JP2022109878A - transmission belt - Google Patents

Abstract

To provide a transmission belt that can achieve improved thermal aging resistance without causing decrease in properties such as hardness, modulus, and wear resistance.SOLUTION: A transmission belt is formed from a cured product of a rubber composition that contains a polymer component (A) containing an ethylene-α-olefin elastomer and a softener (B) with a kinematic viscosity of 30-3500 mm2/s at 100°C. The content of the softener (B) is 3-14 pts.mass relative to 100 pts.mass of the polymer component (A). The softener (B) may have an open-chain aliphatic hydrocarbon skeleton. The cured product may have a rubber hardness (JIS-A) of 85-95 degrees. When the cured product is heated at 150°C for 30 days, the difference in rubber hardness (JIS-A) before and after the heating may be 4 degrees or less. The cured product may have a 100% modulus of 21 MPa or more. The transmission belt may be a low edge cog V belt.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a power transmission belt containing a cured rubber composition containing an ethylene-α-olefin elastomer.

Friction transmission belts and toothed belts have long been used as power transmission means. For example, V-belts and V-ribbed belts are widely used for driving automobile engine accessories, toothed belts for OHC (overhead camshaft) driving, and low-edge cogged V-belts for CVT (continuously variable transmission) driving. there is In these applications, in recent years, demands for increased transmission power and compact layout have become more stringent, and there is a demand for the development of products that can withstand use under high and low temperature conditions. In particular, low-edge cogged V-belts, which are used to drive CVTs in snowmobiles and the like, have a wide range of temperatures from low to high, as they are exposed to heat from the engine and become hot during operation, while the temperature is low when starting. There is a need for a rubber composition that can withstand areas. In addition, high adhesiveness for suppressing separation between the rubber composition and fiber members such as cords and reinforcing fabrics, and bending fatigue resistance that can be used for small-diameter pulleys for compactness are required. Further, high abrasion resistance to withstand abrasion due to contact with pulleys and high lateral pressure resistance to withstand lateral pressure from pulleys are also required. Toothed belts are also required to have a smaller belt width for compactness, and in order to meet this demand, the tooth rubber is required to have high hardness and high modulus. In order to meet such various demands, the use of ethylene-α-olefin elastomers as elastomers constituting rubber compositions is increasing.

For example, Japanese Patent Application Laid-Open No. 2018-141554 (Patent Document 1) describes a rubber component containing an ethylene-α-olefin elastomer, an α,β-unsaturated carboxylic acid metal salt, magnesium oxide, and an organic peroxide. , an inorganic filler, and a cured product of a rubber composition, wherein the ratio of the magnesium oxide is 2 to 20 parts by mass with respect to 100 parts by mass of the rubber component, and the α, β - A transmission belt is disclosed in which the unsaturated carboxylic acid metal salt is 5 parts by mass or more per 100 parts by mass. With such a configuration, the hardness and modulus of the cured product of the transmission belt rubber composition can be increased without impairing cold resistance, heat resistance, adhesiveness, bending fatigue resistance, and wear resistance. Have been described.

JP 2018-141554 A

Patent Document 1 succeeds in increasing the hardness and modulus while maintaining heat resistance, bending fatigue resistance, wear resistance, etc., but there is still a continuing demand for even higher performance. In particular, there is a strong demand for further improvement in heat resistance (suppression of hardness increase and crack suppression at high temperatures).

According to conventional technical knowledge, it has been said that increasing the amount of the softening agent is preferable in order to improve the heat resistance. However, when the softening agent is increased, various physical properties such as hardness, modulus and wear resistance tend to decrease, making it difficult to achieve both.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a power transmission belt which can improve heat aging resistance without deteriorating physical properties such as hardness, modulus and abrasion resistance.

As a result of intensive studies to achieve the above object, the present inventors found that a polymer component (A) containing an ethylene-α ^- olefin elastomer and a softening agent (B ) in a specific ratio, the heat resistance of the cured product of the rubber composition for transmission belts containing ethylene-α-olefin elastomer as the main component is maintained without deteriorating various physical properties such as hardness, modulus, and abrasion resistance. The inventors have found that aging resistance can be improved, and completed the present invention.

That is, the power transmission belt of the present invention is a rubber composition containing a polymer component (A) containing an ethylene-α-olefin elastomer and a softener (B) having a kinematic viscosity at 100°C of 30 to 3500 mm ² /s. Including hardened material. The proportion of the softening agent (B) is 3 to 14 parts by mass with respect to 100 parts by mass of the polymer component (A). The softener (B) may have a chain aliphatic hydrocarbon skeleton. In the softening agent (B), the carbon content derived from the chain aliphatic hydrocarbon may be 50% by mass or more of the total carbon content of the softening agent (B). The softener (B) may be a paraffinic oil and/or a hydrocarbon synthetic oil. The cured product may have a rubber hardness (JIS-A) of 85 to 95 degrees. In the cured product, the difference in rubber hardness (JIS-A) before and after heating at 150° C. for 30 days may be 4 degrees or less. A 100% modulus of the cured product may be 21 MPa or more. The power transmission belt may have a compression rubber layer formed of the cured product. The transmission belt may be a raw edge cogged V-belt used for driving a CVT.

In the present invention, the polymer component (A) containing an ethylene-α-olefin elastomer and the softener (B) having a kinematic viscosity at 100° C. of 30 to 3500 mm ² /s are combined in a specific ratio, so that hardness The heat aging resistance (or heat resistance) of a cured product of a rubber composition for transmission belts containing an ethylene-α-olefin elastomer as a main component can be improved without deteriorating physical properties such as , modulus, and abrasion resistance. Furthermore, by adjusting the range of the kinematic viscosity, the running life of the belt can be improved, and both the properties (the various properties and heat resistance) and belt durability can be achieved at a high level.

FIG. 1 is a schematic perspective view showing an example of the power transmission belt (low-edge cogged V-belt) of the present invention. FIG. 2 is a schematic cross-sectional view of the transmission belt of FIG. 1 cut in the longitudinal direction of the belt. FIG. 3 is a schematic diagram showing the layout of the endurance running test of the low-edge cogged V-belt obtained in the example. FIG. 4 is a schematic cross-sectional view of a V-ribbed belt obtained in an example. FIG. 5 is a schematic diagram showing the layout of the durability running test of the V-ribbed belt obtained in the example.

[Rubber composition]
The power transmission belt of the present embodiment is a cured rubber composition containing a polymer component (A) containing an ethylene-α-olefin elastomer and a softener (B) having a kinematic viscosity at 100°C of 30 to 3500 mm ² /s. Including things.

(polymer component)
The polymer component (A) contains an ethylene-α-olefin elastomer because of its excellent cold resistance, heat resistance and weather resistance.

The ethylene-α-olefin elastomer may contain ethylene units and α-olefin units as structural units, and may further contain diene units. Therefore, ethylene-α-olefin elastomers include ethylene-α-olefin copolymer rubbers, ethylene-α-olefin-diene terpolymer rubbers, and the like.

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

A non-conjugated diene monomer is usually used as the diene monomer for forming the diene unit. Examples of non-conjugated diene monomers include dicyclopentadiene, methylenenorbornene, ethylidenenorbornene, 1,4-hexadiene, and cyclooctadiene. Among these diene monomers, ethylidenenorbornene and 1,4-hexadiene (especially ethylidenenorbornene) are preferred.

