Polyacetal resin composition

Abstract

To provide a polyacetal resin composition capable of reducing formaldehyde release from molded products, effectively preventing deterioration of physical properties under prolonged use in high-temperature drying or high-temperature humid conditions, and having excellent dimensional stability after injection molding.SOLUTION: A polyacetal resin composition contains, with respect to 100 pts.mass of (A) polyacetal resin, 0.03-0.60 pt.mass of (B) ethyleneurea, 0.05-0.50 pt.mass of (C) acrylamide polymer, and 0.0005-0.05 pt.mass of (D) ethylene bisstearamide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyacetal resin composition. [Background technology]

[0002] Polyacetal resin is a material with excellent rigidity, strength, toughness, sliding properties, and creep resistance. Its applications are wide-ranging, including as a resin material for various mechanical parts, such as automotive parts, electrical and electronic parts, and industrial parts.

[0003] Polyacetal resins decompose due to the action of heat, light, oxygen, acid, alkali, etc., generating formaldehyde. Particularly during manufacturing and molding, formaldehyde gas generated by thermal decomposition remains in the resin molded product, and further, formaldehyde is gradually released from the resin product, raising concerns that it could worsen the indoor environment. Particularly for use in automotive interior components, it is necessary to significantly reduce the amount of formaldehyde emitted from the molded product.

[0004] Various techniques have been proposed to suppress the release of formaldehyde from such polyacetal resin molded articles, such as adding hydrazide compounds, urea compounds, guanamine compounds, etc. as formaldehyde scavengers, and adding polyamide resins as heat stabilizers (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2016 / 126514 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-263921 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, the range of uses of polyacetal resins has expanded, and there has been a demand for them to maintain their mechanical strength when placed in various transport and use environments for long periods of time, for example, to suppress deterioration in physical properties when used for long periods of time under high-temperature, dry conditions or high-temperature, high-humidity conditions. Furthermore, as mechanical parts made of polyacetal resins become smaller and more precise, there is a demand for not only improved impact resistance of the mechanical parts but also dimensional stability after molding.

[0007] However, the molded articles of the polyacetal resin compositions proposed in the above-mentioned documents were not necessarily fully satisfactory in terms of suppressing formaldehyde release from the molded articles and suppressing deterioration of physical properties during long-term use under high-temperature dry conditions or high-temperature and high-humidity conditions.

[0008] Therefore, an object of the present invention is to provide a polyacetal resin composition that can suppress the amount of formaldehyde released from a molded article, can sufficiently suppress deterioration in physical properties when the molded article is used for a long period of time under high-temperature dry conditions or high-temperature and high humidity conditions, and has excellent dimensional stability after injection molding. [Means for solving the problem]

[0009] The present inventors have discovered that by adding ethylene urea and an acrylamide polymer as formaldehyde scavengers to a polyacetal resin and adding ethylene bisstearamide in a predetermined ratio relative to the acrylamide polymer, it is possible to suppress the amount of formaldehyde emitted from a molded article, to suppress the deterioration of physical properties when the molded article is used for an extended period under high-temperature dry conditions or high-temperature and high humidity conditions, and to obtain a polyacetal resin composition that has excellent dimensional shrinkage stability during injection molding, and have completed the present invention.

[0010] That is, the present invention is as follows. [1] (A) per 100 parts by mass of polyacetal resin, (B) 0.03 to 0.60 parts by mass of ethylene urea, (C) 0.05 to 0.50 parts by mass of an acrylamide polymer, and (D) A polyacetal resin composition containing 0.0005 to 0.05 parts by mass of ethylene bisstearic acid amide.

[0011] [2] The polyacetal resin composition according to [1], wherein the (A) polyacetal resin is a polyacetal homopolymer.

[0012] [3] The polyacetal resin composition according to [1] or [2], wherein the (A) polyacetal resin has a melt flow rate of 1.0 to 10.0 g / 10 min when measured in accordance with ISO 1133.

[0013] [4] The polyacetal resin composition according to [3], wherein the melt flow rate of the polyacetal resin (A) is 1.0 to 3.0 g / 10 min.

[0014] [5] The polyacetal resin composition according to any one of [1] to [3], wherein the molecular weight distribution of the polyacetal resin has a single peak.

[0015] [6] The polyacetal resin composition according to any one of [1] to [5], which contains 0.05 to 0.20 parts by mass of the acrylamide polymer (C).

[0016] [7] The polyacetal resin composition according to any one of [1] to [6], wherein the mass ratio of (D) ethylene bisstearic acid amide to (C) acrylamide polymer, (D) / (C), is 0.01 to 0.5. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a polyacetal resin composition that can suppress the amount of formaldehyde released from a molded article, and can sufficiently suppress the deterioration of physical properties when the molded article is used for a long period of time under high-temperature dry conditions or high-temperature and high humidity conditions, and that has excellent dimensional stability after injection molding. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the following description, and various modifications can be made within the scope of the gist thereof.

[0019] <Polyacetal resin composition> The polyacetal resin composition of the present embodiment comprises: (A) per 100 parts by mass of polyacetal resin (B) 0.03 to 0.60 parts by mass of ethylene urea, (C) 0.05 to 0.50 parts by mass of an acrylamide polymer, and (D) Contains 0.0005 to 0.05 parts by mass of ethylene bisstearic acid amide. The polyacetal resin composition can suppress the amount of formaldehyde emitted from a molded article produced from the polyacetal resin composition, sufficiently suppress deterioration in physical properties when used for a long period of time under high-temperature dry conditions or high-temperature and high humidity conditions, and also has excellent dimensional stability after injection molding.

[0020] <<(A) Polyacetal resin>> The polyacetal resin (A) contained in the polyacetal resin composition of the present embodiment refers to a polymer having an oxymethylene group in the main chain. Examples of the (A) polyacetal resin include polyacetal homopolymers consisting essentially of oxymethylene units, obtained by homopolymerizing formaldehyde monomer or cyclic oligomers of formaldehyde, such as its trimer (trioxane) or tetramer (tetraoxane); polyacetal copolymers obtained by copolymerizing formaldehyde monomer or cyclic oligomers of formaldehyde, such as its trimer (trioxane) or tetraoxane, with cyclic ethers or cyclic formals, such as ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane, and 1,4-butanediol formal, or cyclic formals of glycols or diglycols; branched polyacetal copolymers obtained by copolymerizing monofunctional glycidyl ethers; and polyacetal copolymers having a crosslinked structure obtained by copolymerizing polyfunctional glycidyl ethers.

[0021] Furthermore, examples of the polyacetal resin (A) that can be used include polyacetal homopolymers having block components obtained by polymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde, such as a formaldehyde monomer trimer (trioxane) or tetramer (tetraoxane), in the presence of a compound having functional groups such as hydroxyl groups at both or one end, for example, polyalkylene glycol; and polyacetal copolymers having block components obtained by copolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde, such as a formaldehyde monomer trimer (trioxane) or tetramer (tetraoxane), with a cyclic ether or a cyclic formal in the presence of a compound having functional groups such as hydroxyl groups at both or one end, for example, hydrogenated polybutadiene glycol. The polyacetal resins can be used singly or in combination of two or more.

[0022] Among these, the (A) polyacetal resin is preferably a polyacetal homopolymer from the viewpoint of improving mechanical strength, and more preferably a polyacetal homopolymer obtained by homopolymerizing formaldehyde monomer.

[0023] In addition, the degree of polymerization and comonomer content of the polyacetal resin (A) in this embodiment are not particularly limited.

[0024] From the viewpoint of exhibiting the excellent properties of the engineering resin, the content of the polyacetal resin is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, relative to 100% by mass of the polyacetal resin composition.

[0025] The polyacetal resin preferably has a melt flow rate (MFR value) of 1.0 to 10.0 g / 10 min when measured according to ISO 1133. The melt flow rate of the polyacetal resin is more preferably set to be in the range of 1.0 g / 10 min to 3.0 g / 10 min. By setting the MFR value of the polyacetal resin within the above range, a polyacetal composition can be obtained that is excellent in mechanical strength, can suppress deterioration of physical properties, and can suppress formaldehyde emission.

