Synthetic fiber treatment agent and synthetic fiber

Abstract

The present invention addresses the problem of more suitably suppressing scattering of a synthetic fiber treatment agent attached to synthetic fibers during a spinning and drawing process, and improving adhesion of the synthetic fibers, to which the synthetic fiber treatment agent has been attached, to a rubber material. The synthetic fiber treatment agent contains a smoothing agent, a nonionic surfactant, and an ionic surfactant. The synthetic fiber treatment agent has a maximum hydrous viscosity of 10,000 mPa·s or more in a non-volatile component concentration range of 40% to 80% by mass, and the kinematic viscosity at 30°C of the synthetic fiber treatment agent, in which the non-volatile component concentration has been adjusted to 25% by mass, is 2 mm2 / s to 12 mm2 / s. The synthetic fiber treatment agent is applied to a process in which the synthetic fiber treatment agent is imparted to synthetic fibers in the form of an aqueous solution having a nonvolatile component concentration of 5% to 25% by mass. The hydrous viscosity is the viscosity at each concentration when the non-volatile component concentration of the synthetic fiber treatment agent is changed in increments of 5% by mass within a range from 30% to 100% by mass.

Description

Treatment agent for synthetic fibers, and synthetic fibers

[0001] The present invention relates to a treating agent for synthetic fibers and synthetic fibers.

[0002] In the spinning and drawing process of synthetic fibers, a treatment is sometimes carried out to attach a treating agent to the surface of the synthetic fibers, for example, to improve smoothness, antistatic properties, etc. Synthetic fibers are also widely used as industrial materials. For example, they are used in the automotive field (tire cords, airbags, etc.), the architectural field (carpets, tents, etc.), the commercial field (advertising cloth, etc.), the agricultural and fisheries field (ropes, fishing nets, etc.), and the civil engineering field (conveyor belts, lifelines, etc.). Among these, they are widely used as reinforcing materials for rubber products. When used as reinforcing materials for rubber products, synthetic fibers are coated with an adhesive and bonded to the rubber material.

[0003] Conventionally, synthetic fiber treatment agents are disclosed in Patent Documents 1 to 4. Patent Document 1 discloses a synthetic fiber treatment agent containing a lubricant component and an emulsifier component, and having a maximum viscosity upon hydration of less than 10,000 mPa·s at 25°C. Patent Document 2 discloses a synthetic fiber spinning oil having a viscosity of 100 cst or less in its original solution at 25°C, a viscosity of 50% aqueous emulsion of 50 cst or less, and an emulsion viscosity at 20°C to 50°C that does not have a maximum value at a concentration of 50% or less. Patent Document 3 discloses an oil containing 50 to 80 wt% of a lubricant component having a sulfur-containing ester compound and 15 to 30 wt% of a nonionic surfactant, and having a maximum viscosity upon hydration of 30,000 centipoise or less. Patent Document 4 discloses a fiber treatment agent containing a lubricant, an ester compound, a phenolic antioxidant, and a phosphite antioxidant as essential components.

[0004] JP 2012-92482 A Patent No. 2540438 JP 8-269870 JP 9-188968

[0005] However, the above-mentioned conventional synthetic fiber treatment agents do not take into consideration the scattering of the treatment agent attached to the synthetic fiber during the spinning and drawing process. With the recent increase in spinning and drawing speed, there is a demand for more effective suppression of scattering of the treatment agent attached to the synthetic fiber. Furthermore, the above-mentioned conventional synthetic fiber treatment agents do not take into consideration the adhesion of the synthetic fiber to the rubber material when the synthetic fiber to which the synthetic fiber treatment agent is attached is used as a reinforcing material for a rubber product. There is a demand for improving the adhesion of the synthetic fiber to the rubber material.

[0006] As a result of research aimed at solving the above problems, the present inventors have found that a synthetic fiber treatment agent containing a lubricant, a nonionic surfactant, and an ionic surfactant and having a specific hydrous viscosity and a specific kinematic viscosity is exactly suitable.

[0007] The synthetic fiber treatment agent of Aspect 1 is a synthetic fiber treatment agent containing a smoothing agent (A), a nonionic surfactant (B), and an ionic surfactant (C), and has a maximum hydrous viscosity of 10,000 mPa·s or more in a nonvolatile content range of 40% by mass to 80% by mass, and a kinematic viscosity at 30°C of 2 mm when the nonvolatile content is adjusted to 25% by mass. ２ / s or more 12mm ２ The gist is that the method is applicable to a process in which the aqueous solution having a non-volatile content of 5% by mass or more and 25% by mass or less is applied to synthetic fibers.

[0008] The hydrous viscosity is the viscosity at each concentration when the nonvolatile content of the synthetic fiber treatment agent is changed in 5 mass% increments within the range from 30 mass% to 100 mass%. In Aspect 2, in the synthetic fiber treatment agent according to Aspect 1, the hydrous viscosity of the synthetic fiber treatment agent is 10,000 mPa s or less when the nonvolatile content is in the range of 85 mass% to 100 mass%.

[0009] Aspect 3 is the synthetic fiber treating agent according to Aspect 1 or 2, wherein the smoothing agent (A) contains an ester compound (A1) having a sulfur atom in the molecule. Aspect 4 is the synthetic fiber treating agent according to any one of Aspects 1 to 3, wherein the maximum viscosity upon water addition is 15,000 mPa s or more.

[0010] In Aspect 5, the synthetic fiber treating agent according to any one of Aspects 1 to 4 has a maximum hydrous viscosity of 20,000 mPa·s or more. In Aspect 6, the synthetic fiber treating agent according to any one of Aspects 1 to 5 has a maximum hydrous viscosity of less than 100,000 mPa·s.

[0011] In Aspect 7, in the treatment agent for synthetic fibers according to any one of Aspects 1 to 6, the treatment agent contains the smoothing agent (A) in an amount of 30% by mass or more and 70% by mass or less, the nonionic surfactant (B) in an amount of 20% by mass or more and 60% by mass or less, and the ionic surfactant (C) in an amount of 0.1% by mass or more and 10% by mass or less, where the total amount of the smoothing agent (A), the nonionic surfactant (B), and the ionic surfactant (C) is taken as 100% by mass.

[0012] Aspect 8 is a synthetic fiber having attached thereto the synthetic fiber treating agent according to any one of Aspects 1 to 7. Aspect 9 is a synthetic fiber according to Aspect 8, which is used to reinforce rubber products.

