JP6533002B1 - Treatment agent for synthetic fiber and method for producing synthetic fiber - Google Patents

Abstract

The present invention provides a synthetic fiber treating agent and synthetic fiber manufacturing method capable of reducing yarn sway occurring in a spinning step of applying a synthetic fiber treating agent by straight oil feeding. SOLUTION: The treating agent for synthetic fiber of the present invention comprises at least one ester compound selected from an ester compound having three or more ester bonds in the molecule and an ester compound having a sulfur element in the molecule as a smoothing agent. It is a processing agent for synthetic fibers used for straight refueling, and it is characterized by having a moisture of 0.1 to 5% by mass. Further, the method for producing a synthetic fiber of the present invention is characterized in that the synthetic fiber treating agent is directly supplied to the synthetic fiber in the spinning step. 【Selection chart】 None

Description

  The present invention relates to a synthetic fiber treating agent capable of effectively reducing yarn swaying in a synthetic fiber spinning step using a straight oiling facility, and a method of producing the synthetic fiber to which such a treating agent is attached.

  Generally, in the process of spinning synthetic fibers, from the viewpoint of reducing friction and preventing damage to the fibers such as thread breakage, a treatment for applying a treating agent for synthetic fibers to the surface of filament yarns of synthetic fibers is performed. is there. When the treatment agent for synthetic fiber is diluted in water (emulsion refueling), the form of the adhesion treatment is applied as it is without diluting or diluting the agent for synthetic fiber with a diluent such as low viscosity mineral oil. There is a case (straight refueling).

  Conventionally, the processing agent for synthetic fibers indicated by patent documents 1-4 is known. Patent Document 1 discloses a treating agent for synthetic fiber degassed by reduced pressure treatment. Patent Document 2 discloses a treatment agent for synthetic fibers having a defined viscosity, which contains a leveling agent, an emulsifying agent, and an antistatic agent. Patent Document 3 discloses a treating agent for synthetic fibers containing a mineral oil, a fatty acid ester, an alkylene oxide adduct of a higher alcohol, and a higher aliphatic unsaturated monocarboxylic acid. Patent Document 4 discloses a treating agent for synthetic fibers which contains an organozinc compound and which contains at least one of an ester compound, a polyether compound and a mineral oil.

Japanese Patent Application Laid-Open No. 11-158770 Unexamined-Japanese-Patent No. 6-57541 Japanese Patent Application Laid-Open No. 61-19871 JP, 2013-7141, A

However, these conventional processing agents for synthetic fibers, when used for straight refueling, have not been able to sufficiently cope with the reduction of yarn fluctuation in the spinning process.
The problem to be solved by the present invention is to provide a synthetic fiber treating agent and synthetic fiber manufacturing method capable of reducing yarn sway generated in a spinning process of applying a synthetic fiber treating agent by straight oil feeding. is there.

  As a result of research conducted to solve the above problems, the present inventors have found that a treating agent for synthetic fiber fed straight in a spinning process contains a predetermined ester compound as a smoothing agent and has a predetermined proportion of water. It was found to be suitable.

  That is, one aspect of the present invention includes at least one ester compound selected from an ester compound having three or more ester bonds in a molecule and an ester compound having a sulfur element in the molecule as a smoothing agent, and is used for straight refueling It is a processing agent for synthetic fibers, Comprising: The water content in the said processing agent for synthetic fibers is 0.1-5 mass%, The processing agent for synthetic fibers characterized by the above-mentioned is provided.

It is preferable that the treatment agent for synthetic fibers further contains a nonionic surfactant and an ionic surfactant.
When the ionic surfactant contains a secondary alkanesulfonic acid compound, and the total content of the leveling agent, the nonionic surfactant, and the ionic surfactant is 100% by mass, the secondary alkanesulfone It is preferable that the content rate of an acid compound is 0.01-10 mass%.

  The organic phosphoric acid ester compound includes the organic phosphoric acid ester compound, and the total content of the leveling agent, the nonionic surfactant, and the ionic surfactant is 100% by mass. The content ratio of is preferably 0.01 to 10% by mass.

The total content of the leveling agent, the nonionic surfactant, and the ionic surfactant is preferably 100 parts by mass, and the diluent is preferably contained in a ratio of 0.1 to 400 parts by mass.
It is preferable that the water content in the said process agent for synthetic fibers is 0.5-2.0 mass%.

