Wet friction material, disc for wet clutch device, wet clutch device, and method for manufacturing wet friction material

Abstract

Provided is a wet friction material that is less susceptible to a decrease in the coefficient of friction. The present invention provides a wet friction material (20C) for use in a wet clutch device used in a wet environment. The wet friction material (20C) includes a fiber base material containing a fiber material and a filler. The filler includes carbon black.

Description

[Technical Field]

[0001] The present invention relates to a wet friction material, a disk for a wet clutch device, a wet clutch device, and a method for manufacturing the wet friction material. [Background technology]

[0002] Conventionally, clutch devices used in wet environments (so-called wet clutch devices) use discs for wet clutch devices that have friction materials (see, for example, Patent Document 1). Patent Document 1 discloses a friction material made of paper. In recent years, a technique has also been known in which a filler such as diatomaceous earth is added to a base material containing a fibrous material (a fibrous base material) in order to improve the coefficient of friction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-179029 Summary of the Invention [Problem to be solved by the invention]

[0004] Through research by the inventors, it has been newly discovered that when a low-friction oil such as MB oil is used in the wet clutch device described above for the purpose of improving fuel efficiency, the friction coefficient of the friction material decreases, resulting in a decrease in clutch capacity (transmittable power).

[0005] The present invention has been made in view of the above points, and its main object is to provide a wet friction material in which the coefficient of friction is less likely to decrease even when low-friction oil is used. [Means for solving the problem]

[0006] The present invention provides a wet friction material for use in a wet clutch device used in a wet environment, the wet friction material including a fiber base material containing a fiber material and a filler, wherein the filler includes carbon black.

[0007] By blending carbon black as a filler, it is possible to reduce the decrease in the friction coefficient of the wet friction material even when using low-friction oil, and thus to suppress the decrease in clutch capacity. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a wet friction material in which the coefficient of friction is less likely to decrease even when low-friction oil is used. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a wet clutch device according to one embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of an input side rotating plate according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will be described below with reference to the drawings. It should be noted that the embodiments described here are, of course, not intended to limit the present invention in any particular way. Furthermore, members and parts that perform the same function are given the same reference numerals, and duplicate descriptions may be omitted or simplified as appropriate. Furthermore, in this specification, the expression "X to Y" (X and Y are arbitrary numerical values) indicating a range includes not only the meaning of X or more and Y or less, but also the meanings of "greater than X" and "smaller than Y."

[0011] <Wet clutch device> FIG. 1 is a cross-sectional view of a wet clutch device 10 according to this embodiment. The wet clutch device 10 is provided on a vehicle such as a motorcycle. The wet clutch device 10 is disposed, for example, between the engine and transmission of the motorcycle. The wet clutch device 10 is a device for transmitting or blocking the rotational driving force of an engine input shaft (crankshaft, not shown) to an output shaft 15. The wet clutch device 10 is a device for transmitting or blocking the rotational driving force of the input shaft to driving wheels (rear wheels) via the output shaft 15.

[0012] The wet clutch device 10 is a clutch device used in a wet environment where it comes into contact with oil. Motorcycle engine oil is preferred as the oil. From the viewpoint of improving fuel economy and engine performance, low-friction oil (oil with low friction characteristics), for example, oil specified in the Society of Automotive Engineers of Japan standard JASO T903, such as MB-grade oil, is preferred. The oil typically contains additives (oil additives) such as friction modifiers. The wet clutch device 10 of this embodiment is integrally formed with the engine and / or transmission, and the oil is engine oil (more specifically, motorcycle engine oil). The wet clutch device 10 is filled with engine oil (not shown). The wet clutch device 10 of this embodiment is a so-called wet multi-plate friction clutch device.

[0013] The wet clutch device 10 of this embodiment includes a clutch housing 30, an input gear 35, a boss 40, and a pressure plate 70.

[0014] As shown in FIG. 1, the clutch housing 30 holds a plurality of input side rotating plates 20 (see FIG. 2). More specifically, the clutch housing 30 has grooves 36. The plurality of input side rotating plates 20 are held in the grooves 36. The claws 20B (see FIG. 2) of the input side rotating plates 20 engage with the grooves 36. The clutch housing 30 is an example of a housing.