[0013] According to the present invention, scattering of a synthetic fiber treatment agent attached to synthetic fibers during the spinning and drawing process can be more effectively suppressed, and the adhesion of the synthetic fibers to rubber materials can be improved.

[0014] First Embodiment A first embodiment of the synthetic fiber treatment agent (hereinafter simply referred to as the treatment agent) of the present invention will be described below. The treatment agent of this embodiment contains a smoothing agent (A), a nonionic surfactant (B), and an ionic surfactant (C).

[0015] (Smoothing Agent (A)) The smoothing agent (A) is not particularly limited, and known smoothing agents used in treatment agents can be used. Examples of the smoothing agent (A) include an ester compound (A1) having a sulfur atom in the molecule, and an ester compound (A2) having an ester bond but no ether bond in the molecule. Among these, it is preferable that the smoothing agent (A) contains the ester compound (A1). By containing the ester compound (A1), the adhesion of the synthetic fiber to which the treatment agent is attached to the rubber material can be further improved.

[0016] (Ester Compound (A1)) The ester compound (A1) is preferably an ester compound having a sulfur atom in the molecule and having a structure formed from a polycarboxylic acid and a monohydric alcohol.

[0017] The ester compound (A1) is preferably an ester compound represented by the following formula (1):

[0018]

[0019] (In formula (1), R ３ and R ４ each independently represents a hydrocarbon having 12 to 24 carbon atoms, and m and n each independently represent an integer of 1 to 4. In the above formula (1), R ３ , R ４ are hydrocarbon groups having 12 to 24 carbon atoms, such as lauryl, tridecyl, isotridecyl, myristyl, isomyristyl, cetyl, isocetyl, stearyl, isostearyl, arachidyl, isoarachidyl, behenyl, isobehenyl, lignoceryl, isolignoceryl, palmitoleyl, oleyl, eicosenyl, docosenyl, and tetracosenyl groups, and among these, branched hydrocarbon groups are preferred.

[0020] Specific examples of the ester compound (A1) include di(2-hexyl-1-decyl)thiodipropionate, di(2-decyl-1-tetradecyl)thiodipropionate, dioleylthiodipropionate, diisostearylthiodipropionate, isostearyl(laurylthiopropionate), and a diester of a compound in which 3 moles of ethylene oxide (hereinafter also referred to as EO) are added to 1 mole of dodecanol with thiodipropionic acid.

[0021] (Ester Compound (A2)) The ester compound (A2) is an ester compound having an ester bond but no ether bond in the molecule. Examples of the ester compound (A2) include a polyhydric alcohol fatty acid ester compound (a1), a polycarboxylic acid fatty alcohol ester compound (a2), and an ester compound (a3) ​​of an aliphatic monohydric alcohol and a fatty acid.

[0022] Specific examples of the polyhydric alcohol fatty acid ester compound (a1) include compounds that are esters of an aliphatic dihydric alcohol having from 2 to 6 carbon atoms, an aliphatic trihydric alcohol having from 3 to 6 carbon atoms, or an aliphatic tetrahydric alcohol having 5 carbon atoms with a fatty acid having from 4 to 32 carbon atoms, and that do not have an ether bond in the molecule. Among these, compounds having a branched hydrocarbon group are preferred.

[0023] Examples of the aliphatic dihydric alcohol having from 2 to 6 carbon atoms include ethylene glycol, propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, and 1,6-hexanediol.

[0024] Examples of the aliphatic trihydric alcohol having 3 to 6 carbon atoms include glycerin, trimethylolpropane, etc. Examples of the aliphatic tetrahydric alcohol having 5 carbon atoms include pentaerythritol, etc.

[0025] The fatty acid (aliphatic monocarboxylic acid) constituting the polyhydric alcohol fatty acid ester (a1) may be saturated or unsaturated. The number of carbon atoms in the fatty acid is preferably 8 to 30, more preferably 10 to 28, and even more preferably 12 to 24. One or more types of fatty acid may be used, and saturated and unsaturated fatty acids may be used in combination.

[0026] Specific examples of the ester compound (A2) include trimethylolpropane trioleate, trimethylolpropane trilaurate, pentaerythritol tetraoctanate, sorbitan monooleate, 2-decyl-1-tetradecyl erucinate, and 2-decyl-1-tetradecyl oleate.

[0027] As for the above-mentioned smoothing agent (A), one kind of smoothing agent (A) can be used alone, or two or more kinds of smoothing agent (A) can be used in appropriate combination.(Nonionic surfactant (B)) As the nonionic surfactant (B), for example, the compound that has (poly)oxyalkylene structure that alkylene oxide is added to alcohols or carboxylic acids, the ether-ester compound that has (poly)oxyalkylene structure that alkylene oxide is added to the ester compound of carboxylic acids and polyhydric alcohol, the compound that alkylene oxide is added to natural fats and oils or the compound that this compound is esterified with carboxylic acids, as amine compound, for example, the compound that has (poly)oxyalkylene structure that alkylene oxide is added to primary organic amine, the compound that has (poly)oxyalkylene structure that alkylene oxide is added to fatty acid amide, the amide compound that condenses amine compound and carboxylic acids, the partial ester compound of carboxylic acids and polyhydric alcohol etc.

[0028] Specific examples of alcohols used as raw materials for the nonionic surfactant (B) include: (1) linear alkyl alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, heneicosanol, docosanol, tricosanol, tetracosanol, pentacosanol, hexacosanol, heptacosanol, octacosanol, nonacosanol, and triacontanol; (2) isopropanol, isobutanol, isohexanol, 2-ethylhexanol, isononanol, isodecanol, isododecanol, isotridecanol, isotetradecanol, isotriacontanol, and isoheptadecanol; (3) branched alkyl alcohols such as tetradecenol, hexadecanol, heptadecanol, octadecanol, isonodecanol, isoeicosanol, isoheneicosanol, isodocosanol, isotricosanol, isotetracosanol, isopentacosanol, isohexacosanol, isoheptacosanol, isooctacosanol, isononacosanol, and isopentadecanol; (4) branched alkenyl alcohols such as isohexadecenol and isooctadecenol; (5) cyclic alkyl alcohols such as cyclopentanol and cyclohexanol; and (6) aromatic alcohols such as phenol, nonylphenol, benzyl alcohol, monostyrenated phenol, distyrenated phenol, and tristyrenated phenol.

