Resin composition and method for producing molded article

Abstract

This resin composition contains a polyvinyl alcohol resin, 0.1 mass% to 1.2 mass% of a surfactant, and at least one of an inorganic filler and silicone particles. The resin composition does not contain a plasticizer or contains not more than 5.0 mass% of a plasticizer, and satisfies at least one of the following conditions (1) and (2):　condition (1) is the inorganic filler content of 1 mass% to 30 mass%; and condition (2) is the content of the silicone particles of 0.01 mass% to 0.45 mass%.

Description

[Technical Field]

[0001] The present invention relates to a resin composition used for a core or the like, and a method for producing a molded article using the core. [Background technology]

[0002] Conventionally, the use of a core made of a water-soluble resin composition or the like has been considered in order to obtain a molded body with a complex inner surface by injection molding. For example, Patent Document 1 discloses a method in which a core having a shape corresponding to the hollow portion of the metal powder sintered body to be produced is placed inside a mold, and a metal powder compound is injection molded (so-called MIM) using the cavity formed by the mold and core. The obtained molded body is removed from the mold together with the core, and after the core is removed, the body is degreased and sintered, thereby producing a metal powder sintered body having a hollow portion or the like.

[0003] In Patent Document 1, the core is made of a water-soluble resin, a water-soluble resin to which a water-soluble filler or a water-insoluble filler has been added, or a water-insoluble resin to which a water-soluble filler has been added. If the core is made of a water-soluble resin or the like, it can be easily removed from the molded body by extracting it by immersing it in water or the like. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-34707 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the core, made of a water-soluble resin, is melted in water after forming the outer green body using the core, the quality of the outer green body may be reduced due to the dissolution of the water-soluble resin. For example, if the outer green body is made of a powder for sintered metal, the volume of the water-soluble resin may change when the core is removed with water, which may cause damage, cracks, or defects in part of the outer green body. Furthermore, if the core has low heat resistance or poor releasability from the outer molded body, the inner surface of the outer molded body may become rough when the core is removed, which may impair the surface smoothness of the inner surface of the obtained molded body. Furthermore, if an additive such as a filler is contained in the core as described in Patent Document 1, the moldability of the core and the pellets used to obtain the core may decrease when the core is molded.

[0006] Therefore, an object of the present invention is to provide a resin composition that can be used to form a core with good moldability, that makes it less likely for chipping to occur in a molded body formed using that core, for example, in powder metal injection molding, and that also provides good surface smoothness on the inner surface of the molded body. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the above problems can be solved by specifying the composition of the resin composition, and have completed the present invention as described below. The present invention provides the following [1] to

[42] . [1] A composition containing a polyvinyl alcohol resin, a surfactant in an amount of 0.1% by mass or more and 1.2% by mass or less, and at least one of an inorganic filler and silicone particles, A resin composition that does not contain a plasticizer or that contains a plasticizer in an amount of 5.0 mass % or less, and that satisfies at least one of the following requirements (1) and (2): (1) The content of the inorganic filler is 1% by mass or more and 30% by mass or less. (2) The content of the silicone particles is 0.01% by mass or more and 0.45% by mass or less. [2] The resin composition according to the above [1], which contains the inorganic filler in an amount of 1% by mass or more and 30% by mass or less. [3] The resin composition according to [1] or [2] above, containing the silicone particles in an amount of 0.01% by mass or more and 0.45% by mass or less. [4] A composition containing a polyvinyl alcohol resin, a surfactant in an amount of 0.1% by mass or more and 1.2% by mass or less, and an inorganic filler in an amount of 1% by mass or more and 30% by mass or less, A resin composition containing no plasticizer or containing 5.0 mass % or less of a plasticizer. [5] Contains a polyvinyl alcohol resin, a surfactant in an amount of 0.1% by mass or more and 1.2% by mass or less, and silicone particles in an amount of 0.01% by mass or more and 0.45% by mass or less, A resin composition containing no plasticizer or containing 5.0 mass % or less of a plasticizer. [6] The resin composition according to any one of the above [1] to [4], wherein the inorganic filler has an average particle size of 30 nm or more and 20 μm or less. [7] The resin composition according to any one of the above [1] to [4] and [6], wherein the inorganic filler is at least one selected from the group consisting of silica, titanium oxide, calcium carbonate, mica, talc, and carbon black. [8] The resin composition according to [7] above, wherein the inorganic filler is at least one selected from the group consisting of silica and titanium oxide. [9] The resin composition according to any one of the above [1] to [4] and [6], wherein the inorganic filler is a water-soluble inorganic filler having a solubility in water at 20°C of 10 g or more and 74 g or less.

[10] The resin composition according to any one of the above items [1] to [4], [6] and [9], wherein the inorganic filler is at least one selected from the group consisting of magnesium sulfate and sodium sulfate.

[11] The resin composition according to any one of the above items [1] to [4] and [6] to

[10] , wherein the inorganic filler has an average particle size of 30 nm or more and 6000 nm or less.

[12] The resin composition according to any one of the above [1] to

[11] , wherein the surfactant is at least one selected from the group consisting of glycerin fatty acid esters, fatty acid metal salts, and fatty acid amides.

[13] The resin composition according to any one of the above [1] to

[12] , wherein the surfactant comprises a fatty acid amide having a fatty acid with 12 to 24 carbon atoms.

[14] The resin composition according to any one of the above [1] to

[13] , wherein the surfactant comprises a metal salt of a fatty acid having 12 to 24 carbon atoms.

[15] The resin composition according to any one of the above [1] to

[14] , wherein the surfactant contains a magnesium metal salt of a fatty acid.

[16] The resin composition according to any one of the above [1] to

[15] , wherein the surfactant comprises a glycerin fatty acid ester having a fatty acid having 12 to 24 carbon atoms.

[17] The resin composition according to any one of the above [1] to

[16] , wherein the surfactant is at least one selected from the group consisting of glycerol monostearate, magnesium stearate, calcium stearate, zinc stearate, and ethylene bisstearamide.

[18] The resin composition according to any one of the above [1] to

[17] , wherein the plasticizer is at least one selected from the group consisting of ethylene glycol, glycerin, diglycerin, and trimethylolpropane.

[19] The resin composition according to any one of the above [1] to

[18] , wherein the degree of polymerization of the polyvinyl alcohol-based resin is 900 or less.

[20] The resin composition according to any one of the above [1] to

[19] , wherein the viscosity of an aqueous solution of the polyvinyl alcohol resin at a concentration of 4% by mass at 23°C is 100 mPa·s or less.

[21] The resin composition according to any one of the above [1] to

[20] , wherein the MFR of the polyvinyl alcohol resin at 210°C under a load of 2160 g is 1.0 g / 10 min or more and 10 g / 10 min or less.

[22] The resin composition according to any one of the above [1] to

[21] , wherein the degree of saponification of the polyvinyl alcohol resin is 70 mol % or more and 99.9 mol % or less.

[23] The resin composition according to any one of the above [1] to

[22] , wherein the polyvinyl alcohol resin is an unmodified polyvinyl alcohol resin.

[24] The resin composition according to any one of the above [1] to

[23] , which is for use in a core.

[25] The resin composition according to the above

[24] , wherein the molding material for obtaining the molded body to be molded on the outside of the core is either a sintered metal material or a super engineering plastic.

[26] The resin composition according to the above

[25] , wherein the molding material is a sintered metal material.

[27] The resin composition according to

[26] above, wherein the degree of saponification of the polyvinyl alcohol-based resin is 72 mol % or more and 90 mol % or less.

[28] The resin composition according to the above

[25] , wherein the molding material is a super engineering plastic.

[29] The resin composition according to the above

[28] , wherein the degree of saponification of the polyvinyl alcohol-based resin is 89 mol % or more and 100 mol % or less.

[30] The resin composition according to the above

[28] or

[29] , wherein the viscosity of a 4% by mass aqueous solution of the polyvinyl alcohol-based resin at 23°C is 12 mPa·s or less.

[31] The resin composition according to any one of the above

[28] to

[30] , wherein the degree of polymerization of the polyvinyl alcohol resin is 300 or more and 1,000 or less.

