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), a polyoxymethylene homopolymer resin composition, 0.5 to 3.0 pts.mass of polyethylene glycol (B) having a number average molecular weight of 1,000 to 7,000, and 0.01 to 0.5 pts.mass of a nitrogen-containing compound (C), wherein a content of alkali metal included 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 physical property balance 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 amount of molded parts made of polyoxymethylene resin used in the automotive interior, etc. Among automotive interior and mechanical parts, molded parts made of polyoxymethylene resin are often used in harsh usage environments, especially under 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 deteriorates and the mechanical properties decrease due to a decrease in molecular weight, which may lead to a decrease in the durability of the gears. 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, etc., there is a need for a material that can suppress the formaldehyde emission amount from polyoxymethylene resin molded products and prevent a decrease in mechanical properties even when in contact with grease for a long time in a high-temperature atmosphere, 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 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 having excellent 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), a polyethylene glycol (B), and a nitrogen-containing compound (C), the content of alkali metal in the resin composition is adjusted to be in the range of 0.1 to 3.0 mass ppm, thereby solving the above-mentioned conventional problems, and thus completing the present invention. 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), A polyoxymethylene homopolymer resin composition containing The content of alkali metal contained in the polyoxymethylene homopolymer resin composition is 0.1 to 3.0 mass ppm. A polyoxymethylene resin composition.

[0009] [2] 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. The polyoxymethylene resin composition according to [1].

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

[0011] [4] A molded article comprising the polyoxymethylene resin composition according to any one of [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 content. 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, and 0.01 to 0.5 parts by mass of a nitrogen-containing compound (C), A polyoxymethylene resin composition containing the above, characterized in that the alkali metal content contained in the polyoxymethylene resin composition is 0.1 to 3.0 mass ppm. The polyoxymethylene resin composition of the present embodiment may further contain various other additives such as an antioxidant.

[0016] Hereinafter, each component that can be contained in the polyoxymethylene resin composition of this embodiment will be described.

[0017] (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. It is preferable that 99.8 mol% or more of the main chain excluding both ends of the polyoxymethylene polymer is composed of oxymethylene groups, and it is more preferable that the main chain excluding both ends is a polyoxymethylene homopolymer composed only of oxymethylene groups. In particular, it is preferable that both ends of the polymer chain are blocked by ester groups and it is a polyoxymethylene homopolymer. 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) (conforming to 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 molding processability, and preferably 10 g / 10 min or less from the viewpoints of high impact resistance and durability. More preferably, it is 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. If it is a polyoxymethylene homopolymer resin (A) with a melt flow rate within this range, it can be suitably used as a material for parts that are subjected to a high load for a long time or parts that require high impact characteristics due to, for example, a collision in an automobile.

[0018] (Production of polyoxymethylene homopolymer resin (A)) The polyoxymethylene homopolymer resin (A) is not particularly limited, and for example, it can be produced by performing the polymerization step and the terminal stabilization step described below.

[0019] <(1) Polymerization step> In the polymerization step, by a known slurry polymerization method (for example, the methods described in JP-B-47-6420 and JP-B-47-10059), in a reactor, a monomer is polymerized using a chain transfer agent and a polymerization catalyst to obtain a crude polyoxymethylene homopolymer resin with unstabilized terminals. Note that as the material of the polyoxymethylene homopolymer resin composition of the present embodiment, this crude polyoxymethylene homopolymer resin itself can be used, but it is preferable to use a material in which the terminals of the crude polyoxymethylene homopolymer resin are stabilized by the terminal stabilization step described below.

[0020] [(1) Monomer] Examples of the monomer used for producing the polyoxymethylene homopolymer resin (A) include monomers of formaldehyde or cyclic oligomers of formaldehyde such as its trimer (trioxane) and tetramer (tetraoxane).

[0021] In the polymerization step, 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 JP-B-5-32374 and JP-T-2001-521916) can be applied.

[0022] When using formaldehyde gas as the monomer in the polymerization step, it is preferable to use a material that contains as few impurities as possible, such as water, methanol, and formic acid, 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 terminal groups is preferably 100 mass ppm or less, more preferably 50 mass ppm or less, based on the total monomer amount.

[0023] [(2) Chain transfer agent] The chain transfer agent used in the production of the polyoxymethylene homopolymer resin is not particularly limited, and examples include alcohols and acid anhydrides. As the chain transfer agent, it is preferable to use one that contains as little as possible impurities having a polymerization termination effect and a chain transfer effect during the polymerization reaction, such as water, methanol, formic acid, acetic acid, etc. 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 using an adsorbent such as activated carbon or zeolite. The chain transfer agent may be used alone as only one type, or two or more types may be used in combination.

[0024] [(3) Polymerization catalyst] The polymerization catalyst used in the production of the polyoxymethylene homopolymer resin is not particularly limited, and examples 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.)

