JP6734074B2 - Gear and its manufacturing method - Google Patents

Description

The present invention relates to a gear and a manufacturing method thereof.

Resin gears are used in a wide range of applications as office automation equipment such as copiers and printers, digital home appliances such as VTRs and DVDs, window glass of automobiles, power transmission mechanism components such as seats and sunroofs, and drive transmission mechanism components.

As described above, many gears used for various purposes require high accuracy. As a method of improving the accuracy of gears, a technique has been disclosed in which deformation is suppressed by defining the thickness of a rim, a hub, and a web (for example, see Patent Document 1).

Further, recently, a resin gear capable of transmitting a larger torque has been demanded for a drive unit of an electric motorcycle. As a gear that transmits such a large torque and has high durability, there is disclosed a gear that uses a polyamide resin reinforced with fibers such as glass (see, for example, Patent Documents 2 to 4).

Polyacetal resin is known as a material that is preferably used for resin gears. The reason is that the polyacetal resin has high mechanical strength, is excellent in oil resistance and organic solvent resistance, can be used in a wide temperature range, and is easily processed.

Among polyacetal resins, polyacetal homopolymers are known to have more excellent mechanical strength and high heat distortion temperature (see, for example, Patent Document 5). Further, a technique has been disclosed in which polyacetal homopolymer is used as a material and a gear having a specific shape is used to improve durability and quietness of the gear (for example, see Patent Document 6). The document also discloses a technique of further improving mechanical properties by using a polyacetal homopolymer containing crystal nucleation inorganic particles as a material.

Japanese Patent No. 3621009 JP, 2003-201398, A JP, 2008-8404, A Patent No. 4209666 JP, 2008-291073, A JP, 2011-5731, A

When a polyamide resin reinforced with fibers such as glass is used as the resin gear, it is difficult to control the orientation state of the fibers in the tooth part, and the mechanical strength and durability of the gear are not constant, so it is stable. There is a problem that it is difficult to obtain the desired performance.

In addition, since the polyacetal homopolymer has a high crystallization rate, the resin solidifies quickly in the mold during injection molding, and the flow length in the mold tends to become short. This tendency is remarkable especially when the crystal nucleation inorganic particles are contained. When such a resin is used for a gear, there is a problem that the tooth tip is not sufficiently filled with the resin. In addition, it is necessary to have a mold structure with a large gate diameter, which results in a decrease in productivity, such as a long cycle time including the pressure holding time and the difficulty of taking multiple pieces. There is.

Then, the present inventors diligently studied to solve the above problems. As a result, in the gear containing the polyacetal resin composition, it was found that by setting the tooth tip density to a specific value, the durability can be further improved, and the productivity during molding can also be improved, and the present invention has been completed. Let

That is, the present invention is as follows.

[1]
A gear containing a polyacetal resin composition, having a tooth tip density of 1.420 g/cm ³ or more.

[2]
The gear according to [1], wherein the polyacetal resin composition contains a polyacetal homopolymer.

[3]
The gear according to [1] or [2], wherein the melt flow rate of the polyacetal resin composition is 0.8 to 3.0 g/10 minutes.

[4]
The gear according to [1] or [2], wherein the melt flow rate of the polyacetal resin composition is 0.8 to 1.4 g/10 minutes.

[5]
The gear according to any one of [1] to [4], which is non-fiber reinforced.

[6]
The method for manufacturing a gear according to any one of [1] to [4], including a step of injection molding a raw material at an injection pressure of 160 to 300 MPa.

[7]
In the injection molding, the method for manufacturing a gear according to [6], wherein the raw material is compressed in the mold after injection.

[8]
The method for producing a gear according to any one of [6] and [7], including a step of heat-treating the molded product in a temperature range of 100 to 160° C. for 2 to 8 hours after injection molding.

According to the present invention, a gear having excellent durability can be obtained with high productivity.

FIG. 1A is a cross-sectional view of an example of the gear according to this embodiment. FIG. 1B is a top view of an example of the gear of this embodiment. FIG. 2 is a schematic view showing an example of a set of polyacetal homopolymer polymerization vessels used in the present embodiment. FIG. 3 is a schematic diagram of an example of a gear strength tester used for evaluation of the gear according to the present embodiment.

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 present invention is not limited to this embodiment, and can be appropriately modified and implemented within the scope of the gist thereof.

[gear]
The gear according to the present embodiment contains a polyacetal resin composition and has a tooth tip density of 1.420 g/cm ³ or more. When the tooth tip density is 1.420 g/cm ³ or more, the durability of the gear becomes more excellent. The tooth tip density is a value measured by the method described in Examples below.

In the gear of the present embodiment, the upper limit of the tip density is not particularly limited, but is preferably 1.430 g/cm ³ or less, more preferably 1.428 g/cm ³ or less, and further preferably 1.426 g/cm ³ or less. is there.

The gear having a tooth top density in the above range is not particularly limited, but can be obtained, for example, by the gear manufacturing method described later.

The gear of the present embodiment is preferably non-fiber reinforced from the viewpoint of dimensional stability and dimensional accuracy of the molded product. Here, the term "non-fiber reinforced" means that the content of reinforcing fibers is 1 part by mass or less based on 100 parts by mass of the polyacetal homopolymer. The reinforcing fiber refers to a known reinforcing fiber such as glass fiber or carbon fiber, and is usually added in an amount of 10% by mass or more in order to increase the mechanical strength of the material.

[Polyacetal resin composition]
The polyacetal resin composition used in this embodiment preferably has a melt flow rate (hereinafter, also referred to as “MFR”) of 0.8 to 3.0 g/10 minutes. Further, from the viewpoint of suppressing creep deformation due to a large load at high temperature, the MFR of the polyacetal resin composition is preferably 0.8 to 2.5 g/10 minutes, more preferably 0.8 to 1.4 g. /10 minutes.

When the MFR of the polyacetal resin composition is 0.8 g/10 minutes or more, the production of the molded product will be more stable, and the durability can be remarkably facilitated. On the other hand, when the MFR of the polyacetal resin composition is 3.0 g/10 minutes or less, the durability is further improved. The method of measuring MFR in this specification uses the method described in Examples below.

