阅读说明：本技术 橡胶增强用线和使用其的橡胶制品 (Rubber reinforcing cord and rubber product using same ) 是由 山口达也 于 2018-04-11 设计创作，主要内容包括：本发明的橡胶增强用线是用于增强橡胶制品的橡胶增强用线。上述橡胶增强用线具备至少1条股线。上述股线包含至少1条丝束和按照覆盖上述丝束的至少一部分表面的方式设置的覆膜。上述覆膜包含橡胶成分和交联剂。上述交联剂包含2种以上的异氰酸酯化合物。(The rubber reinforcing cord of the present invention is a rubber reinforcing cord for reinforcing a rubber product. The rubber reinforcing cord comprises at least 1 strand. The strand comprises at least 1 strand and a coating film provided so as to cover at least a part of the surface of the strand. The coating film contains a rubber component and a crosslinking agent. The crosslinking agent contains 2 or more isocyanate compounds.)

1. A rubber-reinforcing cord for reinforcing a rubber product,

The rubber reinforcing cord comprises at least 1 strand,

The strand comprises at least 1 tow and a coating disposed in a manner to cover at least a portion of a surface of the tow,

The coating film comprises a rubber component and a cross-linking agent,

The crosslinking agent contains 2 or more isocyanate compounds.

2. the rubber-reinforcing cord according to claim 1, wherein the 2 or more isocyanate compounds contain at least any one selected from a blocked isocyanate and a diisocyanate.

3. The rubber-reinforcing cord according to claim 1 or 2, wherein the 2 or more isocyanate compounds comprise a first blocked isocyanate and a second blocked isocyanate having a dissociation temperature different from that of the first blocked isocyanate.

4. The rubber-reinforcing cord according to any one of claims 1 to 3, wherein the crosslinking agent further contains a maleimide crosslinking agent.

5. The rubber-reinforcing cord according to any one of claims 1 to 4, wherein the rubber component contains at least one selected from the group consisting of hydrogenated nitrile rubber and carboxyl-modified hydrogenated nitrile rubber.

6. The rubber-reinforcing cord according to any one of claims 1 to 5, wherein the coating film does not contain a resorcinol-formaldehyde condensate.

7. A rubber product reinforced with the rubber reinforcing cord according to any one of claims 1 to 6.

8. The rubber product according to claim 7, which is a rubber tape comprising a matrix rubber and the rubber-reinforcing thread embedded in the matrix rubber.

Technical Field

The present invention relates to a rubber reinforcing cord (cord) and a rubber product using the same.

Background

Rubber belts and metal chains are used for driving camshafts of internal combustion engines for automobiles, driving auxiliary machines such as injection pumps, and transmitting power to industrial machines. In recent years, attention has been increasingly paid to energy saving, and from the viewpoint of improvement in fuel consumption and the like, use of a rubber belt having excellent power transmission efficiency has been attracting attention. Further, the rubber belt has advantages of high strength and elastic modulus and being usable even under high load conditions, compared with a metal chain. However, the rubber belt may be reduced in strength when repeatedly subjected to stress, and the use thereof is limited.

Generally, a rubber product such as a rubber belt comprises a matrix rubber and a rubber reinforcing cord embedded in the matrix rubber. The strength of the rubber belt depends on the strength of the rubber reinforcing cord. Therefore, the rubber reinforcing cord is an important member for determining the life of the rubber belt.

The rubber reinforcing cord is generally formed of a reinforcing fiber (a yarn bundle including a plurality of filaments) and a coating film for protecting the surface of the reinforcing fiber. This coating film can also improve the adhesion between the rubber-reinforcing cord and the matrix rubber when the rubber-reinforcing cord is embedded in the matrix rubber of the rubber product.

For forming such a coating film, for example, a mixed solution (RFL solution) of a resorcin-formaldehyde condensate and a rubber latex is used. In addition to the RFL liquid, for example, a mixed liquid containing a rubber and a crosslinking agent (at least 1 selected from the group consisting of a diisocyanate compound, an aromatic nitroso compound, and a maleimide crosslinking agent) as disclosed in patent document 1 may be used. Further, as disclosed in patent document 2, a configuration is also known in which a plurality of layers of coatings are provided on a rubber reinforcing cord in order to sufficiently protect the surface of the reinforcing fiber and achieve high adhesion to the matrix rubber.

