Rubber-reinforcing cord and rubber product using same

Abstract

A rubber-reinforcing cord 62 according to the present invention is a rubber-reinforcing cord for reinforcing a rubber product 60, and comprises at least one strand. The strand includes at least one filament bundle and a first coating film that is provided so as to cover at least a part of the surface of the filament bundle. The filament bundle includes a carbon fiber filament. The first coating film contains a rubber component and a crosslinking agent. The rubber-reinforcing cord 62 further contains a liquid component, and the content of the liquid component in the rubber-reinforcing cord 62 is in a range of 0.2-13 mass %.

Description

Rubber reinforcing cord and rubber products using the same

[0001] The present invention relates to a rubber reinforcing cord and a rubber product using the same.

[0002] Rubber reinforcing cords formed using fibers are widely used as reinforcing materials for rubber products that are repeatedly subjected to bending stress, such as rubber belts and tires. Rubber reinforcing cords are used as tension members to enhance the dimensional stability of rubber products, so they desirably have a high tensile modulus and high tensile strength. Rubber reinforcing cords with a high tensile modulus can realize, for example, rubber belts with high torque and high power transmission.

[0003] The manufacturing process for rubber reinforcement cords generally includes a step (RFL treatment step) of applying a treatment agent containing resorcinol-formaldehyde-rubber latex (RFL) to fibers and drying the applied treatment agent. The treatment agent applied to the fibers may also include a material that crosslinks upon heat treatment and does not contain a resorcinol-formaldehyde condensate. The coating formed by such a treatment agent can improve the adhesion of the rubber reinforcement cord to the rubber composition (matrix rubber) that constitutes a rubber product when the cord is embedded in the matrix rubber.

[0004] In order to achieve a high tensile modulus, fibers having a high tensile modulus are used for the rubber reinforcing cord. Examples of such fibers include carbon fibers. For example, Patent Document 1 discloses a rubber reinforcing cord using carbon fibers.

[0005] International Publication No. 2012 / 169207

[0006] However, despite the use of carbon fibers having a high tensile modulus, conventional rubber reinforcing cords using carbon fibers have not yet achieved the expected tensile modulus.

[0007] Therefore, one object of the present invention is to provide a rubber reinforcing cord that contains carbon fiber as a reinforcing fiber and has an improved tensile modulus. Furthermore, another object of the present invention is to provide a rubber product that is reinforced with such a rubber reinforcing cord and has a high tensile modulus.

[0008] One aspect of the present invention provides a rubber reinforcing cord for reinforcing a rubber product, the rubber reinforcing cord comprising at least one strand, the strand including at least one filament bundle and a first coating provided so as to cover at least a portion of a surface of the filament bundle, the filament bundle including carbon fiber filaments, the first coating including a rubber component and a crosslinking agent, the rubber reinforcing cord further including a liquid component, and a content of the liquid component in the rubber reinforcing cord within a range of 0.2 mass % to 13 mass %.

[0009] From another aspect, the present invention provides a rubber product comprising: a matrix rubber; and the above-described rubber-reinforcing cord.

[0010] From another aspect, the present invention provides a method for producing a rubber-reinforcing cord according to the above-mentioned aspect of the present invention, the method comprising: (a) bundling a plurality of filaments including carbon fiber filaments to produce at least one filament bundle; and (b) forming a first coating so as to cover at least a portion of a surface of the filament bundle to produce a strand.

[0011] According to the present invention, it is possible to provide a rubber reinforcing cord that contains carbon fiber as a reinforcing fiber and has an improved tensile modulus. Furthermore, according to the present invention, it is possible to provide a high-strength rubber product that is reinforced with such a rubber reinforcing cord and has a high tensile modulus.

[0012] FIG. 1 is a cross-sectional view showing an example of a strand in a rubber reinforcing cord according to a first embodiment of the present invention. FIG. 1 is a cross-sectional view showing an example of a rubber reinforcing cord according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a rubber reinforcing cord comprising a plurality of strands, as another example of a rubber reinforcing cord according to the first embodiment of the present invention. FIG. 3 is a cross-sectional view showing a rubber reinforcing cord comprising a plurality of strands, as yet another example of a rubber reinforcing cord according to the first embodiment of the present invention. FIG. 4 is a cross-sectional view showing a rubber reinforcing cord comprising a plurality of strands, as yet another example of a rubber reinforcing cord according to the first embodiment of the present invention. FIG. 5 is a partially exploded perspective view schematically showing an example of a rubber product according to a second embodiment of the present invention. FIG. 6 is a cross-sectional view showing the rubber reinforcing cords obtained in Examples 11 to 13 and Comparative Example 3. FIG. 7 is a cross-sectional view showing the rubber reinforcing cords obtained in Example 21 and Comparative Example 8.

[0013] (Background to the Invention) As described in the section [Background Art], carbon fiber has a high tensile modulus and is suitable for use as a fiber for reinforcing cords for rubber belts for power transmission, for example. However, conventional rubber reinforcing cords using carbon fiber have not been able to achieve the expected tensile modulus, despite using fibers with a high tensile modulus. Therefore, the present inventors conducted extensive research on rubber reinforcing cords using carbon fiber and obtained the following findings.

[0014] A rubber reinforcing cord using carbon fiber can be obtained, for example, by applying a coating agent to carbon fiber and then drying the coating. The present inventors conducted research focusing on the drying of the coating agent and discovered that the content of liquid components, such as water, in the coating affects the tensile modulus of the rubber reinforcing cord. For example, rubber reinforcing cords with coatings formed using a coating agent containing a material that crosslinks by heat treatment are typically designed to undergo a curing reaction during the heat treatment required to crosslink the matrix rubber after the rubber reinforcing cord is placed in the matrix rubber during the manufacture of rubber products. However, this curing reaction also progresses when the coating agent is dried to form the coating. If the coating becomes too hard due to this curing reaction, the convergence during twisting, for example, decreases, leading to a decrease in the tensile modulus of the resulting rubber reinforcing cord. Further research by the present inventors into ways to solve this problem revealed that the content of liquid components affects the curing of the coating, which in turn affects the tensile modulus of the rubber reinforcing cord.

[0015] Based on the above newly obtained findings, the present inventors have arrived at the rubber-reinforcing cord of the present invention, which will be described below, and the rubber product of the present invention, which uses such a rubber-reinforcing cord.

[0016] The present invention will be described in detail below, but the following description is not intended to limit the present invention to a specific embodiment.

[0017] (One aspect of the present invention) A rubber reinforcing cord according to a first aspect of the present invention is a rubber reinforcing cord for reinforcing a rubber product, the rubber reinforcing cord having at least one strand, the strand including at least one filament bundle and a first coating provided so as to cover at least a portion of the surface of the filament bundle, the filament bundle including carbon fiber filaments, the first coating including a rubber component and a crosslinking agent, the rubber reinforcing cord further including a liquid component, and a content of the liquid component in the rubber reinforcing cord being within a range of 0.2 mass % or more and 13 mass % or less.

[0018] In a second aspect of the present invention, for example, in the rubber reinforcing cord according to the first aspect, the content of the liquid component in the rubber reinforcing cord may be in the range of 0.2 mass % or more and 5 mass % or less.

