Transmission belt and belt transmission mechanism

Abstract

The present invention relates to a transmission belt comprising a compressed rubber layer. The compressed rubber layer comprises a crosslinked rubber composition, and the crosslinked rubber composition includes a rubber component and short fibers. The rubber component includes chloroprene rubber, and the short fibers include poly(para-phenylene benzobisoxazole)-based short fibers and aramid short fibers. The 4% bending modulus in a direction orthogonal to the orientation direction of the short fibers in the crosslinked rubber composition is 5 MPa or greater, and the 4% bending modulus in a direction parallel to the orientation direction of the short fibers in the crosslinked rubber composition is 2.5 MPa or less.

Description

Transmission belts and belt transmission mechanisms

[0001] This invention relates to a transmission belt and belt transmission mechanism used in small belt-type continuously variable transmissions and the like.

[0002] Power transmission belts used in power transmission mechanisms of machinery and other equipment are broadly classified into friction belts and meshing belts depending on the method of power transmission. Examples of friction belts include V-belts, V-ribbed belts, and flat belts. Examples of meshing belts include toothed belts.

[0003] V-belts, which transmit power by friction, come in two types: raw-edge type V-belts (raw-edge V-belts), which have an exposed rubber layer on the friction transmission surface (V-shaped side), and wrapped type V-belts (wrapped V-belts), which have the friction transmission surface covered by a cover cloth. They are used differently depending on the application due to the difference in the surface properties of the friction transmission surface (the coefficient of friction between the rubber layer and the cover cloth). Raw-edge V-belts include raw-edge V-belts without cogs, raw-edge cogged V-belts with cogs only on the inner circumference to improve flexibility, and raw-edge cogged V-belts (raw-edge double cogged V-belts) with cogs on both the inner and outer circumferences to improve flexibility.

[0004] One application for these V-belts (especially raw-edge cogged V-belts) is a belt-type continuously variable transmission (CVT). As shown in Figures 1A and 1B, the belt-type CVT 30 is a device that continuously changes the gear ratio by winding a V-belt 1A around a drive pulley 31 and a driven pulley 32. The pulleys 31 and 32 each include fixed sheaves 31a and 32a whose axial movement is restricted or fixed, and movable sheaves 31b and 32b that can move in the axial direction. The belt-type CVT 30 has a structure that allows the width of the V-grooves of the pulleys 31 and 32, formed by the fixed sheaves 31a and 32a and the movable sheaves 31b and 32b, to be continuously changed. The V-belt 1A has tapered surfaces at both ends in the width direction that match the inclination of the opposing surfaces of the V-grooves of each pulley 31 and 32, and fits into any position in the pulley radial direction according to the adjusted width of the V-grooves. For example, by narrowing the width of the V-groove on the drive pulley 31 and widening the width of the V-groove on the driven pulley 32, the state shown in Figure 1A is changed to the state shown in Figure 1B. As a result, the V-belt 1A moves towards the outer circumference in the pulley radial direction on the drive pulley 31 side and towards the inner circumference in the pulley radial direction on the driven pulley 32 side. The winding radius on each pulley 31 and 32 changes continuously, allowing for stepless adjustment of the gear ratio.

[0005] V-belts (variable speed belts or CVT belts) used in such applications need to accommodate not only rotational movement between the drive pulley and the driven pulley, but also movement in the pulley radius direction and repeated bending movements due to continuous changes in the winding radius. Therefore, V-belts require high resistance to lateral pressure (high rigidity in the width direction) to suppress deformation of the belt due to lateral pressure from the pulley, as well as high wear resistance and crack resistance.

[0006] To improve the lateral pressure resistance and wear resistance of variable speed transmission belts (CVT belts), a method of forming a compression rubber layer with a crosslinked rubber composition containing short fibers is commonly used. For example, Japanese Patent Publication No. 2004-3609 (Patent Document 1) discloses a transmission belt in which a compression rubber layer is formed using a rubber composition containing 1 to 40 parts by mass of polyp-phenylenebenzobisoxazole (PBO) short fibers per 100 parts by mass of chloroprene rubber, and a rubber composition containing 1 to 40 parts by mass of a mixture of PBO short fibers and aramid short fibers.

[0007] Japanese Patent Publication No. 2004-3609

[0008] However, the rubber composition described in Patent Document 1 contains a large amount of highly rigid short fibers such as PBO short fibers and aramid short fibers, which may have led to problems with mixing depending on the amount of other compounding agents such as crosslinking accelerators (vulcanization accelerators), co-crosslinking agents, and carbon black, thus posing challenges to practical application. Furthermore, as the transmission capacity increases, the operating conditions for CVT belts are becoming more stringent, and conventional formulations are often insufficient in terms of durability, requiring improvement. In particular, increasing the hardness of the belt or incorporating short fibers to improve lateral pressure resistance and abrasion resistance makes it difficult to maintain crack resistance. Thus, it has been difficult to simultaneously satisfy lateral pressure resistance, abrasion resistance, and crack resistance in CVT belts under demanding conditions.

[0009] Therefore, the object of the present invention is to provide a transmission belt and a belt transmission mechanism that can improve lateral pressure resistance, wear resistance, and crack resistance.

[0010] As a result of diligent research to achieve the above objectives, the present inventors have found that the above objectives can be solved by including a crosslinked rubber composition in the compression rubber layer of the transmission belt that contains chloroprene rubber, poly(p-phenylenebenzobisoxazole) short fibers and aramid short fibers, and has a specific flexural modulus, thereby completing the present invention.

[0011] In other words, the present invention includes the following embodiments.

[0012] Embodiment [1]: A transmission belt comprising a compression rubber layer, wherein the compression rubber layer comprises a crosslinked rubber composition, the crosslinked rubber composition comprises a rubber component and short fibers, the rubber component comprises chloroprene rubber, the short fibers comprise poly(p-phenylenebenzobisoxazole) short fibers and aramid short fibers, the 4% flexural modulus in the direction perpendicular to the orientation direction of the short fibers in the crosslinked rubber composition is 5 MPa or more, and the 4% flexural modulus in the direction parallel to the orientation direction of the short fibers in the crosslinked rubber composition is 2.5 MPa or less.

[0013] Embodiment [2]: The transmission belt according to Embodiment [1], wherein the total amount of the poly-p-phenylene-benzobisoxazole short fibers and the aramid short fibers is 15 to 40 parts by mass per 100 parts by mass of the rubber component, and the mass ratio of the poly-p-phenylene-benzobisoxazole short fibers to the aramid short fibers is the former / latter = 10 / 90 to 70 / 30.

[0014] Embodiment [3]: The transmission belt according to Embodiment [1] or [2], wherein the tear strength of the crosslinked rubber composition, measured in accordance with test method C of JIS K 6252-1:2015, is 80 N / mm or more.

[0015] Embodiment [4]: ​​The transmission belt according to any one of Embodiments [1] to [3], wherein the crosslinked rubber composition further comprises a sulfur-based crosslinking agent, and the proportion of the sulfur-based crosslinking agent is 0.5 to 3 parts by mass per 100 parts by mass of the rubber component.

[0016] Embodiment [5]: The transmission belt according to Embodiment [4], wherein the crosslinked rubber composition further comprises a co-crosslinking agent, the proportion of the co-crosslinking agent is 0.5 to 12 parts by mass per 100 parts by mass of the rubber component, and the mass ratio of the co-crosslinking agent to the sulfur-based crosslinking agent is former / latter = 0.3 / 1 to 12 / 1.

[0017] Embodiment [6]: The transmission belt according to any one of Embodiments [1] to [5], wherein the crosslinked rubber composition further comprises an antioxidant, and the proportion of the antioxidant is 3 to 8 parts by mass per 100 parts by mass of the rubber component.

[0018] Embodiment [7]: The transmission belt according to any one of Embodiments [1] to [6], wherein the crosslinked rubber composition further comprises carbon black, the proportion of carbon black is 42 to 58 parts by mass per 100 parts by mass of the rubber component, and the carbon black comprises hard carbon black.

[0019] Embodiment [8]: A transmission belt according to any one of Embodiments [1] to [7], wherein the chloroprene rubber is a sulfur-modified type chloroprene rubber.

[0020] Embodiment [9]: A transmission belt according to any one of Embodiments [1] to [8], which is a low-edge V-belt having cogs on at least the inner circumferential surface side.

[0021] Embodiment

[10] : A belt transmission mechanism comprising a combination of a transmission belt and a pulley as described in any of Embodiments [1] to [9], and provided in a belt-type continuously variable transmission.

[0022] In this application, the numerical range represented by "A to B" means "A or greater and B or less," and is used to include the values ​​A and B at both ends of that range.

[0023] In the present invention, the compression rubber layer of the transmission belt contains a crosslinked rubber composition comprising chloroprene rubber, poly(p-phenylenebenzobisoxazole) short fibers, and aramid short fibers, and having a specific flexural modulus, thereby improving the lateral pressure resistance, abrasion resistance, and crack resistance of the transmission belt.

[0024] Figure 1A is a schematic cross-sectional view illustrating the transmission mechanism of a belt-type continuously variable transmission. Figure 1B is a schematic cross-sectional view illustrating the transmission mechanism of a belt-type continuously variable transmission. Figure 2 is a schematic partial cross-sectional perspective view showing an example of a low-edge cogged V-belt. Figure 3 is a schematic cross-sectional view of the low-edge cogged V-belt of Figure 2 cut in the longitudinal direction of the belt. Figure 4 is a schematic partial cross-sectional perspective view showing an example of a low-edge double cogged V-belt. Figure 5 is a schematic cross-sectional view of the low-edge double cogged V-belt of Figure 4 cut in the longitudinal direction of the belt. Figure 6 is a schematic cross-sectional view showing the definition of the overall thickness of the low-edge double cogged V-belt in the present invention. Figure 7 is a schematic cross-sectional view showing the definition of the belt pitch width of the low-edge cogged V-belt in the present invention. Figure 8 is a schematic perspective view illustrating the method for measuring the 4% flexural modulus (direction perpendicular to short fibers) of a cross-linked rubber molded article obtained in the example. Figure 9 is a schematic perspective view illustrating the method for measuring the 4% flexural modulus (direction parallel to short fibers) of a cross-linked rubber molded article obtained in the example. Figure 10 shows the layout of the testing machine used in the peel resistance and abrasion resistance tests of the raw edge double cogged V-belt obtained in the example. Figure 11 shows the layout of the testing machine used in the crack resistance test of the raw edge double cogged V-belt obtained in the example.

[0025] [Power Transmission Belt] The power transmission belt (power transmission belt) of the present invention is not particularly limited, as long as it includes a compressed rubber layer containing a crosslinked rubber composition. The type of power transmission belt of the present invention is also not particularly limited, as long as it is a belt that transmits power in contact with a pulley, and may be a friction transmission belt or a meshing transmission belt.

[0026] The belt transmission mechanism of the present invention includes the transmission belt of the present invention and a pulley. The transmission belt in the belt transmission mechanism of the present invention is preferably a CVT belt.

[0027] Examples of friction transmission belts include flat belts, V-belts (wrapped V-belts, raw edge V-belts, raw edge cogged V-belts with cogs formed on the inner circumference, raw edge double cogged V-belts with cogs formed on both the inner and outer circumferences), V-ribbed belts, and resin block belts.

[0028] Examples of interlocking power transmission belts include toothed belts and double-sided toothed belts.

[0029] Of these power transmission belts, a friction transmission belt with a V-shaped friction transmission surface is preferred because lateral pressure resistance is important. A V-belt having such a shape may be a raw-edge type belt (raw-edge V-belt) in which the friction transmission surface (V-shaped side surface) is an exposed rubber layer, or a wrapped type belt (wrapped V-belt) in which the friction transmission surface is covered with an outer fabric (cover fabric). Of these friction transmission belts, the power transmission belt of the present invention has high lateral pressure resistance and wear resistance, and can achieve the characteristics required of a raw-edge V-belt at a high level.