[0029] Specific examples of carboxylic acids used as raw materials for the nonionic surfactant (B) include: (1) linear alkyl carboxylic acids such as octylic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, and docosanoic acid; (2) branched alkyl carboxylic acids such as 2-ethylhexanoic acid, isododecanoic acid, isotridecanoic acid, isotetradecanoic acid, isohexadecanoic acid, and isooctadecanoic acid; (3) linear alkenyl carboxylic acids such as octadecenoic acid, octadecadienoic acid, and octadecatrienoic acid; (4) aromatic carboxylic acids such as benzoic acid; and (5) hydroxycarboxylic acids such as ricinoleic acid.

[0030] The alkylene oxide used as a raw material for forming the (poly)oxyalkylene structure of the nonionic surfactant (B) is preferably an alkylene oxide having 2 to 4 carbon atoms. Specific examples of alkylene oxide include EO, propylene oxide (hereinafter also referred to as PO), and butylene oxide (hereinafter also referred to as BO). The number of moles of alkylene oxide added is appropriately set, but is preferably 0.1 to 250 moles, more preferably 1 to 200 moles, and even more preferably 2 to 150 moles. Any combination of the above upper and lower limits is also possible. The number of moles of alkylene oxide added indicates the number of moles of alkylene oxide per mole of the compound to be added in the charged raw material. As for the alkylene oxide, one type of alkylene oxide may be used alone, or two or more types of alkylene oxides may be used in appropriate combination. When two or more types of alkylene oxides are used, the addition form thereof may be any of block addition, random addition, and a combination of block addition and random addition, and is not particularly limited.

[0031] Specific examples of polyhydric alcohols used as raw materials for the nonionic surfactant (B) include ethylene glycol, propylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,2-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2,5-hexanediol, 2-methyl-2,4-pentanediol, 2,3-dimethyl-2,3-butanediol, glycerin, diglycerin, 2-methyl-2-hydroxymethyl-1,3-propanediol, trimethylolpropane, sorbitan, pentaerythritol, and sorbitol.

[0032] Specific examples of the aliphatic amine or primary organic amine used as a raw material for the nonionic surfactant (B) include methylamine, ethylamine, butylamine, octylamine, laurylamine, octadecylamine (stearylamine), octadecenylamine, and coconut amine.

[0033] Specific examples of fatty acid amides used as raw materials for the nonionic surfactant (B) include octylic acid amide, lauric acid amide, palmitic acid amide, stearic acid amide, oleic acid amide, behenic acid amide, and lignoceric acid amide.

[0034] Specific examples of the nonionic surfactant (B) include a compound in which 10 moles of EO are added to 1 mole of hydrogenated castor oil, a compound in which 12 moles of EO are added to 1 mole of hydrogenated castor oil, a compound in which 20 moles of EO are added to 1 mole of hydrogenated castor oil, a compound in which 25 moles of EO are added to 1 mole of hydrogenated castor oil, a compound in which 1 mole of a compound in which 20 moles of EO are added to 1 mole of hydrogenated castor oil is esterified with 2 moles of oleic acid, a compound in which 1 mole of a compound in which 20 moles of EO are added to 1 mole of hydrogenated castor oil is esterified with 3 moles of oleic acid, a compound in which 25 moles of EO are added to 1 mole of hydrogenated castor oil, ...0 moles of EO are added to 1 mole of hydrogenated castor oil, a compound in which 20 moles of EO are added to 1 mole of hydrogenated castor oil, a compound in which 20 moles of EO are added to 1 mole of hydrogenated castor oil, a compound in which 20 moles of EO are added to 1 mole of hydrogenated castor oil, a compound in which 20 moles of EO are Examples of such compounds include a compound obtained by esterifying 1 mole of a compound to which 1 mole of EO has been added, 0.5 moles of adipic acid, and 1 mole of stearic acid, a compound obtained by adding 7 moles of EO to 1 mole of sorbitan monooleate, a compound obtained by adding 20 moles of EO to 1 mole of sorbitan monostearate, a diester of polyethylene glycol (mass average molecular weight 600) and oleic acid, a compound obtained by randomly adding 10 moles of EO and 10 moles of PO to 1 mole of dodecanol, a compound obtained by adding 10 moles of EO to 1 mole of stearylamine, and a compound obtained by adding 15 moles of EO to 1 mole of stearylamine.

[0035] As for these nonionic surfactants (B), one type of nonionic surfactant (B) may be used alone, or two or more types of nonionic surfactants (B) may be used in appropriate combination.

[0036] (Ionic Surfactant (C)) Examples of the ionic surfactant (C) include anionic surfactants, cationic surfactants, and amphoteric surfactants.

[0037] As the anionic surfactant, known surfactants can be appropriately used. Specific examples of anionic surfactants include (1) phosphate salts of aliphatic alcohols, such as lauryl phosphate salts, cetyl phosphate salts, octyl phosphate salts, oleyl phosphate salts, and stearyl phosphate salts; (2) phosphate salts of aliphatic alcohols to which at least one alkylene oxide selected from ethylene oxide and propylene oxide has been added, such as polyoxyethylene lauryl ether phosphate salts, polyoxyethylene oleyl ether phosphate salts, and polyoxyethylene stearyl ether phosphate salts; (3) aliphatic sulfonates or aromatic sulfonates, such as lauryl sulfonate, myristyl sulfonate, cetyl sulfonate, oleyl sulfonate, stearyl sulfonate, tetradecane sulfonate, dodecylbenzene sulfonate, secondary alkyl sulfonate (C13 to 15), secondary alkyl sulfonate (C11 to 14), and α-olefin sulfonate; and (4) lauryl sulfate salts, oleyl sulfate salts, stearyl (5) sulfates of fatty alcohols to which at least one alkylene oxide selected from ethylene oxide and propylene oxide has been added, such as polyoxyethylene lauryl ether sulfate, polyoxyalkylene (polyoxyethylene, polyoxypropylene) lauryl ether sulfate, and polyoxyethylene oleyl ether sulfate; (6) sulfates of castor oil fatty acid sulfate, sesame oil fatty acid sulfate, and thiamin mononitrate. (7) sulfates of fats and oils such as castor oil sulfate, sesame oil sulfate, tall oil sulfate, soybean oil sulfate, rapeseed oil sulfate, and palm oil sulfate; (8) fatty acid salts such as laurates, oleates, and stearates; (9) sulfosuccinates of fatty alcohols such as dioctyl sulfosuccinate;(10) Carboxylic acid ester salts of an aliphatic alcohol to which at least one alkylene oxide selected from ethylene oxide and propylene oxide has been added. Examples of counter ions of the anionic surfactants include alkali metal salts such as potassium salts and sodium salts, ammonium salts, and alkanolamine salts such as triethanolamine.

