Mechanical parts

Abstract

To provide a mechanism component capable of suppressing generation of rust, and further capable of suppressing generation of cracks of a component composed of a polyacetal resin composition even when stress is applied for a long time under a high temperature and high humidity environment while using grease.SOLUTION: The present invention is a mechanical component that has a gear system consisting of a combination of a gear made of a polyacetal resin composition and a metal gear, and is used under a high temperature and high humidity environment, where the polyacetal resin composition comprises a polyacetal resin, and 0.1 to 2.0 parts by mass of polyalkylene glycol per 100 parts by mass of the polyacetal resin; a melt flow rate is 0.8 to 6.0 g / 10 minutes; and grease containing a total of 500 ppm or more of alkali metal and / or alkaline earth metal components is applied to the gear system.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a gear system comprising a combination of a gear made of a polyacetal resin composition and a metal gear, and to a mechanical component used in high-temperature and high-humidity environments. [Background technology]

[0002] Polyacetal resin is a representative engineering plastic that offers an excellent balance of mechanical strength, chemical resistance, and sliding properties, and is also easy to process. It is widely used in electrical equipment, mechanical components such as gears for electrical equipment, automotive parts, and other precision machinery components. Among these, polyacetal resin is particularly often used in electrical equipment, automotive parts, and precision mechanical components such as gears and cams.

[0003] Furthermore, among the automotive parts mentioned above, interior and mechanical parts of automobiles are subjected to high loads over long periods of time and require high impact resistance in the event of collisions, etc., so high molecular weight polyacetal homopolymer resins are generally used. In addition, mechanical parts that operate under constant high loads may be coated with grease to reduce sliding resistance (see, for example, Patent Document 1).

[0004] However, when polyacetal resin is used as a component material for mechanical parts, in environments where grease is in contact with the parts for extended periods at high temperatures, there is a risk of a decrease in the molecular weight of the polyacetal resin, leading to a decline in mechanical properties and the formation of cracks within the parts. In particular, it has been reported that when lithium soap-based grease or calcium soap-based grease is used in high-temperature and high-humidity environments, cracks in the parts tend to form more easily in a short period of time. To solve these problems, for example, Patent Document 2 proposes a mechanism component made of polyacetal resin using urea-based grease. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 5688805 [Patent Document 2] Japanese Patent Publication No. 2021-178944 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, in the case of polyacetal resin mechanical components using urea-based grease, as disclosed in Patent Document 2, prolonged use in high-temperature and high-humidity environments may cause the metal inside the mechanical components to rust, and this rust may lead to abnormal noise and a decrease in transmission efficiency.

[0007] Therefore, the present invention aims to provide a mechanical component that can suppress the occurrence of rust, and furthermore, can suppress the occurrence of cracks in a component made of a polyacetal resin composition even when stress is applied for a long period of time in a high-temperature and high-humidity environment while using grease. [Means for solving the problem]

[0008] The present inventors have diligently studied mechanical components used in high-temperature and high-humidity environments, which have a gear system consisting of a combination of gears made of a polyacetal resin composition and metal gears, in order to solve the problems of the prior art described above. As a result, they have found that by including a specific amount of polyalkylene glycol in the polyacetal resin composition constituting the gear, defining its melt flow rate within a specific range, and applying a grease containing alkali metal and / or alkaline earth metal components to the gear system, it is possible to suppress the occurrence of cracks in the gears even when subjected to stress for a long period of time in a high-temperature and high-humidity environment without causing rust, thus completing the present invention.

[0009] This invention is based on the above findings, and its gist is as follows. [1] A gear system comprising a combination of a gear made of a polyacetal resin composition and a metal gear, a mechanical component used in a high-temperature and high-humidity environment, The polyacetal resin composition comprises a polyacetal resin and 0.1 to 2.0 parts by mass of polyalkylene glycol per 100 parts by mass of the polyacetal resin, and has a melt flow rate of 0.8 to 6.0 g / 10 min. A mechanical component characterized in that the gear system is coated with grease containing a total of 500 ppm or more of alkali metal and / or alkaline earth metal components. [2] The mechanical component according to [1], characterized in that the grease further contains 500 ppm or more of lithium or calcium components. [3] The mechanical component according to [2], characterized in that the grease further contains 2000 ppm or more of lithium or 5000 ppm or more of calcium. [4] The mechanical component according to any one of [1] to [4] above, characterized in that the mechanical component is used in an environment with a temperature of 60°C or higher and a humidity of 60% or higher. [5] The mechanism component according to any one of [1] to [3], characterized in that the polyacetal resin is a polyacetal homopolymer. [6] The mechanism component according to any one of [1] to [5], characterized in that the polyalkylene glycol is polyethylene glycol. [7] The mechanism component according to [6], characterized in that the polyethylene glycol is polyethylene glycol having a number average molecular weight of 10,000 to 25,000. [8] The mechanical component according to any one of [1] to [7] above, characterized in that the mechanical component is an interior component of an automobile. [9] The mechanical component according to any one of [1] to [8] above, characterized in that the mechanical component is a component of a power window and / or wiper. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress the generation of rust, and further, even when stress is applied for a long time in a high-temperature and high-humidity environment while using grease, it is possible to suppress the occurrence of cracks in parts made of a polyacetal resin composition, and a mechanical component can be provided.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram for explaining the test container used when evaluating rust resistance in the examples. [Figure 2] It is a schematic cross-sectional view for explaining the test jig used when evaluating environmental stress cracking resistance (hereinafter referred to as ESC resistance) in the examples. [Figure 3] It is a photograph of the test machine used when evaluating gear durability in the examples.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an exemplification for explaining the present invention, and the present invention is not limited only to the embodiments thereof. That is, the present invention can be variously modified without departing from the gist thereof.

