JPH0418118A - Polyamide fiber having excellent transparency and clear dyeability and production thereof - Google Patents

Abstract

PURPOSE:To provide the subject polyamide fiber containing a specific diamide compound and a salt compound at specific ratios, having excellent transparency, clear dyeability and feeling and suitable as a material for clothes. CONSTITUTION:The objective polyamide fiber contains (A) 0.01-1.0wt.% (based on the polyamide) of a diamide compound expressed by formula I or II (R1 and R4 are 10-20C alkyl; R2 and R3 are H, methyl or ethyl; n is 1-10) and (B) 1-30wt.% (based on the component A) of one or more kinds of salt compounds selected from sulfuric acid ester salt, sulfonic acid salt and polycarboxylic acid salt. The fiber has an elliptic cross-section having a (major diameter)/(minor diameter) ratio of 2-5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention has excellent transparency, vivid dye color development, and texture.
The present invention relates to a polyamide fiber suitable as a material for clothing, and a method for producing the same.

[Conventional technology] In recent years, there has been a strong demand in the clothing filament yarn market for more natural and fashionable fabrics, especially for women's underwear, stockings, casual wear, etc. There is a growing demand for bright colors.

In order to impart vivid coloring properties to polyamide fibers for clothing, it goes without saying that the dye itself should be selected to produce vivid colors, but it is also possible to improve the polyamide substrate itself and improve the cross-sectional shape of the fibers. A method has been proposed.

As a method for improving the polyamide substrate itself, a method of blending a diamide compound is disclosed in JP-A-58-1321.
This is proposed in Publication No. 37, etc.

This publication specifically discloses a method of mixing a powdered diamide compound with a polyamide chip, and a method of adding the diamide compound during polyamide polymerization.

When blending a diamide compound into a polymer at a relatively low concentration, it is possible to mix it uniformly to a certain extent by mixing it with polyamide chips or adding it during polymerization, which results in a corresponding improvement in transparency and vivid coloring. effect can be obtained.

[Problems to be Solved by the Invention] However, diamide compounds generally do not have very good affinity with polyamides, so it is difficult to sufficiently improve mixing uniformity with conventional methods, which causes various troubles during spinning. However, it is also difficult to sufficiently enhance the effect of adding a diamide compound. Moreover, it is difficult to manufacture the master polymer, and further improvements have been desired for industrial production.

That is, since it contains a diamide compound that is not sufficiently compatible with polyamide, it is difficult to suppress yarn breakage during spinning to a low level, and there are also problems in that the area around the spinneret hole during melt spinning is easily contaminated.

In addition, it is difficult to sufficiently increase the uniformity of the diamide compound mixture in the melt-spun fibers, so it is difficult to sufficiently increase the transparency, vivid color development, strength, etc. of the resulting fibers. It's easy to become. In particular, it is difficult to adequately meet the recent market needs, where demands for strength and transparency have become even higher.

Furthermore, since diamide compounds have insufficient compatibility with polyamides, it is difficult to use a master polymer method suitable for industrial production.

Therefore, the present invention solves these problems, and provides a polyamide fiber with excellent bright color development that can improve yarn breakage during melt spinning and further improve performance, and a suitable method for producing the same. .

Another object of the present invention is to provide a polyamide fiber that can produce fibers with excellent quality and good spinnability by a master polymer method, and a method for producing the same.

Furthermore, in order to meet recent market needs, we provide polyamide fibers that are strong and transparent, and can be made into products with a smooth, natural texture.

[Means for Solving the Problems] In order to achieve these objects, claim 1 of the present invention provides 0.01 to 1.0% by weight of the following general formula (
A diamide compound represented by 1) or (2), 1 to 30% by weight of 1 selected from the group of sulfuric acid ester salts, sulfonic acid salts, and polycarboxylic acid salts based on the diamide compound.
A polyamide containing at least one salt compound and having an elliptical fiber cross-sectional shape with a ratio of major axis a to minor axis (a/b) of 2 to 5 and excellent transparency and vivid dye color development. Consists of fibers.

N C(CH2)n CN −(1)/
, \R2R4 0R2R30 111111...(2) R, -C-N -(CH2) n-N-C-R4 (wherein R1 and R4 are an alkyl group having 10 to 2 carbon atoms,
R2 and R3 are a hydrogen atom, a methyl group or an ethyl group, and n is an integer of 1 to 10. ) Furthermore, the manufacturing method of claim 2 includes adding the diamide compound and one or more salt compounds selected from the group of sulfuric acid ester salts, sulfonic acid salts, and polycarboxylic acid salts in a step before polymerization. By this, the concentration of the diamide compound is 0.0.
1 to 1% by weight of a polyamide composition, and melt-spinning the polyamide composition to produce the polyamide fiber according to claim 1. Production of a polyamide fiber with excellent transparency and vivid dye color development. Consists of methods.

