Polyacetal resin composition

Abstract

The invention relates to a polyacetal resin composition. The purpose of the present invention is to provide a polyacetal resin composition which is capable of suppressing the amount of formaldehyde emission from a molded article and sufficiently suppressing deterioration in physical properties when used for a long period of time under high-temperature drying or high-temperature high-humidity conditions, and which has excellent dimensional stability after injection molding. A polyacetal resin composition in which, with respect to 100 parts by mass of (A) a polyacetal resin, the polyacetal resin composition contains (B) 0.03 parts by mass to 0.60 parts by mass of ethylene urea, (C) 0.05 parts by mass to 0.50 parts by mass of an acrylamide polymer, and (D) 0.0005 parts by mass to 0.05 parts by mass of ethylene bis stearamide.

Description

Technical Field

[0001] The present invention relates to polyacetal resin compositions. Background Art

[0002] Polyacetal resin is a material with excellent rigidity, strength, toughness, sliding properties, and creep resistance. It is used in a wide range of applications as a resin material for various mechanical components, including automotive parts, electrical / electronic parts, and industrial parts.

[0003] Polyacetal resins decompose under the influence of heat, light, oxygen, acids, and alkalis, generating formaldehyde. There is a particular concern that formaldehyde gas generated by thermal decomposition during manufacturing or molding may remain within resin molded articles, gradually releasing formaldehyde from these resin products and thus deteriorating the indoor environment. In particular, in automotive interior parts applications, there is a demand to significantly reduce formaldehyde emissions from molded articles.

[0004] Various technologies have been proposed to suppress formaldehyde release from polyacetal resin molded articles. For example, technologies have been proposed that add hydrazide compounds, urea compounds, guanamine compounds, etc. as formaldehyde scavengers, and technologies that add polyamide resins as heat stabilizers (Patent Documents 1 and 2).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2016 / 126514

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2005-263921 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] In recent years, the use of polyacetal resins has expanded, with demands for them to maintain mechanical strength even in various transportation and usage environments over long periods of time. For example, this requires suppressing the degradation of physical properties during long-term use under high-temperature, dry conditions or high-temperature, high-humidity conditions. Furthermore, the miniaturization and precision of mechanical components using polyacetal resins are driving demands for not only improved impact resistance but also dimensional stability after molding.

[0011] However, the molded articles of the polyacetal resin compositions proposed in the above documents are not necessarily fully satisfactory in terms of suppressing the release of formaldehyde from the molded articles and suppressing the degradation of physical properties during long-term use under high-temperature drying or high-temperature and high-humidity conditions.

[0012] 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 the deterioration of physical properties when the molded article is used for a long time under high-temperature drying or high-temperature and high-humidity conditions, and has excellent dimensional stability after injection molding.

[0013] Means used to solve problems

[0014] 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 at a predetermined ratio relative to the acrylamide polymer, a polyacetal resin composition can be obtained that suppresses formaldehyde emission from molded articles, suppresses degradation of physical properties of the molded articles during long-term use under high-temperature drying or high-temperature and high-humidity conditions, and exhibits excellent dimensional shrinkage stability during injection molding. This has led to the completion of the present invention.

[0015] That is, the present invention is as follows.

[0016] [1] A polyacetal resin composition comprising, relative to 100 parts by mass of (A) polyacetal resin:

[0017] 0.03 to 0.60 parts by mass of (B) ethylene urea,

[0018] 0.05 to 0.50 parts by mass of (C) an acrylamide polymer, and

[0019] 0.0005 to 0.05 parts by mass of (D) ethylene bisstearamide.

[0020] [2] The polyacetal resin composition according to [1], wherein the (A) polyacetal resin is a polyacetal homopolymer.

[0021] [3] The polyacetal resin composition according to [1] or [2], wherein the (A) polyacetal resin has a melt flow rate of 1.0 g / 10 min to 10.0 g / 10 min when measured in accordance with ISO 1133.

[0022] [4] The polyacetal resin composition according to [3], wherein the (A) polyacetal resin has a melt flow rate of 1.0 g / 10 min to 3.0 g / 10 min.

[0023] [5] The polyacetal resin composition according to any one of [1] to [3], wherein the peak of the molecular weight distribution of the polyacetal resin is unimodal.

[0024] [6] The polyacetal resin composition according to any one of [1] to [5], wherein the polyacetal resin composition contains 0.05 to 0.20 parts by mass of the (C) acrylamide polymer.

[0025] [7] The polyacetal resin composition according to any one of [1] to [6], wherein the mass ratio of (D) ethylenebisstearamide to the (C) acrylamide polymer is 0.01 to 0.5 ((D) / (C)).

[0026] Effects of the Invention

[0027] According to the present invention, a polyacetal resin composition can be provided that can suppress the amount of formaldehyde released from a molded article, can sufficiently suppress the degradation of physical properties of the molded article when used for a long time under high-temperature drying or high-temperature and high-humidity conditions, and has excellent dimensional stability after injection molding. DETAILED DESCRIPTION

[0028] Hereinafter, a mode for implementing the present invention (hereinafter referred to as "this embodiment") will be described in detail. It should be noted that the present invention is not limited to the following description, and can be implemented with various modifications within the scope of the gist thereof.

[0029] <Polyacetal resin composition>

[0030] The polyacetal resin composition of the present embodiment contains 0.03 to 0.60 parts by mass of (B) ethylene urea, 0.05 to 0.50 parts by mass of (C) acrylamide polymer, and 0.0005 to 0.05 parts by mass of (D) ethylene bisstearamide, per 100 parts by mass of (A) polyacetal resin.

[0031] When the polyacetal resin composition is used, the formaldehyde emission from the molded article produced from the polyacetal resin composition can be suppressed, the degradation of physical properties during long-term use under high-temperature drying or high-temperature and high-humidity conditions can be sufficiently suppressed, and the dimensional stability after injection molding is excellent.

[0032] <<(A) Polyacetal resin>>

[0033] The polyacetal resin (A) contained in the polyacetal resin composition of the present embodiment refers to a polymer having oxymethylene groups in its main chain. Examples of the polyacetal resin (A) include: polyacetal homopolymers substantially containing only oxymethylene units, obtained by polymerizing formaldehyde monomer or cyclic oligomers of formaldehyde such as its trimer (trimethoxymethylene) or tetramer (tetramethoxymethylene); polyacetal copolymers obtained by copolymerizing formaldehyde monomer or cyclic oligomers of formaldehyde such as its trimer (trimethoxymethylene) or tetramer (tetramethoxymethylene) with cyclic ethers or cyclic formals of diols such as ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane, or 1,4-butanediol formal; branched polyacetal copolymers obtained by copolymerizing monofunctional glycidyl ethers; and polyacetal copolymers having a crosslinked structure obtained by copolymerizing polyfunctional glycidyl ethers.

[0034] Furthermore, as the polyacetal resin (A), a polyacetal homopolymer having a block component obtained by polymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trimethoxymethylene) or a tetramer (tetramethoxymethylene) in the presence of a compound having functional groups such as hydroxyl groups at both ends or one end, for example, a polyalkylene glycol; and a polyacetal copolymer having a block component obtained by copolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trimethoxymethylene) or a tetramer (tetramethoxymethylene) with a cyclic ether or a cyclic formal in the presence of a compound having functional groups such as hydroxyl groups at both ends or one end, for example, a hydrogenated polybutadiene diol.

