JP2024022495A - Rubber composition for power transmission belts and power transmission belts - Google Patents

Abstract

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

Description

The present invention relates to a rubber composition capable of forming a compressed rubber layer of a power transmission belt such as a speed change belt, and a power transmission belt equipped with a compressed rubber layer formed from this rubber composition.

Transmission belts used in power transmission mechanisms such as mechanical devices are broadly classified into friction transmission belts and interlocking transmission belts based on the form of power transmission. V-belts, V-ribbed belts, flat belts, and the like are known as friction transmission belts, and toothed belts are known as meshing transmission belts.

One example of the V-belt is a low-edge type belt (low-edge V-belt), which is a rubber layer with an exposed friction transmission surface (V-shaped side surface). Low-edge type belts include low-edge V-belts that do not have cogs, low-edge cogged V-belts that have cogs only on the inner circumferential surface of the belt to improve flexibility, and low-edge cogged V-belts that have cogs only on the inner circumferential surface of the belt to improve flexibility. There is a cog-equipped V-belt called a raw edge cogged V-belt (low-edge double cogged V-belt), which has a cog installed in the belt to improve flexibility.

Applications of these V-belts (particularly low-edge cogged V-belts) include belt-type continuously variable transmissions. As shown in FIG. 1, the belt-type continuously variable transmission 30 is a device in which a V-belt 1 is wound around a driving pulley 31 and a driven pulley 32 to continuously change the gear ratio. Each pulley 31, 32 consists of a fixed sheave 31a, 32a whose movement in the axial direction is restricted or fixed, and a movable sheave 31b, 32b which is movable in the axial direction. It has a structure in which the width of the V groove of the pulleys 31 and 32 formed by the pulleys 31b and 32b can be changed continuously. The V-belt 1 has both end surfaces in the width direction formed of tapered surfaces whose inclinations match the opposing surfaces of the V-grooves of the respective pulleys 31 and 32, and the V-belt 1 has an arbitrary shape in the radial direction of the pulley according to the adjusted width of the V-groove. It fits into the position of. For example, if the state shown in FIG. 1(a) is changed to the state shown in FIG. 1(b) 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 V-belt 1 moves toward the outer periphery in the radial direction of the pulley on the drive pulley 31 side, and toward the inner periphery in the radial direction of the pulley on the driven pulley 32 side, and the winding radius around each pulley 31 and 32 changes continuously. The gear ratio can be adjusted steplessly.

The V-belt (variable speed belt) used in such applications not only rotates around the two axes of the driving pulley and the driven pulley, but also moves repeatedly in the radial direction of the pulley and continuously changes the winding radius. In order to accommodate bending movements, we have developed a belt with abrasion resistance (resistance to wear), heat resistance (resistance to thermal deterioration), flexibility (ease of bending in the circumferential direction of the belt), and lateral pressure resistance (V-shaped Improvements are required in the resistance to pressure acting in the normal direction of the side surfaces) and transmission efficiency (power transmission efficiency or fuel efficiency).

In response to these demands, for example, Japanese Patent Application Publication No. 2017-106617 (Patent Document 1) discloses that by gradually decreasing the crosslinking density of the compressed rubber layer from the outer circumferential side to the inner circumferential side of the belt in the thickness direction, A friction transmission belt is disclosed that can improve side pressure resistance while maintaining fuel efficiency. Furthermore, Japanese Patent Application Laid-open No. 2019-95059 (Patent Document 2) discloses that by containing liquid crystal polyester short fibers in the compressed rubber layer, the flexibility and lateral pressure resistance of the power transmission V-belt can be improved, and the low-edge type V-belt can be improved. It is disclosed that when used in a belt, the abrasion resistance and durability of the belt can also be improved.

Japanese Patent Application Publication No. 2017-106617 JP 2019-95059 Publication

In the examples of Patent Documents 1 and 2, an ethylene-propylene-diene terpolymer (EPDM) is used as the polymer component of the rubber composition. One of the characteristics of EPDM is its high heat resistance due to the fact that it does not have double bonds in its main chain. There is room for improvement with combination agents other than the ingredients, and further research is expected.

Therefore, an object of the present invention is to simultaneously improve the abrasion resistance and transmission efficiency of a rubber composition using an ethylene-α-olefin elastomer such as EPDM as the main polymer component when used in a power transmission belt. It is an object of the present invention to provide a rubber composition capable of providing a rubber composition capable of providing a transmission belt with improved abrasion resistance and transmission efficiency at the same time.

As a result of intensive studies to achieve the above-mentioned object, the present inventors have discovered that a polymer component containing a high viscosity polymer component containing an ethylene-α-olefin elastomer as a main component, an inorganic filler, and short fibers, is 15 to 60 parts by mass based on 100 parts by mass of the polymer component, and the 8% bending stress in the direction parallel to the short fibers of the crosslinked product is adjusted to 2.5 MPa or less. The inventors discovered that by forming a rubber layer, the abrasion resistance and transmission efficiency of the power transmission belt can be improved at the same time, and the present invention was completed.

That is, the rubber composition as aspect [1] of the present invention is
A rubber composition for forming a compressed rubber layer of a power transmission belt, the rubber composition comprising:
Contains polymer components, inorganic fillers and short fibers,
the polymer component includes an ethylene-α-olefin elastomer,
The proportion of the ethylene-α-olefin elastomer is 50% by mass or more in the polymer component,
The uncrosslinked product of the polymer component has a Mooney viscosity of 31 ML (1 + 4) 125 ° C. or higher,
The proportion of the inorganic filler is 20 to 60 parts by mass based on 100 parts by mass of the polymer component, and the crosslinked rubber composition has an 8% bending stress of 2.5 MPa or less in the direction parallel to the short fibers. be.

Aspect [2] of the present invention is a mode in which the above-mentioned aspect [1] further includes a crosslinking agent, and the crosslinking agent includes a sulfur-based crosslinking agent.

Aspect [3] of the present invention is an aspect in which the above-mentioned aspect [1] or [2] further includes a co-crosslinking agent.

Aspect [4] of the present invention is the aspect [3] above, wherein the proportion of the co-crosslinking agent is 1 to 5 parts by mass with respect to 100 parts by mass of the polymer component.

Aspect [5] of the present invention is the inorganic filler containing carbon black, and the carbon black containing soft carbon, and the carbon black containing soft carbon. The ratio is 50 to 200 parts by mass based on 100 parts by mass of the short fibers.

Aspect [6] of the present invention is an embodiment in which the proportion of the softener is 3 parts by mass or less based on 100 parts by mass of the polymer component in any of the above embodiments [1] to [5].

Aspect [7] of the present invention is any one of the aspects [1] to [6], wherein the short fibers include aramid short fibers and aliphatic polyamide short fibers, and the proportion of the aramid short fibers is , the amount is 100 parts by mass or more based on 100 parts by mass of the short aliphatic polyamide fibers.

The present invention also includes, as aspect [8], a power transmission belt in which a compressed rubber layer is formed from the rubber composition of any one of aspects [1] to [7].

In the present invention, a rubber composition for forming a compressed rubber layer of a power transmission belt includes a high viscosity polymer component containing an ethylene-α-olefin elastomer as a main component, an inorganic filler, and short fibers, and The proportion of the inorganic filler is 20 to 60 parts by mass with respect to 100 parts by mass of the polymer component, and the 8% bending stress in the direction parallel to the short fibers of the crosslinked product is adjusted to 2.5 MPa or less. The wear resistance and transmission efficiency can be improved at the same time. Furthermore, by adjusting the type and amount of specific compounding agents (e.g., inorganic fillers, short fibers, crosslinking agents, co-crosslinking agents, softening agents, etc., especially crosslinking agents and short fibers), wear resistance and In addition to transmission efficiency, lateral pressure resistance and flexibility can also be improved.

