Dry friction material, production method therefor, and composition for dry friction material and production method therefor

Abstract

To provide a dry friction material which can be produced more easily than conventional ones, a production method for the dry friction material, a composition for a dry friction material, and a method for producing the composition.SOLUTION: A dry friction material 1 includes a matrix material 11 and a dispersed material 12, the matrix material 11 including a vulcanized rubber, the dispersed material 12 including heat-resistant reinforcing fibers 121 and a friction regulation material, and the heat-resistant reinforcing fibers 121 being oriented in a certain direction. This composition for a dry friction material is formed by extruding a kneaded mixture of an unvulcanized rubber, heat-resistant reinforcing fibers, and a friction regulation material. A production method for this composition for a dry friction material includes an extrusion step of extruding a kneaded mixture of an unvulcanized rubber, heat-resistant reinforcing fibers, and a friction regulation material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a dry friction material, a method for manufacturing the same, a composition for a dry friction material, and a method for manufacturing the same. More specifically, the present invention relates to a dry friction material containing a matrix material and a dispersant, a method for manufacturing the same, a composition for a dry friction material, and a method for manufacturing the same.

Background Art

[0002] Conventionally, dry friction materials have been manufactured by complex methods. For example, (1) a resin liquid preparation step of preparing a resin liquid such as a solution of a thermosetting resin or a dispersion liquid in which a thermosetting resin is dispersed, (2) a resin liquid impregnation step of impregnating a glass roving (glass fiber bundle) with the resin liquid, (3) a resin liquid drying step of drying the resin liquid impregnated in the glass roving, (4) a rubber kneading step of preparing a compounded rubber containing latex, a vulcanizing agent, an additive, etc., (5) a coating step of coating the resin-impregnated glass roving with the compounded rubber, (6) a winding step of winding the glass roving coated with the compounded rubber into a predetermined size to form a ring shape, (7) a hot forming step of putting the wound glass roving into a mold and performing hot forming, (8) a heat treatment step of curing the thermosetting resin of the hot formed product, (9) a polishing step of polishing the obtained green compact, and (10) a punching step of performing necessary punching on the polished product. A manufacturing method including such steps is adopted (see Patent Documents 1 and 2 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Regarding this dry friction material, an annular shape is often used for its general shape. In this regard, an annular shape is also often used for wet friction materials. However, the manufacturing methods of dry friction materials and wet friction materials are very different. For example, a wet friction material can be manufactured by attaching a friction base material segment that exhibits predetermined friction performance to the surface of a plate pre-shaped into an annular shape. In contrast, as described above, for a dry friction material, after arranging the roving material in an annular shape, hot press forming is performed, and further, an annular shape is obtained through shaping such as polishing. Thus, in the case of wet friction materials, a prototype plate is used, whereas in the case of dry friction materials, a prototype plate is not used, and it can be said that a complicated manufacturing process is required in terms of shaping the general shape from the roving material. This is presumably because it is difficult to obtain the performance required for dry friction materials by means of segment attachment or the like. For this reason, there is a demand for a dry friction material that can be manufactured more simply while satisfying the performance required for dry friction materials, a manufacturing method thereof, a composition for dry friction materials, and a manufacturing method thereof.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a dry friction material that can be manufactured simply, a manufacturing method thereof, a composition for dry friction materials, and a manufacturing method thereof, as compared with the prior art.

Means for Solving the Problems

[0006] As described above, the inventor has considered replacing the use of rovings (materials for dry friction materials using glass rovings) with mold materials (materials for dry friction materials that can be molded) for the purpose of a simpler manufacturing method. As a result, it has been found that in conventional dry friction materials, the presence of rovings improves the molding accuracy and the impact resistance. On the other hand, in order to realize a mold material, it is considered possible to blend short fibers as reinforcing fibers instead of rovings, and at that time, it is considered that blending a larger amount of reinforcing fibers contributes to the improvement of molding accuracy and impact resistance. However, in order to obtain a mold material, it is necessary to mix it with various other raw materials, and it has been found that it becomes more difficult to maintain the blending balance with other components (friction modifiers, curable resins, plasticizers, etc.) as the amount of reinforcing fibers to be blended increases. Therefore, the inventor considered that it is necessary to improve the contribution degree of the reinforcing fibers by properties other than the blending amount, and focused on the orientation of the reinforcing fibers as one of such properties. And it has been found that randomly arranged reinforcing fibers reduce the contribution degree of the reinforcing fibers to each performance, and it is considered that a dry friction material that satisfies the required performance can be obtained if the orientation of the reinforcing fibers in the dry friction material can be actively adjusted, and a method for realizing the active orientation of the reinforcing fibers was studied. And by finding this method, the present invention has been completed.