[0030] Low-edge V-belts include low-edge V-belts without cogs and low-edge cogged V-belts with cogs. Furthermore, low-edge cogged V-belts include low-edge cogged V-belts in which cogs are formed only on the inner circumference and low-edge double cogged V-belts in which cogs are formed on both the inner and outer circumferences. In this application, low-edge V-belts without cogs, low-edge cogged V-belts, and low-edge double cogged V-belts are collectively referred to as low-edge V-belts. Among these low-edge V-belts, low-edge V-belts having cogs on at least the inner circumference are preferred because lateral pressure resistance, wear resistance, and crack resistance are important, and low-edge cogged V-belts and low-edge double cogged V-belts used in variable-speed transmission (CVT) belts are particularly preferred. In other words, the transmission belt of the present invention can be used particularly suitably in CVT belts, where a high level of crack resistance is required because the winding radius changes continuously.

[0031] Figure 2 is a schematic partial cross-sectional perspective view showing an example of a low-edge cogged V-belt. Figure 3 is a schematic cross-sectional view of the low-edge cogged V-belt from Figure 2, cut along the longitudinal direction of the belt.

[0032] In this example, the raw-edge cogged V-belt 1 has a cog section on the inner circumferential surface of the belt body, in which cog peaks 1a and cog valleys 1b are formed alternately along the longitudinal direction of the belt (direction A in Figure 3). The cross-sectional shape of the cog peaks 1a in the longitudinal direction is approximately semicircular (curved or wave-shaped), and the cross-sectional shape in the direction perpendicular to the longitudinal direction (width direction or direction B in the figure) is trapezoidal. That is, each cog peak 1a protrudes in an approximately semicircular shape from each cog valley 1b in the cross-section in direction A in the belt thickness direction. The raw-edge cogged V-belt 1 has a laminated structure, in which a reinforcing fabric 2, an elastic rubber layer 3, a core layer (adhesive rubber layer) 4, a compression rubber layer 5, and a reinforcing fabric 6 are sequentially laminated from the outer circumferential side to the inner circumferential side (the side in which the cog section is formed). The cross-sectional shape in the belt width direction is trapezoidal, with the belt width decreasing from the outer circumferential side to the inner circumferential side. Furthermore, a core wire 4a is embedded within the adhesive rubber layer 4, and the cog portion is formed in the compressed rubber layer 5 by a cog-equipped molding die.

[0033] Figure 4 is a schematic partial cross-sectional perspective view showing an example of a low-edge double-cogged V-belt. Figure 5 is a schematic cross-sectional view of the low-edge double-cogged V-belt from Figure 4, cut along the longitudinal direction of the belt.

[0034] In this example, the low-edge double-cogged V-belt 11 has an inner cog section formed on the inner surface of the compressed rubber layer 15, in which inner cog peaks 11a and inner cog valleys 11b are alternately arranged along the longitudinal direction of the belt (direction A in the figure). The cross-sectional shape of the inner cog peaks 11a in the longitudinal direction is approximately semicircular (curved or wave-shaped), and the cross-sectional shape in the direction perpendicular to the longitudinal direction (width direction or direction B in the figure) is trapezoidal. That is, each inner cog peak 11a protrudes in an approximately semicircular shape from each inner cog valley 11b in the cross-section in direction A in the belt thickness direction.

[0035] Furthermore, the outer surface also has an outer cog section in which outer cog peaks 11c and outer cog valleys 11d are formed alternately along the longitudinal direction of the belt. The cross-sectional shape of the outer cog peaks 11c in the longitudinal direction is approximately trapezoidal, and the cross-sectional shape in the direction perpendicular to the longitudinal direction (width direction or direction B in the figure) is approximately rectangular. That is, each outer cog peak 11c protrudes in a approximately trapezoidal shape in the cross-section in direction A from each outer cog valley 11d in the belt thickness direction.

[0036] The low-edge double-cogged V-belt has a laminated structure, in which a stretchable rubber layer 13, a core layer (adhesive rubber layer) 14, a compression rubber layer 15, and a reinforcing fabric 16 are sequentially laminated from the outer circumference to the inner circumference of the belt. The cross-sectional shape in the belt width direction is approximately trapezoidal, with the belt width decreasing from the outer circumference to the inner circumference. Furthermore, a core wire 14a is embedded in the core layer 14, and the inner circumference cog portion and the outer circumference cog portion are formed in the compression rubber layer 15 and the stretchable rubber layer 13, respectively, by a cog-forming mold.

[0037] In the power transmission belt of the present invention (particularly the low-edge V-belt), the overall thickness (average thickness) of the belt is, for example, 5 to 12 mm, preferably 7 to 11.5 mm, and more preferably 8 to 11 mm. In the present invention, when the thickness of the power transmission belt is within this range, the bending rigidity of the belt can be reduced, and both lateral pressure resistance and wear resistance can be achieved even when used in a small belt-type continuously variable transmission.

[0038] Figure 6, based on Figure 5, shows the definition of the overall thickness of the raw edge double cogged V-belt in the present invention. Specifically, in Figure 6, in the raw edge double cogged V-belt 11, the outer circumference cog height H5 indicates the height of the outer circumference cog portion formed on the outer circumference surface, and the outer circumference pitch height H4 indicates the distance from the center of the core wire to the outer circumference surface (the top of the cog portion). In addition, the inner circumference cog height H2 indicates the height of the inner circumference cog portion formed on the inner circumference surface, and the core wire-cog valley thickness H3 indicates the distance from the center of the core wire to the deepest part of the inner circumference cog valley. In contrast, the overall thickness H1 means the sum of the inner circumference cog height H2, the core wire-cog valley thickness H3, and the outer circumference pitch height H4, and represents the thickness at the top of the cog portion (the maximum thickness of the belt).

[0039] In the present application, the overall thickness of a transmission belt (particularly, a low-edge V-belt) means the thickness from the outer peripheral surface to the inner peripheral surface (the thickness at the thickest part of the belt thickness), and in the case of having cogs, as shown in FIG. 6, the top of the cogs becomes the inner peripheral surface or the outer peripheral surface. Therefore, in the case of a low-edge cogged V-belt having cogs only on the inner peripheral surface, the distance from the outer peripheral surface to the top of the cog portion on the inner peripheral surface is the overall thickness. That is, the overall thickness means the distance from the top of the cogs of the compression rubber layer (the convex top on the inner peripheral side) to the back surface of the belt in the case of a low-edge cogged V-belt, and the distance from the top of the cogs of the compression rubber layer (the convex top on the inner peripheral side) to the top of the cogs of the extension rubber layer (the convex top on the outer peripheral side) in the case of a low-edge double-cogged V-belt.

[0040] In the transmission belt (particularly, a low-edge V-belt) of the present invention, the belt pitch width is, for example, 10 to 25 mm, preferably 12 to 24.5 mm, and more preferably 15 to 24 mm.

[0041] FIG. 7 shows the definition of the belt pitch width of the low-edge cogged V-belt in the present invention. That is, FIG. 7 is a schematic cross-sectional view of a low-edge cogged belt 1 in which a reinforcing cloth 2, an extension rubber layer 3, a core layer 4, a compression rubber layer 5, and a reinforcing cloth 6 are sequentially laminated. The belt pitch width W means the width of the belt at the pitch line L of the belt (the position on the line connecting the centers of the core wires 4a buried at equal intervals in the core layer 4). In this example, the pitch width in the low-edge cogged V-belt shown in FIG. 2 is described, but the same applies to other transmission belts.

[0042] [Compression Rubber Layer] The transmission belt (particularly, a low-edge V-belt) of the present invention includes a compression rubber layer formed of a specific crosslinked rubber composition (first crosslinked rubber composition), whereby the side pressure resistance, wear resistance, and crack resistance of the transmission belt can be improved. Specifically, the first crosslinked rubber composition contains a specific rubber component (first rubber component) and a specific short fiber (first short fiber), and has a specific bending elastic modulus.

[0043] (1A) First Rubber Component The first rubber component contains chloroprene rubber (CR) as an essential rubber component from the viewpoint of excellent balance in heat resistance, wear resistance, oil resistance, etc., and high productivity.

[0044] Examples of chloroprene rubber include mercaptan-modified chloroprene rubber, xanthogen-modified chloroprene rubber, and other non-sulfur-modified chloroprene rubbers; as well as sulfur-modified chloroprene rubbers. These chloroprene rubbers can be used individually or in combination of two or more types.

[0045] Of these chloroprene rubbers, sulfur-modified chloroprene rubber is preferred because it can improve abrasion resistance. Furthermore, when sulfur-modified chloroprene rubber is used as the chloroprene rubber, when kneading the uncrosslinked rubber composition, the sulfur bonds in the polymer molecular chains are broken, which suppresses excessive Mooney viscosity even when a large amount of short fibers are incorporated, resulting in good processability. In addition, after crosslinking, energy loss is reduced and internal heat generation is suppressed, improving durability, possibly because the sulfur at the ends of the molecular chains reacts and becomes fixed. For this reason, in demanding operating conditions such as racing ATVs (quad bikes), suppressing heat generation is important, so it is particularly preferable to use sulfur-modified chloroprene rubber that can suppress internal heat generation.

[0046] The first rubber component may further contain other rubbers in addition to chloroprene rubber. Examples of other rubbers include diene rubbers other than chloroprene rubber [natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), hydrogenated nitrile rubber (H-NBR), etc.], ethylene-α-olefin elastomers [ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), etc.], chlorosulfonated polyethylene rubber, alkylated chlorosulfonated polyethylene rubber, epichlorohydrin rubber, acrylic rubber, silicone rubber, urethane rubber, fluororubber, etc. These other rubber components can be used individually or in combination of two or more.

[0047] The proportion of other rubber may be 100 parts by mass or less per 100 parts by mass of chloroprene rubber, preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and more preferably 10 parts by mass or less.

[0048] The proportion of chloroprene rubber may be 50% by mass or more in the first rubber component, preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass (i.e., chloroprene rubber only).

[0049] The proportion of the first rubber component in the first crosslinked rubber composition is, for example, 20 to 80% by mass, preferably 30 to 75% by mass, more preferably 40 to 70% by mass, more preferably 45 to 60% by mass, and most preferably 50 to 55% by mass.

[0050] (1B) First short fibers The first short fibers include poly(p-phenylenebenzobisoxazole) short fibers (PBO) and aramid short fibers, as these can improve lateral pressure resistance, abrasion resistance, and crack resistance. PBO short fibers alone reduce lateral pressure resistance, and aramid short fibers alone reduce abrasion resistance and crack resistance. However, by combining both short fibers, lateral pressure resistance, abrasion resistance, and crack resistance can be improved.

[0051] The PBO-based fibers constituting the PBO-based short fibers can be any fibers formed from a PBO-based resin having a paraphenylenebenzobisoxazole skeleton (paraphenylenebenzobisoxazole units).

[0052] In PBO-based resins, the proportion of paraphenylenebenzobisoxazole units may be 50 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more, more preferably 95 mol% or more, and most preferably 100 mol%.

[0053] Each unit constituting the paraphenylenebenzobisoxazole unit, namely the paraphenylene unit and the benzobisoxazole unit, may have substituents (e.g., alkyl groups such as methyl groups; alkoxy groups such as methoxy groups), but it is preferable that they do not have substituents.

[0054] These PBO-based staple fibers can be used individually or in combination of two or more types. Preferred PBO-based staple fibers are poly(p-phenylenebenzobisoxazole) staple fibers (PBO staple fibers) commercially available as "Zylon®" manufactured by Toyobo Co., Ltd.

[0055] The average fiber diameter of the PBO-based short fibers is, for example, 2 μm or more, preferably 2 to 100 μm, more preferably 3 to 50 μm, more preferably 7 to 40 μm, and most preferably 10 to 30 μm, in order to provide a high reinforcing effect to the belt without reducing its flexibility. If the average fiber diameter is too small, the dispersibility in the rubber will decrease, which may reduce the flexibility of the belt. If the average fiber diameter is too large, the lateral pressure resistance and abrasion resistance of the belt per unit amount may decrease.

[0056] The average fiber length of the PBO-based short fibers is, for example, 1 to 20 mm, preferably 1.3 to 15 mm, more preferably 1.5 to 10 mm, more preferably 2 to 5 mm, and most preferably 2.5 to 4 mm, in order to improve lateral pressure resistance and abrasion resistance without reducing the flexibility of the belt. If the average fiber length is too short, the mechanical properties in the direction of grain cannot be sufficiently improved, which may reduce the lateral pressure resistance and abrasion resistance of the belt. If the average fiber length is too long, the orientation of the PBO-based short fibers in the first crosslinked rubber composition may decrease, which may reduce the flexibility of the belt.

