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, even when a molded article is manufactured by exposing a material to a high temperature for a long period of time, causes little mold contamination and causes little formaldehyde emission and little foreign matter generation in the molded article. The polyacetal resin composition according to the present invention is characterized by containing (A) a polyacetal resin and (B) a semi-aromatic polyamide resin containing a dicarboxylic acid unit and a diamine unit, the dicarboxylic acid unit containing 75 mol% or more of an isophthalic acid unit, the diamine unit containing 75 mol% or more of an isophthalic acid unit, the diamine unit containing 75 mol% or more of an isophthalic acid unit, and the polyacetal resin. The diamine unit contains 50 mol% or more of a diamine unit having 4-10 carbon atoms, and the number average molecular weight Mn of the semi-aromatic polyamide resin is 3000-20000 (inclusive).

Description

[0001] This application is a divisional application of the Chinese patent application with application date of June 9, 2020 and application number 202080041019.4. Technical Field

[0002] The present invention relates to polyacetal resin compositions. Background Art

[0003] Polyacetal resin is a crystalline resin and has been widely used as a material for mechanical parts such as automobile parts, electric / electronic parts, and industrial parts, etc., due to its excellent rigidity, strength, toughness, sliding properties, and creep properties.

[0004] As a technology for improving the thermal stability of polyacetal resin, for example, a method of adding a polyamide oligomer to polyacetal resin (for example, see Patent Document 1 below) and a method of adding a polyamide having an aromatic ring and magnesium hydroxide to polyacetal resin (for example, see Patent Document 2 below) have been proposed.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 50-145458

[0008] Patent Document 2: Japanese Patent Application Publication No. 2013-32416 Summary of the invention

[0009] Problems to be solved by the invention

[0010] Cold runner molds are generally used for molding of polyacetal resin parts. However, when a cold runner mold is used for molding, in addition to the target molded product, an unnecessary runner portion is also molded. Therefore, the unnecessary runner portion needs to be discarded, or crushed by a crusher, etc., and then mixed in a small amount into polyacetal resin pellets, etc., which are the raw materials, for reprocessing and molding.

[0011] Here, when the runner part is re-processed and molded, the runner part is subjected to the heat history generated by molding more than once, which sometimes affects the resin fluidity or thermal stability in the barrel of the molding machine, sometimes causing molding defects such as burrs and warping, making it difficult to produce stably. Under such circumstances, in recent years, in the molding of polyacetal resin parts, the tendency to select hot runner molds has become higher from the perspective of improving production stability and reducing production costs.

[0012] When continuous molding is performed using a hot runner mold, the temperature of the manifold (the part where the molten resin accumulates: the hot runner part) in the mold is usually set to a temperature higher than the temperature of the molding machine barrel. Therefore, polyacetal resin is required to have higher thermal stability than when continuous molding is performed using a cold runner mold.

[0013] In particular, when continuous molding is performed using a hot runner mold, the resin composition stays in the hot runner manifold for a long time at high temperature, which promotes thermal decomposition of the polyacetal resin, deteriorates the low VOC property during long-term molding, and causes contamination of the mold interior due to mold deposits and generation of foreign matter during long-term continuous molding.

[0014] However, these problems have not been recognized in the past, and continuous molding using hot runner molds has caused mold contamination, formaldehyde release, and foreign matter generation.

[0015] Therefore, an object of the present invention is to provide a polyacetal resin composition which reduces mold contamination even when a molded product is produced under conditions where the material is exposed to high temperature for a long period of time and suppresses formaldehyde emission and foreign matter generation from the molded product.

[0016] Means used to solve problems

[0017] The present inventors have conducted intensive studies to solve the above-mentioned problems of the prior art and have found that the above-mentioned problems can be solved by adding a specific semi-aromatic polyamide resin containing a dicarboxylic acid unit containing an isophthalic acid unit and a diamine unit containing a diamine unit having 4 to 10 carbon atoms to a polyacetal resin, thereby completing the present invention.

[0018] That is, the present invention is as follows.

[0019] [1] A polyacetal resin composition, characterized in that the polyacetal resin composition contains: (A) a polyacetal resin; and (B) a semi-aromatic polyamide resin, wherein the semi-aromatic polyamide resin contains a dicarboxylic acid unit and a diamine unit, the dicarboxylic acid unit contains 75 mol % or more of an isophthalic acid unit, the diamine unit contains 50 mol % or more of a diamine unit having 4 to 10 carbon atoms, and the number average molecular weight Mn of the semi-aromatic polyamide resin is 3000 or more and 20000 or less.

[0020] [2] The polyacetal resin composition according to [1], wherein the content of the (B) semi-aromatic polyamide resin is 0.01 part by mass or more and 1.00 part by mass or less per 100 parts by mass of the (A) polyacetal resin.

[0021] [3] The polyacetal resin composition according to [1] or [2], wherein the (B) semi-aromatic polyamide resin is an amorphous polyamide.

[0022] [4] The polyacetal resin composition according to any one of [1] to [3], wherein the (B) semi-aromatic polyamide resin is polyamide 6I.

[0023] [5] The polyacetal resin composition according to any one of [1] to [4], wherein the number average molecular weight Mn of the (B) semi-aromatic polyamide resin is 5,000 or more and 20,000 or less.

[0024] [6] The polyacetal resin composition according to any one of [1] to [5], wherein the number average molecular weight Mn of the (A) polyacetal resin is 75,000 or more and 150,000 or less.

[0025] [7] The polyacetal resin composition according to any one of [1] to [6], wherein the (A) polyacetal resin is a polyacetal homopolymer.

[0026] [8] The polyacetal resin composition according to any one of [1] to [7], wherein the polyacetal resin composition contains 0.01 parts by mass or more and 0.50 parts by mass or less of (B) semi-aromatic polyamide resin relative to 100 parts by mass of (A) polyacetal resin.

[0027] [9] A method for producing a polyacetal resin composition, characterized in that (B) a semi-aromatic polyamide resin is added to (A) a polyacetal resin, wherein the semi-aromatic polyamide resin contains a dicarboxylic acid unit and a diamine unit, the dicarboxylic acid unit contains 75 mol % or more of an isophthalic acid unit, the diamine unit contains 50 mol % or more of a diamine unit having 4 to 10 carbon atoms, and the number average molecular weight Mn of the semi-aromatic polyamide resin is 3,000 or more and 20,000 or less.

[0028]

[10] A method for heat stabilization of a polyacetal resin, characterized in that (B) a semi-aromatic polyamide resin is added to (A) a polyacetal resin, wherein the semi-aromatic polyamide resin contains a dicarboxylic acid unit and a diamine unit, the dicarboxylic acid unit contains 75 mol % or more of an isophthalic acid unit, the diamine unit contains 50 mol % or more of a diamine unit having 4 to 10 carbon atoms, and the number average molecular weight Mn of the semi-aromatic polyamide resin is 3000 or more and 20000 or less.

[0029] Effects of the Invention

[0030] According to the present invention, a polyacetal resin composition can be provided which reduces mold contamination and reduces formaldehyde emission and foreign matter generation in molded products even when the material is exposed to high temperature for a long period of time to produce a molded product. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram showing a hot runner mold molding machine used in the examples. DETAILED DESCRIPTION

[0032] Hereinafter, a mode for carrying out the present invention (hereinafter sometimes referred to as “the present embodiment”) will be described in detail.

[0033] It should be noted that the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist of the invention.

[0034] (Polyacetal resin composition)

[0035] The polyacetal resin composition of the present embodiment contains (A) a polyacetal resin and (B) a semi-aromatic polyamide resin, wherein the semi-aromatic polyamide resin contains a dicarboxylic acid unit and a diamine unit, wherein the dicarboxylic acid unit contains 75 mol % or more of an isophthalic acid unit, and the diamine unit contains 50 mol % or more of a diamine unit having 4 to 10 carbon atoms, and the number average molecular weight Mn of the semi-aromatic polyamide resin is greater than or equal to 3000 and less than or equal to 20000 (sometimes referred to as "(B) semi-aromatic polyamide resin" in the present specification).