[0007] The present invention includes the following inventions. 〔1〕A dry friction material containing a matrix material and a dispersant, wherein the matrix material contains a vulcanized rubber, the dispersant contains a heat-resistant reinforcing fiber and a friction modifier, and the dry friction material is characterized in that the heat-resistant reinforcing fiber is oriented in a certain direction. 〔2〕The dry friction material according to the above 〔1〕, which has an outer edge having a circular or arc shape, wherein the orientation is parallel to the outer edge. 〔3〕The dry friction material according to the above 〔1〕 or 〔2〕, wherein the heat-resistant reinforcing fiber is 50 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the vulcanized rubber. 〔4〕The dry friction material according to any one of the above 〔1〕to 〔3〕, wherein the average fiber length of the heat-resistant reinforcing fiber is 1 to 3 mm. 〔5〕The dry friction material according to any one of the above 〔1〕to 〔4〕, wherein the average fiber diameter of the heat-resistant reinforcing fiber is 15 μm or less. 〔6〕A composition for a dry friction material for obtaining the dry friction material according to any one of the above 〔1〕to 〔5〕, characterized in that it is obtained by extruding a kneaded product of the unvulcanized rubber that becomes the vulcanized rubber, the heat-resistant reinforcing fiber, and the friction modifier. 〔7〕A dry friction material characterized by being obtained by vulcanizing the composition for a dry friction material according to the above 〔6〕. 〔8〕A method for producing a composition for a dry friction material for obtaining the dry friction material according to any one of the above 〔1〕to 〔5〕, characterized by comprising an extrusion step of extruding a kneaded product of the unvulcanized rubber that becomes the vulcanized rubber, the heat-resistant reinforcing fiber, and the friction modifier. 〔9〕A method for producing a dry friction material for obtaining a dry friction material from the composition for a dry friction material obtained by the production method according to the above 〔8〕, characterized by comprising a vulcanization step of vulcanizing the composition for a dry friction material. 〔10〕The method for producing a dry friction material according to the above 〔9〕, wherein the heat-resistant reinforcing fiber is 50 to 300 parts by mass with respect to 100 parts by mass of the unvulcanized rubber. 〔11〕The method for producing a dry friction material according to the above 〔9〕 or 〔10〕, wherein the average fiber length of the heat-resistant reinforcing fiber is 1 to 3 mm. 〔12〕The method for producing a dry friction material according to any one of the above 〔9〕to 〔11〕, wherein the average fiber diameter of the heat-resistant reinforcing fiber is 15 μm or less.

Advantages of the Invention

[0008] According to the dry friction material of the present invention, it can be manufactured more simply than in the prior art. According to the method for producing a dry friction material of the present invention, a dry friction material having excellent performance can be manufactured more simply than in the prior art. According to the composition for dry friction materials of the present invention, dry friction materials can be manufactured more simply than in the prior art. According to the method for manufacturing the composition for dry friction materials of the present invention, the composition for dry friction materials can be surely obtained.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described with reference to the drawings. The matters shown here are exemplary and for exemplarily explaining the embodiments of the present invention, and are described for the purpose of providing an explanation that can most effectively and easily understand the principle and conceptual features of the present invention. In this regard, it is necessary for a fundamental understanding of the present invention and is not intended to show the structural details of the present invention to a greater extent than necessary, and is to clarify to those skilled in the art how some forms of the present invention are actually embodied by the description combined with the drawings.

[0011] [1] Dry friction material The dry friction material (1) of the present invention includes a matrix material (11) and a dispersion material (12). The matrix material (11) includes vulcanized rubber. The dispersion material (12) includes heat-resistant reinforcing fibers (121) and a friction modifier. It is characterized in that the heat-resistant reinforcing fibers (121) are oriented in a certain direction.

[0012] The above-mentioned "matrix material (11)" is a material that constitutes the dry friction material 1 and forms a matrix (continuous phase) with respect to the dispersant 12. The matrix material 11 contains vulcanized rubber. The type of vulcanized rubber is not limited, and examples include acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), styrene-butadiene rubber (SBR), natural rubber (NR), isoprene rubber (IR), chloroprene rubber (CR), polyisobutylene rubber, acrylic rubber (acrylic acid ester·2-chloroethyl vinyl ether copolymer rubber, acrylic acid ester·acrylonitrile copolymer rubber, etc.), urethane rubber, fluororubber (fluorinated olefin·vinylidene fluoride copolymer rubber, etc.), silicone rubber, and the like. These may be used alone or in combination of two or more. Among these, from the viewpoints of friction characteristics and impact resistance, NBR, SBR, BR, NR, IR, and CR are preferable, and NBR and SBR are more preferable.

[0013] In addition to vulcanized rubber, the matrix material 11 can contain other components. Examples of other components include cured resins (resins obtained by curing curable resins). Further, a plasticizer can be blended with the matrix material 11. The type of cured resin is not limited, and examples include phenolic resins (phenol resin, novolak resin, resol resin, melamine-modified phenolic resin, etc.), urea resin, epoxy resin, polyimide resin, unsaturated polyester resin, alkyd resin, polyurethane resin, polyimide resin (curable polyimide resin), and modified resins thereof. These may be used alone or in combination of two or more. Among these, from the viewpoints of friction characteristics and impact resistance, phenolic resin, melamine-modified phenolic resin, etc. are preferable. The melamine-modified phenolic resin is a thermosetting resin using phenol and melamine in combination as monomers. In the melamine-modified phenolic resin, the composition ratio is not limited, but when the total of the phenol-derived unit and the melamine-derived unit is 100%, for example, the melamine-derived unit can be 30 to 80%.

[0014] When the total amount of the dry friction material is 100% by mass, the quantitative ratio of the matrix material is not limited, but for example, it can be 1 to 50% by mass, 2 to 45% by mass, 3 to 40% by mass, 4 to 35% by mass, 5 to 30% by mass, or 6 to 25% by mass. Also, when the matrix material contains a cured resin, the quantitative ratio of the cured resin is not limited. For example, when the total amount of the vulcanized rubber is 100 parts by mass, the cured resin can be 1 to 100 parts by mass, 2 to 75 parts by mass, 3 to 50 parts by mass, 4 to 40 parts by mass, or 5 to 35 parts by mass. Furthermore, when the matrix material contains a plasticizer, the quantitative ratio of the plasticizer is not limited. For example, when the total amount of the vulcanized rubber is 100 parts by mass, the plasticizer can be 0.1 to 50 parts by mass, 1 to 40 parts by mass, 3 to 30 parts by mass, 6 to 25 parts by mass, or 8 to 20 parts by mass.