[0026] From the viewpoint of mechanical strength, the polyacetal resin has a number average molecular weight (Mn) of preferably 10,000 or more, more preferably 25,000 or more, and most preferably 30,000 to 150,000. The weight average molecular weight (Mw) of the polyacetal resin is preferably 30,000 or more, more preferably 100,000 or more, and most preferably 100,000 to 400,000.

[0027] The shape of the molecular weight distribution curve of the polyacetal resin of this embodiment is not particularly limited, but preferably has a single-peaked molecular weight distribution peak. From the viewpoint of improving mechanical strength, the molecular weight distribution curve has a single-peaked shape with a peak top at logM=4.5 to 8.0 (M is molecular weight), more preferably at logM=4.5 to 7.0, and even more preferably at logM=4.5 to 6.0. Here, "unimodal" refers to a shape having only one mountain-like peak. When low molecular weight components are contained, the molecular weight distribution curve in the region of molecular weights of 10,000 or less does not form a part of a mountain-shaped peak, but forms a shoulder to the peak top or a tailing connected to the peak top.

[0028] In this embodiment, the number average molecular weight (Mn), weight average molecular weight (Mw), and molecular weight distribution can be measured by gel permeation chromatography (GPC) using PMMA as a standard substance.

[0029] (Polyacetal homopolymer) The polyacetal resin is preferably a polyacetal homopolymer. The polyacetal homopolymer can be produced, for example, by feeding formaldehyde as a monomer, a chain transfer agent (molecular weight modifier), and a polymerization catalyst into a polymerization reactor containing a hydrocarbon polymerization solvent, and polymerizing them by a slurry polymerization method. In this case, the raw material monomers, chain transfer agent, and polymerization catalyst may contain chain-transferable components (components that generate unstable terminal groups), such as water, methanol, and formic acid, so it is preferable to first adjust the content of these chain-transferable components. The content of these chain-transferable components is preferably 1 to 1,000 ppm by mass, more preferably 1 to 500 ppm by mass, and even more preferably 1 to 300 ppm by mass, relative to the total mass of formaldehyde as a monomer. By adjusting the content of the chain-transferable components to fall within the above range, a polyacetal homopolymer with excellent thermal stability can be obtained.

[0030] The molecular weight of the polyacetal homopolymer can be adjusted by chain transfer using a molecular weight regulator such as a carboxylic acid anhydride or a carboxylic acid, etc. As the molecular weight regulator, propionic anhydride and acetic anhydride are particularly preferred, and acetic anhydride is more preferred. The amount of molecular weight modifier incorporated is adjusted and determined depending on the desired properties (particularly the melt flow rate) of the polyacetal homopolymer. For example, the polyacetal homopolymer is adjusted so that its melt flow rate (MFR value (measured in accordance with ISO 1133)) is preferably in the range of 0.1 to 100 g / 10 min, more preferably in the range of 1.0 g / 10 min to 10 g / 10 min, and even more preferably in the range of 1.0 g / 10 min to 3.0 g / 10 min. By adjusting the MFR value of the polyacetal homopolymer to fall within the above range, a polyacetal homopolymer with excellent mechanical strength can be obtained.

[0031] The polymerization catalyst is preferably an anionic polymerization catalyst, and more preferably an onium salt polymerization catalyst represented by the following general formula (I). [R1R2R3R4M] + X - (I) (In formula (I), R1, R2, R3, and R4 each independently represent an alkyl group, M represents an element having a lone electron pair, and X represents a nucleophilic group.) The polymerization catalyst may be used alone or in combination of two or more.

[0032] Among onium salt-based polymerization catalysts, quaternary phosphonium salt-based compounds such as tetraethylphosphonium iodide and tributylethylphosphonium iodide, and quaternary ammonium salt-based compounds such as tetramethylammonium bromide and dimethyldistearylammonium acetate are preferred.

[0033] The amount of onium salt polymerization catalyst such as a quaternary phosphonium salt compound or a quaternary ammonium salt compound added is preferably 0.0003 to 0.01 mol, more preferably 0.0008 to 0.005 mol, and even more preferably 0.001 to 0.003 mol, per 1 mol of formaldehyde.

[0034] The hydrocarbon polymerization solvent is not particularly limited as long as it does not react with formaldehyde, but examples thereof include pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, benzene, etc., with hexane being particularly preferred. These hydrocarbon solvents may be used alone or in combination of two or more.

[0035] In producing the polyacetal homopolymer, it is preferable to first obtain a crude polyacetal homopolymer by polymerization, and then, as described below, subject the unstable terminal groups to a stabilization treatment.

[0036] The polymerization reactor for producing the crude polyacetal homopolymer is not particularly limited as long as it is an apparatus that can simultaneously supply formaldehyde as a monomer, a chain transfer agent (molecular weight regulator), a polymerization catalyst, and a hydrocarbon polymerization solvent. From the viewpoint of productivity, however, it is preferably a continuous polymerization reactor.

[0037] The terminal groups of the crude polyacetal homopolymer obtained by polymerization are thermally unstable, and therefore it is preferable to subject the unstable terminal groups to stabilization treatment by blocking them with an esterifying agent, an etherifying agent, or the like.

[0038] The stabilization treatment of the terminal groups of a crude polyacetal homopolymer by esterification can be carried out, for example, by charging the crude polyacetal homopolymer, an esterifying agent, and an esterification catalyst into a terminal stabilization reactor containing a hydrocarbon solvent and reacting them. The reaction temperature and reaction time are, for example, preferably 130 to 155°C and 1 to 100 minutes, more preferably 135 to 155°C and 5 to 100 minutes, and even more preferably 140 to 155°C and 10 to 100 minutes.

[0039] As the esterifying agent for blocking and stabilizing the terminal groups of the crude polyacetal homopolymer, an acid anhydride represented by the following general formula (II) can be used. R5COOCOR6···(II) (In formula (II), R5 and R6 each independently represent an alkyl group. R5 and R6 may be the same or different.)

[0040] Examples of the esterifying agent include, but are not limited to, benzoic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, propionic anhydride, and acetic anhydride, and acetic anhydride is preferred. These esterifying agents may be used alone or in combination of two or more.

[0041] The esterification catalyst is preferably an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms, and the amount added can be appropriately selected from the range of 1 to 1,000 ppm by mass relative to the mass of the polyacetal homopolymer. Examples of alkali metal salts of a carboxylic acid having 1 to 18 carbon atoms include, but are not limited to, alkali metal salts of carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of the alkali metal salts include lithium, sodium, potassium, rubidium, and cesium. Among these alkali metal salts of carboxylic acids, lithium acetate, sodium acetate, and potassium acetate are preferred.

[0042] The etherifying agent used to cap and stabilize the end groups of the crude polyacetal homopolymer may be selected from orthoesters of aliphatic or aromatic acids and aliphatic, alicyclic, or aromatic alcohols, such as methyl orthoformate or ethyl orthoformate, methyl orthoacetate or ethyl orthoacetate, methyl orthobenzoate or ethyl orthobenzoate, and orthocarbonates, specifically ethyl orthocarbonate, and may be stabilized using a medium-strength organic acid such as p-toluenesulfonic acid, acetic acid, or oxalic acid.

[0043] When the end groups of the crude polyacetal homopolymer are blocked and stabilized by etherification, examples of the solvent used in the etherification reaction include, but are not limited to, low-boiling aliphatic hydrocarbons such as pentane and hexane, alicyclic and aromatic hydrocarbons such as cyclohexane and benzene, and halogenated lower aliphatic organic solvents such as dichloromethane, chloroform, and carbon tetrachloride.

[0044] The polyacetal homopolymer whose end groups have been stabilized by the above method is dried using a dryer such as a hot air dryer or a vacuum dryer, with air or nitrogen gas adjusted to 100 to 150°C enclosed to remove moisture, thereby obtaining a polyacetal homopolymer as (A) polyacetal resin.

