JP6747924B2 - Friction transmission belt and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a friction transmission belt such as a V-belt or a V-ribbed belt in which a friction transmission surface is inclined in a V shape, and a method for manufacturing the friction transmission belt. It relates to a manufacturing method.

Friction transmission belts such as V-belts, V-ribbed belts and flat belts are known as transmission belts for transmitting power. The V-belt has a rubber layer with an exposed friction transmission surface (Raw-Edge) type (low-edge V-belt) and a friction transmission surface (V-shaped side surface) covered with a cover cloth (Wrapped) type. (Wrapped V-belt), which is used depending on the application because of the difference in surface properties of the friction transmission surface (coefficient of friction between the rubber layer and the cover cloth). Further, the low edge type belt has a low edge cogged V with improved flexibility by providing cogs only on the lower surface (inner peripheral surface) of the belt or on both the lower surface (inner peripheral surface) and upper surface (outer peripheral surface) of the belt. There is a belt.

The low edge V-belt and the low edge cogged V-belt are mainly used for driving general industrial machines, agricultural machines, driving auxiliary machines in automobile engines, and the like. Further, as another application, there is a low edge cogged V-belt called a speed change belt used in a belt type continuously variable transmission such as a motorcycle.

Among these friction transmission belts, V belts and V-ribbed belts whose friction transmission surfaces (V-shaped side surfaces) are formed at V angles are wound around a drive pulley and a driven pulley with tension applied to form a V-shaped belt. The rotating shaft travels between the two shafts in a state where the side surface is in contact with the V groove of the pulley. In the process, the power is transmitted by using the energy accompanying the friction generated by the thrust between the V-shaped side surface and the pulley V groove. At this time, the lateral pressure resistance received from the pulley is one of the important factors that bear the belt durability. Therefore, conventionally, as a prescription for improving the lateral pressure resistance, the compression rubber layer is reinforced by blending short fibers or the like. ing.

For example, in JP-A-10-238596 (Patent Document 1), the rubber hardness of at least one of the stretched and compressed rubber layers is set to 90 to 96°, and the rubber hardness of the adhesive rubber layer is set to 83 to 89°. For the stretched and compressed rubber layers, a V-belt for transmission in which aramid short fibers are oriented in the belt width direction is disclosed. In this document, cracks and separation of rubber layers and cords are prevented from occurring at an early stage, and lateral pressure resistance is improved to improve high-load transmission capability.

However, this transmission V-belt cannot satisfy the recent high demands for the transmission V-belt. In other words, in recent years, in addition to durability (side pressure resistance), it is required to improve fuel economy, and for that reason, it is also necessary to reduce transmission loss and improve fuel economy. This is because lateral pressure resistance and fuel economy are in a trade-off relationship. For example, if the compression rubber layer of the V-belt is mixed with a reinforcing material such as short fibers, carbon black or silica to increase the rubber hardness and enhance the lateral pressure resistance, the bending rigidity is increased, and especially the layout of the small pulley diameter is increased. It is known that transmission loss occurs.

In particular, in a speed change belt used in a belt type continuously variable transmission such as a motorcycle, it is a major issue to make resistance to lateral pressure and fuel saving both compatible, and, for example, Japanese Patent Laid-Open No. 2015-152101 ( Patent Document 2) specifies that the lower cog forming part and the upper cog forming part contain 40 to 80 parts by weight of filler with respect to 100 parts by weight of rubber, and the filler contains 30% or more of silica. A double cogged V-belt made of a rubber composition having dynamic viscoelasticity is disclosed.

However, even with this double-cogged V-belt, it was not possible to achieve both high lateral pressure resistance and high fuel efficiency.

Japanese Unexamined Patent Application Publication No. 2010-196888 (Patent Document 3) discloses a power transmission belt that can withstand use in a small-diameter pulley and can suppress cracks and breaks on the belt surface even if it is repeatedly bent. There is disclosed a power transmission belt having two layers, a near upper layer and a lower layer on the inner peripheral surface side of the belt, and a compression rubber layer in which the hardness of the upper layer is set higher than that of the lower layer. This document describes using different types of rubber materials for the upper layer and the lower layer.

However, this document does not describe compatibility between lateral pressure resistance and fuel economy. Further, even with this power transmission belt, the upper layer and the lower layer are easily separated from each other, and it is not possible to achieve both high lateral pressure resistance and high fuel efficiency.

Japanese Patent Application Laid-Open No. 9-177899 (Patent Document 4) discloses an ACSM composition as a transmission belt that can achieve both sag resistance and crack resistance even when an alkylated chlorosulfonated polyethylene (ACSM) composition is used. Disclosed is a power transmission belt including a compression rubber layer having a composite structure in which a low tan δ layer formed by (1) and a high tan δ layer formed by an ACSM composition are layered in a belt thickness direction. In this document, the compressed rubber layer has a two-layer structure of a low tan δ layer having a sulfur content of 0.5 to 0.8% by weight and a high tan δ layer having a lower sulfur content than the low tan δ layer. , A transmission belt in which the low tan δ layer is arranged on the side close to the core wire is also described. Further, regarding the compressed rubber layer having a two-layer structure, the thickness ratio of the low tan δ layer and the high tan δ layer is not described, and in the drawing, the upper low tan δ layer is twice as thick as the lower high tan δ layer. The above is a large thickness.

However, this document also does not describe compatibility between lateral pressure resistance and fuel economy. In this document, a plurality of layers having different tan δ are combined by changing the compounding amount of the additive, but each layer is a uniform layer.

Japanese Patent Laid-Open No. 10-238596 (claim 1, paragraphs [0008][0048]) JP-A-2015-152101 (Claims, paragraph [0010]) JP, 2010-196888, A (claim 1, paragraph [0010] [0028]). JP-A-9-177899 (claims, paragraphs [0043][0111], examples)

An object of the present invention is to provide a friction transmission belt capable of improving lateral pressure resistance while maintaining fuel economy and a method for manufacturing the same.

As a result of intensive studies to achieve the above-mentioned object, the inventors have gradually reduced the crosslink density of the compressed rubber layer from the outer peripheral side of the belt toward the inner peripheral side in the thickness direction while maintaining fuel efficiency. The present invention has been completed by finding that the lateral pressure resistance can be improved.

That is, the friction transmission belt of the present invention includes a compression rubber layer having a transmission surface at least a portion of which can be in contact with the pulley, and the crosslink density of which gradually decreases in the thickness direction from the belt outer peripheral side toward the inner peripheral side. .. The crosslink density distribution of the compressed rubber layer may be a distribution that decreases continuously or stepwise from the outer peripheral side of the belt toward the inner peripheral side thereof. The compressed rubber layer has a multilayer structure, for example, (a) a two-layer structure of an outer layer on the outer peripheral side of the belt and an inner layer on the inner peripheral side of the belt, or (b) an outer layer on the outer peripheral side of the belt and an inner layer on the inner peripheral side of the belt. And an intermediate layer interposed between the outer layer and the inner layer may have a three-layer structure. The compressed rubber layer has a two-layer structure in which (a) the thickness ratio of the outer layer to the inner layer is about outer layer/inner layer=1.5/1 to 1/1.5, or (b) the outer layer and the inner layer or an intermediate layer. The thickness ratio with respect to the layers may be a three-layer structure in which the outer layer/inner layer or the intermediate layer is approximately 1.5/1 to 1/1.5. In the friction transmission belt of the present invention, when the compressed rubber layer is divided into six equal parts in the thickness direction, the difference in crosslinking density between the first region located on the outermost peripheral side and the sixth region located on the innermost peripheral side is 10 It is about 100 mol/m ³ . Further, when the compressed rubber layer is divided into three equal parts in the thickness direction, the difference in crosslink density between the central region and other regions is about ³ to 50 mol/m ³ . The compressed rubber layer may be a vulcanized product of a rubber composition containing a rubber component, a crosslinking agent and a reinforcing material. The rubber component may include an ethylene-α-olefin elastomer. The cross-linking agent may contain a vulcanizing agent (particularly a sulfur-based vulcanizing agent) and a vulcanization accelerator (particularly a vulcanization accelerator having a molecular weight of 500 or less). The ratio of the reinforcing material may be 50 parts by mass or more with respect to 100 parts by mass of the rubber component. The friction transmission belt of the present invention may be a low edge cogged V-belt.