[0015] The above-mentioned "dispersion material (12)" is a material that is dispersed and present in the matrix material 11 described above. The dispersion material 12 includes heat-resistant reinforcing fibers 121 and friction modifiers. The above-mentioned "heat-resistant reinforcing fiber (121)" is a fiber-shaped material among the dispersion materials 12. The type of the heat-resistant reinforcing fiber 121 is not limited, and inorganic fibers can be preferably used. The type of the inorganic fiber is not limited, and examples include amorphous fibers (such as glass fibers, silica fibers, slag wool, and rock wool), single crystal fibers (such as ceramic fibers, alumina fibers, magnesia fibers, titanate fibers, and wollastonite fibers), polycrystalline fibers (such as ceramic fibers, alumina fibers, and silica-alumina fibers), carbon-based fibers (such as carbon fibers and carbonized fibers), and metal fibers. These may be used alone or in combination of two or more.

[0016] From the viewpoints of friction performance, heat resistance, safety, cost, etc. in dry friction materials, inorganic fibers are preferable, and further, amorphous fibers and / or carbon-based fibers are preferable, and further, glass fibers and / or carbon fibers are preferable, and particularly, glass fibers are preferable. As will be described later, these heat-resistant reinforcing fibers have appropriate rigidity in the fiber itself. For this reason, it is easy to align the directions of the heat-resistant reinforcing fibers by flowing the kneaded material containing the raw materials, and the heat-resistant reinforcing fibers can be oriented in a stretched state without being bent. Also, when the kneaded material is flowed, it is preferable in that the heat-resistant reinforcing fibers are hardly subdivided and their length can be maintained.

[0017] The heat-resistant reinforcing fibers have heat resistance. Although the specific heat-resistant performance is not limited, the melting point or decomposition temperature is preferably 200°C or higher, more preferably 350°C or higher. The upper limit of the melting point or decomposition temperature is not limited, but is usually 3500°C or lower. Also, the fiber represents its shape and means having an elongated shape. Although the specific shape is not limited, the aspect ratio is preferably 50 or more. Also, the length (maximum length) is preferably 500 μm or more, and more preferably 750 μm or more. The upper limit of the aspect ratio is not limited, but can be, for example, 1000 or less. Also, the upper limit of the length of the heat-resistant reinforcing fibers is not limited, but can be, for example, 10 mm or less.

[0018] Also, the heat-resistant reinforcing fiber 121 only needs to exhibit the fiber shape as described above, and further, the average fiber length is preferably 0.5 to 5 mm, more preferably 0.5 to 4 mm, still more preferably 1 to 4 mm, and particularly preferably 1 to 3 mm. If the average fiber length is within the above range, it is easier to orient it in a certain direction, and further, the effect of orienting it in a certain direction can be obtained more remarkably. The average fiber length is defined as the average value of the fiber lengths (maximum lengths) actually measured for 50 randomly selected heat-resistant reinforcing fibers.

[0019] Furthermore, the heat-resistant reinforcing fiber 121 only needs to exhibit a fiber shape as described above, but its fiber diameter is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Also, although the average fiber diameter of the heat-resistant reinforcing fiber is not limited, it is preferably 0.5 to 20 μm, more preferably 2 to 15 μm, even more preferably 3 to 14 μm, and particularly preferably 6 to 13 μm. If the average fiber diameter is within the above range, it is easier to orient in a certain direction, and furthermore, the effect of orientation in a certain direction can be obtained more significantly. In addition, this average fiber diameter shall be the average value of the fiber diameters (maximum diameters) actually measured for each of 50 randomly selected heat-resistant reinforcing fibers.

[0020] The content of the heat-resistant reinforcing fiber 121 in the dry friction material 1 is not limited, but with respect to 100 parts by mass of the vulcanized rubber, the heat-resistant reinforcing fiber is preferably 50 to 300 parts by mass, more preferably 60 to 280 parts by mass, even more preferably 80 to 250 parts by mass, particularly preferably 100 to 220 parts by mass, and especially preferably 120 to 200 parts by mass. If the content of the heat-resistant reinforcing fiber 121 is within the above range, it is easier to orient in a certain direction, and furthermore, the effect of orientation in a certain direction can be obtained more significantly.

[0021] The above-mentioned "aligned" means that the heat-resistant reinforcing fibers 121 within the matrix material 11 are arranged regularly. In other words, it can be said that the longitudinal directions of the heat-resistant reinforcing fibers 121 are aligned according to a predetermined rule. In the present invention, it can be said that the longitudinal directions of the heat-resistant reinforcing fibers 121 are aligned in a certain direction. When the directions are aligned, not only the direction that completely coincides with the predetermined direction but also the directions that intersect within a range of 45 degrees or less with respect to the predetermined direction are included in the same orientation in the present invention. From the viewpoint of improving dimensional stability and impact resistance, this intersection angle is preferably 30 degrees or less, more preferably 20 degrees or less, and even more preferably 15 degrees or less. That is, it is preferable that the orientation is aligned within a closer angle range. Also, the orientation of the heat-resistant reinforcing fibers preferably has all of them in the same orientation, but usually, it is preferable that 50% or more of the heat-resistant reinforcing fibers are in the same orientation. From the viewpoint of improving dimensional stability and impact resistance, this ratio is preferably larger, preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, particularly preferably 90% or more, and especially preferably 95% or more.

[0022] Also, as described above, the orientation direction in the present invention is determined in a certain direction. This certain direction may be one kind of direction, or may be two or three kinds of directions, but since it is preferable to have fewer directions, it is more preferable to have two kinds of orientation directions than to have three kinds of orientation directions, and further, it is even more preferable to have one kind of orientation direction. In the present invention, since the heat-resistant reinforcing fibers contained in the dry friction material are oriented in a certain direction, it is possible to have the same performance as a dry friction material obtained by a conventional method, that is, obtained using roving. In particular, it is possible to obtain a dry friction material excellent in dimensional accuracy and impact resistance. In addition, as will be described later, the orientation of the heat-resistant reinforcing fibers in a certain direction can be obtained by providing an extrusion step of extruding a kneaded product containing unvulcanized rubber and heat-resistant reinforcing fibers in the manufacturing process. Furthermore, the orientation of the heat-resistant reinforcing fibers in a certain direction can be obtained when the heat-resistant reinforcing fibers contained in the composition for dry friction materials used when forming the dry friction material are oriented in a certain direction, or when extrusion is performed to obtain a molded product that becomes a dry friction material and the heat-resistant reinforcing fibers are oriented in a certain direction within the mold in which the molded product is accommodated.

