Rubber reinforcing cord and rubber product using same

Abstract

Provided are a rubber reinforcing cord suitable for improving flex fatigue resistance and a rubber product using the same.　A rubber reinforcing cord 10 includes a carbon fiber strand 11 and glass fiber strands 12. The glass fiber strands 12 are arranged around the carbon fiber strand 11. In a cross-sectional view of the rubber reinforcing cord 10, the ratio of the carbon fiber strand 11 covered by the glass fiber strands 12 is 80% or more.

Description

Cord for rubber reinforcement and rubber product using the same

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

[0002] Rubber products such as rubber belts and tires are repeatedly subjected to bending stress. As a reinforcing material for such rubber products, cords for rubber reinforcement formed using fibers are widely used. Patent Document 1 discloses a cord for rubber reinforcement in which a carbon fiber strand is used for a core portion, and a plurality of glass fiber strands are used for a skin portion around the core portion.

[0003] International Publication No. 2004 / 090224

[0004] According to studies conducted by the present inventors, there is room for improvement in the bending fatigue resistance of cords for rubber reinforcement.

[0005] An object of the present disclosure is to provide a cord for rubber reinforcement suitable for improving bending fatigue resistance and a rubber product using the same.

[0006] The present disclosure provides a cord for rubber reinforcement for reinforcing a rubber product, wherein the cord for rubber reinforcement comprises: a carbon fiber strand; and a plurality of glass fiber strands arranged around the carbon fiber strand, wherein in a cross-sectional view of the cord for rubber reinforcement, a coverage rate of the carbon fiber strand by the plurality of glass fiber strands is 80% or more.

[0007] According to the present disclosure, a cord for rubber reinforcement suitable for improving bending fatigue resistance and a rubber product using the same can be provided.

[0008] This is a cross-sectional view showing an example of a rubber reinforcing cord according to the first embodiment of this disclosure. This is a cross-sectional view showing another example of a rubber reinforcing cord according to the first embodiment of this disclosure. This is a cross-sectional view showing yet another example of a rubber reinforcing cord according to the first embodiment of this disclosure. This is a schematic perspective view showing an example of a rubber product according to the second embodiment of this disclosure. This is a diagram schematically showing the method of bending tests performed on the rubber reinforcing cords of the examples and comparative examples. This is a graph showing the relationship between the number of bends and tensile strength when a flat belt using the rubber reinforcing cord according to the examples and comparative examples is subjected to a bending test. This is a graph showing the relationship between the number of bends and strength retention rate when a flat belt using the rubber reinforcing cord according to the examples and comparative examples is subjected to a bending test.

[0009] Embodiments of the present disclosure will be described below with reference to the drawings. The following description is an example of the present disclosure, and the present disclosure is not limited to the embodiments described below. In this specification, the upper and lower limits of numerical ranges described below may be combined in any way, whether the upper and lower limits are described individually or as a range.

[0010] (First Embodiment) Figure 1 shows an example of a rubber reinforcing cord 10 according to the first embodiment of the present disclosure. The rubber reinforcing cord 10 comprises a carbon fiber strand 11 and a glass fiber strand 12. Multiple glass fiber strands 12 are arranged around the carbon fiber strand 11. In a cross-sectional view of the rubber reinforcing cord 10, the coverage rate of the carbon fiber strand 11 by the glass fiber strand 12 is 80% or more.

[0011] In this specification, the "coverage rate of the carbon fiber strand 11 by the glass fiber strand 12 (hereinafter simply referred to as "coverage rate R")" can be calculated from the following formula (1), where Dt is the total length of the outer circumference 15 of the carbon fiber strand 11 in a cross-sectional view of the rubber reinforcing cord 10, and Db is the total length of the outer circumference portion 16 of the carbon fiber strand 11 that is not covered by the glass fiber strand 12. R = (Dt - Db) / Dt × 100 [%] (1)

[0012] A cross-sectional view of the rubber reinforcing cord 10 can be obtained, for example, by exposing the cross-section of the rubber reinforcing cord 10 using a cutting tool such as a cutter or a grinder, and then observing the exposed cross-section of the rubber reinforcing cord 10 with a scanning electron microscope.

[0013] The rubber reinforcing cord 10 of this embodiment is suitable for improving bending fatigue resistance.

[0014] The coverage rate R may be, for example, 85% or more, 90% or more, or even 95% or more. Alternatively, the coverage rate R may be 99% or more, approximately 100%, or 100%.

