Resin gear

Abstract

Provided is a resin gear which is exceptionally silent and of which the durability can be improved.　A resin gear 1 is constituted from a resin composition. The resin composition is obtained by blending a thermoplastic resin (A), inorganic fibers (B) having an average fiber length of 1‒300 μm, and reinforcing fibers (C) having an average fiber length of 0.3‒30 mm. A module of the resin gear 1 is greater than 0.1 mm and not greater than 0.5 mm.

Description

Resin gear

[0001] The present invention relates to a resin gear composed of a resin composition.

[0002] A gear is a mechanical element necessary for power transmission and is widely used in fields such as smart devices, robots, and automobiles. Among them, in applications where durability and heat resistance of gears are required, gears made of metal materials are used. However, in the case of gears made of metal materials, vibrations and noises caused by the surface roughness of the metal and the high elastic modulus become problems. Therefore, a method for improving the durability, wear resistance, and heat resistance of resin gears has been studied for the purpose of replacing them with resin gears having good surface smoothness and a low elastic modulus.

[0003] For example, Patent Document 1 discloses a resin gear made of carbon fiber reinforced nylon, and it is described that such a resin gear can improve slidability, wear resistance, heat resistance, etc.

[0004] Japanese Unexamined Patent Application Publication No. 2011-131372

[0005] However, resin gears such as those in Patent Document 1 tend to have reduced durability, especially when the module is made small. Therefore, there is a need for a resin gear that is excellent in durability even when the module of the resin gear is made small.

[0006] An object of the present invention is to solve such problems, enhance durability, and provide a resin gear with excellent quietness.

[0007] The present invention provides a resin gear having the following configuration.

[0008] Item 1: A resin gear composed of a resin composition, wherein the resin composition is formulated by blending a thermoplastic resin (A), inorganic fibers (B) having an average fiber length of 1 μm to 300 μm, and reinforcing fibers (C) having an average fiber length of 0.3 mm to 30 mm, and the module of the resin gear exceeds 0.1 mm and is 0.5 mm or less.

[0009] Item 2: The resin gear according to Item 1, wherein the resin composition does not substantially contain aramid fibers.

[0010] Item 3 The resin gear according to item 1 or 2, wherein the tooth width of the resin gear exceeds 0.15 mm and is 40 mm or less.

[0011] Item 4 The resin gear according to any one of items 1 to 3, wherein the thermoplastic resin (A) comprises at least one crystalline resin selected from the group consisting of polyester resins, polyamide resins, polyphenylene sulfide resins, and polyether aromatic ketone resins.

[0012] Item 5 The resin gear according to any one of items 1 to 4, wherein the inorganic fiber (B) is at least one of potassium titanate fiber and wollastonite fiber.

[0013] Item 6 The resin gear according to any one of items 1 to 5, wherein the reinforcing fiber (C) is at least one of carbon fiber and glass fiber.

[0014] Item 7 The resin gear according to any one of items 1 to 6, wherein the total content of the inorganic fiber (B) and the reinforcing fiber (C) is 10% by mass to 65% by mass in 100% by mass of the total amount of the resin composition.

[0015] Item 8 A resin gear according to any one of items 1 to 7, wherein the mass ratio of the inorganic fiber (B) to the reinforcing fiber (C) (inorganic fiber (B) / reinforcing fiber (C)) is 0.05 to 0.9.

[0016] Item 9 The resin gear according to any one of items 1 to 8, wherein the resin composition further contains a solid lubricant (D).

[0017] Item 10 The resin gear according to Item 9, wherein the solid lubricant (D) is a polyolefin resin, and the melting point of the polyolefin resin is 40°C to 220°C lower than the melting point of the thermoplastic resin (A).

[0018] Item 11 The resin gear according to item 9 or 10, wherein the content of the solid lubricant (D) is 0.1% by mass to 10% by mass in 100% by mass of the total amount of the resin composition.

[0019] Item 12 A method for manufacturing a resin gear according to any one of items 1 to 8, comprising the steps of: obtaining a resin composition by blending a thermoplastic resin (A), inorganic fibers (B) having an average fiber length of 1 μm to 300 μm, and reinforcing fibers (C) having an average fiber length of 0.3 mm to 30 mm; and molding the resin composition by injection molding.

[0020] Item 13 A method for manufacturing a resin gear according to any one of items 9 to 11, comprising the steps of: obtaining a resin composition by blending a thermoplastic resin (A), inorganic fibers (B) having an average fiber length of 1 μm to 300 μm, reinforcing fibers (C) having an average fiber length of 0.3 mm to 30 mm, and a solid lubricant (D); and molding the resin composition by injection molding.

[0021] Item 14 A gearbox comprising a resin gear as a component, as described in any one of items 1 to 11.

[0022] According to the present invention, it is possible to provide a resin gear that has improved durability and excellent quietness.

[0023] Figure 1 is a schematic diagram showing a resin gear according to one embodiment of the present invention. Figure 2 is a scanning electron microscope (SEM) image of the cross-section of the tooth tip of the resin gear test piece obtained in Example 8. Figure 3 is a scanning electron microscope (SEM) image of the cross-section of the tooth tip of the resin gear test piece obtained in Comparative Example 8. Figure 4 is a scanning electron microscope (SEM) image of the cross-section of the tooth tip of the resin gear test piece obtained in Example 9. Figure 5 is a scanning electron microscope (SEM) image of the cross-section of the tooth tip of the resin gear test piece obtained in Comparative Example 9.

[0024] Preferred embodiments of the present invention will be described below. However, the following embodiments are merely illustrative, and the present invention is not limited to these embodiments.

[0025] <Resin Gears> The resin gears of the present invention are composed of a resin composition. The resin composition comprises a thermoplastic resin (A), inorganic fibers (B) having an average fiber length of 1 μm to 300 μm, and reinforcing fibers (C) having an average fiber length of 0.3 mm to 30 mm. The resin composition may optionally contain a solid lubricant (D) and other additives.

[0026] Figure 1 is a schematic diagram showing a resin gear according to one embodiment of the present invention. As shown in Figure 1, teeth 2 are provided on the outer circumference of the resin gear 1. A shaft hole 3 is provided in the center of the resin gear 1. In this embodiment, the resin gear 1 is an injection-molded body, and the resin gear 1 is provided with three gates 4. Furthermore, the entire resin gear 1 is made of the above resin composition. Thus, in the resin gear of the present invention, it is desirable that the entire resin gear is made of the above resin composition. Furthermore, while it is desirable that the resin gear of the present invention be an injection-molded body, it may be molded by other molding methods.

