JP2024141138A - Rubber reinforcing fiber cord - Google Patents

Abstract

The present invention provides a rubber reinforcing cord that does not rely on compounds that place a high burden on the environment, has sufficiently high adhesive strength even at high temperatures, and is excellent in cord strength and fatigue resistance.
[Solution] A rubber reinforcing cord is formed by aligning at least two or more first twisted cords and then twisting the first twisted cord to form an organic fiber cord, the surface of which has an adhesive layer treated with a rubber adhesive containing an epoxy compound and latex, wherein at least one of the two or more first twisted cords is made of organic fiber treated with an epoxy compound that does not contain a curing agent, and the epoxy value (X) of the inner layer of the cord and the epoxy value (Y) of the outer layer of the cord satisfy Y/X = 0 to 0.2.
[Selection diagram] None

Description

The present invention relates to a fiber cord for reinforcing rubber.

Synthetic fibers such as aramid fibers, nylon fibers, polyester fibers, and rayon fibers have strength and elasticity, and are flexible and lightweight, so they are used as rubber reinforcing fibers for various tires, belts, conveyors, etc. However, when bonding synthetic fibers to rubber, they need to be treated with an adhesive. Resorcinol-formaldehyde-rubber latex (hereinafter referred to as RFL) has high adhesive strength, and chlorophenol and triazine compounds have the effect of improving adhesive performance at high temperatures, but these compounds have a high environmental impact (for example, Patent Document 1).

On the other hand, if the adhesive performance at high temperatures decreases, the cord will no longer be able to effectively utilize its inherent properties, and when used in rubber materials such as tires, the adhesive surface between the rubber and the cord will peel off and break. To solve these problems, there is a need to develop an adhesive that has sufficient adhesive strength even at high temperatures. Moreover, it is desirable to have an adhesive that has a low environmental impact.

It has long been known to apply epoxy compounds to improve adhesion between fibers and rubber. However, in tire applications, cord strength and fatigue resistance are required, so if the entire cord is treated with an epoxy compound and then cured, the cord becomes too hard, leading to a deterioration in fatigue resistance and a decrease in strength. There is also a method of using epoxy pre-treated yarn in which an epoxy compound is fixed within the fiber structure to maintain the adhesive strength between the adhesive and the fibers, but this poses production challenges because the epoxy treatment is carried out under high moisture conditions.

Patent Document 2 discloses a method in which a fiber cord (not an epoxy pretreated thread) is treated with an aqueous epoxy solution having two or more epoxy groups, then immediately irradiated with ultraviolet light to harden it, and treated with an RFL adhesive to reduce the friction between the fibers when braiding them into a braid or spiral shape, thereby improving workability. However, the fiber surface is not epoxy treated.

Patent Documents 3 and 4 disclose a method for obtaining a rubber reinforcing cord with improved adhesion to rubber by using a fiber composite in which a cured film of a curable epoxy compound and an uncured curable epoxy compound are attached to the fiber surface. However, there is no mention of treating the obtained cord with an epoxy compound.

In addition, in Patent Documents 5 and 6, the under-twisted and over-twisted cord is immersed in a treatment liquid containing an epoxy compound and then treated with an RFL-based adhesive, but this uses an adhesive that has a high environmental impact.

Republished 2020/031408 (Claims, etc.) JP-A-4-352879 (Claims, etc.) JP 2021-1558705 A (Claims, etc.) JP 2021-161569 A (Claims, etc.) Patent No. 4336620 (Claims, etc.) Japanese Patent No. 4565542 (Claims, paragraph 0051, etc.)

The objective of the present invention is to provide a rubber reinforcing cord that does not rely on compounds that have a high environmental impact, has sufficiently high adhesive strength even at high temperatures, and has excellent cord strength and fatigue resistance.

In order to solve the above problems, the inventors conducted extensive research. They succeeded in increasing the adhesion between the outermost cord surface and the adhesive and achieving high adhesive strength at high temperatures by configuring the epoxy compound on the organic fiber surface inside the twisted cord to remain uncured and gradually curing the epoxy compound as it reaches the cord surface.

In other words, the present invention is as follows.