[0015] The diameter of the rubber reinforcing cord 10 is not particularly limited. The diameter of the rubber reinforcing cord 10 may be, for example, 0.5 mm to 5 mm, 0.5 mm to 3 mm, 1.0 mm to 2 mm, or even 1.2 mm to 1.8 mm.

[0016] The diameter of the rubber reinforcement cord 10 can be measured, for example, with a dial thickness gauge.

[0017] The thread count (linear density) of the rubber reinforcing cord 10 is not particularly limited. The thread count of the rubber reinforcing cord 10 may be, for example, 200 tex to 20000 tex, 600 tex to 10000 tex, 1000 tex to 6000 tex, or even 1500 tex to 2500 tex.

[0018] The carbon fiber strand 11 may comprise a bundle of carbon fiber filaments 11a and a first coating 11b covering at least a portion of the surface of the bundle of carbon fiber filaments 11a. The glass fiber strand 12 may comprise a bundle of glass fiber filaments 12a and a second coating 12b covering at least a portion of the surface of the bundle of glass fiber filaments 12a.

[0019] In this specification, "carbon fiber strand" means that the filaments constituting the carbon fiber filament bundle mainly consist of carbon fiber filaments. "Mainly consisting of carbon fiber filaments" means that the filament that accounts for the largest proportion of the cross-sectional area of ​​the carbon fiber filament bundle is a carbon fiber filament. The carbon fiber filament bundle may be substantially composed of carbon fiber filaments. "The carbon fiber filament bundle is substantially composed of carbon fiber filaments" means that the proportion of carbon fiber filaments in the cross-sectional area of ​​the carbon fiber filament bundle is 90% or more, and this proportion may be 95% or more, or even 99% or more. The carbon fiber filament bundle may be composed of carbon fiber filaments only.

[0020] Furthermore, in this specification, "glass fiber strand" means that the filaments constituting the glass fiber filament bundle mainly consist of glass fiber filaments. "Mainly consisting of glass fiber filaments" means that the filament that accounts for the largest proportion of the cross-sectional area of ​​the glass fiber filament bundle is a glass fiber filament. The glass fiber filament bundle may consist substantially of glass fiber filaments. "The glass fiber filament bundle consists substantially of glass fiber filaments" means that the proportion of glass fiber filaments in the cross-sectional area of ​​the glass fiber filament bundle is 90% or more, and this proportion may be 95% or more, or even 99% or more. The glass fiber filament bundle may consist only of glass fiber filaments.

[0021] The rubber reinforcing cord 10 according to this embodiment will be described in more detail below.

[0022] (Carbon fiber strand) The diameter of the filaments contained in the carbon fiber filament bundle 11a of the carbon fiber strand 11 is, for example, 4 μm to 10 μm, and may be 5 μm to 9 μm.

[0023] The number of carbon fiber filaments contained in a single carbon fiber filament bundle 11a is not particularly limited. For example, the number of carbon fiber filaments contained in a single carbon fiber filament bundle 11a may be 1,000 to 80,000, 2,500 to 50,000, 6,000 to 40,000, 6,000 to 25,000, or even 10,000 to 15,000.

[0024] The yarn count (linear density) of the carbon fiber filament bundle 11a is not particularly limited. The yarn count of the carbon fiber filament bundle 11a may be, for example, 60 tex to 8000 tex, and may also be 180 tex to 3500 tex, 300 tex to 2000 tex, or even 600 tex to 1000 tex.

[0025] The carbon fiber filament bundle 11a may or may not be twisted. There is no limit to the number of carbon fiber filament bundles 11a; there may be one or more. The carbon fiber filament bundle 11a may be a bundle of multiple carbon fiber filament bundles. In this case, in each of the multiple carbon fiber filament bundles, the carbon fiber filaments may or may not be under-twisted. Also, each carbon fiber filament bundle 11a may or may not be over-twisted. The number of under-twists and over-twists of the carbon fiber filament bundle 11a may be, for example, 5.0 turns / 25 mm or less and 2.5 turns / 25 mm or less, respectively.

[0026] The surface of the carbon fiber filaments contained in the carbon fiber filament bundle 11a may be pre-treated to increase the 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 resin, urethane resin, and isocyanate compound is further provided between the carbon fiber filament bundle 11a and the first coating 11b. If the carbon fiber filament bundle 11a includes other fiber filaments other than carbon fiber filaments (for example, glass fiber filaments), it is preferable that the surface of those fiber filaments is also pre-treated to enhance the adhesive strength as described above.

