JP6445205B1 - Synthetic fiber treatment agent and synthetic fiber - Google Patents

Abstract

A synthetic fiber treating agent and synthetic fiber having good process passability in a synthetic fiber spinning process and good rubber adhesion in a post-processing process. The treating agent for synthetic fibers of the present invention comprises the following smoothing agent, the following oxycarboxylic acid derivative, a nonionic surfactant, and an ionic surfactant. The smoothing agent comprises at least one ester compound selected from an ester compound of a polyhydric alcohol and a monovalent carboxylic acid, an ester compound of a monohydric alcohol and a polyvalent carboxylic acid, and a monohydric alcohol and elemental sulfur in the molecule. It contains a sulfur-containing ester compound with a polyvalent carboxylic acid. The oxycarboxylic acid derivative is at least one compound selected from oxycarboxylic acids and salts thereof. The synthetic fiber of the present invention is characterized in that the synthetic fiber treating agent is attached. [Selection figure] None

Description

  The present invention relates to a synthetic fiber treating agent that exhibits good process passability in a synthetic fiber spinning process and has good rubber adhesion in a post-processing step, and a synthetic fiber to which such a treating agent is attached.

  In general, in the synthetic fiber spinning process, from the viewpoint of reducing friction and preventing fiber damage such as yarn breakage, a synthetic fiber treating agent containing a surfactant is applied to the surface of the filament yarn of the synthetic fiber. Processing may be performed.

  Conventionally, the processing agent for synthetic fibers disclosed by patent documents 1-4 is known. Patent Document 1 discloses a processing agent for synthetic fibers containing a carboxylate and having a maximum viscosity controlled when containing water. Patent document 2 discloses the processing agent for synthetic fibers containing a quaternary ammonium cation. Patent Document 3 discloses a treating agent for synthetic fibers containing a specific surfactant and having a 40% by mass aqueous emulsion having a viscosity of 20 cst or less. Patent Document 4 discloses a treating agent for synthetic fibers containing an ester compound having a sulfur element, a sorbitan ester compound, and an organic amine compound.

JP 55-148280 A JP 07-258969 A JP 07-216734 A JP, 2006-180190, A

  These conventional synthetic fiber treatment agents improve process passability in the synthetic fiber spinning process, especially suppress tar dirt and fluff around the godet roller in high-temperature spinning processes in recent industrial material applications, and rubber adhesion. It was not possible to fully achieve the compatibility of each function of improvement.

  The problem to be solved by the present invention is to provide a synthetic fiber treating agent and a synthetic fiber having good process passability in a synthetic fiber spinning process and good rubber adhesion in a post-processing process.

  As a result of studies conducted by the present inventors to solve the above-mentioned problems, in particular, as a smoothing agent, an ester of a polyhydric alcohol and a monovalent carboxylic acid or an ester compound of a monohydric alcohol and a polyvalent carboxylic acid, and a specific inclusion. It has been found that a synthetic fiber treating agent containing a sulfur ester compound and a specific oxycarboxylic acid derivative is correctly suitable.

That is, in one aspect of the present invention, there is provided a synthetic fiber treating agent comprising the following smoothing agent, the following oxycarboxylic acid derivative, a nonionic surfactant, and an ionic surfactant.
The smoothing agent includes at least one ester compound selected from an ester compound of a polyhydric alcohol and a monovalent carboxylic acid, an ester compound of a monohydric alcohol and a polycarboxylic acid, and a monohydric alcohol and a sulfur element in the molecule. And a sulfur-containing ester compound with a polyvalent carboxylic acid.

The oxycarboxylic acid derivative is at least one compound selected from oxycarboxylic acids and salts thereof.
The oxycarboxylic acid derivative is preferably an oxycarboxylic acid having 2 to 8 carbon atoms having 1 to 2 hydroxyl groups and 1 to 3 carboxyl groups in the molecule, or a salt thereof.

The total proportion of the oxycarboxylic acid and the salt thereof is preferably 0.001 to 5% by mass in the non-volatile content of the treating agent for synthetic fibers.
The nonionic surfactant contains 1 to 100 moles of a compound having 1 to 100 moles of alkylene oxide added to 1 mole of hardened castor oil, and 1 to 2 moles of alkylene oxide per mole of castor oil. It is preferable to contain the compound which esterified monovalent carboxylic acid in the ratio of 1-3 mol with respect to 1 mol of compounds chosen from the compound added in the ratio of -100 mol.

