Aramid fiber multifilaments, aramid fiber cords, and rubber products

Abstract

To provide an aramid fiber multifilament and an aramid fiber cord capable of impregnating an adhesive into a fiber cord by securing gaps between filaments in a final twist cord, and an aramid fiber cord for reinforcing rubber practically sufficient in belt durability, and good in fray resistance.SOLUTION: An aramid fiber multifilament has a cross-sectional flatness ratio of 18 or more and less than 30. An aramid fiber cord is obtained by twisting the aramid fiber multifilament, where the cross-section occupancy (r) of the aramid fiber in the aramid fiber cord is 30% or more and 48% or less. (A cross-section occupancy (r) here is a value obtained by a cross-section occupancy (r)=(S / A)×100, S is a theoretical cross section of the cord, and A is an apparent cross section of the cord. ) An aramid fiber cord has a Gurley bending resistance obtained by subjecting the aramid fiber cord to adhesive treatment of 100 mN or higher and 200 mN or lower.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to aramid fiber multifilaments, aramid fiber cords used for rubber reinforcement, and rubber products containing the same. [Background technology]

[0002] Aramid fibers are synthetic fibers that possess high functionality such as high strength, high modulus of elasticity, high heat resistance, non-conductivity, and rust resistance, as well as the flexibility and lightness characteristic of organic fibers. For this reason, they are used as rubber reinforcing fibers in various tires, belts, conveyors, etc. When bonding aramid fibers to rubber, it is common to treat aramid fibers (aramid fiber cords) that have undergone under-twisting and over-twisting with adhesives such as resorcinol, formalin, and rubber latex (hereinafter sometimes referred to as RFL).

[0003] However, when fiber cords are used as the core wires of power transmission belts in which the tensile material is exposed on both sides (cut surfaces) of the belt, such as toothed belts, V-ribbed belts, and cut-edge type V-belts, a problem known as fraying can occur, where the filaments making up the cord protrude from the cut surface.

[0004] As a method to solve the fraying problem described above, Patent Document 1 proposes a method to improve fraying by pre-treating untreated fiber cords with an isocyanate compound or epoxy compound, and then treating them with an RFL solution to increase the impregnation of the RFL solution, thereby reducing the void ratio of the treated cord to 0-1.5%. However, Patent Document 1 has the problem of worsening production costs and handling difficulties because the adhesive is treated in two stages. In addition, in order to increase the impregnation of the treatment agent and reduce the void ratio of the treated cord, an organic solvent is used in the first stage of treatment to treat the isocyanate or epoxy compound, but from the standpoint of environmental considerations and worker safety, it is desirable not to use organic solvents.

[0005] Furthermore, Patent Document 2 proposes that by setting the core wire diameter after adhesive treatment to a range of 0.7 to 1.2 mm, high fatigue resistance, pop-out resistance, and belt strength can be achieved. However, controlling only the core wire diameter after adhesive treatment is insufficient to improve the impregnation of the adhesive into the treated cord.

[0006] Furthermore, Patent Document 3 provides two adhesive layers, with the first adhesive layer adhering to the fiber cord at a rate of 3-10% by weight and the second adhesive layer at a rate of 0.1-3% by mass, ensuring good adhesion and fray resistance by bonding the monofilaments to each other even internally. However, the Gurley stiffness of the treated cord is high at 330-660 mN, which poses a challenge to the durability of the belt. In addition, although the adhesive is treated in two stages to improve impregnation, this results in increased manufacturing costs and handling difficulties. Moreover, while this known example specifies polyethylene terephthalate or nylon 66 cords, in the case of aramid fibers, because they are chemically stable, it is difficult to form chemical bonds between the adhesive components and the fiber surface, making it challenging to form an adhesive layer on the monofilaments inside the cord. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-158989 [Patent Document 2] Patent No. 6650545 [Patent Document 3] Japanese Patent Publication No. 2020-033661 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0008] The methods described in Patent Documents 1 to 3 involve modifying the adhesive to improve its impregnation into the fiber cord, and do not involve modifying the adhesive to create voids in the multifilament.

[0009] The present invention aims to provide aramid fiber multifilaments and aramid fiber cords in which gaps are secured between the filaments in the upper twisted cord and adhesive is impregnated into the inside of the fiber cord, as well as aramid fiber cords for rubber reinforcement that have sufficient durability for practical use and good fray resistance. [Means for solving the problem]

[0010] To address the above issues, this research was conducted based on findings obtained from various studies on aramid fibers, namely that the cross-sectional flattening ratio of aramid fiber multifilaments differs depending on the manufacturing method, and, although the details are unclear, the findings that aramid fiber cords for rubber reinforcement with good fray resistance have a cross-sectional flattening ratio of aramid fiber multifilaments and a cross-sectional area occupied by aramid fibers within a specific range. In other words, the present invention is as follows:

[0011] (1) The value obtained by dividing the width of the aramid fiber multifilament by the thickness of the multifilament (cross-sectional flattening ratio) is A is 18.5 or higher and less than 25. Lamid fiber multifilament Aramid fiber cord having under-twisted and over-twisted strands, An aramid fiber cord characterized in that the total fineness of the aramid fiber cord is 6,000 to 12,000 dtex, and the cross-sectional area occupancy rate of aramid fibers in the aramid fiber cord is 30% or more and less than 50%. Here, the cross-sectional area ratio (r) is calculated as (S / A) × 100, where S is the theoretical cross-sectional area of ​​the cord and A is the apparent cross-sectional area of ​​the cord. (2) The aramid fiber multifilament However, it is a curable epoxy compound that has been attached to it, The adhesion rate of the curable epoxy compound is 0% by mass of moisture. Applicable The amount is 0.01% by mass or more and less than 0.1% by mass relative to the aramid fiber multifilament. (1) Aramid fiber cord as described. (3) The above (1)~(2) A rubber-reinforced aramid fiber cord, which is an aramid fiber cord described in any of the above and treated with an adhesive, characterized in that the Gurley stiffness of the aramid fiber cord is 100 mN or more and less than 200 mN. (4) a The lamid fiber cord has one layer of adhesive on its surface. ru (3) Aramid fiber cord for rubber reinforcement, as described.

Advantages of the Invention

[0012] According to the present invention, the cross-sectional flatness ratio of the aramid fiber multifilament is high, and there is a gap of a certain size or more between the filaments in the S-twist cord, making it easier for the adhesive to impregnate the inside of the cord. As a result, it is possible to provide a cord that is less likely to fray (has good fray resistance) from the belt cross-section during belt production. According to the present invention, it is possible to provide a rubber reinforcing cord that has good adhesion to rubber, has a low Gurley stiffness and thus excellent durability of the belt, and also has excellent fray resistance.

Brief Description of the Drawings

[0015] The aramid fiber multifilament of the present invention is preferably one in which a curable epoxy compound has been applied in advance during the spinning process as a mixture with a fiber oil, or in which the curable epoxy compound and the fiber oil have been applied in separate processes. The curable epoxy compound is preferably applied to the aramid fiber multifilament after spinning and neutralization, or after spinning, neutralization, and washing, and after drying the aramid fiber multifilament to adjust the moisture content to 3 to 15% by mass. More preferably, it is 5 to 13% by mass. A moisture content of 15% by mass or less is preferable from the viewpoint of bobbin handling because even if some moisture evaporates after winding, the hardness of the package is maintained at a high level. If the moisture content of the aramid fiber exceeds 15% by mass, the frictional resistance with metal or ceramic rolls in subsequent processing steps increases, which tends to worsen the passability through the process due to abrasion and fuzzing. If the moisture content of the aramid fiber is less than 3% by mass, there is a risk of problems such as static electricity and fuzzing due to abrasion occurring easily.

[0016] The curable epoxy compound can be one or more selected from aliphatic epoxy compounds and epoxy compounds having aromatic rings. When using two or more compounds, they may be mixed or used separately. Furthermore, to improve process passability, the curable epoxy compound and the fiber oil may be mixed and applied, or applied in two stages.

[0017] Aliphatic epoxy compounds include glycidyl ether compounds of polyhydric alcohols such as glycerol, sorbitol, and polyglycerol. Examples include glycerol diglycidyl ether, glycerol triglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether. Among these epoxy compounds, polyfunctional epoxy compounds (polyepoxides) having two or three glycidyl groups are more preferred.

[0018] Examples of epoxy compounds having aromatic rings include bisphenol-type epoxy resins, such as glycidyl ether compounds like bis(4-hydroxyphenyl)methane [bisphenol F], 2,2-bis(4-hydroxyphenyl)propane [bisphenol A], and 2,2-bis(3-methyl-4-hydroxyphenyl)propane [bisphenol C]. Among these, glycidyl ether compounds of bisphenol A and bisphenol F are more preferred because they are liquid at room temperature.

[0019] As a textile lubricant, a lubricant with good compatibility with curable epoxy compounds (water-soluble lubricant) is preferred. Polyalkylene glycol or polyalkylene glycol fatty acid ester is preferred because it has high compatibility with curable epoxy compounds, high smoothness necessary for a textile lubricant, and can reduce abrasion with the traveler when twisting aramid fiber multifilaments. Polyalkylene glycol fatty acid esters are ester compounds of fatty acids and polyalkylene glycols, and include monoester and diester types. Examples of fatty acids include saturated or unsaturated fatty acids such as caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, and behenic acid, as well as unsaturated fatty acids such as palmitoleic acid, oleic acid, vaccenic acid, elaidic acid, and alkenic acid, and 12-hydroxystearic acid. Among these fatty acids, saturated or unsaturated fatty acids with 13 to 22 carbon atoms are preferred because they do not cause the viscosity of the ester compound to become extremely high and are easy to handle.