Disclosure of Invention

Problems to be solved by the invention

However, rubber products reinforced with rubber reinforcing cords have room for further improvement in terms of strength such as strength reduction or ultimate breakage when subjected to repeated stress. Such breakage of the rubber product is caused by fatigue of the rubber reinforcing cord itself, such as separation between the rubber reinforcing cord and the matrix rubber, or cracking in the rubber reinforcing cord. For example, rubber belts have a tight side and a slack side in travel. That is, the rubber belt is repeatedly subjected to tensile stress during travel. Along with this, the rubber reinforcing cord in the rubber belt is also repeatedly subjected to such tensile stress. As a result, the reinforcing cord is fatigued. When the reinforcing fibers constituting the reinforcing cord have poor integrity, that is, when the adhesion between filaments included in the reinforcing fibers is insufficient, the tensile stress cannot be uniformly shared by the entire cord, and the cord is likely to be fatigued. In addition, water and oil easily penetrate between filaments to promote swelling of the coating film, and fatigue of the rubber reinforcing cord is more likely to occur.

Accordingly, an object of the present invention is to provide a rubber reinforcing cord which can maintain the adhesion between filaments of reinforcing fibers and the adhesion between a rubber reinforcing cord and a matrix rubber even when repeatedly subjected to stress, and as a result, is less likely to cause a decrease in strength and breakage of a rubber product. Further, another object of the present invention is to provide a rubber product having improved strength when repeatedly subjected to stress by reinforcing with such a rubber reinforcing cord.

Means for solving the problems

The inventors of the present invention have found, through intensive studies: the crosslinking agent contained in the coating film covering the reinforcing fiber contributes significantly to the above-described problem of the present invention, that is, the adhesiveness between the reinforcing fibers of the rubber reinforcing cord and the adhesiveness between the rubber reinforcing cord and the matrix rubber, and the rubber reinforcing cord of the present invention described below has been completed.

The present invention is a rubber-reinforcing cord for reinforcing a rubber product,

The rubber reinforcing cord comprises at least 1 strand,

The strand comprises at least 1 tow and a coating film provided so as to cover at least a part of the surface of the tow,

The coating film comprises a rubber component and a crosslinking agent,

The crosslinking agent contains 2 or more isocyanate compounds.

The present invention also provides a rubber product reinforced with the rubber reinforcing cord of the present invention.

Effects of the invention

The rubber reinforcing cord of the present invention can maintain the adhesion between the reinforcing fibers and the adhesion between the rubber reinforcing cord and the matrix rubber even when repeatedly subjected to stress in a state of being embedded in the matrix rubber of the rubber product, and as a result, the strength of the rubber product is less likely to be reduced and the rubber product is less likely to be broken. Further, the rubber product of the present invention is reinforced with such a rubber reinforcing cord, and therefore, the strength when repeatedly subjected to stress can be improved.

Drawings

FIG. 1 is a view schematically showing an example of a rubber product of the present invention.

Fig. 2 is a diagram schematically showing a trial and error tensile test performed in the example.

Detailed Description

The following specifically describes embodiments of the present invention.

[ rubber reinforcing cord ]

the rubber-reinforcing cord of the present embodiment is a cord for reinforcing a rubber product. The rubber reinforcing cord comprises at least 1 strand. The strand comprises at least 1 tow (reinforcing fiber) and a coating film provided so as to cover at least a part of the surface of the tow. The coating film contains a rubber component and a crosslinking agent. The crosslinking agent contains 2 or more isocyanate compounds.

the method for manufacturing the reinforcing cord of the present embodiment will be described in more detail below.

In the rubber reinforcing cord of the present embodiment, the filament bundle constituting the cord includes a plurality of filaments. The material of the filament is not particularly limited. As the yarn of the rubber reinforcing yarn in the present embodiment, for example, a glass fiber yarn, a polyvinyl alcohol fiber yarn typified by vinylon fiber, a polyester fiber yarn, a polyamide fiber yarn such as nylon or aramid fiber (aromatic polyamide), a carbon fiber yarn, a poly-p-Phenylene Benzobisoxazole (PBO) fiber yarn, or the like can be used. Among these, filaments of fibers excellent in dimensional stability, tensile strength, modulus and bending fatigue resistance are preferably used. It is preferable to use, for example, at least 1 kind of filament selected from the group consisting of glass filament, aramid filament, polyparaphenylene benzobisoxazole filament and carbon filament, and it is particularly preferable to use glass filament. The tow may be composed of 1 kind of filament or a plurality of kinds of filaments.

