Rubber composition for power transmission belt and power transmission belt

Abstract

To provide a rubber composition capable of simultaneously improving abrasion resistance and transmission efficiency in being used in a transmission belt.SOLUTION: As a rubber composition for forming a compression rubber layer of a transmission belt, a polymer component, an inorganic filler and short fiber are combined. The polymer component includes ethylene-α-olefin elastomer. A ratio of the ethylene-α-olefin elastomer in the polymer component is 50 mass% or more. In an uncrosslinked material of the poly component, Moony viscosity is 31ML(1+4) 125°C or more. A ratio of the inorganic filler to 100 pts. mass of the polymer component is 20-60 pts. mass. In a crosslinked material of the rubber composition, 8% flexural stress in a short fiber parallel direction is 2.5 MPa or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition capable of forming a compressed rubber layer of a transmission belt such as a variable speed belt, and to a transmission belt having a compressed rubber layer formed from this rubber composition. [Background technology]

[0002] Power transmission belts used in power transmission mechanisms of machinery and other devices are broadly classified into friction transmission belts and meshing transmission belts based on the form of power transmission. Known friction transmission belts include V-belts, V-ribbed belts, and flat belts, while known meshing transmission belts include toothed belts.

[0003] One example of a V-belt is a raw-edge type belt (raw-edge V-belt), which has an exposed rubber layer on the friction transmission surface (V-shaped side).Raw-edge type belts include raw-edge V-belts without cogs, raw-edge cogged V-belts with cogs only on the inner circumferential surface of the belt to improve flexibility, and raw-edge cogged V-belts (raw-edge double-cogged V-belts) with cogs on both the inner and outer circumferential surfaces of the belt to improve flexibility.

[0004] One application of these V-belts (particularly raw-edge cog V-belts) is a belt-type continuously variable transmission. As shown in FIG. 1, the belt-type continuously variable transmission 30 is a device that continuously changes the gear ratio by wrapping a V-belt 1 around a drive pulley 31 and a driven pulley 32. Each pulley 31, 32 is composed of a fixed sheave 31a, 32a whose axial movement is restricted or fixed, and a movable sheave 31b, 32b that is movable in the axial direction. The V-belt 1 has a structure that allows the width of the V-groove of the pulleys 31, 32, formed by the fixed sheaves 31a, 32a and the movable sheaves 31b, 32b, to be continuously variable. Both widthwise end surfaces of the V-belt 1 are formed as tapered surfaces whose inclination matches the opposing surfaces of the V-grooves of the pulleys 31, 32. The V-belt 1 can be fitted at any radial position of the pulleys depending on the adjusted V-groove width. For example, by narrowing the width of the V-groove of the drive pulley 31 and widening the width of the V-groove of the driven pulley 32, changing from the state shown in FIG. 1(a) to the state shown in FIG. 1(b), the V-belt 1 moves radially outward on the drive pulley 31 side and radially inward on the driven pulley 32 side, causing the winding radius around each pulley 31, 32 to change continuously, thereby enabling the gear ratio to be adjusted continuously.

[0005] V-belts (variable speed belts) used in such applications are required to have improved abrasion resistance (resistance to wear), heat resistance (resistance to thermal degradation), flexibility (ease of bending in the circumferential direction of the belt), resistance to lateral pressure (resistance to pressure acting in the normal direction of the V-shaped side), and transmission efficiency (power transmission efficiency or fuel economy) in order to cope with not only the rotational running of the belt wrapped around two axes, the drive pulley and the driven pulley, but also the movement in the radial direction of the pulley and the repeated bending motion caused by continuous changes in the wrapping radius.

[0006] In response to these demands, for example, Japanese Patent Laid-Open Publication No. 2017-106617 (Patent Document 1) discloses a friction transmission belt that can improve lateral pressure resistance while maintaining fuel economy by gradually decreasing the crosslink density of the compressed rubber layer from the outer periphery to the inner periphery in the thickness direction of the belt. Furthermore, Japanese Patent Laid-Open Publication No. 2019-95059 (Patent Document 2) discloses that by incorporating liquid crystal polyester short fibers into the compressed rubber layer, the flexibility and lateral pressure resistance of a transmission V-belt can be improved, and when used in a low-edge V-belt, the wear resistance and durability of the belt can also be improved. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-106617 [Patent Document 2] Japanese Patent Application Laid-Open No. 2019-95059 Summary of the Invention [Problem to be solved by the invention]

[0008] In the examples of Patent Documents 1 and 2, ethylene-propylene-diene terpolymer (EPDM) is used as the polymer component of the rubber composition. One of the characteristics of EPDM is its high heat resistance, which is due to the absence of double bonds in the main chain, but there is room for improvement in properties such as abrasion resistance, flexibility, lateral pressure resistance, and power transmission efficiency by using compounding agents other than the polymer component, and further research is expected.

[0009] Therefore, an object of the present invention is to provide a rubber composition that uses an ethylene-α-olefin elastomer such as EPDM as the main polymer component, and that can simultaneously improve abrasion resistance and power transmission efficiency when used in a power transmission belt, and to provide a power transmission belt that simultaneously improves abrasion resistance and power transmission efficiency. [Means for solving the problem]

[0010] As a result of extensive research to achieve the above object, the present inventors have found that the wear resistance and power transmission efficiency of a power transmission belt can be simultaneously improved by forming a compression rubber layer of a power transmission belt from a rubber composition containing a high-viscosity polymer component containing an ethylene-α-olefin elastomer as a main component, an inorganic filler, and short fibers, wherein the proportion of the inorganic filler is 15 to 60 parts by mass per 100 parts by mass of the polymer component, and the 8% bending stress of the cross-linked product in a direction parallel to the short fibers is adjusted to 2.5 MPa or less, and have completed the present invention.

[0011] That is, the rubber composition according to embodiment [1] of the present invention is A rubber composition for forming a compression rubber layer of a transmission belt, comprising a polymer component, an inorganic filler and short fibers; the polymer component comprises an ethylene-α-olefin elastomer; the proportion of the ethylene-α-olefin elastomer in the polymer component is 50% by mass or more, The uncrosslinked polymer component has a Mooney viscosity of 31 ML(1+4) 125°C or more, The proportion of the inorganic filler is 20 to 60 parts by mass relative to 100 parts by mass of the polymer component, and In a crosslinked product of the rubber composition, the 8% bending stress in the direction parallel to the short fibers is 2.5 MPa or less.

[0012] Aspect [2] of the present invention is an aspect of the above aspect [1], further comprising a crosslinking agent, and the crosslinking agent comprises a sulfur-based crosslinking agent.

[0013] Aspect [3] of the present invention is an aspect of the above aspect [1] or [2], further comprising a co-crosslinking agent.

[0014] Aspect [4] of the present invention is an aspect of the aspect [3], in which the proportion of the co-crosslinking agent is 1 to 5 parts by mass per 100 parts by mass of the polymer component.

[0015] Aspect [5] of the present invention is any of aspects [1] to [4], wherein the inorganic filler contains carbon black, the carbon black contains soft carbon, and the proportion of the carbon black is 50 to 200 parts by mass per 100 parts by mass of the short fibers.

[0016] Aspect [6] of the present invention is any one of aspects [1] to [5], wherein the proportion of the softener is 3 parts by mass or less per 100 parts by mass of the polymer component.

[0017] Aspect [7] of the present invention is any of aspects [1] to [6], wherein the staple fibers comprise aramid staple fibers and aliphatic polyamide staple fibers, and the proportion of the aramid staple fibers is 100 parts by mass or more per 100 parts by mass of the aliphatic polyamide staple fibers.

[0018] The present invention also includes, as an embodiment [8], a power transmission belt having a compressed rubber layer formed of the rubber composition according to any one of the embodiments [1] to [7]. [Effects of the Invention]

[0019] In the present invention, the rubber composition for forming the compression rubber layer of the power transmission belt contains a high-viscosity polymer component containing an ethylene-α-olefin elastomer as a main component, an inorganic filler, and short fibers, and the proportion of the inorganic filler is 20 to 60 parts by mass per 100 parts by mass of the polymer component. The 8% bending stress of the cross-linked product in the direction parallel to the short fibers is adjusted to 2.5 MPa or less, thereby simultaneously improving the wear resistance and power transmission efficiency of the power transmission belt. Furthermore, by adjusting the types and amounts of specific compounding agents (e.g., inorganic filler, short fibers, cross-linking agent, co-cross-linking agent, softening agent, etc., particularly cross-linking agent and short fibers, etc.), it is possible to improve not only the wear resistance and power transmission efficiency but also the lateral pressure resistance and flexibility. [Brief explanation of the drawings]

[0020] [Figure 1]FIG. 1 is a schematic cross-sectional view for explaining the transmission mechanism of a belt-type continuously variable transmission. [Figure 2] FIG. 2 is a schematic perspective view showing an example of a power transmission belt of the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view of the power transmission belt of FIG. 2 taken in the belt length direction. [Figure 4] FIG. 4 is a graph showing the behavior of Mooney viscosity to explain the method for measuring the Mooney scorch minimum viscosity (Vm). [Figure 5] FIG. 5 is a schematic perspective view illustrating a method for measuring the 4% bending stress (in the direction perpendicular to the short fibers) of the crosslinked rubber molded article obtained in the example. [Figure 6] FIG. 6 is a schematic perspective view illustrating a method for measuring the 8% bending stress (in a direction parallel to the short fibers) of the crosslinked rubber molded products obtained in the examples. [Figure 7] FIG. 7 shows the layout of the wear durability test of the raw edge double cog V-belt obtained in the example. [Figure 8] FIG. 8 shows the layout of a transmission efficiency test of the raw-edge double-cogged V-belt obtained in the example. DETAILED DESCRIPTION OF THE INVENTION

[0021] [Rubber composition] In the present invention, the rubber composition (first rubber composition) for forming the compressed rubber layer of the transmission belt contains a high-viscosity polymer component (A) containing an ethylene-α-olefin elastomer as a main component, an inorganic filler (B), and short fibers (C).

[0022] (A) Polymer component The polymer component (first polymer component) (A) contains an ethylene-α-olefin elastomer because it has excellent heat resistance, cold resistance, and weather resistance.

[0023] The ethylene-α-olefin elastomer may contain ethylene units and α-olefin units as constituent units, and may further contain diene units. Therefore, the ethylene-α-olefin elastomer includes ethylene-α-olefin copolymer rubber, ethylene-α-olefin-diene terpolymer rubber, etc.