(1) A rubber reinforcing cord comprising at least two or more first-twisted cords arranged in parallel and then second-twisted organic fiber cords, the surface of which is treated with a rubber adhesive containing an epoxy compound and latex to form an adhesive layer,
A rubber reinforcing cord, characterized in that at least one of the two or more first twisted cords is composed of an organic fiber treated with an epoxy compound not containing a curing agent.
(2) The rubber-reinforcing cord according to (1) above, characterized in that the epoxy value (X) of the inner cord layer and the epoxy value (Y) of the outer cord layer satisfy Y/X = 0 to 0.2.
(3) The rubber reinforcing cord according to (2) above, characterized in that the rubber reinforcing cord satisfies one or more of the following (a) and (b):
(a) a post-fatigue strength retention rate of 70% or more; (b) a high-temperature (120°C) adhesive strength of 70 N/cm or more; (4) The rubber reinforcing cord according to any one of (1) to (3), wherein the organic fiber cord contains at least aramid fibers, and the ratio of the aramid fibers is 50% by weight or more.

The present invention makes it possible to provide a rubber reinforcing cord that has high adhesion even at high temperatures (120°C) and excellent fatigue resistance, even though the composition does not contain compounds that have a high environmental impact.

[Organic fiber]
Examples of organic fibers constituting the rubber reinforcing cord of the present invention include aramid fibers, nylon (nylon 6, nylon 66, etc.) fibers, polyester fibers, rayon fibers, etc. Among these organic fibers, organic fiber cords containing at least aramid fibers, which have extremely high strength and elastic modulus, are preferred. Examples include aramid fiber cords, composite cords of aramid fibers and nylon fibers, composite cords of aramid fibers and polyester fibers, etc.

Examples of aramid fibers include para-aramid fibers and meta-aramid fibers, but para-aramid fibers, which have excellent tensile strength, are preferred. Examples of commercially available para-aramid fibers include polyparaphenylene terephthalamide fibers (manufactured by DuPont USA, Toray DuPont Co., Ltd., product name "Kevlar" (registered trademark)) and copolyparaphenylene-3,4'-oxydiphenylene terephthalamide fibers (manufactured by Teijin Limited, product name "Technora" (registered trademark)). Among these para-aramid fibers, polyparaphenylene terephthalamide fibers are particularly preferred.

The above-mentioned aramid fibers may be produced by known methods. The aramid fibers are not particularly limited as long as they have at least one divalent aromatic group, which may be substituted, in the repeating unit of the polymer forming the fiber and have at least one amide bond, and may be called wholly aromatic polyamide fibers or aramid fibers, and the "divalent aromatic group, which may be substituted" means a divalent aromatic group, which may have one or more identical or different substituents.

The aramid fiber used in the present invention is preferably one to which a curable epoxy compound has been added in advance in the spinning process as a mixture with a fiber oil, or one to which a curable epoxy compound and an oil have been added in separate processes. The curable epoxy compound is preferably added to aramid fiber whose moisture content has been adjusted by spinning, neutralization, or by drying after spinning, neutralization, and washing, and the moisture content is preferably 15% by weight or less. If the moisture content exceeds 15% by weight, the curable epoxy compound will be incorporated into the fiber structure, making it difficult to control the curing state of the epoxy compound.

It is also desirable that the textile oils and process chemicals do not contain hardeners. Among hardeners, amine-based hardeners have the effect of accelerating the hardening rate of epoxy compounds, and they lower the epoxy value of the fibers present in the inner layer of the rubber reinforcing cord.

Usually, an epoxy compound applied to an organic fiber cord (twisted yarn cord) hardens on the surface of the cord to form a coating, which physically covers the surface of the cord.
However, in the case of an organic fiber cord containing organic fibers treated with an epoxy compound that does not contain a curing agent (epoxy pre-treated yarn), the epoxy compound inside the cord does not harden, but instead plays a role in guiding the epoxy compound to the inside of the cord in the subsequent step of applying a treatment agent containing the epoxy compound, thereby increasing the epoxy value of the material in the inner layer of the cord (the center side of less than 1/2 of the cord radius).
On the other hand, in the case of an organic fiber cord (twisted cord) that does not use an epoxy pretreated yarn, the applied epoxy compound is present in the outer layer (almost only the surface layer). Even if an epoxy pretreated yarn is used, if the organic fiber cord is not treated with an epoxy compound, the epoxy treatment agent does not penetrate into the inside of the cord.