[0015] As shown in FIG. 1, the input side rotating plate 20 is held in the clutch housing 30. The input side rotating plate 20 is accommodated in the accommodation space of the clutch housing 30 together with the oil described above. The input side rotating plate 20 is provided so as to be displaceable along the axial direction of the clutch housing 30 (i.e., the axial direction of the output shaft 15). The input side rotating plate 20 is rotationally driven by the rotational drive of the input shaft. The input side rotating plate 20 is provided so as to be rotatable integrally with the clutch housing 30. The input side rotating plate 20 is an example of a disc for a wet clutch device.

[0016] The input side rotating plate 20 is a member that is pressed against the output side rotating plate 22 (see FIG. 1), which will be described later. As shown in FIG. 2, the input side rotating plate 20 has a ring-shaped main body 20A and a plurality of claws 20B that extend radially outward from the outer periphery of the main body 20A. The input side rotating plate 20 is formed, for example, by aluminum die casting.

[0017] As shown in FIG. 2, the input side rotating plate 20 has a plurality of wet friction materials 20C. The plurality of wet friction materials 20C are provided on the front and back surfaces of the main body portion 20A, respectively. Here, the plurality of wet friction materials 20C are each in the form of a rectangular sheet. The plurality of wet friction materials 20C are arranged (for example, pressed) at equal intervals in the circumferential direction of the main body portion 20A. The input side rotating plate 20 has a plurality of oil grooves 20D formed between adjacent wet friction materials 20C. The oil grooves 20D are grooves for retaining oil. The depth of the oil grooves 20D is several tens of μm to several hundreds of μm. The configuration of the wet friction materials 20C will be described later.

[0018] As shown in Figure 1, the input gear 35 is attached to the clutch housing 30. The input gear 35 is engaged with a drive gear (not shown) that rotates due to the rotational drive of the input shaft of the engine. The input gear 35 is driven to rotate by the rotational drive of the input shaft. The input gear 35 rotates integrally with the clutch housing 30, independent of the output shaft 15.

[0019] 1, the boss 40 is housed in the clutch housing 30. The boss 40 holds the input rotating plates 20 and a plurality of output rotating plates 22 arranged alternately. The boss 40 is driven to rotate together with the output shaft 15.

[0020] The output side rotating plate 22 is a member that is pressed against the input side rotating plate 20. The output side rotating plate 22 is formed in a ring shape. The output side rotating plate 22 is formed by punching a thin plate material made of, for example, SPCC (Steel Plate Cold Commercial) into a ring shape. In this embodiment, the input side rotating plate 20 is provided with a wet friction material 20C (see FIG. 2 ). However, in other embodiments, the wet friction material 20C may be provided on the output side rotating plate 22 instead of the input side rotating plate 20, or may be provided on both the input side rotating plate 20 and the output side rotating plate 22. In this case, the output side rotating plate 22 is an example of a disk for a wet clutch device.

[0021] As shown in Figure 1, the pressure plate 70 is accommodated in the clutch housing 30. The pressure plate 70 is located between the clutch housing 30 and the boss 40. The pressure plate 70 is provided so as to be able to move toward or away from the boss 40 and to rotate relative to the boss 40. The pressure plate 70 is configured so as to be able to press against the input side rotating plate 20 and the output side rotating plate 22.

[0022] <Wet friction material> The wet friction material 20C is a component used in the wet clutch device 10 that is used in a wet environment. The wet friction material 20C is a component that improves the friction force between the input side rotating plate 20 and the output side rotating plate 22 of the wet clutch device 10. The wet friction material 20C is a component that is provided on the wet clutch device disc (the input side rotating plate 20 and / or the output side rotating plate 22). In this embodiment, the wet friction material 20C is provided only on the input side rotating plate 20.

[0023] The wet friction material 20C can be suitably used in the wet clutch device 10 used in an environment where it comes into contact with low-friction oil, for example, oil specified in the Society of Automotive Engineers of Japan standard JASO T903, for example, MB-grade oil. MB-grade oil is particularly prone to a decrease in the friction coefficient, so using the wet friction material 20C disclosed herein is particularly effective.

[0024] The wet friction material 20C includes (A) a fibrous base material and (B) a filler. The wet friction material 20C of this embodiment further includes (C) a resin binder. The wet friction material 20C may further include other optional components as needed.

