JP2008174889A - Polylactic acid conjugate fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid conjugate fiber excellent in resistance to moist heat degradation, mechanical strength and color tone, and usable in various applications including clothing and industrial materials despite using polylactic acid as a constituent. <P>SOLUTION: The polylactic acid conjugate fiber is a sheath/core-type one composed of polylactic acid as the core component and, as the sheath component, an aromatic polyester having ethylene terephthalate as the main repeating unit accounting for 80 mol% or greater. In this conjugate fiber, the sheath/core ratio (cross section area ratio of core to sheath) is (20:80) to (80:20), and the mechanical strength retention percentage after subjected to exposure treatment at 60°C and 90%RH for 500 h is 80% or greater; wherein the mechanical strength retention percentage(%) means a numerical value represented by (tensile strength after exposure treatment/tensile strength before exposure treatment)×100. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a core-sheath type composite fiber having polylactic acid as a core component and aromatic polyester as a sheath component, having excellent resistance to moist heat decomposition, strength, and good color tone, for clothing use, industrial material use, etc. The present invention relates to a polylactic acid composite fiber that can be used in various applications.

  Among synthetic fibers, particularly polyester fibers are indispensable as clothing and industrial materials because of their excellent dimensional stability, weather resistance, mechanical properties, and the like, and are widely used in various fields and applications.

  Most of the conventional synthetic fibers are made from limited fossil resources and are hardly decomposed in the natural environment, so the disposal method is mainly incineration. On the other hand, since the polylactic acid fiber is completely biodegradable and is finally decomposed into carbon dioxide gas and water in a natural environment, it can be composted and carbon dioxide emission can be reduced. And since it uses plant-derived resources as raw materials, it saves fossil resources.

  However, polylactic acid fibers are inferior in strength and wear resistance to conventional synthetic fibers. In addition, there is a problem that strength is reduced and dyeing spots are generated due to poor heat-and-moisture resistance and large decomposition due to wet heat treatment such as dyeing. In addition, when polylactic acid fiber is used as a cloth for clothing, there is a problem that the texture becomes hard when ironing is performed in the same manner as that of a general-purpose synthetic fiber. Therefore, when ironing a fabric made of polylactic acid fibers, specially low temperature setting and careful attention are required.

  For this reason, conventional polylactic acid fibers are mainly used for disposable daily materials, agriculture, forestry and horticultural materials, and in fields where strength is required for clothing, civil engineering, marine materials, automotive materials, etc. The use of is currently limited.

  One means for solving the problems of such polylactic acid fibers is to increase the mass and thickness to cover the strength and wear resistance.

  In addition, in order to increase the durability of polylactic acid, in Patent Document 1, the end of the polymer is blocked with an end-blocking agent such as carbodiimide in order to reduce the physical properties during wet heat treatment due to hydrolysis of the carboxyl end group in the fiber. It has been proposed to improve hydrolysis resistance. However, the moisture and heat resistance performance was insufficient.

  In Patent Document 2, as a composite fiber composed of polylactic acid and other components, polylactic acid forms all or part of the surface of a single fiber, and an aromatic polyester such as polyethylene terephthalate is used as the other component in the core. The composite fiber used has been proposed. However, this fiber is a binder fiber in which the polylactic acid component occupies the outer periphery of the fiber, and the polylactic acid component is an adhesive component, and has the strength described above for clothing, civil engineering, marine materials, automotive materials, etc. Was not intended for use in the required fields.

Patent Document 3 discloses a core-sheath shape in which polylactic acid is a core portion and aromatic polyester is a sheath portion as a composite fiber composed of polylactic acid and an aromatic polyester, and a terminal blocker is formed in the core portion and / or the sheath portion. Has been proposed to reduce the carboxyl end groups of the entire fiber. However, in this fiber, an end-blocking agent is added to reduce the carboxyl end group, and the fiber tends to turn yellowish and the dyeing quality is likely to deteriorate. If the amount is increased, there is a problem that the spinning operability is deteriorated.
JP 2001-261797 Japanese Patent Laid-Open No. 11-279841 JP 2005-187950 A

  The present invention solves the above-mentioned problems, and has poly-lactic acid as a constituent component, but is excellent in moisture and heat resistance, strength and color tone, and can be used for various uses such as clothing and industrial materials. It is intended to provide a lactic acid composite fiber.

  The inventors of the present invention have arrived at the present invention as a result of studies to solve the above problems.