In the present invention, a laminated sheet obtained by laminating a plurality of unvulcanized sheets for compressed rubber layers (may be simply referred to as unvulcanized sheet or unvulcanized rubber sheet) is pre-cured at a temperature lower than the vulcanization temperature. A method for manufacturing the friction transmission belt including a preliminary vulcanization step of vulcanizing, in the order of increasing the crosslink density of the vulcanized sheet from the inner peripheral side to the outer peripheral side of the belt, that is, each unvulcanized sheet alone The method includes a method of laminating the vulcanized rubber sheet (which may be simply referred to as a vulcanized sheet) vulcanized in the order of increasing crosslink density. It also includes a manufacturing method in which a plurality of unvulcanized sheets for compressed rubber layers having different concentrations of the cross-linking agent are laminated in the order of increasing concentration of the cross-linking agent from the inner peripheral side of the belt toward the outer peripheral side. The laminated sheet may be a laminated body in which the concentration of the cross-linking agent in the unvulcanized sheets adjacent to each other increases by at least 0.1% by mass from the inner peripheral side of the belt toward the outer peripheral side thereof. In the preliminary vulcanization step, preliminary vulcanization may be performed at a temperature lower than the vulcanization temperature by 30° C. or more.

In the present invention, "crosslinking agent" means all additives that act on crosslinking or vulcanization, that is, vulcanizing agent, co-vulcanizing agent (vulcanization aid), vulcanization accelerator, vulcanization retarder, etc. Is used as a generic term.

In the present invention, in the thickness direction, since the crosslink density of the compression rubber layer gradually decreases from the belt outer peripheral side (adhesive rubber layer side) toward the inner peripheral side, it is possible to reduce fuel consumption while maintaining fuel efficiency (transmission efficiency). Lateral pressure (durability) can be improved. Specifically, even if the compression rubber layer is blended with reinforcing materials such as short fibers, carbon black, and silica to increase lateral pressure resistance, the bending rigidity of the belt is kept small, and transmission efficiency is reduced (transmission loss). Can be suppressed.

FIG. 1 is a schematic perspective view showing an example of the friction transmission belt of the present invention. FIG. 2 is a schematic cross-sectional view of the friction transmission belt of FIG. 1 cut in the belt longitudinal direction. FIG. 3 is a schematic diagram for explaining a method of measuring transmission efficiency. FIG. 4 is a schematic diagram for explaining a method for measuring bending stress in the example. FIG. 5 is a schematic diagram for explaining the method of measuring the friction coefficient in the example. FIG. 6 is a schematic diagram for explaining the high load running test in the example. FIG. 7 is a schematic diagram for explaining the high-speed running test in the examples. FIG. 8 is a schematic diagram for explaining the durability running test in the examples. FIG. 9 is a schematic diagram for explaining a region for measuring the crosslink density of the compressed rubber layer in the example. FIG. 10 is a graph showing the crosslink density gradient of the compressed rubber layer of Example 1.

[Structure of friction transmission belt]
The friction transmission belt of the present invention only needs to include a compression rubber layer whose crosslink density gradually decreases from the belt outer peripheral side toward the inner peripheral side, but normally, an adhesive rubber layer in which a core body is embedded in the longitudinal direction of the belt and A compression rubber layer formed on one surface of the adhesive rubber layer and an expanded rubber layer formed on the other surface of the adhesive rubber layer.

Examples of the friction transmission belt of the present invention include V-belts [wrapped V-belts, low-edge V-belts, low-edge cogged V-belts (low-edge cogged V-belts having cogs formed on the inner peripheral side of the low-edge belt, low-edge belts). Low edge double cogged V-belts having cogs formed on both the peripheral side and the outer peripheral side), V-ribbed belts, flat belts and the like. Among these friction transmission belts, a V belt or a V-ribbed belt whose friction transmission surface is inclined in a V shape (at a V angle) is preferable from the viewpoint of receiving a large lateral pressure from the pulleys, and the lateral pressure resistance and The low-edge cogged V-belt is particularly preferable because it is used in a belt-type continuously variable transmission that requires a high degree of compatibility with fuel efficiency.

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

In this example, the friction transmission belt 1 has a plurality of cog portions 1a formed on the inner peripheral surface of the belt main body at predetermined intervals along the longitudinal direction of the belt. The cross-sectional shape in the longitudinal direction (direction A in the figure) is substantially semicircular (curved or corrugated), and the cross-sectional shape in the direction orthogonal to the longitudinal direction (width direction or direction B in the figure) is a trapezoid. The shape. That is, each cog portion 1a projects from the cog bottom portion 1b in the belt thickness direction in a substantially semicircular shape in a cross section in the A direction. The friction transmission belt 1 has a laminated structure, and the reinforcing cloth 2, the stretch rubber layer 3, the adhesive rubber layer 4, the compression rubber layer 4 are compressed from the belt outer peripheral side toward the inner peripheral side (the side where the cog portion 1a is formed). The rubber layer 5 and the reinforcing cloth 6 are sequentially laminated. The cross-sectional shape in the belt width direction is a trapezoidal shape in which the belt width decreases from the outer peripheral side of the belt toward the inner peripheral side. Further, a core body 4a is embedded in the adhesive rubber layer 4, and the cog portion 1a is formed in the compression rubber layer 5 by a cog-forming mold.

[Compressed rubber layer]
In the present invention, a mechanism capable of satisfying both lateral pressure resistance and fuel economy is that the compression rubber layer has a crosslink density that gradually decreases from the outer peripheral side toward the inner peripheral side (has a gradient that decreases in an inclined manner). , Can be estimated as follows.

That is, the crosslink density of the compressed rubber layer has a close correlation with the rubber hardness, which is a physical property (mechanical strength) of the belt, and the compressive stress in the belt width direction. Physical properties (rubber hardness and compressive stress in the belt width direction) also increase. Therefore, if the crosslink density of the compressed rubber layer is high on the belt outer peripheral side (adhesive rubber layer side) and decreases toward the belt inner peripheral side, the physical characteristics of the compressed rubber layer (rubber hardness and belt width direction) (Compressive stress) is high on the outer peripheral side of the belt (adhesive rubber layer side) and decreases toward the inner peripheral side of the belt. Further, when the friction transmission belt is wound around the pulley to travel, the lateral pressure received from the pulley by the side surface of the friction transmission belt is greatest near the core and relatively small on the inner peripheral side of the belt. Therefore, for lateral pressure resistance, it is effective to increase the compressive stress in the belt width direction near the core. On the other hand, with respect to the transmission efficiency (transmission loss) that is an index of fuel economy, it is effective not to increase the bending rigidity of the belt too much (to keep it to a necessary minimum). Therefore, the friction transmission belt of the present invention can secure lateral pressure resistance in the vicinity of the core body, the compression stress on the inner peripheral side of the belt is relatively small, the bending rigidity of the belt does not become too large, and the transmission efficiency decreases. Therefore, fuel efficiency can be secured.

The crosslink density (mesh density or mesh chain density) of the compressed rubber layer may be such that the crosslink density gradually decreases from the outer peripheral side of the belt toward the inner peripheral side, and the crosslink density distribution is continuous from the outer peripheral side of the belt toward the inner peripheral side. It is preferable to decrease gradually or stepwise (particularly continuous).

In the compressed rubber layer having such a crosslink density distribution, when the compressed rubber layer is divided into six equal parts in the thickness direction, the first region located on the outermost side and the sixth region located on the innermost side are crosslinked. The density difference is, for example, about 10 to 100 mol/m ³ , preferably 20 to 80 mol/m ³ , and more preferably 25 to 60 mol/m ³ (particularly 30 to 50 mol/m ³ ). If the difference in cross-linking density is too small, it may be difficult to achieve both lateral pressure resistance and fuel economy, and if it is too large, the mechanical properties of the belt may deteriorate.

When the compressed rubber layer is divided into three equal parts in the thickness direction, the cross-linking density of the central region is, for example, 300 to 400 mol/m ³ , preferably 320 to 390 mol/m ³ , and more preferably 340 to 380 mol/m ³ . ³ (especially 350 to 370 mol/m ³ ). If the crosslink density is too low, the durability may decrease, and if it is too high, the bending resistance may decrease.

Furthermore, when the compressed rubber layer is divided into three equal parts in the thickness direction, the difference in cross-linking density between the central region and other regions is, for example, 3 to 50 mol/m ³ , preferably 5 to 30 mol/m ³ , and more preferably It is about 10 to 25 mol/m ³ (particularly 15 to 20 mol/m ³ ). If the difference in cross-linking density is too small, it may be difficult to achieve both lateral pressure resistance and fuel economy, and if it is too large, the mechanical properties of the belt may deteriorate.

In the present invention, the crosslink density (mesh chain density) of the compressed rubber layer can be calculated according to the Flory-Rehner equation based on the swelling method, and details will be described in Examples described later. It can be measured by the method. Further, in the present invention, the crosslink density of the compressed rubber layer can be measured as the crosslink density of the cog portion (particularly the region including the central portion of the cog portion) when the friction transmission belt is a cog V belt having a cog portion.

