JPS6319628B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing highly twisted polyester yarn with good color development. More specifically, the present invention relates to a method for producing polyester fibers with good color development, which is characterized in that polyester fibers containing inert inorganic fine particles are strongly twisted and then subjected to alkali dissolution treatment. Polyester fibers have excellent physical and chemical properties and are therefore widely used for clothing and industrial purposes. However, polyester fibers have been inferior to other fibers such as acetate, rayon, wool, and silk in terms of color development (depth of black or sharpness of chromatic colors) of dyed fabrics. In particular, since the depth of black color is significantly inferior to that of the other fibers mentioned above, there has been a strong desire for improved black color development (improvement of depth) in the black formal field. As a method to improve the color development of dyed fabrics, which is a drawback of conventional polyester fibers, (1) a method in which organic synthetic fibers are irradiated with plasma in a glow discharge plasma to give the fiber surface an unevenness of 0.1 to 0.5μ (a special method); (1982-99400) (2) A method of applying a thin film of a low refractive index component to the fiber surface (3) A method of applying a thin film of a low refractive index component to the fiber surface (3) A method of applying inorganic fine particles such as silica sol with an average particle size of 80 mμ or less A method of imparting a specific surface structure by subjecting polyethylene terephthalate fibers to which 0.5 to 10% by weight has been added by alkali dissolution treatment
-120728 Publication) have been proposed. Among these methods, method (1) has problems such as high cost due to expensive plasma discharge equipment and no significant effect of improving color development can be expected. Furthermore, since method (2) involves attaching a low refractive index component to the fiber surface, it certainly has a great effect of improving color development, but it has the problem of poor friction fastness. Furthermore, since method (3) can impart a specific surface morphology to the fibers, the effect of improving color development was improved to some extent, but the effect was not sufficient. The present inventors have arrived at the present invention as a result of intensive studies in view of the above-mentioned problems. That is, the present invention provides silicon-containing inorganic fine particles, inorganic fine particles consisting of oxides and/or salts of metals of group group of the periodic table, aluminum oxide, thorium oxide, and zirconium oxide, and having an average primary particle diameter of 5 μm. Contains 0.1 to 4% by weight of the following inert inorganic fine particles and 1 to 50% by weight of a tetraalkylammonium compound and/or sulfonic acid metal salt compound copolyester as a dispersant based on the inert inorganic fine particles, and Twist coefficient defined by the following formula for polyester fibers in which at least 70 mol% of the acid component is terephthalic acid component
This is a method for producing polyester fibers with excellent color development, which is characterized by strongly twisting the fibers so that (K) is 3500 or more, and then subjecting the fibers to an alkali dissolution treatment. K=T√ (where, D: denier number of fiber, T: fiber 1
Number of twists per m) The polyester in the present invention refers to a polyester containing ethylene glycol or 1,4-butanediol as the main glycol component and terephthalic acid or its ester as the main dicarboxylic acid component. A part of this dicarboxylic acid component is, for example, a monoalkali metal salt of 5-sulfoisophthalic acid, a dicarboxylic acid such as isophthalic acid, diphenyldicarboxylic acid, naphthalene dicarboxylic acid, adipic acid, sebacic acid, dotecanedioic acid, or an ester thereof, p
