Rubber reinforcing cords and rubber products using them

Abstract

To provide a rubber-reinforcing cord containing a carbon fiber as a reinforcing fiber and having improved tensile modulus, to provide a rubber product reinforced with the rubber-reinforcing cord and having high tensile modulus, and to provide a method for producing the rubber-reinforcing cord.SOLUTION: The rubber-reinforcing cord 62 of the present invention is a rubber-reinforcing cord for reinforcing the rubber product 60, and includes at least one strand. The strand includes at least one filament bundle and a first coating disposed over at least a portion of a surface of the filament bundle. The filament bundle includes carbon fiber filaments. The first coating 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 the range of 0.2 mass% or more and 13 mass% or less.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

[0002] As a reinforcing material for rubber products that repeatedly receive bending stress, such as rubber belts and tires, a rubber reinforcing cord formed using fibers is widely used. Since the rubber reinforcing cord is used as a tension member to enhance the dimensional stability of rubber products, it is desirable to have a high tensile modulus and a high tensile strength. According to a rubber reinforcing cord having a high tensile modulus, for example, a rubber belt with high torque and high transmission can be realized.

[0003] The manufacturing process of the rubber reinforcing cord generally includes a process of applying a treatment agent containing resorcinol-formaldehyde-rubber latex (RFL) to the fibers and drying them (RFL treatment process). In addition, as a treatment agent to be applied to the fibers, a treatment agent that contains a material crosslinked by heat treatment and does not contain a resorcinol-formaldehyde condensate may be used. By the film formed by such a treatment agent, the rubber reinforcing cord can improve the adhesiveness with the matrix rubber when embedded in the rubber composition (matrix rubber) constituting the rubber product.

[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.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

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

[0007] Therefore, one object of the present invention is to provide a rubber reinforcing cord that contains carbon fibers as reinforcing fibers and has improved tensile modulus. Furthermore, another object of the present invention is to provide a rubber product having a high tensile modulus, which is reinforced by such a rubber reinforcing cord. [Means for solving the problem]

[0008] From one aspect, the present invention, A rubber reinforcing cord for reinforcing rubber products, The aforementioned rubber reinforcing cord comprises at least one strand, The strand comprises 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. It includes, The filament bundle includes carbon fiber filaments, The first coating comprises a rubber component and a crosslinking agent. The aforementioned rubber reinforcing cord further contains a liquid component, The liquid component content in the rubber reinforcing cord is within the range of 0.2% by mass or more and 13% by mass or less. We provide rubber reinforcement cords.

[0009] From another perspective, the present invention Matrix rubber and The above-mentioned rubber reinforcement cord, We provide rubber products including [this product].

[0010] From another perspective, the present invention relates to a method for manufacturing a rubber reinforcing cord in one aspect of the present invention, The aforementioned manufacturing method is (a) Bundling together multiple filaments containing carbon fiber filaments to create at least one filament bundle, (b) Forming a first coating so as to cover at least a portion of the surface of the filament bundle to produce a strand, The present invention provides a method for manufacturing rubber-reinforced cords, including the following: [Effects of the Invention]

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

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

Mode for Carrying Out the Invention

[0013] (Background of the Invention) As described in the column of [Background Art], carbon fiber is a fiber having a high tensile elastic modulus and is suitable as a fiber used for a rubber reinforcing cord, for example, for a rubber belt for power transmission. However, conventional rubber reinforcing cords using carbon fiber have not been able to achieve the expected tensile elastic modulus despite using fibers having a high tensile elastic modulus. Therefore, the present inventor has conducted intensive 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 treatment agent to the carbon fiber and drying it. The present invention focused on the drying of the coating treatment agent and conducted research. As a result, it was found that the content of liquid components such as moisture in the coating affects the tensile elastic modulus of the rubber reinforcing cord. For example, a rubber reinforcing cord provided with a coating formed of a treatment agent containing a material crosslinked by heat treatment is usually designed such that the curing reaction proceeds by heat treatment for crosslinking the matrix rubber after the rubber reinforcing cord is installed in the matrix rubber when manufacturing a rubber product. However, such a curing reaction also proceeds when drying the treatment agent to form a coating. If the coating becomes too hard due to such a curing reaction, for example, the convergence during twisting treatment decreases, leading to a decrease in the tensile elastic modulus of the obtained rubber reinforcing cord. When the present inventor further investigated means for solving such problems, it was found that the content of the liquid component affects the curing of the coating, and as a result, also affects the tensile elastic modulus of the rubber reinforcing cord.

[0015] Based on the newly acquired findings described above, the inventors have arrived at the rubber reinforcing cord of the present invention and the rubber product of the present invention using such a rubber reinforcing cord, as described below.

[0016] The details of the present invention will be described below, but the following description is not intended to limit the present invention to any particular 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 rubber products, The aforementioned rubber reinforcing cord comprises at least one strand, The strand comprises 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. It includes, The filament bundle includes carbon fiber filaments, The first coating comprises a rubber component and a crosslinking agent. The aforementioned rubber reinforcing cord further contains a liquid component, The content of the liquid component in the rubber reinforcing cord is within the range of 0.2% by mass or more and 13% by 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 within the range of 0.2% by mass or more and 5% by mass or less.