The compressed rubber layer may have a single layer structure as long as it has such a crosslink density distribution, but may have a multilayer structure from the viewpoint of productivity. In the present invention, even if it has a multilayer structure, it is possible to use the diffusion of the crosslinking agent (vulcanizing agent and vulcanization accelerator) by the specific manufacturing method described later so as to straddle between the layers constituting the compressed rubber. Since a continuous crosslink density (compressive stress) gradient is provided, stress concentration at the interface of each layer constituting the compressed rubber layer is reduced, and cracks are less likely to occur between the layers. The single-layer structure also includes a structure in which a laminate obtained by laminating a plurality of unvulcanized rubber sheets is integrated by vulcanization so that the boundary between layers becomes unclear.

The multilayer structure can be selected from, for example, about 2 to 10 layers, but from the viewpoint of productivity, it is usually about 2 to 5 layers, preferably 2 to 3 layers structure, and particularly preferably 2 layers structure. From the viewpoint of easy formation of a gradient of cross-linking density, the more the layer structure is, the more preferable. However, in the present invention, even if it is 2 to 3 layers (particularly 2 layers), it is possible to obtain a specific layer by adjusting the manufacturing method of the belt. Since a cross-linking density distribution can be formed, it is easy to prepare a raw material (each unvulcanized rubber sheet).

From the viewpoint of productivity, the compressed rubber layer preferably has a two-layer structure. The compressed rubber layer having a two-layer structure is formed of an outer layer on the outer peripheral side of the belt and an inner layer on the inner peripheral side of the belt, and the thickness ratio of both layers is from the range of outer layer/inner layer=about 2/1 to 1/2. Although it can be selected, it is preferable that both layers have substantially the same thickness, for example, 1.5/1 to 1/1/5, preferably 1.3/1 to 1/1. 3, more preferably about 1.2/1 to 1/1.2 (particularly 1.1/1 to 1/1.1).

In addition, the compression rubber layer has a three-layer structure from the viewpoint that it is easier to form a continuous gradient of crosslink density (or more easily improve the belt transmission efficiency) while maintaining relatively high productivity. Is preferred. The compressed rubber layer having a three-layer structure includes an outer layer on the outer peripheral side of the belt, an inner layer on the inner peripheral side of the belt, and an intermediate layer interposed between the outer layer and the inner layer. The thickness of each layer is preferably substantially the same for the same reason as the two-layer structure. Therefore, the thickness ratio between the outer layer and the other layer (that is, the inner layer or the intermediate layer) can be selected from the range of about 2/1 to 1/2 of the outer layer/other layer (the inner layer or the intermediate layer), For example, 1.5/1 to 1/1.5, preferably 1.3/1 to 1/1.3, more preferably 1.2/1 to 1/1.2 (particularly 1.1/1 to 1) It is about /1.1). The thickness ratio between the intermediate layer and the inner layer (intermediate layer/inner layer) is the same as the above range including the preferred embodiment.

Even in a compressed rubber layer having a multilayer structure of four or more layers, the thickness of each layer is preferably substantially the same for the same reason.

The compressed rubber layer having such a crosslink density may be a vulcanized product of a rubber composition containing a rubber component, a crosslinker and a reinforcing material.

(Rubber component)
As the rubber component, known rubber components and/or elastomers such as diene rubber [natural rubber, isoprene rubber, butadiene rubber, chloroprene rubber, styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (nitrile rubber), hydrogenated nitrile Rubber (including mixed polymer of hydrogenated nitrile rubber and unsaturated carboxylic acid metal salt)], ethylene-α-olefin elastomer, chlorosulfonated polyethylene rubber, alkylated chlorosulfonated polyethylene rubber, epichlorohydrin rubber, acrylic rubber Examples thereof include silicone rubber, urethane rubber, and fluororubber. These polymer components may be used alone or in combination of two or more.

Of these rubber components, the ethylene-α-olefin elastomer (ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer ( Ethylene-α-olefin rubbers) such as EPDM) are preferred. Since the non-polar ethylene-α-olefin elastomer has low compatibility with the vulcanizing agent and the vulcanization accelerator, the vulcanizing agent and the vulcanizing agent are added in the rubber composition containing the ethylene-α-olefin elastomer as the main component. It can be estimated that the vulcanization accelerator easily moves and diffuses easily from the rubber composition having a high vulcanizing agent concentration to the rubber composition having a low vulcanizing agent concentration.

When the rubber component contains an ethylene-α-olefin elastomer, the proportion of the ethylene-α-olefin elastomer in the rubber component may be about 50% by mass or more (particularly 80 to 100% by mass), and 100% by mass (ethylene (-Α-olefin elastomer only) is particularly preferred.

(Crosslinking agent)
The cross-linking agent includes a conventional vulcanizing agent used for vulcanizing the rubber component, a vulcanization aid (or a co-vulcanizing agent co-agent), a vulcanization accelerator, a vulcanization retarder, etc. Be done. Of these, vulcanizing agents, vulcanization aids, and vulcanization accelerators are widely used.

As the vulcanizing agent, a conventional component can be used depending on the type of the rubber component. For example, a sulfur-based vulcanizing agent [powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, sulfur chloride (monochloride) Sulfur, etc.], metal oxides (magnesium oxide, zinc oxide, etc.), organic peroxides (diacyl peroxide, peroxyester, dialkyl peroxide, etc.) and the like. You may use these vulcanizing agents individually or in combination of 2 or more types. When the rubber component is an ethylene-α-olefin elastomer, the vulcanizing agent may be a sulfur-based vulcanizing agent.

Examples of the vulcanization aid include polyfunctional (iso)cyanurate [eg, triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), etc.], polydiene (eg, 1,2-polybutadiene), unsaturated Carboxylic acid metal salts [eg zinc (meth)acrylate, magnesium (meth)acrylate], oximes (eg quinonedioxime), guanidines (eg diphenylguanidine), polyfunctional (meth) Acrylate [eg, ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, etc.], bismaleimides (aliphatic bismaleimide, eg, N,N′-1,2) -Ethylene bismaleimide, 1,6'-bismaleimide-(2,2,4-trimethyl)cyclohexane and the like; arene bismaleimide or aromatic bismaleimide, for example N,N'-m-phenylene bismaleimide, 4-methyl -1,3-phenylene bismaleimide, 4,4'-diphenylmethane bismaleimide, 2,2-bis[4-(4-maleimidophenoxy)phenyl]propane, 4,4'-diphenyl ether bismaleimide, 4,4'- Diphenyl sulfone bismaleimide, 1,3-bis(3-maleimidophenoxy)benzene and the like). These vulcanization aids may be used alone or in combination of two or more. Among these vulcanization aids, bismaleimides (arene bismaleimides such as N,N'-m-phenylene dimaleimide or aromatic bismaleimides) are generally used.

Examples of the vulcanization accelerator include thiuram-based accelerators [eg, tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetrabutylthiuram disulfide (TBTD). ), dipentamethylene thiuram tetrasulfide (DPTT), N,N′-dimethyl-N,N′-diphenyl thiuram disulfide, etc.], thiazole accelerator [eg, 2-mercaptobenzothiazole, 2 -Zinc salt of mercaptobenzothiazole, 2-mercaptothiazoline, dibenzothiazyl disulfide, 2-(4'-morpholinodithio)benzothiazole, etc.]], sulfenamide accelerator [eg, N-cyclohexyl 2-benzothiazylsulfenamide (CBS), N,N'-dicyclohexyl-2-benzothiazylsulfenamide, etc.], bismaleimide-based accelerator (for example, N,N'-m-phenylene bismaleimide, N,N′-1,2-ethylene bismaleimide, etc.), guanidines (diphenylguanidine, di-o-tolylguanidine, etc.), urea-based or thiourea-based accelerators (eg, ethylenethiourea, etc.), dithiocarbamate salts, xanthogenic acid Examples include salts. These vulcanization accelerators can be used alone or in combination of two or more kinds. Among these vulcanization accelerators, TMTD, DPTT, dibenzothiazyl disulfide, CBS and the like are widely used.

The vulcanization accelerator is preferably a vulcanization accelerator having a low molecular weight, because the vulcanization accelerator is excellent in diffusibility in the compressed rubber layer before vulcanization (unvulcanized sheet for compressed rubber layer), and the molecular weight is, for example, 500 or less. It may be present, preferably 100 to 500, more preferably 200 to 400 (particularly 250 to 350).