FIG. 1 is a schematic cross-sectional view for explaining the speed change mechanism of a belt type continuously variable transmission. FIG. 2 is a schematic perspective view showing an example of the power transmission belt of the present invention. FIG. 3 is a schematic cross-sectional view of the power transmission belt of FIG. 2 taken in the belt length direction. FIG. 4 is a graph showing the behavior of Mooney viscosity to explain the method for measuring the minimum Mooney scorch viscosity (Vm). FIG. 5 is a schematic perspective view for explaining a method for measuring 4% bending stress (in the direction orthogonal to the short fibers) of the crosslinked rubber molded body obtained in the example. FIG. 6 is a schematic perspective view for explaining a method for measuring 8% bending stress (in the short fiber parallel direction) of the crosslinked rubber molded body obtained in the example. FIG. 7 shows the layout of the abrasion durability test of the low edge double cogged V-belt obtained in the example. FIG. 8 shows the layout of the transmission efficiency test of the low edge double cogged V-belt obtained in the example.

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

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

The ethylene-α-olefin elastomer may contain ethylene units and α-olefin units as constituent units, and may further contain diene units. Therefore, ethylene-α-olefin elastomers include ethylene-α-olefin copolymer rubber, ethylene-α-olefin-diene terpolymer 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, and octene. Among these α-olefins, α-C _3-4 olefins such as propylene (especially propylene) are preferred.

As the diene monomer for forming the diene unit, a non-conjugated diene monomer is usually used. Examples of the non-conjugated diene monomer include dicyclopentadiene, methylenenorbornene, ethylidenenorbornene, 1,4-hexadiene, and cyclooctadiene. Among these diene monomers, ethylidene norbornene and 1,4-hexadiene (especially ethylidene norbornene) 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 Examples include -diene rubber [ethylene-propylene-diene terpolymer (EPDM)].

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 has excellent heat resistance, cold resistance, and weather resistance. Preferred, particularly EPDM. Therefore, the proportion of EPDM may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more (particularly 95% by mass or more) based on the entire ethylene-α-olefin elastomer. , 100% by mass (EPDM only).

In the ethylene-α-olefin elastomer, the ratio (mass ratio) of ethylene to α-olefin is 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 to 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 (for example 50/50 to 60/40), most preferably 55/45 to 70/30 (especially 55/45 to 65/35) It may be.

In the present application, the ratio (mass ratio) between ethylene and α-olefin can be measured by a conventional method, but may be a ratio based on monomers.

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), The content is preferably 13% by mass or less (for example, 1 to 13% by mass), more preferably 12% by mass or less (for example, 3 to 12% by mass), and even more preferably 10% by mass or less (for example, 5 to 10% by mass). If the diene content is too high, there is a risk that high heat resistance cannot be ensured.

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

The iodine number of the ethylene-α-olefin elastomer containing a diene monomer is, for example, 3 to 40, preferably 5 to 30, and more preferably 10 to 20. If the iodine value is too low, the crosslinking of the rubber composition will be insufficient, resulting in abrasion and adhesion. Conversely, if the iodine value is too high, the scorch of the rubber composition will be short, making it difficult to handle and reducing heat resistance. tends to decrease.

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

The rubber composition of the present invention is characterized in that the uncrosslinked polymer component (A) (particularly the uncrosslinked ethylene-α-olefin elastomer) has a high Mooney viscosity. In the present invention, in order to increase the transmission efficiency, the proportion of the inorganic filler described below is suppressed to a small amount, so by combining it with the polymer component (A) having a high Mooney viscosity, wear resistance can be ensured.

Mooney viscosity is calculated by filling an uncrosslinked polymer component in a cavity in contact with a rotor with grooves on its surface and measuring the torque required to rotate the rotor. It is used as an index to express the properties (ease of processing).

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

In addition, in this application, Mooney viscosity can be measured by a method similar to the Mooney viscosity test of JIS K 6300-1 (2013), and the test conditions are: using an L-shaped rotor, test temperature 125 ° C, preheating for 1 minute, rotor The operating time is 4 minutes. Further, when the polymer component (A) is a combination of multiple types of polymer components, the Mooney viscosity of the entire polymer component (A) is a weighted average value. That is, Mooney viscosity (weighted average) means an average value based on mass ratio, and is the sum of the products of Mooney viscosity and mass fraction of each polymer component.

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

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

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

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

Examples of the inorganic filler (B) 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, Metal oxides such as aluminum; 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; Magnesium carbonate and calcium carbonate metal carbonates; metal sulfates such as calcium sulfate and barium sulfate), 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, and carbonaceous materials and metal oxides are more preferable. Carbon black is particularly preferred in the crosslinked composition because it can improve hardness, modulus, and abrasion resistance.

Carbon black is generally classified into several grades based on differences in primary particle size, iodine adsorption amount, nitrogen adsorption specific surface area, etc. Regarding the classification of carbon black, ASTM classifies it into N0** to N9** based on the amount of iodine adsorbed, but the conventional classification based on the performance of the rubber product in which it is compounded (SAF, HAF, GPF, etc.) ) are also used. N110 (SAF), N220 (ISAF), N330 (HAF), etc., which have small primary particle diameters, are called hard carbons, while N550 (FEF), N660 (GPF), N762 (SRF), etc., which have large primary particle diameters, are soft carbons. It is also sometimes called. There is a close relationship between the amount of iodine adsorbed and the primary particle size, and the smaller the primary particle size, the larger the amount of iodine adsorbed. Carbon black is classified using the SEAST (registered trademark) series manufactured by Tokai Carbon Co., Ltd. as an example, and the iodine adsorption amount and average primary particle diameter are shown in Table 1.

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

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

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

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

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

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

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

The average primary particle diameter of hard carbon is, for example, 10 to 35 nm, preferably 12 to 33 nm, more preferably 15 to 30 nm (eg, 20 to 25 nm), and more preferably 20 to 30 nm (eg, 25 to 30 nm).

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

In the present invention, it is preferable that the carbon black contains soft carbon, since the coefficient of friction and internal heat generation when the belt is bent are reduced, thereby improving transmission efficiency. The proportion of soft carbon in carbon black may be 10% by mass or more, preferably 50% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and most preferably 100% by mass. .

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

The proportion of carbon black is 15 to 60 parts by weight (especially 20 to 58 parts by weight), preferably 20 to 55 parts by weight, more preferably 30 to 52 parts by weight, based on 100 parts by weight of the polymer component (A). , more preferably 40 to 51 parts by weight, most preferably 45 to 50 parts by weight. In applications requiring high transmission efficiency, the proportion of carbon black is preferably 15 to 50 parts by mass, more preferably 18 to 40 parts by mass, and more preferably 18 to 40 parts by mass, based on 100 parts by mass of the polymer component (A). It may be 20 to 30 parts by mass. If the proportion of carbon black is too small, there is a risk that wear resistance and lateral pressure resistance will decrease, and if it is too large, there is a possibility that flexibility and transmission efficiency will decrease.

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

The proportion of the inorganic filler (first inorganic filler) (B) is 18 to 70 parts by weight, preferably 20 to 65 parts by weight, more preferably 30 parts by weight, based on 100 parts by weight of the polymer component (A). ~60 parts by weight, more preferably 40-58 parts by weight, most preferably 45-55 parts by weight. In applications requiring high transmission efficiency, the proportion of the inorganic filler (B) is preferably 15 to 50 parts by weight, more preferably 20 to 40 parts by weight, based on 100 parts by weight of the polymer component (A). , more preferably 25 to 30 parts by mass. If the proportion of the inorganic filler (B) is too small, there is a risk that wear resistance and lateral pressure resistance will decrease, and if it is too large, there is a possibility that flexibility and transmission efficiency will decrease.