[0025] In some embodiments, the wet friction material 20C is preferably a paper-made product formed by papermaking. This makes it easier to distribute the filler (B) uniformly on the surface and inside of the wet friction material 20C. This makes it easier to stably exhibit the effects of the technology disclosed herein (especially the effects of including carbon black as a filler) over a long period of time.

[0026] <(A) Fiber Base Material> The fiber base material constitutes the skeleton of the wet friction material 20C. The fiber base material preferably has a porous structure so that oil can penetrate into the interior thereof. The fiber base material includes a fiber material. There are no particular limitations on the fiber material, and one or more types of fiber materials conventionally known to be usable for this type of application can be appropriately adopted. The fiber material is preferably fibrillated. This improves the integrity and durability of the wet friction material 20C, making it easier to stably exert the effects of the technology disclosed herein over a long period of time.

[0027] The fiber material may be inorganic or organic, or may contain both. Examples of inorganic fibers include metal fibers, glass fibers, ceramic fibers, mineral fibers, and carbon fibers (including PAN-based and pitch-based fibers).

[0028] The organic fibers may be natural fibers or chemically synthesized chemical fibers (artificial fibers). Examples of natural fibers include plant fibers such as pulp fibers, animal fibers, and mineral fibers. The chemical fibers may be recycled fibers, semi-synthetic fibers, or synthetic fibers. Examples of chemical fibers include aramid fibers (including para- and meta-types), cellulose fibers, polyester fibers, polyethylene fibers, polypropylene fibers, acrylic fibers, rayon fibers, polyamide fibers, and polyimide fibers.

[0029] In some embodiments, the fiber base material is preferably composed primarily of organic fibers (a component accounting for 50% or more by mass; the same applies hereinafter). It is particularly preferred that the fiber base material be composed primarily of chemical fibers. In some embodiments, the fiber base material preferably contains inorganic fibers and organic fibers. This allows for well-balanced improvement of various properties of the wet friction material 20C, such as wear resistance, frictional properties, mechanical strength, and durability.

[0030] In some embodiments, the fibrous base material preferably contains aramid fibers. Among organic fibers, aramid fibers have high melting points, hardness, and strength, and are excellent in heat resistance. Therefore, by including aramid fibers, the wet friction material 20C can further improve various properties, for example, it can stably exhibit excellent friction properties over a long period of time. The fibrous base material is preferably composed mainly of aramid fibers. The fibrous base material preferably includes a second organic fiber (e.g., cellulose) in addition to the aramid fibers. In this case, it is preferable that the aramid fibers have the highest content among the fibrous materials.

[0031] In some embodiments, the fibrous base material may not contain cellulose fibers. In this specification, the term "cellulose fibers" refers to any compound having a cellulose skeleton, encompassing cellulose and its derivatives. In this specification, "not containing" means that the proportion of the component is less than 0.1% by mass when the entire wet friction material 20C is taken as 100% by mass.

[0032] In some embodiments, the fibrous base material preferably does not contain at least one of steel fibers and glass fibers, and more preferably does not contain either steel fibers or glass fibers. This can prevent the output rotating plate 22 (the opposing wet clutch device disk) that faces the input rotating plate 20 from contacting and wearing the wet friction material 20C. Furthermore, when the wet friction material 20C is produced by wet papermaking, for example, as described in the manufacturing method below, sinking of the fibrous material during the papermaking process can be prevented, making it easier to obtain a homogeneous wet friction material 20C.

[0033] Although not particularly limited, the proportion of the fibrous material (the total proportion when two or more types are included) is preferably 10% by mass or more, and more preferably 20% by mass or more, when the entire wet friction material 20C is taken as 100% by mass. The proportion of the fibrous material is preferably 80% by mass or less, and more preferably 60% by mass or less. The organic fiber content is preferably 10 to 55% by mass, when the entire wet friction material 20C is taken as 100% by mass. The inorganic fiber content is preferably 0 to 20% by mass, when the entire wet friction material 20C is taken as 100% by mass.

[0034] <(B) Filler> The filler is a component for improving the friction coefficient of the wet friction material 20C. The filler is typically supported (carried) by the above-mentioned fibrous material. The filler is preferably disposed not only on the surface (outer surface) of the fibrous base material but also inside the fibrous base material. The filler may be disposed in a larger amount, by mass, inside the fibrous base material than on the surface of the wet friction material 20C. Note that the filler can also be disposed inside the fibrous base material by incorporating the fibrous material and the filler by wet papermaking, for example, as described in the manufacturing method described below.