[0035] The polyacetal resins can be used alone or in combination of two or more.

[0036] Among them, from the viewpoint of improving mechanical strength, the polyacetal resin (A) is preferably a polyacetal homopolymer, and more preferably a polyacetal homopolymer obtained by polymerizing formaldehyde monomer alone.

[0037] In addition, the degree of polymerization and the comonomer content of the (A) polyacetal resin in the present embodiment are not particularly limited.

[0038] From the viewpoint of exhibiting excellent properties of an engineering resin, the content of the polyacetal resin relative to 100 mass % of the polyacetal resin composition is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more.

[0039] When measured in accordance with ISO 1133, the polyacetal resin preferably has a melt flow rate (MFR) of 1.0 to 10.0 g / 10 minutes. Furthermore, the melt flow rate of the polyacetal resin is more preferably in the range of 1.0 to 3.0 g / 10 minutes. By adjusting the MFR value of the polyacetal resin within this range, a polyacetal composition can be obtained that exhibits excellent mechanical strength, suppresses degradation of physical properties, and reduces formaldehyde emissions.

[0040] From the viewpoint of mechanical strength, the number average molecular weight (Mn) of the polyacetal resin is preferably 10,000 or more, more preferably 25,000 or more, and most preferably 30,000 to 150,000.

[0041] 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.

[0042] The shape of the molecular weight distribution curve of the polyacetal resin of this embodiment is not particularly limited, but preferably the molecular weight distribution peak is unimodal. Furthermore, from the perspective of improving mechanical strength, a unimodal shape having a peak top located in the range of logM = 4.5 to 8.0 (M is the molecular weight) is more preferred, a unimodal shape having a peak top located in the range of logM = 4.5 to 7.0 is even more preferred, and a unimodal shape having a peak top located in the range of logM = 4.5 to 6.0 is even more preferred.

[0043] Here, "single peak" refers to a shape having only one parabolic peak.

[0044] When a low molecular weight component is contained, the molecular weight distribution curve does not form a part of the parabolic peak in the region of molecular weight of 10,000 or less, but forms a shoulder with respect to the peak top, or is connected to the peak top and has a tail.

[0045] In addition, the number average molecular weight (Mn), the weight average molecular weight (Mw), and the molecular weight distribution in this embodiment can be measured by gel permeation chromatography (GPC) using PMMA as a standard substance.

[0046] (Polyacetal homopolymer)

[0047] The polyacetal resin is preferably a polyacetal homopolymer.

[0048] The polyacetal homopolymer can be produced, for example, by supplying formaldehyde as a monomer, a chain transfer agent (molecular weight modifier), and a polymerization catalyst to a polymerization reactor into which a hydrocarbon polymerization solvent has been introduced, and polymerizing the resultant by a slurry polymerization method.

[0049] In this case, the raw monomers, chain transfer agent, and polymerization catalyst may contain components capable of chain transfer (components that generate unstable terminal groups), such as water, methanol, and formic acid. Therefore, it is preferable to first adjust the content of these components capable of chain transfer. The content of these components capable of chain transfer is preferably 1 to 1000 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 the monomer. By adjusting the content of these components capable of chain transfer within this range, a polyacetal homopolymer with excellent thermal stability can be obtained.

[0050] The molecular weight of the polyacetal homopolymer can be adjusted by chain transfer using a molecular weight modifier such as carboxylic anhydride or carboxylic acid. As the molecular weight modifier, propionic anhydride and acetic anhydride are particularly preferred, and acetic anhydride is more preferred.

[0051] The amount of molecular weight modifier introduced is adjusted and determined based on the desired properties of the polyacetal homopolymer (particularly its melt flow rate). For example, the melt flow rate (MFR value (measured in accordance with ISO 1133)) of the polyacetal homopolymer is preferably within the range of 0.1 g / 10 min to 100 g / 10 min, more preferably within the range of 1.0 g / 10 min to 10 g / 10 min, and even more preferably within the range of 1.0 g / 10 min to 3.0 g / 10 min. By adjusting the MFR value of the polyacetal homopolymer within this range, a polyacetal homopolymer with excellent mechanical strength can be obtained.

[0052] As the polymerization catalyst, an anionic polymerization catalyst is preferred, and more preferably a catalyst represented by the following general formula (I): Salt polymerization catalysts.

[0053] [R1R2R3R4M] + X - ···(I)

[0054] (In formula (I), R1, R2, R3, and R4 each independently represent an alkyl group, M represents an element having a lone pair of electrons, and X represents a nucleophilic group.)

[0055] The polymerization catalyst may be used alone or in combination of two or more.

[0056] Among the salt polymerization catalysts, tetraethyl iodide is preferred. , tributylethyl iodide Waiting season Salt compounds; quaternary ammonium salt compounds such as tetramethylammonium bromide and dimethyl distearyl ammonium acetate.

[0057] Relative to 1 mol of formaldehyde, these quaternary Salt compounds and quaternary ammonium salt compounds, etc. The amount of the salt-based polymerization catalyst added is preferably 0.0003 mol to 0.01 mol, more preferably 0.0008 mol to 0.005 mol, and even more preferably 0.001 mol to 0.003 mol.

[0058] The hydrocarbon polymerization solvent is not particularly limited as long as it is a solvent that does not react with formaldehyde. Examples thereof include pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, and benzene, with hexane being particularly preferred. These hydrocarbon solvents may be used alone or in combination of two or more.

[0059] In the production of the polyacetal homopolymer, it is preferred to first obtain a crude polyacetal homopolymer by polymerization, and then subject the crude polyacetal homopolymer to a stabilization treatment for unstable terminal groups as described below.

[0060] The polymerization reactor used to produce the crude polyacetal homopolymer is not particularly limited as long as it is an apparatus capable of simultaneously supplying formaldehyde as a monomer, a chain transfer agent (molecular weight modifier), a polymerization catalyst, and a hydrocarbon polymerization solvent. However, from the viewpoint of productivity, a continuous polymerization reactor is preferred.

[0061] The terminal groups of the crude polyacetal homopolymer obtained by polymerization are thermally unstable. Therefore, it is preferable to perform a stabilization treatment by capping these unstable terminal groups with an esterifying agent or an etherifying agent.

[0062] Stabilization of the terminal groups of the crude polyacetal homopolymer by esterification can be carried out, for example, by separately placing the crude polyacetal homopolymer, an esterification agent, and an esterification catalyst into a terminal stabilization reactor into which a hydrocarbon solvent has been introduced, and reacting them. The reaction temperature and reaction time in this case are, for example, preferably 130°C to 155°C and 1 to 100 minutes, more preferably 135°C to 155°C and 5 to 100 minutes, and even more preferably 140°C to 155°C and 10 to 100 minutes.

[0063] As an esterifying agent for capping and stabilizing the terminal groups of the crude polyacetal homopolymer, an acid anhydride represented by the following general formula (II) can be used.

[0064] R5COOCOR6···(II)

[0065] (In formula (II), R5 and R6 each independently represent an alkyl group. R5 and R6 may be the same as or different from each other.)