  Another aspect of the present invention provides a method for producing a synthetic fiber, which is characterized in that the treatment agent for synthetic fiber is directly fed to the synthetic fiber in a spinning step.

  According to the present invention, it is possible to reduce the yarn fluctuation generated in the spinning process.

First Embodiment
First, a first embodiment in which the treatment agent for synthetic fiber according to the present invention (hereinafter referred to as a treatment agent) is embodied will be described. The treating agent of the present embodiment is a treating agent for synthetic fibers which contains a predetermined ester compound as a smoothing agent and is used for straight refueling, and the water content in the treating agent is 0.1 to 5% by mass. . Preferably, the surfactant further contains a nonionic surfactant and an ionic surfactant, and has a water content of 0.1 to 5% by mass. More preferably, the water content in the treatment agent is 0.5 to 2.0% by mass. Particularly preferably, the water content in the treatment agent is 0.7 to 1.5% by mass. According to such a configuration, the effect of the present invention, that is, the yarn fluctuation generated in the spinning process can be further reduced.

  The amount of water contained in the treatment agent for synthetic fiber may be adjusted by adding water to the treatment agent for synthetic fiber at the time of production or immediately before spinning, by a generally known dehydration method such as decompression or heating. The amount of water may be adjusted. Water to be added as moisture in the processing agent for synthetic fibers may be industrial water, tap water, etc., may be ion exchange resin, water purified by membrane, distillation, etc. It may be water brought in as an ingredient or the like. Among these, water having an electric conductivity of 300 μS / cm or less is preferable, water having 100 μS / cm or less is more preferable, and purified water having 10 μS / cm or less is more preferable. Alternatively, the hardness (as calcium carbonate) of water is preferably 100 mg / L or less, more preferably 10 mg / L or less, and still more preferably 5 mg / L or less. The water to be mixed may be one that has been degassed by a known method such as reduced pressure, or may be one that contains oxygen in the atmosphere, nitrogen, carbon dioxide, and the like. The pH is preferably around neutral, for example, in the range of 5.5 to 8.0. The water content in the synthetic fiber treatment agent can be calculated from the amount of water added and the water content in the raw material of the component of the synthetic fiber treatment agent. If the water content in the raw material is unknown, it may be determined from known analytical methods such as Karl-Fischer titration or gas chromatography.

  As the leveling agent to be used for the processing agent of the present embodiment, one containing at least one ester compound selected from ester compounds having three or more ester bonds in the molecule and ester compounds having sulfur element in the molecule is applied Ru. Such a configuration can reduce the effects of the present invention, that is, the yarn fluctuation generated in the spinning process. In addition, roller stain can be further reduced, and more uniform dyeing can be performed in the post-processing step. Examples of ester compounds having three or more ester bonds in the molecule include (1) trimethylolpropane trilaurate, trimethylolpropane trioleate, glycerin trioleate, pentaerythritol tetraoctanoate, trimethylolpropane-cocotic fatty acid ester Etc., ester compounds of polyvalent alcohol and monohydric carboxylic acid, (2) trioctyl trimellitate, ester compounds of polyvalent carboxylic acid such as triethyl citrate and monohydric alcohol, (3) castor oil, palm oil, Natural fats and oils such as rapeseed oil and the like may be mentioned. Among these ester compounds, trimethylolpropane-coconut fatty acid ester and palm oil are preferable. The ester compound having a sulfur element in the molecule is, for example, an ester of a dihydric carboxylic acid such as (4) diisocetyl thiodipropionate, diisostearyl thiodipropionate, dioleyl thiodipropionate and a monohydric alcohol. Examples thereof include compounds, (5) lauryl mercapto propionate, octyl mercapto propionate, and ester compounds of monohydric carboxylic acids such as oleyl lauryl thiopropionate and monohydric alcohols. Among these ester compounds, diisocetyl thiodipropionate and diisostearyl thiodipropionate are preferable. One of these components may be used alone, or two or more thereof may be used in combination.