[0013] <Mechanical Component> The mechanical component of the present embodiment has a gear system composed of a combination of a gear made of a polyacetal resin composition and a metal gear, and is a mechanical component used in a high-temperature and high-humidity environment. Here, a mechanical component refers to a component used in a machine or device.

[0014] As will be described later, the mechanical component of the present embodiment can suppress the occurrence of cracks even when stress is applied for a long time in a high-temperature and high-humidity environment, and thus can be suitably used particularly as an automotive part. Examples of automotive parts include, for example, automotive interior parts, parts used for power windows, parts used for wipers, and the like. Furthermore, the mechanical components of this embodiment can also be used as components other than those for vehicles, such as mechanical components for information equipment, communication equipment, electrical equipment, electronic equipment, housing equipment, industrial equipment, medical supplies, nursing care supplies, etc.

[0015] Furthermore, in the mechanical component of this embodiment, the polyacetal resin composition comprises a polyacetal resin and 0.1 to 2.0 parts by mass of polyalkylene glycol per 100 parts by mass of the polyacetal resin, and has a melt flow rate of 0.8 to 6.0 g / 10 min, and the gear system is coated with a grease containing alkali metal and / or alkaline earth metal components in a total of 500 ppm or more. The mechanical components of this embodiment, by having the above configuration, can suppress the occurrence of rust in high-temperature and high-humidity environments, and can also suppress the occurrence of cracks even when stress is applied for a long period of time while in contact with grease. The following describes in detail each component that constitutes the mechanical parts of this embodiment.

[0016] <Gear System> As described above, the gear system constituting the mechanical component of this embodiment consists of a combination of a gear made of a polyacetal resin composition and a metal gear. Various types of gears and metal gears can be used in the gear system. The gears mentioned above are not limited to the following, but examples include helical gears, spur gears, internal gears, rack gears, serpentine gears, straight bevel gears, spiral bevel gears, crown gears, face gears, screw gears, worm gears, worm wheel gears, hypoid gears, and Novikov gears. The helical gears and spur gears mentioned above may be single gears, two-stage gears, or combination gears that are combined in multiple stages from a drive motor to eliminate rotational unevenness and reduce speed. Furthermore, while stainless steel and carbon steel are preferred as metal gears, the material is not limited to these, and can be appropriately selected according to the required performance. Additionally, the metal gears can be subjected to treatments such as plating on their metal surfaces.

[0017] Furthermore, the method for manufacturing the gear is not particularly limited, and known methods can be used as appropriate. For example, the polyacetal resin composition described later can be manufactured by molding it using molding methods such as extrusion molding, injection molding, vacuum molding, blow molding, injection compression molding, decorative molding, molding of other materials, gas-assisted injection molding, foam injection molding, low-pressure molding, ultra-thin-wall injection molding (ultra-high-speed injection molding), and in-mold composite molding (insert molding, outsert molding).

[0018] (Polyacetal resin composition) The polyacetal resin composition used for the gears constituting the mechanical components of this embodiment comprises a polyacetal resin and 0.1 to 2.0 parts by mass of polyalkylene glycol per 100 parts by mass of the polyacetal resin, with a melt flow rate (MFR) of 0.8 to 6.0 g / 10 min. This improves the moldability, durability, and impact resistance of the gears made from the polyacetal resin composition, and suppresses the occurrence of cracks in the gears even when subjected to stress for a long period of time in a high-temperature and high-humidity environment. If the MFR of the polyacetal resin composition is less than 0.8 g / 10 min, it becomes difficult to produce stable molded products, which can lead to a decrease in the dimensional accuracy of the gears and a reduction in gear durability. On the other hand, if the MFR of the polyacetal resin composition is greater than 6.0 g / 10 min, although stable molded products can be obtained, it can become difficult to maintain the high impact characteristics and durability required for automotive parts. From a similar viewpoint, the MFR of the polyacetal resin composition is preferably 1.5 to 4.0 g / 10 min, and more preferably 1.8 to 3.0 g / 10 min. The MFR of the polyacetal resin composition was measured under conditions of 190°C and 2160g, in accordance with ASTM-D1238.

[0019] • Polyacetal resin Here, the polyacetal resin contained in the polyacetal resin composition refers to a polymer having oxymethylene groups in its main chain. Examples include: polyacetal homopolymers consisting substantially of oxymethylene units, obtained by homopolymerizing formaldehyde monomers, or cyclic oligomers of formaldehyde such as their trimer (trioxane) or tetramer (tetraoxane); polyacetal copolymers obtained by copolymerizing formaldehyde monomers, or cyclic oligomers of formaldehyde such as their trimer (trioxane) or tetramer (tetraoxane), with cyclic ethers or cyclic formals such as glycols or diglycols such as ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane, and 1,4-butanediol formal; branched polyacetal copolymers obtained by copolymerizing monofunctional glycidyl ethers; and crosslinked polyacetal copolymers obtained by copolymerizing polyfunctional glycidyl ethers.