[0019] In a third aspect of the present invention, for example, in a rubber reinforcing cord according to the first or second aspect, the rubber component may include 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 a rubber reinforcing cord according to any one of the first to third aspects, the crosslinking agent may include at least one selected from the group consisting of maleimide-based crosslinking agents and isocyanate compounds.

[0021] In a fifth aspect of the present invention, for example, in a 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 a rubber-reinforced cord according to any one of the first to fifth aspects, the mass of the first coating may be within the range of 5% or more and 35% or less of the mass of the filament bundle.

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

[0024] In the 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 the 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, a rubber reinforcing cord according to any one of the first to ninth aspects includes a carbon fiber strand as the strand and a plurality of glass fiber strands arranged around the carbon fiber strand, wherein the glass fiber strand may include a bundle of glass fiber filaments containing glass fiber filaments.

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

[0028] A rubber product according to a twelfth aspect of the present invention is: Matrix rubber and A rubber reinforcing cord relating to any one of the 1st to 11th embodiments, Includes.

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

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

[0031] A method for manufacturing a rubber-reinforced cord according to the 15th aspect of the present invention is a method for manufacturing a rubber-reinforced cord according to any one of the 1st to 11th aspects, The aforementioned manufacturing method is (a) Bundling together multiple filaments containing carbon fiber filaments to create at least one filament bundle, (b) Forming a first coating so as to cover at least a portion of the surface of the filament bundle to produce a strand, Includes.

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

[0033] In a 17th aspect of the present invention, for example, in the method for manufacturing a rubber-reinforced cord according to the 15th aspect, the strand may be formed in (b) by twisting the filament bundle and then forming the first coating so as to cover at least a portion of the surface of the twisted filament bundle.

[0034] (First Embodiment) As a first embodiment, an embodiment of the 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 comprises 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 crosslinking agent. The rubber reinforcing cord of this embodiment further contains a liquid component, and the liquid component content in the rubber reinforcing cord is in the range of 0.2% by mass or more and 13% by mass or less. This configuration suppresses the temperature rise of the rubber reinforcing cord when forming the coating, i.e., the curing reaction of the coating, and suppresses or reduces 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 consists of, for example, the solvent contained in the aqueous treatment agent (aqueous treatment agent for the first coating) used when producing the first coating, and residual moisture from the filaments themselves. For example, the above liquid component may consist of a liquid having a boiling point less than or equal to the boiling point of the solvent with the highest boiling point among the solvents contained in the treatment agent used to form the film, and having a heat of vaporization less than or equal to the heat of vaporization of the solvent with the highest heat of vaporization among the solvents contained in the treatment agent used to form the film. As an example, if a first film and a second film are provided as the film, and water is used as the solvent for the treatment agent that forms the first film, and xylene is used as the solvent for the treatment agent that forms the second film, the above liquid component may consist of a liquid having a boiling point less than or equal to the boiling point of xylene and having a heat of vaporization less than or equal to the heat of vaporization of water. The above 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 reinforcing cord of this embodiment, the filament bundle constituting the strand includes multiple filaments. The proportion of carbon fiber filaments to 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 mainly contain carbon fiber filaments, or may consist substantially only of carbon fiber filaments. Here, "the filament bundle mainly contains carbon fiber filaments" means that the filament that accounts for the largest proportion of the cross-sectional area of ​​the filament bundle is the carbon fiber filament. In this case, the proportion of carbon fiber filaments to the cross-sectional area of ​​the filament bundle may be, for example, 50% or more. Also, "the filament bundle consists substantially of carbon fiber filaments" means that the proportion of carbon fiber filaments to 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 reinforcing cords can be used, such as glass fiber filaments.

[0038] There are no particular restrictions on the number of filaments included in a filament bundle. A filament bundle can contain, for example, 1,000 to 48,000 filaments. Preferably, it can contain 6,000 to 48,000 filaments. More preferably, it can 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 forming a coating on such a thick filament bundle, the inside of the filament bundle usually becomes difficult to dry, so the drying temperature during coating formation becomes high and the drying time becomes long, the surface hardening reaction progresses and it becomes hard, making it difficult to obtain a high modulus rubber reinforcing cord. In addition, carbon fibers have a higher modulus than other fibers such as aramid fibers, so they are susceptible to the decrease in modulus that occurs when forming a coating. However, in this embodiment, by setting the liquid component content to within the range of 0.2 mass% or more and 13 mass% or less, even when using a filament bundle containing carbon fiber filaments within the above thickness range, the decrease in the tensile modulus of the rubber reinforcing cord caused by coating formation is suppressed or the degree of decrease is kept small, thereby realizing a high modulus rubber reinforcing cord.