[0066] 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. Acetic anhydride is preferred. These esterifying agents may be used alone or in combination of two or more.

[0067] The esterification catalyst is preferably an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms. The amount of the esterification catalyst added can be appropriately selected within the range of 1 to 1000 ppm by mass relative to the mass of the polyacetal homopolymer. Examples of alkali metal salts of carboxylic acids 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, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, heptadecanoic acid, and stearic acid. Examples of the alkali metal salt include lithium, sodium, potassium, rubidium, and cesium. Among these alkali metal salts of carboxylic acids, lithium acetate, sodium acetate, and potassium acetate are preferred.

[0068] The etherifying agent for capping and stabilizing the terminal groups of the crude polyacetal homopolymer can 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 orthobenzoate, methyl orthobenzoate or ethyl orthobenzoate, and orthocarbonates, specifically ethyl orthocarbonate. Stabilization can be performed using a medium-strength organic acid such as p-toluenesulfonic acid, acetic acid, and oxalic acid.

[0069] Examples of the solvent used in the etherification reaction for capping and stabilizing the terminal groups of the crude polyacetal homopolymer by etherification include, but are not limited to, low-boiling-point 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.

[0070] The polyacetal homopolymer whose terminal groups are stabilized by the above method is dried by enclosing air or nitrogen adjusted to 100° C. to 150° C. in a dryer such as a hot air dryer or a vacuum dryer to remove moisture, thereby obtaining a polyacetal homopolymer as the polyacetal resin (A).

[0071] (Polyacetal copolymer)

[0072] First, the materials used in the production of the polyacetal copolymer, specifically, trioxymethylene, cyclic ether and / or cyclic formal, a polymerization catalyst, a low-molecular-weight acetal compound, and an organic solvent will be described.

[0073] -Trioxymethylene-

[0074] Trioxymethylene is a cyclic trimer of formaldehyde and is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst.

[0075] The trioxane may contain impurities such as water, methanol, formic acid, and methyl formate that may cause chain transfer, and therefore it is preferable to remove these impurities by distillation or other methods to purify them. In this case, the total amount of impurities that may cause chain transfer is preferably adjusted to 1×10 -3 mol or less, more preferably adjusted to 0.5×10 -3 By reducing the total amount of impurities to below the upper limit, the polymerization reaction rate can be sufficiently increased for practical purposes, and the resulting polymer can obtain excellent thermal stability.

[0076] -Cyclic ether and / or cyclic formal-

[0077] Cyclic ethers and / or cyclic formals are components copolymerizable with the above-mentioned trioxymethylene, and examples thereof include ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxetane, 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 the cyclic ethers and / or cyclic formals, 1,3-dioxolane and 1,4-butanediol formal are preferred. These may be used alone or in combination of two or more.

[0078] The amount of the cyclic ether and / or cyclic formal added is preferably in the range of 1 mol% to 20 mol%, more preferably in the range of 1 mol% to 15 mol%, further preferably in the range of 1 mol% to 10 mol%, and even more preferably in the range of 1 mol% to 5 mol%, relative to 1 mol of the above-mentioned trioxymethylene.

[0079] -Polymerization catalyst-

[0080] Examples of polymerization catalysts include Lewis acids such as metal halides. Examples include halides of boron, tin, titanium, phosphorus, arsenic, and antimony. Boron trifluoride, boron trifluoride hydrates, and coordination complexes of boron trifluoride with organic compounds containing oxygen or sulfur atoms are particularly preferred. Preferred examples include boron trifluoride, boron trifluoride ethyl ether complex, and boron trifluoride di-n-butyl ether complex. These catalysts may be used alone or in combination of two or more.

[0081] The amount of the polymerization catalyst added is preferably 0.1×10 -5 mole~0.1×10 -3 molar range, more preferably 0.3×10 -5 mole~0.3×10 -4The range of moles is more preferably 0.5×10 -5 mole~0.15×10 -4 If the amount of the polymerization catalyst added is within the above range, the polymerization reaction can be stably carried out for a long time.

[0082] -Low molecular weight acetal compound-

[0083] The low-molecular-weight acetal compound functions as a chain transfer agent in the polymerization reaction and has a molecular weight of 200 or less, preferably 60 to 170. Specifically, methylal, methoxymethylal, dimethoxymethylal, and trimethoxymethylal are preferred examples. These may be used alone or in combination of two or more.

[0084] From the viewpoint of controlling the molecular weight of the polymer within an appropriate range, the amount of the low molecular weight acetal compound added is preferably 0.1×10 -4 mole~0.6×10 -2 within the molar range.

[0085] -Organic solvents-

[0086] 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). Preferred examples include aliphatic hydrocarbons such as n-hexane, n-heptane, and cyclohexane from the perspective of suppressing the formation of tarry precipitates. These organic solvents may be used alone or in combination of two or more.

[0087] The amount of organic solvent added is preferably 0.1×10 -3 mol to 0.2 mol, more preferably 0.2×10 -3 mole~0.5×10 -1 The range of moles is more preferably 0.5×10 -3 mole~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.

[0088] -Polymerization of polyacetal copolymer-

[0089] The polymerization method of the polyacetal copolymer is not particularly limited, and examples thereof include bulk polymerization and melt polymerization, in addition to the slurry polymerization method described above for the production of the polyacetal homopolymer. The polymerization of the polyacetal copolymer can be carried out in either a batch or continuous manner.

[0090] The polymerization reactor is not particularly limited, and examples thereof include self-cleaning extruders such as a co-kneader, a twin-screw continuous extruder, and a twin-screw paddle continuous mixer. These devices preferably have a jacket through which a heat medium can pass.

[0091] After the various materials are supplied to the polymerization reactor, the temperature of the polymerization reactor during the polymerization reaction is preferably maintained between 63°C and 135°C, more preferably between 70°C and 120°C, and even more preferably between 70°C and 100°C. Furthermore, the residence (reaction) time within the polymerization reactor is preferably between 0.1 and 30 minutes, more preferably between 0.1 and 25 minutes, and even more preferably between 0.1 and 20 minutes. When the polymerization reactor temperature and residence time are within these ranges, a stable polymerization reaction tends to proceed continuously.

[0092] Then, a crude polyacetal copolymer is obtained through a polymerization reaction. The following method can be used to deactivate the polymerization catalyst: the crude polyacetal copolymer discharged from the polymerization reactor is placed in an aqueous or organic solution containing at least one of an amine such as ammonia, triethylamine, or tri-n-butylamine, or a neutralizing and deactivating agent such as an alkali metal or alkaline earth metal hydroxide, an inorganic salt, or an organic acid salt, and the mixture is continuously stirred in a slurry state at a temperature between room temperature and 100°C or below for several minutes to several hours. If the crude polyacetal copolymer is in large lumps, it is preferably pulverized after polymerization before further processing. The mixture is then filtered using a centrifuge and dried under nitrogen to obtain the polyacetal copolymer.

