Underwater sliding member and article

Abstract

Provided is an underwater sliding member which is used in an aqueous liquid at a surface pressure of 0.5 MPa or more and a sliding speed of 10 cm / s or less, and which is a molded member obtained by molding a resin composition that contains a thermoplastic resin having water absorption resistance and does not contain an inorganic filler.

Description

Underwater sliding members and articles

[0001] This disclosure relates to underwater sliding members and articles.

[0002] Molded thermoplastic resin components used in sliding parts are often used under constant loads, and their properties require not only sliding properties but also not only short-term mechanical properties such as rigidity, strength, and toughness, but also long-term durability properties such as creep resistance and fatigue resistance. In recent years, the operating environments for sliding parts have also diversified, and molded thermoplastic resin components used in sliding parts are used, for example, in bathroom and water supply components that come into frequent contact with water, as well as pipe and valve components used in environments where stress is constantly applied, and especially as valve components such as rotary valves for electric vehicle modules. In particular, pipe and valve components are required to have a high level of balance between mechanical strength, long-term properties, and wear resistance in underwater environments, so that they can withstand immersion in hot water and stress generation due to sudden valve closure.

[0003] When thermoplastic resins are used as sliding members, it is known that molded members made of a single material of thermoplastic resin have low wear resistance and excessive wear. To improve wear resistance, sliding members containing fillers in the thermoplastic resin are known. Patent Document 1 discloses a technique to improve rigidity and reduce shrinkage anisotropy by incorporating fibrous inorganic fillers such as glass fibers, carbon fibers, and wollastonite, and granular inorganic fillers such as calcium carbonate as inorganic fillers. Patent Document 2 discloses a technique to incorporate glass fibers, mica, etc., into thermoplastic resin to improve mechanical properties, reduce warping of molded products, and improve the appearance of molded products.

[0004] When using resin sliding members in water, it is expected that the resin should have excellent water resistance and high wear resistance. Patent Document 3 discloses an underwater sliding member made of a laminate of carbon fiber cloth containing a phenolic resin composition consisting of 5 to 40% by weight of one or more fillers selected from graphite, tetrafluoroethylene resin, boron nitride, and amorphous carbon, with the remainder being phenolic resin. Furthermore, Patent Document 4 discloses a resin-based composite sliding member for use in water, which uses a composite material containing carbon fibers and at least one filler selected from graphite, boron nitride, molybdenum disulfide, and tungsten disulfide in a tetrafluoroethylene resin.

[0005] International Publication No. 2005 / 071011, Japanese Patent Publication No. 2003-286402, Japanese Patent Publication No. 2002-323038, Japanese Patent Publication No. 2003-21144

[0006] Thus, high wear resistance is required for sliding members made of thermoplastic resin. On the other hand, referring to the technologies disclosed in Patent Documents 3 and 4, it is known that when used underwater, it is good to include fillers in the resin in order to improve wear resistance while maintaining excellent water resistance. However, in various applications of underwater sliding members, particularly in underwater sliding members used under high surface pressure and low sliding speed, there is room for consideration in resin design that takes into account the effect of fillers. Examples of such underwater sliding members include pipe and valve components for cooling media used in motor and engine cooling systems, especially for long-life coolants (LLC).

[0007] One of the objectives of this disclosure is to provide an underwater sliding member with excellent wear resistance for use in aqueous liquids under high surface pressure and low sliding speed.

