Synthetic fiber cord for rubber reinforcement

Abstract

To provide a synthetic fiber cord for rubber reinforcement that makes it possible to achieve superior initial adhesion strength and superior adhesion strength at high temperature, even when raw materials favorable for reducing environmental burden are employed.SOLUTION: A synthetic fiber cord for rubber reinforcement is obtained by applying to a synthetic fiber a treating agent containing at least a lignin derivative, a water-soluble or water-dispersible crosslinking agent, and a rubber latex, while being free of resorcinol, formaldehyde, and condensates thereof, and then subjecting the treated fiber to heat treatment. The synthetic fiber cord for rubber reinforcement has an adhesion strength at high temperature that is 30% to 100% of the initial adhesion strength, and the synthetic fiber is at least one fiber selected from the group consisting of polyester fiber, nylon fiber, vinylon fiber, and rayon fiber.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a synthetic fiber cord for reinforcing rubber. [Background technology]

[0002] Rubber products such as tires, hoses, and belts use polyester fibers, nylon fibers, vinylon fibers, rayon fibers, and other fibers as reinforcing materials. Resorcinol-formalin-latex (RFL) adhesives (hereinafter sometimes simply referred to as "RFL") containing resorcinol, formalin, and rubber latex have traditionally been widely used to bond these synthetic fibers to rubber compositions in rubber products. However, both resorcinol and formalin are highly toxic substances that pose a significant environmental burden and are harmful to health. Therefore, in recent years, there has been a demand to limit their release into the atmosphere during use and to reduce their usage.

[0003] Prior art techniques disclosed in Patent Documents 1 to 4 address the above-mentioned problems, for example, all of which use biomass-derived materials as part of the raw materials, with the aim of reducing the environmental burden.

[0004] Patent Document 1 discloses a formalin-free adhesive and an adhesive cord using the same.

[0005] Patent Document 2 discloses an adhesive that uses a blocked isocyanate having a predetermined structure to improve overvulcanization adhesive strength.

[0006] Patent Document 3 discloses an adhesive that uses lignosulfonate, an epoxy curing agent, and latex.

[0007] Patent Document 4 discloses an adhesive containing a lignin derivative, a water-soluble or water-dispersible crosslinking agent, and rubber latex, and an adhesive cord using the same. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2018 / 003572 [Patent Document 5] U.S. Patent Application Publication No. 2020-0024416 [Patent Document 3] Japanese Patent Publication No. 2022-554170 [Patent Document 4] International Publication No. 2023 / 095655 Summary of the Invention [Problem to be solved by the invention]

[0009] However, according to Patent Document 1, although the initial adhesive strength is comparable to that of RFL, the adhesive strength at high temperatures is inferior to that when RFL is used. According to Patent Document 2, although the initial adhesive strength and overvulcanization adhesive strength are comparable to that of RFL, the adhesive strength at high temperatures is inferior to that when RFL is used. Furthermore, the use of limited isocyanates is cost-inefficient. According to Patent Document 3, although the initial adhesive strength is comparable to that of RFL when used with polyethylene terephthalate fibers, it is inferior to that when RFL is used with nylon fibers. Furthermore, both adhesive strengths at high temperatures are inferior to that when RFL is used. According to Patent Document 4, although the initial adhesive strength and overvulcanization adhesive strength are comparable to that of RFL, the adhesive strength at high temperatures is inferior to that when RFL is used. In other words, from the perspective of practical use in rubber products such as tires, hoses, and belts, a treatment agent that has both high initial adhesive strength and adhesive strength at high temperatures, which are required for synthetic fiber cords for rubber reinforcement, and that is also advantageous for reducing environmental impact, has not yet been found.

[0010] The present invention has been made as a result of studies aimed at solving the problems in the prior art described above.

[0011] An object of the present invention is to provide a new adhesive treatment agent that does not contain resorcinol or formalin and is made from raw materials that are advantageous in reducing the environmental load, and a synthetic fiber cord for rubber reinforcement that uses the same, which exhibits an initial adhesive strength equal to or greater than that of RFL and also exhibits high adhesive strength at high temperatures. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention employs the following means.