- Oxycarboxylic acids such as oxybenzoic acid and p-β-oxyethoxybenzoic acid or esters thereof may be substituted, and a portion of the aliphatic or alicyclic glycol may be replaced with, for example, alkylene glycols having 2 to 10 carbon atoms, 1 , 4-cyclohexanedimethanol, 1,4-bis(β-oxyethoxy)benzene, bisglycol ether of bisphenol A, polyalkylene glycol, and the like may be substituted with glycols other than the main glycol component. Furthermore, it is also possible to use a small proportion of a chain branching agent such as pentaerythritol, trimethylolpropane, trimelite, or trimesic acid, or a polymerization terminator such as monohydric polyalkylene oxide or phenylacetic acid. To produce polyester from such raw materials,
For example, dimethyl terephthalate may be transesterified with aliphatic or cycloaliphatic glycols, or
An aliphatic or alicyclic glycol ester of terephthalic acid and/or a low polymer thereof is synthesized by directly esterifying terephthalic acid with an aliphatic glycol or by adding ethylene oxide to terephthalic acid, and then The most widely used method is to subject the product to a polymerization reaction using a conventional method. Furthermore, in synthesizing the polyester for carrying out the present invention, catalysts, coloring inhibitors, matting agents, ether bond by-product inhibitors, antioxidants, twist-resistant agents, etc., which are well known in the art, can be appropriately used. The silicon-containing inorganic fine particles in the present invention refer to 500
Contains 20% by weight or more of silicon as silicon oxide after heating at ℃ for 2 hours, does not inhibit the polyester synthesis reaction, does not cause extreme coloring during polyester synthesis, and is substantially insoluble in the polyester. means inorganic fine particles. Such inert inorganic fine particles may be those obtained by crushing naturally occurring raw stones, those obtained by synthesis, or those whose surfaces have been treated, such as mica, talc, kaolin, glass powder, zirconium silicate, silicon oxide, etc. be able to. In the present invention, the inorganic fine particles made of group metal oxides and/or their salts include zinc oxide, cadmium oxide, etc., regardless of whether they are crushed naturally occurring raw stones, synthetically obtained, or surface-treated. , calcium carbonate, calcium sulfate, barium carbonate, barium sulfate, barium phosphate, magnesium phosphate and strontium sulfate. Further, as the inert inorganic fine particles in the present invention, in addition to the silicon-containing inorganic fine particles and group metal oxides and/or salts thereof, aluminum oxide, zirconium oxide, and thorium oxide can be mentioned. Among these inorganic fine particles, silicon oxide and aluminum oxide are particularly preferred because they have a large effect of improving color development. In general, in the production of polyester, titanium oxide is widely used as inert inorganic fine particles in addition to the inert inorganic fine particles of the present invention. However, titanium oxide does not exhibit the effect of improving color development, which is the objective of the present invention. The cause of this is not yet clear, but it is thought that one factor is probably that titanium oxide has a high refractive index, which increases the light reflectance on the fiber surface layer. The average primary particle diameter of the inert inorganic fine particles in the present invention is 5μ or less, preferably 2μ or less, particularly preferably 100mμ or less. If it exceeds 5μ, the effect of improving color development will decrease, which is not preferable. Further, since coarse particles are inevitably mixed in, the number of coarse particles in the polymer increases, which is undesirable because troubles such as sand clogging or yarn breakage occur during the spinning process. Therefore, a method in which coarse particles are removed by classification by a generally well-known method such as a natural sedimentation method, a centrifugal separation method, or an air sieve classification method can be preferably used. Here, the average particle size is 50% by weight of all measured particles.
means the "equivalent spherical diameter" of the particle at the point.
