Resin composition and synthetic resin gear

Abstract

To provide a resin composition that enables molded products such as gears to be formed with favorable dimensional precision.SOLUTION: A resin composition contains a base resin whose principal component is polyphenylene sulfide and an inorganic filler, the shrinkage ratio (STD / SMD) of the TD shrinkage rate STD to the MD shrinkage rate SMD being 3.0 or less, and the shrinkage difference (S3D-SMD), obtained by subtracting the MD shrinkage rate SMD from the 3D shrinkage rate S3D, being 3.0% or less. A synthetic resin gear is formed from the resin composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition and a synthetic resin gear. [Background technology]

[0002] For example, Japanese Patent Application Laid-Open No. 2021-98367 (Patent Document 1) describes a resin molded body obtained by injection molding a resin composition containing a thermoplastic resin as a base resin, a granular inorganic material, and a fibrous inorganic material. In the resin molded body of this publication, the total volume of the granular inorganic material and the fibrous inorganic material is 30% to 70% by volume of the total volume of the resin composition, and when the flow direction of the molten resin composition during injection molding is defined as MD and the direction perpendicular to MD is defined as TD, the ratio of the linear expansion coefficients of the resin molded body (A MD / A TD ) or mold shrinkage ratio (B MD / B TD ) is 0.5 to 1.

[0003] The same publication also describes a scroll rotor for a scroll-type refrigerant compressor used in air-conditioning and heating equipment, etc., as an article molded from the resin composition. The publication further describes that by using a scroll rotor molded from the resin composition, the scroll rotor can be manufactured efficiently and with good productivity, contributing to lower prices for scroll rotors, and ensuring excellent dimensional accuracy and mechanical strength.

[0004] Incidentally, synthetic resin gears (hereinafter referred to as "resin gears") have been widely used as power transmission parts in office automation equipment such as printers and copiers. One resin composition that is used as the material for such gears is a resin composition containing polyphenylene sulfide as its main component, which has excellent moldability, heat resistance, and cost advantages.

[0005] Plastic gears used in office automation equipment are required to have appropriate mechanical properties such as tensile strength and bending strength, as well as gear-specific properties such as high dimensional accuracy to reduce gear meshing error (Japan Gear Manufacturers Association standard JGMA 116-02) and good sliding properties.

[0006] On the other hand, in terms of resin composition materials, it is known that there is a trade-off between the mechanical strength and dimensional accuracy of the molded product, and for example, increasing the mechanical strength has been problematic in that it leads to a decrease in dimensional accuracy. For this reason, in the past, in order to obtain synthetic resin gears that combine strength and dimensional accuracy, improvements were often made to injection molding techniques and mold design techniques. However, with the recent improvement in the quality of office automation equipment, and with the increasing performance and functionality of office automation equipment, higher quality is being demanded of plastic gears as well. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-98367 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a resin composition that can be used to mold a gear or other molded article with good dimensional accuracy, and a gear formed from the resin composition, or to provide a resin composition that can be used to mold a gear or other molded article that has a good balance of good dimensional accuracy and high strength, and a gear formed from the resin composition. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following configuration. 1. A resin composition containing a base resin mainly composed of polyphenylene sulfide and an inorganic filler, Regarding a test piece obtained by injection molding the resin composition in a mold in accordance with JIS K7152-3, the shrinkage rate of the test piece relative to the cavity space of the mold in the M direction parallel to the flow direction of the molten resin during the injection molding is called the MD shrinkage rate S MD The shrinkage rate of the test piece relative to the cavity space in the T direction perpendicular to the flow direction is defined as the TD shrinkage rate S TD When the MD shrinkage ratio S MD The TD shrinkage ratio S TD Shrinkage ratio (S TD / S MD ) is less than or equal to 3.0, The 3D shrinkage ratio S of the test piece relative to the cavity space in the three-dimensional directions of the M direction, the T direction, and the Z direction which is the thickness direction of the test piece 3D From the above, the MD shrinkage rate S MD The shrinkage difference (S 3D -S MD ) is less than 3.0% A resin composition characterized by: 2. The resin composition according to 1, wherein the molded article obtained by molding the resin composition has a tensile strength of 100 MPa or more. 3. The resin composition according to 2., wherein the inorganic filler comprises an isotropic filler having an aspect ratio of less than 5 and a fibrous filler. 4. The resin composition according to 3, wherein the average fiber length of the fibrous filler is 100 μm or more and 500 μm or less. 5. The resin composition according to 3, wherein the volume ratio of the fibrous filler in the inorganic filler is 0.1% or more and 45% or less. 6. The resin composition according to 1., wherein the content of the inorganic filler is 5% by volume or more and 65% by volume or less. 7. A synthetic resin gear formed from the resin composition according to any one of 1. to 6. [Effects of the Invention]

