Code for rubber reinforcement use

Abstract

The code for rubber reinforcement use according to the present invention comprises at least one strand. The strand comprises at least one filament bundle and a coating film that is provided so as to cover at least a part of the surface of the filament bundle. The coating film contains a rubber component (excluding a carboxyl-modified hydrogenated nitrile rubber), a maleimide-based crosslinking agent and an isocyanate compound as essential components, and also contains a filler as an optional component. In the coating film, the total amount of the maleimide-based crosslinking agent and the isocyanate compound is 10 to 100 parts by mass relative to 100 parts by mass of the rubber component, the ratio of the mass of the maleimide-based crosslinking agent to the mass of the isocyanate compound (i.e., a (mass of the maleimide-based crosslinking agent) / (mass of the isocyanate compound) ratio) is more than 1, and the content of the filler is less than 10 parts by mass relative to 100 parts by mass of the rubber component.

Description

Rubber Reinforcement Cord

[0001] The present invention relates to a cord for reinforcing rubber.

[0002] Rubber belts or metal chains are used to drive camshafts in automotive internal combustion engines, drive accessories such as injection pumps, and transmit power in industrial machinery. With growing interest in energy conservation in recent years, the use of rubber belts, which offer superior power transmission efficiency, has been attracting attention from the perspective of improving fuel economy. Rubber belts also have the advantage of being stronger and more elastic than metal chains, allowing them to be used under high-load conditions.

[0003] Generally, rubber products such as rubber belts include a matrix rubber and a rubber reinforcing cord embedded in the matrix rubber. The strength of the rubber belt depends on the strength of the rubber reinforcing cord. Therefore, the rubber reinforcing cord is an important component that determines the lifespan of the rubber belt.

[0004] Fraying of the rubber reinforcing cord may occur from the end surface of a rubber product containing the rubber reinforcing cord. For example, in toothed belts such as timing belts used primarily to drive the camshaft of an internal combustion engine, the rubber reinforcing cord is exposed on the side surface of the belt during the manufacturing process. This can lead to problems such as the rubber reinforcing cord fraying from the exposed portion, causing fibers to protrude from the end surface of the belt. When fibers protrude from the end surface of the belt, the fibers can easily become entangled around a pulley during use. Furthermore, fraying can lead to progressive damage to the rubber belt from the frayed portion. Therefore, to address problems such as reduced durability of rubber products, reinforcing cords that are less susceptible to fraying have been explored.

[0005] Patent Documents 1 to 3 disclose rubber reinforcing cords that are less likely to fray.

[0006] Patent Document 1 discloses a rubber reinforcing cord obtained by using glass fiber filaments as reinforcing fibers and appropriately selecting the number of twists of strands formed by bundling the glass fiber filaments.

[0007] Patent Document 2 discloses a cord obtained by using aramid fibers as reinforcing fibers, treating untwisted aramid fibers with an RFL (resorcinol-formalin-latex) solution, and then gathering and twisting a plurality of treated fibers.

[0008] Patent Document 3 discloses a rubber reinforcing cord obtained by forming a coating on the surface of a bundle of filaments, which are reinforcing fibers, using a specific aqueous treatment agent. The specific aqueous treatment agent used contains rubber latex, a crosslinking agent, and a filler, and the content of the crosslinking agent is in the range of 50 to 150 parts by mass per 100 parts by mass of the solid content contained in the rubber latex, and the content of the filler is in the range of more than 50 to 80 parts by mass.

[0009] JP 2010-111983 A JP 2008-208997 A International Publication No. 2015 / 098105

[0010] The above-mentioned conventional rubber reinforcing cords are not sufficient in terms of improving fray resistance while maintaining excellent flex resistance.

[0011] Therefore, an object of the present invention is to provide a cord for reinforcing rubber that can simultaneously satisfy both excellent fray resistance and excellent flex resistance.