[0040] The surface of the carbon fiber filaments contained in the filament bundle is preferably pre-treated to enhance adhesive strength. A preferred example of a pre-treatment agent is a compound containing at least one functional group selected from the group consisting of epoxy groups and amino groups. Examples of pre-treatment 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, the Epiclon series from DIC, and the Epicote series from Mitsubishi Chemical. Polyurethane resins and isocyanate compounds can also be used as pre-treatment agents. For example, a treatment agent containing at least one selected from the group consisting of epoxy resins, urethane resins, and isocyanate compounds may be used as a pre-treatment agent. By pre-treating with such a treatment agent, a resin layer containing at least one selected from the group consisting of epoxy resins, urethane resins, and isocyanate compounds is further provided between the filament bundle and the first coating. By using carbon fiber filaments with a pre-treated surface, it is possible to improve the adhesion between the matrix rubber and the rubber reinforcing cord. If the filament bundle includes other fiber filaments besides carbon fiber filaments (for example, glass fiber filaments), it is preferable that the surface of those fiber filaments is also pre-treated to improve the adhesive strength as described above.

[0041] There is no limit to the number of filament bundles included in the rubber reinforcement cord; it may be one or multiple. A filament bundle may be made up of multiple filament bundles bundled together. 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 when combined.

[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 it may cover the surface of the filament bundle via another layer (for example, a coating formed by the filament pretreatment described above (for example, the resin layer)).

[0043] The first coating is formed by supplying the first aqueous coating agent, described below, to at least a portion of the surface of the filament bundle and drying it by heat treatment. The supply of the first aqueous coating agent to the surface of the filament bundle can be carried out, for example, by impregnating the filament bundle with the first aqueous coating agent, or by applying the first aqueous coating agent to at least a portion of the surface of the filament bundle. The heat treatment at this time removes almost all of the moisture contained in the filament itself and the solvent (e.g., water) of the aqueous coating agent.

[0044] The first coating contains a rubber component. Preferably, the rubber component 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 it may contain multiple types. In this specification, unless otherwise specified, the term "nitrile rubber" means nitrile rubber that has not been hydrogenated or carboxyl-modified (acrylonitrile-butadiene copolymer rubber).

[0045] The first coating may contain other rubbers in addition to the rubbers mentioned above. Examples of other rubbers include 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 crosslinking agents such as p-quinone dioxime, methacrylate 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, isocyanate compounds such as aromatic or aliphatic organic diisocyanates, polyisocyanates, blocked isocyanates, and blocked polyisocyanates, aromatic nitroso compounds, sulfur, and peroxides. These crosslinking agents may be used individually or in combination of several types. These crosslinking agents are preferably selected considering the type of rubber contained in the first coating and the type of matrix rubber into which the rubber reinforcing cords are embedded. Furthermore, these crosslinking agents are preferably used in the form of an aqueous dispersion in order to ensure a homogeneous presence of the crosslinking agents in the aqueous treatment agent used to produce the first coating.

[0047] The crosslinking agent preferably comprises at least one selected from the group consisting of maleimide-based crosslinking agents and isocyanate compounds. Among maleimide-based crosslinking agents, 4,4'-bismaleimidediphenylmethane is preferably used because it has good stability when dispersed in water, high crosslinking effect, and high heat resistance after crosslinking. As an isocyanate compound, for example, blocked isocyanate is used. By combining maleimide-based crosslinking agents and isocyanate compounds with rubber latex, the adhesion between the reinforcing cord and the matrix rubber can be specifically enhanced. In particular, the combination of 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 covalent 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, in the range of 100 to 200 nm, and more preferably in the range of 130 to 170 nm. The average particle size of silica is preferably in the range of 5 to 200 nm, for example, in the range of 7 to 100 nm, and more preferably in the range of 7 to 30 nm. Here, the average particle size is the value obtained by measuring the particle size of 50 or more particles using a transmission electron microscope and dividing the sum of the particle sizes by the number of particles measured. If the particles are not spherical, the average of the longest and shortest diameters of each particle is used as the particle size.

[0050] The filler, dispersed within the rubber, improves properties such as the tensile strength and tear strength of the coating. In addition to these effects, the filler also improves adhesive strength by increasing the cohesive force of the adhesive components between the fibers and the coating, and between the coating and the matrix rubber. These effects are significantly influenced by the particle size and amount of the filler used.

[0051] The first coating preferably does not contain resorcinol-formaldehyde condensate. In that case, it becomes unnecessary to use environmentally harmful substances such as formaldehyde and ammonia when producing the first coating, thus eliminating the need for environmental measures for workers.

[0052] The first coating may further contain, in addition to the rubber component and crosslinking agent, fillers and other components (for example, metal oxides other than the metal oxides added as fillers, or resins).

[0053] The content of the rubber component and the crosslinking agent in the first coating is 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 crosslinking agent in the first coating can be, for example, within the range of 10% by mass or more and 50% by mass or less.

[0054] The mass of the first coating, which is provided on at least the surface of the filament bundle, is not particularly limited and can be adjusted as appropriate, but it is preferably set to be within the range of 5% or more and 35% or less of the mass of the filament bundle. The mass of the first coating may also be within the range of 10% or more and 25% or less of the mass of the filament bundle, or within the range of 12% or more and 22% or less. 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 prone to fraying, or the function of the first coating in protecting the fibers may decrease, which may result in a reduced lifespan of the rubber product.