In the present invention, the curable epoxy compound may be one or more selected from aliphatic epoxy compounds and epoxy compounds having an aromatic ring. Two or more may be mixed and used, or may be used separately. Furthermore, in order to improve processability, the curable epoxy compound may be mixed with a fiber oil agent and applied, or these two agents may be applied in two stages.

The aliphatic epoxy compound is preferably one or a mixture of two or more selected from glycidyl ether compounds of polyhydric alcohols such as glycerol, sorbitol, polyglycerol, etc. Examples include glycerol diglycidyl ether, glycerol triglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, etc. Examples of epoxy compounds having an aromatic ring include one or a mixture of two or more selected from bisphenol-type epoxy resins, and glycidyl ether compounds such as 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 in the spinning process, and do not impair processability. Glycerol-based polyepoxides such as glycerol diglycidyl ether and glycerol triglycidyl ether are particularly preferred.

As the textile oil, a water-soluble oil is preferred in terms of compatibility with the curable epoxy compound. As the water-soluble oil, one that is highly compatible with the curable epoxy compound, has a high smoothness required for a textile oil, and has an effect of reducing abrasion with the traveler when twisting aramid fibers is preferred. For example, fatty acid polyglycol esters can be mentioned, and one or a mixture selected from monoester type and diester type can be used. In terms of adhesion to rubber and solubility with the curable epoxy compound, the fatty acid constituting the ester is preferably a saturated or unsaturated fatty acid having 7 to 28 carbon atoms, and the polyglycol is preferably a polyethylene glycol having a weight average molecular weight (Mw) of 400 to 1,300, in that an ester compound having excellent solubility with the curable epoxy compound can be obtained.

When the curable epoxy compound and the fiber oil are applied to the aramid fiber as a mixture, it is preferable to use (a) the curable epoxy compound and (b) the water-soluble oil in a ratio of (a)/(b) = 50/50 to 90/10 (weight ratio). (a)/(b) is more preferably 50/50 to 70/30, and even more preferably 55/45 to 65/35.

The amount of the curable epoxy compound attached to the aramid fiber is preferably 10 mmol/kg or more and 50 mmol/kg or less based on the weight of the aramid fiber (on a dry basis). If the amount attached is too small, the post-fatigue strength retention rate of the rubber reinforcing cord and the adhesive strength at high temperatures will decrease, and if the adhesive strength is too high, the economic efficiency and productivity will decrease. More preferably, it is 10 to 30 mmol/kg, and even more preferably, it is 15 to 25 mmol/kg.

The aramid fiber with the curable epoxy compound attached is then wound onto a bobbin in the winding process. After winding, the aramid fiber is kept at room temperature without heat treatment or tension treatment, and the moisture content is maintained at 3 to 15% by weight.

[Organic fiber cord]
It is important that at least one of the two or more first twist cords in the rubber reinforcing cord of the present invention is made of an organic fiber treated with an epoxy compound containing no curing agent. A preferred example of the organic fiber treated with an epoxy compound containing no curing agent is the above-mentioned aramid fiber.

One example of an organic fiber treated with an epoxy compound that does not contain a curing agent is a method in which one or more aramid fibers obtained by the above-mentioned method are aligned, and single-twisted in the S or Z direction to obtain a first-twisted cord, and then two or more of the first-twisted cords are aligned and second-twisted in the same direction as the single-twist (lang twist) or in the opposite direction (pair twist) to obtain a second-twisted cord.

As the under-twisted cord to be twisted with the above under-twisted cord, a under-twisted cord made of organic fibers treated with an epoxy compound containing a curing agent, a under-twisted cord made of organic fibers not treated with an epoxy compound, etc. can be used. One or more types of organic fibers can be selected depending on the purpose of the rubber reinforcing cord, and examples of the organic fibers include aramid fibers, nylon fibers, polyester fibers, etc. The epoxy treatment method for the organic fibers is not particularly limited.

In the present invention, from the viewpoint of increasing the strength of the rubber reinforcing cord, it is preferable that the organic fiber cord contains aramid fiber, and it is preferable that the ratio of aramid fiber in the organic fiber cord is 50% by weight or more.