[0019] In a third aspect of the present invention, for example, in the rubber-reinforcing cord according to the first or second aspect, the rubber component may contain at least one selected from the group consisting of nitrile rubber, hydrogenated nitrile rubber, carboxyl-modified nitrile rubber, and carboxyl-modified hydrogenated nitrile rubber.

[0020] In a fourth aspect of the present invention, for example, in the rubber-reinforcing cord according to any one of the first to third aspects, the crosslinking agent may contain at least one selected from the group consisting of a maleimide-based crosslinking agent and an isocyanate compound.

[0021] In a fifth aspect of the present invention, for example, in the rubber reinforcing cord according to any one of the first to fourth aspects, the first coating may not contain a resorcinol-formaldehyde condensate.

[0022] In a sixth aspect of the present invention, for example, in the rubber reinforcing cord according to any one of the first to fifth aspects, the mass of the first coating may be in the range of 5% or more and 35% or less of the mass of the filament bundle.

[0023] In a seventh aspect of the present invention, for example, the rubber reinforcing cord according to any one of the first to sixth aspects may further include a second coating provided on the first coating.

[0024] In an eighth aspect of the present invention, for example, in the rubber reinforcing cord according to any one of the first to seventh aspects, the thickness of the filament bundle may be 400 tex or more and 3200 tex or less.

[0025] In a ninth aspect of the present invention, for example, in the rubber reinforcing cord according to the eighth aspect, the thickness of the filament bundle may be 800 tex or more and 1600 tex or less.

[0026] In a tenth aspect of the present invention, for example, the rubber reinforcing cord according to any one of the first to ninth aspects may include a carbon fiber strand as the strand, and a plurality of glass fiber strands arranged around the carbon fiber strand, and the glass fiber strand may include a glass fiber filament bundle containing glass fiber filaments.

[0027] In an eleventh aspect of the present invention, for example, in the rubber reinforcing cord related to the tenth aspect, the total cross-sectional area of ​​the carbon fiber strands may be in the range of 20 to 80% of the sum of the total cross-sectional area of ​​the carbon fiber strands and the total cross-sectional area of ​​the glass fiber strands.

[0028] A rubber product according to a twelfth aspect of the present invention includes a matrix rubber and the rubber-reinforcing cord according to any one of the first to eleventh aspects.

[0029] In a thirteenth aspect of the present invention, for example, in the rubber product according to the twelfth aspect, the rubber reinforcing cord may be embedded in the matrix rubber.

[0030] In a fourteenth aspect of the present invention, for example, the rubber product according to the twelfth or thirteenth aspect may be a rubber belt.

[0031] A method for producing a rubber reinforcing cord according to a fifteenth aspect of the present invention is the method for producing a rubber reinforcing cord according to any one of the first to eleventh aspects, and the method includes: (a) bundling a plurality of filaments including carbon fiber filaments to produce at least one filament bundle; and (b) forming a first coating so as to cover at least a portion of the surface of the filament bundle to produce a strand.

[0032] In a sixteenth aspect of the present invention, for example, in the method for manufacturing a rubber reinforcing cord according to the fifteenth aspect, in (b), the first coating may be formed so as to cover at least a part of the surface of the filament bundle, and then the strand may be formed by twisting the filament bundle on which the first coating has been formed.

[0033] In a seventeenth aspect of the present invention, for example, in the method for manufacturing a rubber reinforcing cord according to the fifteenth aspect, in (b), the strand may be formed by twisting the filament bundles and then forming the first coating so as to cover at least a portion of the surface of the twisted filament bundles.

[0034] First Embodiment As a first embodiment, an embodiment of a rubber reinforcing cord of the present invention will be described.

[0035] The rubber reinforcing cord of this embodiment is a cord for reinforcing rubber products. This rubber reinforcing cord has at least one strand. This strand includes at least one filament bundle and a first coating provided so as to cover at least a portion of the surface of the filament bundle. The filament bundle includes carbon fiber filaments. The first coating includes a rubber component and a cross-linking agent. The rubber reinforcing cord of this embodiment further includes a liquid component, and the content of the liquid component in the rubber reinforcing cord is within a range of 0.2% by mass to 13% by mass. This configuration suppresses the temperature rise of the rubber reinforcing cord when forming the coating, i.e., the curing reaction of the coating, and can suppress or minimize the degree of decrease in the tensile modulus of the rubber reinforcing cord caused by the formation of the coating. The liquid component contained in the rubber reinforcing cord is composed, for example, of a solvent contained in the aqueous treatment agent (first coating aqueous treatment agent) used when forming the first coating, and residual moisture contained in the filament itself. For example, the liquid component may be composed of a liquid having a boiling point equal to or lower than the boiling point of the solvent having the highest boiling point among the solvents contained in the treatment agent used to form the coating, and having a heat of vaporization equal to or lower than the heat of vaporization of the solvent having the highest heat of vaporization among the solvents contained in the treatment agent used to form the coating. As an example, if a first coating and a second coating are provided as the coatings, and water is used as the solvent for the treatment agent that forms the first coating, and xylene is used as the solvent for the treatment agent that forms the second coating, the liquid component may be composed of a liquid having a boiling point equal to or lower than the boiling point of xylene and having a heat of vaporization equal to or lower than the heat of vaporization of water. The liquid component may be, for example, water.

[0036] The method for manufacturing the reinforcing cord of this embodiment will be described in more detail below.

[0037] In the rubber reinforcement cord of this embodiment, the filament bundle constituting the strand includes a plurality of filaments. The proportion of carbon fiber filaments in the cross-sectional area of ​​the filament bundle may be, for example, 30% or more. As described above, the filament bundle includes carbon fiber filaments. In this embodiment, the filament bundle may contain carbon fiber filaments as a main component, or may consist essentially of carbon fiber filaments. Here, "the filament bundle contains carbon fiber filaments as a main component" means that the filaments that account for the largest proportion of the cross-sectional area of ​​the filament bundle are carbon fiber filaments. In this case, the proportion of carbon fiber filaments in the cross-sectional area of ​​the filament bundle may be, for example, 50% or more. Furthermore, "the filament bundle is substantially composed of carbon fiber filaments" means that the proportion of carbon fiber filaments in the cross-sectional area of ​​the filament bundle is 90% or more, and may be, for example, 95% or more or 99% or more. As filaments other than carbon fiber filaments, filaments of fibers commonly used as reinforcing fibers for rubber reinforcement cords can be used, such as glass fiber filaments.

[0038] There is no particular limitation on the number of filaments contained in the filament bundle. The filament bundle may contain, for example, 1,000 to 48,000 filaments. Preferably, the filament bundle may contain 6,000 to 48,000 filaments. More preferably, the filament bundle may contain 12,000 to 24,000 filaments.

[0039] The thickness of the filament bundle may be, for example, 400 tex or more and 3200 tex or less, or 800 tex or more and 1600 tex or less. When a coating is formed on such a thick filament bundle, the interior of the filament bundle is usually difficult to dry, which increases the drying temperature and / or the drying time during coating formation, causing the surface curing reaction to proceed and harden the cord, making it difficult to obtain a rubber reinforcement cord with a high elastic modulus. Furthermore, carbon fiber has a higher elastic modulus than other fibers, such as aramid fiber, and is therefore susceptible to the decrease in elastic modulus that occurs during coating formation. However, by setting the liquid component content within the range of 0.2 mass % to 13 mass %, the rubber reinforcement cord of this embodiment can suppress or minimize the decrease in the tensile elastic modulus of the rubber reinforcement cord that occurs due to coating formation, even when a filament bundle containing carbon fiber filaments is used within the above thickness range, thereby achieving a rubber reinforcement cord with a high elastic modulus.