[0035] In this embodiment, the filler contains at least carbon black. According to the inventors' investigations, by including carbon black in the wet friction material 20C, components derived from oil additives contained in oil are less likely to adhere to the wet friction material 20C compared to, for example, a wet friction material 20C that does not contain carbon black or a wet friction material 20C that uses diatomaceous earth or graphite as a filler. This makes it relatively difficult for a reaction film derived from the oil additive to form on the wet friction material 20C. As a result, even when low-friction oil is used, the decrease in the friction coefficient of the wet friction material 20C can be reduced. This, in turn, can suppress a decrease in clutch capacity.

[0036] Carbon black is an amorphous carbon material and has a relatively large specific surface area compared to crystalline carbon materials such as graphite. There are no particular limitations on the carbon black, and one or more conventionally known carbon blacks can be appropriately used. The carbon black may be, for example, furnace black (including oil furnace black and gas furnace black) obtained by the furnace method, channel black obtained by the channel method, acetylene black obtained by the acetylene method, or thermal black obtained by the thermal method.

[0037] The physical properties of the carbon black are not particularly limited, but the carbon content of the carbon black is preferably 90% by mass or more, more preferably 95% by mass or more. The carbon black is typically in powder (particulate) form. The true specific gravity of the carbon black is preferably 1.8 to 1.9.

[0038] The carbon black content is not particularly limited, as it may vary depending on, for example, the properties of the oil in contact and the properties of the fibrous base material. In some embodiments, the carbon black content is preferably 2 to 30% by mass, where the entire wet friction material 20C is taken as 100% by mass. By setting the carbon black content to a predetermined value or more, the effects of the technology disclosed herein can be exhibited at a higher level. From this perspective, the carbon black content is preferably 2% by mass or more, and more preferably 5% by mass or more. Furthermore, by setting the carbon black content to a predetermined value or less, the carbon black is more likely to be firmly supported on the fibrous material, thereby improving the integration with the fibrous base material and durability.

[0039] In addition to carbon black, the filler may further contain one or more materials known to be usable for this type of application. Fillers other than carbon black may be inorganic or organic. Examples of inorganic fillers include whiskers (acicular substances); alkaline earth metal salts such as magnesium oxide, calcium carbonate, and barium sulfate; mineral materials such as talc, clay, silica, mica, mullite, and diatomaceous earth; and metal powders such as iron powder. Examples of organic fillers include rubber materials; crystalline carbon materials such as graphite; activated carbon; and cashew dust. It is particularly preferable to further contain an organic filler and an inorganic filler in addition to carbon black.

[0040] In some embodiments, the filler preferably further includes a rubber material. The rubber may be natural rubber or synthetic rubber. Examples of synthetic rubber include butadiene rubber, styrene-butadiene rubber, isoprene rubber, ethylene-propylene rubber, butyl rubber, acrylonitrile-butadiene rubber, acrylic rubber, urethane rubber, silicone rubber, fluororubber, and polysulfide rubber. By including a rubber material in addition to carbon black, various properties of the wet friction material 20C, such as its integration with the fibrous base material and durability, can be improved.

[0041] In some embodiments, the filler preferably does not contain diatomaceous earth, which increases the carbon black content and makes it easier to achieve a high level of the effects of the technology disclosed herein.

[0042] In some embodiments, the filler preferably does not contain metal powder such as iron powder. This can prevent the output rotating plate 22 (the mating disc for the wet clutch device) that faces the input rotating plate 20 from coming into contact with the wet friction material 20C and wearing out. Furthermore, for example, as described in the manufacturing method below, when the wet friction material 20C is produced by wet papermaking, settling of the filler during the papermaking process can be prevented, making it easier to obtain a homogeneous wet friction material 20C.

[0043] The proportion of the filler (the total proportion when two or more types are included) is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, when the entire wet friction material 20C is taken as 100% by mass. The organic filler is preferably 3 to 55% by mass, when the entire wet friction material 20C is taken as 100% by mass. The inorganic filler is preferably 2 to 40% by mass, when the entire wet friction material 20C is taken as 100% by mass.

[0044] <(C) Resin Binder> The resin binder is a component for improving the integrity of the fiber base material and the filler and the durability of the wet friction material 20 C. There are no particular limitations on the resin binder, and one or more materials that are known to be usable for this type of application may be appropriately used.

