Polyoxymethylene resin composition and molded body

Abstract

To provide a polyoxymethylene resin composition which is excellent in grease resistance and enables reduction of a release amount of formaldehyde from a polyoxymethylene resin molded body, and a molded body which is reduced in the release amount of the formaldehyde.SOLUTION: A polyoxymethylene resin composition is provided, containing, with respect to 100 pts.mass of a polyoxymethylene homopolymer resin (A), 0.5 to 3.0 pts.mass of polyethylene glycol (B) having a number average molecular weight of 1,000 to 7,000, 0.01 to 0.5 pts.mass of a nitrogen-containing compound (C), and 0.01 to 0.5 pts.mass of amorphous polyamide (D) different from the nitrogen-containing compound (C), wherein the content of alkali metal contained in the polyoxymethylene homopolymer resin composition is 0.1 to 3.0 mass ppm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polyoxymethylene resin composition and a molded article.

Background Art

[0002] Polyoxymethylene resin is excellent in mechanical strength, rigidity, oil resistance, organic solvent resistance, slidability, and creep resistance, has a good balance of physical properties in a wide temperature range, and also has excellent processability. Therefore, as a typical engineering plastic, it is widely used as a material for OA equipment, digital household appliances, automotive parts, and other industrial parts. Among these, polyoxymethylene resin is widely used in automotive interior parts and mechanical parts. In recent years, due to the increasing demand for low VOCs from automotive manufacturers and automotive parts suppliers, it is desired to suppress the formaldehyde emission from molded parts made of polyoxymethylene resin used in the automotive interior. Among automotive interior and mechanical parts, molded parts made of polyoxymethylene resin are often used in harsh usage environments, especially at high temperatures or in gear parts that are subjected to high loads for a long time. In such gear parts that always operate under high loads, grease may be applied to reduce sliding resistance. However, when polyoxymethylene resin gears are used in an environment where they are in contact with grease for a long time in a high-temperature atmosphere, due to the influence of substances contained in the grease, the polyoxymethylene resin may deteriorate, resulting in a decrease in mechanical properties due to a decrease in molecular weight, and the durability of the gears may decrease. Furthermore, due to the influence of formaldehyde generated during deterioration, the amount of formaldehyde released from the molded product may increase. That is, in automotive interior and mechanical parts using polyoxymethylene resin, there is a need for a material that can suppress the formaldehyde emission from polyoxymethylene resin molded products and prevent a decrease in mechanical properties even when in contact with grease in a high-temperature atmosphere for a long time, and can maintain the tensile strength over a long period.

[0003] In order to meet such requirements, various techniques have been proposed. For example, a method of adding a carboxylic acid hydrazide compound to a polyoxymethylene homopolymer resin (see, for example, Patent Document 1), a method of adding a carboxylic acid hydrazide compound and polyethylene glycol to a polyoxymethylene copolymer (see, for example, Patent Document 2), and a method of adding a carboxylic acid hydrazide compound and a weather stabilizer to a polyoxymethylene copolymer (see, for example, Patent Document 3) have been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 2, although studies have been conducted on polyoxymethylene homopolymers with high mechanical strength, the reduction of formaldehyde emission from polyoxymethylene resin molded products has not been sufficient. Furthermore, with respect to mechanical properties in an environment where grease contact occurs for a long time under a high-temperature atmosphere and durability of gears and the like to which a high torque is applied, sufficient characteristics have not yet been obtained. In addition, in Patent Documents 1 and 3, although the reduction of formaldehyde emission from polyoxymethylene resin molded products has been improved, since they are made of polyoxymethylene copolymers, durability has not been satisfied.

[0006] Therefore, an object of the present invention is to provide a polyoxymethylene resin composition excellent in grease resistance and capable of reducing the formaldehyde emission from polyoxymethylene resin molded articles, and a molded article with reduced formaldehyde emission.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventors have found that in a resin composition containing a polyoxymethylene homopolymer resin (A), ethylene glycol (B), a nitrogen-containing compound (C), and an amorphous polyamide (D) different from the nitrogen-containing compound (C), the above-described conventional problems can be solved by setting the content of alkali metals in the resin composition in the range of 0.1 to 3.0 mass ppm, and thus the present invention has been completed. That is, the present invention is as follows.

[0008] 〔1〕 Based on 100 parts by mass of the polyoxymethylene homopolymer resin (A), 0.5 to 3.0 parts by mass of polyethylene glycol (B) having a number average molecular weight of 1000 to 7000, 0.01 to 0.5 parts by mass of a nitrogen-containing compound (C), 0.01 to 0.5 parts by mass of an amorphous polyamide (D) different from the nitrogen-containing compound (C), A polyoxymethylene resin composition containing The polyoxymethylene resin composition is characterized in that the content of alkali metals contained in the polyoxymethylene resin composition is 0.1 to 3.0 mass ppm.

[0009] 〔2〕 The polyoxymethylene resin composition according to 〔1〕, wherein the nitrogen-containing compound (C) is at least one selected from the group consisting of an amino-substituted triazine compound, a urea derivative, an amide compound, a low melting point polyamide, an acrylamide copolymer, and a hydrazide compound.

[0010] 〔3〕 The polyoxymethylene resin composition according to the above [1] or [2], wherein the alkali metal is potassium.

[0011] [4] A molded article comprising the polyoxymethylene resin composition according to any one of the above [1] to [3]. [Advantages of the Invention]

[0012] According to the present invention, it is possible to provide a polyoxymethylene resin composition excellent in grease resistance and capable of reducing the formaldehyde emission amount from a polyoxymethylene resin molded article, and a molded article with a reduced formaldehyde emission amount. [Brief Description of the Drawings]

[0013]

Figure 1

[0014] Hereinafter, modes for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. It should be noted that the following present embodiment is an exemplification for explaining the present invention, and is not intended to limit the present invention to the following contents. The present invention can be variously modified and implemented within the scope of its gist.