[0025] Examples of onium salt polymerization catalysts include, but are not limited to, quaternary ammonium salt compounds and quaternary phosphonium salt compounds. In particular, tetramethylammonium bromide, dimethyldistearylammonium acetate, tetraethylphosphonium iodide, and tributylethylphosphonium iodide are preferred.

[0026] [(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 barrel that can heat or cool the reaction mixture, such as a jacket.

[0027] <(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 a known method (for example, the method described in Japanese Patent Publication No. 63-452) and / or blocked with an ester group using an esterifying agent to achieve stabilization.

[0028] The etherifying agent for blocking with an ether group is not particularly limited. Examples include orthoesters.

[0029] Examples of orthoesters include, but are not limited to, orthoesters of aliphatic acids or aromatic acids with aliphatic alcohols, alicyclic alcohols, or aromatic alcohols. Specifically, methyl or ethyl orthoformate, methyl or ethyl orthoacetate, methyl or ethyl orthobenzoate, and orthocarbonates such as ethyl orthocarbonate are included. The etherifying agent may be used alone or in combination of two or more.

[0030] The reaction blocked by an etherifying agent, that is, the etherification reaction, may be carried out by introducing a Lewis acid type catalyst such as a moderately strong organic acid such as p-toluenesulfonic acid, acetic acid and hydrobromic acid, or a moderately strong mineral acid such as dimethyl and diethyl sulfates in an amount of 0.001 part by mass or more and 0.02 part by mass or less based on 1 part by mass of the etherifying agent. In the etherification reaction, although not limited to the following, for example, low-boiling aliphatics such as pentane, hexane, cyclohexane and benzene; alicyclic and aromatic hydrocarbons; and organic solvents such as lower halogenated aliphatic compounds such as methylene chloride, chloroform and carbon tetrachloride can be used.

[0031] As a method for terminally stabilizing the terminal of the crude polyoxymethylene homopolymer resin by blocking it with an ester group, for example, a method using a large amount of acid anhydride described in U.S. Patent No. 3,459,709 and carried out in a slurry state, or a method using a gas of acid anhydride described in U.S. Patent No. 3,172,736 and carried out in a gas phase can be mentioned.

[0032] The esterifying agent for blocking with an ester group is not particularly limited, and examples thereof include organic acid anhydrides.

[0033] Examples of the organic acid anhydride include organic acid anhydrides represented by the following general formula (2). R5COOCOR6···(2) (In the 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.)

[0034] 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 as only one kind, or two or more kinds may be used in combination.

[0035] As a method for end-capping with an ester group in the gas phase, for example, it is preferable to perform end-capping after removing the onium salt-based polymerization catalyst by the method described in JP-A-11-92542. By removing the onium salt-based polymerization catalyst in the polyoxymethylene, when performing end-capping, it is possible to avoid the decomposition reaction of the polyoxymethylene homopolymer resin derived from the onium salt-based polymerization catalyst, improve the polymer yield in the end-stabilization step, and suppress the coloring of the polyoxymethylene homopolymer resin.

[0036] 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 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 in the original 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.

[0037] (Polyethylene glycol (B) having a number average molecular weight of 1000 to 7000) The number average molecular weight of the polyethylene glycol (B) is 1000 to 7000. As the content of the 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 the polyethylene glycol (B) is 0.5 part 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 homopolymer resin (A). The polyalkylene glycol (B) may be used alone or in combination of two or more. The number average molecular weight can be measured using gel permeation chromatography (such as "HLC-8320" manufactured by Tosoh Corporation).

[0038] (Nitrogen-containing compound (C)) The nitrogen-containing compound (C) is preferably 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.

[0039] 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 with respect to 100 parts by mass of the polyoxymethylene homopolymer resin (A). When the content of the nitrogen-containing compound (C) is within the above range, it is possible to provide a polyoxymethylene homopolymer resin composition with a reduced formaldehyde emission amount and a molded article having excellent grease resistance.

[0040] 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.

[0041] 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, etc. Examples of the ureido compound include, but are not limited to, allantoin, etc.

[0042] Examples of the amide compound include, but are not limited to, polyvalent carboxylic acid amides such as isophthalic acid diamide, anthranilamide, polyacrylamide copolymer, etc.

[0043] The low melting point polyamide is a polyamide polymer having a melting point of 200°C or lower, and examples include polyamide 12, polyamide 11, polyamide 6 / 66 copolymer, polyamide 6 / 66 / 12 terpolymer, polyamide 6 / 66 / 610 terpolymer, etc. More preferred is the polyamide 6 / 66 / 610 terpolymer.

[0044] The acrylamide copolymer preferably has a primary amide group content of 30 to 70 mol% and is in the form of particles having 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.

[0045] As the hydrazide compound, it is synthesized by the reaction of carboxylic acid (including aromatic and alicyclic) and hydrazine. The carboxylic acid mono(di)hydrazide compounds synthesized using carboxylic acid 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, etc. 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.