[0040] The surfaces of the carbon fiber filaments contained in the filament bundle are preferably pretreated to enhance adhesive strength. A preferred example of the pretreatment agent is a compound containing at least one functional group selected from the group consisting of an epoxy group and an amino group. Examples of pretreatment agents 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, and glycidylamine-type epoxy resin. Specific examples include the Denacol series from Nagase ChemteX Corporation, the Epiclon series from DIC Corporation, and the Epicoat series from Mitsubishi Chemical Corporation. Polyurethane resins and isocyanate compounds can also be used as pretreatment agents. For example, a pretreatment agent containing at least one selected from the group consisting of an epoxy resin, a urethane resin, and an isocyanate compound may be used. Pretreatment with such a treatment agent further provides a resin layer containing at least one selected from the group consisting of an epoxy resin, a urethane resin, and an isocyanate compound between the filament bundle and the first coating. By using carbon fiber filaments whose surfaces have been pretreated, it is possible to improve the adhesion between the matrix rubber and the rubber reinforcing cord. When the filament bundle contains fiber filaments other than carbon fiber filaments (for example, glass fiber filaments), it is preferable that the surfaces of the fiber filaments are also pretreated as described above to improve the adhesive strength.

[0041] There is no limitation on the number of filament bundles included in the rubber reinforcing cord, and it may be one or more. The filament bundle may be a bundle of multiple filament bundles. In this case, each of the multiple filament bundles may or may not be twisted. Furthermore, the multiple filament bundles may or may not be twisted together.

[0042] The first coating is provided so as to cover at least a portion of the surface of the filament bundle. The first coating may be provided directly on the surface of the filament bundle, or may cover the surface of the filament bundle via another layer (for example, a coating formed by the above-mentioned filament pretreatment (for example, the above-mentioned resin layer)).

[0043] The first coating is formed by applying a first aqueous treatment agent (described below) to at least a portion of the surface of the filament bundle and then drying it by heat treatment. The application of the first aqueous treatment agent to the surface of the filament bundle can be achieved, for example, by impregnating the filament bundle with the first aqueous treatment agent or by applying the first aqueous treatment agent to at least a portion of the surface of the filament bundle. The heat treatment removes most of the moisture contained in the filaments themselves and the solvent (e.g., water) of the aqueous treatment agent.

[0044] The first coating contains a rubber component. The rubber component preferably contains at least one selected from the group consisting of nitrile rubber, hydrogenated nitrile rubber, carboxyl-modified nitrile rubber, and carboxyl-modified hydrogenated nitrile rubber. The first coating may contain only one type of rubber as the rubber component, or may contain multiple types of rubber. In this specification, the term "nitrile rubber" means nitrile rubber (acrylonitrile-butadiene copolymer rubber) that is neither hydrogenated nor carboxyl-modified, unless otherwise specified.

[0045] The first coating may contain other rubbers in addition to the above rubbers, such as butadiene-styrene copolymer, dicarboxylated butadiene-styrene copolymer, vinylpyridine-butadiene-styrene copolymer, chloroprene rubber, butadiene rubber, and chlorosulfonated polyethylene.

[0046] The first coating further contains a crosslinking agent. By including a crosslinking agent in the first coating, the rubber-reinforcing cord of this embodiment can improve adhesion to the matrix rubber. Examples of crosslinking agents include quinone dioxime-based crosslinking agents such as p-quinone dioxime; methacrylate-based crosslinking agents such as lauryl methacrylate and methyl methacrylate; allyl-based crosslinking agents such as DAF (diallyl fumarate), DAP (diallyl phthalate), TAC (triallyl cyanurate), and TAIC (triallyl isocyanurate); maleimide-based crosslinking agents such as bismaleimide, phenylmaleimide, and N,N'-m-phenylenedimaleimide; aromatic or aliphatic organic diisocyanates; isocyanate compounds such as polyisocyanates, blocked isocyanates, and blocked polyisocyanates; aromatic nitroso compounds; sulfur; and peroxides. These crosslinking agents may be used alone or in combination. These crosslinking agents are preferably selected taking into consideration the type of rubber contained in the first coating and the type of matrix rubber in which the rubber reinforcing cords are embedded, etc. These crosslinking agents are preferably used in the form of an aqueous dispersion in order to ensure that the crosslinking agent is uniformly present in the aqueous treatment agent for producing the first coating.

[0047] The crosslinking agent preferably includes at least one selected from the group consisting of maleimide-based crosslinking agents and isocyanate compounds. Among maleimide-based crosslinking agents, 4,4'-bismaleimidodiphenylmethane is preferably used because it has good stability when dispersed in water, a high crosslinking effect, and high heat resistance after crosslinking. Examples of isocyanate compounds include blocked isocyanates. When combined with rubber latex, the maleimide-based crosslinking agent and the isocyanate compound can specifically enhance the adhesion between the reinforcing cord and the matrix rubber. In particular, the combination of a carboxyl-modified hydrogenated nitrile rubber latex and a maleimide-based crosslinking agent is preferred because it can further enhance adhesion.

[0048] The first coating may further contain a filler. Examples of fillers include fine particles of covalently bonded compounds such as carbon black and silica, fine particles of sparingly soluble salts, fine particles of metal oxides, fine particles of metal hydroxides, and fine particles of composite metal oxide salts such as talc. Among these, at least one selected from the group consisting of carbon black and silica is preferred.

[0049] The average particle size of carbon black is preferably in the range of 5 to 300 nm, for example, 100 to 200 nm, and more preferably 130 to 170 nm. The average particle size of silica is preferably in the range of 5 to 200 nm, for example, 7 to 100 nm, and more preferably 7 to 30 nm. Here, the average particle size refers to the value obtained by measuring the particle sizes of 50 or more particles using a transmission electron microscope and dividing the sum of the particle sizes by the number of particles measured. Note that when the particles are not spherical, the particle size is taken as the average of the longest and shortest diameters of each particle.

[0050] The filler, dispersed in the rubber, has the effect of improving the tensile strength, tear strength, and other properties of the coating. In addition to these effects, the filler also improves the adhesive strength between the fiber and coating, and between the coating and the matrix rubber, by increasing the cohesive force of the adhesive components. These effects are significantly influenced by the particle size and amount of the filler.

[0051] The first coating preferably does not contain a resorcinol-formaldehyde condensate, which eliminates the need to use substances that have a large environmental impact, such as formaldehyde and ammonia, when producing the first coating, thereby eliminating the need for environmental measures for workers.

[0052] In addition to the rubber component and the cross-linking agent, the first coating may further contain a filler and other components (for example, a metal oxide other than the metal oxide added as the filler, a resin, etc.).

[0053] The contents of the rubber component and the cross-linking agent in the first coating are not particularly limited. The content of the rubber component in the first coating can be, for example, 50% by mass or more and 90% by mass or less. The content of the cross-linking agent in the first coating can be, for example, 10% by mass or more and 50% by mass or less.