The polyamide used in the present invention may be a linear polyamide obtained by condensation polymerization of a fiber-forming diamine and dicarboxylic acid or ring-opening condensation polymerization of a cyclic lactam. For example, polyhexamethylene adipamide (nylon 66)
, polycapramide (nylon 6), etc. These polyamides may be copolymerized with a copolymerizable monomer to the extent that the fiber properties are not significantly impaired. For example, it may be a polyamide obtained by copolymerizing hexamethylene diammonium adipate with 10% by weight or less of ε-caprolactam.

These polyamides may contain additives that dissolve in the polyamide and do not impair transparency, such as heat-resistant agents, ultraviolet absorbers, etc., or foreign substances that scatter light, such as matting agents, etc. It is required that the inorganic pigment and the organic substance not to be dissolved in the polyamide are substantially not contained. Since these foreign substances cause a significant decrease in the transparency of the fibers, it is preferable to suppress them to an extent that does not halve the improving effect of the diamide compound at most.

Since the polyamide fiber according to the present invention substantially excludes foreign substances and adds the diamide compound, it is stronger than conventional polyamide fibers and can easily provide sufficient durability even for thin fabrics. More preferably, the degree of polymerization is controlled to a high degree.

Generally, the degree of polymerization of the polyamide of the present invention can be used as long as fiber formation is possible. For example, the relative viscosity of 98% sulfuric acid may be within the range of 2.7 to 3.5. If the degree of polymerization is at this level, the strength of the filament yarn for clothing can be set at a desired level, and the polyamide fiber of the present invention can be used. Performance can be demonstrated effectively. Note that if the degree of polymerization becomes too high, the melting temperature will become too high and the melt spinnability will deteriorate, which is not preferred from a practical standpoint.

It is necessary to use a diamide compound represented by the above formula (1) or (2) as a compound that enhances the transparency, vivid color development, and strength of polyamide fibers. With diamide compounds other than these, it is difficult to obtain the high definition color development that is the objective of the present invention.

The diamide compound represented by the general formula (]) or (2) can be prepared by reacting a dicarboxylic acid with an alkyl monoamine or by reacting a monocarboxylic acid with an alkylene diamine.

Typical diamines include methylene diamine, ethylene diamine, propylene diamine, and butylene diamine, including alkylene diamines having 1 to 10 carbon atoms.

Alkyl monoamines include primary amines having an alkyl group having 10 to 20 carbon atoms, such as octadecylamine, methyloctadecylamine, ethyloctadecylamine, etc., and secondary amines in which these are further substituted with methyl or ethyl groups. It will be done.

Further, typical dicarboxylic acids include succinic acid, adipic acid, and sebacic acid, including dicarboxylic acids having 2 to 12 carbon atoms. Monocarboxylic acids have 11 to 21 carbon atoms, such as lauric acid, palmitic acid, and stearic acid.
of alkyl monocarboxylic acids.

The blending amount of the diamide compound needs to be 0.01 to 1.0% by weight, more preferably 0.05 to 1.0% by weight, based on the polyamide fiber. If the amount is too small, it will not be possible to obtain sufficient high-visibility coloring, which is the objective of the present invention.On the other hand, if the amount is too large, the coloring of the fibers due to the diamide compound will become noticeable, and furthermore, the fiber properties will deteriorate due to bleed-out etc. occurs, so it is not suitable for practical use.

In the present invention, it is necessary to blend one or more salt compounds selected from the group of sulfated ester salts, sulfonate salts, and polycarboxylic acid salts together with the diamide compound into the polyamide.

Examples of this salt compound include the following compounds.

The sulfate ester salt is represented by the general formula R(OS 03 M) n. Here, R is a hydrocarbon residue such as an alkyl group, a cycloalkyl group, an allyl group, an aralkyl group,
These hydrocarbon residues include alkyl groups, halogens, hydroxyl groups,
Also included are those having substituents such as amino groups, sulfone groups, and carboxylic acid esters. Further, a portion of these main chains may contain oxygen, sulfur, nitrogen, etc., such as amide bonds, ether bonds, thioether bonds, ester bonds, urethane bonds, and sulfamide bonds. M is a potassium, sodium or ammonium group, and a portion thereof may be hydrogen. n is an integer of 1 or more. Generally, examples include higher alcohol sulfate ester salts, aliphatic amine and aliphatic amide sulfate ester salts, polyethylene glycol ether sulfate ester salts, olefin sulfate ester salts, fatty oil sulfate ester salts, higher fatty acid ester sulfate ester salts, etc. .