[0020] Examples of polyalkylene glycols include polyethylene glycol, a polymer of ethylene oxide; polypropylene glycol, a polymer of propylene oxide; and copolymers of ethylene oxide and propylene oxide. Among these, polyethylene glycol is preferred. This yields an ester compound with excellent solubility for curable epoxy compounds. The weight-average molecular weight (Mw) of polyethylene glycol is preferably 400 to 1,300. This range ensures good mixability with curable epoxy compounds, oil application properties, and process passability.

[0021] The fiber oil applied to the aramid fiber multifilament of the present invention, if its viscosity is too high, can cause monofilaments to stick together due to the viscosity of the oil, leading to a tendency for the multifilaments to become bundled. The viscosity of the fiber oil is preferably 30 mPa·s to 90 mPa·s, and particularly preferably 60 mPa·s to 80 mPa·s. If the viscosity of the fiber oil is less than 30 mPa·s, the oil will not adhere to the filaments, resulting in a significant deterioration in the handling of the filaments. If it exceeds 90 mPa·s, the multifilaments will become bundled, making it difficult to obtain aramid fiber multifilaments with a high cross-sectional flatness ratio.

[0022] The amount of curable epoxy compound adhering to the aramid fiber multifilament of the present invention is preferably 0.01% by mass or more and less than 0.1% by mass, and more preferably 0.02% by mass or more and less than 0.08% by mass, relative to the mass of the aramid fiber (on a dry basis). By setting the amount of adhesion within the above range, the aramid fiber has good process passability and an aramid fiber cord with excellent adhesion to rubber can be obtained. If the amount of epoxy compound adhering to the surface of the aramid fiber is 0.1% by mass or more, the high viscosity of the epoxy compound may cause the monofilaments to stick together, making it difficult to create gaps between the monofilaments when twisted, and potentially making it difficult for the adhesive to penetrate to the monofilaments inside the cord.

[0023] The method for determining the amount of curable epoxy compound attached to aramid fiber multifilaments within the above range is not particularly limited, but for example, one method is to ensure that the oil applied to the aramid fibers contains 5% by mass or more and less than 15% by mass of the curable epoxy compound. More preferably, it is 6% by mass or more and less than 9% by mass.

[0024] The amount of curable epoxy compound adhering to the surface of aramid fibers can be measured, for example, by the following method: Immerse the aramid fibers in acetone and ultrasonically clean them for 10 minutes. Remove the aramid fibers, heat the acetone solution at 85°C to remove the acetone, measure the weight of the residue, and multiply the ratio of the residue to the weight of the aramid fibers when converted to a 0% moisture content by 100 to determine the amount of adhesion (%).

[0025] The aramid fiber multifilament, to which a curable epoxy compound and a fiber lubricant have been applied, is then wound onto a bobbin in the winding process. In the winding process, for example, it is preferable to set the adhesion rate of the epoxy compound to the aramid fiber multifilament (yarn) to the above preferred range, and to set the viscosity of the oil applied to the yarn to the above range. As a result, the monofilaments become less likely to stick together due to the oil, reducing the filament's ability to bundle (making it more prone to unraveling), and the yarn becomes flattened when subjected to surface pressure during winding. After winding, the raw yarn is kept at room temperature without heat treatment or tensioning, and its moisture content is maintained at 3-15% by mass.

[0026] The aramid fiber multifilament of the present invention has a cross-sectional flatness ratio (the ratio obtained by dividing the width of the multifilament by the thickness of the multifilament) of 18 or more and less than 30. More preferably, it is 18.5 or more and less than 25, and particularly preferably 19 or more and less than 22. It is presumed that the properties of the rubber reinforcing fiber cord are improved by setting the cross-sectional flatness ratio within the above range for the following reasons. In other words, if the cross-section is flattened, when the multifilaments are twisted, a cord with an uneven surface is obtained. This results in a cord with many gaps, where the area occupied by the fibers is small relative to the apparent cross-section of the cord, making it easier for the adhesive to penetrate the gaps between the multifilaments that make up the cord. Furthermore, by keeping the cross-sectional flatness ratio within the above range, the impregnation of the adhesive into the gaps between the multifilaments becomes easier, and the bonding between monofilaments by the adhesive results in excellent adhesion and fray resistance in cords used for rubber reinforcement. If the cross-sectional flatness ratio is less than 18, the filaments become highly bundled, which increases the cross-sectional area occupied when twisted. This reduces the gaps into which the treatment solution can be impregnated, resulting in a decrease in the cord's fray resistance. Also, if the cross-sectional flatness ratio is 30 or higher, the single yarns tend to separate easily, and the alignment of the multifilaments when twisted becomes poor, resulting in a decrease in cord strength.

[0027] The aramid fibers used in this invention are not limited in terms of total fineness of the twisted cord, multifilament fineness, or single filament fineness. The total fineness of the twisted cord is preferably 3,000 to 15,000 dtex, and particularly preferably 6,000 to 12,000 dtex. The multifilament fineness is preferably 1,000 to 4,000 dtex, and particularly preferably 1,500 to 2,000 dtex. The single filament fineness is preferably 0.1 to 10 dtex, and particularly preferably 0.6 to 6.0 dtex.