[0027] The module of the resin gear of the present invention is greater than 0.1 mm and less than or equal to 0.5 mm.

[0028] The module of a resin gear can be determined by dividing the diameter of the pitch circle in the resin gear by the number of teeth in the resin gear. The module of a resin gear can be determined, for example, in accordance with JIS B 1701-2:2017. The pitch circle refers to the circle formed by connecting the pitch points where two meshing gears make contact. For example, in resin gear 1 in Figure 1, circle A is the pitch circle, and the diameter of circle A is D. Ａ This corresponds to the pitch circle diameter. In the resin gear shown in Figure 1, the outer circle B of circle A is the tip circle, and the diameter D of circle B is... Ｂ However, this corresponds to the tip diameter.

[0029] Conventionally, resin gears have tended to have reduced durability, especially when the module size was reduced. This tendency was particularly pronounced in resin gears made from molded resin compositions containing long fibers such as carbon fibers.

[0030] In response to this, the present inventors focused on the composition of the resin composition constituting the resin gear and found that by including a thermoplastic resin (A), reinforcing fibers (C) with an average fiber length of 0.3 mm to 30 mm, and further inorganic fibers (B) with an average fiber length of 1 μm to 300 μm, the durability of the resin gear made of resin material can be increased, and it also exhibits excellent noise reduction.

[0031] Furthermore, the inventors have found that when the module of the resin gear is greater than 0.1 mm and less than or equal to 0.5 mm, the resin composition contains a thermoplastic resin (A), reinforcing fibers (C) with an average fiber length of 0.3 mm to 30 mm, and inorganic fibers (B) with an average fiber length of 1 μm to 300 μm, which provides beneficial effects.

[0032] Furthermore, the following can be considered regarding this point. In conventional resin gears, which are molded from a resin composition containing only long fibers such as carbon fibers, it is thought that the long fibers may not be sufficiently filled to the tooth tips of the resin gears, which tend to be thinned, especially when the module is made smaller. As a result, it is thought that conventional resin gears tended to have reduced durability.

[0033] In contrast, in the resin gear of the present invention, the resin composition constituting the resin gear includes not only long fibers such as reinforcing fibers (C) with an average fiber length of 0.3 mm to 30 mm, but also short fibers such as inorganic fibers (B) with an average fiber length of 1 μm to 300 μm. It is thought that not only are the short fibers filled into the thin-walled portion of the tooth tip, but the long fibers are also filled into the thin-walled portion of the tooth tip. As a result, it is possible to reinforce the thin-walled portion of the tooth tip of the resin gear with fibers, and it is thought that the durability of the resin gear can be increased even when the module of the resin gear is reduced.

[0034] Therefore, according to the present invention, it is possible to provide a resin gear that has enhanced durability due to the resin material and excellent quietness.

[0035] The resin composition constituting the resin gear of the present invention preferably contains substantially no aramid fibers. Aramid fibers readily absorb moisture, and their saturation moisture absorption rate exceeds 1% by mass. Therefore, resin gears made of aramid fiber-reinforced resin readily absorb moisture and are prone to dimensional changes due to swelling caused by moisture absorption. In addition, aramid fibers may fibrillate under the high shear environment during injection molding, which can lead to an increase in the melt viscosity of the resin composition, fiber aggregation, mold clogging, and other deteriorations in moldability. Therefore, especially when manufacturing resin gears by injection molding, it is preferable that the resin composition constituting the resin gear contains substantially no aramid fibers. In this specification, "substantially does not contain" the material in the resin composition means, for example, that the content of the material is less than 0.1% by mass in 100% by mass of the total amount of the resin composition. Of course, the resin composition constituting the resin gear of the present invention may contain no aramid fibers at all. Furthermore, since the resin gear of the present invention has the above-described structure, even if it does not substantially contain aramid fibers, it can have improved durability and excellent quietness.

[0036] In the present invention, the module of the resin gear is greater than 0.1 mm, preferably 0.2 mm or more, 0.5 mm or less, and preferably 0.4 mm or less.

[0037] In the present invention, the diameter of the pitch circle in the resin gear is preferably greater than 1 mm, more preferably 3 mm or more, more preferably 280 mm or less, and more preferably 30 mm or less. The diameter of the pitch circle of the resin gear can be calculated by multiplying the number of teeth of the resin gear by a module.

[0038] Furthermore, in the present invention, the tooth width of the resin gear is preferably greater than 0.15 mm, more preferably 0.18 mm or more, preferably 40 mm or less, and more preferably 20 mm or less. The tooth width of the resin gear can be measured, for example, using a caliper or a non-contact microscope.

[0039] The following describes in detail the various components of the resin composition that constitutes the resin gear of the present invention.

[0040] (Thermoplastic resin (A)) The resin composition constituting the resin gear of the present invention includes a thermoplastic resin (A). The thermoplastic resin (A) is not particularly limited as long as it is a thermoplastic resin that can be molded into a resin gear.

[0041] Examples of thermoplastic resins (A) include polyolefin resins such as polypropylene (PP) resin, polyethylene (PE) resin, cyclic polyolefin (COP) resin, and cyclic olefin copolymer (COC) resin; polystyrene (PS) resin, syndiotactic polystyrene (SPS) resin, high-impact polystyrene (HIPS) resin, acrylonitrile-butylene-styrene copolymer (ABS) resin, methyl methacrylate / styrene copolymer (MS), methyl methacrylate / butadiene / styrene copolymer (MBS), styrene / butadiene copolymer (SBR), styrene / isoprene copolymer (SIR), styrene / isoprene / butadiene copolymer (SIBR), styrene / butadiene / styrene copolymer (SBS), styrene / isoprene / styrene copolymer (SIS), and styrene / ethylene / butylene / styrene copolymer. Examples include polystyrene-based resins such as styrene copolymer (SEBS) and styrene / ethylene / propylene / styrene copolymer (SEPS); polyester-based resins such as polylactic acid (PLA) resin, polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, and polycyclohexylene dimethylene terephthalate (PCT) resin; polyacetal (POM) resin; polycarbonate (PC) resin; polyamide resin; polyphenylene sulfide (PPS) resin; polyethersulfone (PES) resin; liquid crystal polyester (LCP) resin; polyether ketone (PEK) resin, polyether ether ketone (PEEK) resin, polyether ketone ketone (PEKK) resin, and polyether ether ketone ketone (PEEKK); and polyetherimide (PEI) resin. As the thermoplastic resin (A), a mixture of two or more compatible thermoplastic resins selected from the above-mentioned thermoplastic resins, i.e., a polymer alloy, may be used.

