JP7487145B2 - Transmission V-belt - Google Patents

Description

The present invention relates to low-edge type transmission V-belts, such as low-edge V-belts and low-edge cogged V-belts.

V-belts that transmit power through friction transmission include the raw-edge type (raw-edge V-belt), which has an exposed rubber layer on the friction transmission surface, and the wrapped type (wrapped V-belt), whose friction transmission surface (V-shaped side) is covered with a cover cloth. They are used differently depending on the application due to the difference in the surface properties of the friction transmission surface (friction coefficient between the rubber layer and the cover cloth). Raw-edge type belts also include raw-edge V-belts that have no cogs, raw-edge cogged V-belts that have cogs only on the underside (inner surface) of the belt to improve flexibility, and raw-edge cogged V-belts (raw-edge double cogged V-belts) that have cogs on both the underside (inner surface) and upper surface (outer surface) of the belt to improve flexibility.

Raw edge V-belts and raw edge cogged V-belts are primarily used to drive general industrial and agricultural machinery, and for driving accessories in automobile engines. Another application is raw edge cogged V-belts, also known as variable speed belts, used in belt-type continuously variable transmissions on motorcycles and other vehicles.

As shown in FIG. 1, the belt-type continuously variable transmission 30 is a device that changes the speed ratio steplessly by wrapping a transmission V-belt 1 around a driving pulley 31 and a driven pulley 32. Each pulley 31, 32 has a fixed pulley piece 31a, 32a whose axial movement is restricted or fixed, and a movable pulley piece 31b, 32b that can move in the axial direction, and the inner peripheral wall of the fixed pulley piece 31a, 32a and the inner peripheral wall of the movable pulley piece 31b, 32b form a V-groove-shaped inclined opposing surface. Each pulley 31, 32 has a structure that allows the width of the V-groove of the pulley 31, 32 formed by the fixed pulley piece 31a, 32a and the movable pulley piece 31b, 32b to be continuously changed. Both end faces in the width direction of the transmission V-belt 1 are formed with tapered surfaces whose inclinations match the V-groove-shaped inclined opposing surfaces of the pulleys 31 and 32, and the belt fits into any vertical position on the opposing surfaces of the V-grooves according to the changed width of the V-grooves. For example, by narrowing the width of the V-groove of the driving pulley 31 and widening the width of the V-groove of the driven pulley 32, the state shown in Fig. 1(a) is changed to the state shown in Fig. 1(b), so that the transmission V-belt 1 moves upward in the V-groove on the driving pulley 31 side and downward in the V-groove on the driven pulley 32 side, and the winding radius around each pulley 31 and 32 changes continuously, thereby allowing the gear ratio to be changed steplessly. The speed-changing belt used for such an application is used in a severe layout where the belt is greatly bent and under high load. In other words, it is specially designed to withstand harsh movements in a high-load environment, such as not only the winding rotation between the two shafts of the drive pulley and the driven pulley, but also the movement in the pulley radial direction and the repeated bending movements caused by continuous changes in the winding radius.

In recent years, there has been a demand for improved properties such as heat resistance, lateral pressure resistance, and flex fatigue resistance (crack resistance) in such V-belts, particularly in speed-change belts used in belt-type continuously variable transmissions.

For example, JP 2010-196888 A (Patent Document 1) discloses a power transmission belt in which the compressed rubber layer is made up of two layers, an upper layer close to the core and a lower layer on the inner peripheral surface side of the belt, with the hardness of the upper layer set higher than that of the lower layer, with the objective of providing a belt that has excellent resistance to bending fatigue while ensuring resistance to lateral pressure. It also describes that hard urethane is preferable as a material that can be used for the upper layer, and gives examples of materials that can be used for the lower layer, such as chloroprene rubber and hydrogenated nitrile rubber.

In addition, Japanese Patent Laid-Open Publication No. 9-303488 (Patent Document 2) discloses a power transmission V-belt that has an objective of providing a power transmission V-belt that is excellent in resistance to lateral pressure and flex fatigue, and also satisfies heat resistance and abrasion resistance, and is characterized in that the compression rubber layer is made of a rubber composition crosslinked by blending hydrogenated nitrile rubber, an unsaturated carboxylic acid metal salt, short fibers, and an organic peroxide, and further has a crack prevention rubber layer laminated thereon that does not contain short fibers. It also describes that the thickness of the crack prevention rubber layer is preferably 0.5 to 3 mm, and in the examples, a raw edge cogged V-belt with a thickness of 14.5 mm is produced.

Polymers other than hydrogenated nitrile rubber that have excellent heat resistance include ethylene-propylene copolymer (EPM) and ethylene-propylene-diene terpolymer (EPDM), as well as other ethylene-α-olefin elastomers. In particular, EPDM has high heat resistance due to the absence of double bonds in the main chain, and due to the presence of double bonds in the side chains derived from the diene component, it can be crosslinked with sulfur in addition to organic peroxides, so there is a possibility that the properties of the crosslinked rubber can be controlled to improve the performance of power transmission belts.

For example, Japanese Patent Application Laid-Open No. 2000-283243 (Patent Document 3) discloses a transmission belt using a rubber containing an ethylene/α-olefin/diene terpolymer containing sulfur as a crosslinking agent, with the objective of providing a transmission belt that has excellent heat resistance and cold resistance, and has a small life variance due to slow crack growth, making it highly reliable. More specifically, it discloses that a V-ribbed belt using EPDM containing sulfur as a crosslinking agent is superior in terms of long life and small life variance to a V-ribbed belt using chloroprene rubber or a V-ribbed belt using EPDM containing an organic peroxide as a crosslinking agent.

JP 2010-196888 A Japanese Patent Application Laid-Open No. 9-303488 JP 2000-283243 A

However, although Patent Document 1 does not explicitly state that improving heat resistance is an issue, in recent years, belt-type continuously variable transmissions have become more compact and cooling functions have been simplified, making it difficult for heat to dissipate. Therefore, improving the heat resistance of variable speed belts has become an important issue, but there are an increasing number of cases where conventional materials such as those exemplified in Patent Document 1 are unable to ensure sufficient heat resistance.

In addition, in Patent Document 2, hydrogenated nitrile rubber containing an unsaturated carboxylic acid metal salt is used as the polymer component of the rubber composition that forms the compression layer, but since it is an expensive polymer, it has the disadvantage of high manufacturing costs. Furthermore, since the crack prevention rubber layer does not contain short fibers, it has the disadvantage of being prone to reducing lateral pressure resistance, and is not a practical configuration.

Furthermore, in Patent Document 3, a transmission belt is formed from a rubber containing an ethylene/α-olefin/diene terpolymer blended with sulfur, which has a certain effect in improving heat resistance, lateral pressure resistance, and flex fatigue resistance, but these properties no longer fully satisfy the stringent requirements of recent years, and further improvements are required.

Therefore, the object of the present invention is to provide a low-edge type V-belt that can improve heat resistance, lateral pressure resistance, and flex fatigue resistance.

As a result of intensive research into achieving the above-mentioned objective, the inventors of the present invention discovered that by forming the compressed rubber layer of a low-edge type V-belt by combining a main body of the compressed rubber layer formed from an ethylene-α-olefin elastomer cross-linked with an organic peroxide and a surface layer of a specific thickness formed from an ethylene-α-olefin elastomer containing diene units cross-linked with a sulfur-based cross-linking agent, it is possible to improve heat resistance, lateral pressure resistance, and flex fatigue resistance, and thus completed the present invention.

That is, the low-edge type V-belt of the present invention includes a compressed rubber layer disposed on the inner peripheral surface side, the compressed rubber layer being formed of a main body of the compressed rubber layer formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide, and an inner surface layer having an average thickness of 0.3 to 3.5 mm that covers the inner peripheral side (belt inner peripheral side) surface of the main body of the compressed rubber layer and is formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing a diene unit and a sulfur-based crosslinking agent. The low-edge type V-belt may further include a tension rubber layer disposed on the outer peripheral surface side. The tension rubber layer may be formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing a diene unit and a sulfur-based crosslinking agent. The tension rubber layer may have a main body of the tension rubber layer formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide, and an outer surface layer covering the outer peripheral side (belt outer peripheral side) surface of the main body of the tension rubber layer and formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing a diene unit and a sulfur-based crosslinking agent. The average thickness of the entire belt of the low-edge type V-belt may be 8 to 18 mm. The hardness of the main body of the compression rubber layer may be 90 to 99 degrees, and the hardness of the inner surface layer may be 70 to 95 degrees. In the main body of the compression rubber layer, the diene content of the ethylene-α-olefin elastomer may be less than 3.5 mass%. In the inner surface layer, the diene content of the ethylene-α-olefin elastomer containing a diene unit may be 3.5 mass% or more. The low-edge type V-belt may have cogs at least on the inner peripheral surface side. The low-edge type V-belt may be a variable speed belt.

In the present invention, the compressed rubber layer of the low-edge type V-belt is composed of a combination of a main body of the compressed rubber layer formed of an ethylene-α-olefin elastomer crosslinked with an organic peroxide and an inner surface layer of a specific thickness formed of an ethylene-α-olefin elastomer containing diene units crosslinked with a sulfur-based crosslinking agent, thereby improving heat resistance, lateral pressure resistance and flex fatigue resistance. Therefore, even when running under harsh conditions in a high-load environment such as a variable speed belt, cracks and pop-outs in the rubber layer (the phenomenon in which the core wire pops out from the side of the belt) are suppressed, improving durability.

FIG. 1 is a schematic diagram for explaining a transmission mechanism of a belt-type continuously variable transmission. FIG. 2 is a schematic, partially sectional perspective view showing an example of a raw edge cogged V-belt of the present invention. FIG. 3 is a schematic cross-sectional view of the raw edge cogged V-belt of FIG. 2 cut in the belt longitudinal direction. FIG. 4 is a schematic diagram showing the layout of a test machine used in the durability running test in the examples.

