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

Abstract

The purpose of the present invention is 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. A dry friction material 1 comprises a matrix material 11 and a dispersed material 12, wherein the matrix material 11 includes a vulcanized rubber and the dispersed material 12 comprises heat-resistant reinforcing fibers 121 and a friction regulation material, the heat-resistant reinforcing fibers 121 being oriented in a certain direction. This composition for a dry friction material is obtained by extruding a kneaded mixture comprising an unvulcanized rubber, heat-resistant reinforcing fibers, and a friction regulation material. This production method for the composition for a dry friction material includes an extrusion step in which a kneaded mixture comprising an unvulcanized rubber, heat-resistant reinforcing fibers, and a friction regulation material is extruded.

Description

Dry friction material and method of manufacturing the same, and composition for dry friction material and method of manufacturing the same

[0001] The present invention relates to a dry friction material and a method for producing the same, and a composition for a dry friction material and a method for producing the same, and more particularly to a dry friction material containing a matrix material and a dispersant and a method for producing the same, and a composition for a dry friction material and a method for producing the same.

[0002] Conventionally, dry friction materials have been manufactured by a complicated method, including, for example, (1) a resin liquid preparation process for preparing a resin liquid such as a thermosetting resin solution or a dispersion liquid in which a thermosetting resin is dispersed, (2) a resin liquid impregnation process for impregnating a glass roving (glass fiber bundle) with the resin liquid, (3) a resin liquid drying process for drying the resin liquid impregnated into the glass roving, (4) a rubber kneading process for preparing a compound rubber containing latex, a vulcanizing agent, additives, etc., (5) a coating process for coating the resin-impregnated glass roving with the compound rubber, (6) a winding process for winding the compound rubber-coated glass roving into a ring shape of a predetermined size, (7) a thermoforming process for thermoforming the wound glass roving into a mold, (8) a heat treatment process for curing the thermosetting resin in the thermoformed molded product, (9) a polishing process for polishing the obtained base molded product, and (10) a drilling process for drilling necessary holes in the polished molded product (see Patent Documents 1 and 2 listed below).

[0003] JP 2000-037797 A JP 2014-214772 A

[0004] Dry friction materials often have a circular ring shape as their general shape, and wet friction materials also often have a circular ring shape. However, the manufacturing methods for dry friction materials and wet friction materials are significantly different. For example, wet friction materials can be manufactured by attaching friction base material segments that exhibit predetermined friction performance to the surface of a plate that has been previously shaped into a circular ring shape. In contrast, dry friction materials, as described above, are manufactured by arranging roving material in a circular shape, thermoforming, and then shaping the material by polishing or other methods to obtain the circular shape. As described above, wet friction materials use a master plate, while dry friction materials do not use a master plate and require a complex manufacturing process in that the general shape is shaped from roving material. This is thought to be due to the difficulty of achieving the performance required for dry friction materials by simply attaching segments, etc. Therefore, there is a need for a dry friction material and a manufacturing method therefor, as well as a composition for a dry friction material and a manufacturing method therefor that can be manufactured more simply while satisfying the performance required for dry friction materials.

[0005] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a dry friction material and a method for producing the same, as well as a composition for a dry friction material and a method for producing the same, which can be produced more simply than conventional methods.

[0006] As described above, the present inventors investigated the replacement of roving materials (dry friction material materials using glass roving) with molding materials (dry friction material materials that can be molded) for a simpler manufacturing process. As a result, they discovered that the presence of roving in conventional dry friction materials improved molding precision and impact strength. On the other hand, to realize a molding material, it was thought that short fibers could be incorporated as reinforcing fibers instead of roving, and in this case, it was thought that incorporating a larger amount of reinforcing fibers would contribute to improved molding precision and impact strength. However, obtaining a molding material requires blending with various other raw materials, and it has been found that the greater the amount of reinforcing fibers incorporated, the more difficult it becomes to maintain a balance with other components (friction modifiers, curable resins, plasticizers, etc.). Therefore, the present inventors believed that the contribution of reinforcing fibers needs to be improved by properties other than their blending amount, and focused on the orientation of the reinforcing fibers as one such property. The inventors then discovered that randomly arranged reinforcing fibers reduced the contribution of the reinforcing fibers to each performance characteristic, and believed that if the orientation of the reinforcing fibers within the dry friction material could be actively adjusted, a dry friction material that satisfied the required performance characteristics could be obtained. They investigated a method for achieving this active orientation of the reinforcing fibers, and by discovering this method, they were able to complete the present invention.