The polyacetal resin composition preferably contains a polyacetal homopolymer. The inclusion of the polyacetal homopolymer tends to further improve the durability of the gear and the quietness during long-time driving.

In the polyacetal resin composition, the content of the polyacetal homopolymer is preferably 80 to 100% by mass, more preferably 90 to 99% by mass, and further preferably 95 to 98% by mass.

[Polyacetal homopolymer]
The polyacetal homopolymer in the present embodiment, the structure of the main chain substantially - refers to only the polymer composed - (CH ₂ O). Here, “substantially” means that the content of the repeating unit (comonomer) other than —(CH ₂ O)— is 0.1 mol% or less.

As a method for confirming that the polyacetal homopolymer is contained, the ¹ H-NMR method is used as shown below. The gear is dissolved with hexafluoroisopropanol (HFIP) for 24 hours to a concentration of 1.5% by mass. ¹ H-NMR measurement is performed using this solution, and the oxymethylene component a and the comonomer component other than the oxymethylene component a (for example, the oxyalkylene component) b are determined from the ratio of the integrated values of the peaks to the oxymethylene component a. The ratio (b/a) of the comonomer component b to 100 mol% of the methylene component can be determined.

[Method for producing polyacetal homopolymer]
(Monomer raw material)
The polyacetal homopolymer used in this embodiment is not particularly limited, but is obtained, for example, by polymerizing formaldehyde, which is a monomer (main monomer) as a main raw material. As formaldehyde, from the viewpoint of continuously obtaining a resin having a stable molecular weight, it is preferable to use purified formaldehyde gas which has a low impurity concentration and is stable. As a method for purifying formaldehyde, a known method can be used. For example, the methods disclosed in Japanese Patent Publication No. 5-32374 and Japanese Patent Publication No. 2001-521916 can be used.

As the formaldehyde gas, it is preferable to use water, methanol, formic acid, or the like that does not contain impurities that stop the polymerization during the polymerization reaction or have a chain transfer action as much as possible. When formaldehyde gas that does not contain such impurities as much as possible is used, it is possible to effectively prevent an unexpected chain transfer reaction, and it becomes easier to obtain a substance having a target molecular weight. Among them, the content of water is preferably 100 ppm or less, and more preferably 50 ppm or less from the viewpoint of making it easier to obtain a substance having a target molecular weight.

(Polymerization method)
The production of the polyacetal homopolymer used in this embodiment is not particularly limited, but it can be carried out by using, for example, a known slurry polymerization method. For example, the polymerization methods disclosed in JP-B-47-6420 and JP-B-47-10059 can be used. Then, by using such a polymerization method, a crude polyacetal homopolymer having an unstable terminal portion can be obtained. It is preferable that the crude polyacetal homopolymer be subjected to a terminal stabilization treatment described below.

(Chain transfer agent)
Alcohols and acid anhydrides are generally used as the chain transfer agent. Further, in order to obtain a block copolymer or a branched polymer, a polyol, a polyether polyol or a polyether polyol/alkylene oxide may be used. Further, as the chain transfer agent, as described above, from the viewpoint of effectively preventing an unexpected chain transfer reaction, it is preferable to use a material that does not contain impurities as much as possible. Among them, the content of water in the chain transfer agent is preferably 2,000 ppm or less, more preferably 1,000 ppm or less.

Examples of the method for obtaining a chain transfer agent containing these impurities very little include, but are not limited to, for example, bubbling of the chain transfer agent with dry nitrogen, and a method of removing impurities by an adsorbent such as activated carbon or zeolite and purifying. To be The chain transfer agents may be used alone or in combination of two or more.

(Polymerization catalyst)
The polymerization catalyst used in the polymerization reaction, that is, the onium salt-based polymerization catalyst is represented by the following formula (1).

_{[R 1 R 2 R 3 R} 4 M +] X - ····· (1)
In the above formula, R ₁ , R ₂ , R ₃ and R ₄ are each independently an alkyl group, M is an element having a lone electron pair, and X is a nucleophilic group.

Among the onium salt-based polymerization catalysts represented by the above formula (1), quaternary ammonium salt-based compounds or Quaternary phosphonium salt compounds are preferred, and tetramethylammonium bromide, dimethyl distearyl ammonium acetate, tetraethylphosphonium iodide and tributylethylphosphonium iodide are more preferred.

(Reactor)
The reactor used for the polymerization is not limited to the following, but examples thereof include a batch-type reaction vessel with a stirrer, a continuous-type cokneader, a twin-screw-type continuous extrusion kneader, and a twin-screw paddle-type continuous mixer. The outer circumference of the cylinder of these reactors preferably has a structure capable of heating and cooling the reaction mixture.

(End stabilization treatment)
Among the terminal stabilization treatments of the above-mentioned crude polyacetal resin, the method of blocking with an ether group is not limited to the following, but examples thereof include the method described in JP-B-63-452. Further, the method of blocking with an acetyl group is not limited to the following, but for example, the method described in US Pat. No. 3,459,709 in which a large amount of acid anhydride is used in a slurry state, and an acid The method described in US Pat. No. 3,172,736, which is carried out in the gas phase using an anhydrous gas, can be mentioned. The etherifying agent used in the above method of blocking with an ether group is not limited to the following, but examples thereof include orthoesters. Examples include orthoesters of aliphatic or aromatic acids with aliphatic, alicyclic or aromatic alcohols. Specific examples of such orthoesters include orthocarbonates such as methylorthoformate, ethylorthoformate, methylorthoacetate, ethylorthoacetate, methylorthobenzoate, ethylorthobenzoate, and ethylorthocarbonate.

The etherification reaction is not limited to, for example, medium strength organic acids such as p-toluenesulfonic acid, acetic acid and hydrobromic acid, and Lewis acids such as medium strength mineral acids such as dimethyl sulfate and diethyl sulfate. The catalyst can be introduced by introducing 0.001 to 0.02 parts by mass with respect to 1 part by mass of the etherifying agent. The solvent used in the etherification reaction is not limited to the following, for example, low-boiling aliphatic, alicyclic and aromatic hydrocarbons such as pentane, hexane, cyclohexane and benzene, and methylene chloride, chloroform and Organic solvents such as halogenated lower aliphatic compounds such as carbon tetrachloride may be mentioned.