[Structure of low edge type V-belt]
The low-edge type V-belt (low-edge type power transmission V-belt) of the present invention is not particularly limited as long as it is a low-edge type V-belt including a compressed rubber layer having a specific two-layer structure of a main body of the compressed rubber layer and a surface layer (inner surface layer). The low-edge type V-belt includes a low-edge V-belt and a low-edge cogged V-belt. Furthermore, the low-edge cogged V-belt can be roughly divided into a low-edge cogged V-belt in which cogs are formed only on the inner peripheral side of the low-edge V-belt, and a low-edge double cogged V-belt in which cogs are formed on both the inner peripheral side and the outer peripheral side of the low-edge V-belt. Of these, the low-edge cogged V-belt and the low-edge double cogged V-belt are preferred because they are required to have both high levels of lateral pressure resistance and bending fatigue resistance, and the low-edge double cogged V-belt is particularly preferred because it is used in harsher conditions and requires a high level.

Figure 2 is a schematic partial cross-sectional perspective view showing an example of a raw-edge cogged V-belt of the present invention, and Figure 3 is a schematic cross-sectional view of the raw-edge cogged V-belt of Figure 2 cut in the belt longitudinal direction.

In this example, the raw edge cogged V-belt 1 has a cog portion formed on the inner peripheral surface of the belt body, in which cog peaks 1a and cog valleys 1b are alternately arranged along the longitudinal direction of the belt (direction A in the figure), and the cross-sectional shape of the cog peaks 1a in the longitudinal direction is approximately semicircular (curved or wavy), 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 approximately semicircularly from the cog valley 1b in the cross section in the A direction in the belt thickness direction. The raw edge cogged V-belt 1 has a laminated structure, and the outer surface layer 2 of the tension rubber layer, the main body 3 of the tension rubber layer, the adhesive rubber layer 4, the main body 5 of the compression rubber layer, and the inner surface layer 6 of the compression rubber layer are laminated in order from the outer periphery side of the belt to the inner periphery side (the side where the cog portion is formed). The cross-sectional shape in the belt width direction is a trapezoid in which the belt width becomes smaller from the outer periphery side of the belt to the inner periphery side. Furthermore, a core 4a is embedded in the adhesive rubber layer 4, and the cog portion is formed in the compressed rubber layer 5 using a cog-equipped molding die.

The overall belt thickness (average thickness) of the low-edge type V-belt of the present invention is, for example, 8 to 18 mm, preferably 9 to 16 mm (particularly 10 to 15 mm), and more preferably 10 to 14 mm (particularly 11 to 13 mm). If the thickness is too thin, there is a risk of reduced resistance to lateral pressure, and if the thickness is too thick, there is a risk of reduced flexibility, reduced transmission efficiency, and reduced resistance to bending fatigue.

In this application, if the compressed rubber layer has a cog portion, the thickness of the entire belt means the thickness at the top of the cog portion (maximum thickness of the belt).

[Compressed rubber layer]
The compressed rubber layer has a main body of the compressed rubber layer formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide, and a surface layer (inner surface layer) that covers the inner peripheral surface of the main body and is formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer and a sulfur-based crosslinking agent. The compressed rubber layer only needs to have the main body of the compressed rubber layer and the inner surface layer, and may have other layers (for example, other rubber layers interposed between the main body of the compressed rubber layer and the inner surface layer), but a two-layer structure of the main body of the compressed rubber layer and the inner surface layer is preferable in terms of mechanical properties and productivity of the compressed rubber layer. In the present invention, by forming the compressed rubber layer into a two-layer structure of the main body and the inner surface layer, it is possible to achieve both lateral pressure resistance and bending fatigue resistance. Furthermore, since the compressed rubber layer contains an ethylene-α-olefin elastomer, it has excellent heat resistance and can improve the durability of the low-edge V-belt when used at high temperatures.

(Compressed rubber layer body)
In the present invention, the main body of the compressed rubber layer (compressed rubber layer main body) is formed from a cured product of a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide, and the rubber hardness of the compressed rubber layer can be increased, thereby improving lateral pressure resistance.

(A1) Ethylene-α-olefin elastomer Ethylene-α-olefin elastomers have excellent heat resistance because they do not contain double bonds in the main chain. Therefore, when the rubber component of the compressed rubber layer body is formed from an ethylene-α-olefin elastomer, the durability of the low-edge V-belt when used at high temperatures can be improved. The ethylene-α-olefin elastomer only needs to contain ethylene units and α-olefin units as constituent units, and may further contain diene units. Ethylene-α-olefin elastomers include ethylene-α-olefin copolymer rubber, ethylene-α-olefin-diene ternary copolymer rubber, and the like.

Examples of the α-olefin for forming the α-olefin unit include linear α-C _3-12 olefins such as propylene, butene, pentene, methylpentene, hexene, octene, etc. Among these α-olefins, α-C _3-4 olefins such as propylene (particularly propylene) are preferred.

As the diene monomer for forming the diene units, a non-conjugated diene monomer is usually used. Examples of non-conjugated diene monomers include dicyclopentadiene, methylenenorbornene, ethylidenenorbornene, 1,4-hexadiene, and cyclooctadiene. Among these diene monomers, ethylidenenorbornene and 1,4-hexadiene are preferred, and ethylidenenorbornene is particularly preferred because it can improve the physical properties (especially hardness) and heat resistance of the crosslinked rubber.

Typical ethylene-α-olefin elastomers include, for example, ethylene-propylene copolymer (EPM) and ethylene-propylene-diene terpolymer (EPDM).

These ethylene-α-olefin elastomers can be used alone or in combination of two or more. Of these, ethylene-propylene copolymers and ethylene-propylene-diene terpolymers are preferred, with ethylene-α-olefin-diene terpolymer rubber being even more preferred because of its excellent crosslinking efficiency due to the diene units and its ability to improve lateral pressure resistance, and ethylene-propylene-diene terpolymer (EPDM) being particularly preferred.

In the ethylene-propylene-diene terpolymer, the ratio (mass ratio) of ethylene to propylene may be from 35/65 to 90/10, preferably from 40/60 to 80/20, more preferably from 45/55 to 70/30, and most preferably from 50/50 to 60/40.

The ethylene content of the ethylene-α-olefin elastomer (particularly ethylene-α-olefin-diene terpolymer rubber such as EPDM) may be 30% by mass or more (e.g., 30 to 80% by mass), preferably 50 to 70% by mass, further preferably 52 to 65% by mass, even more preferably 53 to 60% by mass, and most preferably 54 to 58% by mass. If the ethylene content is too low, there is a risk of reduced heat resistance.

In this application, the ethylene content means the mass ratio of ethylene units among all units constituting the ethylene-α-olefin elastomer, and can be measured by a conventional method, but may also be the monomer ratio.

The diene content of the ethylene-α-olefin elastomer (particularly ethylene-α-olefin-diene terpolymer rubber such as EPDM) may be 10% by mass or less (e.g., 0.1 to 10% by mass), is not particularly limited, and the diene content may be 0% by mass, but from the viewpoint of improving heat resistance and lateral pressure resistance, a diene content smaller than the diene content of the ethylene-α-olefin elastomer in the inner surface layer of the compressed rubber layer described below is preferred. By making the diene content of the ethylene-α-olefin elastomer forming the main body of the compressed rubber layer smaller than the diene content of the ethylene-α-olefin elastomer forming the inner surface layer, it is possible to improve heat resistance and lateral pressure resistance.

The preferred diene content may be less than 3.5% by mass (e.g., 1 to 3.4% by mass), more preferably 1.5 to 3.3% by mass, even more preferably 2 to 3.2% by mass, and most preferably 2.5 to 3% by mass. In the present invention, heat resistance is improved by using a rubber component that does not have a double bond in the main chain, but a high level of heat resistance can be ensured by limiting the double bonds due to diene units introduced as side chains to a small amount. If the diene content is too high, there is a risk that a high level of heat resistance cannot be ensured.

In this application, the diene content means the mass ratio of diene monomer units among all units constituting the ethylene-α-olefin elastomer, and can be measured by a conventional method, but may also be the monomer ratio.

The Mooney viscosity [ML(1+4)125°C] of the uncrosslinked ethylene-α-olefin elastomer may be 80 or less, and is, for example, 10 to 80, preferably 20 to 70, more preferably 30 to 60, and most preferably 35 to 50, from the viewpoint of adjusting the Vm of the rubber composition and improving the dispersibility of carbon black. If the Mooney viscosity is too high, the flowability of the rubber composition may decrease, and the processability during kneading may decrease.

In this application, Mooney viscosity can be measured according to JIS K 6300-1 (2013), and the test conditions are as follows: an L-shaped rotor is used, the test temperature is 125°C, preheating is 1 minute, and the rotor operation time is 4 minutes.

The proportion of ethylene-α-olefin elastomer in the rubber composition may be 10% by mass or more, for example, 10 to 80% by mass, preferably 20 to 70% by mass, more preferably 30 to 60% by mass, and even more preferably 40 to 50% by mass. If the proportion of ethylene-α-olefin elastomer in the rubber composition is too small, there is a risk of reduced heat resistance.

(A2) Organic Peroxide In the present invention, by using an organic peroxide as a crosslinking agent (or vulcanizing agent) for the main body of the compressed rubber layer, the rubber hardness can be improved, and the lateral pressure resistance can be improved.

As the organic peroxide, organic peroxides commonly used as crosslinking agents can be used, such as diacyl peroxides (dilauroyl peroxide, dibenzoyl peroxide, etc.), peroxyketals [1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, etc.], alkyl peroxyesters (t-butylperoxybenzoate, etc.), dialkyl peroxides [di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t- butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,3-bis(2-t-butylperoxyisopropyl)benzene, 2,5-di-methyl-2,5-di(benzoylperoxy)hexane, etc., peroxycarbonates (t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethyl-hexyl carbonate, t-amylperoxy-2-ethyl-hexyl carbonate, etc.). These organic peroxides can be used alone or in combination of two or more.