[0023] More specifically regarding the above orientation, the dry friction material of the present invention has an outer edge 13 having a circular or arc shape, and the above orientation is preferably an orientation parallel to the outer edge 13 (see FIGS. 1 and 2). That is, since the dry friction material is often rotated and slid, the outer edge can be formed to have a circular or arc shape. And when formed in this way, it is preferable that the heat-resistant reinforcing fibers 121 contained in the matrix material 11 are oriented such that their longitudinal direction is parallel to the outer edge. In other words, it is preferable that the longitudinal direction 121a of the heat-resistant reinforcing fibers 121 is substantially parallel to the tangent line 131 to the circular outer edge 13 or the arc-shaped outer edge 13. And for this orientation, it is preferable that 50% or more of the number of heat-resistant reinforcing fibers conforms to the said rule, furthermore 60% or more, furthermore 70% or more, furthermore 80% or more, furthermore 90% or more, furthermore 95% or more conforms to the said rule.

[0024] Similarly, the dry friction material of the present invention has a linear outer edge 14, and the above orientation can be an orientation parallel to the outer edge 14 in its longitudinal direction (see FIG. 3). Also in such a case, it is preferable that the heat-resistant reinforcing fibers 121 contained in the matrix material 11 are oriented parallel to the outer edge, and for the orientation, it is preferable that 50% or more of the number of heat-resistant reinforcing fibers conforms to the said rule, furthermore 60% or more, furthermore 70% or more, furthermore 80% or more, furthermore 90% or more, furthermore 95% or more conforms to the said rule.

[0025] The above-mentioned "friction modifier" is a material among the dispersant 12 that contributes to the function of the dry friction material by its inclusion, and in particular, is a material having a friction adjustment effect. Further, the friction modifier has a non-fiber shape (a shape excluding the fiber shape exhibited by the heat-resistant reinforcing fiber from the whole shape). That is, it has a shape different from that of the heat-resistant reinforcing fiber. The type of the friction modifier is not limited, and examples thereof include inorganic friction modifiers (inorganic friction modifiers made of inorganic materials, composite inorganic friction modifiers mainly composed of inorganic materials but containing organic materials, etc.) and organic friction modifiers (organic friction modifiers made of organic materials, composite inorganic friction modifiers mainly composed of organic materials but containing inorganic materials, etc.). These may be used alone or in combination of two or more.

[0026] The type of the inorganic friction modifier is not limited, and examples thereof include sulfate-based materials {metal sulfates (magnesium sulfate, calcium sulfate, barium sulfate, etc.)}, carbonate-based materials {metal carbonates (magnesium carbonate, calcium carbonate [heavy calcium carbonate, light calcium carbonate], barium carbonate, etc.)}, titanate-based materials {metal titanates (potassium titanate, etc.)}, silicate-based materials {metal silicates (aluminum silicate, zirconium silicate, etc.)}, hydroxide-based materials {metal hydroxides (calcium hydroxide, aluminum hydroxide, etc.)}, oxide-based materials {metal oxides (zinc oxide [zinc white], titanium oxide, iron oxide, aluminum oxide, zirconium oxide, magnesium oxide, etc.)}, sulfide-based materials {metal sulfides (molybdenum disulfide), non-metal sulfides (antimony trisulfide, etc.)}, carbide-based materials {metal carbides (titanium carbide), non-metal carbides (silicon carbide, boron carbide, etc.)}, nitride-based materials {non-metal nitrides (silicon nitride, boron nitride, etc.)}, mineral-based materials (diatomaceous earth, wollastonite, dolomite, silica, mica, talc, kaolin, etc.), carbon-based materials (graphite [black lead], carbon black, coke, etc.), metal materials (aluminum, copper, brass, etc.), and the like. These may be used alone or in combination of two or more.

[0027] The type of organic friction modifier is not limited, and examples thereof include resins (cashew resin, melamine resin, cashew dust, etc.), rubber dust, plant materials {plant bark (cork, etc.), seed shells (walnut shells, coconut shells, etc.)}, etc. These may be used alone or in combination of two or more kinds.

[0028] The friction modifier may have any shape as long as it is non-fibrous. Specifically, the aspect ratio is preferably less than 50 (1 or more). The maximum length is preferably less than 500 μm, and more preferably less than 750 μm. That is, the shape of the friction modifier may be granular, irregular, blocky, needle-like, whisker-like, etc. The size of the friction modifier is not limited, but for example, the average particle size d can be 0.1≦d(μm)<500 μm, or can be 1≦d(μm)≦350, or can be 2≦d(μm)≦200 μm. The average particle size of the friction modifier can be measured in accordance with JIS Z8827-1 (static image analysis method).

[0029] The content of the friction modifier in the dry friction material 1 is not limited, but may be 50 parts by mass or more and 1,000 parts by mass or less, further 60 parts by mass or more and 800 parts by mass or less, further 80 parts by mass or more and 600 parts by mass or less, further 90 parts by mass or more and 400 parts by mass or less, further 100 parts by mass or more and 350 parts by mass or less, or further 150 parts by mass or more and 300 parts by mass or less, relative to 100 parts by mass of the vulcanized rubber.