[0012] 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 coating provided so as to cover at least a portion of the surface of the filament bundle, the coating including a rubber component (excluding carboxyl-modified hydrogenated nitrile rubber), a maleimide-based crosslinking agent, and an isocyanate compound as essential components, and including a filler as an optional component, the coating including: a total of 10 to 100 parts by mass of the maleimide-based crosslinking agent and the isocyanate compound per 100 parts by mass of the rubber component; a mass ratio of the maleimide-based crosslinking agent to the isocyanate compound (mass of the maleimide-based crosslinking agent / mass of the isocyanate compound) exceeding 1; and less than 10 parts by mass of the filler per 100 parts by mass of the rubber component.

[0013] The rubber reinforcing cord of the present invention can simultaneously satisfy both excellent fray resistance and excellent flex resistance.

[0014] FIG. 2 is a diagram schematically showing a method of a bending test carried out on the rubber reinforcing cords of Examples and Comparative Examples.

[0015] Hereinafter, embodiments of the rubber-reinforcing cord of the present invention will be specifically described.

[0016] The rubber reinforcing cord of this embodiment is a cord for reinforcing rubber products. This rubber reinforcing cord includes at least one strand. This strand includes at least one filament bundle (reinforcing fiber) and a coating provided so as to cover at least a portion of the surface of the filament bundle.

[0017] The coating contains a rubber component (excluding carboxyl-modified hydrogenated nitrile rubber), a maleimide-based crosslinking agent, and an isocyanate compound as essential components, and also contains a filler as an optional component. That is, the coating may or may not contain a filler.

[0018] In the coating, the total amount of the maleimide crosslinking agent and the isocyanate compound is 10 to 100 parts by mass per 100 parts by mass of the rubber component, and the mass ratio of the maleimide crosslinking agent to the isocyanate compound (mass of maleimide crosslinking agent / mass of isocyanate compound) exceeds 1. In addition, in the coating, the amount of the filler is less than 10 parts by mass per 100 parts by mass of the rubber component.

[0019] The rubber-reinforcing cord of this embodiment has a coating containing the above-mentioned rubber component and a maleimide-based crosslinking agent and an isocyanate compound used in combination as crosslinking agents. Furthermore, in the coating, the total content of the maleimide-based crosslinking agent and the isocyanate compound, the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound, and the content of the filler are specified within the above-mentioned ranges. The coating contains both the maleimide-based crosslinking agent and the isocyanate compound, which specifically enhances the crosslinking effect (adhesion). As a result, the fray resistance of the rubber-reinforcing cord of this embodiment is improved. Furthermore, by blending the maleimide-based crosslinking agent and the isocyanate compound in the coating so as to satisfy the above-mentioned conditions, the coating is prevented from hardening, thereby maintaining the excellent flex resistance of the rubber-reinforcing cord. Therefore, the rubber-reinforcing cord of this embodiment can improve its fray resistance while maintaining its excellent flex resistance, thereby simultaneously achieving both excellent fray resistance and excellent flex resistance.

[0020] The reinforcing cord of this embodiment will be described in more detail below.

[0021] In the rubber reinforcement cord of this embodiment, the filament bundle constituting the strand includes a plurality of filaments. The material of the filaments is not particularly limited. Examples of filaments that can be used for the rubber reinforcement cord of this embodiment include glass fiber filaments, polyvinyl alcohol fiber filaments typified by vinylon fiber, polyester fiber filaments, polyamide fiber filaments such as nylon and aramid fiber (aromatic polyamide), carbon fiber filaments, and polyparaphenylene benzobisoxazole (PBO) fiber filaments. Among these, it is preferable to use filaments of fibers that have excellent dimensional stability, tensile strength, modulus, and flexural fatigue resistance. For example, it is preferable to use at least one fiber filament selected from the group consisting of glass fiber filaments, aramid fiber filaments, polyparaphenylene benzobisoxazole fiber filaments, and carbon fiber filaments. The filament bundle may be composed of one type of filament or multiple types of filaments.

[0022] There is no particular limit to the number of filaments contained in the filament bundle, and the filament bundle may contain, for example, 200 to 48,000 filaments.