[0036] First, components that may be contained in the polyacetal resin composition of the present embodiment will be described.

[0037] [(A) Polyacetal resin]

[0038] The (A) polyacetal resin contained in the polyacetal resin composition of the present embodiment refers to a polymer having an oxymethylene group in the main chain, and examples thereof include: a polyacetal homopolymer substantially containing only oxymethylene units obtained by homopolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trimer) or a tetramer (tetramer); a polyacetal homopolymer obtained by homopolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trimer) or a tetramer (tetramer) with ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane, 1,2-dioxane, 1,3-dioxane, 1,4 ... , a polyacetal copolymer obtained by copolymerizing a diol such as 4-butanediol formal or a cyclic ether or cyclic formal such as a cyclic formal of a glycol; a polyacetal copolymer with a branched chain obtained by copolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trimer) or a tetramer (tetramer) with a monofunctional glycidyl ether; a polyacetal copolymer with a cross-linked structure obtained by copolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trimer) or a tetramer (tetramer) with a multifunctional glycidyl ether, etc.

[0039] In addition, as the (A) polyacetal resin, there can be used compounds having functional groups such as hydroxyl groups at both ends or at one end, for example, a polyacetal homopolymer having a block component obtained by polymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trimer) or a tetramer (tetramer) in the presence of a polyalkylene glycol; and similarly, compounds having functional groups such as hydroxyl groups at both ends or at one end, for example, a polyacetal copolymer having a block component obtained by copolymerizing a formaldehyde monomer or a cyclic oligomer of formaldehyde such as a trimer (trimer) or a tetramer (tetramer) with a cyclic ether or a cyclic formal in the presence of a hydrogenated polybutadiene diol.

[0040] The above-mentioned polyacetal resins may be used alone or in combination of two or more.

[0041] As described above, the polyacetal resin (A) may be either a polyacetal homopolymer or a polyacetal copolymer. Among them, a polyacetal homopolymer is preferred from the viewpoint of mechanical properties.

[0042] In addition, the degree of polymerization and the comonomer content of the (A) polyacetal resin in the present embodiment are not particularly limited.

[0043] <Polyacetal homopolymer>

[0044] The polyacetal homopolymer can be produced, for example, by feeding formaldehyde as a monomer, a chain transfer agent (molecular weight regulator), and a polymerization catalyst into a polymerization reactor into which a hydrocarbon polymerization solvent has been introduced, and polymerizing the mixture by a slurry polymerization method.

[0045] At this time, the raw material monomers, chain transfer agents, and polymerization catalysts may contain components that can cause chain transfer (components that generate unstable terminal groups), such as water, methanol, and formic acid. Therefore, it is preferred to first adjust the content of these components that can cause chain transfer. The content of these components that can cause chain transfer is preferably in the range of 1 mass ppm to 1000 mass ppm, more preferably 1 mass ppm to 500 mass ppm, and further preferably 1 mass ppm to 300 mass ppm relative to the total mass of formaldehyde as a monomer. By adjusting the content of the components that can cause chain transfer to the above range, a polyacetal homopolymer with excellent thermal stability can be obtained.

[0046] The molecular weight of the polyacetal homopolymer can be adjusted by causing 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.

[0047] The amount of the molecular weight regulator to be introduced is adjusted and determined according to the properties (particularly, melt flow rate) of the target polyacetal homopolymer.

[0048] As the polymerization catalyst, an anionic polymerization catalyst is preferred, and more preferably a catalyst represented by the following general formula (I): Salt polymerization catalyst, [R1R2R3R4M] + X - ...(I) (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).

[0049] The polymerization catalyst may be used alone or in combination of two or more.

[0050] exist Among the salt polymerization catalysts, tetraethyl iodide is preferred. , tributyl ethyl iodide Waiting for the season Salt compounds; quaternary ammonium salt compounds such as tetramethylammonium bromide and dimethyl distearyl ammonium acetate.

[0051] 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.

[0052] The hydrocarbon polymerization solvent is not particularly limited as long as it is a solvent that does not react with formaldehyde, and examples thereof include pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, benzene and the like, with hexane being particularly preferred. These hydrocarbon solvents may be used alone or in combination of two or more.

[0053] In the production of the polyacetal homopolymer, it is preferred that a crude polyacetal homopolymer is first obtained by polymerization and then subjected to a stabilization treatment for unstable terminal groups as described below.

[0054] The polymerization reactor used for producing 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, but a continuous polymerization reactor is preferred from the viewpoint of productivity.

[0055] The terminal groups of the crude polyacetal homopolymer obtained by polymerization are thermally unstable, and therefore, it is preferred to perform a stabilization treatment by capping the unstable terminal groups with an esterifying agent, an etherifying agent, or the like.

[0056] The stabilization treatment of the terminal groups of the crude polyacetal homopolymer by esterification can be carried out, for example, by introducing the crude polyacetal homopolymer, the esterification agent, and the esterification catalyst into a terminal stabilization reactor into which a hydrocarbon solvent is introduced and reacting them. As for the reaction temperature and reaction time at this time, for example, the reaction temperature is preferably 130° C. to 155° C. and the reaction time is 1 minute to 100 minutes, more preferably the reaction temperature is 135° C. to 155° C. and the reaction time is 5 minutes to 100 minutes, and further preferably the reaction temperature is 140° C. to 155° C. and the reaction time is 10 minutes to 100 minutes.

[0057] As an esterifying agent for 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).

[0058] The esterifying agent is not limited to the following, and examples thereof include benzoic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, propionic anhydride, and acetic anhydride, preferably acetic anhydride. These esterifying agents may be used alone or in combination of two or more.

[0059] As the above-mentioned esterification catalyst, an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is preferred, and the amount of the esterification catalyst added can be appropriately selected within the range of 1 mass ppm to 1000 mass ppm relative to the mass of the polyacetal homopolymer. As the alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms, it is not limited to the following substances, and examples thereof include alkali metal salts of carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptanoic acid, octanoic acid, nonanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, heptadecanoic acid, and stearic acid, and examples of the alkali metal include lithium, sodium, potassium, rubidium, and cesium. Moreover, among these carboxylic acid metal salts, lithium acetate, sodium acetate, and potassium acetate are preferred.

[0060] As the etherifying agent for capping the terminal groups of the above-mentioned crude polyacetal homopolymer and stabilizing it, it can be selected from the orthoesters of aliphatic acids or aromatic acids and aliphatic alcohols, alicyclic alcohols 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. It can be stabilized by using medium-strength organic acids such as p-toluenesulfonic acid, acetic acid and oxalic acid; Lewis acid catalysts such as dimethyl sulfate and diethyl sulfate.

[0061] The solvent used for the etherification reaction when the terminal groups of the crude polyacetal homopolymer are capped and stabilized by etherification is not limited to the following solvents, for example, low-boiling aliphatic organic solvents such as pentane, hexane, cyclohexane and benzene, alicyclic hydrocarbon organic solvents and aromatic hydrocarbon organic solvents; halogenated lower aliphatic organic solvents such as dichloromethane, chloroform and carbon tetrachloride, etc.

[0062] The polyacetal homopolymer whose terminal groups are stabilized by the above method is dried by removing moisture using a dryer such as a hot air dryer or a vacuum dryer and sealing air or nitrogen adjusted to 100° C. to obtain a polyacetal homopolymer as the polyacetal resin (A).

[0063] <Polyacetal copolymer>

[0064] First, 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 are described.

[0065] -Trioxane-

[0066] Trioxymethylene refers to a cyclic trimer of formaldehyde, and is generally obtained by reacting an aqueous formaldehyde solution in the presence of an acidic catalyst.

[0067] Since the trioxane may contain impurities such as water, methanol, formic acid, and methyl formate that may cause chain transfer, it is preferred to remove these impurities by distillation or the like to purify the product. In this case, the total amount of impurities that may cause chain transfer is preferably adjusted to 1×10 -3 More preferably, the total amount of impurities causing chain transfer is 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.