[0010] When a gear is molded using the resin composition of the present invention, it is possible to mold a resin gear with high dimensional accuracy that not only has the properties unique to polyphenylene sulfide but also ensures a meshing error of at least grade 3 on the one-pitch meshing scale as defined in the Japanese Gear Manufacturers Association standard JGMA 116-02.Alternatively, when a gear is molded using the resin composition of the present invention, it is possible to mold a resin gear with high dimensional accuracy that not only has the properties unique to polyphenylene sulfide but also ensures a meshing error of at least grade 3 on the one-pitch meshing scale and high mechanical strength, for example, a tensile strength of at least 100 MPa. DETAILED DESCRIPTION OF THE INVENTION

[0011] The resin composition of this embodiment contains polyphenylene sulfide (hereinafter sometimes abbreviated as PPS resin) and an inorganic filler, and is a resin composition used for molding molded articles such as resin gears.

[0012] For example, in Patent Document 1, when the flow direction of the molten resin composition during injection molding of a molded body is defined as MD and the direction perpendicular to MD is defined as TD, the linear expansion coefficient A of the molded body in MD is MD and the linear expansion coefficient A in TD TD Ratio to (A MD / A TD ) or mold shrinkage rate B in MD of the molded body MD and mold shrinkage rate B at TD TD Ratio to (B MD / B TD It is described that by specifying the numerical range of the above, a molded product having excellent dimensional accuracy can be obtained as a "scroll rotor." It is generally known that the anisotropy of injection-molded articles is caused by the molecular orientation of the synthetic resin and the orientation of the inorganic filler contained in the synthetic resin.

[0013] On the other hand, gears are three-dimensional objects with a complex shape provided with a plurality of small protruding teeth. As a result of research and investigation into the anisotropy of molding shrinkage in resin gears molded into complex three-dimensional shapes, the inventors have found that, for example, for a flat test piece as specified in JIS K7152-3, the molding shrinkage rate S in the MD in one plane is MD and TD molding shrinkage S TD It became clear that even if the ratio of the shrinkage rates was calculated, the numerical value of the ratio alone does not have a sufficient correlation with the dimensional accuracy of the gear.

[0014] Furthermore, the present inventors have focused on the molding shrinkage rate in the thickness direction ZD, which is perpendicular to MD and TD, of the above-mentioned flat test specimens and conducted further research. As a result, it has become clear that in a flat test specimen molded from a resin composition containing a PPS resin and an inorganic filler, when the molding shrinkage rate in one plane (the molding shrinkage rates in MD and TD) is small, the molding shrinkage rate in the ZD increases.

[0015] Furthermore, with regard to gear meshing error (Japan Gear Manufacturers Association standard JGMA 116-02), it was revealed that if a gear is considered to be a cylinder, for example, in areas of the gear (molded body) where the fiber orientation of the fibrous inorganic filler is high, the amount of molding shrinkage is small, resulting in a large outer diameter (tooth tip diameter) of the molded gear, while in areas where the fiber orientation is low, the amount of molding shrinkage is large, resulting in a small outer diameter of the molded gear, resulting in outer diameter difference and outer diameter variation in the gear. Here, outer diameter difference of a gear refers to the difference between the maximum and minimum outer diameters of a single gear.

[0016] The gear outer diameter difference and gear meshing error are both affected by differences in molding shrinkage due to differences in fiber orientation. For this reason, for a flat test piece specified in JIS K7152-3, the molding shrinkage ratio S in the three-dimensional directions of MD, TD, and ZD is calculated based on the following formula (1): 3D From this, the molding shrinkage rate S MD The shrinkage difference (S 3D -S MD) is correlated with the gear meshing error, and the shrinkage rate difference (S 3D -S MD ) is 3.0% or less, it has been newly discovered that it is possible to achieve a meshing error of Class 3 or higher in the one-pitch meshing grade specified in JGMA 116-02. MD -D 3D " represents the difference in outer diameter of the gear due to fiber orientation.

[0017]

number

[0018] In addition, the mold shrinkage rate S in the three-dimensional direction mentioned above 3D is a value that does not take into account the direction of shrinkage of the molded body, so the mold shrinkage rate S 3D The shrinkage difference (S 3D -S MD ) alone cannot explain the gear meshing error. Therefore, the inventors have conducted further research and investigations and have decided to use the above-mentioned shrinkage difference (S 3D -S MD ) as well as the MD molding shrinkage S MD TD molding shrinkage ratio S TD The ratio (S TD / S MD ), it was discovered that by setting conditions that also take into account the above, it is possible to identify a material that contains PPS resin and inorganic filler and that can be used to mold gears with meshing error of grade 3 or higher, and this led to the completion of the present invention.