[0007] The present invention includes the following inventions. [1] A dry friction material including a matrix material and a dispersion material, wherein the matrix material includes vulcanized rubber, and the dispersion material includes heat-resistant reinforcing fibers and a friction modifier, and the heat-resistant reinforcing fibers are oriented in a fixed direction. [2] The dry friction material according to [1] above, which has a circular or arc-shaped outer edge, and the orientation is parallel to the outer edge. [3] The dry friction material according to [1] or [2] above, wherein the heat-resistant reinforcing fibers are contained in an amount of 50 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the vulcanized rubber. [4] The dry friction material according to any of [1] to [3] above, wherein the heat-resistant reinforcing fibers have an average fiber length of 1 to 3 mm. [5] The dry friction material according to any of [1] to [4] above, wherein the heat-resistant reinforcing fibers have an average fiber diameter of 15 μm or less. [6] A composition for a dry friction material for obtaining the dry friction material described in any one of [1] to [5] above, characterized by being obtained by extruding a kneaded mixture of unvulcanized rubber to become the vulcanized rubber, the heat-resistant reinforcing fiber, and the friction modifier. [7] A dry friction material characterized by vulcanizing the composition for a dry friction material described in [6] above. [8] A method for producing a composition for a dry friction material for obtaining the dry friction material described in any one of [1] to [5] above, characterized by comprising an extrusion step of extruding a kneaded mixture of unvulcanized rubber to become the vulcanized rubber, the heat-resistant reinforcing fiber, and the friction modifier. [9] A method for producing a dry friction material from the composition for a dry friction material obtained by the production method described in [8] above, 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 [9] above, wherein the heat-resistant reinforcing fibers are used in an amount of 50 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the unvulcanized rubber.

[11] The method for producing a dry friction material according to [9] or

[10] above, wherein the heat-resistant reinforcing fibers have an average fiber length of 1 to 3 mm.

[12] The method for producing a dry friction material according to any one of [9] to

[11] above, wherein the heat-resistant reinforcing fibers have an average fiber diameter of 15 μm or less.

[0008] The dry friction material of the present invention can be produced more easily than conventionally. The method for producing a dry friction material of the present invention allows a dry friction material having excellent performance to be produced more easily than conventionally. The composition for a dry friction material of the present invention allows a dry friction material to be produced more easily than conventionally. The method for producing a composition for a dry friction material of the present invention allows the composition for a dry friction material to be reliably obtained.

[0009] It is a schematic diagram for explaining an example of the dry friction material of the present invention. It is a schematic diagram for explaining another example of the dry friction material of the present invention. It is a schematic diagram for explaining yet another example of the dry friction material of the present invention. It is an explanatory diagram showing the correlation between the content of the heat-resistant reinforcing fiber and each rate of change according to the examples.

[0010] The present invention will be described below with reference to the drawings. The matters shown here are for illustrative purposes and are intended to exemplify embodiments of the present invention, and are set forth in order to provide what is believed to be the most effective and easily understandable explanation of the principles and conceptual features of the present invention. In this regard, it is not intended to show structural details of the present invention beyond the extent necessary for a fundamental understanding of the present invention, and the description, taken together with the drawings, will make clear to those skilled in the art how some aspects of the present invention can be actually embodied.

[0011] [1] Dry Friction Material The dry friction material (1) of the present invention comprises a matrix material (11) and a dispersion material (12), wherein the matrix material (11) comprises vulcanized rubber, and the dispersion material (12) comprises heat-resistant reinforcing fibers (121) and a friction modifier, and wherein the heat-resistant reinforcing fibers (121) are oriented in a fixed direction.

[0012] The "matrix material (11)" is a material constituting the dry friction material 1 and is a material that forms a parent phase (continuous phase) for the dispersion material 12. The matrix material 11 includes 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 ester / 2-chloroethyl vinyl ether copolymer rubber, acrylic ester / acrylonitrile copolymer rubber, etc.), urethane rubber, fluororubber (fluorinated olefin / vinylidene fluoride copolymer rubber, etc.), and silicone rubber. 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 preferred, and NBR and SBR are more preferred.