[0028] If the total fineness is less than 3,000 dtex, the breaking strength of the cord will be low, making the belt more prone to breakage when used under high tension after manufacturing. On the other hand, if it exceeds 15,000 dtex, the cord becomes thicker, making it difficult for the adhesive to penetrate deep into the cord during adhesive treatment.

[0029] Furthermore, if the multifilament fineness is less than 1,000 dtex, it is necessary to increase the number of under-twisted strands that make up the upper twist in order to maintain the strength of the cord. However, increasing the number of under-twisted strands makes it difficult to align the under-twisted cords when the upper twist is applied, raising concerns that the cord strength may decrease. Also, if the multifilament fineness exceeds 4,000 dtex, the under-twisted cords that make up the upper twist become thicker, raising concerns that the adhesive will not easily penetrate the monofilaments inside the cord when the adhesive is applied.

[0030] If the single filament fineness is less than 0.1 dtex, the diameter of the capillary tubes involved in the adhesive treatment when the twisted cord is immersed in the adhesive treatment solution becomes smaller, reducing the penetration of the adhesive treatment solution. If the single filament fineness exceeds 10 dtex, the conformity between the single filaments deteriorates when twisted, resulting in poor alignment and a decrease in cord strength. In addition, the cord becomes stiff when bent, worsening its fatigue resistance.

[0031] The aramid fiber cord of the present invention is typically obtained by twisting the above-mentioned aramid fiber multifilaments to form an untreated cord ("aramid fiber cord before adhesive treatment" or "raw cord"), and then performing adhesive treatment.

[0032] When twisting the cord, the number of twists is preferably 6.0 to 20.0 t / 10cm, and more preferably 7.0 to 10.0 t / 10cm. By setting the number of twists within this range, good fatigue resistance and good cord strength can be obtained.

[0033] Regarding the twisting method of the cord, it is preferable to first align one or more aramid fibers and apply a lower twist in the S direction (or Z direction), and then further align multiple of these fibers and apply an upper twist in the same direction as the single twist (Lang twist) or an upper twist in the opposite direction (multiple twists).

[0034] Furthermore, the aramid fiber cord (upper twist cord) obtained in the present invention preferably has an aramid fiber cross-sectional area occupancy rate of 30% or more and less than 50%, more preferably 35% or more and less than 48%, and particularly preferably 40% or more and less than 45%. Here, the cross-sectional area occupancy rate is the value obtained by dividing the theoretical cross-sectional area of ​​the cord before adhesive treatment by the apparent cross-sectional area and multiplying by 100. The theoretical cross-sectional area is the value obtained from (Equation 1), and the apparent cross-sectional area is the value obtained from (Equation 2).

[0035] (Math 1) Theoretical cross-sectional area (m 2 ) = Total code fineness (dtex) / 10 4 (m) / density (g / m 3 )

[0036] (Math 2) Apparent cross-sectional area (m 2 ) = π × (cord diameter (m) / 2) 2

[0037] By setting the cross-sectional area occupancy within the above range, impregnation of the adhesive treatment solution into the gaps between monofilaments becomes easier, resulting in excellent adhesion and fray resistance in the rubber reinforcement cord. If the cross-sectional area occupancy is less than 30%, the alignment of the filaments constituting the cord will be poor, which may reduce the cord strength. If it is 50% or more, the gaps between monofilaments will be small, which may make it difficult for the adhesive treatment solution to penetrate between the filaments. A preferred method for setting the cross-sectional area occupancy within the above range is, for example, to use the aramid fiber multifilament of the present invention, which has a cross-sectional flatness ratio of 18 or more and less than 30.

[0038] When treating the above-mentioned aramid fiber cord with adhesive, the adhesive treatment solution may use water as the solvent, or an organic solvent such as toluene or xylene may be used. In particular, to reduce the environmental impact during cord manufacturing and from the standpoint of worker safety during manufacturing, it is preferable to use water as the solvent. Water-based adhesive treatment solutions are easy to handle during manufacturing and cause less environmental pollution compared to solvent-based solutions. In addition, from the standpoint of worker safety, water-based solvents are preferable because there is no concern about fire risk or poisoning risk. Furthermore, the aramid fiber cord of the present invention has excellent impregnation properties with water-based treatment solutions, allowing a large amount of adhesive treatment solution to be impregnated into the gaps between monofilaments. As a result, a cord with excellent fatigue resistance is obtained. In the present invention, there is no restriction on the number of times the adhesive treatment solution is applied, but once is preferable. If it is treated two or more times, the durability of the cord may decrease.

[0039] The adhesive is not particularly limited. For example, it may contain RFL (resorcinol-formaldehyde-rubber latex), and may also contain a blocked polyisocyanate compound. RFL is a mixture of an initial condensate of resorcinol-formaldehyde and rubber latex. The initial condensate may be a product obtained by condensing resorcinol and formaldehyde in the presence of an alkaline or acidic catalyst, or a novolac-type resin obtained by reacting resorcinol and formaldehyde in advance in the presence of an acidic or alkaline catalyst. The molar ratio of resorcinol to formaldehyde is preferably 1 / 0.5 to 1 / 3, and more preferably 1 / 1 to 1 / 3. Resorcinol and formaldehyde can also be used individually.