[0027] The first coating 11b may be provided so as to cover at least a portion of the surface of the carbon fiber filament bundle 11a. The first coating 11b may be provided directly on the surface of the carbon fiber filament bundle 11a, or it may cover the surface of the carbon fiber filament bundle 11a via another layer (for example, a coating formed by the above-described pretreatment of the carbon fiber filaments (for example, the resin layer)).

[0028] The first coating 11b can be formed by supplying the first coating-forming treatment agent, described below, to at least a portion of the surface of the carbon fiber filament bundle 11a and drying it by heat treatment. The supply of the first coating-forming treatment agent to the surface of the carbon fiber filament bundle 11a can be carried out, for example, by impregnating the carbon fiber filament bundle 11a with the first coating-forming treatment agent, or by applying the first coating-forming treatment agent to at least a portion of the surface of the carbon fiber filament bundle 11a. In this case, the heat treatment substantially removes the moisture contained in the carbon fiber filament bundle 11a itself and the solvent (e.g., water) of the treatment agent.

[0029] The first coating 11b may contain 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 11b may contain only one type of the above 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).

[0030] The first coating 11b may contain other rubbers in addition to the rubber described above. Examples of other rubbers include butadiene-styrene copolymer, dicarboxylated butadiene-styrene copolymer, vinylpyridine-butadiene-styrene copolymer, chloroprene rubber, butadiene rubber, and chlorosulfonated polyethylene.

[0031] The first coating 11b may further contain a crosslinking agent. The inclusion of a crosslinking agent in the first coating 11b can improve the adhesion of the carbon fiber strand 11. 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 multiple types. These crosslinking agents may be selected considering the type of rubber contained in the first coating 11b and the types of other components that come into contact with the carbon fiber strands 11. These crosslinking agents can be used in the form of a dispersion, allowing them to be homogeneously present in the first coating-forming treatment agent.

[0032] The crosslinking agent may include 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. Blocked isocyanate compounds are used as examples. Maleimide-based crosslinking agents and isocyanate compounds can specifically enhance the adhesion between the reinforcing cord and the matrix rubber when combined with rubber latex. In particular, the combination of carboxyl-modified hydrogenated nitrile rubber latex and a maleimide-based crosslinking agent can further enhance adhesion.

[0033] The first coating 11b 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.

[0034] The average particle size of carbon black is, for example, 5 nm to 300 nm, but may also be 100 nm to 200 nm, or even 130 nm to 170 nm. The average particle size of silica is, for example, 5 nm to 200 nm, but may also be 7 nm to 100 nm, or even 7 nm to 30 nm. Here, the average particle size refers to 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 particle size is the average of the longest and shortest diameters of each particle.

[0035] The filler, dispersed within the rubber, has the effect of improving properties such as the tensile strength and peel 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.

[0036] Preferably, the first coating 11b 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 11b, thus eliminating the need for environmental measures for workers.

[0037] The first coating 11b 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).

[0038] The content of the rubber component and the crosslinking agent in the first coating 11b is not particularly limited. The content of the rubber component in the first coating 11b is, for example, 50% by mass to 90% by mass or less. The content of the crosslinking agent in the first coating 11b is, for example, 10% by mass to 50% by mass or less.

[0039] The first coating agent is a latex of at least one rubber selected from the group consisting of nitrile rubber, hydrogenated nitrile rubber, carboxyl-modified nitrile rubber, and carboxyl-modified hydrogenated nitrile rubber. The first coating agent may contain only one of these rubber latexes, or it may contain multiple types of these rubber latexes.

[0040] The first 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 first coating agent may contain multiple types of these rubber latexes.

[0041] The first film-forming treatment agent may further contain a crosslinking agent. An example of a crosslinking agent included in the first film-forming treatment agent is the same as the example described above as a crosslinking agent included in the first film 11b. It is preferable to use the crosslinking agent in the form of a dispersion in order to ensure that it is homogeneously present in the first film-forming treatment agent.

[0042] The first coating agent may further contain a filler. An example of a filler included in the first coating agent is the same as the example described above as a filler included in the first coating 11b.

[0043] The first coating agent is preferably free of resorcinol-formaldehyde condensates, but may contain resorcinol-formaldehyde condensates.

[0044] In addition to rubber latex and a crosslinking agent, the first treatment agent for film formation may further contain a filler and other components. For example, the first treatment agent for film formation may contain a resin, a plasticizer, an anti-aging agent, a stabilizer, a metal oxide other than the metal oxide added as the aforementioned filler, and the like. However, the first treatment agent for film formation may be free of resin.