That is, the present invention relates to a core-sheath type composite fiber comprising polylactic acid as a core component, and a core-sheath type composite fiber having an aromatic polyester in which 80% by mole or more of ethylene terephthalate as a main repeating unit is a sheath component, The area ratio (core: sheath) is 20:80 to 80:20, and the strength retention after exposure for 500 hours in an environment of temperature 60 ° C. and humidity 90% is 80% or more. The polylactic acid composite fiber is used as a gist.
Here, the strength retention (%) is a value represented by (tensile strength after exposure treatment / tensile strength before exposure treatment) × 100.

  The polylactic acid composite fiber of the present invention has polylactic acid as a constituent component, is excellent in moisture and heat resistance, strength, color tone, and can be obtained with good operability, and is widely used for clothing, industrial materials, etc. Is possible. Moreover, since polylactic acid is a plant-derived raw material, it becomes a fiber that is friendly to the global environment.

Hereinafter, the present invention will be described in detail.
The polylactic acid composite fiber of the present invention is a core-sheath type composite fiber having a cross-sectional shape of a core-sheath shape, wherein the core component is polylactic acid and the sheath component is aromatic polyester. Since the conjugate fiber of the present invention exhibits a single fiber shape, it can be used as a long fiber or a short fiber as a fiber (multifilament) in which a plurality of the conjugate fibers (single fibers) of the present invention are assembled. Moreover, you may use as a monofilament, without making multiple sets gather.

  In addition, when the fiber is composed only of polylactic acid, the heat treatment temperature cannot be increased and false twisting cannot be performed, but the polylactic acid composite fiber of the present invention has an aromatic polyester as a sheath component, False twisting can be performed at a sufficient heat treatment temperature, and a good false twisted yarn can be obtained.

  First, as polylactic acid used for the core component in the present invention, poly-D-lactic acid, poly-L-lactic acid, poly-DL-lactic acid which is a copolymer of poly-D-lactic acid and poly-L-lactic acid, poly-D-lactic acid, Poly L-lactic acid mixture (stereo complex), poly D-lactic acid and hydroxycarboxylic acid copolymer, poly L-lactic acid and hydroxycarboxylic acid copolymer, poly D-lactic acid or poly L-lactic acid Examples thereof include copolymers with aliphatic dicarboxylic acids and aliphatic diols, and blends thereof.

  The polylactic acid is one in which L-lactic acid and D-lactic acid are used alone or in combination as described above, and among them, the melting point is preferably 120 ° C. or higher.

  The melting point of L-lactic acid and D-lactic acid, which are homopolymers of polylactic acid, is about 180 ° C., but in the case of a copolymer of D-lactic acid and L-lactic acid, the proportion of any component is about 10 mol%. Then, the melting point is about 130 ° C.

  Furthermore, if the proportion of any of the components is 18 mol% or more, the melting point is less than 120 ° C., the heat of fusion is less than 10 J / g, and almost completely amorphous properties are obtained. When such an amorphous polymer is used, it becomes difficult to heat-stretch particularly in the production process, and it becomes difficult to obtain high-strength fibers. Even if fibers are obtained, heat resistance and wear resistance It is not preferable because it is inferior to

  Therefore, as polylactic acid, L / D or D / which is the content ratio (molar ratio) of L-lactic acid and D-lactic acid indicated by the content ratio of L-lactic acid or D-lactic acid when polymerizing using lactide as a raw material. L is preferably 82/18 or more, more preferably 90/10 or more, and even more preferably 95/5 or more.

  Among polylactic acids, a mixture (stereo complex) of poly D-lactic acid and poly L-lactic acid as described above is particularly preferable because it has a high melting point of 200 to 230 ° C. and high strength in a high temperature atmosphere. .

  Next, the aromatic polyester that is the sheath component of the composite fiber of the present invention will be described. If the melting point difference between the aromatic polyester and polylactic acid is large, the polylactic acid may be thermally decomposed during composite spinning. For this reason, it is preferable to lower the melting point of the aromatic polyester by copolymerizing other components. However, if the amount of copolymerization is too large and the melting point is too low, the heat and humidity resistance of the sheath component will be reduced. For this reason, in the aromatic polyester, ethylene terephthalate, which is a repeating unit, occupies 80 mol% or more.

  The melting point is preferably 180 to 260 ° C, and more preferably 200 to 240 ° C. The copolymer component may be either an acid component or a glycol component, or both.