[0023] The surfaces of the filaments contained in the filament bundle may be pretreated to enhance adhesive strength. A preferred example of a 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 coating. By pretreating the surface, it is possible to improve the adhesion between the matrix rubber and the rubber reinforcing cord, even when using fiber filaments that are difficult to bond, such as polyparaphenylene terephthalamide fiber filaments. Note that the coating (pretreatment agent film) made of a pretreatment agent formed on the filament surface by pretreatment of the filament is different from the coating that covers at least a portion of the surface of the filament bundle, as specified in this embodiment, and is not included in the coating specified in this embodiment.

[0024] 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.

[0025] The coating is provided so as to cover at least a portion of the surface of the filament bundle. The 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 pretreatment agent film)). The rubber reinforcing cord of this embodiment does not need to be provided with any other coating besides this coating. In other words, in the rubber reinforcing cord of this embodiment, the coating covering the surface of the filament bundle may consist solely of the above-mentioned coating.

[0026] The coating is formed by applying an aqueous coating treatment agent (described below) to at least a portion of the surface of the filament bundle and then drying it by heat treatment. The aqueous coating treatment agent can be applied to the surface of the filament bundle, for example, by impregnating the filament bundle with the aqueous coating treatment agent or by applying the aqueous coating 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 coating treatment agent.

[0027] As described above, the coating contains a rubber component other than the carboxyl-modified hydrogenated nitrile rubber (X-HNBR). The rubber component may be, for example, at least one selected from the group consisting of butadiene-styrene copolymer, dicarboxylated butadiene-styrene polymer, vinylpyridine-butadiene-styrene terpolymer, chloroprene, butadiene rubber, chlorosulfonated polyethylene, nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), and carboxyl-modified nitrile rubber (X-NBR). The rubber component is preferably at least one selected from the group consisting of hydrogenated nitrile rubber and carboxyl-modified nitrile rubber.

[0028] As described above, the coating contains a maleimide-based crosslinking agent and an isocyanate compound. The maleimide-based crosslinking agent and the isocyanate compound function as crosslinking agents in the coating. That is, in this embodiment, the coating uses a maleimide-based crosslinking agent and an isocyanate compound in combination as crosslinking agents. In the coating, the total amount of the maleimide-based crosslinking agent and the isocyanate compound is 10 to 100 parts by mass, preferably 10 to 80 parts by mass, more preferably 30 to 80 parts by mass, and even more preferably 30 to 70 parts by mass, per 100 parts by mass of the rubber component. When the total amount of the maleimide-based crosslinking agent and the isocyanate compound is 10 to 80 parts by mass in the coating, better fray resistance and flex resistance can be achieved. When the total amount of the maleimide-based crosslinking agent and the isocyanate compound is 30 to 80 parts by mass in the coating, even better fray resistance and flex resistance can be achieved. When the total amount of the maleimide crosslinking agent and the isocyanate compound in the coating is 30 to 70 parts by mass, even better fray resistance and flex resistance (particularly, further improvement in flex resistance) can be achieved. The total amount of the maleimide crosslinking agent and the isocyanate compound may be 60 parts by mass or less per 100 parts by mass of the rubber component.

[0029] As described above, the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound in the coating exceeds 1. That is, the content of the maleimide-based crosslinking agent in the coating exceeds 1 times the content of the isocyanate compound. The mass ratio of the maleimide-based crosslinking agent to the isocyanate compound may be 1.5 or more, preferably exceeds 1.5, more preferably 2.0 or more, and even more preferably 3.0 or more. The upper limit of the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound is not particularly limited. The mass ratio is, for example, 20.0 or less, preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 6.0 or less.

[0030] The content of the maleimide-based crosslinking agent in the coating can be appropriately adjusted so as to satisfy the above-mentioned conditions, i.e., so as to satisfy the total mass of the maleimide-based crosslinking agent and the isocyanate compound, and the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound. The content of the maleimide-based crosslinking agent in the coating may be, for example, 5 to 95 parts by mass, 5 to 75 parts by mass, or 5 to 60 parts by mass per 100 parts by mass of the rubber component. Examples of maleimide-based crosslinking agents include bismaleimide, phenylmaleimide, and N,N'-m-phenylenedimaleimide. The maleimide-based crosslinking agent preferably contains 4,4'-bismaleimide diphenylmethane.