[0057] The proportion of PBO-based short fibers is, for example, 1 to 50 parts by mass, preferably 2 to 30 parts by mass, more preferably 3 to 20 parts by mass, more preferably 5 to 15 parts by mass, and most preferably 8 to 12 parts by mass, per 100 parts by mass of the first rubber component. If the proportion of PBO-based short fibers is too low, the abrasion resistance and crack resistance of the belt may decrease. If the proportion of PBO-based short fibers is too high, the lateral pressure resistance of the belt may decrease.

[0058] The aramid fibers constituting the aramid short fibers may be para-aramid fibers or meta-aramid fibers.

[0059] Examples of para-aramid fibers include poly(p-phenylene terephthalamide) fibers (e.g., "Twaron®" manufactured by Teijin Limited, "Kevlar®" manufactured by Toray DuPont Co., Ltd.), and copolymer fibers of poly(p-phenylene terephthalamide) and 3,4'-oxydiphenylene terephthalamide (e.g., "Technora®" manufactured by Teijin Limited).

[0060] Examples of meta-aramid fibers include polymetaphenylene isophthalamide fibers (for example, "Conex®" manufactured by Teijin Limited).

[0061] These aramid short fibers can be used individually or in combination of two or more types. Of these, para-aramid short fibers are preferred because they can improve resistance to lateral pressure.

[0062] The average fiber diameter of the aramid short fibers is, for example, 2 μm or more, preferably 2 to 100 μm, more preferably 3 to 50 μm, more preferably 7 to 40 μm, and most preferably 10 to 30 μm, in order to provide a high reinforcing effect without reducing flexibility. If the average fiber diameter is too small, the flexibility of the belt may decrease due to reduced dispersibility in the rubber. If the average fiber diameter is too large, the lateral pressure resistance and abrasion resistance of the belt per unit amount may decrease.

[0063] The average fiber length of the aramid short fibers is, for example, 1 to 20 mm, preferably 1.3 to 15 mm, more preferably 1.5 to 10 mm, more preferably 2 to 5 mm, and most preferably 2.5 to 4 mm, in order to improve lateral pressure resistance and abrasion resistance without reducing flexibility. If the average fiber length is too short, the mechanical properties in the direction of grain cannot be sufficiently improved, which may reduce lateral pressure resistance and abrasion resistance. If the average fiber length is too long, the orientation of the aramid short fibers in the first crosslinked rubber composition may decrease, which may reduce flexibility.

[0064] In this application, the average fiber diameter and average fiber length of short fibers can be calculated, for example, by performing image analysis on photographs of short fibers taken with an electron microscope such as a transmission electron microscope or a scanning electron microscope, and taking the arithmetic mean of the fiber diameter and fiber length of an appropriate number of samples (e.g., 50 samples).

[0065] The proportion of aramid short fibers is, for example, 1 to 50 parts by mass, preferably 3 to 40 parts by mass, more preferably 5 to 30 parts by mass, more preferably 10 to 20 parts by mass, and most preferably 13 to 17 parts by mass, per 100 parts by mass of the first rubber component. If the proportion of aramid short fibers is too low, the lateral pressure resistance may decrease. If the proportion of aramid short fibers is too high, the abrasion resistance and crack resistance may decrease.

[0066] The total amount of PBO-based short fibers and aramid short fibers is, for example, 15 to 40 parts by mass, preferably 20 to 35 parts by mass, more preferably 22 to 30 parts by mass, and more preferably 23 to 27 parts by mass, per 100 parts by mass of the first rubber component. If the proportion is too low, the lateral pressure resistance may decrease. If the proportion is too high, the crack resistance may decrease.

[0067] The total proportion of PBO-based short fibers and aramid short fibers in the first crosslinked rubber composition is, for example, 1 to 50% by mass, preferably 3 to 40% by mass, more preferably 5 to 30% by mass, more preferably 8 to 20% by mass, and most preferably 10 to 15% by mass.

[0068] The mass ratio of PBO-based staple fibers to aramid staple fibers is, for example, former / latter = 10 / 90 to 70 / 30, preferably 15 / 85 to 60 / 40, more preferably 20 / 80 to 55 / 45, more preferably 30 / 70 to 50 / 50, and most preferably 35 / 65 to 45 / 55. If the ratio of PBO-based staple fibers is too small, the crack resistance of the belt may decrease. If the ratio of PBO-based staple fibers is too large, the lateral pressure resistance of the belt may decrease.

[0069] The first staple fiber may further include other staple fibers in addition to PBO-based staple fibers and aramid staple fibers. Examples of other staple fibers include polyamide staple fibers (aliphatic polyamide staple fibers such as polyamide 6 staple fibers, polyamide 66 staple fibers, and polyamide 46 staple fibers), polyalkylene arylate staple fibers (e.g., polyethylene terephthalate (PET) staple fibers, polyethylene naphthalate staple fibers), liquid crystal polyester staple fibers, polyarylate staple fibers (amorphous all-aromatic polyester staple fibers, etc.), vinylon staple fibers, polyvinyl alcohol-based staple fibers, and other synthetic staple fibers; cellulose staple fibers such as cotton and linen, natural staple fibers such as wool; and inorganic staple fibers such as carbon staple fibers and glass staple fibers. These other staple fibers can be used individually or in combination of two or more types.

[0070] The proportion of other short fibers may be 100 parts by mass or less per 100 parts by mass of the total of PBO-based short fibers and aramid short fibers, preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and more preferably 10 parts by mass or less.

[0071] The total proportion of PBO-based staple fibers and aramid staple fibers may be 50% by mass or more of the first staple fiber, preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass (i.e., PBO-based staple fibers and aramid staple fibers only).

[0072] The first short fibers may be embedded in the first rubber layer, oriented substantially parallel to the belt width direction, in order to suppress compressive deformation of the belt due to pressure from the pulley.

[0073] In this application, "approximately parallel" to the belt width direction means that the angle with respect to the belt width direction is, for example, 10° or less, preferably 8° or less, more preferably 5° or less, more preferably 3° or less, and most preferably 1° or less (for example, 0 to 1°, particularly approximately 0°).

[0074] The first short fibers may be subjected to conventional bonding treatments to enhance their adhesion to the first rubber component. Conventional bonding treatments include immersion in a treatment solution containing an epoxy compound or a polyisocyanate compound, immersion in an RFL treatment solution containing resorcinol (R), formaldehyde (F), and latex (L), and immersion in rubber adhesive. These treatments may be applied individually or in combination of two or more. Of these, immersion in an RFL treatment solution and immersion in rubber adhesive are preferred, and a combination of both methods is particularly preferred.

[0075] The proportion of the first short fibers is, for example, 15 to 40 parts by mass, preferably 20 to 35 parts by mass, more preferably 22 to 30 parts by mass, and more preferably 23 to 27 parts by mass, per 100 parts by mass of the first rubber component.

[0076] The proportion of the first short fibers in the first crosslinked rubber composition is, for example, 1 to 50% by mass, preferably 3 to 40% by mass, more preferably 5 to 30% by mass, more preferably 8 to 20% by mass, and most preferably 10 to 15% by mass.

[0077] (1C) The first crosslinking agent The first crosslinking rubber composition preferably further contains a crosslinking agent (first crosslinking agent).

[0078] Examples of the first crosslinking agent include organic peroxides, sulfur-based crosslinking agents, and metal oxides.

[0079] Examples of organic peroxides include di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 1,1-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,3-bis(t-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyn-3, 1,3-bis(t-butylperoxy-di-isopropyl)benzene, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxybenzoate, and t-butylperoxy-2-ethylhexyl carbonate. These organic peroxides can be used individually or in combination of two or more.

[0080] Examples of sulfur-based crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and sulfur chloride (sulfur monochloride, sulfur dichloride, etc.).

[0081] Examples of metal oxides include magnesium oxide, zinc oxide, and lead oxide.

[0082] These crosslinking agents can be used individually or in combination of two or more.

[0083] When the rubber component is chloroprene rubber, sulfur-free crosslinking with metal oxides is possible. In particular, sulfur-free crosslinking is common for sulfur-modified chloroprene rubber, but in the present invention, by using a sulfur-based crosslinking agent as the first crosslinking agent, the lateral pressure resistance of the belt can be improved, and in combination with the first short fibers, both abrasion resistance and crack resistance of the belt can be achieved. That is, the first crosslinking agent preferably contains a sulfur-based crosslinking agent, and a combination of a sulfur-based crosslinking agent and a metal oxide is particularly preferred. Furthermore, as the sulfur-based crosslinking agent, sulfur such as powdered sulfur is preferred. In addition, as the metal oxide, magnesium oxide and zinc oxide are preferred, and a combination of magnesium oxide and zinc oxide is particularly preferred.

[0084] The proportion of the sulfur-based crosslinking agent is, for example, 0.5 to 3 parts by mass, preferably 0.6 to 2.5 parts by mass, more preferably 0.7 to 2 parts by mass, more preferably 0.8 to 1.5 parts by mass, and most preferably 0.9 to 1.3 parts by mass, per 100 parts by mass of the first rubber component. If the proportion of the sulfur-based crosslinking agent is too low, the lateral pressure resistance and abrasion resistance may decrease. If the proportion of the sulfur-based crosslinking agent is too high, the crack resistance may decrease.

[0085] The proportion of metal oxide is, for example, 1 to 20 parts by mass, preferably 3 to 18 parts by mass, more preferably 5 to 15 parts by mass, more preferably 6 to 13 parts by mass, and most preferably 7 to 12 parts by mass, per 100 parts by mass of the first rubber component. If the proportion of metal oxide is too low, the lateral pressure resistance of the belt may decrease. If the proportion of metal oxide is too high, the crack resistance may decrease.

[0086] When a sulfur-based crosslinking agent and a metal oxide are combined as the first crosslinking agent, the mass ratio of the two may be 50 / 50 to 1 / 99, preferably 40 / 60 to 2 / 98, more preferably 30 / 70 to 3 / 97, more preferably 20 / 80 to 5 / 95, and most preferably 15 / 85 to 7 / 93. If the mass ratio of the sulfur-based crosslinking agent is too small, the crosslinking density may decrease, potentially reducing lateral pressure resistance. If the mass ratio of the sulfur-based crosslinking agent is too large, the flexibility of the belt may decrease, potentially reducing crack resistance.

[0087] The proportion of the first crosslinking agent is, for example, 1 to 25 parts by mass, preferably 3 to 20 parts by mass, more preferably 5 to 18 parts by mass, more preferably 6 to 15 parts by mass, and most preferably 7 to 13 parts by mass, per 100 parts by mass of the first rubber component.

[0088] (1D) First Crosslinking Aid The first crosslinked rubber composition preferably further contains a crosslinking aid (first crosslinking aid). Examples of the first crosslinking aid include cocrosslinking agents and crosslinking accelerators.

[0089] Examples of co-crosslinking agents (crosslinking aids or co-vulcanizing agents) include polyfunctional (iso)cyanurates [e.g., triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), etc.], polydienes (e.g., 1,2-polybutadiene), metal salts of unsaturated carboxylic acids [e.g., polyvalent metal salts of (meth)acrylic acids such as zinc (meth)acrylate and magnesium (meth)acrylate], oximes (e.g., quinone dioxime), guanidines (e.g., diphenylguanidine), polyfunctional (meth)acrylates [e.g., ethylene glycol di(meth)acrylate, alkanediol di(meth)acrylate such as butanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol], Examples include alkane polyols such as tol tetra(meth)acrylate and poly(meth)acrylates, bismaleimides [for example, alkylene bismaleimides such as N,N'-1,2-ethylenedimaleimide, N,N'-hexamethylenebismaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)cyclohexane; N,N'-m-phenylenedimaleimide (MPBM), 4-methyl-1,3-phenyledimaleimide, 4,4'-diphenylmethanedimaleimide, 2,2-bis[arene bismaleimides such as 4-(4-maleimidephenoxy)phenyl, etc.]propane, 4,4'-diphenyletherdimaleimide, 4,4'-diphenylsulfonedimaleimide, 1,3-bis(3-maleimidephenoxy)benzene, etc.].

[0090] These cocrosslinking agents can be used individually or in combination of two or more. Of these, bismaleimides such as MPBM are preferred because they can improve abrasion resistance and lateral pressure resistance.