[0042] In the present invention, from the viewpoint of further improving the toughness, self-lubricity, and quietness of the resin gear, the thermoplastic resin (A) is preferably at least one selected from the group consisting of polyester resins, polyamide resins, polyphenylene sulfide resins, and polyether aromatic ketone resins, more preferably contains at least one polyamide resin, and even more preferably is a polyamide resin because of its excellent melt fluidity and injection moldability.

[0043] The polyamide resin is a polymer having an amide bond (—NH—C(═O)—) in the main chain and is a polymer containing structural units derived from monomer components such as aminocarboxylic acids, diamines, and dicarboxylic acids. The polyamide resin may be composed of one type of structural unit or may be composed of multiple types of structural units. Examples of those composed of one type of structural unit include polymers of aminocarboxylic acids. Examples of those composed of multiple types of structural units include copolymers of diamines and dicarboxylic acids, copolymers of diamines, dicarboxylic acids, and aminocarboxylic acids, and the like.

[0044] When the polyamide resin is a copolymer composed of multiple types of structural units, the copolymerization ratio, copolymerization form, etc. can be arbitrarily selected. Examples of the copolymerization form include random copolymers, block copolymers, alternating copolymers, and the like.

[0045] Specific examples of polyamide resins include, for example, polyamide 6 (polymer of 6-aminocaproic acid), polyamide 66 (polymer of hexamethylenediamine and adipic acid), polyamide 11 (polymer of 11-aminoundecanoic acid), polyamide 12 (polymer of 12-aminododecanoic acid), polyamide 46 (polymer of tetramethylenediamine and adipic acid), polyamide 6 / 66 copolymer (polymer of 6-aminocaproic acid, hexamethylenediamine, and adipic acid), and polyamide 6 / 12 copolymer (polymer of 6-aminocaproic acid and 12-aminododecanoic acid). Examples include aliphatic polyamide resins such as polyamide MXD6 (polymer of m-xylenediamine and adipic acid), polyamide 4T (polymer of tetramethylenediamine and terephthalic acid), polyamide 6T (polymer of hexamethylenediamine and terephthalic acid), polyamide 9T (polymer of 1,9-diaminononane and terephthalic acid), polyamide 10T (polymer of 1,10-diaminodecane and terephthalic acid), and polyamide 6T / 66 copolymer (polymer of hexamethylenediamine, terephthalic acid, and adipic acid). Among these, aliphatic polyamide resins are preferred because their flexibility improves durability against repeated loading due to stress relaxation. These polyamide resins may be used individually or in combination of two or more.

[0046] In this invention, "aliphatic polyamide resin" means a polyamide resin that substantially does not contain constituent units derived from aromatic monomers as constituent units of the polyamide resin. "Semi-aromatic polyamide resin" means a polyamide resin that contains constituent units derived from aliphatic monomers and constituent units derived from aromatic monomers as constituent units of the polyamide resin.

[0047] From the perspective of further improving self-lubricity, the thermoplastic resin (A) is preferably a crystalline resin having a melting point. Also, from the perspective of further suppressing deformation, discoloration, etc. of the thermoplastic resin (A), the melting point of the thermoplastic resin (A) is preferably 150°C or higher. Further, from the perspective of further suppressing thermal decomposition of the thermoplastic resin (A) in melt kneading of the resin composition described later and melt processing in injection molding, etc., the melting point of the thermoplastic resin (A) is preferably 350°C or lower. In this specification, the melting point can be measured in accordance with JIS-K7121.

[0048] The shape of the thermoplastic resin (A) is not particularly limited as long as melt kneading is possible. For example, any of powdery, granular, and pellet状 can be used.

[0049] The content of the thermoplastic resin (A) is preferably 20% by mass to 93.9% by mass, more preferably 33% by mass to 89.9% by mass, and still more preferably 40% by mass to 84.9% by mass in 100% by mass of the total amount of the resin composition.

[0050] (Inorganic fiber (B)) The resin composition constituting the resin gear of the present invention contains an inorganic fiber (B). The inorganic fiber (B) is, for example, a powder composed of fibrous particles. The average fiber length of the inorganic fiber (B) is 1 μm to 300 μm, preferably 1 μm to 200 μm, more preferably 3 μm to 100 μm, and still more preferably 5 μm to 50 μm.

[0051] The average fiber diameter of the inorganic fiber (B) is preferably 0.01 μm to 15 μm or less, more preferably 0.05 μm to 10 μm, and still more preferably 0.1 μm to 7 μm.

[0052] The average aspect ratio of the inorganic fiber (B) is preferably 3 to 200, more preferably 3 to 150, still more preferably 3 to 100, and particularly preferably 3 to 70.

[0053] In this specification, a fibrous particle is defined as a particle in which, when the longest side of the smallest rectangular parallelepiped (circumscribed rectangular parallelepiped) circumscribed around the particle is defined as the major axis L, the next longest side as the minor axis B, and the shortest side as the thickness T (B > T), both L / B and L / T are 3 or greater, with the major axis L corresponding to the fiber length and the minor axis B corresponding to the fiber diameter. A non-fibrous particle is defined as a particle in which L / B is less than 3, and among non-fibrous particles, a particle in which L / B is less than 3 and L / T is 3 or greater is called a plate-like particle.

[0054] Furthermore, the average fiber length and average fiber diameter can be measured by observation using a scanning electron microscope (SEM). For example, by taking images of multiple inorganic fibers (B) with an SEM, 300 inorganic fibers (B) can be arbitrarily selected from the observed images, and their fiber lengths and diameters can be measured. The average fiber length can then be calculated by summing the lengths of all the fibers and dividing by the number of fibers, and the average fiber diameter can be calculated by summing the diameters of all the fibers and dividing by the number of fibers. In addition, the average aspect ratio (average fiber length / average fiber diameter) can be calculated using the average fiber length and average fiber diameter.