  There are no particular limitations on the specific examples of the nonionic surfactant to be used in the treatment agent of the present embodiment, and for example, (1) at least one selected from organic acids, organic alcohols, organic amines, and organic amides having 2 to 2 carbon atoms Compounds to which 4 alkylene oxides are added, more specifically, for example, polyoxyethylene laurate, polyoxyethylene oleate, polyoxyethylene laurate methyl ether, polyoxyethylene octyl ether, polyoxypropylene lauryl ether Methyl ether, polyoxybutylene oleyl ether, polyoxyethylene polyoxypropylene lauryl ether, polyoxyethylene polyoxypropylene nonylphenyl ether, polyoxyethylene lauryl amino ether, polyoxyethylene Ether type nonionic surfactants such as len lauro amide ether, (2) Polyhydric alcohol partial ester type nonionic surfactants such as sorbitan monooleate, sorbitan trioleate, glycerin monolaurate, (3) polyethylene glycol dioleate , Polyoxyethylene sorbitan monooleate, polyoxybutylene sorbitan trioleate, polyoxyethylene glycerine trioleate, polyoxypropylene glycerin castor oil, polyoxyethylene hydrogenated castor oil, polyoxyethylene propylene hydrogenated castor oil trioleate, polyoxyethylene hydrogenated castor oil trilaurate, At least one compound selected from ethylene oxide (hereinafter referred to as EO) adduct of castor oil and EO adduct of hardened castor oil, and monocarboxylic acid Polyoxyalkylene polyhydric alcohol fatty acid ester type nonionic surfactant of an ether ester compound or the like by condensing fine dicarboxylic acid, (4) alkyl amide type nonionic surfactants such as diethanol monolauroyl amide. One of these components may be used alone, or two or more thereof may be used in combination.

  As the ionic surfactant to be provided to the treatment agent of the present embodiment, an anionic surfactant is preferable. There is no restriction | limiting in particular as a specific example of the anionic surfactant used for the processing agent of this embodiment, For example, carboxylic acid soap type ion interfaces, such as (1) octanoic acid potassium salt, oleic acid potassium salt, alkenyl succinic acid potassium salt etc. Activators, (2) Secondary alkanesulfonic acid sodium salts, sodium dodecylbenzenesulfonic acid salts, sulfonic acid ester type ionic surfactants such as dioctyl sulfosuccinate sodium salts, (3) polyoxyethylene lauryl sulfate sodium salts, hexadecyl Examples include sulfuric acid ester type ionic surfactants such as potassium sulfate, tallow sulfurized oil, castor oil sulfurized oil and the like. Among the anionic surfactants, secondary alkanesulfonic acid compounds and organic phosphoric acid compounds are preferably contained. As the secondary alkanesulfonic acid compound, in particular, a secondary alkanesulfonic acid salt represented by the following chemical formula 1 is more preferable, and its sodium salt is more preferable. As the organic phosphoric acid compound, in particular, oleyl phosphate EO5 (the addition mole number of EO is shown. The same applies to the following.) Stearyl aminoether salt and isocetyl phosphate EO10 lauryl aminoether salt are more preferable. One of these components may be used alone, or two or more thereof may be used in combination.

(In chemical formula 1,
a and b are each an integer of 0 or more, and a + b = 5 to 17,
M: alkali metal, ammonium group or organic amine group. )
The treatment agent of the present embodiment may further contain a diluent. Specific examples of the diluent used for the treatment agent of the present embodiment include (1) aromatic hydrocarbons such as xylene, toluene, benzene and phenol, (2) ketones such as acetone and methyl ethyl ketone, and (3) methanol, ethanol, Alcohols such as propanol, 2-ethylhexanol, dodecanol, (4) hexane, heptane, octane, decane, undecane, dodecane, dodecane, tridecane, tridecane, tetradecane, straight chain saturated hydrocarbons such as octadecane, (5) isohexane, isoheptane, Branched hydrocarbons such as isooctane, isodecane, isoundecane, isododecane, isotridecane, isotetradecane, isooctadecane, isoeicosane, (6) cyclic saturated hydrocarbons such as cyclohexane, cyclooctane, cyclododecane, cyclooctadecane, cycloicosane (7) Low molecular weight ester compounds such as methyl octatate, ethyl laurate, propyl palmitate, isobutyl stearate, normal butyl stearate, etc., (8) paraffin hydrocarbons, naphthene hydrocarbons, olefin hydrocarbons, aromatics Solvents other than water, such as mineral oil chosen from at least 1 sort among hydrocarbon, are mentioned. One of these components may be used alone, or two or more thereof may be used in combination. The diluent is preferably volatilized during the spinning process, and more preferably approximately 70% by mass or more before and after spinning. The diluent may be added not only at the time of production of the synthetic fiber treatment agent but also immediately before spinning. Among them, mineral oil having a redwood viscosity of 100 seconds or less at 40 ° C., linear saturated hydrocarbon (C10-C15), isobutyl stearate and normal butyl stearate are preferable.