[0020] Furthermore, as the polyacetal resin, compounds having functional groups such as hydroxyl groups at both or one end, for example, polyacetal homopolymers having a block component obtained by polymerizing a cyclic oligomer of formaldehyde, such as a formaldehyde monomer or its trimer (trioxane) or tetramer (tetraoxane), in the presence of polyalkylene glycol; and polyacetal copolymers having a block component obtained by copolymerizing a cyclic oligomer of formaldehyde, such as a formaldehyde monomer or its trimer (trioxane) or tetramer (tetraoxane), with a cyclic ether or cyclic formal, in the presence of hydrogenated polybutadiene glycol. The polyacetal resins mentioned above can be used individually or in combination of two or more types.

[0021] As described above, the polyacetal resin can be either a polyacetal homopolymer or a polyacetal copolymer, but from the viewpoint of mechanical properties, it is preferable to include a polyacetal homopolymer.

[0022] Furthermore, there are no particular restrictions on the degree of polymerization or comonomer content of the polyacetal resin.

[0023] The aforementioned polyacetal homopolymer can be produced, for example, by feeding formaldehyde as a monomer, a chain transfer agent (molecular weight modifier), and a polymerization catalyst into a polymerization reactor equipped with a hydrocarbon polymerization solvent, and polymerizing them by slurry polymerization. In this process, the raw material monomers, chain transfer agents, and polymerization catalysts may contain chain-transferable components (components that generate unstable end groups), such as water, methanol, and formic acid. Therefore, it is preferable to first adjust the content of these chain-transferable components. The content of these chain-transferable components is preferably in the range of 1 to 1000 ppm by mass, more preferably 1 to 500 ppm by mass, and even more preferably 1 to 300 ppm by mass, relative to the total mass of formaldehyde, which is the monomer. By adjusting the content of the chain-transferable components within the above range, a polyacetal homopolymer with excellent thermal stability can be obtained.

[0024] Furthermore, the molecular weight of the polyacetal homopolymer can be adjusted by chain transfer using a molecular weight modifier such as a carboxylic acid anhydride or carboxylic acid. Propionic anhydride and acetic anhydride are particularly preferred as molecular weight modifiers, with acetic anhydride being more preferred. The amount of molecular weight modifier introduced is adjusted and determined according to the properties of the target polyacetal homopolymer (especially the melt flow rate).

[0025] As the polymerization catalyst, an anionic polymerization catalyst is preferred, and an onium salt polymerization catalyst represented by the following general formula (I) is more preferred. [R 1 R2 R 3 R 4 M]+X- ···(I) (In formula (I), R 1 , R 2 , R 3 and R 4 Each of these independently represents an alkyl group, M represents an element with a lone pair of electrons, and X represents a nucleophilic group. Polymerization catalysts may be used individually or in combination of two or more types.

[0026] Furthermore, among the onium salt polymerization catalysts, quaternary phosphonium salt compounds such as tetraethylphosphonium iodide and tributylethylphosphonium iodide, and quaternary ammonium salt compounds such as tetramethylammonium bromide and dimethyldistearylammonium acetate are preferred.

[0027] The amount of onium salt polymerization catalysts, such as these quaternary phosphonium salt compounds and quaternary ammonium salt compounds, added is preferably 0.0003 to 0.01 mol per mole of formaldehyde, more preferably 0.0008 to 0.005 mol, and even more preferably 0.001 to 0.003 mol.

[0028] Any hydrocarbon polymerization solvent that does not react with formaldehyde is acceptable and is not particularly limited, but examples include pentane, isopentane, hexane, cyclohexane, heptane, octane, nonane, decane, and benzene, with hexane being particularly preferred. These hydrocarbon solvents may be used individually or in combination of two or more.

[0029] Furthermore, in the production of the polyacetal homopolymer, it is preferable to first obtain a crude polyacetal homopolymer by polymerization, and then subject the unstable end groups to a stabilization treatment, as described later.

[0030] The polymerization reactor for producing the crude polyacetal homopolymer is not particularly limited as long as it is a device capable of simultaneously supplying a monomer formaldehyde, a chain transfer agent (molecular weight regulator), a polymerization catalyst, and a hydrocarbon-based polymerization solvent. However, from the perspective of productivity, a continuous polymerization reactor is preferred.

[0031] The terminal groups of the crude polyacetal homopolymer obtained by the polymerization are thermally unstable. Therefore, it is preferable to block and stabilize these unstable terminal groups with an esterifying agent or an etherifying agent.

[0032] The stabilization treatment of the terminal groups of the crude polyacetal homopolymer by esterification can be carried out, for example, by introducing a hydrocarbon-based solvent into a terminal stabilization reactor and respectively charging the crude polyacetal homopolymer, an esterifying agent, and an esterification catalyst, and then reacting them. As the reaction temperature and reaction time at this time, for example, the reaction temperature is preferably 130 to 155°C, and the reaction time is preferably 1 to 100 minutes. More preferably, the reaction temperature is 135 to 155°C, and the reaction time is 5 to 100 minutes. Even more preferably, the reaction temperature is 140 to 155°C, and the reaction time is 10 to 100 minutes.

[0033] As the esterifying agent for blocking and stabilizing the terminal groups of the crude polyacetal homopolymer, an acid anhydride represented by the following general formula (II) can be used. R 5 COOCOR 6 ···(II) (In formula (II), R 5 and R 6 each independently represent an alkyl group. R 5 and R 6 may be the same as or different from each other.)

[0034] The acid anhydride represented by the above general formula (II) is not limited to the following, but examples include benzoic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, phthalic anhydride, propionic anhydride, and acetic anhydride, with acetic anhydride being preferred. These esterifying agents may be used individually or in combination of two or more.