[0040] RFL exhibits excellent penetration and adhesion to raw cords and adhesion to rubber. The method of preparing the adhesive is not particularly limited, but for example, a mixture containing approximately 2 to 20 parts by mass of resorcinol-formaldehyde initial condensate (in terms of solid content) can be blended at a solid content concentration of approximately 5 to 25% by mass per 100 parts by mass of rubber latex (in terms of solid content).

[0041] Examples of rubber latex include vinylpyridine-styrene-butadiene copolymer rubber latex, styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, chloroprene rubber latex, chlorosulfonated polyethylene rubber latex, ethylene-propylene-conjugated diene ternary copolymer rubber latex, acrylate rubber latex, and natural rubber latex.

[0042] Blocked polyisocyanate compounds are reaction products of polyisocyanate compounds and blocking agents. They do not react with water at room temperature, but upon heating, the blocking agent component dissociates to produce active isocyanate groups. Examples of polyisocyanate compounds include tolylene diisocyanate, metaphenylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, polymethylene polyphenyl polyisocyanate, triphenylmethane triisocyanate, etc.; or polyol adduct polyisocyanate compounds containing terminal isocyanate groups obtained by reacting these polyisocyanate compounds with a compound having two or more active hydrogen atoms (e.g., trimethylolpropane, pentaerythritol, etc.) in a molar ratio of isocyanate groups (-NCO) to hydroxyl groups (-OH) greater than 1; aromatic polyisocyanate compounds are particularly preferred. Furthermore, examples of blocking agents include phenols such as phenol, cresol, and resorcinol; lactams such as ε-caprolactam and valerolactam; oximes such as acetooxime, methyl ethyl ketone oxime, and cyclohexanone oxime; and ethyleneimines. Other examples of blocking agents include polyisocyanate compounds that themselves function as blocking agents, such as 2,4-toluenediisocyanate dimers.

[0043] The blocked polyisocyanate compound preferably has a dissociation temperature of 140°C to 300°C, and more preferably 170°C to 200°C. If the dissociation temperature is below 140°C, adhesion to the rubber may be insufficient, and if the dissociation temperature exceeds 300°C, the fatigue resistance of the rubber tends to decrease.

[0044] Examples of rubber latex include vinylpyridine-styrene-butadiene copolymer rubber latex, styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, chloroprene rubber latex, chlorosulfonated polyethylene rubber latex, ethylene-propylene-conjugated diene ternary copolymer rubber latex, acrylate rubber latex, and natural rubber latex, which can be used individually or in mixtures.

[0045] The application of adhesive to the raw cord is preferably carried out using a processing solution in which the adhesive is dissolved or dispersed in a liquid. The total solid content concentration of the adhesive in the processing solution is preferably 5 to 25% by mass, and more preferably 15 to 25% by mass. By keeping it within this range, the stability of the processing solution containing the adhesive is excellent, and the adhesive can be uniformly applied to the aramid fibers. Known viscosity modifiers may also be added to the adhesive.

[0046] Any method can be used to apply the adhesive-containing treatment solution to the aramid fibers, such as immersion, nozzle spraying, or roller application. For example, the treatment can be performed using a Ritzler Computritor or similar device.

[0047] The surface of the aramid fiber cord of the present invention preferably has one adhesive layer. If two or more layers are formed, the number of adhesive treatment steps increases, which is undesirable in terms of productivity and handling. In addition, if the Gurley stiffness becomes too high, stress may concentrate in the bent parts of the cord when the belt is run, which may reduce the durability of the rubber belt. The amount of adhesive attached to the mass of the aramid fiber cord for rubber reinforcement is preferably 2 to 10% by mass, and more preferably 3 to 8% by mass. This amount of adhesive allows for both fray resistance during belt manufacturing and belt durability to be achieved. If the amount of adhesive exceeds 10% by mass, the cord may become too hard, which may reduce the durability of the belt, and if the amount of adhesive falls below 2% by mass, there will be no adhesive attached to the inside of the cord, which may reduce fray resistance. In other words, by making the upper twisted cord as uneven as possible to create gaps between the filaments, the impregnation of the treatment liquid containing the adhesive is improved, and as a result the monofilaments adhere to each other with the treatment liquid, the cord becomes hard, and if the cord becomes too hard, the durability of the belt decreases.

[0048] To control the amount of adhesive applied and the adhesive impregnation rate, for example, methods such as setting the concentration of the adhesive treatment solution, the conditions for removing the solution after immersion in the adhesive treatment solution, or the dipping speed and tension conditions can be employed.