[0008] One embodiment of the present disclosure that solves the aforementioned problems is as follows: [1] An underwater sliding member used in an aqueous liquid with a surface pressure of 0.5 MPa or more and a sliding speed of 10 cm / s or less, which is a molded member made from a resin composition containing a thermoplastic resin having water resistance and not containing an inorganic filler. [2] The underwater sliding member according to [1], used in an aqueous liquid with a surface pressure of 0.8 to 2 MPa. [3] The underwater sliding member according to [1] or [2], used in an aqueous liquid with a sliding speed of 3 to 9 cm / s. [4] The underwater sliding member according to any one of [1] to [3], wherein the thermoplastic resin is a polyacetal resin. [5] A specific wear amount measured under the following condition A at a surface pressure of 0.98 MPa and a sliding speed of 6 cm / s is 10 × 10 －３ mm ３ A water sliding member described in any one of [1] to [4], wherein the pressure is less than or equal to / N·km. [Condition A] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the water sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the members are slid at an ambient temperature of 23°C for a sliding time of 24 hours, and the specific wear amount of the water sliding member is measured after 24 hours. [6] With a surface pressure of 1.96 MPa and a sliding speed of 6 cm / s, the specific wear amount measured under the following condition A is 20 × 10 －３ mm ３An underwater sliding member according to any one of [1] to [5], wherein the coefficient of dynamic friction measured under the following conditions B is 0.35 or less. [Condition A] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the two are slid for 24 hours at an ambient temperature of 23°C, and the specific wear amount of the underwater sliding member is measured after 24 hours. [7] An underwater sliding member according to any one of [1] to [6], wherein the coefficient of dynamic friction measured under the following conditions B is 0.35 or less, with a surface pressure of 0.98 MPa and a sliding speed of 6 cm / s. [Condition B] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the two are slid for 24 hours at an ambient temperature of 23°C, and the coefficient of dynamic friction is measured near the end of the 24 hours. [8] An underwater sliding member according to any one of [1] to [7], wherein the coefficient of dynamic friction measured under the following condition B is 0.35 or less, with a surface pressure of 1.96 MPa and a sliding speed of 6 cm / s. [Condition B] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the two are slid for 24 hours at an ambient temperature of 23°C, and the coefficient of dynamic friction is measured near the end of the 24 hours. [9] An underwater sliding member according to any one of [1] to [8] for use in a rotary valve.

[10] An underwater sliding member according to [9] for use in a rotary valve provided in a cooling system of an electric vehicle.

[11] An article comprising an underwater sliding member used in an aqueous liquid with a surface pressure of 0.5 MPa or more and a sliding speed of 10 cm / s or less, wherein the underwater sliding member is a molded member formed from a resin composition containing a water-resistant thermoplastic resin and no inorganic fillers.

[0009] According to one embodiment of the present disclosure, it is possible to provide an underwater sliding member with excellent wear resistance for use in an aqueous liquid at high surface pressure and low sliding speed.

[0010] Figure 1 is a conceptual diagram showing the sliding test conducted in the embodiment.

[0011] The following describes some embodiments of this disclosure. The examples in the following description do not limit this disclosure.

[0012] The underwater sliding member of this embodiment is an underwater sliding member used in an aqueous liquid with a surface pressure of 0.5 MPa or more and a sliding speed of 10 cm / s or less, and is characterized by being a molded member formed from a resin composition that contains a thermoplastic resin having water resistance and does not contain an inorganic filler.

[0013] The underwater sliding member of this embodiment is intended for members that slide against a mating material in an aqueous liquid, and does not include members used in a dry environment. In this embodiment, "underwater" refers not only to pure water but also to an aqueous liquid. The aqueous liquid is a liquid containing water, and may consist of water alone or a mixture of water and other liquids. For example, it may contain other liquids in a range where water is 10% by mass or more, 30% by mass or more, or 50% by mass or more. Specifically, the aqueous liquid may be a mixture of a water-soluble organic solvent and water, an emulsion containing an aqueous phase and an oil phase, etc. These aqueous liquids may be aqueous liquids that can be used as cooling media including long-life coolant (LLC), aqueous lubricants including emulsion-type lubricants, etc.

[0014] In conventional technology, resin-based underwater sliding members are considered suitable for applications that include inorganic fillers to enhance wear resistance while maintaining water resistance in water. However, underwater sliding members made of thermoplastic resin have been considered to have insufficient wear resistance in water and have therefore been used only in applications with low surface pressure sliding conditions. Furthermore, it has been thought that at low surface pressure, even if the sliding speed is high, the reduction in wear is small. Therefore, considering conventional technology, a sliding member that is a molded part of thermoplastic resin containing inorganic fillers is considered a viable option for use in water at low surface pressure and high sliding speed. However, contrary to this, this disclosure has found that, under high surface pressure sliding conditions, due to the low sliding speed, a sliding member made of thermoplastic resin without inorganic fillers can reduce the amount of wear in water more effectively than a sliding member made of thermoplastic resin containing inorganic fillers.

