JP4605640B2 - Method for producing polylactic acid fiber - Google Patents

Description

The present invention relates to a method for producing polylactic acid fibers. More specifically, the present invention relates to a method for producing high-strength and heat-resistant polylactic acid fibers.

  Conventionally, polyethylene, polypropylene, polyester, polyamide, and the like have been used as materials for fibers and molded products, and consumption has been increasing year by year. Along with this, the amount of waste after use has also increased. Since these wastes are currently disposed of by incineration or landfill, various environmental problems and problems such as securing a disposal site have occurred.

  In order to cope with such problems, in recent years, various kinds of fibers using various biodegradable polymers that decompose resins under natural environment by the action of microorganisms existing in soil or water have been actively studied. ing. Among them, fibers using poly-L-lactic acid have relatively high melting points and crystallinity, and have excellent characteristics such as high strength and elastic modulus when used as fibers. As a result, studies for industrial production have been actively conducted.

  However, the melting point of poly L-lactic acid is about 170 ° C., and when used as clothing fibers, the ironable temperature is limited to low temperatures, and when used as industrial fibers, rubber materials, resin-coated fabrics, etc. There has been a problem that it is not suitable for applications exposed to high temperatures of about 150 ° C. in the manufacturing process.

  On the other hand, lactic acid has optical isomers. When a stereocomplex crystal composed of a mixture of poly (L-lactic acid) and poly (D-lactic acid), which is a polymer of L-lactic acid and D-lactic acid, is formed, poly (L-lactic acid) is formed. Alternatively, it is known that the melting point is higher than that of poly D-lactic acid single crystal. Patent Document 1 discloses, for the first time, that the above unique characteristics are industrially utilized by blending poly-L-lactic acid and poly-D-lactic acid. There is no suggestion. Further, Patent Document 2 discloses a technique for blending poly L-lactic acid and poly D-lactic acid in a solution state and then subjecting to solution spinning. However, in this method, the stability of the blended solution is low, and pot life Has a problem in that stable yarn production cannot be performed due to the short length of the fiber, and the resulting fibers lack quality, or the winding speed is at most several tens of meters / minute, and industrially efficient production cannot be performed. . Furthermore, Patent Document 3 discloses an example of melt spinning using a composition containing equimolar amounts of poly L-lactic acid and poly D-lactic acid, but the physical properties of the obtained fiber are at most 0.5 cN. / DTex, which has not led to a fiber having practical strength.

  Furthermore, Yamane et al. Of Kyoto Institute of Technology polylactic acid fibers containing stereocomplex crystals by heat-treating unstretched yarn obtained by melt spinning a melt blend of poly-L-lactic acid and poly-D-lactic acid or by stretching the stretched yarn obtained by stretching this. (Sen-i Gakkai Preprints 1989). However, in this method, the poly L-lactic acid molecule and the poly D-lactic acid molecule are not sufficiently dispersed as the internal structure of the undrawn yarn and the drawn yarn, and a domain structure is partially formed. In order to produce and grow, it is necessary to heat-treat at 200 ° C. for 2 to 10 minutes after yarn production. For this reason, the molecular orientation inside the fiber is relaxed during the heat treatment, and the strength of the obtained fiber remains at most about 2.3 cN / dTex. In addition, the drawn yarn before the heat treatment can obtain a strength of 4.2 cN / dTex, but a large amount of poly L-lactic acid or poly D-lactic acid single crystal is present, and the formation of stereocomplex crystals is insufficient. Sex was insufficient.

  Patent Document 4 and Patent Document 5 disclose a method of heating and melting a mixture of poly L-lactic acid and poly D-lactic acid or a method of obtaining a highly crystallized polylactic acid molded product by heating and melting each of them and then mixing them. However, there is no specific suggestion regarding fiberization.