[0091] Examples of crosslinking accelerators include thiram-based accelerators [e.g., tetramethylthiram monosulfide (TMTM), tetramethylthiram disulfide (TMTD), tetraethylthiram disulfide (TETD), tetrabutylthiram disulfide (TBTD), dipentamethylenethiram tetrasulfide (DPTT), N,N'-dimethyl-N,N'-diphenylthiram disulfide (MPTD), etc.], sulfenamide-based accelerators [e.g., N-cyclohexyl-2-benzothiadylsulfenamide (CBS), N,N'-dicyclohexyl-2-benzothiadylsulfenamide (DCBS), N-t-butyl-2-benzothiadylsulfenamide (TBBS), etc.], and thiomorpholine-based accelerators [e.g., 4,4'-dithiodimorpholine (DTDM), 2-(4' Examples include morpholinodithio)benzothiazole (MBSS), thiazole-based accelerators (e.g., 2-mercaptobenzothiazole (MBT), zinc salt of MBT (ZMBT), dibenzothiadyl disulfide (MBTS), etc.), urea-based or thiourea-based accelerators (e.g., ethylenethiourea (ETU), trimethylthiourea (TMU), diethylthiourea (DETU), etc.), guanidine-based accelerators (e.g., diphenylguanidine (DPG), di-o-tolylguanidine (DOTG), etc.), dithiocarbamate-based accelerators (e.g., sodium dimethyldithiocarbamate (SDMC), zinc diethyldithiocarbamate (ZDEC), zinc dibutyldithiocarbamate (ZDBC), etc.), and xanthogenic acid-based accelerators (e.g., zinc isopropylxanthogenic acid (ZIX), etc.).

[0092] These crosslinking accelerators can be used individually or in combination of two or more. Among these crosslinking accelerators, thiuram-based accelerators such as TMTD and thiazole-based accelerators such as MBTS are preferred, and thiazole-based accelerators are particularly preferred because they can improve crack resistance.

[0093] The first crosslinking aid preferably contains a co-crosslinking agent, and a combination of a co-crosslinking agent and a crosslinking accelerator is particularly preferred.

[0094] The proportion of the co-crosslinking agent is, for example, 0.5 to 12 parts by mass, preferably 0.6 to 5 parts by mass, more preferably 0.7 to 3 parts by mass, more preferably 0.8 to 2 parts by mass, and most preferably 0.9 to 1.5 parts by mass, per 100 parts by mass of the first rubber component. In particular, from the viewpoint of improving abrasion resistance, the proportion of the co-crosslinking agent is preferably 3 to 12 parts by mass, more preferably 5 to 10 parts by mass, and more preferably 6 to 9 parts by mass, per 100 parts by mass of the first rubber component. If the proportion of the co-crosslinking agent is too low, the lateral pressure resistance and abrasion resistance of the belt may decrease. If the proportion of the co-crosslinking agent is too high, the crack resistance of the belt may decrease.

[0095] In particular, in the present invention, the co-crosslinking agent can be combined with a sulfur-based crosslinking agent to achieve both lateral pressure resistance and crack resistance of the belt. The mass ratio of the co-crosslinking agent to the sulfur-based crosslinking agent is, for example, former / latter = 0.3 / 1 to 12 / 1, preferably 0.5 / 1 to 10 / 1, more preferably 0.7 / 1 to 5 / 1, more preferably 0.8 / 1 to 3 / 1, and most preferably 0.9 / 1 to 2 / 1. In particular, from the viewpoint of improving wear resistance and easily balancing various properties, the above mass ratio is preferably 1 / 1 to 12 / 1, more preferably 3 / 1 to 11 / 1, more preferably 5 / 1 to 10 / 1, and most preferably 7 / 1 to 9 / 1. If the mass ratio of the co-crosslinking agent is too small, the lateral pressure resistance and wear resistance of the belt may decrease. If the mass ratio of the co-crosslinking agent is too large, the crack resistance of the belt may decrease.

[0096] The proportion of the crosslinking accelerator is, for example, 0.1 to 5 parts by mass, preferably 0.3 to 3 parts by mass, more preferably 0.5 to 2 parts by mass, more preferably 0.5 to 1.5 parts by mass, and most preferably 0.6 to 1 part by mass, per 100 parts by mass of the first rubber component. If the proportion of the crosslinking accelerator is too low, the lateral pressure resistance may decrease. If the proportion of the crosslinking accelerator is too high, the crack resistance of the belt may decrease.

[0097] The proportion of the first crosslinking aid is, for example, 0.5 to 15 parts by mass, preferably 0.6 to 10 parts by mass, more preferably 0.8 to 5 parts by mass, more preferably 1 to 3 parts by mass, and most preferably 1.5 to 2 parts by mass, per 100 parts by mass of the first rubber component.

[0098] (1E) The first crosslinked rubber composition may further contain a filler (first filler). Examples of the first filler include reinforcing inorganic fillers and non-reinforcing fillers.

[0099] Examples of reinforcing inorganic fillers include carbon black and silica. The reinforcing inorganic filler may be in powder form.

[0100] Carbon black can generally be classified into hard carbon black, which has a relatively small particle size, and soft carbon black, which has a relatively large particle size. While the classification of carbon black is sometimes based on the average particle size (average primary particle size) in the raw material state, in this application, the classification is based on the primary particle size of the carbon black contained in the rubber composition (particularly in the crosslinked rubber composition). That is, in this application, the primary particle size of each primary particle of carbon black contained in the rubber composition is measured, and carbon black with a primary particle size of 1 nm or more and less than 40 nm is referred to as hard carbon black (or hard carbon), and carbon black with a primary particle size of 40 nm or more (e.g., 40 to 300 nm) is referred to as soft carbon black (or soft carbon).

[0101] The average primary particle size of hard carbon black is, for example, 10 to 38 nm, preferably 15 to 35 nm, more preferably 20 to 33 nm, and more preferably 25 to 30 nm. On the other hand, the average primary particle size of soft carbon black is, for example, 40 to 100 nm, preferably 41 to 80 nm, more preferably 42 to 60 nm, and more preferably 43 to 50 nm.

[0102] In this application, the average particle size of particulate fillers such as carbon black can be measured using, for example, a scanning electron microscope (SEM) or a transmission electron microscope (TEM). This average particle size can be calculated as the arithmetic mean particle size of an appropriate number of samples (e.g., 50 samples) by image analysis.

[0103] In this invention, it is preferable that the carbon black includes hard carbon black, as this can improve lateral pressure resistance and abrasion resistance.

[0104] The proportion of hard carbon black (percentage of particles) may be 10% or more of the carbon black, preferably 50% or more, more preferably 80% or more, more preferably 90% or more, and most preferably 100%.

[0105] In this application, the ratio of hard carbon black to soft carbon black particle numbers can be calculated based on the primary particle size measured using a transmission electron microscope.

[0106] The amount of iodine adsorbed by carbon black is, for example, 5 to 200 g / kg, preferably 10 to 180 g / kg, more preferably 50 to 150 g / kg, and more preferably 100 to 130 g / kg. If the amount of iodine adsorbed is too low, the reinforcing properties may decrease. If the amount of iodine adsorbed is too high, the flexibility of the belt may decrease.

[0107] In this application, the amount of iodine adsorbed by carbon black can be measured in accordance with the standard test method of ASTM D1510-17.

[0108] The BET specific surface area of ​​carbon black is, for example, 50 to 400 m². ２ / g, preferably 70 to 300m ２ / g, more preferably 80 to 200m ２ / g, more preferably 100 to 150m ２ It is / g.

[0109] In this application, the BET specific surface area of ​​a filler such as carbon black refers to the specific surface area measured using nitrogen gas by the BET method.

[0110] The DBP absorption amount (DBP oil absorption amount) of carbon black is, for example, 60 to 500 mL / 100 g, preferably 80 to 400 mL / 100 g, more preferably 100 to 300 mL / 100 g, and more preferably 100 to 200 mL / 100 g.

[0111] In this application, the DBP absorption amount of carbon black refers to the value (OAN) that can be measured for an uncompressible sample, in accordance with JIS K 6217-4 (2017).

[0112] Silica includes dry silica, wet silica, and surface-treated silica. Furthermore, silica can be classified by manufacturing method into categories such as dry-processed white carbon, wet-processed white carbon, colloidal silica, and precipitated silica. These silicas can be used individually or in combination of two or more types. Among these silicas, silica with surface silanol groups (anhydrous silicic acid, hydrated silicic acid) is preferred, and hydrated silicic acid with a high number of surface silanol groups exhibits strong chemical bonding with rubber components.

[0113] The average particle diameter (average primary particle diameter) of silica is, for example, 1 to 500 nm, preferably 3 to 300 nm, more preferably 5 to 100 nm, and more preferably 10 to 50 nm.

[0114] Furthermore, the specific surface area for nitrogen adsorption of silica by the BET method is, for example, 50 to 400 m². ２ / g, preferably 100 to 300m ２ / g, more preferably 150-200m ２ It is / g.

[0115] Examples of non-reinforcing fillers include metal oxides other than metal oxides as crosslinking agents (calcium oxide, barium oxide, iron oxide, copper oxide, titanium oxide, aluminum oxide, etc.), polyvalent metal carbonates (calcium carbonate, magnesium carbonate, etc.), polyvalent metal hydroxides (aluminum hydroxide, etc.), polyvalent metal sulfates (barium sulfate, etc.), silicates (natural or synthetic silicates in which some of the silicon is replaced by polyvalent metal atoms, such as aluminum silicate, magnesium silicate, and aluminum magnesium silicate; minerals mainly composed of silicates, such as clay containing aluminum silicate, talc and mica containing magnesium silicate, etc.), lithopone, silica sand, etc. These non-reinforcing fillers can be used alone or in combination of two or more. Of these, at least one selected from calcium carbonate, magnesium silicate or talc containing magnesium silicate, aluminum silicate or clay containing aluminum silicate is preferred, and calcium carbonate is particularly preferred.

[0116] These fillers can be used alone or in combination of two or more kinds. As the first filler, it is preferable to include a reinforcing inorganic filler, more preferably to include carbon black, and even more preferably to include hard carbon black.

[0117] The proportion of carbon black (especially hard carbon black) is, for example, 42 to 58 parts by mass, preferably 42 to 55 parts by mass, more preferably 42 to 50 parts by mass, still more preferably 43 to 48 parts by mass, and most preferably 44 to 46 parts by mass with respect to 100 parts by mass of the first rubber component. If the proportion of carbon black is too small, the side pressure resistance and abrasion resistance of the belt may decrease. If the proportion of carbon black is too large, the flexibility and crack resistance of the belt may decrease.

[0118] The proportion of carbon black may be 50% by mass or more in the first filler, preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass (that is, only carbon black).

[0119] The proportion of the first filler is, for example, 42 to 100 parts by mass, preferably 42 to 80 parts by mass, more preferably 42 to 60 parts by mass, still more preferably 43 to 50 parts by mass, and most preferably 44 to 46 parts by mass with respect to 100 parts by mass of the first rubber component.

[0120] (1F) First antioxidant The first crosslinked rubber composition may further contain a first antioxidant in terms of improving heat aging resistance. Examples of the first antioxidant include benzimidazole metal salt-based antioxidants, diarylamine-based antioxidants, p-phenylenediamine-based antioxidants, wax-based antioxidants, and the like. These antioxidants can be used alone or in combination of two or more kinds.

[0121] Among these, diarylamine-based antioxidants are preferable. Examples of the diarylamine-based antioxidants include 4,4'-dioctyldiphenylamine (ODPA) and the like of 4,4'-di(C ４－１８ alkyl C ６－１０Examples include aryl amines; bis(aralkyl-aryl)amines such as 4,4'-bis(α,α-dimethylbenzyl)diphenylamine (DCD); and styrene-diphenylamine (SDPA).

[0122] The proportion of the first antioxidant is, for example, 1 to 10 parts by mass, preferably 3 to 8 parts by mass, more preferably 4 to 7 parts by mass, and more preferably 5 to 7 parts by mass, per 100 parts by mass of the first rubber component. If the proportion of the first antioxidant is too low, the crack resistance of the belt may decrease. If the proportion of the first antioxidant is too high, the lateral pressure resistance and abrasion resistance of the belt may decrease.

