JP7681938B2 - Aramid fiber, cord using same, and manufacturing method thereof - Google Patents

Description

The present invention relates to aramid fibers, cords using the same, and methods for manufacturing the same.

Aramid fiber is a synthetic fiber that combines high functionality, such as high strength, high elasticity, high heat resistance, non-conductivity, and rust resistance, with the flexibility and light weight characteristic of organic fibers, and is therefore used as a reinforcing fiber for various tires, belts, conveyors, etc. However, when bonding aramid fiber to rubber, it is necessary to treat it with an adhesive such as resorcinol-formaldehyde-latex (hereinafter referred to as RFL), but RFL has poor adhesion to aramid fiber. Therefore, in order to improve the adhesion of aramid fiber to rubber, an epoxy compound is attached to the surface of the aramid fiber.

For example, Patent Document 1 discloses a method for improving the adhesion of aramid fibers by forming an epoxy coating with a free epoxide content of 10 mmol/kg or less, and describes a method in which an epoxy compound, a curing agent, and a surfactant are applied to an undried yarn, the yarn is then dried, and then cured (paragraph 23, paragraph 27, Examples 1, 3, and 6), or a method in which an epoxy compound is applied to a dried yarn, and then the yarn is cured (paragraph 32, Examples 2, 4, and 7). Example 4 describes a method in which a fatty acid polyglycol ester is applied as a finishing agent to a dried yarn, and then a mixture of an epoxy compound and a curing agent is applied and then cured.
However, in the process of producing the yarn, three or more kinds of agents, namely, an epoxy compound, a curing agent, and a surfactant, are added, which results in poor handleability.

Patent Document 2 discloses that an oil agent containing a curable epoxy compound (such as a low-molecular-weight fatty acid ester having 18 or less carbon atoms, polyether, or mineral oil) is applied to aramid fibers having a moisture content of 15 to 200 mass %, and the fiber skeleton is impregnated with the curable epoxy compound, thereby obtaining a fiber composite having high adhesive strength while maintaining the high heat resistance and high Young's modulus inherent to the aramid fibers, and useful for reinforcing rubber materials and resin materials.
However, when the oil is applied to aramid fibers having a low moisture content, the adhesive strength and tensile strength of the RFL dipped cord are not improved, so the oil cannot be applied to aramid fibers having a low moisture content. In addition, a drying process is required, which increases the production cost.

Patent Document 3 discloses that an aramid fiber having good adhesiveness to a matrix resin can be obtained by attaching to the aramid fiber 0.5 to 3.0 mass % of an oil agent containing a polyalkylene glycol having one end blocked with a higher fatty acid via an ester bond and a higher fatty acid ester of a monohydric higher alcohol in a mass ratio of 70/30 to 95/5.
However, when a polyalkylene glycol having one end blocked with a higher fatty acid is used alone, fuzz is generated in the fiber, resulting in poor product quality, while when a higher fatty acid ester of an alcohol is used alone, the adhesive performance with an epoxy resin is poor. Therefore, in order to obtain an aramid fiber having both good product quality and adhesive performance, it is essential to use both in combination.

Japanese Unexamined Patent Publication No. 59-094640 JP 2012-207326 A JP 2010-275656 A

The present invention aims to provide an aramid fiber that can improve the processability and adhesion to rubber of the aramid fiber even when an oil agent is applied to the aramid fiber with a low moisture content, a cord using the same, and a method for manufacturing the same.

In order to solve the above problems, the present inventors have conducted extensive research and found that by adhering an epoxy compound and an ester compound of a fatty acid and a polyalkylene glycol to an aramid fiber, even if the aramid fiber has a low moisture content and even if an epoxy curing agent is not added, the adhesion of the aramid fiber to rubber after the RFL treatment is good, and thus the present invention has been completed.
That is, the present invention is as follows.