[0015] This embodiment relates to an underwater sliding member used in an aqueous liquid with a surface pressure of 0.5 MPa or more and a sliding speed of 10 cm / s or less. When the surface pressure is high, water is less likely to interpose on the friction surface, so resin fragments generated by friction tend to remain on the friction surface. It is presumed that as the resin fragments tend to remain on the friction surface, they act as a lubricant between the resin fragments and the friction surface of the mating material, reducing the coefficient of dynamic friction and thus reducing the amount of wear. The upper limit of the surface pressure is not limited and varies appropriately depending on the type of resin of the underwater sliding member and the type of mating material, but for example, it is good to have a pressure of 3 MPa or less, 2.5 MPa or less, or 2 MPa or less.

[0016] Given the high surface pressure, it is preferable to set the sliding speed appropriately. If the sliding speed is excessive, water will enter the friction surface and wash away the resin fragments, so the effect of the resin fragments acting as a lubricant between the friction surface of the mating material will not be obtained, and the frictional resistance will increase. The sliding speed is preferably 10 cm / s or less, more preferably 9 cm / s or less, and even more preferably 6 cm / s or less.

[0017] The underwater sliding member is a molded member made from a resin composition containing a thermoplastic resin with water absorption resistance and substantially no inorganic fillers. For example, it is a molded member in which inorganic fillers are not intentionally added during the manufacturing process. If the thermoplastic resin composition of the underwater sliding member contains inorganic fillers, when sliding under high surface pressure, water is less likely to be present on the friction surface, and inorganic filler fragments are scraped off along with resin fragments on the friction surface. Since these inorganic filler fragments are harder than the resin, they scrape off the mating material. If the mating material is soft, the amount of wear increases as the underwater sliding member is further scraped off while the inorganic filler fragments generated on the wear surface scrape off the mating material. If the mating material is hard, the amount of wear may increase as the underwater sliding member is further scraped off by fragments scraped off from the mating material. However, if the thermoplastic resin composition of the underwater sliding member does not contain inorganic fillers, inorganic filler fragments are not generated on the wear surface, so it is considered that the wear surface of the underwater sliding member is less likely to be scraped off.

[0018] In this embodiment, inorganic filler refers to inorganic components added for purposes such as improving mechanical strength and wear resistance. For inorganic fillers used in thermoplastic resins with water resistance, solid inorganic substances with an average particle size of 1 μm or more are typically used. Examples of such inorganic fillers include silica, glass fibers, talc, calcium carbonate, carbon materials such as carbon fibers, mica, kaolin, clay, and wollastonite. However, solid inorganic substances may be included in the molded member for purposes such as improving the smoothness of the resin surface or improving its appearance, as long as they do not function as inorganic fillers. In this case, for a molded member made from a resin composition containing a thermoplastic resin with water resistance but without inorganic fillers, the amount of solid inorganic substance per 100 parts by mass of the thermoplastic resin should preferably be less than 5 parts by mass, less than 1 part by mass, or less than 0.5 parts by mass.

[0019] Examples of the thermoplastic resin having water absorption resistance include polyacetal resin, polyarylene sulfide resin, polycarbonate resin and the like. Examples of the polyarylene sulfide resin include polyphenylene sulfide resin and the like. These resins may be used in combination of two or more. From the concern about environmental conservation, it is preferable that the thermoplastic resin does not contain an organic fluorine compound resin, for example, PFAS (perfluoroalkyl compound and polyfluoroalkyl compound). As such a thermoplastic resin, it is particularly preferable to use polyacetal resin and polyarylene sulfide resin. Here, "water absorption resistance" means, for example, the property of not changing dimensions when immersed in water at a temperature of 23 ° C for 24 hours in the evaluation of water absorption rate according to ISO62.

[0020] In order to improve the physical properties of the resin composition according to the present embodiment according to the intended use, various known additives can be further added as other components. Examples of the additive include various stabilizers (such as antioxidant and antacid), ultraviolet absorber, light stabilizer, formaldehyde scavenger, colorant (such as carbon black), mold release agent, nucleating agent, antistatic agent, other surfactants, different polymers and the like.