As described above, various attempts have been made to obtain a high-strength and high-heat-resistant polylactic acid fiber, but the actual situation has not yet been achieved.
JP-A-61-36321 JP-A 63-264913 JP 63-24014 A Japanese Patent Laid-Open No. 9-25400 JP 2000-17164 A "Sen-i Gakkai Preprints 1989" The Japanese Textile Society, 1989

An object of the present invention is to provide a method for producing a polylactic acid fiber, which could not be achieved by the prior art as described above, and which can provide a high-strength and high-heat-resistant polylactic acid fiber that can be produced with high industrial efficiency. There is to do .

The method for producing a polylactic acid fiber of the present invention for solving the above problems mainly has the following configuration. That is, it is characterized in that a blend of poly L-lactic acid and poly D-lactic acid is melt-spun under the following conditions, once wound or continuously stretched without being wound, and subsequently heat treated at 120 to 180 ° C. It is the manufacturing method of polylactic acid fiber made into.
Blend ratio: poly L-lactic acid / poly D-lactic acid = 30/70 to 70/30
Take-up speed: ≧ 300 m / min Spinning draft: ≧ 50

The polylactic acid fiber obtained by the method for producing a polylactic acid fiber of the present invention is an unprecedented polylactic acid fiber having both high strength and high heat resistance and high quality, and is widely suitable and useful for clothing and industrial use. .
Furthermore, the present invention is a melt spinning method and can be efficiently industrially produced.

Next, the manufacturing method of the polylactic acid fiber of this invention is demonstrated in more detail.
The method for producing polylactic acid fiber of the present invention is characterized by comprising a blend of poly L-lactic acid and poly D-lactic acid.

  The production method of poly L-lactic acid and poly D-lactic acid is a two-stage lactide method in which L-lactic acid or D-lactic acid is used as a raw material to once form lactide which is a cyclic dimer, and then ring-opening polymerization is performed. A one-step direct polymerization method in which the raw material is directly subjected to dehydration condensation in a solvent is known. The polylactic acid used in the present invention may be obtained by any method. In the case of a polymer obtained by the lactide method, the cyclic dimer contained in the polymer is vaporized at the time of melt spinning to cause yarn unevenness. Therefore, the cyclic dimer contained in the polymer at a stage before melt spinning. The content of is desirably 0.3 wt% or less. In the case of the direct polymerization method, there is substantially no problem due to the cyclic dimer.

  The poly L-lactic acid used in the present invention is a polymer having L-lactic acid as a main monomer component, and may be a copolymer poly L-lactic acid containing 15 mol% or less of D-lactic acid component in addition to L-lactic acid. Although good, from the viewpoint of enhancing the formation of stereocomplex crystals, the smaller the D-lactic acid component in the poly L-lactic acid, the more preferable, and the use of homopoly L-lactic acid is more preferable.

  Similarly, poly-D-lactic acid used in the present invention is a polymer containing D-lactic acid as a main monomer component, and is a copolymer poly-D-lactic acid containing 15 mol% or less of L-lactic acid component in addition to D-lactic acid. However, from the viewpoint of enhancing the formability of stereocomplex crystals, the smaller the L-lactic acid component in the poly D-lactic acid, the more preferable, and the use of homopoly D-lactic acid is more preferable.

  Furthermore, the poly L-lactic acid and / or poly D-lactic acid used in the present invention may be copolymerized with other monomer components having ester-forming ability as long as the effects of the present invention are not impaired. Examples of copolymerizable monomer components include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, hydroxycarboxylic acids such as 6-hydroxycaproic acid, ethylene glycol, propylene glycol, butanediol, Compounds containing a plurality of hydroxyl groups in the molecule such as neopentyl glycol, polyethylene glycol, glycerin, pentaerythritol or their derivatives, succinic acid, adipic acid, sebacic acid, fumaric acid, terephthalic acid, isophthalic acid, 2,6 -Compounds containing a plurality of carboxylic acid groups in the molecule, such as naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, 5-tetrabutylphosphonium sulfoisophthalic acid, or derivatives thereof.

  The above-mentioned poly L-lactic acid and poly D-lactic acid preferably have a weight average molecular weight of 50,000 or more, more preferably 100,000 or more, more preferably 150,000 or more. When the weight average molecular weight is less than 100,000, it is difficult to make the fiber excellent in strength properties, which is not preferable. In general, it is difficult to set the average molecular weight of poly L-lactic acid or poly D-lactic acid to 500,000 or more.

