Polyacetal resin composition

Abstract

The present invention provides: a polyacetal resin composition; a metal resin composition; and a method for producing a polyacetal resin composition. The present invention provides a polyacetal resin composition which contains 100 parts by weight of a polyacetal resin (A) and 0.1 to 0.9 part by weight of a fatty acid metal salt (B) having a weight loss rate of 20% by weight of more, the weight loss rate being the ratio of weight loss after the fatty acid metal salt is heated from room temperature to 200°C at a rate of 200°C / minute in the air at atmospheric pressure and is subsequently held at 200°C for 60 minutes.

Description

Polyacetal resin composition

[0001] The present invention relates to a polyacetal resin composition, particularly to a polyacetal resin composition to be kneaded with a metal powder. The present invention also relates to a metal resin composition containing the polyacetal resin composition and the metal powder, a method for producing the polyacetal resin composition, and a method for producing a powder injection molded product using the polyacetal resin composition as a binder resin composition.

[0002] In recent years, powder injection molding has been used to produce metal molded products by injection molding a mixture obtained by kneading a binder resin composition with a metal powder. Powder injection molding is advantageous in terms of the degree of freedom in the shape and material of the molded product, and dimensional accuracy.

[0003] Polyacetal resins are widely used as engineering plastics due to their mechanical properties, friction and wear properties, chemical resistance, heat resistance, and electrical properties. Polyacetal resins can be easily removed by combustion, and the amount of residual ash can be reduced, making them suitable as binder resin compositions for metal powders in powder injection molding.

[0004] Patent Document 1 discloses a polyacetal resin composition containing 100 parts by mass of (A) a polyacetal resin, 0.005 to 0.2 parts by mass of (B) a nitrogen-containing compound, and 0.01 to 0.8 parts by mass of (C) a fatty acid metal salt such as calcium stearate, wherein the ratio of the content of the (C) fatty acid metal salt to the content of the (B) nitrogen-containing compound is 1 to 15.

[0005] JP 2020-041133 A International Publication No. 2017 / 200069

[0006] When a polyacetal resin composition is kneaded with a metal powder (i.e., when used as a binder resin composition for metal powder), a predetermined amount of a nitrogen-containing compound and a fatty acid metal salt is added to the polyacetal resin to improve the thermal stability and flowability of the kneaded product (metal-resin composition) (Patent Document 1). However, it is known that the use of a fatty acid metal salt such as calcium stearate causes significant yellowing of the polyacetal resin composition (Patent Document 2).

[0007] In view of the above, it is desired to suppress yellowing of polyacetal resin compositions containing fatty acid metal salts and improve their color.

[0008] The present invention includes the following aspects. [1] A polyacetal resin composition comprising: 100 parts by weight of a polyacetal resin (A); and 0.1 to 0.9 parts by weight of a fatty acid metal salt (B) having a weight loss rate of 20% by weight or more, wherein the weight loss rate is the weight loss rate when heated in air at atmospheric pressure from room temperature to 200°C at a rate of 200°C / min and maintained at 200°C for 60 minutes. [2] The polyacetal resin composition according to [1], wherein the fatty acid metal salt (B) is magnesium stearate having a weight loss rate of 20% by weight or more, aluminum stearate having a weight loss rate of 20% by weight or more, or a combination thereof. [3] The polyacetal resin composition according to [1] or [2], wherein the polyacetal resin (A) has a melt flow rate of 40 to 100 g / 10 min (temperature 190°C, load 2.16 kg). [4] The polyacetal resin composition according to any one of [1] to [3], which contains 0.14 to 0.6 parts by weight of the fatty acid metal salt (B). [5] The polyacetal resin composition according to any one of [1] to [4], wherein the polyacetal resin (A) is a crude polyoxymethylene copolymer in which the polymerization catalyst has been deactivated after copolymerization has been completed but the unstable terminal groups have not been stabilized. [6] The polyacetal resin composition according to any one of [1] to [5], which further contains 0.01 to 1.0 parts by weight of one or more stabilizers. [7] The polyacetal resin composition according to any one of [1] to [6], which is used by kneading with a metal powder. [8] A metal resin composition comprising the polyacetal resin composition according to any one of [1] to [7], and a metal powder (C).[9] A method for producing a polyacetal resin composition to be used by kneading with a metal powder, comprising: preparing the polyacetal resin composition by melt-kneading 100 parts by weight of a polyacetal resin (A) with 0.1 to 0.9 parts by weight of a fatty acid metal salt (B) having a weight loss rate of 20% by weight or more, wherein the weight loss rate is the weight loss rate when the polyacetal resin composition is heated from room temperature to 200°C at a rate of 200°C / min in air at atmospheric pressure and held at 200°C for 60 minutes, and the fatty acid metal salt (B) is magnesium stearate having a weight loss rate of 20% by weight or more, aluminum stearate having a weight loss rate of 20% by weight or more, or a combination thereof.

