Resin composition for gear and gear made of molded article thereof

Abstract

To provide a resin composition for a gear capable of molding a gear excellent in life, abrasion resistance and low noise property without using a fiber material for reinforcement and excellent in moldability, and to provide a gear excellent in life, abrasion resistance and low noise property.SOLUTION: A resin composition for gears, comprising: a base resin composed of a thermoplastic resin; an impact modifier composed of an elastomer (excluding a silicone-based rubber); and a rheology modifier having a difference in SP value from the base resin of 4.0 or less, wherein the resin composition does not comprise a fiber material for reinforcement.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a gear resin composition and a gear formed from a molded article of the gear resin composition. [Background technology]

[0002] Rotating devices such as reducers used in industrial machinery and transportation equipment are sometimes required to transmit high driving forces even in relatively high-temperature environments, such as around 200°C. Therefore, metals with good heat resistance and torque transmission properties are often selected for the gears used in rotating devices. However, combining metal gears generates noise, such as gear meshing sounds. To reduce this noise, metal cores are sometimes coated with resin to form an integrated unit, or resin gears are sometimes used in combination.

[0003] Patent Document 1 discloses a reduction gear for an electric power steering device, which includes a gear in which a resin part made of a resin composition containing polyphenylene sulfide resin as a base resin and glass fibers with an average diameter of 5 to 9 μm is integrally provided on the outer periphery of a metal core tube, and gear teeth are formed on the outer periphery of the resin part.

[0004] Patent Document 2 describes that a rotating body having teeth on its outer periphery, which are used in torque limiters for reel bases of audio equipment and the like, is formed from a thermoplastic resin composition containing a base resin that is a polyacetal resin or a polyphenylene sulfide resin, a first additive used to improve the sliding properties of the base resin, and a second additive used to further improve the sliding properties, and gives an example of an elastomer as the first additive and a wax as the second additive.

[0005] Furthermore, Patent Document 3 describes a thermoplastic resin material that can suppress the generation of noise caused by stick-slip in molded articles used in home appliances and vehicle interiors, which contains a blend of one or more thermoplastic organic materials and a masterbatch containing one or more thermoplastic materials, a silicone elastomer, and / or an uncured organopolysiloxane polymer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-191050 [Patent Document 2] Japanese Patent Application Publication No. 10-274252 [Patent Document 3] Patent Publication No. 2021-519842 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when a resin composition containing a specific glass fiber, such as that described in Patent Document 1, is combined with a metal gear, for example, abnormal wear may occur between the resin and metal parts, shortening the gear's lifespan and increasing noise. The resin composition described in Patent Document 2 does not take into consideration the dispersibility of additives such as the first additive in the base resin, leaving room for improvement in terms of gear lifespan, wear resistance, noise, and moldability. The thermoplastic material described in Patent Document 3 uses a silicone elastomer, but it has been confirmed that when such a thermoplastic material containing a silicone elastomer is used in gear applications, it is difficult to achieve the required levels of each of the above properties.

[0008] Therefore, an object of the present invention is to provide a gear resin composition with excellent moldability that can be used to mold gears with excellent life, wear resistance, and low noise without using reinforcing fiber materials, and to provide gears with excellent life, wear resistance, and low noise. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that when a resin composition is used in which a predetermined base resin is used in combination with a predetermined impact resistance improver and a predetermined rheology modifier without using a reinforcing fiber material, the resin composition has excellent moldability, and when a molded article thereof is used to form a gear, it exhibits the desired properties.

[0010] A first aspect of the present invention relates to a resin composition for gears, comprising a base resin made of a thermoplastic resin, an impact resistance improver made of an elastomer (excluding silicone-based rubber), and a rheology modifier whose SP value differs from that of the base resin by 4.0 or less, and which does not contain a reinforcing fiber material.

[0011] In the gear resin composition according to the embodiment of the present invention, the thermoplastic resin may be at least one selected from polyphenylene sulfide, polyethylene terephthalate, polybutylene terephthalate, polyamide 6, polyamide 66, and polyoxymethylene.

[0012] In the gear resin composition according to the embodiment of the present invention, the rheology modifier may be at least one selected from fatty acid amides, montanic acid waxes, olefin waxes, stearic acid, sorbitan esters, and glycerin esters.

[0013] In the resin composition for a gear according to the embodiment of the present invention, the elastomer may be at least one selected from vulcanized rubbers.

[0014] The gear resin composition according to the embodiment of the present invention may contain 70 to 98.9% by weight of the base resin, 1 to 25% by weight of the impact resistance improver, and 0.1 to 5% by weight of the rheology modifier.