  The ionic surfactant contains at least one compound selected from an alkali metal sulfonate having a hydrocarbon group having 4 to 22 carbon atoms and an amine phosphate having a hydrocarbon group having 4 to 22 carbon atoms. Is preferred.

  When the total content of the smoothing agent, the nonionic surfactant, the ionic surfactant, and the oxycarboxylic acid derivative is 100% by mass, the smoothing agent is 20 to 85% by mass, and the nonionic surfactant is used. It is preferable to contain 10 to 75 mass% of the agent, 0.1 to 15 mass of the ionic surfactant, and 0.001 to 5 mass% of the oxycarboxylic acid derivative.

  According to another aspect of the present invention, there is provided a synthetic fiber characterized in that the synthetic fiber treating agent is attached.

  According to the present invention, it has good process passability in the synthetic fiber spinning process and good rubber adhesion in the post-processing process.

(First embodiment)
First, a first embodiment in which a synthetic fiber treating agent (hereinafter referred to as a treating agent) according to the present invention is embodied will be described. The treatment agent of this embodiment is a treatment agent comprising a specific smoothing agent, a specific oxycarboxylic acid derivative, a nonionic surfactant, and an ionic surfactant.

  The smoothing agent comprises at least one ester compound selected from an ester compound of a polyhydric alcohol and a monovalent carboxylic acid, an ester compound of a monohydric alcohol and a polyvalent carboxylic acid, and a monohydric alcohol and elemental sulfur in the molecule. It contains a sulfur-containing ester compound with a polyvalent carboxylic acid.

  The oxycarboxylic acid derivative is at least one compound selected from oxycarboxylic acids and salts thereof. These oxycarboxylic acid derivatives may be used alone or in combination of two or more. The oxycarboxylic acid derivative preferably contains an oxycarboxylic acid having 2 to 8 carbon atoms having 1 to 2 hydroxyl groups and 1 to 3 carboxyl groups in the molecule, or a salt thereof. By using such a compound, the effect of the present invention, in particular, rubber adhesion can be further improved in the post-processing step.

  In the non-volatile content of the treatment agent of this embodiment, the total of the proportion of oxycarboxylic acid and the proportion of its salt is preferably 0.001 to 5 mass%. With this configuration, the effects of the present invention, particularly tar dirt, can be further suppressed, and the process passability can be further improved. The non-volatile content refers to an absolutely dry product obtained by sufficiently removing the volatile diluent by heat-treating the diluted solution containing the solvent at 105 ° C. for 2 hours when the treatment agent of this embodiment is mixed with the solvent. Say.

  Specific examples of the compound contained in the smoothing agent to be used in the treatment agent of the present embodiment include (1) 1,4-butanediol dioleate, trimethylolpropane trilaurate, trimethylolpropane trioleate, pentaerythritol tetra Ester compounds of polyhydric alcohols and monovalent carboxylic acids such as octanoate, sorbitan monooleate, sorbitan trioleate, glycerin monolaurate, glycerin trilaurate, glycerin trioleate, (2) dioleyl adipate, Ester compounds of polyvalent carboxylic acids and monohydric alcohols such as trioctyl trimellitate, (3) natural fats and oils such as rapeseed white squeezed oil, palm oil, coconut oil, (4) dioctylthiodipropionate, di Isolauryl thiodipropionate, dilauryl thio Examples include sulfur-containing ester compounds of monohydric alcohols and polyvalent carboxylic acids having a sulfur element in the molecule, such as propionate, diisocetylthiodipropionate, diisostearylthiodipropionate, and dioleylthiodipropionate. It is done.

  Among these, trimethylolpropane trioleate, glycerin trioleate, rapeseed white oil, trioctyl trimellitate, dioleyl adipate, dioleylthiodipropionate, diisocetylthiodipropionate, diisostearylthiodipropio Nartes are preferred.

