JP2024121792A - Rubber composition, its manufacturing method and use - Google Patents

Abstract

To provide a rubber composition having a high ratio of non-petroleum resources and high electrical conductivity.SOLUTION: Prepared is a rubber composition comprising a polymer component containing an ethylene-α-olefin elastomer and carbon black. The rubber composition has a ratio of non-petroleum resources of 30 mass% or more. The ethylene-α-olefin elastomer is composed of raw materials including a raw material derived from non-petroleum resources. A ratio of the carbon black is 40-80 pts.mass relative to 100 pts.mass of the polymer component. The rubber composition may further comprise an inorganic filler derived from a non-petroleum resource. The ethylene-α-olefin elastomer may have a Mooney viscosity [ML(1+4)125°C] of 41 or more. The ethylene-α-olefin elastomer may have an ethylene content of 45 mass% or more. A low edge cogged V belt 1, containing a cross-linked material of the composition, may be produced.SELECTED DRAWING: Figure 1

Description

The present invention relates to an environmentally friendly rubber composition capable of reducing _CO2 emissions, and a production method and use thereof.

Molded products such as tires, hoses, power transmission belts, and conveyor belts made of composites of rubber and fiber materials are used in a variety of applications, including automobiles and general industrial machinery, because they are strong and flexible at the same time. Examples of power transmission belts include meshing power transmission belts such as toothed belts, and friction power transmission belts such as flat belts, V-belts, and V-ribbed belts. V-belts are classified into two types: raw-edge type (raw-edge V-belt), in which the friction transmission surface (V-shaped side surface) is an exposed rubber layer, and wrapped type (wrapped V-belt), in which the friction transmission surface is covered with an outer sheath (cover cloth). They are used according to the application, depending on the surface properties of the friction transmission surface (friction coefficient between the rubber layer and the cover cloth). Furthermore, raw edge V-belts include raw edge V-belts that have no cogs, raw edge cogged V-belts that have cogs only on the underside (inner circumferential surface) of the belt to improve flexibility, and raw edge cogged V-belts (raw edge double cogged V-belts) that have cogs on both the underside (inner circumferential surface) and upper (outer circumferential surface) of the belt to improve flexibility.

A power transmission belt is made of a cross-linked rubber composition, a core formed of twisted cords, and reinforcing fabric. The rubber composition contains polymer components, reinforcing agents such as carbon black, plasticizers, cross-linking agents, and antioxidants, and accounts for the majority of the mass of the power transmission belt. Some power transmission belts contain natural rubber as a polymer component, but in recent years, power transmission belts made of petroleum-derived synthetic rubbers such as chloroprene rubber, hydrogenated nitrile rubber, and EPDM have become mainstream in order to improve durability. Many of the other components, including carbon black, are also petroleum-derived, and power transmission belts have a high content of petroleum-derived resources.

In recent years, manufacturers of industrial products are being asked to provide environmentally friendly products with low _CO2 emissions, as represented by slogans such as SDGs (Sustainable Development Goals), carbon neutral, and green transformation (GX). However, as described above, the rubber composition constituting the transmission belt contains a large amount of petroleum-derived resources, which imposes a large environmental load. Therefore, attempts are being made to reduce the content of petroleum-derived resources.

For example, Patent Document 1 (JP 2011-214663 A) and Patent Document 2 (WO 2011/158586 A) disclose a transmission belt that uses natural rubber as the polymer component and has a relatively small amount of carbon black to increase the ratio of non-petroleum resources.

JP 2011-214663 A International Publication No. 2011/158586

However, natural rubber is inferior to many synthetic rubbers in terms of hardness, abrasion resistance, heat aging resistance, weather resistance, etc., which can reduce the durability of the transmission belt. In addition, all of the documents state that carbon black is preferably 10 parts by mass or less per 100 parts by mass of natural rubber, and even in the examples, only small amounts are included. If the amount of carbon black is reduced, the rubber hardness and abrasion resistance are likely to decrease, and there is a problem that electrical conductivity decreases and the belt becomes more likely to become charged. If the transmission belt becomes charged, it can cause electronic devices such as sensors to malfunction, and it can also cause safety issues such as sparks.

The object of the present invention is therefore to provide a rubber composition having a high non-petroleum resource ratio and high electrical conductivity, as well as a method for producing the same and uses thereof.

Another object of the present invention is to provide a power transmission belt that is made from a high percentage of non-petroleum resources and yet has high durability and electrical conductivity.

As a result of intensive research into achieving the above-mentioned object, the inventors discovered that the non-petroleum resource ratio and electrical conductivity can be improved by combining a polymer component containing an ethylene-α-olefin elastomer with carbon black, forming the ethylene-α-olefin elastomer from raw materials including raw materials derived from non-petroleum resources, adjusting the proportion of the carbon black to 40 to 80 parts by mass per 100 parts by mass of the polymer component, and adjusting the non-petroleum resource ratio of the rubber composition to 30% by mass or more, thereby completing the present invention.

That is, the rubber composition according to embodiment [1] of the present invention is a rubber composition comprising a polymer component containing an ethylene-α-olefin elastomer and carbon black, and having a non-petroleum resource ratio of 30 mass% or more,
The ethylene-α-olefin elastomer is formed from raw materials including raw materials derived from non-petroleum resources, and the proportion of the carbon black is 40 to 80 parts by mass per 100 parts by mass of the polymer component.

Aspect [2] of the present invention is an aspect in which the rubber composition of aspect [1] further contains an inorganic filler derived from a non-petroleum resource.

Aspect [3] of the present invention is an aspect of aspect [1] or [2], in which the average Mooney viscosity [ML(1+4)125°C] of the ethylene-α-olefin elastomer is 41 or more.

Aspect [4] of the present invention is any of aspects [1] to [3] above, in which the ethylene content of the ethylene-α-olefin elastomer is 45 mass% or more.

Aspect [5] of the present invention is any of aspects [1] to [4] above, in which the DBP absorption of the carbon black is 60 mL/100 g or more.

Aspect [6] of the present invention is any of aspects [1] to [5] above, in which the cross-linked product has a rubber hardness Hs (type A) of 92 degrees or more.

Aspect [7] of the present invention is an aspect in which the crosslinked product of the rubber composition of any one of aspects [1] to [6] has a breaking elongation retention rate of 40% or more after heat aging.

Aspect [8] of the present invention is any of aspects [1] to [7] above, in which the electrical resistance of the cross-linked product is 6 MΩ or less.

Aspect [9] of the present invention is an aspect in which the rubber composition of aspects [1] to [8] further contains short cellulose fibers.

The present invention also includes, as aspect [10], a method for producing a rubber composition according to any one of aspects [1] to [9], in which the polymer component and the carbon black are mixed.

The present invention also includes, as aspect [11], a transmission belt containing a cross-linked product of the rubber composition according to any one of the aspects [1] to [9] above.

Aspect [12] of the present invention is an aspect in which the transmission belt of aspect [11] is a raw edge cogged V-belt.

In the present invention, a polymer component containing an ethylene-α-olefin elastomer is combined with carbon black, the ethylene-α-olefin elastomer is formed from raw materials containing raw materials derived from non-petroleum resources, the proportion of the carbon black is adjusted to 40 to 80 parts by mass per 100 parts by mass of the polymer component, and the non-petroleum resource ratio of the rubber composition is adjusted to 30% by mass or more, thereby improving the non-petroleum resource ratio and electrical conductivity. When this rubber composition is used for a transmission belt, the durability and electrical conductivity can be improved while still achieving a transmission belt with a high non-petroleum resource ratio.

FIG. 1 is a schematic, partially sectional perspective view showing an example of a raw edge cogged V-belt of the present invention. FIG. 2 is a schematic cross-sectional view of the raw-edge cogged V-belt of FIG. 1 cut in the belt longitudinal direction. FIG. 3 is a schematic perspective view for explaining a method for measuring the 4% bending stress (in a direction perpendicular to short fibers) of the crosslinked rubber molded articles obtained in the examples. FIG. 4 is a schematic diagram showing the layout of a running test for crack resistance of the raw-edge cogged V-belt obtained in the examples. FIG. 5 is a schematic diagram showing the layout of a running test for the wear resistance of the raw-edge cogged V-belt obtained in the examples.

[Rubber composition]
The rubber composition of the present invention contains a polymer component (A) containing an ethylene-α-olefin elastomer and carbon black (B).

(A) Polymer Component The polymer component (A) contains an ethylene-α-olefin elastomer because it has excellent heat resistance, cold resistance, and weather resistance. Furthermore, the ethylene-α-olefin elastomer is formed from raw materials including raw materials derived from non-petroleum resources. In the present invention, by using such a biomass-derived ethylene-α-olefin elastomer as the polymer component (A), an environmentally friendly rubber composition capable of reducing _CO2 emissions can be prepared.

In this application, non-petroleum resources refer to organic or inorganic resources other than petroleum.

