Composition for sintered molding, green molding, and sintered molding

Abstract

To provide a composition for a sintered molding capable of producing a sintered molding excellent in strength and appearance, extremely low in a void ratio, and suppressed in generation of form-gas.SOLUTION: A composition for a sintered molding includes a sinterable inorganic powder and an organic binder, where the organic binder includes: a thermoplastic resin A which reacts with the inorganic powder; another thermoplastic resin B; a fluidity-imparting agent; and an epoxy resin, a sea-island structure is constituted by an island of the thermoplastic resin, and a sea of the thermoplastic resin B and the fluidity-imparting agent when a section of the composition for a sintered molding is observed, and the sinterable inorganic powder exists in the sea and the epoxy resin exists around the sinterable inorganic powder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Among sintered bodies made from sinterable inorganic powders such as metals, ceramics, and cermets, a technique using a composition for sintered compacts containing a sinterable inorganic powder and a binder is known for producing precise sintered bodies or sintered bodies with complex shapes. The composition for sintered compacts is heated and kneaded to form a raw material for the sintered compact, which is then injection-molded to form a green compact, which is then subjected to a debinding process and then sintered to produce a sintered compact.

[0003] The debinding process is a process for removing the binder from a green compact, which is a compact of a composition for sintered compacts, and can be carried out by a method in which the binder is thermally decomposed and gasified by heating the green compact, or by treating the green compact with a solvent to elute and remove the soluble binder components in the green compact, and then the remaining binder is thermally decomposed and gasified. However, in the thermal debinding methods in which the green compact is heated for debinding as described above, if the thermal decomposition and gasification of the binder contained in the green compact occurs intensively in a short period of time, cracks and blistering may occur in the compact during the debinding process.

[0004] Therefore, in order to suppress cracking and swelling of the molded body during the above-mentioned debinding step, there are techniques for compositions for sintered molded bodies that can suppress cracking and swelling during molding and after sintering, such as using a depolymerizable polymer as a binder.

[0005] For example, Patent Document 1 discloses a sinterable powder injection molding composition containing polymer compounds a: polyoxymethylene, b: ethylene glycidyl methacrylate copolymer, and c: polypropylene as components constituting an organic binder. Furthermore, for example, Patent Document 2 discloses a technique for improving the quality of green compacts, degreased compacts, and sintered compacts by using a polyacetal resin and an epoxy resin together as a binder. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-109994 [Patent Document 2] Japanese Patent Application Publication No. 2023-157969 Summary of the Invention [Problem to be solved by the invention]

[0007] The production of sintered compacts using compositions for sintered compacts is a lengthy process, requiring numerous performance requirements for each step. Green compacts, in particular, are extremely brittle and can affect yield, so strength is essential. Furthermore, uneven distribution of sinterable inorganic powders and binders in the green compacts can lead to localized thermal decomposition and gasification, potentially causing cracks and swelling in the compacts during the debinding process, making it difficult to obtain high-quality sintered compacts with minimal defects. Furthermore, when polyacetal resins, which are suitable for the thermal debinding process, are included, they react with sinterable inorganic powders to generate toxic formaldehyde gas, requiring careful handling.

[0008] Therefore, an object of the present invention is to provide a resin composition that can be used to produce a sintered molded article that is excellent in strength and appearance, has an extremely low porosity, and suppresses the generation of form gas. Another object of the present invention is to provide a green molded body that is excellent in strength and appearance and in which the generation of form gas is suppressed. Another object of the present invention is to provide a sintered molded body that is excellent in strength and appearance, has an extremely low porosity, and suppresses the generation of form gas. [Means for solving the problem]

[0009] The present inventors have conducted extensive research into compositions for sintered compacts containing a sinterable inorganic powder and an organic binder in order to solve the above-mentioned problems. As a result, they have found that it is possible to determine whether a green compact or sintered compact is good from the morphology of the composition for sintered compacts, and have clarified the influence of the materials constituting the composition for sintered compacts on morphology. They have also found that a composition for sintered compacts with a specific morphology can produce green compacts and sintered compacts that are excellent in strength and appearance and that suppress the generation of form gas, and have completed the present invention.

[0010] The present invention has been made based on the above findings, and the gist of the present invention is as follows. [1] A composition for sintered compacts comprising a sinterable inorganic powder and an organic binder, The organic binder includes a thermoplastic resin A that reacts with the inorganic powder, another thermoplastic resin B, a fluidity imparting agent, and an epoxy resin; When a cross section of the composition for sintered compact is observed, the thermoplastic resin A forms an island structure, and the thermoplastic resin B and the fluidity imparting agent form an island structure. the sinterable inorganic powder is present in the sea; A composition for sintered compacts, wherein an epoxy resin is present around the sinterable inorganic powder.

[0011] [2] The composition for sintered compacts according to [1], wherein the sinterable inorganic powder forms an oxide film.

[0012] [3] The composition for sintered compacts according to [1] or [2], wherein the thermoplastic resin A is a polyacetal resin having a thermal decomposition behavior different from that of the thermoplastic resin B and a melt flow index of less than 200 g / 10 min.

[0013] [4] The thermoplastic resin B is a polyolefin having a thermal decomposition behavior different from that of the thermoplastic resin A and a melt flow index of 30 to 70 g / 10 min; The composition for sintered compacts according to any one of [1] to [3], wherein 90% by volume or more of the thermoplastic resin B is polypropylene.

[0014] [5] The composition for sintered compacts according to any one of [1] to [4], wherein the fluidity imparting agent has a melting point of 50 to 90°C.

[0015] [6] The composition for sintered molded bodies according to any one of [1] to [5], wherein the epoxy resin has a melt flow index of 3 to 380 g / 10 min.

[0016] [7] The composition for sintered compacts according to any one of [1] to [6], wherein 95% or more of the sinterable inorganic powder is surrounded by an epoxy resin.

[0017] [8] Of the total volume of the organic binder, The thermoplastic resin A is 10% by volume or less, The thermoplastic resin B is 20% by volume or more and less than 30% by volume, The fluidity imparting agent is 40% by volume or more and less than 50% by volume, The composition for sintered compacts according to any one of [1] to [7], wherein the epoxy resin is contained in an amount of 10% by volume or more and less than 20% by volume.

[0018] [9] The composition for sintered molded bodies according to any one of [1] to [8], wherein the sum of the thermoplastic resin A, the thermoplastic resin B, and the fluidity imparting agent is less than 40% by volume of the total volume of the sinterable inorganic powder, the thermoplastic resin A, the thermoplastic resin B, and the fluidity imparting agent.

[0019]

[10] A green compact obtained by compacting the composition for a sintered compact according to any one of [1] to [9].