  The poly L-lactic acid and poly D-lactic acid used in the present invention may contain components other than the main polymer within a range not impairing the effects of the present invention. For example, inorganic fine particles or organic compounds may be added as necessary as plasticizers, UV stabilizers, matting agents, deodorants, flame retardants, yarn friction reducing agents, antioxidants, or coloring pigments. In particular, benzophenone, benzotriazole, and hindered amine agents can be preferably used as the ultraviolet stabilizer. The blending amount at this time is preferably 0.005 to 1.0 wt% with respect to the fiber weight. Color pigments include inorganic pigments such as titanium oxide and carbon black, as well as cyanine, styrene, phthalocyanine, anthraquinone, perinone, isoindolinone, quinophthalone, quinocridone, and thioindigo. Things can be used.

Further, the polylactic acid fiber obtained by the present invention has a strength of 2.6 cN / dTex or more, preferably 3.5 cN / dTex or more, more preferably 4.8 cN / dTex or more. When widely used for clothing or industrial use, the strength is practically insufficient unless the strength is less than 2.6 cN / dTex. Furthermore, from the same viewpoint, in the polylactic acid fiber obtained by the present invention, the birefringence Δn is preferably 18 × 10 ⁻³ or more, and more preferably 22 × 10 ⁻³ or more.

Method for producing a polylactic acid fiber of the present invention is shall by the melt spinning method. In the case of solution spinning such as dry or wet, industrially efficient production cannot be performed, and the stability of the solution obtained by blending poly-L-lactic acid and poly-D-lactic acid is low and the pot life is short. As a result, the resulting fibers cannot be produced.

Stereocomplex consisting endotherm ΔHl with poly L- lactic acid and poly D- lactic acid based on the crystal fusion of the obtained polylactic L- lactic acid alone crystalline and poly D- lactic acid alone crystals by DSC measurement is obtained from an polylactic acid fiber of the present invention The ratio [Delta] Hh / [Delta] Hl of the endothermic amount [Delta] Hh based on crystal melting of the crystal is 10 or more, preferably [Delta] Hh / [Delta] Hl is 20 or more, more preferably [Delta] Hh / [Delta] Hl is 30 or more. In the case of polylactic acid fibers made of a blend of homopoly L-lactic acid and homopoly D-lactic acid, the peak temperature of ΔHl is around 160 to 180 ° C., and the peak temperature of ΔHh is around 210 ° C. to 230 ° C. There are many cases. Further, when ΔHh / ΔHl is less than 10, since the formation of stereocomplex crystals is insufficient, the fiber is thermally deformed at the melting temperature of the poly L-lactic acid single crystal or the poly D-lactic acid single crystal, resulting in heat resistance. The property becomes insufficient.

Furthermore, from the viewpoint of suppressing yarn slack in processes such as drawing, relaxation, and heat treatment at the time of yarn production, and ensuring setability in the finishing process of the fabric, the polylactic acid fiber obtained by the present invention has a boiling water shrinkage ratio Sb of 3%. Preferably, it is preferably 5% or more.

Polylactic acid fiber manufacturing method of the present invention can be, for example, the following method. The method for obtaining the polylactic acid fiber of the present invention is not limited to the method described below.