"Equivalent Spherical Diameter" (ESD)
Diameter means the diameter of an imaginary sphere having the same volume as the particle, and can be calculated from electron micrographs of the particle or measurements by conventional sedimentation methods. The amount of inert inorganic fine particles added in the present invention is in the range of 0.1 to 4% by weight, particularly preferably in the range of 0.3 to 2% by weight, based on the polyester composition to be produced. If the amount is less than 0.1% by weight, the effect of improving color development will be insufficient, which is undesirable, and if the amount exceeds 4% by weight, the effect of improving color development will be saturated and the effect of increasing the amount added will be lost, which is not preferable. Furthermore, depending on the particle type, if the amount added exceeds 4%, the color development after the alkali dissolution treatment may deteriorate. Further, if the amount exceeds 4%, the number of coarse particles in the resulting polyester will increase, which is not preferable. Further, the inert inorganic fine particles in the present invention can be dispersed in aliphatic glycol, aliphatic alcohol, water, etc. by a known method, but it is particularly preferable to disperse them in glycol, which is a raw material for the polyester. The dispersion slurry of inert inorganic fine particles in the present invention can be prepared by a conventionally known method. For example, a method of dispersing the inert inorganic fine particles of the present invention and ethylene glycol in a high-speed stirrer having a plurality of shearing blades parallel to the direction of rotation as described in JP-A-53-125495 is preferred. Moreover, in order to remove coarse particles in the slurry prepared by the dispersion method, a method of removing coarse particles in the slurry by passing it through a filter can also be preferably used. The amount of the dispersant added in the present invention is in the range of 1 to 50% by weight based on the inert inorganic particles,
Particularly preferred is a range of 3 to 40% by weight. If it is less than 1% by weight, the effect of improving the dispersibility of the inert inorganic particles and the effect of improving the color development of dyed fabrics will be small, and if it exceeds 50% by weight, the inert inorganic particles will re-agglomerate and become coarse particles in the polymer. As the dispersant, a polyester-based dispersant copolymerized with a tetraalkylammonium compound and an alkali metal sulfonic acid salt compound is particularly suitable because it has a large effect of improving color development and preventing agglomeration of inert fine particles. Here, the tetraalkylammonium compounds include tetramethylammonium hydroxide, tetramethylammonium chloride, tetraethylammonium hydroxide, tetraethylammonium chloride, tetraethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium chloride, tetraisopropylammonium oxide, Examples include tetraisopropylammonium chloride, tetrabutylammonium hydroxide, and tetrabutylammonium chloride, among which tetraethylammonium hydroxide is particularly preferred. In addition, as a sulfonic acid metal salt compound copolymerized polyester dispersant, 10 to 50 mol% of a sulfonic acid metal salt compound and 10 mol% of a glycol selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, and polyethylene glycol are used. Water-soluble polyesters containing the above are preferred. Note that a commonly used polyester synthesis method can be applied to the synthesis of the polyester dispersant. Although the dispersant can be added at any stage until the polymerization of the polyester is completed, it is particularly preferable to add the dispersant when preparing a glycol slurry of inert fine particles in order to prevent re-agglomeration of the inert fine particles. Here, the use of a dispersant is effective not only in improving the dispersibility of the additive particles but also in improving the color development of the dyed fabric. Although the reason for this is not clear, it is thought that by adding a dispersant to improve particle dispersibility in the polymer, the alkaline aqueous solution treatment system improves the yarn surface to be more favorable. In the present invention, the glycol slurry of inert inorganic fine particles can be added at any stage until the polymerization of the polyester is completed, but especially before the start of the polymerization reaction of the polyester, the number of coarse inert inorganic fine particles is small. preferable. However, by changing the dispersion medium of inert inorganic fine particles,
If the so-called masterbatch method is used in which inert inorganic fine particles are dispersed at a high concentration in the same polyester as the polyester of the present invention, it can be added either after completion of polymerization or during spinning. The intrinsic viscosity ([η]) of the polyester chips in the present invention is preferably 0.45 or more, particularly preferably 0.60 or more, from the viewpoint of the number of coarse particles of the polyester chips obtained and the strength of the yarn after alkali dissolution treatment. The strong twisting process used in the present invention employs the commonly used Italian method or double twister method, but the effect of improving color development depends on the twist coefficient. The denier number (D) of the highly twisted yarn in the present invention is