[0019] Preferred embodiments of the present invention will now be described in detail. [Resin composition] The resin composition of this embodiment contains a base resin mainly composed of a PPS resin and an inorganic filler. In particular, the resin composition of this embodiment is a resin composition consisting of a PPS resin and an inorganic filler, or a resin composition consisting of a PPS resin, an inorganic filler, and a polytetrafluoroethylene (PTFE) resin. In the present invention, the resin composition may contain various additives in amounts that do not impair the object of the invention.

[0020] [PPS resin] PPS resin is a polymer containing a repeating unit represented by the following structural formula. The PPS resin is preferably contained in a resin composition in an amount of 50% by volume or more. By including a base resin whose main component is PPS resin, the resin composition can have excellent moldability and high heat resistance. Furthermore, the production cost of the resin composition can be reduced.

[0021] [ka]

[0022] The viscosity of the PPS resin is preferably 1 Pa·s or more and 1000 Pa·s or less, and more preferably 10 Pa·s or more and 500 Pa·s or less. The viscosity of the PPS resin is measured in accordance with JIS K7199 using a capillary die (die diameter: 1 mm, die length: 10 mm), at a barrel temperature of 300°C and a shear rate of 1000 s -1 The melt viscosity is obtained by measuring the melt viscosity at 1000 kJ / min.

[0023] In the present invention, the method for producing the PPS resin is not particularly limited. PPS resins include crosslinked (branched) PPS resins and linear (straight-chain) PPS resins, and in the present invention, either the crosslinked PPS resin or the linear PPS resin may be used alone, or both the crosslinked PPS resin and the linear PPS resin may be used in combination.

[0024] [Inorganic filler] The inorganic filler includes at least one of an isotropic filler and a fibrous filler. The inclusion of an isotropic filler in the resin composition reduces the anisotropy of molding shrinkage of the molded article, thereby improving the dimensional accuracy of the gears and reducing meshing errors of the gears when the resin composition is injection molded to produce the gears.

[0025] By including a fibrous filler in the resin composition, it is possible to increase the strength, such as tensile strength and bending strength, of an article molded from the resin composition. By containing an appropriate amount of both an isotropic filler and a fibrous filler in the resin composition, the resin composition can achieve a good balance between appropriate dimensional accuracy during injection molding and appropriate mechanical strength when the molded article is formed.

[0026] The content of the inorganic filler in the resin composition is preferably 5 to 65% by volume, more preferably 7 to 60% by volume, and particularly preferably 10 to 50% by volume. By keeping the content of the inorganic filler within the above range, at least one of the effects of reducing gear meshing error and increasing the mechanical strength of the gears can be stably exhibited.

[0027] Isotropic fillers refer to inorganic fillers with an aspect ratio of less than 5, and have a non-fibrous form such as granular, irregular granular, plate-like, or flat form. It is particularly preferable for isotropic fillers to have a granular form. The aspect ratio of the isotropic filler is preferably 1 or more. Here, the aspect ratio of the isotropic filler refers to the average aspect ratio of the isotropic filler, and is expressed as the ratio of the "major axis / minor axis" of the isotropic filler.

[0028] The isotropic filler has an average particle size of 0.1 μm to 200 μm, preferably 1 μm to 100 μm, and more preferably 5 μm to 70 μm. When the average particle size of the isotropic filler is 0.1 μm or more, the isotropic filler can be uniformly dispersed in the resin composition, and the anisotropy of molding shrinkage of the molded article can be effectively reduced. When the average particle size of the isotropic filler is 200 μm or less, it becomes easier to form a smooth surface for the molded article. Here, the average particle size refers to the particle size at 50% of the cumulative value (D50) in the volume particle size distribution determined by a laser diffraction / scattering method in accordance with JIS Z8825.

[0029] The content of the isotropic filler in the resin composition is preferably 1% by volume or more and 50% by volume or less, and particularly preferably 5% by volume or more and 35% by volume or less. By having an isotropic filler content of 1% by volume or more, the effect of the isotropic filler in improving the dimensional accuracy of the gear can be stably exerted. By having an isotropic filler content of 50% by volume or less, it is possible to prevent or suppress problems such as an unstable filler dispersion during kneading due to a lack of matrix resin, injection molding defects such as short shots due to reduced fluidity during molding, and wear of the molding machine cylinder due to an excess of isotropic filler.