[0020]

[11] A sintered compact obtained by sintering the green compact according to

[10] . [Effects of the Invention]

[0021] According to the present invention, there can be provided a composition for sintered compacts that can be used to produce sintered compacts that are excellent in strength and appearance, have an extremely low porosity, and suppress the generation of form gas. Furthermore, according to the present invention, it is possible to provide a green molded body that is excellent in strength and appearance and in which the generation of form gas is suppressed. Furthermore, the present invention can provide a sintered molded body that is excellent in strength and appearance, has an extremely low porosity, and suppresses the generation of form gas. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an AFM image of a green compact produced in an example. [Figure 2] 1 is an X-ray CT image of a sintered body obtained by sintering a green body produced in an example. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to the embodiment. In other words, the present invention can be modified in various ways without departing from the gist of the present invention.

[0024] <Definition> In the present invention, "epoxy resin is present around the inorganic powder" means that the epoxy resin is present around the inorganic powder selectively compared to other sea phases.

[0025] <Composition for sintered compact> The resin composition for a sintered molded body of the present embodiment is A composition for a sintered compact comprising a sinterable inorganic powder and an organic binder, The organic binder includes a thermoplastic resin A that reacts with the inorganic powder, another thermoplastic resin B, a fluidity imparting agent, and an epoxy resin; When a cross section of the composition for sintered compact is observed, the thermoplastic resin A forms an island structure, and the thermoplastic resin B and the fluidity imparting agent form an island structure. the sinterable inorganic powder is present in the sea; The sinterable inorganic powder is surrounded by an epoxy resin. When the above-mentioned composition for sintered compacts is used to produce a sintered compact, the resulting sintered compact has excellent strength and appearance, an extremely low porosity, and suppressed generation of form gas.

[0026] The composition for a sintered compact of this embodiment contains a sinterable inorganic powder, an organic binder, and the fluidity imparting agent. In addition to the inorganic powder and the organic binder, the composition for a sintered compact of this embodiment can contain other components as described below.

[0027] When a cross section of the composition for sintered compacts is observed, the composition for sintered compacts has a sea-island structure in which thermoplastic resin A is an island and thermoplastic resin B and the fluidity imparting agent are an ocean, with the sinterable inorganic powder present in the ocean. One of the factors contributing to the morphology of the composition for sintered compacts of this embodiment is presumed to be the polarity of the components contained in the composition. Specifically, thermoplastic resin A is thought to exist as islands because it has a different polarity from thermoplastic resin B, the fluidity imparting agent, and the epoxy resin. Furthermore, thermoplastic resin B, the fluidity imparting agent, and the epoxy resin are thought to exist as a sea, which is the main matrix, because they have similar polarities. Furthermore, the epoxy resin is present around (near) the inorganic powder. The inorganic powder is usually present as islands because it is compatible with thermoplastic resin A. However, the selective presence of the epoxy resin around (near) the inorganic powder causes the inorganic powder surface to exhibit a polarity similar to that of the polyolefin and fluidity imparting agent in thermoplastic resin B, resulting in the inorganic powder being present in the ocean. Furthermore, the selective presence of the epoxy resin around (near) the inorganic powder eliminates the risk of decomposition of the inorganic powder due to direct contact with the thermoplastic resin A, such as polyacetal. This suppresses odors such as form gas caused by decomposition of the polyacetal resin, and allows a composition for sintered compacts to be obtained according to the blending ratio, resulting in effects such as improved dimensional accuracy due to shrinkage during debinding and sintering and the ability to fully utilize the properties of the polyacetal resin during debinding. Furthermore, the presence of the inorganic powder in the sea, which is the main matrix, rather than in islands, improves the dispersibility of the inorganic powder in the composition for sintered compacts, resulting in effects such as improved dimensional accuracy during molding, increased strength of the green compact, a sintered compact with a good appearance and increased strength and elongation, and reduced porosity within the sintered compact. Furthermore, it is more preferable that the epoxy resin contains a functional group, such as a vinyl acetate copolymer, that is highly compatible with the thermoplastic resin B. This improves the dispersibility of the thermoplastic resin B in the organic binder that exists as a sea, resulting in effects such as further improving the strength of the green compact and further reducing the porosity inside the sintered compact.

[0028] In the composition for sintered compacts, the sum of the thermoplastic resin A, the thermoplastic resin B, and the fluidity imparting agent is preferably less than 40% by volume of the total volume of the sinterable inorganic powder, the thermoplastic resin A, the thermoplastic resin B, and the fluidity imparting agent. Furthermore, the sum of the thermoplastic resin A, the thermoplastic resin B, and the fluidity imparting agent is more preferably 35% by volume or less, and more preferably 25% by volume or more, of the total volume of the sinterable inorganic powder, the thermoplastic resin A, the thermoplastic resin B, and the fluidity imparting agent.

[0029] (sinterable inorganic powder) The composition for a sintered compact of this embodiment contains a sinterable inorganic powder (hereinafter, sometimes simply referred to as "inorganic powder"). The sinterable inorganic powder may be used alone or in combination of two or more kinds.

[0030] In this embodiment, the sinterable inorganic powder can be selected from any known suitable sinterable inorganic powder. For example, it can be selected from metal powder, alloy powder, metal carbonyl powder, and mixtures thereof. Among these, it is particularly preferable to use metal powder or ceramic powder to impart functionality.

[0031] Examples of the metal powder include powders of aluminum, magnesium, barium, calcium, cobalt, zinc, copper, nickel, iron, silicon, titanium, tungsten, and metal compounds and metal alloys based on these metals, where the metal powder can be not only a completed alloy but also a mixture of individual alloy components.

[0032] Examples of the ceramic powder 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; ferrite; and high-temperature superconducting materials.

[0033] The sinterable inorganic powder may be used alone or in combination with several inorganic materials, such as various metals, metal alloys, or ceramics. Particularly preferred metals and alloys include titanium alloys and stainless steel, and preferred ceramics include Al2O3 and ZrO2. For example, a titanium-6 aluminum-4 vanadium alloy is preferably used as the titanium alloy, and SUS316L is preferably used as the stainless steel.

[0034] In the composition for sintered compacts, the content of the inorganic powder is preferably 45 to 80% by volume, more preferably 50 to 75% by volume, and particularly preferably 55 to 70% by volume.

[0035] The sinterable inorganic powder preferably forms an oxide film, which is thought to allow the epoxy resin (such as EGMA) described below to be more selectively present near the metal and improve the flowability of the composition for sintered compacts.

[0036] In the composition for sintered compacts, the sinterable inorganic powder is surrounded by the epoxy resin, preferably 80% or more of the inorganic powder is surrounded by the epoxy resin, and more preferably 95% or more of the inorganic powder is surrounded by the epoxy resin. The proportion of epoxy resin present around the inorganic powder can be determined by measuring the decomposition rate of thermoplastic resin A. Specifically, it can be determined by the method described in the examples below.

[0037] (organic binder) The composition for a sintered compact of this embodiment contains an organic binder in addition to a sinterable inorganic powder. The organic binder contains at least a thermoplastic resin A that reacts with the inorganic powder, another thermoplastic resin B, an epoxy resin, and a fluidity imparting agent.

[0038] The volume proportion of the organic binder in the composition for sintered compacts of this embodiment is not particularly limited, but is preferably 20 to 55 volume %, more preferably 25 to 50 volume %, and particularly preferably 30 to 45 volume %, relative to 100 volume % of the composition for sintered compacts. By containing the organic binder within the above-mentioned range, when green compacts and sintered compacts are produced using the composition for sintered compacts, the resulting green compacts and sintered compacts have excellent strength and appearance and suppress the generation of form gas.