Among these, a combination of a vulcanizing agent and a vulcanization accelerator is preferable, and the ratio of the vulcanizing agent may be 5 parts by mass or more relative to 100 parts by mass of the vulcanization accelerator, for example, 5 to 100 parts by mass. Parts, preferably 10 to 50 parts by mass, more preferably 15 to 40 parts by mass (particularly 20 to 30 parts by mass).

The cross-linking agent is unevenly distributed in the thickness direction of the compressed rubber layer corresponding to the distribution of the cross-linking density described above, but the proportion of the cross-linking agent (particularly the vulcanizing agent and the vulcanization accelerator) is Overall, for example, 1 to 20 parts by mass, preferably 1.5 to 10 parts by mass, and more preferably 2 to 5 parts by mass (particularly 2.5 to 4 parts by mass) per 100 parts by mass of the rubber component. .. The proportion (concentration) of the crosslinking agent (particularly the vulcanizing agent and the vulcanization accelerator) in the compressed rubber layer is, for example, 0.5 to 8% by mass, preferably 0.8 to 5% by mass, more preferably 1 to 3% by mass. It is about mass% (particularly 1.5 to 2.5 mass%).

(Reinforcement material)
Reinforcing materials include conventional reinforcing fibers and fillers and the like. Examples of the reinforcing fiber include polyolefin fiber (polyethylene fiber, polypropylene fiber, etc.), polyamide fiber (polyamide 6 fiber, polyamide 66 fiber, polyamide 46 fiber, aramid fiber, etc.), polyester fiber [polyethylene terephthalate (PET) fiber, polyethylene C _2-4 alkylene C _6-14 arylate fibers such as naphthalate (PEN) fibers], synthetic fibers such as vinylon fibers and polyparaphenylene benzobisoxazole (PBO) fibers; natural fibers such as cotton, hemp and wool Inorganic fibers such as carbon fibers can be exemplified. These fibers can be used alone or in combination of two or more.

Of these reinforcing fibers, at least one selected from polyamide fibers such as aramid fibers, polyester fibers, and vinylon fibers is preferable, and aramid fibers are particularly preferable. The reinforcing fibers may be fibrillated.

The reinforcing fibers may be usually contained in the compressed rubber layer in the form of short fibers, and the average length of the short fibers is, for example, 0.1 to 20 mm, preferably 0.5 to 15 mm, more preferably 1 to 10 mm. And may be about 1 to 5 mm (particularly 2 to 4 mm). The average fineness of the reinforcing fiber is, for example, 0.3 to 10 dtex, preferably 0.5 to 8 dtex, more preferably 1 to 5 dtex (particularly 2 to 4 dtex).

Examples of the filler include carbonaceous materials (carbon black, graphite, etc.), metal compounds or synthetic ceramics (metal silicates such as calcium silicate and aluminum silicate, metal carbides such as silicon carbide and tungsten carbide, titanium nitride). , Metal nitrides such as aluminum nitride and boron nitride, metal carbonates such as magnesium carbonate and calcium carbonate, metal sulfates such as calcium sulfate and barium sulfate), mineral materials (zeolite, diatomaceous earth, calcined silica, Activated clay, alumina, silica, talc, mica, kaolin, sericite, bentonite, montmorillonite, smectite, clay, etc.) and the like. These fillers can be used alone or in combination of two or more. The shape of the filler is granular, plate-like, or irregular. The number average primary particle diameter of the filler can be appropriately selected from the range of about 10 nm to 10 μm depending on the type. Among these fillers, carbonaceous materials such as carbon black and mineral materials such as silica are widely used, and carbon black is preferred.

The proportion of the reinforcing material may be 40 parts by mass or more (particularly 50 parts by mass or more) with respect to 100 parts by mass of the rubber component, for example, 45 to 100 parts by mass, preferably 50 to 90 parts by mass, and more preferably 55 parts by mass. It is about 80 to 80 parts by mass (particularly 60 to 70 parts by mass). In the present invention, the transmission loss can be reduced even if the proportion of the reinforcing material is large.

The proportion of the reinforcing fiber may be 80 parts by mass or less (for example, 0 to 80 parts by mass) with respect to 100 parts by mass of the rubber component, for example, 60 parts by mass or less (for example, 1 to 60 parts by mass), and preferably 50 parts by mass. The amount is less than or equal to parts (for example, 5 to 50 parts by mass), more preferably about 40 parts by mass or less (for example, 10 to 40 parts by mass). If the proportion of the reinforcing fibers is too large, the transmission loss may not be reduced.

The proportion of the filler may be 10 parts by mass or more based on 100 parts by mass of the rubber component, for example, 20 to 100 parts by mass, preferably 30 to 90 parts by mass, and more preferably 35 to 80 parts by mass (particularly 40 parts by mass). Is about 70 parts by mass).

(Other additives)
The rubber composition forming the compressed rubber layer may further contain other conventional additives. Examples of conventional additives include metal oxides (eg, zinc oxide, magnesium oxide, calcium oxide, barium oxide, iron oxide, copper oxide, titanium oxide, aluminum oxide), softeners (paraffin oil, naphthenic oil). Oils, etc.), processing agents or processing aids (stearic acid, stearic acid metal salts, wax, paraffin, etc.), anti-aging agents (antioxidants, heat anti-aging agents, flex crack inhibitors, ozone deterioration prevention) Agents, etc.), colorants, tackifiers, plasticizers, coupling agents (silane coupling agents, etc.), stabilizers (UV absorbers, heat stabilizers, etc.), flame retardants, antistatic agents, etc. Good. The metal oxide may act as a cross-linking agent or a reinforcing material depending on the type of rubber component, but is classified as another additive in the present invention.

The ratio (total ratio) of the other additives may be 100 parts by mass or less with respect to 100 parts by mass of the rubber component, and is, for example, 1 to 100 parts by mass, preferably about 5 to 50 parts by mass. For example, the ratio of the metal oxide (zinc oxide, etc.) is, for example, 1 to 20 parts by mass, preferably 3 to 10 parts by mass, and more preferably 3 to 8 parts by mass with respect to 100 parts by mass of the rubber component. The ratio of the softening agent (oils such as naphthenic oil) is, for example, 1 to 30 parts by mass, preferably 3 to 20 parts by mass, and more preferably about 5 to 10 parts by mass with respect to 100 parts by mass of the rubber component. .. The proportion of the anti-aging agent is, for example, 0.5 to 15 parts by mass, preferably 1 to 10 parts by mass, more preferably 2.5 to 7.5 parts by mass (particularly 3 to 7 parts) with respect to 100 parts by mass of the rubber component. Mass part).

[Stretched rubber layer]
The stretched rubber layer may be formed of a vulcanized rubber composition containing the rubber component exemplified in the compressed rubber layer, and may contain a reinforcing material as in the compressed rubber layer. Further, the stretched rubber layer may be a layer formed of the same vulcanized rubber composition as the compressed rubber layer.

[Adhesive rubber layer]
The vulcanized rubber composition for forming the adhesive rubber layer includes a rubber component (ethylene-α-olefin elastomer, etc.) and a cross-linking agent (sulfur-based vulcanization such as sulfur), as in the vulcanized rubber composition of the compressed rubber layer. Agents, vulcanization accelerators such as TMTD, DPTT, CBS, etc.), reinforcing materials (carbon black, silica, etc.), softening agents (oils such as naphthenic oils), antiaging agents, etc. It may contain an adhesion improver. In this rubber composition, as the rubber component, a rubber of the same type or the same type as the rubber component of the vulcanized rubber composition of the compression rubber layer is often used. Further, the proportions of the cross-linking agent, the reinforcing material, the softening agent and the anti-aging agent can be selected from the same range as that of the rubber composition of the compressed rubber layer.

[Core]
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 cords are arranged so as to extend in the longitudinal direction of the belt, and usually extend in parallel at a predetermined pitch in parallel with the longitudinal direction of the belt. It is sufficient that at least a part of the core wire is in contact with the adhesive rubber layer, and the adhesive rubber layer embeds the core wire, the core wire is embedded between the adhesive rubber layer and the stretch rubber layer, and the adhesive rubber layer. The core wire may be embedded between the layer and the compressed rubber layer. Of these, the form in which the adhesive rubber layer embeds the core wire is preferable from the viewpoint of improving durability.