[0055] To improve adhesion to the matrix rubber, the rubber reinforcing cord of this embodiment may further comprise a second coating formed on the first coating. The treatment agent for 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 with a treatment agent whose components and solvents differ from those of the aqueous treatment agent for the first coating. 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 added to a single strand (hereinafter sometimes referred to as "undertwist") 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 added to multiple strands (hereinafter sometimes referred to as "overtwist") may also be, for example, in the range of 20 to 160 twists / m, 30 to 120 twists / m, or 40 to 100 twists / m. The undertwist direction and the overtwist direction may be the same Lang twist, or the undertwist direction and the overtwist direction may be opposite Moro twist. There is no limit to the direction of the twist; it may be in the S direction or the Z direction.

[0057] The liquid component content in the rubber reinforcement cord of this embodiment is within the range of 0.2% by mass or more and 13% by mass or less. As mentioned above, this liquid component refers to residual solvents (e.g., water) contained in the aqueous treatment agent used to produce the coating, or moisture contained in the filament itself. In the rubber reinforcement cord of this embodiment, by adjusting the amount of heat during the heat treatment when producing the first coating so that a liquid component remains in the rubber reinforcement cord within the range of 0.2% by mass or more and 13% by mass or less, the temperature rise of the rubber reinforcement cord, i.e., the hardening reaction of the coating, can be suppressed. This prevents the rubber reinforcement cord from becoming too hard due to the hardening reaction of the coating, and suppresses or reduces the degree of decrease in the tensile modulus of the rubber reinforcement cord compared to conventional methods. As a result, the tensile modulus of the rubber reinforcement cord can be improved compared to conventional methods, achieving a higher tensile modulus than before. If the liquid component content is less than 0.2% by mass, that is, if the heat treatment during coating is carried out in such a way that almost all of the solvent in the coating agent and the moisture contained in the fibers are removed, the hardening reaction of the coating on the resulting rubber-reinforced cord will proceed, reducing the tensile modulus of the rubber-reinforced cord, and consequently, the tensile strength of the rubber-reinforced cord will also decrease. On the other hand, if the liquid component content exceeds 13% by mass, it becomes difficult to create the cord by twisting strands, for example.

[0058] To obtain a rubber reinforcing cord with a higher tensile modulus, the liquid component content in the rubber reinforcing cord is preferably 0.2% by mass or more and 5% by mass or less.

[0059] Here, the "liquid component content in rubber-reinforced cord" as specified in this invention is a value that can be determined as follows: A 5m length of cord is taken from the rubber-reinforced cord as a sample, and the sample is measured using an electronic balance. This value is defined as the mass A of the cord. The sample is placed in a dryer heated to 150°C for 30 minutes to remove the solvent from the sample, and after placing it in a desiccator for 30 minutes, the value measured using an electronic balance is defined as the mass B. The difference between mass A and mass B is defined as the mass of the liquid component (AB) contained in the cord. The percentage of the mass of the liquid component (AB) contained in the cord relative to the mass A of the cord ({(AB) / A} × 100) is defined as the liquid component content (%). Here, it is assumed that the solvent of the treatment agent is water, and 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 should be set to completely remove that solvent.

[0060] An example of a method for manufacturing the rubber reinforcing cord of this embodiment is described below. Note that the matters described for the rubber reinforcing cord of this embodiment can also be applied to the following manufacturing method, and therefore, redundant explanations may be omitted. Furthermore, the matters described for the following manufacturing method can also be applied to the rubber reinforcing cord of this embodiment.

[0061] An example of a method for manufacturing the rubber reinforcing cord of this embodiment is: (a) Bundling together multiple filaments containing carbon fiber filaments to create at least one filament bundle, (b) Forming a first coating so as to cover at least a portion of the surface of the filament bundle to produce a strand, Includes.

[0062] First, a filament bundle is prepared by bundling multiple filaments together. Next, an aqueous treatment agent (aqueous treatment agent for the first coating) used to prepare the first coating is prepared. Then, 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 heat treatment is performed to remove the solvent in the aqueous treatment agent for the first coating. As a specific example, first, 12,000 filaments are drawn together to form a single bundle, and the 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 heat treatment. The filament bundle contains 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 Figure 1. Figure 1 shows a strand 10 as an example of a strand, which includes a filament bundle 11 and a first coating 12 covering the surface of the filament bundle 11. The strand 10 shown in Figure 1 may be used as a rubber reinforcing cord. That is, the rubber reinforcing cord of this embodiment may, as an example, have a configuration in which the first coating 12 is formed on the surface of a single filament bundle 11, as shown in Figure 1. However, the rubber reinforcing cord of this embodiment is not limited to this, and a strand may be formed by combining multiple filament bundles and forming the first coating on their surface. Furthermore, there is no limit to the method of supplying the aqueous coating agent to at least a portion of the surface of the filament bundle; for example, the aqueous coating agent may be applied to the surface of the filament bundle, or the filament bundle may be immersed in the aqueous coating agent. The material constituting the first coating 12 may be entirely or partially permeated into the filament bundle 11. In other words, the component indicated by reference numeral 11 in Figure 1 may include a filament bundle and the material for 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 should be appropriately adjusted so that the liquid component content of the cord obtained after heat treatment is 0.2% by mass or more and 13% by mass or less. Preferably, the treatment temperature and treatment time should be appropriately adjusted so that the liquid component content of the cord obtained after heat treatment is 0.2% by mass or more and 5% by mass or less. The treatment temperature is preferably 220°C or lower. The treatment time is not particularly limited, and should be appropriately adjusted considering the heat treatment temperature so that the amount of heat applied is such that the liquid component content in the completed rubber reinforcement 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, an appropriate treatment temperature may be adjusted 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, then the processing time should be set longer if the processing temperature remains the same. Conversely, if the liquid to be removed contains a liquid with a lower heat of vaporization than water, then the processing time should be set shorter if the processing temperature remains the same.