[0039] [Thermoplastic resin A that reacts with inorganic powder] The thermoplastic resin A reacts with the inorganic powder contained in the composition for a sintered molded body of this embodiment. The thermoplastic resin A that reacts with the inorganic powder (hereinafter sometimes simply referred to as "thermoplastic resin A") is not limited, but examples thereof include polyacetal resin (POM), polymethyl methacrylate resin (PMMA), polybutyl methacrylate resin (PBMA), polyamide resin (PA), polyethylene glycol resin (PEG), polyvinylidene fluoride resin (PVDF), and polyvinylidene chloride resin (PVDC).

[0040] The content of thermoplastic resin A in the organic binder is preferably 30% by volume or less, more preferably 20% by volume or less, and even more preferably 10% by volume or less, and may be 5% by volume or more.

[0041] The thermoplastic resin A is preferably a polyacetal resin having a different thermal decomposition behavior from that of the thermoplastic resin B.

[0042] -Polyacetal resin- Examples of the polyacetal resin include polyacetal homopolymers, polyacetal copolymers, and mixtures thereof. Among these, polyacetal copolymers are preferred from the viewpoint of thermal stability. The polyacetal resins may be used singly or in combination. The polyacetal resins may be used in powder form, in addition to the commonly provided pellet form. The particle size of the powder is preferably D50 = 500 μm or less, more preferably D50 = 300 μm or less. The polyacetal resin preferably has a melt flow index measured under conditions of 190°C and 2.16 kg of less than 200 g / 10 min, more preferably 60 g / 10 min or more and less than 200 g / 10 min, and a melting point of 153 to 162°C. The melt flow index can be measured in accordance with ASTM-D-1238 using a MELTINDEXER manufactured by Toyo Seiki under conditions of 190°C and 2.16 kg, and the melting point can be determined by differential scanning calorimetry (DSC) in accordance with JIS K7121.

[0043] The polyacetal homopolymer may be a polymer having oxymethylene units in the main chain, and both ends of the polymer may be blocked with ester or ether groups. The polyacetal homopolymer can be obtained from formaldehyde and a known molecular weight modifier as raw materials, and can be obtained from these raw materials using a known onium salt polymerization catalyst and a hydrocarbon or other solvent by a known slurry method, such as the polymerization methods described in Japanese Patent Publication Nos. 47-6420 and 47-10059. Preferably, the polyacetal homopolymer has oxymethylene units in an amount of 99.8 mol % or more of its main chain, excluding both ends. More preferably, the main chain, excluding both ends, is composed solely of oxymethylene units.

[0044] The polyacetal copolymer includes a polymer having an oxymethylene unit and an oxyethylene unit in the main chain, and can be obtained, for example, by copolymerizing trioxane with a cyclic ether and / or a cyclic formal in the presence of a polymerization catalyst. Trioxane is a cyclic trimer of formaldehyde and is generally obtained by reacting an aqueous solution of formalin in the presence of an acidic catalyst. The cyclic ether and / or cyclic formal is a component copolymerizable with trioxane, and examples thereof include ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxatane, 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. As the cyclic ether and / or cyclic formal, ethylene oxide and 1,3-dioxolane are particularly preferred. These may be used alone or in combination of two or more.

[0045] The polymerization catalyst used in producing the polyacetal copolymer is not particularly limited, but examples thereof include Lewis acids such as boric acid, tin, titanium, phosphorus, arsenic, and antimonides. Among these, it is particularly preferable to use one or more of boron trifluoride, boron trifluoride hydrates, and coordination complex compounds of boron trifluoride with organic compounds containing oxygen or sulfur atoms. More specifically, preferred examples include boron trifluoride, boron trifluoride diethyl etherate, and boron trifluoride-di-n-butyl etherate. These may be used alone or in combination.

[0046] The deactivation of the polymerization catalyst in the production of the polyacetal copolymer can be carried out by introducing the polyacetal resin obtained by the polymerization reaction into an aqueous solution or organic solvent solution containing at least one catalyst neutralizing deactivator, such as an amine such as ammonia, triethylamine, or tri-n-butylamine, or an alkali metal or alkaline earth metal hydroxide, inorganic acid salt, or organic acid salt, and stirring the resulting slurry for typically several minutes to several hours. The slurry after catalyst neutralization and deactivation is filtered and washed to remove unreacted monomer, catalyst neutralizing deactivator, and catalyst neutralization salt, and then dried.

[0047] Furthermore, the polymerization catalyst can be deactivated by contacting the polyacetal copolymer with vapor of ammonia, triethylamine, or the like, or by contacting the polyacetal resin with at least one of hindered amines, triphenylphosphine, calcium hydroxide, or the like in a mixer. Furthermore, without deactivating the polymerization catalyst, the polyacetal copolymer can be heated in an inert gas atmosphere at a temperature below the melting point of the polyacetal copolymer, thereby reducing the volatilization of the polymerization catalyst, and the terminal stabilization treatment described below can be performed using the polyacetal copolymer.

[0048] The above-mentioned operation for deactivating the polymerization catalyst and the operation for reducing the volatilization of the polymerization catalyst can be carried out, if necessary, after pulverizing the polyacetal resin obtained by the polymerization reaction.

[0049] The resulting polyacetal resin can be subjected to terminal stabilization treatment to decompose and remove unstable terminals as follows: For example, the polyacetal resin can be melted using a vented single-screw extruder or a vented twin-screw extruder in the presence of a known basic substance capable of decomposing unstable terminals, such as ammonia, a fatty acid amine such as triethylamine or tributylamine, a hydroxide of an alkali metal or alkaline earth metal typified by calcium hydroxide, an inorganic weak acid salt, or an organic weak acid salt, as a notching agent, to decompose and remove the unstable terminals.

[0050] The polyacetal resin may be recycled. In the material recycling, polyacetal resin used as a product is collected, and any impurities such as grease are removed, and the resulting pulverized polyacetal resin can be used. In addition to material recycling, polyacetal resin used as a product, such as through chemical recycling, may be recycled into monomers, and the polyacetal resin produced from these monomers may be used. The recycled polyacetal resin may be used alone or mixed with non-recycled polyacetal resin.

[0051] The polyacetal resin may also be a modified polyacetal. A modified polyacetal is generally a block copolymer having a modified segment within the polyacetal. The polyacetal segment may be a homopolymer residue consisting of only 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 fall under the category of a polyacetal segment, and examples thereof include polyolefin, polyurethane, polyester, polyamide, polystyrene, and alkyl polyacrylate.

[0052] 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.

[0053] The modified segment of the modified polyacetal is preferably a polyolefin from the viewpoint of reducing residues derived from the organic binder during the degreasing step. Specific examples include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyisoprene, polybutadiene, and hydrogenated polybutadiene. From the same 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 during the degreasing step and suppression of cracking and swelling during the degreasing step. The modified polyacetal resin can be used alone, or two or more modified polyacetal resins can be used, or the modified polyacetal resin can be mixed with an unmodified polyacetal resin.