[0055] Examples of inorganic fibers (B) include potassium titanate fibers, wollastonite fibers, zinc oxide fibers, basic magnesium sulfate fibers, alumina fibers, silicon carbide fibers, and boron fibers. These inorganic fibers may be used individually or in combination of two or more types.

[0056] From the viewpoint of maintaining the reinforcing effect of inorganic fibers (B) while further improving the filling of reinforcing fibers (C) into the tooth tips of resin gears and further improving the durability of resin gears, inorganic fibers (B) are preferably at least one of potassium titanate fibers or wollastonite fibers, and more preferably potassium titanate fibers.

[0057] As the inorganic fiber (B), at least one of the inorganic fibers potassium titanate fiber and wollastonite fiber may be used in combination with fibers such as aluminum borate, magnesium borate, xonotlite, zinc oxide, and basic magnesium sulfate.

[0058] As potassium titanate, a wide range of known potassium titanates can be used. Examples of potassium titanate include potassium tetra-titanate, potassium hexa-titanate, potassium octa-titanate, etc. The dimensions of potassium titanate are not particularly limited as long as they are within the range of the dimensions of the inorganic fiber (B) described above. The average fiber length of potassium titanate is preferably 1 μm to 50 μm, more preferably 3 μm to 30 μm, and even more preferably 10 μm to 20 μm. The average fiber diameter of potassium titanate is preferably 0.01 μm to 1 μm, more preferably 0.05 μm to 0.8 μm, and even more preferably 0.1 μm to 0.7 μm. The average aspect ratio of potassium titanate is preferably 10 or more, more preferably 10 to 100, and even more preferably 15 to 35.

[0059] Wollastonite is an inorganic fiber made of calcium metasilicate. The dimensions of wollastonite are not particularly limited as long as they are within the range of the dimensions of the inorganic fiber (B) described above. The average fiber length of wollastonite is preferably 1 μm to 100 μm, more preferably 10 μm to 70 μm, and even more preferably 20 μm to 40 μm. The average fiber diameter of wollastonite is preferably 0.1 μm to 15 μm, more preferably 1 μm to 10 μm, and even more preferably 2 μm to 7 μm. The average aspect ratio of wollastonite is preferably 3 or more, more preferably 3 to 30, and even more preferably 5 to 15.

[0060] In the present invention, a treatment layer consisting of a surface treatment agent may be formed on the surface of the inorganic fiber (B) from the viewpoint of improving wettability with the thermoplastic resin (A) and further improving the physical properties such as the mechanical properties of the resin gear.

[0061] As the surface treatment agent, known surface treatment agents such as silane coupling agents and titanium coupling agents can be used. Among these, the surface treatment agent is preferably a silane coupling agent, and more preferably an amino-based silane coupling agent, an epoxy-based silane coupling agent, or an alkyl-based silane coupling agent. These surface treatment agents may be used individually or in mixtures of two or more.

[0062] Examples of amino silane coupling agents include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethylamino)propyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane.

[0063] Examples of epoxy silane coupling agents include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyl(dimethoxy)methylsilane, diethoxy(3-glycidyloxypropyl)methylsilane, triethoxy(3-glycidyloxypropyl)silane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0064] Examples of alkyl silane coupling agents include methyltrimethoxysilane, ethyltrimethoxysilane, hexyltrimethoxysilane, heptyltrimethoxysilane, octyltrimethoxysilane, nonyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, eicosyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, hexyltriethoxysilane, heptyltriethoxysilane, octyltriethoxysilane, nonyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane, hexadecyltriethoxysilane, octadecyltriethoxysilane, eicosyltriethoxysilane, and phenyltriethoxysilane.

[0065] As a method for forming a treatment layer consisting of a surface treatment agent on the surface of the inorganic fiber (B), known surface treatment methods can be used. For example, a method can be used in which a surface treatment agent is dissolved in a solvent that promotes hydrolysis (e.g., water, alcohol, or a mixture thereof) to make a solution, and this solution is sprayed onto the inorganic fiber (B).

[0066] The amount of surface treatment agent used when treating the surface of the inorganic fiber (B) is not particularly limited, but for example, the solution of the surface treatment agent can be sprayed so that the amount of surface treatment agent is 0.1 to 20 parts by mass per 100 parts by mass of the inorganic fiber (B). By keeping the amount of surface treatment agent within the above range, the wettability of the inorganic fiber (B) with respect to the thermoplastic resin (A) can be further improved.

[0067] The inorganic fiber (B) content is preferably 1% to 40% by mass, more preferably 2% to 30% by mass, and even more preferably 5% to 20% by mass, based on 100% by mass of the total resin composition. By setting the inorganic fiber (B) content above the lower limit, the noise level of the resin gear can be further improved. Furthermore, by setting the inorganic fiber (B) content below the upper limit, the durability of the resin gear can be further improved.

[0068] The mass ratio of thermoplastic resin (A) to inorganic fiber (B) in the resin composition (thermoplastic resin (A) / inorganic fiber (B)) is preferably 0.5 to 90, more preferably 1 to 20. By setting the mass ratio of thermoplastic resin (A) to inorganic fiber (B) within the above range, it is possible to further suppress the decrease in toughness caused by excessive fiber filling effect on the tooth tips of the resin gear by the inorganic fiber (B), while further improving the moldability of the resin composition.

[0069] (Reinforcement Fiber (C)) The resin composition constituting the resin gear of the present invention includes a reinforcement fiber (C). The reinforcement fiber (C) is not particularly limited as long as it has an average fiber length of 0.3 mm to 30 mm. As the reinforcement fiber (C), inorganic fibers other than inorganic fiber (B), organic fibers, metal fibers, or a combination of two or more of these fibers can be used.

[0070] Examples of inorganic fibers include carbon fibers, graphite fibers, silicon carbide fibers, alumina fibers, tungsten carbide fibers, boron fibers, and glass fibers. Examples of organic fibers include aramid fibers, poly(p-phenylenebenzoxazole) (PBO) fibers, high-density polyethylene fibers, polyamide fibers, and polyester fibers. Examples of metallic fibers include stainless steel and iron fibers. In addition, the reinforcing fiber (C) may be a carbon fiber coated with metal.