[32] The resin composition according to any one of the above

[28] to

[31] , wherein the content of the surfactant is 0.3% by mass or more and 1.0% by mass or less.

[33] The resin composition according to any one of the above

[28] to

[32] , wherein the content of the inorganic filler is from 5% by mass to 30% by mass.

[34] The resin composition according to any one of the above

[28] to

[33] , wherein the super engineering plastic is at least one selected from the group consisting of polyphenylene sulfide, polyether ether ketone, liquid crystal polymer, polyimide, polyamide imide, polyether imide, polyphenyl sulfone, polysulfone, polyether sulfone, polyarylate, and fluororesin.

[35] The resin composition according to any one of the above

[28] to

[34] , wherein the super engineering plastic is at least one selected from the group consisting of polyether ether ketone, polyether sulfone, and polyphenylene sulfide.

[36] The resin composition according to any one of the above [1] to

[35] , wherein the resin composition contains the inorganic filler, the average particle size of the inorganic filler is less than 1000 nm, and the content of the inorganic filler is 5% by mass or more and 30% by mass or less.

[37] The resin composition according to any one of the above [1] to

[35] , wherein the resin composition contains the inorganic filler, the average particle size of the inorganic filler is 1000 nm or more, and the content of the inorganic filler is 1 mass % or more and 15 mass % or less.

[38] A step of molding a core from the resin composition according to any one of the above [1] to

[37] ; placing the core in a mold; a step of injecting a molding material into a cavity formed by the mold and the core to form a molded body; a step of removing the green body from the mold after molding and removing the core; A method for manufacturing a molded body comprising:

[39] The method for producing a molded body according to the above

[38] , wherein the molding material is either a sintered metal material or a super engineering plastic.

[40] The method for producing a molded body according to the above

[38] or

[39] , wherein the molding material is a sintered metal material, and the molded body from which the core has been removed is further sintered to obtain a sintered molded body.

[41] The method for producing a molded article according to any one of the above

[38] to

[40] , wherein the core is removed by elution with water.

[42] A core made of the resin composition according to any one of the above [1] to

[37] . [Effects of the Invention]

[0008] According to the resin composition of the present invention, a core can be molded with good moldability, and for example, in powder metal injection molding, a molded body obtained by using the core is less likely to have defects, and the inner surface of the obtained molded body also has good surface smoothness. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in more detail below using embodiments. <Resin composition> The resin composition of the present invention contains a polyvinyl alcohol resin, a surfactant, and at least one of an inorganic filler and a silicone resin. Therefore, in one embodiment of the present invention, the resin composition of the present invention contains a polyvinyl alcohol-based resin, a surfactant, and an inorganic filler. In another embodiment of the present invention, the resin composition of the present invention contains a polyvinyl alcohol-based resin, a surfactant, and a silicone resin. The resin composition of the present invention may further contain a plasticizer, but does not necessarily need to contain one. Each component constituting the resin composition will be described in detail below.

[0010] (PVA resin) The resin composition of the present invention contains a polyvinyl alcohol-based resin (also referred to as a "PVA-based resin"), which is obtained by polymerizing a vinyl ester and saponifying, i.e., hydrolyzing, the resulting polymer. Examples of vinyl esters that can be used include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, and vinyl benzoate. Of these, vinyl acetate is preferred.

[0011] The PVA resin may be unmodified or modified PVA, but unmodified PVA is preferred in view of availability, ease of molding by heating, and water solubility. Unmodified PVA is polyvinyl alcohol obtained by saponifying polyvinyl ester. Modified PVAs include saponified copolymers of vinyl esters and other monomers, such as monomers other than vinyl esters that have a carbon-carbon double bond, such as vinyl groups. Specific examples include olefins, (meth)acrylic acid and salts thereof, (meth)acrylic acid esters, unsaturated acids other than (meth)acrylic acid, salts and esters thereof, (meth)acrylamides, N-vinylamides, vinyl ethers, nitriles, vinyl halides, allyl compounds, vinylsilyl compounds, isopropenyl acetate, sulfonic acid group-containing compounds, and amino group-containing compounds.

[0012] Examples of olefins include ethylene, propylene, 1-butene, and isobutene. Examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 10 carbon atoms, preferably 1 to 2 carbon atoms. Specific examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of unsaturated acids other than (meth)acrylic acid, and salts and esters thereof include maleic acid and salts thereof, maleic acid esters, itaconic acid and salts thereof, itaconic acid esters, methylenemalonic acid and salts thereof, and methylenemalonic acid esters. Examples of (meth)acrylamides include acrylamide, n-methylacrylamide, N-ethylacrylamide, and N,N-dimethylacrylamide. Examples of N-vinylamides include N-vinylpyrrolidone. Examples of vinyl ethers include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, and n-butyl vinyl ether.

[0013] Examples of nitriles include (meth)acrylonitrile. Examples of vinyl halides include vinyl chloride and vinylidene chloride. Examples of allyl compounds include allyl acetate and allyl chloride. Examples of vinylsilyl compounds include vinyltrimethoxysilane. Examples of sulfonic acid group-containing compounds include (meth)acrylamidoalkanesulfonic acids such as (meth)acrylamidopropanesulfonic acid and salts thereof, and olefinsulfonic acids such as ethylenesulfonic acid, allylsulfonic acid, and methallylsulfonic acid and salts thereof. Examples of the amino group-containing compound include allylamine, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, and polyoxypropylene vinylamine. These comonomers may be used alone or in combination of two or more. When a comonomer is copolymerized to form a modified PVA, the modification amount is preferably 15 mol % or less, more preferably 5 mol % or less. From the viewpoint of exhibiting performance and functionality according to the comonomer through modification, the modification amount is, for example, 1 mol % or more. The modified PVA may be one in which a carboxyl group, a sulfonic acid group, or a pyrrolidone ring group is added to PVA by graft polymerization or the like.

[0014] The degree of polymerization of the PVA-based resin is preferably 900 or less. When the degree of polymerization is 900 or less, the swelling property is low, and when the resin composition is used as a core, swelling of the core before melting it is prevented, and the occurrence of defects in the outer molded body due to swelling of the core can be suppressed. From the viewpoint of low swelling property, the degree of polymerization of the PVA-based resin is more preferably 800 or less. The degree of polymerization of the PVA resin is not particularly limited, but is preferably 300 or more, more preferably 400 or more, and even more preferably 500 or more, from the viewpoint of moldability when molding cores, pellets, etc. from the resin composition. The degree of polymerization of the PVA resin can be measured in accordance with JIS K 6726.

[0015] The degree of saponification of the PVA resin is not particularly limited, but is, for example, 70 mol % or more and 99.9 mol % or less, preferably 72 mol % or more and 95 mol % or less, and more preferably 72 mol % or more and 90 mol % or less. In particular, when the molded body to be molded on the outside of the core is a sintered metal material, the saponification degree of the PVA polymer should be set to 72 mol % or more and 90 mol % or less so that the PVA polymer can be dissolved in warm water at about 60° C. The saponification degree of the PVA polymer is more preferably more than 72 mol % and 90 mol % or less, and even more preferably 78 mol % or more and 90 mol % or less. The saponification degree is measured in accordance with JIS K6726. The saponification degree indicates the proportion of units that are actually saponified to vinyl alcohol units among units that are converted to vinyl alcohol units by saponification. The method for adjusting the saponification degree is not particularly limited, and it can be appropriately adjusted, for example, by adjusting the saponification conditions, i.e., the hydrolysis conditions.

[0016] The PVA resin preferably has an aqueous solution viscosity of 100 mPa·s or less at a concentration of 4% by mass at 23°C. A viscosity of 100 mPa·s results in low swelling, and when the resin composition is used as a core, swelling of the core before melting it is prevented, thereby preventing defects in the outer molded body due to swelling of the core. From the viewpoint of swelling, the aqueous solution viscosity is more preferably 50 mPa·s or less, even more preferably 20 mPa·s or less, even more preferably 15 mPa·s or less, and particularly preferably 12 mPa·s or less. The aqueous solution viscosity is not particularly limited, but from the viewpoints of moldability of the core itself and moldability when obtaining pellets made from the resin composition, it is preferably 2 mPa·s or more, preferably 3 mPa·s or more, and more preferably 4 mPa·s or more. The viscosity of a 4% by mass aqueous solution is measured using a B-type viscometer in accordance with JIS-Z-8803:2011.