[0054] The mass of the first coating applied to at least the surface of the filament bundle is not particularly limited and may be adjusted as appropriate, but is preferably applied so as to be within the range of 5% to 35% of the mass of the filament bundle. The mass of the first coating may be within the range of 10% to 25% or 12% to 22% of the mass of the filament bundle. If the mass of the first coating is too high, problems such as a decrease in the dimensional stability of the rubber reinforcing cord in the rubber product and a decrease in the elastic modulus of the rubber reinforcing cord may occur. On the other hand, if the mass of the first coating is too low, the strands may become more susceptible to fraying, or the function of the first coating to protect the fibers may be reduced, resulting in a shortened lifespan of the rubber product.

[0055] In order to improve adhesion to the matrix rubber, the rubber-reinforcing cord of this embodiment may further include a second coating formed on the first coating. The treatment agent forming the second coating may be the same as or different from the aqueous treatment agent for the first coating. For example, the second coating may be formed using a treatment agent whose components and solvents are different from those of the aqueous treatment agent for the first coating. In order to further improve adhesion to the matrix rubber, it is also possible to provide an additional coating on the second coating.

[0056] The number of twists in the rubber reinforcing cord of this embodiment is not particularly limited. The number of twists applied to a single strand (hereinafter also referred to as "primary twists") may be, for example, in the range of 20 to 160 twists / m, 30 to 120 twists / m, or 40 to 100 twists / m. Similarly, the number of twists applied to multiple strands (hereinafter also referred to as "final twists") may be, for example, in the range of 20 to 160 twists / m, 30 to 120 twists / m, or 40 to 100 twists / m. The twist may be a rung twist in which the primary twist direction and the final twist direction are the same, or a moro twist in which the primary twist direction and the final twist direction are opposite. The twist direction is not limited, and may be either the S direction or the Z direction.

[0057] The liquid component content of the rubber reinforcing cord of this embodiment is within the range of 0.2% by mass or more and 13% by mass or less. As described above, the liquid component refers to, for example, the solvent (e.g., water) contained in the aqueous treatment agent used to prepare the coating, or residual moisture contained in the filament itself. In the rubber reinforcing cord of this embodiment, the heat treatment during the heat treatment for preparing the first coating is performed by adjusting the heat amount so that the liquid component remains within the rubber reinforcing cord within the range of 0.2% by mass or more and 13% by mass or less. This suppresses the temperature rise of the rubber reinforcing cord, i.e., the curing reaction of the coating. This prevents the rubber reinforcing cord from becoming too hard due to the curing reaction of the coating, and suppresses or minimizes the degree of decrease in the tensile modulus of the rubber reinforcing cord compared to conventional methods. As a result, the tensile modulus of the rubber reinforcing cord is improved compared to conventional methods, achieving a higher tensile modulus than conventional methods. If the liquid component content is less than 0.2% by mass, i.e., if the heat treatment during coating production is carried out so as to remove almost all of the solvent in the treatment agent used to produce the coating and the moisture contained in the fibers, the curing reaction of the coating of the obtained rubber-reinforcing cord will proceed, reducing the tensile modulus of the rubber-reinforcing cord and, as a result, reducing the tensile strength of the rubber-reinforcing cord. On the other hand, if the liquid component content exceeds 13% by mass, it will be difficult to produce a cord, for example, by twisting strands.

[0058] In order to obtain a rubber-reinforcing cord having a higher tensile modulus, the content of the liquid component in the rubber-reinforcing cord is preferably 0.2% by mass or more and 5% by mass or less.

[0059] Here, the "content of liquid components in a rubber reinforcing cord" specified in the present invention refers to a value determined as follows. A 5-meter-long cord is collected from the rubber reinforcing cord as a sample, and the sample is measured on an electronic balance; this value is designated as the mass A of the cord. The sample is then placed in a dryer heated to 150°C for 30 minutes to remove the solvent from the sample. The sample is then placed in a desiccator for 30 minutes, after which the value measured on the electronic balance is designated as mass B. The difference between mass A and mass B is designated as the mass (A-B) of the liquid components contained in the cord. The percentage ({(A-B) / A} x 100) of the mass (A-B) of the liquid components contained in the cord relative to the mass A of the cord is designated as the liquid component content (%). Here, assuming that the solvent of the treatment agent is water, a heat treatment at 150°C for 30 minutes is performed to completely remove water from the sample. However, if a solvent other than water is used, an appropriate heating temperature and heating time can be set to completely remove the solvent.

[0060] An example of a manufacturing method for the rubber-reinforcing cord of this embodiment will be described below. Note that, since the matters described for the rubber-reinforcing cord of this embodiment can be applied to the manufacturing method below, duplicated explanations may be omitted. Furthermore, the matters described for the manufacturing method below can be applied to the rubber-reinforcing cord of this embodiment.

[0061] An example of a method for producing a rubber reinforcing cord according to the present embodiment includes: (a) bundling a plurality of filaments including carbon fiber filaments to produce at least one filament bundle; and (b) forming a first coating so as to cover at least a portion of the surface of the filament bundle to produce a strand.

[0062] First, a plurality of filaments are bundled to form a filament bundle. Furthermore, for example, an aqueous treatment agent (aqueous treatment agent for a first coating) used to form the first coating is prepared. Next, for example, the aqueous treatment agent for the first coating is supplied to at least a portion of the surface of the filament bundle, and then a heat treatment is performed to remove the solvent in the aqueous treatment agent for the first coating. Specifically, 12,000 filaments are first aligned into a bundle, and the first aqueous treatment agent for the first coating is supplied to the surface of the bundle. Then, the solvent in the aqueous treatment agent for the first coating is removed by a heat treatment. The filament bundle includes carbon fiber filaments.

[0063] Through the above process, a first coating is formed on at least a portion of the surface of the filament bundle, forming a strand having a cross section such as that shown in FIG. 1 . FIG. 1 shows, as an example of a strand, a strand 10 including a filament bundle 11 and a first coating 12 covering the surface of the filament bundle 11. The strand 10 shown in FIG. 1 may be used as a rubber reinforcement cord. That is, as an example, the rubber reinforcement cord of this embodiment may have a configuration in which the first coating 12 is formed on the surface of a single filament bundle 11, as shown in FIG. 1 . However, the rubber reinforcement cord of this embodiment is not limited to this configuration. A strand may also be formed by combining multiple filament bundles and forming a first coating on their surfaces. Furthermore, there is no limitation on the method for supplying the aqueous treatment agent for the first coating to at least a portion of the surface of the filament bundle. For example, the aqueous treatment agent for the first coating may be applied to the surface of the filament bundle, or the filament bundle may be immersed in the aqueous treatment agent for the first coating. The material constituting the first coating 12 may be fully or partially permeated into the filament bundle 11. That is, the member designated by reference numeral 11 in FIG. 1 may include the filament bundle and the material of the first coating.