(C) Short fibers The rubber composition of the present invention contains short fibers (first short fibers) (C) as an essential component in order to improve the abrasion resistance of the compressed rubber and reduce the coefficient of friction. In particular, if the short fibers are oriented in the belt width direction and embedded in the compressed rubber layer, compressive deformation of the transmission belt against pressure from the pulleys can be suppressed, so that wear resistance can be improved while maintaining transmission efficiency. Examples of the method for orienting the short fibers in the belt width direction include a method of orienting the short fibers by rolling them with rolls.

(Aramid staple fiber)
The short fibers preferably include aramid short fibers in order to improve the lateral pressure resistance and abrasion resistance of the power transmission belt.

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

Examples of para-aramid fibers include poly-paraphenylene terephthalamide fibers (e.g., "Twaron (registered trademark)" by Teijin Corporation, "Kevlar (registered trademark)" by DuPont-Toray Co., Ltd.), Examples include copolymer fibers of phenylene terephthalamide and 3,4'-oxydiphenylene terephthalamide (eg, "Technora (registered trademark)" manufactured by Teijin Ltd.).

Examples of meta-aramid fibers include polymetaphenylene isophthalamide fibers (eg, "Conex (registered trademark)" manufactured by Teijin Ltd.), and the like.

These aramid fibers can be used alone or in combination of two or more. Among these, para-aramid short fibers are preferred because they can easily improve wear resistance and transmission efficiency at the same time by combining with aliphatic polyamide short fibers to be described later.

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

The average fiber length of the aramid short fibers is, for example, 1 to 20 mm, preferably 1.3 to 15 mm, more preferably 1.5 to 10 mm, more preferably 2 to 5 mm, and most preferably 2.5 to 4 mm. If the average fiber length of the aramid short fibers is too short, the mechanical properties in the grain direction (for example, modulus) cannot be sufficiently enhanced, and there is a risk that lateral pressure resistance will decrease.On the other hand, if the average fiber length is too long, the rubber composition There is a risk that the short aramid fibers in the product will be poorly dispersed, and the coefficient of friction on the surface will not be sufficiently reduced, leading to a decrease in transmission efficiency.

The aramid short fibers may be oriented substantially parallel to the width direction of the belt and embedded in the compressed rubber layer in order to suppress compressive deformation of the belt due to pressure from the pulley.

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

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

In the adhesion treatment of aramid short fibers, various adhesive treatments are used, such as a treatment solution containing an initial condensate of phenols and formalin (such as a prepolymer of novolak or resol-type phenolic resin), and a treatment containing a rubber component (or latex). treatment liquid, a treatment liquid containing the above-mentioned initial condensate and a rubber component (latex), a treatment liquid containing a silane coupling agent, an epoxy compound (epoxy resin, etc.), a reactive compound (adhesive compound) such as an isocyanate compound, etc. can do. In a preferred adhesive treatment, the aramid short fibers are treated with a treatment liquid containing the above-mentioned initial condensate and a rubber component (latex), particularly at least a resorcinol-formalin-latex (RFL) liquid. Such treatment liquids may be used alone or in combination of two or more types. After pretreatment with (adhesive compound), treatment with RFL liquid may be performed.

When treated with such a treatment liquid, especially an RFL liquid, the aramid short fibers and the polymer component (A) can be strongly bonded. RFL liquid is a mixture of an initial condensate of resorcinol and formaldehyde and rubber latex. The molar ratio of resorcin and formaldehyde is within a range that can improve the adhesion between the polymer component (A) and short fibers, for example, former/latter = 1/0.3 to 1/3, preferably 1/0.4 to 1/3. The ratio is 1/2, more preferably 1/0.5 to 1/1.5, more preferably 1/0.6 to 1/1, and most preferably 1/0.6 to 1/0.8.

The type of rubber component in the latex is not particularly limited, and diene rubbers (styrene-butadiene-vinylpyridine terpolymer, chloroprene rubber, butadiene rubber, etc.) and chlorosulfonated polyethylene rubber are preferable, and styrene-butadiene- Particularly preferred are vinylpyridine terpolymers.

The proportion of the initial condensate of resorcin and formalin is, for example, 10 to 100 parts by mass, preferably 12 to 50 parts by mass, more preferably 15 to 30 parts by mass, per 100 parts by mass of the rubber component (solid content) of the latex. It is. Note that the total solid content concentration of the RFL liquid can be adjusted within the range of 5 to 40% by mass.

The adhesion rate of the adhesive component (solid content) to the aramid short fibers {[(mass after adhesive treatment − mass before adhesive treatment)/(mass after adhesive treatment)]×100} is, for example, 1 to 25% by mass, preferably is 2 to 20% by weight, more preferably 2.5 to 15% by weight, more preferably 3 to 10% by weight, and most preferably 4 to 8% by weight. If the adhesion rate of the adhesive component is too low, the dispersibility of the aramid short fibers in the rubber composition and the adhesion between the aramid short fibers and the polymer component (A) will be insufficient; on the other hand, if the adhesion rate is too high, the adhesive component There is a possibility that the aramid short fibers may be firmly fixed to each other, and the dispersibility may be reduced.

The proportion of the aramid short fibers is, for example, 5 to 30 parts by weight, preferably 10 to 28 parts by weight, more preferably 15 to 25 parts by weight, and more preferably 17 to 23 parts by weight, based on 100 parts by weight of the polymer component (A). Department. If the proportion of aramid short fibers is too small, there is a risk that wear resistance and lateral pressure resistance will decrease, and if it is too large, the effect of reducing the friction coefficient will be small, and there is a possibility that transmission efficiency will decrease.

In addition, in this application, when short fibers are adhesively treated, the proportion of short fibers means the proportion of short fibers that have been subjected to adhesive treatment (the proportion of short fibers containing adhesive components attached after adhesive treatment).

(Aliphatic polyamide staple fiber)
The short fibers preferably include a combination of the above-mentioned aramid short fibers and aliphatic polyamide short fibers (nylon short fibers) from the viewpoint of achieving both abrasion resistance and transmission efficiency. Nylon short fibers have the effect of lowering the coefficient of friction and improving transmission efficiency, so by combining them with aramid short fibers, it becomes easier to balance wear resistance and transmission efficiency.

Examples of the aliphatic polyamide fibers (nylon fibers) constituting the nylon short fibers include polyamide 46 fibers, polyamide 6 fibers, polyamide 66 fibers, polyamide 610 fibers, polyamide 612 fibers, polyamide 11 fibers, polyamide 12 fibers, etc. .

These nylon fibers can be used alone or in combination of two or more. Among these, nylon fibers having C _4-8 alkylene chains such as polyamide 6 fibers and polyamide 66 fibers are preferred.

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

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

The nylon short fibers may be oriented substantially parallel to the width direction of the belt and embedded in the compressed rubber layer in order to suppress compressive deformation of the belt due to pressure from the pulley.

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

The proportion of the nylon short fibers is, for example, 1 to 25 parts by weight, preferably 3 to 23 parts by weight, more preferably 5 to 20 parts by weight, and most preferably 7 to 15 parts by weight, based on 100 parts by weight of the polymer component (A). Department. If the proportion of nylon short fibers is too small, there is a risk that the effect of improving transmission efficiency will be reduced, and if it is too large, there is a possibility that abrasion resistance and lateral pressure resistance will be reduced.

The proportion of the aramid short fibers can be selected from the range of 10 parts by mass or more (for example, 50 parts by mass or more), specifically 80 parts by mass or more (particularly 100 parts by mass or more), for example, The amount is 100 to 1000 parts by weight, preferably 120 to 500 parts by weight, more preferably 130 to 300 parts by weight, more preferably 150 to 250 parts by weight, and most preferably 170 to 230 parts by weight. If the proportion of aramid fibers is too high (the proportion of nylon short fibers is too small), the effect of improving transmission efficiency may decrease or the flexibility may decrease; If the proportion of fibers is too high), there is a risk that the abrasion resistance and lateral pressure resistance will decrease.