[0030] Examples of the isotropic filler used in this embodiment include glass beads, glass flakes, calcium carbonate, silica, magnesium oxide, aluminum oxide, zinc oxide, boron nitride, magnesium hydroxide, etc., and one of these may be used alone or two or more may be used in combination. In particular, the isotropic filler is preferably glass beads.

[0031] The fibrous filler used in this embodiment includes those having a fibrous (fiber) form and those having a needle (whisker) form. In particular, the fibrous filler preferably has a fibrous form. The aspect ratio of the fibrous filler is preferably 5 or more. Here, the aspect ratio of the fibrous filler is expressed as the ratio of "average fiber length / average fiber diameter" of the fibrous filler.

[0032] The fibrous filler preferably has an average fiber length of 100 μm or more and 500 μm or less. In this case, the average fiber length of the fibrous filler is more preferably 150 μm or more and 400 μm or less, particularly 200 μm or more and 350 μm or less. Here, the average fiber length of the fibrous filler refers to the average remaining fiber length of the fibrous filler remaining in the molded body obtained by molding the resin composition. The average fiber length of the fibrous filler (average remaining fiber length) can be determined by the following method. First, a molded body of the resin composition is heated and decomposed to remove the fibrous filler, and the removed fibrous filler is dispersed in a liquid such as water and then dried. Thereafter, the fibrous filler is photographed using an optical microscope or the like, and the fiber lengths of approximately 500 fibrous fillers are measured from the photographed image and the average is calculated to determine the average fiber length (average remaining fiber length) of the fibrous filler of the resin composition.

[0033] When the average fiber length (average remaining fiber length) of the fibrous filler is 100 μm or more, the mechanical strength of the molded article can be effectively improved. When the average fiber length of the fibrous filler is 500 μm or less, the fibrous filler can be easily dispersed uniformly in the resin composition.

[0034] The fibrous filler has an average fiber diameter of 1 μm or more and 30 μm or less, preferably 5 μm or more and 20 μm or less. When the average fiber diameter of the fibrous filler is 1 μm or more, the mechanical strength of the molded article can be effectively improved. When the average fiber diameter of the fibrous filler is 30 μm or less, the fibrous filler can be easily dispersed uniformly in the resin composition.

[0035] The content of the fibrous filler in the resin composition is 1% by volume or more and 50% by volume or less, preferably 2% by volume or more and 35% by volume or less. By having a fibrous filler content of 1% by volume or more, the effect of increasing mechanical strength due to the fibrous filler can be stably exerted. By having a fibrous filler content of 50% by volume or less, it is possible to prevent or suppress problems such as an unstable filler dispersion state during kneading due to a lack of matrix resin, injection molding defects such as short shots due to reduced fluidity during molding, and wear of the molding machine cylinder due to an excess of fibrous filler.

[0036] In the resin composition, the volume ratio of the fibrous filler is preferably smaller than the volume ratio of the isotropic filler. This improves the mechanical strength of the gear while ensuring high dimensional accuracy. For example, in this embodiment, the volume ratio of the fibrous filler to the total inorganic filler is preferably 0.1% or more and 45% or less.

[0037] Examples of the fibrous filler used in this embodiment include carbon fibers (chopped carbon fibers, milled carbon fibers, etc.), glass fibers, ceramic fibers such as wollastonite, silica fibers, and alumina fibers, and metal fibers such as stainless steel fibers and aluminum fibers. One type of fibrous filler selected from these may be used alone, or two or more types may be used in combination. In particular, the fibrous filler is preferably carbon fiber (particularly, milled carbon fiber) or glass fiber, which can reduce material costs.

[0038] [PTFE resin] The resin composition of this embodiment contains a PTFE resin. The inclusion of the PTFE resin reduces the dynamic friction coefficient of a gear injection-molded from the resin composition, thereby improving the sliding properties of the gear. Specifically, the gear molded from the resin composition of this embodiment can have a dynamic friction coefficient of less than 0.35, preferably less than 0.20. In this case, the content of the PTFE resin in the resin composition is preferably 1% by volume or more and 15% by volume or less, particularly preferably 5% by volume or more and 10% by volume or less. The resin composition of the present invention does not necessarily contain a PTFE resin.

