chain -OCH2- structure was calculated.

[0216] In addition, the sample to be measured is dissolved in a 0.4% TFA-Na / HFIP-d2 solution at a concentration of 0.03% by weight, heated and shaken at 40°C for 2 hours, and the liquid level is adjusted to 40 mm in a 5 mm φ NMR sample tube (manufactured by Wilmad, 535-PP-7, 7 inches in length) without filtration, thus preparing the sample for measurement.

[0217] By using a pressure kneader to mix (A-1), (A-2), (A-3), (A-4), (A-5), and (A-6) at 190°C for 20 minutes, the total terminal amount of the obtained polyacetal resin relative to all polyoxymethylene units was adjusted to the total terminal amount shown in Tables 1 and 2.

[0218] Example 20

[0219] For Example 20 only, SUS316L (average particle size 10 μm) was used as a sinterable inorganic powder and mixed with each of the materials (A) to (F) in the proportions described in Table 2. The mixture was then kneaded for 1 hour at a temperature of 175°C and a blade speed of 30 rpm using a pressure kneader to produce samples of the composition for sintering.

[0220] Then, the obtained sintered molded body is subjected to cryogenic pulverization with the composition, and then HFIP (hexafluoroisopropanol) is added to the obtained pulverized sample to extract polyacetal resin, etc.

[0221] Then, in order to remove oligomer components such as polyolefins, the obtained HFIP solution was concentrated, chloroform and methanol were added, and a reprecipitation treatment was carried out. After filtration, it was air-dried and then dried overnight at 50°C using a vacuum dryer. The resulting polyacetal resin solid was used as the test sample.

[0222] The total amount of terminal components in the polyacetal resin solid was determined using an AVANCEⅢ 900MHz + 5mm TCI CryoProbe manufactured by Burker at an observation frequency of 900MHz, a cumulative number of measurements of 128, and a measurement temperature of 25°C. The total amount (mol%) of the acetyl, formyl, methoxy, and hemiacetal terminals relative to the main chain -OCH2- structure was calculated.

[0223] (The amount of hemiacetal terminus relative to all polyoxymethylene units)

[0224] • Examples 1-19, Comparative Examples 1-5

[0225] Regarding (A), the amount of hemiacetal terminus relative to all polyoxymethylene units of the polyacetal resin was measured using an AVANCEⅢ 900MHz + 5mm TCI CryoProbe manufactured by Burker at an observation frequency of 900MHz, a cumulative number of measurements of 128, and a measurement temperature of 25°C. The amount (mol%) of hemiacetal terminus relative to the main chain -OCH2- structure was calculated.

[0226] In addition, the sample to be measured was dissolved in a 0.4% TFA-Na / HFIP-d2 solution at a concentration of 0.03% by weight, heated and shaken at 40°C for 2 hours, and the liquid level was adjusted to 40 mm in a 5 mm φ NMR sample tube (Wilmad 535-PP-7, 7 inches in length) without filtration, thus preparing the sample for measurement.

[0227] By using a pressure kneader to mix (A-1), (A-2), (A-3), (A-4), (A-5), and (A-6) at 190°C for 20 minutes, the amount of hemiacetal end units of the resulting polyacetal resin relative to all polyoxymethylene units was adjusted to the amount of hemiacetal end units shown in Tables 1 and 2.

[0228] Example 20

[0229] For Example 20 only, SUS316L (average particle size 10 μm) was used as a sinterable inorganic powder and mixed with each of the materials (A) to (F) in the proportions described in Table 2. The mixture was then kneaded for 1 hour at a temperature of 175°C and a blade speed of 30 rpm using a pressure kneader to produce samples of the composition for sintering.

[0230] Then, the obtained sintered molded body is subjected to cryogenic pulverization with the composition, and then HFIP (hexafluoroisopropanol) is added to the obtained pulverized sample to extract polyacetal resin, etc.

[0231] Then, in order to remove oligomer components such as polyolefins, the obtained HFIP solution was concentrated, chloroform and methanol were added, and a reprecipitation treatment was carried out. After filtration, it was air-dried and then dried overnight at 50°C using a vacuum dryer. The resulting polyacetal resin solid was used as the test sample.

[0232] The amount of hemiacetal terminus in the polyacetal resin solid was determined using an AVANCEⅢ 900MHz + 5mm TCI CryoProbe manufactured by Burker, under the conditions of observation frequency of 900MHz, cumulative number of times of 128, and measurement temperature of 25°C, and the amount (mol%) of hemiacetal terminus relative to the main chain -OCH2- structure was calculated.