[0054] [Other thermoplastic resin B] The organic binder contains another thermoplastic resin B (hereinafter, sometimes simply referred to as "thermoplastic resin B"). Examples of the thermoplastic resin B include polyolefin resin, polystyrene resin, polyphenylene ether resin, and polyester resin.

[0055] The content of thermoplastic resin B in the organic binder is preferably 15% by volume or more, more preferably 20% by volume or more, and even more preferably 25% by volume or more. The content of thermoplastic resin B in the organic binder is preferably less than 40% by volume, more preferably 35% by volume or less, and even more preferably 30% by volume or less.

[0056] Furthermore, the thermoplastic resin B preferably contains 90% by volume or more of a polyolefin resin, and more preferably 90% by volume or more of a polypropylene.

[0057] The thermoplastic resin B is preferably a polyolefin resin having a thermal decomposition behavior different from that of the thermoplastic resin A.

[0058] -Polyolefin resin- The polyolefin resin is preferably a homopolymer or copolymer having structural units derived from an alkene having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms.

[0059] Specific examples of the polyolefin resin include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyisoprene, and polybutadiene. Polyolefin resins are preferably polyethylene, polypropylene, and mixtures thereof. From the viewpoints of shape retention and suppression of cracking and swelling during the degreasing process, polyethylene or polypropylene is more preferred. Suitable commercially available polyethylenes include the Suntec HD series (manufactured by Asahi Kasei), the Suntec LD series (manufactured by Asahi Kasei), the Suntec EVA series (manufactured by Asahi Kasei), Neozex, Ultozex, and Evolue (all manufactured by Prime Polymer). Examples of polypropylenes include Sumitomo Noblen (manufactured by Sumitomo Chemical), Novatec PP (manufactured by Japan Polypropylene), the Sunallomer PM series (manufactured by Sunallomer), and Prime Polypro (manufactured by Prime Polymer).

[0060] From the viewpoints of kneadability with sinterable inorganic powders and injection moldability, the polyolefin resin preferably has a melt flow index of 30 to 70 g / 10 min. The melt flow index of the polyolefin resin can be measured in accordance with ISO 19069-2 using a MELTINDEXER manufactured by Toyo Seiki Seisaku-sho at 230°C and 2.16 kg.

[0061] [Fluidity imparting agent] The organic binder further contains a fluidity imparting agent in addition to the thermoplastic resin A and the thermoplastic resin B. By including the fluidity imparting agent, the fluidity of the composition for sintered compacts can be further improved.

[0062] The fluidity imparting agent is a compound other than the polyacetal resin, polyolefin resin, and epoxy resin described above, and examples thereof include waxes. For convenience, in this specification, those with a melting point of 100°C or less are referred to as "waxes" and those with a melting point above 100°C are referred to as "resins."

[0063] Examples of the waxes include paraffin wax, polyethylene wax, polypropylene wax, carnauba wax, polyethylene glycol, polytetramethylene glycol, polytetraethylene glycol, polyisobutylene, microcrystalline wax, montan wax, beeswax, Japan wax, synthetic wax, poly-1,3-dioxolane, poly-1,3-dioxepane, etc. Among these, it is preferable to use paraffin wax, polyethylene glycol, or polytetramethylene glycol, from the viewpoint of achieving even better fluidity of the composition for a sintered molded body during injection molding.

[0064] The content of the fluidity imparting agent in the organic binder is preferably 35% by volume or more, more preferably 40% by volume or more, and even more preferably 45% by volume or more, and preferably less than 60% by volume, more preferably 55% by volume or less, and even more preferably 50% by volume or less.

[0065] The fluidity imparting agent preferably has a melting point of 50 to 90° C. The melting point can be determined by differential scanning calorimetry (DSC) in accordance with JIS K7121.

[0066] [Epoxy resin] The organic binder contains an epoxy resin in addition to the thermoplastic resin A, thermoplastic resin B, and fluidity imparting agent described above. The inclusion of the epoxy resin enhances the interaction (adhesion) between the thermoplastic resin B and the metal powder, thereby improving the dispersibility and sintered density of the metal powder. The epoxy resin refers to a resin composed of an aggregate of multiple epoxy compounds, and the epoxy compound refers to a compound having an epoxy group in the molecule. The multiple epoxy compounds constituting the epoxy resin may have the same or different molecular structures. The type of epoxy resin is not particularly limited, but examples include bisphenol A epoxy, bisphenol F epoxy, novolac epoxy, aliphatic epoxy, and the glycidyl-containing epoxy resins described below. A suitable epoxy resin is a copolymer of a glycidyl ester of an unsaturated acid and an olefin.

[0067] Here, the glycidyl ester of the unsaturated acid is represented by the general formula (1): [ka] (In the formula, R represents an alkenyl group having 2 to 18 carbon atoms, and X represents a carbonyloxy group.) and has a structure formed by forming an ester of an unsaturated acid with an alcohol compound having a glycidyl group. Specific examples of the compound include glycidyl acrylate, glycidyl methacrylate, glycidyl ethacrylate, and glycidyl itaconate. Among these, glycidyl methacrylate is preferably used.

[0068] In addition to the glycidyl esters, examples of the optional unsaturated acid and / or derivative thereof include unsaturated compounds having one or more carboxylic acid groups, unsaturated compounds having one or more carboxylic acid anhydride groups, and esters of compounds having carboxylic acid groups with alkyl alcohols. Specific examples of such 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. Furthermore, examples of the olefin to be copolymerized with the glycidyl ester of an unsaturated acid include α-olefins having 2 to 10 carbon atoms, and among these, ethylene, propylene, and 1-butene are particularly preferred. Furthermore, the method for copolymerizing the glycidyl ester of an unsaturated acid with the olefin is not particularly limited, and can be carried out by a conventionally known method.

[0069] The epoxy resin is particularly preferably an ethylene-glycidyl methacrylate copolymer (EGMA) represented by the following formula (2). [ka] (In the formula, the glycidyl methacrylate group is present in an amount of 3 to 30 parts by weight based on 100 parts by weight of the ethylene-glycidyl methacrylate copolymer.)

[0070] Alternatively, a copolymer containing an epoxy group and other functional groups in the ethylene-glycidyl methacrylate copolymer (EGMA) may be used. A copolymer consisting of three or more functional groups including a methacrylic group, a vinyl acetate group, etc. is also acceptable, and from the viewpoints of compatibility with the organic binder and strength of the green molded body, an ethylene-vinyl acetate-glycidyl methacrylate copolymer (EGMA-VA) is more preferred.

[0071] The ethylene-glycidyl methacrylate copolymer (EGMA) may be commercially available, and suitable examples include Celloxide (manufactured by Daicel Chemical Industries, Ltd.) and Bondfast (manufactured by Sumitomo Chemical Co., Ltd.).