[0030] As described above, the dry friction material of the present invention can be manufactured more simply than in the past. Specifically, as described above, in the conventional manufacturing method using roving, (1) resin liquid preparation step, (2) resin liquid impregnation step, (3) resin liquid drying step, (4) rubber kneading step, (5) coating step, (6) winding step, (7) hot forming step, (8) heat treatment step, (9) polishing step, (10) punching step, a total of 10 steps are required. In contrast, the dry friction material of the present invention can be manufactured by 7 steps, namely, (1) rubber kneading step, (2) extrusion step, (3) winding step, (4) hot forming step, (5) heat treatment step, (6) polishing step, (7) punching step, and significant reduction in man-hours can be achieved.

[0031] [2] Composition for dry friction material The composition for a dry friction material of the present invention is a composition for a dry friction material for obtaining the dry friction material of the present invention, and is characterized by being formed by extruding a kneaded product of unvulcanized rubber that becomes vulcanized rubber, heat-resistant reinforcing fibers, and a friction modifier.

[0032] The composition for a dry friction material of the present invention can be made into a dry friction material by vulcanization. The heat-resistant reinforcing fibers and the friction modifier are as described above. Also, the unvulcanized rubber is a precursor to the vulcanized rubber described above. In order to make it into vulcanized rubber by vulcanization, the above kneaded product can contain a vulcanizing agent (crosslinking agent) and a vulcanization accelerator (crosslinking accelerator).

[0033] The type of vulcanizing agent is not limited, and examples include sulfur-based vulcanizing agents (such as sulfur), organic peroxide-based vulcanizing agents, metal oxide-based vulcanizing agents, sulfur-containing organic compounds, polyamine-based vulcanizing agents, polyol-based vulcanizing agents, metal soap-based vulcanizing agents, triazine-based vulcanizing agents, quinoid-based vulcanizing agents, maleimide-based vulcanizing agents, etc. These may be used alone or in combination of two or more. Among these, examples of sulfur-based vulcanizing agents include sulfur (powdered sulfur, sulfur flowers, surface-treated sulfur, colloidal sulfur, etc.), sulfur chloride, and the like. Examples of organic peroxide-based vulcanizing agents include dicumyl peroxide, cumene peroxide, cumyl peroxide, dicumyl peroxide, bis(α,α-dimethylbenzyl) peroxide, and the like. Further, examples of metal oxide vulcanizing agents include zinc oxide, magnesium oxide, and the like. Examples of sulfur-containing organic vulcanizing agents include morpholine disulfide, alkylphenol disulfide, thiuram polysulfide, and the like. Examples of polyamine-based vulcanizing agents include hexamethylenediamine carbamate, hexamethylenediamine, triethylenetetramine, tetraethylenepentamine, ammonium benzoate, and the like. Further, examples of polyol-based vulcanizing agents include bisphenol, hydroquinone, pentaerythritol, and the like. Examples of metal soap-based vulcanizing agents include sodium stearate, potassium stearate, sodium oleate, potassium oleate, and the like. These may be used alone or in combination of two or more.

[0034] The types of vulcanization accelerators are not limited, but examples include guanidine salts such as hexamethylenetetramine, butyraldehyde-monobutylamine condensate, trichlorotolylidene tetramine, diphenylguanidine, etc.; thiazoles such as imidazoline, mercaptothiazoline, etc.; sulfenamides; thioureas such as thiocarbamide, diethyl thiourea, dibutyl thiourea, etc.; dithiocarbamate salts such as sodium dimethyldithiocarbamate; thiuram compounds; thiodiglycolate esters, and the like. These may be used alone or in combination of two or more.

[0035] The kneading of the unvulcanized rubber, heat-resistant reinforcing fibers, friction modifier, and other necessary formulations can be carried out in any manner. For example, kneading machines such as extruders (single-screw extruders, twin-screw extruders, etc.), kneaders, and mixers (high-speed flow mixers, paddle mixers, ribbon mixers, etc.) can be used. These can be used alone or in combination of two or more. When using two or more kneading machines, they can be used continuously or in a batch manner. Also, each raw material can be kneaded all at once or added in multiple stages in several batches. Also, the kneading temperature during kneading is not limited. For example, it can be 25°C or higher and 400°C or lower, it can be 50°C or higher and 350°C or lower, it can be 75°C or higher and 325°C or lower, and it can be 100°C or higher and 300°C or lower.

[0036] Also, the kneaded product can be extruded (in the extrusion step in the manufacturing method of the dry friction material composition described later) to orient the heat-resistant reinforcing fibers in the kneaded product after extrusion. The extrusion of the kneaded product can be carried out in any manner. For example, it can be carried out using an extruder such as a single-screw extruder, a twin-screw extruder, or a 1.5-screw extruder. Also, for example, the above extrusion can be carried out by using a molding die having a preliminary cavity for accommodating the kneaded product, a molding cavity for molding a precursor of the dry friction material (a shaped article before vulcanization), and a runner connecting these preliminary cavity and molding cavity. That is, the kneaded product (a kneaded product containing unvulcanized rubber, heat-resistant reinforcing fibers, a friction modifier, etc.) is accommodated in the preliminary cavity, and by die pressing, the kneaded product is moved from the preliminary cavity to the molding cavity through the runner, so that extrusion can be carried out when moving from the runner to the molding die cavity. Thereby, the heat-resistant reinforcing fibers in the kneaded product accommodated in the molding cavity can be oriented in a certain direction.

[0037] These extrusion operations may be performed only once or multiple times. Performing multiple extrusions means performing another extrusion operation on the extruded kneaded material (hereinafter also simply referred to as "extrudate"). That is, for example, multiple extrusions can be performed for the purpose of improving the orientation of the heat-resistant reinforcing fibers. On the other hand, it is preferable not to perform an operation that reduces the orientation of the heat-resistant reinforcing fibers on the extrudate. That is, for example, it is preferable not to perform operations such as kneading the extrudate or pelletizing it.