[0013] That is, [1] A synthetic fiber cord for rubber reinforcement, which is obtained by applying a treatment agent to a synthetic fiber, the treatment agent containing at least a lignin derivative (component (A)), a water-soluble or water-dispersible crosslinking agent (component (B)), and rubber latex (component (C)), and not containing resorcinol, formaldehyde, or condensates thereof, and then subjecting the synthetic fiber to a heat treatment, wherein the adhesive strength at high temperatures is 30 to 100% of the initial adhesive strength, and the synthetic fiber is at least one type of fiber selected from the group consisting of polyester fiber, nylon fiber, vinylon fiber, and rayon fiber. [2] The synthetic fiber cord for rubber reinforcement according to [1], wherein the solids weight ratio in the treating agent is [(solids content of component (A)) + (solids content of component (B))]:(solids content of component (C)) = 45:55 to 90:10. [3] The synthetic fiber cord for rubber reinforcement according to [2] above, wherein the solids weight ratio in the treating agent is [(solids content of component (A)) + (solids content of component (B))]:(solids content of component (C)) = 45:55 to 70:30. [4] The synthetic fiber cord for rubber reinforcement according to any one of [1] to [3] above, characterized in that, when the total solid content of the treating agent is taken as 100% by weight, the content of component (A) is 5 to 50% by weight, and the solid content weight ratio of component (A) to component (B) is (solid content of component (A)):(solid content of component (B))=10:1 to 10:30. [5] The synthetic fiber cord for rubber reinforcement according to any one of the above [1] to [4], characterized in that at least one compound selected from the group consisting of oxazoline group-containing compounds, epoxy compounds, and blocked isocyanate compounds is used as component (B). [6] The synthetic fiber cord for rubber reinforcement according to any one of [1] to [5], wherein all or part of component (B) is an HDI-based blocked isocyanate or an MDI-based oxime-blocked isocyanate. [7] The synthetic fiber cord for rubber reinforcement according to any one of the above [1] to [6], wherein the adhesive strength of the synthetic fiber cord for rubber reinforcement under high temperatures is 40 to 100% of the initial adhesive strength. [8] The synthetic fiber cord for rubber reinforcement according to any one of [1] to [7], wherein the weight of the solid content of the treatment agent adhered to the synthetic fiber after the heat treatment is 5.5 to 10 parts by weight, when the weight of the synthetic fiber is 100 parts by weight. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a synthetic fiber cord for rubber reinforcement that exhibits initial adhesive strength equal to or greater than that of RFL and also has excellent adhesive strength at high temperatures, without using raw materials that have a high environmental impact, such as resorcinol and formalin. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below.

[0016] The treating agent used in the present invention must contain at least a lignin derivative (hereinafter referred to as "lignin derivative (A)" or simply "component (A)"), a water-soluble or water-dispersible crosslinking agent (hereinafter referred to as "water-soluble or water-dispersible crosslinking agent (B)" or simply "component (B)"), and a rubber latex (C) (hereinafter referred to as "rubber latex (C)" or simply "component (C)"), and must be free of resorcinol, formaldehyde, and their condensates. The use of such a treating agent is advantageous in terms of adhesion to rubber when treating synthetic fibers.

[0017] The lignin derivative (A) used in the present invention is a chemically treated lignin present in trees, which are biomass. Examples of such compounds include kraft lignin obtained from kraft pulp waste liquor, and lignosulfonic acid or lignosulfonate salts obtained from sulfite pulp waste liquor in the papermaking industry, which uses wood as a raw material. Lignin sulfonate is a compound in which a sulfonic group has been introduced into the side chain of the phenylpropane structure of lignin. Examples of lignosulfonate salts include sodium lignosulfonate, magnesium lignosulfonate, and calcium lignosulfonate. In the present invention, these compounds can be used alone or in combination, but sodium lignosulfonate is most preferred from the standpoint of adhesive strength.

[0018] The water-soluble or water-dispersible crosslinking agent (B) used in the present invention is a compound having a functional group capable of reacting with other compounds upon heating, and is water-soluble or emulsion-type water-dispersible. Examples include oxazoline group-containing compounds, epoxy compounds, blocked isocyanate compounds, alcohols, ketone compounds, carboxylic acid compounds, ether compounds, and amine compounds. Among these, it is preferable to use at least one compound selected from the group consisting of oxazoline group-containing compounds, epoxy compounds, and blocked isocyanate compounds.

[0019] The oxazoline group-containing compound preferably used as component (B) refers to a compound, whether polymer or oligomer, containing an oxazoline group (preferably a 2-oxazoline group) at the end or side chain of the molecular chain. While one or more oxazoline groups can be present in a single molecule, a high number of oxazoline groups per molecule or a high ratio of oxazoline groups to molecular weight is preferred for achieving high adhesiveness. The main chain skeleton of the oxazoline group-containing compound is typically a hydrocarbon chain, an ethylene glycol chain, or a prepolymer of bisphenols such as bisphenol A, phenolic resins, novolac resins, or resol resins, and these molecular skeletons may also contain aromatic or heterocyclic rings. Examples of monomers that can provide the oxazoline group-containing compound include styrene, styrene derivatives, acrylonitrile, methacrylic acid esters, methacrylic acid, ethylene, butadiene, and acrylamide, all of which contain oxazoline groups. These monomers may also be used in combination. The oxazoline group-containing compound may also contain structural units that do not contain oxazoline groups. In addition, a plurality of types of oxazoline group-containing compounds may be used.

[0020] The form of the oxazoline group-containing compound may be liquid, molten, solid, or a solution in an aqueous solvent capable of dissolving these, or may be a suspension dispersed in water (emulsion particles, latex particles, etc.). For example, a method may be used in which the oxazoline group-containing compound is emulsified or dissolved as it is, or, if necessary, after being dissolved in a small amount of solvent, using a known emulsifier such as sodium alkylbenzenesulfonate, dioctyl sulfosuccinate sodium salt, or nonylphenol ethylene oxide adduct.