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

[0014] When the entire dry friction material is taken as 100 mass%, the amount of the matrix material is not limited, but can be, for example, 1 to 50 mass%, 2 to 45 mass%, 3 to 40 mass%, 4 to 35 mass%, 5 to 30 mass%, or 6 to 25 mass%. Furthermore, when the matrix material contains a cured resin, the amount of the cured resin is not limited, but, for example, when the entire vulcanized rubber is taken as 100 mass%, the amount of the cured resin can be 1 to 100 mass%, 2 to 75 mass%, 3 to 50 mass%, 4 to 40 mass%, or 5 to 35 mass%. Furthermore, when the matrix material contains a plasticizer, the amount of the plasticizer is not limited, but for example, when the entire vulcanized rubber is taken as 100 parts by mass, the amount of 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 "dispersed material (12)" is a material that exists dispersedly within the matrix material 11 described above. The dispersed material 12 includes heat-resistant reinforcing fibers 121 and a friction modifier. The "heat-resistant reinforcing fibers (121)" are fibrous materials within the dispersed material 12. The type of heat-resistant reinforcing fibers 121 is not limited, and inorganic fibers can be suitably used. The type of inorganic fiber is not limited, and examples include amorphous fibers (glass fibers, silica fibers, slag wool, rock wool, etc.), single crystal fibers (ceramic fibers, alumina fibers, magnesia fibers, titanate fibers, wollastonite fibers, etc.), polycrystalline fibers (ceramic fibers, alumina fibers, silica-alumina fibers, etc.), carbon-based fibers (carbon fibers, carbonized fibers, etc.), and metal fibers. These may be used alone or in combination of two or more types.

[0016] From the viewpoints of friction performance, heat resistance, safety, cost, etc., in dry friction materials, inorganic fibers are preferred, and amorphous fibers and / or carbon-based fibers are more preferred, with glass fibers and / or carbon fibers being even more preferred, and glass fibers are particularly preferred. As will be described later, these heat-resistant reinforcing fibers themselves have appropriate rigidity. Therefore, by flowing a kneaded material containing raw materials, the heat-resistant reinforcing fibers can be easily aligned in the same direction and can be oriented in an elongated state without being bent. Furthermore, when the kneaded material is flowed, the heat-resistant reinforcing fibers are less likely to be broken down and can maintain their length, which is also preferable.

[0017] The heat-resistant reinforcing fiber has heat resistance. Although the specific heat resistance 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. The term "fiber" refers to its shape, meaning that it has an elongated shape. Although the specific shape is not limited, the aspect ratio is preferably 50 or higher. Furthermore, the length (maximum length) is preferably 500 μm or higher, and more preferably 750 μm or higher. The upper limit of the aspect ratio is not limited, but can be, for example, 1000 or lower. Furthermore, the upper limit of the length of the heat-resistant reinforcing fiber is not limited, but can be, for example, 10 mm or lower.

[0018] Furthermore, the heat-resistant reinforcing fibers 121 may have any fibrous shape as described above, but the average fiber length is preferably 0.5 to 5 mm, more preferably 0.5 to 4 mm, even more preferably 1 to 4 mm, and particularly preferably 1 to 3 mm. The average fiber length within the above range makes it easier to orient the fibers in a certain direction, and the effects of orienting the fibers in a certain direction can be more pronounced. This average fiber length is the average of the fiber lengths (maximum lengths) measured for 50 randomly selected heat-resistant reinforcing fibers.

[0019] Furthermore, the heat-resistant reinforcing fibers 121 may have any fiber shape as described above, but their fiber diameter is preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. The average fiber diameter of the heat-resistant reinforcing fibers is not limited, but 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. The greater the average fiber diameter within the above range, the easier it is to orient the fibers in a certain direction, and the more pronounced the effects of orienting them in a certain direction can be achieved. Note that this average fiber diameter is the average of the fiber diameters (maximum diameters) actually measured for 50 randomly selected heat-resistant reinforcing fibers.