  When the ethylene terephthalate, which is a repeating unit, is less than 80 mol%, the melting point is less than 180 ° C., the moisture and heat resistance of the sheath component is lowered, and it becomes difficult to perform false twisting at a high heat treatment temperature.

  Such an aromatic polyester is a polyester mainly composed of polyethylene terephthalate, and the copolymerization component includes phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, adipic acid, sebacin. Examples include acid components such as acid, azelaic acid, decanedicarboxylic acid, and cyclohexanedicarboxylic acid, and glycol components such as trimethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, dodecamethylene glycol, and cyclohexanedimethanol. It is done.

  And the smaller the amount of carboxyl end groups in the fiber, the better the heat and heat resistance, and the less the strength is reduced even after long-term use in a hot and humid environment. For this reason, the carboxyl end group amount of the whole polylactic acid composite fiber of the present invention is preferably 35 eq / t or less, and more preferably 30 eq / t or less.

  Furthermore, since the sheath component occupying the outer periphery of the composite fiber is easily affected by environmental changes, the amount of carboxyl end groups of the aromatic polyester as the sheath component is preferably 25 eq / t or less, and in particular, 20 eq / t The following is preferable.

  As a method for producing such an aromatic polyester having a low carboxyl end group amount, there is a method of adding an end group blocking agent during spinning. However, if a large amount of the end-group blocking agent is added, the fiber tends to discolor to a yellowish color, which tends to reduce the dyeing quality. Also, the spinning operability is likely to deteriorate.

Therefore, in order to obtain an aromatic polyester having a low amount of carboxyl end groups using existing polymerization equipment at low cost and stably without adding a terminal blocking agent, an antimony compound, a cobalt compound and It is preferable to employ a production method in which the phosphorus compound is in an amount satisfying the following formulas (a) to (c).
(a) 75 ≦ {Sb} ≦ 450
(b) 12 ≦ {Co} ≦ 75
(c) 10 ≦ {P} ≦ 2000
Here, {Sb}, {Co} and {P} represent the contents of the antimony compound, cobalt compound and phosphorus compound in the aromatic polyester raw material, respectively, and the unit is ppm by mass.

  Antimony compounds exhibit sufficient polycondensation activity, but have the disadvantage of deteriorating color tone. Therefore, the color tone is improved by using a cobalt compound in combination.

  For this reason, the addition amount of the antimony compound is reduced within a range in which a sufficient polycondensation reaction rate is exhibited, and the cobalt compound is used in an amount that exhibits a color tone improving effect. However, since the cobalt compound has an action of promoting thermal decomposition in the late stage of the polycondensation reaction, the target raw material cannot be obtained if added in a large amount. From these viewpoints, the addition amounts of the antimony compound and the cobalt compound are preferably in the ranges of the formulas (a) and (b), respectively.

  The phosphorus compound has an effect of suppressing the color tone change and thermal decomposition action of the polyester fiber by the antimony compound and the cobalt compound, and in order to sufficiently exhibit this action, it is preferable to satisfy the formula (c). When the amount of phosphorus compound is small, these effects are insufficient. In many cases, since the inside of the polyester system becomes acidic during the polycondensation reaction, a large amount of diethylene glycol is produced, so that not only the heat-and-moisture resistance is deteriorated but also the strength is lowered.

The above formulas (a) to (c) are the addition amounts during polymerization when obtaining the aromatic polyester of the sheath component, and in the polylactic acid composite fiber of the present invention, the content of these compounds in the entire fiber is expressed by the following formula: It is preferable to satisfy (1) to (3) at the same time.
(1) 15 ≦ [Sb] ≦ 360
(2) 2.5 ≦ [Co] ≦ 60
(3) 2.0 ≦ [P] ≦ 1600
Here, [Sb] represents the content of the antimony compound, [Co] represents the content of the cobalt compound, and [P] represents the content of the phosphorus compound, and the unit is ppm by mass.

  In the present invention, by using an aromatic polyester obtained by a method of adding a compound as described above at the time of polymerization as a raw material, it is possible to produce a fiber excellent in moisture and heat resistance without adding a terminal blocking agent. Is possible. Moreover, if it is a range which does not impair an effect, a terminal blocker may be added (combined) and the heat-and-moisture resistance of a fiber can be improved with a small addition amount.