[10] A method for producing a powder injection molded product, comprising: melt-kneading a metal powder and a binder resin composition to obtain a kneaded body, and injecting the kneaded body into a mold, wherein the binder resin composition is the polyacetal resin composition according to any one of [1] to [7].

[0009] The present invention can suppress yellowing of the polyacetal resin composition and improve its hue. In particular, a kneaded product of the polyacetal resin composition of the present invention and a metal powder (metal-resin composition) is suitable as a raw material for producing small and / or complex products by powder injection molding.

[0010] [Polyacetal Resin Composition] The polyacetal resin composition of the present invention contains 100 parts by weight of a polyacetal resin (A) and 0.1 to 0.9 parts by weight of a fatty acid metal salt (B) having a weight loss rate of 20% by weight or more. Specifically, the fatty acid metal salt (B) is magnesium stearate, aluminum stearate, or a combination thereof, each having a weight loss rate of 20% by weight or more.

[0011] The polyacetal resin composition of the present invention is used by kneading with a metal powder (C), and therefore serves as a binder resin composition for the metal powder (C). The polyacetal resin composition may be in the form of a solid, powder, strand, pellet, or a combination thereof. The polyacetal resin composition of the present invention is used by kneading with the metal powder (C).

[0012] The method for producing a polyacetal resin composition of the present invention includes a step of melt-kneading 100 parts by weight of a polyacetal resin (A) with 0.1 to 0.9 parts by weight of a fatty acid metal salt (B) having a weight loss rate of 20% by weight or more. The fatty acid metal salt (B) is magnesium stearate having a weight loss rate of 20% by weight or more, aluminum stearate having a weight loss rate of 20% by weight or more, or a combination thereof. The melt-kneading step is carried out at a temperature equal to or higher than the melting point of the polyacetal resin composition (generally 180°C or higher) (under atmospheric pressure).

[0013] [Polyacetal Resin (A)] Polyacetal resin (A) is a polymer having an acetal bond: —O—CRH— (where R represents a hydrogen atom or an organic group) in a repeating unit, and is usually an oxymethylene group (—OCH ２ -) as the main structural unit. The polyacetal resin (A) may be a copolymer (block copolymer) or a terpolymer containing one or more repeating structural units other than the oxymethylene group. The polyacetal resin (A) may have not only a linear structure but also a branched or crosslinked structure formed by using a glycidyl ether compound, an epoxy compound, an allyl ether compound, or the like as a comonomer and / or termonomer. Examples of structural units other than the oxymethylene group include an oxyethylene group (-OCH ２ CH ２ -or-OCH(CH ３ )-), oxypropylene group (—OCH ２ CH ２ CH ２ -, -OCH(CH ３ ) CH ２ -or-OCH ２ CH (CH ３ )-), oxybutylene group (—OCH ２ CH ２ CH ２ CH ２ -, -OCH(CH ３） CH ２ CH ２ -, -OCH ２ CH (CH ３ ) CH ２ -, -OCH２ CH ２ CH (CH ３ ) -, -OCH(C ２ H ５ ) CH ２ -or-OCH ２ CH(C ２ H ５ )-) and the like, which may be branched and have 2 to 10 carbon atoms, and among these, an oxyalkylene group having 2 to 4 carbon atoms, which may be branched, or an oxyethylene group (—OCH ２ CH ２ The content of the comonomer (structural unit other than an oxymethylene group) in the polyacetal resin (A) is 0.1 to 20% by weight, 0.1 to 15% by weight, 0.1 to 10% by weight, 0.1 to 8% by weight, 0.1 to 6% by weight, 0.1 to 4% by weight, 0.1 to 2% by weight, 0.1 to 1% by weight, 0.5 to 15% by weight, 0.5 to 10% by weight, 0.5 to 8% by weight, 0.5 to 6% by weight, 0.5 to 4% by weight, 0.5 to 2% by weight, or 0.5 to 1% by weight, based on the weight of the polyacetal resin (A).

[0014] The polyacetal resin (A) may be either terminally stabilized or unterminally stabilized, for example, a crude polyoxymethylene copolymer in which the polymerization catalyst has been deactivated after copolymerization but the unstable terminal groups have not been stabilized.

[0015] Preferably, the polyacetal resin (A) is a copolymer of a cyclic acetal such as trioxane or tetraoxane with ethylene oxide or 1,3-dioxolane, for example, an acetal copolymer using 1,3-dioxolane as a comonomer.