[0021] The epoxy compound preferably used as component (B) is a compound having two or more epoxy groups in one molecule, regardless of whether it is a polymer or oligomer. Examples of such compounds include glycidyl ether epoxy resins obtained from compounds having a hydroxyl group in the molecule, glycidyl amine epoxy resins obtained from compounds having an amino group in the molecule, glycidyl ester epoxy resins obtained from compounds having a carboxyl group in the molecule, cycloaliphatic epoxy resins obtained from compounds having an unsaturated bond in the molecule, heterocyclic epoxy resins such as triglycidyl isocyanurate, and epoxy resins in which two or more types selected from these are present in the molecule. Multiple types of epoxy compounds may also be used.

[0022] Specific examples of glycidyl ether-type epoxy resins include bisphenol A-type epoxy resins obtained by reacting bisphenol A with halogen-containing epoxides such as epichlorohydrin, bisphenol F-type epoxy resins obtained by reacting bisphenol F with the halogen-containing epoxides, biphenyl-type epoxy resins obtained by reacting biphenyl with the halogen-containing epoxides, resorcinol-type epoxy resins obtained by reacting resorcinol with the halogen-containing epoxides, bisphenol S-type epoxy resins obtained by reacting bisphenol S with the halogen-containing epoxides, polyethylene glycol-type epoxy resins, which are reaction products of polyhydric alcohols with the halogen-containing epoxides, polypropylene glycol-type epoxy resins, epoxy resins obtained by oxidizing unsaturated bond moieties such as bis-(3,4-epoxy-6-methyl-dicyclohexylmethyl) adipate and 3,4-epoxycyclohexene epoxide, naphthalene-type epoxy resins, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, and halogen- or alkyl-substituted versions of these. When the epoxy compound is water-soluble, it can be used as is, and when water dispersibility is to be imparted, the same method as for the oxazoline group-containing compound can be used.

[0023] The blocked isocyanate compound preferably used as component (B) is a compound, whether polymer or oligomer, that can liberate a blocking agent upon heating to generate an active isocyanate compound. Examples of blocked isocyanate compounds include reaction products of polyisocyanate compounds having a skeleton such as tolylene diisocyanate (TDI), metaphenylene diisocyanate (MDI), diphenylmethane diisocyanate (HDI), hexamethylene diisocyanate, or triphenylmethane triisocyanate with blocking agents such as phenols (e.g., phenol, cresol, or resorcinol), lactams (e.g., ε-caprolactam or valerolactam), or oximes (e.g., acetoxime, methyl ethyl ketoxime, or cyclohexane oxime). Multiple types of blocked isocyanate compounds may also be used.

[0024] Among these blocked isocyanate compounds, the use of HDI-based blocked isocyanates, which are the reaction product of hexamethylene diisocyanate and a blocking agent, or MDI-based oxime-blocked isocyanates, which are the reaction product of diphenylmethane diisocyanate and an oxime-based blocking agent, is particularly preferred in terms of achieving good adhesive strength and fatigue resistance. Here, diphenylmethane diisocyanate (MDI) can be selected from 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI, with 4,4'-MDI being the most preferred from the standpoint of adhesive strength and fatigue resistance. Polymeric MDI, which is a polynuclear compound, may result in reduced adhesive strength and fatigue resistance and is therefore undesirable. Furthermore, the dissociation temperature of the blocking agent for HDI-based blocked isocyanates or MDI-based oxime-blocked isocyanates is preferably 100 to 160°C. A dissociation temperature within this range is preferred because it exhibits good reactivity during heat treatment and can achieve higher adhesive strength. When the blocked isocyanate compound is water-soluble, it can be used as is, and when water dispersibility is to be imparted, the same method as for the oxazoline group-containing compound can be used.

[0025] Examples of the rubber latex (C) used in the present invention include natural rubber latex, butadiene rubber latex, styrene-butadiene rubber latex, vinylpyridine-styrene-butadiene rubber latex, nitrile rubber latex, hydrogenated nitrile rubber latex, chloroprene rubber latex, chlorosulfonated rubber latex, and ethylene-propylene-diene rubber latex, and these can be used alone or in combination.

[0026] The treatment agent used in this invention does not contain resorcinol, formaldehyde, or their condensates. That is, it does not contain both resorcinol and formaldehyde, nor does it contain condensates of resorcinol and formaldehyde. The absence of resorcinol and formaldehyde can be confirmed, for example, by analyzing the treatment agent applied to a synthetic fiber cord and finding that the reaction product of resorcinol and formaldehyde, i.e., resorcinol-formaldehyde resin, is not detected. Furthermore, the resorcinol content can be measured using HPLC, and the formaldehyde content can be measured using the acetylacetone method.

[0027] Furthermore, in addition to the components (A), (B), and (C), the treating agent used in the present invention may contain other components such as surfactants, antifoaming agents, vulcanization regulators, antioxidants, and pH adjusters, as necessary, within the scope of the object of the present invention.

[0028] The synthetic fiber cord for rubber reinforcement of the present invention preferably has an adhesive strength at high temperatures of 30 to 100%, preferably 40 to 100%, and more preferably 50 to 100% of its initial adhesive strength. A high adhesive strength of 30% or more is preferred because it allows the adhesion between the cord and the rubber to be maintained even when the tire becomes hot during vehicle operation. The initial adhesive strength and adhesive strength at high temperatures can be determined by the methods described in the Examples section.