On the other hand, when the terminal of the polymer is blocked with an ester group, the organic acid anhydride used for esterification is not limited to the following, and examples thereof include an organic acid anhydride represented by the following formula (2).

R ₅ COOCOR ₆ (2)
In the above formula, R ₅ and R ₆ each independently represent an alkyl group. R ₅ and R ₆ may be the same or different.

Among the organic acid anhydrides represented by the above formula (2), propionic anhydride, benzoic anhydride, acetic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride and phthalic anhydride are preferable, and acetic anhydride is more preferable. .. The organic acid anhydride may be used alone or in combination of two or more.

Further, the method of blocking with an ester group in the gas phase is not limited to the following, but for example, the method described in JP-A No. 11-92542 in which terminal blocking is carried out after removal of an onium salt-based polymerization catalyst is possible. preferable. This is because by removing the onium salt-based polymerization catalyst in the polymer resin so that it does not remain as much as possible, it is possible to effectively suppress the promotion of the decomposition reaction of the polymer by the onium salt-based polymerization catalyst during end-capping, and in the stabilization reaction. This is because the polymer yield can be significantly improved and the coloring of the polymer can be effectively prevented.

By blocking the ends of the polymer with ether groups and/or ester groups, it is preferable that the concentration of hydroxyl groups at the ends be reduced to 5×10 ⁻⁷ mol/g or less. More preferably, the concentration of the terminal hydroxyl group is 0.5×10 ⁻⁷ mol/g or less.

[Additive]
The polyacetal resin composition used in the present embodiment is a crystal nucleation inorganic particle, a heat stabilizer, an antioxidant, an acid scavenger, a weathering (light) stabilizer, a mold release agent, within a range that does not impair the gist of the present invention. It may contain additives such as a lubricant, a conductive material/antistatic agent, a thermoplastic resin and a thermoplastic elastomer, and a pigment.

(Crystal nucleation inorganic particles)
The polyacetal resin composition may include crystal nucleation inorganic particles.

The crystal nucleation inorganic particles are not limited to, for example, talc, silica, quartz powder, glass powder, calcium silicate, aluminum silicate, kaolin, pyrophyllite, clay, silicates such as diatomaceous earth and wollastonite, Metal oxides such as iron oxide, titanium oxide and alumina, metal sulfates such as calcium sulfate and barium sulfate, carbonates such as calcium carbonate, magnesium carbonate and dolomite, and silicon carbide, silicon nitride, boron nitride and various metal powders. , Fragmented solids of crystalline nucleation minerals commonly known in polyacetals (eg polyacetal homopolymers). Among these crystal nucleation inorganic particles, the viewpoint of improving the crystallization rate as a crystallization nucleating agent for polyacetal (for example, polyacetal homopolymer) and consequently improving the mechanical properties (mechanical strength, etc.), and the polyacetal ( For example, from the viewpoint of preventing the loss of thermal stability of the polyacetal homopolymer), it is preferable to contain at least one of talc and boron nitride.

The crystal nucleation inorganic particles preferably contain 10 to 90 ppm with respect to the polyacetal resin composition. In order to quantify the crystal nucleation inorganic particles, for example, a method of hydrolyzing a resin composition containing a polyacetal (for example, a polyacetal homopolymer) with hydrochloric acid or the like, or a metal by a high frequency inductively coupled plasma (ICP) emission analysis. A method of quantifying the components can be mentioned. Here, as the measurement of the concentration (ppm) in the present specification, the above-mentioned method of hydrolyzing with hydrochloric acid and quantifying is adopted.

The average particle size of the crystal nucleation inorganic particles is 0.1 to 10 from the viewpoint of forming good crystal nuclei when mixed with a polyacetal (for example, polyacetal homopolymer) and contributing to improvement in strength and durability. It is 0.0 μm, and preferably 0.5 to 5.0 μm. The average particle diameter can be measured by a known method, and for example, a method of cutting out the obtained resin mechanical component and measuring it by a microscope method (polarization microscope or SEM-EDX) can be mentioned. Here, as the measurement of the average particle diameter in the present specification, the method described in Examples below is adopted.

The content of the crystal nucleation inorganic particles is preferably 0.01 to 500 ppm, more preferably 0.05 to 100 ppm, and more preferably 1 to 500 ppm with respect to the polyacetal resin composition (for example, polyacetal homopolymer). More preferably, it is about 90 ppm.

(Heat stabilizer and antioxidant)
The polyacetal resin composition used in the present embodiment preferably contains a heat stabilizer and an antioxidant. The heat stabilizer preferably contains formaldehyde-reactive nitrogen. Further, the antioxidant is preferably a hindered phenol type.

Examples of the heat stabilizer containing formaldehyde-reactive nitrogen include, but are not limited to, polyamides such as nylon 4-6, nylon 6, nylon 6-6, nylon 6-10, nylon 6-12 and nylon 12. Resins, and polymers thereof (for example, nylon 6/6-6/6-10, nylon 6/6-12 and the like) can be mentioned. Other examples include acrylamide and its derivatives, or copolymers of acrylamide and its derivatives with other vinyl monomers. Such copolymers include, but are not limited to, for example, poly-β-alanine copolymers obtained by polymerizing acrylamide and its derivatives with other vinyl monomers in the presence of metal alcoholates.

In addition, amide compounds, amino-substituted triazine compounds, adducts of amino-substituted triazine compounds with formaldehyde, condensates of amino-substituted triazine compounds with formaldehyde, urea, urea derivatives, hydrazine derivatives, imidazole compounds, imide compounds, etc. Can be mentioned.

Specific examples of the amide compound include, but are not limited to, polyvalent carboxylic acid amides such as isophthalic acid diamide, and anthranilamide.

Specific examples of the amino-substituted triazine compound are not limited to the following, for example,
2,4-diamino-sym-triazine,
2,4,6-triamino-sym-triazine,
N-butyl melamine,
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 the adduct of the amino-substituted triazine compound and formaldehyde are not limited to the following, for example,
N-methylol melamine,
N,N'-dimethylol melamine, and N,N',N"-trimethylol melamine are mentioned.