[0016] The polyacetal resin (A) has a melt flow rate, measured in accordance with ASTM-D1238 (temperature 190°C, load 2.16 kg), of 1 to 100 g / 10 min, 10 to 100 g / 10 min, 15 to 100 g / 10 min, 20 to 100 g / 10 min, 25 to 100 g / 10 min, 30 to 100 g / 10 min, 35 to 100 g / 10 min, 40 to 100 g / 10 min, 42 to 100 g / 10 min, 45 to 100 g / 10 min, 40 to 95 g / 10 min, 42 to 95 g / 10 min, or 45 to 95 g / 10 min. Preferably, the polyacetal resin (A) has a melt flow rate of 30 to 100 g / 10 min, 40 to 100 g / 10 min, or 45 to 95 g / 10 min.

[0017] The method for producing the polyacetal resin (A) is not particularly limited, and the polyacetal resin (A) can be produced by a known method. For example, the polyacetal resin (A) having an oxymethylene group and an oxyalkylene group having 2 to 4 carbon atoms as constituent units can be produced by copolymerizing a cyclic acetal of an oxymethylene group, such as a trimer (trioxane) or tetramer (tetraoxane) of formaldehyde, with a cyclic acetal containing an oxyalkylene group having 2 to 5 carbon atoms, such as ethylene oxide, 1,3-dioxolane, 1,3,6-trioxocane, or 1,3-dioxepane.

[0018] For example, polyacetal resin (A) can be obtained by bulk polymerization of a cyclic acetal containing an oxymethylene group and a comonomer cyclic acetal containing an oxyalkylene group having 2 to 5 carbon atoms using a polymerization catalyst. A reaction terminator may be used as needed to deactivate the polymerization catalyst and the growing polymer terminals. Furthermore, a molecular weight regulator may be used as needed to adjust the molecular weight of polyacetal resin (A).

[0019] The types and amounts of the polymerization catalyst, reaction terminator, and molecular weight modifier are not limited as long as they do not impair the effects of the present invention, and known polymerization catalysts, reaction terminators, and molecular weight modifiers may be used as appropriate.

[0020] Examples of the polymerization catalyst include Lewis acids such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, arsenic pentafluoride, and antimony pentafluoride, or complex compounds or salt compounds of these Lewis acids; protonic acids such as trifluoromethanesulfonic acid or perchloric acid; esters of protonic acids such as esters of perchloric acid and lower aliphatic alcohols; anhydrides of protonic acids such as mixed anhydrides of perchloric acid and lower aliphatic carboxylic acids; or triethyloxonium hexafluorophosphate, triphenylmethylhexafluoroarsenate, acetylhexafluoroborate, heteropolyacids or acid salts thereof, isopolyacids or acid salts thereof, and perfluoroalkylsulfonic acids or acid salts thereof.

[0021] Examples of the reaction terminator include a trivalent organic phosphorus compound (e.g., triphenylphosphine), an amine compound, an alkali metal hydroxide, an alkaline earth metal hydroxide, or a combination thereof. Examples of the molecular weight regulator include methylal, methoxymethylal, dimethoxymethylal, trimethoxymethylal, or oxymethylene di-n-butyl ether.

[0022] Furthermore, if necessary, the polyacetal resin (A) may contain known additives such as antioxidants, heat stabilizers, colorants, nucleating agents, plasticizers, fluorescent brighteners, sliding agents, antistatic agents, ultraviolet absorbers, or light stabilizers.

[0023] [Fatty Acid Metal Salt (B)] The fatty acid metal salt (B) is a fatty acid metal salt having a weight loss rate of 20% by weight or more. The "weight loss rate" is measured as follows. Using a thermal analyzer (for example, a thermal analyzer manufactured by TA Instruments: TGA550), (for example, 4 mg) of fatty acid metal salt (B) is heated from room temperature (20°C) to 200°C at a rate of 200°C / min in air at atmospheric pressure, and the weight loss rate when held at 200°C for 60 minutes is defined as the "weight loss rate." For example, the weight of fatty acid metal salt (B) before heating is W ０ The fatty acid metal salt (B) was heated in air at atmospheric pressure from room temperature (20°C) to 200°C at a rate of 200°C / min and held at 200°C for 60 minutes, and its weight was determined as W １Then, the weight loss rate of the fatty acid metal salt (B) is (W ０ -W １ ) / W ０ × 100 (% by weight).