and the number of twists per meter of fiber (T), the twist coefficient (K) K=T√ calculated by the following formula is 3500 or more, preferably 5500 or more. Here, the twist coefficient is a number related to the twist angle of the fibers, and by increasing the twist coefficient, the twist angle increases and the length of the contact area between single fibers per unit length of the fiber bundle increases. As is well known. Therefore, when polyester fibers containing inert inorganic fine particles are strongly twisted and treated with alkali, the color development is greatly improved because the alkali treatment increases the contact area between the single fibers, which has increased due to the strong twisting. Due to weight loss, air gaps are created, and these air gaps become a kind of tunnel for light, increasing the light absorption efficiency. In addition, the fiber surface becomes rough due to alkali treatment of polyester fibers containing inert inorganic fine particles. This is thought to be due to the fact that the tunnel effect caused by the air gaps between the single fibers is made more effective. Therefore, if the twist coefficient of the highly twisted yarn is less than 3500, a sufficient amount of air gaps between the single fibers cannot be obtained. Increasing the twist coefficient improves the color development of dyed products, but excessive twisting also reduces the strength of the fibers, and in practice, K=25,000 is the upper limit. The alkali dissolution treatment of the present invention can be applied to basic alkali metal compounds such as alkali metal hydroxides such as caustic soda and caustic potash, alkali metal compounds that form alkali metal hydroxides when dissolved in water, and alkali metal carbonates. This can be achieved by heating the fiber or knitted fabric in an aqueous solution, or by padding/steaming the fabric with an aqueous solution of a basic alkali metal compound. In the alkali dissolution in the present invention, it is necessary to achieve a weight loss rate of 5 to 50% by weight, preferably 10 to 30% by weight, based on the fiber or woven or knitted fabric by the above-mentioned alkali dissolution treatment method. If it is less than 5% by weight, the effect of improving color development will not be sufficient, which is undesirable, and if it exceeds 50% by weight, the strength of the yarn will decrease too much, which is not preferred. Further, in the alkali dissolution treatment, an alkali dissolution promoter such as cetyltrimethylammonium bromide or lauryldimethylbenzene ammonium chloride can be appropriately used. As detailed above, the effects of the present invention are obtained by (a) subjecting polyester fibers containing a specific dispersant and specific inert inorganic fine particles to (b) strong twisting, and (c) then subjecting them to alkali dissolution treatment. However, the effect of the present invention cannot be achieved only by alkali dissolution treatment of false twisted yarn of silica sol-added yarn as described in Example 1 of JP-A-54-120728. is small. In other words, the above (a), (b), and (c) are essential requirements for improving color development, which is the objective of the present invention, and the reason why the objective of the present invention cannot be achieved even if any one of them is missing is as follows. This is also clear from the examples. The present invention will be specifically explained below with reference to Examples. In addition, parts in Examples mean parts by weight, and % means weight %. In addition, [η] in the following invention,
The number of coarse particles, the method for measuring color development, and the conditions for alkali dissolution are as follows. [Measurement method of intrinsic viscosity [η]] Dissolve the polymer in O-chlorophenol and heat at 25°C.
This is the value measured at [Method for measuring the number of coarse particles] Approximately 10 mg of the sample is sandwiched between 18 mm x 18 mm cover glasses and thermocompressed on a hot plate at 280°C to 300°C to create a film with a diameter of approximately 10 mm. Observe this film with a phase contrast microscope (100x magnification), measure coarse particles with a maximum length of 10 μ or more, calculate the number of coarse particles per 10 mg of sample, and use the average value of 10 measurements per level. [Method for measuring color development] The filament yarn to be evaluated was knitted into a tubular knitted fabric using a 27-gauge tricot sock knitting machine (manufactured by Koike Kikai Seisakusho Co., Ltd.), and then 0.2% nonionic activator was added using a conventional method. Sandets G-900 (manufactured by Sanyo Chemical Co., Ltd.)