[0015] A second aspect of the present invention relates to a gear formed from the aforementioned gear resin composition.

[0016] In the present invention, the configurations of the above-described embodiments can be combined as appropriate. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a gear resin composition with excellent moldability that can be used to mold gears with excellent life, wear resistance, and low noise without using reinforcing fiber materials, and to provide gears with excellent life, wear resistance, and low noise. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic overview of a power-absorbing dynamic gear testing machine used in evaluation tests of gear life in Examples and Comparative Examples. [Figure 2] FIG. 1 is an explanatory diagram schematically illustrating an outline of a power-absorbing dynamic gear testing machine used in an evaluation test of meshing sound pressure levels in Examples and Comparative Examples, and the installation positions of sound-insulating materials. DETAILED DESCRIPTION OF THE INVENTION

[0019] A gear resin composition according to an embodiment of the present invention contains a base resin made of a thermoplastic resin, an impact resistance improver made of an elastomer (excluding silicone-based rubber), and a rheology modifier whose SP value differs from that of the base resin by 4.0 or less, but does not contain a reinforcing fiber material.

[0020] In this way, by using a rheology modifier with an SP value that is 4.0 or less different from the SP value of the base resin together with an impact modifier made of an elastomer, the rheology modifier is uniformly dispersed in the base resin, which allows the impact modifier to be uniformly dispersed throughout the base resin and enhances the affinity at the interface between the base resin and the impact modifier. Therefore, even without the use of reinforcing fibers, the impact modifier uniformly dispersed in the base resin can effectively mitigate the impact force when opposing gear teeth mesh during gear rotation. As a result, impact noise during meshing can be reduced, resulting in quieter operation. Furthermore, the absence of reinforcing fibers can suppress gear wear and shortened lifespan. Furthermore, the uniform dispersion of the rheology modifier in the base resin improves fluidity during molding and mold releasability, resulting in excellent moldability.

[0021] In the present invention, the SP value means the solubility parameter, and its unit is (cal / cm 3 ) 1 / 2 The SP value is calculated based on the composition formula of each material using the estimation method of Fedors (Polym. Eng. Sci., 14(2), 147-154 (1974)).

[0022] The thermoplastic resin used for the base resin can be appropriately selected from those commonly used in gear applications. Examples include polyamide (PA), polyester, polyphenylene sulfide (PPS), polyoxymethylene (POM), polyolefin, styrene-based polymer, polycarbonate (PC), etc. Examples of polyamides include polyamide 6, polyamide 66, and polyamide MXD. Examples of polyesters include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN). From the viewpoints of heat resistance, mechanical properties, electrical properties, moldability, and chemical resistance, at least one selected from PPS, PET, PBT, PA6, PA66, and POM is preferred. From the viewpoints of better heat resistance and impact resistance, PPS is particularly preferred. PPS may be linear or crosslinked, but linear PPS is preferred from the viewpoint of impact resistance. From the same viewpoint, PPS with a high molecular weight (weight-average molecular weight) of 50,000 or more is preferred. Such a high molecular weight PPS preferably has a melt viscosity at 310°C of 50 to 400 Pa·s and a shear rate of 800 to 1200 / sec.

[0023] The content of the base resin in the gear resin composition can be determined appropriately depending on the type and properties of the base resin and other components, but is preferably 70 to 98.9% by weight, more preferably 85 to 98.9% by weight.

[0024] The impact resistance improver is not particularly limited as long as it is made of an elastomer other than silicone-based rubber, and examples of such elastomers include vulcanized rubbers such as styrene-butadiene rubber, acrylic rubber, acrylonitrile-butadiene rubber (NBR), carboxyl-modified acrylonitrile-butadiene rubber, chloroprene rubber, hydrogenated acrylonitrile-butadiene rubber, carboxyl-modified hydrogenated acrylonitrile-butadiene rubber, and carboxyl-modified styrene-butadiene rubber, as well as thermoplastic elastomers such as styrene-based, olefin-based, vinyl chloride-based, urethane-based, ester-based, and amide-based elastomers. Among these, at least one selected from vulcanized rubbers is preferred, and at least one selected from acrylic rubber, acrylonitrile-butadiene rubber (NBR), carboxyl-modified acrylonitrile-butadiene rubber, hydrogenated acrylonitrile-butadiene rubber, and carboxyl-modified hydrogenated acrylonitrile-butadiene rubber is more preferred.

[0025] The shape of the impact resistance improver is not particularly limited, and examples thereof include solid forms such as powder, particles, and small pieces. The size is also not particularly limited, and for example, a maximum length of 5 μm to 0.5 mm can be appropriately selected depending on the application. If the shape and size of the impact resistance improver change during the production process of the gear resin composition, the change will be based on the shape after the change.