[0024] Specifically, the fatty acid metal salt (B) is magnesium stearate, aluminum stearate, or a combination thereof, each of which has a weight loss rate of 20% by weight or more. The upper limit of the weight loss rate of the fatty acid metal salt (B) is not particularly limited, but the weight loss rate of the fatty acid metal salt (B) is, for example, 20 to 80% by weight, 20 to 60% by weight, 20 to 55% by weight, 20 to 50% by weight, 22 to 55% by weight, 22 to 50% by weight, or 22.7 to 49.7% by weight. Alternatively, the weight loss rate of the fatty acid metal salt (B) is 22.7 to 49.5% by weight, or 25 to 50% by weight.

[0025] The content of the fatty acid metal salt (B) in the polyacetal resin composition is 0.1 to 0.9 parts by weight based on 100 parts by weight of the polyacetal resin (A). The content of the fatty acid metal salt (B) in the polyacetal resin composition may be 0.1 to 0.8 parts by weight, 0.1 to 0.6 parts by weight, 0.1 to 0.5 parts by weight, 0.1 to 0.3 parts by weight, 0.1 to 0.2 parts by weight, 0.12 to 0.8 parts by weight, 0.12 to 0.6 parts by weight, 0.12 to 0.5 parts by weight, 0.12 to 0.3 parts by weight, 0.12 to 0.2 parts by weight, 0.14 to 0.9 parts by weight, 0.14 to 0.8 parts by weight, 0.14 to 0.6 parts by weight, 0.14 to 0.5 parts by weight, 0.14 to 0.3 parts by weight, 0.14 to 0.2 parts by weight, or 0.15 to 0.5 parts by weight. Alternatively, the content of the fatty acid metal salt (B) in the polyacetal resin composition may be 0.5 to 0.9 parts by weight.

[0026] [Method for Producing Polyacetal Resin Composition] The method for producing the polyacetal resin composition of the present invention includes a step of melt-kneading the polyacetal resin (A) and the fatty acid metal salt (B) (melt-kneading step). The melt-kneading can be carried out using, for example, a Banbury mixer, a roll, a plastic extruder, a single-screw extruder, a twin-screw extruder, or a kneader.

[0027] The conditions of the melt-kneading step, such as temperature and pressure, may be appropriately selected in consideration of conventionally known methods for producing polyacetal resin compositions. For example, the melt-kneading step may be carried out at a temperature equal to or higher than the melting temperature of the polyacetal resin (A), and is usually preferably carried out at 180 to 240°C or 200 to 220°C.

[0028] The polyacetal resin composition may be prepared by melt-kneading the polyacetal resin (A) and the fatty acid metal salt (B) at once so that the final contents of the polyacetal resin (A) and the fatty acid metal salt (B) are as described above. Alternatively, the polyacetal resin composition may be prepared by first preparing a polyacetal resin composition containing a high concentration of the fatty acid metal salt (B), and then diluting the prepared polyacetal resin composition by melt-kneading it with another polyacetal resin (A).

[0029] [Metal Resin Composition] The metal resin composition of the present invention contains the polyacetal resin composition and metal powder (C). The metal resin composition is produced by melt-kneading the polyacetal resin composition and metal powder (C). The melt-kneading step is carried out at a temperature equal to or higher than the melting point of the polyacetal resin composition (generally 180°C or higher). The metal resin composition (kneaded body) may be in the form of a solid, powder, strand, or pellet.

[0030] The metal-resin composition has a fluidity of 9 g / 10 min or more, particularly 10 g / 10 min or more, measured at 190°C under a load of 10 kg in accordance with ASTM-D 1238. Preferably, the metal-resin composition has a fluidity of 10 to 800 g / 10 min, 10 to 700 g / 10 min, 10 to 600 g / 10 min, 10 to 500 g / 10 min, 10 to 400 g / 10 min, 10 to 300 g / 10 min, 10 to 200 g / 10 min, 10 to 100 g / 10 min, 10 to 90 g / 10 min, 10 to 80 g / 10 min, 10 to 70 g / 10 min, 10 to 60 g / 10 min, or 10 to 50 g / 10 min.

[0031] The bending strain (%) of the metal-resin composition is measured by preparing a molded piece of, for example, 12.7 mm × 63.5 mm × 3.2 mm thick, and performing a three-point bending test on the molded piece at a bending speed of 2 mm / min using an Autograph (registered trademark) AGS-X manufactured by Shimadzu Corporation, and determining the point at which the bending strength is maximum.

[0032] The metal-resin composition has a bending strain of 0.8% or more, particularly 1.0% or more, and preferably 1.0 to 12.0%, 1.0 to 10.0%, 1.0 to 9.0%, 1.0 to 8.5%, 1.0 to 8.0%, 1.0 to 7.0%, 1.0 to 6.0%, 1.0 to 5.0%, or 1.0 to 4.5%.