[0045] (Polyacetal copolymer) First, the materials used in the production of the polyacetal copolymer, specifically, trioxane, cyclic ether and / or cyclic formal, polymerization catalyst, low-molecular-weight acetal compound, and organic solvent will be described.

[0046] -Trioxane- Trioxane is a cyclic trimer of formaldehyde, and is generally obtained by reacting an aqueous solution of formalin in the presence of an acid catalyst. This trioxane may contain impurities that cause chain transfer, such as water, methanol, formic acid, and methyl formate, and is therefore preferably purified by removing these impurities, for example, by distillation. In this case, the total amount of impurities that cause chain transfer is preferably 1 × 10 per 1 mol of trioxane. -3 It is preferable to set the concentration to 0.5×10 mol or less. -3 By reducing the total amount of impurities to the above upper limit or less, the polymerization reaction rate can be increased sufficiently for practical use, and the produced polymer can have excellent thermal stability.

[0047] -Cyclic ether and / or cyclic formal- The cyclic ether and / or cyclic formal are components copolymerizable with the trioxane, and examples thereof include ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxatane, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, and 1,6-hexanediol formal. Among these, 1,3-dioxolane and 1,4-butanediol formal are preferred as the cyclic ether and / or cyclic formal. These may be used alone or in combination of two or more.

[0048] The amount of the cyclic ether and / or cyclic formal added is preferably in the range of 1 to 20 mol % relative to 1 mol of the trioxane, more preferably in the range of 1 to 15 mol %, even more preferably in the range of 1 to 10 mol %, and still more preferably in the range of 1 to 5 mol %.

[0049] -Polymerization catalyst- Examples of polymerization catalysts include Lewis acids such as metal halides and Bronsted acids such as heteropolyacids. Examples of Lewis acids include boric acid, tin, titanium, phosphorus, arsenic, and antimony halides. Particularly preferred are boron trifluoride, boron trifluoride hydrates, and coordination complexes of boron trifluoride with organic compounds containing oxygen or sulfur atoms. Examples of suitable compounds include boron trifluoride, boron trifluoride diethyl etherate, and boron trifluoride-di-n-butyl etherate. Examples of heteropolyacids include phosphomolybdic acid, phosphotungstic acid, phosphomolybdotungstic acid, phosphomolybdovanadic acid, phosphomolybdotungstovanadic acid, phosphotungstovanadic acid, silicotungstic acid, silicomolybdic acid, silicomolybdotungstic acid, and silicomolybdotungstovanadic acid. These may be used alone or in combination of two or more.

[0050] The amount of polymerization catalyst added was 0.1 × 10 per 1 mol of trioxane. -5 ~0.1×10 -3 The preferred range is 0.3 × 10 -5 ~0.3×10 -4 The mol range is more preferable, 0.5 x 10 -5 ~0.15×10 -4 When the amount of the polymerization catalyst added is within the above range, the polymerization reaction can be carried out stably for a long period of time.

[0051] -Low molecular weight acetal compounds- The low-molecular-weight acetal compound functions as a chain transfer agent in the polymerization reaction and is an acetal compound having a molecular weight of 200 or less, preferably 60 to 170. Specific preferred examples include methylal, methoxymethylal, dimethoxymethylal, and trimethoxymethylal. These may be used alone or in combination of two or more.

[0052] The amount of the low-molecular-weight acetal compound added is 0.1×10 per 1 mol of the trioxane, from the viewpoint of controlling the molecular weight of the polymer within a suitable range. -4 ~0.6×10 -2 The molar range is preferred.

[0053] -Organic solvents- The organic solvent is not particularly limited as long as it does not participate in or adversely affect the polymerization reaction. Examples include aromatic hydrocarbons such as benzene (boiling point 80°C), toluene (boiling point 110.63°C), and xylene (boiling point 144°C); aliphatic hydrocarbons such as n-hexane (boiling point 69°C), n-heptane (boiling point 98°C), and cyclohexane (boiling point 80.74°C); halogenated hydrocarbons such as chloroform (boiling point 61.2°C), dichloromethane (boiling point 40°C), and carbon tetrachloride (boiling point 76.8°C); and ethers such as diethyl ether (boiling point 35°C), diethylene glycol dimethyl ether (boiling point 162°C), and 1,4-dioxane (boiling point 101.1°C). In particular, aliphatic hydrocarbons such as n-hexane, n-heptane, and cyclohexane are preferred from the viewpoint of suppressing tar-like deposits. These organic solvents may be used alone or in combination.

[0054] The amount of organic solvent added was 0.1 x 10 per 1 mol of trioxane. -3 The range of 0.2 mol to 0.2 × 10 -3 ~0.5×10 -1 The mol range is more preferable, 0.5 x 10 -3 ~0.3×10 -1 When the amount of the organic solvent added is within the above range, a polyacetal copolymer with excellent productivity can be obtained.

[0055] -Polymerization of polyacetal copolymer- The polymerization method for the polyacetal copolymer is not particularly limited, and examples thereof include the slurry polymerization method described above for the production of the polyacetal homopolymer, as well as bulk polymerization and melt polymerization. In addition, the polymerization of the polyacetal copolymer can be carried out by either a batch system or a continuous system.

[0056] The polymerization reactor is not particularly limited, and examples thereof include self-cleaning extrusion kneaders such as a co-kneader, a twin-screw continuous extrusion kneader, and a twin-screw paddle continuous mixer. These devices preferably have a jacket through which a heat transfer medium can pass.

[0057] After each material is fed into the polymerization reactor, the temperature of the polymerization reactor during the polymerization reaction is preferably maintained at 63 to 135°C, more preferably in the range of 70 to 120°C, and even more preferably in the range of 70 to 100°C. The residence (reaction) time in the polymerization reactor is preferably 0.1 to 30 minutes, more preferably 0.1 to 25 minutes, and even more preferably 0.1 to 20 minutes. If the temperature and residence time of the polymerization reactor are within the above ranges, the polymerization reaction tends to continue stably.

[0058] A crude polyacetal copolymer is then obtained by the polymerization reaction. Here, a method for deactivating the polymerization catalyst includes introducing the crude polyacetal copolymer discharged from the polymerization reactor into an aqueous or organic solution containing at least one neutralizing deactivator, such as ammonia, amines (e.g., triethylamine, tri-n-butylamine), alkali metal or alkaline earth metal hydroxides, inorganic salts, or organic acid salts, and continuously stirring the resulting slurry for several minutes to several hours at room temperature to 100°C or lower. In this case, if the crude polyacetal copolymer is in the form of large blocks, it is preferably crushed and treated after polymerization. The resulting mixture is then filtered using a centrifuge and dried under nitrogen to obtain the polyacetal copolymer.

[0059] The resulting polyacetal copolymer may contain thermally unstable terminal groups [—(OCH)—OH groups] (hereinafter, such polyacetal copolymers may be referred to as “polyacetal copolymers before terminal stabilization”). Therefore, it is preferable to perform a process for decomposing and removing these thermally unstable terminal groups (terminal stabilization) using a terminal stabilizing agent. The terminal stabilizing agent is not particularly limited, and examples thereof include basic substances such as aliphatic amine compounds such as ammonia, triethylamine, and tributylamine; inorganic weak acid salts of alkali metals or alkaline earth metals such as hydroxides, carbonates, phosphates, silicates, and borates of alkali metals or alkaline earth metals such as sodium, potassium, magnesium, calcium, and barium; and organic acid salts of alkali metals or alkaline earth metals such as formates, acetates, stearates, palmitates, propionates, and oxalates. Among these, aliphatic amine compounds are preferred, and triethylamine is more preferred.

[0060] The method for decomposing and removing unstable terminals is not particularly limited, and examples thereof include a method in which the polyacetal copolymer is heat-treated in a molten state in the presence of a terminal stabilizer such as triethylamine at a temperature of not less than the melting point of the polyacetal copolymer but not more than 260° C. The heat-treatment apparatus may be, for example, a single-screw or twin-screw extruder equipped with a vent pressure reduction device, and a twin-screw extruder is preferred.