Examples of the fibers that form the core wire include the same fibers as the short fibers. Among the above fibers, from the viewpoint of high modulus, synthesis of polyester fibers (polyalkylene arylate fibers) containing C _2-4 alkylene arylate such as ethylene terephthalate and ethylene-2,6-naphthalate as a main constituent unit, aramid fibers and the like. Inorganic fibers such as fibers and carbon fibers are commonly used, and polyester fibers (polyethylene terephthalate fibers, polyethylene naphthalate fibers) and polyamide fibers are preferred. The fibers may be multifilament yarns. The fineness of the multifilament yarn may be, for example, about 2000 to 10,000 denier (particularly 4000 to 8,000 denier). The multifilament yarn may be, for example, 100 to 5,000 yarns, preferably 500 to 4,000 yarns, and more preferably about 1,000 to 3,000 yarns.

As the core wire, usually, a twisted cord using multifilament yarn (for example, ply twist, single twist, rung twist, etc.) can be used. The average wire diameter of the core wire (fiber 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. Good.

The core wire may be subjected to an adhesive treatment (or surface treatment) with various treatment liquids in order to improve the adhesiveness with the rubber component (for example, the rubber component of the adhesive rubber layer). Examples of the treatment liquid include a treatment liquid containing an initial condensate of phenols and formaldehyde (a prepolymer of novolac or resol type phenolic resin), a treatment liquid containing a rubber component (or latex), the initial condensate and rubber. Examples include a treatment liquid containing a component (latex), a silane coupling agent, an epoxy compound (epoxy resin, etc.), a treatment liquid containing a reactive compound (adhesive compound) such as an isocyanate compound, and the like.

The core wire may be subjected to an adhesion treatment with the treatment liquid alone, or may be subjected to an adhesion treatment with a combination of two or more treatment liquids. Among the adhesion treatments with these treatment liquids, it is preferable that the cord is adhered with a treatment liquid containing the above-mentioned initial condensate and a rubber component (latex), particularly at least a resorcin-formalin-latex (RFL) liquid. Adhesive treatment is preferred. In the adhesion treatment with the RFL solution, generally, a uniform adhesive layer can be formed on the surface by immersing the core wire in the RFL solution and then heating and drying. Examples of the latex of the RFL liquid include chloroprene rubber, styrene-butadiene-vinylpyridine terpolymer, latex of hydrogenated nitrile rubber (H-NBR), nitrile rubber (NBR) and the like.

Further, as a method of combining two or more kinds of treatment liquids, specifically, for example, a conventional adhesive component [eg, a reactive compound (adhesive compound) such as an epoxy compound (epoxy resin) or an isocyanate compound is included. Pretreatment (pre-dip) with a treatment liquid or the like, followed by treatment with an RFL liquid; after treatment with the RFL liquid, a rubber paste treatment (overcoating) with a treatment liquid containing the rubber component (or latex), and Examples include a method of treating with an RFL solution.

[Transmission efficiency]
When the friction transmission belt provided with the compression rubber layer is used, the transmission efficiency can be greatly improved. The transmission efficiency is an index for the belt to transmit the rotational torque from the drive pulley to the driven pulley. The higher the transmission efficiency, the smaller the transmission loss of the belt and the better the fuel economy. In the biaxial layout in which the belt 11 is hung on the two pulleys of the drive pulley (Dr.) 12 and the driven pulley (Dn.) 13 shown in FIG. 3, the transmission efficiency can be obtained as follows.

When the rotational speed of the drive pulley is ρ ₁ and the pulley radius is r ₁ , the rotational torque T ₁ of the drive pulley can be represented by ρ ₁ ×Te×r ₁ . Te is an effective tension obtained by subtracting the slack side tension (tension on the side where the belt faces the driven pulley) from the tension on the tension side (tension on the side where the belt faces the drive pulley). Similarly, when the rotational speed of the driven pulley is ρ ₂ and the pulley radius is r ₂ , the rotational torque T ₂ of the driven pulley is represented by ρ ₂ ×Te×r ₂ . Then, the transmission efficiency T ₂ /T ₁ is calculated by dividing the rotational torque T ₂ of the driven pulley by the rotational torque T ₁ of the drive pulley, and can be expressed by the following equation.

T ₂ /T ₁ =(ρ ₂ ×Te×r ₂ )/(ρ ₁ ×Te×r ₁ )=(ρ ₂ ×r ₂ )/(ρ ₁ ×r ₁ ).
The value of the transmission efficiency is 1 if there is no transmission loss, and the value is reduced by the loss if there is transmission loss. That is, the closer it is to 1, the smaller the transmission loss of the belt and the better the fuel economy.

[Friction transmission belt manufacturing method]
The friction transmission belt of the present invention is not particularly limited except for a means for imparting a specific cross-linking density distribution to the compressed rubber layer, and the laminating step of each layer (belt sleeve manufacturing method) depends on the belt type. Thus, conventional methods can be used.

For example, in the case of the cogged V-belt, a laminated body composed of a reinforcing cloth (lower cloth) and a sheet for compressed rubber layer (unvulcanized rubber sheet) is arranged with the reinforcing cloth facing downward and tooth portions and groove portions are alternately arranged. Cog pad with a cog part formed by pressing and pressing at a temperature of 60 to 100°C (especially 70 to 80°C) (not completely vulcanized, semi-vulcanized state). After making the pad), both ends of this cog pad may be cut vertically from the top of the cog crest. Further, a cylindrical mold is covered with an inner mother die in which tooth portions and groove portions are alternately arranged, engaged with the tooth portions and groove portions, wound with a cog pad, joined at the top of the cog mountain portion, and wound. After stacking the first adhesive rubber layer sheet (lower adhesive rubber: unvulcanized rubber sheet) on the cog pad, the core wire (twisted cord) forming the core is spirally spun on the first sheet. The adhesive rubber layer sheet 2 (upper adhesive rubber: the same as the above adhesive rubber layer sheet), the stretched rubber layer sheet (unvulcanized rubber sheet), and the reinforcing cloth (upper cloth) are sequentially wound to form a molded body. May be. After that, the jacket is covered, the mold is placed in a vulcanizing can, and the belt sleeve is prepared by vulcanizing at a temperature of about 120 to 200° C. (particularly 150 to 180° C.), and then a V shape is formed using a cutter or the like. You may cut and process.

Means for imparting a specific crosslink density distribution to the compressed rubber layer is, for example, prevulcanization in which a laminated sheet in which a plurality of unvulcanized sheets for compressed rubber layers are laminated is prevulcanized at a temperature lower than the vulcanization temperature. It may be a process. This preliminary vulcanization step is a method of forming a crosslink density distribution by preliminary heating of the unvulcanized laminated sheet as a step prior to the vulcanization step. Specifically, the unvulcanized sheets are laminated in the order in which the crosslink density of the vulcanized sheet increases from the inner circumference side of the belt toward the outer circumference side, that is, the crosslink density decreases from the inner circumference side of the belt toward the outer circumference side. By stacking the unvulcanized sheet forming the vulcanized rubber sheet having a high cross-linking density on the unvulcanized sheet forming the vulcanized rubber sheet, the specific cross-linking density distribution can be easily imparted. Specifically, the crosslink density of each vulcanized sheet obtained by independently vulcanizing each unvulcanized sheet is measured, and the crosslink density may be increased in the order from the inner peripheral side to the outer peripheral side of the belt. .. In particular, the order in which the concentration of the crosslinking agent decreases from the outer peripheral side of the belt to the inner peripheral side of the unvulcanized sheets for the plurality of compressed rubber layers having different concentrations of the crosslinker (or from the inner peripheral side of the belt toward the outer peripheral side). By stacking in the order of increasing concentration of the cross-linking agent), the concentration of the cross-linking agent is reduced from the rubber composition (unvulcanized rubber sheet) having a high concentration of the cross-linking agent (particularly the vulcanizing agent and the vulcanization accelerator). The cross-linking agent diffuses into the rubber composition (unvulcanized rubber sheet), and a concentration gradient in which the concentration of the cross-linking agent decreases more gradually (or continuously) from the outer peripheral side of the belt to the inner peripheral side of the belt occurs. As a result, it is possible to form a compressed rubber layer having a gradient in cross-linking density and physical properties (rubber hardness and compressive stress in the belt width direction) that decreases from the outer peripheral side of the belt to the inner peripheral side of the belt in an inclined manner.

In the laminated sheet in which the unvulcanized sheets for the plurality of compressed rubber layers are laminated, the crosslink density in the vulcanized rubber sheet of each unvulcanized sheet is higher than the unvulcanized rubber sheet on the belt inner peripheral side, on the belt outer peripheral side. It is necessary to stack the unvulcanized rubber sheet so that it will be larger. For example, in the laminated sheet, the crosslink density in each vulcanized product of the unvulcanized sheets adjacent to each other is, for example, at least 1 mol/m ³ (for example, 5 to 200 mol) as it goes from the inner peripheral side to the outer peripheral side. /M ³ ), which is as large as about 10 to 150 mol/m ³ (for example, 15 to 100 mol/m ³ ), preferably 20 to 90 mol/m ³ (for example, 25 to 80 mol). /M ³ ), and more preferably, 30 to 60 mol/m ³ (for example, 40 to 50 mol/m ³ ), which is large.