[0024] Examples of the α-olefins for forming the α-olefin units include linear α-C olefins such as propylene, butene, pentene, methylpentene, hexene, and octene. 3-12 Among these α-olefins, α-C olefins such as propylene 3-4 Olefins (especially propylene) are preferred.

[0025] As the diene monomer for forming the diene unit, a non-conjugated diene monomer is usually used. Examples of the non-conjugated diene monomer include dicyclopentadiene, methylenenorbornene, ethylidenenorbornene, 1,4-hexadiene, and cyclooctadiene. Among these diene monomers, ethylidenenorbornene and 1,4-hexadiene (particularly ethylidenenorbornene) are preferred.

[0026] Representative examples of ethylene-α-olefin elastomers include ethylene-α-olefin rubbers [ethylene-propylene rubber (EPM), ethylene-butene rubber (EBM), ethylene-octene rubber (EOM)], and ethylene-α-olefin-diene rubbers [ethylene-propylene-diene terpolymer (EPDM)].

[0027] These ethylene-α-olefin elastomers can be used alone or in combination. Among these, ethylene-α-C is preferred because of its excellent heat resistance, cold resistance and weather resistance. 3-4Ethylene-α-olefin-diene terpolymer rubbers such as olefin-diene terpolymer rubbers are preferred, with EPDM being particularly preferred. Therefore, the proportion of EPDM may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more (particularly 95% by mass or more), or even 100% by mass (EPDM only) based on the total ethylene-α-olefin elastomer.

[0028] In the ethylene-α-olefin elastomer, the ratio (mass ratio) of ethylene to α-olefin (former / latter) is 40 / 60 to 90 / 10, preferably 45 / 55 to 85 / 15 (e.g., 50 / 50 to 80 / 20), and more preferably 52 / 48 to 70 / 30. In particular, in the ethylene-propylene-diene terpolymer, the ratio (mass ratio) of ethylene to propylene (former / latter) may be 35 / 65 to 90 / 10, preferably 40 / 60 to 80 / 20, more preferably 45 / 55 to 70 / 30, more preferably 50 / 50 to 70 / 30 (e.g., 50 / 50 to 60 / 40), and most preferably 55 / 45 to 70 / 30 (particularly 55 / 45 to 65 / 35).

[0029] In the present application, the ratio (mass ratio) of ethylene to α-olefin can be measured by a conventional method, but may be a ratio based on the monomers.

[0030] The diene content of the ethylene-α-olefin elastomer (particularly, ethylene-α-olefin-diene terpolymer rubber such as EPDM) may be 15% by mass or less (e.g., 0.1 to 15% by mass), preferably 13% by mass or less (e.g., 1 to 13% by mass), further preferably 12% by mass or less (e.g., 3 to 12% by mass), and even more preferably 10% by mass or less (e.g., 5 to 10% by mass). If the diene content is too high, there is a risk that high heat resistance cannot be ensured.

[0031] In the present application, the diene content means the mass proportion of diene monomer units in all units constituting the ethylene-α-olefin elastomer, and can be measured by a conventional method, but may also be a proportion based on the monomer.

[0032] The iodine value of the ethylene-α-olefin elastomer containing a diene monomer is, for example, 3 to 40, preferably 5 to 30, and more preferably 10 to 20. If the iodine value is too low, the crosslinking of the rubber composition becomes insufficient, making it prone to wear and adhesion, while if the iodine value is too high, the scorch of the rubber composition becomes short, making it difficult to handle, and the heat resistance tends to decrease.

[0033] In the present application, the iodine value of the ethylene-α-olefin elastomer can be measured by a conventional method, for example, infrared spectroscopy.

[0034] The rubber composition of the present invention is characterized by a high Mooney viscosity of the uncrosslinked polymer component (A) (particularly, the uncrosslinked ethylene-α-olefin elastomer). In the present invention, the proportion of the inorganic filler described below is kept small to enhance the power transmission efficiency, and therefore, by combining it with the polymer component (A) having a high Mooney viscosity, wear resistance can be ensured.

[0035] Mooney viscosity is used as an index of the fluidity (ease of processing) of an uncrosslinked polymer component, measured by filling the uncrosslinked polymer component in a cavity so that it comes into contact with a rotor with grooves on its surface and measuring the torque required to rotate the rotor.

[0036] The Mooney viscosity [ML(1+4)125°C] of the uncrosslinked polymer component (A) (particularly the uncrosslinked ethylene-α-olefin elastomer) is 31 or more (preferably 33 or more, more preferably 41 or more, and even more preferably 43 or more), for example, 35 to 80, preferably 40 to 78, even more preferably 45 to 75, more preferably 50 to 70, and most preferably 60 to 70. If the Mooney viscosity is too low, the abrasion resistance decreases.

[0037] In this application, Mooney viscosity can be measured by a method conforming to the Mooney viscosity test of JIS K 6300-1 (2013), and the test conditions are as follows: an L-shaped rotor is used, the test temperature is 125°C, preheating is 1 minute, and the rotor operation time is 4 minutes. Furthermore, when polymer component (A) is a combination of multiple polymer components, the Mooney viscosity of the entire polymer component (A) is taken as a weighted average. In other words, the Mooney viscosity (weighted average) means an average value based on mass ratio, and is the sum of the products of the Mooney viscosity of each polymer component and the mass fraction.

[0038] The proportion of the ethylene-α-olefin elastomer in the polymer component (A) may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass (ethylene-α-olefin elastomer only). If the proportion of the ethylene-α-olefin elastomer in the polymer component (A) is too low, there is a risk that the heat resistance and cold resistance will decrease.

[0039] The polymer component (A) may contain, in addition to the ethylene-α-olefin elastomer, other polymer components, such as diene rubbers (natural rubber, isoprene rubber, butadiene rubber, chloroprene rubber, styrene-butadiene rubber (SBR), vinylpyridine-styrene-butadiene copolymer rubber, acrylonitrile-butadiene rubber (nitrile rubber); hydrogenated products of the diene rubbers, such as hydrogenated nitrile rubber (including mixed polymers of hydrogenated nitrile rubber and unsaturated carboxylic acid metal salts)), olefin rubbers (polyoctenylene rubber, ethylene-vinyl acetate copolymer rubber, chlorosulfonated polyethylene rubber, alkylated chlorosulfonated polyethylene rubber), epichlorohydrin rubber, acrylic rubber, silicone rubber, urethane rubber, fluororubber, and the like, as long as the effects of the present invention are not impaired.

[0040] The proportion of the other polymer component in the polymer component (A) may be 50% by mass or less, preferably 20% by mass or less, and more preferably 10% by mass or less.

[0041] (B) Inorganic filler The rubber composition of the present invention contains an inorganic filler (first inorganic filler) (B) as an essential component in order to improve the abrasion resistance and lateral pressure resistance of the compressed rubber layer.

[0042] Examples of inorganic fillers (B) include carbonaceous materials (carbon black, graphite, etc.), metal compounds or synthetic ceramics (metal oxides such as magnesium oxide, calcium oxide, barium oxide, iron oxide, copper oxide, zinc oxide, titanium oxide, and aluminum oxide; metal silicates such as calcium silicate and aluminum silicate; metal carbides such as silicon carbide and tungsten carbide; metal nitrides such as titanium nitride, aluminum nitride, and boron nitride; metal carbonates such as magnesium carbonate and calcium carbonate; metal sulfates such as calcium sulfate and barium sulfate), and mineral materials (zeolite, diatomaceous earth, calcined diatomaceous earth, activated clay, alumina, silica, talc, mica, kaolin, sericite, bentonite, montmorillonite, smectite, clay, etc.). These inorganic fillers can be used alone or in combination.

[0043] Of these inorganic fillers, carbonaceous materials such as carbon black, metal oxides such as magnesium oxide and zinc oxide, and mineral materials such as silica are preferred, and carbonaceous materials and metal oxides are more preferred, with carbon black being particularly preferred from the viewpoint of improving the hardness, modulus, and abrasion resistance of the cross-linked product of the rubber composition.

[0044] Carbon black is generally classified into several grades based on differences in primary particle size, iodine adsorption capacity, and nitrogen adsorption specific surface area. ASTM classifies carbon black into grades N0** to N9** based on iodine adsorption capacity, but traditional classifications (SAF, HAF, GPF, etc.) based on the performance of compounded rubber products are also used. Grades with small primary particle sizes, such as N110 (SAF), N220 (ISAF), and N330 (HAF), are referred to as hard carbon, while grades with large primary particle sizes, such as N550 (FEF), N660 (GPF), and N762 (SRF), are sometimes referred to as soft carbon. Iodine adsorption capacity and primary particle size are closely related, with the smaller the primary particle size, the greater the iodine adsorption capacity. The classification of carbon black is shown in Table 1, using the Seast® series manufactured by Tokai Carbon Co., Ltd. as an example, along with the iodine adsorption capacity and average primary particle size.

[0045] [Table 1]

[0046] In this application, carbon black contained in a rubber composition is not classified by raw material, but carbon black having a primary particle diameter of 40 nm or more is referred to as soft carbon, and carbon black having a primary particle diameter of less than 40 nm is referred to as hard carbon.

[0047] In the present application, the primary particle size of carbon black can be measured using, for example, a transmission electron microscope.

[0048] The primary particle size of the soft carbon may be 40 nm or more, but the maximum primary particle size may be, for example, 300 nm or less, preferably 200 nm or less, and more preferably 100 nm or less. If the maximum primary particle size of the soft carbon is too large, there is a risk that the effect of improving wear resistance will not be achieved.

[0049] The average primary particle size of the soft carbon is, for example, 40 to 100 nm, preferably 41 to 80 nm, further preferably 42 to 60 nm, and even more preferably 43 to 50 nm. If the average primary particle size of the soft carbon is too small, there is a risk that the transmission efficiency (fuel economy) will decrease, and conversely, if it is too large, there is a risk that the effect of improving wear resistance will not be achieved.

[0050] The iodine adsorption amount of the soft carbon may be less than 60 g / kg, for example, 10 g / kg or more and less than 60 g / kg, preferably 20 to 58 g / kg, further preferably 30 to 55 g / kg, and further preferably 40 to 50 g / kg. If the iodine adsorption amount is too high, there is a risk of a decrease in transmission efficiency.

[0051] In the present application, the iodine adsorption amount of carbon black can be measured in accordance with the standard test method of ASTM D1510-17.