Specific examples of the condensate of the amino-substituted triazine compound and formaldehyde include, but are not limited to, a melamine-formaldehyde condensate.

Examples of the urea derivative include, but are not limited to, N-substituted urea, urea condensate, ethylene urea, hydantoin compound, and ureido compound.

Specific examples of the N-substituted urea include, but are not limited to, methylurea substituted with a substituent such as an alkyl group, alkylenebisurea, and aryl-substituted urea.

Specific examples of the urea condensate include, but are not limited to, a condensate of urea and formaldehyde.

Specific examples of the hydantoin compound include, but are not limited to, hydantoin, 5,5-dimethylhydantoin, and 5,5-diphenylhydantoin.

Specific examples of the ureido compound include, but are not limited to, allantoin.

Examples of the hydrazine derivative include, but are not limited to, hydrazide compounds.

Specific examples of the hydrazide compound include, but are not limited to, for example, dicarboxylic acid dihydrazide, and more specifically, but not limited to, for example,
Malonic acid dihydrazide,
Succinic acid dihydrazide,
Glutaric acid dihydrazide,
Adipic acid dihydrazide,
Pimelic acid dihydrazide,
Speric acid dihydrazide,
Azelaic acid dihydrazide,
Sebacic acid dihydrazide,
Dodecanedioic acid dihydrazide,
Isophthalic acid dihydrazide,
Phthalic acid dihydrazide, and 2,6-naphthalenedicarbodihydrazide.

Specific examples of the imide compound include, but are not limited to, succinimide, glutarimide, and phthalimide.

These formaldehyde-reactive nitrogen-containing compounds (including polymers) may be used alone or in combination of two or more.

On the other hand, the above-mentioned antioxidant is not limited to the following, but for example, a hindered phenol-based antioxidant is preferable. Specific examples include, but are not limited to, 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)-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], and pentaerythritol tetrakis[methylene-3-(3',5'-di-t-butyl). -4′-hydroxyphenyl)propionate]methane and the like.

Among them, preferably
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.

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

In the present embodiment, it is preferable that the heat stabilizer and the antioxidant are each contained in an amount of 0.05 to 0.5 parts by mass with respect to 100 parts by mass of the polyacetal (for example, polyacetal homopolymer).

(Acid scavenger)
Examples of the acid scavenger include, but are not limited to, condensates of the above-mentioned amino-substituted triazine compounds and amino-substituted triazine compounds with formaldehyde, and more specifically, melamine-formaldehyde condensates. Other acid scavengers include, but are not limited to, alkali metal and alkaline earth metal hydroxides, inorganic acid salts, carboxylate salts, and alkoxides. Specifically, but not limited to, for example, hydroxides such as sodium, potassium, magnesium, calcium, and barium, and carbonates, phosphates, silicates, borates, and carbonates of the metals listed above. Examples thereof include carboxylates, and layered double hydroxides.

The carboxylic acid of the carboxylic acid salt is preferably a saturated or unsaturated aliphatic carboxylic acid having 10 to 36 carbon atoms, and these carboxylic acids may be substituted with a hydroxyl group. Specific examples of the saturated or unsaturated aliphatic carboxylic acid salt include, but are not limited to, for example, calcium dimyristate, calcium dipalmitate, calcium distearate, (myristic acid-palmitic acid) calcium, (myristin Acid-stearic acid) calcium, and (palmitic acid-stearic acid) calcium. Among them, calcium dipalmitate and calcium distearate are preferable.

Examples of the layered double hydroxide include, but are not limited to, hydrotalcites represented by the following formula.

[(M ²⁺ ) _1-X (M ³⁺ ) _X (OH) ₂ ] ^X+ [(A ^n- ) _x/n ·mH ₂ O] ^X-
In the above formula, M ²⁺ is a divalent metal, M ³⁺ is a trivalent metal, A ⁿ⁻ is an n-valent (n is an integer of 1 or more) anion, and X is in the range of 0<X≦0.33. And m is a positive number.

In the above formula, examples of M ²⁺ are not limited to the following, but examples thereof include Mg ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ^2+. examples of M ^3+, but are not limited to, for ^{example, Al 3+, Fe 3+, Cr} 3+, Co 3+, in 3+ , and the like, as examples of a ^n- is less For example, OH ⁻ , F ⁻ , Cl ⁻ , Br ⁻ , NO ₃ ⁻ , CO ₃ ²⁻ , SO ₄ ²⁻ , Fe(CN) ₆ ³⁻ , CH ₃ COO ⁻ , oxalate ion, Examples thereof include salicylate ion. Of these, CO ₃ ²⁻ and OH ⁻ are preferable. Specific examples thereof include, but are not limited to, for example, natural hydrotalcite represented by Mg _0.75 Al _0.25 (OH) ₂ (CO ₃ ) _0.125 ·0.5H ₂ O, and Mg _4.5 Al ₂ (OH) ₁₃ CO. ₃ · 3.5H ₂ O, include synthetic hydrotalcite represented by _{Mg 4.3 Al 2 (OH) 12.6} CO 3 or the like.

These acid scavengers may be used alone or in combination of two or more.

The content of the acid scavenger is preferably 0.001 to 2.0 parts by mass, and 0.01 to 1.0 parts by mass with respect to 100 parts by mass of the polyacetal (for example, polyacetal homopolymer). It is more preferable that the amount is 0.015 to 0.5 part by mass.

(Weatherproof (light) stabilizer)
The weather resistance (light) stabilizer is preferably one or more selected from the group consisting of benzotriazole-based and oxalic acid anilide-based UV absorbers and hindered amine-based light stabilizers.

The benzotriazole-based ultraviolet absorber is not limited to the following, for example,
2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole,
2-(2'-hydroxy-3',5'-di-t-butyl-phenyl)benzotriazole,
2-[2'-hydroxy-3',5'-bis(α,α-dimethylbenzyl)phenyl]2H-benzotriazole,
2-[2′-hydroxy-3′,5′-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(2′-hydroxy-4′-octoxyphenyl)benzotriazole Are listed.