Typical ethylene-α-olefin elastomers include, for example, ethylene-α-olefin rubber [ethylene-propylene rubber (EPM), ethylene-butene rubber (EBM), ethylene-octene rubber (EOM), etc.], ethylene-α-olefin -Diene rubber [ethylene-propylene-diene terpolymer (EPDM)] and the like can be exemplified.

These ethylene-α-olefin elastomers can be used alone or in combination of two or more. Among these, ethylene-α-olefin-diene terpolymer rubber such as ethylene-α-C _3-4 olefin-diene terpolymer rubber is preferred because of its excellent cold resistance, heat resistance and weather resistance. EPDM is particularly preferred. Therefore, the proportion of EPDM may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more (especially 95% by mass), relative to the entire ethylene-α-olefin elastomer, It may be 100% by mass (only EPDM).

In the ethylene-α-olefin elastomer, the ratio (mass ratio) between ethylene and α-olefin is the former/latter = 40/60 to 90/10, preferably 45/55 to 85/15 (for example, 50/50 to 80 /20), more preferably 52/48 to 70/30. In particular, in the ethylene-propylene-diene terpolymer, the ratio (mass ratio) of ethylene and propylene is the former/latter=35/65 to 90/10, preferably 40/60 to 80/20, more preferably is 45/55 to 70/30, more preferably 50/50 to 70/30 (eg 50/50 to 60/40), most preferably 55/45 to 70/30 (especially 60/40 to 65/35) may be

The diene content of the ethylene-α-olefin elastomer (especially ethylene-α-olefin-diene terpolymer rubber such as EPDM) may be 15% by mass or less (for example, 0.1 to 15% by mass), Preferably 10% by mass or less (eg 0.3 to 10% by mass), more preferably 7% by mass or less (eg 0.5 to 7% by mass), more preferably 5% by mass or less (eg 1 to 5% by mass) , and most preferably 3% by mass or less (eg, 1 to 3% by mass). If the diene content is too high, there is a risk that high heat resistance cannot be ensured.

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

The iodine value of the ethylene-α-olefin elastomer containing a diene monomer is, for example, 3-40, preferably 5-30, more preferably 10-20. If the iodine value is too small, the cross-linking of the rubber composition is insufficient and wear and adhesion tend to occur. tends to decrease.

Mooney viscosity [ML (1+4) 125° C.] of the uncrosslinked ethylene-α-olefin elastomer may be 80 or less, for example 10 to 80, preferably 20 to 70, more preferably 30 to 50, most preferably 35-45. If the Mooney viscosity is too high, the fluidity of the rubber composition may be lowered and the workability in kneading may be lowered.

In the present application, the Mooney viscosity can be measured by a method according to JIS K 6300-1 (2013), and the test conditions are an L-shaped rotor, a test temperature of 125°C, a preheat of 1 minute, and a rotor operating time of 4 minutes. is.

The proportion of the ethylene-α-olefin elastomer in the polymer component may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass (ethylene-α- olefin elastomer only). If the proportion of the ethylene-α-olefin elastomer in the polymer component is too low, the heat resistance and cold resistance may deteriorate.

In addition to the ethylene-α-olefin elastomer, the polymer component includes other rubber components such as diene rubber [natural rubber, isoprene rubber, butadiene rubber, chloroprene rubber, styrene butadiene rubber (SBR), vinylpyridine-styrene-butadiene copolymer rubber, acrylonitrile butadiene rubber (nitrile rubber); hydrogenated nitrile rubber (including mixed polymer of hydrogenated nitrile rubber and unsaturated carboxylic acid metal salt), etc. Hydrogenated diene rubber, etc.], olefin rubber (polyoctenylene rubber, ethylene-vinyl acetate copolymer rubber, chlorosulfonated polyethylene rubber, alkylated chlorosulfonated polyethylene rubber, etc.), epichlorohydrin rubber, acrylic It may contain rubber, silicone rubber, urethane rubber, fluororubber, and the like.

The proportion of other rubber components in the polymer component may be 50% by mass or less, preferably 20% by mass or less, and more preferably 10% by mass or less.

(Softener with kinematic viscosity at 100° C. of 30 to 3500 mm ² /s)
From the viewpoint of preventing the transmission belt from cracking at high temperatures, it is preferable to increase the amount of the softening agent. In addition, the softening agents that have been commonly used so far tend to migrate to the outside or volatilize, and are not sufficiently effective in preventing cracks in transmission belts at high temperatures.

The inventors of the present application have found that by using a softening agent (B) with a high kinematic viscosity for a polymer component containing an ethylene-α-olefin elastomer, various physical properties such as hardness, modulus, and wear resistance can be maintained and heat resistance can be improved. It was found that the improvement of the quality can be compatible. A softening agent with a high kinematic viscosity does not easily migrate to the outside or volatilize even at high temperatures, and can be blended in a small amount. Various physical properties such as hardness, modulus, and wear resistance can be maintained by suppressing the compounding amount.

Furthermore, migration and volatilization of the softener to the outside are considered to occur in various situations such as rubber kneading, cross-linking (vulcanization), and use of the belt. In contrast, in the present invention, the migration and volatilization can be suppressed by using the softening agent (B) having a high kinematic viscosity.

The kinematic viscosity (kinematic viscosity at 100° C.) of such a softening agent (B) is 30 to 3500 mm ² /s, preferably 30 to 3000 mm ² /s, more preferably 30 to 2000 mm ² /s, more preferably 30-1000 mm ² /s, most preferably 30-100 mm ² /s. The kinematic viscosity is, for example, 30 to 1,500 mm ² /s, preferably 32 to 500 mm ² /s, more preferably 32 to 500 mm 2 /s, from the viewpoint that various physical properties such as wear resistance and heat aging resistance can be highly compatible with belt durability. 33-100 mm ² /s, more preferably 35-80 mm ² /s, most preferably 38-50 mm ² /s. If the kinematic viscosity is too low, the heat aging resistance will be lowered, and if it is too high, the flexibility of the belt will be lowered.

In the present application, the kinematic viscosity of the softener (B) at 100°C is a value measured at 100°C using an Ubbelohde viscometer in accordance with JIS K 2283 (2000).

The number average molecular weight of the softener (B) is, for example, 2000-20000, preferably 2200-15000, more preferably 2300-10000, more preferably 2400-5000, most preferably 2500-3000. If the molecular weight is too small, the heat aging resistance will be lowered, and if it is too large, the flexibility of the belt will be lowered.

In addition, in this application, the number average molecular weight of the softening agent (B) can be measured by gel permeation chromatography (GPC) using polystyrene as a standard substance.

The softening agent (B) is not limited in kind as long as it has the above kinematic viscosity, and may be a so-called plasticizer. The softener (B) can be broadly classified into, for example, mineral oil softeners, vegetable oil softeners, and synthetic softeners.

Mineral oil-based softeners include, for example, petroleum-based softeners [paraffinic oils, alicyclic oils (naphthenic oils), aromatic oils, etc.], coal tar-based softeners (coal tar, chroman-indene resin etc.).

Vegetable oil-based softeners include, for example, fatty oil-based softeners (fatty acids or salts thereof, fatty acid esters, fatty acid amides, fatty oils, etc.).