[0038] Also, the shape of the extrudate is not limited and can be columnar (including continuous linear), cylindrical, sheet-like, etc. Among these, columnar or cylindrical is preferable, and columnar is more preferable. Therefore, the die used for extrusion is not limited either, but a die that can form the extrudate into a columnar or cylindrical shape is preferable, and a die that can form it into a columnar shape is more preferable. Also, when the extrudate is columnar, its cross-sectional shape is not limited and can be circular, polygonal (triangular, square), etc. Among these, a circular shape is preferable. Note that the circular shape can include not only a perfect circle but also forms such as an ellipse and a water droplet shape where at least a part of the outer edge is a curved shape.

[0039] Furthermore, when the extrudate is in a cylindrical shape (including continuous linear with a circular cross-section), from the viewpoints of the fluidity of the kneaded material of the unvulcanized rubber, heat-resistant reinforcing fibers, and friction modifier, and the average length of the heat-resistant reinforcing fibers, etc., its diameter is not limited, but for example, it can be 1 mm to 50 mm, it can be 2 mm to 40 mm, it can be 3 mm to 30 mm, it can be 4 mm to 25 mm, and it can be 5 mm to 20 mm.

[0040] The composition for dry friction materials of the present invention is obtained by extruding a kneaded product of unvulcanized rubber that becomes vulcanized rubber, heat-resistant reinforcing fibers, and a friction modifier. According to the composition for dry friction materials of the present invention, a dry friction material having performance equivalent to that of conventional products can be manufactured without using roving. That is, a dry friction material can be easily manufactured without using roving. This effect is considered to be due to the fact that the heat-resistant reinforcing fibers contained in the composition for dry friction materials are oriented in a certain direction by extrusion as described above. However, this orientation is not obtained by individually orienting each of all the contained heat-resistant reinforcing fibers one by one. Therefore, it is extremely difficult to uniquely specify or quantify, for example, how many heat-resistant reinforcing fibers are oriented in the first direction and how many are oriented in the second direction. Therefore, it is not practically possible to directly specify the orientation that contributes to the effect of the present invention for the composition for dry friction materials of the present invention, and there are impossible and impractical circumstances.

[0041] [3] Dry friction material The dry friction material of the present invention is characterized by being obtained by vulcanizing the composition for dry friction materials of the present invention. The above vulcanization (vulcanization step in the manufacturing method of the dry friction material described later) may be performed in any manner, but it can be performed using the above-described vulcanizing agent, vulcanization accelerator, etc. Also, during vulcanization, heating can be performed for the purpose of accelerating vulcanization. The operating temperature during vulcanization is not limited, but for example, it can be 100°C or higher and 400°C or lower, it can be 110°C or higher and 350°C or lower, it can be 115°C or higher and 300°C or lower, and it can be 120°C or higher and 250°C or lower.

[0042] As described above, the dry friction material of the present invention is obtained by vulcanizing the composition for dry friction material of the present invention. That is, the dry friction material of the present invention is obtained by vulcanizing an extrudate obtained by extruding a kneaded product of unvulcanized rubber, heat-resistant reinforcing fibers, and a friction modifier. And the effect of the present invention is considered to be due to the fact that the heat-resistant reinforcing fibers contained in the dry friction material are oriented in a certain direction by extrusion as described above. However, this orientation is not obtained by individually orienting each of all the contained heat-resistant reinforcing fibers one by one. For this reason, it is extremely difficult to uniquely specify or quantify, for example, how many heat-resistant reinforcing fibers are oriented in the first direction and how many are oriented in the second direction. Therefore, it is not practically possible to directly specify the orientation contributing to the effect of the present invention for the dry friction material of the present invention, and there are impossible and impractical circumstances.

[0043] [4] Method for manufacturing a composition for dry friction material, method for manufacturing a dry friction material The method for manufacturing a composition for a dry friction material of the present invention is characterized by comprising an extrusion step of extruding a kneaded product of unvulcanized rubber that becomes vulcanized rubber, heat-resistant reinforcing fibers, and a friction modifier. Further, the method for manufacturing a dry friction material of the present invention is characterized by comprising a vulcanization step of vulcanizing this composition for a dry friction material. Each is as described in [2] above.

[0044] [5] Others The shape, size, etc. of the dry friction material of the present invention are not limited, and its use is also not limited. The dry friction material of the present invention is widely used in various fields such as automobiles, railway vehicles (vehicles in general), aircraft fuselages (fuselages in general), ships and hulls (hulls in general), machine tools, industrial machines, and product manufacturing. More specifically, for example, clutch parts (clutch plates) such as manual clutches (clutch facings), slip clutches, one-way clutches, torque limiters, and thrust dampers can be mentioned. Among these, when used particularly as a torque limiter, it can be a dry friction material that can achieve stability of torque interruption (cutting of excessive torque), suppression of a decrease in the friction coefficient, and the like.

Examples

[0045] Hereinafter, the present invention will be described by way of examples. [1] Preparation of Composition for Dry Friction Material (1) Composition for Dry Friction Material of Experimental Example 1 (42 parts by mass of short glass fibers) Unvulcanized rubber: Styrene-butadiene rubber (SBR) and acrylonitrile-butadiene rubber (NBR) were prepared to a total of 100 parts by mass. Curable resin: As the curable resin that becomes a cured resin, phenol resin was prepared to a total of 20 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Heat-resistant reinforcing fiber: Short glass fibers (average fiber diameter 9 μm, average fiber length 3 mm) were prepared to a total of 42 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Friction modifier: Carbon-based materials (carbon black, graphite), carbonate-based materials (calcium carbonate), oxide-based materials (zinc oxide), mineral-based materials (diatomaceous earth), and resin (cashew dust) were prepared to a total of 201 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Other components: A plasticizer, a vulcanizing agent, and a vulcanization accelerator were prepared to a total of 52.8 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Thereafter, the above unvulcanized rubber, curable resin, heat-resistant reinforcing fiber, friction modifier, and other components were kneaded (rubber kneading step) to obtain a sheet-like material. The obtained sheet-like material was shredded into about 5 mm squares to obtain shredded materials. The obtained shredded materials were put into an extruder and extruded to form a continuous linear shape with a diameter of 5 to 10 mm (extrusion step), and wound into a coil shape as the composition for dry friction material of Experimental Example 1 (extrudate) (winding step).