Of these, dialkyl peroxides such as 1,3-bis(2-t-butylperoxyisopropyl)benzene are commonly used.

The proportion of organic peroxide is, for example, 0.2 to 10 parts by mass, preferably 0.5 to 7 parts by mass, further preferably 1 to 5 parts by mass, even more preferably 1.5 to 3 parts by mass, and most preferably 1.5 to 2.5 parts by mass, per 100 parts by mass of ethylene-α-olefin elastomer. If the proportion of organic peroxide is too low, there is a risk of reduced lateral pressure resistance, and if it is too high, there is a risk of reduced flex fatigue resistance.

(A3) Co-Cross-Linking Agent The rubber composition may further contain a co-cross-linking agent in addition to the ethylene-α-olefin elastomer and the organic peroxide.

Examples of co-crosslinking agents (crosslinking assistants or co-vulcanizing agents) include known crosslinking assistants, such as polyfunctional (iso)cyanurates [e.g., triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), etc.], polydienes (e.g., 1,2-polybutadiene, etc.), metal salts of unsaturated carboxylic acids [e.g., (meth)acrylic acid polyvalent metal salts such as zinc (meth)acrylate and magnesium (meth)acrylate], oximes (e.g., quinone dioxime, etc.), guanidines (e.g., diphenyl guanidine, etc.), polyfunctional (meth)acrylates [e.g., alkane diol di(meth)acrylate such as ethylene glycol di(meth)acrylate and butane diol di(meth)acrylate, trimethylol propane tri(meth)acrylate, pentaerythritol tetraacetate, etc.], and the like. alkane polyol poly(meth)acrylates such as tetra(meth)acrylate, bismaleimides (aliphatic bismaleimides such as alkylene bismaleimides such as N,N'-1,2-ethylene dimaleimide, N,N'-hexamethylene bismaleimide, and 1,6'-bismaleimide-(2,2,4-trimethyl)cyclohexane; arene bismaleimides or aromatic bismaleimides such as N,N'-m-phenylene dimaleimide, 4-methyl-1,3-phenylene dimaleimide, 4,4'-diphenylmethane dimaleimide, 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane, 4,4'-diphenylether dimaleimide, 4,4'-diphenylsulfone dimaleimide, and 1,3-bis(3-maleimidophenoxy)benzene, etc.).

These co-crosslinking agents can be used alone or in combination. Of these, metal salts of unsaturated carboxylic acids such as zinc (meth)acrylate are preferred.

The proportion of the co-crosslinking agent is, for example, 0.5 to 40 parts by mass, preferably 1 to 35 parts by mass, more preferably 3 to 30 parts by mass, even more preferably 5 to 25 parts by mass, and most preferably 10 to 20 parts by mass, relative to 100 parts by mass of the ethylene-α-olefin elastomer. If the proportion of the co-crosslinking agent is too low, there is a risk that the lateral pressure resistance will decrease, and if it is too high, there is a risk that the flex fatigue resistance will decrease.

(A4) Short Fiber The rubber composition may further contain short fibers. Examples of short fibers include polyamide short fibers (polyamide 6 short fibers, polyamide 66 short fibers, polyamide 46 short fibers, aramid short fibers, etc.), polyalkylene arylate short fibers (e.g., polyethylene terephthalate (PET) short fibers, polyethylene naphthalate short fibers, etc.), liquid crystal polyester short fibers, polyarylate short fibers (amorphous fully aromatic polyester short fibers, etc.), vinylon short fibers, polyvinyl alcohol short fibers, polyparaphenylene benzobisoxazole (PBO) short fibers, and other synthetic short fibers; natural short fibers such as cotton, hemp, and wool; and inorganic short fibers such as carbon short fibers. These short fibers can be used alone or in combination of two or more. Among these, aramid short fibers and PBO short fibers are preferred, and aramid short fibers are particularly preferred.

The average fiber length of the short fibers is, for example, 0.1 to 20 mm, preferably 0.3 to 15 mm, more preferably 0.5 to 10 mm, more preferably 1 to 5 mm, and most preferably 2 to 4 mm. The average fiber diameter of the short fibers is, for example, 1 to 50 μm, preferably 5 to 30 μm, more preferably 8 to 20 μm, and more preferably 10 to 15 μm.

The short fibers may be subjected to a general-purpose adhesive treatment to increase the adhesive strength with the ethylene-α-olefin elastomer. Examples of such adhesive treatments include immersion in a treatment liquid containing an epoxy compound or a polyisocyanate compound, immersion in an RFL treatment liquid containing resorcinol, formaldehyde, and latex, and immersion in rubber cement. These treatments may be applied alone or in combination of two or more.

The proportion of short fibers is, for example, 5 to 50 parts by mass, preferably 5 to 40 parts by mass, more preferably 8 to 35 parts by mass, even more preferably 10 to 30 parts by mass, and most preferably 20 to 30 parts by mass, per 100 parts by mass of ethylene-α-olefin elastomer.

(A5) Filler The rubber composition may further contain a filler. Examples of the filler include carbon black, silica, clay, calcium carbonate, talc, and mica. The filler often contains a reinforcing filler, and such a reinforcing filler may be carbon black, reinforcing silica, or the like. These fillers may be used alone or in combination of two or more. In the compressed rubber layer, it is preferable that the filler contains at least a reinforcing filler (particularly carbon black) in order to improve the lateral pressure resistance.

The average particle size of the carbon black is, for example, 5 to 200 nm, preferably 10 to 150 nm.
, more preferably 15 to 100 nm. From the viewpoint of high reinforcing effect, a small particle size, for example,
The average particle size is 5 to 38 nm, preferably 10 to 35 nm, and more preferably 15 to 30 nm.
The carbon black having a small particle size may be, for example, SA
Examples of carbon black include ISAF-F, ISAF-HM, ISAF-LM, HAF-LS, HAF, HAF-HS, etc. These carbon blacks can be used alone or in combination.

The proportion of the filler (particularly carbon black) is, for example, 10 to 200 parts by mass, preferably 20 to 150 parts by mass, further preferably 30 to 100 parts by mass, more preferably 50 to 80 parts by mass, and most preferably 60 to 70 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer. If the proportion of the filler is too low, the elastic modulus may be insufficient, resulting in reduced resistance to lateral pressure, whereas if the proportion is too high, the elastic modulus may be too high, resulting in reduced resistance to bending fatigue.

(A6) Other Components The rubber composition may further contain other components. Examples of the other components include other rubber components [diene rubbers such as natural rubber, isoprene rubber, butadiene rubber, chloroprene rubber, styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (nitrile rubber), and hydrogenated nitrile rubber; chlorosulfonated polyethylene rubber, alkylated chlorosulfonated polyethylene rubber, epichlorohydrin rubber, acrylic rubber, silicone rubber, urethane rubber, and fluororubber, etc.], other crosslinking agents, crosslinking accelerators (or vulcanization accelerators), metal oxides (zinc oxide, magnesium oxide, lead oxide, calcium oxide, barium oxide, acid Examples of the additives include iron oxide, copper oxide, titanium oxide, aluminum oxide, etc.), softeners or plasticizers (oils such as paraffin oil and naphthenic oil), processing agents or processing aids (fatty acids such as stearic acid, fatty acid metal salts such as metal stearates, fatty acid amides such as stearic acid amide, wax, paraffin, etc.), ageing inhibitors (antioxidants, heat ageing inhibitors, flex crack inhibitors, ozone degradation inhibitors, etc.), colorants, tackifiers, lubricants, coupling agents (silane coupling agents, etc.), stabilizers (ultraviolet absorbers, heat stabilizers, etc.), flame retardants, and antistatic agents.

These additives can be used alone or in combination. Metal oxides may also act as cross-linking agents.

The total proportion of the other components is, for example, 1 to 50 parts by mass, preferably 5 to 40 parts by mass, more preferably 10 to 30 parts by mass, and even more preferably 15 to 25 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer.

(A7) Characteristics of the Compressed Rubber Layer Main Body The compressed rubber layer main body has a high rubber hardness, and the rubber hardness is, for example, 90 to 99 degrees, preferably 91 to 98 degrees, further preferably 92 to 98 degrees, more preferably 93 to 97 degrees, and most preferably 94 to 96 degrees. If the rubber hardness of the compressed rubber layer main body is too low, there is a risk that the lateral pressure resistance will decrease, and if it is too high, there is a risk that the flexural fatigue resistance and durability will decrease.

In this application, the rubber hardness of each rubber layer refers to the value Hs (JIS A) measured in accordance with the spring hardness test (A type) specified in JIS K6253 (2012) (Vulcanized rubber and thermoplastic rubber - Determination of hardness), and may be referred to simply as rubber hardness.

The average thickness of the compressed rubber layer body can be appropriately selected depending on the type of belt, but is, for example, 0.5 to 12 mm (particularly 1 to 10 mm), preferably 2 to 9 mm (particularly 3 to 8 mm), further preferably 4 to 7 mm (particularly 5 to 6 mm), and even more preferably 4 to 6 mm (most preferably 4 to 5 mm). In this application, when the compressed rubber layer has a cog portion, the thickness of the compressed rubber layer body means the thickness at the top of the cog portion.

(Inner surface layer of compressed rubber layer)
In the present invention, the surface of the compressed rubber layer main body on the inner peripheral side of the belt is covered with a surface layer (inner surface layer) having an average thickness of 0.3 to 3.5 mm, which is formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing diene units and a sulfur-based crosslinking agent. The inner surface layer has a function of improving resistance to bending fatigue, and the combination of the compressed rubber layer main body and the inner surface layer can improve heat resistance, lateral pressure resistance and bending fatigue resistance.

(B1) Ethylene-α-olefin elastomer containing diene units In the rubber composition forming the inner surface layer of the compression rubber layer, the ethylene-α-olefin elastomer contains diene units since it is crosslinked with a sulfur-based crosslinking agent. That is, the ethylene-α-olefin elastomer of the inner surface layer contains ethylene units, α-olefin units, and diene units as constituent units, and may be an ethylene-α-olefin-diene terpolymer rubber.