In the present invention, the number of twists in the lower twisted cord and the upper twisted cord is preferably 20 to 50 t/10 cm. If the number of twists is less than 20 t/10 cm, the fatigue resistance of the cord tends to decrease, and if the number of twists exceeds 50 t/10 cm, the strength of the cord tends to decrease. The number of twists can be adjusted according to the purpose.

[Rubber reinforcement cord]
The rubber reinforcing cord of the present invention has an adhesive layer formed by treating the surface of an organic fiber cord obtained by aligning at least two or more first twisted cords and then second twisting the cord with a rubber adhesive containing an epoxy compound and latex.
In addition, in a rubber-reinforcing cord, the epoxy value (X) of the inner layer part of the cord and the epoxy value (Y) of the outer layer part of the cord are preferably Y/X = 0 to 0.2. Note that the "outer layer part of the cord" refers to the "surface layer part of the cord treated with a rubber adhesive", and the "inner layer part of the cord" refers to the "inner layer part remaining after removing the surface layer part from the cord treated with a rubber adhesive".

In the rubber reinforcement cord of the present invention, the epoxy value of the outer layer of the cord is low (including 0), but at least one of the first twisted cords contains organic fibers treated with an epoxy compound that does not contain a curing agent, and the epoxy compound contained in the rubber adhesive that treats the surface of the cord is introduced into the inside of the cord, resulting in a high epoxy value in the inner layer of the cord.
That is, a large amount of uncured epoxy compound is present in the inner layer portion of the cord. Specifically, a rubber reinforcing cord in which two or more first twist cords are all made of organic fibers treated with an epoxy compound (without a curing agent) has a high epoxy value (X) in the inner layer portion of the cord, while a rubber reinforcing cord in which only one cord is made of organic fibers treated with an epoxy compound (without a curing agent) has a lower epoxy value (X) in the inner layer portion of the cord than the former. On the other hand, in the case of an organic fiber in which a top twist cord is treated with an epoxy compound (including a curing agent), the epoxy compound is cured on the cord surface, so the epoxy value (Y) in the outer layer portion of the cord is low.

In the present invention, it is presumed that the uncured epoxy compound present in the inner layer of the cord provides an anchoring effect to the bonding strength between the cord and the epoxy. Therefore, it is presumed that the increased adhesive strength between the cord and the adhesive results in a rubber-reinforcing cord with high adhesive strength at high temperatures and excellent fatigue resistance. In addition, if a large amount of uncured epoxy compound is present in the outer layer of the cord, it is assumed that the cord will become fatigued (fatigue resistance will decrease) due to hardening. For this reason, it is important that a large amount of uncured epoxy compound is present in the inner layer of the cord, and by doing so, it is possible to provide a rubber-reinforcing cord with excellent fatigue resistance (high strength retention after fatigue) and excellent high-temperature (120°C) pull-out adhesive strength.

The amount of epoxy compound (A) present in the inner layer of the cord is not particularly limited, but is preferably 5.0 (mmol/kg) or more. If it is less than 5.0 (mmol/kg), the epoxy compound may cure too much, causing the inside of the cord to harden, resulting in a decrease in cord durability. It is more preferably 7.5 (mmol/kg) or more, and even more preferably 10.0 (mmol/kg) or more.

The amount of epoxy compound (B) present in the outer layer of the cord is preferably less than 5.0 (mmol/kg). If it is 5.0 (mmol/kg) or more, the epoxy curing reaction on the cord surface may not proceed sufficiently, resulting in insufficient adhesion between the cord and the epoxy compound. It is more preferably less than 2.5 (mmol/kg).

In a preferred embodiment of the rubber reinforcing cord of the present invention, most of the epoxy compound is present as an uncured product in the inner layer of the rubber reinforcing cord, and the epoxy compound is present as a cured product in the outer layer of the cord. In this case, there is a manufacturing method in which an organic fiber cord is produced using at least one raw yarn pretreated with an epoxy compound that does not contain a curing agent, the surface of the produced organic fiber cord is treated with a rubber adhesive that contains an epoxy compound and latex, and then the cord is heat-treated.

In another preferred embodiment of the rubber reinforcing cord of the present invention, an organic fiber cord is produced using at least one raw yarn pretreated with an epoxy compound that does not contain a curing agent, and the surface of the produced organic fiber cord is treated with a treatment agent containing an epoxy compound, then subjected to a heat treatment, and then further treated with a rubber adhesive containing latex, and then heat-treated again.