[0029] To achieve this high-temperature adhesive strength, the weight ratio of the sum of the solid contents of components (A) and (B) to the solid content of component (C) in the treatment agent applied to synthetic fibers (sometimes referred to as "solid content weight ratio A" for convenience) preferably satisfies [(solid content of component (A)) + (solid content of component (B))]:(solid content of component (C)) = 45:55 to 90:10, more preferably 45:55 to 70:30. When the solid content weight ratio A satisfies 45:55 to 90:10, the high-temperature adhesive strength satisfies 30 to 100% of the initial adhesive strength, which is preferable. Note that the solid content weight ratio A for maximizing the initial adhesive strength is different from the solid content weight ratio A for maximizing the high-temperature adhesive strength, and therefore, there is no problem if the initial adhesive strength is low within a practical range in order to maximize the high-temperature adhesive strength.

[0030] In the adhesive treatment agent used in the present invention, when the total solid content contained in the treatment agent is taken as 100% by weight, the content of the lignin derivative (A) is preferably 5 to 50% by weight, more preferably 7 to 45% by weight, and even more preferably 10 to 40% by weight. If the content of the lignin derivative (A) is less than 5% by weight or more than 50% by weight, the adhesive strength and fatigue resistance may be insufficient. Here, the total solid content refers to the components of the treatment agent excluding the solvent.

[0031] Furthermore, the weight ratio of the solid content of component (A) to the solid content of component (B) (sometimes referred to as "solid content weight ratio B" for convenience) is preferably (solid content of component (A)):(solid content of component (B))=10:1 to 10:30, more preferably 10:5 to 10:25, and even more preferably 10:11 to 10:20. If the amount of component (B) is small so that the solid content weight ratio B exceeds the above range, the initial adhesive strength may be insufficient. If the amount of component (B) is large so that the solid content weight ratio B exceeds the above range, the adhesive strength at high temperatures may be insufficient. Furthermore, the cord may harden, resulting in poor fatigue resistance in rubber. Therefore, when the synthetic fiber cord is used to reinforce rubber products such as tires, belts, and hoses, the durability of the product may be poor, which is undesirable.

[0032] The treatment agent used in the present invention is a solid content dissolved or dispersed in water, with a total solid content concentration of preferably 5 to 25 wt%, more preferably 10 to 20 wt%, and even more preferably 12 to 18 wt%. Outside this range, adhesive strength may decrease. Furthermore, outside this range, a sufficient amount of solid content contained in the treatment agent may not be applied to the synthetic fiber, or cohesive failure may occur within the solid content film after application and drying of the treatment agent, which may result in adhesive strength decrease.

[0033] The synthetic fiber cord for rubber reinforcement of the present invention can be suitably used for reinforcing rubber, and is made by treating the synthetic fiber described below with the treating agent described above.

[0034] In the present invention, the treatment agent is applied to synthetic fibers and then heat-treated. During the heat treatment, for example, volatile components contained in the treatment agent, such as solvents such as water, are distilled off. Furthermore, if a blocked isocyanate compound is used as component (B), the blocking agent is released, causing a reaction involving the isocyanate group, and a chemical reaction involving the crosslinking agent occurs. In other words, synthetic fibers treated with the adhesive treatment agent are in a state where the solid components in the adhesive treatment agent are attached or bonded to the synthetic fibers, with or without being chemically modified. The treatment agent used in the present invention is preferably one containing at least components (A), (B), and (C) in the same bath (one bath). It is not preferable to prepare multiple treatment baths and separate the treatment of components (A), (B), and (C) in separate baths.

[0035] The phrase "applied and then heat-treated" refers to the state after heat treatment has been applied. Alternatively, components (A), (B), and (C) may be chemically modified and converted into other substances, and this description is given in consideration of the fact that it is difficult, impossible, or impractical to describe such substances in some circumstances.

[0036] Here, the amount of the treatment agent adhered to the synthetic fiber after heat treatment is preferably 1 to 15 parts by weight, more preferably 1 to 5 parts by weight, per 100 parts by weight of the synthetic fiber. If the amount is outside this range, the adhesive strength may decrease.

[0037] The synthetic fibers that can be used in the present invention include at least one fiber selected from the group consisting of polyester fiber, nylon fiber, vinylon fiber, and rayon fiber. These can also be used to make a hybrid cord using two or more types of fibers.

[0038] Examples of polyester fibers include fibers made of polyethylene terephthalate and polyethylene naphthalate. Fibers made by melt-spinning and drawing a polyester containing terephthalic acid as the primary difunctional carboxylic acid and ethylene glycol as the primary glycol component are desirable. However, fibers made of polyesters in which part or all of the terephthalic acid is replaced with 2,6-naphthalenedicarboxylic acid, 4,4-dicarboxyphenoxyethane, or the like, or in which part or all of the ethylene glycol is replaced with other diol components such as diethylene glycol, propylene glycol, or butanediol, can also be used. Furthermore, fibers made of polyesters in which small amounts of trifunctional compounds such as trimesic acid, trimellitic acid, boric acid, phosphoric acid, glycerin, and trimethylolpropane are copolymerized may also be used.

