JP7787396B2 - Resin composition for sliding bearing and sliding bearing - Google Patents

Description

The present invention relates to a resin composition for sliding bearings and sliding bearings.

Conventional resin materials used in bearings for office equipment, automobiles, machine tools, etc. include polyamide 6 (PA6), polyamide 66 (PA66), polyacetal (polyoxymethylene) (POM), and polyphenylene sulfide (PPS). The friction and wear characteristics of bearings made from these resin materials are stable at room temperature, but tend to deteriorate rapidly at temperatures around 100°C, making them unsuitable for use as bearings. Furthermore, PA6 and PA66 are highly hygroscopic and have poor dimensional accuracy, while POM can easily decompose during melt molding depending on the type of filler.

As a solution to this problem, bearings have been proposed that use a polyamide resin, the main components of which are terephthalic acid and 1,10-decanediamine, as the constituent resin material (see, for example, Patent Documents 1 and 2).

Patent Document 1 describes a rolling bearing comprising an inner ring, an outer ring, multiple rolling elements interposed between the inner and outer rings, and a cage that holds the rolling elements. The cage is an injection-molded product made from a resin composition containing a polyamide resin made from a dicarboxylic acid component primarily composed of terephthalic acid and a diamine component primarily composed of 1,10-decanediamine, glass fiber or carbon fiber, and a fluororesin, each in a specified blend ratio. The document states that having a cage with this configuration makes it possible to provide a rolling bearing cage that has high rigidity (elastic modulus), minimizes deformation even under conditions of high temperature and high-speed rotation, reduces heat generation due to the lubricating effect of the fluororesin, and is able to prevent seizure and damage even when used at high speeds.

Patent Document 2 describes a semi-aromatic polyamide resin composition containing 100 parts by mass of a semi-aromatic polyamide (A) primarily composed of terephthalic acid and 1,10-decanediamine, 0.5 to 80 parts by mass of a friction modifier (B), 0.5 to 10 parts by mass of a fibrous reinforcing material (C), and 5 to 60 parts by mass of a flame retardant (D), wherein (A) contains 0.3 to 4.0 mol % of a stearic acid component relative to the total monomers constituting (A), and describes a molded article of this semi-aromatic polyamide resin composition for use as a sliding member. It also describes that the average fiber diameter and fiber length of the fibrous reinforcing material (C) are preferably in the ranges of 3 to 30 μm and 0.1 to 7 mm, respectively, and that preferred types of fibrous reinforcing material (C) are glass fiber, organic fiber, and carbon fiber. This composition is said to provide a semi-aromatic polyamide resin composition with improved mechanical properties, heat resistance, and flame retardancy without sacrificing sliding properties.

Patent No. 6697235 Patent No. 6249711

Patent Document 1 does not specifically mention the average fiber diameter or average fiber length of the glass fibers and carbon fibers used, but gives specific examples such as glass fibers with an average fiber diameter of 10 μm and an average fiber length of 3 mm, and carbon fibers with an average fiber diameter of 7 μm and an average fiber length of 6 mm. Patent Document 2, as mentioned above, gives preferred ranges for the average fiber diameter and average fiber length of the fibrous reinforcing material (C) used, and gives specific examples such as glass fibers with an average fiber diameter of 10 μm and an average fiber length of 3 mm, carbon fibers with an average fiber diameter of 7 μm and an average fiber length of 6 mm, and aramid fibers with an average fiber diameter of 12 μm and an average fiber length of 1 mm.

However, when fibrous reinforcing materials with an average fiber diameter of 3 μm or more and an average fiber diameter of 0.1 mm or more, as shown in Patent Documents 1 and 2, are used, the fibrous reinforcing materials are not sufficiently uniformly dispersed in the resin composition. Furthermore, when the resin composition is molded into a product, the linear expansion coefficient of the molded product is affected by the fiber orientation, making it difficult to obtain a desired shape with good dimensional accuracy (hereinafter referred to as "shape accuracy"). In particular, it has been found that at temperatures higher than room temperature, the degree of deformation of the molded product tends to increase due to the influence of the fiber orientation. Furthermore, as a result, when the molded product is used in a sliding part, it is found that play between the molded product and the mating material increases, impairing its function as a mechanical part such as a sliding bearing and reducing its friction and wear characteristics.