[0015] [Polyoxymethylene Resin Composition] The polyoxymethylene resin composition of the present embodiment is Based on 100 parts by mass of the polyoxymethylene homopolymer resin (A), 0.5 to 3.0 parts by mass of polyethylene glycol (B) having a number average molecular weight of 1000 to 7000, 0.01 to 0.5 parts by mass of a nitrogen-containing compound (C), 0.01 to 0.5 parts by mass of an amorphous polyamide (D) different from the nitrogen-containing compound (C), A polyoxymethylene resin composition containing characterized in that the content of alkali metal contained in the polyoxymethylene resin composition is 0.1 to 3.0 mass ppm. The polyoxymethylene resin composition of this embodiment may further contain various other additives such as antioxidants. Hereinafter, each component that can be contained in the polyoxymethylene resin composition of this embodiment will be described.

[0016] (Polyoxymethylene homopolymer resin (A)) The polyoxymethylene resin composition of this embodiment contains a polyoxymethylene homopolymer resin (A). The polyoxymethylene homopolymer resin (A) refers to a polyoxymethylene polymer in which 99.8 mol% or more of the main chain excluding both ends is composed of oxymethylene groups. The polyoxymethylene polymer preferably has 99.8 mol% or more of the main chain excluding both ends composed of polyoxymethylene groups, and more preferably is a polyoxymethylene homopolymer in which the main chain excluding both ends is composed only of polyoxymethylene groups. In particular, it is preferably a polyoxymethylene homopolymer in which both ends of the polymer chain are blocked by ester groups. The polyoxymethylene homopolymer resin (A) may contain 5 parts by mass or less, preferably 3 parts by mass or less, more preferably 1 part by mass or less of a polyoxymethylene copolymer in 100 parts by mass. The melt flow rate (MFR) (in accordance with ISO 1133 D) of the polyoxymethylene homopolymer resin (A) of this embodiment is preferably 0.5 g / 10 min or more from the viewpoint of moldability, and preferably 10 g / 10 min or less, more preferably 1.0 g / 10 min or more and 5.0 g / 10 min or less, and still more preferably 1.5 g / 10 min or more and 2.5 g / 10 min or less from the viewpoints of high impact resistance and durability. If it is a polyoxymethylene homopolymer resin (A) having a melt flow rate within this range, it can be suitably used as a material for parts that are subjected to a high load over a long period of time, or parts that require high impact characteristics due to, for example, a collision in an automobile.

[0017] ((Production of Polyoxymethylene Homopolymer Resin (A))) The polyoxymethylene homopolymer resin (A) is not particularly limited, but can be produced, for example, by carrying out the polymerization step and the terminal stabilization step described below.

[0018] (1) Polymerization Step In the polymerization step, a monomer is polymerized in a reactor using a chain transfer agent and a polymerization catalyst by a known slurry polymerization method (for example, the methods described in Japanese Patent Publication No. Sho 47-6420 and Japanese Patent Publication No. Sho 47-10059) to obtain a crude polyoxymethylene homopolymer resin with unstabilized terminals. As the material of the polyoxymethylene homopolymer resin composition of this embodiment, this crude polyoxymethylene homopolymer resin itself can be used, but it is preferable to use the one in which the terminals of the crude polyoxymethylene homopolymer resin are stabilized by the terminal stabilization step described below.

[0019] [(1) Monomer] Examples of the monomer used for the production of the polyoxymethylene homopolymer resin (A) include monomers of formaldehyde or cyclic oligomers of formaldehyde such as its trimer (trioxane) and tetramer (tetraoxane).

[0020] In the polymerization process, in order to continuously obtain a polyoxymethylene homopolymer resin with a stable molecular weight, it is preferable to use purified formaldehyde gas with a low impurity concentration and high stability. As a method for purifying formaldehyde, known methods (for example, the methods described in Japanese Patent Publication No. 5-32374 and Japanese Patent Publication No. 2001-521916) can be applied.

[0021] When using formaldehyde gas as a monomer in the polymerization process, it is preferable to use those that contain as few impurities as possible, such as water, methanol, formic acid, etc., which have a polymerization termination effect and a chain transfer effect during the polymerization reaction. By using formaldehyde gas with a low content of these impurities, an unexpected chain transfer reaction can be avoided, and a polyoxymethylene homopolymer resin with the desired molecular weight can be obtained. In particular, the content of impurities that induce hydroxyl groups at the polymer end groups is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, based on the total monomer amount.

[0022] [(2) Chain transfer agent] The chain transfer agent used in the production of the polyoxymethylene homopolymer resin is not particularly limited, and examples thereof include alcohols and acid anhydrides. As the chain transfer agent, it is preferable to use those that contain as few impurities as possible, such as water, methanol, formic acid, acetic acid, etc., which have a polymerization termination effect and a chain transfer effect during the polymerization reaction. As a method for obtaining a chain transfer agent with a low content of impurities, for example, a commonly used and commercially available chain transfer agent with a water content exceeding the specified amount is bubbled with dry nitrogen, and the impurities are removed and purified with an adsorbent such as activated carbon or zeolite. The chain transfer agent may be used alone or in combination of two or more.

[0023] [(3) Polymerization catalyst] The polymerization catalyst used in the production of the polyoxymethylene homopolymer resin is not particularly limited, and examples thereof include onium salt-based polymerization catalysts. Examples of the onium salt-based polymerization catalyst include compounds represented by the following general formula (1). [R1R2R3R4M] + X - ··· (1) (In the general formula (1), 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. R1, R2, R3, and R4 may be the same or different.)

[0024] Examples of the onium salt-based polymerization catalyst include, but are not limited to, quaternary ammonium salt-based compounds and quaternary phosphonium salt-based compounds. In particular, tetramethylammonium bromide, dimethyldistearylammonium acetate, tetraethylphosphonium iodide, and tributylethylphosphonium iodide are preferred.