[0068] -Cyclic ether and / or cyclic formal-

[0069] The cyclic ether and / or cyclic formal is a component that can be copolymerized with the above-mentioned trioxymethylene, and examples thereof include: ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxetanes, 1,3-dioxolane, ethylene glycol formal, propylene glycol formal, diethylene glycol formal, triethylene glycol formal, 1,4-butanediol formal, 1,5-pentanediol formal, 1,6-hexanediol formal, etc. Moreover, the cyclic ether and / or cyclic formal is preferably 1,3-dioxolane and 1,4-butanediol formal. These cyclic ethers and / or cyclic formals can be used alone or in combination of two or more.

[0070] 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 more preferably in the range of 1 mol % to 5 mol %, relative to 1 mol of the above-mentioned trioxymethylene.

[0071] -Polymerization Catalyst-

[0072] As the polymerization catalyst, halides of boron, tin, titanium, phosphorus, arsenic and antimony represented by Lewis acid can be cited, and boron trifluoride, boron trifluoride hydrate, and coordination complexes of organic compounds containing oxygen atoms or sulfur atoms and boron trifluoride are particularly preferred. For example, boron trifluoride, boron trifluoride ethyl etherate, and boron trifluoride di-n-butyl etherate can be cited as preferred examples. These polymerization catalysts can be used alone or in combination of two or more.

[0073] 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 -4 The range of moles is 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.

[0074] -Low molecular weight acetal compound-

[0075] The low molecular weight acetal compound functions as a chain transfer agent in the polymerization reaction, and the low molecular weight acetal compound is an acetal compound having a molecular weight of 200 or less, preferably 60 to 170. Specifically, methylal, methoxymethylal, dimethoxymethylal, and trimethoxymethylal can be cited as preferred examples. These low molecular weight acetal compounds can be used alone or in combination of two or more.

[0076] From the viewpoint of controlling the molecular weight of the polymer within a suitable range, the amount of the low molecular weight acetal compound added is preferably 1×10 -4 Mole~0.6×10 -2 within the molar range.

[0077] -Organic Solvents-

[0078] As the organic solvent, there is no particular limitation as long as it does not participate in the polymerization reaction or does not have an adverse effect, and examples thereof 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); 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), and the like. In particular, from the viewpoint of suppressing tarry precipitates, aliphatic hydrocarbons such as n-hexane, n-heptane, and cyclohexane are preferred examples. These organic solvents may be used alone or in combination of two or more.

[0079] 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 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 having excellent productivity can be obtained.

[0080] -Polymerization of polyacetal copolymers-

[0081] 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 may be carried out in either a batch method or a continuous method.

[0082] The polymerization reactor is not particularly limited, and examples thereof include self-cleaning extrusion kneading machines such as a co-kneader, a twin-screw continuous extruder, and a twin-shaft paddle continuous mixer. These devices preferably have a jacket through which a heat medium can pass.

[0083] Each material is supplied to the polymerization reactor, and then the temperature of the polymerization reactor during the polymerization reaction is preferably maintained at 63°C to 135°C, more preferably in the range of 70°C to 120°C, and further preferably in the range of 70°C to 100°C. In addition, the residence (reaction) time in the polymerization reactor is preferably 0.1 minute to 30 minutes, more preferably 0.1 minute to 25 minutes, and further preferably 0.1 minute to 20 minutes. If the temperature and residence time of the polymerization reactor are within the above ranges, there is a tendency for a stable polymerization reaction to continue.

[0084] Then, a crude polyacetal copolymer is obtained by polymerization reaction. Here, as a method for deactivating the polymerization catalyst, the following method can be cited: the crude polyacetal copolymer coming out of the polymerization reactor is put into an aqueous solution or organic solution containing at least one of the neutralizing and deactivating agents such as amines such as ammonia, triethylamine, tri-n-butylamine, hydroxides of alkali metals or alkaline earth metals, inorganic salts, and organic acid salts, and is continuously stirred in a slurry state at room temperature to 100° C. for several minutes to several hours. At this time, when the crude polyacetal copolymer is in the form of large blocks, it is preferably processed by crushing after polymerization. Then, it is filtered using a centrifuge and dried under nitrogen to obtain a polyacetal copolymer.

[0085] The obtained polyacetal copolymer may contain thermally unstable terminal parts [-(OCH2) n -OH group] (hereinafter, such a polyacetal copolymer is sometimes referred to as a "polyacetal copolymer before terminal stabilization"). Therefore, it is preferred to use a terminal stabilizer to carry out a decomposition and removal treatment (terminal stabilization) of the unstable terminal portion. The terminal stabilizer is not particularly limited, and examples thereof include: aliphatic amine compounds such as ammonia, triethylamine, and tributylamine; hydroxides of alkali metals or alkaline earth metals such as sodium, potassium, magnesium, calcium, or barium; inorganic weak acid salts of alkali metals or alkaline earth metals such as carbonates, phosphates, silicates, and borates; 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 them, aliphatic amine compounds are preferred, and triethylamine is more preferred.

[0086] There are no particular restrictions on the method for decomposing and removing the unstable terminal portion, and examples thereof include the following method: heat treatment in the presence of a terminal stabilizer such as triethylamine at a temperature above the melting point of the polyacetal copolymer and below 260° C., in a state where the polyacetal copolymer is molten. Examples of the method for heat treatment include a single-screw or twin-screw extruder having a vent pressure reducing device, preferably a twin-screw extruder.

[0087] The polyacetal copolymer stabilized at the terminal end by the above method is dried by removing moisture using a dryer such as a hot air dryer or a vacuum dryer and sealing air or nitrogen adjusted to 100° C. to obtain a polyacetal copolymer as the polyacetal resin (A).

[0088] The melt flow rate (MFR value (according to ISO1133)) of the polyacetal resin is preferably 0.1 to 100 g / 10 min, more preferably 0.5 to 70 g / 10 min. By adjusting the MFR value of the polyacetal resin to the above range, a polyacetal resin having excellent mechanical strength can be obtained.

[0089] From the viewpoint of suppressing the warpage of the molded article, the number average molecular weight Mn of the polyacetal resin is preferably 25,000 or more, more preferably 50,000 or more, further preferably 60,000 or more, particularly preferably 70,000 or more, and most preferably 75,000 or more. The upper limit is not particularly limited, but from the viewpoint of the ease of molding, it is preferably 150,000 or less, more preferably 140,000 or less, further preferably 130,000 or less, and particularly preferably 120,000 or less. The most preferred range is 75,000 or more and 120,000 or less. By adding (B) a semi-aromatic polyamide resin to a polyacetal resin having a number average molecular weight Mn within the above range, a molded article with suppressed warpage can be obtained.

[0090] From the viewpoint of expressing excellent properties of an engineering resin, the content of the polyacetal resin is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more relative to 100 mass % of the polyacetal resin composition.

[0091] [(B) Semi-aromatic polyamide resin]

[0092] The (B) semi-aromatic polyamide resin contained in the polyacetal resin composition of the present embodiment is a semi-aromatic polyamide resin containing a dicarboxylic acid unit and a diamine unit, wherein the dicarboxylic acid unit contains at least 75 mol % of an isophthalic acid unit, the diamine unit contains at least 50 mol % of a diamine unit having 4 to 10 carbon atoms, and the number average molecular weight Mn of the (B) semi-aromatic polyamide resin is greater than or equal to 3,000 and less than or equal to 20,000.

[0093] In this specification, "polyamide" refers to a polymer having an amide (-NHCO-) ​​bond in the main chain. The semi-aromatic polyamide resin is described in detail below.

[0094] (Dicarboxylic acid unit)

[0095] The dicarboxylic acid unit may contain an aromatic dicarboxylic acid unit, an aliphatic dicarboxylic acid unit, or an alicyclic dicarboxylic acid unit in addition to the isophthalic acid unit.