[0061] The polyacetal copolymer whose terminals have been stabilized by the above method is dried using a dryer such as a hot air dryer or a vacuum dryer, with air or nitrogen gas adjusted to 100 to 150°C enclosed inside, to remove moisture and thereby obtain a polyacetal copolymer as (A) polyacetal resin.

[0062] <<(B) Ethyleneurea>> The (B) ethylene urea contained in the polyacetal resin composition of the present embodiment functions as a formaldehyde scavenger. The method for producing the ethylene urea (B) contained in the polyacetal resin composition of the present embodiment is not particularly limited, and known methods can be used, such as a method of reacting ethylenediamine with carbon dioxide gas, a method of reacting ethylenediamine with urea, a method of reacting ethylenediamine with phosgene, a method of reacting ethylenediamine with dialkyl carbonate, or a method of oxidizing ethylenethiourea.

[0063] The ethylene urea of ​​this embodiment may contain raw materials, intermediates, or solvents as impurities. For example, it may contain ethylenediamine, urea, dialkyl carbonate, 2-aminoethylcarbamic acid, 2-aminoethylcarbamido ester, 2-aminoethylurea, etc. The amount of impurities is preferably less than 10 wt % relative to the weight of the ethylene urea, more preferably less than 5 wt %, and even more preferably less than 1 wt %.

[0064] The content of (B) ethylene urea in this embodiment is 0.03 to 0.60 parts by mass relative to 100 parts by mass of the polyacetal resin. This makes it possible to suppress the amount of formaldehyde released from a molded article obtained from the polyacetal resin composition of this embodiment, to suppress a decrease in mechanical strength during long-term use under high temperature and humidity conditions, and to suppress the formation of mold deposits during molding. From the same viewpoint, the content of (B) ethylene urea is more preferably 0.03 to 0.40 parts by mass, and particularly preferably 0.05 to 0.20 parts by mass.

[0065] <<(C) Acrylamide polymer>> The acrylamide polymer (C) contained in the polyacetal resin composition of the present embodiment functions as a formaldehyde scavenger. (C) The acrylamide polymer can be produced, for example, by homopolymerizing acrylamide or copolymerizing acrylamide with a vinyl group-containing monomer other than acrylamide using an alcoholate of an alkaline earth metal as a catalyst. By using a copolymer of acrylamide and a monomer having a vinyl group (for example, a copolymer having a crosslinked structure) as the (C) acrylamide polymer, the moldability of the polyacetal resin composition can be improved. The (C) acrylamide polymer may be used alone or in combination of two or more.

[0066] The vinyl group-containing monomer other than acrylamide may be a monomer having one or two vinyl groups. Examples of monomers having one vinyl group include n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, cecil methacrylate, pentadecyl methacrylate, stearyl methacrylate, behenyl methacrylate, hydroxypropyl methacrylate, polypropylene glycol methacrylate, and polyethylene glycol methacrylate. Examples of the monomer having two vinyl groups include divinylbenzene, ethylenebisacrylamide, and N,N'-methylenebisacrylamide. Among these vinyl group-containing monomers, N,N'-methylenebisacrylamide is preferred.

[0067] When producing the acrylamide polymer, the amount of the vinyl group-containing monomer added is preferably 0.05 to 20% by mass relative to the total amount of the acrylamide and the vinyl group-containing monomer.

[0068] The (C) acrylamide polymer may be a copolymer having a primary amide group and a secondary amide group. The molar content of primary amide groups in the (C) acrylamide polymer is preferably 30 to 80 mol %, more preferably 30 to 70 mol %, and even more preferably 40 to 70 mol %. If the primary amide groups are in the above range, it is possible to provide a polyacetal resin composition having excellent acrylamide polymer grindability and excellent moldability. The method for measuring primary amide groups is not particularly limited, but the following method can be used, for example: First, a sample polymer and 40% by mass aqueous potassium hydroxide solution are placed in a flask equipped with a stirrer, and the mixture is heated to 105-110°C for 20 minutes while stirring to hydrolyze the primary amide groups to ammonia. Next, the contents of the flask are cooled to below 50°C, and methanol is added to extract the ammonia together with the methanol. The extract is absorbed in a 0.1 N aqueous sulfuric acid solution, and neutralization titration is performed with a 0.1 N aqueous sodium hydroxide solution using methyl red as an indicator to determine the amount of primary amide groups.

[0069] The average particle size of the acrylamide polymer (C) is preferably 0.1 to 20 μm, more preferably 0.1 to 15 μm, and even more preferably 0.1 to 10 μm. When the average particle size of the acrylamide polymer is within the above range, a polyacetal resin composition having excellent moldability can be provided. The average particle size is a value measured by a laser diffraction particle size distribution measuring device.

[0070] The content of the acrylamide polymer (C) in this embodiment is 0.05 to 0.50 parts by mass relative to 100 parts by mass of the polyacetal resin (A). This allows for a polyacetal resin composition with excellent moldability and thermal stability to be obtained. From the same viewpoint, the content of the acrylamide polymer (C) is preferably 0.05 to 0.40 parts by mass, more preferably 0.05 to 0.20 parts by mass, relative to 100 parts by mass of the polyacetal resin (A).

[0071] <<(D) Ethylenebisstearamide>> The method for producing the ethylene bisstearamide (D) contained in the polyacetal resin composition of the present embodiment is not particularly limited, and any known method can be used, such as a method of reacting stearic acid with ethylenediamine. The content of (D) ethylene bisstearamide in this embodiment is 0.0005 to 0.05 parts by mass relative to 100 parts by mass of the polyacetal resin. This makes it possible to obtain a polyacetal resin composition with excellent moldability, and to suppress a decrease in mechanical strength of a molded article obtained from the polyacetal resin composition of this embodiment when used for a long period of time under high temperature and humidity. From the same viewpoint, the content of (D) ethylene bisstearamide is preferably 0.00051 to 0.03 parts by mass, more preferably 0.001 to 0.03 parts by mass, and particularly preferably 0.003 to 0.02 parts by mass relative to 100 parts by mass of the polyacetal resin. Similarly, from the viewpoint of suppressing a decrease in the mechanical strength of a molded article obtained from the polyacetal resin composition of this embodiment during long-term use under high temperature and high humidity conditions, the content of (D) ethylene bisstearic acid amide is preferably 0.00051 to 0.009 parts by mass, more preferably 0.001 to 0.009 parts by mass, and even more preferably 0.001 to 0.007 parts by mass, relative to 100 parts by mass of the polyacetal resin. The mass ratio (D) / (C) of the ethylene bisstearic acid amide (D) to the acrylamide polymer (C) is preferably in the range of 0.01 to 0.5, more preferably in the range of 0.01 to 0.3, and particularly preferably in the range of 0.03 to 0.1. When the mass ratio (D) / (C) is in the above-mentioned range, a molded article obtained from the polyacetal resin composition can be more effectively prevented from decreasing in mechanical strength during long-term use under high-temperature dry conditions and high-temperature and high-humidity conditions, which is preferable.

[0072] <<(E) Other additives>> The polyacetal resin composition of the present invention may contain known additives ((E) other additives) in addition to the above-mentioned components (A) to (D). Examples of (E) other additives include antioxidants, heat stabilizers, formic acid scavengers, weathering stabilizers, mold release agents, lubricants, conductive agents, thermoplastic resins, thermoplastic elastomers, inorganic fillers, organic fillers, pigments, and dyes. These additives may be used alone or in combination of two or more.

[0073] The antioxidant is preferably a hindered phenol-based antioxidant. Examples of the hindered phenol antioxidant include n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)-propionate, n-octadecyl-3-(3'-methyl-5'-t-butyl-4'-hydroxyphenyl)-propionate, n-tetradecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)-propionate, 1,6-hexanediol-bis-[3-(3,5-di Examples of suitable hydroxybenzoates include 1,4-butanediol-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,4-butanediol-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], and pentaerythritol tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]. Among these, triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] and pentaerythritol tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate] are preferred. These antioxidants may be used alone or in combination of two or more.