Synthetic softeners include, for example, synthetic resin softeners (phenol/aldehyde resins, hydrocarbon-based synthetic oils such as liquid ethylene-α-olefin copolymers, liquid polybutene, liquid polybutanediene, liquid rubbers such as liquid isoprene rubber, etc. etc.), synthetic plasticizers (phthalate diesters such as dioctyl phthalate, polyester plasticizers, C _6-18 alkanedicarboxylic acid esters such as dioctyl sebacate, etc.).

These softeners can be used alone or in combination of two or more.

The softener (B) preferably has a chain aliphatic hydrocarbon skeleton because of its high compatibility with the polymer component (A). The chain aliphatic hydrocarbon backbone may be a polyolefin backbone, preferably a polyolefin backbone containing poly-C _2-3 olefins, more preferably an ethylene-α-olefin copolymer backbone, and an ethylene-C _3-4 olefin A copolymer backbone is more preferred, and an ethylene-propylene copolymer backbone is most preferred.

In the softening agent (B) having a chain aliphatic hydrocarbon skeleton, the carbon content derived from the chain aliphatic hydrocarbon (especially the ethylene-α-olefin copolymer) is the total carbon content of the softening agent (B). It may be 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass. If the amount of carbon derived from the chain aliphatic hydrocarbon is too small, the compatibility with the polymer component may decrease, and the heat aging resistance and belt durability may decrease.

In addition, in this application, the carbon content derived from a chain-like aliphatic hydrocarbon can be measured by a conventional method. When the softener (B) is a petroleum-based softener, the carbon content derived from chain aliphatic hydrocarbons can be measured by ndM ring analysis specified in ASTM D3238-17. In the petroleum-based softener, the carbon content may be % Cp (mass ratio of paraffin carbon content to total carbon content) according to the ndM ring analysis, and the paraffin oil has a % Cp of 60 or more. Naphthenic oils have a %Cp of 35 or more and less than 60, and aromatic oils have a %Cp of less than 35.

As the softening agent (B), a paraffinic oil and/or a hydrocarbon synthetic oil are preferred because they are non-staining, have no effect on cross-linking, and are highly compatible with the polymer component (A). Ethylene-α-olefin copolymers are more preferred, and liquid ethylene-propylene copolymers are most preferred.

The ratio of the softening agent (B) is 3 to 14 parts by mass, preferably 3 to 12 parts by mass (especially 3.5 to 12 parts by mass), more preferably 3 to 10 parts by weight, more preferably 3.5 to 8 parts by weight, most preferably 4 to 6 parts by weight (especially 4.5 to 5.5 parts by weight). If the proportion of the softening agent (B) is too small, the plasticity of the rubber and the flexibility of the belt will not be sufficiently improved, and the effect of improving the heat resistance will be reduced.

(other softeners)
The rubber composition may further contain other softening agents. Other softening agents include softening agents having a kinematic viscosity of less than 30 mm ² /s at 100° C. among the mineral oil softening agents, vegetable oil softening agents, and synthetic softening agents exemplified as the softening agent (B). .

Examples of such softening agents (plasticizers or processing aids) include oils such as paraffinic oils, naphthenic oils, and process oils; stearic acid, fatty acids such as stearic acid metal salts or metal salts thereof; stearic acid; fatty acid esters such as esters; fatty acid amides such as stearamide; low molecular weight paraffins; low molecular weight waxes; These other softening agents can be used alone or in combination of two or more.

Among these other softeners, C _8-24 fatty acids (including metal salts, esters and amides thereof) such as stearic acid are preferred.

The ratio of the other softening agent may be 100 parts by mass or less, preferably 80 parts by mass or less (for example, 1 to 80 parts by mass), more preferably 70 parts by mass, relative to 100 parts by mass of the softening agent (B). parts or less (eg 5 to 70 parts by mass), more preferably 50 parts by mass or less (eg 10 to 50 parts by mass), particularly preferably 40 parts by mass or less (eg 20 to 40 parts by mass), most preferably 30 parts by mass or less (eg 10 to 30 parts by mass). If the ratio of other softening agents is too high, the hardness, modulus, and abrasion resistance of the belt may be lowered, or migration to the outside and volatilization may occur.

(crosslinking agent)
The rubber composition may further contain a cross-linking agent. The cross-linking agent (or vulcanizing agent) may be an organic peroxide and/or a sulfur-based cross-linking agent.

Examples of organic peroxides include organic peroxides commonly used for cross-linking rubbers and resins, such as diacyl peroxide, peroxy ester, dialkyl peroxide (e.g., dicumyl peroxide, t-butyl cumyl peroxide, oxide, 1,1-di-butylperoxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane, 1,3-bis(t- butylperoxy-isopropyl)benzene, di-t-butylperoxide, etc.). These organic peroxides can be used alone or in combination of two or more. Furthermore, the organic peroxide is preferably a peroxide having a decomposition temperature of about 150 to 250° C. (eg, 175 to 225° C.), which gives a half-life of 1 minute by thermal decomposition.

Examples of sulfur-based cross-linking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, sulfur chloride (sulfur monochloride, sulfur dichloride, etc.), and the like. These sulfur-based cross-linking agents can be used alone or in combination of two or more. As the sulfur-based cross-linking agent, powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur are preferred, and powdered sulfur is most preferred.

The total proportion of the cross-linking agent is, for example, 1 to 10 parts by mass, preferably 2 to 8 parts by mass, more preferably 2 to 6 parts by mass, more preferably 3 to 6 parts by mass with respect to 100 parts by mass of the polymer component (A). Department.

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

Among these inorganic fillers, carbonaceous materials such as carbon black, metal oxides such as magnesium oxide and zinc oxide, and mineral materials such as silica are preferable. It is particularly preferable to contain at least carbon black from the viewpoint of improving the properties.

Examples of carbon black include SAF, ISAF, HAF, FEF, GPF and HMF. These carbon blacks can be used alone or in combination of two or more. Among these, HAF is preferable because it has a good balance between reinforcing effect and dispersibility and can improve wear resistance.

The average particle size of the carbon black can be selected, for example, from the range of about 5 to 200 nm, for example, about 10 to 150 nm, preferably 15 to 100 nm, more preferably about 20 to 80 nm (especially 30 to 50 nm). If the average particle size of the carbon black is too small, uniform dispersion may become difficult, and if it is too large, the hardness, modulus and abrasion resistance may decrease.

The total proportion of the inorganic filler can be selected from a range of about 10 to 150 parts by mass with respect to 100 parts by mass of the polymer component (A), for example 40 to 100 parts by mass, preferably 50 to 80 parts by mass, more preferably 60 to 70 parts by mass. If the proportion of the inorganic filler is too low, the hardness, modulus and wear resistance of the cured rubber composition may be reduced.

When the inorganic filler contains carbon black and a metal oxide, the ratio of the metal oxide is, for example, 1 to 100 parts by mass, preferably 2 to 50 parts by mass, more preferably 3 parts by mass, with respect to 100 parts by mass of carbon black. to 30 parts by weight, most preferably 5 to 10 parts by weight.