[0064] The conditions for the heat treatment to remove the solvent from the first aqueous coating agent are not particularly limited, but the treatment temperature and treatment time are appropriately adjusted so that the liquid component content of the cord obtained after the heat treatment is 0.2% by mass or more and 13% by mass or less. Preferably, the treatment temperature and treatment time are appropriately adjusted so that the liquid component content of the cord obtained after the heat treatment is 0.2% by mass or more and 5% by mass or less. The treatment temperature is preferably 220°C or less. The treatment time is not particularly limited, and may be appropriately adjusted taking into account the heat treatment temperature so that the applied heat amount is such that the liquid component content of the finished rubber reinforcing cord is within the range specified in this embodiment (0.2% by mass or more and 13% by mass or less). In the heat treatment, the treatment temperature may be adjusted appropriately depending on the liquid to be removed, or the treatment time may be adjusted instead of the treatment temperature. For example, if the processing temperature is set to a temperature suitable for removing water and the liquid to be removed contains a liquid component with a higher heat of vaporization than water, the processing time can be set longer at the same processing temperature, whereas if the liquid to be removed contains a liquid with a lower heat of vaporization than water, the processing time can be set shorter at the same processing temperature.

[0065] In the above step (b), a first coating may be formed so as to cover at least a portion of the surface of the filament bundle, and then the filament bundle on which the first coating is formed may be twisted to form a strand. In this case, the filament bundle on which the first coating is formed is twisted, for example, in one direction. The twisting direction may be the S direction or the Z direction. The number of filaments contained in the filament bundle and the number of twists of the filament bundle have been described above, so explanation will be omitted. In this manner, the rubber reinforcing cord of this embodiment can be manufactured. Note that multiple bundles of filaments on which the first coating is formed may be formed, and these multiple filament bundles may be bundled and then subjected to a final twist. The direction of the final twist may be the same as or different from the twist direction of the filament bundle (direction of the primary twist). Alternatively, multiple filament bundles on which the first coating is formed may be formed, and the bundle of multiple filament bundles may be twisted without twisting each filament bundle individually.

[0066] The first coating may be formed after twisting the filament bundle. That is, in step (b), the strand may be formed by twisting the filament bundle and then forming the first coating so as to cover at least a part of the surface of the twisted filament bundle. In this case, the type, number, and twist degree of the filaments are as described above.

[0067] In a preferred example of the manufacturing method of this embodiment, a filament bundle is coated with or impregnated with an aqueous treatment agent for a first coating to form a first coating, and then twisted in one direction to form a rubber reinforcing cord.

[0068] When forming a second coating on a first coating, a treatment agent for forming the second coating is applied to the first coating, and the solvent in the treatment agent is removed to form the second coating. The type of this second coating can be selected appropriately depending on the matrix rubber of the rubber product to which the rubber reinforcing cord is applied, and is preferably selected particularly from the perspective of improving adhesion. Figure 2 shows a cross-section of an example of a rubber reinforcing cord having a configuration in which a second coating is provided on a first coating. Figure 2 shows, as an example of a rubber reinforcing cord, a rubber reinforcing cord 20 further comprising a second coating 21 formed on the first coating 12 of the strand 10 shown in Figure 1.

[0069] The conditions for the heat treatment to remove the solvent from the second coating treatment agent are not particularly limited, but it is preferable to appropriately adjust the treatment temperature and treatment time so that the content of the liquid component in the cord obtained after the heat treatment satisfies the above range.

[0070] Next, the first aqueous treatment agent for coating will be described.

[0071] The aqueous treatment agent for the first coating preferably contains at least one rubber latex selected from the group consisting of nitrile rubber, hydrogenated nitrile rubber, carboxyl-modified nitrile rubber, and carboxyl-modified hydrogenated nitrile rubber. The aqueous treatment agent may contain only one type of these rubber latexes, or may contain multiple types of these rubber latexes.

[0072] The aqueous treatment agent for the first coating may contain other rubber latexes in addition to the above-mentioned rubber latexes. Examples of other rubber latexes include butadiene-styrene copolymer latexes, dicarboxylated butadiene-styrene copolymer latexes, vinylpyridine-butadiene-styrene terpolymer latexes, chloroprene latexes, butadiene latexes, and chlorosulfonated polyethylene latexes. The aqueous treatment agent may contain multiple types of these rubber latexes.

[0073] The first aqueous treatment agent for forming a coating further contains a crosslinking agent. The crosslinking agent contained in the first aqueous treatment agent for forming a coating is the same as the crosslinking agent contained in the first coating described above, so a description thereof will be omitted here. Note that the crosslinking agent is preferably used in the form of an aqueous dispersion in order to ensure that it is present uniformly in the aqueous treatment agent.

[0074] The first aqueous treatment agent for forming a coating film may further contain a filler. The filler contained in the first aqueous treatment agent for forming a coating film is the same as the filler contained in the first coating film described above, and therefore, a description thereof will be omitted here.

[0075] The first aqueous coating agent preferably does not contain a resorcinol-formaldehyde condensate.

[0076] The first aqueous treatment agent for forming a coating may contain fillers and other components in addition to the rubber latex and crosslinking agent. For example, the first aqueous treatment agent for forming a coating may contain resins, plasticizers, antioxidants, stabilizers, metal oxides other than the metal oxides added as fillers, etc. However, the aqueous treatment agent may not contain resins.

[0077] In the above, as the rubber reinforcing cord of the present embodiment, an example of a rubber reinforcing cord having one strand as shown in Figures 1 and 2 has been described, but the rubber reinforcing cord of the present embodiment is not limited to this. Below, another example of the rubber reinforcing cord of the present embodiment will be described.

[0078] The rubber reinforcing cord of the present embodiment may include a plurality of strands. Fig. 3 shows an example of a rubber reinforcing cord including a plurality of strands as another example of the rubber reinforcing cord of the present embodiment.

[0079] The rubber reinforcing cord 30 shown in FIG. 3 includes a carbon fiber strand 31 and a plurality of glass fiber strands 32 arranged around the carbon fiber strand 31. The carbon fiber strand 31 includes a filament bundle 33 containing carbon fiber filaments and a first coating 34 provided so as to cover at least a portion of the surface of the filament bundle 33. The glass fiber strand 32 includes a filament bundle 35 containing glass fiber filaments and a first coating 36 provided so as to cover at least a portion of the surface of the filament bundle 35. The carbon fiber strand 31 arranged toward the center of the cord contributes to high tensile strength and excellent dimensional stability. The glass fiber strands 32 surrounding the carbon fiber strand 31 can reduce tensile stress and compressive stress, thereby improving the flexural fatigue resistance of the reinforcing cord 30. The filament bundle 33 containing carbon fiber filaments may include carbon fiber filaments, but may also be formed solely from carbon fiber filaments. Furthermore, the filament bundle 35 containing glass fiber filaments may contain glass fiber filaments, but may also be formed solely from glass fiber filaments.

[0080] The total cross-sectional area of ​​the carbon fiber strands 31 is preferably, for example, in the range of 20 to 80% of the sum of the total cross-sectional area of ​​the carbon fiber strands 32 and the total cross-sectional area of ​​the glass fiber strands. As described above, the carbon fiber strands 31 arranged toward the center of the cord contribute to high tensile strength and excellent dimensional stability. However, if the proportion of carbon fiber strands 31 in the cord is too high, flexibility may decrease. Therefore, the total cross-sectional area of ​​the carbon fiber strands 31 is preferably 80% or less, and more preferably 70% or less, of the sum of the total cross-sectional area of ​​the carbon fiber strands 31 and the total cross-sectional area of ​​the glass fiber strands 32. On the other hand, if the proportion of carbon fiber strands 31 in the cord is too low, the effects of the carbon fiber strands 31 may not be fully achieved. Therefore, the total cross-sectional area of ​​the carbon fiber strands 31 is preferably 20% or more, and more preferably 40% or more, of the sum of the total cross-sectional area of ​​the carbon fiber strands 31 and the total cross-sectional area of ​​the glass fiber strands 32.