[0074] Examples of the heat stabilizer include amino-substituted triazine compounds, adducts of amino-substituted triazine compounds and formaldehyde, condensates of amino-substituted triazine compounds and formaldehyde, urea, urea derivatives, hydrazine derivatives, amide compounds, and polyamides.

[0075] Examples of the amino-substituted triazine compound include, but are not limited to, 2,4-diamino-sym-triazine, 2,4,6-triamino-sym-triazine, N-butylmelamine, N-phenylmelamine, N,N-diphenylmelamine, N,N-diallylmelamine, benzoguanamine (2,4-diamino-6-phenyl-sym-triazine), acetoguanamine (2,4-diamino-6-methyl-sym-triazine), and 2,4-diamino-6-butyl-sym-triazine.

[0076] Examples of the urea derivative include, but are not limited to, N-substituted urea, urea condensates, hydantoin compounds, ureido compounds, etc. In the present invention, the urea derivative does not include ethylene urea. Examples of the N-substituted urea include, but are not limited to, methylurea, alkylenebisurea, and aryl-substituted urea having a substituent such as an alkyl group. Examples of the urea condensate include, but are not limited to, a condensate of urea and formaldehyde. Examples of the hydantoin compound include, but are not limited to, hydantoin, 5,5-dimethylhydantoin, and 5,5-diphenylhydantoin. Examples of the ureido compound include, but are not limited to, allantoin.

[0077] The hydrazine derivatives include, but are not limited to, hydrazide compounds. Examples of hydrazide compounds include carboxylic acid monohydrazide compounds, carboxylic acid dihydrazide compounds, alkyl group-substituted monohydrazide compounds, and alkyl group-substituted dihydrazide compounds, which are synthesized by reacting a carboxylic acid (including aromatic or alicyclic) with hydrazine. The carboxylic acid may be a monocarboxylic acid, a dicarboxylic acid, or a compound having three or more carboxylic acids (a polycarboxylic acid). Examples of monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, behenic acid, benzoic acid, salicylic acid, gallic acid, cinnamic acid, pyruvic acid, lactic acid, and amino acids. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, naphthalic acid, malic acid, fumaric acid, maleic acid, tartaric acid, and nitrocarboxylic acid. Examples of polycarboxylic acids include mellitic acid, citric acid, and aconitic acid. Examples of unsaturated carboxylic acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, docosahexaenoic acid, and eicosapentaenoic acid.Examples of carboxylic acid mono(di)hydrazide compounds synthesized using these carboxylic acids include carbodihydrazide, oxalic acid mono(di)hydrazide, malonic acid mono(di)hydrazide, succinic acid mono(di)hydrazide, glutaric acid mono(di)hydrazide, adipic acid mono(di)hydrazide, pimelic acid mono(di)hydrazide, suberic acid mono(di)hydrazide, azelaic acid mono(di)hydrazide, sebacic acid mono(di)hydrazide, phthalic acid mono(di)hydrazide, isophthalic acid mono(di)hydrazide, and terephthalic acid mono(di)hydrazide. , 2,6-naphthalic acid mono(di)hydrazide, malic acid mono(di)hydrazide, fumaric acid mono(di)hydrazide, maleic acid mono(di)hydrazide, tartaric acid mono(di)hydrazide, propionic acid monohydrazide, lauric acid monohydrazide, stearic acid monohydrazide, p-hydroxybenzhydrazide, 1,4-cyclohexanedicarboxylic acid dihydrazide, acetohydrazide, acrylohydrazide, benzohydrazide, nicotinohydrazide, isonicotinohydrazide, isobutylhydrazide, oleic acid hydrazide, etc. Among these, preferred hydrazide compounds are adipic acid mono(di)hydrazide, sebacic acid mono(di)hydrazide, and lauric acid monohydrazide. The term "mono(di)hydrazide" means that one or both of the two carboxylic acids are hydrazide.

[0078] Examples of the amide compound include, but are not limited to, polycarboxylic acid amides such as isophthalic acid diamide, and anthranilamide. Note that the amide compound does not include acrylamide polymers and ethylene bisstearic acid amide.

[0079] Examples of the polyamide include polyamide resins such as nylon (registered trademark) 4-6, nylon 6, nylon 6-6 (polyamide 66), nylon 6-10, nylon 6-12, and nylon 12, and polymers thereof such as nylon 6 / 6-6 / 6-10 and nylon 6 / 6-12.

[0080] Examples of the formic acid scavenger include, but are not limited to, hydroxides, inorganic acid salts, carboxylates, and alkoxides of alkali metals or alkaline earth metals, such as hydroxides of sodium, potassium, magnesium, calcium, and barium; carbonates, phosphates, silicates, borates, and carboxylates of the above metals, and layered double hydroxides. The formic acid scavenger may be used alone or in combination of two or more.

[0081] The carboxylic acid of the carboxylate is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, and these carboxylic acids may be substituted with a hydroxyl group. Examples of saturated or unsaturated aliphatic carboxylic acid salts include, but are not limited to, calcium dimyristate, calcium dipalmitate, calcium distearate, calcium (myristate-palmitate), calcium (myristate-stearate), calcium (palmitate-stearate), and calcium 12-hydroxystearate, and among these, calcium dipalmitate, calcium distearate, and calcium 12-hydroxystearate are preferred.

[0082] The weather resistance stabilizer is not limited to the following, but preferred examples include at least one selected from the group consisting of benzotriazole-based compounds, oxalic acid anilide-based compounds, and hindered amine-based light stabilizers. Examples of the benzotriazole-based compound include, but are not limited to, 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole, 2-(2'-hydroxy-3,5-di-t-butyl-phenyl)benzotriazole, 2-[2'-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2'-hydroxy-3,5-di-t-amylphenyl]benzotriazole, 2-(2'-hydroxy-3,5-di-isoamyl-phenyl)benzotriazole, 2-[2'-hydroxy-3,5-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole. Each of these compounds may be used alone, or two or more may be used in combination.

[0083] Examples of the oxalic acid anilide compound include, but are not limited to, 2-ethoxy-2'-ethyloxalic acid bisanilide, 2-ethoxy-5-t-butyl-2'-ethyloxalic acid bisanilide, 2-ethoxy-3'-dodecyloxalic acid bisanilide, etc. These compounds may be used alone or in combination of two or more.

[0084] Examples of the hindered amine light stabilizer include, but are not limited to, 4-acetoxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(phenylacetoxy)-2,2,6,6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 4-methoxy-2,2,6,6-tetramethylpiperidine, and 4-stearyloxy-2,2,6,6-tetramethylpiperidine. peridine, 4-cyclohexyloxy-2,2,6,6-tetramethylpiperidine, 4-benzyloxy-2,2,6,6-tetramethylpiperidine, 4-phenoxy-2,2,6,6-tetramethylpiperidine, 4-(ethylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, 4-(cyclohexylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, 4-(phenylcarbamoyloxy)-2,2,6,6-tetramethylpiperidine, bis(2,2,6,6-tetramethyl-4-piperidyl)-carbonate, bis (2,2,6,6-tetramethyl-4-piperidyl)-oxalate, bis(2,2,6,6-tetramethyl-4-piperidyl)-malonate, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)-sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)-adipate, bis(2,2,6,6-tetramethyl-4-piperidyl)-terephthalate, 1,2-bis( 2,2,6,6-tetramethyl-4-piperidyloxy)-ethane, α,α'-bis(2,2,6,6-tetramethyl-4-piperidyloxy)-p-xylene, bis(2,2,6,6-tetramethyl-4-piperidyltolylene-2,4-dicarbamate, bis(2,2,6,6-tetramethyl-4-piperidyl)-hexamethylene-1,6-dicarbamate, tris(2,2,6,6-tetramethyl-4-piperidyl)-benzene-1,3,5-tricarboxylate, tris(2,2,6,6-tetramethyl-4-piperidyl)-benzene-1,3,4-tricarboxylate, 1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}butyl]-4-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]2,2,6,6-tetramethylpiperidine, and a condensate of 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol, and β,β,β',β'-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol. The above hindered amine light stabilizers may be used alone or in combination of two or more.