(Short fiber)
The rubber composition may further contain short fibers. Examples of short fibers include polyolefin fibers (polyethylene fibers, polypropylene fibers, etc.), polyamide fibers (polyamide 6 fibers, polyamide 66 fibers, polyamide 46 fibers, aramid fibers, etc.), polyalkylene arylate fibers [polyethylene terephthalate (PET) fibers, poly C _2-4 alkylene C _6-14 arylate-based fibers such as polyethylene naphthalate (PEN) fibers, etc.], vinylon fibers, polyvinyl alcohol-based fibers, synthetic fibers such as polyparaphenylenebenzobisoxazole (PBO) fibers; Natural fibers such as cotton, linen, and wool; and inorganic fibers such as carbon fibers are widely used. These short fibers can be used alone or in combination of two or more. Among these staple fibers, synthetic fibers and natural fibers, especially synthetic fibers (polyamide fibers, polyalkylene arylate fibers, etc.), among which at least aramid fibers are preferred because they are rigid, have high strength and modulus, and easily protrude from the surface. Short fibers containing are preferred. Aramid staple fibers also have high abrasion resistance. Aramid short fibers are commercially available, for example, under the trade names of "Conex", "Nomex", "Kevlar", "Technora", and "Twaron".

Aramid staple fibers may be combined with other synthetic staple fibers, especially aliphatic polyamide staple fibers such as polyamide 6 staple fibers. The mass ratio of aramid short fibers and other synthetic short fibers (especially aliphatic polyamide short fibers) is the former/latter = 90/10 to 10/90, preferably 70/30 to 30/70, more preferably 60 /40 to 40/60.

The short fibers have an average fineness of, for example, 0.1 to 50 dtex, preferably 1 to 10 dtex, more preferably 1.5 to 5 dtex, and more preferably 2 to 3 dtex. If the average fineness is too large, the mechanical properties of the cured product of the rubber composition may deteriorate, and if it is too small, it may be difficult to uniformly disperse the fine particles.

The short fibers have an average length of, for example, 1 to 20 mm, preferably 1.2 to 15 mm (eg, 1.5 to 10 mm), more preferably 2 to 5 mm, more preferably 2.5 to 4 mm. If the average length of the short fibers is too short, when the cured rubber composition is used for a belt, the mechanical properties in the grain direction (e.g., modulus) may not be sufficiently enhanced. As a result, the dispersibility of the short fibers in the rubber composition may decrease, and the bending fatigue resistance may decrease.

From the standpoint of dispersibility and adhesiveness of the short fibers in the rubber composition, at least the short fibers are preferably subjected to adhesion treatment (or surface treatment). Note that not all the staple fibers need to be adhesively treated, and adhesively treated staple fibers and non-adhesively treated staple fibers (untreated staple fibers) may be mixed or used together.

In the adhesive treatment of short fibers, various adhesive treatments, for example, a treatment liquid containing an initial condensate of phenols and formalin (prepolymer of novolac or resol type phenolic resin, etc.), a treatment liquid containing a rubber component (or latex) , a treatment liquid containing the initial condensate and a rubber component (latex), a treatment liquid containing a reactive compound (adhesive compound) such as a silane coupling agent, an epoxy compound (epoxy resin, etc.), an isocyanate compound, or the like. be able to. In a preferred bonding treatment, the short fibers are treated with a treatment liquid containing said precondensate and a rubber component (latex), especially at least a resorcin-formalin-latex (RFL) liquid. Such treatment liquids may be used in combination, for example, short fibers may be pretreated with a conventional adhesive component, e.g. After treatment, it may be treated with an RFL solution.

The ratio of the short fibers is, for example, 5 to 100 parts by mass, preferably 10 to 50 parts by mass, more preferably 20 to 40 parts by mass (especially 25 to 35 parts by mass) with respect to 100 parts by mass of the polymer component (A). may be If the ratio of the short fibers is too low, the mechanical properties of the cured rubber composition may deteriorate. There is

(other additives)
The rubber composition may optionally contain conventional additives, cross-linking aids, cross-linking accelerators, cross-linking retarders, anti-aging agents (antioxidants, heat anti-aging agents, anti-flex cracking agents, anti-ozonants etc.), colorants, tackifiers, plasticizers, coupling agents (silane coupling agents, etc.), stabilizers (ultraviolet absorbers, heat stabilizers, etc.), lubricants, flame retardants, antistatic agents, etc. You can These additives can be used alone or in combination of two or more.

The total proportion of other additives is, for example, 1 to 100 parts by mass, preferably 2 to 50 parts by mass, more preferably 3 to 20 parts by mass, and more preferably 4 to 10 parts by mass with respect to 100 parts by mass of the rubber component. is.

(Characteristics of cured product of rubber composition)
A cured product of the rubber composition has a high rubber hardness and a high modulus. Specifically, the rubber hardness (JIS-A) of the cured product of the rubber composition may be 85 degrees or more, for example, 85 to 95 degrees, preferably 86 to 94 degrees, more preferably 87 to 93 degrees, and more Preferably 88 to 92 degrees, particularly preferably 88 to 91 degrees, most preferably 88 to 90 degrees.

The cured product of the rubber composition has excellent heat aging resistance, and the difference in rubber hardness (JIS-A) before and after heating at 150° C. for 30 days may be 4 degrees or less, preferably 3.5. degrees or less, more preferably 3 degrees or less, more preferably 2.5 degrees or less. If the difference is too large, the heat aging resistance of the belt may deteriorate.

In the present application, the rubber hardness (JIS-A) is measured in accordance with JIS K 6253 (2012) for a cured product press-crosslinked at a temperature of 165° C. and a pressure of 2 MPa for 30 minutes. Measured by the method described in the examples.

The cured product of the rubber composition has a high modulus, and the 100% modulus (tensile stress at 100% elongation) pulled in the grain direction may be 21 MPa or more (especially 23 MPa or more), for example 24 MPa or more (e.g. 24 to 60 MPa), preferably 25 MPa or more (eg, 25 to 50 MPa), more preferably 26 to 40 MPa, more preferably 27 to 30 MPa, most preferably 28 to 29 MPa.

In addition, in this application, 100% modulus can be measured based on JISK6251 (2017), and is measured in detail by the method as described in the below-mentioned Example.

When the rubber composition contains short fibers, the short fibers are usually oriented in a predetermined direction. For example, when the rubber composition is used to form a compressed rubber layer of a transmission belt, short fibers are embedded in the compressed rubber layer oriented in the belt width direction in order to suppress compression deformation of the belt due to pressure from the pulley. is preferred.

When the cured product contains short fibers, the 100% modulus means the tensile stress at 100% elongation in the grain direction. Further, the "grain direction" may be not only the longitudinal direction of the short fibers, but also a direction within ±5° of the longitudinal direction. Therefore, the "grain direction" can also be said to be "the direction substantially parallel to the longitudinal direction of the short fibers".

The rubber composition is used as a cured product crosslinked by a method suitable for the intended use. The cross-linking temperature is, for example, 120-200° C. (especially 150-180° C.).

[Transmission belt]
The type of the transmission belt (power transmission belt) of the present embodiment is not particularly limited as long as it is a belt that transmits power by contacting the pulley, and may be a friction transmission belt or a meshing transmission belt. good.

Examples of friction transmission belts include flat belts, V-belts (wrapped V-belts, raw-edge V-belts, raw-edge cogged V-belts in which cogs are formed on the inner circumference of a raw-edge V-belt, inner and outer circumferences of raw-edge V-belts, raw edge double cogged V-belts with cogs formed on both sides), V-ribbed belts, resin block belts, and the like.