[0096] -Aromatic dicarboxylic acid unit-

[0097] The aromatic dicarboxylic acid constituting the aromatic dicarboxylic acid unit other than the isophthalic acid unit is not limited to the following, and examples thereof include dicarboxylic acids having a phenyl group and a naphthyl group. The aromatic group of the aromatic dicarboxylic acid may be unsubstituted or may have a substituent.

[0098] The substituent is not particularly limited, and examples thereof include an alkyl group having 1 to 4 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, a halogen group such as a chloro group and a bromo group, a silyl group having 1 to 6 carbon atoms, and a sulfonic acid group and its salt (sodium salt, etc.).

[0099] Specifically, the aromatic dicarboxylic acid is not limited to the following, and includes unsubstituted or substituted aromatic dicarboxylic acids having 8 to 20 carbon atoms, such as terephthalic acid, naphthalene dicarboxylic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, and 5-sodium sulfoisophthalic acid. Unsubstituted or substituted aromatic dicarboxylic acids having 6 to 12 carbon atoms are preferred. Among them, terephthalic acid is preferred.

[0100] The aromatic dicarboxylic acid constituting the aromatic dicarboxylic acid unit may be used alone or in combination of two or more.

[0101] -Aliphatic dicarboxylic acid unit-

[0102] The aliphatic dicarboxylic acid constituting the aliphatic dicarboxylic acid unit is not limited to the following, and examples thereof include malonic acid, dimethylmalonic acid, succinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethylglutaric acid, 2,2-diethylsuccinic acid, 2,3-diethylglutaric acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, eicosanedioic acid, and glycolic acid, and the like, and the like. Among these, adipic acid is preferred from the viewpoint of heat resistance and the like.

[0103] The aliphatic dicarboxylic acid constituting the aliphatic dicarboxylic acid unit may be used alone or in combination of two or more.

[0104] -Alicyclic dicarboxylic acid unit-

[0105] The alicyclic dicarboxylic acid constituting the alicyclic dicarboxylic acid unit (hereinafter also referred to as "alicyclic dicarboxylic acid unit") is not limited to the following, and examples thereof include alicyclic dicarboxylic acids having 3 to 10 carbon atoms in the alicyclic structure, and preferably alicyclic dicarboxylic acids having 5 to 10 carbon atoms in the alicyclic structure.

[0106] Examples of the alicyclic dicarboxylic acid include, but are not limited to, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,3-cyclopentanedicarboxylic acid. Among them, 1,4-cyclohexanedicarboxylic acid is preferred.

[0107] In addition, the alicyclic dicarboxylic acid which comprises an alicyclic dicarboxylic acid unit may be used individually by 1 type, or may use 2 or more types together.

[0108] The alicyclic group of the alicyclic dicarboxylic acid may be unsubstituted or may have a substituent. The substituent is not limited to the following groups, and examples thereof include alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl.

[0109] As the dicarboxylic acid unit other than the isophthalic acid unit, it is preferred that an aromatic dicarboxylic acid unit be contained, and it is more preferred that an aromatic dicarboxylic acid unit be contained having 6 to 12 carbon atoms.

[0110] The dicarboxylic acid units contain 75 mol% or more of isophthalic acid units (based on the total molar number of dicarboxylic acid units), more preferably 80 mol% to 100 mol% of isophthalic acid units, further preferably 90 mol% to 100 mol% of isophthalic acid units, and further more preferably 100 mol% of isophthalic acid units.

[0111] In addition, in this specification, the ratio of the predetermined monomer unit which comprises a semi-aromatic polyamide resin can be measured by nuclear magnetic resonance spectroscopy (NMR) etc.

[0112] (Diamine unit)

[0113] The diamine units constituting the (B) semi-aromatic polyamide resin contain at least 50 mol % of diamine units having 4 to 10 carbon atoms.

[0114] Examples of the diamine unit having 4 to 10 carbon atoms include an aliphatic diamine unit, an alicyclic diamine unit, and an aromatic diamine unit.

[0115] -Aliphatic diamine unit-

[0116] The aliphatic diamine constituting the aliphatic diamine unit is not limited to the following, and examples thereof include straight-chain saturated aliphatic diamines having 4 to 10 carbon atoms such as tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, and decamethylenediamine.

[0117] -Alicyclic diamine unit-

[0118] The alicyclic diamine (hereinafter also referred to as “alicyclic diamine”) constituting the alicyclic diamine unit is not limited to the following, and examples thereof include 1,4-cyclohexanediamine, 1,3-cyclohexanediamine, and 1,3-cyclopentanediamine.

[0119] -Aromatic diamine unit-

[0120] The aromatic diamine constituting the aromatic diamine unit is not limited to the following as long as it is a diamine containing an aromatic group, and examples thereof include meta-xylylenediamine and the like.

[0121] Among the diamine units constituting the semi-aromatic polyamide resin (B), an aliphatic diamine unit is preferred, and a diamine unit having a linear saturated aliphatic group having 4 to 10 carbon atoms, such as tetramethylenediamine (carbon number 4), pentamethylenediamine (carbon number 5), hexamethylenediamine (carbon number 6), heptamethylenediamine (carbon number 7), octamethylenediamine (carbon number 8), nonamethylenediamine (carbon number 9), and decamethylenediamine (carbon number 10) is more preferred. A diamine unit having a linear saturated aliphatic group having 6 to 10 carbon atoms is further preferred, and hexamethylenediamine is even more preferred.

[0122] In addition, the diamine may be used alone or in combination of two or more.

[0123] The diamine units contain 50 mol % or more of diamine units having 4 to 10 carbon atoms, preferably 75 mol % or more of diamine units having 4 to 10 carbon atoms, based on 100 mol % of the total diamine units, and are particularly preferably composed only of diamine units having 4 to 10 carbon atoms.

[0124] The total molar ratio of the dicarboxylic acid unit and the diamine unit is preferably 80 mol % or more, more preferably 100 mol %, based on 100 mol % of all monomer units constituting the semi-aromatic polyamide resin.

[0125] The total amount of the isophthalic acid unit and the diamine unit having 4 to 10 carbon atoms is preferably 80 to 100 mol %, more preferably 90 to 100 mol %, and further preferably 100 mol %, based on 100 mol % of all constituent units of the semi-aromatic polyamide resin.

[0126] The molar ratio of the dicarboxylic acid unit is preferably 40 to 60 mol %, and the molar ratio of the diamine unit is preferably 40 to 60 mol %, based on 100 mol % of all monomer units constituting the semi-aromatic polyamide resin.

[0127] As the semi-aromatic polyamide resin, from the viewpoint of low VOC property and suppression of mold deposit, polyamide 4I, 5I, 6I, 7I, 8I, 9I, 10I, and 6I / 6T are preferred, polyamide 4I, 5I, 6I, 7I, and 6I / 6T are more preferred, and polyamide 6I is most preferred.

[0128] The content of the above-mentioned (B) semi-aromatic polyamide resin in the polyacetal resin composition of the present embodiment is preferably 0.01 part by mass or more and 1.00 part by mass or less, more preferably 0.01 part by mass or more and 0.50 part by mass or less, and further preferably 0.05 part by mass or more and 0.50 part by mass or less, relative to 100 parts by mass of the polyacetal resin.

[0129] The number average molecular weight Mn of the (B) semi-aromatic polyamide resin is 3,000 to 20,000, preferably 4,000 to 20,000, more preferably 5,000 to 20,000, and further preferably 5,000 to 18,000.

[0130] When the molecular weight Mn of the semi-aromatic polyamide resin is within the above range, thermal decomposition of the polyacetal resin can be prevented, generation of formaldehyde can be suppressed, and adhesion of mold deposits can be suppressed even during long-term molding because generation of polyamide exudates is reduced.

[0131] (B) The semi-aromatic polyamide resin may be a crystalline resin or an amorphous resin. Among them, an amorphous resin (amorphous polyamide) is preferred from the viewpoint of color tone.