[0025] [(4) Reactor] The reactor used for producing the polyoxymethylene homopolymer resin is not particularly limited. Examples include a batch-type reaction tank equipped with a stirrer, a continuous kneader, a twin-screw continuous extrusion kneader, and a twin-paddle continuous mixer. The reactor preferably has a structure on the outer periphery of the cylinder that can heat or cool the reaction mixture, such as a jacket.

[0026] <(2) Terminal Stabilization Step> In the terminal stabilization step, the terminals of the crude polyoxymethylene homopolymer resin obtained in the polymerization step are blocked with an ether group using an etherifying agent and / or blocked with an ester group using an esterifying agent by a known method (for example, the method described in Japanese Patent Publication No. 63-452) to achieve stabilization.

[0027] Examples of the etherifying agent for blocking with an ether group include, but are not limited to, orthoesters.

[0028] Examples of orthoesters include, but are not limited to, orthoesters of aliphatic or aromatic acids and aliphatic, alicyclic or aromatic alcohols, such as methyl or ethyl orthoformate, methyl or ethyl orthoacetate, methyl or ethyl orthobenzoate, and orthocarbonates such as ethyl orthocarbonate. As the etherifying agent, only one kind may be used alone, or two or more kinds may be used in combination.

[0029] For the reaction of blocking with an etherifying agent, that is, the etherification reaction, a Lewis acid type catalyst such as moderately strong organic acids such as p-toluenesulfonic acid, acetic acid and hydrobromic acid, and moderately strong mineral acids such as dimethyl and diethyl sulfate may be introduced in an amount of 0.001 parts by mass or more and 0.02 parts by mass or less based on 1 part by mass of the etherifying agent. In the etherification reaction, although not limited thereto, for example, low-boiling aliphatic, alicyclic and aromatic hydrocarbons such as pentane, hexane, cyclohexane and benzene; and organic solvents such as lower halogenated aliphatic compounds such as methylene chloride, chloroform and carbon tetrachloride can be used.

[0030] Examples of the method for end-stabilizing the terminal of the crude polyoxymethylene homopolymer resin by blocking it with an ester group include, for example, the method using a large amount of acid anhydride described in U.S. Patent No. 3,459,709 and carried out in a slurry state, and the method carried out in a gas phase using the gas of the acid anhydride described in U.S. Patent No. 3,172,736.

[0031] The esterifying agent for blocking with an ester group is not particularly limited, and examples thereof include organic acid anhydrides.

[0032] Examples of the organic acid anhydride include, for example, organic acid anhydrides represented by the following general formula (2). R5COOCOR6···(2) (In general formula (2), R5 and R6 each independently represent an alkyl group or a phenyl group. R5 and R6 may be the same or different.)

[0033] Examples of the organic acid anhydride include, but are not limited to, propionic anhydride, benzoic anhydride, acetic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, etc., and acetic anhydride is preferred.) (The esterifying agent may be used alone or in combination of two or more.)

[0034] (As a method for end-capping with an ester group in the gas phase, for example, after removing the onium salt-based polymerization catalyst by the method described in JP-A-11-92542, it is preferable to perform end-capping. By removing the onium salt-based polymerization catalyst in the polyoxymethylene, when performing end-capping, the decomposition reaction of the polyoxymethylene homopolymer resin derived from the onium salt-based polymerization catalyst can be avoided, the polymer yield in the end stabilization step can be improved, and the coloring of the polyoxymethylene homopolymer resin can be suppressed.)

[0035] (The terminal of the polyoxymethylene homopolymer resin is blocked with an ether group and / or an ester group, so that the concentration of the terminal hydroxyl group is reduced to 5×10 -7 mol / g or less, preferably. When the concentration of the terminal hydroxyl group is 5×10 -7 mol / g or less, it is preferable because it has excellent thermal stability and can maintain the quality inherent to the polyoxymethylene homopolymer resin. From the same viewpoint, the concentration of the terminal hydroxyl group is more preferably 0.5×10 -7 mol / g or less, and even more preferably 0.3×10 -7 mol / g or less.)

[0036] (Polyethylene glycol (B) having a number average molecular weight of 1000 to 7000) The number average molecular weight of polyethylene glycol (B) is from 1,000 to 7,000. As the content of polyethylene glycol, it is 0.5 to 3.0 parts by mass, preferably 0.5 to 1.0 parts by mass, based on 100 parts by mass of the polyoxymethylene homopolymer resin (A). Further, the content of polyethylene glycol (B) is 0.5 parts by mass or more from the viewpoint of grease resistance and preferably 1.0 part by mass or less from the viewpoint of formaldehyde emission, based on 100 parts by mass of the polyoxymethylene polymer resin (A). These polyalkylene glycols (B) may be used singly or in combination of two or more. The number average molecular weight can be measured using gel permeation chromatography (HLC-8320, manufactured by Tosoh Corporation).

[0037] (Nitrogen-containing compound (C)) The nitrogen-containing compound (C) is preferably at least one selected from the group consisting of amino-substituted triazine compounds, urea derivatives, amide compounds, acrylamide copolymers, and hydrazide compounds. In the present invention, the nitrogen-containing compound (C) does not contain amorphous polyamide (D).

[0038] The content of the nitrogen-containing compound (C) is in the range of 0.01 to 0.5 parts by mass, preferably in the range of 0.05 to 0.4 parts by mass, and more preferably in the range of 0.1 to 0.3 parts by mass, based on 100 parts by mass of the polyoxymethylene homopolymer resin (A). When the content of the nitrogen-containing compound (C) is within the above range, a polyoxymethylene resin composition capable of providing a molded article with reduced formaldehyde emission and excellent grease resistance can be obtained.