[0071] The reinforcing fiber (C) is preferably at least one fiber selected from the group consisting of carbon fiber, glass fiber, and aramid fiber. More preferably, the reinforcing fiber (C) is at least one of carbon fiber and glass fiber, and even more preferably carbon fiber, from the viewpoint of further improving the mechanical strength and durability of the resin gear.

[0072] Carbon fiber is a fiber manufactured by carbonizing raw materials such as acrylic fiber and pitch (a by-product of petroleum, coal, coal tar, etc.) at high temperatures. According to JIS standards, carbon fiber is defined as a fiber obtained by heat carbonization treatment of organic fiber precursors, with a mass ratio of 90% or more being carbon. Carbon fiber made using acrylic fiber is called polyacrylonitrile (PAN) carbon fiber, and carbon fiber made using pitch is called pitch-based carbon fiber.

[0073] Specifically, as the carbon fiber (C) used as the reinforcing fiber, for example, PAN-based carbon fiber, pitch-based carbon fiber, cellulose-based carbon fiber, hydrocarbon-based vapor-grown carbon fiber, graphite fiber, and other carbon fibers can be used. From the viewpoint of higher strength and higher modulus of elasticity, it is preferable to use PAN-based carbon fiber. These reinforcing fibers may be used individually or in combination of two or more types.

[0074] Furthermore, the carbon fiber used is not particularly limited as long as it is carbon fiber for resin reinforcement, and either chopped fiber or milled fiber can be used. However, from the viewpoint of balancing the moldability of the tooth tips of the resin gear with the mechanical strength, short fibers (chopped fiber) are preferable.

[0075] In the present invention, the tensile modulus of the reinforcing fiber (C) is preferably 190 GPa to 600 GPa, more preferably 200 GPa to 450 GPa, and even more preferably 200 GPa to 300 GPa. If the tensile modulus of the reinforcing fiber (C) is too low, the reinforcing effect may be reduced. On the other hand, if the tensile modulus of the reinforcing fiber (C) is too high, the fibers that detach from the resin composition may create significant resistance. The tensile modulus of the reinforcing fiber (C) refers to the value measured in accordance with Method A of JIS R7606 (2000).

[0076] In this invention, if the fiber length of the reinforcing fiber (C) is too long, the fluidity of the resin composition during molding may decrease; therefore, the average fiber length is 30 mm or less.

[0077] The average fiber length of the reinforcing fiber (C) is 0.3 mm to 30 mm, preferably 1 mm to 10 mm, and more preferably 3 mm to 8 mm. The average fiber diameter of the reinforcing fiber (C) is preferably 1 μm to 50 μm, more preferably 3 μm to 20 μm, and even more preferably 5 μm to 15 μm. The reinforcing fiber (C) may be in the form of bundles of reinforcing fibers aggregated with a consolidating agent or the like, as long as they have the average fiber diameters described above.

[0078] Furthermore, the average aspect ratio (average fiber length / average fiber diameter) of the reinforcing fiber (C) is preferably 5 or more, more preferably 10 or more, even more preferably 20 or more, preferably 1200 or less, more preferably 1000 or less, even more preferably 950 or less, and particularly preferably 900 or less.

[0079] The content of reinforcing fibers (C) is preferably 5% to 40% by mass, more preferably 8% to 35% by mass, and even more preferably 10% to 30% by mass, based on 100% by mass of the total resin composition. By setting the content of reinforcing fibers (C) within the above range, the mechanical strength of the resin gear can be further improved.

[0080] The total content of inorganic fibers (B) and reinforcing fibers (C) is preferably 10% to 65% by mass, more preferably 15% to 60% by mass, based on 100% by mass of the total resin composition. By setting the total content of inorganic fibers (B) and reinforcing fibers (C) within the above range, the durability of the resin gear can be further enhanced.

[0081] The mass ratio of inorganic fibers (B) to reinforcing fibers (C) in the resin composition (inorganic fibers (B) / reinforcing fibers (C)) is preferably 0.05 to 0.9, more preferably 0.1 to 0.8. By setting the mass ratio of inorganic fibers (B) to reinforcing fibers (C) within the above range, the durability of the resin gear can be further improved.

[0082] (Solid lubricant (D)) The resin composition constituting the resin gear of the present invention may optionally contain a solid lubricant (D). When the resin composition contains a solid lubricant (D), the quietness of the resin gear can be further improved, and vibrations and noise caused by stick-slip can be reduced.

[0083] The solid lubricant (D) is not particularly limited, but examples include polyolefin resins such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene; graphite; molybdenum disulfide; tungsten disulfide; boron nitride; and fluororesin. These solid lubricants (D) may be used individually or in combination of two or more. In particular, from the viewpoint of achieving a higher level of both durability and quietness in the resin gears, it is more preferable that the solid lubricant (D) is a polyolefin resin.

[0084] Because polyolefin resins have low viscosity and high fluidity, adding a small amount to thermoplastic resin (A) can improve the packing of the resin composition into the mold during injection molding. In particular, it is preferable that the melting point of the polyolefin resin is 40°C to 220°C lower than the melting point of thermoplastic resin (A), more preferably 40°C to 120°C lower, and even more preferably 40°C to 80°C lower. By keeping the melting point difference within the above range, the polyolefin resin melts first and acts lubrically, contributing to improved moldability. In this specification, the melting point can be measured in accordance with JIS-K7121.

[0085] The content of the solid lubricant (D) is preferably 0.1% to 10% by mass, more preferably 1% to 9% by mass, based on 100% by mass of the total resin composition. When the content of the solid lubricant (D) is within the above range, the quietness of the resin gear can be further improved.

[0086] (Other Additives) The resin composition constituting the resin gear of the present invention may contain other additives, as long as they do not hinder the effects of the present invention. As other additives, various additives that are normally blended into resin compositions can be used.