The number of filaments contained in the tow is not particularly limited. The tow may comprise, for example, in the range of 200 to 24000 filaments.

The surface of the filaments included in the tow may be pretreated for improving the bonding strength. One preferable example of the pretreatment agent is a compound containing at least any 1 functional group selected from an epoxy group and an amino group. Examples of the pretreatment agent include aminosilane, epoxysilane, novolac type epoxy resin, bisphenol a type epoxy resin, bisphenol F type epoxy resin, brominated epoxy resin, bisphenol AD type epoxy resin, glycidylamine type epoxy resin, and the like. Specific examples thereof include the Denacol series by Nagase ChemteX, the EPICLON series by DIC, and the Epikote series by Mitsubishi chemical corporation. Further, as the pretreatment agent, a polyurethane resin and an isocyanate compound can be similarly used. For example, a treatment agent containing at least one selected from the group consisting of an epoxy resin, a urethane resin, and an isocyanate compound may be used as the pretreatment agent. By performing a pretreatment using such a treating agent, a resin layer containing at least one selected from the group consisting of an epoxy resin, a urethane resin, and an isocyanate compound is further provided between the tow and the coating film. By pretreating the surface, the adhesiveness between the matrix rubber and the rubber reinforcing cord can be improved even when a fiber such as a poly (p-phenylene terephthalamide) fiber is used, for example, which hardly exhibits adhesion.

The number of strands contained in the rubber reinforcing cord is not limited, and may be 1 or more. The tow may be a product obtained by bundling a plurality of tows. In this case, the plurality of tows may or may not be twisted. Further, the plurality of tows may or may not be twisted in a combined state.

The coating film is provided so as to cover at least a part of the surface of the tow. The coating film may be provided directly on the surface of the filament bundle, or may cover the surface of the filament bundle with another layer (for example, a coating film formed by the pretreatment of the filament (for example, the resin layer)).

The coating is formed by supplying an aqueous coating treatment agent, which will be described later, to at least a part of the surface of the tow, and drying the aqueous coating treatment agent by heat treatment. The supply of the aqueous treatment agent to the surface of the tow can be carried out, for example, by impregnating the tow with the aqueous treatment agent for coating or by applying the aqueous treatment agent for coating to at least a part of the surface of the tow. In this case, the heat treatment substantially removes the moisture contained in the yarn itself and the solvent (e.g., water) of the aqueous treatment agent.

The coating contains a rubber component. Examples of the rubber component include butadiene-styrene copolymer, dicarboxylated butadiene-styrene polymer, vinylpyridine-butadiene-styrene terpolymer, chloroprene, butadiene rubber, chlorosulfonated polyethylene, acrylonitrile-butadiene copolymer, nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), carboxyl-modified nitrile rubber (X-NBR), and carboxyl-modified hydrogenated nitrile rubber (X-HNBR). Among these, hydrogenated nitrile rubber (HNBR) and carboxyl-modified hydrogenated nitrile rubber (X-HNBR) are preferable because of their high oil resistance and water resistance.

The coating film further contains a crosslinking agent. The crosslinking agent contains 2 or more isocyanate compounds. The coating film contains 2 or more isocyanate compounds as a crosslinking agent, and thus the bonding reaction in the coating film, i.e., the reaction in the coating film in which the filaments are bonded, is stepwise and complex. As a result, the film improves the adhesion between filaments. The improvement in the adhesiveness between filaments improves the integrity of the yarn bundle, and therefore, fatigue of the strands constituting the rubber reinforcing yarn can be prevented. Further, since the gaps between the filaments and between the filament bundles are reduced, it is difficult for impurities to enter the gaps between the filaments or the like. This can prevent a decrease in the tensile strength of the rubber-reinforcing cord itself. Further, when the rubber-reinforcing cord of the present embodiment is embedded in the matrix rubber, the adhesiveness between the rubber-reinforcing cord and the matrix rubber is also improved by the coating film.