[0065] In step (b) above, a strand may be formed by twisting the filament bundle with the first coating after forming a first coating so as to cover at least a part of the surface of the filament bundle. In this case, the filament bundle with the first coating is twisted in one direction, for example. The direction of twisting may be the S direction or the Z direction. The number of filaments in the filament bundle and the number of twists of the filament bundle have been described above, so their explanation is omitted. In this way, the rubber reinforcing cord of this embodiment can be manufactured. Note that multiple filament bundles with the first coating may be formed, and these multiple filament bundles may be bundled together and then twisted upwards. The direction of the upward twist may be the same as the direction of the twist of the filament bundle (the direction of the downward twist), or it may be different. Alternatively, multiple filament bundles with the first coating may be formed, and twist may not be applied to each individual filament bundle, but rather to a bundle of multiple filament bundles.

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

[0067] In a preferred example of the manufacturing method of this embodiment, a first coating is formed by applying or impregnating a filament bundle with a first aqueous coating agent, and then twisting it in one direction to form a rubber reinforcing cord.

[0068] When forming a second coating on a first coating, the second coating can be formed by applying a treatment agent for forming the second coating onto the first coating and removing the solvent in the treatment agent. The type of this second coating can be appropriately selected according to the matrix rubber of the rubber product to which the rubber reinforcing cord is applied, and it is particularly desirable to select it from the viewpoint 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 a rubber reinforcing cord 20 as an example of a rubber reinforcing cord, which further comprises 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 of the second coating agent are not particularly limited, but it is preferable to adjust the treatment temperature and treatment time as appropriate so that the liquid component content of the cord obtained after heat treatment satisfies the above range.

[0070] Next, we will describe the first aqueous coating agent.

[0071] The first aqueous coating agent 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 coating agent may contain only one of these rubber latexes, or it may contain multiple types of these rubber latexes.

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

[0073] The first aqueous coating agent further contains a crosslinking agent. The crosslinking agent contained in the first aqueous coating agent is the same as the crosslinking agent contained in the first coating described above, so its explanation is omitted here. It is preferable to use the crosslinking agent in the form of an aqueous dispersion in order to ensure that it is homogeneously present in the aqueous coating agent.

[0074] The first aqueous coating agent may further contain a filler. The filler contained in the first aqueous coating agent is the same as the filler contained in the first coating described above, so its description is omitted here.

[0075] The first aqueous coating agent is preferably free of resorcinol-formaldehyde condensates.

[0076] The first aqueous coating agent may contain, in addition to rubber latex and crosslinking agent, fillers and other components. For example, the first aqueous coating agent may contain resin, plasticizer, antioxidant, stabilizer, metal oxides other than those added as fillers, etc. However, the aqueous coating agent may not contain resin.

[0077] In the above, examples of rubber reinforcing cords of this embodiment mainly consist of a single strand as shown in Figures 1 and 2, but the rubber reinforcing cord of this embodiment is not limited to this. Another example of the rubber reinforcing cord of this embodiment will be described below.

[0078] The rubber reinforcing cord of this embodiment may have multiple strands. Figure 3 shows an example of a rubber reinforcing cord with multiple strands, as another example of the rubber reinforcing cord of this embodiment.

[0079] The rubber-reinforced cord 30 shown in Figure 3 comprises 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 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 to cover at least a portion of the surface of the filament bundle 35. The carbon fiber strand 31, thus positioned towards 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 alleviate tensile and compressive stresses, thereby improving the bending fatigue resistance of the reinforcement cord 30. The filament bundle 33 containing carbon fiber filaments only needs to contain carbon fiber filaments, but may also be formed solely from carbon fiber filaments. Furthermore, the filament bundle 35 containing glass fiber filaments only needs to contain glass fiber filaments, but may also be formed solely from glass fiber filaments.

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

[0081] The number of carbon fiber strands 31 and the number of glass fiber strands 32 can be selected according to the properties required by the code and the properties of the strands. Preferred examples of the ratio of [number of carbon fiber strands] / [number of glass fiber strands] include, for example, [1] / [3-30], [2] / [6-30], and [3] / [10-40].