  When the processing agent of the present embodiment further includes a nonionic surfactant and an ionic surfactant in addition to the above-described smoothing agent, the content ratio of each component is not particularly limited. When the treating agent of the present embodiment contains a secondary alkanesulfonic acid compound as an ionic surfactant, the secondary agent is considered to have a total content of 100% by mass of the smoothing agent, the nonionic surfactant, and the ionic surfactant. It is preferable to make the content rate of an alkanesulfonic acid compound into 0.01 to 10 mass%. According to such a configuration, the effect of the present invention, that is, the yarn fluctuation generated in the spinning process can be further reduced. In addition, more uniform dyeing can be performed in the post-processing step.

  When the treating agent of the present embodiment contains an organic phosphoric acid ester compound as an ionic surfactant, the organic phosphoric acid is contained, assuming that the total content of the smoothing agent, the nonionic surfactant, and the ionic surfactant is 100% by mass. It is preferable to make the content rate of an ester compound into 0.01 to 10 mass%. According to such a configuration, the effect of the present invention, that is, the yarn fluctuation generated in the spinning process can be further reduced. In addition, roller stain can be further reduced, and more uniform dyeing can be performed in the post-processing step.

  When the treatment agent of the present embodiment contains a diluent, if the total content of the smoothing agent, nonionic surfactant and ionic surfactant is 100 parts by mass, the amount of the diluent is 0.1 to 400 parts by mass. Those containing in proportion are preferred. By defining the compounding amount range, the effect of the present invention, that is, the yarn fluctuation generated in the spinning process can be reduced. In addition, roller stain can be further reduced, and more uniform dyeing can be performed in the post-processing step.

Second Embodiment
Next, a second embodiment of the method for producing synthetic fibers according to the present invention will be described. The method for producing the synthetic fiber of the present embodiment is a production method including the step of causing the treatment agent of the first embodiment to adhere to the synthetic fiber by straight oil feeding in the spinning step. Specific examples of the synthetic fiber to be produced are not particularly limited. For example, (1) polyester fibers such as polyethylene terephthalate, polypropylene terephthalate and polylactic acid ester, (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. The fineness of the synthetic fiber to be produced is not particularly limited, but is preferably 150 dtex or more, more preferably 500 dtex or more, and particularly preferably 1000 dtex or more. The strength of the synthetic fiber to be produced is not particularly limited, but is preferably 5.0 cN / dtex or more, more preferably 6.0 cN / dtex or more, and particularly preferably 7.0 cN / dtex or more.

  There is no particular limitation on the ratio of adhering the treating agent of the first embodiment to the synthetic fiber, but 0.1 to 3% by mass (not including diluent and water) of the treating agent of the first embodiment with respect to the synthetic fiber It is preferable to attach it so that it becomes a ratio. With this configuration, the effects of the present invention are further improved. Further, the method for adhering the treatment agent of the first embodiment is not particularly limited, and for example, a known method such as a roller oiling method, a guide oiling method using a measuring pump, an immersion oiling method, a spray oiling method There is no particular limitation as long as the step of attaching is also a spinning step, for example, in the drawing or heat treatment step, the effect of the invention is more expected by use in a production facility or step having a step of passing a roller at 150 ° C. or higher. it can.

According to the treatment agent of the above embodiment and the method for producing the same, the following effects can be obtained.
In the treatment agent of the above embodiment, in the treatment agent used in straight refueling, a predetermined ester compound is contained as a smoothing agent, and the amount of water contained in the treatment agent is specified. Therefore, it is possible to effectively reduce the yarn swing generated by the godet roller in the process of spinning synthetic fibers. In addition, tar stains generated around the godet roller can be effectively reduced, and uniform dyeing is possible in the post-processing step. The synthetic fiber of this embodiment obtained thereby can exhibit excellent process passability. Further, in the case where a nonionic surfactant and an ionic surfactant are further blended in the treatment agent, the above effect is further improved.

The above embodiment may be modified as follows.
-The treatment agent of the present embodiment is usually a stabilizer, an antistatic agent for maintaining the quality of the treatment agent, a binder, an antioxidant, an ultraviolet absorber, etc., as long as the effects of the present invention are not impaired. You may further mix | blend the component used for the processing agent of a synthetic fiber.