[0017] The MFR (melt flow rate) of the PVA resin at 210°C under a load of 2160 g is preferably 0.5 g / 10 min or more and 10 g / 10 min or less. Setting the MFR within the above range improves moldability when molding cores or pellets from the resin composition. This also makes it easier to smooth the core surface, which in turn improves the surface smoothness of the molded article molded using the core. From the viewpoint of improving the moldability of the core, the MFR of the PVA resin is more preferably 1.0 g / 10 min or more and 8 g / 10 min or less, and even more preferably 1.5 g / 10 min or more and 6 g / 10 min or less. MFR (melt flow rate) is measured in accordance with ASTM-D-1238.

[0018] When a PVA-based resin is used for a core and the molding material is a super engineering plastic, the injection molding temperature is generally higher than that for sintered powders, so the saponification degree is preferably 89 mol % or more and 100 mol % or less, and the viscosity of a 4 mass % aqueous solution at 23°C is preferably 12 mPa s or less. From the standpoint of water solubility, the degree of polymerization is preferably 300 or more and 1000 or less, and more preferably 500 or more and 800 or less.

[0019] The content of the PVA resin in the resin composition is, for example, 60% by mass or more, and preferably 60% by mass or more and 98.9% by mass or less, based on the total amount of the resin composition. Furthermore, when the resin composition contains silicone particles, the content of the PVA resin may be 60% by mass or more and 99.89% by mass or less. By setting the content of the PVA resin at or below the above upper limit, surfactants, inorganic fillers, silicone particles, and the like can be contained in the resin composition within desired ranges. Furthermore, setting the content at 60% by mass or more facilitates improving the moldability of the core itself. From these viewpoints, the content of the PVA resin body in the resin composition is more preferably 65% ​​by mass or more, even more preferably 75% by mass or more, and more preferably 98% by mass or less, even more preferably 96% by mass or less.

[0020] (surfactant) The resin composition of the present invention contains a surfactant. By including a surfactant in addition to at least one of an inorganic filler and silicone particles, which will be described later, the resin composition not only has heat resistance but also improves the releasability of the core from the outer molded body when used for a core. As a result, the inner surface of the molded body is not roughened when the core is removed, and a molded body having an inner surface with high surface smoothness can be obtained. A surfactant is a compound that has a hydrocarbon portion (for example, an aliphatic hydrocarbon portion having 12 or more carbon atoms) and a polar group portion (such as a hydroxyl group, an amino group, an ether group, an amide group, an anion, or a cation) in one molecule and has surface activity. Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, and zwitterionic surfactants.

[0021] Examples of nonionic surfactants include ether surfactants, ester surfactants, ether / ester surfactants, amide surfactants, and amine surfactants. Examples of ether surfactants include polyoxyethylene-2-ethylhexyl ether, polyoxyethylene isodecyl ether, polyoxyethylene lauryl ether, polyoxycetyl ether, polyoxyethylene stearyl ether, polyoxyethylene behenyl ether, polyoxypropylene stearyl ether, polyoxyethylene-polyoxypropylene-alkyl ethers and other polyoxyalkylene alkyl ethers, and polyoxyethylene oleyl ether and other polyoxyalkylene alkenyl ethers.

[0022] The ester surfactant is typically a surfactant having a fatty acid ester structure in the molecule, and the number of carbon atoms of the fatty acid in the fatty acid ester is, for example, 12 to 24, and preferably about 14 to 20. Specific examples of the ester surfactant include polyoxyalkylene fatty acid esters such as polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, polyethylene glycol distearate, polyethylene glycol diolate, and polypropylene glycol distearate; glycerin fatty acid esters such as glycerol monolaurate, glycerol monostearate, glycerol monooleate, diglycerol monostearate, triglycerol monostearate, glycerol dilaurate, glycerol distearate, glycerol dioleate, diglycerol distearate, and triglycerol distearate; and sorbitan fatty acid esters such as sorbitan monocaprylate, sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, and sorbitan trioleate.

[0023] Examples of ether / ester surfactants include alkylene oxide-added sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan trioleate.

[0024] Amide surfactants are typically surfactants having a fatty acid amide structure in the molecule, and the number of carbon atoms of the fatty acid in the fatty acid amide is, for example, about 12 to 24, and preferably about 14 to 20. Specific examples of amide surfactants include fatty acid alkanolamides such as coconut fatty acid diethanolamide, beef tallow fatty acid diethanolamide, lauric acid diethanolamide, oleic acid diethanolamide, coconut fatty acid monoethanolamide, and lauric acid monoisopropanolamide, and fatty acid amides such as stearic acid monoamide, oleic acid monoamide, erucic acid monoamide, ethylene bisstearic acid amide, and ethylene bisoleic acid amide.

[0025] Examples of amine surfactants include polyalkylene alkylamines such as polyoxyethylene laurylamine, polyoxyethylene coconut alkylamine, and polyoxyethylene stearylamine, and polyalkylene alkenylamines such as polyoxyethylene oleylamine. Diamine surfactants such as polyoxyethylene alkylpropylene diamine are also suitable.

[0026] Examples of anionic surfactants include alkyl sulfonates such as 2-ethylhexyl sulfonate, decyl sulfonate, dodecyl sulfonate, tetradecyl sulfonate, hexadecyl sulfonate, and octadecyl sulfonate; polyalkylene alkyl ether sulfonates such as polyoxyethylene lauryl ether sulfonate; and ester sulfonates such as dibutyl sulfosuccinate, dioctyl sulfosuccinate, and dodecyl sulfoacetic acid ester.

[0027] Further examples of anionic surfactants include fatty acid metal salts. Examples of fatty acid metal salts include metal salts of fatty acids having 12 to 24 carbon atoms, preferably 14 to 20 carbon atoms, with metals such as sodium, potassium, magnesium, and calcium. The metal may also be zinc. Preferred metals are potassium, magnesium, and zinc, with magnesium being more preferred. Specific examples include sodium laurate, sodium myristate, sodium palmitate, sodium tallow fatty acid, sodium stearate, sodium oleate, potassium laurate, potassium myristate, potassium palmitate, potassium tallow fatty acid, potassium stearate, potassium oleate, magnesium laurate, magnesium myristate, magnesium palmitate, magnesium tallow fatty acid, magnesium stearate, magnesium oleate, calcium laurate, calcium myristate, calcium palmitate, calcium tallow fatty acid, calcium stearate, calcium oleate, and zinc stearate.

[0028] Examples of cationic surfactants include alkylamine salts such as stearylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride, stearyltrimethylammonium chlorite, cetyltrimethylammonium chloride, distearyldimethylammonium chloride, and alkylbenzyldimethylammonium chloride. Examples of amphoteric surfactants include coconut oil dimethylaminoacetic acid betaine, coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine, palm kernel oil fatty acid amidopropyl dimethylaminoacetic acid betaine, and lauric acid amidopropyl dimethylaminoacetic acid betaine. The surfactant may be used alone or in combination of two or more of the above-mentioned surfactants.

[0029] Of the surfactants listed above, those with high lubricity are preferred from the viewpoint of enhancing the releasability of the core from the outer molded body and improving surface smoothness. Of the surfactants listed above, at least one selected from glycerin fatty acid esters, fatty acid amides, and fatty acid metal salts is preferred, and of these, glycerin fatty acid esters are more preferred. Among the glycerin fatty acid esters, glycerin fatty acid monoesters, which are monoesters of glycerol and fatty acids, are more preferred, and glycerol monostearate is the most preferred. Among fatty acid amides, bisfatty acid amides are more preferred, ethylene bisfatty acid amides are even more preferred, and ethylene bisstearic acid amide is even more preferred. Among fatty acid metal salts, metal stearates are more preferred, and magnesium stearate is even more preferred.