[0233] [Examples 1-20, Comparative Examples 1-5]

[0234] SUS316L (average particle size 10 μm) was used as a sinterable inorganic powder and mixed with each material in the proportions described in Tables 1 and 2. The mixture was then kneaded for 1 hour at a temperature of 175°C and a blade speed of 30 rpm using a pressure kneader to produce samples of the composition for sintering.

[0235] Then, the samples of the obtained sintered molding composition were cooled and crushed to obtain raw materials for injection molding. These raw materials were then molded using an injection molding machine (manufactured by Fanuc, ROBOSHOTα-50iA) at a molding temperature of 175℃~190℃, thereby producing multiple green molded test pieces. It should be noted that the dimensions of these green molded test pieces were all 10mm in width, 60mm in height, and 3mm in thickness.

[0236] [evaluate]

[0237] The following evaluations were conducted (1) to (6). The evaluation results are shown in Tables 1 and 2.

[0238] (1) Appearance of the green body

[0239] For each sample of green molded test pieces, 10 pieces were randomly selected, and their appearance was observed and evaluated according to the following criteria.

[0240] 〇 (Good): No cracks or gaps can be observed.

[0241] × (Defective): Cracks, gaps, etc. were observed.

[0242] (2) Mold contamination

[0243] For the production of green molded test pieces of each sample, 500 injection molding cycles were performed, and the contamination adhering to the mold was visually observed at the end of 10 injection cycles, 100 injection cycles, and 500 injection cycles.

[0244] Regarding mold contamination, abnormal conditions on the mold surface, such as white or iridescent colors relative to the mold's color, or the presence of solid substances, are considered contamination and are evaluated according to the following criteria.

[0245] ◎: No contamination was observed on the mold up to 500 injections.

[0246] 〇: No contamination was found on the mold up to 100 injections.

[0247] ×: The mold was contaminated up to the 10th injection.

[0248] (3) Appearance of defatted body

[0249] The prepared green body test pieces were heated and degreased. The prepared green body test pieces were supported at two points with a 50 mm interval and placed in a degreasing oven.

[0250] (3-1) As a first condition, the degreasing furnace was purged with nitrogen, and the temperature was increased to 150°C at a rate of 50°C / hour. Then, the temperature was increased to 150°C–200°C at a rate of 30°C / hour and held for 1 hour. The temperature was then increased to 200°C–400°C at a rate of 30°C / hour, and then increased to 400°C–600°C at a rate of 120°C / hour, followed by furnace cooling, thus obtaining various samples of the degreased body. (Total degreasing process: approximately 15 hours)

[0251] For each degreased body obtained, the appearance of 10 degreased bodies was visually observed and evaluated according to the following criteria.

[0252] 〇 (Excellent): No cracks, bulges or other abnormal appearances can be observed.

[0253] × (Defective): Cracks and bulges were observed.

[0254] (3-2) In addition, for the degreased bodies of samples for which no abnormal appearance such as cracks or bulges were observed under the first condition, as a second condition, the green preforms were placed in a degreasing furnace with two-point support at 50 mm intervals. The furnace was then purged with nitrogen, and the temperature was increased to 150°C at 50°C / hour. Then, the temperature was increased to 150°C–200°C at a rate of 30°C / hour and held for 1 hour. The temperature was then increased to 200°C–300°C at 50°C / hour, then to 300°C–400°C at 100°C / hour, and finally to 400°C–600°C at 120°C / hour, followed by furnace cooling, thus obtaining the degreased bodies of each sample. (Total degreasing process: approximately 12 hours)

[0255] For each degreased body obtained, the appearance of 10 degreased bodies was visually observed and evaluated according to the following criteria.

[0256] 〇 (Excellent): No cracks, bulges or other abnormal appearances can be observed.

[0257] × (Defective): Cracks and bulges were observed.

[0258] It should be noted that the defatted body that is ○ (excellent) under the second condition is also ○ (excellent) under the first condition, so this is omitted from the record.

[0259] (4) Appearance of sintered body

[0260] The degreased bodies of the obtained samples were sintered by slowly heating from room temperature at 200°C / hour under an argon atmosphere and holding at a maximum temperature of 1350°C for 2 hours, thereby obtaining the sintered bodies of the samples.

[0261] For each sample's sintered body, the appearance of 10 sintered bodies was visually observed and evaluated according to the following criteria.