[0039] Examples of the amino-substituted triazine compound include, but are not limited to, 2,4-diamino-sym-triazine, 2,4,6-triamino-sym-triazine, melamine, N-butylmelamine, N-phenylmelamine, N,N-diphenylmelamine, N,N-diallylmelamine, benzoguanamine (2,4-diamino-6-phenyl-sym-triazine), acetoguanamine (2,4-diamino-6-methyl-sym-triazine), 2,4-diamino-6-butyl-sym-triazine, and the like.

[0040] Examples of the urea derivative include, but are not limited to, N-substituted urea, urea condensate, ethylene urea, hydantoin compound, ureido compound, and the like. Examples of the N-substituted urea include, but are not limited to, methylurea having a substituent such as an alkyl group, alkylene bisurea, and aryl-substituted urea. Examples of the urea condensate include, but are not limited to, a condensate of urea and formaldehyde. Examples of the hydantoin compound include, but are not limited to, hydantoin, 5,5-dimethylhydantoin, 5,5-diphenylhydantoin, and the like. Examples of the ureido compound include, but are not limited to, allantoin.

[0041] Examples of the amide compound include, but are not limited to, polyvalent carboxylic acid amides such as isophthalic acid diamide, anthranilamide, polyacrylamide copolymer, and the like.

[0042] The polyacrylamide copolymer preferably has a primary amide group content of 30 to 70 mol% and a particulate form with an average particle diameter of 0.1 to 10 μm. Particularly preferred acrylamide copolymers are crosslinked polyacrylamides having an average particle diameter of 10 μm or less. More preferably, it is a polyacrylamide having an average particle diameter of 5 μm or less, and even more preferably, it is a crosslinked polyacrylamide having an average particle diameter of 3 μm or less.

[0043] The hydrazide compound is synthesized by the reaction of a carboxylic acid (including aromatic and alicyclic) with hydrazine. Carboxylic acid mono(di)hydrazide compounds synthesized using carboxylic acids include, for example, carbohydrazide, 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, sebacic acid mono(di)hydrazide, lauric acid mono(di)hydrazide, malic acid dihydrazide, tartaric acid dihydrazide, propionic acid monohydrazide, lauric acid monohydrazide, stearic acid monohydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, 2,6-naphthalenedicarboxylic acid dihydrazide, p-hydroxybenzoic hydrazide, p-hydroxybenzoic hydrazide, 1,4-cyclohexanedicarboxylic acid dihydrazide, acetohydrazide, acrylohydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, benzohydrazide, nicotinohydrazide, isonicotinohydrazide, isobutylhydrazide, oleic acid hydrazide, and the like. Among these carboxylic acids, dicarboxylic acids such as adipic acid and sebacic acid are preferred, and adipic acid mono(di)hydrazide and sebacic acid mono(di)hydrazide are the most preferred carboxylic acid hydrazide compounds.

[0044] (Amorphous polyamide (D)) The amorphous polyamide (D) different from the nitrogen-containing compound (C) (hereinafter, sometimes simply referred to as "amorphous polyamide (D)") is an amorphous polyamide resin containing a dicarboxylic acid unit containing at least 75 mol% of isophthalic acid units and a diamine unit containing at least 50 mol% of diamine units having 4 to 10 carbon atoms, and the number average molecular weight Mn is 3000 or more and 20000 or less. In this specification, "polyamide" means a polymer having an amide (-NHCO-) bond in the main chain. Hereinafter, the details of the amorphous polyamide will be described.

[0045] (Dicarboxylic acid unit) The dicarboxylic acid unit may contain, in addition to the isophthalic acid unit, an aromatic dicarboxylic acid unit, an aliphatic dicarboxylic acid unit, and an alicyclic dicarboxylic acid unit.

[0046] - Aromatic dicarboxylic acid unit - Examples of the aromatic dicarboxylic acid constituting the aromatic dicarboxylic acid unit other than the isophthalic acid unit include, but are not limited to, dicarboxylic acids having a phenyl group or a naphthyl group. The aromatic group of the aromatic dicarboxylic acid may be unsubstituted or may have a substituent. The above-mentioned substituents are 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 arylalkyl 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 salts (such as a sodium salt). Specific examples of the above-mentioned aromatic dicarboxylic acid include, but are not limited to, aromatic dicarboxylic acids having 8 to 20 carbon atoms which are unsubstituted or substituted with a predetermined substituent such as terephthalic acid, naphthalenedicarboxylic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, and 5-sodium sulfoisophthalic acid. Aromatic dicarboxylic acids having 6 to 12 carbon atoms which are unsubstituted or substituted are preferable. Among these, terephthalic acid is preferable. The aromatic dicarboxylic acid constituting the aromatic dicarboxylic acid unit may be used alone or in combination of two or more.

[0047] - Aliphatic dicarboxylic acid unit - Examples of the aliphatic dicarboxylic acid constituting the aliphatic dicarboxylic acid unit include, but are not limited to, straight-chain or branched saturated aliphatic dicarboxylic acids having 3 to 20 carbon atoms such as 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 diglycolic acid. Among these, adipic acid is preferred from the viewpoint of heat resistance and the like. The aliphatic dicarboxylic acid constituting the aliphatic dicarboxylic acid unit may be used alone as only one kind, or may be used in combination of two or more kinds.

[0048] - Alicyclic dicarboxylic acid unit - Examples of the alicyclic dicarboxylic acid constituting the alicyclic dicarboxylic acid unit (hereinafter also referred to as "alicyclic dicarboxylic acid unit") include, but are not limited to, alicyclic dicarboxylic acids having 3 to 10 carbon atoms in the alicyclic structure, and alicyclic dicarboxylic acids having 5 to 10 carbon atoms in the alicyclic structure are preferred. Examples of the above alicyclic dicarboxylic acid include, but are not limited to, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,3-cyclopentanedicarboxylic acid. Among these, 1,4-cyclohexanedicarboxylic acid is preferred. The alicyclic dicarboxylic acid constituting the alicyclic dicarboxylic acid unit may be used alone as only one kind, or may be used in combination of two or more kinds.