[0030] (inorganic filler) The resin composition of the present invention contains either an inorganic filler or a silicone resin. Therefore, in one embodiment, the resin composition of the present invention contains an inorganic filler. The resin composition contains an inorganic filler, which improves heat resistance, and when used in combination with a surfactant, a molded body having an inner surface with high surface smoothness can be obtained. Furthermore, the resin composition contains an inorganic filler, which reduces swelling in water and the like. Therefore, when the resin composition is used as a core, the core is prevented from melting when molding the outer molded body or from swelling when eluted with water, and defects in the outer molded body due to swelling or melting of the core can be suppressed.

[0031] The inorganic filler may be a water-insoluble inorganic filler or a water-soluble inorganic filler. These inorganic fillers may be used alone or in combination of two or more. Examples of water-insoluble inorganic fillers include silica, titanium oxide, calcium carbonate, mica, talc, and carbon black. Among these, at least one selected from titanium oxide and silica is preferred, from the viewpoint that wastewater generated after use of the resin composition of the present invention dissolved in water is unlikely to have adverse effects on the human body. The use of titanium oxide or silica makes it easier to further improve the surface smoothness of the inner surface of a molded body molded using a core, and also makes it possible to more effectively prevent chipping of the molded body molded using the core.

[0032] Furthermore, the water-soluble inorganic filler preferably has a solubility in water at 20°C of 10 g or more and 74 g or less. The solubility here refers to the solubility in 100 g of water. Examples of such water-soluble inorganic fillers include potassium azide (solubility 50.8 g), barium nitrite (72.8 g), magnesium sulfate (33.7 g), sodium sulfate (19.5 g), and potassium chloride (34.2 g). A filler with a solubility of 74 g or less is less likely to absorb moisture from the PVA used as a binder or from the atmosphere, making it suitable for use in pellet processing, injection molding, and other hot-melt molding processes. From the viewpoints of availability, danger, effects on the human body, transparency of wastewater, etc., the water-soluble inorganic filler is preferably at least one of magnesium sulfate and sodium sulfate. As mentioned above, the inorganic filler may be water-insoluble, and therefore, the solubility of the inorganic filler in water may be 0 g or more.

[0033] The inorganic filler has an average particle size of, for example, 30 nm or more and 20 μm or less. By setting the average particle size to 30 nm or more and 20 μm or less, the heat resistance and low swelling properties of the core molded from the resin composition can be ensured without losing the smoothness of the inner surface of the molded body molded using the core, and chipping of the molded body can be prevented. The average particle size of the inorganic filler is preferably 15 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, and even more preferably 8 μm or less. Among the above, the average particle size of the inorganic filler is preferably 6000 nm or less. When the average particle size is 6000 nm or less, the inorganic filler is prevented from roughening the inner surface of the molded body, and the smoothness of the inner surface of the molded body is further improved. From the viewpoint of improving the smoothness of the inner surface of the molded body, the average particle size of the inorganic filler is more preferably 5000 nm or less, even more preferably 2000 nm or less, and even more preferably less than 1000 nm. Furthermore, from the viewpoint of ensuring low swelling of the core and preventing chipping of the molded body, the average particle size of the inorganic filler is preferably 150 nm or more, more preferably 250 nm or more. The average particle size of the inorganic filler and the silicone particles described below can be measured by the image analysis method of JIS-Z-8827:2018.

[0034] (silicone particles) The resin composition of the present invention may contain silicone particles instead of inorganic fillers, or may contain silicone particles together with inorganic fillers. The use of silicone particles improves releasability from sintered metal materials, super engineering plastics, etc., and the surface smoothness of molded articles. Furthermore, when molding with sintered metal materials, for example, the molded articles are less likely to be chipped. Furthermore, the dissolution rate of the core when dissolved in water can be increased. When the resin composition of the present invention contains silicone particles, the silicone particles are preferably in the form of a fine powder. The average particle size of the silicone particles is not particularly limited, but is preferably 0.1 μm to 35 μm, more preferably 0.2 μm to 20 μm, and even more preferably 0.3 μm to 8 μm.

[0035] The silicone particles are not particularly limited, but examples thereof include silicone rubber particles, silicone resin particles, and silicone rubber-resin composite particles. Examples of silicone rubber particles include silicone rubber particles having a structure in which linear organopolysiloxanes such as linear dimethylpolysiloxanes are crosslinked. Examples of silicone resin particles include particles of silicone resins having a three-dimensional network-like crosslinked structure. Examples of silicone resins include, for example, (CH3SiO 3 / 2 ) n (n is an integer of 1 or more), etc. can be used. Examples of silicone rubber resin composite particles include particles in which the surface of silicone rubber particles is coated with silicone resin.

[0036] (Content of surfactant, inorganic filler, and silicone particles) The resin composition of the present invention contains a surfactant in an amount of 0.1% by mass or more and 1.2% by mass or less, and satisfies at least one of the following requirements (1) and (2). (1) The content of the inorganic filler is 1% by mass or more and 30% by mass or less. (2) The content of the silicone particles is 0.01% by mass or more and 0.45% by mass or less.

[0037] Therefore, in one embodiment, the resin composition of the present invention contains 0.1% by mass or more and 1.2% by mass or less of a surfactant and 1% by mass or more and 30% by mass or less of an inorganic filler. If the surfactant content is less than 0.1% by mass or the inorganic filler content is less than 1% by mass, it will be difficult to achieve the effects of including these ingredients. For example, when used as a core, the resulting molded body may have defects or the surface smoothness of the inner surface of the molded body may be reduced. Furthermore, if the surfactant content exceeds 1.2% by mass or the inorganic filler content exceeds 30% by mass, slippage occurs when the resin composition is molded into a core or the like, and the fluidity and mixability of the resin composition are reduced when the resin composition is molded, resulting in reduced moldability when the resin composition is molded into, for example, a core or pellets.

[0038] The content of the surfactant is preferably 0.2% by mass or more and 1.1% by mass or less, and more preferably 0.3% by mass or more and 1.0% by mass or less, from the viewpoints of improving the moldability of the core and the like, while increasing the surface smoothness of the inner surface of the molded body molded using the core and suppressing defects that occur in the molded body. Furthermore, from the viewpoints of improving the moldability of the core and the like, while increasing the surface smoothness of the molded body molded using the core, and suppressing defects that occur in the molded body, the content of the inorganic filler is preferably from 2% by mass to 25% by mass, more preferably from 3% by mass to 20% by mass, and even more preferably from 4% by mass to 17% by mass.

[0039] When the inorganic filler is on the nano-order (i.e., when the average particle size of the inorganic filler is less than 1000 nm), the content of the inorganic filler is preferably relatively high, from the viewpoint of further improving the surface smoothness while effectively suppressing defects that may occur in the molded body, and among the above, a content of 5% by mass or more and 30% by mass or less is more preferable, and a content of 10% by mass or more and 20% by mass or less is even more preferable. On the other hand, when the inorganic filler is on the micron order (i.e., when the average particle size of the inorganic filler is 1000 nm or more), from the viewpoint of further improving surface smoothness and effectively suppressing defects while maintaining good moldability of cores and the like, the content of the inorganic filler is preferably relatively small, more preferably 1% by mass or more and 15% by mass or less, and even more preferably 3% by mass or more and 10% by mass or less.

[0040] When the resin composition is used for a core and the molding material for molding the molded body is a super engineering plastic, the surfactant content is preferably 0.3% by mass or more and 1.0% by mass or less among the above. By setting the surfactant content within this range, the core is easily separated from the super engineering plastic when it is dissolved. Furthermore, among these, the surfactant content is more preferably 0.6% by mass or more and 1.0% by mass or less. When the resin composition is used for a core and the molding material used to form the molded body is a super engineering plastic, the inorganic filler content is preferably 5% by mass or more and 30% by mass or less, among the above. By setting the inorganic filler content within this range, the heat resistance of the core is improved. In other words, there is an effect of preventing deformation of the core even when the super engineering plastic comes into direct contact with the core. Furthermore, among these, the inorganic filler content is more preferably 10% by mass or more and 20% by mass or less.