[0035] As the esterification catalyst, an alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is preferred, and the amount added can be appropriately selected in the range of 1 to 1000 ppm by mass relative to the mass of the polyacetal homopolymer. The alkali metal salt of a carboxylic acid having 1 to 18 carbon atoms is not limited to the following, but examples include alkali metal salts of carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caprylic acid, enanthic acid, capric acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid, and examples of alkali metals include lithium, sodium, potassium, rubidium, and cesium. Among these alkali metal salts of carboxylic acids, lithium acetate, sodium acetate, and potassium acetate are preferred.

[0036] As an etherifying agent for sequestering and stabilizing the terminal groups of the crude polyacetal homopolymer, one can select from orthoesters of aliphatic or aromatic acids and aliphatic, alicyclic, or aromatic alcohols, such as methyl orthoformate or ethyl orthoformate, methyl orthoacetate or ethyl orthoacetate, methyl orthobenzoate or ethyl orthobenzoate, and orthocarbonates, specifically ethyl orthocarbonate. This can be stabilized using Lewis acid type catalysts such as moderate-strength organic acids like p-toluenesulfonic acid, acetic acid, and oxalic acid, or moderate-strength mineral acids like dimethyl sulfate and diethyl sulfate.

[0037] The solvent used in the etherification reaction to stabilize the terminal groups of the crude polyacetal homopolymer by etherification is not limited to the following, but examples include low-boiling aliphatic organic solvents such as pentane, hexane, cyclohexane, and benzene; alicyclic and aromatic hydrocarbon organic solvents; and halogenated lower aliphatic organic solvents such as methylene chloride, chloroform, and carbon tetrachloride.

[0038] By the above method, the polyacetal homopolymer with stabilized end groups is dried using a dryer such as a hot air dryer or a vacuum dryer, by sealing it with air or nitrogen gas adjusted to 100-150°C to remove moisture and obtain a polyacetal homopolymer as a polyacetal resin.

[0039] • Polyalkylene glycol The polyacetal resin composition contains 0.1 to 2.0 parts by mass of polyalkylene glycol per 100 parts by mass of the polyacetal resin. By including polyalkylene glycol as a stress-relaxing agent in the polyacetal resin composition, the occurrence of cracks in the component due to residual stress can be effectively suppressed.

[0040] Here, the polyalkylene glycol is not particularly limited, but it is preferably polyethylene glycol or polypropylene glycol, and more preferably polyethylene glycol. These polyalkylene glycols may be used individually or in combination of two or more types.

[0041] Furthermore, the number-average molecular weight of the polyalkylene glycol is preferably 5,000 to 20,000, and more preferably 10,000 to 20,000, from the viewpoint of dispersibility. In this embodiment, the number-average molecular weight of polyethylene glycol can be measured by gel permeation chromatography (GPC).

[0042] The polyalkylene glycol content in the polyacetal resin composition must be 0.1 to 10 parts by mass, preferably 0.1 to 5 parts by mass, and more preferably 0.1 to 2 parts by mass, per 100 parts by mass of the polyacetal resin. If the polyalkylene glycol content is 2 parts by mass or less, the gear durability is excellent, and if it is 10 parts by mass or less, the stress cracking resistance (ESC resistance) is excellent.

[0043] • Additives The polyacetal resin composition may be blended with appropriate additives depending on the application. Examples of such additives include antioxidants, polymers or compounds having formaldehyde-reactive nitrogen, formic acid scavengers, hydrazide compounds, and mold release agents. The amount of each additive in the polyacetal resin composition is preferably 0.001 to 0.8 parts by mass, more preferably 0.01 to 0.7 parts by mass, per 100 parts by mass of the polyacetal resin.

[0044] As the aforementioned antioxidant, hindered phenol-based antioxidants are preferred. For example, 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) Examples include [(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',5'-di-t-butyl-4'-hydroxyphenyl)-propionate], and pentaerythritol tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. Preferred antioxidants among these include triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)-propionate] and pentaerythritol tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. A single antioxidant may be used alone, or two or more may be used in combination.

[0045] The polymer or compound having formaldehyde-reactive nitrogen is a polymer or compound (monomer) having a nitrogen atom capable of reacting with formaldehyde within its molecule. Examples include polyamide resins such as nylon 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12, and nylon 12, and polymers thereof, such as nylon 6 / 6-6 / 6-10 and nylon 6 / 6-12. Furthermore, polymers or compounds having formaldehyde-reactive nitrogen include acrylamide and its derivatives, and copolymers of acrylamide and its derivatives with other vinyl monomers. For example, a poly-β-alanine copolymer obtained by polymerizing acrylamide and its derivatives with other vinyl monomers in the presence of a metal alcoholate is an example. Furthermore, polymers or compounds having formaldehyde-reactive nitrogen include amide compounds, amino-substituted triazine compounds, adducts of amino-substituted triazine compounds and formaldehyde, condensates of amino-substituted triazine compounds and formaldehyde, urea, urea derivatives, imidazole compounds, and imide compounds.