[0026] The content of the impact resistance improver in the gear resin composition can be determined appropriately depending on the type and characteristics of the impact resistance improver and other components, but is preferably 1 to 25% by weight, more preferably 5.0 to 10% by weight.

[0027] The rheology modifier can be one whose SP value differs from that of the base resin by 4.0 or less, preferably by 3.0 or less. Therefore, it can be selected appropriately depending on the SP value of the thermoplastic resin used as the base resin. Examples of applicable rheology modifiers include fatty acids, fatty acid amides, esters, waxes, etc.

[0028] Examples of fatty acids include fatty acids having 12 or more carbon atoms. Among these, saturated fatty acids having 16 or more carbon atoms are preferred, with palmitic acid, stearic acid, behenic acid, montanic acid, adipic acid, and sebacic acid being more preferred, and stearic acid being particularly preferred.

[0029] Examples of fatty acid amides include saturated or unsaturated monovalent or divalent or higher polyvalent aliphatic amides having 12 to 60 carbon atoms. For example, primary amides such as lauric amide, palmitic amide, stearic amide, behenic amide, hydroxystearic amide, oleic amide, and erucic amide; Examples of the secondary amides include methylene bisstearamide, ethylene biscapric amide, ethylene bislauric amide, ethylene bisstearamide, ethylene bishydroxystearamide, ethylene bisbehenic amide, ethylene bisoleic amide, ethylene biserucic amide, hexamethylene bisstearamide, hexamethylene bisbehenic amide, hexamethylene bisoleic amide, and hexamethylene hydroxystearic amide; and the like.

[0030] As the fatty acid amide, secondary amides are preferred, secondary amides of saturated fatty acids are more preferred, and ethylene bisstearic acid amides are even more preferred.

[0031] Examples of esters include sorbitan esters and glycerin esters.

[0032] Examples of waxes include shellac wax, beeswax, spermaceti, shellac wax, wool wax, carnauba wax, Japan wax, rice wax, candelilla wax, oat wax, and olefin-based waxes. Of these, olefin-based waxes are preferred. Examples of olefin-based waxes include microcrystalline wax, paraffin wax, Montan acid wax, Fischer-Tropsch wax, polyethylene wax, and polypropylene wax.

[0033] Among these, at least one selected from fatty acid amides, olefin waxes, stearic acid, sorbitan esters, and glycerin esters is preferred, and at least one selected from fatty acid amides is more preferred.

[0034] Among the above rheology modifiers, the SP values ​​of representative ones are as follows: Fatty acid amides: 9.5-11.0 Olefin wax: 7.9~8.4 Stearic acid: 11.2 Sorbitan ester: 12.1 to 12.8 Glycerin ester: 10.8-11.5

[0035] The SP values ​​of typical thermoplastic resins used as base resins are generally as follows: PPS: 12.1~12.7 PET: 10.2~10.9 PBT: 9.9~10.2 PA6: 12.4~12.9 PA66: 12.4-12.9 POM: 10.8~11.3

[0036] Furthermore, the difference in SP value between the elastomer constituting the impact modifier and the rheology modifier is preferably 4.0 or less, more preferably 3.0 or less. The difference in SP value between the impact modifier and the base resin is also preferably similar. The SP values ​​of typical elastomers are generally as follows: The higher the acrylonitrile content of NBR, the higher the SP value tends to be. NBR is generally classified according to the acrylonitrile (AN) content into low NBR (less than 25% by weight), medium NBR (25% to 30% by weight), medium-high NBR (more than 30% to 35% by weight), and high NBR (more than 35% by weight). Examples of SP values ​​taking each classification into consideration are also shown below. The SP value of silicone-based rubber is said to be 7.3 to 7.6. Acrylic rubber: 9.2~9.7 NBR: 8.7~10.5 (Low NBR (AN content is 18% by weight): 8.7 to 8.8 Medium NBR (AN content is 25% by weight): 8.9 to 9.5 Medium to medium-high NBR (AN content is 30% by weight): 9.4 to 9.9 High NBR (AN content is 39% by weight): 10.3-10.5)