[0093] The resulting polyacetal copolymer may contain thermally unstable terminal portions [-(OCH2)n-OH groups] (hereinafter, such polyacetal copolymers may be referred to as "polyacetal copolymers before terminal stabilization"). Therefore, it is preferable to use a terminal stabilizer to decompose and remove these thermally unstable terminal portions (terminal stabilization). Terminal stabilizers are not particularly limited, but examples include: 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, or barium; and alkaline substances such as 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, with triethylamine being even more preferred.

[0094] The method for decomposing and removing the unstable terminal portions is not particularly limited. For example, the following method can be used: heat-treating the polyacetal copolymer in a molten state at a temperature of not less than the melting point of the polyacetal copolymer and not more than 260° C. in the presence of a terminal stabilizer such as triethylamine. The apparatus for performing the heat treatment can be, for example, a single-screw or twin-screw extruder equipped with a vent pressure reducing device, preferably a twin-screw extruder.

[0095] The polyacetal copolymer stabilized at the terminal end by the above method is dried by enclosing air or nitrogen at 100° C. to 150° C. in a dryer such as a hot air dryer or a vacuum dryer to remove moisture, thereby obtaining the polyacetal copolymer as the polyacetal resin (A).

[0096] <<(B)Ethylene urea>>

[0097] (B) Ethylene urea contained in the polyacetal resin composition of the present embodiment functions as a formaldehyde scavenger.

[0098] 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. For example, the ethylene urea can be produced by reacting ethylenediamine with carbon dioxide, reacting ethylenediamine with urea, reacting ethylenediamine with phosgene, reacting ethylenediamine with a dialkyl carbonate, or oxidizing ethylenethiourea.

[0099] The ethylene urea of this embodiment may contain raw materials, intermediates, and solvents as impurities. For example, it may contain ethylenediamine, urea, dialkyl carbonate, 2-aminoethylcarbamic acid, 2-aminoethylcarbamate, 2-aminoethylurea, etc. The amount of impurities relative to the weight of the ethylene urea is preferably less than 10% by weight, more preferably less than 5% by weight, and even more preferably less than 1% by weight.

[0100] The content of (B) ethylene urea in this embodiment is 0.03 to 0.60 parts by mass per 100 parts by mass of the polyacetal resin. This can suppress formaldehyde emissions from molded articles obtained from the polyacetal resin composition of this embodiment, inhibit a decrease in mechanical strength during long-term use under high temperature and high humidity conditions, and suppress the formation of mold deposits during molding. From the same perspective, 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.

[0101] <<(C) Acrylamide polymer>>

[0102] The (C) acrylamide polymer contained in the polyacetal resin composition of the present embodiment functions as a formaldehyde scavenger.

[0103] (C) The acrylamide polymer can be produced by, for example, homopolymerizing acrylamide or copolymerizing acrylamide with a monomer having a vinyl group other than acrylamide using an alkaline earth metal alkoxide as a catalyst.

[0104] By using a copolymer of acrylamide and a monomer having a vinyl group (for example, a copolymer having a cross-linked structure) as the (C) acrylamide polymer, the moldability of the polyacetal resin composition can be improved.

[0105] (C) The acrylamide polymer may be used alone or in combination of two or more.

[0106] Examples of the monomer having a vinyl group other than acrylamide include monomers having one or two vinyl groups.

[0107] Examples of the monomer having one vinyl group include n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, ethyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, cetyl methacrylate, pentadecyl methacrylate, stearyl methacrylate, behenyl methacrylate, hydroxypropyl methacrylate, polypropylene glycol methacrylate, and polyethylene glycol methacrylate.

[0108] Examples of the monomer having two vinyl groups include divinylbenzene, ethylenebisacrylamide, and N,N′-methylenebisacrylamide.

[0109] Among these monomers having a vinyl group, N,N'-methylenebisacrylamide is preferred.

[0110] When producing the acrylamide polymer, the amount of the vinyl group-containing monomer added is preferably 0.05% by mass to 20% by mass relative to the total amount of the acrylamide and the vinyl group-containing monomer.

[0111] The acrylamide polymer (C) may be a copolymer having a primary amide group and a secondary amide group.

[0112] The molar content of primary amide groups in the acrylamide polymer (C) is preferably 30 to 80 mol%, more preferably 30 to 70 mol%, and even more preferably 40 to 70 mol%. When the molar content of primary amide groups is within this range, a polyacetal resin composition having excellent crushability and moldability of the acrylamide polymer can be provided.

[0113] 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 a 40% by mass aqueous potassium hydroxide solution are placed in a flask equipped with a stirrer. The mixture is heated at 105°C to 110°C for 20 minutes while stirring to hydrolyze the primary amide groups into ammonia. The contents of the flask are then cooled to below 50°C, and methanol is added to extract the ammonia along with the methanol. This extract is then absorbed into a 0.1N aqueous sulfuric acid solution and neutralized and titrated with a 0.1N aqueous sodium hydroxide solution using methyl red as an indicator to determine the amount of primary amide groups.

[0114] 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.

[0115] In addition, the said average particle diameter is the value measured with the laser diffraction type particle size distribution measuring apparatus.

[0116] In this embodiment, the content of the acrylamide polymer (C) is 0.05 to 0.50 parts by mass per 100 parts by mass of the polyacetal resin (A). This allows for a polyacetal resin composition with excellent moldability and thermal stability. From the same perspective, the content of the acrylamide polymer (C) is preferably 0.05 to 0.40 parts by mass, and more preferably 0.05 to 0.20 parts by mass.

[0117] <<(D)Ethylene bisstearamide>>

[0118] The method for producing the (D) ethylene bisstearamide contained in the polyacetal resin composition of the present embodiment is not particularly limited, and a known method can be used. For example, it can be obtained by reacting stearic acid with ethylenediamine.

[0119] The content of (D) ethylene bisstearamide in this embodiment is 0.0005 to 0.05 parts by mass per 100 parts by mass of the polyacetal resin. This allows for a polyacetal resin composition with excellent moldability, and can suppress the reduction in mechanical strength of molded articles obtained from the polyacetal resin composition of this embodiment during long-term use under high temperature and high humidity conditions. From the same perspective, 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.

[0120] The mass ratio (D) / (C) of the ethylene bisstearamide (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. A mass ratio (D) / (C) within this range is preferred because it further suppresses the reduction in mechanical strength of molded articles obtained from the polyacetal resin composition during long-term use under high-temperature drying conditions and high-temperature, high-humidity conditions.

[0121] <<(E)Other additives>>

[0122] The polyacetal resin composition of the present invention may contain, in addition to the above-mentioned components (A) to (D), known additives ((E) other additives). Examples of (E) other additives include antioxidants, heat stabilizers, formic acid scavengers, weather stabilizers, mold release agents, lubricants, conductive agents, thermoplastic resins, thermoplastic elastomers, inorganic or organic fillers, pigments, and dyes. These additives may be used alone or in combination of two or more.

[0123] As the antioxidant, hindered phenol antioxidants are preferred.

[0124] Examples of the hindered phenol antioxidant include n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, n-octadecyl 3-(3-methyl-5-tert-butyl-4-hydroxyphenyl)propionate, n-tetradecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,4-butanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. Among them, triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] are preferred.

[0125] These antioxidants may be used alone or in combination of two or more.

[0126] 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.