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

[0021] The term "oriented" as used herein means that the heat-resistant reinforcing fibers 121 in the matrix material 11 are arranged with regularity. In other words, the longitudinal directions of the heat-resistant reinforcing fibers 121 are aligned according to a predetermined rule. In the present invention, this means that the longitudinal directions of the heat-resistant reinforcing fibers 121 are aligned in a certain direction. When the directions are aligned, this includes not only directions that are completely aligned with the predetermined direction, but also directions that intersect with the predetermined direction at an angle of 45 degrees or less. From the viewpoint of improving dimensional stability and impact resistance, this intersecting angle is preferably 30 degrees or less, more preferably 20 degrees or less, and even more preferably 15 degrees or less. In other words, an orientation that is aligned within a closer angle range is preferable. Furthermore, it is preferable that all of the heat-resistant reinforcing fibers are oriented in the same direction, but typically, it is preferable that 50% or more of the heat-resistant reinforcing fibers are oriented in the same direction. From the viewpoint of improving dimensional stability and impact resistance, this proportion 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] Furthermore, as described above, the orientation direction in the present invention is fixed to a certain direction. This certain direction may be one, two, or three directions. However, it is preferable to have as few directions as possible. Therefore, it is preferable to have two orientation directions rather than three orientation directions, and it is even more preferable to have one orientation direction. In the present invention, the heat-resistant reinforcing fibers contained in the dry friction material are oriented in a certain direction, so that the dry friction material can have performance equivalent to that obtained by a conventional method, i.e., a dry friction material obtained using roving. In particular, the dry friction material can have excellent dimensional accuracy and impact resistance. Furthermore, the uniform orientation of the heat-resistant reinforcing fibers can be obtained by including an extrusion process in the manufacturing process, in which a kneaded material containing unvulcanized rubber and heat-resistant reinforcing fibers is extruded, as will be described later. Furthermore, the heat-resistant reinforcing fibers can be oriented in a certain direction when the heat-resistant reinforcing fibers contained in the composition for a dry friction material used to mold the dry friction material are oriented in a certain direction, or when extrusion is performed to obtain a molded product that will become the dry friction material, and the heat-resistant reinforcing fibers are oriented in a certain direction within a mold containing the molded product.

[0023] More specifically, the dry friction material of the present invention has a circular or arc-shaped outer edge 13, and the orientation is preferably parallel to the outer edge 13 (see FIGS. 1 and 2 ). That is, since dry friction materials are often subjected to rotational sliding, the outer edge can be formed to have a circular or arc-shaped configuration. When formed in this manner, the heat-resistant reinforcing fibers 121 contained in the matrix material 11 are preferably oriented so that their longitudinal direction is parallel to the outer edge. In other words, the longitudinal direction 121a of the heat-resistant reinforcing fibers 121 is preferably approximately parallel to a tangent 131 to the circular or arc-shaped outer edge 13. It is preferable that 50% or more of the heat-resistant reinforcing fibers conform to this rule, and more preferably 60% or more, even 70% or more, even 80% or more, even 90% or more, and even 95% or more of the heat-resistant reinforcing fibers conform to this rule.

[0024] Similarly, the dry friction material of the present invention may have a linear outer edge 14, and the orientation may be parallel to the outer edge 14 in the longitudinal direction (see FIG. 3). In such a case, the heat-resistant reinforcing fibers 121 contained in the matrix material 11 are preferably oriented parallel to the outer edge, and the orientation of the heat-resistant reinforcing fibers is preferably such that 50% or more, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and even more preferably 95% or more of the heat-resistant reinforcing fibers conform to the rule.

[0025] The "friction modifier" is a material in the dispersion material 12 that contributes to the performance of the dry friction material through its inclusion, and is particularly a material that has a friction-modifying effect. The friction modifier is in a non-fibrous form (a form obtained by excluding the fibrous form exhibited by the heat-resistant reinforcing fibers from the overall form). That is, it has a form different from that of the heat-resistant reinforcing fibers. The type of friction modifier is not limited, and examples include inorganic friction modifiers (inorganic friction modifiers made of inorganic materials, complex inorganic friction modifiers mainly made of inorganic materials but also containing organic materials, etc.) and organic friction modifiers (inorganic friction modifiers made of organic materials, complex inorganic friction modifiers mainly made of organic materials but also containing inorganic materials, etc.). These may be used alone or in combination of two or more types.

[0026] The type of 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 oxide], titanium oxide), Examples of suitable materials include carbon, 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, carbon black, coke, etc.), and metal materials (aluminum, copper, brass, etc.). 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.

[0028] The friction modifier may be in a non-fibrous form. 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 friction modifier may be in the form of granules, irregular shapes, chunks, needles, whiskers, or the like. The size of the friction modifier is not limited, but the average particle size d can be, for example, 0.1≦d (μm)<500 μm, or 1≦d (μm)≦350, or 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 produced more simply than conventional methods. Specifically, as described above, conventional manufacturing methods using roving require ten steps, namely, (1) a resin liquid blending step, (2) a resin liquid impregnation step, (3) a resin liquid drying step, (4) a rubber kneading step, (5) a coating step, (6) a winding step, (7) a thermoforming step, (8) a heat treatment step, (9) a polishing step, and (10) a perforation step. In contrast, the dry friction material of the present invention can be produced through seven steps, namely, (1) a rubber kneading step, (2) an extrusion step, (3) a winding step, (4) a thermoforming step, (5) a heat treatment step, (6) a polishing step, and (7) a perforation step, thereby achieving a significant reduction in the number of steps.