[0041] The resin composition of the present invention may contain silicone particles, as described above. In this case, the resin composition of the present invention contains 0.1% by mass or more and 1.2% by mass or less of a surfactant and 0.01% by mass or more and 0.45% by mass or less of silicone particles, as described above. If the surfactant content is less than 0.1% by mass or the silicone particle content is less than 0.01% by mass, it will be difficult to achieve the effects of adding these components, and when used as a core, for example, the releasability from sintered metal materials, super engineering plastics, etc. will be reduced, resulting in defects in the resulting molded body. Also, the surface smoothness of the inner surface of the molded body will be reduced. Furthermore, if the surfactant content exceeds 1.2% by mass or the silicone particle content exceeds 0.45% by mass, slippage occurs when the resin composition is molded into a core or the like, and the fluidity and mixability of the resin composition are reduced when the resin composition is molded, resulting in reduced moldability when the resin composition is molded into, for example, a core or pellets.

[0042] When silicone particles are used, the details of the surfactant content are the same as when the inorganic filler is used, and therefore the description thereof will be omitted. The content of silicone particles is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and preferably 0.4% by mass or less, more preferably 0.3% by mass or less. When silicone particles are used, the inorganic filler may not be used and the silicone particles may be used instead of the inorganic filler. Similarly, when an inorganic filler is used, the silicone particles may not be used.

[0043] The resin composition may contain both an inorganic filler and silicone particles. In this case, the contents of the inorganic filler and silicone particles may satisfy either or both of the above (1) or (2), but preferably satisfy both. Even when used in combination, the details of the contents of the inorganic filler and silicone particles are as explained above. From the viewpoint of moldability, it is preferable that the content of the inorganic filler in the resin composition is 30% by mass or less and the content of the silicone particles is 0.45% by mass or less.

[0044] (plasticizer) In the present invention, the resin composition may or may not contain a plasticizer, but when it contains a plasticizer, the content of the plasticizer is 5.0 mass % or less. By containing a plasticizer, the resin composition has high moldability, and the moldability when molding, for example, pellets or cores made of the resin composition is improved. On the other hand, if the resin composition contains more than 5.0% by mass of plasticizer, the heat resistance of the resin composition decreases, and problems such as the surface of the core melting when molding the outer molded body, causing the inner surface of the outer molded body to become rough and reducing surface smoothness, are more likely to occur. In the resin composition, the content of the plasticizer is preferably small from the viewpoint of surface smoothness, and is preferably 0% by mass to 4% by mass, and more preferably 0% by mass to 2% by mass, where 0% by mass means that the resin composition does not contain a plasticizer. However, when the resin composition contains a plasticizer, the content is preferably a certain amount or more, for example, 1 mass % or more, from the viewpoint of exerting the effect of the plasticizer.

[0045] When the resin composition is used for a core and the molding material used to mold a molded body is a super engineering plastic, the plasticizer content is preferably from 0% to 3% by mass among the above ranges. By keeping the plasticizer content within this range, direct contact with the super engineering plastic does not adversely affect the surface smoothness of the super engineering plastic molded body due to a decrease in surface smoothness of the core. Furthermore, among these ranges, the plasticizer content is more preferably from 0% to 2% by mass.

[0046] The plasticizer may be a polyhydric alcohol. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, trimethylolpropane, polyethylene glycol, and polypropylene glycol. Here, the polyethylene glycol and polypropylene glycol may have an average molecular weight of 200 or more and 600 or less, preferably 250 or more and 500 or less. Only one type of polyhydric alcohol may be added as the plasticizer, or two or more types may be added. Of the plasticizers mentioned above, at least one selected from ethylene glycol, glycerin, diglycerin, and trimethylolpropane is preferred, and at least one selected from glycerin, diglycerin, and trimethylolpropane is more preferred.

[0047] (Other ingredients) The resin composition may contain an antioxidant. Known antioxidants such as phenolic antioxidants, phosphorus-based antioxidants, amine-based antioxidants, and sulfur-containing antioxidants can be used as the antioxidant. Among these, a combined use of a phenolic antioxidant and a phosphorus-based antioxidant is preferred. An antioxidant having both a phenolic functional group and a phosphorus-based functional group in one molecule can also be suitably used. The content of the antioxidant in the resin composition is, for example, 0.1% by mass or more and 5% by mass or less, and preferably 0.2% by mass or more and 2% by mass or less.

[0048] Examples of the phenolic antioxidant include acrylate compounds such as 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate and 2,4-di-t-amyl-6-(1-(3,5-di-t-amyl-2-hydroxyphenyl)ethyl)phenyl acrylate, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2'-methyl-4-methylphenyl acrylate, 2,4-di-t-butyl ...butyl-2-hydroxyphenyl)ethyl)phenyl acrylate, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,2'-methyl-4-methylphenyl acrylate, 2,4-di- Styrene-bis(4-methyl-6-t-butylphenol), 4,4'-butylidene-bis(4-methyl-6-t-butylphenol), 4,4'-butylidene-bis(6-t-butyl-m-cresol), 4,4'-thiobis(3-methyl-6-t-butylphenol), bis(3-cyclohexyl-2-hydroxy-5-methylphenyl)methane, 3,9-bis(2-(3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy)-1,1-dimethylethyl)-2,4,8,10-tetraoxas Alkyl-substituted phenolic compounds such as pyro[5,5]undecane, 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis(methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate)methane, or triethylene glycol bis(3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate), 6-(4-hydroxyphenyl)- and triazine group-containing phenolic compounds such as 6-(4-hydroxy-3,5-di-t-butylanilino)-2,4-bis-octylthio-1,3,5-triazine, 6-(4-hydroxy-3,5-dimethylanilino)-2,4-bis-octylthio-1,3,5-triazine, 6-(4-hydroxy-3-methyl-5-t-butylanilino)-2,4-bis-octylthio-1,3,5-triazine, and 2-octylthio-4,6-bis-(3,5-di-t-butyl-4-oxyanilino)-1,3,5-triazine.

[0049] Examples of phosphorus-based antioxidants include triphenyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, tris(nonylphenyl) phosphite, tris(dinonylphenyl) phosphite, tris(2-t-butyl-4-methylphenyl) phosphite, tris(cyclohexylphenyl) phosphite, 2,2-methylenebis(4,6-di-t-butylphenyl)octyl phosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(3,5-di-t-butyl-4-hydroxybenzyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and Examples of the phosphate include monophosphite compounds such as 10-decyloxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene, and diphosphite compounds such as 4,4'-butylidene-bis(3-methyl-6-t-butylphenyl-di-tridecyl phosphite), 4,4'-isopropylidene-bis(phenyl-di-alkyl(C12-C15) phosphite), 4,4'-isopropylidene-bis(diphenyl monoalkyl(C12-C15) phosphite), 1,1,3-tris(2-methyl-4-di-tridecyl phosphite-5-t-butylphenyl)butane, and tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene phosphite. Among these, monophosphite compounds are preferred.

[0050] The antioxidant having both a phenolic functional group and a phosphorus functional group is not particularly limited, but examples thereof include phosphite compounds having a phenolic skeleton. Specifically, 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenz[d,f][1,3,2]dioxaphosphepine, 2,10-dimethyl-4,8-di-t-butyl-6-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propoxy]-12H-dibenzo[d,g][1,3,2]dioxaphosphene, 2,4,8,10-tetra-t-butyl-6-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propoxy]dibenzo[d,f][1,3,2]dioxaphosphene, 2,4,8,10-tetra-t-pentyl-6-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propoxy]-12H-dibenzo[d,g][1,3,2]dioxaphosphene, )propoxy]-12-methyl-12H-dibenzo[d,g][1,3,2]dioxaphosphocin, 2,10-dimethyl-4,8-di-t-butyl-6-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-12H-dibenzo[d,g][1,3,2]dioxaphosphocin, 2,4,8,10-tetra-t-pentyl-6-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-12-methyl-12H-dibenzo[d,g][1,3,2]dioxaphosphocin, 2,4,8,10-tetra-t-butyl-6-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]-dibenzo[d,f][1,3, 2]dioxaphosphepin, 2,10-dimethyl-4,8-di-t-butyl-6-(3,5-di-t-butyl-4-hydroxybenzoyloxy)-12H-dibenzo[d,g][1,3,2]dioxaphosphocin, 2,4,8,10-tetra-t-butyl-6-(3,5-di-t-butyl-4-hydroxybenzoyloxy)-12-methyl-12H-dibenzo[d,g][1,3,2]dioxaphosphocin, 2,10-dimethyl-4,8-di-t-butyl-6[3-(3-methyl-4-hydroxy-5-t-butylphenyl)propoxy]-12H-dibenzo[d,g][1,3,2]dioxaphosphocin, 2,10-di-t-pentyl-4,Examples include 8-di-t-butyl-6[3-(3,5-di-t-butyl-4-hydroxyphenyl)propoxy]-12H-dibenzo[d,g][1,3,2]dioxaphosphocin and 2,4,8,10-tetra-t-butyl-6-[2,2-dimethyl-3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-dibenzo[d,f][1,3,2]dioxaphosphepine.