(1) A para-aramid fiber having an oil agent applied thereto,
The aramid fiber has a moisture content of 3 to 15 mass% after application of an oil agent , the oil agent contains (a) and (b), and no epoxy curing agent is added.
(a) an aliphatic epoxy compound; (b) an ester compound of a fatty acid and a polyalkylene glycol represented by the following general formula (I) and/or the following general formula (II):

(In the formula, R ¹ is an alkyl group or alkenyl group having 5 to 30 carbon atoms, R ² is an alkylene group having 2 to 3 carbon atoms, and m is an integer of 5 to 100 representing the average number of moles of oxyalkylene groups (R ² -O) added. Note that in (R ² -O), the same oxyalkylene group may be added, or two or more types of oxyalkylene groups may be added.)

(In the formula, R ¹ and R ³ are both alkyl or alkenyl groups having 5 to 30 carbon atoms and may be the same or different. R ² is an alkylene group having 2 to 3 carbon atoms, and n is an integer of 5 to 100 representing the average number of moles of oxyalkylene groups (R ² -O) added. In addition, in (R ² -O), the same oxyalkylene group may be added, or two or more types of oxyalkylene groups may be added.)
(2) (b) The aramid fiber according to the above (1), wherein in the general formula (I) or (II), R ² is an alkylene group having 2 carbon atoms.
(3) (b) The aramid fiber according to (1) or (2) above, wherein, in the general formula (I) or (II), m and n are each 9 to 30.
(4) (b) The aramid fiber according to any one of (1) to (3), wherein the ester compound of a fatty acid and a polyalkylene glycol is an ester compound represented by general formula (I) as a main component, R ¹ is an alkyl group or alkenyl group having 9 to 26 carbon atoms, R ² is an alkylene group having 2 carbon atoms, and m is 9 to 21.
(5) (b) The aramid fiber according to any one of (1) to (3), wherein the ester compound of a fatty acid and a polyalkylene glycol is an ester compound represented by general formula (I) as a main component, R ¹ is an alkyl group or alkenyl group having 13 to 22 carbon atoms, R ² is an alkylene group having 2 carbon atoms, and m is 9 to 30.
(6) The aramid fiber according to any one of (1) to (5) above, wherein the epoxy compound (a) is one or a mixture of two selected from glycerol diglycidyl ether and glycerol triglycidyl ether.
(7) An aramid fiber cord comprising an aramid fiber having the oil agent according to any one of (1) to (6) applied thereto , and a resorcin-formaldehyde-rubber latex (RFL) adhesive applied thereto .
(8) A method for producing aramid fibers, comprising a step of applying an oil solution (excluding an epoxy curing agent) consisting of a mixture of (a) an aliphatic epoxy compound and (b) an ester compound of a fatty acid and a polyalkylene glycol to para-aramid fibers that have been dried to a moisture content of 15% by mass or less after spinning and neutralization, followed by winding the aramid fibers to which the oil solution has been applied around a bobbin in a winding step, and maintaining the moisture content of the wound aramid fibers at 3 to 15% by mass.
(9) A method for producing aramid fibers, comprising: (a) a step of providing an aliphatic epoxy compound to para-aramid fibers that have been spun, neutralized, and then dried to a moisture content of 15% by mass or less; and (b) a step of providing an ester compound of a fatty acid and a polyalkylene glycol (but not including a step of providing an epoxy curing agent), followed by winding up the aramid fibers provided with the epoxy compound and the ester compound on a bobbin in a winding step, and maintaining the moisture content of the wound aramid fibers at 3 to 15% by mass.
(10) A method for producing an aramid fiber cord, comprising unwinding the aramid fibers obtained by the production method according to (8) or (9) from a bobbin and twisting the aramid fibers.
(11) A method for producing an aramid fiber cord, comprising unwinding the aramid fibers obtained by the production method according to (8) or (9) from a bobbin, twisting the aramid fibers, and applying an adhesive to the twisted yarn cord.
(12) A method for producing an aramid fiber cord, comprising unwinding the aramid fibers obtained by the production method according to (8) or (9) from a bobbin, applying an adhesive thereto, and twisting the cord to which the adhesive has been applied.