[0045] The resin binder preferably contains a thermosetting resin binder from the viewpoint of durability, etc. Examples of the resin binder include phenolic resins, epoxy resins, and melamine resins. Of these, phenolic resins are preferred.

[0046] When the wet friction material 20C contains a binder, the proportion of the binder (the total proportion when two or more types are contained) is preferably 5% by mass or more, more preferably 10% by mass or more, when the entire wet friction material 20C is taken as 100% by mass. The proportion of the binder is preferably 60% by mass or less, more preferably 50% by mass or less.

[0047] <Applications of wet friction material 20C> As described above, the technology disclosed herein provides an input rotating plate 20 (wet clutch device disc) for use in a wet clutch device 10 used in a wet environment, the input rotating plate 20 (wet clutch device disc) having a wet friction material 20C containing a filler including carbon black. The technology disclosed herein also provides a wet clutch device 10 including an input rotating plate 20 (wet clutch device disc), oil in contact with the input rotating plate 20, and a clutch housing (housing) 30 that accommodates these, in which the input rotating plate 20 (wet clutch device disc) has a wet friction material 20C containing a filler including carbon black. By including the wet friction material 20C, the wet clutch device 10 can have superior vehicle performance (engine output) and fuel economy and a reduced environmental impact, compared to a wet clutch device not including the wet friction material 20C.

[0048] <Method of manufacturing the wet friction material 20C> Next, a method for manufacturing the above-described wet friction material 20C will be described. The manufacturing method of this embodiment includes a preparation step (step S10), a preparation step (step S20), and a papermaking step (step S30) in this order. The manufacturing method disclosed herein may further include other steps at any stage. For example, after the papermaking step, a cutting step may be further included in which the obtained sheet material is cut into a predetermined shape and size.

[0049] The preparation step (step S10) is a step of preparing at least a fiber material and carbon black as a filler. The fiber material and carbon black can be prepared, for example, by purchasing commercially available products. The fiber material and carbon black may be those described above.

[0050] The preparation step (step S20) is a step of preparing a slurry by mixing at least the fiber material prepared in the preparation step with carbon black. As an example, first, the fiber material and a filler containing carbon black are added to a solvent and mixed. This disperses the fiber material and carbon black in the solvent. The solvent is typically water, but it may also be a mixed solvent mainly composed of water. As the solvent other than water that constitutes the mixed solvent, an organic solvent that is uniformly miscible with water, such as a lower alcohol such as methanol, ethanol, or propanol, or a lower ketone, can be used. For mixing, a conventional stirring and mixing device such as a magnetic stirrer, a planetary mixer, or a disper can be used as appropriate.

[0051] The slurry may further contain fillers other than the carbon black described above, binders, etc., as long as the effects of the technology disclosed herein are not significantly impaired. The slurry more preferably contains a rubber material as a filler. The rubber material is preferably in the form of an emulsion, from the viewpoint of suppressing subsidence in the papermaking process (step S30) described below. The slurry may also contain an organic binder (e.g., phenolic resin) as a binder.

[0052] The slurry preferably does not contain at least one of steel fiber and glass fiber as a fibrous material, and more preferably does not contain either steel fiber or glass fiber. The slurry preferably does not contain metal powder as a filler. This makes it easier to prepare a homogeneous slurry, and makes it easier to obtain a homogeneous wet friction material 20C in the papermaking process (step S30).

[0053] The papermaking step (step S30) is a step of wet-processing the slurry prepared in the preparation step. Wet-processing can be performed using, for example, a conventionally known papermaking machine. The papermaking conditions may be the same as conventional ones. In one example, first, the solvent contained in the slurry is roughly removed, and the solid content in the slurry is processed (molded) into a sheet. This results in a wet paper. Next, the obtained wet paper is dried to further remove the solvent. This results in a sheet material (wet friction material 20C) that includes a fibrous base material containing a fibrous material and a filler carried by the fibrous material.

[0054] Although the preferred embodiments of the present invention have been described above, the above-described embodiments are merely examples, and the present invention can be embodied in various other forms.

[0055] For example, in the above-described embodiment, the boss 40 and the pressure plate 70 are each configured to hold the output side rotating plate 22, but this is not limiting. In a modified example, for example, only the boss 40 may be configured to hold the output side rotating plate 22, or only the pressure plate 70 may be configured to hold the output side rotating plate 22.