[0127] Examples of the amino-substituted triazine compound include, but are not limited to, 2,4-diamino-s-triazine, 2,4,6-triamino-s-triazine, N-butylmelamine, N-phenylmelamine, N,N-diphenylmelamine, N,N-diallylmelamine, benzoguanamine (2,4-diamino-6-phenyl-s-triazine), methylguanamine (2,4-diamino-6-methyl-s-triazine), and 2,4-diamino-6-butyl-s-triazine.

[0128] Examples of the urea derivatives include, but are not limited to, N-substituted ureas, urea condensates, hydantoin compounds, and urea-based compounds. It should be noted that, in the present invention, the urea derivatives do not include ethylene urea.

[0129] 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, condensates 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 urea-based compound include, but are not limited to, allantoin.

[0130] Examples of the hydrazine derivatives include, but are not limited to, hydrazide compounds.

[0131] Examples of hydrazide compounds include carboxylic acid monohydrazide compounds, carboxylic acid dihydrazide compounds, alkyl-substituted monohydrazide compounds, and alkyl-substituted dihydrazide compounds synthesized by the reaction of carboxylic acids (including aromatic and alicyclic groups) with hydrazine. The carboxylic acids may be monocarboxylic acids, dicarboxylic acids, or compounds having three or more carboxylic acids (polycarboxylic acids). Examples of monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, lauric acid, myristic acid, palmitic acid, heptadecanoic 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, naphthalene dicarboxylic 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, and isophthalic acid mono(di)hydrazide. Hydrazide, terephthalic acid mono(di)hydrazide, 2,6-naphthalene dicarboxylic 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-hydroxybenzohydrazide, 1,4-cyclohexanedicarboxylic acid dihydrazide, acetic acid hydrazide, acrylhydrazide, benzohydrazide, nicotinic acid hydrazide, isonicotinic acid hydrazide, isobutylhydrazide, oleohydrazide, etc. Among them, the hydrazide compound is preferably adipic acid mono(di)hydrazide, sebacic acid mono(di)hydrazide, or lauric acid monohydrazide.

[0132] It should be noted that "mono(di)hydrazide" means that one or both of the two carboxylic acids are hydrazide-formed.

[0133] Examples of the amide compound include, but are not limited to, polycarboxylic acid amides such as isophthalic acid diamide and anthranilamide. It should be noted that the amide compound does not include acrylamide polymers and ethylene bisstearamide.

[0134] 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.

[0135] Examples of the formic acid scavenger include, but are not limited to, hydroxides, inorganic acid salts, carboxylates, or alkoxides of alkali metals or alkaline earth metals. Examples include hydroxides of sodium, potassium, magnesium, calcium, or barium; and carbonates, phosphates, silicates, borates, carboxylates, and layered double hydroxides of the aforementioned metals.

[0136] In addition, the formic acid scavenger may be used alone or in combination of two or more.

[0137] The carboxylic acid of the carboxylate is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, which may be substituted with a hydroxyl group. Examples of the saturated or unsaturated aliphatic carboxylate include, but are not limited to, calcium dimyristate, calcium dipalmitate, calcium distearate, (myristic acid-palmitic acid) calcium, (myristic acid-stearate) calcium, (palmitic acid-stearate) calcium, and calcium 12-hydroxystearate. Preferred examples include, but are not limited to, calcium dipalmitate, calcium distearate, and calcium 12-hydroxystearate.

[0138] Preferred examples of the weathering stabilizer include, but are not limited to, at least one selected from the group consisting of benzotriazole compounds, oxalic anilide compounds, and hindered amine light stabilizers.

[0139] Examples of the benzotriazole compounds include, but are not limited to, 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2-hydroxy-3,5-di-tert-amylphenyl]benzotriazole, 2-(2-hydroxy-3,5-diisopentylphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(2-hydroxy-4-octyloxyphenyl)benzotriazole. These compounds may be used alone or in combination of two or more.

[0140] Examples of the oxalic acid anilide compounds include, but are not limited to, N-(2-ethoxyphenyl)-N'-(2-ethylphenyl)oxamide, N-(2-ethoxy-5-tert-butylphenyl)-N'-(2-ethylphenyl)oxamide, and N-(2-ethoxyphenyl)-N'-(3-dodecylphenyl)oxamide. These compounds may be used alone or in combination of two or more.

[0141] Examples of hindered amine light stabilizers include 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, 4-stearoyloxy-2,2,6,6-tetramethylpiperidine, 4-cyclohexyloxy-2,2,6,6-tetramethylpiperidine, 4-benzyloxy-2,2,6,6-tetramethylpiperidine, and 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-piperidinyl) carbonate, bis(2,2,6,6-tetramethyl-4-piperidinyl) oxalate, bis(2,2,6,6-tetramethyl-4-piperidinyl) malonate, bis(1,2,6,6,6-pentamethyl-4-piperidinyl) sebacate, bis(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate Ester, 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-piperidyl)toluene-2,4-diaminocarboxylate, bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylene-1,6-diaminocarboxylate, benzene-1,3,5-tricarboxylic acid Examples include, but are not limited to, tris(2,2,6,6-tetramethyl-4-piperidinyl) ester, tris(2,2,6,6-tetramethyl-4-piperidinyl) benzene-1,3,4-tricarboxylate, 1-[2-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}butyl]-4-[3-(3,5-di-tert-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. These hindered amine light stabilizers may be used alone or in combination of two or more.

[0142] Among the above, preferred weathering stabilizers are 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]benzotriazole, 2-(2-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-tert-amylphenyl)benzotriazole, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, 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.

[0143] Preferred examples of the release agent and lubricant include, but are not limited to, alcohols, fatty acids and their esters, olefin compounds with an average degree of polymerization of 10 to 500, and silicones. The release agent and lubricant may be used alone or in combination of two or more.

[0144] Examples of the conductive agent include, but are not limited to, conductive carbon black, metal powder, and fiber. The conductive agent may be used alone or in combination of two or more.

[0145] Examples of the thermoplastic resin include, but are not limited to, polyolefin resins, acrylic resins, styrene resins, polycarbonate resins, and uncured epoxy resins. The thermoplastic resin may be used alone or in combination of two or more.

[0146] Examples of the thermoplastic elastomer include, but are not limited to, polyurethane elastomers, polyester elastomers, polystyrene elastomers, and polyamide elastomers. The thermoplastic elastomer may be used alone or in combination of two or more.

[0147] Examples of the dyes and pigments include inorganic pigments, organic pigments, metallic pigments, fluorescent pigments, and the like, but are not limited thereto.

[0148] The inorganic pigments are generally used for coloring resins, and examples thereof include, but are not limited to, zinc sulfide, titanium oxide, barium sulfate, titanium yellow, cobalt blue, fired pigments, carbonates, phosphates, acetates, carbon black, and acetylene black.

[0149] Examples of the organic pigments include condensed azo pigments, quinone pigments, monoazo pigments, disazo pigments, polyazo pigments, anthraquinone pigments, heterocyclic pigments, perinone pigments, quinacridone pigments, thioindigo pigments, perylene pigments, diazol pigments, and dapoxetine pigments. Pigments include, but are not limited to, oxazine, phthalocyanine, and the like.