Sulfonate salts have the general formula R' (s03M)m. Here, R' is a hydrocarbon residue such as an alkyl group, a cycloalkyl group, or an aralkyl group having at least two aromatic nuclei, and these hydrocarbon residues include an alkyl group, a halogen, a hydroxyl group, an amino group, Also included are those having substituents such as carboxylic acid groups and sulfuric acid carboxylic acid esters. Further, a part of these main chains may contain oxygen, sulfur, nitrogen, etc., such as amide bonds, ether bonds, thioether bonds, ester bonds, urethane bonds, and sulfamide bonds. M is a potassium, sodium or ammonium group, and a portion thereof may be hydrogen.

m is an integer of 1 or more. Generally, aliphatic ester sulfonates, aliphatic amide sulfonates, ether bond-containing sulfonates, alkylnaphthalene sulfonates, naphthalene formaldehyde condensate sulfonates, and the like can be mentioned.

Polycarboxylic acid salts are represented by the general formula R' (COOM)p. R' is a hydrocarbon residue such as an alkyl group, a cycloalkyl group, an allyl group, or an aralkyl group;
It also includes those having substituents such as halogen, hydroxyl group, amino group, sulfone group, and carboxylic acid ester. Also,
A portion of these main chains may contain oxygen, sulfur, nitrogen, etc., such as amide bonds, ether bonds, thioether bonds, ester bonds, urethane bonds, and sulfamide bonds.

M is a potassium, sodium or ammonium group, and a portion thereof may be hydrogen. p is an integer of 2 or more, preferably 5 to 500. Most commonly, polyacrylic acid, polymethacrylic acid, partially saponified polyacrylic esters, partially saponified polymethacrylic esters, and combinations of acrylic acid, methacrylic acid or maleic acid with other vinyl compounds, such as vinyl acetate. Examples include, but are not limited to, sodium or potassium salts of polycarboxylic acids such as polymerized polymers, and sodium alginate.

These salt compounds are added at the same time as the diamide compound, but the amount thereof needs to be 1 to 30% by weight based on the diamide compound. If this amount is too small,
It is difficult to obtain the desired effects of improving performance and improving yarn breakage during melt spinning, and it is also difficult to produce a master polymer.

On the other hand, if the amount is too high, bleed-out tends to occur, and the transparency of the resulting polyamide fibers is impaired, making it difficult to obtain highly vivid color development.

The above-mentioned diamide compound and salt compound may be added in a step before polymerization of polyamide, and in particular, the diamide compound and salt compound may be added in high concentration to the polymerization raw material in a step before polymerization to form a diamide compound. A master polymer in which a master polymer having a content of 2 to 15% by weight is produced, and this master polymer is mixed with an unmodified polyamide and then melt-spun to produce a polyamide fiber containing a diamide compound and a salt compound at a predetermined concentration. law is preferred.

The base polymer used as the master polymer is preferably a polyamide obtained by ring-opening condensation polymerization of a cyclic amide, such as polycapramide. Since diamide compounds are generally in the form of powder, it is not easy to uniformly disperse them in polyamide raw materials, and it is particularly difficult to disperse them in polyamide raw materials (nylon salts) consisting of diamines and dicarboxylic acids.

However, polyamides made from cyclic amides are particularly suitable for master polymers that need to be blended at high concentrations because they can be relatively uniformly dispersed in aqueous solutions or melts of cyclic monomers such as ε-caprolactam. It is.

The amount of diamide compound added to the master polymer is 2 to 1
5% by weight is suitable, preferably 5-10% by weight. If it exceeds 15% by weight, separation and aggregation of the diamide compound will occur during polymerization of the master polymer, making it difficult to discharge and pelletize. If the amount is less than 2% by weight, the original effects of the master polymer method cannot be exhibited.

When adding diamide compounds and salt compounds to lactam, it is best to thoroughly knead them with a small amount of lactam aqueous solution to form a paste, and then add and mix with the lactam aqueous solution that is the raw material for the master polymer. preferable.