It was scoured by boiling in boiling water containing 0.2% soda ash for 5 minutes, then washed with water and dried. Next, using a baking test device (MODEL-DK-1H, manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.) adjusted to 180°C, dry heat treatment was carried out in a non-tensioned state for 30 seconds to set the cylindrical knitted fabric. Next, dyeing was carried out for 60 minutes in an aqueous solution of Sumikaron Black S-BB (disperse dye manufactured by Sumitomo Chemical Co., Ltd.) at 130°C in a bath ratio of 1:30 consisting of 10% OWF acetic acid 0.5cc/sodium acetate 0.2g/. After that, according to the usual method, hydrosulfite 2g / caustic soda 2g / nonionic activator (Sandet G-900)
Reduction cleaning was performed for 20 minutes in an aqueous solution of 2 g/ml at 80°C, followed by water washing and drying. The color development was evaluated using a digital colorimetric color difference calculator (manufactured by Suga Test Instruments Co., Ltd.) by stacking six or more tube knitted fabrics and using the L value measured in a state where no irradiation light was transmitted.
The darker the color, the smaller the L value, and the lighter the color, the larger the value. [Alkali dissolution conditions] 1 part by weight of the tubular knitted fabric was immersed in 50 parts by weight of a boiling aqueous solution of sodium hydroxide (3% by weight), treated for a specified period of time with stirring, washed with water, and then neutralized with a 1% aqueous acetic acid solution. Then, it was further washed with water and dried.
The alkali dissolution treatment time was preliminarily studied and set to achieve a predetermined weight loss rate. In addition, the weight loss rate is calculated by heating the tubular knitted fabric at 100℃ before treatment.
After drying in hot air for 20 minutes, the weight was measured [the weight at this time was referred to as (A)], and the tubular knitted fabric after the reduction process was similarly dried at 100°C for 20 minutes and the weight was measured [the weight at this time was taken as (A)]. The weight is defined as (B)], and the weight loss was calculated from the formula A-B/A×100=weight loss rate (%). Example 1 100 parts of dimethyl terephthalate, 60 parts of ethylene glycol, 0.05 part of manganese acetate tetrahydrate, and 0.04 part of antimony trioxide were charged into a transesterification can.
The temperature was raised from 140° C. to 230° C. over a period of 4 hours under a nitrogen gas atmosphere, and the transesterification reaction was carried out while the generated methanol was continuously distilled out of the system. Subsequently, 0.05 part of trimethyl phosphate was added to the obtained product. In addition, 20% of dry process silicon oxide and tetraethylammonium hydroxide with an average primary particle size of 12 mμ
The weight ratio of aqueous solution and ethylene glycol is 5:
2.5:92.5 mixture with Janke & Kunkel Ultra
A slurry dispersed in Turrax T45 DX (10,000 rpm) for 45 minutes was added as silicon oxide to the resulting polyester at a concentration of 1.0%. The system was then gradually depressurized to 760°C over 1 hour and 30 minutes.
Depressurize from mmHg to 1mmHg and at the same time 30 hours for 1 hour.
The temperature was raised from 230°C to 280°C over a period of minutes. 1mmHg
Under the following reduced pressure, at a polymerization temperature of 280°C for an additional 2 hours,
Polymerization was carried out for a total of 3 hours and 30 minutes. After the reaction was completed, the polymer was discharged into water to obtain a rod-shaped polymer having a diameter of 3 mm. Furthermore, the polymer was cut to a length of 5 mm and [η] was
0.670, and the number of coarse particles was 10. The obtained polyethylene terephthalate was heated to 160℃
After drying under reduced pressure for 5 hours, the spinning temperature was 290℃ and the take-up speed was
Spinning at 900 m/min, then stretching at a stretching ratio of 3.45 times,
It was drawn at a pin temperature of 100°C to obtain a drawn yarn of 75 denier/36 filaments. This drawn yarn was twisted using an Italian twisting machine to a number of twists of 20,000, and then set in saturated steam at a temperature of 95° C. for 20 minutes.
Next, a tubular knitted fabric was created by the method described above. The product was then refined and subjected to alkali dissolution treatment to achieve a weight loss rate of 25%, and then evaluated for color development. The yarn strength after the alkali dissolution treatment was 2.9 g/d, which was at an acceptable level. Further, the color development properties are shown in Table 1. From the results in Table 1, it is clear that the combination of silicon oxide addition, strong twisting, and alkali dissolution treatment has a good effect on improving color development. Comparative Example 1 The same procedure as in Example 1 was carried out except that silicon oxide was not added, and the coloring property was evaluated after polymerization, spinning, strong twisting, knitting, and alkali dissolution treatment. Table 1 shows the L value.