The α-olefin for forming the α-olefin units can be selected from the α-olefins exemplified in the section on ethylene-α-olefin elastomer (A1) in the compressed rubber layer main body, including preferred embodiments.

The diene monomer for forming the diene units can be selected from the diene monomers exemplified in the section on the ethylene-α-olefin elastomer (A1) in the compressed rubber layer main body, including the preferred embodiments. Ethylidene norbornene is preferred from the standpoint of crosslinking efficiency in sulfur crosslinking.

Typical ethylene-α-olefin elastomers include, for example, ethylene-propylene copolymer (EPM) and ethylene-propylene-diene terpolymer (EPDM).

These ethylene-α-olefin elastomers can be used alone or in combination. Of these, ethylene-propylene-diene terpolymers (EPDM) are preferred.

In the ethylene-propylene-diene terpolymer, the ratio (mass ratio) of ethylene to propylene may be from 35/65 to 90/10, preferably from 40/60 to 80/20, more preferably from 45/55 to 70/30, and most preferably from 50/50 to 60/40.

The ethylene content of ethylene-α-olefin elastomers containing diene units (particularly ethylene-α-olefin-diene terpolymer rubbers such as EPDM) may be 30% by mass or more (e.g., 30 to 80% by mass), preferably 50 to 70% by mass, further preferably 52 to 65% by mass, even more preferably 53 to 60% by mass, and most preferably 54 to 58% by mass. If the ethylene content is too low, there is a risk of reduced heat resistance.

The diene content of the ethylene-α-olefin elastomer containing diene units (particularly ethylene-α-olefin-diene terpolymer rubber such as EPDM) may be higher than the diene content of the ethylene-α-olefin elastomer in the main body of the compressed rubber layer. The diene content of the ethylene-α-olefin elastomer containing diene units may be 3.5% by mass or more, for example, 3.5 to 10% by mass, preferably 3.6 to 6% by mass, more preferably 3.8 to 5.5% by mass, and more preferably 4 to 5% by mass. If the diene content is too low, crosslinking may be insufficient, resulting in a decrease in lateral pressure resistance, and if the diene content is too high, there is a risk of a decrease in heat resistance.

The diene content of the ethylene-α-olefin elastomer forming the inner surface layer may be 1.1 times or more the diene content of the compression rubber layer body, for example 1.1 to 5 times, preferably 1.2 to 3 times, more preferably 1.3 to 2 times, and even more preferably 1.5 to 1.8 times.

The Mooney viscosity of the uncrosslinked ethylene-α-olefin elastomer, including preferred embodiments, can be selected from the viscosities described in the section on the ethylene-α-olefin elastomer (A1) in the compressed rubber layer body.

The proportion of the α-olefin elastomer containing diene units in the rubber composition may be 10% by mass or more, for example, 10 to 80% by mass, preferably 20 to 70% by mass, more preferably 35 to 65% by mass, and even more preferably 45 to 55% by mass. If the proportion of the ethylene-α-olefin elastomer containing diene units in the rubber composition is too low, there is a risk of reduced flex fatigue resistance, and if it is too high, there is a risk of reduced lateral pressure resistance.

(B2) Sulfur-Based Crosslinking Agent In the present invention, by using a sulfur-based crosslinking agent as a crosslinking agent in the inner surface layer of the compressed rubber layer, the hardness of the inner surface layer can be adjusted to be lower than that of the main body of the compressed rubber layer, and the flexural fatigue resistance (crack resistance) can be improved.

Examples of sulfur-based crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, and sulfur chlorides (sulfur monochloride, sulfur dichloride, etc.). These sulfur-based crosslinking agents can be used alone or in combination of two or more. Of these, powdered sulfur is the most commonly used.

The proportion of the sulfur-based crosslinking agent is, for example, 0.1 to 10 parts by mass, preferably 0.2 to 5 parts by mass, further preferably 0.3 to 3 parts by mass (e.g., 0.5 to 2 parts by mass), more preferably 1 to 3 parts by mass (e.g., 0.8 to 1.5 parts by mass), and most preferably 1.5 to 2.5 parts by mass, relative to 100 parts by mass of the ethylene-α-olefin elastomer containing diene units. If the proportion of the sulfur-based crosslinking agent is too low, there is a risk that the lateral pressure resistance will decrease, and if it is too high, there is a risk that the flexural fatigue resistance will decrease.

(B3) Crosslinking Accelerator The rubber composition may further contain a crosslinking accelerator in addition to the ethylene-α-olefin elastomer containing diene units and the sulfur-based crosslinking agent.

Examples of crosslinking accelerators include thiuram accelerators [e.g., tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetrabutylthiuram disulfide (TBTD), dipentamethylenethiuram tetrasulfide (DPTT), N,N'-dimethyl-N,N'-diphenylthiuram disulfide, etc.], thiazole accelerators [e.g., 2-mercaptobenzothiazole, zinc salt of 2-mercaptobenzothiazole, 2-mercaptobenzothiazole, zinc salt of 2-mercaptobenzothiazole, etc.], -mercaptothiazoline, dibenzothiazyl disulfide, 2-(4'-morpholinodithio)benzothiazole, etc.], sulfenamide accelerators [e.g., N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N,N'-dicyclohexyl-2-benzothiazylsulfenamide, etc.], guanidines (diphenylguanidine, di-o-tolylguanidine, etc.), urea or thiourea accelerators (e.g., ethylenethiourea, etc.), dithiocarbamates, xanthogenates, etc. These crosslinking accelerators can be used alone or in combination of two or more. Of these crosslinking accelerators, TMTD, DPTT, CBS, etc. are commonly used.

The proportion of the crosslinking accelerator is, for example, 0.2 to 10 parts by mass, preferably 0.5 to 7 parts by mass, more preferably 1 to 5 parts by mass, even more preferably 1.5 to 3 parts by mass, and most preferably 1.5 to 2.5 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer containing diene units. If the proportion of the crosslinking accelerator is too low, there is a risk of reduced lateral pressure resistance, and if it is too high, there is a risk of reduced flex fatigue resistance.

(B4) Short Fibers The rubber composition may further contain short fibers, which can be selected from the short fibers exemplified in the section on short fibers (A4) in the compressed rubber layer main body, including preferred embodiments.

The proportion of short fibers is, for example, 5 to 50 parts by mass, preferably 5 to 40 parts by mass, more preferably 8 to 35 parts by mass, even more preferably 10 to 30 parts by mass, and most preferably 15 to 25 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer containing diene units.

(B5) Filler The rubber composition may further contain a filler. The filler, including preferred embodiments, can be selected from the fillers exemplified in the section on the filler (A5) in the compressed rubber layer main body.

The proportion of the filler (particularly carbon black) is, for example, 10 to 200 parts by mass, preferably 20 to 150 parts by mass, more preferably 30 to 100 parts by mass, more preferably 50 to 80 parts by mass, and most preferably 60 to 70 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer containing diene units. If the proportion of the filler is too low, the elastic modulus may be insufficient, resulting in reduced resistance to lateral pressure, whereas if the proportion is too high, the elastic modulus may be too high, resulting in reduced resistance to bending fatigue.

(B6) Other Components The rubber composition may further contain other components. In addition to the other components exemplified as the other components (A6) in the compressed rubber layer main body, a co-crosslinking agent and the like can be used as the other components.

The total proportion of the other components is, for example, 1 to 50 parts by mass, preferably 5 to 40 parts by mass, more preferably 8 to 30 parts by mass, and even more preferably 10 to 20 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer containing diene units.

(B7) Characteristics of the Inner Surface Layer of the Compressed Rubber Layer The hardness of the inner surface layer of the compressed rubber layer is, for example, 70 to 95 degrees, preferably 80 to 94 degrees, further preferably 85 to 94 degrees (e.g., 85 to 93 degrees), and more preferably 90 to 94 degrees (most preferably 92 to 94 degrees). If the rubber hardness of the inner surface layer is too low, there is a risk of reduced lateral pressure resistance, and if it is too high, there is a risk of reduced flexural fatigue resistance.

The difference in rubber hardness between the main body of the compressed rubber layer and the inner surface layer (rubber hardness of the main body of the compressed rubber layer - rubber hardness of the inner surface layer) is, for example, 0 to 30 degrees, preferably 3 to 20 degrees, more preferably 5 to 15 degrees, more preferably 6 to 10 degrees, and most preferably 7 to 9 degrees. In applications where lateral pressure resistance and durability are important, the difference may be, for example, 1 to 10 degrees, preferably 1 to 5 degrees, and more preferably 1 to 3 degrees. If the difference in rubber hardness between the main body of the compressed rubber layer and the inner surface layer is too small, there is a risk that bending fatigue resistance will decrease, and conversely, if it is too large, there is a risk that lateral pressure resistance will decrease.

The average thickness of the inner surface layer is 0.3 to 3.5 mm (particularly 0.5 to 3.5 mm), preferably 0.5 to 3 mm, more preferably 0.6 to 3 mm, more preferably 0.7 to 1.5 mm, and most preferably 0.8 to 1.2 mm. In applications where durability is important, the average thickness is, for example, 0.5 to 5 mm, preferably 1 to 3 mm, more preferably 1.5 to 2.5 mm, and more preferably 1.8 to 2.2 mm. If the inner surface layer is too thin, it may be difficult to adjust the rubber sheet, reducing productivity and decreasing bending fatigue resistance, while if it is too thick, there is a risk of decreasing lateral pressure resistance.

In this application, the average thickness of the inner surface layer can be measured using a microscope, and in detail, can be measured by the method described in the examples below.

The average thickness of the inner surface layer is, for example, 2 to 44% (particularly 3 to 30%), preferably 4 to 25%, further preferably 5 to 20%, more preferably 6 to 20% (e.g. 6 to 15%), and most preferably 7 to 20% (e.g. 7 to 12%) of the total belt thickness, and from the standpoint of durability, is preferably 10 to 25% (particularly 15 to 20%).