[0038] As the cationic surfactant, known ones can be appropriately used, and specific examples of the cationic surfactant include lauryl trimethyl ammonium chloride, cetyl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, behenyl trimethyl ammonium chloride, and didecyl dimethyl ammonium chloride.

[0039] As the amphoteric surfactant, known surfactants can be appropriately used. Specific examples of amphoteric surfactants include betaine-type amphoteric surfactants. Specific examples of the ionic surfactant (C) include sodium α-olefin (having 14 to 18 carbon atoms) sulfonate, sodium secondary alkyl (having 12 to 18 carbon atoms) sulfonate, a salt of an oleyl phosphate ester and a compound in which 4 moles of EO are added to 1 mole of laurylamine, and a salt of an isocetyl phosphate ester and a compound in which 10 moles of EO are added to 1 mole of laurylamine.

[0040] These ionic surfactants (C) may be used singly or in combination of two or more types. (Contents of Smoothing Agent (A), Nonionic Surfactant (B), and Ionic Surfactant (C)) The contents of the smoothing agent (A), nonionic surfactant (B), and ionic surfactant (C) in the treatment agent are not particularly limited. When the total content of the smoothing agent (A), nonionic surfactant (B), and ionic surfactant (C) is taken as 100% by mass, it is preferable that the smoothing agent (A) be contained in an amount of 30% by mass to 70% by mass, the nonionic surfactant (B) be contained in an amount of 20% by mass to 60% by mass, and the ionic surfactant (C) be contained in an amount of 0.1% by mass to 10% by mass.

[0041] When the content ratios of the smoothing agent (A), the nonionic surfactant (B), and the ionic surfactant (C) in the treatment agent are within the above ranges, scattering of the treatment agent adhered to the synthetic fiber during the spinning and drawing process can be easily suppressed, and the adhesion of the synthetic fiber to the rubber material to which the treatment agent is adhered can be easily improved.

[0042] In one aspect of this embodiment, the content of the smoothing agent (A) in the treatment agent is, for example, 38% by mass or more, 40% by mass or more, 50% by mass or more, 54.5% by mass or more, or 55% by mass or more. Similarly, the content of the smoothing agent (A) in the treatment agent is, for example, 55% by mass or less, 54.5% by mass or less, 50% by mass or less, 40% by mass or less, or 38% by mass or less.

[0043] In one aspect of this embodiment, the content of the nonionic surfactant (B) in the treatment agent is, for example, 30% by mass or more, 38% by mass or more, 39% by mass or more, 40% by mass or more, 41% by mass or more, 43% by mass or more, 44% by mass or more, 44.5% by mass or more, 45% by mass or more, 47% by mass or more, 53% by mass or more, 55% by mass or more, or 57% by mass or more. Similarly, the content of the nonionic surfactant (B) in the treatment agent is, for example, 57% by mass or less, 55% by mass or less, 53% by mass or less, 47% by mass or less, 45% by mass or less, 44.5% by mass or less, 44% by mass or less, 43% by mass or less, 41% by mass or less, 40% by mass or less, 39% by mass or less, 38% by mass or less, or 30% by mass or less.

[0044] In one aspect of this embodiment, the content of the ionic surfactant (C) in the treatment agent is, for example, 2% by mass or more, 2.2% by mass or more, 2.5% by mass or more, 3% by mass or more, 3.3% by mass or more, 4% by mass or more, 4.5% by mass or more, 6% by mass or more, or 6.5% by mass or more. Similarly, the content of the ionic surfactant (C) in the treatment agent is, for example, 6.5% by mass or less, 6% by mass or less, 4.5% by mass or less, 4% by mass or less, 3.3% by mass or less, 3% by mass or less, 2.5% by mass or less, 2.2% by mass or less, or 2% by mass or less.

[0045] (Hydrated Viscosity) The maximum hydrous viscosity of the treatment agent is 10,000 mPa·s or more when the nonvolatile content is in the range of 40% to 80% by mass. The hydrous viscosity is the viscosity at each concentration when the nonvolatile content of the treatment agent is changed in 5% increments from 30% to 100% by mass.

[0046] When the nonvolatile content is in the range of 40% by mass to 80% by mass, the maximum viscosity upon watering is preferably 15,000 mPa·s or more, more preferably 20,000 mPa·s or more, and preferably less than 100,000 mPa·s.

[0047] When the nonvolatile content is in the range of 40% by mass or more and 80% by mass or less, and the maximum hydrous viscosity is 15,000 mPa·s or more, scattering of the treatment agent adhered to the synthetic fiber during the spinning and drawing process is more easily suppressed. Furthermore, since it becomes easier to apply an adhesive to the surface of the synthetic fiber to which the treatment agent has been adhered, the adhesion of the synthetic fiber to the rubber material to which the treatment agent has been adhered can be improved. When the maximum hydrous viscosity is 20,000 mPa·s or more, scattering of the treatment agent adhered to the synthetic fiber during the spinning and drawing process is even more easily suppressed.

[0048] The viscosity of the treatment agent when hydrated is preferably 10,000 mPa·s or less when the nonvolatile content is in the range of 85% by mass to 100% by mass. When the viscosity of the treatment agent when hydrated is 10,000 mPa·s or less when the nonvolatile content is in the range of 85% by mass to 100% by mass, the adhesion of the synthetic fiber to which the treatment agent is attached to the rubber material can be further improved.