[0150] The dyes and pigments may be used alone or in combination of two or more. It should be noted that the addition ratio of the dyes and pigments varies greatly depending on the color tone and is therefore difficult to determine. Generally, the dyes and pigments are used in an amount of 0.05 to 5 parts by mass relative to 100 parts by mass of the polyacetal resin.

[0151] In addition, other resins than the above-mentioned thermoplastic resins are not particularly limited, and examples thereof include polyolefin resins, acrylic resins, styrene resins, polycarbonate resins, and uncured epoxy resins.

[0152] In addition, other resins other than the thermoplastic resin may be used alone or in combination of two or more.

[0153] As the inorganic filler, for example, fibrous, granular, plate-like, and hollow fillers may be used, but the inorganic filler is not limited thereto.

[0154] 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, and brass. Furthermore, short-fiber whiskers such as potassium titanate whiskers and zinc oxide whiskers are also included.

[0155] Examples of the above-mentioned powdery filler include: silicates such as talc, carbon black, silicon dioxide, 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 aluminum oxide; metal sulfates such as calcium sulfate and barium sulfate; carbonates such as magnesium carbonate and dolomite; and silicon carbide, silicon nitride, boron nitride, and various metal powders, but are not limited thereto.

[0156] Examples of the plate-like filler include mica, glass flakes, and various metal foils, but are not limited thereto.

[0157] Examples of the hollow filler include, but are not limited to, glass hollow microspheres, silica hollow microspheres, white sand hollow microspheres, and metal hollow microspheres.

[0158] Examples of the organic filler include, but are not limited to, high-melting-point organic fibrous fillers such as aromatic polyamide resins, fluorine-containing resins, and acrylic resins.

[0159] These fillers may be used alone or in combination of two or more. As these fillers, any of surface-treated fillers and unsurface-treated fillers can be used, but from the perspective of the smoothness and mechanical properties of the molded surface, fillers that have been surface-treated using a surface treatment agent are sometimes preferably used.

[0160] The surface treatment agent is not particularly limited, and conventionally known surface treatment agents can be used.

[0161] Surface treatment agents include, but are not limited to, various coupling agents such as silanes, titanates, aluminums, and zirconiums; and surfactants such as resin acids, organic carboxylic acids, and salts of organic carboxylic acids. Specific examples include, but are not limited to, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyl tristearoyl titanate, diisopropoxyaluminum ethyl acetoacetate, and n-butyl zirconate.

[0162] When conventionally known additives are included, the content of the (A) polyacetal resin 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.

[0163] The molding method of the polyacetal resin composition of this embodiment is not particularly limited, and examples thereof include well-known molding methods, such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, heterogeneous material molding, 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, substrate-on-substrate injection molding), meltblowing molding, etc.

[0164] The shape of the molded article is not particularly limited, and examples thereof include injection molded articles (including on-substrate injection molded articles and insert molded articles), fibers / non-woven fabrics, sheets / films, and profile extrusions.

[0165] The use of the molded body is not particularly limited. For example, it can be suitably used in mechanical parts represented by gears, cams, sliders, rods, shafts, bearings and guides, especially automobile interior parts represented by door peripheral parts, seat belt peripheral parts, combination switch parts, and switches.

[0166] [Method for producing polyacetal resin composition]

[0167] The method for producing the polyacetal resin composition of the present embodiment is not particularly limited.

[0168] For example, the polyacetal resin composition can be obtained by mixing (A) polyacetal resin, (B) ethylene urea, (C) acrylamide polymer, (D) ethylene bisstearamide, and, if necessary, the above-specified components ((E) other additives) using, for example, a Henschel mixer, a tumbler, or a V-type mixer, and then kneading using a kneading machine such as a single-screw or multi-screw extruder, a heated roll, a kneader, or a Banbury mixer. Furthermore, (C) acrylamide polymer is preferably added to (D) ethylene bisstearamide during polymerization. From the perspectives of thermal stability and productivity, kneading is preferably performed using an extruder equipped with a vent pressure reducing device. Furthermore, to produce the polyacetal resin composition in large quantities and stably, a single-screw or twin-screw extruder is preferably used. In this case, pelletized polyacetal resin compositions (hereinafter sometimes referred to as "polyacetal resin pellets") can be obtained.

[0169] Alternatively, each component may be continuously supplied to an extruder alone or in combination using a quantitative feeder or the like without pre-mixing.

[0170] Alternatively, a high-concentration masterbatch containing each component may be prepared in advance and diluted with the polyacetal resin during extrusion melt kneading.

[0171] The kneading temperature may be determined according to the preferred processing temperature of the polyacetal resin used, and is usually set within the range of 140°C to 260°C, preferably within the range of 180°C to 230°C.

[0172] The method for drying the polyacetal resin pellets obtained above is not particularly limited, and examples thereof include drying methods using a box dryer (normal pressure, vacuum), a tunnel dryer, a belt dryer, a rotary dryer, a ventilated rotary dryer, a tank-type stirring dryer, a fluidized bed dryer, a multi-stage disk dryer, a spray dryer, an airflow dryer, an infrared dryer, a high-frequency dryer, and the like.

[0173] Among them, box-type dryers, rotary and ventilation rotary dryers, tank-type stirring dryers, fluidized bed dryers, multi-stage disc dryers, and airflow dryers are preferred, and fluidized bed dryers are more preferred from the viewpoint of productivity.

[0174] The drying temperature, measured as the temperature of the heat medium, is preferably 80° C. or higher, more preferably 100° C. or higher. Furthermore, the drying time, starting from the point in time 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.

[0175] [Molding of polyacetal resin composition]

[0176] The polyacetal resin composition of this embodiment can be molded and used as a molded article. The molding method is not particularly limited, and the composition can be molded using any of the known molding methods, such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, heterogeneous 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, on-substrate injection molding). Among these, injection molding is preferred from the perspective of stable productivity.

[0177] Furthermore, even when the polyacetal resin composition of the present embodiment is used for continuous molding using a mold molding method in which the material is exposed to high temperature for a long period of time, such as molding using a hot runner mold, mold contamination is minimal.

[0178] [Application of molded articles of polyacetal resin compositions]

[0179] The polyacetal resin composition of this embodiment has excellent quality stability and can be used as molded articles for a variety of applications. For example, it can be used in mechanical parts such as gears, cams, sliders, levers, shafts, bearings, and guides; resin parts that are injection-molded onto substrates; resin parts that are insert-molded (chassis, trays, and side panels); parts for printers and copiers; parts for digital cameras and digital video equipment; parts for music, imaging, and information equipment; parts for communications equipment; parts for electrical equipment; and parts for electronic equipment.

[0180] In addition, molded articles of the polyacetal resin composition of this embodiment are suitable for use in fuel peripheral parts such as fuel tanks, fuel pump modules, valves, and tank flanges, door peripheral parts, seat belt peripheral parts, combination switch parts, and switches as automotive parts.

[0181] Furthermore, the molded article of the polyacetal resin composition of the present embodiment can also be suitably used as industrial parts such as housing equipment.

[0182] While the embodiment for carrying out the present invention has been described above, the present invention is not limited to the embodiment and various modifications can be made to the present invention without departing from the spirit and scope of the present invention.

[0183] Example

[0184] 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.