  The polylactic acid fiber of the present invention can be obtained by subjecting a blend of poly L-lactic acid and poly D-lactic acid to ordinary melt spinning. As a blending method of poly L-lactic acid and poly D-lactic acid, for example, there is a method in which a chip blend (dry blend) product of poly L-lactic acid chips and poly D-lactic acid chips is subjected to melt spinning. Can use a normal melt extruder such as a pressure melter type or a single-screw or twin-screw extruder type. However, it is easy to form a stereocomplex crystal by sufficiently kneading poly L-lactic acid and poly D-lactic acid. 1-axis or 2-axis extruder type is preferred. Furthermore, a method of incorporating a static kneader into the polymer flow path, a chip blend of a poly L-lactic acid chip and a poly D-lactic acid chip is melted and kneaded in a biaxial extruder type kneader and then formed into chips. A method in which a chip made of a blend of poly L-lactic acid and poly D-lactic acid pre-kneaded in advance is prepared in advance, and the pre-kneaded chip is subjected to melt spinning is preferable. Alternatively, poly L-lactic acid and poly D-lactic acid may be mixed after being melted in separate melt extruders. In any of the above cases, kneading is expected due to the shear stress when passing through the filtration layer or the spinneret, but especially when poly-L-lactic acid and poly-D-lactic acid are mixed after being melted in separate melt extruders, they are kneaded. From the viewpoint of strengthening, it is preferable to incorporate a static kneader after mixing.

The blend ratio of poly L-lactic acid and poly D-lactic acid used in the method for producing polylactic acid fiber of the present invention is a weight ratio of poly L-lactic acid: poly D-lactic acid between 30:70 and 70:30. However, from the viewpoint of promoting the formation of stereocomplex crystals and improving the content ratio, it is preferably between 40:60 and 60:40, and more preferably 50:50.

  After the above blend of poly-L-lactic acid and poly-D-lactic acid is melted by an extruder type or pressure melter type melt extruder, it is measured by a metering pump and filtered in a spinning pack or the like. , And discharged from a base having a desired base shape and the number of bases. The discharged yarn is cooled and solidified by passing through a gas having a temperature lower than the melting point of the polymer, and then taken up by applying an oil agent. By increasing the molecular orientation during spinning, polylactic acid stereocomplex crystals Since it becomes easy to form, it is preferable to take over at 300 m / min or more. From the same viewpoint, the spinning draft is preferably 50 or more. Moreover, it is preferable to use an airflow suction device in order to remove the sublimate from the discharged yarn at the upstream side of cooling or at the cooling section. Furthermore, it is preferable from the viewpoint of increasing the strength of the fiber that a heating zone is provided immediately before spinning and before cooling and solidification to heat the yarn to a temperature higher than the melting point of the polymer. For cooling, either a circular chimney or a uniflo chimney can be used. The undrawn yarn taken up is then subjected to drawing. Either a two-step method of winding once before stretching or a direct spinning stretching method in which stretching is performed without winding after spinning may be used, but from the viewpoint of productivity, the direct spinning stretching method may be used. Is preferred.

  The stretching step may be a single step or a multi-stage of two or more stages, but it is preferable to perform a multi-stage stretching of two or more stages from the viewpoint of increasing the strength. Further, if the draw ratio is too high, a fiber whitening phenomenon occurs and the strength decreases. Therefore, it is preferable to set the draw ratio so that the fiber whitening phenomenon does not occur. As the stretching heat source, any commonly used method may be employed. For example, a hot roller, a contact hot plate, a non-contact hot plate, a heat medium bath, a pin, or the like may be used.

  Subsequent to stretching, it is preferable to perform heat treatment at a temperature lower by about 10 to 80 ° C. than the melting point of the polymer before winding. Arbitrary methods, such as a hot roller, a contact-type hot plate, and a non-contact type hot plate, can be adopted for the heat treatment. From the viewpoint of dimensional stability, it is preferable that a relaxation treatment of 0 to 20% is performed subsequent to the heat treatment.

In the polylactic acid fiber obtained by this invention, arbitrary forms, such as a monofilament, a multifilament, a staple, and a nonwoven fabric, can be selected according to a use. When used as a multifilament, the single fiber fineness may be selected in accordance with the use form, but it is usually preferably 0.1 dTex or more and 22 dTex or less. Moreover, it is preferable that the total fineness of a multifilament shall be 5 dTex or more and 3330 dTex or less. Furthermore, the cross-sectional shape is arbitrary such as round, flat, hollow, Y-type, T-type, and polygonal, but a round cross-section is preferable from the viewpoint of easily achieving high strength.

  Hereinafter, based on an Example, this invention is demonstrated more concretely.