[Tension rubber layer]
The tension rubber layer may be formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer, and the crosslinking agent may be an organic peroxide or a sulfur-based crosslinking agent. Of these, a sulfur-based crosslinking agent is preferred from the viewpoint of durability. Furthermore, the layer structure of the tension rubber layer is not particularly limited, and may be a single-layer structure or a two-layer structure. A single-layer structure is preferred from the viewpoint of reducing the number of steps and improving the productivity of the belt, and a two-layer structure is preferred from the viewpoint of suppressing cracks on the back surface of the belt.

When the tension rubber layer has a single-layer structure, the tension rubber layer may be formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing a diene unit and a sulfur-based crosslinking agent, or may be formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide. Of these, from the viewpoint of durability, it is preferable that the tension rubber layer is formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing a diene unit and a sulfur-based crosslinking agent. The rubber composition forming the tension rubber layer of the single-layer structure can be selected from the rubber compositions exemplified in the section on the inner surface layer of the compression rubber layer, including preferred embodiments. The rubber composition forming the tension rubber layer of the single-layer structure may be a different rubber composition from the rubber composition forming the inner surface layer of the compression rubber layer, or may be the same rubber composition. From the viewpoint of productivity, etc., the same rubber composition is preferable. The hardness of the tension rubber layer may be, for example, 70 to 95 degrees, preferably 80 to 93 degrees, and more preferably 85 to 90 degrees.

The average thickness of the single-layered tension rubber layer can be selected from the range of about 0.5 to 6 mm (particularly 1 to 4 mm) depending on the type of belt. In the case of a low-edge double-cogged belt, it may be, for example, 2 to 6 mm, preferably 2.5 to 5 mm, and more preferably 3 to 4 mm, and in the case of a low-edge cogged belt, it may be 0.5 to 3 mm, preferably 0.8 to 2.5 mm, and more preferably 1 to 2 mm.

When the tension rubber layer has a two-layer structure, the tension rubber layer may have a two-layer structure consisting of a main body of the tension rubber layer formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide, and a surface layer (outer surface layer) that covers the outer peripheral surface of the main body and is formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing diene units and a sulfur-based crosslinking agent. By adjusting the tension rubber layer to have such a two-layer structure, in combination with the two-layer compressed rubber layer, it is possible to suppress not only the occurrence of cracks on the inner peripheral surface but also the occurrence of cracks on the outer peripheral surface, thereby further improving the durability of the low-edge type V-belt.

The rubber composition forming the main body of the tension rubber layer (tension rubber layer main body), including the preferred embodiments, can be selected from the rubber compositions exemplified in the section on the main body of the compressed rubber layer. The rubber composition forming the tension rubber layer main body may be a different rubber composition from the rubber composition forming the compressed rubber layer main body, or it may be the same rubber composition. From the standpoint of productivity, etc., it is preferable that the rubber composition be the same.

The average thickness of the tension rubber layer body is, for example, 0.5 to 5.5 mm, preferably 1 to 4 mm, more preferably 1.5 to 3 mm, and even more preferably 2 to 3 mm.

The rubber composition forming the outer surface layer of the tension rubber layer, including the preferred embodiments, can be selected from the rubber compositions exemplified in the section on the inner surface layer of the compression rubber layer. The rubber composition forming the outer surface layer of the tension rubber layer may be a different rubber composition from the rubber composition forming the inner surface layer of the compression rubber layer, or may be the same rubber composition. From the standpoint of productivity, etc., it is preferable that the rubber composition be the same.

The average thickness of the outer surface layer of the tension rubber layer is 0.3 to 3.5 mm, preferably 0.5 to 3.5 mm, more preferably 0.6 to 3 mm (particularly 1 to 2 mm), even more preferably 0.7 to 1.5 mm, and most preferably 0.8 to 1.2 mm. If the thickness of the outer surface layer is too thin, there is a risk of reduced resistance to bending fatigue, and if it is too thick, there is a risk of reduced resistance to lateral pressure and durability.

The hardness of the outer surface layer of the tension rubber layer is, for example, 70 to 95 degrees, preferably 80 to 94 degrees, more preferably 85 to 94 degrees (e.g., 85 to 93 degrees), and even more preferably 90 to 94 degrees (most preferably 92 to 94 degrees). If the rubber hardness of the outer surface layer is too low, there is a risk of reduced resistance to lateral pressure, and if it is too high, there is a risk of reduced resistance to bending fatigue.

The difference in rubber hardness between the tension rubber layer main body and the outer surface layer (rubber hardness of the tension rubber layer main body - rubber hardness of the outer surface layer) is, for example, 0 to 30 degrees, preferably 3 to 20 degrees, more preferably 5 to 15 degrees, more preferably 6 to 10 degrees, and most preferably 7 to 9 degrees. In applications where lateral pressure resistance and durability are important, the difference may be, for example, 1 to 10 degrees, preferably 1 to 5 degrees, and more preferably 1 to 3 degrees. If the difference in rubber hardness between the tension rubber layer main body and the outer surface layer is too small, there is a risk of reduced flex fatigue resistance, and conversely, if it is too large, there is a risk of reduced lateral pressure resistance and durability.

[Adhesive rubber layer]
The low-edge type V-belt of the present invention may not include an adhesive rubber layer, but it is preferable that the V-belt includes an adhesive rubber layer, since it can increase the adhesive strength between the core and the compression rubber layer main body, and between the core and the tension rubber layer (or the tension rubber layer main body) and suppress peeling between the core and the layer. The adhesive rubber layer may be formed of a rubber composition containing an ethylene-α-olefin elastomer and a crosslinking agent.

(C1) Ethylene-α-olefin elastomer The ethylene-α-olefin elastomer can be selected from the ethylene-α-olefin elastomers exemplified in the section on the ethylene-α-olefin elastomer (A1) in the main body of the compressed rubber layer, including the preferred embodiments.

The proportion of ethylene-α-olefin elastomer in the rubber composition may be 10% by mass or more, for example, 10 to 80% by mass, preferably 20 to 70% by mass, more preferably 30 to 60% by mass, and even more preferably 45 to 55% by mass. If the proportion of ethylene-α-olefin elastomer in the rubber composition is too low, there is a risk of reduced flex fatigue resistance, and if it is too high, there is a risk of reduced lateral pressure resistance.

(C2) Crosslinking agent As the crosslinking agent, the organic peroxides exemplified in the section on organic peroxides (A2) in the main body of the compressed rubber layer, and the sulfur-based crosslinking agents exemplified in the section on sulfur-based crosslinking agents (B2) in the inner surface layer of the compressed rubber layer can be used. These crosslinking agents can be used alone or in combination of two or more. Among these, organic peroxides are preferred.

The proportion of the crosslinking agent is, for example, 0.2 to 10 parts by mass, preferably 0.5 to 7 parts by mass, more preferably 1 to 5 parts by mass, even more preferably 1.5 to 3 parts by mass, and most preferably 1.5 to 2.5 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer. If the proportion of the crosslinking agent is too low, there is a risk that the lateral pressure resistance will decrease, and if it is too high, there is a risk that the flex fatigue resistance will decrease.

(C3) Co-crosslinking agent or crosslinking accelerator As the co-crosslinking agent, the co-crosslinking agent exemplified in the section on the co-crosslinking agent (A3) in the main body of the compressed rubber layer can be used. As the crosslinking accelerator, the crosslinking accelerator exemplified in the section on the crosslinking accelerator (B3) in the inner surface layer of the compressed rubber layer can be used. These co-crosslinking agents and crosslinking accelerators can be used alone or in combination of two or more. Among these, the co-crosslinking agent is preferred, and a metal salt of an unsaturated carboxylic acid such as zinc (meth)acrylate is particularly preferred.

The total proportion of the co-crosslinking agent and crosslinking accelerator is, for example, 0.2 to 10 parts by mass, preferably 0.5 to 7 parts by mass, more preferably 1 to 5 parts by mass, even more preferably 1.5 to 3 parts by mass, and most preferably 1.5 to 2.5 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer. If the proportion is too low, the lateral pressure resistance may decrease, and if the proportion is too high, the flexural fatigue resistance may decrease.

(C4) Filler The rubber composition may further contain a filler. Examples of the filler include carbon black, silica, clay, calcium carbonate, talc, and mica. These fillers may be used alone or in combination of two or more. Among these, a combination of carbon black and silica is preferred.

The carbon black can be selected from the carbon blacks exemplified in the section on filler (A5) in the compressed rubber layer body, including preferred embodiments.

Silica includes dry silica, wet silica, surface-treated silica, etc. Silica can also be classified according to the manufacturing method, for example, into dry method white carbon, wet method white carbon, colloidal silica, precipitated silica, gel method silica (silica gel), etc. These silicas can be used alone or in combination of two or more. Of these, wet method white carbon, which is mainly composed of hydrated silica, is preferred because it has many surface silanol groups and has a strong chemical bond with rubber.

The average particle size of the silica is, for example, 1 to 1000 nm, preferably 3 to 300 nm, more preferably 5 to 100 nm, and even more preferably 10 to 50 nm. If the silica particle size is too large, the mechanical properties of the adhesive rubber layer may be reduced, and if it is too small, it may be difficult to disperse uniformly.

The silica may be either non-porous or porous, but the nitrogen adsorption specific surface area measured by the BET method is, for example, 50 to 400 m ² /g, preferably 70 to 350 m ² /g, more preferably 100 to 300 m ² /g, and even more preferably 150 to 250 m ² /g. If the specific surface area is too large, it may be difficult to disperse uniformly, and if the specific surface area is too small, the mechanical properties of the adhesive rubber layer may be reduced.

The proportion of carbon black is, for example, 5 to 100 parts by mass, preferably 10 to 80 parts by mass, more preferably 15 to 50 parts by mass, and even more preferably 20 to 40 parts by mass, per 100 parts by mass of silica. If the proportion of silica is too low, there is a risk that the effect of improving adhesion will not be achieved.