As a typical example, for example, a laminated sheet is a laminate of an outer layer unvulcanized sheet for forming an outer layer of a compressed rubber layer and an inner layer unvulcanized sheet for forming an inner layer of a compressed rubber layer. In some cases, the crosslinking density of the vulcanized product of the unvulcanized sheet for the outer layer is 3 mol/m ³ or more (particularly 5 to 100 mol/m ³⁾ more than the crosslinking density of the vulcanized product of the unvulcanized sheet for the inner layer. It may be large, for example, 10 to 80 mol/m ³ , preferably 20 to 60 mol/m ³ , and more preferably 30 to 50 mol/m ³ (particularly 35 to 45 mol/m ³ ) even if large. Good.

Further, when the laminated sheet is a laminated body of an unvulcanized sheet for outer layer, an unvulcanized sheet for intermediate layer for forming an intermediate layer of the compressed rubber layer, and an unvulcanized sheet for inner layer, two adjacent sheets are provided. Crosslink density in the vulcanizate of the unvulcanized sheet forming the layer on the outer peripheral side relative to the unvulcanized sheet forming the layer on the inner peripheral side between the layers [that is, the unvulcanized sheet for the outer layer relative to the unvulcanized sheet for the intermediate layer] Crosslink density in the vulcanizate of the vulcanized sheet and crosslink density in the vulcanizate of the unvulcanized sheet for the intermediate layer with respect to the unvulcanized sheet for the inner layer] is 1 mol/m ³ or more (particularly 5 to 100 mol/ m ³ ) about 10 to 80 mol/m ³ , preferably 20 to 60 mol/m ³ , and more preferably 30 to 50 mol/m ³ (particularly 35 to 45 mol/m ³ ). May be. The crosslink density in each vulcanized product of each unvulcanized rubber sheet can be measured by the method (swelling method) described in Examples described later.

The concentration of the cross-linking agent in each unvulcanized rubber sheet is preferably set so that the concentration of the unvulcanized rubber sheet on the outer peripheral side of the belt is higher than the concentration of the unvulcanized rubber sheet on the inner peripheral side of the adjacent belt. For example, in the laminated sheet, the concentration of the cross-linking agent in the unvulcanized sheets adjacent to each other is increased by at least about 0.05 mass% (eg, 0.1 mass%) from the inner circumference side to the outer circumference side of the belt. It may be a body, for example, 0.1 to 3% by mass, preferably 0.3 to 2% by mass, and more preferably 0.5 to 1.5% by mass (particularly 0.6 to 1% by mass). It may be a laminated body.

As a typical example, for example, a laminated sheet is a laminate of an unvulcanized sheet for an outer layer for forming an outer layer of a compressed rubber layer and an unvulcanized sheet for an inner layer for forming an inner layer of a compressed rubber layer. In this case, the concentration of the crosslinking agent in the unvulcanized sheet for the outer layer may be 0.05% by mass or more (particularly 0.1% by mass or more) higher than the concentration of the crosslinking agent in the unvulcanized sheet for the inner layer. The amount may be increased by about 0.1 to 3% by mass, preferably 0.3 to 2% by mass, and more preferably 0.5 to 1.5% by mass (particularly 0.6 to 1% by mass).

If the laminated sheet is a laminate of the outer layer unvulcanized sheet, the intermediate layer unvulcanized sheet for forming the intermediate layer of the compressed rubber layer, and the inner layer unvulcanized sheet, adjacent The concentration of the cross-linking agent in the unvulcanized sheet forming the outer peripheral layer relative to the unvulcanized sheet forming the inner peripheral layer between the two layers [that is, the unvulcanized sheet for the outer layer relative to the unvulcanized sheet for the intermediate layer] If the concentration of the crosslinking agent of the vulcanized sheet and the concentration of the crosslinking agent of the unvulcanized sheet for the intermediate layer with respect to the unvulcanized sheet for the inner layer] is 0.05 mass% or more (particularly 0.1 mass% or more), Well, for example, it may be increased by about 0.1 to 3% by mass, preferably 0.3 to 2% by mass, more preferably 0.5 to 1.5% by mass (particularly 0.6 to 1% by mass).

The heating temperature in the pre-vulcanization step may be a temperature lower than the vulcanization temperature, for example, a temperature lower than the vulcanization temperature by 30° C. or more (for example, a temperature lower than the vulcanization temperature by about 30 to 100° C.). It may be. The specific heating temperature may be 50° C. or higher, for example, 50 to 160° C., preferably 80 to 150° C., more preferably 100 to 140° C. (particularly 110 to 130° C.). The heating time can be selected according to the temperature, but is, for example, 1 to 60 minutes, preferably 3 to 30 minutes, more preferably 5 to 20 minutes.

When the friction transmission belt is a cogged V belt, the pre-vulcanization step may be a step independent of the press-pressing step for forming the cog portion, and the press-pressing step for forming the cog portion may be performed. You may also combine. In the case of an independent process, the preliminary vulcanization process is usually processed as a pre-process of the belt vulcanization process and continuously with the vulcanization process. On the other hand, when it also serves as the press-pressing step, in the press-pressing step, the pressure is applied for a longer time than the pressurizing time for forming the normal cog portion to promote the diffusion of the cross-linking agent at the same time when the cog portion is formed. May be.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In the following examples, the raw materials used in the examples and the measuring or evaluating methods for each physical property are shown below. In addition, "part" and "%" are based on mass unless otherwise specified.

[material]
EPDM: "Nordel IP4640" manufactured by Dow Chemical Company
Aramid short fiber: "Twaron" manufactured by Teijin Ltd., modulus 88 cN, fineness 2.2 dtex, fiber length 3 mm
Naphthenic oil: "NS-90" manufactured by Idemitsu Kosan Co., Ltd.
Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd.
Anti-aging agent: "Nocrac AD-F" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanizing agent: Sulfur Vulcanizing accelerator 1: Thiazole type accelerator (dibenzothiazyl disulfide), "NOXCELLER DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd., molecular weight 332.5
Vulcanization accelerator 2: Thiuram-based accelerator (tetramethylthiuram disulfide TMTD), "NOXCELLER TT" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., molecular weight 240.44
Vulcanization accelerator 3: Sulfenamide-based accelerator (N-cyclohexyl-2-benzothiazylsulfenamide CBS), "NOXCELLER CZ-G" manufactured by Ouchi Shinko Chemical Industry Co., Ltd., molecular weight 264.42
Core wire: A fiber obtained by adhesion-bonding a total denier cord of 6,000, which is made by twisting PET fibers of 1,000 denier in a 2×3 twist structure with an upper twist coefficient of 3.0 and a lower twist coefficient of 3.0.

[Measurement of physical properties of vulcanized rubber]
(1) Hardness The compressed rubber layer sheet was press-vulcanized at a temperature of 170° C. for 20 minutes to produce a vulcanized rubber sheet (length 100 mm, width 100 mm, thickness 2 mm). According to JIS K6253 (2012), the hardness was measured using a durometer A type hardness tester using a laminate obtained by stacking three vulcanized rubber sheets as a sample.

(2) Abrasion amount A vulcanized rubber sheet (50 mm×50 mm×8 mm thickness) produced by press vulcanizing a compressed rubber layer sheet at a temperature of 170° C. for a time of 20 minutes is hollow with an inner diameter of 16.2±0.05 mm. It was cut out with a drill to prepare a cylindrical sample having a diameter of 16.2 ± 0.2 mm and a thickness of 6 to 8 mm. According to JIS K6264 (2005), the abrasion loss of the vulcanized rubber was measured using a rotating cylindrical drum device (DIN abrasion tester) wound with a polishing cloth.

(3) Compressive stress The sheet for compressed rubber layer was press-vulcanized at a temperature of 170° C. for 20 minutes to prepare a vulcanized rubber molded body (length 25 mm, width 25 mm, thickness 12.5 mm). The short fibers were oriented in the direction perpendicular to the compression surface (thickness direction). This vulcanized rubber molded body is vertically sandwiched by two metal compression plates (the upper compression plate is positioned as the initial position in a sandwiched state where the vulcanized molded body is not pressed by the compression plate), and the upper side The compression plate of No. 2 was pressed against the vulcanized rubber molded body at a speed of 10 mm/min (pressing surface 25 mm x 25 mm) to distort the vulcanized rubber molded body by 20%, and after holding for 1 second in this state, the compression plate was moved upward. Was returned to the initial position (pre-compression). After repeating this preliminary compression three times, when the strain in the thickness direction of the vulcanized rubber molded product is 2% from the stress-strain curve measured in the fourth compression test (conditions are the same as those of the preliminary compression) Was measured as a compressive stress. The preliminary compression was performed three times in order to reduce variations in the measured data.