For the above reasons, the rubber-reinforcing cord of the present embodiment is provided with a coating film containing 2 or more isocyanate compounds as a crosslinking agent, and thus, even when repeatedly subjected to stress in a state embedded in the matrix rubber of a rubber product, the adhesiveness between filaments and between strands and the adhesiveness between the rubber-reinforcing cord and the matrix rubber can be improved, and the strength reduction and breakage of the rubber product are less likely to occur.

Examples of the isocyanate compound include aromatic or aliphatic organic diisocyanates, polyisocyanates, blocked isocyanates, and blocked polyisocyanates. The 2 or more isocyanate compounds in the coating film preferably contain at least one selected from blocked isocyanates and diisocyanates. It is preferable to use 2 kinds of blocked isocyanates whose blocking agents have dissociation temperatures different from each other. That is, in other words, the 2 or more kinds of isocyanate compounds in the coating film preferably include a first blocked isocyanate and a second blocked isocyanate having a dissociation temperature different from that of the first blocked isocyanate. Here, the difference in dissociation temperature between the first blocked isocyanate and the second blocked isocyanate is preferably 10 ℃ or more, more preferably 20 ℃ or more, and still more preferably 30 ℃ or more.

The coating film may further contain a crosslinking agent other than the isocyanate compound. Examples of the crosslinking agent other than the isocyanate compound include quinone dioxime-based crosslinking agents such as p-quinone dioxime; methacrylic ester-based crosslinking agents such as lauryl methacrylate and methyl methacrylate; allyl crosslinking agents such as DAF (diallyl fumarate), DAP (diallyl phthalate), TAC (triallyl cyanurate) and TAIC (triallyl isocyanurate); maleimide crosslinking agents such as bismaleimide, phenylmaleimide and N, N' -m-phenylenedimaleimide; aromatic nitroso compounds, sulfur and peroxides. Among these, a maleimide-based crosslinking agent is preferable. That is, the coating film is preferably formed by using 2 or more kinds of isocyanate compounds in combination with a maleimide crosslinking agent. When 2 or more kinds of isocyanate compounds are used in combination with the maleimide-based crosslinking agent, the maleimide-based crosslinking agent may function as a crosslinking aid for the isocyanate compound, and the reactivity may be further improved.

The cover film may further contain a filler material. Examples of the filler include fine particles of a covalent bond compound such as carbon black and silica, fine particles of a hardly soluble salt, fine particles of a metal oxide, fine particles of a metal hydroxide, and fine particles of a composite metal oxide salt such as talc. The filler is dispersed in the rubber, and thus has an effect of improving the properties of the coating film, such as tensile strength and tear strength. In addition to these effects, the filler has an effect of increasing the adhesive strength by increasing the cohesive force of the adhesive component between the fiber and the coating film and between the coating film and the matrix rubber.

The coating is preferably free of resorcinol-formaldehyde condensates. When the coating does not contain a resorcinol-formaldehyde condensate, it is not necessary to use a substance having a large environmental load such as formaldehyde or ammonia in the production of the coating. Therefore, no environmental measures are required for the operator. However, the coating film may contain a resorcinol-formaldehyde condensate.

The coating film may further contain a filler and other components (for example, a metal oxide other than the metal oxide added as the filler, a resin, and the like) in addition to the rubber component and the crosslinking agent.

The content of the rubber component and the crosslinking agent in the coating is not particularly limited. The content of the rubber component in the coating film may be, for example, 50 to 97 mass%. The content of the crosslinking agent in the coating film may be, for example, 3 to 50% by mass. The total content of the rubber component and the crosslinking agent in the coating film is preferably 53 mass% or more. The coating film may be formed substantially only of the rubber component and the crosslinking agent. The substantially only rubber component and crosslinking agent means that: the total content of the rubber component and the crosslinking agent in the coating film is 99 mass% or more. Further, the coating film may be formed only of the rubber component and the crosslinking agent.

the mass of the coating film provided on at least the surface of the tow is not particularly limited, and may be appropriately adjusted, and is preferably set to be within a range of 1% to 35% of the mass of the tow. The mass of the coating film may be in the range of 10 to 25% by mass of the tow, or in the range of 12 to 20% by mass. When the coating quality is too high, there may be a case where there are problems such as a decrease in dimensional stability of the rubber reinforcing cord and a decrease in elastic modulus of the rubber reinforcing cord in the rubber product. On the other hand, when the coating film quality is too low, the strands are likely to become loose or the function of protecting the fibers with the coating film is reduced, and as a result, the life of the rubber product may be reduced.

