JPH0143071B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a rubber-reinforcing carbon fiber treated cord that has excellent adhesion to rubber. [Prior Art] In addition to rayon, polyamide, polyester, etc., conventional rubber reinforcing cords used for tires, belts, etc. have recently been made of organic fibers such as aramid (aromatic polyamide fiber), glass fiber, etc. Inorganic fibers such as steel fibers are used. In particular, rubber reinforcing cords used for tires must be made of high-strength, high-elastic, and lightweight fiber materials from the viewpoint of tire maneuverability, running stability, ride comfort, tire durability, and fuel efficiency. is preferred. Carbon fiber has extremely high specific modulus and specific strength compared to the above-mentioned reinforcing fibers, and has characteristics that allow it to be used to make extremely excellent rubber reinforcing cords. However, carbon fibers have the drawback of insufficient adhesion to rubber, and various improvements have been made in the past. For example, a method of impregnating carbon fiber with an elastomer and twisting it to produce a reinforcing cord (US Pat. No. 3,648,452)
A method in which carbon fibers are treated with an epoxy compound and then treated with an adhesive such as a latex (hereinafter referred to as RFL) solution of an initial condensate of resorcinol and formalin (Japanese Patent Application Laid-Open No. 102678/1983), a method in which polyisocyanate is treated in a first treatment bath containing
Processing method using a second processing bath containing RFL (JP-A-Sho
50-102679) have been proposed. However, none of these methods provides sufficient adhesion and rubber adhesion for practical use. In particular, carbon fibers have a high modulus of elasticity, so they have extremely poor resistance to repeated fatigue due to stretching, compression, etc., but this point has not been sufficiently improved. According to the inventors' study, the cause of the above-mentioned insufficient performance is carbon fiber and rubber.
Either the elastomer, epoxy resin, or polyisocyanate interposed between the RFLs does not combine with the carbon fibers, or even if they do, they do not have the effect of penetrating the rubber or RFL between the single fibers that make up the carbon fiber bundle, and the carbon fibers This is because the adhesiveness within the bundle is poor. Another method for infiltrating RFL into carbon fiber bundles is to use a water-soluble epoxy resin, but in this method, RFL is applied as an aqueous dispersion, so the water-soluble epoxy resin falls off during processing. This reduces the effectiveness by half and has the disadvantage of contaminating the RFL liquid. [Object of the Invention] The present invention has been made in order to solve the above-mentioned drawbacks of the prior art. An object of the present invention is to provide a rubber-reinforcing carbon fiber treated cord that has excellent adhesion to rubber and resistance to repeated fatigue (bending fatigue), and is adhered to the outer periphery in a layer. [Structure of the Invention] Therefore, the present invention provides the following formula (1) A: - (C ₂ H ₄ O -) _l or - (C ₂ H ₄ O) _o - ( - C ₃ H ₆ O
-) A mixture containing 5 to 20% by weight of a compound having _n l, n; 18 to 50 m; 2 to 50 (1≦n/m≦25) and an epoxy resin is added to the carbon fiber bundle in an amount of 0.1 to 1% by weight. %
Further, 15 to 30% by weight of latex (RFL), an initial condensate of resorcinol and formalin, is attached, and is represented by the following formula (2).
The amount of RFL attached to the outer circumference of the carbon fiber cord is 10~
The gist is a carbon fiber treated cord for rubber reinforcement that is 30% by weight. Amount of RFL attached to the outer periphery (%) = b / a - c × 100 ... (2) a; Cross-sectional area of the entire RFL-attached carbon fiber cord b; Cross-sectional area of the RFL-attached outer periphery of the carbon fiber cord c; Carbon fiber cord Total cross-sectional area of constituent single fibers of carbon fibers The structure of the present invention will be described in detail below. (1) The compound having the above formula (1) used in the present invention is
It is a compound made from styrene, methylphenol, ethylene oxide, and propylene oxide, and the number of moles of added alkylene oxide and the amount of this compound used are important for infiltrating RFL between single fibers in a carbon fiber bundle. . In particular, it needs to be changed depending on the type of epoxy resin used for mixing. When A in the compound of formula (1) is an ethylene oxide compound, the number of moles added is 18 to 50. The number of moles added is
If it is less than 18, the amount of RFL deposited by RFL treatment will not be sufficient and the ability to penetrate into the carbon fiber bundle will decrease, and if it exceeds 50, there will be a tendency for it to fall off during RFL treatment, and RFL treatment will be difficult. This is not desirable as it contaminates the bath. Further, when A is a block polymer of ethylene oxide and propylene oxide, the number of moles of ethylene oxide added (n) is in the range of 18 to 50, the number of moles of propylene oxide added (m) is in the range of 2 to 50, and both It is necessary that the number of moles added is 1≦n/m≦25. If n/m is less than 1, RFL