[0039] The polyester fiber may also be modified with various modifiers, for example, terminal carboxyl group blocking agents such as carbodiimide compounds, epoxy compounds, isocyanate compounds, and oxazoline compounds.

[0040] Alternatively, the polyester fiber may be pre-treated with a polyepoxide compound during the spinning process. Examples of the polyepoxide compound include compounds containing at least two epoxy groups in one molecule in an epoxy equivalent amount of 1000 g / eq or less. Specific examples include reaction products of polyhydric alcohols such as pentaerythritol, ethylene glycol, polyethylene glycol, propylene glycol, glycerol, and sorbitol with halogen-containing epoxides such as epichlorohydrin; reaction products obtained by converting the carbon-carbon double bonds of unsaturated compounds to epoxy rings using peroxide or hydrogen peroxide; and aromatic polyepoxides such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexenecarboxylate, bis(3,4-epoxy-6-methyl-cyclohexylmethyl)adipate, phenol novolac type, hydroquinone type, biphenyl type, bisphenol S type, brominated novolac type, xylene-modified novolac type, phenol glyoxal type, trisoxyphenylmethane type, trisphenol PA type, and bisphenol type polyepoxides. Particularly preferred are sorbitol glycidyl ether type and cresol novolac type polyepoxide compounds.

[0041] These polyepoxide compounds are usually used as an emulsion or solution, i.e., the compound is dissolved in a solvent and used as a solution, or emulsified with a common emulsifier such as sodium alkylbenzenesulfonate, dioctyl sulfosuccinate sodium salt, or nonylphenol ethylene oxide adduct and used as an emulsion.

[0042] Such polyepoxide compounds are applied together with spinning oil during the synthetic fiber spinning process. The amount of polyepoxide compound attached to the polyester fiber is preferably in the range of 0.1 to 5% by weight, where the weight of the polyester fiber to which the polyepoxide compound is applied is 100% by weight. When the amount of polyepoxide compound attached is within this range, the effects of the polyepoxide compound are fully exerted, and satisfactory adhesion between the polyester fiber and rubber is obtained. Furthermore, when the amount is within this range, the polyester fiber does not become too hard, and the tenacity is less likely to decrease in the twisting process described below.

[0043] Examples of nylon fibers that can be used in the present invention include fibers made of nylon 6, nylon 66, nylon 46, nylon 610, or nylon 612. Among these, fibers made of nylon 66, which has a relative viscosity in sulfuric acid of 3.0 or more, more preferably 3.5 or more, are preferred. Furthermore, nylon fibers can contain copper compounds, as well as conventionally known inorganic and organic copper salts and elemental copper metal. Instead of copper compounds, other heat-resistant additives such as amine compounds, mercapto compounds, phosphorus compounds, and hindered phenol compounds may also be used.

[0044] Furthermore, when synthetic fiber cords for rubber reinforcement using nylon fibers are used as tire cords, polymers with a high degree of polymerization are used to obtain fibers with high strength and toughness, and nylon resins constituting the fibers preferably have a relative viscosity in sulfuric acid of 3.0 to 5.0.

[0045] The vinylon fiber or rayon fiber used in the present invention may be any known fiber.

[0046] The synthetic fibers used in the present invention are not subject to restrictions on fineness, number of filaments, cross-sectional shape, etc., but typically have a total fineness of 200 to 5,000 dtex, 30 to 1,000 filaments, and a circular cross-section yarn, with a total fineness of 250 to 3,000 dtex, 50 to 500 filaments, and a circular cross-section yarn being preferred. If the total fineness is less than 200 dtex, the cord strength may be insufficient, and if it exceeds 5,000 dtex, the cord may become too thick and handleability may decrease. Furthermore, if it is less than 30 filaments, the cord may become too stiff and handleability may decrease, and if it exceeds 1,000 filaments, the cord may become too fluffed and quality may decrease.

[0047] From the viewpoint of improving fatigue resistance, the synthetic fiber cord for rubber reinforcement of the present invention can be obtained by twisting the above synthetic fibers to form a twisted cord, and then dipping the twisted cord in the adhesive treatment agent of the present invention and heat-treating it either as is or after weaving it into a blind. For example, twisted cords used for carcass tire cords can be made by first twisting in the S direction or Z direction, and then combining two or three first-twist cords and twisting them together, usually with the same number of second twists in the opposite direction to the first twist, to form a multi-twisted twisted cord. The twisted cords are used as warp yarns, and cotton yarn or organic fiber covered with cotton yarn is used as weft yarns, which are woven into a blind to form a green curtain. The green curtain is then dipped in the adhesive treatment agent and heat-treated to obtain a dipped curtain.

[0048] On the other hand, in the case of cords for hoses or belts, for example, a twisted cord is formed by first twisting, or two or three of these first twisted cords are combined and then twisted in the opposite direction to the first twist, usually with the same number of second twists, to form a twisted cord, which is then dipped in an adhesive treating agent and heat-treated while still in the twisted cord form to form a dipped cord.