[0051] The resin composition may also contain various additives, such as colorants, antifoaming agents, ultraviolet absorbers, and preservatives, that can be used in combination with the PVA resin.

[0052] [Method of producing resin composition] The resin composition can be obtained, for example, by adding a surfactant and at least one of an inorganic filler and silicone particles, and other additives such as a plasticizer, which are blended as necessary, to a PVA-based resin and mixing them. The method for mixing the components of the resin composition is not particularly limited, but mixing may be performed using a known kneading device, such as an extrusion molding machine, or, for example, in the case where the resin composition is injection molded to obtain a core as described below, mixing may be performed inside the cylinder of an injection molding machine.

[0053] [Core molding] The resin composition of the present invention is, for example, a resin composition for a core. The core is formed by molding an outer molded body in an injection molding process, and then removed from the outer molded body by elution or the like. The method for producing a core from the resin composition is not particularly limited, but molding by injection molding is preferred. Injection molding may be performed using a known injection molding machine, which includes, for example, a mold such as a metal mold for molding a core, and an injection unit connected to the mold for supplying a molding material (resin composition) to the mold. The injection unit includes, for example, a cylinder and a screw disposed inside the cylinder. The injection unit rotates the screw to mix the components introduced into the cylinder and send them to the front of the cylinder, supplying the fluidized resin composition (molding material) to a mold. In the mold, the supplied resin composition (molding material) is injected into a cavity formed by the mold to produce a core. The molding temperature for injection molding the core is not particularly limited, but is, for example, about 160 to 220°C. The resin composition may be pelletized before being placed in an injection molding machine. The pelletized resin composition may then be placed in an injection molding machine to injection mold a core. The pelletizing process is not particularly limited, but may be performed by extrusion molding, for example. The pelletizing process may be performed at an extrusion temperature of about 160 to 220°C, for example.

[0054] [Method of manufacturing molded body] The core obtained as described above may be used to produce a molded body. The molded body may be produced, for example, by injection molding, which may be performed using a known injection molding machine. As described above, the injection molding machine may include, for example, a molding die such as a metal mold and an injection unit.

[0055] In the method for producing a molded body, the core obtained as described above is placed in a mold, and then a molding material is injected into the cavity formed by the mold and the core to form a molded body. Thereafter, the molded body is removed from the mold, and the core is removed to obtain the molded body. Here, the molded body is preferably removed from the mold together with the core as a composite. The method for removing the core from the removed composite is not particularly limited, but it is preferable to remove the core by eluting at least a portion of the core. Specifically, the core is removed from the composite by immersing the composite in water, preferably in warm water heated to about 40°C or higher and 80°C or lower, thereby eluting at least a portion of the core. The water in which the composite is immersed may be stirred. The water from which the core is removed may be water alone, or may be acidic water or alkaline water to which various acidic substances, alkaline substances, etc. have been added. Furthermore, when sintering as described below is carried out, the core may be removed by thermal decomposition caused by heating during sintering.

[0056] The molding material used to obtain the molded body is preferably either a sintered metal material or a super engineering plastic. The sintered metal material is a sintering composition containing, for example, a metal powder and a binder. Examples of the metal powder include, but are not limited to, nickel powder, titanium powder, aluminum powder, copper powder, iron powder, carbonyl iron powder, stainless steel powder, and nickel alloys such as Inconel. Examples of the binder include olefin-based resins such as polyethylene and polypropylene, and polymer components such as polystyrene and polyamide. The polymer component may also contain various additives such as paraffin wax, stearic acid, and amide-based lubricants.

[0057] When a sintered metal material is used as the molding material, a sintered molded body made of metal powder is obtained by sintering the molded body (preferably the molded body from which the core has been removed) removed from the mold. The sintering temperature is not particularly limited, but may be any temperature at which the binder is thermally decomposed, for example, about 250 to 2500°C, preferably about 500 to 2000°C. The molded article obtained by using a sintered metal material can have good surface smoothness on the inner surface and be less susceptible to chipping by using the above resin composition for the core.

[0058] Examples of super engineering plastics include polymers that can retain optical anisotropy even in a fluid state. Specific examples of super engineering plastics include highly heat-resistant plastics such as polyphenylene sulfide (PPS), polyetheretherketone (PEEK), liquid crystal polymer (LCP), polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polyphenylsulfone (PPSU), polysulfone (PSF), polyethersulfone (PES), polyarylate (PAR), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE). Among these, PEEK, PES, and PPS are preferred. By using Super Engineering Plastics, molded articles with good heat resistance, durability, mechanical strength, etc. Furthermore, even when a molded article is obtained using Super Engineering Plastics as a molding material, by using the above-mentioned resin composition, a molded article with high releasability from the core and high inner surface smoothness can be obtained.

[0059] The outer molded body formed by the core is, for example, a molded body having a hollow portion, and more specifically, a cylindrical body, a cylindrical body with a bottom, or a hollow or unique cavity shape for molding, for example, a golf club head. By using a core for the outer molded body, it is possible to obtain a molded body having a hollow portion of a complex shape. Furthermore, the shape of various molded bodies such as cylindrical bodies may be straight, but is not limited to a straight shape and may be any shape such as L-shape, S-shape, or T-shape. These L-shape, S-shape, and other cylindrical bodies can be used as, for example, joints. Furthermore, the cylindrical body or the bottomed cylindrical body may have a shape in which the diameter changes along the axial direction. In the present invention, even when molding a molded article having a complex shape, by using a core made of the resin composition having the above-mentioned blend, the molded article can be easily released from the core, and the surface roughness of the molded article can be reduced, thereby increasing the smoothness of the inner surface.Furthermore, damage to the molded article can also be effectively prevented.

[0060] Specifically, the surface roughness of the inner surface of the molded body having a hollow portion obtained by the above manufacturing method (a sintered molded body when the molding material is a sintered metal material) is preferably 0.5 mm or less. By making it 0.5 mm or less, the inner surface smoothness of the molded body is improved, making it possible to use the molded body practically. From the viewpoint of improving the inner surface smoothness of the molded body, the above surface roughness is more preferably 0.3 mm or less, and even more preferably 0.2 mm or less. The lower the above surface roughness, the better, with the lower limit being 0 mm. The surface roughness is the arithmetic mean surface roughness Ra measured using a contact surface roughness measuring instrument (such as Talysurf or Surfcom). [Example]

[0061] The present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way.

[0062] The evaluation methods in this example are as follows. [Moldability] In each of the Examples and Comparative Examples, the pelletizing process and the moldability during core molding were evaluated according to the following evaluation criteria. A: No problems occurred during pelletizing or core molding, and the moldability was excellent. B: Molding became unstable at least during pelletizing and / or core molding, but pellets and cores could be molded without any practical problems. C: There were problems with the moldability of the pellets or cores, such as damage to the pellets during pelletizing and inability to mold the cores properly.

[0063] [Surface roughness of sintered compact] The surface roughness of the inner peripheral surface of the cylindrical sintered compacts obtained in each Example and Comparative Example was measured and evaluated according to the following criteria: The surface roughness is the arithmetic mean surface roughness Ra measured using a contact-type surface roughness measuring instrument (Talysurf manufactured by Taylor Hobson or Surfcom manufactured by Tokyo Seimitsu). (Evaluation criteria) AA: Surface roughness is 0.2 mm or less A: Surface roughness is greater than 0.2 mm and less than 0.3 mm B: Surface roughness is greater than 0.3 mm and less than 0.5 mm C: Surface roughness greater than 0.5 mm

[0064] [Damage in sintered compacts] The appearance of the finally obtained sintered compact was observed to check for the presence or absence of defects on the inner surface of the compact, and the compact was evaluated according to the following evaluation criteria. A: No defects. B: Fine defects adhered to the core, causing minute irregularities on the inner surface. C: There was a relatively large defect that could be visually confirmed.