The linoleic oxalate ultraviolet absorber is not limited to the following, for example,
2-ethoxy-2'-ethyl oxalic acid bisanilide,
2-ethoxy-5-t-butyl-2'-ethyl oxalic acid bisanilide and 2-ethoxy-3'-dodecyl oxalic acid bisanilide can be mentioned.

Among them, 2-[2'-hydroxy-3',5'-bis-(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(2'-hydroxy-3',5' are preferable. -Di-t-butyl-phenyl)benzotriazole.

These benzotriazole ultraviolet absorbers may be used alone or in combination of two or more.

The hindered amine light stabilizer is not limited to the following, for example,
N,N′,N″,N′″-Tetrakis-(4,6-bis-(butyl-(N-methyl 2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazine -2-yl)-4,7-diazadecane-1,10-diamine,
Dibutylamine·1,3,5-triazine·N,N′-bis(2,2,6,6,tetramethyl-4-piperidyl-1,6-hexamethylenediamine and N-(2,2,6 6, tetramethyl-4-piperidyl) butylamine polycondensation product,
Poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl )Imino}hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl)imino}],
A condensate of dimethyl succinate and 4-hydroxy-2,2,6,6,tetramethyl-1-piperidineethanol,
A reaction product of decanedioic acid bis(2,2,6,6-tetramethyl-1(octyloxy)-4-piperidinyl) ester, 1,1-dimethylethyl hydroperoxide and octane,
Bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate,
Methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate,
Bis(2,2,6,6-tetramethyl-4-piperidyl)-sebacate,
1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl-4-piperidinol and β,β,β′,β′,-tetramethyl-3,9-[2,2 A condensate with 4,8,10-tetraoxaspiro(5,5)undecane]diethanol may be mentioned.

Among them, preferably bis(2,2,6,6-tetramethyl-4-piperidyl)-sebacate,
Bis-(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, and 1,2,3,4-butanetetracarboxylic acid and 1,2,2,6,6-pentamethyl- It is a condensate of 4-piperidinol and β,β,β′,β′,-tetramethyl-3,9-[2,4,8,10-tetraoxaspiro(5,5)undecane]diethanol.

These hindered amine light stabilizers may be used alone or in combination of two or more.

The content of the weather resistance (light) stabilizer is preferably 0.001 to 5.0 parts by mass, and 0.01 to 4.0 parts by mass with respect to 100 parts by mass of the polyacetal (for example, polyacetal homopolymer). More preferably, it is 0.015 to 3.0 parts by mass.

(Release agent/lubricant)
The release agent/lubricant is not limited to the following, but alcohols, fatty acids and their fatty acid esters, polyoxyalkylene glycols, olefin compounds having an average degree of polymerization of 10 to 500, and silicones are preferably used.

The content of the release agent/lubricant is preferably 0.001 to 5.0 parts by mass, and 0.01 to 4.0 parts by mass with respect to 100 parts by mass of the polyacetal (for example, polyacetal homopolymer). More preferably, it is 0.015 to 3.0 parts by mass.

(Conductive material/antistatic agent)
Examples of the conductive agent include, but are not limited to, conductive carbon black, carbon nanotubes, nanofibers, nanoparticles, metal powders and fibers. Examples of the above-mentioned antistatic agent include, but are not limited to, aliphatic polyethers (excluding compounds having terminal fatty acid esters), aliphatic polyethers having terminal fatty acid esters, and fatty acid Polyalkylene with fatty acid ester of polyhydric alcohol having free hydroxyl group obtained from polyhydric alcohol, boric acid ester of glycerin monofatty acid ester, ethylene oxide adduct of amine compound, basic carbonate and anion exchanger thereof as a base Examples of the antistatic agent include a polyol and an alkali metal salt-dissolved polyalkylene polyol.

The content of the conductive material/antistatic agent is preferably 0.001 to 5.0 parts by mass, and 0.01 to 4.0 parts by mass with respect to 100 parts by mass of polyacetal (for example, polyacetal homopolymer). More preferably, it is 0.015 to 3.0 parts by mass.

(Thermoplastic resin and thermoplastic elastomer)
Examples of the thermoplastic resin include, but are not limited to, polyacetal copolymer, polyolefin resin, acrylic resin, styrene resin, polycarbonate resin, polytetrafluoroethylene, polyamide, polyurethane, polylactic acid, and uncured epoxy resin. To be Also, these modified products may be included. Examples of the thermoplastic elastomer include, but are not limited to, polyurethane elastomers, polyester elastomers, polystyrene elastomers, and polyamide elastomers.

The content of the thermoplastic resin and the thermoplastic elastomer is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less with respect to 100 parts by mass of the polyacetal (for example, polyacetal homopolymer).

(Pigment)
Examples of the above-mentioned pigment include, but are not limited to, inorganic and organic pigments, metallic pigments, and fluorescent pigments. The inorganic pigment refers to those generally used for coloring resins, but is not limited to the following, for example, zinc sulfide, titanium oxide, barium sulfate, titanium yellow, cobalt blue, a fire pigment, Examples thereof include carbonates, phosphates, acetates, carbon black, acetylene black, and lamp black. Examples of the organic pigment include, but are not limited to, condensed azo pigments, inone pigments, flotacyanine pigments, monoazo pigments, diazo pigments, polyazo pigments, anthraquinone pigments, heterocyclic pigments, pennon pigments, quinacridone pigments, and thioindico pigments. , Berylylene-based, dioxazine-based, and phthalocyanine-based pigments.

The content of the pigment is preferably 0.001 to 5.0 parts by mass, and more preferably 0.01 to 4.0 parts by mass with respect to 100 parts by mass of the polyacetal (for example, polyacetal homopolymer). More preferably, it is 0.015 to 3.0 parts by mass, and further preferably.

(Surface treatment)
When the above crystal nucleation inorganic particles are added, a known surface treatment agent may be used in order to further improve the affinity and dispersibility with the polyacetal (for example, polyacetal homopolymer) used in the present embodiment. Examples of such surface treatment agents include, but are not limited to, silane coupling agents such as aminosilane and epoxysilane, titanate coupling agents, fatty acids (saturated fatty acids, unsaturated fatty acids), alicyclic carboxylic acids, resin acids. , As well as metal soaps. In the polyacetal resin composition used in the present embodiment, the amount of the surface treatment agent added is preferably 3% by mass or less, and more preferably 2% by mass or less, from the viewpoint of suppressing deterioration in physical properties and thermal stability. More preferably, it is substantially not added.