(4) Bending stress The compressed rubber layer sheet was press-vulcanized at a temperature of 170° C. for 20 minutes to prepare a vulcanized rubber molded body (length 60 mm, width 25 mm, thickness 6.5 mm). The short fibers were oriented in the direction parallel to the width of the vulcanized rubber molding. As shown in FIG. 4, this vulcanized rubber molded body 21 was placed on and supported by a pair of rolls (6 mmφ) 22a, 22b that were rotatable at intervals of 20 mm, and the central portion of the upper surface of the vulcanized rubber molded body was supported. In, the metal pressing member 23 was placed in the width direction (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 the vulcanized rubber molded body 21 can be smoothly pressed by the tip. Further, at the time of pressing, a frictional force acts between the lower surface of the vulcanized rubber molded body 21 and the rolls 22a, 22b along with the compressive deformation of the vulcanized rubber molded body 21, but the rolls 22a, 22b can be rotated. This reduces the effect of friction. The state where the tip of the pressing member 23 is in contact with the upper surface of the vulcanized rubber molded body 21 and is not pressed is "0", and from this state, the pressing member 23 is vulcanized rubber molded downward at a speed of 100 mm/min. The stress when the upper surface of the body 21 was pressed and the strain in the thickness direction of the vulcanized rubber molded body 21 became 10% was measured as the bending stress.

(5) Crosslink Density The crosslink density (mesh chain density) of the compressed rubber layer was measured by the swelling method. Specifically, the compressed rubber layer sheet was press-vulcanized at a temperature of 170° C. for 20 minutes to produce a vulcanized rubber sheet (length 100 mm, width 100 mm, thickness 2 mm). The obtained vulcanized rubber sheet is swelled in a toluene solvent at a temperature of 25° C. for 72 hours, the sample volume before and after the swelling is measured, and the obtained value is a network chain according to the following Flory-Rehner formula. The density was calculated.

ν=−{ln(1−Vr)+Vr+μVr ² }×10 ⁶ /[Vs{Vr ^1/3 −(2/f)Vr}]
(In the formula, ν: network chain density (mol/m ³ ), Vr: rubber volume fraction in swollen sample, Vs: molecular volume of solvent, μ: interaction coefficient of solvent and rubber, f: functional number of crosslinking And 106 cm ³ as Vs, 0.49 as μ, and ³ as f).

[Measurement of belt physical properties]
(1) Friction coefficient measurement As shown in FIG. 5, the friction coefficient of the belt is obtained by fixing one end of the cut belt 31 to the load cell 32 and placing a load 33 of 3 kgf on the other end of the belt. The belt 31 was wound around the pulley 34 with the belt winding angle of 45°. Then, the belt 31 on the load cell 32 side was pulled at a speed of 30 mm/sec for about 15 seconds, and the average friction coefficient of the friction transmission surface was measured. During the measurement, the pulley 34 was fixed so as not to rotate.

(2) High load running test (transmission efficiency)
In this running test, the transmission efficiency of the belt was evaluated when the belt was run in a state where the belt was greatly bent (a state in which the belt was wound around a small pulley).

As shown in FIG. 6, the high load running test was performed using a biaxial running tester including a driving (Dr.) pulley 42 having a diameter of 50 mm and a driven (Dn.) pulley 43 having a diameter of 125 mm. The low-edge cogged V-belt 41 is hung on each pulley 42, 43, the driven pulley 43 is applied with a load of 3 N·m at a rotation speed of the drive pulley 42 of 3000 rpm, and the belt 41 is run in a room temperature atmosphere. .. Immediately after running, the rotational speed of the driven pulley 43 was read from the detector, and the transmission efficiency was calculated from the above formula. In Table 3, when the transmission efficiency of Comparative Example 1 is “1”, the transmission efficiency of each Example and Comparative Example is shown as a relative value converted. If this value is larger than 1, the transmission efficiency of the belt 41 is shown. That is, it was determined that the fuel economy was high.

(3) High-speed running test (transmission efficiency)
In this running test, the transmission efficiency of the belt was evaluated when the belt was run while sliding on the pulley in the radial direction of the pulley. In particular, when the number of rotations of the drive pulley increases, the centrifugal force strongly acts on the belt. Further, the belt tension is low at the position on the loose side (see FIG. 7) of the drive pulley, and due to the combined action with the centrifugal force, the belt tends to pop out to the outside in the radial direction of the pulley at this position. If this pop-out is not performed smoothly, that is, if a strong frictional force acts between the frictional transmission surface of the belt and the pulley, the frictional force causes a transmission loss of the belt, resulting in a reduction in transmission efficiency.

As shown in FIG. 7, the high-speed running test was performed using a biaxial running tester including a driving (Dr.) pulley 52 having a diameter of 95 mm and a driven (Dn.) pulley 53 having a diameter of 85 mm. Next, the low-edge cogged V-belt 51 is hung on each pulley 52, 53, the rotation speed of the drive pulley 52 is 5000 rpm, and the driven pulley 53 is loaded with 3 N·m, and the belt 51 is run in a room temperature atmosphere. Let Immediately after running, the rotational speed of the driven pulley 52 was read from the detector, and the transmission efficiency was calculated from the above formula. In Table 3, when the transmission efficiency of Comparative Example 1 is set to "1", it is shown as a relative value converted from the transmission efficiency of each Example and Comparative Example. If this value is larger than 1, the transmission efficiency (fuel saving) is shown. Sex) was judged to be high.

(4) Durability running test (side pressure resistance)
As shown in FIG. 8, the durability running test was performed using a biaxial running tester including a driving (Dr.) pulley 62 having a diameter of 50 mm and a driven (Dn.) pulley 63 having a diameter of 125 mm. The low-edge cogged V-belt 61 is hung on each pulley 62, 63, the rotation speed of the driving pulley 62 is 5000 rpm, and the driven pulley 63 is loaded with 10 N·m, and the belt 61 is kept at an ambient temperature of 80° C. for a maximum of 24 hours. I made it run. It was determined that the durability was not a problem if the belt 61 was running for 24 hours. In addition, the side surface of the compressed rubber (the surface in contact with the pulley) after running was visually observed to check for cracks.

(5) Crosslinking Density Gradient of Compressed Rubber Layer As shown in FIG. 9, the compressed rubber layer of the produced belt is sliced in the vertical direction at the substantially central portion 71 of the cog portion, and further sliced into 6 equal parts in the belt thickness direction. And taken out to prepare a test piece. Since the thickness of the compressed rubber layer of the belt of the example is about 6 mm, the thickness of the test piece is about 1 mm. The crosslink density (swelling method) was measured for each test piece. The cross-link density gradient of the compressed rubber layer was measured only in Example 1.

Examples 1-6 and Comparative Examples 1-3
(Formation of rubber layer)
The rubber compositions A to D (compressed rubber layer) in Table 1, the rubber composition A (extended rubber layer) in Table 1, and the rubber composition E (adhesive rubber layer) in Table 2 are each known in Banbury mixer or the like. Rubber kneading was carried out using the method, and the kneaded rubber was passed through a calendar roll to prepare a rolled rubber sheet (sheet for compressed rubber layer, sheet for expanded rubber layer, sheet for adhesive rubber layer). Regarding the obtained sheet for compressed rubber layer, the results of measuring the physical properties of vulcanized rubber are also shown in Table 1. In Table 1, the vulcanizing agent concentration is the ratio of the total amount of the vulcanizing agent and the vulcanization accelerator to the total amount of the rubber composition.

(Manufacture of belt)
A laminated sheet of a reinforcing rubber cloth and a sheet for a compressed rubber layer composed of two or three kinds of rubber compositions having different vulcanizing agent concentrations (a sheet composed of the rubber composition disposed on the outer peripheral side of the belt is referred to as "compressed rubber layer 1", a belt). A laminated body in which a sheet made of a rubber composition arranged on the inner peripheral side is a "compressed rubber layer 2", and a sheet made of a rubber composition arranged between the compressed rubber layers 1 and 2 is a "compressed rubber layer 3"). Was produced. At this time, in Examples 1 to 4 and Comparative Examples 1 to 2 (examples in which the laminated sheet has a two-layer structure), the thickness of the compressed rubber layer sheet was 3 mm, and Examples 5 to 6 and Comparative Example 3 (the above In the case where the laminated sheet has a three-layer structure), the thickness of the compressed rubber layer sheet was 2 mm each, and the laminated sheet was prepared to have a thickness of 6 mm in any of the Examples and Comparative Examples.