[0046] Specific examples of the aforementioned amide compounds include polycarboxylic acid amides such as isophthalic acid diamide and anthranilamide. Specific examples of the amino-substituted triazine compounds include 2,4-diamino-sym-triazine, 2,4,6-triamino-sym-triazine, N-butylmelamine, N-phenylmelamine, N,N-diphenylmelamine, N,N-diallylmelamine, benzoguanamine (2,4-diamino-6-phenyl-sym-triazine), acetoguanamine (2,4-diamino-6-methyl-sym-triazine), and 2,4-diamino-6-butyl-sym-triazine. Specific examples of adducts between the amino-substituted triazine compound and formaldehyde include N-methylolmelamine, N,N'-dimethylolmelamine, and N,N',N''-trimethylolmelamine. Specific examples of condensates between the amino-substituted triazine compound and formaldehyde include melamine-formaldehyde condensates. Examples of the urea derivatives include N-substituted ureas, urea condensates, ethylene urea, hydantoin compounds, and ureido compounds. Specific examples of the N-substituted ureas include methylurea substituted with alkyl groups, alkylenebisurea, and aryl-substituted ureas. Specific examples of the urea condensates include condensates of urea and formaldehyde. Specific examples of the hydantoin compounds include hydantoin, 5,5-dimethylhydantoin, and 5,5-diphenylhydantoin. Specific examples of the ureido compounds include allantoin. Specific examples of the imidazole compounds mentioned above include imidazole, 1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole. Specific examples of the aforementioned imide compounds include succinimide, glutarimide, and phthalimide. These polymers or compounds containing formaldehyde-reactive nitrogen may be used individually or in combination of two or more.

[0047] The formic acid scavenger described above is capable of efficiently neutralizing formic acid and includes, for example, the above-mentioned amino-substituted triazine compound, a condensate of an amino-substituted triazine compound and formaldehyde, such as a melamine-formaldehyde condensate. Furthermore, examples of formic acid scavenging agents include hydroxides, inorganic salts, carboxylates, or alkoxides of alkali metals or alkaline earth metals. For example, hydroxides of metals such as sodium, potassium, magnesium, calcium, or barium, and carbonates, phosphates, silicates, borates, and carboxylates of the above metals are examples. The carboxylic acid in the above carboxylate salt is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, and these carboxylic acids may have hydrogen atoms substituted with hydroxyl groups. Specific examples of saturated or unsaturated aliphatic carboxylates include calcium dimyristate, calcium dipalmitate, calcium distearate, calcium (myristate-palmitate), calcium (myristate-stearate), and calcium (palmitate-stearate). Among these, calcium dipalmitate, calcium distearate, and magnesium silicate are preferred.

[0048] The hydrazide compound constituting the polyacetal homopolymer resin composition is not particularly limited as long as it has a hydrazine structure (NN) with a single bond between nitrogen atoms, and known compounds can be used. For example, hydrazine; hydrazine hydrate; carboxylic acid monohydrazides such as succinate monohydrazide, glutarate monohydrazide, adipic acid monohydrazide, pimelic acid monohydrazide, superiric acid monohydrazide, azelaic acid monohydrazide, and sebacate monohydrazide; saturated oxalate dihydrazide, malonic acid dihydrazide, succinate dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, superiric acid dihydrazide, azelaic acid dihydrazide, sebacate dihydrazide, and dodecanediic acid dihydrazide. Aliphatic carboxylic acid dihydrazides; dihydrazides of monoolefinic unsaturated dicarboxylic acids such as maleic acid dihydrazide, fumaric acid dihydrazide, and itaconic acid dihydrazide; aromatic carboxylic acid dihydrazides such as isophthalic acid dihydrazide, phthalic acid dihydrazide, and 2,6-naphthalenedicarbodide dihydrazide; pyromellitic acid dihydrazides; trihydrazides such as trimer acid trihydrazide, cyclohexanetricarboxylic acid trihydrazide, benzenetricarboxylic acid trihydrazide, nitrilotriacetic acid trihydrazide, and citrate trihydrazide; pyrome Tetrahydrazides such as tetrahydrazide litate, tetrahydrazide naphthoate, tetrahydrazide ethylenediaminetetraacetate, and tetrahydrazide 1,4,5,8-tetrahydrazide naphthoate; polyhydrazides such as polyhydrazides obtained by reacting low polymers having a lower alkyl ester group of carboxylic acid with hydrazine or hydrazine hydrate (hydrazine hydrate); dihydrazides carbonate; bissemicarbazides; diisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate, and polyisocyanates derived therefrom. Examples include polyfunctional semicarbazides obtained by reacting a compound with an excess of an N,N-substituted hydrazine such as N,N-dimethylhydrazine and / or one of the exemplified hydrazides; aqueous polyfunctional semicarbazides obtained by reacting an isocyanate group in a reaction product of the polyisocyanate compound with an active hydrogen compound containing a hydrophilic group, such as polyether polyols or polyethylene glycol monoalkyl ethers, with one of the dihydrazides mentioned above in excess; mixtures of the polyfunctional semicarbazides and aqueous polyfunctional semicarbazides; and bisacetyldihydrazones.

[0049] As the aforementioned release agent, for example, alcohols, fatty acids and their fatty acid esters are preferably used, and a preferred release agent is ethylene glycol distearate.

[0050] Other compounding agents The polyacetal resin composition may be further enriched with known compounding agents (other compounding agents) as needed, as long as the objectives of the present invention are not impaired. Examples of such other compounding agents include inorganic fillers, nucleating agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, and the like.