[0033] [Metal Powder (C)] The metal of the metal powder (C) is iron, aluminum, magnesium, cobalt, zinc, copper, nickel, titanium, tungsten, or a metal compound or metal alloy based on these. Preferably, the metal powder (C) is a powder of stainless steel (SUS), and the stainless steel is an austenitic stainless steel (SUS300 series), a ferritic or martensitic stainless steel (SUS400 series), or a precipitation-hardened stainless steel (SUS600 series). Precipitation-hardened stainless steel (SUS600 series) is particularly preferred. The particle size (average particle size) of the metal powder (C) is not particularly limited, but is 1 to 100 μm, 1 to 50 μm, 1 to 25 μm, or 1 to 10 μm, as measured by electron microscopy or laser diffraction / scattering particle size distribution measurement.

[0034] The content of the metal powder (C) in the metal-resin composition is 60 to 95 wt%, 65 to 95 wt%, 70 to 95 wt%, 80 to 95 wt%, 85 to 95 wt%, or 70 to 90 wt%, based on the weight of the metal-resin composition. In other words, the content of the polyacetal resin composition in the metal-resin composition is 5 to 40 wt%, 5 to 35 wt%, 5 to 30 wt%, 5 to 20 wt%, 5 to 15 wt%, or 10 to 30 wt%. Alternatively, the content of the metal powder (C) in the metal-resin composition is 60 wt% or more but less than 95 wt%, 65 wt% or more but less than 90 wt%, 70 wt% or more but less than 90 wt%, 60 to 85 wt%, 65 to 85 wt%, or 70 to 85 wt%, based on the weight of the metal-resin composition. Note that "● to ▲" represent a range from ● or more to ▲ or less. For example, 60 to 95% by weight means 60% by weight or more and 95% by weight or less.

[0035] [Method for producing powder injection molded article] The method for producing a powder injection molded article of the present invention includes a step of melt-kneading a metal powder (C) and a binder resin composition to obtain a kneaded body, and injecting the kneaded body into a mold, where the binder resin composition is the polyacetal resin composition. The production method may also include a step of removing the binder resin composition from the molded kneaded body in a degreasing furnace by heating the molded kneaded body or exposing it to a gaseous acid, and a step of sintering the molded body in a sintering furnace to form a powder injection molded article.

[0036] [Optional Components] Optional additives such as other stabilizers, nucleating agents, release agents, fillers, pigments, lubricants, plasticizers, UV absorbers, flame retardants, or flame retardant aids may be added to the polyacetal resin composition as needed, within the scope of the present invention. Examples of optional additives include glass fiber, glass flakes, glass beads, wollastonite, mica, talc, boron nitride, calcium carbonate, kaolin, silicon dioxide, clay, asbestos, silica, diatomaceous earth, graphite, molybdenum disulfide, glass fiber, middle fiber, potassium titanate fiber, boron fiber, carbon fiber, aramid fiber, potassium titanate whiskers, carbon black, and pigments.

[0037] In one embodiment, the polyacetal resin composition of the present invention further comprises, relative to 100 parts by weight of the polyacetal resin (A), 0.01 to 1.0 parts by weight, 0.01 to 0.7 parts by weight, 0.01 to 0.5 parts by weight, 0.01 to 0.3 parts by weight, 0.01 to 0.1 parts by weight, 0.1 to 0.5 parts by weight, or 0.1 to 0.3 parts by weight of one or more stabilizers. The stabilizer includes an antioxidant, a heat stabilizer, or a combination thereof. The antioxidant is triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], or a combination thereof, preferably triethylene glycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate]. The heat stabilizer is melamine, methylol melamine, alkylated melamine, benzoguanamine, a water-soluble melamine-formaldehyde resin, or a combination thereof, preferably melamine.

[0038] In one embodiment, the polyacetal resin composition of the present invention further comprises 0.01 to 1.0 parts by weight, 0.01 to 0.7 parts by weight, 0.01 to 0.5 parts by weight, 0.1 to 0.5 parts by weight, or 0.1 to 0.3 parts by weight of triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] and 0.01 to 1.0 parts by weight, 0.01 to 0.7 parts by weight, 0.01 to 0.5 parts by weight, 0.01 to 0.3 parts by weight, or 0.01 to 0.1 parts by weight of melamine.

[0039] An example of the present invention will be described below. The materials used in the example and comparative examples are shown below.