The obtained laminate was placed in a flat cogged mold in which tooth portions and groove portions were alternately arranged with the reinforcing cloth facing downward, and press-pressed at 75° C. to press the cog portion to form a cog pad (completely Was not vulcanized and is in a semi-vulcanized state). Next, both ends of this cog pad were cut vertically from the top of the cog peak.

A cylindrical mold is covered with an inner mother die in which tooth portions and groove portions are alternately arranged, and the tooth portions and groove portions are engaged to wind a cog pad and joints are made at the top of the cog mountain portion. An adhesive rubber layer sheet (lower adhesive rubber: unvulcanized rubber) is laminated on top, and then the core wire is spun into a spiral shape, and the adhesive rubber layer sheet (upper adhesive rubber: the adhesive rubber layer sheet The same), a stretched rubber layer sheet (unvulcanized rubber), and a reinforcing cloth (upper cloth) were sequentially wound to produce a molded body. After that, the jacket was covered, the mold was placed in a vulcanization can, and pre-vulcanization was performed at a temperature of 120° C. for 10 minutes, and then vulcanization was performed at a temperature of 170° C. for 20 minutes to obtain a belt sleeve. This sleeve is cut into a V shape by a cutter, and a belt having a structure shown in FIG. 1, that is, a low edge cogged V belt (size: upper width 22.0 mm, thickness 11. 0 mm, outer peripheral length 800 mm) was produced.

Table 3 shows the evaluation results of the belts obtained in Examples and Comparative Examples. Further, with respect to the belt obtained in Example 1, the results of measuring the crosslink density gradient of the compressed rubber layer are shown in Table 4 and FIG.

As is clear from the results of Table 3, in the transmission belts of Examples 1 to 6, no abnormality was observed in the durability test and the transmission efficiency was high as compared with the comparative example. The reason for this is that the cross-linking density of the compressed rubber layer on the outer peripheral side of the belt is high (=compressive stress is large) and the cross-linking density on the inner peripheral side of the belt is low (=compressive stress is small). It is considered that the transmission efficiency was achieved at the same time. Particularly, in Examples 5 and 6, the transmission efficiency is improved as compared with Examples 2 and 3 in which the compressed rubber layers 1 and 2 have the same rubber composition and do not include the compressed rubber layer 3 as the intermediate layer. did. The reason for this is not clear, but it is presumed that the fact that the compression rubber layer has a three-layer structure facilitates the formation of a gradient in crosslink density as compared with the case of a two-layer structure.

On the other hand, in Comparative Example 1, cracks were generated inside the compressed rubber layer. Since the compressed rubber layers 1 and 2 are composed of the same rubber composition (compound B) and have no cross-linking density gradient, stress is concentrated at the interface between the compressed rubber layer 1 and the compressed rubber layer 2 and cracks are generated. it is conceivable that.

Further, Comparative Example 2 is an example in which the crosslink density of the compressed rubber layer on the outer peripheral side of the belt is low (=small compressive stress) and the crosslink density on the inner peripheral side of the belt is high (=large compressive stress). The efficiency was low and cracks occurred between the compressed rubber layers. This is because the compressive stress of the compressed rubber layer on the core wire side, where the lateral pressure is large, is small, so that bending deformation (dishing) due to lateral pressure causes the transmission efficiency to drop, and the layer with different physical properties due to the deformation. It is considered that cracks were generated at the interface.

In Comparative Example 3, the compression rubber layer has a three-layer structure, but the crosslink density of the compression rubber layer on the outer peripheral side of the belt is low (=small compressive stress) and the crosslink density on the inner peripheral side of the belt is high (=compressive stress is high). However, as in Comparative Example 2, the transmission efficiency was low and cracks occurred between the compressed rubber layers.

As is clear from Table 4 and FIG. 10, the cross-linking density of the compressed rubber layer of Example 1 is the largest on the core wire side (belt outer peripheral side) and continuous toward the cog side (belt inner peripheral side). It was confirmed that the gradient was significantly smaller.

The friction transmission belt of the present invention can be applied to, for example, V-belts (wrapped V-belts, low-edge V-belts, low-edge cogged V-belts), V-ribbed belts, flat belts, and the like. In particular, V-belts (shift belts) used in transmissions (continuously variable transmissions) in which the transmission ratio changes continuously during belt running, such as continuously variable motorcycles, ATVs (four-wheel buggies), snowmobiles, etc. It is preferably applied to a low edge cogged V-belt and a low edge double cogged V-belt used in a transmission.

1... Friction transmission belt 2, 6... Reinforcing cloth 3... Stretching rubber layer 4... Adhesive rubber layer 4a... Core 5... Compression rubber layer

Claims (16)

A friction transmission belt including a compression rubber layer, at least a portion of which has a transmission surface capable of contacting a pulley, and a cross-linking density of which gradually decreases from an outer peripheral side of the belt toward an inner peripheral side in a thickness direction, the compression rubber comprising: A friction transmission belt, wherein the layer is a vulcanized product of a rubber composition containing a crosslinking agent, and the crosslinking agent contains a vulcanization accelerator having a molecular weight of 500 or less . The friction transmission belt according to claim 1, wherein the cross-linking density distribution of the compressed rubber layer decreases continuously or stepwise from the outer peripheral side of the belt toward the inner peripheral side thereof. The friction transmission belt according to claim 1, wherein the compressed rubber layer has a multilayer structure. The compressed rubber layer has a two-layer structure of (a) an outer layer on the outer peripheral side of the belt and an inner layer on the inner peripheral side of the belt, or (b) an outer layer on the outer peripheral side of the belt, an inner layer on the inner peripheral side of the belt, the outer layer and the above-mentioned outer layer. The friction transmission belt according to claim 1, which has a three-layer structure including an intermediate layer interposed between the inner layers. The compression rubber layer has a two-layer structure in which (a) the outer layer and the inner layer have a thickness ratio of outer layer/inner layer=1.5/1 to 1/1.5, or (b) the thickness of the outer layer and the inner layer or the intermediate layer. The friction transmission belt according to claim 4, wherein each of the ratios is a three-layer structure of outer layer/inner layer or intermediate layer=1.5/1 to 1/1.5. When the compressed rubber layer is divided into six equal parts in the thickness direction, the difference in crosslinking density between the first region located on the outermost peripheral side and the sixth region located on the innermost peripheral side is 10 to 100 mol/m ³ . The friction transmission belt according to claim 1. The friction transmission belt according to claim 1, wherein when the compressed rubber layer is divided into three equal parts in the thickness direction, the difference in cross-linking density between the central region and other regions is 3 to 50 mol/m ³ . The friction transmission belt according to any one of claims 1 to 7, wherein the compressed rubber layer is a vulcanized product of a rubber composition containing a rubber component, a crosslinking agent and a reinforcing material. The friction transmission belt according to claim 8, wherein the rubber component contains an ethylene-α-olefin elastomer, and the crosslinking agent contains a vulcanizing agent and a vulcanization accelerator. Friction transmission belt according to claim 9, wherein the vulcanizing agent is a sulfur-based vulcanizing agent. The friction transmission belt according to claim 8, wherein the proportion of the reinforcing material is 50 parts by mass or more with respect to 100 parts by mass of the rubber component. The friction transmission belt according to any one of claims 1 to 11, which is a low edge cogged V belt. The production of the friction transmission belt according to claim 1, further comprising a pre-vulcanization step of pre-vulcanizing a laminated sheet in which a plurality of unvulcanized sheets for compressed rubber layers are laminated, at a temperature lower than the vulcanization temperature. The method is a method for laminating unvulcanized sheets in the order of increasing crosslink density after vulcanization from the inner circumference side to the outer circumference side of the belt. The manufacturing method according to claim 13, wherein a plurality of unvulcanized sheets for compressed rubber layers having different concentrations of the cross-linking agent are laminated in the order of increasing concentration of the cross-linking agent from the inner circumference side to the outer circumference side of the belt. The production method according to claim 13 or 14, wherein the laminated sheet is a laminated body in which the concentration of the crosslinking agent in the unvulcanized sheets adjacent to each other increases by at least 0.1% by mass from the inner peripheral side of the belt toward the outer peripheral side thereof. The manufacturing method according to claim 13, wherein the preliminary vulcanization is performed at a temperature lower than the vulcanization temperature by 30° C. or more.