As shown in Comparative Example 2 The raw yarn obtained in Example 1 was knitted without being subjected to strong twisting and subjected to an alkali dissolution treatment, and then the color development was evaluated. The L values are shown in Table 1. Comparative Example 3 The drawn yarn obtained in Example 1 was heated to a heater length of 110 cm.
Heater temperature using spindle type false twisting machine
200℃, false twisting speed 100m/min, number of twists
After false twisting at 2400 tpm, knitting and alkali dissolution treatment, color development was evaluated. The L values are shown in Table 1. Comparative Example 4 The highly twisted knitted fabric obtained in Example 1 was evaluated for color development without being subjected to alkali dissolution treatment. The L values are summarized in Table 1.

[Table] Examples 2 to 13, Comparative Examples 4 to 7 Polymerization, spinning, and strength were carried out in the same manner as in Example 1, except that the particle type and average primary particle size were changed as shown in Table 2 instead of silicon oxide. Color development was evaluated after twisting, knitting, and alkali dissolution treatment.
Table 2 shows the number of coarse particles and color development of the polyester chips obtained. From Table 2, it is clear that the number of coarse particles in the chips and the color development of the cloth are good when the particle types and average primary particle diameters according to the present invention are used.

【table】

[Table] Examples 14 to 17, Comparative Examples 8 to 9 Polymerization, spinning, strong twisting, and knitting were carried out in the same manner as in Example 1, except that the amount of silicon oxide added in Example 1 was changed as shown in Table 3. And color development was evaluated after performing alkali dissolution treatment. Table 3 shows the number of coarse particles and color development of the obtained polyester chips.
It was shown to. It is clear that color development is good when the amount of silicon oxide added is 0.1 to 4%.

[Table] Examples 18 to 22, Comparative Examples 10 to 11 Knitting and alkali dissolution treatment were carried out in the same manner as in Example 1, except that the yarn obtained in Example 1 was strongly twisted under the conditions shown in Table 4. After that, the color development was evaluated. From Table 4, it is clear that when the strong twist processing conditions are a twist coefficient of 3,500 or more, especially 5,500 or more, the color development is good.

【table】

[Table] Examples 23 to 25, Comparative Examples 12 to 13 The highly twisted knitted fabric obtained in Example 1 was subjected to alkali dissolution treatment by changing the alkali dissolution treatment time so that the weight loss rate was as shown in Table 5. The subsequent color development was evaluated.
From Table 5, when the alkali weight loss rate is 5 to 50%,
It is clear that the yarn strength after the alkali dissolution treatment is within a satisfactory range and the color development level is good.

[Table] Examples 26 to 28 [η] of polyester chips in Example 1
The coloring property was evaluated after polymerization, spinning, strong twisting, knitting, and alkali weight loss processing in the same manner as in Example 1 except that the following changes were made as shown in Table 6. Table 6 shows the [η], the number of coarse particles, the strength of the yarn, the strength of the yarn after the alkali dissolution treatment, and the color development of the polyester chips obtained. If [η] is 0.50 or more,
It is clear that the yarn strength after the alkaline dissolution treatment is particularly good.

[Table] Examples 29 to 30 Polymerization was carried out in the same manner as in Example 1, except that the timing of addition of the silicon oxide ethylene glycol slurry was changed as shown in Table 7. Table 7 shows the number of coarse particles in the obtained polyester chips. From the results of Table 7 and Example 1, it is clear that it is particularly preferable to add the silicon oxide ethylene glycol slurry before the start of polymerization.

[Table] Examples 31 to 41, Comparative Example 14 Table 8 shows the type and amount of dispersant in Example 1.