[0045] The ratio of the mass of the first coating 11b to the mass of the carbon fiber filament bundle 11a (hereinafter referred to as the "deposition rate of the first coating 11b") is not particularly limited, and may be appropriately adjusted. The deposition rate of the first coating 11b is, for example, 5% to 35%, and may be 10% to 30%, or even 15% to 25%. When it is desired to sufficiently obtain the effects of suppressing fraying and protecting the carbon fiber strand 11, the deposition rate of the first coating 11b is preferably 5% or more. When it is desired to obtain sufficient dimensional stability of the carbon fiber strand 11 while obtaining an appropriate elastic modulus, the deposition rate of the first coating 11b is preferably 35% or less.

[0046] In order to improve the adhesiveness of the carbon fiber strand 11, an additional coating may be further provided on the first coating 11b. The treatment agent for forming the additional coating may be the same as or different from the first treatment agent for film formation. For example, the additional coating may be formed with a treatment agent whose components or solvent are different from those of the first treatment agent for film formation. In order to further improve the adhesiveness of the carbon fiber strand 11, a further coating may be provided on the additional coating.

[0047] (Glass Fiber Strand) The diameter of the filaments contained in the glass fiber filament bundle 12a of the glass fiber strand 12 is, for example, 4 μm to 12 μm, and may be 6 μm to 10 μm.

[0048] The number of glass fiber filaments contained in one glass fiber filament bundle 12a is not particularly limited. The number of glass fiber filaments contained in one glass fiber filament bundle 12a is, for example, in the range of 100 to 5000, and may be in the range of 200 to 3000, 300 to 2000, or even 500 to 1500.

[0049] The thread count (linear density) of the glass fiber filament bundle 12a is not particularly limited. The thread count of the glass fiber filament bundle 12a may be, for example, 20 tex to 350 tex, and may also be 40 tex to 210 tex, 60 tex to 150 tex, or even 60 tex to 80 tex.

[0050] The glass fiber filament bundle 12a may or may not be under-twisted. If the glass fiber filaments contained in the glass fiber filament bundle 12a are under-twisted, the number of under-twists in the glass fiber strands 12 may be, for example, 0.5 turns / 25 mm to 4.0 turns / 25 mm, 1.0 turns / 25 mm to 3.5 turns / 25 mm, or even 1.5 turns / 25 mm to 2.5 turns / 25 mm. The glass fiber filament bundle 12a may or may not be over-twisted. If the glass fiber filament bundle 12a is over-twisted, the number of over-twists in the glass fiber filament bundle 12a may be, for example, 0.1 turns / 25 mm to 3.0 turns / 25 mm, 0.5 turns / 25 mm to 3.0 turns / 25 mm, or even 1.0 turns / 25 mm to 2.0 turns / 25 mm.

[0051] When the glass fiber filament bundle 12a is under-twisted and over-twisted, the twisting method of the glass fiber filament bundle 12a may be a Lang twist where the under-twist direction and the over-twist direction are the same, or it may be a Moro twist where the under-twist direction and the over-twist direction are opposite. There is no limit to the direction of the twist; it may be in the S direction or the Z direction.

[0052] The surface of the glass fiber filaments contained in the glass fiber filament bundle 12a may be pre-treated to increase adhesive strength. Examples of pre-treatment agents are the same as those described above for the carbon fiber filaments of the carbon fiber filament bundle 11a.

[0053] The second coating 12b may be provided so as to cover at least a portion of the surface of the glass fiber filament bundle 12a. The second coating 12b may be provided directly on the surface of the glass fiber filament bundle 12a, or it may cover the surface of the glass fiber filament bundle 12a via another layer (for example, a coating similar to the coating formed by the pretreatment of the glass fiber filaments described above (for example, the resin layer)).

[0054] Examples of the material constituting the second coating 12b and the second coating-forming treatment agent are the same as the examples described above for the material constituting the first coating 11b and the first coating-forming treatment agent.

[0055] The ratio of the mass of the second coating 12b to the mass of the glass fiber filament bundle 12a (hereinafter referred to as the "adhesion rate of the second coating 12b") is not particularly limited and can be adjusted as appropriate. The adhesion rate of the second coating 12b is, for example, 5% to 35%, and may be 10% to 30%, or even 15% to 25%. If the effect of suppressing fraying and protecting the glass fiber strand 12 is to be sufficiently obtained, the adhesion rate of the second coating 12b is preferably 5% or more. If the dimensional stability of the glass fiber strand 12 is to be sufficiently obtained while obtaining an appropriate modulus of elasticity, the adhesion rate of the second coating 12b is preferably 35% or less.