[0123] (1G) First Other Component The first crosslinked rubber composition may contain conventional additives as the first other component. Examples of conventional additives include softeners (or plasticizers) [oils (paraffin oil, naphthenic oil, etc.), aliphatic carboxylic acid plasticizers, aromatic carboxylic acid ester plasticizers, oxycarboxylic acid ester plasticizers, phosphate ester plasticizers, ether plasticizers, ether ester plasticizers, etc.], processing agents (or processing aids) (stearic acid, metal stearic acid salts, waxes, paraffin, fatty acid amides, etc.), metal powders (zinc powder, etc.), crosslinking retarders, antioxidants, flex crack inhibitors, ozone degradation inhibitors, adhesion improvers, colorants, tackifiers, coupling agents (silane coupling agents, etc.), stabilizers (ultraviolet absorbers, heat stabilizers, etc.), flame retardants, antistatic agents, etc. These additives can be used individually or in combination of two or more.

[0124] The proportion of the softening agent may be 20 parts by mass or less per 100 parts by mass of the first rubber component, for example, 0.1 to 20 parts by mass, preferably 1 to 15 parts by mass, more preferably 1.5 to 10 parts by mass, more preferably 2 to 7 parts by mass, and most preferably 3 to 5 parts by mass.

[0125] The proportion of the processing agent is, for example, 0.1 to 20 parts by mass, preferably 0.3 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and more preferably 0.8 to 2 parts by mass, per 100 parts by mass of the first rubber component.

[0126] The total proportion of the first additive is, for example, 5 to 300 parts by mass, preferably 10 to 200 parts by mass, more preferably 30 to 150 parts by mass, and more preferably 50 to 100 parts by mass, per 100 parts by mass of the first rubber component.

[0127] (1H) Characteristics of the first crosslinked rubber composition In the transmission belt of the present invention, the 4% flexural modulus (or 4% flexural stress) in the direction perpendicular to and parallel to the orientation direction of the short fibers in the crosslinked rubber composition is adjusted to a specific range. This improves the lateral pressure resistance, abrasion resistance, and crack resistance of the belt.

[0128] The 4% flexural modulus in the direction perpendicular to the orientation direction of the short fibers in the first crosslinked rubber composition is 5 MPa or higher, for example, 5 to 15 MPa, preferably 5.3 to 12 MPa, more preferably 5.5 to 10 MPa, more preferably 6 to 8 MPa, and most preferably 6.5 to 7.5 MPa. If the 4% flexural modulus is too low, the lateral pressure resistance of the belt will decrease.

[0129] In this application, the 4% flexural modulus in the direction perpendicular to the short fibers can be measured by arranging the pressing member so that its longitudinal direction intersects the orientation direction (length direction) of the short fibers at a right angle, and then pressing with the pressing member. More specifically, it can be measured by the method described in the embodiments described later.

[0130] Furthermore, in this application, "direction perpendicular to the short fiber" may refer not only to the direction perpendicular to the length direction of the short fiber (perpendicular direction), but also to directions within a range of ±5° from the perpendicular direction.

[0131] The 4% flexural modulus in the direction parallel to the short fibers (short fiber parallel direction) of the first crosslinked rubber composition is 2.5 MPa or less, for example, 0.5 to 2.5 MPa, preferably 1 to 2 MPa, more preferably 1 to 1.8 MPa, more preferably 1.1 to 1.5 MPa, and most preferably 1.2 to 1.4 MPa. If the 4% flexural modulus is too high, the flexibility and crack resistance of the belt will decrease.

[0132] In this application, the 4% flexural modulus in the direction parallel to the short fibers can be measured by arranging the pressing member so that its length is aligned with the orientation direction (length direction) of the short fibers and pressing with the pressing member. More specifically, it can be measured by the method described in the embodiments described later.

[0133] Furthermore, in this application, "direction parallel to the short fibers" may refer not only to the longitudinal direction of the short fibers, but also to directions within a range of ±5° from the longitudinal direction.

[0134] The tear strength of the first crosslinked rubber composition may be 80 N / mm or more, for example, 80 to 150 N / mm, preferably 85 to 140 N / mm, more preferably 90 to 130 N / mm, more preferably 100 to 120 N / mm, and most preferably 110 to 115 N / mm. If the tear strength is too low, cracks may easily occur when the belt is run, which may reduce durability.

[0135] In this application, the tear strength of the first crosslinked rubber composition can be measured in accordance with test method C (method using a crescent-shaped test piece) of JIS K 6252-1:2015 (vulcanized rubber and thermoplastic rubber - method for determining tear strength), and in detail, it can be measured by the method described in the examples below.

[0136] The rubber hardness (Type A) of the first crosslinked rubber composition may be 55 or higher, for example, 85 to 98, preferably 86 to 95, more preferably 87 to 93, more preferably 88 to 92, and most preferably 89 to 91. If the rubber hardness of the first crosslinked rubber composition is too low, there is a risk that the lateral pressure resistance will decrease. If the rubber hardness of the first crosslinked rubber composition is too high, there is a risk that the crack resistance will decrease.

[0137] In this application, the rubber hardness of the crosslinked rubber composition is expressed as the value (Type A) measured using a Type A durometer in accordance with the spring durometer hardness test specified in JIS K 6253 (2012) (Vulcanized rubber and thermoplastic rubber - Method for determining hardness), and may simply be referred to as rubber hardness. In detail, the rubber hardness can be measured by the method described in the examples below.

[0138] The average thickness of the compression rubber layer is, for example, 2 to 10 mm, preferably 3 to 8 mm, and more preferably 4 to 7 mm. In this application, the thickness of the compression rubber layer refers to the maximum thickness (thickness at the top of the cog portion).

[0139] [Stretchable Rubber Layer] The power transmission belt of the present invention (especially the low-edge V-belt) may further include a stretchable rubber layer formed of a second crosslinked rubber composition containing a second rubber component.

[0140] (2A) Second rubber component The second rubber component can be selected from the rubber components exemplified as the first rubber component, including preferred embodiments. The second rubber component may be a different rubber component from the first rubber component, but it is preferably a rubber component of the same series or type as the first rubber component, and more preferably a rubber component of the same type.

[0141] The proportion of the second rubber component is, for example, 20 to 80% by mass, preferably 30 to 75% by mass, more preferably 35 to 70% by mass, more preferably 40 to 60% by mass, and most preferably 45 to 50% by mass in the second crosslinked rubber composition.

[0142] (2B) The second short fiber crosslinked rubber composition may further contain a second short fiber. Examples of fibers constituting the second short fiber include the short fibers exemplified as the first short fiber. The short fiber can be used alone or in combination of two or more types. Among the short fibers, polyamide short fibers such as aramid short fibers and aliphatic polyamide short fibers are preferred, and a combination of aramid short fibers and aliphatic polyamide short fibers is particularly preferred.

[0143] The average fiber diameter and average fiber length of the second short fiber can be selected from the average fiber diameter and average fiber length of the aramid short fiber in the first short fiber, including a preferred range.

[0144] The second short fibers may be embedded in the rubber composition (rubber layer) oriented in the belt width direction in order to suppress compressive deformation of the belt due to pressure from the pulley.

[0145] The second short fiber may be subjected to a conventional bonding treatment to enhance its adhesion to the second rubber component. The conventional bonding treatment method can be selected from the methods exemplified as bonding treatments for the first short fiber, including preferred embodiments.

[0146] The proportion of the second short fibers is, for example, 15 to 40 parts by mass, preferably 20 to 35 parts by mass, more preferably 22 to 30 parts by mass, and more preferably 23 to 27 parts by mass, per 100 parts by mass of the second rubber component.

[0147] (2C) Second Crosslinking Agent The second crosslinked rubber composition may further contain a second crosslinking agent. Examples of the second crosslinking agent include the crosslinking agents exemplified as the first crosslinking agent. The crosslinking agents can be used alone or in combination of two or more. Among the crosslinking agents, the second crosslinking agent is preferably a metal oxide, more preferably magnesium oxide and zinc oxide, and even more preferably a combination of magnesium oxide and zinc oxide.

[0148] The proportion of the second crosslinking agent is, for example, 1 to 20 parts by mass, preferably 3 to 18 parts by mass, more preferably 5 to 15 parts by mass, more preferably 6 to 13 parts by mass, and most preferably 7 to 12 parts by mass, per 100 parts by mass of the second rubber component.

[0149] (2D) Second Crosslinking Aid The second crosslinked rubber composition may further contain a second crosslinking aid. The second crosslinking aid can be selected from the crosslinking aids exemplified as the first crosslinking aid, including preferred embodiments.

[0150] The proportion of the cocrosslinking agent is, for example, 1 to 20 parts by mass, preferably 2 to 15 parts by mass, more preferably 3 to 10 parts by mass, and more preferably 5 to 7 parts by mass, per 100 parts by mass of the second rubber component.

[0151] The proportion of the crosslinking accelerator is, for example, 0.1 to 5 parts by mass, preferably 0.3 to 3 parts by mass, more preferably 0.5 to 2 parts by mass, and more preferably 0.5 to 1.5 parts by mass, per 100 parts by mass of the second rubber component.

[0152] The proportion of the second crosslinking aid is, for example, 1 to 25 parts by mass, preferably 3 to 20 parts by mass, more preferably 4 to 15 parts by mass, and more preferably 5 to 10 parts by mass, per 100 parts by mass of the second rubber component.

[0153] (2E) Second Filler The second crosslinked rubber composition may further contain a second filler. Examples of the second filler include the fillers exemplified above as the first filler. The fillers can be used alone or in combination of two or more. Of the fillers, the second filler preferably contains a reinforcing inorganic filler, more preferably contains carbon black, and even more preferably contains soft carbon black.

[0154] The proportion of carbon black (especially soft carbon black) is, for example, 10 to 200 parts by mass, preferably 20 to 100 parts by mass, more preferably 30 to 80 parts by mass, and more preferably 40 to 60 parts by mass, per 100 parts by mass of the second rubber component.

[0155] The proportion of carbon black in the second filler 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 (i.e., carbon black only).

[0156] The proportion of the second filler is, for example, 10 to 200 parts by mass, preferably 20 to 100 parts by mass, more preferably 30 to 80 parts by mass, and more preferably 40 to 60 parts by mass, per 100 parts by mass of the second rubber component.

[0157] (2F) Second Anti-aging Agent The second crosslinked rubber composition may further contain a second anti-aging agent. Examples of the second anti-aging agent include the anti-aging agents exemplified above as the first anti-aging agent. The anti-aging agents can be used alone or in combination of two or more. The proportion of the second anti-aging agent is, for example, 1 to 15 parts by mass, preferably 5 to 10 parts by mass, and more preferably 7 to 9 parts by mass, per 100 parts by mass of the second rubber component.

[0158] (2G) Second Other Component The second crosslinked rubber composition may contain conventional additives as a second other component. Examples of conventional additives include those exemplified as conventional additives in the first other component. The additives can be used alone or in combination of two or more.

[0159] The proportion of metal powder is, for example, 1 to 30 parts by mass, preferably 3 to 20 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of the second rubber component.

[0160] The proportion of the softening agent may be 20 parts by mass or less per 100 parts by mass of the second rubber component, for example, 1 to 20 parts by mass, preferably 2 to 10 parts by mass, and more preferably 3 to 7 parts by mass.

[0161] The proportion of the processing agent is, for example, 0.1 to 10 parts by mass, preferably 0.3 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the second rubber component.

[0162] The total proportion of the second other component is, for example, 5 to 300 parts by mass, preferably 10 to 200 parts by mass, more preferably 30 to 150 parts by mass, and more preferably 50 to 100 parts by mass, per 100 parts by mass of the second rubber component.

[0163] [Core layer] The transmission belt of the present invention (in particular the low-edge V-belt) may further include a core layer.

[0164] The core layer only needs to contain a core wire as a core, and may be a core layer formed only of core wires. However, a combination of a core wire and an adhesive rubber layer (third adhesive rubber layer) formed of a third crosslinked rubber composition containing a third rubber component is preferred in order to suppress delamination between layers and improve belt durability. When forming a core layer by combining a core wire and a third adhesive rubber layer, it is sufficient that at least a part of the core wire is in contact with the third adhesive rubber layer. The core layer may take any of the following forms: a form in which the third adhesive rubber layer embeds the core wire, a form in which the core wire is embedded between the third adhesive rubber layer and the stretch rubber layer, or a form in which the core wire is embedded between the third adhesive rubber layer and the compression rubber layer. Of these, the form in which the third adhesive rubber layer embeds the core wire is preferred in order to improve durability (i.e., the third adhesive rubber layer is interposed between the stretch rubber layer and the compression rubber layer to bond the stretch rubber layer and the compression rubber layer, and the entire core wire is embedded in the third adhesive rubber layer).