[0021] In one embodiment, the underwater sliding member has a specific wear rate (hereinafter also referred to as specific wear rate a) measured under the following condition A at a surface pressure of 0.98 MPa and a sliding speed of 6 cm / s. －３ mm ３ / N·km or less. The specific wear rate a is preferably 20×10 －３ mm ３ / N·km or less, 15×10 －３ mm ３ / N·km or less, 10×10 －３ mm ３ / N·km or less, or 5×10 －３ mm ３ / N·km or less. In the range of a surface pressure of 0.98 MPa and a sliding speed of 6 cm / s, if the specific wear rate a is at this level, excellent wear resistance can be provided even when applied to underwater sliding members for various uses. Note that condition A is part of condition 1 of the sliding test performed in the examples described later.

[0022] In another embodiment, when the underwater sliding member is measured under the following condition A with a surface pressure of 1.96 MPa and a sliding speed of 6 cm / s, the specific wear amount (hereinafter also referred to as specific wear amount b) is 10 × 10 －３ mm ３ It is preferable that it be less than or equal to / N·km. The specific wear amount b is 10 × 10 －３ mm ３ / N・km or less, 8×10 －３ mm ３ / N・km or less, 5×10 －３ mm ３ / N·km or less, or 2 × 10 －３ mm ３ It is preferable that the specific wear amount b be less than or equal to / N·km. With a surface pressure of 1.96 MPa and a sliding speed of 6 cm / s, a specific wear amount of this magnitude b can provide excellent wear resistance when applied to underwater sliding members for various applications.

[0023] [Condition A] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the sliding is performed at an ambient temperature of 23°C for a sliding time of 24 hours. The specific wear amount of the underwater sliding member is measured after 24 hours.

[0024] In another embodiment, the underwater sliding member is preferably such that the dynamic friction coefficient (hereinafter also referred to as the dynamic friction coefficient a) measured under the following condition B with a surface pressure of 0.98 MPa and a sliding speed of 6 cm / s is 0.35 or less. If the dynamic friction coefficient a is within this range, it can be applied to underwater sliding members for various applications and will have excellent wear resistance.

[0025] In another embodiment, the underwater sliding member is preferably such that the coefficient of dynamic friction (hereinafter also referred to as the coefficient of dynamic friction b) measured under the following condition B with a surface pressure of 1.96 MPa and a sliding speed of 6 cm / s is 0.35 or less. If the coefficient of dynamic friction b is within this range, it can be applied to underwater sliding members for various applications and will have excellent wear resistance.

[0026] [Condition B] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the two are slid for 24 hours at an ambient temperature of 23°C. The coefficient of dynamic friction is measured near the end of the 24-hour period.

[0027] In some embodiments, it is preferable to satisfy at least one of the above-mentioned specific wear amount a, specific wear amount b, dynamic friction coefficient a, and dynamic friction coefficient b, but it is preferable to satisfy at least two of these, and even better to satisfy three, and even better to satisfy all four. Underwater sliding members that satisfy these physical properties can be applied to underwater sliding members for various applications and will have excellent wear resistance.

[0028] In this embodiment, the underwater sliding member can be manufactured by molding a resin composition containing a thermoplastic resin having water resistance. In the manufacturing process, solid inorganic substances are not intentionally added so as to function as inorganic fillers. Additives may be optionally included in the resin composition containing the thermoplastic resin having water resistance. There are no particular limitations on the method for manufacturing the underwater sliding member using the resin composition, and known methods can be employed. For example, the resin composition can be put into an extruder, melt-kneaded to form pellets, and then these pellets can be put into an injection molding machine equipped with a predetermined mold and injection molded.

[0029] The underwater sliding member of this embodiment is suitable for use under high surface pressure and low sliding speed conditions in water. For example, the underwater sliding member can be used in articles used in underwater or water-intervening environments such as valves, pumps, gears, and bearings. Specifically, the underwater sliding member can be used in bathroom-related parts and water supply-related parts that are frequently in contact with water; pipe parts and valve parts used in environments where stress is constantly applied, especially rotary valves for aqueous liquids; and electrical appliances such as electric shavers that require water resistance. In particular, the underwater sliding member can be preferably used in rotary valves, which are often used under high surface pressure and low sliding speed conditions. A rotary valve comprises a rotor, case, shaft, and side cover, and at least one of these parts is preferably the underwater sliding member of this embodiment. This enhances wear resistance in the sliding between the rotor and the inner surface of the case, between the rotor and the shaft, between the shaft and the side cover, and between the side cover and the rotor, reducing wear on the parts and preventing a decrease in the liquid tightness of the rotary valve.