[0056] To improve the adhesion of the glass fiber strands 12, an additional coating may be provided on the second coating 12b. The treatment agent for forming the additional coating may be the same as or different from the treatment agent for forming the second coating. For example, the additional coating may be formed using a treatment agent whose components and solvents are different from those of the treatment agent for forming the second coating. To further improve the adhesion of the glass fiber strands 12, an additional coating may be provided on the additional coating.

[0057] (Relationship between carbon fiber strands and glass fiber strands) The number of carbon fiber strands 11 and the number of glass fiber strands 12 can be selected according to the required properties of the rubber reinforcing cord 10 and the properties of the carbon fiber strands 11 and glass fiber strands 12. Preferred examples of the ratio of [number of carbon fiber strands] / [number of glass fiber strands] include [1] / [3 to 30], [2] / [6 to 30], and [3] / [10 to 40].

[0058] As shown in Figures 2 and 3, a third coating 13 may be provided around a plurality of glass fiber strands 12. Examples of materials constituting the third coating 13 are the same as those described above for materials constituting the first coating 11b.

[0059] As shown in Figure 2 (rubber reinforcing cord 20) and Figure 3 (rubber reinforcing cord 30), the third coating 13 may be provided around a plurality of glass fiber strands 12 so as to be in contact with the carbon fiber strands 11. An example of such a configuration is to loosely arrange a plurality of glass fiber strands 12 around the carbon fiber strands 11. In this case, the third coating-forming agent is made more likely to penetrate from the outside to the inside of the glass fiber strands 12, making it easier for the third coating 13 to form in contact with the surface of the carbon fiber strands 11 (i.e., the first coating 11b).

[0060] The third coating 13 may be provided around the multiple glass fiber strands 12 so as not to come into contact with the carbon fiber strands 11. An example of such a configuration is to densely arrange the multiple glass fiber strands 12 around the carbon fiber strands 11. In this case, the third coating-forming agent is less likely to penetrate from the outside of the glass fiber strands 12 (the side opposite to the carbon fiber strands 11) to the inside (the side of the glass fiber strands 12 that is on the carbon fiber strands 11), making it less likely for the third coating 13 to form in contact with the surface of the carbon fiber strands 11 (i.e., the first coating 11b). Furthermore, densely arranging multiple glass fiber strands 12 around the carbon fiber strand 11 includes arranging the multiple glass fiber strands 12 such that the gaps between the glass fiber strands 12 are small enough so that the third coating 13 does not seep into the gaps between adjacent glass fiber strands 12, and arranging the multiple glass fiber strands 12 so that there are no gaps between adjacent glass fiber strands 12.

[0061] The ratio of the mass of the third coating 13 to the total mass of the carbon fiber strands 11 and glass fiber strands 12 (hereinafter referred to as the "adhesion rate of the third coating 13") can be adjusted as appropriate. The adhesion rate of the third coating 13 may be, for example, 1% to 10%, 1% to 5%, or even 2% to 5%.

[0062] The ratio of the total mass of the first coating 11b, the second coating 12b, and the third coating 13 to the total mass of the carbon fiber strands 11 and the glass fiber strands 12 (hereinafter referred to as the "total coating adhesion rate") can be adjusted as appropriate. The total coating adhesion rate may be, for example, 1% to 40%, and may be 5% to 30%, 10% to 30%, or even 20% to 25%.

[0063] (Second Embodiment) The second embodiment will now be described. Matters described in the first embodiment will be omitted as appropriate.

[0064] Figure 4 shows an example of a rubber product 40 according to the second embodiment of this disclosure. The rubber product 40 comprises a matrix rubber 41 and a rubber reinforcing cord 42. The rubber reinforcing cord 42 is the rubber reinforcing cord of the first embodiment. Because the rubber product 40 of this embodiment is equipped with the rubber reinforcing cord of the first embodiment, it can have high bending fatigue resistance.

[0065] The rubber product 40 is not particularly limited. Examples of rubber products in 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 in this embodiment may be a toothed belt, a flat belt, a round belt, a V-belt, or a V-ribbed belt.