[0039] [MD shrinkage rate, TD shrinkage rate and 3D shrinkage rate] Regarding the resin composition of this embodiment, when a small square plate test piece (type D2) of 60 mm in length × 60 mm in width × 2 mm in thickness as specified in JIS K7152-3 was produced using an injection molding machine, the molding shrinkage rate of the test piece in the M direction was determined as the MD shrinkage rate S MD The molding shrinkage of the test piece in the T direction is defined as the TD shrinkage S TD Furthermore, the molding shrinkage of the test piece in the three dimensions of the M, T, and Z directions is defined as the 3D shrinkage S 3D It is stipulated that:

[0040] In the above definition, the M direction refers to the direction parallel to the flow direction of the molten resin flowing inside the mold during injection molding. The T direction refers to the direction perpendicular to the M direction (the flow direction of the molten resin) within the 60 mm x 60 mm front or back surface of the test specimen, and is also the width direction perpendicular to the M direction and the thickness direction of the test specimen. The Z direction refers to the thickness direction of the test specimen, and is the direction perpendicular to the M direction and the T direction. The molding shrinkage rate is the ratio "(L0 - L1) / L0" of the shrinkage dimension of the test specimen (i.e., the difference between the cavity space dimension L0 and the test specimen dimension L1) to the cavity space dimension L0 of the mold.

[0041] In this case, the resin composition of the present embodiment has a 3D shrinkage ratio S 3D From this, the MD shrinkage ratio S of the test piece in the M direction MDThe shrinkage difference (S 3D -S MD This satisfies the condition (first condition) that the value of the shrinkage rate difference (S 3D -S MD ) represents the difference in outer diameter of the gear when the gear is considered as a cylinder, as explained above with reference to formula (1). 3D -S MD By using a resin composition in which the porosity is 3.0% or less, the dimensional accuracy during injection molding of gears can be improved, and as a result, gears with reduced outer diameter differences can be manufactured.

[0042] Furthermore, the resin composition of this embodiment has an MD shrinkage ratio S MD TD shrinkage rate S TD Shrinkage ratio (S TD / S MD ) is 3.0 or less (second condition). By injection-molding gears using a resin composition that satisfies not only the first condition regarding shrinkage difference but also the second condition regarding shrinkage ratio, the dimensional accuracy of the injection molding can be further improved, and gears with meshing error of grade 3 or higher on the one-pitch meshing grade specified in JGMA 116-02 can be consistently manufactured.

[0043] The difference in shrinkage rate (S 3D -S MD ) and shrinkage ratio (S TD / S MD ) can be adjusted to fall within the above ranges by, for example, changing the content ratio (volume ratio) of the PPS resin and the inorganic filler, the content ratio (volume ratio) of the isotropic filler and the fibrous filler in the inorganic filler, the materials of the isotropic filler and the fibrous filler, the aspect ratio and average particle size of the isotropic filler, the fiber length and fiber diameter of the fibrous filler, etc.

[0044] [Plastic gears] The resin gear of this embodiment is formed by injection molding a resin composition that satisfies both of the above-mentioned conditions 1 and 2. This resin gear has a gear body and a plurality of teeth arranged at a constant pitch on the outer periphery of the gear body.

[0045] As described above, the resin gear of this embodiment contains at least one of an isotropic filler and a fibrous filler, and preferably both an isotropic filler and a fibrous filler, as the inorganic filler in an appropriate proportion that satisfies the first and second conditions described above, thereby reducing the meshing error specified in JGMA 116-02. In particular, in this embodiment, the resin gears can be manufactured with high dimensional accuracy due to the inclusion of isotropic filler, so that the gear meshing error can be made to be grade 3 or higher in one-pitch meshing grade.

[0046] At the same time, the resin gear of this embodiment can have high mechanical strength, with a tensile strength of 100 MPa or more, preferably 120 MPa or more, due to the inclusion of fibrous filler, and / or can have high mechanical strength, with a bending strength of 165 MPa or more, preferably 185 MPa or more.

[0047] Therefore, while there has conventionally been a trade-off between the mechanical strength and dimensional accuracy of molded articles in terms of materials, the resin gear of this embodiment can achieve a good balance between good dimensional accuracy and high mechanical strength by using a resin composition that satisfies the above-mentioned first and second conditions. Resin gears with small meshing error and high tensile strength and / or bending strength as described above are suitable for use in gears for office automation equipment and gears for automobile parts, which are subject to high temperatures and high pressures. [Example]