[0049] The synthetic fiber cord for rubber reinforcement of the present invention includes both the case where it is included in the above-mentioned dipped roll and the case where it is in the form of a dipped cord.

[0050] The synthetic fiber cord for rubber reinforcement of the present invention may be treated with a precoating agent before the synthetic fiber is treated with the treating agent.

[0051] The precoating agent preferably contains at least an epoxy compound, and the total solids concentration in the precoating agent is preferably 0.1 to 6%. More preferably, the precoating agent contains at least an epoxy compound and a blocked isocyanate compound, and the ratio of the solids weight of the blocked isocyanate compound to the solids weight of the epoxy compound contained in a unit weight of the precoating agent ((solids weight of blocked isocyanate compound) / (solids weight of epoxy compound)) is 3 or less, and the total solids concentration in the precoating agent is preferably 0.1 to 6% by weight. Outside this range, the adhesive strength may decrease. Furthermore, the amount of precoating agent applied to the synthetic fibers is preferably 0.1 to 3 parts by weight in terms of the solids weight of the precoating agent per 100 parts by weight of the synthetic fibers. Outside this range, the adhesive strength may decrease.

[0052] A preferred method for applying the precoating agent is to dip the object to be treated into a bath filled with the precoating agent, followed by drying the water at a temperature of preferably 100 to 150° C., and then subjecting the object to heat treatment at 200 to 255° C. For controlling the amount of solids attached and softening treatment, the same methods as those that can be used for treating agents can be used.

[0053] The treating agent used in the present invention, which is characterized as described above, is a novel treating agent that does not contain resorcinol, formalin, or condensates thereof and is made from raw materials that are advantageous in reducing the environmental impact. Synthetic fiber cords for rubber reinforcement that use this treating agent exhibit initial adhesive strength equal to or greater than that of RFL, and also exhibit high adhesive strength at high temperatures. As a result, it is possible to provide extremely excellent synthetic fiber cords for rubber reinforcement.

[0054] The synthetic fiber cord for rubber reinforcement of the present invention is obtained by applying the above-mentioned treating agent to a synthetic fiber and then subjecting it to a heat treatment. The synthetic fiber cord for rubber reinforcement of the present invention can be used to reinforce rubber products such as tires, belts, and hoses.

[0055] Next, the method for obtaining the synthetic fiber cord for rubber reinforcement of the present invention will be described with reference to an example.

[0056] An example of a method for producing the synthetic fiber cord for rubber reinforcement of the present invention is a method in which synthetic fibers are dipped into a bath filled with a treating agent containing at least components (A), (B), and (C), and not containing resorcinol, formaldehyde, or condensates thereof, to apply the treating agent, followed by heat treatment. The synthetic fibers may be in the form of either a twisted cord or a green cloth. A preferred method involves dipping the twisted cord or green cloth into the treating agent in a bath, subsequently drying the water at a temperature preferably between 100 and 150°C, and then heat treating at 200 and 255°C. The preferred embodiments of components (A), (B), and (C) are those described above.

[0057] Here, "dipping" refers to applying a treatment agent to a twisted yarn cord or a raw curtain reel by running the twisted yarn cord or the raw curtain reel through a bath equipped with rollers and filled with the treatment agent. "Heat treatment" refers to heating the twisted yarn cord or the raw curtain reel by running the twisted yarn cord or the raw curtain reel through an oven equipped with rollers and capable of being set to a predetermined temperature. As a dip treatment machine for carrying out such dipping and heat treatment, for example, a commercially available machine from Ritzler can be used. Note that, in addition to dipping, any other method can be used to attach a treatment agent to synthetic fibers, such as spraying the treatment agent from a nozzle.

[0058] In order to control the amount of treatment agent applied to the synthetic fibers, means such as squeezing with a pressure roller, scraping with a scraper, blowing with air, and suction may be used.

[0059] Furthermore, after the heat treatment, a mechanical softening treatment step can be carried out in which the synthetic fiber cord is brought into sliding contact with the edge to soften the cord, thereby making it possible to obtain any desired cord stiffness.

[0060] The synthetic fiber cord for rubber reinforcement of the present invention obtained in this manner exhibits initial adhesive strength equal to or greater than that obtained when treated with RFL, while using raw materials that have a low environmental impact, and also exhibits high adhesive strength at high temperatures, making it suitable for use in rubber reinforcement applications such as tires. [Example]

[0061] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples specifically described below, the measured values ​​were determined by the following methods.

[0062] (1) Amount of treatment agent attached According to the dip pick-up mass method of JIS L1017 (2002), the solid weight of the treatment agent (if heat treatment was performed, the solid weight after heat treatment) was determined per 100 parts by weight of synthetic fiber.

[0063] (2)Initial adhesive strength In accordance with JIS L1017 (2002) Appendix 1, 3.1T test (method A), the synthetic fiber cord sample was embedded in the unvulcanized rubber compound shown in the following item (3), and subjected to a test at 150°C for 30 minutes at 50 kg / cm. 2 After press vulcanization, the specimens were allowed to cool, and the synthetic fiber cord was pulled out of the rubber block at a speed of 300 mm / min in a 20°C atmosphere. The load required for the pull-out was measured for each specimen, and the arithmetic average value of 10 specimens was taken as the initial adhesive strength.