[0165] (Third adhesive rubber layer) The third adhesive rubber layer is formed of a third crosslinked rubber composition containing a third rubber component.

[0166] (3A) Third rubber component The third rubber component can be selected from the rubber components exemplified as the first rubber component, including preferred embodiments. The third rubber component may be a different rubber component from the first rubber component, but it is preferably a rubber component of the same series or type as the first rubber component, and more preferably a rubber component of the same type.

[0167] The proportion of the third rubber component in the third crosslinked rubber composition is, for example, 20 to 80% by mass, preferably 30 to 75% by mass, more preferably 40 to 70% by mass, and more preferably 50 to 60% by mass.

[0168] (3B) Third Crosslinking Agent The third crosslinked rubber composition may further contain a third crosslinking agent. Examples of the third crosslinking agent include the crosslinking agents exemplified as the first crosslinking agent. The crosslinking agent can be used alone or in combination of two or more. Among the crosslinking agents, the third crosslinking agent is preferably a metal oxide, more preferably magnesium oxide and zinc oxide, and even more preferably a combination of magnesium oxide and zinc oxide.

[0169] The proportion of the third crosslinking agent is, for example, 1 to 20 parts by mass, preferably 3 to 18 parts by mass, more preferably 5 to 15 parts by mass, and more preferably 8 to 10 parts by mass, per 100 parts by mass of the third rubber component.

[0170] (3C) Third Crosslinking Agent The third crosslinked rubber composition may further contain a third crosslinking agent. The third crosslinking agent can be selected from the crosslinking agents exemplified as the first crosslinking agent, including preferred embodiments. Among the third crosslinking agents, thiram-based accelerators are particularly preferred as crosslinking accelerators.

[0171] The proportion of the cocrosslinking agent is, for example, 0.3 to 10 parts by mass, preferably 0.5 to 5 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of the third rubber component.

[0172] The proportion of the crosslinking accelerator is, for example, 0.1 to 5 parts by mass, preferably 0.3 to 3 parts by mass, and more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the third rubber component.

[0173] The proportion of the third crosslinking aid is, for example, 0.5 to 15 parts by mass, preferably 1 to 10 parts by mass, and more preferably 2 to 5 parts by mass, per 100 parts by mass of the third rubber component.

[0174] (3D) Third Filler The third crosslinked rubber composition may further contain a third filler. Examples of the third filler include the fillers exemplified above as the first filler. The fillers can be used alone or in combination of two or more. Of the fillers, the third filler preferably contains a reinforcing inorganic filler, more preferably contains carbon black and silica, and even more preferably contains soft carbon black and silica.

[0175] The proportion of carbon black (especially soft carbon black) is, for example, 5 to 100 parts by mass, preferably 10 to 80 parts by mass, and more preferably 20 to 40 parts by mass, per 100 parts by mass of the third rubber component.

[0176] The proportion of silica is, for example, 3 to 100 parts by mass, preferably 5 to 50 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of the third rubber component.

[0177] The proportion of the third filler is, for example, 10 to 200 parts by mass, preferably 20 to 100 parts by mass, more preferably 30 to 80 parts by mass, and more preferably 40 to 60 parts by mass, per 100 parts by mass of the third rubber component.

[0178] (3E) Third Anti-aging Agent The third crosslinked rubber composition may further contain a third anti-aging agent. Examples of the third anti-aging agent include the anti-aging agents exemplified above as the first anti-aging agent. The anti-aging agent can be used alone or in combination of two or more types. The proportion of the third anti-aging agent is, for example, 1 to 10 parts by mass, preferably 2 to 8 parts by mass, and more preferably 3 to 5 parts by mass, per 100 parts by mass of the third rubber component.

[0179] (3F) Third Other Component The third crosslinked rubber composition may contain conventional additives as the third other component. Conventional additives include those exemplified as conventional additives in the first other component, as well as short fibers. The additives can be used alone or in combination of two or more.

[0180] The proportion of the softening agent may be 20 parts by mass or less per 100 parts by mass of the third rubber component, for example, 1 to 20 parts by mass, preferably 2 to 10 parts by mass, and more preferably 3 to 7 parts by mass.

[0181] The proportion of the processing agent is, for example, 0.1 to 10 parts by mass, preferably 0.3 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the third rubber component.

[0182] The proportion of the adhesion improver is, for example, 1 to 20 parts by mass, preferably 2 to 10 parts by mass, and more preferably 3 to 7 parts by mass, per 100 parts by mass of the third rubber component.

[0183] The total proportion of the third other component is, for example, 5 to 300 parts by mass, preferably 10 to 200 parts by mass, more preferably 30 to 150 parts by mass, and more preferably 50 to 100 parts by mass, per 100 parts by mass of the third rubber component.

[0184] (Core wire) The core wire is not particularly limited, but typically, core wires (twisted cords) arranged at predetermined intervals in the belt width direction can be used. The core wires may be embedded at equal intervals (or pitches) from one end to the other in the belt width direction of the core layer.

[0185] The core wires are arranged extending in the longitudinal direction (circumferential direction) of the belt, and multiple core wires may be arranged parallel to the longitudinal direction of the belt. However, from the standpoint of productivity, they are usually arranged spirally, extending in parallel at a predetermined pitch, approximately parallel to the longitudinal direction of the cogted V-belt. When the core wires are arranged spirally, the angle of the core wires with respect to the longitudinal direction of the belt may be, for example, 5° or less, and from the standpoint of belt running performance, it is preferable that it is as close to 0° as possible.

[0186] The pitch of the core wires (the distance between the centers of adjacent core wires) should be greater than the core wire diameter, and depending on the core wire diameter, it is, for example, 0.5 to 3 mm, preferably 0.6 to 2 mm, and more preferably 0.8 to 1.5 mm.

[0187] Examples of fibers constituting the core wire include those exemplified as fibers constituting the first short fibers. Among these fibers, synthetic fibers such as polyester fibers (polyalkylene arylate fibers) and aramid fibers, and inorganic fibers such as carbon fibers are often used from the viewpoint of high modulus, with polyalkylene arylate fibers and aramid fibers being preferred, and aramid fibers being particularly preferred.

[0188] The fiber may be a multifilament yarn. The fineness of the multifilament yarn is, for example, 300 to 10,000 dtex, preferably 500 to 5,000 dtex, and more preferably 1,000 to 3,000 dtex. The multifilament yarn may contain, for example, about 100 to 5,000 filaments, preferably about 300 to 3,000 filaments, and more preferably about 500 to 2,000 filaments.

[0189] For the core wire, a twisted cord using multifilament yarn can usually be used. The twisted cord may be a double-twisted, single-twisted, or Lang-twisted cord, but a double-twisted cord is preferred.

[0190] The number of undertwisted yarns can be multiple, but preferably 2 to 6, more preferably 2 to 4, more preferably 2 to 3, and most preferably 3. If there are too many undertwisted yarns, the bending fatigue resistance may decrease.

[0191] The twist coefficient (under-twist coefficient) of each under-twisted yarn is, for example, 0.3 to 5, preferably 0.5 to 3, more preferably 0.7 to 2, and more preferably 0.8 to 1.5.

[0192] The twist coefficient of the twisted cord (the upper twist coefficient of the upper twisted yarn) is, for example, 0.5 to 5, preferably 1 to 4, more preferably 2 to 3.5, and even more preferably 2.5 to 3.5.

[0193] The ratio of the upper twist coefficient to the lower twist coefficient (upper twist coefficient / lower twist coefficient) is, for example, 0.5 to 10, preferably 1 to 8, more preferably 1.5 to 5, more preferably 2 to 4, and most preferably 2.5 to 3.5.

[0194] In this application, the twist coefficients for the under-twist coefficient and the over-twist coefficient can be calculated based on the following formulas.

[0195] TF = TN × D ０．５ / 960 [In the formula, TF: twist coefficient, TN: number of twists per meter, D: fineness (tex) of the yarn]

[0196] The total fineness of the twisted cord is, for example, 1,000 to 30,000 dtex, preferably 3,000 to 20,000 dtex, and more preferably 5,000 to 10,000 dtex.

[0197] The average diameter of the core wire (twisted cord after bonding treatment) is, for example, 0.5 to 3 mm, preferably 0.6 to 2 mm, and more preferably 0.7 to 1 mm.

[0198] In this application, the average diameter of the core wires refers to the average diameter of the core wires within the belt. The average diameter of the core wires is determined by taking a cross-sectional image of the belt in the width direction using a scanning electron microscope (SEM), measuring the length of all core wires in the belt in the width direction in the captured image, and calculating the arithmetic mean. However, if a portion of the core wire is missing on the side of the belt, it will not be included in the measurement.

[0199] The core wire may be bonded (or surface-treated) in the same manner as the first short fiber in order to improve its adhesion to the third rubber component. Preferably, the core wire is bonded with at least RFL liquid.

[0200] [Reinforcement Fabric] The power transmission belt of the present invention (in particular, the low-edge V-belt) may further include a reinforcement fabric. Examples of the form of the reinforcement fabric include laminating it on the surface of the stretchable rubber layer and / or the compression rubber layer, and embedding it in the stretchable rubber layer and / or the compression rubber layer (for example, the form described in Japanese Patent Publication No. 2010-230146).

[0201] The reinforcing fabric may be made of conventional fabric (fabric material or cloth). Examples of conventional fabrics include woven fabrics, knitted fabrics (weft knitted fabrics, warp knitted fabrics), and nonwoven fabrics. Of these, woven fabrics such as plain weave, twill weave, and satin weave, and woven or knitted fabrics with intersection angles exceeding 90° and not exceeding 120° are preferred, and woven fabrics commonly used as cover fabrics for transmission belts in general industrial and agricultural machinery [plain weave fabrics with right-angle intersections, and plain weave fabrics with intersection angles exceeding 90° and not exceeding 120° (wide-angle canvas)] are particularly preferred. Furthermore, in applications where durability is required, the fabric may be wide-angle canvas.

[0202] Examples of fibers constituting the fabric include the fibers exemplified as constituting the first short fibers of the first rubber layer. The fibers may be single yarns using only one type of fiber, or composite yarns (such as blended yarns) combining two or more types of fibers. Among the fibers, polyalkylene arylate short fibers and cellulose short fibers are preferred.

[0203] The reinforcing fabric may be subjected to adhesive treatment, such as treatment with RFL liquid (including immersion treatment), or friction treatment in which adhesive rubber is rubbed into the stretched rubber layer and / or the fabric, if necessary. After laminating the adhesive rubber and the fabric, the reinforcing fabric may be laminated or embedded in the compression rubber layer in a laminated form.

[0204] The average thickness of the reinforcing fabric is, for example, 0.1 to 1.5 mm, preferably 0.2 to 1 mm, and more preferably 0.3 to 0.7 mm.

[0205] [Manufacturing Method for Transmission Belts] The manufacturing method for the transmission belt of the present invention (in particular, the raw edge V-belt) is not particularly limited, and the manufacturing method for the raw edge cogged V-belt is also not particularly limited. Regarding the lamination process of each layer (manufacturing method for the belt sleeve), conventional methods can be used depending on the type of belt. A typical manufacturing method for raw edge cogged V-belts is described below.

[0206] First, a laminate is prepared consisting of a reinforcing cloth (bottom cloth) and a sheet for the main body of the compressed rubber layer (uncrosslinked rubber sheet). This laminate is then brought into contact with a flat cog mold, with the reinforcing cloth facing downwards, where teeth and grooves corresponding to the inner circumferential cog portion (cog peaks 1a and cog bottoms 1b shown in Figure 2) are arranged alternately. This laminate is then pressed at a temperature of 60 to 100°C (especially 70 to 80°C) to produce a cog pad with the inner circumferential cog portion molded onto it (a pad that is not completely crosslinked, but in a semi-crosslinked state). Finally, both ends of this cog pad are cut vertically at appropriate points (especially the tops of the cog peaks) to obtain the required length.