[0052] The primary particle diameter of the hard carbon may be less than 40 nm, but the maximum primary particle diameter may be, for example, 38 nm or less, preferably 35 nm or less, and more preferably 30 nm or less.

[0053] The average primary particle size of the hard carbon is, for example, 10 to 35 nm, preferably 12 to 33 nm, further preferably 15 to 30 nm (for example, 20 to 25 nm), and even more preferably 20 to 30 nm (for example, 25 to 30 nm).

[0054] The iodine adsorption amount of the hard carbon may be 60 g / kg or more, for example, 60 to 150 g / kg, preferably 80 to 130 g / kg, further preferably 100 to 130 g / kg, and further preferably 120 to 125 g / kg.

[0055] In the present invention, the carbon black preferably contains soft carbon, since this reduces the coefficient of friction and the internal heat generation when the belt is bent, thereby improving the transmission efficiency. The proportion of soft carbon in the carbon black may be 10% by mass or more, preferably 50% by mass or more, further preferably 80% by mass or more, even more preferably 90% by mass or more, and most preferably 100% by mass.

[0056] The proportion of carbon black in the inorganic filler (B) may be 10% by mass or more, preferably 50% by mass or more, further preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0057] The amount of carbon black is 15 to 60 parts by mass (particularly 20 to 58 parts by mass) per 100 parts by mass of the polymer component (A), preferably 20 to 55 parts by mass, more preferably 30 to 52 parts by mass, even more preferably 40 to 51 parts by mass, and most preferably 45 to 50 parts by mass. In applications requiring high power transmission efficiency, the amount of carbon black may be preferably 15 to 50 parts by mass, more preferably 18 to 40 parts by mass, and even more preferably 20 to 30 parts by mass per 100 parts by mass of the polymer component (A). If the amount of carbon black is too low, abrasion resistance and lateral pressure resistance may decrease, while if the amount is too high, flexibility and power transmission efficiency may decrease.

[0058] In addition to carbon black, the inorganic filler (B) may further contain a metal oxide such as zinc oxide. The proportion of the metal oxide relative to 100 parts by mass of carbon black is, for example, 1 to 100 parts by mass, preferably 1.5 to 50 parts by mass, further preferably 2 to 30 parts by mass, even more preferably 3 to 20 parts by mass, and most preferably 4 to 10 parts by mass.

[0059] The proportion of the inorganic filler (first inorganic filler) (B) is 18 to 70 parts by mass, preferably 20 to 65 parts by mass, more preferably 30 to 60 parts by mass, more preferably 40 to 58 parts by mass, and most preferably 45 to 55 parts by mass, per 100 parts by mass of the polymer component (A). In applications requiring high power transmission efficiency, the proportion of the inorganic filler (B) may be preferably 15 to 50 parts by mass, more preferably 20 to 40 parts by mass, and more preferably 25 to 30 parts by mass, per 100 parts by mass of the polymer component (A). If the proportion of the inorganic filler (B) is too low, there is a risk of reduced abrasion resistance and lateral pressure resistance, while if it is too high, there is a risk of reduced flexibility and power transmission efficiency.

[0060] (C) Short Fiber The rubber composition of the present invention contains short fibers (first short fibers) (C) as an essential component in order to improve the wear resistance of the compressed rubber and reduce the coefficient of friction. In particular, when the short fibers are oriented in the belt width direction and embedded in the compressed rubber layer, compressive deformation of the power transmission belt due to pressure from the pulley can be suppressed, thereby improving the wear resistance while maintaining the transmission efficiency. Examples of methods for orienting the short fibers in the belt width direction include a method in which the short fibers are rolled with a roll to orient them.

[0061] (Aramid short fiber) The short fibers preferably contain aramid short fibers in order to improve the side pressure resistance and abrasion resistance of the power transmission belt.

[0062] The aramid fibers constituting the aramid short fibers may be para-aramid fibers or meta-aramid fibers.

[0063] Examples of para-aramid fibers include polyparaphenylene terephthalamide fibers (e.g., Twaron (registered trademark) from Teijin Limited, Kevlar (registered trademark) from Toray DuPont Co., Ltd., etc.), and copolymer fibers of polyparaphenylene terephthalamide and 3,4'-oxydiphenylene terephthalamide (e.g., Technora (registered trademark) from Teijin Limited, etc.).

[0064] Examples of meta-aramid fibers include polymetaphenylene isophthalamide fibers (such as "Conex (registered trademark)" from Teijin Limited).

[0065] These aramid fibers can be used alone or in combination of two or more. Among these, para-aramid short fibers are preferred because they can easily improve wear resistance and power transmission efficiency at the same time when combined with aliphatic polyamide short fibers described below.

[0066] The average fineness of the aramid short fibers is, for example, 0.1 to 50 dtex, preferably 1 to 10 dtex, more preferably 1.5 to 5 dtex, and even more preferably 2 to 3 dtex. The average fiber diameter of the aramid short fibers is 2 μm or more, for example, 2 to 100 μm, preferably 3 to 50 μm, more preferably 7 to 40 μm, and even more preferably 10 to 30 μm. If the average fineness and average fiber diameter are too small, there is a risk that the coefficient of friction of the surface of the compressed rubber layer cannot be sufficiently reduced.

[0067] The average fiber length of the aramid short fibers is, for example, 1 to 20 mm, preferably 1.3 to 15 mm, further preferably 1.5 to 10 mm, even more preferably 2 to 5 mm, and most preferably 2.5 to 4 mm. If the average fiber length of the aramid short fibers is too short, the mechanical properties (e.g., modulus) in the grain direction cannot be sufficiently improved, and there is a risk of a decrease in lateral pressure resistance. Conversely, if the average fiber length is too long, there is a risk of poor dispersion of the aramid short fibers in the rubber composition, a failure to sufficiently reduce the surface friction coefficient, and a decrease in power transmission efficiency.

[0068] The aramid short fibers may be embedded in the compression rubber layer while being oriented substantially parallel to the belt width direction in order to suppress compressive deformation of the belt due to pressure from the pulleys.

[0069] In this application, "substantially parallel" to the belt width direction means that the angle with respect to the belt width direction is, for example, within 10°, preferably within 8°, even more preferably within 5°, even more preferably within 3°, and most preferably within 1° (for example, 0 to 1°, particularly approximately 0°).

[0070] From the viewpoint of dispersibility and adhesiveness of the aramid short fibers in the rubber composition, the aramid short fibers may be subjected to an adhesive treatment (or surface treatment).

[0071] The aramid short fibers can be treated with various adhesive treatments, such as a treatment liquid containing a precondensate of phenols and formalin (e.g., a prepolymer of novolac or resol-type phenolic resin), a treatment liquid containing a rubber component (or latex), a treatment liquid containing the precondensate and a rubber component (latex), or a treatment liquid containing a reactive compound (adhesive compound) such as a silane coupling agent, an epoxy compound (e.g., an epoxy resin), or an isocyanate compound. In a preferred adhesive treatment, the aramid short fibers are treated with a treatment liquid containing the precondensate and a rubber component (latex), particularly with at least a resorcinol-formalin-latex (RFL) liquid. Such treatment liquids may be used alone or in combination. For example, the aramid short fibers may be pretreated with a conventional adhesive component, for example, a reactive compound (adhesive compound) such as an epoxy compound (e.g., an epoxy resin), or an isocyanate compound, and then treated with the RFL liquid.

[0072] Treatment with such a treatment liquid, particularly an RFL liquid, can strongly bond the aramid short fibers to the polymer component (A). The RFL liquid is a mixture of a precondensate of resorcinol and formaldehyde and rubber latex. The molar ratio of resorcinol to formaldehyde is within a range that can improve the adhesion between the polymer component (A) and the short fibers, for example, the former / latter = 1 / 0.3 to 1 / 3, preferably 1 / 0.4 to 1 / 2, further preferably 1 / 0.5 to 1 / 1.5, even more preferably 1 / 0.6 to 1 / 1, and most preferably 1 / 0.6 to 1 / 0.8.

[0073] The type of rubber component in the latex is not particularly limited, and diene rubbers (styrene-butadiene-vinylpyridine terpolymer, chloroprene rubber, butadiene rubber, etc.) and chlorosulfonated polyethylene rubbers are preferred, with styrene-butadiene-vinylpyridine terpolymer being particularly preferred.

[0074] The proportion of the precondensate of resorcinol and formalin is, for example, 10 to 100 parts by mass, preferably 12 to 50 parts by mass, and more preferably 15 to 30 parts by mass, relative to 100 parts by mass of the rubber component (solid content) of the latex. The total solid content concentration of the RFL liquid can be adjusted within the range of 5 to 40% by mass.

[0075] The adhesion rate of the adhesive component (solid content) to the aramid short fibers {[(mass after adhesion treatment-mass before adhesion treatment) / (mass after adhesion treatment)]×100} is, for example, 1 to 25 mass%, preferably 2 to 20 mass%, further preferably 2.5 to 15 mass%, further preferably 3 to 10 mass%, and most preferably 4 to 8 mass%. If the adhesion rate of the adhesive component is too low, the dispersibility of the aramid short fibers in the rubber composition and the adhesion between the aramid short fibers and the polymer component (A) may be insufficient. Conversely, if the adhesion rate is too high, the adhesive component may strongly bond the aramid short fibers to each other, thereby reducing dispersibility.

[0076] The proportion of the aramid short fibers relative to 100 parts by mass of the polymer component (A) is, for example, 5 to 30 parts by mass, preferably 10 to 28 parts by mass, further preferably 15 to 25 parts by mass, and further preferably 17 to 23 parts by mass. If the proportion of the aramid short fibers is too low, there is a risk that the abrasion resistance and lateral pressure resistance will decrease, whereas if it is too high, there is a risk that the effect of reducing the friction coefficient will be small and the transmission efficiency will decrease.

[0077] In the present application, when short fibers are subjected to an adhesive treatment, the proportion of short fibers means the proportion of adhesively treated short fibers (the proportion of short fibers containing adhesive components attached after the adhesive treatment).

[0078] (Aliphatic polyamide short fiber) The short fibers preferably include a combination of the aramid short fibers and aliphatic polyamide short fibers (nylon short fibers) because this easily achieves both wear resistance and power transmission efficiency. Nylon short fibers have the effect of reducing the friction coefficient and improving power transmission efficiency, so by combining them with aramid short fibers, it becomes easier to achieve a balance between wear resistance and power transmission efficiency.