In the rubber-reinforcing cord of the present embodiment, in order to improve the adhesion to the matrix rubber, another coating film (hereinafter referred to as "second coating film") for improving the adhesion to the rubber product may be further formed on the surface thereof. When sufficient adhesion to the matrix rubber of the rubber product cannot be obtained only by the coating, it is preferable to form a second coating on the surface of the double-twisted yarn in order to improve adhesion to the matrix rubber. The second coating may be composed of any component that can improve adhesion to the matrix rubber. For example, a halogen-containing polymer adhesive (e.g., Chemlok manufactured by LORD Co., Ltd.), an adhesive containing H-NBR rubber and a crosslinking agent (e.g., maleimide-based crosslinking agent), and the like are preferably used.

The number of twists of the rubber-reinforcing cord of the present embodiment is not particularly limited. The number of twists (hereinafter, sometimes referred to as "first twists") applied to 1 strand may be, for example, in the range of 20 to 160 times/m, 30 to 120 times/m, or 40 to 100 times/m. Further, the number of twists (hereinafter, also referred to as double twists) to be applied to the plurality of strands may be similarly in the range of, for example, 20 to 160 times/mn, 30 to 120 times/m, or 40 to 100 times/m. The first twist direction and the second twist direction can be the same forward twist, and the first twist direction and the second twist direction can also be reverse common twist. The twisting direction is not limited, and may be the S direction or the Z direction.

[ method for producing rubber-reinforcing cord ]

An example of the method for producing the rubber reinforcing cord of the present embodiment is described below. Note that, the matters described for the rubber reinforcing cord of the present embodiment can be applied to the following manufacturing method, and therefore, the overlapping description may be omitted. Note that the matters described in the following manufacturing method can be applied to the rubber reinforcing cord of the present embodiment. An example of the manufacturing method includes the following steps.

First, a plurality of filaments are bundled to produce a tow, and an aqueous coating treatment agent for producing a coating is prepared. Next, an aqueous coating treatment agent is supplied to at least a part of the surface of the tow. Thereafter, a heat treatment for removing the solvent in the aqueous coating treatment agent is performed.

Through the above steps, a coating is formed on at least a part of the surface of the tow. The method of supplying the aqueous coating treatment agent to at least a part of the surface of the tow is not limited, and for example, the aqueous coating treatment agent may be applied to the surface of the tow or the tow may be immersed in the aqueous coating treatment agent.

The heat treatment conditions for removing the solvent of the aqueous coating treatment agent are not particularly limited, and drying under such conditions that the reaction of the crosslinking agent in the coating is completely carried out is not to be avoided. Therefore, when drying is performed at a relatively high temperature (for example, 80 ℃ or higher), it is preferable to set the drying time to a short time (for example, 5 minutes or less). For example, in the case of an atmosphere of 150 ℃ or lower, the drying time may be set to 5 minutes or less. In one example, the drying is carried out in an atmosphere of 80 to 280 ℃ for 0.1 to 2 minutes.

The tow having the coating film formed thereon may be twisted in one direction. The twisting direction may be the S direction or the Z direction. The number of filaments included in the tow and the number of twists of the tow are as described above, and therefore, the description thereof is omitted. In this way, the rubber reinforcing cord of the present embodiment can be manufactured. It is also possible to form a plurality of bundles of filaments on which a coating film is formed, and bundle the plurality of bundles and apply a double twist. The direction of the secondary twist may be the same as or different from the twisting direction (primary twist direction) of the tow. Further, a plurality of tows having a coating film formed thereon may be formed, and the plurality of tows may be bundled and twisted without being twisted separately.

The coating may be formed after twisting the tow. The types, the numbers, and the twist numbers of the filaments are as described above.

In a preferred example of the production method of the present embodiment, the yarn bundle is coated or impregnated with the aqueous coating agent, and then the bundled product is twisted in one direction to form the rubber reinforcing cord.

When another coating is further formed on the coating, a treatment agent for forming the other coating may be applied to the formed coating, and the solvent in the treatment agent may be removed. The type of the other coating film may be appropriately selected depending on the matrix rubber of the rubber product to which the rubber reinforcing cord is to be applied, and is particularly desired to be selected from the viewpoint of improving the adhesiveness.

Next, the aqueous treating agent for coating will be described.