The aramid fiber of the present invention has an epoxy compound and an ester compound of fatty acid and polyalkylene glycol attached to the aramid fiber as an oil agent, and when the oil agent is applied to an aramid fiber having a moisture content of 15 mass% or less, the bundling property of the aramid fiber is improved, and the friction coefficient is reduced, so that the processability and productivity are dramatically improved. The ester compound of fatty acid and polyalkylene glycol not only functions as a diluent for the epoxy compound and an oil agent for fibers, but also has the advantage of not inhibiting the effect of improving the adhesion to rubber by the epoxy compound. The oil agent does not contain an epoxy curing agent, so that the oil agent is easy to handle in the manufacturing process and the epoxy compound is excellent in stability.
Furthermore, the cord made by twisting the aramid fibers of the present invention has excellent adhesive strength with rubber when treated with RFL.
Furthermore, according to the method for producing aramid fibers of the present invention, the step of mixing many kinds of ester compounds can be simplified, so that economical aramid fibers can be provided.

Aramid fibers include para-aramid fibers and meta-aramid fibers. The oil of the present invention is preferably used for para-aramid fibers, which have excellent tensile strength. Examples of commercially available para-aramid fibers include polyparaphenylene terephthalamide (PPTA) fibers (manufactured by DuPont USA and Toray DuPont Co., Ltd., product name "Kevlar" (registered trademark), etc.), and copolyparaphenylene-3,4'-oxydiphenylene terephthalamide fibers (manufactured by Teijin Limited, product name "Technora" (registered trademark)).

The oil agent of the present invention is preferably applied to aramid fibers that have been spun and neutralized, or spun, neutralized and washed, and dried to adjust the moisture content to 15% by mass or less. By applying the oil agent to aramid fibers with a moisture content of 15% by mass or less, one drying step can be omitted. In addition, the moisture content of the aramid fibers is preferably 3% by mass or more, and if it is less than 3% by mass, fluffing due to abrasion is likely to occur. On the other hand, if the moisture content of the aramid fibers exceeds 15% by mass, free water is likely to adhere to the surface of the aramid fibers, making it difficult for the oil agent to adhere to the fiber surface, and the strength of the twisted yarn cord tends to decrease. In addition, the packaging quality deteriorates after the moisture on the surface of the aramid fibers dries.

The oil agent of the present invention comprises (a) an epoxy compound and (b) an ester compound of a fatty acid and a polyalkylene glycol, and does not contain an epoxy curing agent. These components (a) and (b) may be applied separately in two steps, or may be applied as a mixture. When applied in two steps, the order in which components (a) and (b) are applied is not particularly limited, but it is preferable to apply component (a) and then component (b) in terms of improving processability. A more preferred application form is to apply components (a) and (b) as a mixture. When applied separately, the two-step process results in poor handling.

The epoxy compound (a) used in the present invention may be one or more selected from aliphatic epoxy compounds and epoxy compounds having an aromatic ring. When two or more types are used, they may be used in combination or separately.

As the aliphatic epoxy compound, one or a mixture of two or more selected from glycidyl ether compounds of polyhydric alcohols such as glycerol, sorbitol, polyglycerol, etc. are preferred. Examples include glycerol diglycidyl ether, glycerol triglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, etc. More preferred epoxy compounds are polyfunctional epoxy compounds having two or three glycidyl groups.

As an epoxy compound having an aromatic ring, one or a mixture of two or more selected from bisphenol type epoxy resins is preferred. Examples include glycidyl ether compounds such as 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.

Among the above epoxy compounds, aliphatic epoxy compounds are preferred because they have low viscosity and can be applied during the spinning process, and they can improve processability. Glycerol-based epoxy compounds such as glycerol diglycidyl ether and glycerol triglycidyl ether are particularly preferred.

The (b) ester compound of fatty acid and polyalkylene glycol used in the present invention is represented by the following general formula (I) and/or the following general formula (II). General formula (I) is a monoester type, and general formula (II) is a diester type. By incorporating these ester compounds into the oil, it is possible to reduce wear with the traveler during twisting of aramid fibers and improve adhesion to rubber during RFL treatment.