  Hereinafter, examples and the like will be described in order to make the configuration and effects of the present invention more specifically, but the present invention is not limited to these examples. In the following examples and comparative examples, "part" means "mass part" and "%" means mass%.

Test division 1 (adjustment of processing agent for synthetic fiber)
Preparation of a treating agent for synthetic fiber (Example 1) 50 parts of trimethylolpropane-cocoal fatty acid ester (L-1), 5 parts of diisostearyl thiodipropionate (LS-1) as a smoothing agent, non-ionic Compound (N-3) obtained by esterifying 10 parts of EO added with 10 moles of EO (N-1) per 1 mol of hardened castor oil as surfactant and 20 moles added of EO with 1 mol of hardened castor oil with 3 moles of oleic acid Part, 25 parts of EO added per 1 mol of hardened castor oil is crosslinked with adipic acid, and 5 parts of a compound (MW 5000) (N-6) end-esterified with stearic acid, polyethylene glycol (molecular weight 600) dioleate (N-7) Sodium hydroxide (a + b = 8 to 11) (S-) of the structure of the above-mentioned chemical formula 1 as an ionic surfactant 1) 5 parts of oleyl phosphate (EO5) stearylaminoether salt (P-1) were mixed uniformly to obtain a mixture.

  Furthermore, when the mixture is 100 parts by mass, 1.00 parts by mass of ion exchange water, and then 10 parts by mass of linear saturated hydrocarbon (C12-15) (M-1) as a diluent are added and uniformly mixed, The treatment agent for synthetic fiber of Example 1 was prepared such that the water content in the treatment agent was 0.9%. The ion-exchanged water used had an electric conductivity of 0.2 μS / cm and a hardness of 0 mg / L.

Preparation of Treating Agent for Synthetic Fiber (Example 2) The agent was prepared in the same manner as the treating agent for synthetic fiber of Example 1. However, in addition to the raw materials shown in Table 1, 0, 1 based on 100 parts of the processing agent before addition of the diluent, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane as an antioxidant. It was added in the proportion of 8 parts.

Preparation of processing agents for synthetic fibers (Examples 3 to 8 and Comparative Examples 1 to 3) For the synthetic fibers of Examples 3 to 8 and Comparative Examples 1 to 3 in the same manner as the preparation of the synthetic fiber processing agent of Example 1 The treatment agents were prepared and the results are shown in Table 1. In addition, in Table 1, while showing the kind of each component in the processing agent for synthetic fibers, the compounding ratio (%) at the time of setting components other than a diluent and water to 100% is shown. In addition, the addition ratio (parts) of the diluent and water when the components other than the diluent and water in the processing agent for synthetic fiber are 100 parts is shown. It also shows the water content (%) in the treatment agent.

In Table 1,
L-1: trimethylolpropane-coconut fatty acid ester,
L-2: Palm oil,
LS-1: diisostearylthiodipropionate,
LS-2: diisocetyl thiodipropionate,
rL-1: isostearyl oleate,
N-1: 10 mol of EO added to 1 mol of hardened castor oil,
N-2: 20 mol of EO added to 1 mol of hardened castor oil,
N-3: a compound obtained by esterifying 20 mol of EO added to 1 mol of hardened castor oil with 3 mol of oleic acid,
N-4: A compound obtained by esterifying 40 moles of EO added to 1 mole of hydrogenated castor oil with 2 moles of oleic acid,
N-5: a compound obtained by esterifying 25 moles of EO added to 1 mole of castor oil with 3 moles of lauric acid,
N-6: a compound obtained by adding 25 moles of EO to 1 mole of hardened castor oil is crosslinked with adipic acid and terminated with stearic acid (MW 5000)
N-7: polyethylene glycol (molecular weight 600) dioleate,
N-8: sorbitan monooleart,
S-1: Sodium secondary alkane sulfonate (a + b = 8 to 11 in the above [Chemical formula 1]),
S-2: secondary alkanesulfonic acid sodium (a + b = 1 to 14 in the above [Chemical formula 1]),
rS-1: sodium dioctyl sulfosuccinate,
P-1: oleyl phosphate (EO5) stearyl amino ether salt,
P-2: Isocetyl phosphate (EO 10) lauryl amino ether salt,
M-1: linear saturated hydrocarbon (C12-15),
M-2: mineral oil (red wood viscosity at 40 ° C. for 80 seconds),
M-3: isobutyl stearate,
M-4: Normal butyl stearate,
Indicates