In the present invention, the number of times the rubber adhesive containing the epoxy compound and latex is treated is not particularly limited. From the viewpoint of economy, one time (one-bath treatment) is preferred, but two or more times may be used. The adhesive treatment is preferably performed on twisted fiber cords. From the viewpoint of rubber adhesion and fatigue resistance of the cord, the amount of adhesive applied is preferably 3 to 20% by weight (based on the weight of the cord), more preferably 5 to 15% by weight, and even more preferably 6 to 10% by weight.

A rubber adhesive containing an epoxy compound and latex is used as the adhesive (first adhesive) that forms the adhesive layer. The inclusion of latex can enhance adhesion to rubber. Other components may include a blocked polyisocyanate compound. The epoxy compound may be the same as the epoxy compound described above.

Examples of latex that can be used include vinylpyridine-styrene-butadiene, isoprene, styrene-butadiene, ethylene-propylene-diene, acrylonitrile-butadiene, chloroprene, chlorosulfonated polyethylene, acrylate, and natural rubber latex. These latexes may be used alone or in combination of two or more. The use of latex can improve the adhesion between the organic fiber cord and the rubber member.

The rubber reinforcing cord of the present invention may be further treated with a second adhesive. The known RFL (a mixture of resorcinol, formaldehyde initial condensate, and rubber latex) can be used as the second adhesive. RFL has excellent permeability and adhesion to organic fiber cords and excellent adhesion to rubber. For example, an RFL treatment solution containing a mixture containing about 2 to 20 parts by weight of resorcinol-formaldehyde initial condensate (solid content equivalent) per 100 parts by weight of rubber latex (solid content equivalent), with a solid content concentration of about 5 to 25% by weight, can be mentioned.

The application of the adhesive containing RFL to the untreated cord is preferably carried out using a treatment liquid in which the second adhesive is dissolved or dispersed in a liquid. The total solids concentration of the adhesive in the treatment liquid is preferably 5 to 25% by weight, more preferably 15 to 25% by weight. Within this range, the stability of the treatment liquid containing the adhesive is excellent, and the adhesive can be applied uniformly to the organic fibers. A known viscosity modifier can also be added to the second adhesive.

A known method can be used to apply the treatment liquid containing the adhesive to the aramid fibers. The amount of adhesive applied and the adhesive impregnation rate can be controlled, for example, by setting the concentration of the adhesive treatment liquid, the conditions for removing the liquid after immersion in the adhesive treatment liquid, and conditions such as the dipping speed and tension.

Usually, after applying an adhesive containing RFL to the aramid fibers, they are dried and heat treated. The heat treatment conditions are preferably a drying temperature of 100-160°C, a residence time of 0.5-5 minutes, a heat treatment temperature of 200-260°C, and a residence time of 0.5-5 minutes.

When applying the adhesive and then drying and heat treating, it is preferable to apply a tension of 0.15 g/dtex to 0.80 g/dtex and perform tension heat treatment. This optimizes the alignment of the filaments in the twisted cord, and increases its strength. In addition, since excessive tension is not applied to the twisted cord, damage to the yarn caused by abrasion during processing is minimized, and the cord strength can be maintained at a higher value.

The aramid fiber cord obtained as described above is 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. to obtain a composite cord.

The rubber reinforcing cord of the present invention has high adhesion to rubber and a high adhesive impregnation rate, so adhesive transfer is unlikely to occur between the dipped cord and rubber, and no adhesive residue is generated during the cord manufacturing process, making it possible to maximize the properties of the organic fiber cord. Taking advantage of these properties, the cord can be suitably used to reinforce rubber products such as cords and sudare for various tires for 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.

Examples of 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, 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 explained below using examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, "%" means "% by weight." The measurements in the examples were performed according to the following methods.

(1) Initial Strength Measurement was carried out using a tensile tester (manufactured by A&D Co., Ltd., product name: Tensilon, model: RTM1T) under the following conditions based on the procedure of the method of JIS L1017:2002.
[Measurement conditions]
Measurement environment temperature: 20±3℃
Humidity: 65±5%
Test speed: 100 mm/min. Chuck distance: 250 mm

(2) Evaluation of T-adhesion (adhesion between cord and rubber) In accordance with the adhesion-A method of JIS L1017:2002, 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.