  Specific examples of the nonionic surfactant used for the treatment agent of the present embodiment include, for example, (1) a compound obtained by adding an alkylene oxide having 2 to 4 carbon atoms to an organic acid, an organic alcohol, an organic amine, and / or an organic amide, For example, polyoxyethylene monolaurate, polyoxyethylene monooleate, polyoxyethylene laurate methyl ether, polyoxyethylene octyl ether, polyoxypropylene lauryl ether methyl ether, polyoxybutylene oleyl ether, polyoxyethylene polyoxy Propylene lauryl ether, polyoxyethylene polyoxypropylene nonylphenyl ether, polyoxyethylene lauryl amino ether, polyoxyethylene lauroamide ether, polyoxyethylene Ether type nonionic surfactants such as ethanolamine monooleylamide, (2) polyethylene glycol dioleate, polyoxyethylene sorbitan monooleate, polyoxybutylene sorbitan trioleate, polyoxypropylene castor oil, polyoxyethylene hydrogenated castor oil, poly Oxyethylenepropylene hydrogenated castor oil trioleate, polyoxyethylene hydrogenated castor oil trilaurate, ether ester compound obtained by condensing ethylene oxide adduct of hardened castor oil and fumaric acid, ethylene oxide adduct of castor oil and ethylene oxide adduct of hardened castor oil Ether ester compound, bispolyoxyethylene lauryl adipa obtained by condensing at least one kind of compound with monocarboxylic acid and dicarboxylic acid , Bis polyoxyethylene oleyl adipate, polyoxyalkylene ether ester type nonionic surfactants and the like, (3) alkyl amide type nonionic surfactants such as diethanol monolauroyl amide, and the like. These nonionic surfactants may be used alone or in combination of two or more.

  As the nonionic surfactant, a monovalent carboxylic acid was esterified at a ratio of 1 to 3 mol with respect to 1 mol of at least one compound selected from an alkylene oxide adduct of castor oil and an alkylene oxide adduct of hardened castor oil. Those containing a compound are preferred. Examples of the alkylene oxide used in the ether ester compound include ethylene oxide, propylene oxide, butylene oxide, and the like. Examples of monovalent carboxylic acids include lauric acid, myristic acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, isostearic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, arachidic acid, eicosenoic acid, behen. An acid, erucic acid, etc. are mentioned.

  Among these, the compound which added C2-C4 alkylene oxide in the ratio of 1-100 mol with respect to 1 mol of hardened castor oil, and C1-C4 alkylene oxide with 1-100 mol per mol of castor oil. What contains the compound which esterified monovalent carboxylic acid in the ratio of 1-3 mol with respect to 1 mol of compounds chosen from the compound added in the ratio is more preferable. With this configuration, the effects of the present invention, in particular, the yarn fluff can be further suppressed, and the process passability can be further improved.

  More preferable ether ester compounds include compounds obtained by adding 20 moles of ethylene oxide to 1 mole of hardened castor oil and 3 moles of oleic acid, and those obtained by adding 40 moles of ethylene oxide to 1 mole of hardened castor oil. And a compound obtained by esterifying 25 mol of ethylene oxide to 1 mol of castor oil with 3 mol of lauric acid.

  Specific examples of the ionic surfactant used in the treatment agent of the present embodiment include (1) carboxylic acid soap type ionic surfactants such as potassium octoate, potassium oleate, potassium alkenyl succinate, (2 ) Pentadecyl sulfonic acid sodium salt, dodecyl benzene sulfonic acid sodium salt, dioctyl sulfosuccinic acid sodium salt and other sulfonic acid ester type ionic surfactants, (3) polyoxyethylene lauryl sulfate sodium salt, hexadecyl sulfate potassium salt, beef fat sulfide Sulfate, ionic surfactants such as oil, castor oil sulfide oil, (4) sodium salt of octyl phosphate, potassium salt of polyoxyethylene lauryl phosphate, triethanolamine salt of oleyl phosphate, polyoxyethylene oleyl phosphate Polyoxyethylene lauryl amine salt, dibutyl ethanolamine salts of polyoxyethylene oleyl phosphate. These ionic surfactants may be used alone or in combination of two or more.

  Examples of the ionic surfactant include those containing at least one compound selected from an alkali metal sulfonate having a hydrocarbon group having 4 to 22 carbon atoms and an amine phosphate having a hydrocarbon group having 4 to 22 carbon atoms. preferable. Among these, sodium alkyl sulfonate, oleyl phosphate ethylene oxide (hereinafter referred to as EO) 15 (the number of moles added of ethylene oxide is the same) stearyl amino ether salt, isocetyl phosphate EO 10 lauryl amino ether salt are particularly preferable.

  Specific examples of the oxycarboxylic acid derivative include oxycarboxylic acids such as citric acid, lactic acid, tartaric acid, glycolic acid, malic acid, and salts thereof. Examples of the salt include potassium salt, sodium salt, triethanolamine salt, diethanolamine salt, alkylamine salt and the like. Among these, citric acid, lactic acid, potassium citrate salt, potassium lactate salt, and triethanolamine tartrate are preferable.