[0064] (3) Adhesive strength at high temperatures In accordance with JIS L1017 (2002) Appendix 1, 3.1T test (method A), the synthetic fiber cord sample was embedded in the unvulcanized rubber compound shown below and subjected to a test at 150°C for 30 minutes at 50 kg / cm. 2After press vulcanization and cooling, the synthetic fiber cord was pulled out of the rubber block at a rate of 300 mm / min in a high-temperature atmosphere at 120°C, and the load required for the pullout was determined for each sample. The arithmetic average of 10 samples was used as the high-temperature adhesive strength. Here, the pullout load in a high-temperature atmosphere at 120°C can be measured using a tensile tester with the ability to heat the sample in a high-temperature chamber; for example, it can be measured by combining A&D's high-temperature testing machine (TLF) with a Tensilon universal testing machine (RTF).

[0065] The composition of the unvulcanized rubber compound used for evaluating the initial adhesive strength and adhesive strength at high temperatures is as follows:

[0066] Natural rubber (RSS1): 70 parts by weight SBR (#1502, manufactured by JSR Corporation): 30 parts by weight HAF carbon black: 40 parts by weight Stearic acid: 2 parts by weight Sulfur: 2 parts by weight Zinc oxide: 5 parts by weight 2,2'-dithiobenzothiazole: 3 parts by weight Naphthenic acid process oil: 3 parts by weight.

[0067] (4) Tire evaluation A tire having a tire size of 225 / 40R18 was produced as an evaluation tire, and a high load test was carried out using this tire by the following method.

[0068] After conducting a running test using a drum testing machine under conditions of an air pressure of 120 kPa, 102% of the maximum load, and a running speed of 81 km / h, the running time when the tire failed was measured. The evaluation results were given an "A" if the running time reached 80 hours, a "B" if it was between 50 and 80 hours, a "C" if it was between 40 and 50 hours, and a "D" if it was less than 40 hours. C is the pass level, and A is the best.

[0069] (Examples 1 to 20, Comparative Examples 1 to 5) Glycerol polyglycidyl ether ("Denacol" EX313, manufactured by Nagase ChemteX Corporation), blocked isocyanate compound (DM-6400, manufactured by Meisei Chemical Industry Co., Ltd.), and rubber latex (Pyratex, manufactured by Nippon A&L Inc.) were mixed in a solids ratio of 20:40:40, and then diluted with water to obtain a precoat agent (P) with a total solids content of 4.0 wt%.

[0070] As shown in the table, each of components (A), (B), and (C) was dissolved or dispersed in water and mixed so that the solid content of each component was the proportion shown in the table (total solid content being 100% by weight), to prepare a treatment agent with a total solid content of 15% by weight.

[0071] Next, the synthetic fiber cords shown in the table as the treated materials were immersed in the precoating agent (P) using a Computreator treatment machine (manufactured by Ritzler Co., Ltd.), dried at 120°C for 2 minutes, and then heat-treated at 245°C for 1 minute. Subsequently, the cords were immersed in the treatment agent prepared above, dried at 120°C for 2 minutes, and then heat-treated at 240°C for 1 minute to obtain treated synthetic fiber cords.

[0072] The solid content of the precoating agent and the treating agent applied to the obtained synthetic fiber cord was 1.5 parts by weight per 100 parts by weight of the synthetic fiber cord to be treated, and 2.5 parts by weight of the treating agent per 100 parts by weight of the synthetic fiber cord to be treated.

[0073] Examples 21 to 23 A synthetic fiber cord was obtained in the same manner as in Example 1, except that the synthetic fiber was changed to one shown in the table, the treatment with a precoating agent was not performed, and the solid content of the treatment agent applied to the synthetic fiber cord was changed to 5.0 parts by weight per 100 parts by weight of the synthetic fiber cord.

[0074] Details of the materials used are as follows:

[0075] Polyester fiber (in the table, "Polyester"): Two strands of polyester fiber (manufactured by Toray Industries, Inc.) with a total fineness of 1670 dtex were twisted together with a first twist of 40 times per 10 cm and a second twist of 40 times per 10 cm.

[0076] Nylon fiber ("Nylon" in the table): Two nylon fibers (manufactured by Toray Industries, Inc.) with a total fineness of 1400 dtex were twisted together with a first twist of 40 times per 10 cm and a second twist of 40 times per 10 cm.

[0077] Vinylon fiber (in the table, "Vinylon"): Two vinylon fibers with a total fineness of 1670 dtex were twisted together with a first twist of 40 times / 10 cm and a second twist of 40 times / 10 cm.

[0078] Rayon fiber (in the table, "Rayon"): Two rayon fibers with a total fineness of 1840 dtex were twisted together with a first twist of 40 times / 10 cm and a second twist of 40 times / 10 cm.