[0087] Other additives include, for example, plate-like fillers such as mica, sericite, illite, talc, kaolinite, montmorillonite, boehmite, smectite, vermiculite, titanium dioxide, sodium titanate, magnesium potassium titanate, lithium potassium titanate, and boehmite; fibrous reinforcing materials other than the inorganic fibers (B) or reinforcing fibers (C) mentioned above; release agents such as saturated fatty acid esters, unsaturated fatty acid esters, and polyolefin waxes; colorants such as pigments and dyes such as carbon black and titanium dioxide; flame retardants such as brominated flame retardants and phosphorus-based flame retardants; ultraviolet absorbers such as benzophenone compounds, benzotriazole compounds, hydroxyphenyltriazine compounds, cyclic iminoester compounds, and cyanoacrylate compounds; heat stabilizers such as phenolic antioxidants, phosphite antioxidants, and carbodiimide compound-based hydrolysis inhibitors; thermal conductors such as graphite powder, aluminum oxide, and magnesium oxide; and antistatic agents such as polyether ester amide and glycerin monostearate. These other additives may be used individually or in combination of two or more.

[0088] The content of other additives is not particularly limited as long as it does not hinder the effects of the present invention. The content of other additives is preferably 10% by mass or less, and more preferably 5% by mass or less, based on 100% by mass of the total resin composition.

[0089] (Method for producing the resin composition) The resin composition constituting the resin gear of the present invention can be produced by heating and mixing (especially by melt kneading) a mixture containing a thermoplastic resin (A), inorganic fibers (B), and reinforcing fibers (C), and optionally a solid lubricant (D) and other additives. For melt kneading, known melt kneading equipment such as a twin-screw extruder can be used.

[0090] Specifically, resin compositions can be manufactured by (1) pre-mixing each component in a mixer (tumbler, Henschel mixer, etc.), melt-kneading in a melt-kneading device, and pelletizing with a pelletizing means (pelletizer, etc.); (2) preparing a masterbatch of desired components, mixing in other components as needed, melt-kneading in a melt-kneading device, and pelletizing; or (3) supplying each component to a melt-kneading device and pelletizing.

[0091] The processing temperature in melt mixing is not particularly limited as long as it is a temperature at which the thermoplastic resin (A) can melt. Typically, the cylinder temperature of the melt mixing apparatus used for melt mixing is adjusted to this range. Thus, a resin composition exhibiting the desired effect is produced.

[0092] <Method of Manufacturing and Use of Resin Gears> The resin gears of the present invention can be obtained by injection molding the above-mentioned resin composition. The method of injection molding the resin composition is not particularly limited, and various methods used in the art can be employed. For example, the resin gears of the present invention can be manufactured by introducing a pellet-shaped resin composition into an injection molding machine equipped with a predetermined mold and performing injection molding. Alternatively, the resin gears of the present invention may be manufactured by a combination of methods, in which the resin composition is formed into a plate-like or rod-like shape by injection molding, and then shaped by general molding processes such as cutting. The resin gears of the present invention may also be obtained by molding the above-mentioned resin composition by other molding methods.

[0093] The resin gears obtained by the manufacturing method of the present invention exhibit excellent rigidity and high mechanical strength. Furthermore, these resin gears also exhibit excellent durability and quiet operation.

[0094] In the present invention's method for manufacturing resin gears, resin gears having a module greater than 0.1 mm and less than or equal to 0.5 mm are manufactured. In the present invention's method for manufacturing resin gears, it is preferable to manufacture resin gears having a tooth width greater than 0.15 mm and less than or equal to 40 mm, a pitch circle diameter greater than 1 mm and less than or equal to 280 mm, and a number of teeth of 3T or more.

[0095] As described above, the resin gears of the present invention can be suitably used for small-module (miniature) gears. Examples of small gears include gears used in watches, AV equipment and amusement equipment, gears used in planetary gear reducers and harmonic drive gear reducers with high reduction ratios, and gears in geared motors of small drive mechanisms for smartphones, tablets, PCs, etc.

[0096] Furthermore, the resin gears of the present invention can be suitably used in automotive parts applications, such as gears for electric power steering devices with gear reduction mechanisms, gears for electric parking brakes, and the like. In electrical and electronic component applications, they can be suitably used in gears for housings of washing machines, vacuum cleaners, robots, and the like.

[0097] Examples of gears to which the resin gears of the present invention can be applied include spur gears, helical gears, internal gears, helical internal gears, spiral gears, screw gears, bevel gears, face gears, hypoid gears, worm gears, racks, and the like.

[0098] The gear reducer of the present invention includes the resin gear of the present invention as a component. Examples of gear reducers include planetary gear reducers and harmonic drive gear reducers with high reduction ratios. Because the gear reducer of the present invention includes the resin gear of the present invention as a component, it can be made more durable and quieter.

[0099] The present invention will be described in detail below based on examples and comparative examples, but is not limited thereto. The raw materials used in these examples and comparative examples are as follows.

[0100] (Thermoplastic resin (A)) PA-1: Polyamide 12, manufactured by Ube Industries, Ltd., product name "UBESTA3030U", melting point 178℃ PA-2: Polyamide MXD6, manufactured by Mitsubishi Engineering Plastics Corporation, product name "Lenny 6000", melting point 238℃ PA-3: Polyamide 66, manufactured by DuPont, product name "Zytel 103HSL", melting point 264℃ PEEK: Polyether ether ketone resin, manufactured by Victorex, product name "PEEK 450G", melting point 343℃

[0101] (Inorganic Fibers (B)) 8KT: Potassium titanate fiber, manufactured by Otsuka Chemical Co., Ltd., product name "Tismo D102", average fiber length 15 μm, average fiber diameter 0.5 μm 6KT: Potassium titanate fiber, manufactured by Otsuka Chemical Co., Ltd., product name "Tismo N102", average fiber length 15 μm, average fiber diameter 0.5 μm

[0102] (Reinforcement Fiber (C)) CF: PAN-based carbon fiber, manufactured by ZOLTEK, product name "Panex35-65", average fiber length 6 mm, average fiber diameter 7 μm, tensile modulus 242 GPa GF: Glass fiber, manufactured by Nippon Electric Glass Co., Ltd., product name "Glass Chopped Strand ECS03 T-297", average fiber length 3 mm, average fiber diameter 13 μm, tensile modulus 75 GPa

[0103] (Solid lubricant (D)) PE: High-density polyethylene, melting point 129°C

[0104] (Examples 1, 2, and Comparative Examples 1 to 4) In Examples 1, 2, and Comparative Examples 1 to 4, each material was melt-kneaded using a twin-screw extruder at a cylinder temperature of 270°C to 300°C in the blending ratios shown in Table 1 to obtain pellets. The obtained pellets were injection-molded into JIS test pieces and resin gear test pieces using an injection molding machine at a cylinder temperature of 270°C to 300°C and a mold temperature of 60°C to 100°C to obtain evaluation samples.