The proportion of the filler is, for example, 10 to 200 parts by mass, preferably 20 to 150 parts by mass, more preferably 30 to 100 parts by mass, more preferably 50 to 80 parts by mass, and most preferably 60 to 70 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer. If the proportion of the filler is too low, the elastic modulus may be insufficient, resulting in reduced resistance to lateral pressure, whereas if the proportion is too high, the elastic modulus may be too high, resulting in reduced resistance to bending fatigue.

(C5) Adhesion Improver The rubber composition may further contain an adhesion improver. Examples of the adhesion improver include resorcinol-formaldehyde co-condensates (RF condensates), amino resins (condensates of nitrogen-containing cyclic compounds and formaldehyde, e.g., melamine resins such as hexamethylol melamine, hexaalkoxymethyl melamine (hexamethoxymethyl melamine, hexabutoxymethyl melamine, etc.), urea resins such as methylol urea, benzoguanamine resins such as methylol benzoguanamine resin, etc.), and co-condensates thereof (resorcinol-melamine-formaldehyde co-condensates, etc.).

These adhesion improvers can be used alone or in combination. Of these, hexaalkoxymethylmelamines such as hexamethoxymethylmelamine are preferred.

The proportion of the adhesion improver is, for example, 0.3 to 20 parts by mass, preferably 0.5 to 10 parts by mass, further preferably 1 to 7 parts by mass, even more preferably 1.5 to 5 parts by mass, and most preferably 2 to 4 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer. If the proportion of the adhesion improver is too low, there is a risk that the effect of improving adhesion will not be achieved, and if it is too high, there is a risk that the lateral pressure resistance will decrease.

(C6) Other Components The rubber composition may further contain other components. As the other components, the other components exemplified as the other components (A6) in the compressed rubber layer main body can be used.

The total proportion of the other components is, for example, 1 to 50 parts by mass, preferably 5 to 40 parts by mass, more preferably 10 to 30 parts by mass, and even more preferably 20 to 25 parts by mass, per 100 parts by mass of the ethylene-α-olefin elastomer.

(C7) Characteristics of the Adhesive Rubber Layer The adhesive rubber layer preferably has a lower hardness than the main body of the compressed rubber layer, and more preferably has a lower hardness than the inner surface layer of the compressed rubber layer (or the outer surface layer of the tension rubber layer). By adjusting the adhesive rubber layer to such a low hardness, it becomes possible for it to deform significantly when a shear stress acts on it, and peeling between the core body and the main body of the compressed rubber layer and the main body of the tension rubber layer can be suppressed.

The rubber hardness of the adhesive rubber layer is, for example, 60 to 85 degrees, preferably 65 to 84 degrees, more preferably 70 to 83 degrees, and even more preferably 75 to 82 degrees. If the rubber hardness is too low, there is a risk of reduced resistance to lateral pressure, and if it is too high, there is a risk of reduced adhesion.

The difference in rubber hardness between the main body of the compressed rubber layer and the adhesive rubber layer (rubber hardness of the main body of the compressed rubber layer - rubber hardness of the adhesive rubber layer) may be 5 degrees or more, for example, 5 to 30 degrees, preferably 8 to 25 degrees, further preferably 10 to 23 degrees, more preferably 12 to 20 degrees, and most preferably 13 to 17 degrees. If the difference in rubber hardness between the main body of the compressed rubber layer and the adhesive rubber layer is too small, there is a risk that the heat resistance, lateral pressure resistance, and flexural fatigue resistance cannot be improved, and conversely, if it is too large, there is a similar risk.

The average thickness of the adhesive rubber layer is, for example, 0.8 to 3 mm, preferably 1.2 to 2.8 mm, and more preferably 1.5 to 2.5 mm.

[Core body]
The core body is not particularly limited, but usually, a cord (twisted cord) arranged at a predetermined interval in the belt width direction can be used. The cord is arranged extending in the longitudinal direction of the belt, and usually, the cord is arranged extending in parallel with the longitudinal direction of the belt at a predetermined pitch. The cord may be in any of the following forms as long as at least a part of the cord is in contact with the adhesive rubber layer: the cord is embedded in the adhesive rubber layer, the cord is embedded between the adhesive rubber layer and the tension rubber layer, and the cord is embedded between the adhesive rubber layer and the compression rubber layer. Of these, the cord is preferably embedded in the adhesive rubber layer from the viewpoint of improving durability.

As the fibers constituting the core wire, the short fibers exemplified in the section on short fibers (A4) in the compressed rubber layer body can be used. Among the above-mentioned fibers, from the viewpoint of high modulus, polyester fibers (polyalkylene arylate fibers) whose main constituent unit is C _2-4 alkylene arylate such as ethylene terephthalate and ethylene-2,6-naphthalate, synthetic fibers such as aramid fibers, inorganic fibers such as carbon fibers, etc. are generally used, and polyester fibers (polyethylene terephthalate fibers, polyethylene naphthalate fibers, etc.) and polyamide fibers are preferred. The fibers may be used in the form of multifilament yarns. The fineness of the multifilament yarns may be, for example, about 2000 to 10000 dtex (particularly 4000 to 8000 dtex). The multifilament yarns may contain, for example, 100 to 5000 filaments, preferably 500 to 4000 filaments, and more preferably about 1000 to 3000 filaments.

The core wire can usually be a twisted cord (e.g., double twist, single twist, Lang twist, etc.) using multifilament yarn. The average wire diameter of the core wire (diameter of the twisted cord) can be, for example, 0.5 to 3 mm, preferably 0.6 to 2 mm, and more preferably about 0.7 to 1.5 mm.

The core wire may be adhesively treated (or surface treated) in the same manner as the short fibers to improve adhesion to the rubber component. It is preferable to adhesively treat the core wire with at least RFL liquid.

[Reinforcing fabric]
The low-edge type V-belt of the present invention has excellent resistance to bending fatigue even without a reinforcing cloth because the inner surface layer of the compressed rubber layer enhances the resistance to bending fatigue. Therefore, in the present invention, the number of steps can be reduced without providing a reinforcing cloth, and productivity can be improved. On the other hand, the inner surface layer and the tensile rubber layer may be further combined with a reinforcing cloth to further improve the resistance to bending fatigue.

When the low-edge type V-belt of the present invention includes a reinforcing cloth, the reinforcing cloth may be laminated on both the compressed rubber layer and the tension rubber layer (or on the cogs when the cogs are formed integrally with the compressed rubber layer) (the inner circumferential surface of the compressed rubber layer and the outer circumferential surface of the tension rubber layer), the reinforcing cloth may be laminated on the surface of either the compressed rubber layer or the tension rubber layer, or the reinforcing layer may be embedded in the compressed rubber layer and/or the tension rubber layer (such as the form described in JP 2010-230146 A). The reinforcing cloth is often laminated on the surface of at least one of the compressed rubber layer and the tension rubber layer (the inner circumferential surface of the compressed rubber layer and the outer circumferential surface of the tension rubber layer), for example, on both the inner circumferential surface (lower surface) of the compressed rubber layer and the outer circumferential surface (upper surface) of the tension rubber layer.

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

[Manufacturing method of raw edge type V-belt]
The method for producing the raw edge type V-belt of the present invention is not particularly limited, and for the lamination process of each layer (the method for producing the belt sleeve), a conventional method can be used depending on the type of belt.

For example, a typical method for manufacturing a cogged V-belt is as follows: first, a laminate of a sheet for the inner surface layer of the compressed rubber layer (uncrosslinked rubber sheet) and a sheet for the main body of the compressed rubber layer (uncrosslinked rubber sheet) is placed in contact with a flat cog-equipped mold in which teeth and grooves are alternately arranged, and the inner surface layer sheet is pressed at a temperature of about 60 to 120°C (particularly 80 to 100°C) to produce a cog pad (a pad that is not completely crosslinked, but is in a semi-crosslinked state) with shaped cogs. Both ends of this cog pad may be cut vertically at appropriate points (particularly the tops of the cog peaks). Furthermore, a cylindrical mold may be covered with an inner matrix having alternating tooth and groove portions, and a cog pad may be wound around the inner matrix by engaging the tooth and groove portions and joining both ends (particularly the tops of the cog peaks). A second adhesive rubber layer sheet (lower adhesive rubber: uncrosslinked rubber sheet) may then be laminated on top of the wound cog pad. The core wire (twisted cord) that forms the core body may then be spun helically, and the first adhesive rubber layer sheet (upper adhesive rubber: uncrosslinked rubber sheet) and the tension rubber layer sheet (uncrosslinked rubber sheet) may then be wound on top of the first adhesive rubber layer sheet in sequence to produce a molded body.

Then, a jacket is placed over the molded body, the mold is placed in a vulcanizer, and crosslinked at a temperature of about 120 to 200°C (particularly 150 to 180°C) to prepare a belt sleeve. After that, it may be cut into a V shape using a cutter or the like.

The adhesive rubber layer can be formed from multiple adhesive rubber layer sheets, and the core wire (twisted cord) that forms the core body can be spun in association with the stacking order of the multiple adhesive rubber layer sheets depending on the embedding position in the adhesive rubber layer. Also, as mentioned above, it is not necessary to form cogs, and reinforcing cloth (lower cloth and upper cloth) can be further stacked.

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 are shown below.