  In addition, the physical property in an Example is the value measured with the following method.

(1) Strength Te (cN / dtex):
Using a “Tensilon” tensile tester type manufactured by Orientec Co., Ltd., the sample length was 25 cm and the tensile speed was 30 cm / min.

(2) Birefringence Δn:
Using a BH-2 polarizing microscope manufactured by OLYMPUS Co., Ltd., the wavelength of the light source was adjusted to 589 nm with a filter and measured by the compensator method.

(3) Boiling water shrinkage ratio Sb (%):
When the yarn to be measured is treated under normal pressure in boiling water for 15 minutes with no load, the yarn length before and after treatment is measured under a load of 0.0882 cN / dTex, and the yarn length before treatment is measured. The shrinkage ratio of the yarn length was obtained.

(4) Endothermic quantity ΔHl (J / g) based on crystal melting of poly L-lactic acid single crystal and poly D-lactic acid single crystal and absorption based on crystal melting of stereocomplex crystal composed of poly L-lactic acid and poly D-lactic acid Amount of heat ΔHh (J / g):
Using a “SSC5200 / DSC120” differential scanning calorimeter manufactured by Seiko Denshi Kogyo Co., Ltd., it was obtained from a DSC curve obtained by measuring at a temperature rising rate of 10 ° C./min.

(5) 200 ° C. heat resistance:
A fabric of 10 cm square was formed using the fiber to be tested, and the state of the fabric after being brought into contact with an iron whose temperature was adjusted to 200 ° C. for 30 seconds was observed.
A: The shape of the fabric before treatment was maintained without heat fusion between single yarns.
X: Thermal fusion between single yarns, thermal deformation or thermal melting of the fabric was observed.

Example 1
L-lactide was mixed with 150 ppm of tin octylate, polymerized in a reaction vessel equipped with a stirrer for 10 minutes at 192 ° C. in a nitrogen atmosphere, further chipped with a twin-screw kneading extruder, and then in a nitrogen atmosphere at 140 ° C. Was subjected to solid-phase polymerization to obtain a poly L-lactic acid homopolymer (PLLA1) chip having a melting point of 176 ° C. and a weight average molecular weight of 151,000. As the poly D-lactic acid homopolymer, a poly D-lactic acid (PDLA) chip manufactured by PURAC having a weight average molecular weight of 302,000 was used. This PLLA1 and PDLA are chip-blended in a weight ratio of PLLA1: PDLA = 50/50, then dried under reduced pressure at 100 ° C. for 12 hours, melt-kneaded and chipped with a twin-screw kneading extruder, and PLLA1 (50 parts) And a pre-kneading chip of a mixture consisting of PLDA (50 parts).

This pre-kneaded chip is dried under reduced pressure at 100 ° C. for 12 hours, melt melt extruded using a pressure melter type melt spinning machine, melted at a spinning temperature of 260 ° C., and spun from a die having twelve 0.3φ discharge holes. Immediately after passing through an atmosphere in a heating cylinder having a length of 100 mm and a temperature of 280 ° C., cooling with a chimney wind at a wind speed of 30 m / min, applying an oil agent, and taking it out at a speed of 1000 m / min, 84 dTex / 12 fil. The undrawn yarn was once wound up. This unstretched yarn was stretched by one stage using a pair of Nelson rollers at 80 ° C. and 120 ° C. for a total draw ratio of 2.8 times, and the drawn yarn was wound up. The evaluation results of the drawn yarn are shown in Table 1.
The drawn yarn wound up had sufficient strength for practical use, and further had good heat resistance as can be seen from the results of the 200 ° C. heat resistance test.

(Example 2)
In the same manner as in Example 1, 84 dTex / 12 fil of undrawn yarn was once wound. The undrawn yarn was stretched in two stages using three pairs of Nelson rollers at 80 ° C., 120 ° C., and 180 ° C. with a total draw ratio of 3.6 times, and the drawn yarn was wound up. The evaluation results of the drawn yarn are shown in Table 1.
The drawn yarn wound up had sufficient strength for practical use, and further had good heat resistance as can be seen from the results of the 200 ° C. heat resistance test.