In detail, the non-petroleum resource may be biomass, for example, a plant that is easily renewable. The biomass-derived ethylene-α-olefin elastomer may be formed of ethylene produced from bioethanol derived from a plant such as sugar cane as the ethylene component. Plants absorb _CO2 from the atmosphere during their growth process, and this can offset the _CO2 emissions when the plant is made into a product, thereby reducing the substantial _CO2 emissions. Therefore, in the present invention, the use of an ethylene-α-olefin elastomer having a high non-petroleum resource ratio as the polymer component can reduce the _CO2 emissions.

The non-petroleum resource ratio of the ethylene-α-olefin elastomer is not particularly limited as long as it can be adjusted so that the non-petroleum resource ratio of the rubber composition is 30% by mass or more, and may be 10% by mass or more, but is, for example, 10 to 100% by mass, preferably 30 to 90% by mass, further preferably 50 to 85% by mass, more preferably 60 to 80% by mass, and most preferably 65 to 75% by mass. If the non-petroleum resource ratio is too low, it may be difficult to adjust the non-petroleum resource ratio of the rubber composition to 30% by mass or more.

In the present application, the non-petroleum resource ratio of the ethylene-α-olefin elastomer can be measured by a method for estimating the non-petroleum resource ratio by measuring the concentration of ^{the 14C} radioisotope, taking advantage of the fact that carbon in plants contains the ^14C radioisotope at the same concentration as that in the atmosphere, whereas petroleum does not contain any ^14C radioisotope, and specifically, the measurement can be performed in accordance with ASTM D6866-22.

Ethylene-α-olefin elastomers 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, etc.

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

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

Typical ethylene-α-olefin elastomers include, for example, ethylene-α-olefin rubber [ethylene-propylene rubber (EPM), ethylene-butene rubber (EBM), ethylene-octene rubber (EOM)] and ethylene-α-olefin-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 rubbers such as ethylene-α-C _3-4 olefin-diene terpolymer rubbers are preferred from the viewpoint of excellent heat resistance, cold resistance, and weather resistance, and EPDM is particularly preferred. Therefore, the proportion of EPDM may be 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more (particularly 95% by mass or more), and may be 100% by mass (only EPDM) based on the total ethylene-α-olefin elastomers.

In the ethylene-α-olefin elastomer, the ethylene content (proportion of ethylene units) in the ethylene-α-olefin elastomer may be 45% by mass or more, for example, 45 to 80% by mass, preferably 50 to 78% by mass, further preferably 55 to 75% by mass, more preferably 60 to 73% by mass, and most preferably 65 to 72% by mass. If the ethylene content is too low, there is a risk of reduced abrasion resistance when used in a transmission belt, and if the ethylene content is too high, there is a risk of reduced processability and crack resistance.

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

Furthermore, in this application, when there are multiple types of ethylene-α-olefin elastomers, the ethylene content means an average value based on the mass ratio (average ethylene content). In other words, the average ethylene content is the sum of the products of the ethylene contents and the mass fractions of the respective ethylene-α-olefin elastomers.

In the ethylene-α-olefin elastomer, the ratio (mass ratio) of ethylene to α-olefin is 40/60 to 90/10, preferably 45/55 to 85/15, more preferably 50/50 to 80/20, and more preferably 55/45 to 75/25. In particular, in the ethylene-propylene-diene terpolymer, the ratio (mass ratio) of ethylene to propylene may be 45/55 to 80/20, preferably 50/50 to 78/22, more preferably 60/40 to 77/23, more preferably 65/35 to 75/25, and most preferably 70/30 to 75/25.

The diene content of ethylene-α-olefin elastomers (particularly ethylene-α-olefin-diene terpolymer rubbers such as EPDM) is, for example, 0.1 to 15 mass%, preferably 1 to 10 mass%, further preferably 2 to 7 mass%, more preferably 3 to 6 mass%, and most preferably 4 to 5 mass%. If the diene content is too high, there is a risk that a high level of heat resistance cannot be ensured. If the diene content is too low, there is a risk that the processability and crack resistance will decrease when used in a transmission belt, and conversely, if the diene content is too high, there is a risk that the abrasion resistance will decrease.

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

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

The Mooney viscosity [ML(1+4)125°C] of the ethylene-α-olefin elastomer (uncrosslinked ethylene-α-olefin elastomer) may be 41 or more, for example, 41 to 85, preferably 43 to 80, further preferably 45 to 70, more preferably 50 to 60, and most preferably 53 to 57. If the Mooney viscosity is too low, there is a risk of reduced abrasion resistance when used in a transmission belt, and conversely, if it is too high, there is a risk of reduced processability and crack resistance.

In this application, the Mooney viscosity can be measured by a method conforming to the Mooney viscosity test of JIS K 6300-1 (2013), and the test conditions are as follows: an L-shaped rotor is used, the test temperature is 125°C, preheating is 1 minute, and the rotor operation time is 4 minutes. The Mooney viscosity is used as an index of the fluidity (ease of processing) of rubber by filling a cavity with uncrosslinked ethylene-α-olefin elastomer so that it is in contact with a rotor with grooves on its surface, and measuring the torque required to rotate the rotor.

Furthermore, in this application, when there are multiple types of ethylene-α-olefin elastomers, the Mooney viscosity means the average value based on the mass ratio (average Mooney viscosity). In other words, the average Mooney viscosity is the sum of the products of the Mooney viscosities of the respective ethylene-α-olefin elastomers and the mass fractions.

The proportion of ethylene-α-olefin elastomer in 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 ethylene-α-olefin elastomer in the polymer component is too low, there is a risk of reduced heat resistance and cold resistance.

Ethylene-α-olefin elastomers derived from biomass are commercially available as bio-EPDMs, such as ARLANXEO's "Keltan eco 5470," "Keltan eco 6950," and "Keltan eco 8550." In these bio-EPDMs, all of the ethylene components are made from raw materials derived from sugar cane, so the ethylene content directly corresponds to the non-petroleum resource ratio of each bio-EPDM.

The polymer component (A) may contain, in addition to the ethylene-α-olefin elastomer, other rubber components, such as diene rubbers [natural rubber, isoprene rubber, butadiene rubber, chloroprene rubber, styrene butadiene rubber (SBR), vinylpyridine-styrene-butadiene copolymer rubber, acrylonitrile butadiene rubber (nitrile rubber); hydrogenated products of the diene rubbers, such as hydrogenated nitrile rubber (including a mixed polymer of hydrogenated nitrile rubber and an unsaturated carboxylic acid metal salt)], 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., as long as the effects of the present invention are not impaired.

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

The proportion of polymer component (A) in the rubber composition is, for example, 10 to 80 mass%, preferably 20 to 70 mass%, further preferably 25 to 60 mass%, even more preferably 30 to 50 mass%, and most preferably 35 to 45 mass%.

(B) Carbon Black Carbon black (B) is formed from petroleum-derived raw materials, and the non-petroleum resource ratio is 0 mass%. In contrast, in the present invention, as described above, an ethylene-α-olefin elastomer formed from raw materials containing non-petroleum-derived raw materials is used as the polymer component, and therefore it is possible to increase the non-petroleum resource ratio while containing a relatively large amount of carbon black. As a result, when the rubber composition of the present invention is used for a transmission belt, a transmission belt having high hardness, excellent heat aging resistance, abrasion resistance, and flex fatigue resistance, and high electrical conductivity can be provided.

The three most important basic properties of carbon black (B) are the primary particle size, aggregate structure, and surface properties (BET specific surface area, iodine adsorption amount, etc.).

In the present invention, the average primary particle size of carbon black (B) can be selected from the range of about 10 to 100 nm, for example, 10 to 70 nm, 13 to 50 nm, more preferably 15 to 40 nm, even more preferably 18 to 30 nm, and most preferably 20 to 25 nm. If the average primary particle size of carbon black (B) is too small, the dispersibility of carbon black in the rubber composition may decrease, and conversely, if it is too large, the reinforcing properties of carbon black may decrease.

In this application, the average primary particle size of carbon black (B) can be measured by number using, for example, a transmission electron microscope.

The term "aggregate" refers to a chain-like aggregation of multiple primary particles that branch out, and DBP (dibutyl phthalate) absorption is used as a method for evaluating the degree of branching, i.e., the degree of structure development. Carbon black (B) with a developed structure has larger voids between aggregates and a larger DBP absorption. In the present invention, carbon black (B) with a large DBP absorption (developed structure) has aggregates that are easily linked together to form paths through which electricity can pass, and the electrical resistance of the crosslinked rubber composition is easily reduced, improving electrical conductivity. It can be estimated that electrical conductivity can be improved even if the non-petroleum resource ratio of the rubber composition is increased.

The DBP absorption of carbon black (B) is preferably large in order to improve electrical conductivity, and may be 60 mL/100 g or more. For example, it may be selected from the range of about 60 to 500 mL/100 g, and is preferably 80 mL/100 g or more, more preferably 100 mL/100 g or more, more preferably 105 mL/100 g or more, and most preferably 110 mL/100 g or more, and may be 100 to 200 mL/100 g (preferably 105 to 180 mL/100 g, and more preferably 110 to 150 mL/100 g). If the DBP absorption is too small, there is a risk that the electrical conductivity of the crosslinked rubber will decrease.