In this way, the method of adding too much before polymerization allows the diamide compound to be more easily dispersed uniformly in the unmodified polyamide than the method of sprinkling the diamide compound in a powder state on polyamide pellets and melt-spinning it, so that the desired performance of the present invention can be achieved. It is effective for improving thread breakage during spinning and melt spinning.

Nylon 6 fibers can also be produced by adding diamide compounds and salt compounds in the same amount as the final fiber during the polyamide polymerization stage, but it is difficult to produce nylon 66 fibers because uniform dispersion is difficult. It is. On the other hand, the master polymer method makes it possible to produce nylon 66 in which diamide compounds are uniformly dispersed, making it possible to produce nylon 66 fibers with vivid color development. Also,
The master polymer method also has the advantage of being easily adaptable to small quantities of products.

Polymerization of a master polymer containing a diamide compound and a salt compound may be carried out in the same manner as ordinary lactam polymerization. That is, a lactam aqueous solution or melt may be heated to carry out ring-opening condensation polymerization, and an alkali, acid, or other catalyst may be used.

Further, when producing a master polymer, the diamide compound and the salt compound must be added at or before polymerization of polycapramide. On the other hand, in the method of adding and mixing a powdered diamide compound at a high concentration to unmodified polyamide pellets after polymerization, the mixture is made into master pellets using a melt molding machine such as an extruder.
It is difficult to disperse diamide compounds sufficiently uniformly,
It becomes difficult to obtain the desired highly transparent polyamide fiber.

The obtained master polymer pellets are mixed with unmodified polyamide in an amount such that the concentration in the polyamide fibers becomes a predetermined amount. Fibers may be obtained by melt spinning using a conventional melt spinning machine and a conventional method.

In order to make the fiber cross-sectional shape an elliptical shape with a ratio of major axis a to minor axis (a/b) of 2 to 5, the shape of the mouthpiece discharge hole may be slit-like, and its width/length The ratio varies depending on the melting state of the polymer and the spinning conditions, but is generally between 5 and 20.
It is sufficient to use degree.

If the cross-sectional shape of the fiber is so flat (ribbon-like) that the ratio (a/b) of major axis/breadth axis exceeds 5, melt spinnability and winding performance will deteriorate, and furthermore, it will be difficult to unwind from a wound package. Due to the unraveling and twisting that occurs during this process, light reflection becomes uneven, which tends to cause unevenness in the appearance of the fabric, making it difficult to obtain excellent fabric products.

In addition, if the ratio (a/b) of the major axis/minor axis is less than 2, the effect of the elliptical shape is difficult to exhibit, and the transparency and
It is difficult to improve bright color development, texture, etc.

The following conditions may be used for melt spinning.

In the modified polyamide containing a diamide compound and a salt compound used in the present invention, the diamide compound in the polymer tends to seep out around the discharge hole during melt spinning, so there is a strong tendency to contaminate the die hole and form carbide. This can easily lead to problems such as thread shaking and thread breakage. Therefore, it is preferable to seal the area around the mouth hole with an inert gas such as nitrogen or steam to prevent deterioration such as carbonization. This tendency to contaminate the nozzle discharge hole also depends on the state of dispersion and dissolution of the diamide compound in the polyamide.In the powder blending method, where uniform dispersion is difficult, the contamination is noticeable even when sealed with an inert gas, and thread breakage occurs frequently. It's easy.

Next, the yarn that has been melt-spun and cooled and solidified is applied with a spinning oil agent in order to improve its passability through the process, but it is preferable to strictly control the variation in water applied at the same time as the oil agent. If there is a large variation in the amount of water applied, there will be a difference in the crystallization of the polyamide fiber when it absorbs water, which will change the light transmittance and become a cause of variation in the transparency of the yarn. Variation in transparency causes streaks when the filament yarn is made into a fabric, which significantly reduces the commercial value. Although the required moisture content varies depending on the target product and yarn type, it is preferably 20% or more lower than that of unmodified yarn of the same thickness. As for the lubricating method, nozzle lubricating, in which lubricant is applied in measured amounts in fixed amounts, is preferable to roller lubricating using a rotating roller.

Since the polyamide fiber of the present invention is mainly used for clothing, it is preferable that the single yarn fineness is 20 denier or less in terms of the feel and feel of the final product.

This polyamide fiber is woven or knitted by a conventional method for producing clothing fabrics, and then dyed to form a product fabric.