[0031] The content of the isocyanate compound in the coating can be appropriately adjusted so as to satisfy the above-mentioned conditions, i.e., so as to satisfy the total mass of the maleimide-based crosslinking agent and the isocyanate compound, and the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound. The content of the isocyanate compound in the coating may be, for example, 5 to 95 parts by mass, 5 to 75 parts by mass, or 5 to 60 parts by mass per 100 parts by mass of the rubber component. Examples of the isocyanate compound include aromatic or aliphatic organic diisocyanates, polyisocyanates, blocked isocyanates, and blocked polyisocyanates. The isocyanate compound preferably includes a blocked isocyanate.

[0032] For example, the coating preferably contains 30 to 80 parts by mass of the maleimide crosslinking agent and the isocyanate compound in total per 100 parts by mass of the rubber component, and the mass ratio of the maleimide crosslinking agent to the isocyanate compound is greater than 1 and not greater than 10. When the coating satisfies this configuration, a rubber-reinforcing cord that is particularly excellent in both fray resistance and flex resistance can be achieved.

[0033] The coating may further contain a filler. That is, the amount of filler in the coating may be more than 0 parts by mass and less than 10 parts by mass per 100 parts by mass of the rubber component. 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 complex metal oxide salts such as talc. When the filler is dispersed in the rubber, it has the effect of improving properties such as the tensile strength and tear strength of the coating. In addition to these effects, the filler also has the effect of improving the adhesive strength between the fiber and the coating and between the coating and the matrix rubber by increasing the cohesive force of the adhesive components. As described above, the content of the filler in the coating is less than 10 parts by mass, preferably 7 parts by mass or less, per 100 parts by mass of the rubber component. When the coating contains a filler, excellent flex resistance can be maintained by having the content of the filler in the coating be less than 10 parts by mass per 100 parts by mass of the rubber component. When the coating contains a filler, the content of the filler in the coating may be more than 0 parts by mass and 3 parts by mass or more per 100 parts by mass of the rubber component. Alternatively, the coating may not contain a filler (i.e., the content is 0 parts by mass).

[0034] It is preferable that the coating does not contain resorcinol-formaldehyde condensates. If the coating does not contain resorcinol-formaldehyde condensates, it becomes unnecessary to use substances that have a large environmental impact, such as formaldehyde and ammonia, when producing the coating. Therefore, environmental measures for workers are not required.

[0035] The coating may contain other components in addition to the above components.

[0036] The total content of the rubber component, isocyanate compound, bismaleimide compound, and filler (hereinafter sometimes simply referred to as "four components") in the coating is not particularly limited. The total content of the four components in the coating is desirably 70% by mass or more, and more desirably 90% by mass or more. The coating may be formed substantially only from the four components. "Formed substantially only from the four components" means that the total content of the four components in the coating is 95% by mass or more. The coating may also be formed only from the four components.

[0037] The proportion of the coating in the entire rubber reinforcing cord is not particularly limited and may be adjusted as appropriate, but is preferably provided so that it is within the range of 1 to 35% of the mass of the entire rubber reinforcing cord. The mass of the coating may be within the range of 10 to 30% or 15 to 30% by mass of the entire rubber reinforcing cord. If the mass of the 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 coating is too low, the strands may become more susceptible to fraying and the coating's ability to protect the fibers may be reduced, resulting in a shortened lifespan of the rubber product.

[0038] The rubber reinforcing cord of this embodiment may have another coating (hereinafter referred to as a "second coating") formed on its surface to improve adhesion to the matrix rubber. If the above-described coating alone does not provide sufficient adhesion to the matrix rubber of a rubber product, it is preferable to form a second coating on the surface of the twisted cord to enhance adhesion to the matrix rubber. The components of the second coating may be any that can improve adhesion to the matrix rubber. For example, a halogen-containing polymer adhesive (e.g., Chemlok, manufactured by Lord Corporation) or an adhesive containing H-NBR rubber and a crosslinking agent (e.g., a maleimide crosslinking agent) is preferably used.

[0039] 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.