In this application, the DBP absorption of carbon black (B) refers to the value (OAN) that can be measured for a non-compressed sample in accordance with JIS K 6217-4 (2017).

The BET specific surface area of the carbon black (B) is, for example, 10 to 160 m ² /g, preferably 30 to 150 m ² /g, further preferably 50 to 140 m ² /g, more preferably 80 to 130 m ² /g, and most preferably 100 to 120 m ² /g. If the BET specific surface area is too small, the hardness and modulus of the crosslinked rubber may decrease, whereas if it is too large, the hardness of the crosslinked rubber may become too high.

In this application, the BET specific surface area refers to the specific surface area measured using nitrogen gas by the BET method.

The iodine adsorption amount of carbon black (B) is, for example, 15 to 150 g/kg, preferably 30 to 140 g/kg, further preferably 50 to 135 g/kg, more preferably 100 to 130 g/kg, and most preferably 110 to 125 g/kg. If the iodine adsorption amount is too small, the hardness and modulus of the crosslinked rubber may decrease, and conversely, if it is too large, it may become difficult to prepare carbon black (B) itself.

In this application, the iodine adsorption amount of carbon black (B) can be measured in accordance with the standard test method of ASTM D1510-17.

The proportion of carbon black (B) is 40 to 80 parts by mass, preferably 45 to 78 parts by mass, more preferably 50 to 75 parts by mass, even more preferably 55 to 73 parts by mass, and most preferably 60 to 70 parts by mass, per 100 parts by mass of polymer component (A). If the proportion of carbon black (B) is too low, when used in a transmission belt, the crosslinked rubber becomes too soft, resulting in reduced durability and reduced electrical conductivity. Conversely, if the proportion is too high, the crosslinked rubber becomes too hard, resulting in reduced resistance to bending fatigue and reduced rolling properties.

(C) Inorganic filler derived from non-petroleum resources The rubber composition of the present invention may further contain, as an inorganic filler, an inorganic filler (C) derived from a non-petroleum resource in addition to the carbon black (B). This inorganic filler (C) is derived from a mineral, i.e., a non-petroleum resource, and has a non-petroleum resource ratio of 100% by mass, so that the non-petroleum resource ratio of the rubber composition can be increased. Therefore, by combining the carbon black (B) with the inorganic filler (C) derived from a non-petroleum resource, the non-petroleum resource ratio of the rubber composition can be increased while improving the reinforcing effect of the filler.

Examples of the inorganic filler (C) include metal compounds or synthetic ceramics (metal oxides such as magnesium oxide, calcium oxide, barium oxide, iron oxide, copper oxide, zinc oxide, titanium oxide, and aluminum oxide; metal silicates such as calcium silicate; metal carbides such as silicon carbide and tungsten carbide; metal nitrides such as titanium nitride, aluminum nitride, and boron nitride; metal carbonates such as magnesium carbonate and calcium carbonate; metal sulfates such as calcium sulfate and barium sulfate, etc.), and mineral materials (clay, zeolite, diatomaceous earth, calcined diatomaceous earth, activated clay, alumina, silica, talc, mica, sericite, bentonite, montmorillonite, smectite, etc.). Metal oxides such as zinc oxide may act as crosslinking agents, crosslinking promoters, or co-crosslinking agents. These inorganic fillers can be used alone or in combination of two or more.

Of these, silica (C1), metal carbonates (C2), and metal oxides (C3) are preferred.

Silica (C1) includes dry silica, wet silica, surface-treated silica, and the like. Silica can also be classified into dry-process white carbon, wet-process white carbon, colloidal silica, precipitated silica, and the like, depending on the manufacturing method. Silica (C1) may be amorphous silica. These silicas can be used alone or in combination of two or more. Among these silicas, silicas having surface silanol groups (anhydrous silicic acid, hydrous silicic acid) are preferred, and hydrous silicic acid with many surface silanol groups has a strong chemical bond with the rubber component.

The average primary particle diameter of silica (C1) is, for example, 1 to 500 nm, preferably 3 to 300 nm, more preferably 5 to 100 nm, and even more preferably 10 to 50 nm.

In this application, the average primary particle size of silica (C1) can be measured, for example, using a scanning electron microscope or a transmission electron microscope, and the arithmetic average particle size of an appropriate number of samples (for example, 50 samples) can be calculated by image analysis.

The nitrogen adsorption specific surface area of the silica (C1) measured by the BET method is, for example, 50 to 400 m ² /g, preferably 100 to 300 m ² /g, and more preferably 150 to 200 m ² /g.

Silica (C1) may be used as a filler to replace part of the carbon black (B). In that case, the proportion of silica may be 100 parts by mass or less relative to 100 parts by mass of carbon black (B), for example, 5 to 100 parts by mass, preferably 10 to 90 parts by mass, more preferably 30 to 80 parts by mass, more preferably 40 to 70 parts by mass, and most preferably 50 to 65 parts by mass. The proportion of silica (C1) is, for example, 1 to 40 parts by mass, preferably 5 to 35 parts by mass, more preferably 10 to 30 parts by mass, and more preferably 20 to 28 parts by mass relative to 100 parts by mass of polymer component (A). If the proportion of silica (C1) is too high, there is a risk that the durability of the belt will decrease when used in a transmission belt.

Calcium carbonate is preferred as the metal carbonate (C2). The proportion of the metal carbonate (C2) is, for example, 5 to 100 parts by mass, preferably 10 to 80 parts by mass, more preferably 20 to 60 parts by mass, even more preferably 30 to 50 parts by mass, and most preferably 35 to 45 parts by mass, per 100 parts by mass of the polymer component (A). If the proportion of the metal carbonate (C2) is too low, there is a risk that the effect of increasing the non-petroleum resource ratio will be reduced, and conversely, if it is too high, there is a risk that the rubber hardness, electrical conductivity, etc. will decrease.

As the metal oxide (C3), zinc oxide is preferred. The proportion of the metal oxide (C3) is, for example, 0.1 to 50 parts by mass, preferably 0.5 to 30 parts by mass, further preferably 1 to 20 parts by mass, even more preferably 2 to 10 parts by mass, and most preferably 3 to 7 parts by mass, relative to 100 parts by mass of the polymer component (A). If the proportion of the metal oxide (C3) is too low, there is a risk that the effect of increasing the non-petroleum resource ratio will be reduced, and conversely, if it is too high, there is a risk that the rubber hardness, electrical conductivity, etc. will decrease.

The proportion of the inorganic filler (C) may be, for example, 300 parts by mass or less relative to 100 parts by mass of carbon black (B), and is, for example, 10 to 200 parts by mass, preferably 20 to 150 parts by mass, further preferably 30 to 100 parts by mass, more preferably 50 to 90 parts by mass, and most preferably 60 to 80 parts by mass. If the proportion of the inorganic filler (C) is too low, there is a risk that the effect of increasing the non-petroleum resource ratio will be reduced, and conversely, if it is too high, there is a risk that the rubber hardness, electrical conductivity, etc. will decrease.

The proportion of the inorganic filler (C) may be 200 parts by mass or less relative to 100 parts by mass of the polymer component (A), for example, 5 to 150 parts by mass, preferably 10 to 100 parts by mass, further preferably 20 to 80 parts by mass, more preferably 30 to 70 parts by mass, and most preferably 40 to 50 parts by mass. If the proportion of the inorganic filler (C) is too low, there is a risk that the effect of increasing the non-petroleum resource ratio will be reduced, and conversely, if it is too high, there is a risk that the rubber hardness, electrical conductivity, etc. will decrease.

(D) Short Fiber The rubber composition of the present invention may further contain short fiber (D). Examples of the short fiber (D) include synthetic fibers such as polyolefin fibers (polyethylene fibers, polypropylene fibers, etc.), polyamide fibers (polyamide 6 fibers, polyamide 66 fibers, polyamide 46 fibers, aramid fibers, etc.), polyalkylene arylate fibers [poly C _2-4 alkylene C _6-14 arylate fibers such as polyethylene terephthalate (PET) fibers and polyethylene naphthalate (PEN) fibers], vinylon fibers, polyvinyl alcohol fibers, and polyparaphenylene benzobisoxazole (PBO) fibers; natural fibers such as cotton, hemp, and wool; and inorganic fibers such as carbon fibers. These short fibers can be used alone or in combination of two or more.

The rubber composition of the present invention contains a relatively large amount of carbon black (B), which improves the physical properties of the rubber, and therefore does not require the use of high-rigidity short fibers. Even if inexpensive short fibers such as cotton, PET, and aliphatic polyamide (nylon) are used, the durability of the belt can be improved and the economy can be improved. In particular, the use of cellulosic fibers derived from plants can increase the non-petroleum resource ratio. Therefore, as fibers forming the short fibers (D), polyalkylene arylate fibers such as PET fibers, nylon fibers such as polyamide 6 fibers, and cellulosic fibers such as cotton are preferred, with polyalkylene arylate fibers and cellulosic fibers being particularly preferred, and cellulosic fibers being the most preferred because they can increase the non-petroleum resource ratio and also improve heat resistance.