[0132] [Other additives]

[0133] The polyacetal resin composition of the present embodiment may contain other additives in addition to the above-mentioned substances, such as antioxidants, formic acid scavengers, weather stabilizers, release agents, lubricants, conductive agents, thermoplastic resins, thermoplastic elastomers, dyes or pigments, or well-known additives such as inorganic fillers or organic fillers.

[0134] These additives may be used alone or in combination of two or more.

[0135] The content of the other additives in the polyacetal resin composition of the present embodiment is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, relative to 100 parts by mass of the polyacetal resin.

[0136] In particular, the polyacetal resin composition of the present embodiment preferably contains a hindered phenol compound as an antioxidant. The hindered phenol compound is not limited to the following substances, and examples thereof include 1,2-bis[3-(4-hydroxy-3,5-di-tert-butylphenyl)propionyl]hydrazine, N,N'-hexamethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide], 1,3,5-tris[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 4-[[4,6-bis(octylthio)-1,3,5-triazine-2-yl]amino]-2,6-di-tert-butylphenol, 3-(3',5'-di-tert-butyl-4' -hydroxyphenyl) propionate n-octadecyl ester, 3-(3'-methyl-5'-tert-butyl-4'-hydroxyphenyl) propionate n-octadecyl ester, 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate n-tetradecyl ester, 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], pentaerythritol tetrakis[3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate], and the like. Preferred are triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate] and pentaerythritol tetrakis[3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate], and more preferred is triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate].

[0137] The melting point of the hindered phenol compound is preferably 30 to 120° C., more preferably 50 to 120° C., and even more preferably 50 to 100° C. When the melting point of the hindered phenol compound is within the above range, a polyacetal resin composition having better thermal stability can be provided.

[0138] In the polyacetal resin composition of the present embodiment, the hindered phenol compound is preferably contained in an amount of 0.001 to 0.3 parts by mass, more preferably 0.005 to 0.3 parts by mass, and further preferably 0.005 to 0.27 parts by mass relative to 100 parts by mass of the polyacetal resin (A). If the content of the hindered phenol compound is within the above range, a polyacetal resin composition having better thermal stability can be provided.

[0139] The formic acid scavenger is not limited to the following substances, and examples thereof include: hydroxides, inorganic acid salts, carboxylates or alkoxides of alkali metals or alkaline earth metals. Examples thereof include: hydroxides of sodium, potassium, magnesium, calcium or barium; carbonates, phosphates, silicates, borates, carboxylates, and layered double hydroxides of the above metals.

[0140] 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. The saturated or unsaturated aliphatic carboxylate is not limited to the following substances, for example, calcium dimyristate, calcium dipalmitate, calcium distearate, calcium myristate, calcium palmitate, calcium stearate, and calcium 12-hydroxystearate, among which calcium dipalmitate, calcium distearate, and calcium 12-hydroxystearate are preferably used.

[0141] The formic acid scavenger may be used alone or in combination of two or more.

[0142] The weather stabilizer is not limited to the following, and for example, at least one selected from the group consisting of benzotriazole compounds, oxalic acid anilide compounds, and hindered amine light stabilizers can be cited as a preferred weather stabilizer.

[0143] As the above-mentioned benzotriazole compound, it is not limited to the following substances, for example, 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-di-isoamylphenyl)benzotriazole, 2-[2'-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, 2-(2'-hydroxy-4'-octyloxyphenyl)benzotriazole, 2-(2'-hydroxy-3,5-di-tert-butylphenyl)benzotriazole, etc. can be listed. Each of these compounds can be used alone or in combination of two or more.

[0144] The oxalic acid anilide compound is not limited to the following substances, and examples thereof include 2-ethoxy-2'-ethyl oxalic acid dianilide, 2-ethoxy-5-tert-butyl-2'-ethyl oxalic acid dianilide, 2-ethoxy-3'-dodecyl oxalic acid dianilide, etc. These compounds may be used alone or in combination of two or more.

[0145] The hindered amine light stabilizer is not limited to the following, and examples thereof 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, 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, di(2,2,6,6-tetramethyl-4-piperidinyl) carbonate, di(2,2,6,6-tetramethyl-4-piperidinyl) oxalate, di(2,2,6,6-tetramethyl-4-piperidinyl) malonate, di(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, di(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, bis(2,2,6,6-tetramethyl-4-piperidinyl) terephthalate, bis(2,2,6,6-tetramethyl-4-piperidinyl) adipate, bis(2,2,6,6-tetramethyl-4-piperidinyl) terephthalate, 1,2-bis(2,2,6,6-tetramethyl-4-piperidinyloxy)ethane, α,α'-bis(2,2,6,6-tetramethyl-4-piperidinyloxy)-p-xylene, bis(2,2,6,6-tetramethyl-4-piperidinyl) toluene-2,4-dicarbamate, bis(2,2,6,6-tetramethyl-4-piperidinyl) hexamethylene-1,6-dicarbamate, tris(2,2,6,6-tetramethyl-4-piperidinyl) benzene-1,3,5-tricarboxylate Benzene-1,3,4-tricarboxylic acid tris(2,2,6,6-tetramethyl-4-piperidinyl) ester, 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, 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, and di(2,2,6,6-tetramethyl-4-piperidinyl) sebacate. The above hindered amine light stabilizers may be used alone or in combination of two or more.

[0146] Among them, the 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, di(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, di(N-methyl-2,2,6,6-tetramethyl-4-piperidyl)sebacate, di(2,2,6,6-tetramethyl-4-piperidyl)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.

[0147] The mold release agent and lubricant are not limited to the following substances, and examples thereof include alcohols, fatty acids and fatty acid esters thereof, N,N'-ethylenebisfatty acid amides derived from higher fatty acids having 12 to 22 carbon atoms, olefin compounds having an average degree of polymerization of 10 to 500, and polysiloxane. The mold release agent and lubricant may be used alone or in combination of two or more.

[0148] The conductive agent is not limited to the following substances, and examples thereof include conductive carbon black, metal powder, and fiber. The conductive agent may be used alone or in combination of two or more.

[0149] The thermoplastic resin is not limited to the following substances, and examples thereof include 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. It should be noted that the thermoplastic resin does not include the polyacetal resin and the semi-aromatic polyamide resin.

[0150] In addition, the thermoplastic resin also includes modified products of the above-mentioned resins.

[0151] Thermoplastic elastomers are not limited to the following, and examples thereof include polyurethane elastomers, polyester elastomers, polystyrene elastomers, and polyamide elastomers. Thermoplastic elastomers may be used alone or in combination of two or more.

[0152] The dye or pigment is not limited to the following, and examples thereof include inorganic pigments, organic pigments, metallic pigments, fluorescent pigments, and the like.

[0153] Inorganic pigments are pigments generally used for coloring resins, and are not limited to the following substances. Examples thereof include zinc sulfide, titanium oxide, barium sulfate, titanium yellow, cobalt blue, fired pigments, carbonates, phosphates, acetates, carbon black, acetylene black, lamp black, and the like.

[0154] Examples of organic pigments include, but are not limited to, condensed azo pigments, quinone pigments, phthalocyanine pigments, monoazo pigments, disazo pigments, polyazo pigments, anthraquinone pigments, heterocyclic pigments, perinone pigments, quinacridone pigments, thioindigo pigments, perylene pigments, diazolone pigments, and phthalocyanine pigments. Pigments such as oxazine and phthalocyanine.

[0155] The dye or pigment may be used alone or in combination of two or more.

[0156] The addition ratio of the dye or pigment varies greatly depending on the color tone and is therefore difficult to specify, but the dye or pigment is usually used in an amount within a range of 0.05 to 5 parts by mass based on 100 parts by mass of the polyacetal resin.

[0157] The inorganic filler is not limited to the following, and examples thereof include fibrous, granular, plate-like, and hollow fillers.