[0079] Examples of aliphatic polyamide fibers (nylon fibers) constituting the nylon staple fibers include polyamide 46 fibers, polyamide 6 fibers, polyamide 66 fibers, polyamide 610 fibers, polyamide 612 fibers, polyamide 11 fibers, and polyamide 12 fibers.

[0080] These nylon fibers can be used alone or in combination. Among these, C such as polyamide 6 fiber and polyamide 66 fiber is preferred. 4-8 Nylon fibers having alkylene chains are preferred.

[0081] The average fiber diameter of the nylon short fibers is 2 μm or more, for example, 2 to 100 μm, preferably 3 to 50 μm, further preferably 7 to 40 μm, even more preferably 10 to 35 μm, and most preferably 20 to 30 μm. If the average fiber diameter is too small, there is a risk that the coefficient of friction of the surface of the compressed rubber layer cannot be sufficiently reduced.

[0082] The average fiber length of the nylon short fibers may be 1 mm or more (for example, 1 to 20 mm), and is preferably 1.5 mm or more (particularly 2 mm or more) from the viewpoint of improving flex fatigue resistance and crack resistance, further preferably 1.5 to 10 mm, even more preferably 2 to 5 mm, and most preferably 2.5 to 4 mm.

[0083] The nylon short fibers may be embedded in the compression rubber layer so as to be oriented substantially parallel to the belt width direction in order to suppress compressive deformation of the belt due to pressure from the pulleys.

[0084] From the viewpoint of dispersibility and adhesiveness of the nylon staple fibers in the rubber composition, the nylon staple fibers may be subjected to an adhesive treatment (or surface treatment). The adhesive treatment, including preferred embodiments, can be selected from the adhesive treatments exemplified as the adhesive treatment for the aramid staple fibers. The adhesion rate of the adhesive component can also be selected from the adhesion rate of the aramid staple fibers. The adhesive treatment for the nylon staple fibers may be different from the adhesive treatment for the aramid staple fibers, but from the viewpoint of simplicity, it is preferable that the two be the same adhesive treatment.

[0085] The proportion of the nylon short fibers relative to 100 parts by mass of the polymer component (A) is, for example, 1 to 25 parts by mass, preferably 3 to 23 parts by mass, more preferably 5 to 20 parts by mass, and most preferably 7 to 15 parts by mass. If the proportion of the nylon short fibers is too low, the effect of improving the transmission efficiency may decrease, while if it is too high, the wear resistance and lateral pressure resistance may decrease.

[0086] The proportion of aramid short fibers can be selected from the range of 10 parts by mass or more (e.g., 50 parts by mass or more), specifically 80 parts by mass or more (particularly 100 parts by mass or more), per 100 parts by mass of nylon short fibers, and is, for example, 100 to 1,000 parts by mass, preferably 120 to 500 parts by mass, further preferably 130 to 300 parts by mass, more preferably 150 to 250 parts by mass, and most preferably 170 to 230 parts by mass. If the proportion of aramid fibers is too high (if the proportion of nylon short fibers is too low), the effect of improving transmission efficiency may be reduced and flexibility may be reduced, while if the proportion of aramid fibers is too low (if the proportion of nylon short fibers is too high), abrasion resistance and lateral pressure resistance may be reduced.

[0087] (Percentage of other short fibers and total amount of short fibers) The staple fibers (C) may further contain other staple fibers (staple fibers other than aramid staple fibers and nylon staple fibers). Examples of other staple fibers include polyolefin staple fibers (polyethylene staple fibers, polypropylene staple fibers, etc.), polyester staple fibers (e.g., polyalkylene arylate staple fibers [polyC such as polyethylene terephthalate (PET) staple fibers, polyethylene naphthalate (PEN) staple fibers, etc.], 2-4 Alkylene C 8-14 Examples of other staple fibers include synthetic staple fibers such as vinylon staple fibers, polyvinyl alcohol staple fibers, and polyparaphenylenebenzobisoxazole (PBO) staple fibers; natural staple fibers such as cotton, hemp, and wool; and inorganic staple fibers such as carbon fibers. These other staple fibers can be used alone or in combination. Among these other staple fibers, polyester staple fibers such as PET staple fibers are preferred.

[0088] The proportion of other staple fibers in the staple fibers (C) may be 50% by mass or less, preferably 30% by mass or less, and more preferably 10% by mass or less. The staple fibers (C) may be substantially free of other staple fibers, and preferably free of other staple fibers such as polyester staple fibers. That is, the staple fibers (C) may consist only of aramid staple fibers and nylon staple fibers. If the proportion of other staple fibers is too high, it may be difficult to improve the transmission efficiency.

[0089] The proportion of short fibers (C) (proportion of the total amount of short fibers) is 15 to 40 parts by mass, preferably 20 to 35 parts by mass, and more preferably 25 to 35 parts by mass, per 100 parts by mass of polymer component (A). If the proportion of short fibers (C) is too low, abrasion resistance and lateral pressure resistance will decrease, and the friction coefficient will not be sufficiently reduced, which may result in an inability to improve transmission efficiency. On the other hand, if the proportion of short fibers (C) is too high, flexibility may decrease.

[0090] In the present invention, when the inorganic filler (B) contains carbon black, adjusting the mass ratio of the carbon black to the short fibers (C) can achieve both abrasion resistance and power transmission efficiency. The proportion of carbon black can be selected from a range of approximately 10 to 500 parts by mass per 100 parts by mass of the short fibers (C), for example, 50 to 200 parts by mass, preferably 80 to 190 parts by mass, more preferably 100 to 180 parts by mass (e.g., 140 to 175 parts by mass), and even more preferably 150 to 170 parts by mass. If the proportion of carbon black is too high (if the proportion of short fibers (C) relative to carbon black is too low), the anisotropy of the rubber composition may decrease, making it difficult to achieve both flexibility and lateral pressure resistance, and the power transmission efficiency may decrease. On the other hand, if the proportion of carbon black is too low (if the proportion of short fibers (C) is too high), abrasion resistance and flexibility may decrease and cracks may be more likely to occur.

[0091] (D) Crosslinking agent The rubber composition of the present invention may contain a crosslinking agent (D), and preferably contains a sulfur-based crosslinking agent, in particular, from the viewpoint of improving flexibility (flexural fatigue resistance or crack resistance) and power transmission efficiency.

[0092] Examples of sulfur-based crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and sulfur chlorides (sulfur monochloride, sulfur dichloride, etc.). These sulfur-based crosslinking agents can be used alone or in combination. Among these, sulfurs such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur are preferred, and powdered sulfur is particularly preferred.

[0093] The proportion of the sulfur-based crosslinking agent can be selected from the range of, for example, about 1 to 10 parts by mass relative to 100 parts by mass of the polymer component (A), and is preferably 1.2 parts by mass or more, for example, 1.2 to 5 parts by mass, preferably 1.3 to 3 parts by mass, further preferably 1.5 to 2.5 parts by mass, even more preferably 1.6 to 2.3 parts by mass, and most preferably 1.8 to 2.2 parts by mass. If the proportion of the sulfur-based crosslinking agent is too low, there is a risk of a decrease in rubber hardness, lateral pressure resistance, and abrasion resistance, while if it is too high, there is a risk of a decrease in flex fatigue resistance and also of bloom (precipitation on the surface) occurring.

[0094] The crosslinking agent (D) may further contain an organic peroxide as another crosslinking agent (or vulcanizing agent). Examples of organic peroxides include those typically used for crosslinking rubbers and resins, such as diacyl peroxides, peroxy esters, and dialkyl peroxides (e.g., dicumyl peroxide, t-butylcumyl peroxide, 1,1-dibutylperoxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane, 1,3-bis(t-butylperoxy-isopropyl)benzene, and di-t-butyl peroxide). These organic peroxides can be used alone or in combination. Furthermore, the organic peroxide is preferably a peroxide with a thermal decomposition temperature of about 150 to 250°C (e.g., 175 to 225°C) that provides a half-life of one minute.

[0095] The proportion of organic peroxide may be 100 parts by mass or less, preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the sulfur-based crosslinking agent. If the proportion of organic peroxide is too high, the flex fatigue resistance of the cured product may decrease. It is particularly preferable that the crosslinking agent (D) is substantially free of organic peroxide, and most preferably free of organic peroxide.

[0096] The proportion of the sulfur-based crosslinking agent (particularly sulfur compounds such as powdered sulfur) in the crosslinking agent (D) may be 50% by mass or more, preferably 70% by mass or more, further preferably 90% by mass or more, and even more preferably 100% by mass. If the proportion of the sulfur-based crosslinking agent is too low, the flexibility of the compression rubber layer may decrease.

[0097] The proportion of the crosslinking agent (D) can be selected, for example, from a range of about 1 to 10 parts by mass relative to 100 parts by mass of the polymer component (A), and is, for example, 1.2 to 10 parts by mass, preferably 1.3 to 8 parts by mass, even more preferably 1.5 to 5 parts by mass, even more preferably 1.6 to 3 parts by mass, and most preferably 1.8 to 2.5 parts by mass.

[0098] (E) Co-crosslinking agent (crosslinking aid or co-vulcanizing agent) The rubber composition of the present invention may further contain a co-crosslinking agent (E). In particular, when the crosslinking agent (D) contains a sulfur-based crosslinking agent (especially a sulfur-based compound such as powdered sulfur), crosslinking with the sulfur-based crosslinking agent makes it difficult to increase hardness, and the lateral pressure resistance and heat resistance tend to decrease. Therefore, by combining the sulfur-based crosslinking agent with the co-crosslinking agent (E), it is possible to maintain the lateral pressure resistance and heat resistance while taking advantage of the action of the sulfur-based crosslinking agent to improve flexibility and power transmission efficiency. In particular, when the co-crosslinking agent (E) contains a bismaleimide compound, the effect of improving the lateral pressure resistance and wear resistance is significant.

[0099] Examples of bismaleimide compounds include aliphatic bismaleimides (e.g., N,N'-1,2-ethylenedimaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)cyclohexane, etc.), and aromatic bismaleimides (e.g., N,N'-m-phenylene dimaleimide, 4-methyl-1,3-phenylene dimaleimide, 4,4'-diphenylmethane dimaleimide, 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane, 4,4'-diphenylether dimaleimide, 4,4'-diphenylsulfone dimaleimide, 1,3-bis(3-maleimidophenoxy)benzene, etc.)).