[0049] Here, the synthetic fibers to which a treatment agent has been applied in the spinning and drawing process may further undergo, for example, a twisting process and a weaving process, after which an adhesive is applied and the fibers are bonded to a rubber material. As the fibers pass through the twisting and weaving processes, the treatment agent attached to the synthetic fibers tends to have a higher nonvolatile content concentration. That is, the treatment agent attached to synthetic fibers that have been weaving tends to have a relatively higher nonvolatile content concentration than the treatment agent attached in the spinning and drawing process. When the nonvolatile content concentration of the treatment agent becomes relatively high, the viscosity of the surface of the synthetic fibers increases, making it difficult to apply the adhesive uniformly. Therefore, by setting the nonvolatile content concentration of the treatment agent to be 85% by mass or more and 100% by mass or less and the viscosity upon hydration to be 10,000 mPa·s or less, the adhesive can be applied more uniformly to the synthetic fibers. This further improves the adhesion of the synthetic fibers to the rubber material.

[0050] The non-volatile content of the treatment agent refers to the bone-dry content of the treatment agent when it has reached a constant weight after being heat-treated at 105°C to remove the solvent, etc. The state of the non-volatile content of the treatment agent is defined as a non-volatile content concentration of 100% by mass. When the non-volatile content is diluted by adding ion-exchanged water and stirring, the non-volatile content is defined as the proportion of the non-volatile content to the total mass including the ion-exchanged water.

[0051] The viscosity upon hydration was measured by adding ion-exchanged water starting from a state in which the nonvolatile content of the treatment agent was 100% by mass, and measuring the viscosity of the treatment agent at 30°C with an E-type viscometer every time the nonvolatile content decreased by 5% by mass. The viscosity upon hydration was measured three times for each nonvolatile content concentration, and the average value was calculated.

[0052] (Kinematic Viscosity) The treatment agent has a kinematic viscosity of 2 mm at 30°C when the nonvolatile content is adjusted to 25% by mass. ２ / s or more 12mm ２ The kinematic viscosity of the treatment agent adjusted to a nonvolatile content of 25% by mass at 30°C is 2 mm / s or less. ２ / s or more 12mm ２ / s or less, scattering of the treatment agent adhered to the synthetic fiber can be more effectively suppressed, and the adhesion of the synthetic fiber to the rubber material with the treatment agent adhered thereto can be improved.

[0053] The kinematic viscosity of the treatment agent was measured using a treatment agent diluted with ion-exchanged water to a non-volatile content of 25% by mass by the Cannon-Fenske method at 30°C. The treatment agent was diluted with ion-exchanged water by adding the treatment agent in small amounts to ion-exchanged water stirred at 550 rpm with a stirring blade, and stirring was continued until the treatment agent was completely dissolved.

[0054] In the present invention, the method for adjusting the hydrous viscosity and kinematic viscosity values ​​to the above-mentioned ranges is not particularly limited. For example, they can be adjusted by selecting the types of the lubricant (A), the nonionic surfactant (B), and the ionic surfactant (C) or adjusting their content ratios. They can also be adjusted by adding a viscosity modifier or the like in the other component (D) described below.

[0055] (Other Component (D)) The treatment agent may contain other component (D). Examples of other component (D) include components typically used in treatment agents, such as stabilizers, antistatic agents, binders, antioxidants, ultraviolet absorbers, pH adjusters, viscosity adjusters, and appearance adjusters.

[0056] Specific examples of the other component (D) include malic acid, tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate, bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid](ethylenebisoxy)bisethylene, dibutylethanolamine, ethylene glycol, and glycerin.

[0057] The content of the other component (D) in the nonvolatile content of the treatment agent is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 2.5% by mass or less. The other component (D) may be 0% by mass.

[0058] (Storage form) The treatment agent may be configured as a one-component treatment agent containing the above-mentioned components (A) to (D), or from the viewpoint of improving the formulation stability, it may be configured as a two-component treatment agent or a three-component treatment agent.

[0059] (Solvent) The treatment agent of the present embodiment may be mixed with a solvent, if necessary, to prepare a treatment-agent-containing composition for synthetic fibers (hereinafter also referred to as a "treatment-agent-containing composition"). The treatment agent may be stored or distributed in the form of a treatment-agent-containing composition.

[0060] The solvent has a boiling point of 105°C or less at 1 atmosphere. Examples of the solvent include water and organic solvents. Specific examples of water include ion-exchanged water, distilled water, hard water, and soft water. Among these, it is preferable to use ion-exchanged water or distilled water.

[0061] Specific examples of the organic solvent include lower alcohols such as ethanol and propanol, and low-polarity solvents such as hexane. These solvents may be used alone or in combination of two or more. Among these, polar solvents such as water and lower alcohols are preferred from the viewpoint of excellent dispersibility or solubility of each component, and water is more preferred from the viewpoint of excellent handleability.

[0062] (Application Form) The treatment agent of this embodiment is applied to a process in which the treatment agent is applied to synthetic fibers in the form of an aqueous liquid having a non-volatile content of 5% by mass or more and 25% by mass or less. For example, the treatment agent of this embodiment is applied to synthetic fibers in the form of an aqueous liquid having a non-volatile content of 5% by mass or more and 25% by mass or less in a spinning and drawing process. By applying the treatment agent to synthetic fibers in the form of an aqueous liquid having a non-volatile content of 5% by mass or more and 25% by mass or less, scattering of the treatment agent can be more effectively suppressed. Furthermore, the adhesion of the synthetic fibers to which the treatment agent is attached to rubber materials can be improved.

[0063] The aqueous liquid refers to a treatment agent diluted with a solvent containing water. The proportion of water in the solvent is preferably 90% by mass or more. The aqueous liquid can be prepared by adding a solvent containing water to the treatment agent. The aqueous liquid may also be prepared by adding a solvent containing water to the nonvolatile components.

[0064] <Functions and Effects of First Embodiment> (1-1) The treatment agent of the first embodiment contains a smoothing agent (A), a nonionic surfactant (B), and an ionic surfactant (C). The maximum value of the hydrous viscosity is 10,000 mPa·s or more in a range of nonvolatile content of 40% by mass or more and 80% by mass or less, and the kinematic viscosity at 30°C when the nonvolatile content is adjusted to 25% by mass is 2 mm ２ / s or more 12mm ２ The treatment agent is applied to the synthetic fibers in the form of an aqueous liquid having a nonvolatile content of 5% by mass or more and 25% by mass or less.

[0065] Therefore, scattering of the treatment agent attached to the synthetic fiber during the spinning and drawing process can be more effectively suppressed, and the adhesiveness of the synthetic fiber to which the treatment agent is attached to the rubber material can be improved.