[0066] The rubber product 40 of this embodiment is formed by embedding the rubber reinforcing cord 42 of this embodiment into a matrix rubber 41. The method of embedding the rubber reinforcing cord 42 into the matrix rubber 41 is not particularly limited, and known methods may be applied. The rubber product 40 of this embodiment (for example, a rubber belt) can have high bending fatigue resistance because the rubber reinforcing cord 42 is embedded in it. Therefore, the rubber product 40 is particularly suitable for applications that require 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.

[0067] The matrix rubber 41 used in the rubber product 40 of this embodiment 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 41 may also contain carboxyl-modified hydrogenated nitrile rubber. It is preferable from the viewpoint of adhesion that the coating of the rubber reinforcing cord 10 (for example, the third coating 13) and the matrix rubber 41 of the rubber product 40 contain the same type of rubber or are made of the same type of rubber.

[0068] Figure 4 shows a toothed belt as an example of a rubber product 40. The toothed belt shown in Figure 4 comprises a belt body 41a and a plurality of teeth 41b protruding from the belt body 41a at regular intervals in a predetermined direction. The rubber reinforcing cord 42 is embedded inside the belt body 41a so as to be parallel to the longitudinal direction of the belt body 41a.

[0069] As described above, this specification discloses the following technologies.

[0070] (First Technology) A rubber reinforcing cord for reinforcing rubber products, wherein the rubber reinforcing cord comprises: a carbon fiber strand; and a plurality of glass fiber strands arranged around the carbon fiber strand, and in a cross-sectional view of the rubber reinforcing cord, the coverage rate of the carbon fiber strand by the plurality of glass fiber strands is 80% or more.

[0071] (Second technology) The rubber reinforcing cord according to technology 1, wherein the carbon fiber strand comprises a bundle of carbon fiber filaments and a first coating covering at least a portion of the surface of the bundle of carbon fiber filaments.

[0072] (Third technology) The carbon fiber filament bundle is untwisted, the rubber reinforcing cord as described in Technology 2.

[0073] (Fourth technology) A rubber-reinforced cord according to any one of technologies 1 to 3, wherein each glass fiber strand comprises a bundle of glass fiber filaments and a second coating covering at least a portion of the surface of the bundle of glass fiber filaments.

[0074] (Fifth technology) The rubber reinforcing cord according to technology 4, wherein each glass fiber filament bundle is under-twisted in the range of 0.5 turns / 25 mm to 4.0 turns / 25 mm, and over-twisted in the range of 0.1 turns / 25 mm to 3.0 turns / 25 mm around the carbon fiber strand.

[0075] (Technology 6) Each bundle of glass fiber filaments is twisted in a Lang twist, as described in Technology 5, for rubber reinforcement cord.

[0076] (Seventh technology) A rubber-reinforced cord according to any one of technologies 1 to 6, comprising a third coating around the plurality of glass fiber strands so as to be in contact with the carbon fiber strands.

[0077] (Eighth technology) A rubber-reinforced cord according to any one of technologies 1 to 6, wherein a third coating is provided around the plurality of glass fiber strands so as not to come into contact with the carbon fiber strands.

[0078] (Technology 9) A rubber product comprising a matrix rubber and a rubber reinforcing cord described in any one of Technologies 1 to 8.

[0079] (Technology No. 10) The rubber product according to Technology No. 9, wherein the rubber reinforcing cord is embedded in the matrix rubber.

[0080] (Technology No. 11) The rubber product is a rubber belt, as described in Technology No. 9 or No. 10.

[0081] The embodiments of this disclosure will be described in more detail below with reference to examples and comparative examples.

[0082] [Manufacturing of Rubber Reinforcement Cord] (Example 1) Toray Industries' "T700SC-12000" (average diameter of carbon fiber filaments: 7 μm, number of carbon fiber filaments: 12,000 strands (untwisted), count: 700 tex) was prepared as a carbon fiber filament bundle. A primary treatment solution (first coating-forming treatment agent) with the composition shown in Table 1 below was applied to this carbon fiber filament bundle and dried. In this way, a carbon fiber strand with a first coating formed on the surface of the carbon fiber filament bundle was obtained. When applying the primary treatment solution, the amount of primary treatment solution applied was adjusted with a target value of 20% for the ratio of the mass of the first coating to the mass of the carbon fiber filament bundle.

[0083]

[0084] The abbreviations in Table 1 are as follows: HNBR: Hydrogenated nitrile rubber latex (Zetpol 2230LX, manufactured by Zeon Corporation) BMI: Bismaleimide aqueous dispersion (40% solids by mass) NCO: Blocked isocyanate (Elastron BN-27, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Si: Water-dispersible colloidal silica (Snowtex ST-S, manufactured by Nissan Chemical Industries, Ltd.)