[0031] [2] Composition for dry friction material The composition for dry friction material of the present invention is a composition for dry friction material for obtaining the dry friction material of the present invention, and is characterized by being obtained by extruding a kneaded mixture of unvulcanized rubber to be used as the vulcanized rubber, heat-resistant reinforcing fibers, and a friction modifier.

[0032] The dry friction material composition of the present invention can be made into a dry friction material by vulcanization. The heat-resistant reinforcing fiber and friction modifier are as described above. The unvulcanized rubber is a precursor to the vulcanized rubber described above. To produce the vulcanized rubber by vulcanization, the 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 thereof 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, and maleimide-based vulcanizing agents. These may be used alone or in combination of two or more. Examples of sulfur-based vulcanizing agents include sulfur (powdered sulfur, sulfur flowers, surface-treated sulfur, colloidal sulfur, etc.) and sulfur chloride. Examples of organic peroxide-based vulcanizing agents include dicumyl peroxide, cumene peroxide, cumyl peroxide, dicumyl peroxide, and bis(α,α-dimethylbenzyl) peroxide. Examples of metal oxide vulcanizing agents include zinc oxide and magnesium oxide. Examples of sulfur-containing organic vulcanizing agents include morpholine disulfide, alkylphenol disulfide, and thiuram polysulfide. Examples of polyamine vulcanizing agents include hexamethylenediamine carbamate, hexamethylenediamine, triethylenetetramine, tetraethylenepentamine, and ammonium benzoate. Examples of polyol vulcanizing agents include bisphenol, hydroquinone, and pentaerythritol. Examples of metal soap vulcanizing agents include sodium stearate, potassium stearate, sodium oleate, and potassium oleate. These may be used alone or in combination of two or more.

[0034] The type of vulcanization accelerator is not limited, and examples thereof include hexamethylenetetramine, butylaldehyde-monobutylamine condensates, tricrotonylidenetetramine, guanidine salts such as diphenylguanidine, thiazoles such as imidazoline and mercaptothiazoline, sulfenamide, thiocarbamide, thioureas such as diethyl thiourea and dibutyl thiourea, dithiocarbamates such as sodium dimethyl dithiocarbamate, thiuram compounds, thioglycolic acid esters, etc. These may be used alone or in combination of two or more.

[0035] The unvulcanized rubber, heat-resistant reinforcing fiber, friction modifier, and other optional compounds may be kneaded in any manner. For example, kneaders such as extruders (single-screw extruders, twin-screw extruders, etc.), kneaders, mixers (high-speed fluid mixers, paddle mixers, ribbon mixers, etc.) can be used. These kneaders may be used alone or in combination of two or more. When two or more kneading gases are used, they may be used continuously or in a batch system. Furthermore, the raw materials may be kneaded all at once or may be added in multiple stages in multiple batches. Furthermore, the kneading temperature during kneading is not limited, but may be, for example, 25°C to 400°C, 50°C to 350°C, 75°C to 325°C, or 100°C to 300°C.

[0036] Furthermore, by extruding the kneaded material (the extrusion step in the manufacturing method for a dry friction material composition described later), the heat-resistant reinforcing fibers in the resulting extruded kneaded material can be oriented. The kneaded material can be extruded in any manner, including, for example, a single-screw extruder, a twin-screw extruder, or a 1.5-screw extruder. For example, the extrusion can be performed using a mold equipped with a preliminary cavity for accommodating the kneaded material, a molding cavity for molding a precursor (a shaped material before vulcanization) of the dry friction material, and a runner connecting the preliminary cavity and the molding cavity. That is, the kneaded material (a kneaded material containing unvulcanized rubber, heat-resistant reinforcing fibers, friction modifiers, etc.) is accommodated in the preliminary cavity, and the kneaded material is transferred from the preliminary cavity to the molding cavity via the runner by pressing, thereby extruding the kneaded material as it moves from the runner to the mold cavity. This allows the heat-resistant reinforcing fibers in the kneaded material accommodated in the molding cavity to 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 product (hereinafter also simply referred to as "extrudate"). That is, for example, extrusion can be performed multiple times 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 an operation such as kneading or pelletizing the extrudate.