[0048] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. First, each of the resin compositions of Examples 1 to 9 and Comparative Examples 1 to 5 was prepared by mixing a PPS resin (A900B1 manufactured by Toray Industries, Inc.), glass fiber (CSF 3PE-941HS manufactured by Nitto Boseki Co., Ltd., fiber length 3000 μm, fiber diameter 13 μm), chopped carbon fiber (Tenax-J HT C702 manufactured by Teijin Limited, fiber length 6000 μm, fiber diameter 7 μm), milled carbon fiber (Tenax-J HT C702 manufactured by Teijin Limited, fiber length 6000 μm, fiber diameter 7 μm), and a cellulose ester resin (C6000, C ... The coating was prepared as described below using glass beads (Unitika Glass Beads Co., Ltd., UB-02EG, particle size 45 μm), wollastonite (Nippon Talc Co., Ltd., WP-200, fiber length 40 μm, fiber diameter 13 μm), mica (Yamaguchi Mica Co., Ltd., AB-25S, particle size 24 μm), and PPS / PTFE30 (Idemitsu Fine Composites Co., Ltd., N501F3).

[0049] Examples 1 and 2 The resin compositions of Examples 1 and 2 were prepared by injection molding a material in which PAN-based carbon fiber was pre-mixed with PPS resin, a material in which glass beads were pre-mixed with PPS resin, and a material in which PTFE resin was added to PPS resin (PPS / PTFE30), so that the volume ratios of PPS resin, fibrous filler (chopped carbon fiber), isotropic filler (glass beads), and PTFE resin were as shown in Table 1 below.

[0050] Example 3 A material in which PAN-based carbon fiber was pre-mixed with PPS resin, and a material in which glass beads were pre-mixed with PPS resin were injection molded to prepare the resin composition of Example 3, in which the volume ratios of PPS resin, fibrous filler (chopped carbon fiber), and isotropic filler (glass beads) were as shown in Table 1 below.

[0051] Example 4 A material in which glass fiber was pre-mixed with PPS resin, and a material in which glass beads were pre-mixed with PPS resin, were injection molded to prepare the resin composition of Example 4, in which the volume ratios of PPS resin, fibrous filler (glass fiber), and isotropic filler (glass beads) were as shown in Table 1 below.

[0052] Example 5 A material in which PAN-based carbon fiber was pre-mixed with PPS resin, and a material in which glass beads were pre-mixed with PPS resin were injection molded to prepare the resin composition of Example 5, in which the volume ratios of PPS resin, fibrous filler (chopped carbon fiber), and isotropic filler (glass beads) were as shown in Table 1 below.

[0053] Example 6 A material in which glass fiber was pre-mixed with PPS resin, and a material in which glass beads were pre-mixed with PPS resin, were injection molded to prepare the resin composition of Example 6, in which the volume ratios of PPS resin, fibrous filler (glass fiber), and isotropic filler (glass beads) were as shown in Table 1 below.

[0054] Example 7 The resin composition of Example 7 was prepared by kneading the glass beads into the PPS resin so that the volume ratio of the PPS resin and the isotropic filler (glass beads) was as shown in Table 1 below.

[0055] Example 8 The resin composition of Example 8 was prepared by kneading the PPS resin with wollastonite so that the volume ratio of the PPS resin and the fibrous filler (wollastonite) was as shown in Table 1 below.

[0056] Example 9 The resin composition of Example 9 was prepared by kneading crushed PAN-based carbon fiber into PPS resin so that the volume ratio of PPS resin and fibrous filler (milled carbon fiber) was as shown in Table 1 below.

[0057] (Comparative Example 1) A material in which PAN-based carbon fiber was pre-mixed with PPS resin, and a material in which glass beads were pre-mixed with PPS resin were injection molded to prepare the resin composition of Comparative Example 1, in which the volume ratios of PPS resin, fibrous filler (chopped carbon fiber), and isotropic filler (glass beads) were as shown in Table 2 below.

[0058] (Comparative Example 2) The resin composition of Comparative Example 2 was prepared by kneading mica into the PPS resin so that the volume ratio of the PPS resin and mica was as shown in Table 2 below.

[0059] (Comparative Example 3) A material in which glass fiber was pre-mixed with PPS resin, a material in which glass beads were pre-mixed with PPS resin, and a material in which PTFE resin was added to PPS resin (PPS / PTFE30) were injection molded to prepare the resin composition of Comparative Example 3, in which the volume ratios of PPS resin, fibrous filler (glass fiber), isotropic filler (glass beads), and PTFE resin were as shown in Table 2 below.

[0060] Comparative Example 4 The resin composition of Comparative Example 4 was prepared by kneading the glass fiber into the PPS resin so that the volume ratio of the PPS resin and the fibrous filler (glass fiber) was as shown in Table 2 below.