(Method for producing polyacetal resin composition)
The polyacetal resin composition used in this embodiment can be produced, for example, by the following method.

The polymer powder subjected to the above-mentioned end stabilization treatment is generally pelletized using an extruder after drying for the purpose of improving handling. After mixing polyacetal (for example, polyacetal homopolymer) and, if necessary, crystal nucleation inorganic particles and other additives with a Henschel mixer, a tumbler, a V-shaped blender, etc., a uniaxial or multiaxial kneading extruder, etc. The polyacetal resin composition used in the present embodiment can be obtained by melt-kneading with. Of these, a twin-screw extruder equipped with a pressure reducing device is preferable.

Further, the polyacetal resin composition can also be produced by using a quantitative feeder or the like without premixing, and collectively or dividing the crystal nucleation inorganic particles, and continuously feeding them to an extruder. ..

In addition, a high-concentration masterbatch composed of polyacetal (for example, polyacetal homopolymer) and other components (hereinafter, referred to as "additive") is prepared in advance, and the masterbatch is prepared at the time of extrusion melt kneading or molding. It is also possible to obtain a polyacetal resin composition by adding to a polyacetal (for example, a polyacetal homopolymer).

[Gear manufacturing method]
The gear according to the present embodiment includes, for example, polyacetal (for example, polyacetal homopolymer), and optionally crystal nucleation inorganic particles, a heat stabilizer, an antioxidant, an acid scavenger, a weathering (light) stabilizer, and a mold release agent. It is obtained by molding a polyacetal resin composition containing additives such as agents/lubricants, conductive materials/antistatic agents, thermoplastic resins and thermoplastic elastomers, and pigments.

The method of manufacturing the gear according to the present embodiment is not limited to the following. For example, in addition to normal injection molding, injection compression molding, gas assist injection molding, foam injection molding, in-mold composite molding (metal insert molding, Examples thereof include a method of molding a raw material (for example, the polyacetal resin composition described above) by any of molding methods such as metal outsert molding. Among them, from the viewpoint of productivity, durability and quality, injection molding and/or injection compression molding, or a molding method combining these with in-mold composite molding is preferable.

The conditions for injection molding are not limited to the following, but preferably the molding temperature is 180 to 220°C, the mold temperature is 30 to 120°C, and the injection time is 0.1 to 10 seconds.

The gear manufacturing method according to the present embodiment preferably includes a step of injection molding the raw material at an injection pressure of 160 to 300 MPa. The injection pressure is more preferably 180 to 300 MPa, further preferably 200 to 300 MPa. In injection molding, if the injection pressure is too high, molding defects such as jetting may occur, so the injection pressure is usually set to about 150 MPa or less at the highest. However, by setting the injection pressure within the above range, it is possible to fill the resin into the tooth tips of the gears even if a polyacetal resin composition having an extremely high viscosity of MFR of 3.0 g/10 minutes or less is used as a raw material. As a result, the tooth tip density can be controlled within a specific range, and a gear having excellent durability can be manufactured with high productivity. It was found that the problem of jetting can be improved by increasing the gate diameter.

In the method of manufacturing the gear according to the present embodiment, it is preferable to set the holding pressure to be higher than usual from the viewpoint of improving the tooth tip density and improving the durability of the gear. The holding pressure is preferably 100 MPa or more, more preferably 120 MPa, particularly preferably 150 MPa or more. Although the pressure holding time varies depending on the structure of the mold, it is preferably 40 seconds or more from the viewpoints of applying sufficient pressure to the resin injected into the mold and maintaining the molding cycle. 50 seconds or more is more preferable, and 60 seconds or more is particularly preferable.

In the gear manufacturing method according to the present embodiment, from the viewpoint of improving the tooth tip density and improving the durability of the gear, in injection molding, it is preferable to further compress the raw material in the mold after injection. In normal injection molding, a resin is injected into a mold after a mold closing step, and then a pressure holding step, a cooling step, and a mold opening step are performed to obtain a molded product. Here, the in-mold compression is a molding method characterized in that, in injection molding, a resin is pressure-molded from an injection start time to a mold opening time. The preferable timing of in-mold compression is to apply sufficient pressure to the resin injected into the mold and to maintain the molding cycle. From the above two points, the resin is pressure-molded during the pressure-holding step. It is preferable.

The gear manufacturing method according to the present embodiment preferably includes a step of further heat treating (annealing) the molded product from the viewpoint of removing the residual strain of the molded product and improving the mechanical strength. From the viewpoint of suppressing the variation in annealing, the preferable condition of the heat treatment is 100° C. or more and 160° C. or less, 2 hours or more and 8 hours or less, and more preferably 120° C. or more and 160° C. or less, 3 hours or more and 5 hours or less.

[Uses of gears]
The gear according to the present embodiment is significantly superior in durability and productivity as compared with the one using a conventional polyacetal (for example, polyacetal homopolymer) or polyamide resin, and thus is used in various applications. be able to.

In particular, the gears are not limited to the following, for example, helical gears, spur gears, internal gears, rack gears, spiral gears, straight bevel gears, bevel gears, spiral bevel gears, crown gears. , Face gears, screw gears, worm gears, worm wheel gears, hypoid gears, and Novikov gears. Further, the helical gear and the spur gear may be a single gear, a two-stage gear, and a combination gear having a structure in which driving motors are combined in multiple stages to reduce speed without uneven rotation.

Examples of parts in which such gears are preferably used include, but are not limited to, gears, cams, sliders, levers, arms, clutches, felt clutches, idler gears, pulleys, rollers, rollers, key stems, key tops, shutters, These include reels, shafts, joints, shafts, bearings, and guides. In addition, outsert-molded resin parts, insert-molded resin parts, chassis, trays, and side plates are also included.