In the above general formula (I) or (II), the number of carbon atoms in ^R1 and ^R3 is 5 to 30. If it is less than 5, the convergence of the aramid fiber is low, resulting in poor processability, and if it exceeds 30, the hydrophobicity of the ester compound is high, resulting in the inability to mix with the epoxy compound or the affinity being low. In consideration of the adhesion of the ester compound to rubber and the solubility with the epoxy compound, the number of carbon atoms in ^R1 and ^R3 in the formula is preferably 7 to 28, more preferably 9 to 26, even more preferably 11 to 24, and particularly preferably 13 to 22.

Specific examples of fatty acids constituting the ester compounds represented by general formula (I) or (II) 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, and unsaturated fatty acids such as palmitoleic acid, oleic acid, vaccenic acid, and elaidic acid. Among these fatty acids, saturated or unsaturated fatty acids having 13 to 22 carbon atoms are preferred, since the viscosity of the ester compounds with polyalkylene glycols does not become extremely high and they are easy to handle.

In the above general formula (I) or (II), m and n (average number of moles of oxyalkylene groups added) are 5 to 100. If they are less than 5, mixing with the epoxy compound becomes difficult, and the adhesive strength with the rubber when treated with RFL decreases. Also, if they exceed 100, the viscosity of the oil increases, and the oil application becomes poor, which is not preferable. m and n are preferably 5 to 50, more preferably 9 to 30, even more preferably 11 to 19, and particularly preferably 13 to 17.

Examples of polyalkylene glycols include polyethylene glycol, which is a polymer of ethylene oxide, polypropylene glycol, which is a polymer of propylene oxide, and copolymers of ethylene oxide and propylene oxide. Among these, polyethylene glycol is preferred because it gives an ester compound that has excellent solubility for epoxy compounds.

The weight average molecular weight (Mw) of the polyethylene glycol is preferably 400 to 1300, more preferably 400 to 920, even more preferably 480 to 840, and particularly preferably 570 to 750. If the weight average molecular weight (Mw) of the polyethylene glycol is 400 or more, the hydrophilicity of the ester compound increases, making it easier to mix with the epoxy compound. On the other hand, if the weight average molecular weight (Mw) exceeds 1300, the viscosity of the ester compound increases, the oil imparting ability in the process decreases, and the process passability deteriorates. The weight average molecular weight of the polyethylene glycol can be measured by gel permeation chromatography (GPC).

Preferred specific examples of the ester compounds represented by general formula (I) or (II) include polyethylene glycol (m=10-20) lauric acid monoester and/or diester, polyethylene glycol (m=10-20) oleic acid monoester and/or diester, polyethylene glycol (m=10-20) stearate monoester and/or diester, etc.

In the oil agent of the present invention, the ratio (mass ratio) of (a) epoxy compound to (b) ester compound of fatty acid and polyalkylene glycol can generally be selected in the range of 80/20 to 20/80, more preferably in the range of 70/30 to 30/70, and even more preferably in the range of 65/35 to 45/55. If the ratio of (b) ester compound to (a) epoxy compound is high, the adhesion of the epoxy compound to rubber is hindered, and conversely, if it is low, the convergence of the aramid fiber is reduced, and the processability is deteriorated. If the (b) ester compound is present in excess in the oil agent, it tends to hinder the adhesion of the aramid fiber to rubber, so the ratio of (a) epoxy compound to (b) ester compound is particularly preferably in the range of 65/35 to 55/45.

The oil agent of the present invention may contain known smoothing agents, surfactants such as nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants, antistatic agents, etc., within the scope of not impairing the effects of the present invention. In addition, an epoxy curing agent is not necessary because adhesion to rubber is possible as long as the epoxy compound is present on the fiber surface. However, this does not prevent the blending of known epoxy curing agents as necessary. Examples of epoxy curing agents include amine compounds and tertiary amine compounds. Examples include dimethyloctylamine, dimethyldecylamine, dimethyllaurylamine, and long-chain alkyl polyoxyethylene tertiary amines in which ethylene oxide is added to an aliphatic primary amine.

The amount of the mixed oil agent adhered to the aramid fiber, and the amount (total amount) of the epoxy compound and the ester compound of fatty acid and polyalkylene glycol adhered to the aramid fiber is preferably 0.3 to 5 mass% based on the fiber mass (dry basis), more preferably 0.4 to 3 mass%, and particularly preferably 0.5 to 2 mass%. If it is less than 0.3 mass%, the aramid fiber coating effect becomes insufficient, and if it exceeds 5 mass%, it is likely to wrap around the roll due to adhesion.