[Materials used]
EPDM1: "EP93" manufactured by JSR Corporation, ethylene content 55% by mass, diene content 2.7% by mass
EPDM2: "EP24" manufactured by JSR Corporation, ethylene content 54% by mass, diene content 4.5% by mass
Short fibers (para-aramid short fibers): "Twaron (registered trademark)" manufactured by Teijin Limited, average fiber diameter 14 μm, average fiber length 3 mm
Carbon black: "Show Black N550" manufactured by Cabot Japan Co., Ltd.
Silica: "Ultrasil VN-3" manufactured by Evonik Degussa Japan Ltd., specific surface area 155 to 195 m ² /g
Plasticizer (paraffin oil): "Diana Process Oil PW90" manufactured by Idemitsu Kosan Co., Ltd.
Zinc oxide: "Zinc oxide type 2" manufactured by Sakai Chemical Industry Co., Ltd., average particle size 0.55 μm
Stearic acid: "Camellia Stearate" manufactured by NOF Corporation
Magnesium oxide: Kyowa Mag 150 manufactured by Kyowa Chemical Industry Co., Ltd.
Antioxidant: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine ("Nocrac CD" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
Co-crosslinking agent: zinc methacrylate ("Sunester SK-30" manufactured by Sanshin Chemical Industry Co., Ltd.)
Organic peroxide: 1,3-bis(t-butylperoxyisopropyl)benzene, theoretical active oxygen content 9.45%
Sulfur: "Sulfur" manufactured by Bigen Chemical Co., Ltd.
Crosslinking accelerator: Tetramethylthiuram disulfide ("Noccela TT" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
Adhesion improver (hexamethoxymethylmelamine): "POWERPLAST PP-1890S" manufactured by Singh Plasticisers & Resins Pvt. Ltd.
Core wire: A treated cord made by plying 1100 dtex PET multifilament yarn in a 2 x 3 twist configuration with a top twist factor of 3.0 and a bottom twist factor of 3.0 to create a twisted cord with a total fineness of 6600 dtex, which has been subjected to an adhesive treatment.

[Formation of rubber layer]
The rubber compositions in Table 1 were kneaded using a known method such as a Banbury mixer, and the kneaded rubber was passed through a calendar roll to produce a rolled rubber sheet (uncrosslinked rubber sheet). The short fibers were adhesively treated with an RFL liquid (containing resorcinol and formaldehyde, and vinylpyridine-styrene-butadiene rubber latex as a latex), and short fibers with a solid adhesion rate of 6% by mass were used. As the RFL liquid, 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, and 29.0 parts by mass of water were used.

[Production of Raw Edge Double Cogged V-Belt]
A flat cog-equipped mold in which convex portions and concave portions are alternately arranged was laminated with an uncrosslinked rubber sheet forming the inner surface layer of the compressed rubber layer and an uncrosslinked rubber sheet forming the main body of the compressed rubber layer, and then pressed under heating at 100 ° C to prepare a semi-crosslinked cog pad with a cog portion formed. An inner mold in which convex portions and concave portions are alternately arranged was placed over a cylindrical mold, and the cog pad was wrapped around the inner mold and attached by joining both ends. An uncrosslinked rubber sheet (R3) forming an adhesive rubber layer was wound around the attached cog pad, and then the core wire was spun in a spiral shape. An uncrosslinked rubber sheet (R3) forming an adhesive rubber layer and an uncrosslinked rubber sheet forming a tension rubber layer were further wound around the core wire to form a molded body. An outer mold and a flexible jacket for forming a cog shape on the outer periphery of the belt were placed over this molded body, and the mold was placed in a vulcanizing can and crosslinked at a temperature of 170 ° C for 40 minutes to obtain a belt sleeve. This belt sleeve was cut into a V shape with a cutter to produce a low-edge double-cogged V-belt (size: upper width 20 mm, thickness (distance from inner cog crest to outer cog crest) 12 mm, V angle 30 degrees, cog height (inner side) 4.5 mm, cog height (outer side) 3 mm, belt outer length 650 mm), which is a variable speed belt having cogs on the inner and outer sides of the belt.

[Manufacture of Raw Edge Cogged V-Belt]
In the case of producing a raw edge cogged V-belt having cogs only on the inner peripheral surface and no cogs on the outer peripheral surface, the same procedure as for producing a raw edge double cogged V-belt was used except that the molded body was covered only with a flexible jacket without covering it with an outer matrix. The size of the raw edge cogged V-belt was an upper width of 19 mm, a thickness (distance from the inner cog crest to the outer periphery of the belt) of 10 mm, a V angle of 30 degrees, a cog height (inner peripheral side) of 4.5 mm, and a belt outer peripheral length of 640 mm.

[Measurement of thickness of inner and outer surface layers]
The raw edge cogged V-belt was cut parallel to the belt width direction at the cog top, and the cross section was observed under a microscope at 20 times magnification to measure the thickness of the inner surface layer and the outer surface layer. The thickness was measured at five points so as to divide the belt length into about five equal parts, and the arithmetic average was taken as the thickness of the inner surface layer and the outer surface layer of the belt. Note that the cut points of the raw edge V-belt that does not have a cog portion on the inner and outer peripheral sides of the belt are not limited to the cog tops, but are five points so as to divide the belt length into about five equal parts.

[Durability test]
The durability running test was performed using a biaxial running test machine equipped with a driving (DR) pulley 22 with a diameter of φ100 mm and a driven (DN) pulley 23 with a diameter of φ80 mm, as shown in FIG. 4. A V-belt 21 was hung on each pulley with an axial load of 0.6 kN, and the belt was run at an ambient temperature of 100°C until the end of its life. The rotation speed of the driving pulley was constant at 7,000 rpm for 0 to 20 seconds, fluctuated between 7,000±350 rpm for 20 to 40 seconds, and was again constant at 7,000 rpm for 40 to 60 seconds, and the load on the driven pulley was 15 Nm. This cycle of 60 seconds was repeated until the end of the test.

[Example 1]
A rubber composition (R1) containing an organic peroxide was used as the tension rubber layer, a rubber composition (R1) containing an organic peroxide was used as the main body of the compression rubber layer, and a rubber composition (R2) containing sulfur was used as the inner surface layer of the compression rubber layer, and a raw edge double cogged V-belt was manufactured in which the tension rubber layer had a single layer structure and the compression rubber layer had a two layer structure. In the obtained belt, the main body of the compression rubber layer had a thickness of 6.2 mm, the inner surface layer had a thickness of 0.3 mm, and the tension rubber layer had a thickness of 3.5 mm.

[Example 2]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 1, except that the thickness of the main body of the compressed rubber layer in the obtained belt was changed to 6.0 mm, and the thickness of the inner surface layer was changed to 0.5 mm. That is, in the obtained belt, the thickness of the main body of the compressed rubber layer was 6.0 mm, the thickness of the inner surface layer was 0.5 mm, and the thickness of the tension rubber layer was 3.5 mm.

[Example 3]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 1, except that the thickness of the main body of the compressed rubber layer in the obtained belt was changed to 5.5 mm and the thickness of the inner surface layer was changed to 1.0 mm. That is, in the obtained belt, the thickness of the main body of the compressed rubber layer was 5.5 mm, the thickness of the inner surface layer was 1.0 mm, and the thickness of the tension rubber layer was 3.5 mm.

[Example 4]
A raw edge double cogged V-belt having a two-layer structure in both the tension rubber layer and the compression rubber layer was manufactured in the same manner as in Example 3, except that the main body of the tension rubber layer was made of a rubber composition (R1) containing an organic peroxide, and the outer surface layer of the tension rubber layer was made of a rubber composition (R2) containing sulfur. In the obtained belt, the main body of the compression rubber layer had a thickness of 5.5 mm, the inner surface layer had a thickness of 1.0 mm, the main body of the tension rubber layer had a thickness of 3.0 mm, and the outer surface layer had a thickness of 0.5 mm.

[Example 5]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 4, except that the thickness of the main body of the tension rubber layer in the obtained belt was changed to 2.5 mm and the thickness of the outer surface layer was changed to 1.0 mm. That is, in the obtained belt, the thickness of the main body of the compression rubber layer was 5.5 mm, the thickness of the inner surface layer was 1.0 mm, the thickness of the main body of the tension rubber layer was 2.5 mm, and the thickness of the outer surface layer was 1.0 mm.

[Example 6]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 5, except that the thickness of the main body of the compressed rubber layer was changed to 4.5 mm and the thickness of the inner surface layer was changed to 2.0 mm. That is, in the obtained belt, the thickness of the main body of the compressed rubber layer was 4.5 mm, the thickness of the inner surface layer was 2.0 mm, the thickness of the main body of the tension rubber layer was 2.5 mm, and the thickness of the outer surface layer was 1.0 mm.

[Example 7]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 5, except that the thickness of the main body of the compressed rubber layer was changed to 3.5 mm and the thickness of the inner surface layer was changed to 3.0 mm. That is, in the obtained belt, the thickness of the main body of the compressed rubber layer was 3.5 mm, the thickness of the inner surface layer was 3.0 mm, the thickness of the main body of the tension rubber layer was 2.5 mm, and the thickness of the outer surface layer was 1.0 mm.

[Example 8]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 4, except that the thickness of the tension rubber layer was changed to 1.5 mm and the thickness of the outer surface layer was changed to 2.0 mm. That is, in the obtained belt, the thickness of the compression rubber layer was 5.5 mm, the thickness of the inner surface layer was 1.0 mm, the thickness of the tension rubber layer was 1.5 mm, and the thickness of the outer surface layer was 2.0 mm.

[Comparative Example 1]
A rubber composition (R1) containing an organic peroxide was used as the tension rubber layer, and a rubber composition (R1) containing an organic peroxide was used as the compression rubber layer, to produce a raw edge double cogged V-belt in which the tension rubber layer and the compression rubber layer both have a single layer structure.

[Comparative Example 2]
A rubber composition (R2) containing sulfur was used for the tension rubber layer, and a rubber composition (R2) containing sulfur was used for the compression rubber layer, to produce a raw edge double cogged V-belt in which the tension rubber layer and the compression rubber layer both have a single layer structure.

[Comparative Example 3]
A raw edge double cogged V-belt was manufactured in which the tension rubber layer was made of a rubber composition (R1) containing an organic peroxide, the main body of the compression rubber layer was made of a rubber composition (R2) containing sulfur, and the inner surface layer of the compression rubber layer was made of a rubber composition (R1) containing an organic peroxide, and the tension rubber layer had a single layer structure and the compression rubber layer had a two layer structure. That is, in Example 3, the rubber compositions of the main body and the inner surface layer of the compression rubber layer were interchanged.