[0049] The alicyclic group of the alicyclic dicarboxylic acid may be unsubstituted or may have a substituent. Examples of the substituent include, but are not limited to, alkyl groups having 1 to 4 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, and tert-butyl group.

[0050] As the dicarboxylic acid unit other than the isophthalic acid unit, it preferably contains an aromatic dicarboxylic acid unit, and more preferably contains an aromatic dicarboxylic acid having 6 to 12 carbon atoms.

[0051] The above dicarboxylic acid unit contains 75 mol% or more of the isophthalic acid unit (based on the total number of moles of the dicarboxylic acid unit), more preferably contains 80 to 100 mol%, even more preferably contains 90 to 100 mol%, and even more preferably is 100 mol%.

[0052] In addition, in this specification, the ratio of a predetermined monomer unit constituting the amorphous polyamide can be measured by nuclear magnetic resonance spectroscopy (NMR) or the like.

[0053] (Diamine unit) The diamine unit constituting the amorphous polyamide (D) contains at least 50 mol% of a diamine having 4 to 10 carbon atoms. Examples of the diamine having 4 to 10 carbon atoms include an aliphatic diamine unit, an alicyclic diamine unit, and an aromatic diamine unit.

[0054] -Aliphatic diamine unit- The aliphatic diamine constituting the aliphatic diamine unit is not limited to the following, and examples thereof include linear saturated aliphatic diamines having 4 to 10 carbon atoms such as tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, and decamethylenediamine.

[0055] - Alicyclic diamine unit- The alicyclic diamine constituting the alicyclic diamine unit (hereinafter also referred to as "alicyclic diamine") is not limited to the following, and examples thereof include 1,4 - cyclohexanediamine, 1,3 - cyclohexanediamine, and 1,3 - cyclopentanediamine.

[0056] -Aromatic diamine unit- 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. For example, metaxylylenediamine and the like can be mentioned.

[0057] Among the diamine units constituting the amorphous polyamide (D), preferably an aliphatic diamine unit, more preferably a diamine unit having a linear saturated aliphatic group with 4 to 10 carbon atoms such as tetramethylenediamine (4 carbon atoms), pentamethylenediamine (5 carbon atoms), hexamethylenediamine (6 carbon atoms), heptamethylenediamine (7 carbon atoms), octamethylenediamine (8 carbon atoms), nonamethylenediamine (9 carbon atoms), decamethylenediamine (10 carbon atoms), etc., and even more preferably a diamine unit having a linear saturated aliphatic group with 6 to 10 carbon atoms, and even more preferably hexamethylenediamine. Note that only one kind of diamine may be used alone, or two or more kinds may be used in combination.

[0058] The above diamine unit preferably contains 50 mol% or more, more preferably 75 mol% or more, and particularly preferably consists only of diamine units with 4 to 10 carbon atoms, based on a total of 100 mol% of the diamine units.

[0059] The total molar ratio of the above dicarboxylic acid unit and the above diamine unit is preferably 80 mol% or more, more preferably 100 mol%, based on 100 mol% of all monomer units constituting the amorphous polyamide. The total amount of the above isophthalic acid unit and the diamine unit with 4 to 10 carbon atoms is preferably 80 to 100 mol%, more preferably 90 to 100 mol%, and even more preferably 100 mol%, based on 100 mol% of all constituent units of the amorphous polyamide.

[0060] The molar ratio of the above dicarboxylic acid units is preferably 40 to 60 mol%, and the molar ratio of the above diamine units is preferably 40 to 60 mol%, based on 100 mol% of all the monomer units constituting the above amorphous polyamide.

[0061] From the viewpoints of improving grease resistance and reducing formaldehyde emission, amorphous polyamides such as polyamide 4I, 5I, 6I, 7I, 8I, 9I, 10I, 6I / 6T are preferred, polyamide 4I, 5I, 6I, 7I, 6I / 6T are more preferred, and polyamide 6I is most preferred.

[0062] The content of the amorphous polyamide (D) is preferably 0.01 part by mass or more and 0.5 part by mass or less, more preferably 0.03 part by mass or more and 0.4 part by mass or less, and still more preferably 0.05 part by mass or more and 0.2 part by mass or less, based on 100 parts by mass of the polyoxymethylene resin.

[0063] The number average molecular weight Mn of the amorphous polyamide (D) is 3,000 or more and 20,000 or less, and more preferably 3,500 or more and 18,000 or less. When the number average molecular weight Mn of the amorphous polyamide is within the above range, thermal decomposition of the polyoxymethylene resin can be prevented, and grease resistance can be improved and formaldehyde emission can be reduced. The number average molecular weight Mn can be measured using gel permeation chromatography ("HLC-8320", manufactured by Tosoh Corporation).

[0064] (Alkali metal) In the polyoxymethylene homopolymer resin composition of this embodiment, an alkali metal is contained. The state of existence of the alkali metal in the polyoxymethylene homopolymer resin composition is not limited, and examples include alkali metal ions and alkali metal compounds. The content of the alkali metal in the polyoxymethylene homopolymer resin composition is determined by the method described in the examples and is 0.1 to 3.0 mass ppm. When the polyoxymethylene homopolymer resin composition contains an alkali metal within the above numerical range, it has excellent grease resistance, and furthermore, the amount of formaldehyde released from the polyoxymethylene resin molded article can be reduced.

[0065] Examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium, and the like. Among these, the alkali metal is particularly preferably potassium.

[0066] From the viewpoint of grease resistance, the alkali metal content is preferably 0.1 mass ppm or more, more preferably 0.2 mass ppm or more, and even more preferably 0.3 mass ppm or more. Also, from the viewpoint of formaldehyde emission, the alkali metal content is preferably 3.0 mass ppm or less, more preferably 2.0 mass ppm or less, and even more preferably 1.0 mass ppm or less.