[0049] It is preferable to dry the raw cord coated with adhesive at a temperature of 100-160°C for 0.5-5 minutes, and then heat-treat it at 200-260°C for 0.5-5 minutes. Drying within the above range allows the adhesive to react with the fiber surface to a sufficient extent, making it particularly easy to form a resorcinol-formaldehyde crosslinked structure. Furthermore, by performing the heat treatment within the above range, the adhesive can exhibit sufficient adhesive strength without degradation.

[0050] Furthermore, when applying adhesive and then drying and heat-treating, it is preferable to apply tension of 0.05 g / dtex to 0.15 g / dtex during tension heat treatment. By applying tension of 0.05 g / dtex or more during tension heat treatment, the alignment of the filaments in the upper twist cord can be optimized, thereby increasing its strength. On the other hand, by applying tension of 0.15 g / dtex or less during tension heat treatment, excessive tension load is not applied to the upper twist cord, minimizing damage to the yarn due to friction during the process and allowing the cord strength to be maintained at a higher level.

[0051] In the present invention, the aramid fiber cord for rubber reinforcement preferably has a Gurley stiffness of 100 mN or more and less than 200 mN, more preferably 110 mN to 180 mN, and particularly preferably 120 mN to 160 mN. If the Gurley stiffness is less than 100 mN, the adhesive will not be impregnated into the cord, and the fibers will easily fray from the cross-section of the belt during belt manufacturing. On the other hand, if it is 200 mN or more, the cord will be stiff, and stress will concentrate at the points where the cord bends during belt operation, reducing the durability of the belt. The method for setting the Gurley stiffness within the above range is not particularly limited, but for example, it can be achieved by providing only one adhesive layer on the aramid fiber cord of the present invention to prevent the cord from becoming too stiff, and setting the amount of adhesive applied within the above preferred range. In addition, by using only one adhesive layer, manufacturing costs can be reduced. Furthermore, the amount of adhesive applied can be set within the above range by adjusting the air pressure using air or the pressure of the nip roll during adhesive processing.

[0052] The aramid fiber cord obtained as described above can be used on its own, but it can also be twisted with fiber cords made of nylon fibers such as nylon 6 and nylon 66, polyester fibers such as polyethylene terephthalate, vinylon fibers, polyketone fibers, etc., and used as a composite cord.

[0053] The aramid fiber cord of the present invention exhibits a high impregnation rate of adhesive into the gaps between monofilaments, making it less prone to fraying of the fibers from the belt cross-section during rubber belt manufacturing. Furthermore, during adhesive treatment, the adhesive components are less likely to be unevenly distributed on the outer layer of the cord, and are more easily impregnated uniformly into the interior, thus achieving both fray resistance and fatigue resistance in the aramid fiber cord. Taking advantage of these characteristics, it can be suitably used as reinforcement for rubber products such as cords and blinds in various tires of automobiles and aircraft; various belts such as transmission belts, V-belts, and timing belts; and various hoses such as radiator hoses, heater hoses, and power steering hoses.

[0054] Examples of the above-mentioned rubbers include acrylic rubber (ACM), acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (HNBR), isoprene rubber (IR), urethane rubber (AU, EU), ethylene-propylene rubber (EPM), ethylene-propylene-diene copolymer rubber (EPDM), chloroprene rubber (CR), styrene-butadiene rubber (SBR), butadiene rubber (BR), natural rubber (NR), silicone rubber, fluororubber, and polysulfide rubber. In addition to the main component rubber, the rubber may also contain various compounding agents commonly used in the rubber industry, such as inorganic fillers like carbon black, silica, and aluminum hydroxide, organic fillers like coumarone resin and phenolic resin, vulcanization accelerators, antioxidants, and softeners. [Examples]

[0055] The present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, "%" refers to "mass%". The measurements in the examples were taken according to the following method.

[0056] (1) Moisture content of aramid fiber The mass of approximately 5g of the sample (mass before drying) is measured, it is heated at 300°C for 20 minutes, left at 25°C and 65% RH for 5 minutes, and then the mass (mass after drying) is measured again. The moisture content used here is the dry base moisture content obtained by [mass before drying - mass after drying] / [mass after drying].

[0057] (2) Adhesive attachment rate The mass (A) of the twisted cord per unit length was measured in advance, and the mass (B) of the cord of the same length after the adhesive treatment was measured. The amount of adhesive attachment was determined by the following calculation formula as the difference. Adhesive attachment rate = [(B - A) / A] × 100 (%)

[0058] (3) Filament cross-sectional flatness ratio After suspending the multifilament by applying a load of 100 g for 1 minute, using a microscope, the average value when measuring the width at N = 10 is defined as W (mm). With the same load applied, using a thickness measuring machine manufactured by Fuji Works Co., Ltd., the average value when measuring the thickness at N = 10 is defined as L (mm). The filament cross-sectional flatness ratio R (-) is defined by the following formula. R = W / L