[0037] Suitable examples of combinations of the above components are as follows: Base resin: PPS (SP value: 12.1 to 12.7) Impact resistance improver: Acrylic rubber (SP value: 9.2 to 9.7) or NBR (SP value: 8.7 to 10.5) Rheology modifier: fatty acid amide (SP value: 9.5-9.9) In this example, the difference in SP value between PPS and the rheology modifier is 2.2 to 3.2, the difference (absolute value) in SP value between the impact modifier and the rheology modifier is 0.2 to 0.7 or 0.6 to 1.2, and the difference with PPS is 2.4 to 3.5 or 1.6 to 3.0. Since the SP value of each component is 3.5 or less, the dispersibility of the impact modifier and rheology modifier in PPS is good. Furthermore, when the PPS is linear and has a high molecular weight, the PPS itself has low fluidity during molding. However, the inclusion of a uniformly dispersed rheology modifier improves fluidity during molding and also provides good moldability, resulting in excellent moldability. Furthermore, the impact modifier is uniformly dispersed in the PPS by the rheology modifier, and the resulting molded article is endowed with the impact resistance and fatigue resistance provided by the impact modifier without impairing the excellent heat resistance, mechanical properties, and other characteristics of the PPS, making it suitable for gear applications.

[0038] The content of the rheology modifier in the gear resin composition can be determined appropriately depending on the type and characteristics of the rheology modifier and other components, but is preferably 0.1 to 5% by weight, more preferably 0.5 to 3% by weight.

[0039] In addition to the above-mentioned components, the gear resin composition may contain other components besides the reinforcing fiber material and silicone rubber, as long as they do not affect the above-mentioned properties. Examples of such additives include internal lubricants (e.g., solid lubricants such as PTFE powder and molybdenum sulfide), colorants, and flame retardants.

[0040] Although the gear resin composition does not include a reinforcing fiber material, the present invention includes a small amount of the reinforcing fiber material contained therein that does not affect the above-mentioned properties. Furthermore, the impact resistance improver does not include a silicone rubber elastomer, but the present invention includes a small amount of the reinforcing fiber material contained therein that does not affect the above-mentioned properties.

[0041] The gear resin composition according to the embodiment of the present invention can be obtained, for example, by mixing the above-described components in a mixer or the like according to a conventional method. If necessary, the mixture obtained in the mixer can be made into pellets or the like using a twin-screw kneading extruder or the like according to a conventional method.

[0042] A gear according to an embodiment of the present invention comprises a molded article made from the aforementioned gear resin composition. The molded article can be obtained by injection molding the aforementioned gear resin composition into a mold having a cavity in the shape of the desired gear, according to a standard method. The aforementioned gear resin composition has good fluidity due to the rheology modifier being uniformly contained in the base resin, preventing underfilling during injection molding. The rheology modifier also present on the surface of the molded article provides good moldability and moldability. The composition also has excellent life, wear resistance, and low noise. These properties can be evaluated using the methods described in the Examples section below.

[0043] Furthermore, because of the excellent properties described above, gears formed from the molded article of the gear resin composition described above are suitable for various gears used in, for example, electric bicycles (electrically assisted bicycles, etc.), electric motorcycles, electric wheelchairs, senior cars, kick scooters, etc., as well as idler gears used in automobiles, industrial machinery, etc. [Example]

[0044] Hereinafter, embodiments of the present invention will be described based on examples.

[0045] Example 1 90% by weight of PPS (Polyplastics Co., Ltd., DURAFIDE® 0220A9) thermoplastic resin, 9% by weight of acrylic rubber (Zeon Corporation, Nipol® AR71) flakes as impact modifier, and 1% by weight of fatty acid amide (Lion Corporation, Armowax EBS) as rheology modifier were mixed in a mixer, and then pelletized using a twin-screw extruder (Plastics Engineering Research Institute Co., Ltd., BT-30, screw diameter: φ30 mm, screw L / D=30, die temperature: 300°C, output rate: 12 kg / h). The impact modifier was finely pulverized by the shear force of the extruder, and it was confirmed that the components were uniformly mixed.

[0046] The resulting resin composition was used to injection-molde test gears using an injection molding machine (UH-1000, manufactured by Nissei Plastic Industrial Co., Ltd., clamping force: 60 tons). The molding conditions were: molding machine barrel temperature 300°C, mold temperature 150°C, dwell pressure 150 MPa, and cooling time 20 seconds. The molding mold used had a three-point pin gate, module m=1, and two cavities. The specifications of the test gears are shown in Table 2.

[0047] (Examples 2 to 4, Comparative Examples 1 to 6) In the same manner as in Example 1, a pellet-shaped resin composition was prepared according to the formulation shown in Table 1, and the obtained resin composition was used to injection-molde a test gear.