[0066] (1-2) The viscosity of the treatment agent when mixed with water is 10,000 mPa·s or less when the nonvolatile content is in the range of 85% by mass to 100% by mass, thereby further improving the adhesion of the synthetic fiber to the rubber material.

[0067] (1-3) The smoothing agent (A) contains an ester compound (A1) having a sulfur atom in the molecule, which can further improve the adhesion of synthetic fibers to rubber materials.

[0068] Second Embodiment Next, a second embodiment of the synthetic fiber according to the present invention will be described. The synthetic fiber of this embodiment is a synthetic fiber to which the treatment agent of the first embodiment has been adhered. That is, this embodiment provides a treated synthetic fiber comprising a synthetic fiber and a treatment agent adhered thereto. The treatment agent may be applied to the synthetic fiber in the form of a dilution diluted with the above-mentioned solvent, such as an organic solvent solution or an aqueous liquid. The synthetic fiber is obtained by adhering a dilution such as an aqueous liquid to the synthetic fiber, for example, in a spinning and drawing process. The solvent from the dilution adhered to the synthetic fiber may be evaporated in a drawing process or drying process after the spinning process.

[0069] Specific examples of synthetic fibers to which the treatment agent of this embodiment can be applied include, but are not limited to, (1) polyester fibers such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and composite fibers containing these polyester resins, (2) polyamide fibers such as nylon 6 and nylon 66, (3) polyacrylic fibers such as polyacrylic and modacrylic, and (4) polyolefin fibers such as polyethylene and polypropylene. Of these, the treatment agent is preferably applied to polyester fibers and polyamide fibers.

[0070] There are no particular restrictions on the proportion of the treatment agent applied to the synthetic fibers, but it is preferable to apply the treatment agent at a proportion of 0.1% by mass to 3% by mass (excluding solvents such as water) relative to the synthetic fibers. This configuration further improves the effects of the present invention. There are also no particular restrictions on the method for applying the treatment agent, and known methods such as roller oiling, guide oiling using a metering pump, immersion oiling, and spray oiling can be used.

[0071] In the present invention, the synthetic fibers are not particularly limited in their applications, but are preferably used in industrial materials. For example, they can be used for airbag fibers, seatbelt fibers, tire cord fibers, carpet fibers, tent fibers, advertising fabric fibers, fishing net fibers, conveyor belt fibers, rope fibers, etc. They can also be used in fields such as automobiles, construction, commerce, agriculture / fisheries, and civil engineering.

[0072] Among the above industrial materials, when used to reinforce rubber products such as tire cords, the adhesive used to bond to the rubber material is not particularly limited. Any known adhesive used to bond to rubber materials can be used. Examples of known adhesives used to bond to rubber materials include epoxy compounds, isocyanate compounds, and resorcinol-formaldehyde-latex (RFL) solutions. Among these, epoxy compounds are preferred. Also included are mixtures of these adhesives and mixtures of adhesives and surfactants. When applying the adhesive, a solution diluted with water or an organic solvent may be applied, or the adhesive may be applied as is.

[0073] The procedure for applying the treatment agent and adhesive of the present invention to synthetic fibers is not particularly limited. For example, the treatment agent may be applied to synthetic fibers during spinning, such as in the spinning and drawing process, and then twisted synthetic fibers are woven to produce a woven fabric, and an adhesive may be applied to the woven fabric to bond the woven fabric to the rubber material. Alternatively, the treatment agent and adhesive may be mixed in advance to prepare a mixed solution, and then the mixed solution may be applied to synthetic fibers during spinning, and then twisted synthetic fibers are woven to produce a woven fabric, and the woven fabric and rubber material may be bonded. Alternatively, the treatment agent and adhesive may be applied separately to synthetic fibers during spinning, and then twisted synthetic fibers are woven to produce a woven fabric, and the woven fabric and rubber material may be bonded.

[0074] <Functions and Effects of the Second Embodiment> (2-1) The synthetic fiber has the treatment agent of the first embodiment attached thereto. Therefore, the adhesion of the synthetic fiber to rubber materials can be improved. The synthetic fiber can be suitably used for reinforcing rubber products.

[0075] Examples will be given below to more specifically illustrate the configuration and effects of the present invention, but the present invention is not limited to these examples. In the following examples and comparative examples, % means % by mass.

[0076] Test Section 1 (Preparation of Treatment Agent) (Treatment Agent 1) As shown in Table 1, the lubricating agent (A) consisted of 45% trimethylolpropane trioleate (A-1) and 5% di(2-hexyl-1-decyl)thiodipropionate (A1-7), and the nonionic surfactants (B) were 10% of a compound (B-2) in which 12 moles of EO were added to 1 mole of hydrogenated castor oil, 5% of a compound (B-3) in which 20 moles of EO were added to 1 mole of hydrogenated castor oil, 20% of a compound (B-5) in which 1 mole of a compound in which 20 moles of EO were added to 1 mole of hydrogenated castor oil was esterified with 2 moles of oleic acid, and 1 mole of a compound (B-7) in which 25 moles of EO were added to 1 mole of hydrogenated castor oil was esterified with 0.5 moles of adipic acid and 1 mole of stearic acid. Treatment agent 1 was prepared by mixing 5% of a compound (B-12) in which 10 moles of EO were added to 1 mole of stearylamine, 4% of a compound (B-12) in which 10 moles of EO were added to 1 mole of stearylamine, 1.8% of a secondary alkyl (having from 12 to 18 carbon atoms) sodium sulfonate (C-2) as an ionic surfactant (C), 1.5% of a salt (C-4) of an isocetyl phosphate ester and a compound in which 10 moles of EO were added to 1 mole of laurylamine, and 0.7% of bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid](ethylenebisoxy)bisethylene (D-3), 1% of dibutylethanolamine (D-4), and 1% of ethylene glycol (D-5) as other components (D) so that the total amount was 100% by mass.

[0077] (Treatment Agents 2 to 30) Treatment Agents 2 to 30 were prepared in the same manner as Treatment Agent 1, containing the smoothing agent (A), nonionic surfactant (B), ionic surfactant (C), and other component (D) in the proportions shown in Tables 1 and 2.

[0078] The type and content of the smoothing agent (A), the type and content of the nonionic surfactant (B), the type and content of the ionic surfactant (C), and the type and content of the other component (D) are shown in the "Smoothing agent (A)" column, the "Nonionic surfactant (B)" column, the "Ionic surfactant (C)" column, and the "Other component (D)" column in Tables 1 and 2, respectively.