Examples of meshing transmission belts include toothed belts and double-sided toothed belts.

These power transmission belts may contain a cured product of the rubber composition, but usually the belt body (especially the compression rubber layer and/or the stretched rubber layer) is formed of the cured rubber composition. .

Among the power transmission belts, power transmission belts such as cogged V-belts and toothed belts, for which there are strict demands for increased transmission power and compact layout, are preferred, and cogged V-belts are particularly preferred.

The cogged V-belt of this embodiment includes an adhesive rubber layer in contact with at least a portion of a core wire extending in the longitudinal direction of the belt, an extension rubber layer formed on one surface of the adhesive rubber layer, and the adhesive rubber layer. It is formed on the other surface and has a plurality of projections (cogs) formed on its inner peripheral surface at predetermined intervals along the longitudinal direction of the belt, and its side surface is frictionally engaged with the pulley. and a compression rubber layer. Such cogged V-belts include cogged V-belts in which the cog portions are formed only in the compression rubber layer, double cogged V-belts in which the same cog portions are formed on the outer peripheral surface of the extension rubber layer in addition to the compression rubber layer. Includes belt. The cogged V-belt is preferably a V-belt in which the side surface of the compression rubber layer is in contact with the pulley (particularly, a speed change belt used in a transmission in which the gear ratio changes steplessly while the belt is running). Examples of cogged V-belts include a low edge cogged V belt in which cogs are formed on the inner peripheral side of a raw edge belt, a low edge double cogged V belt in which cogs are formed on both the inner peripheral side and the outer peripheral side of a raw edge belt, and the like. mentioned. Among these, low edge cogged V-belts used for driving CTVs are particularly preferred.

FIG. 1 is a schematic perspective view showing an example of the power transmission belt (low-edge cogged V-belt) of the present embodiment, and FIG. 2 is a schematic cross-sectional view of the power transmission belt of FIG. 1 cut in the belt longitudinal direction.

In this example, the raw-edge cogged V-belt 1 has a plurality of cog portions 1a formed on the inner peripheral surface of the belt body at predetermined intervals along the longitudinal direction of the belt (direction A in the drawing). The cross-sectional shape of the cog portion 1a in the longitudinal direction is substantially semicircular (curved or wavy), and the cross-sectional shape in the direction perpendicular to the longitudinal direction (the width direction or the B direction in the drawing). is trapezoidal. That is, each cog portion 1a protrudes from the cog bottom portion 1b in the belt thickness direction in a substantially semicircular cross-section in the A direction. The raw-edge cogged V-belt 1 has a laminated structure, and from the outer circumference of the belt to the inner circumference (the side on which the cog portion 1a is formed), a reinforcing cloth 2, an elastic rubber layer 3, and an adhesive rubber layer 4 are formed. , a compression rubber layer 5 and a reinforcing cloth 6 are sequentially laminated. The cross-sectional shape in the belt width direction is a trapezoidal shape in which the belt width decreases from the belt outer circumference side to the belt inner circumference side. Further, a core 4a is embedded in the adhesive rubber layer 4, and the cog portion 1a is formed in the compression rubber layer 5 by a mold with cogs.

The height and pitch of the cogs are similar to those of conventional cogged V-belts. In the compression rubber layer, the height of the cog portion is 50 to 95% (particularly 60 to 80%) of the thickness of the entire compression rubber layer, and the pitch of the cog portions (the distance between the centers of adjacent cog portions ) is 50 to 250% (especially 80 to 200%) of the height of the cog portion. The same is true when forming the cog portion in the stretchable rubber layer.

In this example, the stretched rubber layer 3 and the compressed rubber layer 5 are formed of the cured rubber composition. As for the adhesive rubber layer, the core and the reinforcing cloth, a conventional adhesive rubber layer, the core and the reinforcing cloth can be used. For example, the following adhesive rubber layer, the core and the reinforcing cloth may be used.

(Adhesive rubber layer)
The rubber composition for forming the adhesive rubber layer contains a rubber component, a cross-linking agent (such as a sulfur-based vulcanizing agent such as sulfur), a co-cross-linking agent or a cross-linking agent, similarly to the cross-linked rubber composition for the compression rubber layer and the stretched rubber. Auxiliary agents (maleimide cross-linking agents such as N,N'-m-phenylene dimaleimide, etc.), cross-linking accelerators (TMTD, DPTT, CBS, etc.), inorganic fillers (carbon black, silica, etc.), softening agents (paraffin-based oils such as oils), processing agents or processing aids, antioxidants, adhesion improvers [resorcin-formaldehyde cocondensates, amino resins (condensates of nitrogen-containing cyclic compounds and formaldehyde, such as hexamethylolmelamine, Melamine resins such as hexaalkoxymethylmelamine (hexamethoxymethylmelamine, hexabutoxymethylmelamine, etc.), urea resins such as methylol urea, benzoguanamine resins such as methylolbenzoguanamine resin, etc.), co-condensates thereof (resorcin-melamine-formaldehyde co- condensates, etc.)], colorants, tackifiers, plasticizers, coupling agents, stabilizers, flame retardants, antistatic agents, and the like. In the adhesion improver, the resorcin-formaldehyde cocondensate and amino resin may be an initial condensate (prepolymer) of resorcin and/or a nitrogen-containing cyclic compound such as melamine and formaldehyde.

In addition, in this rubber composition, as the polymer component, a polymer of the same system or type as the polymer component of the rubber composition of the compression rubber layer and the extension rubber layer is often used. Moreover, the proportions of the cross-linking agent, co-cross-linking agent or cross-linking aid, cross-linking accelerator, softening agent and anti-aging agent can each be selected from the same range as in the rubber compositions of the compression rubber layer and the extension rubber layer. In addition, in the rubber composition of the adhesive rubber layer, the proportion of the inorganic filler is 10 to 100 parts by mass, preferably 20 to 80 parts by mass, more preferably 30 to 50 parts by mass with respect to 100 parts by mass of the polymer component. . The proportion of the adhesion improver (resorcinol-formaldehyde cocondensate, hexamethoxymethylmelamine, etc.) is 0.1 to 20 parts by weight, preferably 1 to 10 parts by weight, more preferably 1 to 10 parts by weight, per 100 parts by weight of the polymer. is 2 to 8 parts by mass.

(Core body)
The core body is not particularly limited, but usually core wires (twisted cords) arranged at predetermined intervals in the belt width direction can be used. The cords are arranged to extend in the longitudinal direction of the belt, and are generally arranged in parallel with the longitudinal direction of the belt at a predetermined pitch. At least a part of the core wire needs to be in contact with the adhesive rubber layer. The core wire may be embedded between the adhesive rubber layer and the compression rubber layer (on the side of the compression rubber layer). Among these, the configuration in which the core wire is embedded in the adhesive rubber layer is preferable from the viewpoint of improving the durability.

As the fiber constituting the core wire, the same fiber as the short fiber can be exemplified. Among the above-mentioned fibers, from the viewpoint of high modulus, polyester fibers (polyalkylene arylate-based fibers) having C _2-4 alkylene-arylate such as ethylene terephthalate and ethylene-2,6-naphthalate as the main structural unit, aramid fibers, etc. Inorganic fibers such as synthetic fibers and carbon fibers are widely used, and polyester fibers (polyethylene terephthalate-based fibers, polyethylene naphthalate-based fibers) and polyamide fibers are preferred. The fibers may be multifilament yarns. The fineness of the multifilament yarn is, for example, 2200-13500 dtex (especially 6600-11000 dtex). A multifilament yarn may for example comprise 100 to 5000, preferably 500 to 4000, more preferably 1000 to 3000 monofilaments.