(Other short fibers and percentage of total short fibers)
The short fibers (C) may further contain other short fibers (short fibers other than aramid short fibers and nylon short fibers). Other short fibers include, for example, polyolefin short fibers (polyethylene short fibers, polypropylene short fibers, etc.), polyester short fibers {for example, polyalkylene arylate short fibers [polyethylene terephthalate (PET) short fibers, polyethylene naphthalate short fibers, etc. Synthetic short fibers such as _vinylon short fibers, _polyvinyl alcohol short fibers, and polyparaphenylenebenzobisoxazole (PBO) short fibers Fibers include natural short fibers such as cotton, linen, and wool; and inorganic short fibers such as carbon fiber. These other short fibers can be used alone or in combination of two or more. Among these other short fibers, polyester short fibers such as PET short fibers are preferred.

The proportion of other short fibers in the short fibers (C) may be 50% by mass or less, preferably 30% by mass or less, and more preferably 10% by mass or less. The short fibers (C) may not substantially contain other short fibers, and preferably do not contain other short fibers such as polyester short fibers. That is, the short fibers (C) may consist only of aramid short fibers and nylon short fibers. If the proportion of other short fibers is too large, it may be difficult to improve transmission efficiency.

The ratio of the short fibers (C) (ratio of the total amount of short fibers) is 15 to 40 parts by weight, preferably 20 to 35 parts by weight, more preferably 25 to 35 parts by weight, based on 100 parts by weight of the polymer component (A). Part by mass. If the proportion of the short fibers (C) is too small, the abrasion resistance and lateral pressure resistance will decrease, and the coefficient of friction will not be sufficiently reduced, so there is a risk that the transmission efficiency will not improve. On the other hand, if the proportion of short fibers (C) is too high, there is a possibility that the flexibility will be reduced.

In the present invention, when the inorganic filler (B) contains carbon black, both wear resistance and transmission efficiency can be achieved by adjusting the mass ratio of carbon black and short fibers (C). The proportion of carbon black can be selected from a range of about 10 to 500 parts by mass, for example 50 to 200 parts by mass, preferably 80 to 190 parts by mass, more preferably 100 to 180 parts by mass, based on 100 parts by mass of short fibers (C). Parts by weight (for example, 140 to 175 parts by weight), more preferably 150 to 170 parts by weight. If the proportion of carbon black is too high (the proportion of short fibers (C) to carbon black is too small), the anisotropy of the rubber composition will decrease, making it difficult to achieve both flexibility and lateral pressure resistance. Otherwise, the transmission efficiency may decrease. On the other hand, if the proportion of carbon black is too low (the proportion of short fibers (C) is too high), there is a risk that the abrasion resistance and flexibility will decrease and cracks will be likely to occur.

(D) Crosslinking agent The rubber composition of the present invention may contain a crosslinking agent (D), in particular a sulfur-based Preferably, a crosslinking agent is included.

Examples of the sulfur-based crosslinking agent include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, and sulfur chloride (sulfur monochloride, sulfur dichloride, etc.). These sulfur-based crosslinking agents can be used alone or in combination of two or more. Among these, sulfurs such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersed sulfur are preferred, and powdered sulfur is particularly preferred.

The proportion of the sulfur-based crosslinking agent can be selected, for example, from a range of about 1 to 10 parts by weight, and preferably 1.2 parts by weight or more, for example 1.2 to 5 parts by weight, based on 100 parts by weight of the polymer component (A). , preferably 1.3 to 3 parts by weight, more preferably 1.5 to 2.5 parts by weight, more preferably 1.6 to 2.3 parts by weight, most preferably 1.8 to 2.2 parts by weight. be. If the proportion of sulfur-based crosslinking agent is too small, rubber hardness, lateral pressure resistance, and abrasion resistance may decrease; if it is too large, flex fatigue resistance may decrease, and bloom (on the surface) may occur. There is also a possibility that precipitation) may occur.

The crosslinking agent (D) may further contain an organic peroxide as another crosslinking agent (or vulcanizing agent). Examples of organic peroxides include organic peroxides normally used for crosslinking rubbers and resins, such as diacyl peroxide, peroxy ester, dialkyl peroxide (e.g. dicumyl peroxide, t-butylcumyl peroxide). , 1,1-di-butylperoxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane, 1,3-bis(t-butyl (peroxy-isopropyl)benzene, di-t-butyl peroxide, etc.). These organic peroxides can be used alone or in combination of two or more. Further, the organic peroxide is preferably a peroxide whose decomposition temperature is about 150 to 250°C (for example, 175 to 225°C) to obtain a half-life of 1 minute due to thermal decomposition.

The proportion of the organic peroxide may be 100 parts by mass or less, preferably 50 parts by mass or less, more preferably 30 parts by mass or less, more preferably 10 parts by mass or less, based on 100 parts by mass of the sulfur-based crosslinking agent. It is. If the proportion of the organic peroxide is too large, there is a risk that the bending fatigue resistance of the cured product will decrease. The crosslinking agent (D) is particularly preferably substantially free of organic peroxide, most preferably free of organic peroxide.

The proportion of the sulfur-based crosslinking agent (especially sulfur such as powdered sulfur) in the crosslinking agent (D) may be 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and more. Preferably it is 100% by mass. If the proportion of the sulfur-based crosslinking agent is too small, the flexibility of the compressed rubber layer may decrease.

The proportion of the crosslinking agent (D) can be selected from a range of about 1 to 10 parts by weight, for example, 1.2 to 10 parts by weight, preferably 1.3 to 8 parts by weight, based on 100 parts by weight of the polymer component (A). Parts by weight, more preferably 1.5 to 5 parts by weight, more preferably 1.6 to 3 parts by weight, most preferably 1.8 to 2.5 parts by weight.

(E) Co-crosslinking agent (crosslinking aid or co-vulcanizing agent co-agent)
The rubber composition of the present invention may further contain a co-crosslinking agent (E). In particular, when the crosslinking agent (D) contains a sulfur-based crosslinking agent (especially sulfur such as powdered sulfur), it is difficult to increase the hardness by crosslinking with the sulfur-based crosslinking agent, and the lateral pressure resistance decreases. However, by combining a sulfur-based crosslinking agent and a co-crosslinking agent (E), the effect of the sulfur-based crosslinking agent can be enhanced while maintaining lateral pressure resistance and heat resistance. By taking advantage of this, flexibility and transmission efficiency can be improved. Among these, when the co-crosslinking agent (E) contains a bismaleimide compound, the effect of improving lateral pressure resistance and abrasion resistance is large.

Examples of the bismaleimide compound include aliphatic bismaleimide (for example, N,N'-1,2-ethylene dimaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)cyclohexane, etc.), aromatic Group bismaleimides {for example, N,N'-m-phenylene dimaleimide, 4-methyl-1,3-phenylene dimaleimide, 4,4'-diphenylmethane dimaleimide, 2,2-bis[4-(4-maleimide) phenoxy)phenyl]propane, 4,4'-diphenyl ether dimaleimide, 4,4'-diphenylsulfone dimaleimide, 1,3-bis(3-maleimidophenoxy)benzene, etc.).

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

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

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

The proportion of the other co-crosslinking agent may be 100 parts by mass or less, preferably 50 parts by mass or less, more preferably 30 parts by mass or less, more preferably 10 parts by mass or less, based on 100 parts by mass of the bismaleimide compound. It is. If the proportion of other co-crosslinking agents is too large, the effect of improving lateral pressure resistance and abrasion resistance may decrease.