[0051] Examples of inorganic fillers include fibrous, powder, plate-like, and hollow inorganic fillers. Examples of fibrous inorganic fillers include inorganic fibers such as glass fibers, carbon fibers, silicone fibers, silica-alumina fibers, zirconia fibers, boron nitride fibers, silicon nitride fibers, boron fibers, potassium titanate fibers, stainless steel, aluminum, titanium, copper, brass, and other metal fibers. Whiskers with short fiber lengths, such as potassium titanate whiskers and zinc oxide whiskers, are also exemplified as fibrous inorganic fillers. Examples of powder-like inorganic fillers include carbon black, silica, quartz powder, glass beads, glass powder, calcium silicate, magnesium silicate, aluminum silicate, kaolin, clay, diatomaceous earth, silicates such as wollastonite, metal oxides such as iron oxide, titanium oxide, and alumina, metal sulfates such as calcium sulfate and barium sulfate, carbonates such as magnesium carbonate and dolomite, and other materials such as silicon carbide, silicon nitride, boron nitride, and various metal powders. Examples of plate-shaped inorganic fillers include mica, glass flakes, and various metal foils. Examples of hollow inorganic fillers include glass balloons, silica balloons, shirasu balloons, and metal balloons. These inorganic fillers may be used individually or in combination of two or more. Furthermore, the inorganic filler may or may not be surface-treated, but surface-treated fillers are sometimes preferred from the viewpoint of smoothness of the molded surface and mechanical properties. Conventional known surface treatment agents can be used for surface treatment of the inorganic filler. Examples include various coupling agents such as silane-based, titanate-based, aluminum-based, and zirconium-based agents. Specifically, examples include N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyltrisstearoyl titanate, diisopropoxyammonium ethyl acetate, and n-butyl zirconate. In addition, high-melting-point organic fibrous substances such as aromatic polyamide resins, fluororesins, and acrylic resins may be added together with or in place of the inorganic filler.

[0052] Examples of the aforementioned nucleating agent include boron nitride and talc.

[0053] Examples of the conductive agent include conductive carbon black, metal powder, or fibers.

[0054] Examples of the thermoplastic resins include polyolefin resins, acrylic resins, styrene resins, polycarbonate resins, and uncured epoxy resins. Modified products of these resins are also included in thermoplastic resins. Examples of thermoplastic elastomers include polyurethane elastomers, polyester elastomers, polystyrene elastomers, and polyamide elastomers.

[0055] Examples of the aforementioned pigments include inorganic pigments, organic pigments, metallic pigments, and fluorescent pigments. Inorganic pigments can be any pigment commonly used for coloring resins, such as zinc sulfide, titanium dioxide, barium sulfate, titanium yellow, cobalt blue, pyrolytic pigments, carbonates, phosphates, acetates, carbon black, acetylene black, and lamp black. Examples of organic pigments include condensed azo, quinone, phthalocyanine, monoazo, diazo, polyazo, anthraquinone, heterocyclic, perinone, quinacridone, thioindico, perylene, and dioxazine pigments.

[0056] (Method for producing polyacetal resin composition) The method for producing the polyacetal resin composition used in this embodiment is not particularly limited, and conventionally known methods can be applied. For example, the polyacetal resin and the polyalkylene glycol can be pre-mixed using a Henschel mixer, tumbler, V-type blender, etc., and then melt-mixed using a single-screw or multi-screw compounding extruder, etc., or other methods generally known as methods for producing resin compositions. When melt-mixing the polyacetal resin composition, it is preferable to use a twin-screw compounding extruder equipped with a vacuum device. Furthermore, it is also possible to obtain a raw material composition within the extruder by continuously supplying each component individually or in groups of several types to the extruder using a quantitative feeder or the like, without pre-mixing the polyacetal resin and the polyalkylene glycol, and then producing a polyacetal resin composition from that raw material composition. Furthermore, a polyacetal resin composition can also be obtained by preparing a high-concentration masterbatch consisting of the above components in advance and then further diluting it with the polyacetal resin during extrusion melt kneading or injection molding.

[0057] <Grease> The grease used for the mechanical components in this embodiment is applied to the gear system, and the grease contains a total of 500 ppm or more of alkali metal and / or alkaline earth metal components. By using a grease containing a total of 500 ppm or more of alkali metal and / or alkaline earth metal components, rust formation can be suppressed even in high-temperature and high-humidity environments. Here, when applying the grease to the gear system, it is preferable to apply it to at least the meshing surfaces of the gears. This is because it can more effectively suppress the occurrence of rust.

[0058] The grease contains alkali metal and / or alkaline earth metal components in a total of 500 ppm or more, but from the viewpoint of more effectively suppressing rust formation in high-temperature and high-humidity environments, it is preferable to contain lithium and / or calcium components in a total of 500 ppm or more, and more preferably to contain lithium components in a total of 2,000 ppm or more and / or calcium components in a total of 5,000 ppm or more. In this embodiment, the content of alkali metals and alkaline earth metal components in the grease can be semi-quantified by inductively coupled plasma mass spectrometry (ICP-MS).

[0059] The grease is not particularly limited in terms of other components, as long as it contains the alkali metal and / or alkaline earth metal components. For example, it may contain molybdenum, aluminum, fluorine, urea compounds, etc., as its main components. Regarding the grease mentioned above, commercially available products can be used as appropriate. [Examples]

[0060] The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0061] (Components of each sample) The components contained in each sample of the examples and comparative examples are shown below.