The above-mentioned oiling agent has an advantage that, even when applied to aramid fibers having a moisture content of 15% by mass or less, the adhesiveness to rubber when RFL is treated is exhibited and the bundling property of the spun aramid fibers is improved. On the other hand, when the moisture content is less than 3% by mass, the fibers frequently wind around the roll due to static electricity, and furthermore, the strength is reduced due to excessive heat treatment. The moisture content of the aramid fibers to which the above-mentioned oiling agent is applied is more preferably 3 to 14% by mass, and particularly preferably 5 to 13% by mass.
On the other hand, in the method of impregnating and penetrating an epoxy compound into the skeleton of aramid fibers having a moisture content of 15% by mass or more, a step of drying the spun aramid fibers once to maintain the moisture content at 15% by mass or less is required. In contrast, the oil agent used in the present invention exhibits adhesion to rubber even when applied to aramid fibers having a moisture content of 15% by mass or less, and therefore has a great advantage in terms of the production cost of the aramid fibers.

In the method for producing aramid fibers of the present invention (first production method), after spinning and neutralization, aramid fibers are dried to a moisture content of 15% by mass or less, and then an oil solution consisting of (a) an epoxy compound and (b) an ester compound of a fatty acid and a polyalkylene glycol (however, this does not include a step of adding an epoxy curing agent) is applied to the aramid fibers, which are then wound around a bobbin in a winding step, and the moisture content of the wound aramid fibers is maintained at 3 to 15% by mass.

The method for producing aramid fibers (second production method) of the present invention includes the steps of (a) applying an epoxy compound to aramid fibers that have been spun, neutralized, and then dried to a moisture content of 15% by mass or less, and (b) applying an oil agent consisting of an ester compound of a fatty acid and a polyalkylene glycol (however, does not include a step of applying an epoxy curing agent), and then winding the aramid fibers to which the epoxy compound and the oil agent have been applied onto a bobbin in a winding step, and maintaining the moisture content of the aramid fibers after winding at 3 to 15% by mass.

The first and second manufacturing methods of the present invention are characterized in that they do not include a curing agent application step for curing the applied epoxy compound. In other words, there is no need to externally add a curing agent for curing the epoxy compound. Conventionally, it was thought that adding a curing agent to cure the epoxy compound was effective in improving the adhesiveness of aramid fibers, but according to the present invention, even in a state where the epoxy compound is not 100% cured and uncured epoxy compound is attached to the surface of the aramid fibers, it is possible to improve the adhesiveness to rubber and resin to an equal or greater level than in the past.

The oil-treated aramid fiber can be treated with an adhesive such as resorcinol, formalin, or rubber latex (RFL) treatment to produce aramid fiber suitable for reinforcing rubber or resin. If necessary, the adhesive-treated aramid fiber can be cut to a specified length (0.1 to 10 mm) to produce short aramid fiber suitable for reinforcing rubber or resin.

The resorcinol-formalin-rubber latex (RFL) treatment agent may be, for example, an RFL treatment solution containing about 5 to 25 mass% of a mixture containing about 2 to 20 mass parts of resorcinol-formaldehyde initial condensate per 100 mass parts of rubber latex.

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, acrylate rubber latex, and natural rubber latex. Examples of resorcinol-formaldehyde initial condensates include novolak condensates obtained by condensing resorcinol-formaldehyde under an acid catalyst or an alkali catalyst. The RFL treatment liquid may contain one or more compounds selected from blocked polyisocyanate compounds, ethyleneimine compounds, and reaction products of polyisocyanate and ethyleneimine.