[0038] The shape of the extrudate is not limited, and can be columnar (including continuous linear), tubular, sheet-like, etc., with columnar or tubular being preferred, and columnar being more preferred. Therefore, the die used for extrusion is not limited, but a die capable of shaping the extrudate into a columnar or tubular shape is preferred, and a die capable of shaping into a columnar shape is more preferred. When the extrudate is columnar, its cross-sectional shape is not limited, and can be circular, polygonal (triangular, rectangular), etc., with circular being preferred. The circular shape includes not only perfect circles, but also ellipses, teardrop shapes, etc., in which at least a portion of the outer edge is curved.

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

[0040] The dry friction material composition of the present invention is prepared by extruding a mixture of unvulcanized rubber (to be vulcanized), heat-resistant reinforcing fibers, and a friction modifier. The dry friction material composition of the present invention allows for the production of dry friction materials with performance equivalent to that of conventional products without using roving. In other words, dry friction materials can be produced easily without using roving. This effect is believed to be due to the heat-resistant reinforcing fibers contained in the dry friction material composition being oriented in a certain direction by extrusion, as described above. However, this orientation is not achieved by individually orienting all of the contained heat-resistant reinforcing fibers one by one. For this reason, it is extremely difficult to unambiguously identify or quantify, for example, the number of heat-resistant reinforcing fibers oriented in a first direction and the number of heat-resistant reinforcing fibers oriented in a second direction. Therefore, it is practical, impossible, or impractical to directly identify the orientation that contributes to the effects of the dry friction material composition of the present invention.

[0041] [3] Dry Friction Material The dry friction material of the present invention is characterized by being obtained by vulcanizing the dry friction material composition of the present invention. The vulcanization (the vulcanization step in the manufacturing method of the dry friction material described later) may be carried out in any manner, but may be carried out using the vulcanizing agent, vulcanization accelerator, etc. described above. Furthermore, heating may be carried out during vulcanization to accelerate vulcanization. The operating temperature during vulcanization is not limited, but may be, for example, 100°C to 400°C, 110°C to 350°C, 115°C to 300°C, or 120°C to 250°C.

[0042] As described above, the dry friction material of the present invention is obtained by vulcanizing the dry friction material composition of the present invention. That is, the dry friction material of the present invention is obtained by vulcanizing an extrudate obtained by extruding a mixture of unvulcanized rubber, heat-resistant reinforcing fibers, and a friction modifier. The effects of the present invention are believed to be due to the heat-resistant reinforcing fibers contained in the dry friction material being oriented in a certain direction by extrusion, as described above. However, this orientation is not achieved by individually orienting all of the contained heat-resistant reinforcing fibers one by one. For this reason, it is extremely difficult to unambiguously identify or quantify, for example, the number of heat-resistant reinforcing fibers oriented in a first direction and the number of heat-resistant reinforcing fibers oriented in a second direction. Therefore, it is practical, impossible, or impractical to directly identify the orientation that contributes to the effects of the present invention in the dry friction material of the present invention.

[0043] [4] Manufacturing method for dry friction material composition, manufacturing method for dry friction material The manufacturing method for a dry friction material composition of the present invention is characterized by including an extrusion step of extruding a mixture of unvulcanized rubber to be vulcanized, heat-resistant reinforcing fibers, and a friction modifier. Furthermore, the manufacturing method for a dry friction material of the present invention is characterized by including a vulcanization step of vulcanizing the dry friction material composition. Each of these is as described in [2] above.

[0044] [5] Others The dry friction material of the present invention is not limited in shape, size, etc., 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 (aircraft in general), ships and hulls (hulls in general), machine tools, industrial machinery, and product manufacturing. More specific examples include clutch parts (clutch plates) such as manual clutches (clutch facings), slip clutches, and one-way clutches, torque limiters, and thrust dampers. Among these, when used as a torque limiter in particular, the dry friction material can be made to realize stable torque interruption (cutting off excessive torque) and suppression of a decrease in the friction coefficient.