  In addition, since the heat-and-moisture resistance of the aromatic polyester of the sheath component greatly affects the heat-and-moisture resistance of the entire fiber, it is preferable to add the end group blocking agent to the sheath component. A terminal blocking agent may be added to the polylactic acid as a core component. However, since polylactic acid is originally inferior in heat and moisture resistance, the effect of improving heat and moisture resistance is small.

  Furthermore, the polylactic acid composite fiber according to the present invention is such that the content of the compound as described above satisfies the above formulas (1) to (3) at the same time. The b value indicating the color tone is preferably 4.0 or less, and more preferably 1.0 or less.

  When the b value is 4.0 or less, a fiber product exhibiting a desired color after dyeing can be obtained. The b value is a value indicating the yellow-blue color tone (+ is yellowish,-is blueish) of the fiber, and the closer to 0, the less yellowish the color tone is preferable for the fiber.

  Next, the shape of the polylactic acid composite fiber of the present invention will be described. The polylactic acid conjugate fiber of the present invention is a core-sheath type conjugate fiber in which a cross-sectional shape, that is, a shape of a cross section cut perpendicularly to the length direction of the fiber exhibits a core-sheath shape, Is a core component, and aromatic polyester is a sheath component. At this time, the core part may be one or plural. In other words, examples of the core-sheath shape include composite forms such as a concentric core-sheath type having one core part, an eccentric core-sheath type, and a sea-island type having a plurality of core parts.

  By adopting such a core-sheath type composite shape, aromatic polyester excellent in moisture and heat decomposability, strength and wear resistance can cover the fiber surface, so that polylactic acid is inferior in these performances. As a whole, the fiber is excellent in resistance to wet thermal decomposition, strength and wear resistance. In addition, since twisted yarn, intertwisted yarn, false twisted yarn, aligned yarn, blended yarn, looped yarn, covering yarn, interlaced yarn, etc. can be heat treated at high temperature, sufficient twisting etc. It can be set as the processed yarn to which is given.

  The composite fiber of the present invention is not limited to a round cross section as long as it has a core-sheath type composite shape as described above, but is not limited to a round cross section, a flat cross section, a polygonal shape, a multileaf shape, a gourd shape, an alphabet shape (T type, Y-shaped, etc.), well-shaped, etc. Moreover, you may have a hollow part in these shapes.

  As for the core-sheath ratio, the thicker the aromatic polyester as the sheath component, the more excellent the moisture and heat decomposability, the strength and the abrasion resistance. On the other hand, the more the proportion of the polylactic acid in the core component, the more environmentally friendly fibers. For this reason, the core-sheath ratio (cross-sectional area ratio) is preferably 20:80 to 80:20, and more preferably 30:70 to 70:30.

  In such a shape, when the thickness of the thickest part of the sheath component is a, the thickness of the thinnest part is b, and the degree of eccentricity is a / b, the degree of eccentricity is 2.0 or less. Among them, it is preferable to set it to 1.5 or less. If the degree of eccentricity is too large, the spinning operability is deteriorated and physical properties such as strength are likely to be lowered.

  In addition, the cross-sectional area of the fiber and the thickness of the core-sheath component were measured from a micrograph by photographing the cross-section of the fiber (cross-section cut perpendicular to the length direction of the fiber) with an optical microscope at a magnification of 500 times. The average value of the number of samples (n = 20).

The polylactic acid composite fiber of the present invention is excellent in moisture and heat resistance. Specifically, as a heat treatment, strength retention after exposure to a high temperature and high humidity environment of 60 ° C. and 90% humidity for 500 hours Is 80% or more.
Here, the strength retention (%) is a value represented by (tensile strength after treatment / tensile strength before treatment) × 100.

In the present invention, the tensile strength of the fiber is measured at a gripping interval of 20 cm using a constant speed extension type tester according to a standard time test of tensile strength and elongation rate of JIS-L1013. Next, after carrying out a wet heat treatment in an environment of 60 ° C. and 90% humidity for 500 hours, the strength of the fiber is obtained again by the same method. And it calculates as follows.
Strength retention (%) = (S / M) × 100
S: Tensile strength (cN / dtex) of polylactic acid composite fiber after exposure treatment
M: Tensile strength (cN / dtex) of polylactic acid composite fiber before exposure treatment

  The strength retention is preferably 80% or more, and more preferably 85% or more. If the strength retention is less than 80%, the strength decreases greatly during washing and ironing for clothing, and during industrial materials usage during exposure to high temperature and high humidity. As a result, the fibers are cut or the quality is deteriorated. By setting the strength retention rate to 80% or more, it can be suitably used as an industrial material application, and can be used for many applications.