Cellulosic fibers include cellulose fibers (cellulose fibers derived from plants, animals, bacteria, etc.) and fibers of cellulose derivatives. Examples of cellulose fibers include cellulose fibers (pulp fibers) derived from natural plants such as wood pulp (coniferous and broadleaf pulp, etc.), bamboo fibers, sugarcane fibers, seed hair fibers [cotton fibers (cotton linters), kapok, etc.], ginseng bark fibers (hemp, paper mulberry, Mitsumata, etc.), and leaf fibers (Manila hemp, New Zealand hemp, etc.); cellulose fibers derived from animals such as sea squirt cellulose; bacterial cellulose fibers; and algae cellulose. Examples of cellulose derivative fibers include cellulose ester fibers; regenerated cellulose fibers (rayon, cupra, lyocell, etc.). These cellulose fibers can be used alone or in combination of two or more types. Of these cellulose fibers, cellulose fibers such as cotton fibers are preferred.

The average fiber diameter of the short fibers (D) is, for example, 1 to 1000 μm, preferably 3 to 100 μm, more preferably 5 to 50 μm, and even more preferably 10 to 30 μm. If the fiber diameter is too large, the hardness and modulus of the crosslinked rubber may decrease, and if the fiber diameter is too small, it may be difficult to disperse the fibers uniformly.

The average fiber length of the short fibers (particularly cellulose-based short fibers) (D) is, for example, 1 to 20 mm, preferably 3 to 10 mm, more preferably 4 to 8 mm, and even more preferably 5 to 7 mm. If the average length of the short fibers (D) is too short, there is a risk that the mechanical properties (e.g., modulus, etc.) in the grain direction cannot be sufficiently improved when used in a transmission belt, and conversely, if it is too long, there is a risk that the dispersibility of the short fibers (D) in the rubber composition will decrease.

From the viewpoint of dispersibility and adhesiveness of the short fibers (D) in the rubber composition, it is preferable that at least the short fibers (D) are subjected to an adhesive treatment (or surface treatment). It is not necessary that all the short fibers (D) are adhesively treated, and adhesively treated short fibers and non-adhesively treated short fibers (untreated short fibers) may be mixed or used in combination.

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

The proportion of short fibers (D) is, for example, 5 to 100 parts by mass, preferably 10 to 50 parts by mass, more preferably 15 to 40 parts by mass, and even more preferably 20 to 30 parts by mass, per 100 parts by mass of polymer component (A). If the proportion of short fibers (D) is too low, the hardness and modulus of the crosslinked rubber may decrease, and conversely, if it is too high, it may be difficult to disperse the fibers uniformly.

(E) Crosslinking Agent The rubber composition of the present invention may further contain a crosslinking agent (E). The crosslinking agent (or vulcanizing agent) (E) may be a sulfur-based crosslinking agent and/or an organic peroxide.

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

The organic peroxides include those that are normally used for crosslinking rubber and resin, such as diacyl peroxides, peroxy esters, and dialkyl peroxides (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-butylperoxy-isopropyl)benzene, and di-t-butyl peroxide). These organic peroxides can be used alone or in combination of two or more. Furthermore, the organic peroxide is preferably a peroxide whose decomposition temperature that provides a half-life of one minute by thermal decomposition is about 150 to 250°C (e.g., 175 to 225°C).

Among these, sulfur-based crosslinking agents are preferred because they can improve the wear resistance and lateral pressure resistance of the belt. Note that, when collected as natural minerals, sulfur-based crosslinking agents are considered to be non-petroleum resources, but in recent years, they have mainly been refined from components separated by desulfurization of petroleum, so in this application, they are considered to be components with a non-petroleum resource ratio of 0% by mass.

The proportion of the crosslinking agent (E) is, for example, 1 to 10 parts by mass, preferably 1.5 to 8 parts by mass, more preferably 2 to 6 parts by mass, and more preferably 2 to 5 parts by mass, relative to 100 parts by mass of the polymer component (A). When the crosslinking agent (E) is a sulfur-based crosslinking agent, the proportion of the crosslinking agent may be, for example, 0.5 to 5 parts by mass, preferably 1 to 3 parts by mass, and more preferably 1.5 to 2.5 parts by mass, relative to 100 parts by mass of the polymer component (A). If the proportion of the crosslinking agent (E) is too small, when used in a transmission belt, the wear resistance and lateral pressure resistance of the transmission belt may decrease, and if the proportion is too large, the scorch resistance, rolling resistance, and crack resistance may decrease.

(F) Crosslinking Auxiliary Agent The rubber composition of the present invention may further contain a crosslinking auxiliary agent (F) in addition to the crosslinking agent (E) (particularly, a sulfur-based crosslinking agent). The crosslinking auxiliary agent is formed from a petroleum-derived raw material, and the non-petroleum resource ratio is 0 mass%. Examples of the crosslinking auxiliary agent include a crosslinking accelerator (F1) and a co-crosslinking agent (F2).

(F1) Crosslinking accelerator Examples of the crosslinking accelerator (F1) include thiuram accelerators [e.g., tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetrabutylthiuram disulfide (TBTD), dipentamethylenethiuram tetrasulfide (DPTT), N,N'-dimethyl-N,N'-diphenylthiuram disulfide, etc.], sulfenamide accelerators [e.g., N-cyclohexyl-2-benzothiazylsulfenamide (CBS), N,N'-dicyclohexyl-2-benzothiazylsulfenamide, N-t-butyl-2-benzothiazylsulfenamide (TBBS)], thiomorpholine accelerators [e.g., 4,4'-dithiodimorpholine (DTDM), 2-(4'-morpholinodithio)benzothiazylsulfenamide, etc.], and the like. azole, etc.], thiazole-based accelerators [for example, 2-mercaptobenzothiazole (MBT), zinc salt of MBT, 2-mercaptobenzothiazole dibenzothiazyl disulfide (MBTS), 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-(4'-morpholinodithio)benzothiazole, etc.], urea- or thiourea-based accelerators [for example, ethylenethiourea, trimethylthiourea (TMU), diethylthiourea (EDE), etc.], guanidine-based accelerators (diphenylguanidine, di-o-tolylguanidine, etc.), dithiocarbamic acid-based accelerators [for example, sodium dimethyldithiocarbamate, zinc diethyldithiocarbamate (EZ), zinc dibutyldithiocarbamate (BZ), etc.], xanthogenate-based accelerators (zinc isopropylxanthogenate, etc.), etc.], etc. These crosslinking accelerators can be used alone or in combination of two or more. Among these crosslinking accelerators, TMTD, DPTT, CBS, MBTS, etc. are commonly used.

Of these, a combination of a thiuram accelerator and a sulfenamide accelerator is preferred. When the two are combined, the mass ratio of the thiuram accelerator to the sulfenamide accelerator is the former/latter = 10/1 to 1/10, preferably 3/1 to 1/3, more preferably 2/1 to 1/2, and even more preferably 1.5/1 to 1/1.5.

The proportion of the crosslinking accelerator (F1) is, for example, 0.2 to 10 parts by mass, preferably 0.5 to 7 parts by mass, more preferably 1 to 5 parts by mass, even more preferably 1.2 to 3 parts by mass, and most preferably 1.3 to 2 parts by mass, relative to 100 parts by mass of the polymer component (A). If the proportion of the crosslinking accelerator (F1) is too low, when used in a transmission belt, there is a risk of a decrease in abrasion resistance and lateral pressure resistance, and if the proportion is too high, there is a risk of a decrease in scorch resistance, rolling ability, and crack resistance.

(F2) Co-Crosslinking Agent Examples of the co-crosslinking agent (co-agent for crosslinking or co-vulcanizing agent) (F2) include known crosslinking assistants, such as polyfunctional (iso)cyanurates [e.g., triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), etc.], polydienes (e.g., 1,2-polybutadiene, etc.), metal salts of unsaturated carboxylic acids [e.g., polyvalent metal salts of (meth)acrylic acid, such as zinc (meth)acrylate and magnesium (meth)acrylate], oximes (e.g., quinone dioxime, etc.), guanidines (e.g., diphenyl guanidine, etc.), polyfunctional (meth)acrylates [e.g., alkane diol di(meth)acrylate, such as ethylene glycol di(meth)acrylate and butane diol di(meth)acrylate, trimethylol propane tri(meth)acrylate, phenyl di(meth)acrylate, etc. ... alkane polyol poly(meth)acrylates such as pentane erythritol tetra(meth)acrylate, bismaleimides [for example, alkylene bismaleimides such as N,N'-1,2-ethylene dimaleimide, N,N'-hexamethylene bismaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)cyclohexane, etc.; arene bismaleimides such as N,N'-m-phenylene dimaleimide (MPBM), 4-methyl-1,3-phenylene dimaleimide, 4,4'-diphenylmethane dimaleimide, 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane, 4,4'-diphenyl ether dimaleimide, 4,4'-diphenyl sulfone dimaleimide, 1,3-bis(3-maleimidophenoxy)benzene, etc.], and the like.