[0065] [Removability and surface roughness of Super Engineering plastic moldings] After molding a molded body using Super Engineering Plastic, the resulting molded body was cut in half along the axial direction together with the core. The peelability between the core and the molded body was then checked and evaluated according to the following criteria. The molded body was cut in half, and the core was removed, and the surface roughness of the inner surface was measured and evaluated. The measurement method and evaluation criteria for surface roughness were the same as those for the sintered molded body described above. (peelability) A: The core could be easily peeled off from the molded body with fingers. C: The core could not be easily peeled off from the molded body with fingers.

[0066] Example 1 The following polyvinyl alcohol, antioxidant, surfactant, and inorganic filler were used. 1) Polyvinyl alcohol: Sekisui Specialty Chemicals, trade name "SELVOL205", saponification degree 89, polymerization degree 500 to 800, MFR 3.5 g / 10 min at 210°C under a load of 2160 g, viscosity of a 4% by mass aqueous solution at 23°C of 5.2 to 6.2 mPa·s 2) Antioxidant: Sumitomo Chemical Co., Ltd., trade name "Sumilizer GP", 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenz[d,f][1,3,2]dioxaphosphepine 3) Surfactant: Kao Corporation, product name "Electrostripper TS5", glycerol monostearate 4) Inorganic filler: Ishihara Sangyo Kaisha, product name "Tipake PF690", titanium oxide, average particle size: 300 nm

[0067] An antioxidant, a surfactant, and an inorganic filler were added to polyvinyl alcohol in the amounts shown in Table 1, and the mixture was pelletized at an extrusion temperature of 190 to 210°C using an extrusion molding machine (manufactured by Toshiba Machine Co., Ltd., product number "TEM26SX") to obtain pellets. The resulting pellets were used to mold a core using an injection molding machine (product number "J30ADS" manufactured by Japan Steel Works, Ltd.) Using the same molding machine, the core was placed in a mold, and sintering clay containing sintering stainless steel powder and a polyethylene binder was placed along the periphery of the core. The mold was then closed, and molding was carried out at a temperature of 180 to 200°C. Next, the composite including the core and outer compact was removed from the mold and immersed in warm water at 60°C. The core was dissolved over approximately 6 hours while the water was stirred. The remaining outer compact was sintered by heating at a temperature of 1300°C for 60 seconds to obtain a stainless steel cylindrical body (sintered compact).

[0068] Example 2 Pellets were obtained in the same manner as in Example 1, except that the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was formed. The evaluation results of the obtained molded body are shown in Table 1. In this example, a core was further molded, and then the core was used to obtain a molded body (cylindrical body) made of PEEK resin at a molding temperature of 250°C using PEEK resin as the molding material.

[0069] Example 3 Pellets were obtained in the same manner as in Example 1, except that the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was formed. In this example, a core was further molded, and then the core was used to obtain a molded body (cylindrical body) made of PEEK resin at a molding temperature of 250°C using PEEK resin as the molding material.

[0070] Example 4 Pellets were obtained in the same manner as in Example 1, except that the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was formed.

[0071] Example 5 Pellets were obtained in the same manner as in Example 1, except that 5% by mass of diglycerin was added as a plasticizer for polyvinyl alcohol and the blending amounts of each component were changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0072] Example 6 Pellets were obtained in the same manner as in Example 1, except that 5% by mass of glycerin was added as a plasticizer for polyvinyl alcohol and the blending amounts of each component were changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0073] Example 7 Pellets were obtained in the same manner as in Example 1, except that 5% by mass of trimethylolpropane (TMP) was added as a plasticizer for polyvinyl alcohol and the blending amounts of each component were changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0074] Example 8 Pellets were obtained in the same manner as in Example 1, except that the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was formed.

[0075] Example 9 Pellets were obtained in the same manner as in Example 1, except that the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was formed.

[0076] Example 10 Pellets were obtained in the same manner as in Example 1, except that the surfactant was changed to "Magnesium Stearate MG" (magnesium stearate) manufactured by NOF Corporation and the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0077] Example 11 Pellets were obtained in the same manner as in Example 1, except that the surfactant was changed to "Alflow H50" (ethylene bisstearic acid amide) manufactured by NOF Corporation and the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0078] Example 12 Pellets were obtained in the same manner as in Example 1, except that the surfactant was changed to "SC-P" (calcium stearate), a product of Sakai Chemical Industry Co., Ltd., and the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0079] Example 13 Pellets were obtained in the same manner as in Example 1, except that the surfactant was changed to "SPZ100F" (zinc stearate) manufactured by Sakai Chemical Industry Co., Ltd., and the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0080] Example 14 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to silica particles manufactured by Fuji Silysia Chemical Ltd. (product name "Sylysia 358", average particle size: 5000 nm) and the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded. In this example, a core was further molded, and then the core was used to obtain a molded body (cylindrical body) made of PEEK resin at a molding temperature of 250°C using PEEK resin as the molding material.

[0081] Example 15 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to silica particles manufactured by Fuji Silysia Chemical Ltd. (product name "Sylysia 780", average particle size: 8000 nm) and the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded. In this example, a core was further molded, and then the core was used to obtain a molded body (cylindrical body) made of PEEK resin at a molding temperature of 250°C using PEEK resin as the molding material.

[0082] Example 16 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to silica particles (product name "Sylysia 358") manufactured by Fuji Silysia Chemical Ltd., and the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0083] Example 17 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to silica particles (product name "Sylysia 358") manufactured by Fuji Silysia Chemical Ltd., and the addition ratio of each component was changed as shown in Table 1. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded. During the injection molding to form the core, the pellets slipped on the screw inside the cylinder, making the injection molding unstable, but the core was still able to be molded.

[0084] Example 18 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to carbon black particles (product name "SEAST-S", average particle size: 30 nm) manufactured by Tokai Carbon Co., Ltd., and the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0085] Example 19 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to carbon black particles (product name "SEAST-S") manufactured by Tokai Carbon Co., Ltd., and the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0086] Example 20 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to high-purity anhydrous magnesium sulfate particles (particle size 20 μm) manufactured by Tomita Pharmaceutical Co., Ltd., and the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a cylindrical body was molded using PEEK resin.

[0087] Example 21 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to high-purity anhydrous sodium sulfate particles manufactured by Tomita Pharmaceutical Co., Ltd., and the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a cylindrical body was molded using PEEK resin.

[0088] Example 22 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to anhydrous magnesium sulfate particles (particle size 20 μm) manufactured by Tomita Pharmaceutical Co., Ltd., and silicone particles (product name "KMP590") manufactured by Shin-Etsu Chemical Co., Ltd. were added, and the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a cylindrical body was molded using PEEK resin.

[0089] Example 23 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to silicone particles (trade name "KMP590") manufactured by Shin-Etsu Chemical Co., Ltd., and the addition ratio of each component was changed as shown in Table 2. Pellets were then obtained in the same manner as in Example 1. A core was then molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0090] Example 24 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to silicone particles (product name "X-52-854") manufactured by Shin-Etsu Chemical Co., Ltd., and the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0091] Example 25 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to silicone particles (trade name "KMP590") manufactured by Shin-Etsu Chemical Co., Ltd., and the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded. During the injection molding to form the core, the pellets slipped on the screw inside the cylinder, making the injection molding unstable, but we managed to mold the core.

[0092] Example 26 Pellets were obtained in the same manner as in Example 1, except that the inorganic filler was changed to silicone particles (product name "X-52-854") manufactured by Shin-Etsu Chemical Co., Ltd., and the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded. During the injection molding to form the core, the pellets slipped on the screw inside the cylinder, making the injection molding unstable, but the core was still able to be molded.