[0059] (4) Raw cord cross-sectional occupancy After applying a load of 1 kg / strand to the S-twisted cord for 1 minute, using a microscope, at N = 30, measure the width of the part with the widest unevenness of the cord cross-section, and the average value is defined as D (mm). The apparent cross-sectional area A (mm 2 ) is defined by the following formula. A = π × (D / 2) 2 The theoretical cross-sectional area S (mm 2 ) of the cord is defined by the following formula. S = (X / M) × 10 2 Here, X is the fineness (g / 10000 m), and M is the density (g / m 3 ). The cross-sectional occupancy r (%) of the cord is defined by the following formula. r = (S / A) × 100

[0060] (5) Gurley stiffness It was measured in accordance with JIS L1096 using a Gurley type flexibility tester manufactured by Yasuda Seiki Seisakusho Co., Ltd. A 1m length of aramid fiber cord was cut, a metal hook was attached to one end, and a 2000g weight was attached to the other end. The aramid fiber cord was then suspended in the air for 24 hours under conditions of 25°C and 40% relative humidity to maintain its vertical position, and a sample was obtained for measurement. This was cut into 30mm (1.2 inch) pieces to make test specimens, and the hardness of the Gurley cord was measured using a "Gurley's stiffness tester" manufactured by Yasuda Seiki Co., Ltd. Figure 1 shows a perspective view of the "Gurley's stiffness tester".

[0061] (6) Evaluation of the adhesive impregnation state of the dip cord The adhesive-treated cords were untwisted down to the undertwist, and the degree of adhesive impregnation within the undertwist was observed under a microscope and qualitatively evaluated on a three-point scale. The degree of impregnation was determined by whether a brown dipping solution was present in the individual threads inside the untwisted undertwist cord. The evaluation criteria are as follows: 3; The inside of the under-twisted cord is impregnated with adhesive, just like the outside (darker in color), and no fraying of the single threads is observed. 2; The inside of the under-twisted cord has less adhesive impregnation (lighter color) than the outside, resulting in less fraying of the single threads. 1; No adhesive impregnation was observed inside the under-twisted cord, making the single threads prone to unraveling.

[0062] (7) Fray resistance test Evaluation samples were prepared by vulcanizing rubber reinforcing fiber cords and combining them with unvulcanized EPDM rubber of the composition shown in Table 1. The samples were then cut to expose the cord cross-sections. The evaluation samples were fixed so that the cord cross-sections were facing directly upwards. Rectangular pieces of TRUSCO sandpaper (GBS-150) were placed on the cord cross-sections with their longer sides perpendicular to the longitudinal direction of the cords. A 1kg load was suspended from the center of each of the shorter sides of the sandpaper. One end of the suspended load was pulled down so that the sandpaper moved 5cm across the cord cross-section, which counted as one rub. The loads at both ends were alternately pulled down for a total of 10 rubs. After 10 rubs, the rubbed areas were observed under a microscope, the state of fraying of the filaments was visually inspected under a microscope, and the number of filaments protruding from the cross-section was counted.

[0063] [Table 1]

[0064] (8) Belt durability The belt prepared in (7) was wrapped between a drive pulley with a diameter of 140 mm and a driven pulley with a diameter of 70 mm. The drive pulley was loaded with a load of 75 ps, the driven pulley was loaded with a shaft load of 500 kg, and the drive pulley 12 was driven to a rotational speed of 7000 rpm. The belt was run for 100 hours, and a belt sample was obtained after the run. The tensile strength of the belt sample after the run was measured, and the ratio to the belt strength before the run was calculated as a percentage to determine the belt strength retention rate.

[0065] (Example 1) One kilogram of poly(p-phenylene terephthalamide) (molecular weight approximately 20,000), obtained by conventional methods, was dissolved in four kilograms of concentrated sulfuric acid, and the mixture was subjected to a shearing rate of 30,000 seconds through a die with 1,000 holes, each with a diameter of 0.1 mm. -1The material was extruded in this manner, spun in water at 4°C, neutralized with a 10% by mass sodium hydroxide aqueous solution at 10°C for 15 seconds, and then heated and dried at 200°C to obtain a poly(p-phenylene terephthalamide) fiber (single fiber fineness 1.67 dtex, filament count 1,000, total fineness 1,670 dtex) with a moisture content of 50% by mass.

[0066] The bundles of poly(p-phenylene terephthalamide) fibers described above were coated with a fiber lubricant consisting of a mixture of sorbitol polyglycidyl ether and polyethylene glycol (mass ratio: 7.7 / 92.3) at a concentration of 0.65% relative to the fiber mass when converted to a 0% moisture content. The bundles were then rolled up and packaged.

[0067] Bundles of poly(p-phenylene terephthalamide) fibers were unwound from the package, the width and thickness of the multifilaments were measured, and the filament cross-sectional flattening ratio R was calculated.

[0068] Two bundles of poly(p-phenylene terephthalamide) fibers, unwound from the package, were joined together and twisted in the S direction at 8t / 10cm to obtain a lower twist cord. Then, three lower twist cords were joined together and twisted in the S direction at 9t / 10cm to obtain a higher twist cord (twist configuration 1670dtex / / 2 / 3, Lang twist cord).