  In the treatment agent of this embodiment, the content ratio of the above-described smoothing agent, nonionic surfactant, ionic surfactant, and oxycarboxylic acid derivative is not particularly limited. When the total content of the smoothing agent, nonionic surfactant, ionic surfactant, and oxycarboxylic acid derivative described above is 100% by mass, the smoothing agent is 20 to 85% by mass, and the nonionic surfactant is 10 to 10%. It is preferable to contain 75% by mass, 0.1 to 15% by mass of an ionic surfactant, and 0.001 to 5% by mass of an oxycarboxylic acid derivative. By defining within this range, the effect of the present invention can be further improved.

(Second Embodiment)
A second embodiment in which the synthetic fiber according to the present invention is embodied will be described. The synthetic fiber of this embodiment is a synthetic fiber to which the treatment agent of the first embodiment is attached. The synthetic fiber is not particularly limited. For example, (1) Polyester fiber such as polyethylene terephthalate, polypropylene terephthalate, and polylactic acid ester, (2) Polyamide fiber such as nylon 6 and nylon 66, (3) Polyacryl, Examples thereof include polyacrylic fibers such as modacrylic, and (4) polyolefin fibers such as polyethylene and polypropylene.

  The ratio of attaching the treatment agent (not including the solvent) of the first embodiment to the synthetic fiber is not particularly limited, but the treatment agent of the first embodiment is a proportion of 0.1 to 3% by mass with respect to the synthetic fiber. It is preferable to make it adhere. Moreover, a well-known method can be employ | adopted suitably for the method of attaching the processing agent of 1st Embodiment. For example, a roller oiling method, a guide oiling method using a metering pump, an immersion oiling method, a spray oiling method and the like can be mentioned. As a form at the time of making the processing agent of 1st Embodiment adhere to a synthetic fiber, you may provide as an organic solvent solution, an aqueous liquid, etc., for example.

According to the synthetic fiber treatment agent and the synthetic fiber of the above embodiment, the following effects can be obtained.
In the said embodiment, it comprised as a processing agent for synthetic fibers containing a specific smoothing agent, a specific oxycarboxylic acid derivative, a nonionic surfactant, and an ionic surfactant. Therefore, good process passability is exhibited in the synthetic fiber spinning process. In particular, by reducing tar dirt around the godet roller and fluff of synthetic fiber yarns, good processability can be exhibited. In addition, good rubber adhesion can be exhibited in the post-processing step. Such an effect is particularly effective in a post-processing step in a tire cord application or the like.

In addition, you may change the said embodiment as follows.
In the treatment agent of the present embodiment, components that are used in ordinary treatment agents such as stabilizers, binders, antioxidants, ultraviolet absorbers and the like for maintaining the quality of the treatment agent within a range that does not impair the effects of the present invention. May be further blended.

  Hereinafter, in order to make the configuration and effects of the present invention more specific, examples and the like will be described. However, the present invention is not limited to these examples. In the following Examples and Comparative Examples, “part” means “part by mass” and “%” means “% by mass”.

Test category 1 (oxycarboxylic acid derivatives)
Table 1 shows the contents of the oxycarboxylic acid derivatives (OA-1 to OA-5 and rOA-1, rOA-2) used in the present Examples and Comparative Examples. In Table 1, the number of hydroxyl groups, the number of carboxyl groups, the number of carbon atoms, and the types of counter ions constituting the oxycarboxylic acid derivative are shown.

In Table 1,
OA-1: citric acid,
OA-2: lactic acid,
OA-3: potassium citrate salt,
OA-4: potassium lactate salt,
OA-5: triethanolamine salt of tartaric acid,
rOA-1: ricinoleic acid sodium salt,
rOA-2: hydroxystearic acid potassium salt,
Indicates.

Test category 2 (Preparation of synthetic fiber treatment agent)
-Preparation of treating agent for synthetic fiber (Example 1) 60 parts trimethylolpropane trioleate (L-1), 5 parts dioleylthiodipropionate (LS-1) as a smoothing agent, nonionic surfactant 10 parts of compound (N-1) esterified with 3 moles of oleic acid with 20 moles of EO added to 1 mole of hardened castor oil, 25 parts of EO added to 1 mole of hardened castor oil, crosslinked with adipic acid, and stearic acid 5 parts of the compound (rN-1) terminal-esterified with 1 mol, 5 parts of the compound (rN-2) added with 20 mol of EO to 1 mol of hardened castor oil, 10.9 parts of polyethylene glycol (molecular weight 600) dioleate (rN-4), 2 parts sodium alkyl sulfonate (I-1), oleyl phosphate (EO15) stearylamino as ionic surfactant A synthetic fiber treating agent of Example 1 was prepared by uniformly mixing 2 parts of an ether salt (I-2) and 0.1 part of citric acid (OA-1) as an oxycarboxylic acid derivative. Table 2 shows the ratio of each component when the total of the blending ratio of the smoothing agent, the oxycarboxylic acid derivative, the nonionic surfactant, and the ionic surfactant and the ratio of such components is 100%.