  In addition, in the polylactic acid and the aromatic polyester, the heat stabilizer, crystal nucleating agent, matting agent, terminal blocking agent, pigment, light-proofing agent, weathering agent, lubricant, antioxidant are included within the range not impairing the object of the present invention. Agents, antibacterial agents, fragrances, plasticizers, dyes, surfactants, flame retardants, surface modifiers, various inorganic and organic electrolytes, and other similar additives may be added to the fibers.

  And as above-mentioned, the polylactic acid composite fiber of this invention can also be processed into a twisted yarn, a twisted yarn, a false twisted yarn, a draw yarn, a blended yarn, a loop processing yarn, a covering yarn, an interlace yarn, etc. In the case of such a processed yarn, only the polylactic acid composite fiber of the present invention may be used, or it may be mixed with other fibers.

  For example, as other fibers to be mixed, synthetic fibers such as polyester, nylon, acrylic and aramid, rayon fibers such as viscose, cupra and polynosic, solvent-spun cellulose fibers such as lyocell, silk, cotton, hemp, wool and others Of animal hair fibers.

  Among them, the polylactic acid composite fiber of the present invention is preferably subjected to false twisting. As the false twisting method, a belt nip, a disk-type friction false twisting device, a spindle pin type, a turning process using a fluid such as compressed air, and the like can be used.

  In these processing methods, the heating method and surface material of the heater when performing heat treatment are not particularly limited, but it is preferable that ceramic finish is applied to reduce frictional resistance during false twisting. The satin finish reduces the frictional resistance and can suppress the occurrence of fluff and yarn breakage.

  The heat treatment temperature (heater temperature) is preferably 100 to 170 ° C., more preferably 110 to 160 ° C., and more preferably 130 to 150 ° C., although it depends on the melting point of the core and sheath polymers. preferable. When the heat treatment temperature is less than 100 ° C., the heat setting effect is insufficient, the stretchability when woven or knitted is inferior, the texture becomes paper-like and the fabric quality is lowered, which is not preferable. On the other hand, the higher the heat treatment temperature, the more advantageous in terms of heat setting, but if it exceeds 170 ° C, the cross-section of the single yarn is excessively deformed due to softening of the polylactic acid arranged in the core, and the pseudo-fusion-like unsolved Twists are generated. Moreover, since deterioration of the fiber due to heat and a decrease in wet heat resistance proceed, it is not preferable.

  Next, the method for producing the polylactic acid composite fiber of the present invention will be described with reference to production examples in the case of using long fibers. First, polylactic acid and aromatic polyester are respectively introduced into separate extruders, melted, and compositely spun using a conventional composite spinning device. Then, after the spun yarn is cooled and solidified, the POY method of winding as a semi-undrawn yarn without drawing by high-speed spinning of 2000 m / min or higher, or the high-speed spinning method of 2000 m / min or higher, or 2000 m / min. It can be obtained by a two-step method in which melt spinning is performed with a low-speed spinning of less than a minute, and the yarn is once wound up and then the yarn is drawn and heat-treated, or a one-step method in which the yarn is continuously drawn without being drawn once. When stretching is performed, the stretching ratio, temperature, and the like may be set as appropriate according to the physical properties and application of the target fiber.

  When the false twisting is performed, the stretched fiber is wound up once, or subsequently introduced into the false twisting device, and the false twisting is performed. And what is necessary is just to set the heat processing temperature, the number of twists, etc. suitably according to the physical property and use of the target fiber.

  In addition, when setting it as a short fiber, it uses as a fiber bundle which gathered thousands-millions. After melt spinning, cooling, and applying an oil agent, it is once wound without stretching. The undrawn yarn is focused on a bundle of hundreds of thousands to 2 million dtex, drawn at a draw ratio of 2-5 times, a draw temperature of 40-80 ° C., and heat treated at 80-160 ° C. Subsequently, after mechanical crimping by a push-in type crimper, it is cut into a target length with a cutter such as an EC cutter to obtain short fibers.