Specific applications of the gears include, but are not limited to, mechanical parts for office automation equipment, mechanical parts for cameras or video equipment, mechanical parts for music, video or information equipment, mechanical parts for communication equipment, and electrical equipment. Mechanical parts for equipment, mechanical parts for electronic devices, mechanical parts for automobiles (door peripheral parts, seat peripheral parts, air conditioner peripheral parts), bicycle mechanical parts (drive motor transmission etc.), switch parts, stationery mechanical parts, housing Examples include mechanical parts for equipment, mechanical parts for vending machines, mechanical parts for sports/leisure/recreation related equipment, and mechanical parts for industrial equipment.

Further, the gear according to the present embodiment can be applied to all electric vehicles from the viewpoint of being able to maintain remarkably excellent durability as compared with the conventional gear. Here, examples of the electric vehicle include, but are not limited to, senior four-wheeled vehicles, motorcycles, and electric motorcycles. Above all, an electrically assisted bicycle is preferable from the viewpoint of requiring high durability as the power transmission gear.

The gear according to the present embodiment is preferably used with grease applied. This can greatly improve durability and noise reduction.

Hereinafter, the gear according to the present embodiment will be described more specifically by way of examples and comparative examples, but the present embodiment is not limited to these examples.

[Preparation of evaluation sample]
<Preparation of polyacetal homopolymer powder>
FIG. 2 is a schematic view showing a set of polyacetal homopolymer polymerization vessels. As shown in FIG. 2, a polyacetal homopolymer was produced using a jacketed 5 L tank polymerization machine equipped with a stirrer.

FIG. 2 illustrates a polyacetal homopolymer polymerizer used in the present embodiment, and includes a stirring blade-equipped motor (a), a jacketed reactor (b), a slurry circulation pump (c), and supply of formaldehyde gas. (1), Supply of chain transfer agent and polymerization solvent (2), Supply of polymerization catalyst (3), and Slurry collection (4).

The reactor (b) with a jacket was filled with 2 L of n-hexane (solvent for etherification reaction), and a circulation line was provided. The length of this line was 6φ×2.5 m, and the slurry was circulated at 20 L/hour by the slurry circulation pump (c). Dehydrated formaldehyde gas of 200 g/hour was directly fed into this (1). Dimethyl distearyl ammonium acetate (polymerization catalyst) is supplied to the circulation line immediately before the reactor (b) (3), and acetic anhydride (chain transfer agent) is withdrawn for the purpose of supplementing the slurry equivalent to the above process in order to supplement the slurry. -Added to hexane. Then, while continuously feeding (2) these polymerization catalyst and chain transfer agent, polymerization was carried out at 58° C. to obtain a slurry containing a crude polymer. The added polymerization catalyst and chain transfer agent were adjusted according to the MFR of the resin composition as the final target. The obtained slurry was reacted in a 1:1 mixture of hexane and acetic anhydride at 140° C. for 2 hours to acetylate the molecular terminal, thereby performing terminal stabilization treatment. The polymer after the reaction was collected by filtration, depressurized to 2 mmHg or less, and dried for 3 hours in a vacuum dryer set at 80° C. to obtain a polyacetal homopolymer powder.

<Preparation of Polyacetal Resin Composition Pellets>
A polyacetal homopolymer powder and an additive (heat stabilizer 0.3 part by mass, antioxidant 0.3 part by mass, crystal nucleation inorganic particles 0 or 20 or 50 ppm relative to 100 parts by mass of polyacetal homopolymer) and Henschel are used. Mix for 1 minute using a mixer. Then, using a screw type twin screw extruder with a vent (BT-30, manufactured by Plastic Industry Co., Ltd.; L/D=44) set to 200° C., the screw rotation speed was set to 100 rpm, and the mixture was melt-kneaded at 24 amperes. Thus, a polyacetal resin composition pellet was obtained. The operation was carried out from the introduction of the raw materials to the collection of the pellet-shaped sample while avoiding the mixing of oxygen (while degassing).

<Production of gears>
The polyacetal resin composition pellets obtained above were set to a cylinder temperature of 200° C. and a mold temperature of 100° C. using an injection molding machine equipped with a helical gear mold (see FIGS. 1A and 1B), Injection molding was performed to obtain a JIS4 class test gear.

Regarding the setting of the holding pressure, the standard condition was 120 MPa.60 seconds (holding pressure: expressed as medium), and in some examples, 150 MPa.60 seconds (holding pressure: expressed as high).

In addition, in some of the examples, a step of applying a compression force of 10 kN to the web surface of the gear for 2 seconds after 10 seconds from the start of holding pressure (compression molding: expressed as "exist") was performed.

<Evaluation of polyacetal resin composition>
1. MFR Measurement of Polyacetal Resin Composition After drying the polyacetal resin composition pellets obtained above at 80° C. for 3 hours, MFR (ASTM D-1238-57T) was obtained under the conditions of a load of 2.16 kg and a cylinder temperature of 190° C. Compliant) was measured. In general, a large MFR value is an index of high fluidity and excellent moldability.

<Evaluation of gears>
1. Test Device For the evaluation of durability and noise reduction, a power absorption type gear strength tester as shown in FIG. 3 capable of adjusting the shaft intervals was used. An appropriate drive motor and power absorption device (powder clutch/brake) were selected according to the test conditions.

FIG. 3 illustrates a gear strength tester used for evaluation of the gear according to the present embodiment, and includes a drive motor (a1), a bearing support base (a2), a tachometer (a3), and a power absorption device (b1). , A bearing support (b2), a torque meter (b3), a microphone (c1), a sound level meter (c2), a soundproof box (d1), a metal gear (A), and a test gear (B).

As shown in FIG. 3, in the gear strength tester, the drive motor (a1) is connected to the metal gear (A) via the shaft (module: 0.8, pitch circle diameter: 100 mm, tooth width: 30 mm, twist angle). : 20 degree) helical gears are installed so that it can be operated at any rotation speed. The metal gear (A) and the test gear (B) are engaged with each other with a backlash amount of 0.1 mm. The test gear (B) is connected to the power absorbing device (b1) via a shaft and has a structure capable of applying an arbitrary load torque.