[0040] An example of a manufacturing method for the rubber reinforcing cord of this embodiment will be described below. Note that the matters described for the rubber reinforcing cord of this embodiment can be applied to the manufacturing method below, so duplicated explanations may be omitted. Furthermore, the matters described in the manufacturing method below can be applied to the rubber reinforcing cord of this embodiment. This example of the manufacturing method includes the following steps.

[0041] First, a plurality of filaments are bundled to form a filament bundle, and then an aqueous treatment agent for coating is prepared. Next, the aqueous treatment agent for coating is applied to at least a portion of the surface of the filament bundle. After that, a heat treatment is performed to remove the solvent from the aqueous treatment agent for coating.

[0042] The above process forms a coating on at least a portion of the surface of the filament bundle. The method for supplying the aqueous treatment agent for coating to at least a portion of the surface of the filament bundle is not limited, and for example, the aqueous treatment agent for coating may be applied to the surface of the filament bundle, or the filament bundle may be immersed in the aqueous treatment agent for coating.

[0043] The conditions for the heat treatment to remove the solvent from the aqueous coating treatment agent are not particularly limited, but it is necessary to avoid drying under conditions that would cause the reaction of the crosslinking agent in the coating to proceed completely. Therefore, when drying is performed at a relatively high temperature (e.g., 80°C or higher), it is preferable to keep the drying time short (e.g., 5 minutes or less). For example, in an atmosphere of 150°C or less, the drying time may be 5 minutes or less. In one example, drying may be performed for 0.1 to 2 minutes in an atmosphere of 80°C to 280°C.

[0044] The coated filament bundle may be twisted 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 further explanation will be omitted. In this manner, the rubber reinforcing cord of this embodiment can be manufactured. Note that multiple coated filament bundles may be formed, and these multiple filament bundles may be bundled together and then twisted. 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 coated filament bundles may be formed, and twisting may be applied to the bundle of multiple filament bundles without twisting each filament bundle individually.

[0045] The coating may be formed after twisting the filament bundle, with the type, number and twisting degree of the filaments being as described above.

[0046] 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 coating, and then the bundle is twisted in one direction to form a rubber reinforcing cord.

[0047] Next, the aqueous treatment agent for coating will be described.

[0048] The aqueous treatment agent for coating preferably contains a latex of the rubber that constitutes the rubber component of the coating. For example, when the rubber component of the coating is a carboxyl-modified nitrile rubber, the aqueous treatment agent for coating contains a latex of the carboxyl-modified nitrile rubber. The aqueous treatment agent for coating may contain only one type of rubber latex or multiple types of rubber latexes depending on the rubber component of the coating.

[0049] The aqueous coating agent further contains a bismaleimide compound and an isocyanate compound. These components are the same as those described above, so further explanation is omitted here. It is preferable to use these components in the form of an aqueous dispersion in order to ensure that they are uniformly present in the aqueous coating agent.

[0050] The aqueous treatment agent for forming a coating may further contain a filler. Examples of the filler that may be contained in the aqueous treatment agent for forming a coating are the same as those described above as the filler contained in the coating, and therefore, further description thereof will be omitted here.

[0051] The aqueous coating treatment agent preferably does not contain resorcinol-formaldehyde condensation products.

[0052] The aqueous treatment agent for coating may further contain other components in addition to those described above. For example, the aqueous treatment agent for coating may further contain, as other components, a resin, a plasticizer, an antioxidant, a stabilizer, and the like.

[0053] The rubber reinforcing cord of this embodiment is used to reinforce rubber products. The rubber product reinforced with the rubber reinforcing cord of this embodiment is not particularly limited. Examples of rubber products reinforced with the rubber reinforcing cord of this embodiment include automobile or bicycle tires and power transmission belts. Examples of power transmission belts include meshing power transmission belts and friction power transmission belts. Examples of meshing power transmission belts include toothed belts such as automotive timing belts. Examples of friction power transmission belts include flat belts, round belts, V-belts, and V-ribbed belts. That is, the rubber product reinforced with the rubber reinforcing cord of this embodiment may be a toothed belt, flat belt, round belt, V-belt, or V-ribbed belt.