The amount of adhesion becomes insufficient, and the ability to penetrate into the carbon fiber bundle decreases. If n/m exceeds 25, it is not preferable because it tends to contaminate the RFL treatment bath. In the present invention, the compound of formula (1) is used in a mixture with an epoxy resin and, if necessary, other resins such as rubber latex. The mixing ratio is 5 to 20% by weight of the solid content of the resulting mixture (hereinafter referred to as mixture R), and if the epoxy resin used is water-soluble or nearly water-soluble, the ratio is low; In the case of resin, a high proportion is beneficial for increasing the amount of RFL infiltration and preventing contamination of the RFL treatment bath, but normally, if it is less than 5% by weight, the RFL may not penetrate into the carbon fiber bundle. If it exceeds 20% by weight, it is not preferable because it will cause mixture R to drop into the RFL treatment bath. Mixture R is obtained by mixing a predetermined amount of the compound of formula (1) and an epoxy resin to form a liquid, and then forming a solution by dissolving acetone and methyl ethyl ketone, or forming an emulsion while vigorously stirring the liquid. After that, it is made into an aqueous dispersion and applied to the carbon fiber bundle. The amount of mixture R attached to the carbon fiber bundle is
It is 0.1 to 1% by weight. If it is less than 0.1% by weight, it will cause RFL adhesion spots and decrease in the amount of adhesion, and if it is more than 1% by weight, it will prevent RFL from impregnating inside the carbon fiber bundle. In particular, 0.2 to 0.5% by weight is preferable in terms of penetration and uniformity of adhesion. The method of adhering the mixture R to the carbon fiber bundle is usually contact with a roller,
Any method can be used, such as a coating method by spraying from a nozzle or dipping the carbon fiber bundle in a liquid bath. When using the immersion method, typically 0.5
After processing at a liquid temperature of about 10 to 30°C as a solution of ~20 g/l, it is dried at a temperature and time that removes the solvent or water. Usually, it is carried out for 0.5 to 3 minutes at about 50 to 120℃. The epoxy resin used here has at least one epoxy group in one molecule, and is a bisphenol type, a phenol novolac type, a polyphenol type, a nitrogen-containing epoxy type, etc., and particularly preferably a bisphenol type. Specifically, it is a bisphenol A type having an epoxy equivalent of 150 to 450. Further, the carbon fiber bundle may be, for example, a single fiber diameter of 5 to
Consisting of 1000 to 10000 wires of 10μm, 1000
~4000 denier fiber bundle. Carbon fiber cord consists of carbon fiber bundles. (2) 15 to 30% by weight of RFL is applied to the carbon fiber bundle to which the mixture R thus obtained is applied. RFL is a known adhesive in which the molar ratio of resorcinol and formaldehyde (formalin) is 1:0.1 to 1:8, preferably 1:0.5 to 1:
The range is 5. Latexes include natural rubber latex, styrene-butadiene copolymer latex, vinylpyridine-styrene-butadiene terpolymer latex, nitrile rubber latex, etc. These latexes are used alone or in combination, and in particular, vinyl Pyridine-styrene-butadiene terpolymer latex is preferred. If the amount of RFL attached is less than 15% by weight, the adhesion to the rubber will be low, and if it is more than 30% by weight, the treated carbon fiber cord will be hard and its bending fatigue strength will be low. The blending ratio of the resorcinol/formalin initial condensate and latex in RFL is 1:1 to 1:15 in terms of solid weight ratio, preferably 1:3 to 1:
It is 12. To attach RFL, for example, a carbon fiber bundle to which mixture R has been attached is immersed in an aqueous dispersion of 10 to 35% by weight of RFL at 10 to 25°C, and the amount of adhesion is preferably adjusted using a squeezing roller. , 80～
Dry in air at 110℃ for 2 to 3 minutes, then dry at 200℃
It can be obtained by heat treatment at 230℃ for 1 to 2 minutes, but preferably the same RFL is applied again after drying.
It is preferable to perform heat treatment after immersing in a liquid and drying under the same conditions. As a result, the amount of RFL adhered to the outer peripheral portion of the carbon fiber cord can be made to be 10 to 30% by weight as determined by the following formula (2). Amount of RFL adhesion on the outer periphery (%): After taking a photograph of the cross section of the carbon fiber treated cord at 100x magnification using an electron microscope, the adhesion status on the outer periphery can be calculated from the adhesion thickness using the following formula (2). Calculate by. Amount of RFL attached to the outer periphery (%) = b / a - c × 100 ... (2) a; Cross-sectional area of the entire RFL-attached carbon fiber cord b; Cross-sectional area of the RFL-attached outer periphery of the carbon fiber cord c; Carbon fiber cord Total cross-sectional area of single fibers of carbon fibers.If the amount of adhesion on the outer periphery is less than 10% by weight, the adhesion with rubber will be low, and if it is more than 30% by weight, RFL will not penetrate into the fiber bundle. If it is insufficient, friction between the single fibers in the carbon fiber bundle tends to occur, resulting in poor fatigue properties and poor post-processability, which is undesirable. Particularly preferred is 15 to 25% by weight. Examples and comparative examples are shown below. Note that unless otherwise specified, "%" and "part" represent weight. Examples 1 to 3 Comparative Examples 1 to 2 Using a compound (hereinafter referred to as compound (1)) in which A in formula (1) is a polyoxyethylene group and added 25 moles, a bisphenol A-based epoxy resin was used. A certain Epicote 828 (Yuka Ciel Epoxy Co., Ltd.)