[0067] (Antioxidant) The polyoxymethylene homopolymer resin composition of this embodiment preferably contains an antioxidant. By containing an antioxidant in the polyoxymethylene homopolymer resin composition, the grease resistance and formaldehyde emission can be further improved. Examples of the antioxidant include, but are not limited to, n-octadecyl-3-(3’,5’-di-t-butyl-4’-hydroxyphenyl)-propionate, n-octadecyl-3-(3’-methyl-5-t-butyl-4’-hydroxyphenyl)-propionate, n-tetradecyl-3-(3’,5’-di-t-butyl-4’-hydroxyphenyl)-propionate, 1,6-hexanediol-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], 1,4-butanediol-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate], tetrakis-[methylene-3-(3’,5’-di-t-butyl-4’-hydroxyphenyl)propionate]methane, 3,9-bis[2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]2,4,8,10-tetraoxaspiro(5,5)undecane, N,N’-bis-3-(3’,5’-di-t-butyl-4-hydroxyphenol)propionylhexamethylenediamine, N,N’-tetramethylenebis-3-(3’-methyl-5’-t-butyl-4-hydroxyphenol)propionyl diamine, N,N’-bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl]hydrazine, N-salicyloyl-N’-salicylidene hydrazine, 3-(N-salicyloyl)amino-1,2,4-triazole, N,N’-bis[2-{3-(3,5-di-butyl-4-hydroxyphenyl)propionyloxy}ethyl]oxyamide, and the like. Among these antioxidants, triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate] and tetrakis-[methylene-3-(3’,5’-di-t-butyl-4’-hydroxyphenyl)propionate]methane are preferred. These may be used alone or in combination of two or more.

[0068] The content of the antioxidant is preferably in the range of 0.01 to 0.50 parts by mass, more preferably in the range of 0.03 to 0.40 parts by mass, and even more preferably in the range of 0.05 to 0.30 parts by mass with respect to 100 parts by mass of the polyoxymethylene homopolymer resin (A).

[0069] (Other components) In the polyoxymethylene homopolymer resin composition of the present embodiment, various additives such as dyes and various reinforcing materials can be added, for example, preferably in an amount of 2 parts by mass or less with respect to 100 parts by mass of the polyoxymethylene homopolymer resin composition, as long as the properties of the polyoxymethylene homopolymer resin (A) are not impaired.

[0070] (Method for producing polyoxymethylene homopolymer resin composition) The polyoxymethylene homopolymer resin composition of the present embodiment can be produced by mixing the above-described components (A) to (D), an optional antioxidant, and other additive components, etc., for example, with a Henschel mixer, tumbler, V-shaped blender, etc., and then melt-kneading using a single-screw extruder, twin-screw extruder, heating roll, kneader such as a kneader, Banbury mixer, etc., and can be obtained as products in various forms such as strand shape and pellet shape. Also, without prior mixing, each component can be continuously fed into the extruder alone or in several kinds together by a metering feeder or the like. Further, a high-concentration masterbatch composed of each component can be prepared in advance and diluted with a polyoxymethylene homopolymer resin during extrusion melt-kneading. The kneading temperature may follow the preferred processing temperature of the polyoxymethylene homopolymer resin (A) used, and generally, it is in the range of 180°C or higher and 240°C or lower, preferably in the range of 190°C or higher and 220°C or lower. The pellets and the like of the polyoxymethylene homopolymer resin composition obtained as described above may be dried in advance and then used for the production of a molded article. The drying method is not particularly limited, and examples thereof include drying methods using a box dryer (atmospheric pressure, vacuum), a rotary and ventilated rotary dryer, a trough-type stirring dryer, a fluidized bed dryer, and the like. As the drying temperature, the temperature of the heat medium is preferably 80°C or higher, more preferably 100°C or higher. Further, as the drying time, when the temperature of the polyoxymethylene homopolymer resin composition pellets reaches 100°C or higher as the start time, 0.1 to 10 hours is preferable, 0.5 to 6 hours is more preferable, and 1 to 5 hours is even more preferable.

[0071] (Molded article) The molded article of the present embodiment contains the polyoxymethylene homopolymer resin composition of the present embodiment described above. Since the molded article contains the polyoxymethylene homopolymer resin composition of the present embodiment, it is excellent in grease resistance and the formaldehyde emission amount is reduced. Using the pellet-shaped product obtained as described above, the target molded article can be molded. The method for manufacturing a molded article is not particularly limited, and known molding methods commonly used, such as injection molding, extrusion molding, vacuum molding, blow molding, injection compression molding, decorative molding, molding with other materials, gas-assisted injection molding, foaming injection molding, low-pressure molding, ultra-thin-wall injection molding (ultra-high-speed injection molding), in-mold composite molding (insert molding, out-insert molding), etc., can be applied.

Examples

[0072] Hereinafter, the present embodiment will be described with specific examples and comparative examples, but the present embodiment is not limited to the examples described later.