The fabric may be dyed using acid dyes, metal-containing dyes, disperse dyes, etc. that are commonly used for polyamides for clothing, and it is preferable to use highly vivid color dyes in order to fully utilize the vivid coloring properties.

[Function] In the present invention, the specific salt compound that is blended into the fiber together with the specific diamide compound cannot produce effects such as improving transparency or strength if it is blended alone, but it can be used in combination with the diamide compound. By this, the effect of the diamide compound can be increased.

In other words, the melting and dispersibility of the diamide compound in the polyamide is extremely good, so that the scattering of light due to external foreign matter inside the yarn and undissolved coarse particles of the diamide compound is greatly suppressed, resulting in extremely good transparency. It can be a thread. Furthermore, since these foreign particles do not reduce the physical properties of the yarn, especially its strength, it is possible to create a yarn with even greater strength, making it possible to use strong polyamide fibers as filament yarns for clothing. becomes.

Further, the above salt compound can significantly suppress the adverse effects such as an increase in yarn breakage during spinning caused by blending the diamide compound.

This adverse effect is thought to be due to the fact that the diamide compound has a strong tendency to separate and aggregate in the polymer during melt-spinning, and that it oozes around the spinneret hole and contaminates the area around the spinneret hole during melt-spinning. Moreover, the above salt compound can increase the amount of the diamide compound that can be uniformly mixed into the polyamide raw material monomer, and therefore can be easily used as a master polymer.

Furthermore, by making the cross section of the fibers into a specific elliptical shape, the effects of the diamide compound can be further enhanced, and the product can have a smooth and natural texture.

Therefore, according to the present invention, it is possible to obtain a brightly colored product having a feel suitable for summer clothing.

According to the method of claim 2, if both a diamide compound and a salt compound are added to the polyamide polymerization raw material in a step before polymerization, the dispersion state of the diamide compound in the fiber can be made more uniform, improving fiber performance and spinnability. The effect of improvement can be further enhanced.

[Example] - Example 1 In an 85% aqueous solution of ε-caprolactam, 0.5% by weight of ethylene bisstearamide and 0.1% by weight of β-naphthalenesulfonic acid formalin condensate based on ε-caprolactam. (“Demol N” manufactured by Kao Atlas ■
) was added and stirred thoroughly, followed by heating and ring-opening condensation polymerization using a conventional method to obtain master polyamide pellets (sample A) having a relative viscosity of 2.78 using 98% sulfuric acid.

This modified polyamide is subjected to an extruder type spinning machine,
Slit width is 0. After melt spinning at 1000 m/min from spinnerets with rectangular discharge holes of 3 mm and different slit lengths, the fibers are subsequently drawn to an elongation of 40 to 45% to determine the ratio of the major axis to the minor axis of the yarn cross section. Nylon 6 yarns of 30 denier and 6 filaments with different (a/b) were obtained (No. 1 to 4).

For comparison, the modified polyamide was similarly melt-spun using a circular discharge hole to form nylon 6 yarn (N
o, 5).

Furthermore, as a comparison, polyamide polymerized without adding a diamide compound or β-naphthalene sulfonic acid formalin condensate was melt-spun in the same manner from a circular or rectangular discharge hole, and the polyamide was melt-spun with a round or elliptical cross section. (No. 5.7).

The transparency of the yarn obtained by each of these methods is as follows:
．． 1,000 pieces of light were arranged in a 5cm grid, and white light was applied from the vertical direction, and the amount of transmitted light was measured using a photoelectric photometer and expressed as the ratio of transmitted light to incident light (transmitted light intensity).

Furthermore, a tubular knitted fabric was created from these yarns and Diaci
d Ali! It was stained with Aline SK7 Blup B in a conventional manner, and its bright color development was evaluated using a one-to-one comparison method.

The polyamide fiber according to the present invention had extremely excellent light transmittance, excellent dyeing and vivid color development, and a smooth texture. Moreover, there was less yarn breakage during spinning.

On the other hand, in the case of No. 3 (the ratio of major axis/minor axis of the fiber cross section exceeds 5), the transparency and bright dyeability were excellent, but the yarn breakage during spinning was particularly frequent, and the yarn was continuously spun. It was difficult to do so.

In addition, in the case of No. 4 (when the major axis/minor axis ratio of the fiber cross section is less than 2), in the case of No. 5 (in the case of round cross-section fiber), and in the case of No. 017 (in the case of elliptical cross-section filament but with a diamide compound) Although the case (without compounding) was better than N016, which is a round cross-section yarn without addition of a diamide compound, it was insufficient in terms of transparency and vivid dyeability.