[0048] The components used in the examples and comparative examples shown in Table 1 are as follows. (1) PPS 0220A9 Polyplastics Co., Ltd., DURAFIDE (registered trademark) 0220A9, linear type, melt viscosity at 310°C: 500 Pa·s, shear rate: 1000 / sec, SP value: 12.3 (2) Elastomer Acrylic rubber Acrylic rubber sheet (Nipol (registered trademark) AR71, manufactured by Nippon Zeon Co., Ltd., thickness: 2 mm) cut into 2 mm square pieces, SP value: 9.3 NBR Zeon Corporation, Nipol (registered trademark) 1141C, powder, medium NBR, SP value: 8.9 Silicone rubber Shin-Etsu Chemical Co., Ltd., KR22OL, flakes, SP value: 7.4 (3) Rheology modifier Fatty acid amides Lion Corporation, Armowax EBS, ethylene bisstearic acid amide type, SP value: 9.7 Silicone-based Wacker Asahi Kasei Silicone Co., Ltd., GENIOPLAST (registered trademark), silicone-based, SP value: 7.5

[0049] (evaluation) <Gear life> In accordance with JIS B1759, a gear life evaluation test was conducted using the test gears obtained in the examples and comparative examples. Using a power-absorbing dynamic gear testing machine (manufactured by Starlite Industrial Co., Ltd.) shown in Figure 1, gears of the same type were meshed under a constant load (tooth root bending stress) under the measurement conditions shown in Table 2, and the total number of gear rotations from the start of the test until rotation stopped due to gear fracture or wear on the tooth surface was determined. The measurement results are shown in Table 1. In this test, a load (tooth root bending stress) was applied by the rotational resistance of the powder clutch of the power-absorbing dynamic gear testing machine. The Lewis equation described on page 8 of the "DURACON Gears" product catalog (September 2006 edition) published by Polyplastics Co., Ltd. was used to calculate the tooth root bending stress. Grease lubrication was performed by initially applying grease to the gear meshing area (tooth flanks) before the start of the test.

[0050] <Wear resistance> The test was conducted under the conditions shown in Table 2, in the same manner as the gear life evaluation test. However, the test machine was stopped 330 hours (9.9 million revolutions) after the start of the test, and the matagi tooth thickness of four teeth was measured at six locations, and the average value was taken as the matagi tooth thickness. The difference in matagi tooth thickness before and after the test was calculated as the matagi tooth thickness change, and wear resistance was evaluated.

[0051] <Engagement sound pressure level> Similar to the gear life evaluation test, the test was conducted under the conditions shown in Table 2. However, after 300 hours had passed since the start of the test, the meshing portion of the gears of the testing machine was tightly surrounded by sound-insulating material to block out external noise (see Figure 2 for an outline of the installation location of the sound-insulating material (broken line area)), and the sound pressure level of the meshing sound generated by the test gears of the testing machine was measured inside the space surrounded by the sound-insulating material using a sound level meter (NL42, manufactured by Rion Co., Ltd.), and the sound pressure during steady-state operation was recorded as the meshing sound pressure level.

[0052] <Mold releasability> In Examples 1 to 4 and Comparative Examples 1 to 6, after injection molding, the releasability when releasing from the mold was evaluated visually according to the following criteria. ◯: Smooth release from the mold; ×: The ejector pin bit into the molded product, or resistance was encountered during ejection, causing the molded product to deform.

[0053] Table 1 shows the formulations and evaluation results of Examples 1 to 4 and Comparative Examples 1 to 6.

[0054] [Table 1]

[0055] [Table 2]

[0056] As shown in Table 1, the resin compositions containing the specified components such as those in Examples 1 to 4 have excellent moldability, and gears made from molded articles obtained using these resin compositions have excellent life, wear resistance, and low noise.

Claims

1. A resin composition for a gear, comprising: a base resin made of a thermoplastic resin; an impact resistance improver made of an elastomer (excluding silicone-based rubber); and a rheology modifier having an SP value that differs from that of the base resin by 4.0 or less, and containing no reinforcing fiber material.

2. 2. The gear resin composition according to claim 1, wherein the thermoplastic resin is at least one selected from the group consisting of polyphenylene sulfide, polyethylene terephthalate, polybutylene terephthalate, polyamide 6, polyamide 66, and polyoxymethylene.

3. 3. The gear resin composition according to claim 1, wherein the rheology modifier is at least one selected from the group consisting of fatty acid amides, montanic acid waxes, olefin waxes, stearic acid, sorbitan esters, and glycerin esters.

4. 3. The gear resin composition according to claim 1, wherein the elastomer is at least one selected from vulcanized rubbers.

5. 3. The gear resin composition according to claim 1, comprising 70 to 98.9% by weight of the base resin, 1 to 25% by weight of the impact resistance improver, and 0.1 to 5% by weight of the rheology modifier.

6. A gear comprising a molded article of the gear resin composition according to claim 1 or 2.

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