Twisted cords using multifilament yarns (for example, plied, single-twisted, Lang-twisted, etc.) can be used as the cord. The average wire diameter of the cord (diameter of the twisted cord) may be, for example, 0.5 to 3 mm, preferably 0.6 to 2 mm, more preferably 0.7 to 1.5 mm.

The cord may be adhesively treated (or surface treated) in a manner similar to the short fibers of the compression and extension rubber layers to improve adhesion with the polymer component. As with the short fibers, it is preferable to bond the core wires with at least the RFL liquid.

(reinforcement cloth)
In the friction transmission belt, when reinforcing cloth is used, it is not limited to the form of laminating the reinforcing cloth on the surface of the compression rubber layer. It may be laminated, or may be in the form of embedding the reinforcing layer in the compression rubber layer and/or the extension rubber layer (for example, the form described in JP-A-2010-230146). The reinforcing cloth can be formed of, for example, a cloth material (preferably a woven cloth) such as a woven cloth, a wide-angle canvas, a knitted cloth, a nonwoven cloth, etc. If necessary, the adhesion treatment, for example, treatment with an RFL liquid (immersion treatment etc.), the adhesive rubber may be rubbed into the cloth material, or the adhesive rubber and the cloth material may be laminated and then laminated on the surface of the compression rubber layer and/or the tension rubber layer.

[Manufacturing method of power transmission belt]
The method of manufacturing the power transmission belt of this embodiment is not particularly limited, and a conventional method can be used. In the case of a raw-edge cogged V-belt, for example, a laminate consisting of a reinforcing cloth (lower cloth) and a compressed rubber layer sheet (uncrosslinked rubber sheet) is arranged alternately in teeth and grooves with the reinforcing cloth facing downward. The cog pad is placed in a flat mold with cogs and pressed at a temperature of about 60 to 100°C (especially 70 to 80°C) to mold the cog part (not completely crosslinked, semi-crosslinked). After making the cog pad, the ends of the cog pad may be cut vertically from the top of the cog peaks. Furthermore, the cylindrical mold is covered with an inner matrix (a mold made of cross-linked rubber) in which teeth and grooves are alternately arranged. After laminating the first adhesive rubber layer sheet (lower adhesive rubber: uncrosslinked rubber sheet) on the wound cog pad, the core wire (twisted cord) forming the core is spirally Then, a second adhesive rubber layer sheet (upper adhesive rubber: the same as the adhesive rubber layer sheet), a stretched rubber layer sheet (uncrosslinked rubber sheet), and a reinforcing cloth (upper cloth) are sequentially laid thereon. A compact may be produced by winding. After that, a jacket (jacket made of crosslinked rubber) was placed on the mold, and the mold was placed in a vulcanization can, and crosslinked at a temperature of 120 to 200°C (especially 150 to 180°C) to prepare a belt sleeve. After that, a cutting step may be performed in which a compressed rubber layer is formed by cutting with a cutter or the like so as to have a V-shaped cross section.

For raw-edge cogged V-belts that do not contain reinforcing fabrics, a laminate may be prepared by pre-pressing a sheet for the compression rubber layer and a sheet for the first adhesive rubber layer.

In the stretched rubber layer sheet and the compressed rubber layer sheet, as a method for orienting the orientation direction of the short fibers in the belt width direction, a conventional method, for example, a rubber roll between a pair of calender rolls provided with a predetermined gap, is used. Both sides of the rolled sheet with short fibers oriented in the rolling direction are cut parallel to the rolling direction, and the rolled sheet is rolled so as to have a belt forming width (length in the belt width direction). A method of cutting in a direction perpendicular to the direction and jointing the side surfaces cut in a direction parallel to the rolling direction can be used. For example, the method described in JP-A-2003-14054 can be used. The uncrosslinked sheet in which the short fibers are oriented by such a method is arranged and crosslinked in the above-described method so that the orientation direction of the short fibers is the width direction of the belt.

EXAMPLES The present invention will be described in more detail below based on examples, but the present invention is not limited by these examples. Details of raw materials used in the examples are shown below.

[material]
(Softener)
Softener 1: "Lucant LX004" manufactured by Mitsui Chemicals, Inc., liquid ethylene-α-olefin copolymer, kinematic viscosity at 100° C. 40 mm ² /s, average molecular weight 2,700
Softener 2: "Lucant LX010" manufactured by Mitsui Chemicals, Inc., liquid ethylene-α-olefin copolymer, kinematic viscosity at 100° C. 100 mm ² /s, average molecular weight 4,200
Softener 3: "Lucant LX400" manufactured by Mitsui Chemicals, Inc., liquid ethylene-α-olefin copolymer, kinematic viscosity at 100° C. of 2,000 mm ² /s, average molecular weight of 13,000
Softener 4: “Lucant LX900Z” manufactured by Mitsui Chemicals, Inc., liquid ethylene-α-olefin copolymer, kinematic viscosity at 100° C. of 3,400 mm ² /s, average molecular weight of 17,000
Softener 5: "Diana Process Oil PS430" manufactured by Idemitsu Kosan Co., Ltd., paraffin oil, kinematic viscosity at 100° C. 33 mm ² /s, % Cp (mass ratio of paraffin carbon content to total carbon content) 72, % Cn ( Mass ratio of naphthenic carbon content to total carbon content) 22, % Ca (mass ratio of aromatic carbon content to total carbon content) 6
Softener 6: "Diana Process Oil PW90" manufactured by Idemitsu Kosan Co., Ltd., paraffin oil, kinematic viscosity at 100° C. 11 mm ² /s, %Cp72, %Cn28, %Ca0
Softener 7: "SUNTHENE4240" manufactured by Nippon Sun Oil Co., Ltd., naphthenic oil, kinematic viscosity at 100° C. 18 mm ² /s, %Cp45, %Cn40, %Ca15
Softener 8: "SUNTHENE450" manufactured by Nippon Sun Oil Co., Ltd., naphthenic oil, kinematic viscosity at 100° C. 9 mm ² /s, % Cp50, % Cn38, % Ca12
Stearic acid: "Tsubaki Stearate" manufactured by NOF Corporation.

(other ingredients)
EPDM1: "Nordel IP3640" manufactured by Dow Chemical Company, ethylene content 55% by mass, diene content 1.8% by mass
EPDM2: "Nordel IP3745" manufactured by Dow Chemical Company, ethylene content 70% by mass, diene content 0.5% by mass
Zinc oxide: "Type 2 zinc oxide" manufactured by Sakai Chemical Industry Co., Ltd.
Aramid staple fiber: "Twaron" manufactured by Teijin Limited, fineness 2.2 dtex, average fiber length 3 mm
Nylon staple fiber: "Leona" manufactured by Asahi Kasei Co., Ltd., average fiber diameter 27 μm, average fiber length 3 mm
Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd.
Antiaging agent: "Nocrac CD" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Organic peroxide: "P-40MB (K)" manufactured by NOF Corporation
Cross-linking accelerator: Ouchi Shinko Kagaku Kogyo Co., Ltd. "Noccellar TT"
Sulfur: "Powder Sulfur" manufactured by Bigen Chemical Co., Ltd.
Silica: "Ultrasil VN3" manufactured by Evonik Degussa Japan Co., Ltd., BET specific surface area 175 m ² /g
Resorcinol resin: "Penacolite Resin (B-18-S)" manufactured by INDSPEC Chemical Corporation
Hexamethoxymethylol melamine: "POWERPLAST PP-1890S" manufactured by SINGH PLASTICISER & RESINS
Cotton canvas with rubber: Treated canvas obtained by rubbing the adhesive rubber shown in Table 2 into canvas (basis weight: 280 g/m ² ) plain-woven from 20-count cotton threads at a thread density of 75 threads/50 mm.