Compound (1) was mixed in varying proportions as shown in Table 3 below. Mixing involves compound (1) and epoxy resin.
Dissolve at 60℃ and pour water at a rate of 10c.c./min under stirring at 5000rpm to finally create an aqueous dispersion containing 60% solids of the mixture of compound (1) and epoxy resin. A master solution was prepared. This solution was further diluted with water to make a 15 g/l aqueous dispersion, and a 3600 denier carbon fiber bundle (tensile strength 350 Kgf/mm ² , elastic modulus
24×10 ³ Kgf/mm ² ) was continuously immersed so that the solid content of the mixture was 0.4%, and dried at 110°C. The obtained carbon fiber bundle was mixed with the composition shown in Table 2.
Continuously immersed in a bath with 25% RFL concentration at 25 °C,
RFL was attached, dried at 85°C for 2 minutes, and then heat treated at 210°C for 2 minutes. Regarding the obtained RFL-attached carbon fiber bundle, the total amount of adhesion and the adhesion ratio on the outer periphery of the carbon fiber bundle were investigated, and the results were as shown in Table 3. The obtained carbon fiber cord was tested as follows:
The ply peeling force, bending fatigue strength retention rate, and pull-out force were measured, and the results were as shown in Table 4. In the case of the range of the present invention, excellent adhesion to rubber and fatigue resistance were exhibited. Hereinafter, the ratio of RFL adhesion to the outer periphery of the carbon fiber cord will be simply referred to as the adhesion ratio of the outer periphery of carbon fiber. Pulling test: A carbon fiber cord was embedded in an unvulcanized rubber compound with a composition shown in Table 1 below, with a cord length of 8 mm, and heated at 150°C.
After vulcanization for 30 minutes, the adhesive strength was determined by a pull-out test that measured the force with which the cord was pulled out of the vulcanized rubber. 2-ply peel test: 20 cords were arranged parallel to the longitudinal direction of the rubber sheet on the surface layer of a rubber sheet with a width of 25 mm, a length of 200 mm, and a thickness of 1.0 mm made of the unvulcanized rubber compound shown in Table 1 below. The top is covered with the above rubber sheet, and then 20 cords are similarly arranged in parallel in the longitudinal direction of the rubber sheet, and then covered with the rubber sheet again.
A laminate of rubber/cord/rubber/cord/rubber with a ply structure was prepared and heated at 150℃ under a pressure of 30Kg/ ^cm2 .
After vulcanization for 30 minutes, a peel test was performed between the cord layers to determine the adhesive strength of each cord, and the state of the peel interface was observed. Figure 1 shows the shape of the sample used here. 1st
In the figure, a is a rubber layer, b is a cord layer, and the cord is peeled between the cord layers b along the longitudinal direction. Bending fatigue test: In order to measure the bending fatigue properties of the cord in rubber, a so-called daytime bending fatigue test was conducted in which the cord was embedded in rubber and bent with a constant stroke. The compounded rubber shown in Table 1 was used as the rubber. The rubber block that was subjected to the daytimer type bending fatigue test was 25.4 mm wide, 76.2 mm long, and 6.35 mm thick.
This was prepared by embedding three cords in the longitudinal direction of the rubber block at 6.35 mm intervals and vulcanizing at 148°C for 30 minutes. After bending this rubber block 100,000 times with a stroke of 30 mm, the rubber block was divided into three equal parts, a rubber block with a cord was collected, and the rubber block with a cord was pulled at a pulling speed of 300 mm/nin and a distance between chucks of 30 mm. The bending fatigue resistance of the cord was determined by determining the strength and determining the 100% of the tensile strength when not fatigued. Table 1 Rubber compound natural rubber RSS #3 100 parts Zinc white 5 parts Stearic acid 2 parts Carbon black (GPF) 50 parts Anti-aging agent ^*1 1 part Aromatic oil 7 parts Sulfur 2.25 parts Vulcanization accelerator DM ^*2 1 part Notes *1 Santoflex 13 (manufactured by Mitsubishi Monsanto) *2 Dibenzothiazyl disulfide Table 2 Soft water with RFL 387.6 parts Sodium hydroxide (10% aqueous solution) 6.3 parts Resorcinol 23.1 parts Formalin (37%) 25.6 parts Nipole 2518FS (40%) ) ^*1 543.5 parts Ammonia water (28%) 13.9 parts Total 1000.0 parts Note *1 Vinylpyridine/styrene/butadiene copolymer rubber latex (manufactured by Nippon Zeon Co., Ltd.)