[0073] Hereinafter, the evaluation method will be described. 〔Evaluation method〕 ((1) Grease resistance) From the polyoxymethylene resin composition pellets of the examples or comparative examples, using a 5-ounce molding machine (manufactured by Toshiba Machine Co., Ltd., trade name "IS-100GN") with the cylinder temperature set at 215 °C, an ISO dumbbell test piece for grease resistance evaluation was molded under the conditions of a mold temperature of 90 °C, an injection time of 35 seconds, and a cooling time of 15 seconds. Six test pieces were prepared for each polyoxymethylene resin composition. The following tests were conducted on these six test pieces. Three of the above ISO dumbbell test pieces were immersed in grease. Using ISOFLEX TOPAS L32 (manufactured by NOK Klüber Co., Ltd.) as the evaluation grease, the immersion conditions were carried out at a temperature of 100 °C for 1000 hours. The evaluation was carried out by performing a tensile test in accordance with ISO 527 with n = 3 and evaluated according to the following criteria. Tensile strength n3 average value after grease immersion test / Tensile strength n3 average value before grease immersion test × 100 = Tensile strength retention rate (%) A: Tensile strength retention rate is 100.0% or more B: Tensile strength retention rate is 95.0% or more and less than 99.9% C: Tensile strength retention rate is less than 95.0%

[0074] ((2) Measurement of formaldehyde emission from hot runner molded products (VOC property)) From the polyoxymethylene resin composition pellets of the examples or comparative examples, using a hot runner mold molding machine having the configuration shown in FIG. 1, molding was carried out according to the following molding conditions (a). First, the polyoxymethylene resin composition pellets were put into an injection molding machine, and the molten resin was injected into the manifold part to obtain a molded product. Then, the formaldehyde emission amount released by the following VDA 275 method was measured. (a) Molding conditions · Injection molding machine: Toshiba Machine Co., Ltd. IS-100GN · Cylinder set temperature: 200 °C · Manifold set temperature: 200 °C (nozzle automatic opening and closing type) · Mold set temperature: 80 °C · Mold type: Hot runner type ·Test piece size: 100 mm × 40 mm × 3 mm (no gas vent at the tip of the molten resin flow path end, with weld part) ·Molding cycle: Injection time / Cooling time = 30 / 15 seconds The molded products from the start of molding to 30 shots were discarded, and the amount of formaldehyde released (formaldehyde emission) from the molded products of the 31st to 35th shots was measured. The n5 average value is described in the table. ※VDA275 method: Put 50 mL of distilled water and a test piece of a specified size into a polyethylene container, seal it, extract formaldehyde into the distilled water while heating at 60 °C for 3 hours, and then cool it to room temperature. After cooling, add 5 mL of a 0.4 mass% aqueous solution of acetylacetone and 5 mL of a 20 mass% aqueous solution of ammonium acetate to 5 mL of the distilled water that has absorbed formaldehyde to obtain a mixed solution, heat it at 40 °C for 15 minutes, and carry out the reaction between formaldehyde and acetylacetone. Further, after cooling the mixed solution to room temperature, use a UV spectrophotometer to quantify the amount of formaldehyde in the distilled water from the absorption peak at 412 nm. The amount of formaldehyde released from the molded product (mg / kg) was determined by the following formula. Amount of formaldehyde released from the molded product (mg / kg) = Amount of formaldehyde in the distilled water (mg) / Mass of the polyoxymethylene resin molded product used for the measurement (kg) From the perspective of practicality, the polyoxymethylene resin composition of this embodiment preferably has a formaldehyde emission of 5 mg / kg or less.

[0075] ((3) Content of alkali metal contained in the polyoxymethylene homopolymer resin composition) Precisely weigh about 0.1 g of the polyoxymethylene homopolymer resin composition pellets of the example or comparative example into a decomposition container made of TFM, add sulfuric acid and nitric acid, perform pressurized acid decomposition with a microwave decomposition device, make the volume of the decomposition solution constant at 50 mL, and use it for ICP-MS measurement. An Agilent Technologies device (Agilent 7900) was used for ICP-MS measurement.

[0076] [Components used in Examples and Comparative Examples] (Polyoxymethylene Homopolymer Resin (A)) (A) As the polyoxymethylene homopolymer resin, (A-1) to (A-5) were used. The production methods of (A-1) to (A-5) are shown below. <Production Method of (A-1)> A polymerization reactor equipped with stirring blades was filled with n-hexane, and purified formaldehyde (monomer) and a polymerization catalyst (dimethyl distearylammonium acetate) were continuously fed at 5.0×10 -5 mol per 1 mol of the monomer, and a molecular weight regulator (acetic anhydride) was continuously fed at 0.24×10 -3 mol per 1 mol of the monomer, respectively, and a polymerization reaction was carried out. The polymerization reaction temperature at this time was 58°C. The obtained crude polyoxymethylene homopolymer was put into a reaction vessel filled with a 1.5:1 mixed solvent of n-hexane and acetic anhydride, and potassium acetate was added as an esterification catalyst at 65 ppm by mass based on the crude polyoxymethylene homopolymer, and stirring was carried out at 150°C for 2 hours to esterify the unstable terminals of the crude polyoxymethylene homopolymer. The slurry concentration at this time was 16% by mass. After the terminal stabilization treatment of the crude polyoxymethylene homopolymer was completed, the polyoxymethylene homopolymer was taken out from the reaction vessel and put into a 1.5:1 mixed solvent of n-hexane and acetic anhydride, and washing at 60°C was repeated 3 times. Thereafter, the polyoxymethylene homopolymer was dried under reduced pressure at 120°C for 3 hours under the condition of -700 mmHg to obtain a powdery polyoxymethylene homopolymer resin (A-1) with an MFR of 2.2 g / 10 min.

[0077] <Production Method of (A-2)> A polyoxymethylene homopolymer resin (A-2) was obtained in the same manner as (A-1) except that the addition amount of potassium acetate was 200 ppm by mass.

[0078] <Production Method of (A-3)> A polyoxymethylene homopolymer resin (A-3) was obtained in the same manner as (A-1) except that the addition amount of potassium acetate was 500 ppm by mass.

[0079] <Method for Producing (A-4)> A polyoxymethylene homopolymer resin (A-4) was obtained in the same manner as (A-1), except that potassium acetate was not added.

[0080] <Method for Producing (A-5)> A polyoxymethylene homopolymer resin (A-5) was obtained in the same manner as (A-1), except that the addition amount of potassium acetate was 950 mass ppm.