[0054] A rubber product reinforced with the rubber reinforcing cord 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 known methods may be applied. A rubber product (e.g., a rubber belt) in which the rubber reinforcing cord of this embodiment is embedded has excellent flex resistance and high durability. Therefore, the rubber reinforcing cord of this embodiment is particularly suitable for reinforcing rubber products such as timing belts for vehicle engines and belts for driving vehicle accessories.

[0055] Hereinafter, the embodiments of the present invention will be described more specifically with reference to examples and comparative examples.

[0056] [Manufacturing of Rubber Reinforcement Cord] (Example 1) 12,000 carbon fiber filaments were bundled to form a filament bundle. The average diameter of the carbon fiber filaments was 7 μm. The filament bundle was immersed in an aqueous coating treatment agent having the composition shown in Table 1 and then dried at 200°C for 2 minutes to obtain a carbon fiber cord having a coating. The rubber component contained in the treatment agent was carboxyl-modified nitrile rubber (X-NBR). This carbon fiber cord was twisted in one direction at a rate of 80 turns / m. Next, to improve adhesion to the matrix rubber, a halogen-containing polymer adhesive (Chemlock 402 (manufactured by Lord Corporation)) was applied to the coating and dried to form a second coating on top of the coating. In this way, the rubber reinforcing cord of Example 1 was obtained. The mass of the coating (excluding the second coating) in the rubber reinforcing cord was 20% of the mass of the entire rubber reinforcing cord.

[0057] Examples 2 to 11 Rubber-reinforcing cords of Examples 2 to 11 were produced under the same conditions as in Example 1, except that the composition of the aqueous treatment agent for coating was changed to the composition shown in Table 1.

[0058] Comparative Examples 1 to 14 Rubber-reinforcing cords of Comparative Examples 1 to 14 were produced in the same manner as in Example 1, except that the composition of the aqueous treatment agent for coating was changed to the composition shown in Table 2.

[0059] (Examples 12 to 16) Rubber-reinforcing cords of Examples 12 to 16 were produced under the same conditions as in Example 1, except that the composition of the aqueous treatment agent for coating was changed to the composition shown in Table 3. The rubber component contained in the treatment agent was hydrogenated nitrile rubber (HNBR).

[0060] (Comparative Examples 15 to 20) Rubber-reinforcing cords of Comparative Examples 15 to 20 were produced in the same manner as in Example 1, except that the composition of the aqueous treatment agent for coating was changed to the composition shown in Table 4. The rubber component contained in the treatment agent was hydrogenated nitrile rubber (HNBR).

[0061]

[0062]

[0063]

[0064]

[0065] [Evaluation of Rubber Reinforcement Cords] (Fray Resistance) First, the rubber reinforcing cords of each Example and Comparative Example were cut to a length of 200 mm to prepare samples for evaluating fray resistance. These samples were placed on the surface of a sheet-like (25 mm x 200 mm x 3 mm thick) matrix rubber precursor having the composition shown in Table 5 below, with the longitudinal direction of the sample aligned with the long side direction of the matrix rubber precursor and adjacent samples parallel to each other, with no gaps between them. Next, another sheet-like matrix rubber precursor of the same size as the matrix rubber precursor was placed on top of the matrix rubber precursor so as to sandwich the sample placed as above.

[0066] Next, the pair of precursors sandwiching the sample therebetween were hot-pressed from both sides at 150° C. for 20 minutes. The matrix rubber precursor contained a vulcanizing agent, and the matrix rubber was vulcanized by the hot press to produce a rubber sample in which the rubber reinforcing cord sample was embedded.

[0067] Next, the prepared rubber sample was cut in a direction parallel to the length direction of the rubber sample using a cutter, and the state of the end surface was visually evaluated. The evaluation was on a 5-point scale, with "5" indicating a smooth cut surface and no fraying of the carbon fibers at the cut surface, "4" indicating a smooth cut surface but a few carbon fibers fraying at the cut surface, "3" indicating a smooth cut surface but a few aramid fibers fraying at the cut surface and cracks in the cord, "2" indicating a smooth cut surface but several dozen carbon fibers fraying and protruding from the cut surface or a crack in the cord that protrudes from the crack as a starting point, and "1" indicating a cut surface that is not smooth at all. The evaluation results of the fray resistance of the rubber reinforcing cords of each Example and Comparative Example are shown in Tables 1 to 4.