[0082] In a rubber-reinforced cord as described above, comprising a carbon fiber strand and a plurality of glass fiber strands arranged around the carbon fiber strand, a second coating may be further formed on top of the first coating. That is, as shown in Figure 4, the rubber-reinforced cord 40 may have a configuration comprising 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 top of the first coating 35 of the glass fiber strand 32. In this case, as shown in Figure 4, it is preferable to arrange the plurality of glass fiber strands 32 densely around the carbon fiber strand 31 so that the second coating 41 does not come into contact with the surface of the carbon fiber strand 31 (i.e., the first coating 34 of the carbon fiber strand 31). By having the second coating 41 not come into contact with the surface of the carbon fiber strand 31 in this way, the bending fatigue resistance of the rubber-reinforced cord can be further improved. Furthermore, the above-mentioned dense arrangement of multiple glass fiber strands 32 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 such 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 such that there are no gaps between the glass fiber strands 32.

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

[0084] (Second Embodiment) As a second embodiment, an embodiment of the 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 fibers as reinforcing fibers and has an improved tensile modulus compared to conventional rubber reinforcing cords containing carbon fibers. By including such a rubber reinforcing cord, the rubber product of this embodiment can become a high-strength rubber product with a high tensile modulus.

[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 tires for automobiles and bicycles, and rubber belts such as power transmission belts. Examples of power transmission belts include interlocking power transmission belts and friction power transmission belts. Examples of interlocking power transmission belts include toothed belts, such as timing belts for automobiles. Examples of friction power transmission belts include flat belts, round belts, V-belts, V-ribbed belts, etc. In other words, the rubber product of this embodiment may be a toothed belt, a flat belt, a round belt, a V-belt, or a V-ribbed belt.

[0087] The rubber product of this embodiment is formed by embedding the rubber reinforcing cord of this embodiment into a rubber composition (matrix rubber). The method of embedding the rubber reinforcing cord into the matrix rubber is not particularly limited, and known methods may be applied. The rubber product of this embodiment (for example, a rubber belt) has the rubber reinforcing cord of this embodiment embedded in it. 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 high elastic modulus and strength, such as rear-wheel drive for two-wheeled vehicles, timing belts for vehicle engines, auxiliary drive belts for vehicles, and large industrial equipment.

[0088] The rubber contained in the rubber composition into 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 (for example, 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. It is preferable from the viewpoint of adhesion that the coating of the rubber reinforcing cord and the rubber composition of the rubber product contain the same type of rubber or are 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 body 61 and a plurality of rubber reinforcing cords 62. The belt body 61 includes a belt portion 63 and a plurality of teeth 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. [Examples]

[0090] The embodiments of the present invention will be described in more detail below with reference to examples and comparative examples.

[0091] [Manufacturing of rubber reinforcement cords] (Examples 1-10 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 aqueous coating agent with the composition shown in Table 1 was applied to this filament bundle. Subsequently, the residence time in a drying oven set at 150°C was adjusted to control the liquid component content. In this way, strands with a first coating formed on the surface of the filament bundle were formed. The amount of the first aqueous coating 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 in a Z-twist at a rate of 60 turns / m. A second coating was formed on the surface of the resulting cord. For the second coating agent, a composition of Chemloc 233X (manufactured by Rhode Japan Inc.) and xylene mixed in a mass ratio of 1:1 was used. The second coating was formed to be 5% of the mass of the cord before the second coating was formed (i.e., in this case, the strands on which the first coating was formed on the surface of the filament bundle). The second coating agent was dried at 130°C for 1 minute. In this way, a rubber-reinforced cord was obtained. The obtained rubber-reinforced cord had a cross-section similar to that of the reinforced cord shown in Figure 2.

[0092] (Comparative Example 2) As the first aqueous coating agent, as shown in Table 1, an RFL treatment agent was used, which was prepared by mixing 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), and adjusting the resulting mixture with ammonia to a pH of 10. This RFL treatment agent was applied to filament bundles prepared in the same manner as in Examples 1-10 and Comparative Example 1. Then, the bundles were treated in a drying oven set to 200°C for a residence time of 2 minutes. Strands were formed in this manner. The amount of RFL treatment agent applied was adjusted so that the mass of the formed first coating was 20% of the mass of the filament bundle. Then, twisting and formation of the second coating were performed in the same manner as in Examples 1-10 and Comparative Example 1.

[0093] (Examples 11-13 and Comparative Example 3) Except for using a treatment agent with the composition shown in Table 2 as the first aqueous coating agent, twisting four strands in a Z-twist at a rate of 40 turns / m during the twisting process, and forming a second coating after twisting, rubber-reinforced cords for Examples 11-13 and Comparative Example 3 were obtained in the same manner as for Examples 1-10 and Comparative Example 1. The obtained rubber-reinforced cords had the cross-section shown in Figure 7. Figure 7 shows a cross-section of a rubber-reinforced cord 70 having a structure in which four carbon fiber strands 73, each with 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 on top of them.