The object of the present invention is therefore to provide a resin composition for sliding bearings that can provide molded articles with stable friction and wear properties both at room temperature and at high temperatures of around 100°C, and to provide a sliding bearing having a sliding part molded from this resin composition for sliding bearings.

The inventors conducted extensive research to solve the aforementioned problems. As a result, they discovered that the aforementioned problems can be solved by using a resin composition containing a specific base resin, a specific fibrous inorganic filler, and a solid lubricant. The gist of the present invention is as follows:

(1) A resin composition for a sliding bearing comprising a base resin, a fibrous inorganic filler, and a solid lubricant, wherein the base resin is a semi-aromatic polyamide resin whose main components are terephthalic acid and 1,10-decanediamine, and the fibrous inorganic filler has an average fiber diameter of 3 μm or less and an average fiber length of 2 to 50 μm.
(2) The sliding bearing resin composition according to the preceding paragraph (1), wherein the fibrous inorganic filler has a Mohs hardness of 4 or less.
(3) The sliding bearing resin composition according to the preceding item (1) or (2), in which the fibrous inorganic filler is at least one type of whisker selected from calcium carbonate whiskers, zinc oxide whiskers, potassium titanate whiskers, and magnesium sulfate whiskers.
(4) The sliding bearing resin composition according to any one of (1) to (3), wherein the solid lubricant is at least one selected from the group consisting of fluororesin, graphite, molybdenum disulfide, zinc sulfide, metal oxides, and metal carbonates.
(5) The sliding bearing resin composition according to any one of (1) to (4) above, comprising 55 to 88% by mass of the base resin, 5 to 20% by mass of the fibrous inorganic filler, and 7 to 35% by mass of the solid lubricant.
(6) A sliding bearing having, in a sliding part, an article molded from the resin composition for a sliding bearing according to any one of (1) to (5) above.

The present invention provides a resin composition for sliding bearings that can provide molded articles with stable friction and wear properties both at room temperature and at high temperatures of around 100°C, as well as a sliding bearing having a sliding part molded from this resin composition for sliding bearings.

1A is a plan view schematically illustrating the dumbbell test pieces prepared in the examples and comparative examples, and FIG. 1B is a side view of the plan view shown in FIG.

A resin composition for sliding bearings according to an embodiment of the present invention (hereinafter sometimes simply referred to as the "resin composition") contains a base resin, a fibrous inorganic filler, and a solid lubricant. The base resin is a semi-aromatic polyamide resin whose main components are terephthalic acid and 1,10-decanediamine. The fibrous inorganic filler has an average fiber diameter of 3 μm or less and an average fiber length of 2 to 50 μm.

When a resin composition contains a fibrous inorganic filler with an average fiber diameter equal to or smaller than that of conventional fibrous reinforcing materials such as glass fiber or carbon fiber, the resin composition is more likely to achieve uniform dispersion of the fibrous inorganic filler within the resin composition and its molded body, and the orientation of the fibrous inorganic filler can be suppressed, thereby improving the shape precision of the molded body. Furthermore, as described below, the specific semi-aromatic polyamide resin used as the base resin has a glass transition temperature (Tg) of 120°C or higher and can maintain good mechanical properties even at high temperatures of around 100°C. The solid lubricant can impart low friction properties. Thus, by using the specific fibrous inorganic filler, in combination with the functions of the specific semi-aromatic polyamide resin and solid lubricant, the resin composition is believed to be able to provide a molded body with stable friction and wear properties both at room temperature and at high temperatures of around 100°C.

The semi-aromatic polyamide resin used as the base resin is primarily composed of terephthalic acid, a dicarboxylic acid component, and 1,10-decanediamine, a diamine component, and may be, for example, a polycondensate of a dicarboxylic acid component and a diamine component. Examples of such semi-aromatic polyamide resins that can be used include those described in Patent Documents 1 and 2, and Japanese Patent No. 5,804,313.

Terephthalic acid preferably accounts for 50 mol% or more of the dicarboxylic acid component, more preferably 95 mol% or more, and even more preferably 100 mol%. The dicarboxylic acid component may contain aromatic dicarboxylic acids and aliphatic dicarboxylic acids other than terephthalic acid. Examples of other semi-aromatic dicarboxylic acids include phthalic acid, isophthalic acid, and naphthalenedicarboxylic acid. Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid.