(3) High-Temperature Adhesion Strength In accordance with the adhesion strength-A method of JIS L1017:2002, the treated cord was embedded in unvulcanized rubber, and press-vulcanized under pressure at 150°C for 30 minutes to measure the initial adhesion strength. The cord was then pulled out from the rubber block at 120°C at a speed of 300 mm/min, and the load required for the pullout was expressed in N/cm.

(4) Strength after fatigue, strength retention after fatigue A belt-type flex fatigue tester (Ueshima Seisakusho) was used to measure according to JIS L1017:2002. The cords treated by the method of the present invention were driven into a 4 mm thick rubber sheet at 16 cords/inch, sandwiched between 0.4 mm rubber sheets, arranged in parallel in two layers, and vulcanized at 150°C for 30 minutes with a press pressure of 50 kg/cm2. The vulcanized rubber sheet was cut into a belt shape of 1 inch width x 410 mm length, attached to a roller with a diameter of 1 inchφ, and a load of 50 kg was applied, and the reciprocating motion was repeated at a speed of 180 rpm for 24 hours. The belt sample after fatigue loading was immersed in toluene to swell, and then the cord was taken out from the layer of the two-layer rubber sheet on the side where the roller was installed, and the strength was measured according to the method of JIS L1017:2002 to obtain the strength after fatigue. The ratio of the post-fatigue strength to the initial strength was defined as the post-fatigue strength retention rate (%).

(5) Epoxy value measurement method Separately, 10 g of sample (actual weight Ag) is placed in a beaker, and the free epoxy compounds attached to the surface of the sample are extracted with acetone, and then the acetone is removed and the weight of the extract is measured. 20 ml of a hydrochloric acid/1,4-dioxane mixed solution (15/1000 (volume ratio)) and 30 ml of ethanol are added to the extract, and neutralization titration (titration amount: C ml) is performed with a 0.5 mol/L NaOH solution. A blank titration (titration amount: D ml) is performed on the hydrochloric acid/1,4-dioxane mixed solution not containing the extract, and the number of millimoles of free epoxy groups present per kg of sample is calculated as the amount of free epoxy compounds using the following formula.
[Amount of free epoxy compound (mmol/kg)]=0.5×1000×(D−C)/A

(6) Measurement method of epoxy value of inner and outer layers of cord Outer layer: 10 g of the surface layer of the RFL-treated cord was sampled, and the epoxy value of the sample was measured. Inner layer: The surface layer of the RFL-treated cord was removed, and 10 g of the innermost layer of the cord was sampled, and the epoxy value of the sample was measured.
The cord center (distance of 50% of the cord diameter) was determined as the diameter of the cord measured by the method described in JIS L1017:2002 8.1 Cord Gauge. The fiber cord used in the experiment had a diameter of 0.5 to 1.0 mm.

Example 1
1 kg of polyparaphenylene terephthalamide (hereinafter, abbreviated as PPTA) (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 wt% aqueous sodium hydroxide solution at 10°C for 15 seconds, and then dried by heating to obtain a PPTA fiber with a moisture content of 10 wt% (total fineness 1,670 dtex).

An oil agent (epoxy compound/polyglycol ester = 30/70 (weight ratio)) was applied to the resulting bundle of PPTA fibers so that the amount was 1% of the fiber weight when converted to a moisture content of 0%, and then the bundle was wound up and packaged.

The obtained PPTA fiber of 1,670 dtex (epoxy pretreated yarn, initial elastic modulus 520 cN/dtex) was twisted in the Z direction at 40 t/10 cm to produce a first twisted cord, and two of these first twisted cords were twisted in the S direction at 40 t/10 cm to produce a second twisted yarn cord.
The resulting twisted cord was immersed in a first adhesive treatment liquid mainly composed of vinylpyridine-styrene-conjugated diene rubber latex and an epoxy compound, heat-treated at 140° C. for 2 minutes to remove moisture, and then heat-treated at 230° C. for 1 minute. The cord was then immersed in a second adhesive treatment liquid mainly composed of resorcin-formalin-rubber latex (RFL), heat-treated at 140° C. for 2 minutes to remove moisture, and then heat-treated at 230° C. for 1 minute to complete an aramid fiber cord. The results are shown in Table 1.