[0045] The present invention will be described below with reference to examples. [1] Preparation of Dry Friction Material Composition (1) Dry Friction Material Composition 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 in a total amount of 100 parts by mass. Curable resin: Phenolic resin was prepared as the curable resin to be cured in a total amount of 20 parts by mass per 100 parts by mass of the total unvulcanized rubber. Heat-resistant reinforcing fiber: Short glass fibers (average fiber diameter 9 μm, average fiber length 3 mm) were prepared in a total amount of 42 parts by mass per 100 parts by mass of the total 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 resins (cashew dust) were prepared in a total amount of 201 parts by mass per 100 parts by mass of the total unvulcanized rubber. Other components: a plasticizer, a vulcanizing agent, and a vulcanization accelerator were prepared in a total amount of 52.8 parts by mass per 100 parts by mass of the total amount of unvulcanized rubber. The unvulcanized rubber, curable resin, heat-resistant reinforcing fiber, friction modifier, and other components were then kneaded (rubber kneading process) to obtain a sheet-like material. The obtained sheet-like material was shredded into approximately 5 mm square pieces to obtain shredded material. The shredded material was fed into an extruder and extruded into a continuous wire with a diameter of 5 to 10 mm (extrusion process), and wound into a coil to obtain the dry friction material composition (extrudate) of Experimental Example 1 (winding process).

[0046] (2) Dry friction material composition 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 in a total amount of 100 parts by mass per 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, a dry friction material composition (extrudate) of Experimental Example 2 was obtained in the same manner as in Experimental Example 1.

[0047] (3) Dry friction material composition of Experimental Example 3 (short glass fiber 168 parts by mass) 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 fiber (average fiber diameter 9 μm, average fiber length 3 mm) was prepared in a total amount of 168 parts by mass per 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, a dry friction material composition (extrudate) of Experimental Example 3 was obtained in the same manner as in Experimental Example 1.

[0048] (4) Dry friction material composition of Experimental Example 4 (short glass fiber 217 parts by mass) 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 fiber (average fiber diameter 9 μm, average fiber length 3 mm) was prepared in a total amount of 217 parts by mass per 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, a dry friction material composition (extrudate) of Experimental Example 4 was obtained in the same manner as in Experimental Example 1.

[0049] (5) Dry friction material composition of Experimental Example 5 (short glass fiber 271 parts by mass) 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 fiber (average fiber diameter 9 μm, average fiber length 3 mm) was prepared in a total amount of 271 parts by mass per 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, a dry friction material composition (extrudate) of Experimental Example 5 was obtained in the same manner as in Experimental Example 1.

[0050] [2] Manufacturing of Dry Friction Materials (1) A mold for dry friction materials was prepared, having a ring-shaped cavity with an inner diameter of 194 mm and an outer diameter of 217 mm. Each dry friction material composition (continuous linear extrudate) of Experimental Examples 1 to 5 obtained in [1] above was placed in the mold, and then the dry friction material composition was cut so as not to leave any excess material, and the mold was closed. Subsequently, the composition was molded at a mold temperature of 150 to 200°C while applying a pressure of 50 MPa (thermoforming process) to obtain a ring-shaped molded product. (2) The obtained ring-shaped molded product was heated to 200 to 300°C for heat treatment to obtain a crude product (heat treatment process). (3) The obtained crude product was polished to obtain a polished product. (4) The polished product was drilled at 60-degree intervals to form circular through-holes (drilling process), obtaining the dry friction materials of Experimental Examples 1 to 5.

[0051] (5) Dry Friction Material Composition of Experimental Example 6 (168 parts by mass of short glass fibers) Unvulcanized rubber: Prepared in the same manner as in Experimental Example 3. Curable resin: Prepared in the same manner as in Experimental Example 3. Heat-resistant reinforcing fiber: A total of 168 parts by mass of short glass fibers (average fiber diameter 9 μm, average fiber length 3 mm) was prepared per 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. Then, the 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 approximately 5 mm square pieces to obtain shredded material. The obtained shredded material was used to obtain a dry friction material of Experimental Example 6 by the same procedures as in (1) to (4) above.

[0052] [3] Evaluation (1) Evaluation of Flatness and Smoothness Ten dry friction materials of Experimental Example 3 (molded into extrudates) were compared with ten dry friction materials of Experimental Example 6 (molded into pellets) to evaluate flatness and smoothness. As a result, the inner and outer peripheral surfaces of all the dry friction materials of Experimental Example 3 were smoother and smoother than those of Experimental Example 6.

[0053] (2) Evaluation of Impact Resistance Five dry friction materials of Experimental Example 3 (molded into extrudates) and five dry friction materials of Experimental Example 6 (molded into pellets) were each dropped from a height of 1 m. As a result, none of the dry friction materials of Experimental Example 3 broke. In contrast, five out of five dry friction materials of Experimental Example 6 broke into three pieces due to the impact of the drop. In other words, they were broken by the drop.