-Preparation of treatment agent for synthetic fiber (Example 2) It was prepared in the same manner as the treatment agent for synthetic fiber of Example 1. However, in addition to the raw materials shown in Table 2, 0.5 part of 1,3,5-tris (4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid as an antioxidant is added to 100 parts of the treating agent. The ratio was added.

-Preparation of synthetic fiber treatment agents (Examples 3-11 and Comparative Examples 1-4) Similar to the preparation of the synthetic fiber treatment agent of Example 1, the synthetic fibers of Examples 3-11 and Comparative Examples 1-4 A treating agent was prepared. Each raw material is shown in Table 2. The total of the proportion of oxycarboxylic acid and the proportion of its salt in the nonvolatile content of each treatment agent is shown in the * 1 column of Table 2.

In Table 2,
L-1: trimethylolpropane trioleate,
L-2: Glycerin trioleate,
L-3: Rapeseed white squeezed oil,
L-4: Trioctyl trimellitate,
L-5: Georail adipate,
LS-1: dioleylthiodipropionate,
LS-2: diisocetylthiodipropionate,
LS-3: diisostearyl thiodipropionate,
rL-1: Isostearyl oleate,
N-1: Compound obtained by esterifying 20 mol of EO to 1 mol of hardened castor oil with 3 mol of oleic acid,
N-2: Compound obtained by esterifying 40 mol of EO to 1 mol of hardened castor oil with 2 mol of oleic acid,
N-3: Compound obtained by esterifying 25 mol of EO to 1 mol of castor oil with 3 mol of lauric acid,
rN-1: Compound obtained by adding 25 mol of EO to 1 mol of hardened castor oil, cross-linked with adipic acid, and terminal-esterified with stearic acid (MW 5,000),
rN-2: 20 mol of EO added to 1 mol of hardened castor oil,
rN-3: 10 mol of EO added to 1 mol of hardened castor oil,
rN-4: polyethylene glycol (molecular weight 600) dioleate,
rN-5: polyoxyethylene (5 mol) sorbitan monooleate,
I-1: Sodium alkyl sulfonate
I-2: oleyl phosphate (EO15) stearyl amino ether salt,
I-3: Isocetyl phosphate (EO10) lauryl amino ether salt,
OA-1: citric acid,
OA-2: lactic acid,
OA-3: potassium citrate salt,
OA-4: potassium lactate salt,
OA-5: triethanolamine salt of tartaric acid,
rOA-1: ricinoleic acid sodium salt,
rOA-2: hydroxystearic acid potassium salt,
Indicates.

Test category 3 (Evaluation of treatment agents for synthetic fibers)
About the processing agent for synthetic fibers, process passability and rubber adhesiveness were evaluated. More specifically, the process passability was evaluated as fuzz and heat-resistant tar.

-Evaluation of fluff Each treatment agent prepared in Test Category 2 was diluted uniformly with ion-exchanged water or an organic solvent as necessary to obtain a 15% solution. A polyethylene terephthalate chip is dried by a conventional method, melt-spun using an extruder, and is applied to a running yarn after being discharged from a die and cooled and solidified. It was made to adhere by the roller oil supply method set so that it might become mass%. Thereafter, the yarn was converged with a guide and drawn through a drawing roll and a relaxation roll at 230 ° C. so that the total draw ratio was 5.3 times, and a 1670 dtex 288 filament drawn yarn was obtained as 10 kg-wheated cheese.

  In the spinning process, before winding the yarn as cheese, the number of fluffs per hour was measured with a fluff counting device (manufactured by Toray Engineering Co., Ltd.) and evaluated according to the following criteria. The results are shown in Table 2.

-Evaluation standard of fluff A: The number of fluff measured is zero.
A: The number of fluffs measured is less than 2 (however, 0 is not included).
X: The measured number of fluff is 2 or more and less than 10.
XX: The measured number of fluff is 10 or more.