[0085] Among the above, preferred weather resistance stabilizers are 2-[2'-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2'-hydroxy-3,5-di-t-butylphenyl)benzotriazole, 2-(2'-hydroxy-3,5-di-t-amylphenyl)benzotriazole, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate, bis-(N -methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate, condensation product of 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β',β',-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol.

[0086] The release agent and the lubricant are not limited to the following, but preferred examples include alcohols, fatty acids and their fatty acid esters, olefin compounds having an average degree of polymerization of 10 to 500, and silicones. The release agent and the lubricant may be used alone or in combination of two or more.

[0087] The conductive agent may be, but is not limited to, conductive carbon black, metal powder, or fiber. One type of conductive agent may be used alone, or two or more types may be used in combination.

[0088] Examples of the thermoplastic resin include, but are not limited to, polyolefin resin, acrylic resin, styrene resin, polycarbonate resin, and uncured epoxy resin. One type of thermoplastic resin may be used alone, or two or more types may be used in combination.

[0089] Examples of the thermoplastic elastomer include, but are not limited to, polyurethane elastomers, polyester elastomers, polystyrene elastomers, and polyamide elastomers. One type of thermoplastic elastomer may be used alone, or two or more types may be used in combination.

[0090] Examples of the dyes and pigments include, but are not limited to, inorganic pigments, organic pigments, metallic pigments, fluorescent pigments, and the like.

[0091] The inorganic pigments refer to those generally used for coloring resins, and include, but are not limited to, zinc sulfide, titanium oxide, barium sulfate, titanium yellow, cobalt blue, combustion pigments, carbonates, phosphates, acetates, carbon black, acetylene black, and the like.

[0092] Examples of the organic pigments include, but are not limited to, condensed azo, quinone, monoazo, diazo, polyazo, anthraquinone, heterocyclic, pennone, quinacridone, thioindigo, perylene, dioxazine, and phthalocyanine pigments.

[0093] The dyes and pigments may be used singly or in combination of two or more. The proportion of the dyes and pigments added varies greatly depending on the color tone, making it difficult to specify, but they are generally used in the range of 0.05 to 5 parts by mass per 100 parts by mass of the polyacetal resin.

[0094] Resins other than the thermoplastic resins are not particularly limited, but examples thereof include polyolefin resins, acrylic resins, styrene resins, polycarbonate resins, and uncured epoxy resins. The resins other than the thermoplastic resin may be used singly or in combination of two or more.

[0095] The inorganic filler may be, but is not limited to, a fibrous, powdery, plate-like or hollow filler. Examples of the fibrous filler include, but are not limited to, inorganic fibers such as glass fibers, carbon fibers, silicone fibers, silica-alumina fibers, zirconia fibers, boron nitride fibers, silicon nitride fibers, boron fibers, potassium titanate fibers, and metal fibers such as stainless steel, aluminum, titanium, copper, brass, etc. Also included are short whiskers such as potassium titanate whiskers and zinc oxide whiskers. Examples of the powdery particulate filler include, but are not limited to, silicates such as talc, carbon black, silica, quartz powder, glass beads, glass powder, calcium silicate, magnesium silicate, aluminum silicate, kaolin, clay, diatomaceous earth, and wollastonite; metal oxides such as iron oxide, titanium oxide, and alumina; metal sulfates such as calcium sulfate and barium sulfate; carbonates such as magnesium carbonate and dolomite; and other materials such as silicon carbide, silicon nitride, boron nitride, and various metal powders. Examples of the plate-like filler include, but are not limited to, mica, glass flakes, and various metal foils. Examples of the hollow filler include, but are not limited to, glass balloons, silica balloons, shirasu balloons, and metal balloons.

[0096] The organic filler is not limited to the following, but examples thereof include high-melting-point organic fibrous fillers such as aromatic polyamide resins, fluororesins, and acrylic resins. These fillers may be used alone or in combination of two or more. Both surface-treated and untreated fillers can be used as these fillers, but in terms of the smoothness of the molding surface and mechanical properties, it may be preferable to use fillers that have been surface-treated with a surface treatment agent.

[0097] The surface treatment agent is not particularly limited, and any conventionally known surface treatment agent can be used. Examples of surface treatment agents that can be used include, but are not limited to, various coupling treatment agents such as silane-based, titanate-based, aluminum-based, and zirconium-based, resin acids, organic carboxylic acids, organic carboxylates, surfactants, etc. Specific examples include, but are not limited to, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyl tristearoyl titanate, diisopropoxyaluminum ethyl acetate, and n-butyl zirconate.

[0098] When conventionally known additives are contained, the content of the polyacetal resin (A) in 100% by mass of the polyacetal resin composition is preferably 75% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0099] The molding method for the polyacetal resin composition of the present embodiment is not particularly limited, and examples thereof include known molding methods such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, molding with other materials, gas-assisted injection molding, foam injection molding, low-pressure molding, ultra-thin-wall injection molding (ultra-high-speed injection molding), in-mold composite molding (insert molding, outsert molding), and melt-blow molding. The shape of the molded article is not particularly limited, and examples thereof include injection molded articles (including outsert molded articles and insert molded articles), fibers / nonwoven fabrics, sheets / films, and profile extrusion articles. The use of the molded body is not particularly limited, and it can be suitably used for, for example, mechanical parts such as gears, cams, sliders, levers, shafts, bearings, and guides, and in particular, automotive interior parts such as door surrounding parts, seat belt surrounding parts, combination switch parts, and switches.

[0100] [Method for producing polyacetal resin composition] The method for producing the polyacetal resin composition of the present embodiment is not particularly limited. For example, the polyacetal resin composition can be obtained by mixing (A) polyacetal resin, (B) ethylene urea, (C) acrylamide polymer, (D) ethylene bisstearic acid amide, and, if necessary, the above-mentioned predetermined components ((E) other additives) in, for example, a Henschel mixer, a tumbler, a V-shaped blender, or the like, and then kneading the mixture using a kneading machine such as a single-screw or multi-screw extruder, a heated roll, a kneader, or a Banbury mixer. It is also preferable to add (D) ethylene bisstearic acid amide during polymerization of (C) acrylamide polymer. From the viewpoints of thermal stability and productivity, kneading using an extruder equipped with a vent pressure reduction device is preferred as a kneading method. To stably produce large quantities of polyacetal resin compositions, a single-screw or twin-screw extruder is preferably used, and in this case, a pelletized polyacetal resin composition (hereinafter, sometimes referred to as "polyacetal resin pellets") can be obtained. Alternatively, each component may be continuously fed into the extruder either individually or in batches of several components using a metering feeder or the like, without pre-mixing. Alternatively, a high-concentration masterbatch consisting of each component may be prepared in advance and diluted with the polyacetal resin during extrusion melt kneading.

[0101] The kneading temperature may be determined in accordance with the preferred processing temperature of the polyacetal resin used, and is generally set in the range of 140 to 260°C, preferably 180 to 230°C.

[0102] The method for drying the polyacetal resin pellets obtained above is not particularly limited, and examples thereof include drying methods using a box dryer (atmospheric pressure, vacuum), tunnel and band dryer, rotary and ventilated rotary dryer, grooved agitator dryer, fluidized bed dryer, multi-stage disk dryer, spray dryer, flash dryer, infrared dryer, and high-frequency dryer. Among these, a box-type dryer, a rotary and ventilated rotary dryer, a groove-type agitator dryer, a fluidized bed dryer, a multi-stage disk dryer, and a flash dryer are preferred, and a fluidized bed dryer is more preferred from the viewpoint of productivity. The drying temperature, as the temperature of the heat medium, is preferably 80° C. or higher, more preferably 100° C. or higher. The drying time, starting from the point when the product temperature of the polyacetal resin pellets reaches 100° C. or higher, is preferably 0 to 10 hours, more preferably 0 to 6 hours, and even more preferably 1 to 6 hours.