[0079]

[0080]

[0081] Details of the smoothing agent (A), nonionic surfactant (B), ionic surfactant (C), and other component (D) shown in Tables 1 and 2 are as follows: <Smoothing Agent (A)> A-1: ​​Trimethylolpropane trioleate A-2: Trimethylolpropane trilaurate A-3: Pentaerythritol tetraoctanate A-4: Sorbitan monooleate A-5: 2-decyl-1-tetradecyl erucinate A-6: 2-decyl-1-tetradecyl oleate A1-7: Di(2-hexyl-1-decyl)thiodipropionate A1-8: Di(2-decyl-1-tetradecyl)thiodipropionate A1-9: Dioleylthiodipropionate A1-10: Diisostearylthiodipropionate A1-11: Isostearyl(laurylthiopropionate) A1-12: a diester of a compound in which 3 moles of EO are added to 1 mole of dodecanol and thiodipropionic acid. The smoothing agents A-1 to A-6 are ester compounds (A2) that have an ester bond but no ether bond in the molecule. The smoothing agents A1-7 to A1-12 are ester compounds (A1) that have a sulfur atom in the molecule and have a structure formed from a polycarboxylic acid and a monohydric alcohol.

[0082] <Nonionic surfactants (B)> B-1: A compound obtained by adding 10 moles of EO to 1 mole of hydrogenated castor oil. B-2: A compound obtained by adding 12 moles of EO to 1 mole of hydrogenated castor oil. B-3: A compound obtained by adding 20 moles of EO to 1 mole of hydrogenated castor oil. B-4: A compound obtained by adding 25 moles of EO to 1 mole of hydrogenated castor oil. B-5: A compound obtained by esterifying 1 mole of a compound obtained by adding 20 moles of EO to 1 mole of hydrogenated castor oil with 2 moles of oleic acid. B-6: A compound obtained by esterifying 1 mole of a compound obtained by adding 20 moles of EO to 1 mole of hydrogenated castor oil with 3 moles of oleic acid. B-7: A compound obtained by esterifying 1 mole of a compound obtained by adding 25 moles of EO to 1 mole of hydrogenated castor oil with 0.5 moles of adipic acid and 1 mole of stearic acid. B-8: A compound obtained by adding 7 moles of EO to 1 mole of sorbitan monooleate. B-9: A compound in which 20 moles of EO are added to 1 mole of sorbitan monostearate B-10: A diester of polyethylene glycol (mass average molecular weight 600) and oleic acid B-11: A compound in which 10 moles of EO and 10 moles of PO are randomly added to 1 mole of dodecanol B-12: A compound in which 10 moles of EO are added to 1 mole of stearylamine B-13: A compound in which 15 moles of EO are added to 1 mole of stearylamine <Ionic surfactants (C)> C-1: Sodium α-olefin (having 14 to 18 carbon atoms) sulfonate C-2: Sodium secondary alkyl (having 12 to 18 carbon atoms) sulfonate C-3: A salt of an oleyl phosphate ester and a compound in which 4 moles of EO are added to 1 mole of laurylamine C-4: A salt of an isocetyl phosphate ester and a compound in which 10 moles of EO are added to 1 mole of laurylamine <Other components (D)> D-1: Malic acid D-2: Tris(4-tert-butyl-3-hydroxy-2,D-3: Bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionic acid](ethylenebisoxy)bisethylene D-4: Dibutylethanolamine D-5: Ethylene glycol D-6: Glycerin Test Category 2 (Evaluation of kinematic viscosity and hydrous viscosity of treatment agents) The kinematic viscosity of the treatment agents was measured using an aqueous solution prepared by diluting each treatment agent with ion-exchanged water to a non-volatile content of 25% by mass. The measurement was carried out using the Cannon-Fenske method at 30°C. The treatment agents were diluted with ion-exchanged water by adding the treatment agent in small amounts to the ion-exchanged water stirred at 550 rpm using a stirring blade, and stirring was continued until the agent was completely dissolved.

[0083] The viscosity of each treatment agent with water was measured at 30°C using an E-type viscometer every time the nonvolatile content of the treatment agent was reduced by 5% by mass by adding ion-exchanged water, starting from a state where the nonvolatile content of the treatment agent was 100% by mass. The measurement of the water-added viscosity was performed three times for each nonvolatile content concentration, and the average value was calculated. The measurement results of the kinematic viscosity and water-added viscosity are shown in Tables 3 and 4.

[0084]

[0085]

[0086] In Tables 3 and 4, the value marked with * on the left shoulder indicates the maximum water-added viscosity. Also, ** indicates that the viscosity exceeded 100,000 mPa·s and could not be measured. In the water-added viscosity range, where the treatment agent concentration is high, the treatment agent is dispersed as an oily component, and the viscosity is maintained in a relatively low state. As the treatment agent concentration decreases, the treatment agent undergoes a phase transition to a state in which it is dispersed in water, and the viscosity becomes relatively high. Furthermore, in the range of low treatment agent concentration, the treatment agent remains dispersed in water, and the viscosity becomes relatively low.

[0087] Test Section 3 (Evaluation of Amount of Adhesion of Treatment Agent) For each treatment agent, aqueous solutions with non-volatile content concentrations of 5 mass%, 10 mass%, 15 mass%, 20 mass%, 25 mass%, and 70 mass% were prepared, and these were designated as Examples 1 to 100 and Comparative Examples 1 to 80.

[0088] After drying polyethylene terephthalate chips using conventional methods, they were melt-spun using an extruder, discharged from the spinneret, and cooled and solidified. An aqueous solution of the treatment agent from each Example and Comparative Example was applied to the running yarn using a guide oiling method using a metering pump. Oil was added so that the amount of treatment agent attached was 0.6% by mass (amount excluding diluents and water). The yarn was then focused using a guide, stretched through a 250°C stretch roll and a relaxation roll to a total stretch ratio of 2.0, and wound up at a speed of 5,000 m / min. The amount of treatment agent attached to the stretched yarn was measured, and evaluation was performed using the following criteria, with 100% being the target amount. The closer the amount of treatment agent attached to the target amount, the more effectively the treatment agent was suppressed from scattering. The results are shown in the "OPU" column of Tables 5 to 7. Note that OPU stands for oil pickup.