[0040] [Polyacetal Resin (A)] The polyacetal resin (A-1) used in the examples and comparative examples was an oxymethylene copolymer of trioxane and 1,3-dioxolane, and was prepared as follows: To 100 parts by weight of trioxane, 4.5 parts by weight of 1,3-dioxolane, a benzene solution (0.62 mol / kg-benzene) of boron trifluoride diethyl etherate as a catalyst in an amount of 0.06 mmol relative to 1 mol of total monomers, and a benzene solution (25 wt%) of methylal as a molecular weight modifier in an amount of 2,000 ppm relative to the total monomers were continuously added, and polymerization was continuously carried out in a twin-screw kneader equipped with self-cleaning paddles and having a jacket set at a temperature of 65°C, so that the residence time in the polymerization machine was 15 minutes. To the produced polymer, triphenylphosphine was added as a benzene solution (25 wt %) in an amount of 2 mol per 1 mol of the added boron trifluoride diethyl etherate, and after deactivating the catalyst, the polymer was pulverized to obtain polyacetal resin (A-1) (polyacetal resin 1).

[0041] The polyacetal resin (A-2) used in the examples was an oxymethylene copolymer of trioxane and 1,3-dioxolane, and was prepared as follows: To 100 parts by weight of trioxane, 4.0 parts by weight of 1,3-dioxolane, a benzene solution (0.62 mol / kg-benzene) of boron trifluoride diethyl etherate as a catalyst (0.06 mmol relative to 1 mol of total monomers), and a benzene solution (25 wt%) of methylal as a molecular weight modifier (2,500 ppm relative to total monomers) were continuously added, and polymerization was continuously carried out in a twin-screw kneader equipped with self-cleaning paddles and a jacket set at a temperature of 65°C, so that the residence time in the polymerization machine was 15 minutes. To the produced polymer, triphenylphosphine was added as a benzene solution (25 wt %) in an amount of 2 mol per 1 mol of the added boron trifluoride diethyl etherate, and after deactivating the catalyst, the polymer was pulverized to obtain polyacetal resin (A-2) (polyacetal resin 2).

[0042] The melt flow rates of the polyacetal resins (A-1) and (A-2) were determined as follows. To 100 parts by weight of polyacetal resins (A-1) and (A-2), 0.3 parts by weight of triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (manufactured by BASF, trade name IRGANOX (registered trademark) 245) as a stabilizer and 0.05 parts by weight of melamine (manufactured by Mitsui Chemicals, Inc.) were added and mixed, and the mixture was melt-kneaded in a kneader "Labo Plastomill (registered trademark) 4C150" manufactured by Toyo Seiki Seisaku-sho, Ltd. at a set temperature of 220°C and a rotation speed of 30 rpm for 20 minutes under a nitrogen gas flow (nitrogen flow rate 5000 mL / min). The mixture was crushed, and the flowability was measured using a melt indexer "L241" manufactured by Takara Kogyo Co., Ltd. at a temperature of 190°C and a load of 2.16 kg in accordance with ASTM-D1238. As a result of the measurement, the melt flow rate of polyacetal resin (A-1) was 45 g / 10 min, and the melt flow rate of polyacetal resin (A-2) was 88 g / 10 min.

[0043] [Fatty Acid Metal Salts (B)] Fatty acid metal salt (B-1) is magnesium stearate "IMN" manufactured by Dainichi Chemical Industry Co., Ltd. (Magnesium Stearate 1). The weight loss rate of (B-1) magnesium stearate 1 is 49.7% by weight. Fatty acid metal salt (B-2) is aluminum stearate "Aluminum Stearate 300" manufactured by NOF Corporation (Aluminum Stearate 1). The weight loss rate of (B-2) aluminum stearate 1 is 22.7% by weight. Fatty acid metal salt (B-3) is aluminum stearate "Aluminum Stearate 600" manufactured by NOF Corporation (Aluminum Stearate 2). The weight loss rate of (B-3) aluminum stearate 2 is 28.5% by weight. Fatty acid metal salt (B-4) is aluminum stearate "Aluminum Stearate 900" manufactured by NOF Corporation (Aluminum Stearate 3). The weight loss rate of (B-4) aluminum stearate 3 is 25.7% by weight. The fatty acid metal salt (B-5) is magnesium stearate "Magnesium Stearate" manufactured by NOF Corporation (Magnesium Stearate 2). The weight loss rate of (B-5) magnesium stearate 2 is 14.3% by weight. The fatty acid metal salt (B-6) is magnesium stearate "Magnesium Stearate GP" manufactured by NOF Corporation (Magnesium Stearate 3). The weight loss rate of (B-6) magnesium stearate 3 is 12.8% by weight. The fatty acid metal salt (B-7) is magnesium stearate "M" manufactured by Dainichi Chemical Industry Co., Ltd. (Magnesium Stearate 4). The weight loss rate of (B-7) magnesium stearate 4 is 12.4% by weight.