[0062] (A) Polyacetal resin composition (A-1) A polymerization reactor equipped with stirring blades was filled with n-hexane, and purified formaldehyde gas (water content: 110 ppm), a polymerization catalyst (dimethyldistearylammonium acetate), and a molecular weight regulator (acetic anhydride) were continuously fed to carry out the polymerization reaction. The polymerization reaction temperature at this time was 58°C. The obtained crude polyacetal homopolymer was placed in a reaction vessel filled with a 1:1 mixed solvent of n-hexane and acetic anhydride, and stirred at 150°C for 2 hours to esterify the unstable ends of the crude polyacetal homopolymer. At this time, the mass ratio (slurry concentration) of the polymer to the "1:1 mixed solvent of n-hexane and acetic anhydride" was 20 parts polymer to 100 parts of the "1:1 mixed solvent of n-hexane and acetic anhydride". After the end-stabilization treatment of the polyacetal homopolymer was completed, the polyacetal homopolymer and the "1:1 mixed solvent of n-hexane and acetic anhydride" were removed from the reaction vessel, and the polyacetal homopolymer was repeatedly washed with n-hexane to remove the acetic anhydride. The washing was repeated until the concentration of acetic anhydride in the polyacetal homopolymer was 10 ppm by mass or less. Subsequently, the polyacetal homopolymer was dried under reduced pressure at 120°C for 3 hours at -700 mmHg to remove the n-hexane solvent used for washing. Further drying was performed for 5 hours using a heated drying oven set to 120°C to remove moisture contained in the polyacetal homopolymer, yielding a polyacetal homopolymer powder (P1). Subsequently, polyacetal homopolymer powder (P1), polyethylene glycol (PEG-5000, manufactured by NOF Corporation, number average molecular weight 18,000), antioxidant (Irganox 245, manufactured by BASF), nitrogen-containing compound (terpolymer of polyamide 6 / 66 / 610), and hydrazide compound (dihydrazide sebacate, manufactured by Nippon Finechem Co., Ltd.) were mixed in a Henschel mixer for 1 minute. Then, the mixture was melt-kneaded at 200°C in a vented screw-type twin-screw extruder (BT-30, manufactured by Plastics Industry Co., Ltd., L / D=44) at a screw rotation speed of 100 rpm and 24 amperes to obtain pellets of polyacetal resin composition (sample of polyacetal resin composition (A-1)). From raw material input to pellet collection, the operation was carried out while avoiding oxygen contamination as much as possible. The MFR of the obtained polyacetal resin composition sample (A-1) was measured in accordance with ASTM-D1238 using a MELT INDEXER manufactured by Toyo Seiki under conditions of 190°C and 2.16 kg. The measured MFRs are shown in Table 1.

[0063] (A-2)~(A-4) Samples (A-2) to (A-4) of the polyacetal resin composition were obtained under the same conditions as sample (A-1), except that the amount of polyethylene glycol was adjusted so that the polyethylene glycol content was as shown in Table 1. The MFRs of the obtained polyacetal resin compositions, samples (A-2) to (A-4), were measured in accordance with ASTM-D1238 using a MELT INDEXER manufactured by Toyo Seiki under conditions of 190°C and 2.16 kg. The measured MFRs are shown in Table 1.

[0064] (A-5)~(A-7) Except for adjusting the amounts of polymerization catalyst and chain transfer agent so that the MFR was the value shown in Table 1, the preparation of polyacetal homopolymer powders (P2), (P3), and (P4) was carried out in the same manner as for the preparation of polyacetal homopolymer powder (P1), and polyacetal homopolymer powders (P2), (P3), and (P4) were obtained. Resin compositions (A-5) to (A-7) were obtained by performing the same procedure as for sample (A-1) of polyacetal resin composition, except that polyacetal homopolymer powders (P2), (P3), and (P4) were used instead of polyacetal homopolymer powder (P1). The MFR of the obtained polyacetal resin composition was measured in accordance with ASTM-D1238 using a MELT INDEXER manufactured by Toyo Seiki under conditions of 190°C and 2.16 kg. The measured MFRs are shown in Table 1.

[0065] [Table 1]

[0066] (Forming of multi-purpose test specimens) Multipurpose test specimens were prepared using the obtained polyacetal resin compositions (A-1) to (A-7). Polyacetal resin compositions (A-1) to (A-7) were each molded using an injection molding machine (J110AD, manufactured by Japan Steel Works Ltd.) under the following injection conditions: cylinder temperature 210°C, mold temperature 90°C, injection pressure 70 MPa, injection time 60 seconds, and cooling time 15 seconds, using an ISO mold (compliant with ISO 294-3) to obtain dumbbell-shaped multipurpose test specimens.

[0067] (B) Grease (B-1) Lithium soap-based grease: Chemie Technik ELKALUB VP926, thickener (lithium soap) (B-2) Calcium soap-based grease: Shell Rhodina 0616, thickener (calcium soap) (B-3) Lithium soap-based grease: Maltemp AC-K manufactured by Kyodo Yushi Co., Ltd., thickener (lithium soap) (B-4) Urea-based grease: Excelite No. 2 manufactured by Kyodo Yushi Co., Ltd., thickener (urea compound)

[0068] [Examples 1-7, Comparative Examples 1-3] Samples of multipurpose test pieces prepared from polyacetal resin compositions (A-1) to (A-7) and greases (B-1) to (B-4) were combined as shown in Table 2 to form the examples and comparative examples.