[0207] Next, an inner mold, in which teeth and grooves corresponding to the cog portion are arranged alternately, is placed over the outer circumference of the cylindrical mold, and the cog pad is wrapped around it by engaging the teeth and grooves of the inner mold and joining at both ends (especially the tops of the cog peaks). After laminating a sheet for the first adhesive rubber layer (lower adhesive rubber: uncrosslinked rubber sheet) on the outer circumference of this cog pad, a core wire (twisted cord) that will form 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 stretch rubber layer (uncrosslinked rubber sheet) are sequentially wrapped around its outer circumference to produce an uncrosslinked molded body. Furthermore, if necessary, a reinforcing cloth (upper cloth) may be laminated on top of the stretch rubber layer.

[0208] Subsequently, the uncrosslinked molded body is covered with a jacket and placed in a known crosslinking apparatus (such as a vulcanizing vessel), where crosslinking is performed at a temperature of 120 to 200°C (preferably 150 to 190°C, and more preferably 160 to 185°C) to produce a crosslinked belt sleeve. Then, using a cutter or the like, it is cut into a V shape to obtain an endless low-edge cogged V-belt.

[0209] In the case of a raw edge double cogged V-belt, an outer matrix with teeth and grooves corresponding to the outer cog portion arranged alternately is placed over the outer circumference of the uncrosslinked molded body, and a jacket is then placed over it to perform crosslinking. This results in a crosslinked belt sleeve with cog portions formed on the outer surface as well, which can then be cut into a V shape to obtain a raw edge double cogged V-belt.

[0210] The adhesive rubber layer can be formed from multiple sheets for the adhesive rubber layer. The core wire (stranded cord) forming the core body may be spun in relation to the lamination order of the multiple sheets for the adhesive rubber layer, depending on its embedding position in the adhesive rubber layer.

[0211] 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, the method for producing the uncrosslinked rubber sheet, and the methods for measuring or evaluating each physical property are shown below.

[0212] [Materials Used] (Rubber Components) Chloroprene Rubber A: "PM-40" manufactured by Denka Co., Ltd. (Sulfur-modified type) Chloroprene Rubber B: "DCR-107" manufactured by Denka Co., Ltd. (Sulfur-modified type) Chloroprene Rubber C: "DCR-34" manufactured by Denka Co., Ltd. (Mercaptan-modified type) Chloroprene Rubber D: "M-40" manufactured by Denka Co., Ltd. (Mercaptan-modified type) Carboxylate-modified NBR latex (COOH-modified NBR): "Nipol 1571CL" manufactured by Nippon Zeon Co., Ltd. Vinylpyridine-styrene-butadiene copolymer latex (VP latex): "Nipol 2518FS" manufactured by Nippon Zeon Co., Ltd.

[0213] (Hardening agent) Polycarbodiimide dispersion: "Carbodilite E-02" manufactured by Nisshinbo Chemical Co., Ltd., 40% by mass of active ingredient, NCN (carbodiimide) equivalent 445 Polymeric isocyanate (polymeric MDI): "Millionate® MR-200" manufactured by Tosoh Corporation, NCO content 30% by mass Block polyisocyanate: "Elastron BN-27" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., NCO content 30% by mass

[0214] (Short Fibers) The following short fibers were used. All short fibers were subjected to an adhesion treatment by immersion in RFL solution [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 Nippon Zeon Co., Ltd.), and 78.8 parts by mass of water] and drying. The adhesion rate of the adhesive component (solid content) was adjusted to 6% by mass relative to the short fibers before treatment.

[0215] Para-aramid staple fibers: "Twaron®" manufactured by Teijin Limited, average fiber diameter 12 μm, fiber length 3 mm Nylon 66 staple fibers: "Leona" manufactured by Asahi Kasei Corporation, average fiber diameter 27 μm, fiber length 3 mm PBO staple fibers: "Zylon" manufactured by Toyobo Co., Ltd., average fiber diameter 12 μm, fiber length 3 mm

[0216] (Fillers) Carbon Black FEF: "Seast SO" manufactured by Tokai Carbon Co., Ltd. Carbon Black ISAF: "Seast 6" manufactured by Tokai Carbon Co., Ltd. Silica: "NipsilvN3" manufactured by Tosoh Silica Co., Ltd.

[0217] (Additives) Naphthenic oil: Diana Process Oil NS-90S manufactured by Idemitsu Kosan Co., Ltd. Adhesion improver A (resorcinol formaldehyde cocondensate): Powerplast PP-1860 manufactured by Singh Plasticisers & Resins Adhesion improver B (hexamethoxymethylmelamine): Powerplast PP-1890S manufactured by Singh Plasticisers & Resins Magnesium oxide: Kyowa Mag 150 manufactured by Kyowa Chemical Industry Co., Ltd. Crosslinking accelerator MBTS (dibenzothiadyl disulfide): Noxellar DM manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Crosslinking accelerator TMTD (tetramethylthiuram disulfide): Noxellar TT manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Anti-aging agent A (octyl diphenylamine): "Nonflex OD-3" manufactured by Seiko Chemical Co., Ltd. Anti-aging agent B (4,4'-bis(α,α-dimethylbenzyl)diphenylamine): "Nonflex DCD" manufactured by Seiko Chemical Co., Ltd. Anti-aging agent C (microcrystalline wax): "Santight C" manufactured by Seiko Chemical Co., Ltd. Zinc powder: "M-11" manufactured by Sakai Chemical Industry Co., Ltd. Softener: "ADEKA Sizer C-8" manufactured by ADEKA Corporation Stearic acid: "Beads Stearic Acid Tsubaki" manufactured by NOF Corporation Stearic acid amide: "Amid AP-1" manufactured by Nippon Chemical Corporation Zinc oxide: "Zinc oxide (JIS standard type 2)" manufactured by Hakusui Tech Co., Ltd. Co-crosslinking agent (N,N'-m-phenylenedimaleimide): "Balnock PM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur (powdered sulfur): "MIDAS" manufactured by Migen Chemical Co., Ltd.

[0218] (Core wire) Aramid core wire: Two bundles of 1100 dtex aramid fibers (Teijin Limited's "Technora") were combined and twisted with a twist coefficient of 1.0 to produce a pre-twisted yarn. Three of these pre-twisted yarns were combined and twisted in the opposite direction to the pre-twist with a twist coefficient of 3.0 to produce a multi-twisted cord with a total fineness of 6600 dtex (the diameter of the processed cord is approximately 0.95 mm and the tensile strength per core wire is 1300 N).

[0219] (Method for bonding core wires) (A) Preparation of the first treatment agent The first treatment agent having the composition shown in Table 2 was prepared by mixing the RFL liquid having the composition shown in Table 1 with the polycarbodiimide dispersion and water in the proportions shown in Table 2 and stirring at room temperature for 10 minutes.

[0220]

[0221]

[0222] (B) Preparation of the second treatment agent The RFL solution with the composition shown in Table 3 was mixed with blocked polyisocyanate and water in the proportions shown in Table 4, and stirred at room temperature for 10 minutes to prepare the second treatment agent with the composition shown in Table 4.

[0223]

[0224]

[0225] (C) Preparation of the third treatment agent The rubber composition for the adhesive rubber layer described later was dissolved in toluene in the proportions shown in Table 5, and polymeric isocyanate was added to prepare the third treatment agent (rubber glue).

[0226]

[0227] (D) The untreated twisted cord was immersed in the first treatment agent for 10 seconds and dried at 150°C for 2 minutes (first treatment step). Next, the twisted cord treated with the first treatment agent was immersed in the second treatment agent for 10 seconds and dried at 230°C for 2 minutes (second treatment step). Finally, the twisted cord treated with the second treatment agent was immersed in the third treatment agent for 3 seconds and dried at 100°C for 1 minute. This immersion and drying process was repeated three times. After that, it was further heated at 230°C for 2 minutes to obtain the core wire (third treatment step).

[0228] (Reinforcement fabric) Plain woven canvas made from 10-count cotton yarn at a thread density of 70 threads / 50mm (weight 180g / m) ２ A treated canvas (thickness approximately 0.5 mm, basis weight approximately 450 g / m²) was obtained by rubbing the adhesive rubber composition onto the canvas. ２ ) was used as reinforcing fabric.

[0229] [Preparation of Uncrosslinked Rubber Sheets for Rubber Layers] Rubber compositions for forming the adhesive rubber layer, stretchable rubber layer, and compression rubber layer were prepared according to the mixing ratios shown in Tables 6 to 8. Specifically, the materials were kneaded using a Banbury mixer, and the resulting kneaded rubber was passed through a calender roll to produce rolled rubber sheets (sheets for the adhesive rubber layer, stretchable rubber layer, and compression rubber layer).

[0230]

[0231]

[0232] [Rubber Hardness] Uncrosslinked rubber compositions having the compositions shown in Tables 12 and 13 were press-heated at a temperature of 170°C and a pressure of 2 MPa for 20 minutes to produce crosslinked rubber sheets (100 mm × 100 mm × 2 mm thickness). A laminate of three crosslinked rubber sheets was used as a sample, and the rubber hardness (Type A) of the crosslinked rubber sheets was 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 - Method for determining hardness -). The measurement temperature was 23°C.

[0233] [4% flexural modulus (direction perpendicular to short fibers)] An uncrosslinked rubber composition having the composition shown in Tables 12 and 13 was press-heated at a temperature of 170°C and a pressure of 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 direction of the crosslinked rubber molded body. As shown in Figure 8, the crosslinked rubber molded body 21 was supported on a pair of rotatable rolls (6 mm in diameter) 22a and 22b spaced 20 mm apart, and a metal pressing member 23 was placed on the center of the upper surface of the crosslinked rubber molded body in the width direction (direction perpendicular to the orientation direction of the short fibers). The tip of the pressing member 23 had a semicircular cross-sectional shape with a diameter of 10 mm, and the crosslinked rubber molded body 21 could be smoothly pressed with its tip. Furthermore, during pressing, frictional force acted between the lower surface of the cross-linked rubber molded body 21 and the rolls 22a and 22b due to the compressive deformation of the cross-linked rubber molded body 21. However, by making the rolls 22a and 22b rotatable, the effect of friction was reduced. The initial position was set with the tip of the pressing member 23 in contact with the upper surface of the cross-linked rubber molded body 21, but without pressing. From this state, the pressing member 23 was pressed downwards at a speed of 100 mm / min against the upper surface of the cross-linked rubber molded body 21, and the bending modulus of elasticity at a bending strain of 4% was measured. The measurement temperature was 23°C. The larger the bending modulus of elasticity in the direction perpendicular to the short fibers (4% bending modulus of elasticity), the better the lateral pressure resistance of the belt can be judged, and 5 MPa or higher is considered good.

[0234] [4% Flexural Modulus (Parallel to Short Fibers)] In the above method for measuring the 4% flexural modulus in the direction perpendicular to the short fibers, as shown in Figure 9, the short fibers were oriented perpendicular to the longitudinal direction of the cross-linked rubber molded body when manufacturing the cross-linked rubber molded body (i.e., the orientation direction of the short fibers was parallel to the metal pressing member 23). Otherwise, the 4% flexural modulus was measured in the same manner. The smaller the 4% flexural modulus in the direction parallel to the short fibers, the better the flexibility of the belt can be judged. A value of 2.5 MPa or less can be judged as a practically acceptable level.

[0235] [Tear Strength] Tear strength was measured in accordance with test method C (method using crescent-shaped test specimens) of JIS K 6252-1:2015 (Vulcanized rubber and thermoplastic rubber - Method for determining tear strength). Specifically, crosslinked rubber sheets with a thickness of approximately 2 mm were prepared using uncrosslinked rubber compositions having the compositions shown in Tables 12 and 13 (crosslinking conditions: 170°C, 2 MPa, 20 minutes), and left to stand at the test temperature of 23°C for 24 hours or more. After that, crescent-shaped test specimens were prepared by punching out with a punching blade so that the row direction (orientation direction) of the short fibers was perpendicular to the long side direction of the test specimen, with a 1 mm deep cut in the center of the recess of the test specimen. The thickness was measured at three locations near the cut of the test specimen, and the median value was determined. Subsequently, using a tensile testing machine (Shimadzu Corporation's "Autograph AG-5000A"), the tear force was recorded while pulling both ends of the long side of the test specimen at a speed of 500 mm / min. The test was performed five times (measured on five test specimens), and the tear strength of each specimen was calculated using the following formula, and the arithmetic mean was adopted.