[0100] These bismaleimide compounds can be used alone or in combination of two or more. Among these, aromatic bismaleimides (arene bismaleimides) such as N,N'-m-phenylenedimaleimide are preferred because of their excellent heat resistance.

[0101] The co-crosslinking agent (E) may further contain other co-crosslinking agents in addition to the bismaleimide compound.

[0102] Other co-crosslinking agents include, for example, polyfunctional (iso)cyanurates [e.g., triallyl isocyanurate (TAIC), triallyl cyanurate (TAC)], polydienes (e.g., 1,2-polybutadiene), metal salts of α,β-unsaturated carboxylic acids [e.g., zinc (meth)acrylate, magnesium (meth)acrylate], oximes (e.g., quinone dioxime), guanidines (e.g., diphenyl guanidine), and polyfunctional (meth)acrylates [e.g., ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate].

[0103] The proportion of the other co-crosslinking agent may be 100 parts by mass or less, preferably 50 parts by mass or less, further preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the bismaleimide compound. If the proportion of the other co-crosslinking agent is too high, the effect of improving lateral pressure resistance and abrasion resistance may be reduced.

[0104] The proportion of the bismaleimide compound in the co-crosslinking agent (E) may be 50% by mass or more, preferably 70% by mass or more, further preferably 90% by mass or more, and even more preferably 100% by mass. If the proportion of the bismaleimide compound is too low, the effect of improving lateral pressure resistance and abrasion resistance may decrease.

[0105] The proportion of the co-crosslinking agent (E) can be selected from the range of, for example, about 0.1 to 10 parts by mass relative to 100 parts by mass of the polymer component (A), and is, for example, 0.5 to 8 parts by mass, preferably 1 to 7 parts by mass, further preferably 1.5 to 5 parts by mass, even more preferably 2 to 4 parts by mass, and most preferably 2.5 to 3.5 parts by mass. If the proportion of the co-crosslinking agent (E) is too low, there is a risk that the lateral pressure resistance and abrasion resistance will decrease, and if it is too high, there is a risk that the flexibility and transmission efficiency will decrease.

[0106] (F) Crosslinking accelerator The rubber composition of the present invention may further contain a crosslinking accelerator (F) in addition to the crosslinking agent (particularly, a sulfur-based crosslinking agent).

[0107] Examples of the crosslinking accelerator (F) include thiuram accelerators [e.g., tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetrabutylthiuram disulfide (TBTD), dipentamethylenethiuram tetrasulfide (DPTT), N,N'-dimethyl-N,N'-diphenylthiuram disulfide, etc.], sulfenamide accelerators [e.g., N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N,N'-dicyclohexyl-2-benzothiazylsulfenamide, Nt-butyl-2-benzothiazylsulfenamide (TBBS)], thiomorpholine accelerators [e.g., 4,4'-dithiodimorpholine (DTDM), 2-(4'-morpholinodithio)benzothiazyl] azoles, etc.), thiazole-based accelerators [e.g., 2-mercaptobenzothiazole (MBT), zinc salt of MBT, 2-mercaptobenzothiazoledibenzothiazyl disulfide (MBTS), 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-(4'-morpholinodithio)benzothiazole, etc.], urea- or thiourea-based accelerators [e.g., ethylenethiourea, trimethylthiourea (TMU), diethylthiourea (EDE)], guanidine-based accelerators (diphenylguanidine, di-o-tolylguanidine), dithiocarbamate-based accelerators [e.g., sodium dimethyldithiocarbamate, zinc diethyldithiocarbamate (EZ), zinc dibutyldithiocarbamate (BZ)], xanthate-based accelerators (e.g., zinc isopropylxanthate), etc. These crosslinking accelerators can be used alone or in combination. Among these crosslinking accelerators, TMTD, DPTT, CBS, MBTS, etc. are commonly used, and thiuram accelerators such as TMTD are preferred.

[0108] The proportion of the crosslinking accelerator (F) is, for example, 0.1 to 10 parts by mass, preferably 0.3 to 5 parts by mass, more preferably 1 to 3 parts by mass, and most preferably 1.5 to 2.5 parts by mass, relative to 100 parts by mass of the polymer component (A). If the proportion of the crosslinking accelerator is too low, the lateral pressure resistance of the compression rubber layer may decrease, while if it is too high, the flexibility may decrease.

[0109] (G) Softener The rubber composition of the present invention may not contain a softener (G), but may further contain a softener (G) as needed to improve flexibility. The softener (G) may be a so-called plasticizer or processing aid.

[0110] Examples of the softener (G) include mineral oil-based softeners {e.g., petroleum-based softeners [e.g., paraffinic oils, alicyclic oils (naphthenic oils), aromatic oils, etc.], coal tar-based softeners [e.g., coal tar, coumarone-indene resin, etc.], etc.}, vegetable oil-based softeners {e.g., fatty acid or metal salts thereof such as stearic acid and metal stearates; fatty acid esters such as stearic acid esters; fatty acid amides such as stearic acid amide; fatty oils, etc.}, and pine oil-based softeners. Fat-derived softeners [pine tar, rosin, sub(factice), etc.], synthetic softeners {e.g., synthetic resin softeners [hydrocarbon-based synthetic oils (low molecular weight paraffin, low molecular weight wax, phenol-aldehyde resin, liquid ethylene-α-olefin copolymer, etc.), liquid rubber (liquid polybutene, liquid polybutadiene, liquid isoprene rubber, etc.)], synthetic plasticizers (phthalate diesters such as dioctyl phthalate, polyester-based plasticizers, C-type plasticizers such as dioctyl sebacate, etc.) 6-18 Alkanedicarboxylic acid esters, etc.}.

[0111] These softeners (G) can be used alone or in combination of two or more. Among these, petroleum-based softeners such as paraffin oil, C softeners such as stearic acid, etc. 8-24 Fatty acids (including their metal salts, esters, and amides) are preferred, and petroleum-based softeners and C 8-24 Combinations with fatty acids are particularly preferred.

[0112] Softener (G) is a petroleum-based softener and C 8-24 When combined with fatty acids, C 8-24 The proportion of the fatty acids relative to 100 parts by mass of the petroleum-based softener is, for example, 10 to 1000 parts by mass, preferably 30 to 300 parts by mass, further preferably 50 to 200 parts by mass, even more preferably 70 to 150 parts by mass, and most preferably 80 to 120 parts by mass.

[0113] The proportion of the softener (G) is preferably, for example, 3 parts by mass or less per 100 parts by mass of the polymer component (A), from the viewpoint of not reducing the effects of the polymer component (A) having a high Mooney viscosity on lateral pressure resistance and abrasion resistance; and from the viewpoint of achieving both lateral pressure resistance and abrasion resistance and flexibility, the proportion is, for example, 0.1 to 3 parts by mass, preferably 0.5 to 2.8 parts by mass, even more preferably 0.8 to 2.5 parts by mass, even more preferably 1 to 2.3 parts by mass, and most preferably 1.5 to 2.2 parts by mass.

[0114] (H) Other ingredients The rubber composition of the present invention may further contain another component (H). Examples of the other component (H) include conventional additives compounded into rubber, such as crosslinking retarders, antioxidants (antioxidants, heat-aging inhibitors, flex crack inhibitors, antiozonants, etc.), colorants, tackifiers, lubricants, coupling agents (silane coupling agents, etc.), stabilizers (ultraviolet absorbers, heat stabilizers, etc.), flame retardants, and antistatic agents. These additives can be used alone or in combination. Among these, antioxidants (first antioxidants) are commonly used.

[0115] The total proportion of the other components (H) is, for example, 0.1 to 15 parts by mass, preferably 0.3 to 10 parts by mass, and more preferably 0.5 to 7 parts by mass, relative to 100 parts by mass of the polymer component (A). The proportion of the antioxidant is, for example, 0.1 to 5 parts by mass, preferably 0.5 to 4 parts by mass, more preferably 1 to 3 parts by mass, and most preferably 1.5 to 2.5 parts by mass, relative to 100 parts by mass of the polymer component (A).

[0116] (I) Properties of the rubber composition The Mooney scorch minimum viscosity (minimum value of Mooney viscosity) of the rubber composition of the present invention (uncrosslinked rubber composition) measured at 125°C is, for example, 70 to 130, preferably 80 to 128, further preferably 90 to 125, even more preferably 100 to 120, and most preferably 110 to 118. If the Mooney scorch minimum viscosity is too low, there is a risk that the abrasion resistance and lateral pressure resistance will decrease, and if the Mooney scorch minimum viscosity is too high, there is a risk that the flexibility will decrease.

[0117] In the present application, the Mooney scorch minimum viscosity can be measured in accordance with the Mooney scorch test of JIS K 6300-1 (2013), and in detail, can be measured by the method described in the examples below.

[0118] The hardness (Hs) of the crosslinked product of the rubber composition of the present invention (crosslinked rubber composition) is, for example, 83 to 95°, preferably 85 to 94°, further preferably 87 to 93°, even more preferably 88 to 92°, and most preferably 89 to 91°. If the hardness of the crosslinked product is too low, there is a risk that the lateral pressure resistance will decrease, and conversely, if the hardness is too high, there is a risk that the flexibility will decrease.

[0119] In this application, the rubber hardness of the crosslinked rubber composition refers to the value Hs (Type A) measured using a Type A durometer in accordance with the spring type durometer hardness test specified in JIS K 6253 (2012) (Vulcanized rubber and thermoplastic rubber - Determination of hardness), and may be simply referred to as rubber hardness. In detail, it can be measured by the method described in the examples below.

[0120] The short fibers (C) contained in the rubber composition of the present invention are usually oriented in a predetermined direction in the compressed rubber layer. For example, when the rubber composition forms the compressed rubber layer of a friction transmission belt such as a raw-edge cog V-belt, the short fibers (C) are preferably embedded in the compressed rubber layer oriented in the belt width direction to suppress compressive deformation of the belt due to pressure from a pulley.

[0121] In the crosslinked rubber composition of the present invention, the 8% bending stress in the direction parallel to the short fibers can be regarded as an index of the ease of bending the belt in the circumferential direction. In order to improve the flexibility of a belt having a compressed rubber layer, the 8% bending stress in the direction parallel to the short fibers is 2.5 MPa or less, for example, 1 to 2.5 MPa, preferably 1.5 to 2.4 MPa, more preferably 1.8 to 2.3 MPa, and even more preferably 2 to 2.2 MPa. If the 8% bending stress in the direction parallel to the short fibers is too small, there is a risk that the lateral pressure resistance will decrease, and conversely, if it is too high, there is a risk that the flexibility will decrease.