(core wire for raw edge cogged V-belt)
Two multifilament bundles of aramid fibers with a fineness of 1,680 dtex are aligned to prepare a lower-twisted yarn, and the three prepared lower-twisted yarns are combined and ply-twisted in the opposite direction to the lower-twist. twisted cord.

(Core wire for V-ribbed belt)
Two polyester fiber multifilament bundles with a fineness of 1,100 dtex are combined and twisted in one direction to make a first twisted yarn, and the three prepared first twisted yarns are combined and twisted in the opposite direction to the first twist. A plied cord with a fineness of 6,600 dtex (a S-twisted cord in which the ply twist is in the S direction and a Z-twisted cord in which the ply twist is in the Z direction are produced).

Examples 1-8 and Comparative Examples 1-5
[Rubber hardness]
An uncrosslinked rubber sheet having the composition shown in Table 1 was press-crosslinked at a temperature of 165° C. and a pressure of 2 MPa for 30 minutes to prepare a crosslinked rubber sheet (100 mm×100 mm×2 mm thickness). The rubber hardness was measured according to JIS K 6253 (2012) using a durometer A-type hardness tester using a laminate obtained by stacking three crosslinked rubber sheets as a sample. A rubber hardness of 87 degrees or more was regarded as acceptable. Table 3 shows the results.

[M100 (tensile stress at 100% elongation)]
An uncrosslinked rubber sheet having the composition shown in Table 1 was press-crosslinked at 165° C. for 30 minutes to prepare a crosslinked rubber sheet (100 mm×100 mm×2 mm thick). This crosslinked rubber sheet was punched out with a super dumbbell cutter (manufactured by Dumbbell Co., Ltd.) to prepare a dumbbell-shaped No. 3 test piece. Using the prepared test piece, M100 (100% modulus) was measured according to JIS K 6251 (2017). The tensile speed was 500 mm/min, and the test temperature was 23°C. The measurement was performed in a direction (parallel grain direction) in which the longitudinal direction of the test piece and the grain (longitudinal direction of the short fibers) were parallel. M100 made 25MPa or more the pass. Table 3 shows the results.

[Rubber hardness change after heat aging]
An uncrosslinked rubber sheet having the composition shown in Table 1 was press-crosslinked at a temperature of 165° C. and a pressure of 2 MPa for 30 minutes to prepare a crosslinked rubber sheet (100 mm×100 mm×2 mm thickness). This crosslinked rubber sheet was punched out with a super dumbbell cutter (manufactured by Dumbbell Co., Ltd.) to prepare a dumbbell-shaped No. 3 test piece. Based on JIS K 6257 (2017), the prepared test piece was left in a gear-type aging tester set at 150°C for a predetermined number of days and then taken out. After leaving the removed test piece at 23° C. for 24 hours, the rubber hardness was measured using a durometer A-type hardness tester, and the amount of change from the rubber hardness before heat aging was calculated. A change amount of 4 degrees or less after 30 days was regarded as a pass.

[Manufacture of raw-edge cogged V-belt]
An uncrosslinked compression rubber layer sheet having the composition shown in Table 1 and an uncrosslinked first adhesive rubber layer having the composition shown in Table 2 were placed on the outer periphery of a cog-equipped mold in which teeth and grooves were alternately arranged. The laminate obtained by laminating the sheet for the compression rubber layer was wound with the uncrosslinked sheet for the compression rubber layer facing the mold side. After covering the outer periphery of the laminate with a flexible jacket, the mold was placed in a vulcanization can, and steam was injected around the flexible jacket to pressurize and heat (approximately 75°C). A laminate obtained by laminating the uncrosslinked sheet for the compression rubber layer and the uncrosslinked sheet for the adhesive rubber layer was press-fitted into the cog portion of the mold. The mold was then removed from the vulcanization can and the flexible jacket removed. Then, a raw edge cogged V-belt cord is spirally wound around the outer periphery of the uncrosslinked adhesive rubber layer sheet, and an uncrosslinked second adhesive rubber layer sheet having the composition shown in Table 2 is further wound around the outer periphery. A laminate obtained by laminating an uncrosslinked stretchable rubber layer sheet having the composition shown in Table 1 was wound with the uncrosslinked second adhesive rubber layer sheet facing the cord side. After covering the outer periphery of the laminate with a flexible jacket, the mold was placed in a vulcanization can, and pressure and heat were applied for 40 minutes by injecting steam around the flexible jacket and inside the mold. (about 170° C.) to produce a belt sleeve. The produced belt sleeve was cut into a V shape with a cutter, and a raw edge cogged V belt having a cog on the inner peripheral surface of the belt (upper width 20.4 mm, thickness (thickness at the top of the cog) 9.3 mm, Perimeter length 811 mm) was produced.

[Durability running test of raw edge cogged V belt]
The durability running test was conducted using a biaxial running test machine including a drive (Dr.) pulley with a diameter of 115 mm and a driven (Dn.) pulley with a diameter of 95 mm, as shown in FIG. A low-edge cogged V-belt was stretched over each pulley, the rotation speed of the drive pulley was 7000 rpm, the load of the driven pulley was 6 N·m, the shaft load was 400 N, and the belt was run at an ambient temperature of 150°C. The running test machine was temporarily stopped every 24 hours, and the raw edge cogged V-belt was visually observed to measure the presence or absence of cracks and the length of the cracks. When the length of the crack became 2 mm or more, it was determined that the life had expired and the running was terminated. The mass of the belt was measured before running and after the running test was completed, and the wear rate of the belt was calculated by the following formula. A test piece having a crack generation time of 60 hours or more, a life time of 180 hours or more, and a wear rate of 4.5% or less was regarded as acceptable. Table 3 shows the results.

Abrasion rate (%)=[(belt mass before running−belt mass after running)/belt mass before running]×100.

[Comprehensive evaluation]
Rubber hardness, M100, change in rubber hardness after heat aging, and durability running test were comprehensively evaluated according to the following criteria. Table 3 shows the results.

◎: All evaluation items passed ○: Only one evaluation item failed ×: Two or more evaluation items failed

As is clear from the results in Table 3, Comparative Example 1 using Softener 6 with a low kinematic viscosity had a large change in rubber hardness due to heat aging and a short service life. Comparative Example 2, in which the amount of the softener was large, had a low rubber hardness and M100, and a high wear rate. Examples 1 to 8, which used a softening agent with a high kinematic viscosity, had a small change in rubber hardness due to heat aging and a long service life. Examples 6-8, which had a relatively high amount of softener, had a slightly higher wear rate, and Examples 7 and 8 had shorter life times.