Test division 2 (evaluation of synthetic fiber treatment agent)
· Evaluation of heat-resistant tar After drying the chips of polyethylene terephthalate according to a conventional method, melt spinning is performed using an extruder, and the processing agent is added to the running yarn after discharging from the die and cooling and solidifying. It was made to adhere by the used guide oiling method. It was refueled so that the adhesion amount of the synthetic fiber treatment agent became 0.6 mass% (diluent, water not included). Then, it was converged with a guide and stretched through a stretching roll at 245 ° C. and a relaxation roll so as to have a total draw ratio of 5.5 times to obtain a stretched yarn of 1100 dtex 192 filaments as a 10 kg cut cheese. The heat resistance (tar) was evaluated as described below as soiling (tar) of a godet roller (GR) after spinning for 48 hours. The results are shown in Table 1.

· Evaluation criteria for GR stain ◎: Almost no stain (tar) is observed.
○: Slight (tar) is slightly recognized.
X: Dirt (tar) is recognized.

Evaluation of yarn sway In the spinning step, yarn sway on a godet roller was observed and evaluated according to the following criteria. The results are shown in Table 1.

-Evaluation criteria for yarn shake :: No yarn shake on the roller is recognized.
○: Slight vibration on the roller is observed.
X: Yarn on the roller is observed.

-Evaluation of dyeability The 360 fibers obtained in the above spinning process are used as warp yarns, and polyester yarns of 560 dtex-96 filaments are used as weft yarns, using a sheet belt loom with a weft density of 21 yarns / inch and a width of 51 mm. Immerse in the following dye solution (a solution in which 3.4 g of Dinix Red S-4G, 3.3 g of Dinix Yellow S-6G, and 3.3 g of Dinix S-2G were added to 1 L of water) without refining and continuous Then, staining was performed by performing a treatment for 2 minutes in a coloring bath at 220 ° C. The dyeability was evaluated according to the following criteria from the number of staining defects per 2000 m of the seat belt at this time. The results are shown in Table 1.

Evaluation criteria for dyeability ◎: number of staining defects 0 to 3.
○: number of staining defects 4 to 10.
X: The number of staining defects is 11 or more.

  As is clear from the results in Table 1, the synthetic fiber treatment agent of each example was good in all of the evaluation of yarn sway, roller stain, and dyeability. According to the present invention, in the process of spinning synthetic fibers, the effect of reducing yarn sway on the godet roller and dirt of the godet roller can be reduced, and synthetic fibers with good dyeability can be obtained.

Claims (7)

  A treating agent for synthetic fibers used for straight refueling, comprising at least one ester compound selected from ester compounds having three or more ester bonds in the molecule and ester compounds having sulfur element in the molecule as a leveling agent. A processing agent for synthetic fiber, wherein the water content in the processing agent for synthetic fiber is 0.1 to 5% by mass.   The processing agent for synthetic fibers according to claim 1, further comprising a nonionic surfactant and an ionic surfactant. The ionic surfactant comprises a secondary alkanesulfonic acid compound,
The total content of the leveling agent, the nonionic surfactant, and the ionic surfactant is 100% by mass, and the content ratio of the secondary alkanesulfonic acid compound is 0.01 to 10% by mass. The processing agent for synthetic fibers as described in item 2. The ionic surfactant comprises an organic phosphoric acid ester compound,
The total content ratio of the leveling agent, the nonionic surfactant, and the ionic surfactant is 100% by mass, and the content ratio of the organic phosphoric acid ester compound is 0.01 to 10% by mass. The processing agent for synthetic fibers as described in 2 or 3.   The total content of the leveling agent, the nonionic surfactant, and the ionic surfactant is 100 parts by mass, and the diluent is contained in a ratio of 0.1 to 400 parts by mass. The processing agent for synthetic fibers according to any one of the preceding claims.   The water content in the said process agent for synthetic fibers is 0.5-2.0 mass%, The process agent for synthetic fibers as described in any one of Claims 1-5.   A method for producing a synthetic fiber, comprising straight feeding the synthetic fiber according to any one of claims 1 to 6 in the spinning step.