[0044] [Metal Powder (C)] Metal powder (C) is SUS630 powder (average particle size: approximately 10 μm) manufactured by Epson Atmix Corporation.

[0045] Example 1 As shown in Table 1, the polyacetal resin composition of Example 1 was prepared by adding 0.3 parts by weight of triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (manufactured by BASF, trade name IRGANOX® 245) as a stabilizer, 0.05 parts by weight of melamine (manufactured by Mitsui Chemicals, Inc.), and 0.15 parts by weight of magnesium stearate (B-1) to 100 parts by weight of polyacetal resin (A-1), and melt-kneading the mixture in a kneader "Labo Plastomill® 4C150" manufactured by Toyo Seiki Seisaku-sho, Ltd., at a set temperature of 220°C and a rotation speed of 30 rpm for 20 minutes under a nitrogen gas flow (nitrogen flow rate: 100 mL / min). The polyacetal resin composition was then crushed using a granulator "Gran Cutter® SPC-400" manufactured by Harmo Corporation. This was dried in an oven at 120° C. for 12 hours.

[0046] The metal resin composition of Example 1 was prepared by kneading 20 g of the polyacetal resin composition (10 wt % based on the weight of the metal resin composition) and 180 g of the metal powder (C) (90 wt %) in a kneader "Laboplastomill (registered trademark) 4C150" manufactured by Toyo Seiki Seisaku-sho, Ltd., at a set temperature of 180°C and a rotation speed of 60 rpm for 40 minutes under a nitrogen gas flow (nitrogen flow rate 5000 mL / min), followed by cooling and solidification. To measure the bending strain properties and flow properties, this kneaded body (metal resin composition) was crushed using a granulator "Grand Cutter (registered trademark) SPC-400" manufactured by Harmo Corporation.

[0047] As in Example 1, the polyacetal resin compositions of Examples 2 to 23 were prepared by melt-kneading the polyacetal resins (A-1, A-2) and the fatty acid metal salts (B-1 to B-4) shown in Table 1, respectively, using 0.3 parts by weight of triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (manufactured by BASF, trade name IRGANOX (registered trademark) 245) as stabilizers, 0.05 parts by weight of melamine (manufactured by Mitsui Chemicals, Inc.), and the types and amounts (parts by weight) of the fatty acid metal salts (B-1 to B-4).

[0048] The metal resin compositions of Examples 2 to 17 contained 20 g of the polyacetal resin composition (10 wt % based on the weight of the metal resin composition) and 180 g of the metal powder (C) (90 wt %), and were prepared in the same manner as in Example 1. The metal resin compositions of Examples 18 to 23 contained 60 g of the polyacetal resin composition (30 wt % based on the weight of the metal resin composition) and 140 g of the metal powder (C) (70 wt %), and were prepared in the same manner as in Example 1.

[0049] Comparative Examples 1 to 9 In the same manner as in Example 1, polyacetal resin compositions of Comparative Examples 1 to 9 were prepared using the polyacetal resin (A-1) shown in Table 2, 0.3 parts by weight of triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] (manufactured by BASF, trade name IRGANOX (registered trademark) 245) as stabilizers, 0.05 parts by weight of melamine (manufactured by Mitsui Chemicals, Inc.), and the types and amounts (parts by weight) of fatty acid metal salts (B-1, B-5 ​​to B-7).

[0050] The metal resin compositions of Comparative Examples 1 to 7 contained 20 g of the polyacetal resin composition (10 wt % based on the weight of the metal resin composition) and 180 g of the metal powder (C) (90 wt %), and were prepared in the same manner as in Example 1. The metal resin compositions of Comparative Examples 8 and 9 contained 60 g of the polyacetal resin composition (30 wt % based on the weight of the metal resin composition) and 140 g of the metal powder (C) (70 wt %), and were prepared in the same manner as in Example 1.

[0051] The weight loss rates of fatty acid metal salts B-1 to B-7 determined by thermogravimetric analysis, the color (b value) of the polyacetal resin composition, and the bending strain and fluidity properties of the metal resin composition were measured as follows.

[0052] [Measurement and Evaluation Methods] (1) Thermogravimetric Analysis of Fatty Acid Metal Salts The thermogravimetric analysis of fatty acid metal salts (B) was performed using a thermal analyzer, TGA550, manufactured by TA Instruments. 4 mg of a sample of fatty acid metal salt (B) was heated from room temperature (20°C) to 200°C at a rate of 200°C / min in air at atmospheric pressure, and the weight loss rate when the sample was held at 200°C for 60 minutes was recorded as the "weight loss rate." The weight loss rate was determined for each of the fatty acid metal salts (B-1 to B-7).