[0069] The twist coefficient (K) for the under-twisted cord and the over-twisted cord was calculated using the following formula. K = t × D 1 / 2 / 303 [However, t is the number of twists per unit length (twists / 10m), and D is the fineness (dtex).]

[0070] Furthermore, the mixture was added so that the solid content mass ratio was resorcinol / formaldehyde / rubber latex = 16 / 4 / 80, and thoroughly stirred to obtain an aqueous adhesive treatment solution with a solid content concentration of 20%. The rubber latex used was "Nipol 1571CL" manufactured by Nippon Zeon Co., Ltd.

[0071] The fabricated cord was immersed in an adhesive treatment solution containing RFL for 7 seconds using a computer processing machine (manufactured by Ritzler), dried at 140°C for 108 seconds, and then heat-treated at 230°C for 108 seconds to obtain a dip-treated aramid fiber cord (dip cord).

[0072] The cord had 5.7% by mass of solid content from the adhesive treatment solution, i.e., adhesive, adhering to it. The adhesive impregnation state of the cord was rated as 3 on a 3-point scale. For the cord obtained in this way, the Gurley stiffness, resin adhesion amount, belt fray resistance test, and belt fatigue strength retention rate were measured using the method described above. The results are shown in Table 2.

[0073] (Example 2) Using the twisted cord obtained in Example 1, a dip cord was prepared by changing the adhesive treatment process to a step of treating with blocked isocyanate in the first bath and resorcinol, formalin, and latex in the second bath. In the first bath, the isocyanate compound was treated with adhesive to achieve a solid content concentration of 10% and an adhesive adhesion rate of 5%.

[0074] (Example 3) In the oil agent applied to the yarn, sorbitol polyglycidyl ether / polyethylene glycol was mixed in a ratio of 4 / 6 to obtain a yarn with an adhesion rate of 0.2%. Otherwise, the same dip cord as in Example 1 was obtained.

[0075] (Comparative Example 1) In the oil agent applied to the yarn, sorbitol polyglycidyl ether / polyethylene glycol / fatty acid ester was mixed in a ratio of 2.9 / 4.4 / 2.6 to obtain a yarn with an adhesion rate of 1.5%. Otherwise, the same dip cord as in Example 1 was obtained.

[0076] (Comparative Example 2) Using the yarn from Example 1, a top-twisted cord with a cord configuration of 1670 dtex / / 2 / 5 was obtained. Otherwise, the dip cord was the same as in Example 1.

[0077] The evaluation results are summarized in Table 2. Note that Example 3 is a reference example.

[0078] [Table 2]

[0079] Table 2 shows that the aramid fiber cord of the present invention has a larger cross-sectional flattening ratio of the filaments constituting the cord (raw cord) compared to the cord of Comparative Example 1, and the cross-sectional occupancy rate of the raw cord is smaller (i.e., there is more space within the cord). Furthermore, when the cord is in a dip-cord state, the degree of impregnation of the adhesive treatment solution into the interior of the under-twisted cord is high. This indicates that the adhesive has penetrated deep into the cord due to the large amount of space within the raw cord. Furthermore, because the aramid fiber cord of the present invention has good impregnation of the adhesive into the cord, the Gurley stiffness is less than 200 mN and the cord does not become stiff. Therefore, stress does not concentrate at the bent parts of the cord when the belt runs, improving the durability of the belt. [Industrial applicability]

[0080] The aramid fiber multifilament of the present invention, and the aramid fiber cord obtained by twisting the multifilament, can be suitably used as a fiber cord for reinforcing rubber products such as tires, belts, and hoses. [Explanation of Symbols]

[0081] 1. Chuck 2 Test specimens 3 Rotating Rods 4 scale plates 5 needles

Claims

1. An aramid fiber cord is formed by applying a lower twist and an upper twist to an aramid fiber multifilament, wherein the value obtained by dividing the width of the aramid fiber multifilament by the thickness of the multifilament (cross-sectional flatness ratio) is 18.5 or more and less than 25. The aramid fiber cord is characterized in that the total fineness of the aramid fiber cord is 6,000 to 12,000 dtex, and the cross-sectional area occupancy rate of aramid fibers in the aramid fiber cord is 30% or more and less than 50%. Here, the cross-sectional area ratio (r) is calculated as (S / A) × 100, where S is the theoretical cross-sectional area of ​​the cord and A is the apparent cross-sectional area of ​​the cord.

2. The aramid fiber cord according to claim 1, wherein the aramid fiber multifilament is coated with a curable epoxy compound, and the coating rate of the curable epoxy compound is 0.01% by mass or more and less than 0.1% by mass with respect to the aramid fiber multifilament with 0% by mass of moisture.

3. A rubber-reinforced aramid fiber cord, which is an aramid fiber cord according to any one of claims 1 to 2 and treated with an adhesive, characterized in that the Gurley stiffness of the aramid fiber cord is 100 mN or more and less than 200 mN.

4. The aramid fiber cord for rubber reinforcement according to claim 3, having one layer of adhesive on the surface of the aramid fiber cord.

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