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

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

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

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

The proportion of the crosslinking accelerator (F) is, for example, 0.1 to 10 parts by weight, preferably 0.3 to 5 parts by weight, more preferably 1 to 3 parts by weight, based on 100 parts by weight of the polymer component (A). Most preferably it is 1.5 to 2.5 parts by mass. If the proportion of the crosslinking accelerator is too small, the lateral pressure resistance of the compressed rubber layer may be reduced, and if it is too large, the flexibility may be reduced.

(G) Softener The rubber composition of the present invention does not need to contain a softener (G), but may further contain a softener (G) as necessary to improve flexibility. You can stay there. The softener (G) may be a so-called plasticizer or a processing aid.

Examples of the softener (G) include mineral oil-based softeners {for example, petroleum-based softeners [paraffinic oils, alicyclic oils (naphthenic oils), aromatic oils, etc.], coal tar-based softeners [Coal tar, coumaron-indene resin, etc.]}, vegetable oil-based softeners {e.g., fatty oil-based softeners [fatty acids or metal salts thereof such as stearic acid and metal salts of stearate; fatty acid esters such as stearate esters; stearin Fatty acid amides such as acid amide; fatty oils, etc.]; Softeners derived from pine resin [pine tar, rosin, factice, etc.], synthetic softeners {for example, synthetic resin softeners [hydrocarbon-based synthetic oils (low Molecular weight paraffins, low molecular weight waxes, phenol/aldehyde resins, liquid ethylene-α-olefin copolymers, etc.), liquid rubbers (liquid polybutene, liquid polybutadiene, liquid isoprene rubber, etc.), synthetic plasticizers (phthalates such as dioctyl phthalate) acid diesters, polyester plasticizers, C _6-18 alkanedicarboxylic acid esters such as dioctyl sebacate, etc.).

These softeners (G) can be used alone or in combination of two or more. Among these, petroleum-based softeners such as paraffin oil, C _8-24 fatty acids such as stearic acid (including their metal salts, esters, and amides) are preferred, and petroleum-based softeners and C _8-24 fatty acids are preferred. A combination of these is particularly preferred.

When the softener (G) is a combination of a petroleum softener and a C _8-24 fatty acid, the proportion of the C _8-24 fatty acid is, for example, 10 to 1000 parts by mass per 100 parts by mass of the petroleum softener. parts, preferably 30 to 300 parts by weight, more preferably 50 to 200 parts by weight, more preferably 70 to 150 parts by weight, most preferably 80 to 120 parts by weight.

The proportion of the softener (G) is, for example, 3 parts by mass per 100 parts by mass of the polymer component (A) from the viewpoint of not reducing the effects of lateral pressure resistance and abrasion resistance due to the polymer component (A) having a high Mooney viscosity. From the viewpoint of achieving both lateral pressure resistance, abrasion resistance, and flexibility, it is preferably 0.1 to 3 parts by mass, preferably 0.5 to 2.8 parts by mass, and more preferably 0. .8 to 2.5 parts by weight, more preferably 1 to 2.3 parts by weight, most preferably 1.5 to 2.2 parts by weight.

(H) Other components The rubber composition of the present invention may further contain other components (H). Other components (H) include additives commonly used in rubber, such as crosslinking retarders, anti-aging agents (antioxidants, heat anti-aging agents, flex cracking inhibitors, anti-ozonants, etc.) , colorants, tackifiers, lubricants, coupling agents (such as silane coupling agents), stabilizers (such as ultraviolet absorbers and heat stabilizers), flame retardants, and antistatic agents. These additives can be used alone or in combination of two or more. Among these, anti-aging agents (first anti-aging agents) are commonly used.

The total proportion of other components (H) is, for example, 0.1 to 15 parts by weight, preferably 0.3 to 10 parts by weight, and more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the polymer component (A). 7 parts by mass. The proportion of the anti-aging agent is, for example, 0.1 to 5 parts by weight, preferably 0.5 to 4 parts by weight, more preferably 1 to 3 parts by weight, and most preferably, based on 100 parts by weight of the polymer component (A). is 1.5 to 2.5 parts by mass.

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

In the present application, the Mooney scorch minimum viscosity can be measured in accordance with the Mooney scorch test of JIS K 6300-1 (2013), and more specifically, by the method described in the Examples below.

The hardness (Hs) of the crosslinked product (crosslinked rubber composition) of the rubber composition of the present invention is, for example, 83 to 95°, preferably 85 to 94°, more preferably 87 to 93°, and more preferably 88 to 92°. , most preferably 89-91°. If the hardness of the crosslinked product is too small, there is a risk that the lateral pressure resistance will be reduced, and if the hardness is too large, there is a risk that the flexibility will be reduced.

In this application, the rubber hardness of the crosslinked rubber composition is determined based on the spring durometer hardness test specified in JIS K 6253 (2012) (Vulcanized rubber and thermoplastic rubber - How to determine hardness). , indicates the value Hs (type A) measured using a type A durometer, and is sometimes simply written as rubber hardness. In detail, it can be measured by the method described in Examples below.

The short fibers (C) contained in the rubber composition of the present invention are usually oriented in a predetermined direction in the compressed rubber layer. For example, when the rubber composition forms a compressed rubber layer of a friction transmission belt such as a low edge cogged V belt, the compressed rubber layer is oriented in the width direction of the belt in order to suppress compressive deformation of the belt in response to pressure from a pulley. It is preferable that short fibers (C) are embedded in the layer.

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

In the crosslinked rubber composition of the present invention, from the viewpoint of improving lateral pressure resistance, the 4% bending stress in the direction perpendicular to the short fibers is, for example, 2.5 to 4.5 MPa, preferably 2.7 to 4 MPa, more preferably 3 ~3.5MPa. If the 4% bending stress in the direction orthogonal to the short fibers is too small, the lateral pressure resistance of the belt may be reduced, and if it is too high, the flexibility may be reduced.

In this application, the bending stress is 8% bending stress in the direction parallel to the short fibers, and the length direction of the holding member is arranged to be the orientation direction (length direction) of the short fibers, and 4% bending stress can be measured by arranging the length direction of the holding member in a direction perpendicular to the orientation direction (length direction) of the short fibers. It can be measured by the method described.

Furthermore, in the present application, the "short fiber parallel direction" is not limited to the length direction of the short fibers, but may also be a direction within a range of ±5° in the length direction. Further, the "short fiber orthogonal direction" may be not only a direction perpendicular to the length direction of the short fiber (perpendicular direction), but also a direction within a range of ±5° in the perpendicular direction.

[Transmission belt]
The power transmission belt of the present invention is not particularly limited as long as it has a compressed rubber layer capable of contacting pulleys and this compressed rubber layer is formed of the crosslinked rubber composition. The power transmission belt may include a rubber layer), a compressed rubber layer formed on one surface of the core layer, and a stretchable rubber layer formed on the other surface of the core layer. Furthermore, among power transmission belts, friction transmission belts that require wear resistance are preferred.

Friction transmission belts include, for example, V-belts [wrapped V-belts, low-edge V-belts, raw-edge cogged V-belts (low-edge cogged V-belts with cogs formed on the inner periphery of the low-edge V-belt, inner periphery of low-edge V-belts). Examples include a low edge double cogged V belt in which cogs are formed on both the side and outer circumferential sides), a V-ribbed belt, and a flat belt. Among these, V-belts or V-ribbed belts whose transmission surfaces are inclined in a V-shape (or at a V angle) are preferable, and are required to have both wear resistance and transmission efficiency at a high level. For example, V-belts used in belt-type continuously variable transmissions (eg, raw edge cogged V-belts) are preferred.

Furthermore, the raw edge cogged V-belt of the present invention includes a raw-edge cogged V-belt in which cogs are formed only on the inner circumferential side of the low-edge V-belt, and a raw-edge cogged V-belt in which cogs are formed on both the inner circumferential side and the outer circumferential side of the low-edge V-belt. It can be broadly divided into low edge double cogged V-belts. Among these, the low-edge double cogged V-belt is particularly preferred because it is used in more severe conditions and is required to have both lateral pressure resistance and flexibility at a high level.