[0085] Furthermore, as a glass fiber filament bundle, a filament bundle was prepared by bundling 200 strands of "K glass filament" (average diameter: 7 μm) manufactured by Nippon Sheet Glass Co., Ltd. Three of these filament bundles were then pre-twisted 2.0 times / 25 mm using a Z-twist. A second coating was formed on the surface of this glass fiber filament bundle using the same primary treatment solution (second coating-forming treatment agent) as used for forming the first coating on the carbon fiber filament bundle, thereby obtaining glass fiber strands. When applying the primary treatment solution, the amount of primary treatment solution applied was adjusted with a target value of 20% for the ratio of the mass of the first coating to the mass of the glass fiber filament bundle.

[0086] Next, fifteen glass fiber strands were arranged around one carbon fiber strand, and a cord was obtained by applying a Z-twist at a rate of 1.5 turns / 25 mm. A secondary treatment solution (third coating-forming treatment agent) (Road Co., Ltd.'s "chemlok 233X") was applied to the obtained cord and dried to form a third coating on the surface of the cord. In this way, a rubber-reinforced cord according to Example 1 was obtained. The count of the rubber-reinforced cord according to Example 1 was 2410 tex. When applying the secondary treatment solution, the amount of primary treatment solution applied was adjusted with a target value of 4% for the ratio of the mass of the third coating to the mass of the cord.

[0087] (Example 2) In the preparation of the glass fiber strands, five filament bundles were under-twisted to form a glass fiber filament bundle, and in the preparation of the cord, nine glass fiber strands were arranged around one carbon fiber strand and then over-twisted. The rubber reinforcement cord according to Example 2 was obtained in the same manner as in Example 1. The count of the rubber reinforcement cord according to Example 2 was 2377 tex.

[0088] (Comparative Example 1) A rubber-reinforced cord according to Comparative Example 1 was obtained in the same manner as in Example 1, except that in the preparation of the glass fiber strands, nine filament bundles were under-twisted to form a glass fiber filament bundle, and in the preparation of the cord, five glass fiber strands were arranged around one carbon fiber strand and then over-twisted. The count of the rubber-reinforced cord according to Comparative Example 1 was 2411 tex.

[0089] Table 2 shows the manufacturing conditions for the rubber reinforcing cords in the examples and comparative examples.

[0090]

[0091] The rubber reinforcing cords obtained in the examples and comparative examples were evaluated as follows.

[0092] [Observation using a scanning electron microscope] The rubber reinforcing cords of the examples and comparative examples were embedded in hydrogenated nitrile rubber and cut with a cutter to expose the cross-section of the rubber reinforcing cord. The exposed cross-section of the rubber reinforcing cord was observed using a scanning electron microscope (SEM). During the SEM observation, the coverage rate R of the carbon fiber strands by the glass fiber strands was calculated. In calculating the coverage rate R, the cross-section of each rubber reinforcing cord was observed at 10 different locations along its length, and the average of the coverage rates at these 10 locations was taken as the coverage rate R. In all of the rubber reinforcing cords of Examples 1 and 2 and Comparative Example 1, a portion of the third coating was in contact with the first coating of the carbon fiber strand.

[0093] [Diameter Measurement] The diameters of the rubber reinforcing cords in the examples and comparative examples were calculated using a commonly used dial thickness gauge. For the diameter calculation, the diameter of each rubber reinforcing cord was measured at five different locations along its length, and the average of the five diameters was taken as the diameter of the rubber reinforcing cord.

[0094] [Adhesion Test] First, two rubber pieces (25 mm wide x 50 mm long x 5 mm thick) made of hydrogenated nitrile rubber were prepared. Next, the rubber reinforcing cords of the example and comparative example were sandwiched between the two rubber pieces so that the rubber reinforcing cords were parallel to the longitudinal direction of the rubber pieces, and the pieces were bonded by heating at 150°C for 20 minutes. The test pieces obtained in this way were pulled in the longitudinal direction using a commonly used tensile testing machine, and the fracture surface due to the tensile test was observed with an optical microscope to determine the fracture mode of the test piece. In all test pieces, fracture occurred in the matrix rubber (hereinafter, this fracture mode will be referred to as "rubber fracture").