These co-crosslinking agents can be used alone or in combination of two or more. Among these, bismaleimides such as MPBM are preferred because they can improve abrasion resistance and lateral pressure resistance when used in transmission belts.

The proportion of the co-crosslinking agent (F2) is, for example, 0.1 to 30 parts by mass, preferably 0.2 to 20 parts by mass, more preferably 0.3 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and most preferably 0.8 to 3 parts by mass, relative to 100 parts by mass of the polymer component (A). When the crosslinking agent (E) is a sulfur-based crosslinking agent, the proportion of the co-crosslinking agent (F2) may be, for example, 0.1 to 3 parts by mass, preferably 0.3 to 2 parts by mass, and more preferably 0.5 to 1.5 parts by mass, relative to 100 parts by mass of the polymer component. If the proportion of the co-crosslinking agent (F2) is too low, there is a risk of a decrease in abrasion resistance and lateral pressure resistance when used in a transmission belt, and if the proportion is too high, there is a risk of a decrease in crack resistance.

The proportion of the crosslinking aid is, for example, 0.3 to 30 parts by mass, preferably 0.5 to 20 parts by mass, more preferably 1 to 10 parts by mass, even more preferably 1.5 to 5 parts by mass, and most preferably 2 to 3 parts by mass, relative to 100 parts by mass of the polymer component (A).

(G) Plasticizer The rubber composition of the present invention may further contain a plasticizer (G). Examples of the plasticizer (G) include aliphatic carboxylic acid ester plasticizers (adipate ester plasticizers, sebacic acid ester plasticizers, etc.), aromatic carboxylic acid ester plasticizers (phthalate ester plasticizers, trimellitic acid ester plasticizers, etc.), oxycarboxylic acid ester plasticizers, phosphate ester plasticizers, ether plasticizers, ether ester plasticizers, and other oils. These plasticizers can be used alone or in combination of two or more. Of these, ether ester plasticizers are preferred.

Furthermore, the plasticizer (G) is preferably a plasticizer derived from a resource other than petroleum, and is particularly preferably a plant-derived plasticizer (plant-based plasticizer).

The proportion of the plasticizer (G) is, for example, 0.1 to 30 parts by mass, preferably 0.2 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, even more preferably 0.5 to 3 parts by mass, and most preferably 0.8 to 2 parts by mass, per 100 parts by mass of the polymer component (A).

(H) Processing Agent or Processing Aid Examples of the processing agent or processing aid (H) include fatty acids such as stearic acid, fatty acid metal salts such as metal stearates, fatty acid amides such as stearic acid amide, wax, paraffin, etc. Among these, processing agents or processing aids derived from non-petroleum resources such as plant-derived or animal-derived are preferred, and fatty acids such as stearic acid are particularly preferred.

The proportion of the processing agent or processing aid (H) is, for example, 10 parts by mass or less, preferably 0.1 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, even more preferably 0.2 to 2 parts by mass, and most preferably 0.3 to 1 part by mass, based on 100 parts by mass of the polymer component (A), calculated as solid content.

(I) Other Components The rubber composition of the present invention may further contain other components. Examples of other components include carbonaceous materials other than carbon black (graphite, carbon nanotubes, etc.), softeners (paraffin oil, naphthenic oil, etc.), anti-aging agents (antioxidants, heat anti-aging agents, flex crack inhibitors, anti-ozonants, etc.), colorants, tackifiers, lubricants, coupling agents (silane coupling agents, etc.), stabilizers (ultraviolet absorbing agents, heat stabilizers, etc.), flame retardants, antistatic agents, etc. These other components can be used alone or in combination of two or more.

Of these, anti-aging agents are preferred. Anti-aging agents are made from petroleum-derived raw materials, and the non-petroleum resource ratio is 0% by mass. The proportion of anti-aging agent, calculated as solid content, is, for example, 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass, even more preferably 0.3 to 3 parts by mass, and even more preferably 0.5 to 1.5 parts by mass, per 100 parts by mass of the rubber component.

The total proportion of the other components is, for example, 0.1 to 100 parts by mass, preferably 0.2 to 50 parts by mass, more preferably 0.3 to 20 parts by mass, and even more preferably 0.5 to 10 parts by mass, relative to 100 parts by mass of polymer component (A).

(J) Properties of Cross-Linked Product of Rubber Composition The cross-linked product of the rubber composition of the present invention may have a rubber hardness Hs (type A) of 92 degrees or more, for example, 92 to 98 degrees, preferably 92.5 to 97 degrees, and more preferably 93 to 95 degrees, from the viewpoint of improving abrasion resistance and lateral pressure resistance when used in a transmission belt. If the rubber hardness is too low, the abrasion resistance and lateral pressure resistance may decrease when used in a transmission belt, and conversely, if the rubber hardness is too high, the crack resistance may decrease.

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

The crosslinked product of the rubber composition of the present invention has excellent resistance to heat aging, and the breaking elongation after heating at 120°C for 14 days (breaking elongation retention after heat aging) may be 40% or more (particularly 50% or more) of the breaking elongation before heating, for example 40 to 90%, preferably 45 to 80%, more preferably 48 to 70%, and even more preferably 50 to 60%. If the breaking elongation retention after heat aging is too low, there is a risk of reduced crack resistance.

In this application, the breaking elongation retention rate after heat aging can be measured in accordance with JIS K 6251 (2017), and in detail, can be measured by the method described in the examples below.

Despite its high non-petroleum resource ratio, the crosslinked product of the rubber composition of the present invention has excellent electrical conductivity, and the electrical resistance value may be 6 MΩ or less, for example, 5 MΩ or less, preferably 1 MΩ or less, further preferably 0.1 MΩ or less, more preferably 0.05 MΩ or less, and most preferably 0.03 MΩ or less, for example, about 0.01 to 0.05 MΩ. If the electrical resistance value is too high, the crosslinked product becomes easily charged.

In this application, the electrical resistance value of the cross-linked product can be measured as the electrical resistance value measured when a voltage is applied to both ends of the cross-linked rubber sheet using an insulation resistance meter, and in detail, can be measured by the method described in the examples below.

(K) Manufacturing Method of Rubber Composition The rubber composition of the present invention can be prepared by mixing (or kneading) each component by a conventional method. In order to mix them uniformly, however, it is preferable to knead a raw material (or raw material composition) containing the polymer component (A) and the carbon black (B).

All the compounding ingredients may be mixed at once (one-pass mixing), but in order to prevent scorching (unintentional crosslinking), the mixing may be performed in two stages: a parent mixing (A mixing) in which the components excluding the crosslinking agent and crosslinking aid are mixed, and a finish mixing (B mixing) in which the parent mixing rubber composition is mixed with the crosslinking agent and crosslinking aid. By mixing in two stages, it becomes easier to uniformly disperse the compounding ingredients in the rubber composition while preventing scorching. The mixing may be performed under heating or cooling to prevent scorching or to maintain the viscosity of the rubber composition at an appropriate level. In the parent mixing, the temperature of the rubber composition is preferably 130°C or less, more preferably 70 to 130°C, even more preferably 80 to 120°C, and most preferably 90 to 110°C. In the finish mixing, the temperature of the rubber composition is preferably 100°C or less, more preferably 50 to 100°C, even more preferably 65 to 95°C, and most preferably 70 to 90°C. If the temperature of the rubber composition during kneading is too high, scorching may occur, and if it is too low, the dispersibility of the compounding ingredients may decrease.

The kneading method may be a conventional kneading method, such as a method using a mixing roller, a kneader, a Banbury mixer, or an extruder (such as a single-screw or twin-screw extruder).

The rubber composition of the present invention is used as a crosslinked product crosslinked by a method appropriate for the application. The crosslinking temperature is, for example, 120 to 200°C (particularly 150 to 180°C).

[Power transmission belt]
The rubber composition of the present invention can be used for various molded articles formed from a polymer component containing an ethylene-α-olefin elastomer. Since the ethylene-α-olefin elastomer is combined with carbon black, the rubber composition is also excellent in electrical conductivity, heat resistance, cold resistance, weather resistance, hardness, and abrasion resistance, and is therefore preferably used for a transmission belt.

The type of the power transmission belt (power transmission belt) of the present invention is not particularly limited as long as it is a belt that contacts a pulley to transmit power, and may be a friction power transmission belt or a meshing power transmission belt.

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

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

These transmission belts may contain a cross-linked product of the rubber composition, but in order to effectively achieve the effects of the present invention, it is preferable that the belt body (particularly the compression rubber layer and/or the tension rubber layer) is formed from a cross-linked product of the rubber composition.

Among the above-mentioned power transmission belts, the application to V-belts in which the mass ratio of the rubber composition in the entire belt is large is preferred. Furthermore, raw edge V-belts are preferred because the contact surface with the pulley is made of rubber and static electricity can be easily released, and raw edge cogged V-belts are particularly preferred because improved crack resistance is required to prevent cog valley cracks.