[0053] (2) Hue of Polyacetal Resin Composition The crushed polyacetal resin composition was molded into a plate using an Epson Techform "C,Mobile Model 0813" at a manifold temperature of 230°C and a body heater temperature of 220°C, and the plate was used to evaluate the hue. The hue was evaluated by measuring the L, a, and b values ​​using a Nippon Denshoku Industries color meter "SE6000," and the b value was taken as the hue value. A lower b value indicates less yellowness. In the present invention, a b value of 4.0 or less is considered to suppress yellowing and to have a good hue.

[0054] (3) Bending strain A molded piece measuring 12.7 mm x 63.5 mm x 3.2 mm thick was prepared from the crushed kneaded body (metal-resin composition) using a small desktop injection molding machine "HAAKE MiniJet" manufactured by Thermo Fisher Scientific Co., Ltd., at a cylinder temperature of 220 ° C. A three-point bending test was performed on the molded piece using an "Autograph (registered trademark) AGS-X" manufactured by Shimadzu Corporation, at a bending speed of 2 mm / min, and the point at which the bending strength was maximum was used as the bending strain (%). The bending strain value of the metal-resin composition is preferably 1.0% or more.

[0055] (4) Fluidity The fluidity of the crushed kneaded body (metal-resin composition) was measured at a temperature of 190°C and a load of 10 kg in accordance with ASTM-D1238 using a melt indexer "L241" manufactured by Takara Kogyo Co., Ltd. The fluidity value of the metal-resin composition is preferably 10 g / 10 min or more.

[0056]

[0057]

[0058] As shown in Tables 1 and 2, all of the polyacetal resin compositions of Examples 1 to 23 had b values ​​of 4.0 or less, and yellowing was suppressed and hue was improved. On the other hand, the b values ​​of Comparative Examples 1 to 9 exceeded 4.0, and no improvement in hue was observed.

[0059] In particular, the polyacetal resin compositions of Examples 1 to 15 and 18 to 21 had excellent hue with suppressed yellowing, and the metal resin compositions had favorable properties in both bending strain (1.0% or more) and fluidity (10 g / 10 min or more).

Claims

1. 100 parts by weight of polyacetal resin (A), 0.1 to 0.9 parts by weight of a fatty acid metal salt (B) having a weight reduction rate of 20% or more; Including, The weight loss rate of the polyacetal resin composition is the weight loss rate when the temperature is raised from room temperature to 200°C at 200°C / min in air at atmospheric pressure and the composition is kept at 200°C for 60 minutes.

2. 2. The polyacetal resin composition according to claim 1, wherein the fatty acid metal salt (B) is magnesium stearate having a weight reduction rate of 20% by weight or more, aluminum stearate having a weight reduction rate of 20% by weight or more, or a combination thereof.

3. 3. The polyacetal resin composition according to claim 1, wherein the polyacetal resin (A) has a melt flow rate of 40 to 100 g / 10 min (temperature: 190° C., load: 2.16 kg).

4. 3. The polyacetal resin composition according to claim 1, comprising 0.14 to 0.6 parts by weight of the fatty acid metal salt (B).

5. 3. The polyacetal resin composition according to claim 1, wherein the polyacetal resin (A) is a crude polyoxymethylene copolymer in which a polymerization catalyst has been deactivated after copolymerization but unstable terminal groups have not been stabilized.

6. 3. The polyacetal resin composition according to claim 1 or 2, further comprising 0.01 to 1.0 parts by weight of one or more stabilizers.

7. 3. The polyacetal resin composition according to claim 1 or 2, which is used by kneading with a metal powder.

8. The polyacetal resin composition according to claim 1 or 2, Metal powder (C); A metal-resin composition comprising:

9. A method for producing a polyacetal resin composition to be kneaded with a metal powder, comprising the steps of: The method includes a step of preparing the polyacetal resin composition by melt-kneading 100 parts by weight of a polyacetal resin (A) and 0.1 to 0.9 parts by weight of a fatty acid metal salt (B) having a weight reduction rate of 20% or more by weight, The weight loss rate is the weight loss rate when the temperature is increased from room temperature to 200° C. at 200° C. / min in air at atmospheric pressure and the sample is held at 200° C. for 60 minutes. The method for producing said fatty acid metal salt (B) is magnesium stearate having a weight reduction rate of 20% by weight or more, aluminum stearate having a weight reduction rate of 20% by weight or more, or a combination thereof.

10. A method for producing a powder injection molded product, comprising a step of melt-kneading a metal powder and a binder resin composition and injecting the resulting kneaded body into a mold, The above-mentioned production method, wherein the binder resin composition is the polyacetal resin composition according to claim 1 or 2.