[0158] The fibrous filler is not limited to the following substances, and examples thereof include inorganic fibers such as glass fiber, carbon fiber, silica-alumina fiber, zirconium oxide fiber, boron nitride fiber, potassium titanate fiber, and metal fibers such as stainless steel, aluminum, titanium, copper, and brass. In addition, short-fiber whiskers such as potassium titanate whiskers and zinc oxide whiskers are also included.

[0159] Powdered fillers are not limited to the following substances, and examples thereof include: talc, carbon black, silicon dioxide, quartz powder, glass beads, glass powder, and silicates such as calcium 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.

[0160] Examples of the plate-like filler include, but are not limited to, mica, glass flakes, and various metal foils.

[0161] Examples of the hollow filler include, but are not limited to, glass hollow microspheres, silica hollow microspheres, volcanic ash hollow microspheres, and metal hollow microspheres.

[0162] The organic filler is not limited to the following, and examples thereof include high melting point organic fibrous fillers such as aromatic polyamide resins, fluorine-containing resins, and acrylic resins.

[0163] These fillers can be used alone or in combination of two or more. As these fillers, any one of a filler that has been surface treated or a filler that has not been surface treated can be used. From the perspective of the smoothness of the molding surface and mechanical properties, it is sometimes preferred to use a filler that has been surface treated using a surface treatment agent.

[0164] The surface treatment agent is not particularly limited, and a conventionally known surface treatment agent can be used.

[0165] The surface treatment agent is not limited to the following substances, and for example, various coupling treatment agents such as silanes, titanates, aluminum-containing agents, zirconium-containing agents, resin acids, organic carboxylic acids, organic carboxylic acid salts and other surfactants can be used. Specifically, it is not limited to the following substances, and for example, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, tristearoyltitanate isopropyl, diisopropoxyethyl acetoacetate aluminum, n-butyl zirconate and the like can be listed.

[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] The method for producing the polyacetal resin composition of the present embodiment preferably includes, for example, adding (B) a semi-aromatic polyamide resin to (A) a polyacetal resin, wherein the semi-aromatic polyamide resin contains a dicarboxylic acid unit and a diamine unit, wherein the dicarboxylic acid unit contains 75 mol % or more of an isophthalic acid unit, and the diamine unit contains 50 mol % or more of a diamine unit having 4 to 10 carbon atoms, and the number average molecular weight Mn of the semi-aromatic polyamide resin is 3000 or more and 20000 or less. As the (A) polyacetal resin, the above-mentioned polyacetal resins can be listed, and the same polyacetal resins as above are preferred. As the (B) semi-aromatic polyamide resin, the above-mentioned semi-aromatic polyamide resins can be listed, and the same semi-aromatic polyamide resins as above are preferred.

[0169] In the method for producing the polyacetal resin composition, for example, (A) polyacetal resin, (B) semi-aromatic polyamide resin and the above-mentioned prescribed components as required are mixed in, for example, a Henschel mixer, a drum, a V-type mixer, etc., and then kneaded using a single-screw or multi-screw extruder, a heating roller, a kneader, a Banbury mixer or other mixers. Among them, from the viewpoint of thermal stability and productivity, it is preferred to use an extruder with a vent pressure reducing device for kneading. In addition, in order to produce the polyacetal resin composition in large quantities and stably, it is preferred to use a single-screw or twin-screw extruder, in which case, a polyacetal resin composition made into pellets (hereinafter, sometimes referred to as "polyacetal resin pellets") can be obtained.

[0170] Alternatively, the components may be continuously fed individually or in combination into an extruder using a quantitative feeder or the like without mixing them in advance.

[0171] Alternatively, a high-concentration masterbatch containing each component may be prepared in advance and diluted with the polyacetal resin during extrusion melt kneading.

[0172] The kneading temperature may be determined according to the preferred processing temperature of the polyacetal resin used, and is usually set within a range of 140°C to 260°C, preferably within a range of 180°C to 230°C.

[0173] There is no particular limitation on the method for drying the polyacetal resin pellets obtained above, and examples thereof include: drying methods using a box dryer (normal pressure, vacuum), a tunnel and belt dryer, a rotary and ventilated rotary dryer, a tank stirring dryer, a fluidized bed dryer, a multi-stage disc dryer, a spray dryer, an airflow dryer, an infrared dryer, a high-frequency dryer, and the like.

[0174] Among them, box dryers, rotary and ventilation rotary dryers, tank stirring dryers, fluidized bed dryers, multi-stage disk dryers, and airflow dryers are preferred, and fluidized bed dryers are more preferred from the viewpoint of productivity.

[0175] The drying temperature is preferably 80° C. or higher, more preferably 100° C. or higher. The drying time is preferably 0 to 10 hours, more preferably 0 to 6 hours, and even more preferably 1 to 6 hours, when the drying time is started when the product temperature of the polyacetal resin pellets reaches 100° C. or higher.

[0176] [Molding of polyacetal resin composition]

[0177] The polyacetal resin composition of the present embodiment can be molded and used in the form of a molded product. As a molding method, there is no particular limitation, and known molding methods can be cited, for example, any method in the 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), composite molding in a mold (insert molding, injection molding on a substrate) can be used for molding. Among these, from the viewpoint of production stability, injection molding is preferred.

[0178] Furthermore, even when the polyacetal resin composition of the present embodiment is used for continuous molding by 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, there is little contamination of the mold.

[0179] [Application of molded articles of polyacetal resin composition]

[0180] The molded article of the polyacetal resin composition of the present embodiment has excellent quality stability, and thus can be used as a molded article for various purposes. For example, it can be used for: mechanism parts represented by gears, cams, sliders, levers, shafts, bearings, and guide rails; resin parts injection-molded on a substrate or resin parts insert-molded (chassis, trays, side panel parts); parts for printers or copiers; parts for digital cameras or digital video equipment; parts for music, imaging, or information equipment; parts for communication equipment; parts for electrical equipment; and parts for electronic equipment.

[0181] In addition, the molded article of the polyacetal resin composition of this embodiment is suitable for use in fuel-related parts represented by fuel tanks, fuel pump modules, valves, tank flanges, etc. as automobile parts; door-related parts; seat belt peripheral parts; combination switch parts; switches.

[0182] 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.

[0183] (Method for thermal stabilization of polyacetal resin)

[0184] The method for heat stabilization of a polyacetal resin according to the present embodiment comprises adding (B) a semi-aromatic polyamide resin to (A) a polyacetal resin, wherein the semi-aromatic polyamide resin contains a dicarboxylic acid unit and a diamine unit, wherein the dicarboxylic acid unit contains 75 mol % or more of an isophthalic acid unit, and the diamine unit contains 50 mol % or more of a diamine unit having 4 to 10 carbon atoms, and the number average molecular weight Mn of the semi-aromatic polyamide resin is 3000 or more and 20000 or less.

[0185] Examples of the polyacetal resin include the same ones as those mentioned above, and the same ones as those mentioned above are preferred.

[0186] Examples of the semi-aromatic polyamide resin include the same ones as those mentioned above, and the same ones as those mentioned above are preferred.

[0187] The method for heat stabilizing polyacetal according to the present embodiment can heat stabilize the polyacetal resin by, for example, preparing the polyacetal resin into a polyacetal resin composition by the method for producing a polyacetal resin composition described above.

[0188] Example

[0189] Hereinafter, the present embodiment will be described with reference to specific examples and comparative examples thereof, but the present embodiment is not limited to the following examples.

[0190] In addition, the measurement and evaluation methods applied in Examples and Comparative Examples are as follows.

[0191] <Measurement of Formaldehyde (HCHO) Emission from Molded Articles (Low VOC Properties)>

[0192] Use with Figure 1 The polyacetal resin pellets were molded in a hot runner mold molding machine having the structure shown in the figure according to the molding conditions (a) described below. Then, the amount of formaldehyde released was measured by the VDA275 method described below.