[0081] The number of carbon fiber strands 31 and the number of glass fiber strands 32 can be selected depending on the properties required of the cord and the properties of the strands. Preferred examples of the ratio [number of carbon fiber strands] / [number of glass fiber strands] include [1] / [3 to 30], [2] / [6 to 30], and [3] / [10 to 40].

[0082] Even in the rubber reinforcing cord including a carbon fiber strand and a plurality of glass fiber strands arranged around the carbon fiber strand as described above, a second coating may be further formed on the first coating. That is, as in the rubber reinforcing cord 40 shown in Fig. 4 , the cord may have a configuration including a carbon fiber strand 31 and a plurality of glass fiber strands 32 arranged around the carbon fiber strand 31, with a second coating 41 further provided on the first coating 35 of the glass fiber strand 32. In this case, as in the rubber reinforcing cord 40 shown in Fig. 4 , it is preferable to arrange the plurality of glass fiber strands 32 closely around the carbon fiber strand 31 so that the second coating 41 does not contact the surface of the carbon fiber strand 31 (i.e., the first coating 34 of the carbon fiber strand 31). Such a configuration in which the second coating 41 does not contact the surface of the carbon fiber strand 31 can further improve the bending fatigue resistance of the rubber reinforcing cord. The above-mentioned arrangement of multiple glass fiber strands 32 densely around the carbon fiber strand 31 includes, for example, a configuration in which the glass fiber strands 32 are arranged around the carbon fiber strand 31 so that the gaps between the glass fiber strands 32 are small enough that the second coating 41 does not come into contact with the surface of the carbon fiber strand 31, or a configuration in which the glass fiber strands 32 are arranged around the carbon fiber strand 31 so that there are no gaps between the glass fiber strands 32.

[0083] As in the rubber reinforcing cord 50 shown in FIG. 5, the second coating 41 may be in contact with the surface of the carbon fiber strand 31 through the gaps between the glass fiber strands 32.

[0084] Second Embodiment As a second embodiment, an embodiment of a rubber product of the present invention will be described.

[0085] The rubber product of this embodiment includes a matrix rubber and the rubber reinforcing cord of the first embodiment. As described in the first embodiment, the rubber reinforcing cord of the first embodiment includes carbon fiber as a reinforcing fiber, and has an improved tensile modulus of elasticity compared to conventional rubber reinforcing cords containing carbon fiber. By including such a rubber reinforcing cord, the rubber product of this embodiment can become a high-strength rubber product having a high tensile modulus of elasticity.

[0086] The rubber product of this embodiment is a rubber product reinforced with the rubber reinforcing cord described in the first embodiment. There are no particular limitations on the rubber product. Examples of the rubber product of this embodiment include automobile and bicycle tires, and rubber belts such as transmission belts. Examples of transmission belts include meshing transmission belts and friction transmission belts. Examples of meshing transmission belts include toothed belts, such as automotive timing belts. Examples of friction transmission belts include flat belts, round belts, V-belts, and V-ribbed belts. That is, the rubber product of this embodiment may be a toothed belt, flat belt, round belt, V-belt, or V-ribbed belt.

[0087] The rubber product of this embodiment is formed by embedding the rubber reinforcing cord of this embodiment in a rubber composition (matrix rubber). The method for embedding the rubber reinforcing cord in the matrix rubber is not particularly limited, and any known method may be used. The rubber product of this embodiment (e.g., a rubber belt) has the rubber reinforcing cord of this embodiment embedded therein. As a result, the rubber product of this embodiment has a high tensile modulus of elasticity. Therefore, the rubber product of this embodiment is particularly suitable for applications requiring a high modulus of elasticity and strength, such as rear-wheel drive belts for motorcycles, timing belts for vehicle engines, belts for driving vehicle accessories, and large industrial equipment.

[0088] The rubber contained in the rubber composition in which the rubber reinforcing cord of this embodiment is embedded is not particularly limited, and may be chloroprene rubber, chlorosulfonated polyethylene rubber, ethylene propylene rubber, hydrogenated nitrile rubber, etc. The hydrogenated nitrile rubber may be hydrogenated nitrile rubber in which a zinc acrylate derivative (e.g., zinc methacrylate) is dispersed. At least one rubber selected from hydrogenated nitrile rubber and hydrogenated nitrile rubber in which a zinc acrylate derivative is dispersed is preferred from the viewpoint of water resistance and oil resistance. The matrix rubber may further contain carboxyl-modified hydrogenated nitrile rubber. Note that, from the viewpoint of adhesion, it is preferable that the coating of the rubber reinforcing cord and the rubber composition of the rubber product contain or be made of the same type of rubber.

[0089] As an example of a rubber product, a toothed belt is shown in Figure 6. The toothed belt 60 shown in Figure 6 includes a belt main body 61 and a plurality of rubber reinforcing cords 62. The belt main body 61 includes a belt portion 63 and a plurality of tooth portions 64 protruding from the belt portion 63 at regular intervals. The rubber reinforcing cords 62 are embedded inside the belt portion 63 so as to be parallel to the longitudinal direction of the belt portion 63. The rubber reinforcing cords 62 are the rubber reinforcing cords of this embodiment.

[0090] Hereinafter, the embodiments of the present invention will be described more specifically with reference to examples and comparative examples.

[0091] [Manufacturing of Rubber Reinforcement Cord] (Examples 1 to 10 and Comparative Example 1) 12,000 carbon fiber filaments (average diameter: approximately 7 μm) were bundled together and used as a filament bundle. A first coating aqueous treatment agent having the composition shown in Table 1 below was applied to this filament bundle. The residence time in a drying oven set at 150°C was then adjusted to control the liquid component content. In this manner, a strand was formed on the surface of the filament bundle, with a first coating formed on the surface. The amount of the first coating aqueous treatment agent applied was adjusted so that the mass of the formed first coating was 20% of the mass of the filament bundle. One strand thus prepared was twisted into a Z-twist at a rate of 60 twists / m. A second coating was formed on the surface of the resulting cord. The second coating treatment agent was a 1:1 mixture of Chemlok 233X (manufactured by Lord Japan Inc.) and xylene by mass. The second coating was formed so that its mass was 5% of the mass of the cord before the second coating was formed (i.e., in this case, the strand having the first coating formed on the surface of the filament bundle). The treatment agent for the second coating was dried at 130°C for 1 minute. In this way, a rubber reinforcing cord was obtained. The obtained rubber reinforcing cord had a cross section similar to that of the reinforcing cord shown in Figure 2.

[0092] (Comparative Example 2) As the aqueous treatment agent for the first coating, as shown in Table 1, 50 parts by mass of vinylpyridine-modified styrene butadiene latex (Nippon A&L), 50 parts by mass of styrene butadiene latex (Nipol LX110, Nippon Zeon), and 10 parts by mass of resorcinol-formaldehyde condensate (Sumikanol 700S, Sumitomo Chemical) were mixed, and the resulting mixture was adjusted with ammonia to a pH of 10 to form an RFL treatment agent. This RFL treatment agent was applied to a filament bundle prepared in the same manner as in Examples 1 to 10 and Comparative Example 1. Thereafter, the filament bundle was treated in a drying oven set at 200 ° C. so that the residence time was 2 minutes. A strand was formed in this way. The amount of RFL treatment agent applied was adjusted so that the mass of the first coating formed was 20% of the mass of the filament bundle. Thereafter, twisting treatment and formation of a second coating were performed in the same manner as in Examples 1 to 10 and Comparative Example 1.