[0122] In the crosslinked rubber composition of the present invention, in order to improve lateral pressure resistance, the 4% bending stress in the direction perpendicular to the short fibers is, for example, 2.5 to 4.5 MPa, preferably 2.7 to 4 MPa, and more preferably 3 to 3.5 MPa. If the 4% bending stress in the direction perpendicular to the short fibers is too small, the lateral pressure resistance of the belt may decrease, and conversely, if it is too high, the flexibility may decrease.

[0123] In the present application, the bending stress can be measured by arranging the pressing member so that the length direction is the same as the orientation direction (length direction) of the short fibers for an 8% bending stress in the direction parallel to the short fibers, and by arranging the pressing member so that the length direction is perpendicular to the orientation direction (length direction) of the short fibers for a 4% bending stress in the direction perpendicular to the short fibers. More specifically, the bending stress can be measured by the method described in the examples below.

[0124] In the present application, the term "short fiber parallel direction" refers not only to the length direction of the staple fibers but also to a direction within a range of ±5° from the length direction. The term "short fiber perpendicular direction" refers not only to a direction perpendicular to the length direction of the staple fibers (perpendicular direction) but also to a direction within a range of ±5° from the perpendicular direction.

[0125] [Power transmission belt] The power transmission belt of the present invention is not particularly limited as long as it has a compressed rubber layer that can come into contact with a pulley and this compressed rubber layer is formed from the crosslinked rubber composition, and may be a power transmission belt that includes a core layer (adhesive rubber layer), a compressed rubber layer formed on one surface of this core layer, and a tension rubber layer formed on the other surface of the core layer. Furthermore, among power transmission belts, friction power transmission belts that require wear resistance are preferred.

[0126] Examples of friction power transmission belts include V-belts [wrapped V-belts, raw-edge V-belts, raw-edge cogged V-belts (raw-edge cogged V-belts with cogs formed on the inner periphery of the raw-edge V-belt, and raw-edge double-cogged V-belts with cogs formed on both the inner and outer periphery of the raw-edge V-belt)], V-ribbed belts, flat belts, etc. Among these, V-belts or V-ribbed belts with a power transmission surface formed in a V-shape (or at a V angle) are preferred, and V-belts that are required to achieve high levels of both wear resistance and power transmission efficiency, such as V-belts used in belt-type continuously variable transmissions (e.g., raw-edge cogged V-belts), are preferred.

[0127] Furthermore, the raw-edge cogged V-belt of the present invention can be broadly divided into raw-edge cogged V-belts, in which cogs are formed only on the inner circumferential side of the raw-edge V-belt, and raw-edge double-cogged V-belts, in which cogs are formed on both the inner and outer circumferential sides of the raw-edge V-belt. Of these, raw-edge double-cogged V-belts are particularly preferred because they are used in more severe conditions and are required to have high levels of both lateral pressure resistance and flexibility.

[0128] FIG. 2 is a schematic perspective view showing an example of a power transmission belt (raw-edge double-cogged V-belt) of the present invention, and FIG. 3 is a schematic cross-sectional view of the power transmission belt of FIG. 2 cut in the belt length direction.

[0129] In this example, raw edge double cog V-belt 1 has an inner cog portion formed on the inner surface of the belt body along the length direction of the belt (direction A in the figure), with inner cog crests 1a and inner cog valleys 1b arranged alternately, and the cross section of these inner cog crests 1a in the length direction is approximately semicircular (curved or wavy), and the cross section in the direction perpendicular to the length direction (the width direction or direction B in the figure) is trapezoidal. That is, in the cross section along direction A, each inner cog crest 1a protrudes in an approximately semicircular shape in the belt thickness direction from the inner cog valley 1b.

[0130] The outer circumferential surface also has an outer cog portion formed with outer cog peaks 1c and outer cog valleys 1d arranged alternately along the length of the belt, and the cross section of the outer cog peaks 1c in the length direction is generally trapezoidal, while the cross section in the direction perpendicular to the length direction (the width direction or direction B in the figure) is generally rectangular. That is, in the cross section along direction A, each outer cog peak 1c protrudes in a generally trapezoidal shape in the belt thickness direction from the outer cog valley 1d.

[0131] The raw-edge double-cogged V-belt has a layered structure, with a tension rubber layer 2, a core layer (bonded rubber layer) 3, a compression rubber layer 4, and a reinforcing fabric 5 layered in this order from the outer periphery to the inner periphery. The cross-sectional shape in the belt width direction is a generally trapezoidal shape, with the belt width decreasing from the outer periphery to the inner periphery. Furthermore, a core 3a is embedded within the core layer 3, and the inner and outer cogs are formed into the compression rubber layer 4 and the tension rubber layer 2, respectively, using a cog-forming mold. In this example, only the inner periphery is covered with a reinforcing fabric, but the surface of the tension rubber layer 2 may also be covered with a second reinforcing fabric. Furthermore, the reinforcing fabric is not essential, and a structure without a reinforcing fabric on either the inner or outer periphery is also possible.

[0132] [Tension rubber layer] The power transmission belt (particularly, the raw-edge cogged V-belt) of the present invention may further include a tension rubber layer formed of a second rubber composition (second crosslinked rubber composition) containing a second polymer component.

[0133] The second polymer component, including preferred embodiments thereof, can be selected from the polymer components exemplified as the first polymer component (A). The second polymer component may be a polymer component different from the first polymer component (A), but is usually the same as the first polymer component.

[0134] The second rubber composition forming the tension rubber layer preferably contains a second inorganic filler, since this further improves lateral pressure resistance and abrasion resistance. When the second inorganic filler is contained in both the compression rubber layer and the tension rubber layer, lateral pressure resistance and abrasion resistance are further improved. The second inorganic filler, including preferred embodiments, can be selected from the inorganic fillers exemplified for the first inorganic filler (B). The second inorganic filler may be different from the first inorganic filler (B), but is usually the same as the first inorganic filler (B). The proportion of the second inorganic filler, including preferred proportions, can be selected from the proportion of the first inorganic filler (B).

[0135] The second rubber composition forming the tension rubber layer preferably contains second short fibers, since this further improves lateral pressure resistance and abrasion resistance. When the tension rubber layer contains the second short fibers as well as the compression rubber layer, the lateral pressure resistance and abrasion resistance are further improved. The second short fibers, including preferred embodiments, can be selected from the short fibers exemplified as the first short fibers (C). The second short fibers may be different from the first short fibers (C), but are usually the same as the first short fibers (C). The proportion of the second short fibers, including preferred proportions, can be selected from the proportion of the first short fibers (C).

[0136] The second rubber composition forming the tension rubber layer may also further contain the crosslinking agent (D), co-crosslinking agent (E), crosslinking accelerator (F), softener (G), and other components (H) exemplified in the first rubber composition forming the compression rubber layer.

[0137] The properties of the tension rubber layer, including the preferred ranges, can be selected from the properties of the compression rubber layer described above (Mooney scorch minimum viscosity, hardness, bending stress, etc.).

[0138] The second rubber composition forming the tension rubber layer may be of the same type or the same (particularly the same) as the first rubber composition forming the compression rubber layer.

[0139] [Core layer] The power transmission belt (particularly, the raw-edge cogged V-belt) of the present invention may further include a core layer.

[0140] The core layer may contain a core, and may be a core layer formed only of a core. However, from the viewpoint of suppressing interlayer peeling and improving belt durability, a core layer containing a core and an adhesive rubber layer formed of a cross-linked rubber composition is preferred.

[0141] In the core layer, at least a portion of the core needs to be in contact with the adhesive rubber layer, and the core may be embedded in the adhesive rubber layer, embedded between the adhesive rubber layer and the tension rubber layer, or embedded between the adhesive rubber layer and the compression rubber layer. Of these, the core is preferably embedded in the adhesive rubber layer in view of improving durability.

[0142] (Adhesive rubber layer) The adhesive rubber layer may be formed from a crosslinked product of a third rubber composition containing a third polymer component (third crosslinked rubber composition).

[0143] The third polymer component, including preferred embodiments thereof, can be selected from the polymer components exemplified as the first polymer component (A). The third polymer component may be a polymer component different from the first polymer component, but is usually the same type as the first polymer component (A).

[0144] The Mooney viscosity [ML(1+4)125°C] of the uncrosslinked third polymer component (particularly the uncrosslinked ethylene-α-olefin elastomer) may be, for example, 10 to 30, and preferably 15 to 25 or so.

[0145] The third rubber composition forming the adhesive rubber layer may also further contain the inorganic filler (B), crosslinking agent (D), co-crosslinking agent (E), crosslinking accelerator (F), softener (G), and other components (H) exemplified in the first rubber composition forming the compressed rubber layer.

[0146] The adhesive rubber layer preferably has a lower rubber hardness than the compressed rubber layer. The rubber hardness of the adhesive rubber layer is, for example, 60 to 85°, preferably 65 to 84°, further preferably 70 to 83°, and even more preferably 75 to 82°. If the rubber hardness is too low, there is a risk that the resistance to lateral pressure will be insufficient, while if it is too high, there is a risk that the adhesiveness will decrease. By adjusting the adhesive rubber layer to such a low hardness, it becomes possible for it to deform significantly when shear stress is applied, and peeling between the core and the compressed rubber layer and the tension rubber layer can be suppressed.

[0147] The average thickness of the adhesive rubber layer is, for example, 0.8 to 3 mm, preferably 1.2 to 2.8 mm, and more preferably 1.5 to 2 mm.

[0148] (Core body) The core is not particularly limited, but typically, a core wire (twisted cord) arranged at a predetermined interval in the width direction of the belt can be used. The core wires are arranged in the longitudinal direction of the belt and may be arranged in parallel with the longitudinal direction of the belt at a predetermined pitch. However, from the viewpoint of productivity, they are usually arranged in a spiral shape, extending in parallel with the longitudinal direction of the belt at a predetermined pitch, in raw-edge cogged V-belts and the like. When arranged in a spiral shape, the angle of the core wire with respect to the longitudinal direction of the belt may be, for example, 5° or less, and from the viewpoint of belt running performance, the closer to 0° the angle is, the more preferable. Furthermore, the pitch or interval, which is the distance between the centers of adjacent cores (particularly the spinning pitch of the core wire), is preferably set in the range of 0.5 to 3.0 mm, more preferably in the range of 0.8 to 2.0 mm, and most preferably in the range of 1.0 to 1.6 mm.