[0068] (Flexibility) The rubber reinforcing cords of each Example and Comparative Example were embedded in a matrix rubber having the composition shown in Table 5 below to prepare samples (size: 300 mm x 10 mm x 3 mm) for evaluating flexibility.

[0069]

[0070] A bending test was conducted on each sample, in which the sample was bent 50,000 times. The bending test was conducted using a bending tester 10 shown in FIG. 1. The tensile strength of each sample was measured before and after the bending test. Here, the tensile strength was measured using a commonly used tensile tester and a commonly used cord grip, and the breaking strength (unit: N / cord) obtained at that time was used.

[0071] The bending tester 10 was equipped with one flat pulley 11 with a diameter of 10 mm, a motor (not shown), and four guide pulleys 12. First, the prepared sample 13 was placed on the five pulleys. Then, a weight was attached to one end 13a of the sample 13, and a load of 10 N was applied to the sample 13. In this state, the other end 13b of the sample 13 was reciprocated 50,000 times in the direction of the arrow shown in FIG. 1, thereby repeatedly bending the sample 13 at the flat pulley 11. The bending test was carried out at room temperature. After the bending test of the sample 13 was carried out in this manner, the tensile strength of the sample after the bending test was measured.

[0072] The tensile strength of the sample after the bending test was determined as a percentage of the tensile strength of the sample before the bending test, i.e., the strength retention (%). The higher the strength retention value, the better the bending resistance. The evaluation results of the bending resistance of the rubber reinforcing cords of each Example and Comparative Example are shown in Tables 1 to 4.

[0073] (Regarding evaluation results) In the coatings of the rubber-reinforcing cords of Examples 1 to 16, the total amount of the maleimide-based crosslinking agent and the isocyanate compound was 10 to 100 parts by mass per 100 parts by mass of the rubber component, the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound exceeded 1, and the amount of the filler per 100 parts by mass of the rubber component was less than 10 parts by mass. These rubber-reinforcing cords of Examples 1 to 16 had fray resistance of 4 or more and strength retention of 70% or more, and excellent results were obtained in both fray resistance and flex resistance.

[0074] In the coatings of the rubber-reinforcing cords of Examples 1 to 6, 9, 10, and 12 to 16, the total amount of the maleimide-based crosslinking agent and the isocyanate compound was 10 to 80 parts by mass per 100 parts by mass of the rubber component, and the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound exceeded 1. These rubber-reinforcing cords of Examples 1 to 6, 9, 10, and 12 to 16 had fray resistance of 4 or more and strength retention of 80% or more, and thus achieved even better results in both fray resistance and flex resistance.

[0075] In the coatings of the rubber-reinforcing cords of Examples 2 to 5, 9, 10, and 13 to 15, the total amount of the maleimide-based crosslinking agent and the isocyanate compound was 30 to 80 parts by mass per 100 parts by mass of the rubber component, and the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound was more than 1 and not more than 10. In these rubber-reinforcing cords of Examples 2 to 5, 9, 10, and 13 to 15, the fray resistance was scored out of 5 and the strength retention rate was 80% or more, and particularly excellent results were obtained in both fray resistance and flex resistance.