[0185] The measurement and evaluation methods used in Examples and Comparative Examples are shown below.

[0186] <Measurement of Formaldehyde Emission from Molded Articles>

[0187] The prepared polyacetal resin pellets were molded according to the molding conditions (a) below, and the formaldehyde emission from the molded articles was measured using the VDA275 method (b) below.

[0188] (a) Molding conditions

[0189] Injection molding machine: Toshiba Machine Co., Ltd. IS-100GN

[0190] Barrel set temperature: 220℃

[0191] Mold setting temperature: 80℃

[0192] Mold type: cold runner type

[0193] Test piece size: 100mm×40mm×3mm

[0194] Molding cycle: injection time / cooling time = 30 seconds / 15 seconds

[0195] The formaldehyde emission from the molded articles was measured by the method shown below (VDA 275 method).

[0196] (b) VDA 275 method:

[0197] 50 mL of distilled water and a test piece of predetermined dimensions (100 mm × 40 mm × 3 mm) were placed in a polyethylene container, which was sealed. The container was heated at 60°C for 3 hours to extract formaldehyde into the distilled water, and then cooled to room temperature.

[0198] After cooling, 5 mL of a 0.4 mass % aqueous solution of acetylacetone and 5 mL of a 20 mass % aqueous solution of ammonium acetate were added to 5 mL of distilled water that absorbed formaldehyde to obtain a mixed solution, which was heated at 40° C. for 15 minutes to react formaldehyde with acetylacetone.

[0199] Then, the mixed solution was cooled to room temperature, and the amount of formaldehyde absorbed into the distilled water was quantified using a UV spectrophotometer based on the absorption peak at 412 nm.

[0200] The formaldehyde emission (mg / kg) from the molded article was calculated using the following formula.

[0201] Formaldehyde emission from molded products (mg / kg)

[0202] = Amount of formaldehyde absorbed in distilled water (mg) / Mass of the polyacetal resin molded article used for measurement (kg)

[0203] <Charpy Impact Value>

[0204] The Charpy impact value was measured as an indicator of mechanical strength.

[0205] Test specimens were produced using an EC100SX machine manufactured by Toshiba Machine Co., Ltd. under the following conditions: barrel temperature: 205°C, injection time: 35 seconds, cooling time: 15 seconds, and mold temperature: 90°C. ISO dumbbell test specimens for physical property evaluation were molded. The following tests were performed on these specimens. Charpy impact strength (ISO 179 / 1eA) was measured the day after molding.

[0206] <Tensile elongation retention in high temperature and high humidity environment>

[0207] Test specimens were produced using a Toshiba Machine EC100SX under the following conditions: 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. ISO dumbbell test specimens for physical property evaluation were molded. The resulting molded products were allowed to stand for 500 hours in an environment of 90°C and 80% humidity. The tensile elongation was then measured using an Autograph. The elongation retention was calculated using a sample left at room temperature of 23°C as a reference.

[0208] <Tensile strength retention in high-temperature dry environment>

[0209] Test specimens were produced using a Toshiba Machine EC100SX under the following conditions: a barrel temperature of 205°C, an injection time of 35 seconds, a cooling time of 15 seconds, and a mold temperature of 90°C. ISO dumbbell test specimens for physical property evaluation were then molded. The resulting molded products were then allowed to stand for 1500 hours in an environment of 95°C and 20% humidity. The tensile strength was then measured using an Autograph. The tensile strength retention was calculated using a sample that had been allowed to stand at room temperature of 23°C as a reference.

[0210] <Mold Deposits (MD)>

[0211] The produced polyacetal resin pellets were molded according to the molding conditions (a) below, and the mold deposit properties at this time were evaluated according to the evaluation criteria (b) below.

[0212] (a) Molding conditions

[0213] Injection molding machine: Si-30V manufactured by Toyo Machinery & Metal Co., Ltd.

[0214] Barrel set temperature: 200℃

[0215] Mold setting temperature: 43℃

[0216] Molding cycle: injection time / cooling time = 20 seconds / 20 seconds

[0217] (b) Evaluation criteria

[0218] Based on the following evaluation criteria, the mold deposit adhesion condition in the mold cavity at the 1000th shot from the start of molding was observed.

[0219] A: No MD adhesion is observed in the mold cavity

[0220] B: A small amount of MD was observed in the mold cavity

[0221] C: A large amount of film-like MD is observed in the mold cavity

[0222] <Molding shrinkage>

[0223] The mold shrinkage was measured as an indicator of dimensional stability after injection molding.

[0224] The produced polyacetal resin pellets were molded under the molding conditions (a) below, and the molding shrinkage at this time was evaluated by the method (b) below.

[0225] (a) Molding conditions

[0226] Injection molding machine: Toshiba Machine Co., Ltd. IS-100GN

[0227] Barrel set temperature: 220℃

[0228] Mold setting temperature: 80℃

[0229] Mold type: cold runner type

[0230] Test piece mold size: vertical 100mm × horizontal 40mm × thickness 3mm

[0231] Molding cycle: injection time / cooling time = 30 seconds / 15 seconds

[0232] (b) Evaluation method

[0233] The longitudinal and lateral dimensions of ten obtained molded articles were measured, and the molding shrinkage was determined by the following method.

[0234] Molding shrinkage (%) = ((1-(average longitudinal dimension of 10 molded products / vertical dimension of test piece mold 100 mm))) + ((average transverse dimension of 1-10 molded products / transverse dimension of test piece mold 40 mm))) / 2×100

[0235] [Raw Materials]

[0236] The raw material components used in Examples and Comparative Examples are shown below.

[0237] <(A) Polyacetal resin>

[0238] A-1: Polyacetal homopolymer (MFR: 2.0 g / 10 min)

[0239] A-2: Polyacetal homopolymer (MFR: 10.0 g / 10 min)

[0240] The preparation methods of A-1 and A-2 are described below.

[0241] (A-1: Preparation of polyacetal homopolymer)

[0242] A polymerization reactor equipped with a stirring blade was filled with n-hexane, and purified formaldehyde gas (water content: 110 ppm), a polymerization catalyst (dimethyldistearylammonium acetate), and a molecular weight modifier (acetic anhydride) were continuously supplied to allow polymerization to proceed. The polymerization temperature was set at 58°C.

[0243] The resulting crude polyacetal homopolymer was placed in a reaction vessel filled with a 1:1 mixture of n-hexane and acetic anhydride and stirred at 150°C for 2 hours to esterify the unstable ends of the crude polyacetal homopolymer. The mass ratio (slurry concentration) of the polymer to the 1:1 mixture of n-hexane and acetic anhydride at this point was 20 parts polymer per 100 parts n-hexane and acetic anhydride.

[0244] After the terminal stabilization treatment of the polyacetal homopolymer is completed, the "1:1 mixture of n-hexane and acetic anhydride" and the polyacetal homopolymer are removed from the reaction vessel and repeatedly washed with n-hexane to remove the acetic anhydride. This washing process is repeated until the acetic anhydride concentration in the polyacetal homopolymer reaches 10 ppm by mass or less.