[0089] Evaluation criteria for adhesion amount: 4 (Excellent): 95% or more; 3 (Good): 85% or more but less than 95%; 2 (Acceptable): 75% or more but less than 85%; 1 (Unacceptable): Less than 75%. Test Section 4 (Evaluation of Adhesion to Rubber Materials) The aqueous solution of the treatment agent of each Example and Comparative Example was applied to oil-free polyethylene terephthalate fiber having 1670 dtex, 288 filaments, and an intrinsic viscosity of 0.93 in a spinning process using an oiling roller oiling method, so that the amount applied was 5.0% by mass as non-volatile matter. The water was then dried to obtain a test yarn. Two test yarns were twisted with a twist number of 40 twists per 10 cm and 40 twists per 10 cm to obtain a twisted yarn cord.

[0090] This twisted yarn cord was immersed in a first adhesive (epoxy compound (trade name: DENACOL EX-512, manufactured by Nagase ChemteX Corporation) / blocked isocyanate (trade name: ELASTRON BN-27, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) = 5 / 5 (solid content ratio)), and then heat-treated.

[0091] Next, the cord was further immersed in a second adhesive (an RFL solution of resorcinol (Kishida Chemical Co., Ltd., trade name Resorcinol) / formalin (Kishida Chemical Co., Ltd., trade name Formaldehyde Liquid (37%)) / latex (Nipol 2518FS, Nippon Zeon Co., Ltd., trade name Nipol 2518FS) = 1.5 / 0.5 / 8 (solids ratio)), followed by heat treatment to obtain a reinforcing cord treated with the adhesive. This reinforcing cord was closely aligned with unvulcanized rubber measuring 2.5 cm in length and 12.5 cm in width, and unvulcanized rubber was placed on top of it. This was then press-vulcanized at 150 ° C and 4 MPa for 30 minutes to prepare a test piece for evaluating rubber adhesion. The test piece was allowed to cool, and the reinforcing cord and rubber were peeled at a peel rate of 50 mm / min. The degree of adhesion of the rubber to the reinforcing cord was visually observed, and the adhesion was evaluated according to the following evaluation criteria. The results are shown in the "Rubber Adhesion" column of Tables 5 to 7.

[0092] - Evaluation criteria for rubber material adhesion 3 (Good): When the rubber is adhered to such an extent that the reinforcing cord is not visible 2 (Fair): When the rubber is adhered to such an extent that the reinforcing cord is barely visible 1 (Poor): When the reinforcing cord is clearly visible

[0093]

[0094]

[0095]

[0096] As shown in Tables 1 to 7, it was confirmed that the kinematic viscosity values ​​of treatment agents 21 to 24 (comparative examples 21 to 44) were outside the range of the present invention, and that scattering of the treatment agent could not be suppressed, and that the adhesion of the synthetic fiber to which the treatment agent was attached to the rubber material was poor.

[0097] For treatment agents 25 to 30 (comparison examples 45 to 80), the maximum values ​​of the hydrous viscosity in the nonvolatile content range of 40% by mass or more and 80% by mass or less were outside the numerical range of the present invention, and it was confirmed that scattering of the treatment agent could not be suppressed and that the adhesion to rubber materials was poor.

[0098] Furthermore, among treatment agents 1 to 30, those with a treatment agent concentration of 70% by mass when applied to the synthetic fibers (Comparative Examples 1 to 20, 26, 32, 38, 44, 50, 56, 62, 68, 74, and 80) had poor adhesion because the treatment agent concentration when applied to the synthetic fibers was too high. As a result, it was confirmed that these treatment agents were poor in the evaluation of the amount of adhesion and that the synthetic fibers to which the treatment agent was applied had poor adhesion to the rubber material.

[0099] On the other hand, according to the treatment agents 1 to 20 (Examples 1 to 100) of the present invention, scattering of the treatment agent attached to the synthetic fiber during the spinning and drawing process can be more effectively suppressed, and the adhesion of the synthetic fiber to which the treatment agent is attached to the rubber material can be improved.

Claims

1. A synthetic fiber treatment agent containing a smoothing agent (A), a nonionic surfactant (B), and an ionic surfactant (C), the maximum viscosity upon hydration is 10,000 mPa·s or more in the range of nonvolatile content of 40% by mass to 80% by mass, and the kinematic viscosity at 30°C when the nonvolatile content is adjusted to 25% by mass is 2 mm ２ / s or more 12mm ２ / s or less, and is applied to a process in which the synthetic fiber treatment agent is applied to synthetic fibers in the form of an aqueous liquid having a non-volatile content of 5% by mass or more and 25% by mass or less, and the hydrated viscosity is the viscosity at each concentration when the non-volatile content of the synthetic fiber treatment agent is changed in increments of 5% by mass within a range from 30% by mass to 100% by mass.

2. The synthetic fiber treatment agent according to claim 1, wherein the viscosity of the synthetic fiber treatment agent when hydrated is 10,000 mPa·s or less when the nonvolatile content is in the range of 85% by mass or more and 100% by mass or less.

3. The synthetic fiber processing agent according to claim 1, wherein the smoothing agent (A) contains an ester compound (A1) having a sulfur atom in the molecule.

4. The synthetic fiber treatment agent according to claim 1, wherein the maximum viscosity upon addition of water is 15,000 mPa·s or more.

5. The synthetic fiber treating agent according to claim 4, wherein the maximum viscosity upon addition of water is 20,000 mPa·s or more.

6. The synthetic fiber treatment agent according to claim 1, wherein the maximum viscosity upon addition of water is less than 100,000 mPa·s.

7. The synthetic fiber treatment agent according to claim 1, wherein the synthetic fiber treatment agent contains the smoothing agent (A) in an amount of 30% by mass or more and 70% by mass or less, the nonionic surfactant (B) in an amount of 20% by mass or more and 60% by mass or less, and the ionic surfactant (C) in an amount of 0.1% by mass or more and 10% by mass or less, when the total content of the smoothing agent (A), the nonionic surfactant (B), and the ionic surfactant (C) is taken as 100% by mass.

8. Synthetic fibers characterized by having the synthetic fiber treatment agent according to any one of claims 1 to 7 adhered thereto.

9. The synthetic fiber according to claim 8, which is used to reinforce rubber products.

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