Comparative Example 3, which contained a small amount of softening agent, had a short service life probably because the plasticity of the rubber and the flexibility of the belt were not sufficiently improved.

Comparative Examples 4 and 5, which used naphthenic oil, had a large change in rubber hardness due to heat aging and a short service life. It is believed that this is because the oil has low compatibility with EPDM, so that it tends to bloom on the belt surface during high-temperature running, and it cannot remain in the rubber composition for a long time because of its high volatility. In general, naphthenic oils tend to have low kinematic viscosity due to their low %Cp and high degree of branching, and are considered to be less effective in achieving both physical properties and heat aging resistance of transmission belts.

Examples 9-16 and Comparative Examples 6-10
[Rubber hardness]
Samples were prepared in the same manner as in Example 1 using uncrosslinked rubber sheets having the compositions shown in Table 4, and rubber hardness was measured. A rubber hardness of 85 degrees or more was regarded as acceptable. Table 5 shows the results.

[M100 (tensile stress at 100% elongation)]
An uncrosslinked rubber sheet having the composition shown in Table 4 was used to prepare a test piece in the same manner as in Example 1, and M100 (100% modulus) was measured. M100 made 21 MPa or more the pass. Table 5 shows the results.

[Rubber hardness change after heat aging]
An uncrosslinked rubber sheet having the composition shown in Table 4 was used to prepare a test piece in the same manner as in Example 1, and the amount of change in rubber hardness before and after heat aging was calculated. A change amount of 4 degrees or less after 30 days was regarded as a pass.

[Manufacture of V-ribbed belt]
First, a 1-ply rubberized cotton canvas was wrapped around the outer periphery of a cylindrical molding mold with a smooth surface, and an unfilled rubber composition made of a rubber composition shown in Table 2 was applied to the outside of the cotton canvas. A sheet for a sulfuric adhesive rubber layer was wound. Next, an S-twisted cord and a Z-twisted cord are arranged in parallel from above the adhesive rubber layer sheet at a pitch of 1.13 mm, and the two twisted cords (S-twisted and Z-twisted) are helically twisted. It is spun and wound, and an unvulcanized adhesive rubber layer sheet formed of the rubber composition and an unvulcanized compression rubber layer sheet formed of the rubber composition shown in Table 4 are placed thereon in this order. Wrapped around. The molding mold was placed in a vulcanizing can and vulcanized in a state in which the vulcanizing jacket was arranged on the outside of the compressed rubber layer sheet. The cylindrical vulcanized rubber sleeve obtained by vulcanization is taken out from the molding mold, and the compressed rubber layer of the vulcanized rubber sleeve is simultaneously ground with a grinder to form a plurality of V-shaped grooves, and then the vulcanized rubber sleeve is sliced. A V-ribbed belt (3PK1100) having a circumferential length of 1100 mm and having three ribs was obtained by cutting in the circumferential direction with a cutter as shown in FIG.

A schematic sectional view of the obtained V-ribbed belt (a sectional view cut along the belt width direction) is shown in FIG. As shown in FIG. 4, the obtained V-ribbed belt has, in order from the belt lower surface (inner peripheral surface) to the belt upper surface (back surface), a compression rubber layer 12 having a V rib portion 13 and a core wire in the longitudinal direction of the belt. 11 are embedded in the adhesive rubber layer 14 and the extension layer 15 made of cotton canvas with rubber are laminated. In the core wire 11, S-twisted cords and Z-twisted cords are alternately arranged in parallel.

[V-ribbed belt durability running test]
The test layout is shown in Figure 5, in which a drive pulley (Dr.) with a diameter of 120 mm, a tension pulley (Ten.) with a diameter of 45 mm, a driven pulley (Dn.) with a diameter of 120 mm, and an idler pulley (IDL.) with a diameter of 85 mm are arranged in order. An endurance running test was conducted using a machine. A V-ribbed belt is hung on each pulley of the testing machine, the rotation speed of the drive pulley is 4900 rpm, the belt winding angle around the idler pulley is 120°, the belt winding angle around the tension pulley is 90°, and the driven pulley load is 8. 8 kW, a constant load (560 N) was applied to the tension pulley, and the belt was run at an ambient temperature of 150°C. The running test machine was temporarily stopped every 12 hours, and the V-ribbed belt was visually observed to confirm the presence or absence of cracks. When the number of cracks was 5 or more, it was judged that the life had expired and the running was terminated. A case where the crack generation time was 260 hours or more and the life time was 350 hours or more was regarded as acceptable. Table 5 shows the results.

[Comprehensive evaluation]
Rubber hardness, M100, change in rubber hardness after heat aging, and durability running test were comprehensively evaluated according to the following criteria. Table 5 shows the results.

◎: All evaluation items passed ○: Only one evaluation item failed ×: Two or more evaluation items failed

As in the evaluation of the low-edge cogged V-belt, Examples 9 to 16 using a softening agent with high kinematic viscosity showed little change in rubber hardness due to heat aging and had a long life. In addition, when comparing Examples 9 to 12, the higher the kinematic viscosity of the softener, the shorter the time until cracking occurs. it is conceivable that. It is suggested that the optimum kinematic viscosity of softeners has a peak around 40 mm ² /s.

The transmission belt of the present invention is, for example, a flat belt, a V belt (wrapped V belt, raw edge V belt, raw edge cogged V belt, raw edge double cogged V belt, etc.), V ribbed belt, friction transmission belt such as resin block belt; It can be used for meshing transmission belts such as belts with teeth and double-sided toothed belts. In particular, the power transmission belt of the present invention can be preferably used as a power transmission belt such as a cogged V-belt or a toothed belt for which there are strict demands for increased transmission power and a compact layout, and a low-edge cogged V-belt used for driving a CTV. It can be used particularly effectively as

DESCRIPTION OF SYMBOLS 1... Transmission belt 2, 6... Reinforcement cloth 3... Extension rubber layer 4... Adhesion rubber layer 4a... Core body 5... Compression rubber layer

Claims (9)

It contains a polymer component (A) containing an ethylene-α-olefin elastomer, and a softening agent (B) having a kinematic viscosity at 100° C. of 30 to 3500 mm ² /s, and the ratio of the softening agent (B) is A power transmission belt containing 3 to 14 parts by mass of a cured rubber composition per 100 parts by mass of the polymer component (A). 2. The power transmission belt according to claim 1, wherein said softener (B) has a chain aliphatic hydrocarbon skeleton. 3. The power transmission belt according to claim 1, wherein the softening agent (B) contains 50% by mass or more of carbon derived from the chain aliphatic hydrocarbon in the total carbon content of the softening agent (B). The transmission belt according to any one of claims 1 to 3, wherein the softener (B) is paraffinic oil and/or hydrocarbon synthetic oil. The transmission belt according to any one of claims 1 to 4, wherein the cured product has a rubber hardness (JIS-A) of 85 to 95 degrees. The transmission belt according to any one of claims 1 to 5, wherein the cured product has a difference of 4 degrees or less in rubber hardness (JIS-A) before and after heating at 150°C for 30 days. The transmission belt according to any one of claims 1 to 6, wherein the cured product has a 100% modulus of 21 MPa or more. The transmission belt according to any one of claims 1 to 7, which has a compressed rubber layer formed of the cured product. The transmission belt according to any one of claims 1 to 8, which is a low-edge cogged V-belt used for driving a CVT.

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