[0105] The obtained pellets were injection molded into JIS test pieces and resin gear test pieces using an injection molding machine to create evaluation samples. The cylinder temperature of the injection molding machine was set to 270°C to 300°C, and the mold temperature was set to 60°C to 100°C.

[0106] In the resin gear test pieces of Example 1 and Comparative Example 1, the module was set to 0.2 mm, the number of teeth to 90T, the pitch circle diameter to 18.0 mm, the tip circle diameter to 18.4 mm, the tooth width to 2.0 mm, and the pressure angle to 20°.

[0107] Furthermore, in the resin gear test pieces of Example 2 and Comparative Example 2, the module was set to 0.4 mm, the number of teeth to 45T, the pitch circle diameter to 18.0 mm, the tip circle diameter to 18.8 mm, the tooth width to 2.0 mm, and the pressure angle to 20°.

[0108] Furthermore, in the resin gear test pieces of Comparative Examples 3 and 4, the module was set to 0.6, the number of teeth to 30T, the pitch circle diameter to 18.0 mm, the tip circle diameter to 19.2 mm, the tooth width to 2.0 mm, and the pressure angle to 20°.

[0109] <Evaluation> The evaluation samples obtained in Example 1, Example 2, and Comparative Examples 1 to 4 were evaluated as follows.

[0110] (Bending Strength) The bending strength of the obtained JIS test specimens was measured in accordance with JIS K7271. More specifically, the bending strength was measured using an Autograph (Shimadzu Corporation, product name "AG-5000") by a three-point bending test with a support distance of 60 mm.

[0111] (Gear Testing) The obtained resin gear test pieces were evaluated for quietness and lifespan (measurement of number of rotations) using a gear durability tester. The conditions for evaluating quietness were a load torque of 0.005 N·m and a rotation speed of 500 rpm, with sound collected at 15 mm from the top of the gear, in an unlubricated and untemperature-controlled atmosphere. The conditions for evaluating lifespan were a load torque of 0.25 N·m and a rotation speed of 1500 rpm, in an unlubricated and untemperature-controlled atmosphere. The number of rotations was determined from the total number of rotations until tooth cracking or fracture occurred. Gears corresponding to the dimensions of each example and comparative example were used for the mating material (carbon steel, S45C). The tooth root strength was calculated from the stress obtained by fixing the resin gear test piece to a digital force gauge (IMADA Corporation, product name "ZTA-500N"), applying a load to the tooth tip side at a speed of 10 mm / min, and measuring the maximum load value at the time of tooth root fracture.

[0112] The results are shown in Table 1 below.

[0113]

[0114] Table 1 shows that in the resin gears of Comparative Examples 1 and 4, which contain only reinforcing fibers (C) and no inorganic fibers (B), reducing the module size compared to the resin gear of Comparative Example 4, as in the resin gear of Comparative Example 1, results in particularly poor durability and noise reduction are observed.

[0115] In contrast, the resin gear of Example 1, which further contains inorganic fibers (B) in addition to reinforcing fibers (C) and is not included in the resin gear of Comparative Example 1, showed improved durability and quietness even when the module was made smaller, similar to the resin gear of Comparative Example 1. From this, it can be concluded that in resin gears with a small module, the inclusion of inorganic fibers (B) in addition to reinforcing fibers (C) provides fiber reinforcement all the way to the tooth tips of the resin gear. Furthermore, the resin gear of Example 2, which has the same composition as Example 1 but a larger module than the resin gear of Example 1, also showed improved durability and quietness. Moreover, even when comparing the resin gears of Example 2 and Comparative Example 2, the resin gear of Example 2 showed superior results in terms of durability and quietness.

[0116] (Examples 3 to 5) In Example 3, each material was melt-kneaded using a twin-screw extruder at a cylinder temperature of 270°C to 290°C in the mixing ratios shown in Table 2 to obtain pellets. The obtained pellets were injection-molded into JIS test pieces and resin gear test pieces using an injection molding machine at a cylinder temperature of 230°C to 270°C and a mold temperature of 120°C to 140°C to obtain evaluation samples.

[0117] In Example 4, the materials were melt-kneaded using a twin-screw extruder at a cylinder temperature of 240°C to 300°C in the mixing ratios shown in Table 2 to obtain pellets. The obtained pellets were injection-molded into JIS test pieces and resin gear test pieces using an injection molding machine at a cylinder temperature of 270°C to 320°C and a mold temperature of 110°C to 130°C to obtain evaluation samples.

[0118] In Example 5, the materials were melt-kneaded using a twin-screw extruder at a cylinder temperature of 370°C to 390°C in the mixing ratios shown in Table 2 to obtain pellets. The obtained pellets were injection-molded into JIS test pieces and resin gear test pieces using an injection molding machine at a cylinder temperature of 380°C to 410°C and a mold temperature of 170°C to 190°C to obtain evaluation samples.

[0119] In the resin gear test pieces of Examples 3 to 5, the module was set to 0.2 mm, the number of teeth to 90T, the pitch circle diameter to 18.0 mm, the tip circle diameter to 18.4 mm, the tooth width to 2.0 mm, and the pressure angle to 20°.

[0120] The evaluation samples obtained in Examples 3 to 5 were also evaluated in the same manner as in Example 1.

[0121] The results are shown in Table 2 below.

[0122]

[0123] Table 2 shows that even in the resin gears of Examples 3 to 5, which use a thermoplastic resin (A) different from that of Examples 1 and 2, it was confirmed that durability could be improved and noise reduction could be achieved.

[0124] (Examples 6, 7, and Comparative Examples 5 and 6) In Examples 6 and Comparative Example 5, evaluation samples were prepared and evaluated in the same manner as in Example 1, except that the formulation ratios were as shown in Table 3 below. In Examples 7 and Comparative Example 6, evaluation samples were prepared and evaluated in the same manner as in Example 2, except that the formulation ratios were as shown in Table 3 below.

[0125] The results are shown in Table 3 below.