[0076] On the other hand, when the maleimide-based crosslinking agent and / or isocyanate compound were not added to the coating of the rubber reinforcing cords of Comparative Examples 1 to 20 (Comparative Examples 1 to 6, 9, and 15 to 17), the fray resistance was poor. Furthermore, in the rubber reinforcing cords of Comparative Examples 7, 8, 10 to 12, and 18 to 20, in which the total amount of crosslinking agent exceeded 100 parts by mass, fray resistance was improved, but the coating became hard, resulting in poor strength retention. Furthermore, in Comparative Example 14, in which the total amount of crosslinking agent was within the range of 10 to 100 parts by mass per 100 parts by mass of the rubber component, but the mass ratio of maleimide-based crosslinking agent to isocyanate compound was 1 or less, fray resistance was improved, but the coating became hard, resulting in poor strength retention. Furthermore, in the coating of the rubber reinforcing cord of Comparative Example 13, the total amount of crosslinking agent satisfied the range of 10 to 100 parts by mass per 100 parts by mass of the rubber component, and the mass ratio of the maleimide-based crosslinking agent to the isocyanate compound exceeded 1. However, since the carbon black was contained in an amount of 10 parts by mass or more per 100 parts by mass of the rubber component, while the fray resistance was improved, the coating became hard and the strength retention rate was poor.

[0077] The present invention can be used for a rubber reinforcing cord for reinforcing rubber products.

Claims

1. A rubber reinforcing cord for reinforcing a rubber product, The rubber reinforcing cord comprises at least one strand, The strand includes at least one filament bundle and a coating disposed so as to cover at least a portion of a surface of the filament bundle; The coating contains a rubber component (excluding carboxyl-modified hydrogenated nitrile rubber), a maleimide-based crosslinking agent, and an isocyanate compound as essential components, and contains a filler as an optional component; In the coating, the total amount of the maleimide-based crosslinking agent and the isocyanate compound is 10 to 100 parts by mass per 100 parts by mass of the rubber component, a mass ratio of the maleimide-based crosslinking agent to the isocyanate compound (mass of the maleimide-based crosslinking agent / mass of the isocyanate compound) is greater than 1; and The filler is less than 10 parts by mass based on 100 parts by mass of the rubber component. Rubber reinforcement cord.

2. In the coating, a mass ratio of the maleimide-based crosslinking agent to the isocyanate compound (mass of the maleimide-based crosslinking agent / mass of the isocyanate compound) is 1.5 or more. The rubber reinforcing cord according to claim 1.

3. In the coating, the maleimide-based crosslinking agent is contained in an amount of 5 to 95 parts by mass and the isocyanate compound is contained in an amount of 5 to 95 parts by mass per 100 parts by mass of the rubber component. The rubber reinforcing cord according to claim 1 or 2.

4. In the coating, the total amount of the maleimide-based crosslinking agent and the isocyanate compound is 10 to 80 parts by mass per 100 parts by mass of the rubber component. The rubber reinforcing cord according to claim 1 or 2.

5. In the coating, the maleimide-based crosslinking agent is contained in an amount of 5 to 75 parts by mass and the isocyanate compound is contained in an amount of 5 to 75 parts by mass per 100 parts by mass of the rubber component. The rubber reinforcing cord according to claim 4.

6. In the coating, The total amount of the maleimide-based crosslinking agent and the isocyanate compound is 30 to 80 parts by mass per 100 parts by mass of the rubber component, and a mass ratio of the maleimide-based crosslinking agent to the isocyanate compound (mass of the maleimide-based crosslinking agent / mass of the isocyanate compound) is greater than 1 and less than or equal to 10; The rubber reinforcing cord according to claim 1 or 2.

7. In the coating, The total amount of the maleimide-based crosslinking agent and the isocyanate compound is 30 to 70 parts by mass based on 100 parts by mass of the rubber component. The rubber reinforcing cord according to claim 6.

8. The rubber component is at least one selected from the group consisting of butadiene-styrene copolymer, dicarboxylated butadiene-styrene polymer, vinylpyridine-butadiene-styrene terpolymer, chloroprene, butadiene rubber, chlorosulfonated polyethylene, nitrile rubber, hydrogenated nitrile rubber, and carboxyl-modified nitrile rubber. The rubber reinforcing cord according to claim 1 or 2.

9. The rubber component is at least one selected from the group consisting of hydrogenated nitrile rubber and carboxyl-modified nitrile rubber. The rubber reinforcing cord according to claim 8.

10. The maleimide-based crosslinking agent includes 4,4'-bismaleimidodiphenylmethane. The rubber reinforcing cord according to claim 1 or 2.

11. The isocyanate compound includes a blocked isocyanate. The rubber reinforcing cord according to claim 1 or 2.