[0061] (Comparative Example 5) The resin composition of Comparative Example 5 was prepared by kneading the PAN-based carbon fiber into the PPS resin so that the volume ratio of the PPS resin and the fibrous filler (chopped carbon fiber) was as shown in Table 2 below.

[0062] [Volume fraction of inorganic filler, volume ratio of fibrous filler, average fiber length in molded body] For each of the resin compositions of Examples 1 to 9 and Comparative Examples 1 to 5, the volume fraction of the inorganic filler (fibrous filler and isotropic filler) contained in the resin composition, the volume ratio of the fibrous filler in the inorganic filler, and the average fiber length (average remaining fiber length) in the molded body molded from each resin composition are shown in Tables 1 and 2.

[0063] [Mold shrinkage rate] Using the resin compositions of Examples 1 to 9 and Comparative Examples 1 to 5, small square plate test pieces (Type D2) of 60 mm x 60 mm x 2 mm were prepared from each resin composition by injection molding in accordance with JIS K7152-3. Thereafter, the MD, TD, and ZD dimensions of the mold used for injection molding and the MD, TD, and ZD dimensions of the small square plate test pieces were measured, and the shrinkage ratio (S TD / S MD ) and shrinkage rate difference (S 3D -S MD For each resin composition, test specimens were prepared and the shrinkage ratio (S TD / S MD ) · Shrinkage rate difference (S 3D -S MD ) was calculated three times, and the shrinkage ratio (S TD / S MD ) and shrinkage rate difference (S 3D -S MD The average values of each of these are shown in Tables 1 and 2.

[0064] [Gear meshing test] Helical gear-shaped test pieces were injection-molded using each of the resin compositions of Examples 1 to 9 and Comparative Examples 1 to 5. The resulting helical gear-shaped test pieces were attached to a gear meshing tester (manufactured by Osaka Precision Machinery Co., Ltd., model GTR-4LS) to measure the gear pitch meshing error. Furthermore, the measured pitch meshing error was used to determine the pitch meshing grade in accordance with the JGMA 116-02 standard. The pitch meshing error and pitch meshing grade for each resin composition are shown together in Tables 1 and 2.

[0065] [Tensile strength] Dumbbell-shaped test pieces were injection molded using each of the resin compositions of Examples 1 to 9 and Comparative Examples 1 to 5. The obtained test pieces were attached to a testing machine, and a tensile test was carried out in accordance with JIS K7161, with a chuck distance of 115 mm and a tensile speed of 5 mm / min at a temperature of 23°C, to measure the tensile stress at break of the test pieces. For each resin composition, the tensile stress at break was measured three times, and the average value of the three measurements is shown as the tensile strength in Tables 1 and 2.

[0066] [Bending strength] Dumbbell-shaped test pieces were injection-molded using each of the resin compositions of Examples 1 to 9 and Comparative Examples 1 to 5, and both ends of the resulting molded bodies were cut to prepare 80 mm long strip-shaped test pieces. The resulting test pieces were attached to a testing machine and subjected to a three-point bending test in accordance with JIS K7171, with a support distance of 64 mm and a bending speed of 15 mm / min at a temperature of 23°C, to measure the fracture stress of the test pieces. The three-point bending test was performed three times for each resin composition, and the average value of the three measurements is shown in Tables 1 and 2 as the bending strength.

[0067] [Kinematic friction coefficient] Cylindrical test specimens were injection molded according to JIS K7218-1986 using the resin compositions of Examples 1 to 9 and Comparative Examples 1 to 5. The test specimens were attached to a Suzuki friction and wear tester, and friction and wear tests were carried out under the following conditions: a temperature of 150°C, a mating material of SUS303 with a ten-point surface roughness Ra of 0.5 μm, a surface pressure of 2 MPa, a sliding speed of 300 mm / sec, a test time of 3 hours, and no lubricant, to determine the dynamic friction coefficient. The dynamic friction coefficients determined for each resin composition are shown in Tables 1 and 2.

[0068] [Table 1]

[0069] [Table 2]

[0070] As shown in Table 1, the shrinkage ratio (S TD / S MD ) is 3.0 or less, and the shrinkage rate difference (S 3D -S MD It was confirmed that the resin compositions of Examples 1 to 9, which satisfy both the first condition that the meshing error is 3.0% or less, can be used to mold gears with high dimensional accuracy, with meshing grade of 3 or higher (meshing error of 16.0 μm or less).

[0071] Furthermore, among Examples 1 to 9 that satisfy the first and second conditions, it was confirmed that the molded bodies of the resin compositions of Examples 1 to 6, which contain chopped carbon fiber or glass fiber as the fibrous filler and glass beads as the isotropic filler, have high mechanical strength, with a tensile strength of 100 MPa or more and a bending strength of 165 MPa or more.