[0072] Furthermore, EGMA can be synthesized by various methods. For example, it can be produced by bulk polymerization, emulsion polymerization, solution polymerization, etc. using a free radical initiator. Representative polymerization methods include those described in JP-B-46-45085 and JP-A-61-127709, etc., in which polymerization is carried out at a pressure of 500 kg / cm in the presence of a polymerization initiator that generates free radicals. 2 As described above, the polymer can be produced at a temperature of 40 to 300° C. Other examples include a method in which an unsaturated epoxy compound and a radical generator are mixed with a resin made of at least one monomer selected from ethylene and olefinic unsaturated compounds other than ethylene, and the mixture is melt-graft-copolymerized in an extruder, and a method in which an unsaturated epoxy compound and an olefinic unsaturated compound are copolymerized in an inert medium such as water or an organic solvent in the presence of a radical generator.

[0073] The copolymer of the glycidyl ester of an unsaturated acid 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 acid glycidyl ester units. When the content of the unsaturated acid glycidyl ester units is 1% by weight or more, the interaction with other resin components and metal powders is strengthened, resulting in high dispersibility. Furthermore, when the content of the unsaturated acid glycidyl ester units is 25% by weight or less, the copolymer exhibits excellent thermal stability during kneading and injection molding.

[0074] The content of the glycidyl ester of the unsaturated acid can be determined by measuring the infrared absorption spectrum of a press sheet of the ethylene polymer having an epoxy group. The absorbance of the characteristic absorption in the infrared absorption spectrum is corrected by the thickness of the sheet used for the measurement, and the content of the unsaturated compound having a glycidyl group is determined by a calibration curve method based on the corrected absorbance. The peak of the characteristic absorption is at 910 cm -1 This can be used as an indicator as it often appears near

[0075] The melt flow index of the epoxy resin is preferably 3 to 380 g / 10 min. The melt flow index of the EGMA can be measured under conditions of 190°C and 2.16 kg with reference to ASTM-D-1238.

[0076] When EGMA is used 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.

[0077] The content of the epoxy resin in the organic binder is preferably 5% by volume or more, more preferably 10% by volume or more, and even more preferably 15% by volume or more, and preferably less than 30% by volume, more preferably 25% by volume or less, and even more preferably 20% by volume or less.

[0078] It is more preferable that the epoxy resin contains a functional group, such as a vinyl acetate copolymer, that is highly compatible with the thermoplastic resin B. This improves the dispersibility of the thermoplastic resin B in the organic binder that exists as a sea, resulting in effects such as further improving the strength of the green compact and further reducing the porosity inside the sintered compact.

[0079] [Holm Catcher] When the organic binder contains a polyacetal resin, it may further contain a form catcher agent. The form catcher agent has the function of capturing or suppressing the effects of products that have an adverse effect on productivity and appearance, such as residual formaldehyde and formic acid produced by denaturing the formaldehyde, when producing molded articles using the polyacetal resin. By including a form-catcher agent in the organic binder, the composition containing the polyacetal resin of this embodiment not only improves the appearance and texture of the molded body due to its formaldehyde-trapping function, but also prevents depolymerization of the polyacetal resin by the form-catcher agent preferentially interacting with the metal powder and eliminating reaction sites, thereby achieving an unexpected improvement in the appearance and texture of moldable products, as well as maintaining productivity and improving quality.

[0080] Examples of the form-catcher agent include nitrogen-containing compounds, metal salts of inorganic acids, metal oxides, metal salts of organic acids, etc. Among these, the form-catcher agent is preferably a compound that contains as little acid as possible as an impurity and / or is unlikely to generate acid. The form catcher agent may be used alone or in combination of two or more kinds. The form catcher agents such as the nitrogen-containing compounds, metal salts of inorganic acids, metal oxides, and metal salts of organic acids can also function as heat stabilizers.

[0081] Examples of the nitrogen-containing compound 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, and imide compounds.

[0082] 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 such as nylon 6 / 6-6 / 6-10 or nylon 6 / 6-12. Further examples of the polyamide resin include acrylamide and its derivatives, and copolymers of acrylamide and its derivatives with other vinyl monomers, such as a poly-β-alanine copolymer obtained by polymerizing acrylamide and its derivatives with other vinyl monomers in the presence of a metal alcoholate.

[0083] Examples of the amide compound include polycarboxylic acid amides such as isophthalic acid diamide, and anthranilamide.

[0084] 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.

[0085] Examples of the adducts of the amino-substituted triazine compounds and formaldehyde include N-methylolmelamine, N,N'-dimethylolmelamine, and N,N',N"-trimethylolmelamine.

[0086] Specific examples of the condensation product of the amino-substituted triazine compound and formaldehyde include melamine-formaldehyde condensation products.

[0087] Examples of the urea derivatives include N-substituted urea, urea condensates, ethylene urea, hydantoin compounds, and ureido compounds. Specific examples of N-substituted ureas include methyl urea substituted with a substituent such as an alkyl group, alkylene bis urea, and aryl-substituted urea. 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.

[0088] The hydrazine derivatives may include, for example, hydrazide compounds. Specific examples of the hydrazide compounds include dicarboxylic acid dihydrazides, and more specifically, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, isophthalic acid dihydrazide, phthalic acid dihydrazide, and 2,6-naphthalenedicarbodihydrazide.

[0089] Examples of the imidazole compound include imidazole, 1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole. Examples of the imide compound include succinimide, glutarimide, and phthalimide.

[0090] Examples of form catcher agents other than those mentioned above include metal salts of inorganic acids, metal oxides, and metal salts of organic acids, such as hydroxides of sodium, potassium, magnesium, calcium, barium, etc., carbonates, phosphates, silicates, borates, and carboxylates of the above metals, and layered double hydroxides.

[0091] The carboxylic acid of the carboxylate 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.

[0092] Examples of the layered double hydroxide include, for example, 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- represents an anion of n valence (n is an integer of 1 or more), 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 - , CO32- , SO4 2- , Fe(CN)6 3- , CH3COO - , oxalate ion, salicylate ion, etc. n- Examples of - , CO3 2- is preferred. Specific examples of hydrotalcites include Mg 0.75 Al 0.25 (OH)2(CO3) 0.125 Natural hydrotalcite, Mg, expressed as 0.5H2O 4.5 Al2(OH) 13 CO3·3.5H2O, Mg 4.3 Al2(OH) 12.6 Examples include synthetic hydrotalcites represented by CO3.

[0093] (Compatibilizer) The composition for a sintered compact of this embodiment may contain a compatibilizer in addition to the sinterable inorganic powder and organic binder described above. By containing a compatibilizer, the quality of the composition for a sintered compact can be further improved.

[0094] The compatibilizer has properties different from those of the resin and fluidity imparting agent described above, and has the effect of further increasing the compatibility between the metal, resin, and fluidity imparting agent, for example, by virtue of an effect similar to that of a surfactant. Examples of compatibilizers include Sannix (Sanyo Chemical), Sunflex (Sanyo Chemical), Tafmer DF&A (Mitsui Chemicals), Tafmer XM (Mitsui Chemicals), Tafmer BL (Mitsui Chemicals), Tafmer M (Mitsui Chemicals), Tafmer PN (Mitsui Chemicals), and Maricon (Osaka Gas Chemicals).