1,10-decanediamine is preferably contained in the diamine component at 50 mol% or more, more preferably at 95 mol% or more, and even more preferably at 100 mol%. The diamine component may contain aliphatic diamine components, alicyclic diamine components, and aromatic diamine components other than 1,10-dodecanediamine. Examples of other aliphatic diamine components include 1,2-ethanediamine, 1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,11-undecanediamine, and 1,12-dodecanediamine. Examples of alicyclic diamine components include cyclohexanediamine. Examples of aromatic diamine components include xylylenediamine.

The semi-aromatic polyamide resin may be (a) a polycondensation product of the aforementioned dicarboxylic acid component and diamine component, or (b) one or more components selected from an aminocarboxylic acid component and a lactam component that can be condensed with the aforementioned dicarboxylic acid component and diamine component. In these cases, the content of units composed of terephthalic acid and 1,10-decanediamine in the semi-aromatic polyamide resin is preferably 50 to 100 mol%, more preferably 95 to 100 mol%, and particularly preferably 100 mol% in the case of (a), and preferably 50 to 98 mol%, more preferably 95 to 98 mol% in the case of (b).

The Tg of the semi-aromatic polyamide resin described above is preferably 120°C or higher. The Tg of the semi-aromatic polyamide resin can be measured using a differential scanning calorimeter (DSC) in accordance with JIS K7121. A measurement sample is prepared by rapidly cooling the semi-aromatic polyamide resin from a heated molten state to room temperature in an inert gas atmosphere. When the measurement sample is measured with DSC, the baseline shift temperature that appears on the resulting DSC curve can be taken as the Tg.

From the standpoint of mechanical properties and moldability, the weight-average molecular weight of the semi-aromatic polyamide resin is preferably 15,000 to 50,000, and more preferably 26,000 to 50,000.

Using terephthalic acid as the primary component can impart good heat resistance and high rigidity to semi-aromatic polyamide resins. Using 1,10-decanediamine as the primary component, coupled with the use of an aromatic carboxylic acid, can impart good moisture absorption to semi-aromatic polyamide resins. This allows for good shape precision and dimensional stability in molded articles. Because both terephthalic acid and 1,10-decanediamine have highly symmetric chemical structures, using them as the primary components can enhance crystallinity. As a result, crystallization during molding is rapid, shortening the molding cycle and improving demoldability. Thus, semi-aromatic polyamide resins primarily composed of terephthalic acid and 1,10-decanediamine are well suited for producing molded articles. Furthermore, 1,10-decanediamine is preferably derived from castor oil, which is obtained from the inedible plant known as castor bean. By using plant-based biomass-derived materials in this way, environmentally friendly resin compositions and sliding bearings can be provided.

The fibrous inorganic filler has an average fiber diameter of 3 μm or less and an average fiber length of 2 to 50 μm. As mentioned above, this configuration makes it possible to uniformly disperse the fibrous inorganic filler in the resin composition, suppressing the effects of fiber orientation. This, combined with the good shape precision and dimensional stability properties of the semi-aromatic polyamide resin mentioned above, allows for good shape precision in the molded article. It can also provide a reinforcing effect to the molded article. The average fiber diameter and average fiber length can be measured and calculated using an electron microscope or optical microscope.

Here, the orientation of fibers (fibrous inorganic fillers) in molded articles is speculated as follows, but is not limited to this speculation. The orientation of fibers in molded articles tends to be affected by the flow direction of the resin composition during melt molding. For example, the length of the fibers tends to be oriented parallel to the flow direction of the molten resin composition during molding. Therefore, while the fibers suppress linear expansion in the direction parallel to the flow direction of the resin composition, they tend not to suppress linear expansion in the direction perpendicular to the flow direction. As a result, when temperatures rise from room temperature to approximately 100°C, the difference in linear expansion coefficient between the flow direction and the perpendicular direction in the molded article increases, resulting in significant deformation, reduced dimensional stability, and an inability to ensure shape precision. For example, fibrous reinforcing materials such as glass fibers and carbon fibers described in Patent Documents 1 and 2 are strongly affected by fiber orientation due to their large average fiber diameters and average fiber lengths, which is thought to reduce the dimensional stability of molded articles and make it difficult to ensure shape precision. In contrast, the specific fibrous inorganic filler described above has specific dimensions that are smaller than conventional fillers, which is thought to significantly suppress the orientation of the fibrous inorganic filler within the molded body as described above. Furthermore, large fibers like those in conventional fibrous reinforcing materials have low dispersibility and are unevenly distributed within the molded body, which, combined with the orientation of the fibers, is thought to result in greater deformation.