[0103] [Molding of polyacetal resin composition] The polyacetal resin composition of this embodiment can be molded and used as a molded article. The molding method is not particularly limited, and can be any of known molding methods, such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, other material molding, gas-assisted injection molding, foam injection molding, low-pressure molding, ultra-thin-wall injection molding (ultra-high-speed injection molding), and in-mold composite molding (insert molding, outsert molding). Among these, injection molding is preferred from the viewpoint of stable productivity. Furthermore, even when the polyacetal resin composition of the present embodiment is used for continuous molding in a molding method in which the material is exposed to high temperatures for a long period of time, such as molding using a hot runner mold, contamination of the mold is minimal.

[0104] [Uses of molded articles made from polyacetal resin compositions] Molded articles of the polyacetal resin composition of the present embodiment have excellent quality stability and can therefore be used as molded articles for a variety of applications, such as mechanical parts typified by gears, cams, sliders, levers, shafts, bearings, and guides, outsert-molded resin parts or insert-molded resin parts (chassis, trays, side panel parts), printer or copier parts, digital camera or digital video device parts, music, video, or information device parts, communication device parts, electrical device parts, and electronic device parts.

[0105] Furthermore, molded articles of the polyacetal resin composition of the present embodiment are suitable for use as automobile parts, such as fuel-related parts typified by gasoline tanks, fuel pump modules, valves, and gasoline tank flanges; door-related parts; seatbelt-related parts; combination switch parts; and switches. Furthermore, molded articles of the polyacetal resin composition of the present embodiment can also be suitably used as industrial parts, such as housing equipment.

[0106] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and can be modified in various ways without departing from the spirit and scope of the present invention. [Example]

[0107] Hereinafter, the present embodiment will be described with reference to specific examples and comparative examples, but the present embodiment is not limited to the following examples. The measurement and evaluation methods used in the examples and comparative examples are shown below.

[0108] <Measurement of formaldehyde emissions from molded products> The prepared polyacetal resin pellets were molded under the following molding conditions (a), and the amount of formaldehyde released from the molded product was measured by the VDA275 method (b). (a) Molding conditions ·Injection molding machine: Toshiba Machine Co., Ltd. IS-100GN Cylinder temperature setting: 220℃ Mold temperature setting: 80℃ Mold type: Cold runner type Test piece size: 100 x 40 mm x 3 mm Molding cycle: Injection time / Cooling time = 30 seconds / 15 seconds The amount of formaldehyde released from the molded article was measured using the method shown below (VDA275 method). (b) VDA275 method: 50 mL of distilled water and a test piece of the specified size (100 mm x 40 mm x 3 mm) were placed in a polyethylene container, which was then sealed. The container was heated at 60°C for 3 hours to extract formaldehyde into the distilled water, and then cooled to room temperature. After cooling, 5 mL of a 0.4% by mass aqueous solution of acetylacetone and 5 mL of a 20% by mass aqueous solution of ammonium acetate were added to 5 mL of distilled water that had absorbed formaldehyde to obtain a mixed solution, which was then heated at 40°C for 15 minutes to allow the formaldehyde and acetylacetone to react with each other. Furthermore, after the mixture was cooled to room temperature, the amount of formaldehyde absorbed in the distilled water was quantified using a UV spectrophotometer from the absorption peak at 412 nm. The amount of formaldehyde released from the molded article (mg / kg) was calculated using the following formula. Formaldehyde emission from molded products (mg / kg) = Amount of formaldehyde absorbed in distilled water (mg) / Mass of polyacetal resin molded product used for measurement (kg)

[0109] <Charpy impact value> The Charpy impact value was measured as an index of mechanical strength. Test pieces were prepared using a Toshiba Machine EC100SX mold at a cylinder temperature of 205°C, an injection time of 35 seconds, a cooling time of 15 seconds, and a mold temperature of 90°C to mold ISO dumbbell test pieces for evaluating physical properties. The following tests were performed on these test pieces. Charpy impact strength was measured the day after molding in accordance with ISO179 / 1eA.

[0110] <Tensile elongation retention rate under high temperature and humidity conditions> Test pieces were prepared using a Toshiba Machine EC100SX machine at a cylinder temperature of 205°C, injection time of 35 seconds, cooling time of 15 seconds, and mold temperature of 90°C to mold ISO dumbbell test pieces for physical property evaluation. The resulting molded pieces were left to stand at 90°C and 80% humidity for 500 hours, after which the tensile elongation was measured using an autograph, and the elongation retention was calculated using a sample left to stand at room temperature of 23°C as the standard.

[0111] <Tensile strength retention rate under high temperature and dry conditions> Test pieces were prepared using a Toshiba Machine EC100SX machine at a cylinder temperature of 205°C, injection time of 35 seconds, cooling time of 15 seconds, and mold temperature of 90°C to mold ISO dumbbell test pieces for physical property evaluation. The resulting molded pieces were left to stand at 95°C and 20% humidity for 1,500 hours, after which their tensile strength was measured using an autograph, and the strength retention was calculated using a sample left to stand at room temperature of 23°C as the standard.

[0112] <Mold deposit (MD) properties> The prepared polyacetal resin pellets were molded under the molding conditions (a) below, and the mold deposit property at this time was evaluated according to the evaluation criteria (b) below. (a) Molding conditions ·Injection molding machine: Si-30V manufactured by Toyo Machinery & Metals Co., Ltd. Cylinder temperature setting: 200℃ Mold temperature setting: 43℃ Molding cycle: Injection time / Cooling time = 20 seconds / 20 seconds (b) Evaluation criteria The state of mold deposits inside the mold cavity was observed on the 1000th shot from the start of molding, based on the following evaluation criteria. A: No MD adhesion is observed inside the mold cavity. B: A small amount of MD is observed in the mold cavity. C: A large amount of film-like MD is observed inside the mold cavity.

[0113] <Molding shrinkage rate> The molding shrinkage was measured as an index of dimensional stability after injection molding. The prepared polyacetal resin pellets were molded under the molding conditions (a) below, and the molding shrinkage rate at this time was evaluated by the method (b) below. (a) Molding conditions ·Injection molding machine: Toshiba Machine Co., Ltd. IS-100GN Cylinder temperature setting: 220℃ Mold temperature setting: 80℃ Mold type: Cold runner type Test piece mold size: length 100 x width 40 mm x thickness 3 mm Molding cycle: Injection time / Cooling time = 30 seconds / 15 seconds b) Evaluation method The longitudinal and lateral dimensions of the 10 molded articles obtained were measured, and the molding shrinkage was calculated by the following method. Molding shrinkage rate (%) = ((1-(average vertical dimension of 10 molded products / vertical size of test piece mold 100 mm)) + ((1 - average value of horizontal dimensions of 10 molded products / test piece mold horizontal size 40 mm))) / 2 x 100

[0114] [Raw material ingredients] The raw material components used in the examples and comparative examples are shown below.

[0115] <(A) Polyacetal resin> A-1: Polyacetal homopolymer (MFR: 2.0 g / 10 min) A-2: Polyacetal homopolymer (MFR: 10.0 g / 10 min)

[0116] The methods for producing A-1 and A-2 are described below. (A-1: Preparation of polyacetal homopolymer) A polymerization reactor equipped with a stirring blade was filled with n-hexane, and purified formaldehyde gas (water content: 110 ppm), a polymerization catalyst (dimethyl distearyl ammonium acetate), and a molecular weight modifier (acetic anhydride) were continuously fed into the reactor to carry out a polymerization reaction at a temperature of 58°C. The obtained crude polyacetal homopolymer was placed in a reaction vessel filled with a 1:1 mixed solvent of n-hexane and acetic anhydride, and the mixture was stirred at 150°C for 2 hours to esterify the unstable terminals of the crude polyacetal homopolymer. The mass ratio (slurry concentration) of the polymer to the "1:1 mixed solvent of n-hexane and acetic anhydride" was 100 parts by weight of the "1:1 mixed solvent of n-hexane and acetic anhydride" to 20 parts by weight of the polymer. After the end-stabilization treatment of the polyacetal homopolymer was completed, the "1:1 mixed solvent of n-hexane and acetic anhydride" and the polyacetal homopolymer were removed from the reaction vessel, and n-hexane solvent was added to repeatedly wash the polyacetal homopolymer to wash off the acetic anhydride. The washing was repeated until the acetic anhydride concentration in the polyacetal homopolymer reached 10 ppm by mass or less. Thereafter, the polyacetal homopolymer was dried under reduced pressure at 120°C for 3 hours at -700 mmHg to remove the n-hexane solvent used for washing, and further dried for 5 hours using a heating dryer set at 120°C to remove water contained in the polyacetal homopolymer, yielding (A-1) polyacetal homopolymer in powder form (average particle size: 200 μm) with an MFR of 2.0 g / 10 min. The average particle size of the polyacetal polymer was measured by a laser diffraction particle size distribution measuring device.