Polymerization, spinning, strong twisting, knitting, and alkali dissolution treatment were carried out in the same manner as in Example 1, except for the following changes, and color development was evaluated. Table 8 shows the number of coarse particles and coloring properties of the obtained polyester. From Table 8, tetraalkylammonium compounds,
It is clear that polyester dispersants are effective in preventing particle aggregation and improving the color development of fabrics.

[Table] Example 42 100 parts of dimethyl terephthalate, 93 parts of 1,4-butanediol, and 0.03 parts of tetrabutyl titanate were charged into a transesterification tank and heated to 140 parts under a nitrogen gas atmosphere.
Methanol produced by raising the temperature from ℃ to 225℃,
The transesterification reaction was carried out while continuously distilling tetrahydrofuran and water out of the system, and the reaction was completed 4 hours after the start of the reaction. 0.03 part of tetrabutyl titanate was added to the obtained product, and 20% of the slurry dry process silicon oxide and tetraethylammonium hydroxide with an average primary particle size of 12 mμ was added.
The weight ratio of aqueous solution and 1,4-butanediol is 5:
2.5:92.5 mixture with Janke & Kunkel Ultra
A slurry dispersed in a Turrax T45 DX (10000 rpm) for 45 minutes was added as silicon oxide to the resulting polyester at 1.0%. The system was then gradually depressurized to 760mmH over 1 hour.
Reduce the pressure from g to 1 mmHg and simultaneously over 1 hour.
The temperature was raised from 225℃ to 250℃. Polymerization was carried out for an additional 2 hours at a polymerization temperature of 250° C. under reduced pressure of 1 mmHg or less, for a total of 3 hours. Diameter 3 after reaction
It was discharged into water so that a rod-shaped polymer of mm was obtained. Further, the polymer was cut to a length of 5 mm to obtain polyester chips. The intrinsic viscosity of the obtained polyester chip was 0.815, and the number of coarse particles was 15. Furthermore, after drying the obtained polyester chips at 140℃ for 5 hours under reduced pressure, the spinning temperature was 260℃ and the take-up speed was
The yarn was spun at 1200 m/min and then drawn at a draw ratio of 2.8 times to obtain a yarn of 75 denier/36 filaments. The strength of this drawn yarn is 3.8g/d, and the elongation is 30.5%.
It was hot. This drawn yarn was subjected to heavy twisting, tube knitting, and scouring in the same manner as in Example 1, and then subjected to tensionless heat treatment at a temperature of 170° C. for 30 seconds using a baking tester. This was immersed in boiling water containing 5% sodium hydroxide with stirring, washed with water, neutralized, and washed with water to obtain a cylindrical knitted fabric with a weight loss rate of 25%. The obtained tubular knitted fabric was evaluated for L value in the same manner as in Example 1. As a result, the L value was 12.6, showing very good color development. Comparative Example 15 Polymerization, spinning, strong twisting, and
Color development was evaluated after knitting and alkali dissolution treatment. The L value was 13.7, which was poor.

Claims (1)

[Scope of Claims] 1. Average primary particle diameter selected from the group consisting of silicon-containing inorganic fine particles, inorganic fine particles consisting of oxides and/or salts of metals of group group of the periodic table, aluminum oxide, thorium oxide, and zirconium oxide. Inert inorganic fine particles with a size of 5μ or less from 0.1 to
4% by weight and 1 to 50% by weight of a tetraalkylammonium compound and/or sulfonic acid alkali metal salt compound copolymer polyester as a dispersant based on the inert fine particles, and at least 70 mol% of the total acid component is terephthalic acid. A method for producing polyester fibers with excellent color development, which comprises strongly twisting polyester fibers as an acid component so that the twist coefficient (K) defined by the following formula is 3500 or more, and then subjecting the fibers to an alkali dissolution treatment. K=T√(where, D: denier number of fiber,
T: Number of twists per meter of fiber).