There are no particular limitations on such fibrous inorganic fillers, as long as they have the average fiber diameter and fiber length described above. However, from the perspective of aggressiveness toward mating materials when the molded article is used as the sliding part of a plain bearing, fillers with a Mohs hardness of 4 or less are preferred. Glass fiber and general carbon fiber have a Mohs hardness of greater than 5. Therefore, using a fibrous inorganic filler with a Mohs hardness of 4 or less can suppress the aggressiveness toward mating materials in the sliding part of a plain bearing that occurs when using conventional fibrous reinforcing materials such as glass fiber and general carbon fiber, while also imparting a certain degree of reinforcing effect to molded articles containing the fibrous inorganic filler. Furthermore, when whiskers, as described below, are included as a fibrous inorganic filler with a Mohs hardness of 4 or less, the anisotropy of the thermal expansion coefficient caused by conventional fibrous reinforcing materials can be more effectively suppressed in injection-molded articles of the resin composition.

Specific examples of fibrous inorganic fillers include whiskers, such as calcium carbonate whiskers, zinc oxide whiskers, potassium titanate whiskers, and magnesium sulfate whiskers.

The above-mentioned fibrous inorganic fillers may be used alone or in combination of two or more. When whiskers are used as the fibrous inorganic filler, the fibrous inorganic filler is preferably at least one selected from calcium carbonate whiskers, zinc oxide whiskers, potassium titanate whiskers, and magnesium sulfate whiskers.

Solid lubricants that can improve the sliding properties of the compact can be used, and examples include fluororesin, graphite, molybdenum disulfide, zinc sulfide, metal oxides, and metal carbonates. There are no particular limitations on the form of the solid lubricant, as long as it can impart lubricity, and examples include powders.

The fluororesin that constitutes the fluororesin may be, for example, those described in Patent Documents 1 and 2. Examples include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-ethylene copolymer (ETFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF). Of these, PTFE, PFA, and FEP are preferred, with PTFE being particularly preferred. While virgin PTFE may be used, from the standpoint of moldability, a powder of sintered virgin material, such as recycled PTFE, is preferred.

Examples of metal oxides include silica, magnesium oxide, and zinc oxide.

Examples of metal carbonates include calcium carbonate, barium carbonate, potassium carbonate, and sodium carbonate.

The solid lubricant used is preferably at least one selected from fluororesin, graphite, molybdenum disulfide, zinc sulfide, metal oxides, and metal carbonates, and more preferably at least fluororesin.

The content of each of the aforementioned components can be determined as appropriate depending on the intended use of the sliding bearing, but from the perspective of friction and wear characteristics and shape precision when used in the sliding part of a sliding bearing, it is preferable for the resin composition to contain 55 to 88 mass% of base resin, 5 to 20 mass% of fibrous inorganic filler, and 7 to 35 mass% of solid lubricant, relative to the total amount of the resin composition.

In addition to the components described above, the resin composition may contain other components as needed. Examples of such components include elastomers, colorants, flame retardants, weathering agents, antioxidants, heat stabilizers, mold release agents, lubricants, nucleating agents, plasticizers, and antistatic agents. The total content of these optional components can be, for example, 0.1 to 5% by mass of the total amount of the resin composition.

The above-mentioned resin compositions can be obtained by mixing and kneading the components according to standard methods. Furthermore, after kneading, the mixture can be formed into various forms, such as pellets or powder, as needed. For example, the components that make up the resin composition can be mixed using a general-purpose mixer, and the resulting mixture can be melt-kneaded in a melt extruder such as a single-screw kneading extruder or a twin-screw kneading extruder. The molten material can then be extruded into strands and pelletized to obtain pellets for molding. Alternatively, the molten mixture obtained by a specified method can be hot-cut or underwater-cut into pellets to obtain pellets for molding. Alternatively, the molten mixture can be extruded into a block, and the molded product can be pulverized into a powder to obtain powder for molding.