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, the measurement and evaluation of the characteristic value in an Example were performed as follows.
(1) Intrinsic Viscosity The intrinsic viscosity was determined from the solution viscosity measured at a temperature of 20 ° C. using an equimolar mixture of phenol and ethane tetrachloride as a solvent.
(2) Melting point A differential scanning calorimeter DSC-7 manufactured by Perkin Elmer was used and measured at a heating rate of 20 ° C./min. When the melting point peak was unclear, the temperature at the time of melting was visually measured using a microscope with a hot stage.
(3) Content of L-lactic acid and D-lactic acid The L-lactic acid and D-lactic acid contents were measured by a high performance liquid chromatography method using a mixed solution of ultrapure water and 1N sodium hydroxide in an equal mass as a solvent. Sumichiral OA6100 was used for the column, and it detected with the UV absorption measuring device.
(4) Amount of carboxyl end group 0.1 g of the obtained composite fiber was dissolved in 10 ml of benzyl alcohol, 10 ml of chloroform was added to this solution, and then titrated with a 1/10 N potassium hydroxide benzyl alcohol solution.
(5) Antimony, cobalt and phosphorus contents in fiber After the obtained composite fiber is heated and melted on an aluminum plate, it is formed into a molded body having a flat surface by a compression press machine, and a fluorescent X-ray measuring device (Rigaku Denki Kogyo) Quantitative analysis was performed on a 3270 model.
(6) Core-sheath ratio (cross-sectional area ratio)
Measurement was performed by the method described above.
(7) Strength (Before and after exposure treatment, strength retention)
The obtained conjugate fiber was measured by the method described above. In addition, it measured similarly about the obtained false twisted yarn.
(8) b value (color tone)
The obtained conjugate fiber was knitted in a cylinder, and the b value was measured using a color difference meter CR-100 manufactured by Minolta in an undyed state. In addition, the cylinder knitting was performed at 28 gauge using a single-neck cylinder knitting machine CR-A manufactured by Glory Industries Co., Ltd.
(9) Spinning operability Spinning was performed continuously with 16 spindles for 168 hours, and the following four stages were evaluated according to the number of yarn breakage.
No thread break ◎
1-2 times ○
3-5 times △
6 times or more ×
(10) Iron resistance The obtained composite fiber is knitted in the same manner as in (8), sprayed with water so that the entire knitted fabric is uniformly moistened, and pressed for 15 seconds with an iron set at a surface temperature of 140 ° C The texture after the evaluation was subjected to sensory evaluation in the following three stages.
○: The texture is not cured.
Δ: A slight texture hardening is observed.
X: Curing of considerable texture is seen.
(11) Dyeing spots The obtained conjugate fiber was knitted and dyed in the same manner as in (8), and the presence or absence of the dyeing spots was visually determined and evaluated in the following three stages. The dyeing conditions were as follows: 1.0% omf of Terasil Navy Blue SGL (Ciba Specialty Chemicals dyestuff for raw yarn) and dyeing solution having a bath ratio of 1:50 were dyed by a conventional method at 100 ° C. for 30 minutes.
○: No staining spots are seen.
Δ: Slightly stained spots are observed.
X: Considerable stained spots are seen.
(12) Texture The obtained composite fiber was knitted in the same manner as in (8), treated with boiling water for 30 minutes and then dried, and the texture of the knitted fabric was subjected to sensory evaluation on the basis of the following criteria by 10 panelists. The obtained false twisted yarn was also knitted and evaluated in the same manner.
A: Excellent soft feeling.
○: Excellent soft feeling.
Δ: Slightly soft.
X: A soft feeling is not seen.
(13) False twist operability
False twisting was performed continuously for 24 hours with 24 spindles, and the following four levels were evaluated according to the number of yarn breaks.
○: 0 to 4 times △: 5 to 9 times ×: 10 times or more