(Example 3)
The same PLLA1 chip and PDLA chip as in Example 1 were prepared, the PLLA1 and PDLA were chip-blended at a weight ratio of PLLA: PDLA = 50/50, and then dried under reduced pressure at 100 ° C. for 12 hours. Without preparing a pre-kneading tip from this blend tip, the two are melted and kneaded by using a uniaxial extruder type melt spinning machine with a cylinder temperature of 260 ° C., and discharged, cooled and taken off under the same conditions as in Example 1. The undrawn yarn of 84dTex / 12fil was once wound up. The undrawn yarn was stretched in two stages using three pairs of Nelson rollers at 80 ° C., 120 ° C., and 180 ° C. with a total draw ratio of 3.0, and the drawn yarn was wound up. The evaluation results of the drawn yarn are shown in Table 1.
The drawn yarn wound up had sufficient strength for practical use, and further had good heat resistance as can be seen from the results of the 200 ° C. heat resistance test.

(Example 4 )
A drawn yarn was produced in the same manner as in Example 1 except that the weight ratio of PLLA1 and PDLA was PLLA1: PDLA = 60/40. The evaluation results of the drawn yarn are shown in Table 1. The wound drawn yarn had sufficient strength for practical use, and also had good heat resistance as can be seen from the results of the 200 ° C. heat resistance test.

(Comparative Example 1)
A drawn yarn was produced in the same manner as in Example 1 except that the weight ratio of PLLA to PDLA was PLLA1: PDLA = 100/0 (homopoly L-lactic acid chip was subjected to melt spinning). The evaluation results of the drawn yarn are shown in Table 1.
The wound drawn yarn had sufficient strength for practical use, but the heat resistance was insufficient as can be seen from the results of the 200 ° C. heat resistance test.

(Comparative Example 2)
A drawn yarn was produced in the same manner as in Example 1 except that the weight ratio of PLLA and PDLA was PLLA1: PDLA = 80/20. The evaluation results of the drawn yarn are shown in Table 1.
The wound drawn yarn had sufficient strength for practical use, but the heat resistance was insufficient as can be seen from the results of the 200 ° C. heat resistance test.

(Comparative Example 3)
An 84 dTex / 12 fil undrawn yarn was once wound in the same manner as in Example 1 except that the undrawn yarn was wound at a spinning speed of 50 m / min. The undrawn yarn was subjected to two-stage drawing using three pairs of Nelson rollers at 80 ° C., 120 ° C., and 180 ° C., respectively, and the drawn yarn was wound up. The evaluation results of the drawn yarn are shown in Table 1.
Although the wound drawn yarn had sufficient strength for practical use, the heat resistance was insufficient as can be seen from the result of the 200 ° C. heat resistance test.

(Comparative Example 4)
After winding the drawn yarn in the same manner as in Comparative Example 3, a constant-length heat treatment was performed for 5 minutes using a dry heat oven in which the processing chamber temperature was adjusted to 200 ° C. The evaluation results of the drawn yarn are shown in Table 1.
The wound drawn yarn had good heat resistance as can be seen from the result of the 200 ° C. heat resistance test, but the strength was as low as 1.8 cN / dTex, which was insufficient in practice.

Claims (3)

A blend of poly-L-lactic acid and poly-D-lactic acid is melt-spun under the following conditions, and once wound up, stretched or continuously stretched without winding, and subsequently heat treated at 120 to 180 ° C. A method for producing a polylactic acid fiber.
Blend ratio: poly L-lactic acid / poly D-lactic acid = 30/70 to 70/30
Take-up speed: ≧ 1000 m / min Spinning draft: ≧ 50   The method for producing a polylactic acid fiber according to claim 1, wherein the weight average molecular weights of poly L-lactic acid and poly D-lactic acid used for melt spinning are 5 to 500,000.   The method for producing polylactic acid fibers according to claim 1 or 2, wherein the content of the cyclic dimer of poly L-lactic acid used for melt spinning is 0.3 wt% or less.