The cord made by twisting the aramid fiber of the present invention may be a cord made by unwinding an aramid fiber bundle with an oil applied thereto from a bobbin and twisting it, or a cord made by twisting an aramid fiber bundle similarly unwound from a bobbin and applying an adhesive to the twisted cord, or a cord made by twisting an aramid fiber bundle similarly unwound from a bobbin and applying an adhesive to the twisted cord. The treatment with the adhesive may be performed once or more than once. It may be performed on the aramid fiber bundle or the first twisted cord, or it may be performed on the twisted cord obtained by adding a second twist to the first twisted cord, or it may be performed on the twisted cord obtained by adding a second twist to the first twisted cord. In addition, it is preferable to dry and heat-treat the aramid fiber to which the adhesive containing RFL as the main component is applied under the same conditions as in the past (100 to 260°C).

Examples of cords include single-twisted cords made by aligning two or more aramid fiber bundles and twisting them appropriately, and double-twisted cords made by bundling two or more first-twisted cords made by twisting them appropriately and then twisting them. The aramid fiber cord may also be a composite cord made of nylon fibers such as nylon 6 and nylon 66, polyester fibers such as polyethylene terephthalate, vinylon fibers, polyketone fibers, and the like. The aramid fiber cord of the present invention exerts particularly excellent effects when used for tire cords and blinds.

In the present invention, the method of applying the oil or RFL treatment liquid to the aramid fibers is not particularly limited, and any conventionally known method may be used, such as immersion oiling, spray oiling, roller oiling, and guide oiling using a metering pump.

The aramid fiber of the present invention has an epoxy compound and an ester compound of a fatty acid and a polyalkylene glycol, which can function as a diluent for diluting the epoxy compound, attached thereto as an oil agent, either as a mixture or in stages. The epoxy compound mainly contributes to improving the adhesion of the aramid fiber to rubber, and the diluent mainly contributes to improving the processability of the aramid fiber.

The cord made by twisting the aramid fibers of the present invention is free from traveler wear during twisting, has high breaking strength, and has excellent adhesive strength with rubber, so it can be widely used as a reinforcing cord for rubber products such as belts, tires, and hoses.

Examples of the above rubber 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, polysulfide rubber, etc. In addition to the main component rubber, the rubber may contain various compounding agents such as inorganic fillers such as carbon black, silica, and aluminum hydroxide, organic fillers such as coumarone resin and phenolic resin, vulcanization accelerators, antioxidants, and softeners that are commonly used in the rubber industry.

The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, "%" means "mass %". The measurements in the examples were performed according to the following methods.

(1) Moisture content of aramid fiber The mass (mass before drying) of about 5 g of a sample is measured, 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].

(2) Amount of Adhered Oil Using a Soxhlet extractor, the oil content of the fiber bundle was extracted with a cyclohexane solvent, and after evaporating the solvent, the mass of the oil was measured and calculated.

(3) Traveler Abrasion Evaluation During Twisting The processability of the aramid fiber was evaluated based on the presence or absence of traveler abrasion during twisting. Two aramid fiber multifilaments (fineness: 1,670 dtex) were twisted with a twist number of 32 t/10 cm for the first twist and 32 t/10 cm for the second twist to produce a PPTA fiber cord. At this time, 1,000 m of the yarn was twisted with a nylon traveler for 1 hour. If the matte finish of the traveler was worn, it was judged as having abrasion, and if the matte finish of the traveler was not worn, it was judged as not having abrasion.

(4) Evaluation of T-adhesion (adhesion between cord and rubber) According to the adhesion-A method of JIS L 1017:2002, the treated cord was embedded in unvulcanized rubber, and press-vulcanized under pressure at 150°C for 30 minutes to measure the initial adhesion. After cooling, the cord was pulled out from the rubber block at a speed of 300 mm/min, and the load required for the pull-out was displayed in N/cm.

(Examples 1 to 3)
1 kg of polyparaphenylene terephthalamide (molecular weight: about 20,000) obtained by a conventional method was dissolved in 4 kg of concentrated sulfuric acid, extruded from a spinneret having 1,000 holes with a diameter of 0.1 mm at a shear rate of 30,000 sec ^-1 , spun into water at 4°C, neutralized with a 10 mass% aqueous sodium hydroxide solution at 10°C for 15 seconds, and then dried by heating at 200°C to obtain polyparaphenylene terephthalamide fiber (total fineness: 1,670 dtex) with a moisture content of 10 mass%.