[0093] (Comparative Example 1) Pellets were obtained in the same manner as in Example 1, except that the addition ratio of each component was changed as shown in Table 2. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was formed. In Comparative Example 1, although pellet processing was possible, the pellets were weak and easily cracked by external force, and the pellet shape could not be stably maintained, raising doubts about their practicality.

[0094] (Comparative Example 2) Pellets were produced in the same manner as in Example 1, except that the inorganic filler was changed to silica particles manufactured by Fuji Silysia Chemical Ltd. (product name "Sylysia 358") and the addition ratio of each component was changed as shown in Table 2. However, during pellet production, the supply of raw materials into the extruder became increasingly unstable, and the PVA resin slipped on the screw inside the extruder, making it impossible to stably process pellets by extrusion molding, and it was not possible to produce pellets suitable for injection molding.

[0095] (Comparative Example 3) Pellets were obtained in the same manner as in Example 1, except that 10% by mass of diglycerin was added as a plasticizer for polyvinyl alcohol and the blending amounts of each component were changed as shown in Table 2. Thereafter, a core was molded in the same manner as in Example 1, and then a stainless steel cylindrical body was molded.

[0096] Comparative Example 4 Pellets were obtained in the same manner as in Example 1, except that no surfactant was used and the amounts of each component were changed to those shown in Table 2. Thereafter, a core was formed in the same manner as in Example 1, and then a stainless steel cylindrical body was formed. In this comparative example, a core was further molded, and then a molded body (cylindrical body) made of PEEK resin was obtained using the core and a molding temperature of 250°C using PEEK resin as a molding material.

[0097] (Comparative Example 5) An attempt was made to obtain pellets in the same manner as in Example 1, except that the inorganic filler was changed to silicone particles manufactured by Shin-Etsu Chemical Co., Ltd. (product name "KMP590") and the addition ratio of each component was changed as shown in Table 2. However, slippage occurred in the extruder, and extrusion molding was not possible.

[0098] (Comparative Example 6) An attempt was made to obtain pellets in the same manner as in Example 1, except that the inorganic filler was changed to silicone particles manufactured by Shin-Etsu Chemical Co., Ltd. (product name "KX-62-854") and the addition ratio of each component was changed as shown in Table 2. However, slippage occurred in the extruder, and extrusion molding processing was not possible.

[0099] (Comparative Example 7) An attempt was made to obtain pellets in the same manner as in Example 1, except that the inorganic filler was changed to commercially available calcium chloride particles (particle size 50 μm, solubility in water at 20°C 74.5 g), silicone particles (product name "KMP590") from Shin-Etsu Chemical Co., Ltd. were added, and the addition ratio of each component was changed as shown in Table 2. However, the moisture emitted a lot of smoke, the material was burnt, and the pellets were not formed satisfactorily.

[0100] [Table 1]

[0101] [Table 2]

[0102] As is clear from each example, by molding a core using a resin composition containing a surfactant and at least one of an inorganic filler and silicone particles in a predetermined content, and containing no plasticizer or containing a plasticizer in an amount not greater than a predetermined amount, good moldability was achieved when molding the core and pellets. Furthermore, in powder metal injection molding (MIM), the molded body molded using the core had good internal smoothness, and chipping of the molded body was prevented. In contrast, in each of the comparative examples, when the content of any one of the surfactant, plasticizer, and inorganic filler or silicone particles was outside the specified range, the moldability when molding the core and pellets decreased, or the surface smoothness of the molded body molded using the core decreased.

Claims

1. The composition contains a polyvinyl alcohol resin, a surfactant in an amount of 0.1% by mass or more and 1.2% by mass or less, and at least one of an inorganic filler and silicone particles, A resin composition containing no plasticizer or containing 5.0% by mass or less of a plasticizer, and having a content of the silicone particles of 0.01% by mass or more and 0.45% by mass or less.

2. The resin composition according to claim 1, wherein the inorganic filler is a water-soluble inorganic filler having a solubility in water at 20°C of 10 g or more and 74 g or less.

3. The resin composition according to claim 1 or 2, wherein the surfactant is at least one selected from the group consisting of glycerin fatty acid esters, fatty acid metal salts, and fatty acid amides.

4. The resin composition according to any one of claims 1 to 3, which is used for a core.

5. The composition contains a polyvinyl alcohol resin, a surfactant in an amount of 0.1% by mass or more and 1.2% by mass or less, and at least one of an inorganic filler and silicone particles, The composition does not contain a plasticizer or contains a plasticizer in an amount of 5.0% by mass or less, and satisfies at least one of the following requirements (1) and (2): The resin composition, wherein the inorganic filler is a water-soluble inorganic filler having a solubility in water at 20°C of 10 g or more and 74 g or less. (1) The content of the inorganic filler is 1% by mass or more and 30% by mass or less. (2) The content of the silicone particles is 0.01% by mass or more and 0.45% by mass or less.

6. The resin composition according to claim 5, wherein the surfactant is at least one selected from the group consisting of glycerin fatty acid esters, fatty acid metal salts, and fatty acid amides.

7. The resin composition according to claim 5 or 6, which is for use in a core.

8. The composition contains a polyvinyl alcohol resin, a surfactant in an amount of 0.1% by mass or more and 1.2% by mass or less, and at least one of an inorganic filler and silicone particles, The composition does not contain a plasticizer or contains a plasticizer in an amount of 5.0% by mass or less, and satisfies at least one of the following requirements (1) and (2): The resin composition, wherein the surfactant is at least one selected from the group consisting of a glycerin fatty acid ester, a fatty acid metal salt, and a fatty acid amide. (1) The content of the inorganic filler is 1% by mass or more and 30% by mass or less. (2) The content of the silicone particles is 0.01% by mass or more and 0.45% by mass or less.

9. The resin composition according to claim 8, which is for use in a core.

10. The composition contains a polyvinyl alcohol resin, a surfactant in an amount of 0.1% by mass or more and 1.2% by mass or less, and at least one of an inorganic filler and silicone particles, The composition does not contain a plasticizer or contains a plasticizer in an amount of 5.0% by mass or less, and satisfies at least one of the following requirements (1) and (2): A resin composition for use in cores. (1) The content of the inorganic filler is 1% by mass or more and 30% by mass or less. (2) The content of the silicone particles is 0.01% by mass or more and 0.45% by mass or less.

11. A resin composition described in any one of claims 1 to 10, wherein the degree of saponification of the polyvinyl alcohol-based resin is 72 mol% or more and 90 mol% or less.

12. The resin composition according to any one of claims 1 to 11, comprising the inorganic filler in an amount of 1% by mass or more and 30% by mass or less.

13. The resin composition according to any one of claims 1 to 12, wherein the inorganic filler has an average particle size of 30 nm or more and 20 µm or less.

14. The resin composition according to any one of claims 1 to 13, wherein the inorganic filler is at least one selected from the group consisting of silica, titanium oxide, calcium carbonate, mica, talc, and carbon black.

15. The resin composition according to any one of claims 1 to 14, wherein the plasticizer is at least one selected from the group consisting of ethylene glycol, glycerin, diglycerin, and trimethylolpropane.

16. The resin composition according to any one of claims 1 to 15, wherein the degree of polymerization of the polyvinyl alcohol-based resin is 900 or less.

17. The resin composition according to any one of claims 1 to 16, wherein the polyvinyl alcohol-based resin has a 4% by mass aqueous solution viscosity of 100 mPa·s or less at 23 ° C.

18. The resin composition according to any one of claims 1 to 17, wherein the polyvinyl alcohol-based resin has an MFR of 1.0 g / 10 min or more and 10 g / 10 min or less at 210 ° C. and a load of 2160 g.

19. A step of molding a core from the resin composition according to any one of claims 1 to 18; placing the core in a mold; a step of injecting a molding material into a cavity formed by the mold and the core to form a molded body; a step of removing the green body from the mold after molding and removing the core; A method for manufacturing a molded body comprising:

20. The method for producing a molded article according to claim 19, wherein the molding material is either a sintered metal material or a super engineering plastic.

21. 21. The method for producing a molded body according to claim 19 or 20, wherein the molding material is a sintered metal material, and the molded body from which the core has been removed is further sintered to obtain a sintered molded body.

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