[0030] While the use of polyacetal resin has been restricted in high-temperature underwater environments, its high strength in relatively low-temperature underwater environments makes it suitable for use as a sliding member. For example, components of the drive system of electric vehicles are often used in environments where the temperature does not exceed 100°C. Polyacetal resin underwater sliding members can be preferably used in such applications. Specifically, they are suitable for use in rotary valves in the cooling systems of electric vehicles. In the cooling systems of electric vehicles, there is a method of supplying a cooling medium to the motor to cool it, but the cooling medium for the motor does not get as hot as the cooling medium for the engine. Therefore, the underwater sliding member of this embodiment can be used in the rotary valve placed in the flow path of the cooling medium in the cooling system of an electric vehicle, and it is particularly preferable to use an underwater sliding member made of polyacetal resin. Examples of electric vehicles include electric cars, plug-in hybrid cars, trains, and electric bicycles. For similar reasons, the underwater sliding member of this embodiment can also be used in cooling systems for stationary power sources, etc.

[0031] In this embodiment, the mating member of the underwater sliding member may be any of a resin member, a metal member, a ceramic member, a glass member, etc., and the underwater sliding member of this embodiment may be used as the mating member.

[0032] As another aspect of this embodiment, an article can be provided that includes an underwater sliding member used in an aqueous liquid at a surface pressure of 0.5 MPa or more and a sliding speed of 10 cm / s or less. The underwater sliding member is a molded member formed by molding a resin composition that includes a water-absorbent thermoplastic resin and does not contain an inorganic filler. Details of the underwater sliding member are as described above. Examples of the article include bathroom-related parts and plumbing-related parts, pipe parts and valve parts, particularly rotary valves for aqueous liquids, household appliances, and electric vehicles, and details are as described above.

[0033] Hereinafter, the present disclosure will be described more specifically by way of examples, but the present disclosure is not limited to the following examples.

[0034] (Examples 1 to 3, Comparative Example 1) In each example and comparative example, the following thermoplastic resins were prepared. Example 1, 3: Polyacetal resin 1, manufactured by Polyplastics Co., Ltd., Duracon (registered trademark) POM M90-44 (unfilled). Example 2: Polyacetal resin 2, manufactured by Polyplastics Co., Ltd., Duracon (registered trademark) POM NW-02 (sliding property improving material). Comparative Example 1: Polyacetal resin 3, manufactured by Polyplastics Co., Ltd., Duracon (registered trademark) POM TW-51 (sliding property improving material containing 51 parts by mass of an inorganic filler with respect to 100 parts by mass of the resin).

[0035] [Evaluation] Using the pellet-shaped resin compositions prepared in each example and comparative example, cylindrical test pieces 10 (outer diameter: 2.56 cm, inner diameter: 2.0 cm, height: 1.5 cm) were molded with an injection molding machine. Also, a cylindrical stainless steel member 20 having the same shape and size as the test piece 10 was prepared (see FIG. 1).

[0036] (Sliding Test) As shown in Figure 1, the cylindrical test piece 10 was placed on top and the cylindrical stainless steel member 20 on the bottom, with their upper and lower surfaces in contact, and then immersed in water. The lower stainless steel member 20 was then continuously rotated under the following conditions 1 and 2. Condition 1: Sliding speed: 30 cm / s Surface pressure: 0.49 MPa Ambient temperature: 23°C Sliding time: 24 hours Condition 2: Sliding speed: 3-9 cm / s Surface pressure: 0.98 MPa or 1.96 MPa Ambient temperature: 23°C Sliding time: 24 hours

[0037] (Evaluation of wear amount) In each example and comparative example, the amount of wear [g] was calculated from the difference in mass of the test piece 10 before and after the sliding test. The calculated amount of wear [g] was then compared to the specific gravity of the material [g / cm³]. ３ Using ], volume [mm ３ Convert this to [units], and divide this volume value by the applied load [N] and sliding distance [km] to obtain the specific wear amount [mm]. ３ The value [ / N・km] was calculated. The calculation results are shown in Table 1.

[0038]

[0039] (Evaluation of Dynamic Friction Coefficient) In each example and comparative example, the following apparatus was used to perform a 24-hour sliding test from the start of the sliding test to obtain data on the change in the dynamic friction coefficient over time. The values ​​immediately after the start of the test and the values ​​near the end of the test after 24 hours (where the behavior of change stabilized) were determined as the dynamic friction coefficient values, and the amount of change was calculated. The results are shown in Table 2. Apparatus: Thrust-type friction and wear tester EFM-III-EN (manufactured by Orientec Co., Ltd.)