The raw edge cogged V-belt of the present invention may comprise an adhesive rubber layer that is in contact with at least a portion of the core wire extending in the longitudinal direction of the belt, an extension rubber layer formed on one side of the adhesive rubber layer, and a compression rubber layer formed on the other side of the adhesive rubber layer, the inner circumferential surface of which has a plurality of convex portions (cogs) formed at predetermined intervals along the longitudinal direction of the belt, and the side surface of which frictionally engages with a pulley. Such raw edge cogged V-belts include raw edge cogged V-belts in which the cogs are formed only in the compression rubber layer, and raw edge double cogged V-belts in which similar cogs are formed on the outer circumferential surface of the extension rubber layer in addition to the compression rubber layer.

Figure 1 is a schematic partial cross-sectional perspective view showing an example of a transmission belt (raw-edge cogged V-belt) of the present invention, and Figure 2 is a schematic cross-sectional view of the transmission belt of Figure 1 cut in the belt longitudinal direction.

In this example, the raw edge cogged V-belt 1 has a plurality of cogs 1a formed at a predetermined interval along the longitudinal direction of the belt (direction A in the figure) on the inner peripheral surface of the belt body, and the cross-sectional shape of the cogs 1a in the longitudinal direction is approximately semicircular (curved or wavy), and the cross-sectional shape in the direction perpendicular to the longitudinal direction (direction B in the figure) is an inverted trapezoid. That is, each cog (cog crest or cog top) 1a protrudes in the belt thickness direction from the cog bottom (cog valley) 1b in an approximately semicircular shape in the cross section in the A direction. The raw edge cogged V-belt 1 has a layered structure, and the reinforcing cloth 2, the tension rubber layer 3, the adhesive rubber layer 4, the compression rubber layer 5, and the reinforcing cloth 6 are layered in order from the outer periphery of the belt to the inner periphery (the side where the cogs 1a are formed). The cross-sectional shape in the belt width direction is an inverted trapezoid in which the belt width becomes smaller from the outer periphery of the belt to the inner periphery. Furthermore, a core 4a is embedded in the adhesive rubber layer 4, and the cog portion 1a is formed into the compressed rubber layer 5 using a cog-equipped molding die.

The height and pitch of the cogs are the same as in conventional cog V-belts. In the compressed rubber layer, the height of the cogs is 50-95% (particularly 60-80%) of the total thickness of the compressed rubber layer, and the pitch of the cogs (the distance between the centers of adjacent cogs) is 50-250% (particularly 80-200%) of the height of the cogs. The same applies when cogs are formed in a tension rubber layer.

In this example, the tension rubber layer 3 and compression rubber layer 5 are formed from a cross-linked product of the rubber composition. Conventional adhesive rubber layers, cores, and reinforcing fabrics can be used for the adhesive rubber layer, core, and reinforcing fabric, and may be, for example, the adhesive rubber layer, core, and reinforcing fabric shown below.

(Adhesive rubber layer)
The rubber composition for forming the adhesive rubber layer, like the crosslinked rubber composition for the compression rubber layer and the tension rubber layer, contains a polymer component, a crosslinking agent (sulfur-based vulcanizing agent, etc.), a co-crosslinking agent (maleimide-based crosslinking agent, such as N,N'-m-phenylenedimaleimide, etc.), a crosslinking accelerator (TMTD, CBS, MBTBS, etc.), an inorganic filler (carbon black, silica, etc.), a softener (oils such as paraffin-based oil), a processing agent or processing aid, an antiaging agent, an adhesion improver [resorcinol-formaldehyde cocondensate, amino resin (nitrogen Condensates of nitrogen-containing cyclic compounds with formaldehyde, for example, melamine resins such as hexamethylol melamine, hexaalkoxymethyl melamine (hexamethoxymethyl melamine, hexabutoxymethyl melamine, etc.), urea resins such as methylol urea, benzoguanamine resins such as methylol benzoguanamine resin, etc.), cocondensates thereof (resorcin-melamine-formaldehyde cocondensates, etc.), colorants, tackifiers, plasticizers, coupling agents, stabilizers, flame retardants, antistatic agents, etc. In the adhesion improver, the resorcin-formaldehyde cocondensates and amino resins may be initial condensates (prepolymers) of nitrogen-containing cyclic compounds such as resorcin and/or melamine with formaldehyde.

In addition, in this rubber composition, the polymer component is often the same type or the same polymer as the polymer component of the rubber composition of the compression rubber layer and the tension rubber layer. The polymer component of the adhesive rubber layer may also be an ethylene-α-olefin elastomer formed from raw materials including raw materials derived from non-petroleum resources, but since the polymer component is smaller than that of the compression rubber layer, from the standpoint of economy, an ethylene-α-olefin elastomer derived from petroleum resources may also be used.

The proportions of the crosslinking agent, crosslinking aid, softener and anti-aging agent can be selected from the same ranges as those of the rubber composition of the compression rubber layer and the tension rubber layer. In addition, in the rubber composition of the adhesive rubber layer, the total proportion of the inorganic filler is 10 to 100 parts by mass, preferably 20 to 80 parts by mass, and more preferably 30 to 50 parts by mass, per 100 parts by mass of the polymer component. In addition, the total proportion of the adhesion improver (resorcinol-formaldehyde co-condensate, hexamethoxymethylmelamine, etc.) is 0.1 to 20 parts by mass, preferably 1 to 10 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of the polymer component.

(Core body)
The core body is not particularly limited, but usually, a core wire (twisted cord) arranged at a predetermined interval in the belt width direction can be used. The core wire is arranged extending in the longitudinal direction of the belt, and a plurality of core wires parallel to the belt longitudinal direction may be arranged, but from the viewpoint of productivity, it is usually arranged in a spiral shape extending in parallel at a predetermined pitch approximately parallel to the belt longitudinal direction of the raw edge cogged V-belt. When arranged in a spiral shape, the angle of the core wire with respect to the belt longitudinal direction may be, for example, 5° or less, and from the viewpoint of belt running property, the closer to 0°, the more preferable. In addition, the pitch of the core wire is preferably set in the range of 1.0 to 2.5 mm, more preferably in the range of 1.5 to 2.0 mm. The core wire may be embedded in the adhesive rubber layer, embedded between the adhesive rubber layer and the tension rubber layer (tension layer side), or embedded between the adhesive rubber layer and the compression rubber layer (compression rubber layer side). Of these, the adhesive rubber layer is preferred in terms of improving durability.

Examples of fibers constituting the core wire include the same fibers as the short fibers. Among the fibers, polyester fibers (polyalkylene arylate fibers) having C _2-4 alkylene-arylate such as ethylene terephthalate and ethylene-2,6-naphthalate as the main structural unit, synthetic fibers such as aramid fibers, and inorganic fibers such as carbon fibers are widely used from the viewpoint of high modulus, and polyester fibers (polyethylene terephthalate fibers, polyethylene naphthalate fibers) 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 (particularly 500 to 2000 dtex). The number of filaments contained in the multifilament yarn can be selected from the range of about 50 to 5000, for example, 50 to 1500, preferably 100 to 1000, and more preferably 300 to 500.

As the core wire, a twisted cord (e.g., multiple twist, single twist, Lang twist, etc.) using multifilament yarn can usually be used. The fineness of the core wire (twisted cord) is, for example, 3000 to 30000 dtex, preferably 10000 to 25000 dtex, and more preferably 15000 to 20000 dtex. The number of filaments contained in the core wire (twisted cord) can be selected from a range of about 500 to 15000, for example, 500 to 12000, preferably 2000 to 10000, and more preferably 4000 to 6000. The average wire diameter of the core wire (diameter of the twisted cord) may be, for example, 0.5 to 3.0 mm, preferably 1.0 to 2.0 mm, and more preferably 1.5 to 1.7 mm.

The core wire may be adhesively treated (or surface treated) in the same manner as the short fibers of the compressed rubber layer and the tensioned rubber layer to improve adhesion to the polymer component. It is preferable that the core wire is adhesively treated with at least an RFL liquid, like the short fibers.

(Reinforcing fabric)
In the case of using a reinforcing cloth in a friction transmission belt, the reinforcing cloth is not limited to being laminated on the surface of the compressed rubber layer, and may be laminated on the surface of the tension rubber layer (the surface opposite to the adhesive rubber layer), or may be embedded in the compressed rubber layer and/or tension rubber layer (for example, the form described in JP 2010-230146 A). The reinforcing cloth may be formed of, for example, a fabric material (preferably a woven fabric) such as a woven fabric, a wide-angle canvas, a knitted fabric, or a nonwoven fabric, and if necessary, may be subjected to the above-mentioned adhesion treatment, for example, treatment with an RFL liquid (dipping treatment, etc.), or friction in which adhesive rubber is rubbed into the fabric material, or the adhesive rubber and the fabric material are laminated, and then laminated on the surface of the compressed rubber layer and/or tension rubber layer.

[Manufacturing method of power transmission belt]
The method for producing the power transmission belt of the present invention is not particularly limited, and any conventional method can be used depending on the type of belt.