[0095] (Other ingredients) The composition for sintered compacts of this embodiment may contain other components in addition to the above-mentioned inorganic powder, organic binder, and other components. Examples of other components include additives such as heat stabilizers and antioxidants. These may be used alone or in combination of two or more. The amount of other components is not limited as long as it does not impair the effects of the present invention. The amount of other components is not limited, but may be, for example, 0.003 to 1.8 parts by weight per 100 parts by weight of the organic binder.

[0096] -Heat stabilizer- Examples of the heat stabilizer include fatty acid metal salts, etc. As mentioned above, fatty acid metal salts can also function as form catchers. Examples of fatty acids for fatty acid metal salts include capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, liglyceric acid, cerotic acid, heptacosanoic acid, montanic acid, undecylenic acid, oleic acid, elaidic acid, cetoleic acid, erucic acid, brassidic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid, propiolic acid, stearic acid, 12-hydroxydodecanoic acid, 3-hydroxydecanoic acid, 16-hydroxyhexadecanoic acid, 10-hydroxyhexadecanoic acid, 12-hydroxyoctadecanoic acid, and 10-hydroxy-8-octadecanoic acid. The metal compound is a hydroxide or chloride of an alkali metal or alkaline earth metal, such as sodium, lithium, potassium, calcium, magnesium, barium, zinc, aluminum, or strontium. Among these, the fatty acid is preferably myristic acid, palmitic acid, or stearic acid, and the metal compound is preferably calcium hydroxide, oxide, or chloride. Specific examples of fatty acid metal salts include calcium myristate, calcium palmitate, and calcium stearate.

[0097] -Antioxidants- Examples of antioxidants include n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, n-octadecyl-3-(3'-methyl-5'-t-butyl-4'-hydroxyphenyl)propionate, n-tetradecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, 1,6-hexanediol-bis-(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), 1,4-butanediol-bis-(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, triethylene glycol-bis-(3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate), tetrakis(2-methyl-4-hydroxyphenyl)propionate, ... Examples of suitable hydroxyphenyl esters include bis(methylene 3-(3'-t-butyl-4-hydroxyphenyl)propionate)methane, N,N'-bis-(3-(3,5-di-t-butyl-4-hydroxyphenol)propionyl)hydrazine, N,N'-tetramethylene-bis-3-(3'-methyl-5'-t-butyl-4-hydroxyphenol)propionyldiamine, N,N'-bis-3-(3',5'-di-t-butyl-4-hydroxyphenol)propionylhexamethylenediamine, 3-(N-salicyloyl)amino-1,2,4-triazole, N,N'-bis-(2-(3-(3,5-dibutyl-4-hydroxyphenyl)propionyloxy)ethyl)oxyamide, and N,N'-hexamethylene-bis-(3-(3,5-di-t-butyl-4-hydroxyphenyl)propanamide). These antioxidants may be used alone or in combination of two or more.

[0098] (Method of manufacturing a composition for sintered compact) The method for producing the composition for sintered compacts of this embodiment is not particularly limited, and can be produced by known methods. For example, the sinterable inorganic powder, organic binder, and other optional components described above can be mixed using, for example, a Henschel mixer, tumbler, or V-shaped blender, and then melt-kneaded in a semi-molten state using a kneader such as a single-screw extruder, twin-screw extruder, heated roll, kneader, or Banbury mixer. This produces a product in various forms, such as strands or pellets. When kneading using a pressure kneader, the kneading temperature is preferably set to 160°C to 210°C, more preferably 170°C to 190°C. The blade rotation speed is preferably 10 rpm to 50 rpm, more preferably 15 rpm to 40 rpm. The kneading time is preferably 45 minutes or more and 2 hours or less. Kneading within the above conditions can improve the compatibility between the resins and suppress the organic binder phenomenon caused by thermal decomposition. Furthermore, the order in which the inorganic powder and the organic binder are kneaded may be any order, such as adding the materials simultaneously or adding them in portions, but from the viewpoint of the interaction (adhesion) between the polyolefin resin and the metal powder, it is preferable to knead the sinterable inorganic powder and the epoxy resin first.

[0099] <Green compact> The green compact of this embodiment is obtained by molding the composition for sintered compact of this embodiment described above. The obtained green compact has excellent strength and appearance, and the generation of form gas is suppressed.

[0100] The green molded body of this embodiment can be obtained by using a composition for a sintered molded body in a screw-type or piston-type injection molding machine. In the injection molding, the cylinder temperature is preferably set to 160 to 210°C, more preferably 170 to 190°C. Setting the temperature to 160°C or higher can improve the fluidity of the resin, while setting it to 210°C or lower can reduce mold contamination due to resin decomposition. The mold temperature is preferably 30 to 90°C, more preferably 50 to 70°C. Setting the mold temperature to 30°C or higher can improve dimensional stability during molding, while setting it to 90°C or lower can prevent poor appearance of the green molded body due to waxes with a melting point of 100°C or lower.

[0101] <Sintered compact> The sintered compact of this embodiment is obtained by sintering the green compact of this embodiment described above. The obtained sintered compact has excellent strength and appearance, an extremely low porosity, and suppressed generation of form gas.

[0102] The green compact can be placed in a sealed debinding / sintering furnace and debound and sintered under the desired conditions to produce a debound body and a sintered compact. In the case of debinding by heating, the debinding is carried out by raising the temperature from room temperature to about 500-600°C in a nitrogen or argon atmosphere. A fluidity imparting agent may be dissolved in a solvent before heating. The temperature is then raised to the sintering temperature of the sinterable inorganic powder to obtain a sintered compact.

[0103] In the case of degreasing with acid, degreasing is carried out by passing nitric acid gas through a nitrogen atmosphere and raising the temperature from room temperature to 110 to 120° C. Then, the temperature is raised to the sintering temperature of the sinterable inorganic powder to obtain a sintered compact. [Example]

[0104] 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.

[0105] <Components of each sample> The components contained in each sample of the examples and comparative examples are shown below.