[0046] (Alkali metal) In the polyoxymethylene homopolymer resin composition of the present 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 product can be reduced.

[0047] Examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium, and the like. Among these, the alkali metal is particularly preferably potassium.

[0048] 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.

[0049] (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.

[0050] 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).

[0051] (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.

[0052] (Manufacturing method of polyoxymethylene homopolymer resin composition) The polyoxymethylene homopolymer resin composition of the present embodiment can be produced by mixing the above-described components (A) to (C), 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, Banbury mixer, etc., and can be obtained as products in various forms such as strand shape and pellet shape. Also, without pre-mixing, each component can be continuously fed into the extruder alone or in several kinds together using a metering feeder, etc. 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) to be 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 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.

[0053] (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, a 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 method, extrusion molding method, 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

[0054] 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.

[0055] 〔Evaluation method〕 Hereinafter, the evaluation method will be described.

[0056] ((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 a cylinder temperature set at 215°C, ISO dumbbell test pieces for grease resistance evaluation were 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 conducting a tensile test in accordance with ISO 527 with n = 3 and evaluating 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%

[0057] ((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 ·Specimen 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.

[0058] ((3) Content of alkali metals 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.

[0059] [Components used in the examples and comparative examples] ((A) Polyoxymethylene homopolymer resin) (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 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 added in amounts of 5.0×10 -5 mol per 1 mol of monomer, and a molecular weight regulator (acetic anhydride) was added in an amount of 0.24×10 -3 mol per 1 mol of monomer, and they were continuously fed and subjected to a polymerization reaction. 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 mass ppm based on the crude polyoxymethylene homopolymer, and stirring was carried out at 150°C for 2 hours to esterify the unstable ends of the crude polyoxymethylene homopolymer. The slurry concentration at this time was 16 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.

[0060] <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 mass ppm.

[0061] <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 mass ppm.

[0062] <Method for preparing (A-4)> A polyoxymethylene homopolymer resin (A-4) was obtained in the same manner as (A-1), except that potassium acetate was not added.

[0063] <Method for preparing (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.

[0064] (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))

[0065] (Nitrogen-containing compound (C)) (C-1) Polyamide 6 / 66 / 610 terpolymer (PA / 6 / 66 / 610) (C-2): Acrylamide copolymer (C-3): Hydrazide compound (Sebacic acid dihydrazide (SDH), manufactured by Nippon Fine Chemical Co., Ltd.)

[0066] <Method for preparing (C-2)> 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 the reaction was completed, the solid matter was pulverized with a jet mill and washed with acetone. Then, it was dried under reduced pressure at 120 °C for 20 hours under a reduced pressure of -700 mmHg. The content of primary amide groups was 44.7 mol%, and the average particle size was 5.0 μm. The average particle size of the acrylamide copolymer (C-2) was measured with a laser diffraction particle size distribution measuring device.

[0067] [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-2), 0.05 part by mass of a hydrazide compound (C-3), 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 using a 30φ single-screw extruder, extruded into strands, cooled, and pelletized to obtain pellets of a polyoxymethylene homopolymer resin composition. The extrusion conditions were as follows: the cylinder set temperature was 200 °C, the discharge rate 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-mentioned (1) grease resistance and the above-mentioned (2) formaldehyde emission amount from the hot runner molded product were evaluated by the respective evaluation methods. The evaluation results are shown in Table 1.

[0068] 〔Examples 2 to 7〕 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.

[0069] 〔Comparative Examples 1 to 8〕 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.

[0070]

Table 1

[0071]

Table 2

[0072] As is clear from the evaluation results in Table 1, in the resin composition containing polyoxymethylene homopolymer resin (A), polyethylene glycol (B), and nitrogen-containing compound (C), in the examples where the potassium content in the resin composition is in the range of 0.1 to 3.0, a polyoxymethylene homopolymer resin composition excellent in grease resistance and having a reduced formaldehyde emission amount from the hot runner molded article was obtained.

Industrial Applicability

[0073] The polyoxymethylene homopolymer resin composition of the present invention has industrial applicability as parts for automobiles, various electrical and electronic equipment parts, and other various industrial parts.

Claims

1. A polyoxymethylene homopolymer resin composition containing, with respect to 100 parts by mass of a polyoxymethylene homopolymer resin (A), 0.5 to 3.0 parts by mass of a polyethylene glycol (B) having a number average molecular weight of 1,000 to 7,000, and 0.01 to 0.5 parts by mass of a nitrogen-containing compound (C), characterized in that the content of alkali metal contained in the polyoxymethylene homopolymer resin composition is 0.1 to 3.0 mass ppm. A polyoxymethylene resin composition.

2. The polyoxymethylene resin composition according to claim 1, characterized in that 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, characterized in that the alkali metal is potassium.

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

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