Example 2
In the same manner as in Example 1, a ply-twisted yarn cord was prepared.
The resulting twisted yarn cord was immersed in a first adhesive treatment liquid mainly composed of vinylpyridine-styrene-conjugated diene rubber latex and an epoxy compound, heat-treated at 215° C. for 2 minutes to remove moisture, and then heat-treated at 230° C. for 1 minute. The cord was further immersed in a second adhesive treatment liquid mainly composed of resorcin-formalin-rubber latex (RFL), heat-treated at 140° C. for 2 minutes to remove moisture, and then heat-treated at 230° C. for 1 minute to complete an aramid fiber cord.

(Comparative Example 1)
A commercially available polyparaphenylene terephthalamide fiber (total fineness 1,670 dtex, Kevlar® 29, manufactured by DuPont-Toray Co., Ltd.) was used.

(Comparative Example 2)
In the same manner as in Example 1, PPTA fibers (total fineness: 1,670 dtex) having a moisture content of 10% by weight were obtained.
An oil agent (epoxy compound/polyglycol ester mixture = 30/70 (weight ratio)) containing a curing agent (organic amine) was applied to the obtained PPTA fiber bundle in an amount of 1.0% based on the fiber weight when converted to a moisture content of 0%, and then the bundle was wound up and packaged. Using the obtained PPTA fiber, an aramid fiber cord was obtained in the same manner as in Example 1.

(Comparative Example 3)
In the same manner as in Example 1, PPTA fibers (total fineness: 1,670 dtex) having a moisture content of 50% by weight were obtained.
An oil agent (epoxy compound/polyglycol ester mixture=30/70 (weight ratio)) was applied to the obtained bundle of PPTA fibers in an amount of 1.0% based on the fiber weight when converted to a moisture content of 0%, and then the bundle was wound up and packaged. Using the obtained PPTA fibers, an aramid fiber cord was obtained in the same manner as in Example 1.

The evaluation results are summarized in Table 1.

From the results in Table 1, it can be seen that the aramid twisted yarn cord of the present invention, which has a large amount of uncured epoxy compound in the inner layer of the cord, is superior in strength retention after cord fatigue and adhesive strength at high temperatures compared to the aramid twisted yarn cords of Comparative Examples 2 and 3, which have a small amount of uncured epoxy compound in the inner layer of the cord. It can also be seen that the aramid twisted yarn cord of Comparative Example 1, in which the raw yarn is not pretreated with an epoxy compound, is inferior in all of strength retention after cord fatigue, T-adhesion strength, and adhesive strength at high temperatures. Therefore, it can be seen that increasing the amount of uncured epoxy compound in the inner layer of the cord is effective in improving the strength retention after cord fatigue and adhesive strength at high temperatures of the aramid twisted yarn cord.

The present invention has been specifically described above using examples, but the above-mentioned embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited to the above-mentioned embodiments, and various modifications are possible within the scope of the claims.

The rubber reinforcing cord of the present invention can be suitably used as a tire reinforcing cord. It goes without saying that it can also be used for other rubber products such as belts and hoses.

Claims (4)

A rubber reinforcing cord comprising at least two or more first twisted cords arranged in parallel and then second twisted, the surface of which is treated with a rubber adhesive containing an epoxy compound and latex to form an adhesive layer,
A rubber reinforcing cord, characterized in that at least one of the two or more first twisted cords is composed of an organic fiber treated with an epoxy compound not containing a curing agent. The rubber reinforcing cord according to claim 1, characterized in that the epoxy value (X) of the inner layer of the cord and the epoxy value (Y) of the outer layer of the cord are Y/X = 0 to 0.2. The rubber-reinforcing cord according to claim 2, characterized in that the rubber-reinforcing cord satisfies at least one of the following (a) and (b):
(a) Strength retention after fatigue is 70% or more. (b) High temperature (120°C) adhesive strength is 70 N/cm or more. The rubber reinforcing cord according to any one of claims 1 to 3, characterized in that the organic fiber cord contains at least aramid fiber, and the ratio of the aramid fiber is 50% by weight or more.