[0072] Furthermore, the molded articles of Examples 1 to 4 had mechanical strengths of 120 MPa or more in tensile strength and 185 MPa or more in bending strength. In particular, the molded articles of Examples 2 and 4, which contained 20 vol% or more of isotropic filler (glass beads) and 7 vol% or more of chopped carbon fiber or 10 vol% or more of glass fiber, had bending strengths of 190 MPa or more.

[0073] As described above, the composite material contains a fibrous filler of chopped carbon fiber or glass fiber and an isotropic filler (glass beads), and has a shrinkage ratio (S TD / S MD ) is 3.0 or less, and the shrinkage rate difference (S 3D -S MD It was confirmed that the resin compositions of Examples 1 to 6, in which the content of SiO 2 was 3.0% or less, made it possible to mold resin gears that had a good balance between high dimensional accuracy and high mechanical strength.

[0074] In this case, the fibrous filler (chopped carbon fiber or glass fiber) preferably has an original fiber length of 3000 μm or more. The isotropic filler (glass beads) preferably has an average particle size of, for example, 0.1 μm or more and 200 μm or less, particularly 5 μm or more and 70 μm or less.

[0075] Furthermore, it was confirmed that the resin compositions of Examples 1 to 6, which combine dimensional accuracy and mechanical strength, had an average fiber length in the molded product of 100 μm or more. That is, by molding a gear using a resin composition with an average fiber length (average remaining fiber length) of 100 μm or more, preferably a resin composition with an average fiber length of 200 μm to 350 μm, the molded gear can stably possess high dimensional accuracy and high mechanical strength.

[0076] Furthermore, it was confirmed that the resin compositions of Examples 1 to 3 and 5 containing chopped carbon fiber could be used to mold molded articles with a dynamic friction coefficient of less than 0.35. In particular, it was confirmed that the resin compositions of Examples 1 and 2 containing chopped carbon fiber and PTFE resin could be used to mold molded articles with a dynamic friction coefficient of less than 0.20.

[0077] In contrast, in the resin compositions of Comparative Examples 1 to 5, which did not satisfy at least one of the first and second conditions, the meshing grade of the molded gears was Grade 4 or lower, resulting in a decrease in dimensional accuracy during injection molding.

[0078] The present invention is not limited to the above-described embodiments, and various modifications are possible as long as they have substantially the same configuration as that described in the claims of the present invention and provide similar effects. For example, in the above-described embodiment, the molded article obtained by injection molding the resin composition is described as a gear, but in the present invention, the molded article molded from the resin composition is not limited to a gear, and the resin composition of the present invention may be used to mold an article other than a gear.

Claims

1. A resin composition containing a base resin mainly composed of polyphenylene sulfide and an inorganic filler, Regarding a test piece obtained by injection molding the resin composition in a mold in accordance with JIS K7152-3, the shrinkage rate of the test piece relative to the cavity space of the mold in the M direction parallel to the flow direction of the molten resin during the injection molding is defined as the MD shrinkage rate S ＭＤ The shrinkage rate of the test piece relative to the cavity space in the T direction perpendicular to the flow direction is defined as the TD shrinkage rate S ＴＤ When the MD shrinkage ratio S ＭＤ The TD shrinkage rate S ＴＤ The shrinkage ratio (S ＴＤ / S ＭＤ ) is 3.0 or less, The 3D shrinkage ratio S of the test piece relative to the cavity space in the three-dimensional directions of the M direction, the T direction, and the Z direction which is the thickness direction of the test piece. ３Ｄ From the above, the MD shrinkage rate S ＭＤ The shrinkage difference (S ３Ｄ -S ＭＤ ) is 3.0% or less A resin composition characterized by:

2. 2. The resin composition according to claim 1, wherein a molded article obtained by molding the resin composition has a tensile strength of 100 MPa or more.

3. 3. The resin composition according to claim 2, wherein the inorganic filler comprises an isotropic filler having an aspect ratio of less than 5 and a fibrous filler.

4. 4. The resin composition according to claim 3, wherein the average fiber length of the fibrous filler is 100 μm or more and 500 μm or less.

5. 4. The resin composition according to claim 3, wherein the volume ratio of the fibrous filler in the inorganic filler is 0.1% or more and 45% or less.

6. 2. The resin composition according to claim 1, wherein the content of the inorganic filler is 5% by volume or more and 65% by volume or less.

7. A synthetic resin gear formed from the resin composition according to any one of claims 1 to 6.

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