[0046] (2) Composition for Dry Friction Material of Experimental Example 2 (100 parts by mass of short glass fibers) Unvulcanized rubber: Prepared in the same manner as in Experimental Example 1. Curable resin: Prepared in the same manner as in Experimental Example 1. Heat-resistant reinforcing fiber: Short glass fibers (average fiber diameter 9 μm, average fiber length 3 mm) were prepared to a total of 100 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Friction modifier: Prepared in the same manner as in Experimental Example 1. Other components: Prepared in the same manner as in Experimental Example 1. Thereafter, in the same manner as in Experimental Example 1, a composition for dry friction material (extrudate) of Experimental Example 2 was obtained.

[0047] (3) Composition for dry friction material of Experimental Example 3 (168 parts by mass of short glass fibers) Unvulcanized rubber: Prepared in the same manner as in Experimental Example 1. Curing resin: Prepared in the same manner as in Experimental Example 1. Heat-resistant reinforcing fiber: Short glass fibers (average fiber diameter 9 μm, average fiber length 3 mm) were prepared so as to total 168 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Friction modifier: Prepared in the same manner as in Experimental Example 1. Other components: Prepared in the same manner as in Experimental Example 1. Thereafter, in the same manner as in Experimental Example 1, a composition for dry friction material (extrudate) of Experimental Example 3 was obtained.

[0048] (4) Composition for dry friction material of Experimental Example 4 (217 parts by mass of short glass fibers) Unvulcanized rubber: Prepared in the same manner as in Experimental Example 1. Curing resin: Prepared in the same manner as in Experimental Example 1. Heat-resistant reinforcing fiber: Short glass fibers (average fiber diameter 9 μm, average fiber length 3 mm) were prepared so as to total 217 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Friction modifier: Prepared in the same manner as in Experimental Example 1. Other components: Prepared in the same manner as in Experimental Example 1. Thereafter, in the same manner as in Experimental Example 1, a composition for dry friction material (extrudate) of Experimental Example 4 was obtained.

[0049] (5) Composition for dry friction material of Experimental Example 5 (271 parts by mass of short glass fibers) Unvulcanized rubber: Prepared in the same manner as in Experimental Example 1. Curing resin: Prepared in the same manner as in Experimental Example 1. Heat-resistant reinforcing fiber: Short glass fibers (average fiber diameter 9 μm, average fiber length 3 mm) were prepared so as to total 271 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Friction modifier: Prepared in the same manner as in Experimental Example 1. Other components: Prepared in the same manner as in Experimental Example 1. Thereafter, in the same manner as in Experimental Example 1, a composition for dry friction material (extrudate) of Experimental Example 5 was obtained.

[0050] [2] Manufacture of dry friction material (1) A mold for dry friction material with a ring-shaped cavity having an inner diameter of 194 mm and an outer diameter of 217 mm was prepared. After placing each composition for dry friction material (continuous linear extrudate) of Experimental Examples 1 to 5 obtained in [1] above in the mold, the composition for dry friction material was cut so as not to cause excess and the mold was closed. Thereafter, while applying a pressure of 50 MPa, molding was performed at a mold temperature of 150 to 200 °C (hot molding process) to obtain a ring-shaped molded product. (2) The obtained ring-shaped molded product was heated to 200 to 300 °C and heat-treated to obtain a crude product (heat treatment process). (3) The obtained crude product was polished to obtain a polished product. (4) Through holes (circular) were drilled in the obtained polished product at every 60 degrees (drilling process) to obtain the dry friction materials of Experimental Examples 1 to 5.

[0051] (5) Composition for dry friction material of Experimental Example 6 (168 parts by mass of glass short fibers) Unvulcanized rubber: Prepared in the same manner as in Experimental Example 3. Curing resin: Prepared in the same manner as in Experimental Example 3. Heat-resistant reinforcing fiber: Glass short fibers (average fiber diameter 9 μm, average fiber length 3 mm) were prepared so as to total 168 parts by mass with respect to 100 parts by mass of the total amount of unvulcanized rubber. Friction modifier: Prepared in the same manner as in Experimental Example 3. Other components: Prepared in the same manner as in Experimental Example 3. Thereafter, the unvulcanized rubber, curing resin, heat-resistant reinforcing fiber, friction modifier and other components were kneaded (rubber kneading process) to obtain a sheet-like material. The obtained sheet-like material was shredded into approximately 5 mm squares to obtain shredded materials. Using the obtained shredded materials, the dry friction material of Experimental Example 6 was obtained by the same operations as in (1) to (4) above.

[0052] [3] Evaluation (1) Evaluation of flatness and smoothness The dry friction materials of 10 Experimental Examples 3 (extrudates are molded) and the dry friction materials of 10 Experimental Examples 6 (pellets are molded) were compared, and the flatness and smoothness were evaluated. As a result, for all the dry friction materials of Experimental Example 3, their inner peripheral surfaces and outer peripheral surfaces were smoother and more even than those of the dry friction materials of Experimental Example 6.