[0193] (a) Molding conditions

[0194] ・Injection molding machine: Toshiba Machine Co., Ltd. IS-100GN

[0195] ・Barrel setting temperature: 220℃

[0196] ・Manifold set temperature: 230℃ (nozzle automatic opening and closing type)

[0197] ・Mold setting temperature: 80℃

[0198] ・Mold type: hot runner type

[0199] ・Test piece size: 100mm×40mm×3mm (no exhaust part at the front end of the molten resin flow path, with welding part)

[0200] ・Molding cycle: injection time / cooling time = 30 seconds / 15 seconds

[0201] The molded products from the start of molding to the fifth injection were discarded, and the amount of formaldehyde released from the molded products of the sixth injection (referred to as the initial state) and the test piece of the 5000th injection was measured by the method described below (VDA275 method).

[0202] ※VDA275 method:

[0203] 50 mL of distilled water and a test piece of a predetermined size (100 mm×40 mm×3 mm) were placed in a polyethylene container and sealed, and formaldehyde was extracted into distilled water while heating at 60° C. for 3 hours, and then cooled to room temperature.

[0204] After cooling, 5 mL of 0.4 mass % aqueous solution of acetylacetone and 5 mL of 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.

[0205] Then, the mixed solution was cooled to room temperature, and then the amount of formaldehyde in the distilled water was quantified using a UV spectrophotometer based on the absorption peak at 412 nm.

[0206] The amount of formaldehyde released from the molded product (mg / kg) was calculated using the following formula.

[0207] Amount of formaldehyde released from molded products (mg / kg) = Amount of formaldehyde in distilled water (mg) / Mass of polyacetal resin molded products used for measurement (kg)

[0208] From the viewpoint of practicality, the low VOC property of the polyacetal resin composition of the present embodiment is preferably 12 mg / kg or less at the initial stage, and preferably 15 mg / kg or less at the 5000th injection.

[0209] It should be noted that “-” in the table means no evaluation.

[0210] <Mold fouling properties>

[0211] Use with Figure 1 The polyacetal resin pellets thus prepared were molded using a hot runner mold molding machine having the structure shown below under the molding conditions (a) below. The mold deposit properties at this time were then evaluated using the evaluation criteria (b) below.

[0212] (a) Molding conditions

[0213] ・Injection molding machine: Toshiba Machine Co., Ltd. IS-100GN

[0214] ・Barrel setting temperature: 220℃

[0215] ・Manifold set temperature: 230℃ (nozzle automatic opening and closing type)

[0216] ・Mold setting temperature: 80℃

[0217] ・Mold type: hot runner type

[0218] ・Test piece size: 70mm×60mm×3mm (no exhaust part at the front end of the molten resin flow path, with welding part)

[0219] ・Molding cycle: injection time / cooling time = 20 seconds / 20 seconds

[0220] (b) Evaluation criteria

[0221] The mold deposit adhesion in the mold cavity was observed at the 1000th and 5000th injections from the start of molding according to the following evaluation criteria.

[0222] Score 1: Deposits were observed in more than 20% of the mold cavity.

[0223] Score 2: Debris is observed in an area greater than or equal to 15% and less than 20% of the mold cavity

[0224] Score 3: Deposits were observed in an area of ​​10% or more and less than 15% within the mold cavity.

[0225] Score 4: Deposits were observed in an area of ​​5% or more and less than 10% within the mold cavity.

[0226] Score 5: No deposits were observed, or deposits were observed in less than 5% of the mold cavity.

[0227] Components of mold deposits include components derived from formaldehyde generated by thermal decomposition of polyacetal resin and components derived from bleeds of low molecular weight polyamide. By suppressing the generation of both, adhesion of mold deposits can be suppressed even during long-term molding.

[0228] From the viewpoint of practicality, the mold deposit property of the polyacetal resin composition of the present embodiment preferably has a score of 3 or more at the 1000th injection, and preferably has a score of 3 or more at the 5000th injection.

[0229] It should be noted that “-” in the table means no evaluation.

[0230] <Evaluation of the number of retained foreign matter>

[0231] The number of foreign matter on the surface of the molded test piece during the mold fouling evaluation was visually confirmed.

[0232] The first shot and the 5000th shot were measured, and the number of foreign matter was obtained by counting the number of colored matter larger than 0.1 mm on one side of the molded product.

[0233] From the viewpoint of practicality, the number of foreign matter in the polyacetal resin composition of the present embodiment is preferably 1 or less in the first injection, and preferably 10 or less in the 5000th injection.

[0234] It should be noted that “-” in the table means no evaluation.

[0235] <Warp Properties>

[0236] The produced polyacetal resin flat plate was molded using a cold runner mold molding machine under the following (a) molding conditions, and the warpage at this time was evaluated using the following (b) evaluation criteria.

[0237] (a) Molding conditions

[0238] ・Injection molding machine: Sumitomo Heavy Industries, Ltd. SH-75

[0239] ・Barrel setting temperature: 200℃

[0240] ・Mold setting temperature: 60℃

[0241] ・Mold type: Cold runner type

[0242] ・Test piece size: 150mm×150mm×2mm (no exhaust part at the front end of the molten resin flow path, with welding part)

[0243] ・Molding cycle: Cooling time = 30 seconds

[0244] (b) Evaluation criteria

[0245] The plate was placed on a flat surface with the gate facing upward, and the warpage (height) relative to the vertex when one vertex was fixed was measured using a height gauge (HDM-A manufactured by Mitutoyo). The warpage was evaluated based on the following criteria.

[0246] Score 1: The warpage is 16 mm or more.

[0247] Score 2: The warpage is greater than or equal to 12 mm and less than 16 mm.

[0248] Score 3: Warpage is greater than or equal to 8 mm and less than 12 mm.

[0249] Score 4: Warpage is greater than or equal to 4 mm and less than 8 mm.

[0250] Score 5: Warpage is less than 4 mm.

[0251] The higher the warpage score, the higher the productivity during injection molding and the better the molding yield. If the score is 1 or 2, the continuous productivity of injection molding will decrease and the yield will decrease.

[0252] [Raw materials]

[0253] The raw material components used in Examples and Comparative Examples are as follows.

[0254] <(A) Polyacetal resin>

[0255] A-1. Polyacetal homopolymer

[0256] 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 regulator (acetic anhydride) were continuously fed respectively, and a polymerization reaction was performed.

[0257] The polymerization reaction temperature at this time was set to 58°C.

[0258] 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 stirred at 150° C. for 2 hours to esterify the unstable terminals of the crude polyacetal homopolymer.

[0259] The mass ratio (slurry concentration) of the polymer and the "1:1 mixed solvent of n-hexane and acetic anhydride" at this time was 20 parts of the polymer with respect to 100 parts of the "1:1 mixed solvent of n-hexane and acetic anhydride".

[0260] After the terminal stabilization treatment of the polyacetal homopolymer was completed, the "1:1 mixed solvent of n-hexane and acetic anhydride" and the polyacetal homopolymer were taken out from the reaction vessel, and the n-hexane solvent was added to repeatedly wash the polyacetal homopolymer, thereby washing away the acetic anhydride.

[0261] Regarding the number of times of washing, washing was repeated until the acetic anhydride concentration in the polyacetal homopolymer became 10 mass ppm or less.

[0262] 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, and then dried in a heating dryer set at 120°C for 5 hours to remove water contained in the polyacetal homopolymer, thereby obtaining a powdered polyacetal homopolymer (A-1a) having an MFR of 10 g / 10 min and an Mn of 78,000 (average particle size of 200 μm).

[0263] The average particle size of the polyacetal homopolymer is measured by a laser diffraction particle size distribution analyzer.

[0264] (A-1b) A powdery polyacetal homopolymer having MFR = 22 g / 10 min and Mn of 64,000 was obtained by the same production method as A-1a.

[0265] A-2. Polyacetal copolymer

[0266] Tenac 3510 manufactured by Asahi Kasei Corporation was used. MFR=2.7 g / 10 minutes, Mn=28,000.

[0267] <(B) Semi-aromatic polyamide resin>

[0268] B-1. Polyamide 6I

[0269] The polymerization reaction of polyamide was carried out by the "hot melt polymerization method" as follows.