The above bundle of polyparaphenylene terephthalamide fibers was treated with an oil solution consisting of a mixture of an epoxy compound and a polyalkylene glycol fatty acid ester, as shown in Table 1, in an amount of 0.7% based on the fiber mass when converted to a moisture content of 0%, and then the fibers were wound up and packaged.

A bundle of polyparaphenylene terephthalamide fibers unwound from a package was twisted in the Z direction at 32t/10cm to obtain a first twisted cord, and then two first twisted cords were aligned and twisted in the S direction at 32t/10cm to obtain a second twisted cord.

Next, the prepared cord was immersed in an adhesive treatment solution containing RFL as the main component using a Computorita treatment machine (manufactured by Ritzler), dried at 100°C for 150 seconds, and then heat-treated at 220°C for 123 seconds to obtain an RFL-treated aramid fiber cord.

Example 4
Polyparaphenylene terephthalamide fibers were obtained in the same manner as in Example 1, and glycerol polyglycidyl ether was applied to the obtained bundle of polyparaphenylene terephthalamide fibers, and then polyethylene glycol monooleate was applied thereto, followed by winding up and packaging.
Two bundles of polyparaphenylene terephthalamide fibers unwound from a package were aligned and twisted in the Z direction at 32 t/10 cm to obtain a first twisted cord, and then two first twisted cords were aligned and twisted in the S direction at 32 t/10 cm to obtain a second twisted cord.
The prepared twisted cord was immersed in an RFL treatment solution using a Computorita treatment machine (manufactured by Ritzler) in the same manner as in Example 1, and was dried and heat-treated under the same conditions as in Example 1 to obtain an RFL-treated aramid fiber cord.

(Comparative Example 1)
Polyparaphenylene terephthalamide fibers were obtained in the same manner as in Example 1, and the obtained bundles of polyparaphenylene terephthalamide fibers were coated with an oil solution consisting of a mixture of an epoxy compound and a diluting oil solution shown in Table 1, and then wound up into a package.
Two bundles of polyparaphenylene terephthalamide fibers unwound from a package were aligned and twisted in the Z direction at 32 t/10 cm to obtain a first twisted cord, and then two first twisted cords were aligned and twisted in the S direction at 32 t/10 cm to obtain a second twisted cord.
The prepared twisted cord was immersed in an RFL treatment solution using a Computorita treatment machine (manufactured by Ritzler) in the same manner as in Example 1, and was dried and heat-treated under the same conditions as in Example 1 to obtain an RFL-treated aramid fiber cord.

(Comparative Example 2)
Polyparaphenylene terephthalamide fibers (total fineness: 1,670 dtex) having a moisture content of 50% by mass were obtained by changing the drying conditions in Example 1. The obtained bundle of polyparaphenylene terephthalamide fibers was applied with an oil solution consisting of a mixture of an epoxy compound and a diluting oil solution shown in Table 1, and then wound up into a package.
Two bundles of polyparaphenylene terephthalamide fibers unwound from a package were aligned and twisted in the Z direction at 32 t/10 cm to obtain a first twisted cord, and then two first twisted cords were aligned and twisted in the S direction at 32 t/10 cm to obtain a second twisted cord.
The prepared twisted cord was immersed in an RFL treatment solution using a Computorita treatment machine (manufactured by Ritzler) in the same manner as in Example 1, and was dried and heat-treated under the same conditions as in Example 1 to obtain an RFL-treated aramid fiber cord.

The evaluation results are summarized in Table 1.

From the results in Table 1, the aramid fibers of the examples to which the oil of the present invention was applied had good traveler abrasion resistance during twisting, and also had very good T-adhesive strength.
On the other hand, the aramid fiber to which an oil solution in which a glycerol-based epoxy compound was diluted with a polyethylene glycol-polypropylene glycol copolymer was applied had good rubber adhesion, but the traveler was worn during twisting, and the processability was poor. The aramid fiber to which an oil solution in which a sorbitol-based epoxy compound was diluted with a polyethylene glycol-oleic acid ester was applied to an aramid fiber having a moisture content of 50 mass % had no wear of the traveler during twisting, and had excellent processability, but had poor adhesion to rubber.