[0149] Examples of fibers constituting the core wire include the same fibers as the short fibers. Among the fibers, C fibers such as ethylene terephthalate and ethylene-2,6-naphthalate are preferred in terms of high modulus. 2-4 Alkylene-C 8-14 Polyester fibers (polyalkylene arylate fibers) containing arylate as the main structural unit, synthetic fibers such as aramid fibers, and inorganic fibers such as carbon fibers are commonly used, with polyester fibers (polyethylene terephthalate fibers, polyethylene naphthalate fibers, etc.) and aramid fibers being preferred. These fibers may be used in the form of multifilament yarns containing multiple filaments. The fineness of the multifilament yarns is, for example, 200 to 5000 dtex (particularly 500 to 2000 dtex). The multifilament yarns may contain, for example, 50 to 1500 filaments, preferably 100 to 1000 filaments, and more preferably 300 to 500 filaments.

[0150] The core wire can usually be a twisted cord (e.g., double twist, single twist, Lang twist, etc.) using multifilament yarn. The average wire diameter of the core wire (diameter of the twisted cord) may be, for example, 0.5 to 3 mm, preferably 0.6 to 2 mm, and more preferably about 0.7 to 1.5 mm. The total fineness of the core wire (twisted cord) may be, for example, 2,000 to 17,000 dtex, preferably 4,000 to 15,000 dtex, and more preferably 5,000 to 13,000 dtex (particularly 6,000 to 8,000 dtex). The core wire (twisted cord) may contain, for example, 500 to 12,000 filaments, preferably 1,000 to 5,000 filaments, and more preferably 2,000 to 3,000 filaments.

[0151] The core wire may be subjected to an adhesive treatment (or surface treatment) in the same manner as the short fibers (C) in order to improve adhesion to the polymer component. The core wire is preferably subjected to an adhesive treatment with at least an RFL liquid.

[0152] [Reinforcing fabric] The power transmission belt (particularly the raw-edge cogged V-belt) of the present invention may include, but is not necessarily required to include, a reinforcing fabric, which may be, for example, laminated on the inner circumferential surface of the compression rubber layer, laminated on the outer circumferential surface of the tension rubber layer, or embedded in the compression rubber layer and / or tension rubber layer.

[0153] The reinforcing fabric can be formed from fabric materials (especially woven fabrics) such as woven fabrics, wide-angle canvas, knitted fabrics, and nonwoven fabrics, and if necessary, can be subjected to an adhesive treatment, for example, treatment with RFL liquid (dipping treatment, etc.), a friction treatment in which adhesive rubber is rubbed into the fabric material, or the adhesive rubber and the fabric material can be laminated together and then laminated or embedded in the compression rubber layer and / or tension rubber layer in the above-mentioned form.

[0154] [Manufacturing method of power transmission belt] The method for manufacturing the power transmission belt of the present invention is not particularly limited, and any conventional method can be used. For example, the method for manufacturing the raw-edge cogged V-belt of the present invention is also not particularly limited, and any conventional method can be used for the lamination process of each layer (method for manufacturing the belt sleeve) depending on the type of belt. For example, a typical method for manufacturing a raw-edge cogged V-belt will be described below.

[0155] First, a laminate of a reinforcing fabric (lower fabric) and a sheet for the main body of the compressed rubber layer (an uncrosslinked rubber sheet) is placed, with the reinforcing fabric facing downward, in contact with a flat cog mold in which teeth and grooves corresponding to the inner cogs (cog crests 1a and cog bottoms 1b shown in Figure 2) are alternately arranged, and the laminate is pressed at a temperature of 60 to 100°C (particularly 70 to 80°C) to produce a cog pad with shaped inner cogs (a pad that is not completely crosslinked, but is in a semi-crosslinked state). Then, both ends of this cog pad are cut vertically at appropriate points (particularly the tops of the cog crests) to obtain the required length.

[0156] Next, an inner mold, which has teeth and grooves corresponding to the cog portions arranged alternately, is placed over the outer periphery of a cylindrical mold, and a cog pad is wrapped around it by engaging the teeth and grooves of the inner mold and joining both ends (particularly the tops of the cog crests).A sheet for the first adhesive rubber layer (lower adhesive rubber: uncrosslinked rubber sheet) is then laminated around the outer periphery of this cog pad, and the core wire (twisted cord) that forms the core body is spun spirally, and a sheet for the second adhesive rubber layer (upper adhesive rubber: uncrosslinked rubber sheet) and a sheet for the tension rubber layer (uncrosslinked rubber sheet) are sequentially wrapped around the outer periphery to produce an uncrosslinked molded body.

[0157] The uncrosslinked molded body is then placed in a known crosslinking device (such as a vulcanizer) with the jacket on, and crosslinked at a temperature of 120 to 200°C (particularly 150 to 180°C) to produce a crosslinked belt sleeve.Then, using a cutter or the like, the crosslinked belt sleeve is cut into a V shape to obtain an endless raw-edge cog V-belt.

[0158] In the case of a raw-edge double-cogged V-belt, an outer mold having teeth and grooves corresponding to the outer cogs arranged alternately is placed on the outer periphery of the uncrosslinked molded body, and then a jacket is placed over the uncrosslinked molded body and crosslinked molding is performed to obtain a crosslinked belt sleeve having cogs formed on the outer periphery as well.Then, the crosslinked belt sleeve is cut into a V shape to obtain a raw-edge double-cogged V-belt.

[0159] The adhesive rubber layer can be formed from multiple adhesive rubber layer sheets, and the core wire (twisted cord) that forms the core body may be spun in relation to the stacking order of the multiple adhesive rubber layer sheets, depending on the embedding position in the adhesive rubber layer. [Example]

[0160] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. Details of the materials used in the examples and the evaluation methods for the examples and comparative examples are shown below.

[0161] [Materials used] (polymer component) EPDM1: “EP123” manufactured by JSR Corporation, ethylene content 58% by mass, diene content 4.5% by mass, Mooney viscosity 19.5ML(1+4) 125℃ EPDM2: Dow Chemical Company's "Nordel 6530XFC", ethylene content 55% by mass, diene content 8.5% by mass, Mooney viscosity 30ML (1+4) 125℃ EPDM3: "Nordel 3745P" manufactured by Dow Chemical Company, ethylene content 70% by mass, diene content 0.5% by mass, Mooney viscosity 45ML (1+4) 125℃ EPDM4: Dow Chemical Company's "Nordel 6565XFC", ethylene content 55% by mass, diene content 8.5% by mass, Mooney viscosity 65ML (1+4) 125℃

[0162] (short fibers) The following staple fibers were used. All staple fibers were immersed in an RFL liquid [a mixture of 2.6 parts by mass of resorcinol, 1.4 parts by mass of 37% formalin, 17.2 parts by mass of vinylpyridine-styrene-butadiene copolymer latex (manufactured by Zeon Corporation), and 78.8 parts by mass of water] and then dried to undergo an adhesion treatment. The adhesion rate of the adhesive component (solid content) was adjusted to 6% by mass of the staple fibers after the adhesion treatment.

[0163] Para-aramid staple fiber: Twaron manufactured by Teijin Limited, fineness 2.2 dtex, average fiber length 3 mm Nylon staple fiber: "Leona" manufactured by Asahi Kasei Corporation, average fiber diameter 27 μm, average fiber length 3 mm Polyester staple fiber: "Tetoron" manufactured by Teijin Limited, average fiber diameter 25 μm, average fiber length 3 mm

[0164] (filler) Carbon black FEF: "Seast SO" manufactured by Tokai Carbon Co., Ltd., average primary particle diameter 43 nm Carbon black HAF: "Seast 3" manufactured by Tokai Carbon Co., Ltd., average primary particle size 28 nm Silica: Evonik Degussa "Ultrasil VN3", BET specific surface area 175m2 / g

[0165] (additives) Paraffin oil: Idemitsu Kosan Co., Ltd. "Diana Process Oil PW90" Antioxidant ODPA (octyldiphenylamine): "Nonflex OD-3" manufactured by Seiko Chemical Co., Ltd. Antioxidant DCD (4,4'-bis(α,α-dimethylbenzyl)diphenylamine): "Nocrac CD" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Zinc oxide: Sakai Chemical Industry Co., Ltd. "Zinc oxide type 2" Stearic acid: "Camellia Stearate" manufactured by NOF Corporation Resorcinol-formalin copolymer: INDSPEC Chemical Corporation "Penacolite Resin B-18-S" Hexamethoxymethylolmelamine: "POWERPLAST PP-1890S" manufactured by SINGH PLASTICISER & RESINS Crosslinking accelerator TMTD (tetramethylthiuram disulfide): "Noccela TT" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Crosslinking accelerator CBS (N-cyclohexyl-2-benzothiazolylsulfenamide): "Noccela CZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Crosslinking accelerator MBTS (di-2-benzothiazolyl disulfide): "Noccela DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Co-crosslinking agent MPBM (N,N'-m-phenylenedimaleimide): "Valnoc PM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur (powdered sulfur): "MIDAS" manufactured by Bigen Chemical Co., Ltd.

[0166] (reinforced fabric) 2 / 2 twill nylon canvas (thickness 0.50 mm) adhesively treated with the RFL liquid.

[0167] (core wire) This treated cord is made by combining two 1100dtex PET fiber bundles (384 filaments) and first twisting them at a twist factor of 3.0 to form three first twisted yarns, which are then top twisted at a twist factor of 3.0 to form a ply-twisted cord with a total fineness of 6600dtex, and then applying the same adhesive treatment as for staple fibers.The twist factor (TF) is calculated using the following formula.

[0168] TF=TN×D 0.5 / 960

[0169] [In the formula, TN represents the number of twists per meter, and D represents the fineness (tex) of the yarn.]

[0170] (Adhesive rubber layer composition) As the adhesive rubber layer composition, the rubber compositions shown in Table 2 were used.

[0171] [Table 2]

[0172] Examples 1 to 12 and Comparative Examples 1 to 3 [Mooney Scorch minimum viscosity (Vm)] Using uncrosslinked rubber compositions having the compositions shown in Table 3 or Table 4, the minimum Mooney scorch viscosity was measured according to the Mooney scorch test of JIS K 6300-1 (2013). An L-shaped rotor was used, and the test temperature was 125°C. A polyester film ("Lumirror" manufactured by Toray Industries, Inc.) with a thickness of approximately 0.04 mm was placed between the surface where the test piece (the uncrosslinked rubber composition) and the die came into contact. The die was preheated for 1 minute after closing, and then the rotor was rotated, and the progress of the Mooney viscosity was recorded. The recorded Mooney viscosity generally exhibited the behavior shown in Figure 4, and the value at which the Mooney viscosity reached its minimum was taken as the minimum Mooney scorch viscosity (Vm).