For example, a typical manufacturing method for a raw edge cogged V-belt is described below. First, a laminate of a reinforcing fabric (lower fabric) and a sheet for a compressed rubber layer (uncrosslinked rubber sheet) is placed in contact with a flat cog-equipped mold in which teeth and grooves corresponding to the cogs (cog crests 1a and cog bottoms 1b) are alternately arranged, with the reinforcing fabric facing down, and pressed at a temperature of about 60-100°C (particularly 70-80°C) to produce a cog pad (a pad that is not completely crosslinked, but is in a semi-crosslinked state) with the cogs shaped. Then, both ends of this cog pad are cut vertically at appropriate points (particularly the tops of the cog crests) to obtain the required length.

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

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

In this case, the reinforcing fabric and the sheet for the compressed rubber layer may be laminated on the outer periphery of the inner mold without preparing a cog pad. In this method, the reinforcing fabric and the sheet for the compressed rubber layer are pressed into the grooves of the inner mold during cross-linking molding to form the cog portion.

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

In addition, the method of orienting the short fibers in the tension rubber layer sheet and the compression rubber layer sheet in the belt width direction can be a conventional method, such as rolling the rubber into a sheet by passing it between a pair of calendar rolls with a specified gap, cutting both sides of the rolled sheet with the short fibers oriented in the rolling direction parallel to the rolling direction, cutting the rolled sheet perpendicular to the rolling direction to the belt forming width (length in the belt width direction), and joining the sides cut parallel to the rolling direction. For example, the method described in JP 2003-14054 A can be used. The uncrosslinked sheet in which the short fibers have been oriented in this way can be crosslinked in the above method by arranging the short fibers so that they are oriented in the belt width direction.

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

[Materials used]
(polymer)
EPDM-A: "Keltan eco 5470" manufactured by ARLANXEO, ethylene content 70% by mass, diene content 4.6% by mass, Mooney viscosity [ML(1+4)125°C] 55
EPDM-B: "Nordel 4520" manufactured by Dow Chemical Company, ethylene content 50% by mass, diene content 4.9% by mass, Mooney viscosity [ML(1+4)125°C] 20
EPDM-C: "Nordel 4640" manufactured by Dow Chemical Company, ethylene content 55% by mass, diene content 4.9% by mass, Mooney viscosity [ML(1+4)125°C] 40
EPDM-D: “EP24” manufactured by JSR Corporation, ethylene content 54% by mass, diene content 4.5% by mass

(Filler)
Carbon black ISAF: "Seat 6" manufactured by Tokai Carbon Co., Ltd., DBP absorption capacity 114 mL/100 g, BET specific surface area 119 m ² /g, iodine adsorption capacity 121 g/kg
Carbon black HAF: "Seat 3" manufactured by Tokai Carbon Co., Ltd., DBP absorption capacity 101 mL/100 g, BET specific surface area 79 m ² /g, iodine adsorption capacity 80 g/kg
Carbon black FEF: "N550" manufactured by Cabot Japan Co., Ltd.
Silica: "Ultrasil VN3" manufactured by Evonik Degussa, BET specific surface area 175 m ² /g
Calcium carbonate: "Super #1500" manufactured by Maruo Calcium Co., Ltd.
Zinc oxide: "Zinc oxide type 2" manufactured by Sakai Chemical Industry Co., Ltd.
Cellulosic staple fiber: "Cotton cut yarn" manufactured by Hashimoto Co., Ltd., average fiber length 6 mm
Polyester staple fiber: "Tetoron" manufactured by Teijin Limited, average fiber diameter 25 μm, average fiber length 3 mm

(Crosslinking agent and crosslinking coagent)
Sulfur: "MIDAS" manufactured by Bigen Chemical Co., Ltd.
Crosslinking accelerator TMTD (tetramethylthiuram disulfide): "Noccela TT" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Crosslinking accelerator CBS (N-cyclohexyl-2-benzothiazolylsulfenamide): "Noccela CZ" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Crosslinking accelerator MBTS (2,2'-dibenzothiazolyl disulfide): "Noccela DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Co-crosslinking agent MPBM (m-phenylenedimaleimide): "Valnoc PM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

(Other ingredients)
Vegetable plasticizer (polyethylene glycol-di-2-ethylhexoate): "Leonon DEH-40" manufactured by Lion Specialty Chemicals Co., Ltd.
Paraffin oil: "Diana Process Oil PW-90" manufactured by Idemitsu Kosan Co., Ltd.
Stearic acid: "Camellia Stearate" manufactured by NOF Corporation
Antioxidant DCD (4,4'-bis(α,α-dimethylbenzyl)diphenylamine): "Nocrac CD" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Anti-aging agent ODPA (octyldiphenylamine): "Nonflex OD-3" manufactured by Seiko Chemical Co., Ltd.
Adhesion improver A (resorcinol-formaldehyde co-condensate): "Penacolite Resin (B-18-S)" manufactured by INDSPEC Chemical Corporation
Adhesion improver B (hexamethoxymethylmelamine): "POWERPLAST PP-1890S" manufactured by SINGH PLASTICISER & RESINS

[Core wire (processing code)]
The cord is made by bonding a multi-ply cord (5760 filaments) with a total fineness of 18300 dtex, which is made by combining three 1220 dtex PET fiber bundles (384 filaments) and twisting them at a twist factor of 3.0 to form five first twisted yarns, which are then twisted at a twist factor of 3.0. The cord diameter is 1.6 mm.

[Reinforcing fabric covering the outer surface (treated canvas)]
The canvas (approximately 180 g/ ^m2 ) is plain woven using No. 10 cotton yarn for the warp and weft with a warp and weft density of 70 threads/50 mm, and has been treated with friction treatment by imprinting adhesive rubber on both sides (approximately 0.5 mm thick and approximately 450 g/ ^m2 ).

Examples 1 to 5 and Comparative Examples 1 to 4
[Rubber hardness Hs of crosslinked rubber]
The rubber composition having the composition shown in Table 2 was kneaded in two stages, a temperature of 105°C for the main kneading and a temperature of 80°C for the finishing kneading, and then rolled into a sheet. The resulting uncrosslinked rubber sheet was press-crosslinked at a temperature of 165°C, a pressure of 2 MPa, and a time of 30 minutes to produce a crosslinked rubber sheet (100 mm x 100 mm x 2 mm thick). Three of the resulting crosslinked rubber sheets were stacked together to form a laminate, which was used as a sample. The rubber hardness Hs (Type A) of the crosslinked rubber sheet was measured using a Type A durometer in accordance with the spring durometer hardness test specified in JIS K 6253 (2012) (vulcanized rubber and thermoplastic rubber - Determination of hardness). The results are shown in Table 2.

[4% bending stress (perpendicular to short fibers)]
An uncrosslinked rubber composition having the composition shown in Table 2 was press-heated at a temperature of 165° C. and a pressure of 2 MPa for 30 minutes to prepare a crosslinked rubber molded body (60 mm×25 mm×6.5 mm thick). The short fibers were oriented parallel to the length direction of the crosslinked rubber molded body. As shown in FIG. 3, this crosslinked rubber molded body 21 was placed on a pair of rotatable rolls (diameter 6 mm) 22a, 22b spaced 20 mm apart to support it, and a metal pressing member 23 was placed in the width direction (direction perpendicular to the orientation direction of the short fibers) at the center of the upper surface of the crosslinked rubber molded body. The tip of the pressing member 23 has a semicircular shape with a diameter of 10 mm, and the tip can smoothly press the crosslinked rubber molded body 21. In addition, 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 during pressing, but the effect of friction is reduced by making the rolls 22a, 22b rotatable. The initial position was a state in which the tip of the pressing member 23 was in contact with but not pressing against the upper surface of the crosslinked rubber molded body 21, and from this state the pressing member 23 was pressed downward against the upper surface of the crosslinked rubber molded body 21 at a speed of 100 mm/min, and the stress at which the bending strain reached 4% was measured as the bending stress. The measurement temperatures were 23° C. and 120° C. It can be determined that the greater the 4% bending stress in the direction perpendicular to the short fibers, the higher the resistance to buckling deformation called dishing during belt running.

[Breaking elongation retention after heat aging]
The rubber composition having the composition shown in Table 2 was kneaded in two stages, a temperature of 105 ° C. for the main kneading and a temperature of 80 ° C. for the finishing kneading, and then rolled into a sheet. The obtained uncrosslinked rubber sheet was press-crosslinked at a temperature of 165 ° C. and a pressure of 2 MPa for 30 minutes to produce a crosslinked rubber sheet (100 mm × 100 mm × 2 mm thick). The obtained crosslinked rubber sheet was punched with a super dumbbell cutter (manufactured by Dumbbell Co., Ltd.) to prepare a dumbbell-shaped No. 3 test piece. In accordance with JIS K 6257 (2017), the prepared test piece was left in a gear-type aging tester set at 120 ° C. for 14 days and then removed. The removed test piece was left at 23 ° C. for 24 hours, and then the breaking elongation was measured in accordance with JIS K 6251 (2017). The tensile speed was 500 mm / min, and the test temperature was 23 ° C. The breaking elongation retention was calculated using the following formula. The results are shown in Table 2.

Breaking elongation retention rate (%) = (breaking elongation after heat aging / breaking elongation before heat aging) x 100.