[0054] (3) Evaluation of molding accuracy For each of 10 dry friction materials of Experimental Examples 1 to 5 (molded extrudates), the inner diameters of six locations at an angle of 60 degrees were measured, and the average value of the inner diameters was calculated. Furthermore, the average values ​​of the inner diameters of these six locations were further averaged to calculate the average inner diameter value of each of Experimental Examples 1 to 5. Then, the designed inner diameter value X of the mold was calculated. １ Average inner diameter value Y (mm) １ (mm) change rate [(X １ -Y １ ) / X １ × 100] was calculated and shown as "Inner diameter change rate (%)" in Table 1. Similarly, for each of 10 dry friction materials of Experimental Examples 1 to 5 (molded extrudates), the outer diameters were measured at six points at 60-degree intervals, and the average value of the outer diameters was calculated. Furthermore, the average values ​​of the outer diameters at these six points were further averaged to calculate the average outer diameter value of each of Experimental Examples 1 to 5. Then, the designed outer diameter value X ２ Average outer diameter Y (mm) ２ (mm) change rate [(X ２ -Y ２ ) / X ２ × 100] was calculated and shown as "Rate of change in outer diameter (%)" in Table 1. Furthermore, the results are shown in Figure 4 as a correlation between the content of heat-resistant reinforcing fiber and each rate of change.

[0055]

[0056] (4) Effects of Examples From the evaluation results of the above [3] (1), even though the dry friction material had the same composition and the same content of heat-resistant reinforcing fibers, the dry friction material of Experimental Example 3, in which the heat-resistant reinforcing fibers were oriented in a unidirectional manner, exhibited excellent flatness and smoothness. In contrast, the dry friction material of Experimental Example 6, in which the heat-resistant reinforcing fibers were not oriented, exhibited inferior flatness and smoothness. Furthermore, from the evaluation results of the above [3] (2), even though the dry friction material had the same composition and the same content of heat-resistant reinforcing fibers, the dry friction material of Experimental Example 3, in which the heat-resistant reinforcing fibers were oriented in a unidirectional manner, exhibited excellent impact resistance. In contrast, the dry friction material of Experimental Example 6, in which the heat-resistant reinforcing fibers were not oriented, exhibited inferior impact resistance. Furthermore, from the results of Experimental Examples 1 to 3 among the evaluation results of the above [3] (3), it was found that increasing the content of unidirectionally oriented heat-resistant reinforcing fibers improved shaping accuracy (see Table 1 and FIG. 4). On the other hand, from the results of Experimental Examples 3 to 5 among the evaluation results of [3] (3) above, it can be seen that when the content of heat-resistant reinforcing fibers oriented in a certain direction is excessively increased, the shaping accuracy tends to gradually decrease, although it is better than Experimental Example 2 (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 the rate of change of both the outer diameter and the inner diameter is significantly inferior, even though the content of heat-resistant reinforcing fibers is equivalent to that of Experimental Example 3.

[0057] 1: dry friction material, 11: matrix material, 12: dispersed material, 121: heat-resistant reinforcing fiber, 121a: longitudinal direction, 13: outer edge, 131: tangent line.

Claims

1. A dry friction material comprising a matrix material and a dispersion material, wherein the matrix material comprises vulcanized rubber, the dispersion material comprises heat-resistant reinforcing fibers and a friction modifier, and the heat-resistant reinforcing fibers are oriented in a fixed direction.

2. The dry friction material according to claim 1, which has a circular or arcuate outer edge, and the orientation is parallel to the outer edge.

3. The dry friction material according to claim 1 or 2, wherein the heat-resistant reinforcing fiber is contained in an amount of 50 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the vulcanized rubber.

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

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

6. A composition for dry friction materials for obtaining the dry friction material according to claim 1, characterized in that the composition is obtained by extruding a mixture of unvulcanized rubber to become the vulcanized rubber, the heat-resistant reinforcing fiber, and the friction modifier.

7. A dry friction material obtained by vulcanizing the composition for dry friction materials according to claim 6.

8. A method for producing a composition for a dry friction material to obtain the dry friction material described in claim 1, comprising an extrusion step of extruding a mixture of unvulcanized rubber to become the vulcanized rubber, the heat-resistant reinforcing fiber, and the friction modifier.

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

10. The method for producing a dry friction material according to claim 9, wherein the heat-resistant reinforcing fiber is 50 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the vulcanized rubber.

11. The method for producing 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 producing 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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