[0270] 1500 g of an equimolar salt of isophthalic acid and hexamethylenediamine and 1.5 mol % of adipic acid relative to 100 mol of isophthalic acid were dissolved in 1500 g of distilled water to prepare a uniform aqueous solution containing 50.19 mass % of the raw material monomers.

[0271] The solution was concentrated by slowly discharging water vapor at a temperature of 110° C. to 150° C. while stirring until the solution concentration reached 70% by mass. Then, the internal temperature was raised to 220° C. At this time, the autoclave was pressurized to 1.8 MPa. This state was maintained for 1 hour until the internal temperature reached 245° C., and the reaction was continued for 1 hour while the pressure was maintained at 1.8 MPa by slowly discharging water vapor.

[0272] Next, the pressure was reduced over 30 minutes. Then, the autoclave was kept at a reduced pressure of 650 Torr for 10 minutes using a vacuum device. At this time, the final internal temperature of the polymerization was 265°C.

[0273] Then, the strands were formed from the lower spinneret (nozzle) by nitrogen pressure, water-cooled, cut, discharged in pellets, and dried at 100° C. in a nitrogen atmosphere for 12 hours to obtain a polyamide with Mn=3760 and Mw / Mn=2.0.

[0274] As B-2. polyamide, polyamide 6I having a molecular weight Mn = 5380 was used. This polyamide 6I is a polyamide comprising a dicarboxylic acid unit containing 100 mol % of isophthalic acid units and a diamine unit containing 100 mol % of hexamethylenediamine units having 6 carbon atoms.

[0275] As B-3. polyamide, polyamide 6I having a molecular weight Mn = 16046 was used. This polyamide 6I is a polyamide comprising a dicarboxylic acid unit containing 100 mol % of isophthalic acid units and a diamine unit containing 100 mol % of hexamethylenediamine units having 6 carbon atoms.

[0276] As B-4. polyamide, polyamide 6I having a molecular weight Mn = 18739 was used. This polyamide 6I is a polyamide comprising a dicarboxylic acid unit containing 100 mol % of isophthalic acid units and a diamine unit containing 100 mol % of hexamethylenediamine units having 6 carbon atoms.

[0277] As B-5. polyamide 6I / 6T, Grivory G16 manufactured by EMS was used. Molecular weight Mn = 8247. Polyamide 6I / 6T is a polyamide comprising 100 mol % of dicarboxylic acid units containing isophthalic acid units and terephthalic acid units (isophthalic acid units are less than 75 mol %) and 100 mol % of diamine units having 4 to 10 carbon atoms.

[0278] As B-6. MXD6, Reny MXD6 manufactured by Mitsubishi Gas Chemical Co., Ltd. was used. Molecular weight Mn = 30500. MXD6 is a polyamide containing a dicarboxylic acid unit in which 0 mol % of isophthalic acid unit is contained and a diamine unit in which 100 mol % of a diamine unit has 4 to 10 carbon atoms.

[0279] As B-7. polyamide, polyamide 66 having a molecular weight Mn = 15766 was used. Polyamide 66 is a polyamide containing a dicarboxylic acid unit in which 0 mol % of isophthalic acid unit is contained and a diamine unit in which 100 mol % of a diamine unit having 4 to 10 carbon atoms is contained.

[0280] As B-8. polyamide, polyamide 12 having a molecular weight Mn = 11572 was used. Polyamide 12 is a polyamide containing 0 mol% of isophthalic acid units and 0 mol% of diamine units having 4 to 10 carbon atoms.

[0281] [Example 1]

[0282] Using a Henschel mixer, 100 parts by mass of the powdered polyacetal homopolymer (A-1) as the polyacetal resin produced above, 0.01 parts by mass of (B-2) polyamide 6I, and 0.15 parts by mass of triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate] as a hindered phenol antioxidant were uniformly mixed to obtain a mixture.

[0283] The mixture was fed from the top feed port of a twin-screw extruder with a 40 mm exhaust hole 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, exhaust pressure reduction of -0.08 MPa, and a discharge volume of 50 kg / hour. The mixture was formed into pellets by thermal cutting at the extruder die outlet, and then the pellets were put into warm water adjusted to 40°C, stirred for a certain period of time, and then the moisture was removed by a centrifugal separator. The pellets were put into a fluidized bed hot air dryer and dried at a hot air temperature of 150°C for 3 hours to obtain polyacetal resin pellets.

[0284] The formaldehyde emission, mold deposit properties, and amount of foreign matter of the molded sheets of the obtained polyacetal resin pellets were evaluated by the above-mentioned methods.

[0285] The evaluation results are shown in Table 1 below.

[0286] [Examples 2 to 28, Comparative Examples 1 to 13]

[0287] Polyacetal resin pellets were obtained in the same manner as in Example 1 except that the type of (A) the polyacetal resin and the type and addition amount of (B) the semi-aromatic polyamide resin were changed to the ratios shown in Table 1 below.

[0288] The low VOC property, mold deposit property, and foreign matter count of the molded sheets of the obtained polyacetal resin pellets were evaluated by the above-mentioned methods.

[0289] In addition, the warpage properties of the compositions obtained in Example 9, Example 18, Comparative Example 1, Comparative Example 7, Comparative Example 11, and Comparative Example 12 were evaluated by the above-mentioned method and the results are shown in Table 2.

[0290]

[0291]

[0292] As shown in Table 1, it can be seen that the molded articles containing the polyacetal resin compositions obtained in Examples 1 to 28 have low formaldehyde emission during long-term continuous molding, and can significantly reduce mold deposits and foreign matter generation caused by retention. In addition, the warpage of the polyacetal resin composition of Example 9 is particularly significantly suppressed.

[0293] On the other hand, it was confirmed that the molded articles containing the polyacetal resin compositions obtained in Comparative Examples 1 to 13 released a large amount of formaldehyde during long-term continuous molding, and it was difficult to simultaneously suppress mold deposits and foreign matter caused by the accumulation.

[0294] Industrial Applicability

[0295] The polyacetal resin composition of the present invention can be suitably used in a wide range of fields such as automobiles, electric and electronic industries, and other industries.

Claims

1. A method for heat stabilization of a polyacetal resin, characterized in that: (B) a semi-aromatic polyamide resin is added to (A) a polyacetal resin, The semi-aromatic polyamide resin contains a dicarboxylic acid unit and a diamine unit, wherein the dicarboxylic acid unit contains 75 mol % or more of an isophthalic acid unit, and the diamine unit contains 50 mol % or more of a diamine unit having 4 to 10 carbon atoms, and the number average molecular weight Mn of the semi-aromatic polyamide resin is 5000 or more and 20000 or less.

2. A method for heat stabilization during continuous molding of a polyacetal resin, which is the method according to claim 1, wherein: The thermal stabilization of the polyacetal resin is thermal stabilization during continuous molding of the polyacetal resin.

3. A method, which is the method according to claim 2, wherein: The heat stabilization during the continuous molding means that a molded article obtained by continuously molding the polyacetal resin has excellent low VOC properties.

4. A method, which is the method according to claim 3, wherein: The polyacetal resin is continuously injection molded 5000 times or more, and the formaldehyde emission of the molded article obtained by the 5000th injection molding is 15 mg / kg or less as measured by the VDA275 method.

5. A method, which is the method according to claim 2, wherein: When the polyacetal resin is continuously molded, mold contamination caused by mold deposits is reduced.

6. A method, which is the method according to claim 5, wherein: When the polyacetal resin was continuously injection molded for more than 5,000 times, it was observed that the range of mold deposit adhesion was less than 15% of the mold cavity.

7. A method, which is the method according to claim 2, wherein: The number of foreign matters on the surface of a molded article obtained by continuously molding the polyacetal resin is reduced.

8. A method, which is the method according to claim 7, wherein: The polyacetal resin is continuously injection-molded 5000 times or more, and the number of colored substances of 0.1 mm or more on the surface of a molded article obtained by the 5000th injection is 10 or less.

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