[0093] (Examples 11 to 13 and Comparative Example 3) Rubber reinforcing cords of Examples 11 to 13 and Comparative Example 3 were obtained in the same manner as Examples 1 to 10 and Comparative Example 1, except that a treatment agent having the composition shown in Table 2 was used as the first coating aqueous treatment agent, that four strands were twisted in a Z twist at a rate of 40 turns / m in the twisting process, and that a second coating was formed after twisting. The obtained rubber reinforcing cords had a cross section as shown in Fig. 7. Fig. 7 shows a cross section of a rubber reinforcing cord 70 having a structure in which four carbon fiber strands 73, each having a first coating 72 formed on the surface of a carbon fiber filament bundle 71, are twisted together, and a second coating 74 is further provided thereon.

[0094] (Examples 14, 15, and Comparative Example 4) Rubber reinforcing cords of Examples 14, 15, and Comparative Example 4 were obtained in the same manner as in Examples 1 to 10 and Comparative Example 1, except that the number of carbon fiber filaments bundled to produce one filament bundle was changed to 24,000, that a treatment agent having the composition shown in Table 3 was used as the first coating aqueous treatment agent, and that in the twisting treatment, one strand was twisted into a Z twist at a rate of 40 turns / m. The obtained rubber reinforcing cords had the same cross section as the reinforcing cord shown in FIG. 2.

[0095] (Examples 16 and 17, and Comparative Example 5) A carbon fiber strand in which a first coating was formed on the surface of a filament bundle made of carbon fiber filaments was used as the strand arranged in the center. A glass fiber strand in which a first coating was formed on the surface of a filament bundle made of glass fiber filaments was used as the strand arranged on the periphery of this carbon fiber strand. The carbon fiber strands were produced in the same manner as the strands produced in Examples 1 to 10 and Comparative Example 1. However, the aqueous treatment agent for the first coating used had the composition shown in Table 4. The glass fiber strand was produced by bundling 600 K-glass filaments (manufactured by Nippon Sheet Glass Co., Ltd.) having an average diameter of 7 μm to produce a filament bundle, and forming a first coating similar to that of the carbon fiber strand on the surface of this filament bundle. Fifteen of these glass fiber strands were used, each twisted at a rate of 80 times / m. Drying conditions for forming the first coating were set so that the glass fiber strands had a liquid component content similar to that of the carbon fiber strands. One carbon fiber strand was placed in the center, and 15 glass fiber strands were placed around it, and a second coating was then formed. The second coating was produced in the same manner as in Examples 1 to 10 and Comparative Example 1. The obtained rubber reinforcing cords (rubber reinforcing cords of Examples 16, 17, and Comparative Example 5) had cross sections similar to those of the reinforcing cords shown in FIG. 4.

[0096] (Examples 18 to 20, Comparative Example 6) Except for using a treatment agent having the composition shown in Table 5 as the aqueous treatment agent for the first coating and not forming a second coating, the rubber reinforcing cords of Examples 18 to 20 and Comparative Example 6 were obtained in the same manner as in Examples 1 to 10 and Comparative Example 1. The obtained rubber reinforcing cords were reinforcing cords not provided with a second coating, and had the same cross section as the reinforcing cord shown in Figure 1.

[0097] (Comparative Example 7) Except for not forming the second coating, a rubber reinforcing cord of Comparative Example 7 was obtained in the same manner as in Comparative Example 2. The obtained rubber reinforcing cord was a reinforcing cord not provided with a second coating, and had the same cross section as the reinforcing cord shown in Fig. 1 .

[0098] (Example 21 and Comparative Example 8) Except for not forming a second coating, the rubber-reinforcing cords of Example 21 and Comparative Example 8 were obtained in the same manner as in Examples 11 to 13 and Comparative Example 3, using a treatment agent having the composition shown in Table 6 as the aqueous treatment agent for the first coating. The obtained rubber-reinforcing cords had a cross-sectional structure in which the second coating 74 was not provided in the cross section of the reinforcing cord 70 shown in Figure 7. That is, the rubber-reinforcing cords of Example 21 and Comparative Example 8 had cross sections as shown in Figure 8.

[0099] (Example 22, Example 23, and Comparative Example 9) Rubber reinforcing cords of Example 22, Example 23, and Comparative Example 9 were obtained in the same manner as in Examples 1 to 10 and Comparative Example 1, except that the number of carbon fiber filaments bundled to produce one filament bundle was changed to 6,000, a treatment agent having the composition shown in Table 7 was used as the first coating aqueous treatment agent, one strand was twisted into an S twist or a Z twist at a rate of 80 turns / m in the twisting treatment (Example 22: S twist, Example 23 and Comparative Example 9: Z twist), and no second coating was formed. The obtained rubber reinforcing cords were reinforcing cords not provided with a second coating, and had the same cross section as the reinforcing cord shown in FIG. 1.

[0100] (Example 24, Example 25, and Comparative Example 10) Rubber reinforcing cords of Example 24, Example 25, and Comparative Example 10 were obtained in the same manner as in Examples 1 to 10 and Comparative Example 1, except that the number of carbon fiber filaments bundled to produce one filament bundle was changed to 3,000, a treatment agent having the composition shown in Table 8 was used as the first coating aqueous treatment agent, one strand was twisted into a Z twist at a rate of 120 turns / m in the twisting treatment, and a second coating was not formed. The obtained rubber reinforcing cords were reinforcing cords not provided with a second coating, and had the same cross section as the reinforcing cord shown in FIG. 1.

[0101] (Examples 26, 27, and Comparative Example 11) A carbon fiber strand in which a first coating was formed on the surface of a filament bundle made of carbon fiber filaments was used as the strand arranged in the center. A glass fiber strand in which a first coating was formed on the surface of a filament bundle made of glass fiber filaments was used as the strand arranged on the periphery of this carbon fiber strand. The carbon fiber strands were produced in the same manner as the strands produced in Examples 1 to 10 and Comparative Example 1. However, as the aqueous treatment agent for the first coating, a treatment agent having the composition shown in Table 9 was used, and the twist direction was S-twist in Examples 23 and 27. The glass fiber strand was produced by bundling 600 K-glass filaments (manufactured by Nippon Sheet Glass Co., Ltd.) having an average diameter of 7 μm to produce a filament bundle, and forming a first coating similar to that of the carbon fiber strand on the surface of this filament bundle. Fifteen of these glass fiber strands were used, each of which was first twisted at a rate of 80 turns / m. The drying conditions for forming the first coating were set so that the glass fiber strands had a liquid component content similar to that of the carbon fiber strands. One carbon fiber strand was placed in the center, and 15 glass fiber strands were placed around it. Note that a second coating was not formed. The obtained rubber reinforcing cords (rubber reinforcing cords of Examples 26 and 27, and Comparative Example 11) had the same cross section as the reinforcing cord shown in Figure 3.