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

In this example, the low edge double cogged V-belt 1 has inner cog peaks 1a and inner cog valleys 1b arranged alternately along the length direction of the belt (direction A in the figure) on the inner circumferential surface of the belt body. The cross section of the inner cog ridge 1a in the longitudinal direction is approximately semicircular (curved or wavy), and is perpendicular to the longitudinal direction. The cross-sectional shape in the direction (width direction or B direction in the figure) is trapezoidal. That is, each inner circumferential cog ridge 1a protrudes in a substantially semicircular shape from the inner circumferential cog valley 1b in the belt thickness direction in the cross section in the A direction.

Further, the outer circumferential surface also has an outer circumferential cog portion in which outer circumferential cog peaks 1c and outer circumferential cog valleys 1d are alternately arranged along the length direction of the belt, and the outer circumferential cog peaks 1c are formed in a longitudinal direction. The cross-sectional shape in is approximately trapezoidal, and the cross-sectional shape in the direction perpendicular to the length direction (width direction or direction B in the figure) is approximately rectangular. That is, each outer circumferential cog ridge 1c protrudes in a substantially trapezoidal shape from the outer circumferential cog valley 1d in the belt thickness direction in the cross section in the A direction.

The raw edge double cogged V belt has a laminated structure, and from the outer circumferential side to the inner circumferential side of the belt are a stretch rubber layer 2, a core layer (adhesive rubber layer) 3, a compressed rubber layer 4, and a reinforcing cloth 5. Laminated in sequence. The cross-sectional shape in the belt width direction is approximately trapezoidal, with the belt width decreasing from the outer circumferential side to the inner circumferential side. Further, a core body 3a is embedded in the core layer 3, and the inner circumferential cog portion and the outer circumferential cog portion are formed in the compressed rubber layer 4 and the stretchable rubber layer 2, respectively, using a cog-equipped mold. . In this example, only the inner peripheral surface is covered with the reinforcing cloth, but the surface of the stretchable rubber layer 2 may also be covered with the second reinforcing cloth. Further, the reinforcing cloth is not essential, and a structure in which neither the inner circumferential surface nor the outer circumferential surface is provided with reinforcing cloth may be used.

[Stretch rubber layer]
The power transmission belt (particularly the low edge cogged V-belt) of the present invention further includes a stretchable rubber layer formed of a second rubber composition (second crosslinked rubber composition) containing a second polymer component. Good too.

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

The second rubber composition forming the stretch rubber layer preferably contains a second inorganic filler from the standpoint of further improving lateral pressure resistance and abrasion resistance. When not only the compressed rubber layer but also the stretchable rubber layer contains the second inorganic filler, the lateral pressure resistance and abrasion resistance are further improved. The second inorganic filler, including preferred embodiments, can be selected from the inorganic fillers exemplified as the first inorganic filler (B). The second inorganic filler may be a different inorganic filler from the first inorganic filler (B), but is usually the same as the first inorganic filler (B). The proportion of the second inorganic filler can be selected from the proportions of the first inorganic filler (B), including preferred proportions.

The second rubber composition forming the stretchable rubber layer preferably contains second short fibers from the standpoint of further improving lateral pressure resistance and abrasion resistance. When not only the compressed rubber layer but also the stretched rubber layer contains the second short fibers, the lateral pressure resistance and abrasion resistance are further improved. The second short fibers, including preferred embodiments, can be selected from the short fibers exemplified in the first short fibers (C). The second short fibers may be different short fibers from the first short fibers (C), but are usually the same as the first short fibers (C). The proportion of the second short fibers can be selected from the proportions of the first short fibers (C), including preferred proportions.

The second rubber composition forming the stretched rubber layer also contains the crosslinking agent (D), co-crosslinking agent (E), crosslinking accelerator (F), It may further contain a softener (G) and other components (H).

The properties of the stretchable rubber layer, including preferred ranges, can be selected from the properties of the compressed rubber layer described above (minimum Mooney scorch viscosity, hardness, bending stress, etc.).

The second rubber composition forming the stretchable rubber layer may be the same or the same (especially the same) as the first rubber composition forming the compressed rubber layer.

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

The core layer only needs to contain a core, and may be a core layer formed of only a core, but from the viewpoint of suppressing interlayer peeling and improving belt durability, Preferably, the core layer includes an adhesive rubber layer formed of a crosslinked rubber composition.

In the core layer, it is sufficient that at least a portion of the core is in contact with the adhesive rubber layer, and the core may be buried in the adhesive rubber layer, or the core may be buried between the adhesive rubber layer and the stretchable rubber layer. The core body may be embedded between the adhesive rubber layer and the compressed rubber layer. Among these, preferred is a configuration in which the adhesive rubber layer embeds the core body from the viewpoint of improving durability.

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

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

Incidentally, the Mooney viscosity [ML(1+4) 125° C.] of the uncrosslinked third polymer component (particularly the uncrosslinked ethylene-α-olefin elastomer) is, for example, about 10 to 30, preferably about 15 to 25. Good too.

The third rubber composition forming the adhesive rubber layer also contains the inorganic filler (B), crosslinking agent (D), co-crosslinking agent (E), It may further contain a crosslinking accelerator (F), a softener (G), and other components (H).

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

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

(Core body)
The core is not particularly limited, but usually core wires (twisted cords) arranged at predetermined intervals in the belt width direction can be used. The core wires are arranged to extend in the length direction of the belt, and may be arranged in parallel at a predetermined pitch in parallel to the length direction of the belt, but from the viewpoint of productivity, usually The belts, such as a raw edge cogged V-belt, are arranged substantially parallel to the length direction of a belt, extending in parallel at a predetermined pitch, and arranged in a spiral shape. In the case of spiral arrangement, the angle of the core wire with respect to the belt length direction may be, for example, 5° or less, and from the viewpoint of belt runnability, it is preferably closer to 0°. Further, the pitch or interval (particularly the spinning pitch of the core wire), which is the distance between the centers of adjacent core bodies, is preferably set in the range of 0.5 to 3.0 mm, and 0.8 to 2. It is more preferable to set it in the range of .0 mm, and most preferably to set it in the range of 1.0 to 1.6 mm.

Examples of the fibers constituting the core wire include the same fibers as the short fibers. Among the above-mentioned fibers, from the viewpoint of high modulus, polyester fibers (polyalkylene arylate fibers) whose main constituent units are C _2-4 alkylene-C _8-14 arylates such as ethylene terephthalate and ethylene-2,6-naphthalate; Synthetic fibers such as aramid fibers and inorganic fibers such as carbon fibers are often used, and polyester fibers (polyethylene terephthalate fibers, polyethylene naphthalate fibers, etc.) and aramid fibers are preferred. These fibers may be used in the form of multifilament yarns containing multiple filaments. The fineness of the multifilament yarn is, for example, 200 to 5000 dtex (especially 500 to 2000 dtex). The multifilament yarn may contain, for example, 50 to 1500 filaments, preferably 100 to 1000 filaments, and more preferably 300 to 500 filaments.

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

The core wire may be adhesively treated (or surface treated) in the same manner as the staple fiber (C) in order to improve adhesion with the polymer component. Preferably, the core wire is adhesively treated with at least RFL liquid.

[Reinforcement cloth]
The power transmission belt (particularly the raw edge cogged V-belt) of the present invention may, but need not necessarily, include a reinforcing fabric. Examples of the form of the reinforcing cloth include a form in which it is laminated on the inner circumferential surface of a compressed rubber layer, a form in which it is laminated on the outer circumferential surface of a stretchable rubber layer, a form in which it is embedded in a compressed rubber layer and/or a stretchable rubber layer, and the like.