Example 1
A slurry of terephthalic acid (TPA) and ethylene glycol (EG) (TPA: EG molar ratio = 1: 1.6) is continuously supplied to the esterification reactor, and the reaction is carried out under conditions of a temperature of 250 ° C and a pressure of 50 hPa. A polyester oligomer having an esterification reaction rate of 95% was continuously obtained for 8 hours. In addition, isophthalic acid (IPA) and EG were supplied to the esterification reactor so that the molar ratio of IPA: EG was 1: 3.5, and the esterification reaction was performed at a temperature of 200 ° C. until the reaction rate reached 95%. A liquid was obtained.
A polyester oligomer and an IPA-EG solution are charged into a polymerization reactor so that the IPA copolymerization amount is 8 mol%, and then, as a catalyst, 150 mass ppm of antimony trioxide with respect to ethylene terephthalate constituting the polyester, cobalt acetate. Was added at 25 ppm by mass, and triethyl phosphate as a phosphorus component was added at 50 ppm by mass. Depressurize the reactor to conduct a polymerization reaction at a final pressure of 0.9 hPa and a temperature of 270 ° C. for 4 hours. Aromatic polyester (copolymerized polyethylene terephthalate) having an intrinsic viscosity of 0.64, a melting point of 230 ° C., and a carboxyl end group content of 12 eq / t Got.
A polylactic acid having a content ratio of L-lactic acid to D-lactic acid of 98.8 / 1.2, a melting point of 170 ° C., and an intrinsic viscosity of 1.88 was used.
Polylactic acid is the core component, aromatic polyester is the sheath component, and the core-sheath ratio (cross-sectional area ratio core: sheath) is 50:50, and is supplied to the compound spinning device and melted at a spinning temperature of 260 ° C. Spinning was performed. The spinneret has 24 spinning holes with a hole diameter of 0.40 mm, and the spun yarn is cooled by an air flow and passed through an oiling device so that an oil agent is applied so that the amount of adhesion is 0.5 mass%. And focused with a focusing guide. Subsequently, the yarn was taken up by a roller having a speed of 3000 m / min, and then taken up by a take-up machine to obtain a 122 dtex semi-undrawn yarn.
The obtained yarn was drawn at a drawing speed of 667 m / min, a draw ratio of 1.51, a preheating roller temperature of 90 ° C., and a heat setting temperature of 150 ° C. to obtain 84 dtex / 24fil polylactic acid composite fiber.

Examples 2-3 and Comparative Example 1
The same procedure as in Example 1 was performed except that the core-sheath ratio of the composite fiber was changed as shown in Table 1.

Example 4
The aromatic polyester is made of copolymerized polyethylene terephthalate with a carboxylic acid component of 80 mol% terephthalic acid and 20 mol% isophthalic acid, an intrinsic viscosity of 0.62, a melting point of 200 ° C, and a carboxyl end group content of 13 eq / t. It implemented like Example 1 except having changed into 240 degreeC.

Example 5
Aromatic polyester, carboxylic acid component terephthalic acid 100 mol%, glycol component EG94 mol%, cyclohexanedimethanol (CHDM) 6 mol%, limiting viscosity 0.61, melting point 255 ° C, carboxyl end group amount 13eq This was carried out in the same manner as in Example 1 except that / t copolymerized polyethylene terephthalate was used and the spinning temperature was changed to 270 ° C.

Example 6
The same procedure as in Example 1 was performed except that the addition amount of cobalt acetate during polymerization was 2 ppm by mass with respect to ethylene terephthalate constituting the polyester.

Comparative Example 2
The same procedure as in Example 1 was performed except that the amount of antimony trioxide added during polymerization was 1500 ppm by mass with respect to ethylene terephthalate constituting the polyester.

Comparative Example 3
The same procedure as in Example 1 was performed except that the amount of antimony trioxide added during polymerization was 15 ppm by mass with respect to ethylene terephthalate constituting the polyester.

Comparative Example 4
The same procedure as in Example 1 was performed except that the addition amount of cobalt acetate at the time of polymerization was 250 ppm by mass with respect to ethylene terephthalate constituting the polyester.

Comparative Example 5
The same procedure as in Example 1 was conducted except that the amount of triethyl phosphate added during polymerization was 5000 ppm by mass with respect to ethylene terephthalate constituting the polyester.

Comparative Example 6
The same procedure as in Example 1 was conducted except that the amount of triethyl phosphate added during polymerization was 2.5 ppm by mass with respect to ethylene terephthalate constituting the polyester.

Comparative Example 7
This was carried out in the same manner as in Example 1 except that polylactic acid alone was supplied to a single component spinning apparatus, melt spinning was performed at a spinning temperature of 220 ° C., and single component fiber containing only polylactic acid was obtained.

Comparative Example 8
The aromatic polyester is 70% by mole of terephthalic acid and 30% by mole of isophthalic acid as the carboxylic acid component, copolymerized polyethylene terephthalate having an intrinsic viscosity of 0.61, melting point of 130 ° C, and carboxyl end group content of 15 eq / t, and spinning temperature. It implemented similarly to Example 1 except having changed into 235 degreeC.