2. Test Gear The test gear (B) in FIG. 3 is a helical gear having a module 0.8, a pitch circle diameter of 100 mm, and a twist angle of 15 degrees, and a gate having a diameter of 1.5 mm is provided at three points on the boss portion. (See FIG. 1B), and the intervals are uniform every 120 degrees in the circumferential direction. Further, as shown in FIG. 1A, the upper rib height g1 and the lower rib height g2 have the same size.

3. Measurement of the tooth tip density of the gear The tooth tip density of the gear is determined by cutting the tooth portion G at the boundary with the rim F shown in FIG. 1B, and substituting in water using an electronic hydrometer (ELEKTRON TEK, SD-200L). It was measured by the method. The measurement was performed on any 5 teeth, and the average value thereof was used as the tip density.

4. Test Method Using Gear Strength Tester A torque of 2 N·m was applied and a continuous 100-hour test was performed. The rotation speed was fixed at 100 rpm. The test was performed in a constant temperature room at room temperature of 23° C. and humidity of 50%.

(1) Durability As for durability, the appearance of the gear before and after the test was evaluated according to the following criteria.

⊚: No deformation was observed with the naked eye of the gear before and after the test, and there was no particular problem.

◯: Deformation of the gear was visually confirmed before and after the test, but there was no problem in operability.

Δ: There was some problem in operability.

X: Malfunction of the teeth due to damage of teeth and deformation of shaft hole.

Hereinafter, Examples and Comparative Examples will be described with reference to Table 1 below. Unless otherwise specified, experiments were performed according to the above-described preparation and evaluation methods.

[Examples 1 to 4, Comparative Examples 1 to 3]
Under the conditions shown in Table 1, a polyacetal resin composition was produced by the method described above, and a gear (injection-molded resin gear) was produced by injection molding the polyacetal resin composition.

From Table 1, Examples 1 to 4 in which the tooth tip density of the injection-molded resin gear is within a specific range (1.420 g/cm ³ or more) due to the effects of injection pressure, annealing, etc. ) And productivity were well balanced and confirmed. In particular, Examples 1 and 2 using the polyacetal resin composition having an MFR of 0.8 to 1.5 g/10 minutes were also confirmed to have significantly excellent durability under high torque. On the other hand, Comparative Examples 1 to ^{3 in} which the tip density of the injection-molded resin gear is out of the specific range (less than 1.420 g/cm ³ ) are compared with Examples 1 to 4 having the same gear shape, It was confirmed that the durability was significantly inferior.

[Examples 5 to 8]
Under the conditions shown in Table 1, a polyacetal resin composition was produced by the method described above, and a gear (injection-molded resin gear) was produced by injection molding the polyacetal resin composition.

As shown in Table 1, in the gear manufacturing methods of Examples 5 to 8, instead of annealing conditions, the density of the tooth tip portion was 1.420 g/cm ³ depending on the compression molding, the pressure holding effect, and the combination thereof. The above points differ from the gear manufacturing method of the first embodiment. It was confirmed that the gears of Examples 5 to 8 have the same gear shape and can obtain equivalent durability as compared with the gear of Example 1 in which the polyacetal resin composition has the same MFR value. Above all, it was confirmed that the gear of Example 7 in which the compression molding and the annealing conditions were combined was remarkably excellent in the balance between durability and productivity.

[Examples 9 to 11]
Under the conditions shown in Table 1, a polyacetal resin composition was produced by the method described above, and a gear (injection-molded resin gear) was produced by injection molding the polyacetal resin composition.

Further, as shown in Table 1, the method for manufacturing the gears of Examples 9 to 11 uses the polyacetal resin composition containing 50 ppm of talc as the crystal nucleation inorganic particles, in that the gears of Examples 1 to 8 are used. Manufacturing method. The gears of Examples 9 to 11 have the same gear shape and have a balance of durability and productivity as compared with the gears of Example 4 and Comparative Example 3 in which the MFR value of the polyacetal resin composition is the same. It was confirmed to be excellent. Above all, it was confirmed that the gear of Example 9 in which the MFR value of the polyacetal resin composition was 0.8 to 1.5 g/10 minutes was remarkably excellent in durability.

The gear according to the present invention has an excellent balance of durability and productivity as compared with conventional fiber-reinforced polyamide resins and the like. Therefore, the gear according to the present invention can be suitably used in the automobile field, the electric/electronic field, and other industrial fields.

a Agitating motor with agitating blades,
b jacketed reactor,
c Slurry circulation pump,
1 Supply of formaldehyde gas,
2 Supply of chain transfer agent and polymerization solvent,
3 Supply of polymerization catalyst,
4 Slurry collection,
a1 drive motor,
a2 bearing support,
a3 tachometer,
b1 power absorption device,
b2 bearing support,
b3 torque meter,
c1 microphone,
c2 sound level meter,
d1 soundproof box,
A metal gear,
B test gear,
C boss,
D Web,
E rib,
F rim,
G tooth,
H shaft hole,
e web thickness,
f rim height,
g1 Upper rib height,
g2 Lower rib height,
h Boss thickness,
i Rim thickness.

Claims (6)

A method for producing a non-fiber reinforced resin gear containing a polyacetal resin composition,
Ri der addendum density 1.420g / cm ³ or more of said gears,
A method for manufacturing a gear made of non-fiber reinforced resin, in which a raw material is injection molded at an injection pressure of 160 to 300 MPa . The method for producing a non-fiber-reinforced resin gear according to claim 1, wherein the polyacetal resin composition contains a polyacetal homopolymer. The method for producing a non-fiber reinforced resin gear according to claim 1, wherein the melt flow rate of the polyacetal resin composition is 0.8 to 3.0 g/10 minutes. The method for producing a non-fiber-reinforced resin gear according to claim 1, wherein the melt flow rate of the polyacetal resin composition is 0.8 to 1.4 g/10 minutes. The method for producing a non-fiber reinforced resin gear according to any one of claims 1 to 4, wherein in the injection molding, a raw material is compressed in a mold after being injected. Comprising the step of 2-8 hours heat-treated molded product in the temperature range of 100 to 160 ° C. after the injection molding method for producing a non-fiber-reinforced resin gear according to any one of claims 1 to 5.