[0056] The technology disclosed herein can be applied to various types of clutch devices. In the above-described embodiment, a so-called external disengagement type clutch device in which the pressure plate 70 is located between the boss 40 and the clutch housing 30 in the axial direction of the output shaft 15 has been described as an example, but the present invention is not limited to this. For example, the technology disclosed herein can be similarly applied to a so-called internal disengagement type clutch device in which the pressure plate 70 is located on the opposite side of the boss 40 from the clutch housing 30 in the axial direction of the output shaft 15.

[0057] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A wet friction material used in a wet clutch device used in a wet environment, the wet friction material comprising a fiber base material containing a fiber material and a filler, wherein the filler contains carbon black. Item 2: The wet friction material according to Item 1, wherein the proportion of the carbon black is 2% by mass or more and 30% by mass or less when the entire wet friction material is taken as 100% by mass. Item 3: The wet friction material according to Item 1 or 2, wherein the wet clutch device is used in an environment where it comes into contact with motorcycle engine oil. Item 4: The wet friction material according to any one of Items 1 to 3, wherein the wet clutch device is used in an environment where it comes into contact with motorcycle engine oil (for example, oil specified in the Society of Automotive Engineers of Japan standard JASO T903). Item 5: The wet friction material according to any one of Items 1 to 4, wherein the fiber base material contains aramid fibers. Item 6: The wet friction material according to any one of Items 1 to 5, wherein the fiber base material does not contain at least one of steel fiber and glass fiber. Item 7: The wet friction material according to any one of Items 1 to 6, wherein the filler further contains a rubber material. Item 8: The wet friction material according to any one of Items 1 to 7, which is a paper-made product formed by papermaking. Item 9: A disc for a wet clutch device used in a wet clutch device used in a wet environment, the disc having a wet friction material containing a filler including carbon black. Item 10: A wet clutch device comprising: a wet clutch device disc; oil in contact with the wet clutch device disc; and a housing in which the wet clutch device disc and the oil are accommodated, wherein the wet clutch device disc has a wet friction material containing a filler including carbon black. Item 11: A method for producing a wet friction material used in a wet clutch device used in a wet environment, the method comprising: a preparation step of preparing a fiber material and carbon black as a filler; a preparation step of mixing the fiber material and the carbon black to prepare a slurry; and a papermaking step of wet-processing the slurry. [Explanation of symbols]

[0058] 10. Wet clutch device 15 Output shaft 20 Input side rotating plate (disc for wet clutch device) 20C wet friction material 22 Output side rotating plate 30 Clutch housing (housing) 35 input gear 36 Groove 40 Boss 70 Pressure Plate

Claims

1. A wet friction material used in a wet clutch device used in a wet environment, A fiber substrate including a fiber material and a filler, The wet friction material contains carbon black as a filler.

2. When the entire wet friction material is taken as 100% by mass, the proportion of the carbon black is 2% by mass or more and 30% by mass or less. The wet friction material according to claim 1.

3. The wet clutch device is used in an environment where it comes into contact with motorcycle engine oil. The wet friction material according to claim 1 or 2.

4. The wet clutch device is used in an environment where it comes into contact with motorcycle engine oil (for example, oil specified in the Society of Automotive Engineers of Japan standard JASO T903). The wet friction material according to claim 3.

5. The fiber substrate includes aramid fibers. The wet friction material according to claim 1 or 2.

6. The fiber substrate does not contain at least one of steel fiber and glass fiber. The wet friction material according to claim 1 or 2.

7. The filler further comprises a rubber material. The wet friction material according to claim 1 or 2.

8. A paper product formed by papermaking, The wet friction material according to claim 1 or 2.

9. A wet clutch device disc used in a wet clutch device used in a wet environment, A wet friction material containing a filler including carbon black. Disc for wet clutch device.

10. a wet clutch device disc; oil in contact with the wet clutch device disc; a housing that accommodates the wet clutch device disc and the oil; Equipped with The wet clutch device disc has a wet friction material containing a filler including carbon black.

11. A method for manufacturing a wet friction material used in a wet clutch device used in a wet environment, comprising: A preparation step of preparing a fiber material and carbon black as a filler; a preparation step of mixing the fiber material and the carbon black to prepare a slurry; a papermaking process of wet-processing the slurry; A method for producing a wet friction material, comprising:

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