[Table] Example 2
Implementation 18 82 0.4 20 24
Example 3
Comparison 25 75 0.4 21 25
Example 2
Note)
* According to formula (2) above.

【table】

[Table] Example 4 Comparative Examples 3 to 4 The procedure was carried out in exactly the same manner as in Example 1, except that A in the formula (1) above was a polyoxyethylene group and three types of compounds were used in which the number of moles was 10, 20, and 70. Three types of carbon fiber cords were obtained with an RFL adhesion amount of 20% and an adhesion ratio of 24% on the carbon fiber outer periphery. The obtained cord was similarly measured for two-ply peeling force, bending fatigue strength retention rate, and pulling force, and the results were as shown in Table 5 below. In the case of the range of the present invention, excellent adhesion to rubber and fatigue resistance were exhibited.

[Table] Example 5 Comparative Examples 5 to 8 The amount of the mixture of the compound of formula (1) and epoxy resin, which is the same as in Example 2, attached to the carbon fiber bundle was 0.05%,
Three types of carbon fiber cords were obtained in exactly the same manner as in Example 2, except that the RFL adhesion amount was 21%, and the adhesion ratio on the outer periphery of the carbon fiber was 23%. In addition, when the adhesion amount of the mixture to carbon fiber is 0.5%, the RFL adhesion amount is 8%.
and 35%, and the adhesion ratio on the outer periphery of carbon fibers was changed to 18% and 24%, respectively.
A carbon fiber cord was obtained in the same manner as in Example 2, except that the bath concentration for treating the second RFL-attached carbon fiber bundle was 13%. The two-ply peel force, flexural fatigue strength retention rate, and pull-out force of the resulting cords were similarly measured, and the results are shown in Table 6, indicating that the cords within the scope of the present invention had excellent properties.

[Table] Comparative Examples 9 to 10 In Example 3, the case where the second RFL adhesion bath was not used was such that the amount of adhesion on the outer circumferential part of the carbon fiber was 5% and 35% with 18% RFL adhesion carbon fiber, and
A carbon fiber cord was obtained in the same manner as in Example 3 except that a 20% bath was used. 2 of the obtained code
When the ply peeling force, bending fatigue strength retention rate, and pulling force were examined, the values were lower than those of Example 3, as shown in Table 7.

〔Effect of the invention〕

As explained above, the carbon fiber treated cord of the present invention has very good adhesion to rubber and excellent resistance to repeated fatigue, and furthermore, the carbon fiber itself has high strength and high modulus. Therefore, it is useful as a reinforcing tire cord, such as a cord for a tire belt layer or a carcass layer, or as a reinforcing cord for a conveyor belt, etc.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the shape of a sample used in a 2-ply peel test. a...Rubber layer, b...Cord layer.

Claims (1)

[Claims] 1. The following formula (1) A: - (C ₂ H ₄ O -) _l or - (C ₂ H ₄ O) _o - ( - C ₃ H ₆ O
-) A mixture containing 5 to 20% by weight of a compound having _n l, n; 18 to 50 m; 2 to 50 (1≦n/m≦25) and an epoxy resin is added to the carbon fiber bundle in an amount of 0.1 to 1% by weight. %
Further, 15 to 30% by weight of latex (RFL), an initial condensate of resorcinol and formalin, is attached, and is represented by the following formula (2).
The amount of RFL attached to the outer circumference of the carbon fiber cord is 10~
Carbon fiber treated cord for rubber reinforcement which is 30% by weight. Amount of RFL attached to the outer periphery (%) = b / a - c × 100 ... (2) a; Cross-sectional area of the entire RFL-attached carbon fiber cord b; Cross-sectional area of the RFL-attached outer periphery of the carbon fiber cord c; Carbon fiber cord Total cross-sectional area of the constituent carbon fiber single fibers