A sliding bearing according to an embodiment of the present invention has, in its sliding section, an article molded from the aforementioned resin composition for sliding bearings. There are no particular limitations on the method for molding the molded article, but injection molding is preferred. There are no particular limitations on the structure of the injection molding mold, and for example, a single-point side gate mold, a multi-point pin gate mold, a disc gate mold, etc. can be used. With the aforementioned resin composition, a molded article with good shape precision can be obtained even with a single-point side gate mold, which has a simple mold structure and is cost-effective, but which generally tends to cause welds in the molded article. If a weld occurs in the molded article, the orientation of the fibers in the vicinity of the weld becomes disrupted, reducing shape precision. However, the aforementioned specific fibrous inorganic filler can suppress the effects of orientation, thereby preventing a decrease in shape precision.

The shape precision of an injection-molded article obtained by injection molding a resin composition can be confirmed, for example, by the ratio (TD/MD) of the linear expansion coefficient in the flow direction (MD) of the resin composition in the injection-molded article to the direction perpendicular to this flow direction (TD). When the linear expansion coefficient ratio (TD/MD) is between 1.00 and 1.50, shape precision tends to be good. As a result, the molded article tends to have stable friction and wear properties both at room temperature and at high temperatures around 100°C. This ratio can be calculated, for example, by measuring the linear expansion coefficient using the method described in the Examples section below.

The shape of the sliding part (molded body) that makes up the sliding bearing can be determined appropriately depending on the application, and examples include cylindrical shapes such as bushings, and U-shapes. Of these, the resin composition described above can be suitably used for cylindrical shapes such as bushings, which require particular dimensional stability and shape precision (roundness) at high temperatures of around 100°C.

The sliding parts that make up the sliding bearing are molded from the aforementioned resin composition, resulting in good shape precision and dimensional stability from room temperature to high temperatures of around 100°C. This allows for stable sliding against the mating material, ensuring stable friction and wear characteristics both at room temperature and at high temperatures of around 100°C. Consequently, sliding bearings with this sliding part are well suited to applications that use bushings and other components, such as office equipment, automobiles, electric motors, medical equipment, home appliances, and industrial equipment.

The following describes embodiments of the present invention based on examples.

(Examples 1 to 12, Comparative Examples 1 to 8)
The components in the formulations shown in Tables 1 and 2 were dry mixed and then kneaded using a twin-screw kneading extruder (TEM-26SX, manufactured by Shibaura Machine Co., Ltd.) to obtain pellets of a resin composition for a sliding bearing. The obtained pellets of the resin composition for a sliding bearing were placed in a hot-air drying oven (PHH-201, manufactured by Espec Corporation) and dried at 120°C for 16 hours. After that, an injection molding machine (PS60E5H, manufactured by Nissei Plastic Industrial Co., Ltd.) was used to prepare various test pieces to be used for the various evaluations described below. The molding temperatures were all 310°C for the cylinder temperature and 150°C for the mold temperature.

The components shown in Tables 1 and 2 are as follows:
(1) Base resin: PA10T
XecoT (registered trademark) XN400, manufactured by Unitika Ltd., a semi-aromatic polyamide mainly composed of terephthalic acid and 1,10-decanediamine, Tg: 121°C;
・PA66
Leona, polyamide 66, manufactured by Asahi Kasei Corporation, Tg: 50°C,
・PPS
FZ2100, polyphenylene sulfide, Tg: 90°C, manufactured by DIC Corporation
(2) Solid lubricant: Polytetrafluoroethylene (Kitamura Co., Ltd., KTL-620, powder of sintered PTFE (recycled PTFE)
Graphite: Nippon Graphite Industries Co., Ltd., CPB,
(3) Fibrous inorganic filler (referred to as "inorganic filler" in Tables 1 and 2)
Calcium carbonate whiskers: Whiskers manufactured by Maruo Calcium Co., Ltd., average fiber diameter: 1.0 μm, average fiber length: 20 μm, Mohs hardness: 3 or less,
Zinc oxide whiskers: Panatetra, manufactured by Amtec Co., Ltd., average fiber diameter: 1.5 μm, average fiber length: 20 μm, Mohs hardness: 4 or less,
(4) Fibrous reinforcing material: Glass fiber manufactured by Asahi Fiberglass Co., Ltd., 03JAFT692, average fiber diameter: 10 μm, average fiber length: 3 mm, Mohs hardness: 6.5
Aramid fiber: Teijin Limited, product name: Conex, average fiber diameter: 12 μm, average fiber length: 1 mm,