-Evaluation of heat resistant tar The heat resistance of the treating agent was evaluated as follows as dirt (tar) of the godet roller after spinning for 48 hours in the spinning step. The results are shown in Table 2.

・ Evaluation criteria for heat-resistant tar: No dirt (tar) is observed.
○: Dirt (tar) is hardly recognized.
X: Dirt (tar) is slightly observed.
Xx: Dirt (tar) is recognized.

・ Evaluation of rubber adhesion Two synthetic fibers to which the synthetic fiber treating agent obtained in the spinning process is attached are twisted at a twist number of 40 twists / 10 cm and 40 twists / 10 cm, and a twisted cord It was. This twisted yarn cord was bonded to the first adhesive (epoxy compound (trade name Denacol EX-512, manufactured by Nagase ChemteX Corporation) / blocked isocyanate (trade name, Elastron BN-27, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) = 5/5 ( It was heat-treated after being immersed in the solid content ratio)). Furthermore, the second adhesive (resorcin (trade name resorcinol, manufactured by Kishida Chemical Co., Ltd.) / Formalin (trade name, formaldehyde solution (37%) manufactured by Kishida Chemical Co., Ltd.) / Latex (trade name, Nipol 2518FS manufactured by Nippon Zeon Co., Ltd.) = 1 .5 / 0.5 / 8 (solid content ratio RFL solution). Thereafter, heat treatment was performed to obtain a reinforcing cord treated with an adhesive. Based on the T test (A method) described in JIS-L1017 (chemical fiber tire cord test method), the adhesive strength of the reinforcing cord was measured and evaluated according to the following criteria. The results are shown in Table 2.

-Evaluation standard of rubber adhesion ◎: Adhesive strength is 16 kg or more.
○: Adhesive strength is 15 kg or more and less than 16 kg.
X: Adhesive strength is 14 kg or more and less than 15 kg.
XX: Adhesive strength is less than 14 kg.

  As is apparent from the results in Table 2, according to the present invention, tar dirt and fluff around the godet roller can be reduced in the synthetic fiber spinning process, and rubber adhesion in the post-processing process can be further improved. There is an effect that can be done.

Claims (7)

A treating agent for synthetic fibers comprising the following smoothing agent, the following oxycarboxylic acid derivative, a nonionic surfactant, and an ionic surfactant.
Smoothing agent: at least one ester compound selected from an ester compound of a polyhydric alcohol and a monovalent carboxylic acid, an ester compound of a monohydric alcohol and a polycarboxylic acid, and a monohydric alcohol and a sulfur element in the molecule Contains a sulfur-containing ester compound with a polyvalent carboxylic acid.
Oxycarboxylic acid derivative: At least one compound selected from oxycarboxylic acid and salts thereof.   2. The synthetic fiber according to claim 1, wherein the oxycarboxylic acid derivative is an oxycarboxylic acid having 2 to 8 carbon atoms having 1 to 2 hydroxyl groups and 1 to 3 carboxyl groups in the molecule, or a salt thereof. Processing agent.   The processing agent for synthetic fibers according to claim 1 or 2, wherein the total proportion of the oxycarboxylic acid and the salt thereof is 0.001 to 5% by mass in the nonvolatile content of the processing agent for synthetic fibers. .   The nonionic surfactant contains 1 to 100 moles of a compound having 1 to 100 moles of alkylene oxide added to 1 mole of hardened castor oil, and 1 to 2 moles of alkylene oxide per mole of castor oil. The compound according to any one of claims 1 to 3, comprising a compound obtained by esterifying a monovalent carboxylic acid at a ratio of 1 to 3 moles with respect to 1 mole of a compound selected from compounds added at a ratio of ~ 100 moles. Treatment agent for synthetic fibers.   The ionic surfactant contains at least one compound selected from an alkali metal sulfonate having a hydrocarbon group having 4 to 22 carbon atoms and an amine phosphate having a hydrocarbon group having 4 to 22 carbon atoms. Item 5. A treating agent for synthetic fibers according to any one of Items 1 to 4.   When the total content of the smoothing agent, the nonionic surfactant, the ionic surfactant, and the oxycarboxylic acid derivative is 100% by mass, the smoothing agent is 20 to 85% by mass, and the nonionic surfactant is used. 10 to 75% by mass of the agent, 0.1 to 15% by mass of the ionic surfactant, and 0.001 to 5% by mass of the oxycarboxylic acid derivative. The processing agent for synthetic fibers described in 1.   A synthetic fiber to which the synthetic fiber treating agent according to any one of claims 1 to 6 is attached.