The aramid fiber of the present invention can be suitably used to reinforce rubber products such as tires, belts, and hoses.

Claims (12)

A para-aramid fiber having an oil agent applied thereto,
The aramid fiber has a moisture content of 3 to 15 mass% after application of an oil agent , the oil agent contains (a) and (b), and no epoxy curing agent is added.
(a) an aliphatic epoxy compound; (b) an ester compound of a fatty acid and a polyalkylene glycol represented by the following general formula (I) and/or the following general formula (II):

(In the formula, R ¹ is an alkyl group or alkenyl group having 5 to 30 carbon atoms, R ² is an alkylene group having 2 to 3 carbon atoms, and m is an integer of 5 to 100 representing the average number of moles of oxyalkylene groups (R ² -O) added. Note that in (R ² -O), the same oxyalkylene group may be added, or two or more types of oxyalkylene groups may be added.)

(In the formula, R ¹ and R ³ are both alkyl or alkenyl groups having 5 to 30 carbon atoms and may be the same or different. R ² is an alkylene group having 2 to 3 carbon atoms, and n is an integer of 5 to 100 representing the average number of moles of oxyalkylene groups (R ² -O) added. In addition, in (R ² -O), the same oxyalkylene group may be added, or two or more types of oxyalkylene groups may be added.)
(b) The aramid fiber according to claim 1, wherein in the general formula (I) or (II), R ² is an alkylene group having 2 carbon atoms. (b) The aramid fiber according to claim 1 or 2, wherein in general formula (I) or (II), m and n are 9 to 30. (b) The aramid fibers according to any one of claims 1 to 3, wherein the ester compound of a fatty acid and a polyalkylene glycol is an ester compound represented by general formula (I) as a main component, R ¹ is an alkyl group or alkenyl group having 9 to 26 carbon atoms, R ² is an alkylene group having 2 carbon atoms, and m is 9 to 21. (b) The ester compound of a fatty acid and a polyalkylene glycol is an ester compound represented by the general formula (I) as a main component, and R ¹ is an alkyl or alkenyl group having 13 to 22 carbon atoms, R ² 4. The aramid fiber according to claim 1, wherein: is an alkylene group having 2 carbon atoms; and m is 9 to 30. 6. The aramid fiber according to claim 1 , wherein the epoxy compound (a) is one or a mixture of two selected from glycerol diglycidyl ether and glycerol triglycidyl ether. An aramid fiber cord comprising an aramid fiber having the oil agent according to any one of claims 1 to 6 applied thereto and a resorcinol-formaldehyde-rubber latex (RFL) adhesive applied thereto .
A method for producing aramid fibers, comprising the steps of: applying an oil solution (excluding an epoxy curing agent) consisting of a mixture of (a) an aliphatic epoxy compound and (b) an ester compound of a fatty acid and a polyalkylene glycol to para-aramid fibers that have been spun, neutralized, and then dried to a moisture content of 15% by mass or less; and then winding the aramid fibers to which the oil solution has been applied around a bobbin in a winding step, thereby maintaining the moisture content of the wound aramid fibers at 3 to 15% by mass. A method for producing aramid fibers, comprising the steps of (a) providing an aliphatic epoxy compound to para- aramid fibers that have been spun, neutralized, and then dried to a moisture content of 15% by mass or less, and (b) providing an ester compound of a fatty acid and a polyalkylene glycol (but not including a step of providing an epoxy curing agent), and then winding the aramid fibers to which the epoxy compound and the ester compound have been provided on a bobbin in a winding step, and maintaining the moisture content of the wound aramid fibers at 3 to 15% by mass. 10. A method for producing an aramid fiber cord, comprising unwinding the aramid fiber obtained by the method according to claim 8 or 9 from a bobbin and twisting it into a yarn. 10. A method for producing an aramid fiber cord, comprising unwinding the aramid fiber obtained by the method according to claim 8 from a bobbin, twisting the aramid fiber, and applying an adhesive to the twisted cord. 10. A method for producing an aramid fiber cord, comprising unwinding the aramid fiber obtained by the method according to claim 8 or 9 from a bobbin, applying an adhesive thereto, and twisting the cord to which the adhesive has been applied.