[0117] (A-2: Preparation of polyacetal homopolymer) A powder-like (average particle size of 200 μm) polyacetal homopolymer (A-2) with an MFR of 10.0 g / 10 min was obtained using the same production method as for polyacetal homopolymer (A-1), except that the molecular weight was changed by adjusting the amount of molecular weight modifier (acetic anhydride) added, etc.

[0118] <(B) Ethylene urea> B-1: Ethylene urea (Tokyo Chemical Industry Co., Ltd.)

[0119] <(C) Acrylamide polymer> C-1: Acrylamide polymer (primary amide group content: 50.4 mol%, average particle size: 5.1 μm) (C-1) The acrylamide polymer was prepared as follows. 2,400 g of acrylamide, 267 g of N,N'-methylenebisacrylamide, and 0.54 g of zirconium tetraisopropoxide (1 / 10,000 mol relative to acrylamide) as a catalyst were placed in a 5 L batch reactor equipped with a stirrer, and the mixture was reacted at 125°C for 4 hours while stirring in a N2 stream. After the reaction was completed, the solid matter was pulverized in a jet mill and washed with acetone. Thereafter, the mixture was dried at 120° C. for 20 hours under reduced pressure of −700 mmHg to obtain an acrylamide polymer (C-1). The resulting acrylamide polymer (C-1) had a primary amide group content of 50.4 mol % and an average particle size of 5.1 μm, as measured by a laser diffraction particle size distribution analyzer.

[0120] <(D) Ethylene bisstearic acid amide> D-1: Ethylene bisstearic acid amide (Tokyo Chemical Industry Co., Ltd.) <(E) Other additives> E-1: Sebacic acid dihydrazide (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.) E-2: Allantoin (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.) E-3: Hydantoin (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.) E-4: Polyamide 66 (heat stabilizer, manufactured by Asahi Kasei Corporation) E-5: Triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate] (hindered phenol antioxidant, manufactured by Songwon Corporation)

[0121] [Example 1, Examples 3 to 13] The powdered polyacetal resin (A-1) polyacetal homopolymer, (B-1) ethylene urea, (C-1) acrylamide polymer, and (E) other additives, including triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] as a hindered phenol-based antioxidant, were mixed uniformly in the amounts shown in Table 1 using a Henschel mixer to obtain a mixture. Note that (D) ethylene bisstearamide was added during the polymerization of (C) acrylamide polymer. This mixture was fed from the top feed port of a 40 mm vented twin-screw extruder with an L (screw length) / D (screw inner diameter) = 48 set at 200°C, melt-kneaded at a screw rotation speed of 200 rpm, a vent vacuum of -0.08 MPa, and a discharge rate of 50 kg / hr, and pelletized at the extruder die outlet using a hot-cut method.The pellets were then placed in warm water adjusted to 40°C and stirred for a certain period of time, after which the water was removed using a centrifuge.The pellets were then placed in a fluidized bed hot air dryer and dried for 3 hours at a hot air temperature of 100°C to obtain polyacetal resin pellets. Using the obtained polyacetal resin pellets, the amount of formaldehyde released from the molded article, the mechanical properties after tests in a high-temperature dry environment and a high-temperature high-humidity environment, the mold deposit property, and the molding shrinkage rate were evaluated and measured by the methods described above. The evaluation results are shown in Table 1 below.

[0122] Example 2 Polyacetal resin pellets were obtained in the same manner as in Example 1, except that (D) ethylene bisstearic acid amide was added by mixing it simultaneously with the powdery (A-1) polyacetal homopolymer and the like. Using the obtained polyacetal resin pellets, the amount of formaldehyde released from the molded article, the mechanical properties after tests in a high-temperature dry environment and a high-temperature high-humidity environment, the mold deposit property, and the molding shrinkage rate were evaluated and measured by the methods described above. The evaluation results are shown in Table 1 below.

[0123] [Comparative Examples 1 to 2, Comparative Examples 5 to 11, and 13] The same procedure as in Example 2 was carried out except that the composition was as shown in Table 2, to obtain polyacetal resin pellets. Using the obtained polyacetal resin pellets, the amount of formaldehyde released from the molded article, the mechanical properties after tests in a high-temperature dry environment and a high-temperature high-humidity environment, the mold deposit property, and the molding shrinkage rate were evaluated and measured by the methods described above. The evaluation results are shown in Table 2 below.

[0124] [Comparative Examples 3 to 4, Comparative Example 12] The same procedure as in Example 1 was carried out except that the composition was as shown in Table 2, to obtain polyacetal resin pellets. Using the obtained polyacetal resin pellets, the amount of formaldehyde released from the molded article, the mechanical properties after tests in a high-temperature dry environment and a high-temperature high-humidity environment, the mold deposit property, and the molding shrinkage rate were evaluated and measured by the methods described above. The evaluation results are shown in Table 2 below.

[0125] [Table 1]

[0126] [Table 2]

[0127] As shown in Table 1, the molded articles made of the polyacetal resin compositions obtained in Examples 1 to 13 are excellent in suppressing formaldehyde emission from the molded articles, in mechanical strength retention in a high-temperature, dry environment and a high-temperature, high-humidity environment, and in dimensional stability after molding. In addition, they are also excellent in mold deposit resistance. On the other hand, as shown in Table 2, the molded articles made of the polyacetal resin compositions obtained in Comparative Examples 1 to 13 did not suppress the amount of formaldehyde emitted from the molded articles, and the retention of mechanical properties in high-temperature, dry environments and high-temperature, high-humidity environments decreased. In addition, the mold deposit properties and dimensional stability after molding were poor, resulting in a poor balance of performance. [Industrial Applicability]

[0128] The polyacetal resin composition of the present invention can be suitably used in a wide range of fields, such as automobiles, electrical and electronics, and other industrial fields.

Claims

1. (A) per 100 parts by mass of polyacetal resin, (B) 0.03 to 0.60 parts by mass of ethylene urea, (C) 0.05 to 0.50 parts by mass of an acrylamide polymer, and (D) A polyacetal resin composition containing 0.0005 to 0.05 parts by mass of ethylene bisstearic acid amide.

2. The polyacetal resin composition according to claim 1, wherein the polyacetal resin (A) is a polyacetal homopolymer.

3. 3. The polyacetal resin composition according to claim 1, wherein the polyacetal resin (A) has a melt flow rate of 1.0 to 10.0 g / 10 min when measured in accordance with ISO 1133.

4. The polyacetal resin composition according to claim 3, wherein the polyacetal resin (A) has a melt flow rate of 1.0 to 3.0 g / 10 min.

5. The polyacetal resin composition according to claim 1 or 2, wherein the molecular weight distribution of the polyacetal resin (A) has a single peak.

6. 3. The polyacetal resin composition according to claim 1, comprising 0.05 to 0.20 parts by mass of the acrylamide polymer (C).

7. 3. The polyacetal resin composition according to claim 1, wherein the mass ratio (D) / (C) of the ethylene bisstearic acid amide (D) to the acrylamide polymer (C) is 0.01 to 0.5.

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