[0069] [evaluation] The following evaluations (1) to (3) were performed on each sample in the examples and comparative examples. The evaluation results are shown in Table 2. (1) Rust resistance As shown in Figure 1, a 200 mL PP bottle 11 was filled with (a) each sample of the dumbbell-shaped multipurpose test piece, cut into three parts using nippers or the like 12, (b) a 5 mL vial 13 with 2 mL of water added, and (c) a round metal bar (Φ3 × 100 mm) 15 made of S45C with grease 14 shown in Table 2 applied to the center, and then sealed with sealing tape. Next, the PP bottle was placed in a gear oven (PH-102M, manufactured by ESPEC Corporation) and heated to 80°C. After 48 hours, the PP bottle 11 was removed, and the presence or absence of rust on the metal rod 15 inside the bottle 11 was checked. For evaluation, we rated the product as follows: "○ (Good)" if no rust was observed, "△ (Poor)" if rust was observed in only one place, and "× (Inferior)" if rust was observed in multiple places.

[0070] (2)ESC resistance As shown in Figure 2, each sample 21 of the dumbbell-shaped multipurpose test specimen was attached to the jig 22, and the grease shown in Table 2 was applied to the center of the dumbbell. The specimens were then placed in a constant temperature and humidity chamber maintained at 80°C and 80% humidity, and the time until cracks occurred was measured for 10 test specimens. The average value (time) was then calculated. For the evaluation, the longer the time until cracks appear, the better the ESC resistance was judged to be. 1400 hours or more was rated "○ (Good)", 1000 hours or more but less than 1400 hours was rated "△ (Poor)", and less than 1000 hours was rated "× (Poor)".

[0071] (3) Gear durability Using polyacetal resin compositions (A-1) to (A-7) as raw materials, gear test pieces with a tooth tip diameter of 52 mm, pitch circle diameter of 50 mm, tooth tip thickness of 8 mm, and 50 teeth were fabricated using a FANUC Corporation S-2000iB injection molding machine at a cylinder temperature of 210°C, injection pressure of 70 MPa, injection time of 25 seconds, cooling time of 15 seconds, and mold temperature of 90°C. After preparing the gear test specimens, the time until the gear specimens broke was measured using a gear durability testing machine manufactured by Nakagawa Seisakusho, under a load torque of 9 Nm, a rotation speed of 100 rpm, and in air at 23°C. Gear durability (gear endurance time) was calculated as the average value (time) of the time until the gears broke for five test specimens. For evaluation, the longer the time it took for the gear test piece to break, the better the gear's durability was judged to be. A rating of 25 hours or more was given as "○ (Good)," and a rating of less than 25 hours was given as "△ (Poor)." As shown in Figure 3, the gear durability testing machine comprises a gear test piece 32 equipped with a drive unit 31 and a metal gear (S45C) 34 equipped with a variable torque meter unit 33. The mechanism rotates the metal gear 34 when the gear test piece 32 is rotated. For the durability test, the torque on the metal gear 34 was set to a predetermined value and the test was conducted. In addition, the grease shown in Table 2 was applied to the resin gear 32 during the test.

[0072] [Table 2]

[0073] The results in Table 2 show that the combination of molded polyacetal resin compositions (test pieces) obtained in Examples 1 to 7 with grease can suppress rust formation in high-temperature and high-humidity environments, further suppress crack formation, and exhibit excellent durability in gears requiring high durability. On the other hand, it was confirmed that achieving both rust resistance and crack prevention was difficult with the combination of molded articles (test pieces) of the polyacetal resin compositions obtained in Comparative Examples 1 to 3 and grease. [Industrial applicability]

[0074] According to the present invention, it is possible to provide a mechanical component that can suppress the occurrence of rust, and furthermore, can suppress the occurrence of cracks in a component made of a polyacetal resin composition even when stress is applied for a long period of time in a high-temperature and high-humidity environment while using grease. [Explanation of Symbols]

[0075] 11 PP bottles 12. A sample of a dumbbell-shaped multi-purpose test specimen, divided into three parts. 13 vials 14 Grease 15 Metal round bar 21 Dumbbell-shaped multi-purpose test specimen 22 Jig 31 Drive Unit 32 Gear Test Pieces 33 Variable Torque Meter Unit 34 metal gears

Claims

1. A mechanical component having a gear system consisting of a combination of a gear made of a polyacetal resin composition and a metal gear, The polyacetal resin composition comprises a polyacetal resin and 0.1 to 2.0 parts by mass of polyalkylene glycol per 100 parts by mass of the polyacetal resin, and has a melt flow rate of 0.8 to 6.0 g / 10 min. A mechanical component characterized in that the gear system is coated with grease containing a total of 500 ppm or more of alkali metal and / or alkaline earth metal components.

2. The mechanical component according to claim 1, characterized in that the grease further contains 500 ppm or more of a lithium component or a calcium component.

3. The mechanical component according to claim 2, characterized in that the grease further contains 2,000 ppm or more of lithium components, or 5,000 ppm or more of calcium components.

4. The mechanical component according to any one of claims 1 to 3, characterized in that the mechanical component is used in an environment with a temperature of 60°C or higher and a humidity of 60% or higher.

5. The mechanism component according to any one of claims 1 to 4, characterized in that the polyacetal resin is a polyacetal homopolymer.

6. The mechanism component according to any one of claims 1 to 5, characterized in that the polyalkylene glycol is polyethylene glycol.

7. The mechanism component according to claim 6, characterized in that the polyethylene glycol is polyethylene glycol having a number average molecular weight of 10,000 to 25,000.

8. The mechanical component according to any one of claims 1 to 7, characterized in that the mechanical component is an interior component of an automobile.

9. The mechanical component according to any one of claims 1 to 7, characterized in that the mechanical component is a component of a power window and / or wiper.

Images