[0173] [Rubber hardness Hs of cross-linked rubber] An uncrosslinked rubber composition having the composition shown in Table 3 or Table 4 was press-heated at 160°C for 30 minutes to prepare a crosslinked rubber sheet (100 mm x 100 mm x 2 mm thick). Three crosslinked rubber sheets were stacked to form a laminate, which was used as a sample. The hardness of the crosslinked rubber sheet was measured using a Type A durometer in accordance with the spring durometer hardness test specified in JIS K 6253 (2012).

[0174] [4% bending stress (perpendicular to short fibers)] An uncrosslinked rubber composition having the composition shown in Table 3 or Table 4 was press-heated at 160°C and 2 MPa for 20 minutes to produce a crosslinked rubber molded body (60 mm × 25 mm × 6.5 mm thick). The short fibers were oriented parallel to the length of the crosslinked rubber molded body. As shown in Figure 5, this crosslinked rubber molded body 21 was supported on a pair of rotatable rolls (6 mm diameter) 22a and 22b spaced 20 mm apart, and a metal presser member 23 was placed across the center of the top surface of the crosslinked rubber molded body in the width direction (perpendicular to the short fiber orientation direction). The tip of the presser member 23 had a semicircular shape with a diameter of 10 mm, allowing it to smoothly press against the crosslinked rubber molded body 21. During pressing, frictional forces act between the underside of the crosslinked rubber molded body 21 and the rolls 22a and 22b as the crosslinked rubber molded body 21 compresses and deforms. However, the rotatable rolls 22a and 22b minimize the effects of this friction. The initial position was a state in which the tip of the pressing member 23 was in contact with but not pressing against the top surface of the crosslinked rubber molded body 21, and from this state the pressing member 23 was pressed downward against the top surface of the crosslinked rubber molded body 21 at a speed of 100 mm / min, and the stress at which bending strain reached 4% was measured as bending stress. The measurement temperature was set to 120°C, simulating the temperature of the belt during running. It can be determined that the greater the 4% bending stress in the direction perpendicular to the short fibers, the higher the resistance to buckling deformation known as dishing during belt running.

[0175] [8% bending stress (parallel to short fibers)] In the above-mentioned method for measuring the 4% bending stress in the direction perpendicular to the short fibers, as shown in Figure 6, the measurement was performed in the same manner except that when producing the crosslinked rubber molding, the short fibers were oriented perpendicular to the length direction of the rubber molding (i.e., the metal pressing member 23 and the orientation direction of the short fibers were parallel), and the stress at which the bending strain reached 8% was taken as the bending stress. If the 8% bending stress in the direction parallel to the short fibers is small, the flexibility of the belt can be determined to be good. A value of 2.5 MPa or less is considered to be a practical acceptable level.

[0176] [Manufacturing raw edge double cog V-belts] Using the uncrosslinked rubber compositions shown in Table 3 or Table 4 for the compression rubber layer and the tension rubber layer, and the uncrosslinked rubber composition shown in Table 2 for the adhesive rubber layer, a raw edge double cogged V-belt (size: upper width 20.0 mm, thickness 10.0 mm, belt outer circumference length 800 mm) was produced by the method described in the above embodiment (crosslinking temperature 160°C, time 20 minutes).

[0177] [Abrasion durability test (change in upper width and mass)] The wear durability test was conducted using a biaxial running test machine consisting of a 50 mm diameter drive (Dr.) pulley and a 125 mm diameter driven (Dn.) pulley, as shown in Figure 7. A raw-edge double-cogged V-belt was hung between these two pulleys, and the belt was run for 20 hours at an ambient temperature of 80°C under an axial load of 800 N, a drive pulley rotation speed of 5600 rpm, and a load on the driven pulley of 9 N m. The belt was measured before and after running, and the change in top width (wear loss) and the rate of mass change were evaluated.

[0178] [Transmission efficiency (power transmission efficiency) test] The transmission efficiency test was conducted by using a motor to drive a continuously variable transmission with a 250 mm centerline between the drive and driven shafts. Figure 8 shows the layout of the test machine. It is a two-axle running test machine consisting of a drive (Dr.) pulley connected to the drive shaft and a driven (Dn.) pulley connected to the driven shaft. The driven pulley clamps the belt with a spring, while the drive pulley has a fixed groove width. The no-load speed ratio (the pitch diameter of the driven pulley divided by the pitch diameter of the drive pulley) was adjusted to 1.2. Digital tachometers and torque meters were attached to the drive and driven shafts. The drive shaft rotation speed and torque were recorded while varying the drive shaft rotation speed from 3000 to 5000 rpm and the drive shaft torque from 2 to 4 N·m. The ambient temperature was 25°C.

[0179] As shown in the formula below, the power P1 of the drive shaft is calculated as the product of the torque T1 and the rotational speed ρ1 of the drive shaft. Similarly, the power P2 of the driven shaft is calculated as the product of the torque T2 and the rotational speed ρ2 of the driven shaft. The transmission efficiency η is calculated by dividing the power P2 of the driven shaft by the power P1 of the drive shaft.

[0180] P1=T1×ρ1 P2=T2×ρ2 η(%)=[P2 / P1]×100=[(T2×ρ2) / (T1×ρ1)]×100

[0181] The transmission efficiency is calculated when the drive shaft rotation speed is 3000 rpm and the drive shaft torque is 2 N·m. The transmission efficiency value is 100% if there is no transmission loss, and if there is transmission loss, the value will be smaller by the amount of that loss. In other words, the closer to 100%, the smaller the transmission loss and the better the fuel efficiency.

[0182] The evaluation results of Examples 1 to 12 and Comparative Examples 1 to 3 are shown in Table 3 or Table 4.

[0183] [Table 3]

[0184] [Table 4]

[0185] Comparative Example 1 is an example in which the Mooney viscosity of the polymer component is low and the inorganic filler is contained in a large amount, but the flexibility and transmission efficiency were low. Comparative Example 2 is an example in which the Mooney viscosity of the polymer component is low, but the abrasion resistance was low. Comparative Example 3 is an example in which the Mooney viscosity of the polymer component is high, but the inorganic filler is contained in a small amount, but the abrasion resistance was low.

[0186] In contrast, Examples 1 to 12, in which the Mooney viscosity of the polymer component and the amount of inorganic filler were adjusted within appropriate ranges, were able to simultaneously improve wear resistance and transmission efficiency. A comparison of Examples 1 to 6, in which the amount of inorganic filler was kept constant and the Mooney viscosity of the polymer component was changed, confirmed a tendency for wear resistance to improve as the Mooney viscosity of the polymer component increased.

[0187] Example 8 is an example in which polyester staple fibers were used instead of the nylon staple fibers of Example 3, but the transmission efficiency was lower than that of Example 3. Example 9 is an example in which the proportion of para-aramid staple fibers of Example 3 was reduced, but the 4% bending stress in the direction perpendicular to the staple fibers and the abrasion resistance were lower than those of Example 3. Example 10 is an example in which carbon black HAF (hard carbon) was used instead of carbon black FEF (soft carbon) of Example 3, but the transmission efficiency was lower than that of Example 3. Example 11 is an example in which the proportion of carbon black was lower than that of Example 3, but the abrasion resistance was lower than that of Example 3. Example 12 is an example in which the proportion of co-crosslinking agent was higher than that of Example 3, but the transmission efficiency was lower than that of Example 3.

[0188] Among these Examples 1 to 12, Example 6 had high wear resistance and an excellent balance with transmission efficiency. [Industrial Applicability]

[0189] The rubber composition of the present invention can be used for various molded articles, and in particular can be used as power transmission belts, for example, friction power transmission belts such as flat belts, wrapped V-belts, raw-edge V-belts, raw-edge cog-V-belts, and V-ribbed belts, and meshing power transmission belts such as toothed belts and double-sided toothed belts. In particular, when used as a compressed rubber layer in a power transmission belt, it can simultaneously improve abrasion resistance and transmission efficiency, and is therefore useful as a compressed rubber layer in speed-change belts used in motorcycles, four-wheeled buggies, snowmobiles, agricultural machinery, and the like, which are becoming increasingly powerful. [Explanation of symbols]

[0190] 1...Raw edge double cog V-belt 2...Tension rubber layer 3...Core layer 3a… Core body 4...Compressed rubber layer 5...Reinforcing fabric

Claims

1. A rubber composition for forming a compression rubber layer of a transmission belt, comprising a polymer component, an inorganic filler and short fibers; the polymer component comprises an ethylene-α-olefin elastomer; the ethylene-α-olefin elastomer is an ethylene-α-C 3-4 olefin-diene terpolymer rubber; the proportion of the ethylene-α-olefin elastomer in the polymer component is 90% by mass or more, The uncrosslinked polymer component has a Mooney viscosity of 34 to 65 ML(1+4) 125°C, The proportion of the inorganic filler is 25 to 55 parts by mass per 100 parts by mass of the polymer component; and A crosslinked product of the rubber composition has an 8% bending stress in a direction parallel to the short fibers of 1.6 to 2.4 MPa.

2. The rubber composition according to claim 1, further comprising a crosslinking agent, wherein the crosslinking agent comprises a sulfur-based crosslinking agent.

3. The rubber composition according to claim 1 or 2, further comprising a co-crosslinking agent.

4. 4. The rubber composition according to claim 3, wherein the proportion of the co-crosslinking agent is 1 to 5 parts by mass per 100 parts by mass of the polymer component.

5. The rubber composition according to claim 1 or 2, wherein the inorganic filler contains carbon black, and the carbon black contains soft carbon, and the proportion of the carbon black is 50 to 200 parts by mass per 100 parts by mass of the short fibers.

6. 3. The rubber composition according to claim 1, wherein the content of the softener is 3 parts by mass or less per 100 parts by mass of the polymer component.

7. 3. The rubber composition according to claim 1, wherein the short fibers comprise aramid short fibers and aliphatic polyamide short fibers, and the proportion of the aramid short fibers is 100 parts by mass or more per 100 parts by mass of the aliphatic polyamide short fibers.

8. A power transmission belt having a compressed rubber layer formed from the rubber composition according to claim 1 or 2.

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