[0236] Ts = F / d [wherein Ts represents the tear strength (N / mm), F represents the maximum tear force (N), and d represents the median thickness of the test specimen (mm)]

[0237] [Running Test 1 (Peeling Resistance and Abrasion Resistance Test)] The peeling resistance and abrasion resistance tests were conducted using a two-axis running test machine with a layout consisting of a 50 mm diameter drive pulley (Dr.) and a 125 mm diameter driven pulley (Dn.), as shown in Figure 10. A low-edge V-belt was mounted on these two pulleys, and the belt was run for 72 hours at an ambient temperature of 25°C with an axial load (static axial load) of 392 N, a drive pulley rotation speed of 5600 rpm, and a driven pulley load torque of 9 N·m. The belt was visually inspected after running to check for peeling between the core wire and the adhesive rubber layer, and judged according to the criteria shown in Table 8. In addition, the upper width of the belt was measured before and after running, and the change in upper width (decrease in upper width) was calculated to evaluate abrasion resistance. The smaller the change in upper width, the better the abrasion resistance, and this was judged according to the criteria shown in Table 9.

[0238]

[0239]

[0240] [Running Test 2 (Crack Resistance Test)] The crack resistance test was conducted using a three-axis running test machine with a layout consisting of a 98 mm diameter drive pulley (Dr.), a 78 mm diameter driven pulley (Dn.), and an 80 mm diameter rear idler pulley (Id.), as shown in Figure 11. A low-edge V-belt was mounted on this test machine so that the contact angle of the belt with respect to the rear idler pulley (the central angle with respect to the arc in which the belt and pulley are in contact) was 15 degrees. The belt was run with an axial load (dead load) of 392 N, a drive pulley rotation speed of 3600 rpm, and no load, at an ambient temperature of 120°C. In the test, after running for an appropriate amount of time, the test machine was stopped and the sides of the belt (especially the cog grooves) were visually observed. If a crack occurred, the depth of the crack (length of the crack in the direction of the belt thickness) was measured. If no cracks occurred or the crack depth was less than 2.0 mm, driving was resumed. If the crack depth reached 2.0 mm or more, it was determined that the belt's lifespan had ended and the test was terminated. The longer the time until the end of the test, the better the crack resistance was judged to be, and the criteria shown in Table 10 were used for evaluation.

[0241]

[0242] [Overall Assessment] Based on the assessment of each evaluation item, an overall assessment was made according to the criteria shown in Table 11.

[0243] [Belt Fabrication] A laminate of reinforcing fabric and a sheet for the compression rubber layer (uncrosslinked rubber) was placed with the reinforcing fabric facing downwards on a flat cog mold in which teeth and grooves corresponding to the inner circumference cog portion were arranged alternately. The laminate was pressed at 75°C to form the cog portion, creating a cog pad (not fully crosslinked, but in a semi-crosslinked state). Next, both ends of this cog pad were cut vertically from the top of the cog peaks.

[0244] Next, an inner mold, in which teeth and grooves corresponding to the cog portion were arranged alternately, was placed over a cylindrical mold. The cog pad was then wound around the inner mold, engaging with the teeth and grooves, and joined at the top of the cog peaks. A first adhesive rubber layer sheet (lower adhesive rubber, uncrosslinked rubber, same as the adhesive rubber layer sheet) was laminated around the outer circumference of the wound cog pad. Subsequently, the core wire was spun in a spiral shape, and a second adhesive rubber layer sheet (upper adhesive rubber, same as the adhesive rubber layer sheet) and a stretchable rubber layer sheet (uncrosslinked rubber) were sequentially wound around its outer circumference to produce an uncrosslinked molded body. The short fibers of the stretchable rubber layer and the compression rubber layer were oriented in the belt width direction. The core wire pitch was 1.1 mm.

[0245] Subsequently, an outer matrix, with teeth and grooves arranged alternately to correspond to the outer cog portion, was placed over the outer circumference of the uncrosslinked molded body. With the jacket then placed over it, the mold was set in a vulcanizing can and crosslinked at a temperature of 180°C, 0.9 MPa, and for 40 minutes to obtain a belt sleeve (crosslinking conditions in Tables 12 and 13: C1). In Example 20 only, crosslinking was performed under the conditions of 153°C, 0.41 MPa, and for 20 minutes (crosslinking conditions in Table 13: C2). This belt sleeve was cut with a cutter to a V-shaped cross section of a predetermined width in the longitudinal direction of the belt. Then, this belt sleeve was finished into a belt with the structure shown in Figure 4, that is, a low-edge double-cogged V-belt (size: top width 20 mm, thickness 10 mm, V angle 30 degrees, outer circumference length 817 mm, pitch width 18 mm, outer circumference cog height (H5) 1.8 mm, inner circumference cog height (H2) 4.5 mm) which is a CVT belt with cogs on the inner circumference side of the belt.

[0246] The evaluation results of the belts obtained in Examples 1 to 20 and Comparative Examples 1 to 7 are shown in Tables 12 and 13.

[0247]

[0248]

[0249] Examples 1 to 5 showed an excellent balance of peel resistance, abrasion resistance, and crack resistance. In Example 3, although the flexural modulus in the direction perpendicular to the short fibers was relatively low, it had a good balance with other physical properties, resulting in the longest durability life among the examples where peeling did not occur in running test 1.

[0250] On the other hand, compared to Example 3, Examples 1, 2, and 4, which contained higher amounts of sulfur and co-crosslinking agent, tended to show a slight decrease in tear strength and crack resistance. Conversely, as the co-crosslinking agent / sulfur ratio increased, wear resistance tended to improve, and Example 1 showed the smallest change in upper width in running test 1.

[0251] Furthermore, Example 5, like Comparative Example 3, uses a small amount of carbon black, but by increasing the amount of sulfur and co-crosslinking agent, the bending modulus of elasticity in the direction perpendicular to the short fibers is maintained at a high level. No delamination occurred in running test 1, and the durability life was also relatively long.

[0252] Of Examples 1 to 5, Example 1 received an overall rating of A, demonstrating the best balance of various characteristics.

[0253] Comparative Examples 1 and 2 were examples that did not contain aramid short fibers, and had a low flexural modulus in the direction perpendicular to the short fibers, resulting in delamination.

[0254] Comparative Example 3 is an example in which the proportion of carbon black is lower than that of Example 3, resulting in a lower flexural modulus in the direction perpendicular to the short fibers, and delamination occurred.

[0255] Comparative Example 4 is an example with a higher proportion of carbon black compared to Example 1, Comparative Example 5 is an example with a higher proportion of co-crosslinking agent compared to Examples 1-3, and Comparative Example 6 is an example with a higher proportion of short fibers and co-crosslinking agent compared to Example 3. In all examples, the flexural modulus in the direction parallel to the short fibers was high, and the crack resistance was reduced.

[0256] Comparative Example 7 is an example that does not contain PBO short fibers compared to Example 3, and its abrasion resistance and crack resistance were reduced.

[0257] Examples 6 to 9 show cases where the amount of sulfur was changed. When the amount of sulfur was low, the change in upper width became larger, possibly due to a decrease in wear resistance. On the other hand, when the amount of sulfur was high, crack resistance decreased.

[0258] Example 10 is an example where the amount of crosslinking accelerator is large, resulting in reduced crack resistance.

[0259] Example 11 is an example in which the crosslinking accelerator was changed from MBTS (thiazole-based) to TMTD (thiuram-based), resulting in decreased crack resistance. Thiazole-based accelerators are preferred as they can improve crack resistance.

[0260] Examples 12 and 13 show cases where the chloroprene rubber was changed from sulfur-modified to mercaptan-modified, and the change in upper width was larger, possibly due to a decrease in abrasion resistance.

[0261] Examples 14 to 16 show cases where the amount of antioxidant was changed. When the amount of antioxidant was low, crack resistance decreased, possibly due to increased thermal curing. On the other hand, when the amount of antioxidant was high, the change in upper width increased, possibly due to decreased wear resistance.

[0262] Examples 17-19 show variations in the type and proportion of carbon black. The larger the proportion of carbon black FEF, which is classified as soft carbon black, the greater the change in the upper width, possibly due to a decrease in wear resistance.

[0263] Example 20 is an example in which the crosslinking conditions were changed. The 4% flexural modulus and abrasion resistance in the direction perpendicular to the short fibers decreased, but practical levels were maintained.

[0264] The power transmission belt of the present invention can be used for various types of power transmission belts, such as friction power transmission belts like V-belts and V-ribbed belts; and meshing power transmission belts like toothed belts and double-sided toothed belts. In particular, the power transmission belt of the present invention may be applied to raw edge V-belts and raw edge cogged V-belts having cogs. Because the power transmission belt of the present invention has excellent resistance to lateral pressure, wear resistance and crack resistance, it can be used in V-belts (gear belts or CVT belts) used in transmissions (continuously variable transmissions) where the gear ratio changes steplessly during belt operation, such as raw edge cogged V-belts and raw edge double cogged V-belts used in continuously variable transmissions of motorcycles, ATVs (four-wheel buggies), and snowmobiles. The power transmission belt of the present invention is particularly suitable for use in raw edge cogged V-belts and raw edge double cogged V-belts used in continuously variable transmissions of racing ATVs under demanding operating conditions.

[0265] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2025-025757 filed on 20 February 2025 and Japanese Patent Application No. 2026-012244 filed on 28 January 2026, the contents of which are incorporated herein by reference.

[0266] 1... Raw edge cogged V-belt 11... Raw edge double cogged V-belt 1a, 11a, 11c... Cog peaks 1b, 11b, 11d... Cog valleys 2, 6, 16... Reinforcement fabric 3, 13... Stretchable rubber layer 4, 14... Core layer 4a, 14a... Core wire 5, 15... Compression rubber layer

Claims

1. A power transmission belt comprising a compression rubber layer, wherein the compression rubber layer comprises a crosslinked rubber composition, the crosslinked rubber composition comprises a rubber component and short fibers, the rubber component comprises chloroprene rubber, the short fibers comprise poly(p-phenylenebenzobisoxazole) short fibers and aramid short fibers, the 4% flexural modulus in the direction perpendicular to the orientation direction of the short fibers in the crosslinked rubber composition is 5 MPa or more, and the 4% flexural modulus in the direction parallel to the orientation direction of the short fibers in the crosslinked rubber composition is 2.5 MPa or less.

2. The transmission belt according to claim 1, wherein the total amount of the poly(p-phenylene benzobisoxazole) short fibers and the aramid short fibers is 15 to 40 parts by mass per 100 parts by mass of the rubber component, and the mass ratio of the poly(p-phenylene benzobisoxazole) short fibers to the aramid short fibers is 10 / 90 to 70 / 30.

3. The transmission belt according to claim 1 or 2, wherein the tear strength of the crosslinked rubber composition, measured in accordance with test method C of JIS K 6252-1:2015, is 80 N / mm or more.

4. The transmission belt according to any one of claims 1 to 3, wherein the crosslinked rubber composition further comprises a sulfur-based crosslinking agent, and the proportion of the sulfur-based crosslinking agent is 0.5 to 3 parts by mass per 100 parts by mass of the rubber component.

5. The transmission belt according to claim 4, wherein the crosslinked rubber composition further comprises a co-crosslinking agent, the proportion of the co-crosslinking agent is 0.5 to 12 parts by mass per 100 parts by mass of the rubber component, and the mass ratio of the co-crosslinking agent to the sulfur-based crosslinking agent is former / latter = 0.3 / 1 to 12 / 1.

6. The transmission belt according to any one of claims 1 to 5, wherein the crosslinked rubber composition further comprises an antioxidant, and the proportion of the antioxidant is 3 to 8 parts by mass per 100 parts by mass of the rubber component.

7. The transmission belt according to any one of claims 1 to 6, wherein the crosslinked rubber composition further comprises carbon black, the proportion of carbon black being 42 to 58 parts by mass per 100 parts by mass of the rubber component, and the carbon black comprising hard carbon black.

8. The transmission belt according to any one of claims 1 to 7, wherein the chloroprene rubber is a sulfur-modified type chloroprene rubber.

9. A transmission belt according to any one of claims 1 to 8, which is a low-edge V-belt having cogs on at least the inner circumferential surface side.

10. A belt transmission mechanism comprising a combination of a transmission belt and a pulley as described in any one of claims 1 to 9, and provided in a belt-type continuously variable transmission.

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