(evaluation)
<Friction characteristics and wear resistance>
The pellet-shaped resin compositions obtained in the above-mentioned Examples and Comparative Examples were molded into cylindrical test pieces with a diameter of 5 mm using the above-mentioned injection molding machine.
A pin-on-disk test was carried out using a pin-on-disk friction and wear tester (Auto Pin Disk APD-101, manufactured by Starlite Industrial Co., Ltd.), the dynamic friction coefficient of each test piece was measured, and the specific wear rate was calculated. The test conditions were as follows:
Surface pressure (load on sample): 2.0 MPa
Speed (set value): 1.0 m/sec. Counterpart disc temperature: 25°C and 100°C
Lubrication: No lubrication Mating disc: SUS303 (surface roughness before test: Rz ≒ 1.5 to 2.5 μm)

The evaluation criteria for the frictional properties are as follows:
○: Friction coefficient at 25°C and 100°C is 0.30 or less,
×: The coefficient of friction at 25° C. or 100° C. is greater than 0.30. The evaluation criteria for wear resistance are as follows.
◯: The specific wear rate at 25°C and 100°C is 1.5 [×10 ⁻⁶ mm ³ /N·m] or less. ×: The specific wear rate at 25°C or 100°C is greater than 1.5 [×10 ⁻⁶ mm ³ /N·m].

The specific wear rate was calculated from the wear progress curve, which shows the change in wear rate (height) over time, using the following formula (1): In this experiment, T′ was set to 6 hours (21,600 s) after the start of the test, and T was set to 2 hours (7,200 s) after the start of the test.
K=(H'-H)/{P・V・(T'-T)} (1)
K: specific wear rate [mm ³ /N·m]
H': wear amount (height) at test time T' [mm]
H: Amount of wear (height) at test time T [mm]
P: Surface pressure [N/mm ² ]
V: Velocity [m/s]
T': Test time in steady state [s]
T: Test time in steady state [s]
Steady state: After the test time, the rate of wear has stabilized

<Shape accuracy (roundness)>
Using the pellet-shaped resin compositions obtained in the above-mentioned Examples and Comparative Examples, dumbbell test specimens conforming to ISO 527 were molded using the above-mentioned injection molding machine with a fan-gate type, single-side-gate injection mold. As shown in Figures 1(a) and 1(b), immediately after demolding from the fan-gate type, single-side-gate injection mold, dumbbell test specimen 1 has gate 2 and runner 3 connected. Gate 2 is located at one end of dumbbell test specimen 1 in the longitudinal direction, and one end of runner 3 is connected to dumbbell test specimen 1 via gate 2. The dimensions of the main parts of dumbbell test specimen 1 are as shown in Figures 1(a) and 1(b). Dimensions in Figure 1 are in millimeters. As shown in FIG. 1( a), in relation to the gate position, the length (long axis) direction of the dumbbell test piece 1 is the flow direction (MD) of the molten resin composition (the direction of the arrow indicated by reference numeral 4 in FIG. 1( a)), and the direction perpendicular to the length direction, i.e., the flow direction, in the planar direction of the dumbbell test piece 1 is the vertical direction (TD) (the direction of the arrow indicated by reference numeral 5 in FIG. 1( a)). The gate 2 and the runner 3 were cut out to obtain the dumbbell test piece 1. From the obtained dumbbell test piece 1, rectangular column-shaped test pieces measuring 4 mm × 5 mm × 10 mm were cut out in the flow direction (MD) and the vertical direction (TD), respectively, and analyzed using a thermomechanical analyzer (TMA) (EXSTAR, manufactured by Hitachi High-Tech Science Corporation) in accordance with JIS K7197. The linear expansion coefficient was measured from 25°C to 100°C using a tester (TMA/SS6100). The evaluation criteria for shape precision (roundness) are as follows: The closer the ratio of linear expansion coefficients TD/MD is to 1.00, the higher the shape precision (roundness).
Good: The ratio of linear expansion coefficients TD/MD is 1.00 or more and 1.50 or less. Poor: The ratio of linear expansion coefficients TD/MD is more than 1.50.