[Comparative Example 4]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 5, except that the thickness of the inner surface layer of the compressed rubber layer was changed to 4.0 mm. That is, in the obtained belt, the main body thickness of the compressed rubber layer was 2.5 mm, the inner surface layer thickness was 4.0 mm, the main body thickness of the tension rubber layer was 2.5 mm, and the outer surface layer thickness was 1.0 mm.

[Example 9]
A raw edge double cogged V-belt was produced in the same manner as in Example 3, except that a rubber composition (R2) containing sulfur was used as the tension rubber layer. That is, in the obtained belt, the main body thickness of the compression rubber layer was 5.5 mm, the inner surface layer thickness was 1.0 mm, and the tension rubber layer thickness was 3.5 mm.

[Example 10]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 6, except that a rubber composition (R6) containing sulfur and having a rubber hardness lower than that of the rubber composition (R2) was used as the outer surface layer of the tension rubber layer and the inner surface layer of the compression rubber layer. That is, in the obtained belt, the thickness of the main body of the compression rubber layer was 4.5 mm, the thickness of the inner surface layer was 2.0 mm, the thickness of the main body of the tension rubber layer was 2.5 mm, and the thickness of the outer surface layer was 1.0 mm.

[Example 11]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 6, except that a rubber composition (R7) containing sulfur and having a rubber hardness greater than that of the rubber composition (R2) was used as the outer surface layer of the tension rubber layer and the inner surface layer of the compression rubber layer. That is, in the obtained belt, the main body of the compression rubber layer had a thickness of 4.5 mm, the inner surface layer had a thickness of 2.0 mm, the main body of the tension rubber layer had a thickness of 2.5 mm, and the outer surface layer had a thickness of 1.0 mm.

[Example 12]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 6, except that a rubber composition (R8) containing sulfur and having a rubber hardness greater than that of the rubber composition (R7) was used as the outer surface layer of the tension rubber layer and the inner surface layer of the compression rubber layer. That is, in the obtained belt, the main body of the compression rubber layer had a thickness of 4.5 mm, the inner surface layer had a thickness of 2.0 mm, the main body of the tension rubber layer had a thickness of 2.5 mm, and the outer surface layer had a thickness of 1.0 mm.

[Example 13]
A raw edge double cogged V-belt was produced in the same manner as in Example 11, except that a rubber composition (R4) containing an organic peroxide and having a rubber hardness lower than that of the rubber composition (R1) was used as the main body of the tension rubber layer and the main body of the compression rubber layer. That is, in the obtained belt, the main body of the compression rubber layer had a thickness of 4.5 mm, the inner surface layer had a thickness of 2.0 mm, the main body of the tension rubber layer had a thickness of 2.5 mm, and the outer surface layer had a thickness of 1.0 mm.

[Example 14]
A raw edge double cogged V-belt was manufactured in the same manner as in Example 11, except that a rubber composition (R5) containing an organic peroxide and having a rubber hardness greater than that of the rubber composition (R1) was used as the main body of the tension rubber layer and the main body of the compression rubber layer. That is, in the obtained belt, the main body of the compression rubber layer had a thickness of 4.5 mm, the inner surface layer had a thickness of 2.0 mm, the main body of the tension rubber layer had a thickness of 2.5 mm, and the outer surface layer had a thickness of 1.0 mm.

[Example 15]
A raw-edge cogged V-belt was manufactured in the same manner as in Example 9, except that the belt shape was a raw-edge cogged V-belt. That is, in the obtained belt, the main body of the compressed rubber layer had a thickness of 5.5 mm, the inner surface layer had a thickness of 1.0 mm, and the tension rubber layer had a thickness of 1.5 mm.

The evaluation results of the raw edge type V-belts obtained in Examples 1 to 15 and Comparative Examples 1 to 4 are shown in Tables 2 and 3.

Examples 1 to 15 had a lifespan of 90 hours or more in a durability running test at high temperatures. The reason for this is thought to be that the main body of the compressed rubber layer is formed from a cured product of a rubber composition containing an organic peroxide, and the inner surface layer of the compressed rubber layer is formed from a cured product of a rubber composition containing sulfur, which allows both lateral pressure resistance and flex fatigue resistance to be achieved.

In contrast, in Comparative Example 1, where the compressed rubber layer does not have an inner surface layer, cracks occurred in the compressed rubber layer due to insufficient flex fatigue resistance. In Comparative Example 2, where the entire compressed rubber layer is formed from a cured product of a rubber composition containing sulfur, pop-out (a phenomenon in which the core wire protrudes from the side of the belt) occurred, possibly due to reduced lateral pressure resistance. In Comparative Example 3, where the inner surface layer of the compressed rubber layer is formed from a cured product of a rubber composition containing an organic peroxide, cracks occurred in the compressed rubber layer due to insufficient flex fatigue resistance. In Comparative Example 4, where the main body of the compressed rubber layer is formed from a cured product of a rubber composition containing organic peroxide and the inner surface layer of the compressed rubber layer is formed from a cured product of a rubber composition containing sulfur, but the thickness of the inner surface layer of the compressed rubber layer is as thick as 4.0 mm, pop-out occurred and the lifespan decreased, possibly due to insufficient lateral pressure resistance.

The results of Examples 1 to 3 show that as the thickness of the inner surface layer of the compressed rubber layer increases, the lifespan increases, possibly due to improved crack resistance.

Comparing Examples 5 to 7 with Comparative Example 4, it was found that if the thickness of the inner surface layer of the compressed rubber layer is too thick, the life time is reduced. When the belt thickness is 12 mm, the most preferable result was that the thickness of the inner surface layer of the compressed rubber layer was about 1 mm (thickness of the inner surface layer / total belt thickness = about 8%).

Example 4 is an example in which the thickness of the outer surface layer of the tension rubber layer is thinner than that of Example 5, but there was no change in the life time. Also, Example 8 is an example in which the thickness of the outer surface layer of the tension rubber layer is thicker than that of Example 5, but the life time was shorter, possibly due to a decrease in resistance to lateral pressure.

A comparison between Example 3 and Example 5 shows that providing an outer surface layer on the tension rubber layer also improves the durability life. Also, a comparison between Example 3 and Example 9 shows that when the tension rubber layer is a single layer, it is preferable to form the tension rubber layer from a cured product of a rubber composition containing sulfur.

Example 10 is an example in which the hardness of the inner and outer surface layers is reduced compared to Example 6, but the lifespan is shorter, possibly due to a decrease in resistance to lateral pressure.

Example 11 is an example in which the hardness of the inner and outer surface layers is increased compared to Example 6, and the life time was the longest, possibly due to the improved resistance to lateral pressure.

Example 12 is an example in which the hardness of the inner and outer surface layers is increased even more than in Example 11, but the lifespan is shortened, possibly due to a decrease in the crack resistance of the inner and outer surface layers.

Example 13 is an example in which the hardness of the main body of the compressed rubber layer and the main body of the tension rubber layer is reduced compared to Example 11, but the lifespan is shorter, possibly due to a decrease in resistance to lateral pressure.

Example 14 is an example in which the hardness of the main body of the compressed rubber layer and the main body of the tension rubber layer is increased compared to Example 11, but the lifespan is shortened, possibly due to a decrease in the crack resistance of the main body of the compressed rubber layer and the main body of the tension rubber layer.

As in Example 15, a sufficient durability life was obtained with the raw-edge cogged V-belt, but the durability life was lower than that of the raw-edge double-cogged V-belt of Example 9, and it is considered preferable to apply it to a raw-edge double-cogged V-belt, which can more effectively improve lateral pressure resistance and flex fatigue resistance.

The low-edge type V-belt of the present invention can be applied to low-edge V-belts, low-edge cogged V-belts with cogs, etc., and is particularly suitable for use in V-belts (speed-changing belts) used in transmissions (continuously variable transmissions) in which the gear ratio changes continuously while the belt is in motion, such as low-edge cogged V-belts and low-edge double cogged V-belts used in continuously variable transmissions in motorcycles, ATVs (four-wheeled buggies), snowmobiles, etc.

1 ... Raw edge cogged V-belt 2 ... Outer surface layer of tension rubber layer 3 ... Main body of tension rubber layer 4 ... Adhesive rubber layer 4a ... Core body 5 ... Main body of compression rubber layer 6 ... Inner surface layer of compression rubber layer

Claims (6)

A raw edge type V-belt having cogs at least on the inner peripheral surface side,
A compression rubber layer is provided on the inner peripheral surface side,
the compressed rubber layer has a body of the compressed rubber layer formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide, and an inner surface layer having an average thickness of 0.3 to 3.5 mm, which covers the inner peripheral surface of the body of the compressed rubber layer and is formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing a diene unit and a sulfur-based crosslinking agent;
In the main body of the compressed rubber layer, the diene content of the ethylene-α-olefin elastomer is less than 3.5% by mass,
In the inner surface layer, the diene content of the ethylene-α-olefin elastomer containing diene units is 3.5% by mass or more . The low-edge type V-belt according to claim 1 further includes a tension rubber layer disposed on the outer peripheral surface side, the tension rubber layer being formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing diene units and a sulfur-based crosslinking agent. The low-edge type V-belt according to claim 1 further includes a tension rubber layer disposed on the outer peripheral surface side, the tension rubber layer having a main body of the tension rubber layer formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer and an organic peroxide, and an outer surface layer covering the outer peripheral surface of the main body of the tension rubber layer and formed of a cured product of a rubber composition containing an ethylene-α-olefin elastomer containing diene units and a sulfur-based crosslinking agent. A raw edge type V-belt according to any one of claims 1 to 3, in which the average thickness of the entire belt is 8 to 18 mm. A raw edge type V-belt according to any one of claims 1 to 4, in which the hardness of the main body of the compressed rubber layer is 90 to 99 degrees, and the hardness of the inner surface layer is 70 to 95 degrees. The raw edge type V-belt according to any one of claims 1 to 5 , which is a variable speed belt.

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