- Example 2 Into an 85% aqueous solution of ε-caprolactam, 10% by weight of ethylene bisstearamide and 1% by weight of β-naphthalene sulfonic acid formalin condensate (Demol N manufactured by Kao Atlas ■) were added. '') was added and stirred thoroughly, followed by heating and ring-opening condensation polymerization using a conventional method to obtain master polyamide pellets (sample A) having a relative viscosity of 2.45 using 98% sulfuric acid.

Further, addition and polymerization were carried out in the same manner as above, except that sodium polyacrylate ("Dispex" manufactured by Toagosei Kogyo ■) was used as the salt compound, and the relative viscosity of sulfuric acid was 2.
5 master polyamide pellets (Sample B) were obtained.

Furthermore, when ethylene bisstearamide (10% by weight relative to ε-caprolactam) was added to an 85% aqueous solution of ε-caprolactam and polymerization was carried out in the same manner,
As the polymerization progressed, the diamide compound separated from the melt polymer, making it virtually impossible to pelletize it. Therefore, the amount of diamide compound added was reduced to 3% and polymerization was performed again in the same manner to obtain master polyamide pellets (sample C) with a relative viscosity of 2.5.

Furthermore, as a comparison, an attempt was made to prepare master pellets by sprinkling the same ethylene bisstearamide (powder) on unmodified ε-polycapramide pellets and subjecting them to an extruder.

The extruder had poor biting properties, and the limit was to add 2.5% by weight (Sample D).

For these four types of master pellets (samples A-D), sulfuric acid was prepared so that the concentration of ethylene bisstearamide in the polyamide filament was 0.4% by weight, and the sulfuric acid solution contained substantially no foreign substances that scatter light. It was mixed with unmodified polyε-capramide pellets having a relative viscosity of 2.80, subjected to an extruder spinning machine, and melt-spun under the same conditions as in Example 1 to obtain a fiber cross-section with a/b of 4.
A polyε-capramide yarn of 0 denier and 6 filaments was obtained (NL 8-11).

The transparency and spinnability of these yarns were evaluated in the same manner as in Example 1.

Separately, an attempt was made to directly sprinkle 0.4% by weight of powdered ethylene bisstearamide onto polyε-capramide pellets and perform melt spinning in the same manner, but the extruder biting stability was extremely poor. Due to large pressure fluctuations, thread breakage occurred frequently and continuous spinning was not possible.

The polyε-capramide blended with the ethylene bisstearamide dispersion and meltability improver of the present invention exhibited excellent transparency and spinning stability.

[Effects of the invention] According to the present invention, when a specific diamide compound is added in combination with a specific salt compound and the cross section of the fiber is made into a specific elliptical shape, the original effect of the addition of the diamide compound can be fully exhibited. It is possible to produce nylon fibers with improved spinnability and improved transparency, vivid color development, strength and elongation properties, and texture.

Therefore, even as a thin fabric, it can be made into a product that is strong, has excellent transparency and vivid color development, and has a smooth and natural texture.

In addition, it is easy to manufacture using the master polymer method, making industrial production even easier.

According to the method of claim 2, the uniform dispersibility of the diamide compound can be further improved, so that transparency, vivid color development, strength and elongation properties, etc. can be further improved.

Claims (1)

[Claims] (1) 0.01 to 1.0% by weight of a diamide compound represented by the following general formula (1) or (2) based on the polyamide, 1 to 30% by weight of a sulfuric ester salt, or sulfone based on the diamide compound Contains one or more salt compounds selected from the group of acid salts and polycarboxylic acid salts, and has an elliptical fiber cross-sectional shape with a ratio of major axis a to minor axis b (a/b) of 2 to 5. A polyamide fiber with excellent transparency and vivid color development due to its shape. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(1) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(2) (However, R_1 and R_4 are alkyl groups with 10 to 20 carbon atoms, R_2 , R_3 is a hydrogen atom, a methyl group or an ethyl group, and n is an integer of 1 to 10.) (2) In a step before polymerization, the diamide compound and a sulfuric ester salt,
and one or more salt compounds selected from the group of sulfonic acid salts and polycarboxylic acid salts to produce a polyamide composition in which the concentration of the diamide compound is 0.01 to 1.0% by weight. 2. A method for producing polyamide fibers having excellent transparency and vivid dye color development, characterized by producing the polyamide fibers according to claim 1 by melt-spinning said polyamide composition.