<Aggression by opponents>
After the pin-on-disk test performed in the evaluation of the friction characteristics and wear resistance described above, the contact surface with the mating disk test piece was measured for ten-point average roughness (Rz) in accordance with JIS B0601-1982 using a surface roughness tester (SURFCOM 1500DX3, manufactured by Tokyo Seimitsu Co., Ltd.). The test conditions were as follows:
Measurement length: 8,000 mm (evaluation length: 5,000 mm)
・Measurement speed: 0.300mm
・Shape removal: least squares straight line

The evaluation criteria for opponent aggression are as follows:
◯: Ten-point average roughness (Rz) after pin-on-disk test at 25°C and 100°C is 10 or less. ×: Ten-point average roughness (Rz) after pin-on-disk test at 25°C or 100°C is more than 10.

Tables 1 and 2 show that resin compositions for sliding bearings containing the specified components have good friction characteristics and wear resistance at 25°C and 100°C, and also good shape precision (roundness). Therefore, it is clear that the resin compositions for sliding bearings are suitable as components for sliding bearings that have good friction and wear characteristics from the normal temperature of 25°C to around 100°C. In particular, it is believed that the inclusion of the aforementioned fibrous inorganic filler in the resin composition for sliding bearings suppresses the effects of fiber orientation in the molded product, resulting in good maintenance of shape precision (roundness).

In addition, because the base resin contains a specific biomass-derived semi-aromatic polyamide resin, it is possible to provide an environmentally friendly resin composition and sliding bearing. Furthermore, it has been found that the use of a fibrous inorganic filler with a Mohs hardness of 4 or less, combined with the lubricating properties of the fluororesin solid lubricant, makes it possible to provide a resin composition and sliding bearing that also reduces aggressiveness toward mating surfaces.

1 Dumbbell test piece 2 Gate 3 Runner 4 Flow direction 5 Vertical direction

Claims (3)

A resin composition for a sliding bearing comprising a base resin, a fibrous inorganic filler, and a solid lubricant,
the base resin is a semi-aromatic polyamide resin containing terephthalic acid and 1,10-decanediamine as main components,
the fibrous inorganic filler has an average fiber diameter of 3 μm or less, an average fiber length of 2 to 50 μm , and a Mohs hardness of 4 or less, and is at least one type of whisker selected from calcium carbonate whiskers, zinc oxide whiskers, potassium titanate whiskers, and magnesium sulfate whiskers ;
the solid lubricant is at least one selected from the group consisting of fluororesin, graphite, molybdenum disulfide, zinc sulfide, metal oxides, and metal carbonates;
The composition contains 55 to 88 mass % of the base resin, 5 to 20 mass % of the fibrous inorganic filler, and 7 to 35 mass % of the solid lubricant,
The resin composition for a sliding bearing has a friction coefficient of 0.3 or less and a specific wear rate of 1.5×10 ⁻⁶ mm ³ /N·m or less at 100°C, as measured under the following test conditions using an injection-molded article of the resin composition for a sliding bearing.
Test conditions:
A pin-on-disc test was carried out under the following conditions using a pin-on-disc friction and wear tester (Auto Pin Disk APD-101, manufactured by Starlite Industrial Co., Ltd.), the dynamic friction coefficient of the test piece was measured, and the specific wear rate was calculated from the wear progress curve based on the following formula (1).
Test piece: φ5 mm cylindrical injection molded body
Surface pressure (load on sample): 2.0 MPa
Speed (set value): 1.0 m/s
・Matching disc temperature: 100℃
Lubrication: No lubrication
Counterpart disc: SUS303 (surface roughness before test: Rz ≒ 1.5 to 2.5 μm)
・K=(H'-H)/{P・V・(T'-T)} (1)
K: specific wear rate [mm ³ /N·m]
H': wear amount (height) at test time T' [mm]
H: Wear amount (height) at test time T [mm]
P: Surface pressure [N/mm ² ]
V: Velocity [m/s]
T': Test time [s] in the steady state, 6 hours (21600 s) after the start of the test
T: Test time in steady state [s], 2 hours (7200 s) after the start of the test
Steady state: After the test time, the wear rate stabilizes Using an injection-molded article of the resin composition for a sliding bearing, the friction coefficient at 25°C measured under the test conditions (with the exception of a mating disc temperature of 25°C) is 0.3 or less, and the specific wear rate is 1.5 x 10 ^-6 mm ³ 2. The resin composition for a sliding bearing according to claim 1, wherein the sliding bearing resin composition has a viscosity of 1/2 N·m or less. A sliding bearing having, in a sliding part, an article molded from the resin composition for sliding bearings according to claim 1 or 2 .