[0245] The polyacetal homopolymer was then dried under reduced pressure at 120°C for 3 hours at -700 mmHg to remove the n-hexane solvent used for washing. The polyacetal homopolymer was then dried in a heating dryer set at 120°C for 5 hours to remove moisture contained in the polyacetal homopolymer. This yielded a powdered polyacetal homopolymer (A-1) having an MFR of 2.0 g / 10 minutes (average particle size of 200 μm).

[0246] The average particle size of the polyacetal polymer was measured using a laser diffraction particle size distribution analyzer.

[0247] (A-2: Preparation of polyacetal homopolymer)

[0248] A powdery polyacetal homopolymer (A-2) having an MFR of 10.0 g / 10 min (average particle size of 200 μm) was obtained by the same production method as for the polyacetal homopolymer (A-1), except that the molecular weight was changed by adjusting the amount of the molecular weight modifier (acetic anhydride) added.

[0249] <(B) Ethylene urea>

[0250] B-1: Ethylene urea (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0251] <(C) Acrylamide polymer>

[0252] C-1: Acrylamide polymer (primary amide group content: 50.4 mol%, average particle size: 5.1 μm)

[0253] (C-1) Acrylamide polymer was prepared as follows.

[0254] In a 5 L batch reactor equipped with a stirrer, 2400 g of acrylamide, 267 g of N,N'-methylenebisacrylamide, and 0.54 g of tetraisopropoxyzirconium as a catalyst (1 / 10000 mol relative to acrylamide) were added and reacted at 125°C for 4 hours with stirring in a N2 stream.

[0255] After the reaction was completed, the solid matter was pulverized using a jet mill and washed with acetone.

[0256] Then, the mixture was dried under reduced pressure at 120° C. for 20 hours at a reduced pressure of −700 mmHg to obtain an acrylamide polymer (C-1).

[0257] The obtained acrylamide polymer (C-1) had a primary amide group content of 50.4 mol % and an average particle size of 5.1 μm. The average particle size was measured using a laser diffraction particle size distribution analyzer.

[0258] <(D) Ethylene bisstearamide>

[0259] D-1: Ethylene bisstearamide (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0260] <(E) Other additives>

[0261] E-1: Sebacic acid dihydrazide (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0262] E-2: Allantoin (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0263] E-3: Hydantoin (heat stabilizer, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0264] E-4: Polyamide 66 (heat stabilizer, manufactured by Asahi Kasei Corporation)

[0265] E-5: Triethylene glycol bis(3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate) (hindered phenol antioxidant, manufactured by SONGWON Co., Ltd.)

[0266] [Example 1, Example 3 to Example 13]

[0267] The powdered polyacetal homopolymer (A-1) produced above, which is the polyacetal resin; ethylene urea (B-1); acrylamide polymer (C-1); and triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] as a hindered phenolic antioxidant (E) as another additive were uniformly mixed in the amounts shown in Table 1 below to obtain a mixture. Ethylene bisstearamide (D) was added during the polymerization of the acrylamide polymer (C).

[0268] The mixture was fed from the top feed port of a twin-screw extruder with a 40 mm vent port and L (screw length) / D (screw inner diameter) = 48, set at 200°C, and melt-kneaded under the conditions of a screw speed of 200 rpm, a vent pressure reduction of -0.08 MPa, and a discharge rate of 50 kg / hour. The mixture was then pelletized by thermal cutting at the extruder die outlet. The pellets were then placed in warm water adjusted to 40°C and stirred for a certain period of time. The moisture was removed by a centrifugal separator, and the pellets were placed in a fluidized bed hot air dryer and dried at a hot air temperature of 100°C for 3 hours to obtain polyacetal resin pellets.

[0269] The obtained polyacetal resin pellets were used to evaluate and measure formaldehyde emission from molded articles, mechanical properties after testing in a high-temperature dry environment and a high-temperature, high-humidity environment, mold deposit resistance, and mold shrinkage by the above-mentioned methods.

[0270] The evaluation results are shown in Table 1 below.

[0271] [Example 2]

[0272] Polyacetal resin pellets were obtained by the same procedures as in Example 1, except that (D) ethylene bisstearamide was mixed and added simultaneously with the powdered polyacetal homopolymer (A-1). Using the obtained polyacetal resin pellets, formaldehyde emission from molded articles, mechanical properties after testing under high-temperature dry conditions and high-temperature, high-humidity conditions, mold deposit resistance, and mold shrinkage were evaluated and measured using the above-described methods.

[0273] The evaluation results are shown in Table 1 below.

[0274] [Comparative Examples 1 to 2, Comparative Examples 5 to 11, Comparative Example 13]

[0275] Except for adjusting the composition as shown in Table 2, the same operation as in Example 2 was carried out to obtain polyacetal resin pellets.

[0276] The obtained polyacetal resin pellets were used to evaluate and measure formaldehyde emission from molded articles, mechanical properties after testing in a high-temperature dry environment and a high-temperature, high-humidity environment, mold deposit resistance, and mold shrinkage by the above-mentioned methods.

[0277] The evaluation results are shown in Table 2 below.

[0278] [Comparative Examples 3 to 4, Comparative Example 12]

[0279] Except for adjusting the composition as shown in Table 2, the same operation as in Example 1 was carried out to obtain polyacetal resin pellets.

[0280] The obtained polyacetal resin pellets were used to evaluate and measure formaldehyde emission from molded articles, mechanical properties after testing in a high-temperature dry environment and a high-temperature, high-humidity environment, mold deposit resistance, and mold shrinkage by the above-mentioned methods.

[0281] The evaluation results are shown in Table 2 below.

[0282] [Table 1]

[0283]

[0284] [Table 2]

[0285]

[0286] As shown in Table 1, the molded articles comprising the polyacetal resin compositions obtained in Examples 1 to 13 exhibit excellent formaldehyde emission suppression, mechanical strength retention under high-temperature dry conditions and high-temperature, high-humidity conditions, and dimensional stability after molding. Furthermore, they exhibit excellent mold deposit resistance.

[0287] On the other hand, as shown in Table 2, the molded articles comprising the polyacetal resin compositions obtained in Comparative Examples 1 to 13 may not be able to suppress the amount of formaldehyde released from the molded articles, may suffer from a decrease in mechanical property retention in a high-temperature dry environment and a high-temperature, high-humidity environment, may have poor mold deposit resistance and dimensional stability after molding, and may have a poor performance balance.

[0288] Industrial Applicability

[0289] The polyacetal resin composition of the present invention can be suitably used in a wide range of fields such as automobiles, electrical and electronic industries, and other industries.

Claims

1. A polyacetal resin composition, wherein The polyacetal resin composition comprises, relative to 100 parts by mass of the (A) polyacetal resin: 0.03 to 0.60 parts by mass of (B) ethylene urea, 0.05 to 0.50 parts by mass of (C) an acrylamide polymer, and 0.0005 to 0.05 parts by mass of (D) ethylene bisstearamide.

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

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

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

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

6. The polyacetal resin composition according to claim 1 or 2, wherein The polyacetal resin composition includes 0.05 to 0.20 parts by mass of the (C) acrylamide polymer.

7. The polyacetal resin composition according to claim 1 or 2, wherein The mass ratio (D) / (C) of the (D) ethylene bisstearamide to the (C) acrylamide polymer is 0.01 to 0.5.

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