[0079] (A)-1: Lignin derivative (manufactured by Nippon Paper Industries Co., Ltd., sodium lignosulfonate, "Vanilex" N) (A)-2: Lignin derivative (sodium lignosulfonate, "Vanilex" RN, manufactured by Nippon Paper Industries Co., Ltd.) (B)-1: Blocked isocyanate (Meisei Chemical Industry Co., Ltd., DM-6400, oxime-blocked diphenylmethane diisocyanate, dissociation temperature 120 to 160°C) (B)-2: Blocked isocyanate (Meisei Chemical Industry Co., Ltd., SU-268A, a blocking agent adduct of hexamethylene diisocyanate, dissociation temperature 100 to 130°C) (B)-3: Carbodiimide group-containing polymer (Nisshinbo Chemical Co., Ltd., Carbodilite V-02 (B)-4: Oxazoline group-containing compound (manufactured by Nippon Shokubai Co., Ltd., "Epocross" K-2035E (B)-5: Epoxy compound (Nagase ChemteX Corporation, "Denacol" EX313) (B)-6: Blocked isocyanate (Meisei Chemical Industry Co., Ltd., DM-3031CONC, lactam-blocked diphenylmethane diisocyanate, dissociation temperature 160-180°C) (B)-7: Blocked isocyanate (Meisei Chemical Industry Co., Ltd., DM-7000, lactam block polymeric MDI, dissociation temperature 160 to 180°C) (C)-1: Rubber latex ("Pilatex" manufactured by Nippon A&L Co., Ltd.).

[0080] (Conventional example) Treatment and evaluation were carried out in the same manner as in Example 1, except that the treatment agent used was changed to an RFL adhesive obtained by the following procedure.

[0081] Specifically, the treatment agent was prepared by mixing resorcinol / formalin at a molar ratio of 1 / 1.5 in the presence of caustic soda, adjusting the solids concentration to 10% by weight, and aging for two hours to obtain a precondensation product of resorcinol and formalin. Next, this precondensation product (hereinafter simply referred to as "RF") was mixed with rubber latex (hereinafter simply referred to as "L") (Piratex, manufactured by Nippon A&L Co., Ltd.) at a ratio of RF / L = 1 / 5 (solids weight ratio) and aged for 24 hours. This mixture was diluted with water to obtain an RFL adhesive with a solids weight of 15%.

[0082] The synthetic fiber cord for rubber reinforcement obtained as described above was embedded in unvulcanized rubber and vulcanized, after which the initial adhesive strength and adhesive strength at high temperatures were measured. The results are shown in Tables 1 to 3.

[0083] As shown in Tables 1 and 2, the synthetic fiber cord for rubber reinforcement of the present invention, despite not containing resorcinol or formalin in the treatment agent, exhibits initial adhesion to rubber that is equal to or better than that when RFL is used, and also exhibits high adhesion at high temperatures.

[0084] [Table 1]

[0085]

Table 2

[0086]

Table 3

Claims

1. A synthetic fiber cord for rubber reinforcement, which is obtained by applying a treatment agent to a synthetic fiber, the treatment agent containing at least a lignin derivative (hereinafter referred to as "component (A)"), a water-soluble or water-dispersible crosslinking agent (hereinafter referred to as "component (B)"), and rubber latex (hereinafter referred to as "component (C)"), and which does not contain resorcinol, formaldehyde, or condensates thereof, and then subjecting the synthetic fiber cord to a heat treatment, wherein the adhesive strength at high temperatures is 30 to 100% of the initial adhesive strength, and the synthetic fiber is at least one type of fiber selected from the group consisting of polyester fiber, nylon fiber, vinylon fiber, and rayon fiber.

2. 2. The synthetic fiber cord for rubber reinforcement according to claim 1, wherein the treatment agent has a solids weight ratio of [(solids content of component (A)) + (solids content of component (B))]:(solids content of component (C)) = 45:55 to 90:

10.

3. 3. The synthetic fiber cord for rubber reinforcement according to claim 2, wherein the treatment agent has a solids weight ratio of [(solids content of component (A)) + (solids content of component (B))]:(solids content of component (C)) = 45:55 to 70:

30.

4. 4. The synthetic fiber cord for rubber reinforcement according to claim 1, wherein, when the total solid content of the treating agent is taken as 100% by weight, the content of component (A) is 5 to 50% by weight, and the solid content weight ratio of component (A) to component (B) is (solid content of component (A)):(solid content of component (B))=10:1 to 10:

30.

5. 5. The synthetic fiber cord for rubber reinforcement according to claim 1, wherein component (B) is at least one compound selected from the group consisting of oxazoline group-containing compounds, epoxy compounds, and blocked isocyanate compounds.

6. 6. The synthetic fiber cord for rubber reinforcement according to claim 1, wherein all or part of component (B) is an HDI-based blocked isocyanate or an MDI-based oxime-blocked isocyanate.

7. 7. The synthetic fiber cord for rubber reinforcement according to claim 1, wherein the adhesive strength of the synthetic fiber cord for rubber reinforcement at high temperatures is 40 to 100% of the initial adhesive strength.

8. 8. The synthetic fiber cord for rubber reinforcement according to claim 1, wherein the weight of the solid content of the treating agent adhered to the synthetic fiber after the heat treatment is 1 to 15 parts by weight, when the weight of the synthetic fiber is 100 parts by weight.

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