The reinforcing fabric can be formed of fabric materials (especially woven fabrics) such as woven fabrics, wide-angle canvases, knitted fabrics, and non-woven fabrics, and if necessary, can be treated with adhesive treatment, for example, treated with RFL liquid (dipping treatment, etc.). ), or a friction treatment in which the adhesive rubber is rubbed into the cloth material, or after the adhesive rubber and the cloth material are laminated, it may be laminated or embedded in the compressed rubber layer and/or the stretchable rubber layer in the form described above. .

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

First, a laminate of a reinforcing fabric (lower fabric) and a compressed rubber layer main body sheet (uncrosslinked rubber sheet) is placed with the reinforcing fabric on the lower side, and The inner periphery is placed in contact with a flat cog-equipped mold in which teeth and grooves corresponding to the cog bottom 1b) are arranged alternately, and pressurized at a temperature of 60 to 100°C (particularly 70 to 80°C). A cog pad (a pad that is not completely crosslinked, but is in a semi-crosslinked state) with a molded cog portion is produced. Then, both ends of this cog pad are cut vertically from appropriate locations (particularly from the top of the cog crest) to obtain the required length.

Next, an inner mother mold having teeth and grooves corresponding to the cog portions alternately arranged is placed over the outer periphery of the cylindrical mold, and the cog pad is wound around the inner mother mold by engaging with the teeth and grooves of the inner mother mold. After joining at both ends (particularly the top of the cog crest) and laminating the first adhesive rubber layer sheet (lower adhesive rubber: uncrosslinked rubber sheet) around the outer periphery of this cog pad, the core wire (twisted) forming the core is Cord) is spirally spun, and a second adhesive rubber layer sheet (upper adhesive rubber: uncrosslinked rubber sheet) and a stretched rubber layer sheet (uncrosslinked rubber sheet) are sequentially wrapped around the outer circumference to form an uncrosslinked rubber sheet. Create a body.

After that, the uncrosslinked molded body is covered with a jacket and placed in a known crosslinking device (such as a vulcanization can), and crosslinked at a temperature of 120 to 200°C (particularly 150 to 180°C) to form a crosslinked belt sleeve. Create. Then, using a cutter or the like, the belt is cut into a V shape to obtain an endless raw edge cogged V belt.

In the case of a raw edge double cogged V-belt, the outer periphery of the uncrosslinked molded body is covered with an outer mold in which tooth parts and groove parts corresponding to the outer peripheral cog parts are arranged alternately, and then a jacket is covered and crosslinking molding is performed. By carrying out this process, a crosslinked belt sleeve having a cog portion also formed on the outer circumferential surface is obtained, and by cutting into a V shape, a low edge double cogged V belt is obtained.

Note that the adhesive rubber layer can be formed of multiple adhesive rubber layer sheets, and the core wire (twisted cord) forming the core can be formed of multiple adhesive rubber layer sheets depending on the position where it is buried in the adhesive rubber layer. Spinning may be performed in conjunction with the stacking order.

The present invention will be explained in more detail below based on Examples, but the present invention is not limited by these Examples. The details of the materials used in the examples and the evaluation methods for the examples and comparative examples are shown below.

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

(short fiber)
The following short fibers were used as the short fibers. Both short fibers were prepared using 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 (manufactured by Nippon Zeon Co., Ltd.), and water. 78.8 parts by mass of mixed solution] and dried. The adhesion rate of the adhesive component (solid content) was adjusted to 6% by mass based on the short fibers after the adhesive treatment.

Para-aramid short fiber: "Twaron" manufactured by Teijin Ltd., fineness 2.2 dtex, average fiber length 3 mm
Nylon short fiber: "Leona" manufactured by Asahi Kasei Corporation, average fiber diameter 27 μm, average fiber length 3 mm
Polyester short fiber: "Tetron" manufactured by Teijin Ltd., average fiber diameter 25 μm, average fiber length 3 mm

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

(Additive)
Paraffin oil: “Diana Process Oil PW90” manufactured by Idemitsu Kosan Co., Ltd.
Anti-aging agent ODPA (octyl diphenylamine): "Nonflex OD-3" manufactured by Seiko Chemical Co., Ltd.
Antiaging agent DCD (4,4'-bis(α,α-dimethylbenzyl)diphenylamine): “Nocrack CD” manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Zinc oxide: “Zinc oxide type 2” manufactured by Sakai Chemical Industry Co., Ltd.
Stearic acid: “Tsubaki Stearic Acid” manufactured by NOF Corporation
Resorcinol/formalin copolymer: “Penacolite Resin B-18-S” manufactured by INDSPEC Chemical Corporation
Hexamethoxymethylolmelamine: “POWERPLAST PP-1890S” manufactured by SINGH PLASTICISER & RESINS
Crosslinking accelerator TMTD (tetramethylthiuram disulfide): “Noxeler TT” manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Crosslinking accelerator CBS (N-cyclohexyl-2-benzothiazolylsulfenamide): “Noxela CZ” manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Crosslinking accelerator MBTS (di-2-benzothiazolyl disulfide): “Noxela DM” manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Co-crosslinking agent MPBM (N,N'-m-phenylene dimaleimide): "Barnock PM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Sulfur (powdered sulfur): “MIDAS” manufactured by Bigen Chemical Co., Ltd.

(reinforcing cloth)
A 2/2 twill weave nylon canvas (thickness 0.50 mm) that has been adhesively treated with the RFL liquid.

(core wire)
Two 1100 dtex PET fiber bundles (384 filaments) are combined and three first twisted yarns are first twisted with a twist coefficient of 3.0, and short fibers are added to a plied cord with a total fineness of 6600 dtex that is final twisted with a twist coefficient of 3.0. Processed cord with the same adhesive treatment. Note that the twist coefficient (TF) is a value calculated using the following formula.

TF=TN×D ^0.5 /960

[In the formula, TN indicates the number of twists per 1 m, and D indicates the fineness (tex) of the yarn. ]

(Composition for adhesive rubber layer)
As the adhesive rubber layer composition, the rubber compositions shown in Table 2 were used.

Examples 1 to 12 and Comparative Examples 1 to 3
[Mooney scorch minimum viscosity (Vm)]
Using an uncrosslinked rubber composition having the composition shown in Table 3 or Table 4, the minimum Mooney scorch viscosity was measured in accordance with the Mooney scorch test of JIS K 6300-1 (2013). An L-shaped rotor was used, and the test temperature was 125°C. Note that a polyester film ("Lumirror" manufactured by Toray Industries, Inc.) having a thickness of about 0.04 mm was placed between the surface where the test piece (the uncrosslinked rubber composition) and the die were in contact. After closing the die, it was preheated for 1 minute, then the rotor was rotated, and the change in Mooney viscosity was recorded. The recorded Mooney viscosity generally exhibited behavior as shown in FIG. 4, and the value when the Mooney viscosity reached its lowest value was adopted as the Mooney scorch minimum viscosity (Vm).

[Rubber hardness Hs of crosslinked rubber]
An uncrosslinked rubber composition having the composition shown in Table 3 or 4 was press-heated at a temperature of 160° C. for 30 minutes to produce a crosslinked rubber sheet (100 mm x 100 mm x 2 mm thickness). Using a laminate of three cross-linked rubber sheets as a sample, measure the hardness of the cross-linked rubber sheet using a type A durometer in accordance with the spring type durometer hardness test specified in JIS K 6253 (2012). did.