[0081] (Polyethylene glycol (B) having a number average molecular weight of 1000 to 7000) (B-1): Polyethylene glycol with a number average molecular weight of 5000 (PEG (molecular weight 5000))

[0082] (Nitrogen-containing compound (C)) (C-1): Acrylamide copolymer (C-2): Hydrazide compound (Sebacic acid dihydrazide (SDH), manufactured by Nippon Fine Chemical Co., Ltd.)

[0083] (Method for Producing C-1) Into a 5 L batch reactor equipped with a stirrer, 2400 g of acrylamide, 267 g of methylenebisacrylamide, and 0.54 g of zirconium tetraisopropoxide (1 / 10000 mol relative to acrylamide) as a catalyst were added, and the mixture was reacted at 125 °C for 4 hours while stirring in a nitrogen stream. After completion of the reaction, the solid matter was pulverized with a jet mill and washed with acetone. Thereafter, it was dried under reduced pressure at 120 °C for 20 hours with a reduced pressure degree of -700 mmHg. The content of primary amide groups was 44.7 mol%, and the average particle diameter was 5.0 μm. The average particle diameter of the acrylamide copolymer (C-1) was measured with a laser diffraction particle size distribution measuring device.

[0084] (Amorphous polyamide resin (D)) (D-1): Polyamide 6I (PA-6I)

[0085] <Method for Producing (D-1)> The polymerization reaction of polyamide was carried out as follows by the "thermal melting polymerization method". 1500 g of an equimolar salt of isophthalic acid and hexamethylenediamine, and 1.5 mol% of adipic acid with respect to 100 mol of isophthalic acid were dissolved in 1500 g of distilled water to prepare a homogeneous aqueous solution containing 50.19% by mass of the raw material monomers. While stirring at a temperature of 110 to 150 °C, water vapor was gradually removed to concentrate the solution to a concentration of 70% by mass. Then, the internal temperature was raised to 220 °C. At this time, the autoclave was pressurized to 1.8 MPa. While gradually removing water vapor and maintaining the pressure at 1.8 MPa, the reaction was carried out for 1 hour until the internal temperature reached 245 °C for 1 hour. Next, the pressure was reduced over 30 minutes. Then, the inside of the autoclave was maintained under a reduced pressure of 650 torr for 10 minutes with a vacuum device. At this time, the final internal temperature of the polymerization was 265 °C. Then, it was pressurized with nitrogen and made into strands from the lower spinning nozzle (nozzle), cooled, cut, discharged in pellet form, and dried at 100 °C in a nitrogen atmosphere for 12 hours to obtain polyamide. Mn = 3,760 and Mw / Mn = 2.0.

[0086] [Example 1] To 100 parts by mass of a polyoxymethylene homopolymer resin (A-1), 0.5 part by mass of polyethylene glycol (B-1), 0.2 part by mass of an acrylamide copolymer (C-1), 0.05 part by mass of a hydrazide compound (C-2), 0.05 part by mass of polyamide 6I (D-1), and 0.1 part by mass of an antioxidant triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate] were uniformly mixed using a Henschel mixer to obtain a mixture. The mixture was melt-kneaded with a 30φ single-screw extruder, extruded into strands, cooled, and pelletized to obtain pellets of a polyoxymethylene homopolymer resin composition. The extrusion conditions were: the cylinder set temperature was 200 °C, the discharge amount was 5 kg / hr, the screw rotation speed was 50 rpm, and the vent vacuum degree was -720 mmHg. The obtained resin composition pellets were dried at 80 °C for 4 hours. When potassium (K) was measured by ICP-MS analysis after subjecting the obtained resin composition pellets to acid decomposition in a closed system, it was 0.30 mass ppm. Using the dried resin composition pellets, the above (1) grease resistance and the above (2) formaldehyde emission from the hot runner molded article were evaluated by the respective evaluation methods. The evaluation results are shown in Table 1.

[0087] 〔Examples 2 to 9〕 The composition of the resin composition was changed as described in Table 1. Other conditions were the same as those in [Example 1]. The evaluation results are shown in Table 1.

[0088] 〔Comparative Examples 1 to 9〕 The composition of the resin composition was changed as described in Table 2. Other conditions were the same as those in [Example 1]. The evaluation results are shown in Table 2.

[0089]

Table 1

[0090]

Table 2

[0091] As is clear from the evaluation results in Table 1, in a resin composition containing a polyoxymethylene homopolymer resin (A), a polyethylene glycol (B), a nitrogen-containing compound (C), and an amorphous polyamide (D) different from the nitrogen-containing compound (C), in Examples where the potassium content in the resin composition was in the range of 0.1 to 3.0, a polyoxymethylene homopolymer resin composition excellent in grease resistance and having a reduced formaldehyde emission from the hot runner molded article was obtained.

Industrial Applicability

[0092] The polyoxymethylene homopolymer resin composition of the present invention has industrial applicability as automotive parts, various electrical and electronic equipment parts, and other various industrial parts, etc.

Claims

1. Based on 100 parts by mass of the polyoxymethylene homopolymer resin (A), 0.5 to 3.0 parts by mass of polyethylene glycol (B) having a number average molecular weight of 1,000 to 7,000, 0.01 to 0.5 parts by mass of a nitrogen-containing compound (C), 0.01 to 0.5 parts by mass of an amorphous polyamide (D) different from the nitrogen-containing compound (C), A polyoxymethylene homopolymer resin composition containing the same, The polyoxymethylene resin composition is characterized in that the content of alkali metal contained in the polyoxymethylene homopolymer resin composition is 0.1 to 3.0 mass ppm.

2. The polyoxymethylene resin composition according to claim 1, wherein the nitrogen-containing compound (C) is at least one selected from the group consisting of an amino-substituted triazine compound, a urea derivative, an amide compound, a low melting point polyamide, an acrylamide copolymer, and a hydrazide compound.

3. The polyoxymethylene resin composition according to claim 1, wherein the alkali metal is potassium.

4. A molded article characterized by containing the polyoxymethylene resin composition according to any one of claims 1 to 3.

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