[0102] [Liquid Component Content] Within 30 minutes after the heat treatment performed after applying the first aqueous coating agent to the filament bundle, a 5-m-long cord was taken as a sample from the resulting rubber reinforcing cord. The sample was measured using an electronic balance, and this value was taken as the cord's mass A. The sample was then placed in a dryer heated to 150°C for 30 minutes to remove the solvent from the sample, and then placed in a desiccator for 30 minutes, after which the value measured using the electronic balance was taken as the cord's mass B. The difference between mass A and mass B was taken as the mass (A-B) of the liquid component contained in the cord. The percentage ({(A-B) / A} x 100) of the mass (A-B) of the liquid component contained in the cord relative to the cord's mass A was calculated, and this was taken as the liquid component content (%). Tables 1 to 9 show the liquid component contents of the rubber reinforcing cords of Examples and Comparative Examples.

[0103] [Tensile Test] A tensile test was conducted on the rubber reinforcing cords of each Example and Comparative Example using a commonly used tensile tester and a commonly used cord grip to measure the load at 0.8% elongation and tensile strength. The conditions for the cord tensile test were a chuck distance of 250 mm, an initial load of 10 N, and a pulling speed of 300 mm / min. The maximum load was taken as the tensile strength, and the load at which the cord had elongated 0.8% (2 mm) was taken as the load at 0.8% elongation. The tensile modulus of the rubber reinforcing cords of each Example and Comparative Example was evaluated using the load at 0.8% elongation. Tables 1 to 9 show the results of the tensile tests on the rubber reinforcing cords of the Examples and Comparative Examples.

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110]

[0111]

[0112]

[0113] The liquid component contents of the rubber reinforcing cords of Examples 1 to 27 were in the range of 0.2% by mass or more and 13% by mass or less. On the other hand, the liquid component contents of the rubber reinforcing cords of Comparative Examples 1 to 11 were less than 0.2% by mass.

[0114] The results of the tensile tests were compared between Examples and Comparative Examples with the same strand configuration. As shown in Table 1, the rubber reinforcing cords of Examples 1 to 10, in which the liquid component content of the reinforcing cord was in the range of 0.2% by mass or more and 13% by mass or less, had a higher load at 0.8% elongation and a higher tensile modulus than the rubber reinforcing cord of Comparative Example 1, in which the liquid component content of the reinforcing cord was less than 0.2% by mass, and the rubber reinforcing cord of Comparative Example 2, in which the first coating was formed with an RFL treatment agent and the liquid component content of the reinforcing cord was less than 0.2% by mass. Furthermore, the rubber reinforcing cords of Examples 1 to 10 had tensile strengths comparable to or greater than those of the rubber reinforcing cords of Comparative Examples 1 and 2. The rubber reinforcing cords of the Examples and Comparative Examples shown in Tables 2 to 4 also showed results similar to those of the rubber reinforcing cords shown in Table 1.

[0115] For Examples 18 to 27 and Comparative Examples 6 to 11, in which the second coating was not provided, the results of the tensile tests were compared between Examples and Comparative Examples with the same strand configuration. As shown in Table 5, the rubber reinforcing cords of Examples 18 to 20, in which the liquid component content of the reinforcing cord was in the range of 0.2% by mass or more and 13% by mass or less, had a higher load at 0.8% elongation and a higher tensile modulus than the rubber reinforcing cord of Comparative Example 6, in which the liquid component content of the reinforcing cord was less than 0.2% by mass, and the rubber reinforcing cord of Comparative Example 7, in which the first coating was formed with an RFL treatment agent and the liquid component content of the reinforcing cord was less than 0.2% by mass. Furthermore, the rubber reinforcing cords of Examples 18 to 20 had tensile strengths comparable to or greater than those of the rubber reinforcing cords of Comparative Examples 6 and 7. The rubber reinforcing cords of the Examples and Comparative Examples shown in Tables 6 to 9 also showed results similar to those of the rubber reinforcing cords shown in Table 5.

[0116] The rubber-reinforcing cord of the present invention can achieve a high tensile modulus and is therefore applicable to the reinforcement of various rubber products. Furthermore, the rubber products of the present invention can withstand high loads and are therefore applicable to a variety of uses.

Claims

1. A rubber reinforcing cord for reinforcing a rubber product, the rubber reinforcing cord comprising at least one strand, the strand including at least one filament bundle and a first coating provided so as to cover at least a portion of a surface of the filament bundle, the filament bundle including carbon fiber filaments, the first coating including a rubber component and a crosslinking agent, the rubber reinforcing cord further including a liquid component, and a content of the liquid component in the rubber reinforcing cord being within a range of 0.2% by mass or more and 13% by mass or less.

2. The rubber reinforcing cord according to claim 1, wherein the content of the liquid component in the rubber reinforcing cord is within a range of 0.2 mass % or more and 5 mass % or less.

3. The rubber reinforcing cord according to claim 1, wherein the rubber component comprises at least one selected from the group consisting of nitrile rubber, hydrogenated nitrile rubber, carboxyl-modified nitrile rubber, and carboxyl-modified hydrogenated nitrile rubber.

4. The rubber reinforcing cord according to claim 1, wherein the crosslinking agent comprises at least one selected from the group consisting of maleimide-based crosslinking agents and isocyanate compounds.

5. The rubber reinforcing cord according to claim 1, wherein the first coating does not contain a resorcinol-formaldehyde condensate.

6. The rubber reinforcing cord according to claim 1, wherein the mass of the first coating is within the range of 5% to 35% of the mass of the filament bundle.

7. The rubber reinforcing cord according to claim 1, further comprising a second coating provided on said first coating.

8. The rubber reinforcing cord according to claim 1, wherein the filament bundle has a thickness of 400 tex or more and 3200 tex or less.

9. The rubber reinforcing cord according to claim 8, wherein the filament bundle has a thickness of 800 tex or more and 1600 tex or less.

10. The rubber reinforcing cord according to claim 1, comprising a carbon fiber strand as the strand, and a plurality of glass fiber strands arranged around the carbon fiber strand, and the glass fiber strand includes a glass fiber filament bundle including glass fiber filaments.

11. The rubber reinforcing cord according to claim 10, wherein the total cross-sectional area of ​​the carbon fiber strands is in the range of 20 to 80% of the sum of the total cross-sectional area of ​​the carbon fiber strands and the total cross-sectional area of ​​the glass fiber strands.

12. A rubber product comprising: a matrix rubber; and the rubber-reinforcing cord according to any one of claims 1 to 11.

13. The rubber product according to claim 12, wherein the rubber reinforcing cord is embedded in the matrix rubber.

14. The rubber product according to claim 12, which is a rubber belt.

15. A method for producing a rubber reinforcing cord according to any one of claims 1 to 11, comprising: (a) bundling a plurality of filaments, including carbon fiber filaments, to produce at least one filament bundle; and (b) forming a first coating so as to cover at least a portion of the surface of the filament bundle to produce a strand.

16. The method for producing a rubber reinforcing cord according to claim 15, wherein in (b), the first coating is formed so as to cover at least a portion of the surface of the filament bundle, and then the strand is formed by twisting the filament bundle on which the first coating has been formed.

17. The method for producing a rubber reinforcing cord according to claim 15, wherein in (b), after twisting the filament bundles, the strand is formed by forming the first coating so as to cover at least a portion of the surface of the twisted filament bundles.