[0095] [Flexural Fatigue Resistance] The rubber reinforcing cords of the examples and comparative examples were embedded in a matrix rubber made of hydrogenated nitrile rubber to form a flat belt with a width of 10 mm, a length of 300 mm, and a thickness of 3 mm. The resulting flat belts were subjected to flexural tests by bending them 10,000 times, 20,000 times, and 50,000 times, respectively. The flexural tests were performed using the flexural testing machine M shown in Figure 5.

[0096] The bending test machine M shown in Figure 5 comprises a motor M1, a bending jig M2, and a guide pulley P1 (10 mm in diameter). In addition to guide pulley P1, guide pulleys P2 and P3 (both 10 mm in diameter) are also provided within the bending jig M2. First, the fabricated flat belt S was placed over guide pulleys P2 and P3 within the bending jig M2. A cord grip (not shown) at one end of the flat belt S was connected to a fixed end via a connector (not shown), and the cord grip (not shown) at the other end of the flat belt S was connected to a weight W via another connector (not shown). The connector connecting the flat belt S and the weight W was placed over guide pulley P1. Then, the motor M1 was operated to reciprocate the bending jig M2 in the direction shown in Figure 5, thereby repeatedly bending the flat belt S at guide pulleys P2 and P3. The bending test was performed at room temperature. After performing the bending test of the flat belt S in this manner, the tensile strength of the flat belt S was measured. The weight W was 2 kg. The reciprocating motion of the bending jig M2 was performed at a frequency of 40 Hz.

[0097] [Tensile Test] The tensile strength of the flat belts of the examples and comparative examples was measured before and after the bending test. Here, the tensile strength is the breaking strength (unit: N / cord) obtained when the tensile test was performed using a commonly used tensile testing machine and a commonly used cord grip. The tensile strength was tested under the conditions of a tensile speed of 300 mm / min and a grip distance of 250 mm.

[0098] From the results of the bending test, the percentage of the tensile strength of the flat belt after the bending test (hereinafter referred to as the "strength retention rate") was calculated, with the tensile strength of the flat belt before the bending test set to 100%.

[0099] Table 3 shows the evaluation results of the rubber reinforcing cords of the examples and comparative examples, and the flat belts made using them. Figure 6 shows the change in tensile strength when the flat belt is repeatedly bent in a bending test, and Figure 7 shows the change in strength retention rate when the flat belt is repeatedly bent in a bending test.

[0100]

[0101] The rubber reinforcing cords of this disclosure are suitable for improving flexural fatigue resistance and are therefore applicable to reinforcing various rubber products. Furthermore, the rubber products of this disclosure are suitable for improving flexural fatigue resistance and are therefore applicable to various uses.

Claims

1. A rubber reinforcing cord for reinforcing rubber products, wherein the rubber reinforcing cord comprises a carbon fiber strand and a plurality of glass fiber strands arranged around the carbon fiber strand, and in a cross-sectional view of the rubber reinforcing cord, the coverage rate of the carbon fiber strand by the plurality of glass fiber strands is 80% or more.

2. The rubber reinforcing cord according to claim 1, wherein the carbon fiber strand comprises a bundle of carbon fiber filaments and a first coating covering at least a portion of the surface of the bundle of carbon fiber filaments.

3. The rubber reinforcing cord according to claim 2, wherein the carbon fiber filament bundle is untwisted.

4. The rubber reinforcing cord according to claim 1, wherein each glass fiber strand comprises a bundle of glass fiber filaments and a second coating covering at least a portion of the surface of the bundle of glass fiber filaments.

5. The rubber reinforcing cord according to claim 4, wherein each glass fiber filament bundle is under-twisted in the range of 0.5 turns / 25 mm to 4.0 turns / 25 mm, and over-twisted in the range of 0.1 turns / 25 mm to 3.0 turns / 25 mm around the carbon fiber strand.

6. The rubber reinforcing cord according to claim 5, wherein each bundle of glass fiber filaments is twisted in a Lang twist.

7. The rubber reinforcing cord according to claim 1, further comprising a third coating around the plurality of glass fiber strands so as to be in contact with the carbon fiber strands.

8. The rubber-reinforced cord according to claim 1, further comprising a third coating around the plurality of glass fiber strands so as not to come into contact with the carbon fiber strands.

9. A rubber product comprising a matrix rubber and a rubber reinforcing cord as described in claim 1.

10. The rubber product according to claim 9, wherein the rubber reinforcing cord is embedded in the matrix rubber.

11. The rubber product according to claim 9, wherein the rubber product is a rubber belt.

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