[0106] -Thermoplastic resin A- (A-1) Polyacetal resin A jacketed, twin-screw paddle-type continuous polymerization reactor (Kurimoto, Ltd., diameter 2B, L / D = 14.8) capable of passing a heat transfer medium was adjusted to a temperature of 80°C. 69 g / hr of a catalyst preparation prepared by diluting boron trifluoride-di-n-butyl etherate with cyclohexane to 0.26% by mass as the polymerization catalyst, 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 fed into the polymerization reactor to carry out polymerization. The material discharged from the polymerization reactor was poured into a 0.5% by mass aqueous triethylamine solution to deactivate the polymerization catalyst, followed by filtration, washing, and drying. The mixture was then fed into a vented twin-screw extruder (L / D = 40) set at 200°C, and a 0.8% by mass aqueous solution of triethylamine was added to the terminal stabilization zone to a concentration of 20 ppm in terms of nitrogen. The mixture was stabilized by degassing under reduced pressure at 90 kPa and pelletized in a pelletizer. The mixture was then dried at 100°C for 2 hours to obtain polyacetal resin (A-1). The resulting 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 A polyacetal resin (A-2) was produced in the same manner as in the polyacetal resin (A-1), except that the flow rate of methylal as a molecular weight modifier was set to 5.72 g / hr. The resulting polyacetal resin (A-2) had a melting point of 164°C and a melt flow index of 20 g / 10 min. (A-3) Polyacetal resin Polyacetal resin (A-3) was produced in the same manner as polyacetal resin (A-1), except that the flow rate of methylal as a molecular weight modifier was set to 7.1 g / hr. The resulting polyacetal resin (A-3) had a melting point of 164°C and a melt flow index of 71 g / 10 min. (A-4) Polyacetal resin Polyacetal resin (A-4) was produced in the same manner as polyacetal resin (A-1), except that the flow rate of methylal as a molecular weight modifier was set to 7.62 g / hr. The resulting polyacetal resin (A-4) had a melting point of 164°C and a melt flow index of 81 g / 10 min. (A-5) Polyacetal resin A polyacetal resin (A-5) was produced in the same manner as in the polyacetal resin (A-1), except that the flow rate of methylal as a molecular weight modifier was 9.4 g / hr. The resulting polyacetal resin (A-5) had a melting point of 164°C and a melt flow index of 121 g / 10 min. (A-6) Polyacetal resin A polyacetal resin (A-6) was produced in the same manner as in the polyacetal resin (A-1), except that the flow rate of methylal as a molecular weight modifier was 10.6 g / hr. The resulting polyacetal resin (A-6) had a melting point of 164°C and a melt flow index of 200 g / 10 min.

[0107] -Thermoplastic resin B- (B-1) Polypropylene: Novatec BC06C manufactured by Japan Polypropylene Corporation (B-2) Polypropylene: SunAllomer PMB60A manufactured by SunAllomer Co., Ltd. (B-3) Polypropylene: Sumitomo Noblen UH501E1 manufactured by Sumitomo Chemical Co., Ltd. (B-4) Polyethylene: Asahi Kasei Corporation Suntec™ HDPE J300

[0108] -Epoxy resin- (C-1) Aliphatic epoxy: Celloxide 2021P manufactured by Daicel Chemical Industries, Ltd. (C-2) EGMA: Bondfast BF-2C manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 6% by weight Melt flow index 3g / 10min (C-3) EGMA: Bondfast BF-E manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 12% by weight Melt flow index 3g / 10min (C-4) EGMA: Bondfast BF-30C manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 19% by weight Melt flow index 30g / 10min (C-5) EGMA: Bondfast CG5001 manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 19% by weight Melt flow index 380g / 10min (C-6) EGMA-VA: Bondfast BF-2B manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 12% by weight VA ratio 5% by weight Melt flow index 3g / 10min (C-7) EGMA-VA: Bondfast BF-7B manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 12% by weight VA ratio 5% by weight Melt flow index 7g / 10min (C-8) EGMA-MA: Bondfast BF-7L manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 3% by weight MA ratio 27% by weight Melt flow index 7g / 10min (C-9) EGMA-MA: Bondfast BF-7M manufactured by Sumitomo Chemical Co., Ltd. GMA ratio 6% by weight MA ratio 27% by weight Melt flow index 7g / 10min

[0109] -Fluidity imparting agent- Paraffin wax: Paraffin wax-145 manufactured by Nippon Seiro Co., Ltd., melting point: 63°C

[0110] <Measurement method> The samples of the examples and comparative examples were measured as follows.

[0111] (Melt Flow Index) The melt flow indexes of thermoplastic resin A, thermoplastic resin B, and epoxy resin were measured under conditions of 190°C and 2160g using a MELTINDEXER manufactured by Toyo Seiki Seisakusho Co., Ltd., with reference to ASTM-D-1238.

[0112] (Melting Point) The melting point was determined by differential scanning calorimetry (DSC) using a differential scanning calorimeter (manufactured by Netsche Japan) in accordance with JIS K7121.

[0113] (Decomposition rate of polyacetal resin when preparing a composition for sintered compact) Since the coating of the sinterable inorganic powder with epoxy resin suppresses the decomposition of the polyacetal resin by the inorganic powder, the decomposition rate of the polyacetal resin is equivalent to the coating rate of the epoxy resin on the inorganic powder. The decomposition rate of the polyacetal resin was measured using a Hitachi High-Technologies Corporation STA7200RV Tg-DTA device to measure the weight loss rate during the preparation of the composition for sintered compacts, and evaluated according to the following criteria. Note that the lower the decomposition rate of the polyacetal resin, the greater the coating rate of the epoxy resin on the inorganic powder. Excellent: Decomposition rate of polyacetal resin is less than 5% by weight Good: Decomposition rate of polyacetal resin is 5% by weight or more but less than 20% by weight Poor: Decomposition rate of polyacetal resin is 20% by weight or more

[0114] (Cross-section observation of green compact) Cross sections of the green compacts were prepared by Ar ion milling using a Hitachi High-Tech IM4000 ion milling system. The cross sections were observed using a Keyence VHX-6000 optical microscope, a JEOL JSM-IT800 electron microscope, and an Oxford Instruments MFP-3D Origin+ AFM. The cross sections were then identified using a Renishaw In via Qontor micro-Raman spectrometer. The cross sections of the green compacts preferably have a sea-island structure where thermoplastic resin A is an island and thermoplastic resin B and the flowability modifier are a sea. The inorganic powder is present in the sea, and the epoxy resin is present around the inorganic powder. Furthermore, it is more preferable that thermoplastic resin B and the flowability modifier, which exist as a sea, are dispersed within the sea. The morphology of each green compact sample was observed and evaluated according to the following criteria. All green compact specimens were ISO 2740 test specimens. Excellent: Thermoplastic resin A is an island, and thermoplastic resin B and the fluidity imparting agent form an island-sea structure. The inorganic powder is present in the sea, the epoxy resin is present around the inorganic powder, and thermoplastic resin B and the fluidity imparting agent are dispersed even within the sea. Good: Thermoplastic resin A is an island, and thermoplastic resin B and the fluidity imparting agent form an island-sea structure, with the inorganic powder present in the sea and the epoxy resin surrounding the inorganic powder. Poor: 80% or more by volume of the inorganic powder is not present in the sea, or epoxy resin is not present around the inorganic powder.