[0053] (2) Evaluation of impact resistance The dry friction materials of 5 Experimental Examples 3 (extrudates are molded) and the dry friction materials of 5 Experimental Examples 6 (pellets are molded) were each dropped from a height of 1 m. As a result, none of the dry friction materials of Experimental Example 3 cracked. In contrast, all 5 of the dry friction materials of Experimental Example 6 were broken into 3 pieces by the impact of the fall. That is, they cracked due to the fall.

[0054] (3) Evaluation of shaping accuracy For the dry friction materials of each 10 Experimental Examples 1 to 5 (extrudates are molded), the inner diameters at 6 locations every 60 degrees were measured, and the average value of the inner diameters was calculated. Further, the average values of these 6 inner diameters were averaged again to calculate the average inner diameter values of each of Experimental Examples 1 to 5. Then, the change rate [(X1 - Y1) / X1 × 100] of the average inner diameter value Y1 (mm) with respect to the designed inner diameter value X1 (mm) of the mold was calculated and shown in Table 1 as "Inner diameter change rate (%)". Similarly, for the dry friction materials of each 10 Experimental Examples 1 to 5 (extrudates are molded), the outer diameters at 6 locations every 60 degrees were measured, and the average value of the outer diameters was calculated. Further, the average values of these 6 outer diameters were averaged again to calculate the average outer diameter values of each of Experimental Examples 1 to 5. Then, the change rate [(X2 - Y2) / X2 × 100] of the average outer diameter value Y2 (mm) with respect to the designed outer diameter value X2 (mm) of the mold was calculated and shown in Table 1 as "Outer diameter change rate (%)". Furthermore, this result was shown in FIG. 4 as the correlation between the content of the heat-resistant reinforcing fiber and each change rate.

[0055]

Table 1

[0056] (4) Effects of the examples From the evaluation results of the above [3](1), it can be seen that among the dry friction materials of Experimental Example 3 with the same composition and the same content of heat-resistant reinforcing fibers, but with the heat-resistant reinforcing fibers oriented in a certain direction, the flatness and smoothness are excellent. In contrast, it can be seen that the dry friction material of Experimental Example 6 without the orientation of heat-resistant reinforcing fibers is inferior in flatness and smoothness. Also, from the evaluation results of the above [3](2), it can be seen that among the dry friction materials of Experimental Example 3 with the same composition and the same content of heat-resistant reinforcing fibers, but with the heat-resistant reinforcing fibers oriented in a certain direction, the impact resistance is excellent. In contrast, it can be seen that the dry friction material of Experimental Example 6 without the orientation of heat-resistant reinforcing fibers is inferior in impact resistance. Furthermore, among the evaluation results of the above [3](3), from the results of Experimental Examples 1 to 3, it can be seen that the shaping accuracy is improved by increasing the content of heat-resistant reinforcing fibers oriented in a certain direction (see Table 1 and Figure 4). On the other hand, among the evaluation results of the above [3](3), from the results of Experimental Examples 3 to 5, it can be seen that when the content of heat-resistant reinforcing fibers oriented in a certain direction is excessively increased, although it is better than Experimental Example 2, the shaping accuracy gradually shows a tendency to decrease (see Table 1 and Figure 4). Furthermore, in the dry friction material of Experimental Example 6, since the heat-resistant reinforcing fibers are not oriented, it can be seen that although the content of heat-resistant reinforcing fibers is equivalent to that of Experimental Example 3, the change rate is significantly inferior both in the outer diameter and the inner diameter.

Explanation of Symbols

[0057] 1; Dry friction material, 11; Matrix material, 12; Dispersion material, 121; Heat-resistant reinforcing fiber, 121a; Longitudinal direction, 13; Outer edge, 131; Tangent line.

Claims

1. A dry friction material containing a matrix material and a dispersion material, wherein the matrix material contains vulcanized rubber, the dispersion material contains heat-resistant reinforcing fibers and a friction modifier, and the dry friction material is characterized in that the heat-resistant reinforcing fibers are oriented in a certain direction.

2. Having an outer edge in a circular or arc shape, The dry friction material according to claim 1, wherein the orientation is parallel to the outer edge.

3. The dry friction material according to claim 1 or 2, wherein the heat-resistant reinforcing fibers are 50 to 300 parts by mass based on 100 parts by mass of the vulcanized rubber.

4. The dry friction material according to claim 3, wherein the average fiber length of the heat-resistant reinforcing fibers is 1 to 3 mm.

5. The dry friction material according to claim 4, wherein the average fiber diameter of the heat-resistant reinforcing fibers is 15 μm or less.

6. A composition for a dry friction material for obtaining the dry friction material according to claim 1, characterized in that it is formed by extruding a kneaded product of the unvulcanized rubber to be the vulcanized rubber, the heat-resistant reinforcing fibers, and the friction modifier.

7. A dry friction material characterized in that it is obtained by vulcanizing the composition for a dry friction material according to claim 6.

8. A method for manufacturing a composition for a dry friction material for obtaining the dry friction material according to claim 1, characterized by comprising an extrusion step of extruding a kneaded product of the unvulcanized rubber to be the vulcanized rubber, the heat-resistant reinforcing fibers, and the friction modifier.

9. A method for manufacturing a dry friction material for obtaining a dry friction material from the composition for a dry friction material obtained by the manufacturing method according to claim 8, characterized by comprising a vulcanization step of vulcanizing the composition for a dry friction material.

10. The method for manufacturing a dry friction material according to claim 9, wherein the heat-resistant reinforcing fibers are 50 to 300 parts by mass based on 100 parts by mass of the vulcanized rubber.

11. The method for manufacturing a dry friction material according to claim 9 or 10, wherein the average fiber length of the heat-resistant reinforcing fibers is 1 to 3 mm.

12. The method for manufacturing a dry friction material according to claim 11, wherein the average fiber diameter of the heat-resistant reinforcing fibers is 15 μm or less.

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