[Electrical resistance value]
The rubber composition having the composition shown in Table 2 was kneaded in two stages, a temperature of 105°C for the main kneading and a temperature of 80°C for the finishing kneading, and then rolled into a sheet. The resulting uncrosslinked rubber sheet was press-crosslinked at a temperature of 165°C for 30 minutes to produce a crosslinked rubber sheet having a thickness of 2 mm. A sample for measuring electrical resistance value having a length of 100 mm, a width of 5 mm, and a thickness of 2 mm was punched out from the resulting rubber sheet. After attaching electrode terminals of an insulation resistance meter to both ends of the sample in the longitudinal direction, a voltage of 500 V was applied, and the electrical resistance value after 1 minute was measured. The measurement was performed at room temperature of 23°C and a relative humidity of 50%. The results are shown in Table 2.

[Belt manufacturing]
A laminate in which an uncrosslinked compression rubber layer sheet having a composition shown in Table 2 and an uncrosslinked first adhesive rubber layer sheet having a composition shown in Table 1 were laminated in this order was wound around the outer periphery of a cog-equipped mold in which teeth and grooves were alternately arranged, with the compression rubber layer sheet facing the mold. Then, a core wire was spirally wound around the outer periphery of the uncrosslinked first adhesive rubber layer sheet, and a laminate in which an uncrosslinked second adhesive rubber layer sheet having a composition shown in Table 1 and an uncrosslinked tensile rubber layer sheet having a composition shown in Table 2 were laminated around the outer periphery of the uncrosslinked first adhesive rubber layer sheet was wound around the outer periphery with the uncrosslinked second adhesive rubber layer sheet facing the core. Furthermore, a laminate in which treated canvas was wrapped twice around the outer periphery of the tensile rubber layer sheet was produced. After covering the outer periphery of the laminate with a flexible jacket, the mold was placed in a vulcanizing can, and pressurized and heated (about 170°C) for 40 minutes by injecting steam around the flexible jacket and into the inside of the mold, to produce a belt sleeve. The prepared belt sleeve was cut into a V shape with a cutter to prepare a raw edge cogged V-belt (upper width 16.6 mm, thickness (thickness at the top of the cog) 13.5 mm, outer periphery length 1140 mm) having cogs on the inner peripheral surface of the belt.

[Evaluation of crack resistance (time until cracks occur)]
As shown in FIG. 4, a three-axis running test machine consisting of a driving (Dr.) pulley with a diameter of 125 mm, a driven (Dn.) pulley with a diameter of 125 mm, and an idler (Id.) pulley with a diameter of 85 mm was used. A low-edge cogged V-belt was hung on each pulley, and an initial tension of 798 N was applied to the belt, and the contact angle at the idler pulley (the central angle with respect to the arc where the belt and pulley are in contact) was adjusted to 90°. The belt was run at a rotation speed of 4900 rpm, a load of 8.8 kW on the driven pulley, no load on the idler pulley, and an ambient temperature of 85° C., and the time until a crack with a depth (length in the belt thickness direction) of 1 mm or more occurred was measured. The longer the time until the crack occurred, the better the crack resistance, and 150 hours or more was considered to be acceptable.

[Evaluation of wear resistance (wear rate)]
As shown in Fig. 5, a biaxial running tester consisting of a driving (Dr.) pulley with a diameter of 180 mm and a driven (Dn.) pulley with a diameter of 180 mm was used. A low-edge cogged V-belt was hung on each pulley, and the belt was run for 70 hours at an ambient temperature of 23°C with an axial load of 1764N, a rotation speed of the driving pulley of 1140 rpm, and a load of the driven pulley of 70 Nm. The mass of the belt was measured before and after running, and the mass change rate (wear rate) was evaluated. The smaller the wear rate, the better the wear resistance, and a wear rate of 0.35% or less was considered to be acceptable.

Wear rate (%) = [(belt mass before running - belt mass after running) / belt mass before running] x 100.

[Overall Judgment]
The overall judgment was made as follows: Raw-edge cogged V-belts that satisfied the following conditions: non-petroleum resource rate of 30 mass% or more, rubber hardness of 92 or more, 4% bending stress of 2.4 MPa or more, breaking elongation retention after heat aging of 40% or more, electrical resistance of 6 MΩ or less, time until cracks occur of 150 hours or more, and abrasion rate of 0.35% or less were judged as ◯ (pass), and raw-edge cogged V-belts that did not satisfy at least one of the above conditions were judged as × (fail).

The evaluation results of the obtained raw edge cogged V-belt are shown in Table 2.

Examples 1 to 8 had a high non-petroleum resource ratio, low electrical resistance, and low wear rate.

Comparing Examples 1 to 4, Example 1 had the highest non-petroleum resource content, and also had high levels of crack resistance and abrasion resistance. Although Examples 2 to 4 use EPDM that is not bio-EPDM (EPDM with a non-petroleum resource content of 0%) as part of the polymer component, which reduces the non-petroleum resource content, the rubber properties and belt evaluation are comparable to those of Example 1, and it was found that it is possible to mix in non-bio-EPDM and use it while taking into account cost, etc.

In addition, it was found that it is also effective to increase the non-petroleum resource ratio by replacing part of the carbon black with silica in Example 4, as in Example 5.

As in Example 6, it was found that the electrical resistance value increased by using carbon black with a lower DBP absorption amount than in Example 4.

As in Example 7, by replacing part of the carbon black in Example 1 with silica, it was found that it was possible to increase the non-petroleum resource ratio while keeping the electrical resistance value relatively low, as in Example 5.

As in Example 8, by using polyester staple fibers instead of cellulosic staple fibers in Example 4, the overall evaluation was ◯, but it was found that the non-petroleum resource ratio decreased and the 4% bending stress at 120°C decreased.

On the other hand, in Comparative Example 1 in which no bio-EPDM was used at all, the non-petroleum resource ratio was significantly low, making it impossible to sufficiently reduce CO ₂ emissions.

Comparative Examples 2 and 3 are examples in which an attempt was made to increase the non-petroleum resource ratio by replacing part of the carbon black with silica without using any bio-EPDM, but the electrical resistance was high and the abrasion resistance was also at a low level. Comparative Example 4 used bio-EPDM, but the proportion of carbon black was low, resulting in a high electrical resistance.

These results show that simply replacing part of the carbon black with silica results in high electrical resistance and makes it difficult to sufficiently increase the non-petroleum resource ratio. It was found that the use of bio-EPDM is essential to sufficiently increase the non-petroleum resource ratio while keeping electrical resistance low.

The rubber composition of the present invention can be used for molded articles using rubber, such as tires, hoses, power transmission belts, and conveyor belts, but is particularly preferably used for power transmission belts. Power transmission belts can be, for example, friction power transmission belts such as flat belts, V-belts (wrapped V-belts, low-edge V-belts, low-edge cogged V-belts, low-edge double cogged V-belts, etc.), V-ribbed belts, and resin block belts; meshing power transmission belts such as toothed belts and double-sided toothed belts; and the like. In particular, application to V-belts in which the mass ratio of the rubber composition to the entire belt is large is preferred. Furthermore, low-edge V-belts are preferred because the contact surface with the pulley is made of rubber and is easy to release static electricity, and low-edge cogged V-belts are particularly preferred because improved crack resistance is required to prevent cog valley cracks.

1 ... Raw edge cogged V-belt 2, 6 ... Reinforcing fabric 3 ... Tension rubber layer 4 ... Adhesive rubber layer 4a ... Core body 5 ... Compression rubber layer

Claims (12)

A rubber composition comprising a polymer component containing an ethylene-α-olefin elastomer and carbon black, and having a non-petroleum resource ratio of 30 mass% or more,
The ethylene-α-olefin elastomer is formed from raw materials including raw materials derived from non-petroleum resources, and the proportion of the carbon black is 40 to 80 parts by mass per 100 parts by mass of the polymer component. The rubber composition according to claim 1, further comprising an inorganic filler derived from a non-petroleum resource. The rubber composition according to claim 1 or 2, wherein the ethylene-α-olefin elastomer has an average Mooney viscosity [ML(1+4)125°C] of 41 or more. The rubber composition according to claim 1 or 2, wherein the ethylene content of the ethylene-α-olefin elastomer is 45% by mass or more. The rubber composition according to claim 1 or 2, wherein the carbon black has a DBP absorption of 60 mL/100 g or more. The rubber composition according to claim 1 or 2, wherein the cross-linked product has a rubber hardness Hs (type A) of 92 degrees or more. The rubber composition according to claim 1 or 2, in which the crosslinked product has a breaking elongation retention rate of 40% or more after heat aging. The rubber composition according to claim 1 or 2, wherein the electrical resistance of the crosslinked product is 6 MΩ or less. The rubber composition according to claim 1 or 2, further comprising short cellulose fibers. The method for producing a rubber composition according to claim 1 or 2, in which the polymer component and the carbon black are mixed. A transmission belt comprising a crosslinked product of the rubber composition according to claim 1 or 2. The power transmission belt according to claim 11, which is a raw edge cogged V-belt.

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