[0115] (Strength of green compact) The green compact was subjected to a bending test using an Instron tensile tester with a support distance of 60 mm and a test speed of 1 mm / min, and evaluated according to the following criteria. Excellent: Bending strength is 30 MPa or more and bending strain is 0.4% or more Good: Bending strength is 25 MPa or more and bending strain is over 0.35% (excluding cases where bending strength is 30 MPa or more and bending strain is 0.4% or more (included in excellent)) Poor: Bending strength is less than 25 MPa or bending strain is 0.35% or less

[0116] (Appearance of sintered compact) The degreased body of each sample was sintered in an argon atmosphere by gradually increasing the temperature from room temperature at 200°C / hr and holding at a maximum temperature of 1350°C for 2 hours to obtain a sintered compact sample. The appearance of 10 sintered compacts of each sample was visually observed and evaluated according to the following criteria. Good: No cracks, swelling or other abnormalities in appearance are observed Poor: Cracks and swelling are observed

[0117] (Tensile properties of sintered compacts) To evaluate the strength of the sintered compact, the tensile properties were evaluated. The six sintered compacts were subjected to a tensile test using an Instron tensile tester with a chuck distance of 50 mm and a test speed of 3 mm / min, and were evaluated according to the following criteria. Good: All measured samples have a tensile strength of 490 MPa or more and a tensile elongation of 45% or more Poor: Two or more of the measured samples have a tensile strength of less than 450 MPa or a tensile elongation of less than 30%

[0118] (Porosity inside sintered compact) The sintered compacts were subjected to X-ray CT measurement using a large X-ray CT device (TXS-34500FDmHS, microfocus tube) with a voxel size of 8 x 8 x 13 mm and a resolution of 10 mm, and were evaluated according to the following criteria. Excellent: Porosity is 0.01% or less Good: Porosity is greater than 0.01% and less than 0.05% Poor: Porosity greater than 0.05%

[0119] <Examples 1 to 20 and Comparative Examples 1 to 6> SUS316L (average particle size 10 μm) was used as the sinterable inorganic powder. The epoxy resin, flowability additive, and SUS316L were first kneaded in a pressure kneader at 175°C and a blade rotation speed of 30 rpm for 30 minutes. Then, polyacetal resin and polyolefin resin were added, and the materials were kneaded in a pressure kneader at 175°C and a blade rotation speed of 30 rpm for 1 hour to obtain the blending ratios shown in Tables 1 to 3 below. This produced each sample of the sintered compact composition. The resulting sintered compact composition samples were then cooled and crushed to obtain injection molding materials. The resulting injection molding materials were molded at temperatures of 175 to 190°C using an injection molding machine (ROBOSHOT α-50iA, manufactured by Fanuc Corporation) to produce multiple green compact test pieces. The green compact test pieces of each sample were then thermally debound. The resulting green compact test pieces were placed in a debinding furnace. First, the debinding furnace was purged with nitrogen gas and heated to 150°C at 50°C / hr. The temperature was then increased from 150 to 200°C at a rate of 30°C / hr, held for 1 hour, then increased from 200 to 400°C at 30°C / hr, and then increased from 400 to 600°C at 120°C / hr. The furnace was then cooled to obtain debound samples (total debinding process time: approximately 15 hours). The debound samples were then sintered by gradually increasing the temperature from room temperature at 200°C / hr in an argon atmosphere and holding the temperature at a maximum of 1350°C for 2 hours, yielding sintered compact samples. The blending compositions and evaluation results are shown in Tables 1 to 3 below.

[0120] <Comparative Example 7> For Comparative Example 7 only, SUS316L (average particle size 10 μm) was used as the sinterable inorganic powder, and after mixing with the other materials in the proportions shown in Table 3 below, the mixture was kneaded in a pressure kneader at 175°C and a blade rotation speed of 30 rpm for 1 hour to produce a sample of a composition for sintered compacts (total debinding process time: approximately 15 hours). The debound sample obtained was sintered by gradually increasing the temperature from room temperature at 200°C / hr in an argon atmosphere and holding it at a maximum temperature of 1350°C for 2 hours to obtain a sample of a sintered compact. The blending compositions and evaluation results are shown in Table 3 below.

[0121] [Table 1]

[0122] [Table 2]

[0123] [Table 3]

[0124] FIG. 1 shows a cross section of the green compact of Example 1 observed using an AFM. The darkest phase is polyacetal resin (thermoplastic resin A), the brightest phase is sinterable inorganic powder, the phase near the inorganic powder is epoxy resin, and the other phases are polyolefin resin (thermoplastic resin B) and a fluidity imparting agent. Morphologies similar to those in Figure 1 were observed in other fields of view.

[0125] Additionally, the results of X-ray CT of a sintered green compact obtained by sintering a green compact with the above morphology are shown in Figure 2. It can be seen that even thick green compacts such as ISO2740 undergo a debinding and sintering process, and that there are almost no voids that could become defects.

[0126] It is clear from Tables 1 to 3 that the resin composition for sintered molded bodies of the present invention makes it possible to produce sintered molded bodies that are excellent in strength and appearance, have extremely low porosity, and suppress the generation of form gas. [Industrial Applicability]

[0127] According to the present invention, there can be provided a composition for sintered compacts that can be used to produce sintered compacts that are excellent in strength and appearance, have an extremely low porosity, and suppress the generation of form gas.

Claims

1. A composition for a sintered compact comprising a sinterable inorganic powder and an organic binder, The organic binder includes a thermoplastic resin A that reacts with the inorganic powder, another thermoplastic resin B, a fluidity imparting agent, and an epoxy resin; When a cross section of the composition for sintered compact is observed, the thermoplastic resin A forms islands, and the thermoplastic resin B and the fluidity imparting agent form an island-sea structure. the sinterable inorganic powder is present in the sea; A composition for sintered compacts, wherein the epoxy resin is present around the sinterable inorganic powder.

2. The composition for sintered compacts according to claim 1 , wherein the sinterable inorganic powder forms an oxide film.

3. 2. The composition for sintered compacts according to claim 1, wherein the thermoplastic resin A is a polyacetal resin having a thermal decomposition behavior different from that of the thermoplastic resin B and a melt flow index of less than 200 g / 10 min.

4. the thermoplastic resin B is a polyolefin having a thermal decomposition behavior different from that of the thermoplastic resin A and a melt flow index of 30 to 70 g / 10 min; 2. The composition for sintered compacts according to claim 1, wherein 90% by volume or more of said thermoplastic resin B is polypropylene.

5. 2. The composition for sintered compacts according to claim 1, wherein the fluidity imparting agent has a melting point of 50 to 90°C.

6. 2. The composition for sintered compacts according to claim 1, wherein the epoxy resin has a melt flow index of 3 to 380 g / 10 min.

7. 2. The composition for sintered compacts according to claim 1, wherein the epoxy resin is present around 95% or more of the sinterable inorganic powder.

8. Of the total volume of the organic binder, The thermoplastic resin A is 10% by volume or less, The thermoplastic resin B is 20% by volume or more and less than 30% by volume, The fluidity imparting agent is 40% by volume or more and less than 50% by volume, The composition for sintered compacts according to claim 1 , wherein the epoxy resin is present in an amount of 10% by volume or more and less than 20% by volume.

9. 2. The composition for sintered molded bodies according to claim 1, wherein the sum of the thermoplastic resin A, the thermoplastic resin B, and the fluidity imparting agent is less than 40 volume % of the total volume of the sinterable inorganic powder, the thermoplastic resin A, the thermoplastic resin B, and the fluidity imparting agent.

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

11. A sintered compact obtained by sintering the green compact according to claim 10.

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