[0094] (Examples 14, 15, and Comparative Example 4) Except for changing the number of carbon fiber filaments bundled to produce one filament bundle to 24,000, using a treatment agent with the composition shown in Table 3 as the first aqueous coating agent, and twisting each strand in a Z-twist at a rate of 40 turns / m during the twisting process, rubber-reinforced cords for Examples 14, 15, and Comparative Example 4 were obtained in the same manner as for Examples 1 to 10 and Comparative Example 1. The obtained rubber-reinforced cords had a cross-section similar to that of the reinforcement cord shown in Figure 2.

[0095] (Examples 16, 17, and Comparative Example 5) As the strand positioned in the center, a carbon fiber strand was used, in which a first coating was formed on the surface of a filament bundle made of carbon fiber filaments. As the strand positioned on the outer periphery of this carbon fiber strand, a glass fiber strand was used, in which a first coating was formed on the surface of a filament bundle made of glass fiber filaments. The carbon fiber strand was prepared in the same manner as the strands prepared in Examples 1 to 10 and Comparative Example 1. However, the aqueous treatment agent for the first coating had the composition shown in Table 4. For the glass fiber strand, a filament bundle was prepared by bundling 600 K glass filaments (manufactured by Nippon Sheet Glass Co., Ltd.) with an average diameter of 7 μm, and a first coating similar to that of the carbon fiber strand was formed on the surface of this filament bundle to prepare the glass fiber strand. Fifteen of these glass fiber strands, which were initially twisted at a rate of 80 turns / m, were used. For the glass fiber strand, the drying conditions during the formation of the first coating were set so that the liquid component content was similar to that of the carbon fiber strand. A single carbon fiber strand was placed in the center, and 15 glass fiber strands were arranged around it to form a second coating. The second coating was prepared in the same manner as in Examples 1-10 and Comparative Example 1. The resulting rubber-reinforced cords (rubber-reinforced cords of Examples 16, 17, and Comparative Example 5) had a cross-section similar to that of the reinforcement cord shown in Figure 4.

[0096] (Examples 18-20, Comparative Example 6) Except for using a treatment agent with the composition shown in Table 5 as the first aqueous coating agent and not forming a second coating, rubber reinforcing cords for Examples 1-10 and Comparative Example 1 were obtained in the same manner as for Comparative Examples 18-20 and Comparative Example 6. The obtained rubber reinforcing cords were reinforcing cords without a second coating and had a cross-section similar to that of the reinforcing cord shown in Figure 1.

[0097] (Comparative Example 7) A rubber reinforcing cord for Comparative Example 7 was obtained in the same manner as for Comparative Example 2, except that a second coating was not formed. The obtained rubber reinforcing cord was a reinforcing cord without a second coating and had a cross-section similar to that of the reinforcing cord shown in Figure 1.

[0098] (Example 21 and Comparative Example 8) Except for not forming a second coating, rubber reinforcing cords for Example 21 and Comparative Example 8 were obtained using the same method as in Examples 11-13 and Comparative Example 3, with the first aqueous coating agent having the composition shown in Table 6. 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 for Example 21 and Comparative Example 8 had the cross-section shown in Figure 8.

[0099] (Examples 22, 23, and Comparative Example 9) Except for changing the number of carbon fiber filaments bundled to produce one filament bundle to 6,000, using a treatment agent with the composition shown in Table 7 as the first aqueous coating agent, twisting each strand 80 times / m in an S-twist or Z-twist during the twisting process (Example 22: S-twist, Example 23 and Comparative Example 9: Z-twist), and not forming a second coating, the rubber-reinforced cords of Examples 22, 23, and Comparative Example 9 were obtained in the same manner as Examples 1 to 10 and Comparative Example 1. The obtained rubber-reinforced cords were reinforced cords without a second coating and had a cross-section similar to the reinforced cord shown in Figure 1.

[0100] (Examples 24, 25, and Comparative Example 10) Except for changing the number of carbon fiber filaments bundled to produce one filament bundle to 3000, using a treatment agent with the composition shown in Table 8 as the first aqueous coating agent, twisting each strand in a Z-twist at a rate of 120 turns / m during the twisting process, and not forming a second coating, rubber-reinforced cords for Examples 24, 25, and Comparative Example 10 were obtained in the same manner as for Examples 1 to 10 and Comparative Example 1. The obtained rubber-reinforced cords were reinforced cords without a second coating and had a cross-section similar to that of the reinforced cord shown in Figure 1.

[0101] (Examples 26, 27, and Comparative Example 11) As the strand positioned in the center, a carbon fiber strand was used, in which a first coating was formed on the surface of a filament bundle made of carbon fiber filaments. As the strand positioned on the outer periphery of this carbon fiber strand, a glass fiber strand was used, in which a first coating was formed on the surface of a filament bundle made of glass fiber filaments. The carbon fiber strand was prepared in the same manner as the strands prepared in Examples 1 to 10 and Comparative Example 1. However, the aqueous treatment agent for the first coating had the composition shown in Table 9, and for Examples 23 and 27, the twist direction was S-twist. For the glass fiber strand, a filament bundle was prepared by bundling 600 K glass filaments (manufactured by Nippon Sheet Glass Co., Ltd.) with an average diameter of 7 μm, and a first coating similar to that of the carbon fiber strand was formed on the surface of this filament bundle to prepare the glass fiber strand. Fifteen of these glass fiber strands, which had been under-twisted at a rate of 80 turns / m, were used. The drying conditions for the first coating were set so that the liquid component content of the glass fiber strands was similar to that of the carbon fiber strands. One carbon fiber strand was placed in the center, and 15 glass fiber strands were arranged around it. No second coating was formed. The resulting rubber-reinforced cords (rubber-reinforced cords of Examples 26, 27, and Comparative Example 11) had a cross-section similar to the reinforcement cord shown in Figure 3.