[0262] 〇 (Excellent): No cracks, bulges or other abnormal appearances can be observed.

[0263] × (Defective): Cracks and bulges were observed.

[0264] (5) Density of sintered body

[0265] For each sintered sample, the density (g / cm³) of 10 sintered bodies was determined using an electronic hydrometer (manufactured by Alfa Mirage) at a water temperature of 25°C, according to JIS Z 8807. 3 ).

[0266] (6) Dimensional accuracy of sintered body

[0267] For each sample of sintered body, the diameter of 30 sintered bodies was measured using a micrometer. Then, based on the "normal tolerance for width" specified in JIS B0411, the measured values ​​were evaluated according to the following evaluation criteria.

[0268] ◎: Grade is high (tolerance error is less than ±0.05mm).

[0269] 〇: The grade is medium (greater than the allowable error ±0.05mm and less than or equal to the allowable error ±0.1mm).

[0270] △: The grade is low (greater than the allowable error ±0.1mm and less than or equal to the allowable error ±0.2mm).

[0271] ×: Outside of permitted limits.

[0272]

[0273]

[0274] As can be seen from the results in Tables 1 and 2, in Examples 1 to 20, all evaluation items showed well-balanced and excellent results. On the other hand, Comparative Examples 1 to 5 showed worse results than the Examples in at least one evaluation item. In particular, the mold contamination and the dimensional accuracy of the sintered body were worse than those of the Examples.

[0275] Industrial practicality

[0276] 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 special equipment and processes, without causing mold contamination during molding, and can suppress cracking and bulging during molding and after sintering, as well as green molded bodies and sintered molded bodies using the composition for sintered molded bodies.

Claims

1. A composition for sintering molded bodies, said composition comprising a sinterable inorganic powder and an organic binder, characterized in that, The organic binder comprises at least polyacetal resin, polyolefin resin, and epoxy resin. The polyacetal resin has a total terminal amount of 0.1 mol% or more and 0.75 mol% or less relative to all polyoxymethylene units, and the polyacetal resin has a hemiacetal terminal amount of 0.05 mol% or more and 0.20 mol% or less relative to all polyoxymethylene units.

2. The composition for sintered molded bodies as described in claim 1, characterized in that, The polyacetal resin has a terminal amount of more than 0.31 mol% and less than 0.50 mol% relative to the total amount of all polyoxymethylene units.

3. The composition for sintered bodies as described in claim 1, characterized in that, The polyacetal resin has a hemiacetal end content of more than 0.14 mol% and less than 0.20 mol% relative to all polyoxymethylene units.

4. The composition for sintered molded articles as described in claim 1 or 2, characterized in that, The melt flow index of the polyacetal resin is 80 g / 10 min to 200 g / 10 min.

5. The composition for sintered molded bodies as described in claim 1 or 2, characterized in that, The organic binder contains at least one formaldehyde scavenger.

6. The composition for sintered bodies as described in claim 1 or 2, characterized in that, The epoxy resin is a copolymer of an olefin and an unsaturated compound having a glycidyl group.

7. The composition for sintered bodies as described in claim 6, characterized in that, The glycidyl unsaturated compound in the epoxy resin is 1% to 25% by weight relative to the total weight of the epoxy resin.

8. The composition for sintered bodies as described in claim 1 or 2, characterized in that, The melt flow index of the epoxy resin is 3 g / 10 min to 400 g / 10 min.

9. The composition for sintered molded articles as described in claim 1 or 2, characterized in that, It also contains compatibilizers.

10. The composition for sintered molded articles as described in claim 1 or 2, characterized in that, In the total volume of the sinterable inorganic powder and the organic binder, the ratio of the organic binder is less than 40% by volume.

11. A green molded body, characterized in that, The green body is obtained by molding the sintered body according to claim 1 or 2 using a composition.

12. A sintered molded body, characterized in that, The sintered body is obtained by sintering the green body as described in claim 11.

13. A composition for sintering molded bodies, said composition comprising a sinterable inorganic powder and an organic binder, characterized in that, The organic binder comprises at least polyacetal resin, polyolefin resin, and epoxy resin. The amount of hemiacetal terminal resin in the compounded sintered body composition is 0.14 mol% to 0.20 mol% relative to all polyoxymethylene units. The polyacetal resin has a terminal amount of more than 0.1 mol% and less than 0.75 mol% relative to the total amount of all polyoxymethylene units.

Images