[0126]

[0127] Table 3 shows that even when glass fiber is used as the reinforcing fiber (C), comparing the resin gears of Examples 6 and 7, which further contain inorganic fiber (B) in addition to reinforcing fiber (C), with the resin gears of Comparative Examples 5 and 6, which do not contain inorganic fiber (B), using the same module, it can be seen that durability and quietness are improved even when the module is reduced in size.

[0128] (Examples 8, 9 and Comparative Examples 7 to 9) In Example 8, a resin gear test piece was prepared in the same manner as in Example 1, except that the module was 0.2 mm, the number of teeth was 30T, the pitch circle diameter was 6 mm, the tip circle diameter was 6.4 mm, the tooth width was 1.5 mm, and the pressure angle was 20°. The durability was evaluated in the same manner as in Example 1, except that the load torque was 0.035 N·m and the rotational speed was 1000 rpm.

[0129] Furthermore, in Example 9 and Comparative Examples 7-9, resin gear test pieces were prepared in the same manner as in Example 8, except that the compounding ratios shown in Table 4 below were used, and the durability was evaluated.

[0130] Furthermore, in Examples 8, 9, and Comparative Examples 7 to 9, SEM images of the cross-section of the tooth tips of the resin gear test pieces were observed to determine the long fiber filling rate (filling rate of reinforcing fibers (C)).

[0131] Figure 2 shows an SEM image of the cross-section of the tooth tip of the resin gear test piece obtained in Example 8. Figure 3 shows an SEM image of the cross-section of the tooth tip of the resin gear test piece obtained in Comparative Example 8.

[0132] As is clear from Figures 2 and 3, the resin gear test piece of Example 8, which contains both reinforcing fibers (C) (long carbon fibers) and inorganic fibers (B), shows a greater long fiber filling rate at the tooth tip compared to the resin gear test piece of Comparative Example 8, which contains only reinforcing fibers (C) (long carbon fibers), even though the long fiber content is the same.

[0133] Figure 4 is an SEM image of the cross-section of the tooth tip of the resin gear test piece obtained in Example 9. Figure 5 is an SEM image of the cross-section of the tooth tip of the resin gear test piece obtained in Comparative Example 9.

[0134] As is clear from Figures 4 and 5, similarly, when the reinforcing fiber (C) is glass fiber, the resin gear test piece of Example 9, which contains both reinforcing fiber (C) (long-fiber glass fiber) and inorganic fiber (B), shows a larger long-fiber filling rate at the tooth tip compared to the resin gear test piece of Comparative Example 9, which contains only reinforcing fiber (C) (long-fiber glass fiber), even though the long-fiber content is the same.

[0135] The SEM images were taken by embedding the resin gear specimens in epoxy resin, then mechanically polishing and ion milling the specimens to allow observation of their cross-sections, and finally capturing the images using a scanning electron microscope (SEM, Hitachi High-Tech Corporation, S4800, magnification: 250x). The long fiber packing ratio was determined by binarizing the captured SEM images using OpenCV in Python and calculating the ratio of the number of white pixels in the SEM image to the total number of pixels in the SEM image.

[0136] The results are shown in Table 4 below.

[0137]

[0138] As is clear from the comparison between Example 8 and Comparative Example 8, or between Example 9 and Comparative Example 9, in resin gears made of a resin composition containing both reinforcing fibers (C) and inorganic fibers (B), the long fiber filling rate at the tooth tip is higher compared to resin gears made of a resin composition containing only reinforcing fibers (C), even though the long fiber content is the same. This confirms that the durability of the resin gears is improved.

[0139] 1... Resin gear 2... Teeth 3... Shaft hole 4... Gate

Claims

1. A resin gear comprising a resin composition, wherein the resin composition is a mixture of a thermoplastic resin (A), inorganic fibers (B) having an average fiber length of 1 μm to 300 μm, and reinforcing fibers (C) having an average fiber length of 0.3 mm to 30 mm, and the module of the resin gear is greater than 0.1 mm and less than or equal to 0.5 mm.

2. The resin gear according to claim 1, wherein the resin composition substantially does not contain aramid fibers.

3. The resin gear according to claim 1 or claim 2, wherein the tooth width of the resin gear exceeds 0.15 mm and is 40 mm or less.

4. The resin gear according to claim 1 or claim 2, wherein the thermoplastic resin (A) comprises at least one crystalline resin selected from the group consisting of polyester resins, polyamide resins, polyphenylene sulfide resins, and polyether aromatic ketone resins.

5. The resin gear according to claim 1 or claim 2, wherein the inorganic fiber (B) is at least one of potassium titanate fiber and wollastonite fiber.

6. The resin gear according to claim 1 or claim 2, wherein the reinforcing fiber (C) is at least one of carbon fiber and glass fiber.

7. The resin gear according to claim 1 or claim 2, wherein the total content of the inorganic fiber (B) and the reinforcing fiber (C) is 10% by mass to 65% by mass in 100% by mass of the total amount of the resin composition.

8. The resin gear according to claim 1 or claim 2, wherein the mass ratio of the inorganic fiber (B) to the reinforcing fiber (C) (inorganic fiber (B) / reinforcing fiber (C)) is 0.05 to 0.

9.

9. The resin gear according to claim 1 or claim 2, wherein the resin composition further contains a solid lubricant (D).

10. The resin gear according to claim 9, wherein the solid lubricant (D) is a polyolefin resin, and the melting point of the polyolefin resin is 40°C to 220°C lower than the melting point of the thermoplastic resin (A).

11. The resin gear according to claim 9, wherein the content of the solid lubricant (D) is 0.1% by mass to 10% by mass of the total amount of the resin composition.

12. A method for manufacturing a resin gear according to claim 1 or claim 2, comprising the steps of: obtaining a resin composition by blending a thermoplastic resin (A), inorganic fibers (B) having an average fiber length of 1 μm to 300 μm, and reinforcing fibers (C) having an average fiber length of 0.3 mm to 30 mm; and molding the resin composition by injection molding.

13. A method for manufacturing a resin gear according to claim 9, comprising the steps of: obtaining a resin composition by blending a thermoplastic resin (A), inorganic fibers (B) having an average fiber length of 1 μm to 300 μm, reinforcing fibers (C) having an average fiber length of 0.3 mm to 30 mm, and a solid lubricant (D); and molding the resin composition by injection molding.

14. A gearbox comprising a resin gear as described in claim 1 or claim 2 as a component.

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