[0102] [Concentration of liquid components] Within 30 minutes of the heat treatment performed after applying the first aqueous coating agent to the filament bundle, a 5m length of cord was taken as a sample from the obtained rubber-reinforced cord. The sample was weighed using an electronic balance, and this value was defined as the cord mass A. Next, the sample was placed in a dryer heated to 150°C for 30 minutes to remove the solvent from the sample, and after being placed in a desiccator for 30 minutes, the value measured using an electronic balance was defined as the mass B. The difference between mass A and mass B was defined as the mass of the liquid component contained in the cord (AB). The percentage of the mass of the liquid component contained in the cord (AB) relative to the cord mass A ({(AB) / A} × 100) was calculated to determine the liquid component content (%). Tables 1 to 9 show the liquid component content of the rubber-reinforced cords for the examples and comparative examples.

[0103] [Tensile test] Tensile tests were conducted on the rubber reinforcing cords of each example and comparative example using a commonly used tensile testing machine and a commonly used cord grip, and the load at 0.8% elongation and tensile strength were measured. The conditions for the cord tensile test were a chuck spacing of 250 mm, an initial load of 10 N, and a tensile speed of 300 mm / min. The maximum load was defined as the tensile strength, and the load at which the cord elongated by 0.8% (2 mm) was defined as the load at 0.8% elongation. The tensile modulus of elasticity of the rubber reinforcing cords of each example and comparative example was evaluated based on 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] [Table 1]

[0105] [Table 2]

[0106] [Table 3]

[0107] [Table 4]

[0108] [Table 5]

[0109] [Table 6]

[0110] [Table 7]

[0111] [Table 8]

[0112] [Table 9]

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

[0114] The results of tensile tests were compared between examples and comparative examples with the same strand structure. 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, showed a higher load at 0.8% elongation and a higher tensile modulus compared to 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 by 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 strength comparable to or greater than that 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 similar results to the rubber reinforcing cords shown in Table 1.

[0115] For Examples 18-27 and Comparative Examples 6-11, where the second coating was not applied, the tensile test results were compared with other examples and comparative examples that had the same strand structure. As shown in Table 5, the rubber reinforcing cords of Examples 18-20, in which the liquid component content of the reinforcing cord was between 0.2% by mass and 13% by mass, showed a higher load at 0.8% elongation and a higher tensile modulus compared to 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 by 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 18-20 had tensile strength comparable to or greater than that of the rubber reinforcing cords of Comparative Examples 6 and 7. The rubber reinforcing cords of the examples and comparative examples shown in Tables 6-9 also showed similar results to the rubber reinforcing cords shown in Table 5. [Industrial applicability]

[0116] The rubber reinforcing cord of the present invention can achieve a high tensile modulus, making it applicable to reinforcing various rubber products. Furthermore, the rubber products of the present invention can withstand high loads, making them applicable to a wide range of uses.

Claims

1. A rubber reinforcing cord for reinforcing rubber products, The aforementioned rubber reinforcing cord comprises at least one strand, The strand comprises 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. It includes, The filament bundle includes carbon fiber filaments, The first coating comprises a rubber component and a crosslinking agent. The aforementioned rubber reinforcing cord further contains a liquid component, The liquid component content in the rubber reinforcing cord is within the range of 0.2% by mass or more and 13% by mass or less. Rubber reinforcement cord.

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

3. The rubber component includes 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 rubber reinforcing cord according to claim 1.

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

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

6. The mass of the first coating is within the range of 5% or more and 35% or less of the mass of the filament bundle. The rubber reinforcing cord according to claim 1.

7. The present invention further includes a second coating provided on the first coating, The rubber reinforcing cord according to claim 1.

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

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

10. A method for manufacturing a rubber reinforcing cord according to any one of claims 1 to 9, The aforementioned manufacturing method is (a) Bundling together multiple filaments containing carbon fiber filaments to produce at least one filament bundle, (b) Forming a first coating so as to cover at least a portion of the surface of the filament bundle to produce a strand, A method for manufacturing rubber-reinforced cords, including the method described above.

11. In (b) above, after forming the first coating so as to cover at least a portion of the surface of the filament bundle, the strand is formed by twisting the filament bundle on which the first coating has been formed. A method for manufacturing a rubber reinforcing cord according to claim 10.

12. In (b) above, the strand is formed by twisting the filament bundle and then forming the first coating so as to cover at least a portion of the surface of the twisted filament bundle. A method for manufacturing a rubber reinforcing cord according to claim 10.

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