  Table 1 shows the characteristic values and evaluation results of the polylactic acid composite fibers obtained in Examples 1 to 6 and Comparative Examples 1 to 6 and 8, and the polylactic acid fiber obtained in Comparative Example 7.

As is clear from Table 1, the polylactic acid composite fibers obtained in Examples 1 to 6 have both high strength and strength retention, good color tone (low b value), spinning operability and ironing resistance. , Texture and dyeability were excellent.
On the other hand, since the ratio of the sheath component of the fiber of Comparative Example 1 was too small, the fiber of Comparative Example 7 was composed only of polylactic acid. Therefore, both the strength retention was low, and the iron resistance, texture, and dyeability were low. All of the evaluations were low. In the fibers of Comparative Examples 2 to 6, the content of antimony compound, cobalt compound and phosphorus compound in the fiber was not appropriate, and the amount of carboxyl end groups was high. Therefore, all had low strength retention, spinning operability and iron resistance. , Texture and dyeability were low. In the fiber of Comparative Example 8, the aromatic polyester of the sheath component had many copolymerization components and had a low melting point, so that the strength retention was low, the spinning operability was poor, the iron resistance, the texture, and the dyeability. The evaluation was also low.

Examples 7-9, 12 Comparative Examples 9-14
For the polylactic acid composite fibers obtained in Examples 1 to 3 and 6 and Comparative Examples 1 to 6, using a spindle pin type false twisting device (LS-6 type manufactured by Mitsubishi Heavy Industries), false twisting speed of 100 m / min. Then, false twisting was performed under the conditions of a heat treatment temperature of 140 ° C., a twist number of 3050 TM, and an overfeed rate of 0.5% to obtain false twisted yarn.

Example 10
The polylactic acid composite fiber obtained in Example 4 was subjected to false twisting in the same manner as in Example 7 except that the heat treatment temperature during false twisting was changed to 130 ° C. to obtain false twisted yarn.

Example 11
The polylactic acid composite fiber obtained in Example 5 was false twisted in the same manner as in Example 7 except that the heat treatment temperature during false twisting was changed to 150 ° C. to obtain false twisted yarn.

Comparative Example 15
The polylactic acid fiber obtained in Comparative Example 7 was subjected to false twisting in the same manner as in Example 7 except that the heat treatment temperature during false twisting was changed to 110 ° C. to obtain false twisted yarn.

Comparative Example 16
The polylactic acid composite fiber obtained in Comparative Example 8 was subjected to false twisting in the same manner as in Example 7 except that the heat treatment temperature during false twisting was changed to 125 ° C. to obtain false twisted yarn.

  Table 2 shows the characteristic values and evaluation results of false twisted yarns obtained in Examples 7 to 12 and Comparative Examples 9 to 16.

As is apparent from Table 2, the false twisted yarns obtained in Examples 7 to 12 were both high in strength and strength retention, and excellent in both false twist operability and texture.
On the other hand, since the false twisted yarns of Comparative Examples 9 to 16 were made using the fibers of Comparative Examples 1 to 8, both the strength and strength retention were low, and the false twist operability and texture were inferior.

Claims (4)

A core-sheath type composite fiber comprising polylactic acid as a core component and an aromatic polyester in which ethylene terephthalate as a main repeating unit accounts for 80 mol% or more as a sheath component, and a core-sheath ratio (cross-sectional area ratio core: sheath) 20:80 to 80:20, and a polylactic acid composite fiber characterized by having a strength retention of 80% or more after being exposed for 500 hours in an environment of a temperature of 60 ° C. and a humidity of 90% .
Here, the strength retention (%) is a value represented by (tensile strength after exposure treatment / tensile strength before exposure treatment) × 100. The polylactic acid composite fiber according to claim 1, wherein the amount of carboxyl end groups of the whole fiber is 35 eq / t or less. The polylactic acid composite fiber according to any one of claims 1 to 2, wherein the fiber contains an antimony compound, a cobalt compound, and a phosphorus compound that simultaneously satisfy the following formulas (1) to (3).
(1) 15 ≦ [Sb] ≦ 360
(2) 2.5 ≦ [Co] ≦ 60
(3) 2.0 ≦ [P] ≦ 1600
Here, [Sb] represents the content of the antimony compound, [Co] represents the content of the cobalt compound, and [P] represents the content of the phosphorus compound, and the unit is ppm by mass. The polylactic acid composite fiber according to any one of claims 1 to 3, wherein false twisting is applied.