[4% bending stress (direction perpendicular to short fibers)]
An uncrosslinked rubber composition having the composition shown in Table 3 or 4 was press-heated at a temperature of 160° C. and a pressure of 2 MPa for 20 minutes to produce a crosslinked rubber molded body (60 mm x 25 mm x 6.5 mm thickness). The short fibers were oriented parallel to the length direction of the crosslinked rubber molded body. As shown in FIG. 5, this cross-linked rubber molded body 21 is placed and supported on a pair of rotatable rolls (diameter 6 mm) 22a, 22b with an interval of 20 mm. A metal pressing member 23 was placed in the width direction (direction perpendicular to the orientation direction of the short fibers). The tip of the pressing member 23 has a semicircular shape with a diameter of 10 mm, and can smoothly press the crosslinked rubber molded body 21 with the tip. Further, during pressing, frictional force acts between the lower surface of the crosslinked rubber molded body 21 and the rolls 22a, 22b as the crosslinked rubber molded body 21 is compressed and deformed, but by making the rolls 22a, 22b rotatable, , which reduces the influence of friction. The initial position is a state in which the tip of the holding member 23 is in contact with the upper surface of the crosslinked rubber molded body 21 and is not pressed, and from this state, the holding member 23 is moved downward at a speed of 100 mm/min to the crosslinked rubber molded body 21. The upper surface was pressed and the stress when the bending strain became 4% was measured as the bending stress. The measurement temperature was 120°C, assuming the belt temperature during running. It can be determined that the larger the 4% bending stress in the direction perpendicular to the short fibers, the higher the resistance to buckling deformation called dishing during belt running.

[8% bending stress (short fiber parallel direction)]
In the above method for measuring 4% bending stress in the direction perpendicular to the short fibers, as shown in FIG. , the metal holding member 23 and the orientation direction of the short fibers were made parallel), and the stress at which the bending strain reached 8% was taken as the bending stress, but measurements were made in the same manner. If the 8% bending stress in the direction parallel to the short fibers is small, it can be determined that the belt has good flexibility. 2.5 MPa or less can be judged as a practical passing level.

[Production of raw edge double cogged V belt]
Using the uncrosslinked rubber compositions shown in Table 3 or 4 as the compressed rubber layer and the stretched rubber layer, and using the uncrosslinked rubber composition shown in Table 2 as the adhesive rubber layer, using the method described in the above embodiment (crosslinking temperature A low edge double cogged V belt (size: upper width 20.0 mm, thickness 10.0 mm, belt outer circumference length 800 mm) was produced at 160° C. for 20 minutes.

[Abrasion durability test (upper width change and mass change rate)]
The wear durability test was conducted using a two-axis running test machine consisting of a driving (Dr.) pulley with a diameter of 50 mm and a driven (Dn.) pulley with a diameter of 125 mm, as shown in FIG. A low edge double cogged V-belt is suspended between these two pulleys, the shaft load is 800N, the rotation speed of the driving pulley is 5600rpm, the load of the driven pulley is 9N・m, and the belt is run for 20 hours at an ambient temperature of 80℃. I let it happen. The top width of the belt before and after running was measured, and the amount of change in top width (abrasion loss) and mass change rate were evaluated.

[Transmission efficiency (power transmission efficiency) test]
The transmission efficiency test was conducted by driving a continuously variable transmission in which the distance between the drive shaft and the driven shaft was 250 mm. Figure 8 shows the layout of the test machine. The test machine is a two-axis running test machine consisting of a driving (Dr.) pulley connected to a drive shaft and a driven (Dn.) pulley connected to a driven shaft. be. The driven pulley uses a spring to apply a force that pinches the belt, while the driving pulley has a fixed groove width, and the gear ratio (the value obtained by dividing the pitch diameter of the driven pulley by the pitch diameter of the driving pulley) at no load is 1.2. It was adjusted so that A digital tachometer and torque meter were installed on the drive shaft and driven shaft. Then, the rotation speed and torque of the drive shaft and the driven shaft were recorded while varying the rotation speed of the drive shaft from 3000 to 5000 rpm and the torque of the drive shaft from 2 to 4 N·m. The ambient temperature was 25°C.

As shown in the following equation, the power P ₁ of the drive shaft is obtained as the product of the torque T ₁ of the drive shaft and the rotational speed ρ ₁ . Similarly, the power P ₂ of the driven shaft is determined as the product of the driven shaft torque T ₂ and the rotation speed ρ ₂ . The transmission efficiency η is obtained by dividing the power P ₂ of the driven shaft by the power P ₁ of the drive shaft.

P ₁ =T ₁ ×ρ ₁
P ₂ =T ₂ ×ρ ₂
η (%)=[ _P2 / _P1 ]×100=[( _T2 × _ρ2 )/( _T1 × _ρ1 )]×100

The transmission efficiency is determined when the rotational speed of the drive shaft is 3000 rpm and the torque of the drive shaft is 2 N·m. Note that the value of transmission efficiency is 100% if there is no transmission loss, and if there is transmission loss, the value becomes smaller by the amount of the loss. In other words, the closer it is to 100%, the smaller the transmission loss and the better the fuel efficiency.

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

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

On the other hand, in Examples 1 to 12, in which the Mooney viscosity of the polymer component, the amount of the inorganic filler, etc. were adjusted within appropriate ranges, wear resistance and transmission efficiency were simultaneously improved. A comparison of Examples 1 to 6 in which the Mooney viscosity of the polymer component was varied while keeping the amount of inorganic filler constant, confirmed that the wear resistance tends to improve as the Mooney viscosity of the polymer component increases.

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

Among these Examples 1 to 12, Example 6 had high wear resistance and excellent balance with transmission efficiency.

The rubber composition of the present invention can be used for various molded products, and in particular, transmission belts, such as friction transmission belts such as flat belts, wrapped V-belts, low-edge V-belts, raw-edge cogged V-belts, and V-ribbed belts, and toothed It can be used as an interlocking power transmission belt such as a double-sided toothed belt or a double-sided toothed belt. In particular, when used as a compressed rubber layer in power transmission belts, it can simultaneously increase wear resistance and transmission efficiency, so it is used in motorcycles, four-wheeled buggies, snowmobiles, agricultural machinery, etc. where horsepower is increasing. It is useful for the compressed rubber layer of variable speed belts.

1... Raw edge double cogged V belt 2... Stretch rubber layer 3... Core layer 3a... Core body 4... Compressed rubber layer 5... Reinforcement cloth

Claims (8)

A rubber composition for forming a compressed rubber layer of a power transmission belt, the rubber composition comprising:
Contains polymer components, inorganic fillers and short fibers,
the polymer component includes an ethylene-α-olefin elastomer,
The proportion of the ethylene-α-olefin elastomer is 50% by mass or more in the polymer component,
The uncrosslinked product of the polymer component has a Mooney viscosity of 31 ML (1 + 4) 125 ° C. or higher,
The proportion of the inorganic filler is 20 to 60 parts by mass based on 100 parts by mass of the polymer component, and the crosslinked rubber composition has an 8% bending stress of 2.5 MPa or less in the direction parallel to the short fibers. A rubber composition. The rubber composition according to claim 1, further comprising a crosslinking agent, and the crosslinking agent comprising a sulfur-based crosslinking agent. The rubber composition according to claim 1 or 2, further comprising a co-crosslinking agent. The rubber composition according to claim 3, wherein the proportion of the co-crosslinking agent is 1 to 5 parts by weight based on 100 parts by weight of the polymer component. 3. The inorganic filler contains carbon black, the carbon black contains soft carbon, and the proportion of the carbon black is 50 to 200 parts by mass based on 100 parts by mass of the short fibers. rubber composition. 3. The rubber composition according to claim 1, wherein the proportion of the softener is 3 parts by mass or less based on 100 parts by mass of the polymer component. 3. The short fibers include aramid short fibers and aliphatic polyamide short fibers, and the proportion of the aramid short fibers is 100 parts by mass or more based on 100 parts by mass of the aliphatic polyamide short fibers. rubber composition. A power transmission belt comprising a compressed rubber layer formed of the rubber composition according to claim 1 or 2.

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