The aqueous coating treatment agent preferably contains a rubber latex of a rubber component constituting the coating. For example, in the case where the rubber component of the coating film is at least 1 rubber selected from the group consisting of hydrogenated nitrile rubber and carboxyl-modified hydrogenated nitrile rubber, the aqueous treating agent for coating film contains a latex of at least 1 rubber selected from the group consisting of hydrogenated nitrile rubber and carboxyl-modified hydrogenated nitrile rubber. The aqueous coating treatment agent may contain only 1 kind of rubber latex or may contain a plurality of kinds of rubber latexes depending on the rubber component of the coating.

The aqueous coating treatment agent further contains a crosslinking agent. The crosslinking agent contained in the aqueous coating treatment agent is the same as the crosslinking agent contained in the coating as described above, and therefore, the description thereof is omitted here. In order to be uniformly present in the aqueous treatment agent, the crosslinking agent is preferably used in the form of an aqueous dispersion.

The aqueous coating treatment agent may further contain a filler. Examples of the filler optionally contained in the aqueous treating agent for coating are the same as those described above as the filler contained in the coating, and therefore, the description thereof is omitted here.

The aqueous coating treatment agent preferably does not contain a resorcinol-formaldehyde condensate. However, the aqueous coating treatment agent may contain a resorcinol-formaldehyde condensate.

The aqueous treatment agent for coating may contain a filler and other components in addition to the rubber latex and the crosslinking agent. For example, the aqueous coating treatment agent may contain a resin, a plasticizer, an antioxidant, a stabilizer, a metal oxide other than the metal oxide added as the filler, and the like. However, the aqueous treatment agent may contain no resin.

[ rubber products ]

the rubber product of the present embodiment is a rubber product reinforced with the rubber reinforcing cord of the present embodiment. The rubber product is not particularly limited. Examples of the rubber product of the present embodiment include tires and transmission belts of automobiles and bicycles. Examples of the transmission belt include a meshing transmission belt, a friction transmission belt, and the like. Examples of the engaging transmission belt include a toothed belt typified by a timing belt for an automobile or the like. Examples of friction drive belts include flat belts, circular belts, V-ribbed belts, and the like. That is, the rubber product of the present embodiment may be a toothed belt, a flat belt, a circular belt, a V-belt, or a V-ribbed belt.

The rubber product of the present embodiment is formed by embedding the rubber reinforcing cord of the present embodiment in a rubber composition (matrix rubber). The method for embedding the rubber reinforcing cord in the matrix rubber is not particularly limited, and a known method can be applied. The rubber product (for example, a rubber belt) according to the present embodiment has the rubber reinforcing cord according to the present embodiment embedded therein. Therefore, the rubber product of the present embodiment has high bending fatigue resistance. Therefore, the rubber product of the present embodiment is particularly suitable for applications such as a synchronous belt of an engine for a vehicle, a belt for driving auxiliary machines for a vehicle, and the like.

The rubber contained in the rubber composition in which the rubber reinforcing cord of the present embodiment is to be embedded is not particularly limited, and may be chloroprene rubber, chlorosulfonated polyethylene rubber, ethylene propylene rubber, hydrogenated nitrile rubber, or the like. The hydrogenated nitrile rubber may be a hydrogenated nitrile rubber having dispersed therein a zinc acrylate derivative, such as zinc methacrylate. From the viewpoint of water resistance and oil resistance, at least 1 rubber selected from the group consisting of hydrogenated nitrile rubbers and hydrogenated nitrile rubbers in which zinc acrylate derivatives are dispersed is preferable. The matrix rubber may further comprise a hydrogenated nitrile rubber modified with carboxyl groups. In view of adhesiveness, the coating of the rubber-reinforcing cord and the rubber composition of the rubber product preferably contain or consist of the same rubber.

Fig. 1 shows a toothed belt as an example of a rubber product. The toothed belt 1 shown in fig. 1 includes a belt main body 11 and a plurality of rubber reinforcing cords 12. The belt body 11 includes a belt portion 13 and a plurality of teeth 14 projecting from the belt portion 13 at fixed intervals. The rubber reinforcing cord 12 is embedded inside the belt portion 13 so as to be parallel to the longitudinal direction of the belt portion 13. The rubber reinforcing cord 12 is the rubber reinforcing cord of the present embodiment.