[0040]

[0041] Table 1 shows that under condition 1, which involves low surface pressure, the comparative example containing inorganic fillers exhibits less resin-to-surface wear than the example without inorganic fillers. On the other hand, under condition 2, which involves high surface pressure, when the sliding speed is 3 to 9 cm / s, the example without inorganic fillers exhibits less resin-to-surface wear than the comparative example containing inorganic fillers.

[0042] Table 2 shows that in Example 3, which does not contain inorganic fillers, the coefficient of dynamic friction is smaller under Condition 2, which has high surface pressure and low sliding speed, compared to Condition 1, which has low surface pressure and high sliding speed.

[0043] Although the present invention has been described with reference to several embodiments described above, the present invention is not limited to these embodiments. Various modifications can be made to the structure and details of the present invention within the scope of the invention. This disclosure is related to the subject matter described in Japanese Patent Application No. 2024-228817, filed on 25 December 2024, all of which are incorporated herein by reference.

[0044] 10 test pieces, 20 stainless steel components

Claims

1. An underwater sliding member for use in an aqueous liquid with a surface pressure of 0.5 MPa or more and a sliding speed of 10 cm / s or less, wherein the molded member is made from a resin composition containing a thermoplastic resin having water absorption resistance and not containing an inorganic filler.

2. The underwater sliding member according to claim 1, which is used in an aqueous liquid at a surface pressure of 0.8 to 2 MPa.

3. The underwater sliding member according to claim 1, which is used in an aqueous liquid at a sliding speed of 3 to 9 cm / s.

4. The underwater sliding member according to claim 1, wherein the thermoplastic resin is a polyacetal resin.

5. The specific wear amount measured under the following condition A, with a surface pressure of 0.98 MPa and a sliding speed of 6 cm / s, was 10 × 10 －３ mm ３ An underwater sliding member according to any one of claims 1 to 4, wherein the friction coefficient is less than or equal to / N·km. [Condition A] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the members are slid at an ambient temperature of 23°C for a sliding time of 24 hours, and the specific wear amount of the underwater sliding member is measured after 24 hours.

6. The specific wear amount measured under the following condition A, with a surface pressure of 1.96 MPa and a sliding speed of 6 cm / s, was 20 × 10⁻¹⁶. －３ mm ３ An underwater sliding member according to any one of claims 1 to 4, wherein the friction coefficient is less than or equal to / N·km. [Condition A] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the members are slid at an ambient temperature of 23°C for a sliding time of 24 hours, and the specific wear amount of the underwater sliding member is measured after 24 hours.

7. An underwater sliding member according to any one of claims 1 to 4, wherein the coefficient of dynamic friction measured under the following condition B is 0.35 or less, with a surface pressure of 0.98 MPa and a sliding speed of 6 cm / s. [Condition B] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the two are slid for an ambient temperature of 23°C for a sliding time of 24 hours, and the coefficient of dynamic friction is measured near the end of the 24-hour period.

8. An underwater sliding member according to any one of claims 1 to 4, wherein the coefficient of dynamic friction measured under the following condition B is 0.35 or less, with a surface pressure of 1.96 MPa and a sliding speed of 6 cm / s. [Condition B] In an aqueous liquid, the upper surface of a stainless steel cylindrical member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm) is brought into contact with the lower surface of the underwater sliding member (inner diameter: 2.0 cm, outer diameter: 2.56 cm, height: 1.5 cm), and the members are slid for 24 hours at an ambient temperature of 23°C, and the coefficient of dynamic friction is measured near the end of the 24-hour period.

9. An underwater sliding member for use in a rotary valve, according to any one of claims 1 to 4.

10. The underwater sliding member according to claim 9, for use in a rotary valve provided in the cooling system of an electric vehicle.

11. An article comprising an underwater sliding member used in an aqueous liquid with a surface pressure of 0.5 MPa or more and a sliding speed of 10 cm / s or less, wherein the underwater sliding member is a molded member formed from a resin composition containing a thermoplastic resin having water resistance and not containing inorganic fillers.

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