JP4483956B2 - Method for producing polylactic acid fiber - Google Patents

Description

  The present invention relates to an efficient method for producing polylactic acid fibers excellent in strength at 25 ° C. and high-temperature mechanical properties.

  Recently, there has been a strong demand for the development of polymer materials that can be decomposed in the natural environment in response to environmental problems on a global scale, and research and development of various polymers such as aliphatic polyesters and attempts to put them into practical use are active. It has become. Attention has been focused on polymers that are degraded by microorganisms, that is, biodegradable polymers.

  On the other hand, most of the conventional polymers are made from petroleum resources, but they have been stored in the ground since the geological era due to the fact that the petroleum resources will be depleted in the future and that they are consumed in large quantities. There is concern that carbon dioxide will be released into the atmosphere and global warming will become more serious. However, if a polymer can be synthesized using plant resources that grow by taking in carbon dioxide from the atmosphere, it is possible not only to suppress global warming by carbon dioxide circulation, but also to solve the problem of resource depletion at the same time. . For this reason, attention has been focused on polymers using plant resources as raw materials, that is, polymers using biomass.

  From the above two points, biodegradable polymers using biomass attract great attention and are expected to replace conventional polymers made from petroleum resources. However, biodegradable polymers using biomass generally have problems such as low mechanical properties and heat resistance and high cost. As a biodegradable polymer using biomass that can solve these problems, polylactic acid is currently attracting the most attention. Polylactic acid is a polymer made from lactic acid obtained by fermenting starch extracted from plants. Among biodegradable polymers using biomass, it has the best balance of mechanical properties, heat resistance, and cost. And development of the fiber using this is performed at a rapid pitch.

  The development of polylactic acid fiber is preceded by agricultural materials and civil engineering materials that make use of biodegradability, but the use of clothing and industrial materials is expected as the subsequent large-scale applications. In particular, high-strength polylactic acid fibers are required for industrial material applications, and examples of the production method include a method of applying high-strength fibers such as polyethylene terephthalate (PET) and nylon, which are general-purpose synthetic fibers, to polylactic acid. It is done. However, this manufacturing method is premised on multi-stage stretching, and the capital investment is large, and since a plurality of high-temperature, large-diameter Nelson-type hot rollers are used, it becomes an energy-intensive process, resulting in high costs. It was. For this reason, for example, as described in Patent Document 1 and the like, an energy saving type using a hot plate other than the final heat treatment has been proposed. However, since the number of rollers is increased, high efficiency and low cost are not required. It was enough. Further, since a hot plate is used as a heating means, there is a problem that fluff and yarn breakage frequently occur when the drawing speed is increased. On the other hand, Patent Document 2 describes that high-strength polylactic acid fibers can be obtained even by one-stage drawing, but since the draw ratio is too high with respect to the elongation of the undrawn yarn, yarn breakage frequently occurs due to excessive deformation. There was a problem that the thread spots became large.

  In addition, in the conventional method for producing high-strength polylactic acid fiber, although a product having a high strength at room temperature (25 ° C.) was obtained, there was a problem that the high-temperature mechanical properties were low. Here, the poor high-temperature mechanical properties indicate that the polylactic acid polymer softens rapidly when it exceeds 60 ° C. which is the glass transition temperature (Tg) of the polylactic acid polymer. In fact, when the tensile test of polylactic acid fiber is performed at different temperatures, it softens rapidly from around 70 ° C, shows a shape close to flow at 90 ° C, and not only lowers strength but also greatly reduces mechanical dimensional stability. (FIG. 5). On the other hand, in nylon 6, which is a conventional polymer, such a softening phenomenon is gradual and exhibits sufficient mechanical properties even at 90 ° C. (FIG. 5).

  Thus, since polylactic acid fibers have poor high-temperature mechanical properties, various problems have actually occurred. For example, when used for warp of a woven fabric, the yarn is glued for the purpose of improving the weaving property of the yarn and improving the weaving property. Will occur. In addition, when false twist is applied to the polylactic acid fiber, the yarn softens rapidly on the hot plate, so the yarn does not twist and the crimp characteristics are inferior, and the yarn breaks on the hot plate, False twisting itself may be difficult. Furthermore, due to such troubles on the hot plate, the hot plate temperature can only be raised up to 110 ° C, and not only the crimping property is low due to insufficient heat setting, but also the shrinkage rate of the yarn in boiling water. It is also difficult to reduce (boiling) to 20% or less, which is a practical level.

For this reason, a high-efficiency and low-cost process for obtaining polylactic acid fibers having high strength at 25 ° C. and excellent high-temperature mechanical properties has been desired.
JP 2000-248426 A Japanese Patent Laid-Open No. 8-222016

  The present invention provides an efficient method for producing polylactic acid fibers having strength at 25 ° C. and excellent high-temperature mechanical properties.

The above object is characterized in that, when a polylactic acid undrawn yarn having a crystal size of 6 nm or more is drawn, the drawing temperature is 85 ° C. or more, the heat treatment temperature is 120 ° C. or more, and the draw ratio (DR) is in the following range. In the production method of lactic acid fibers, or when a polylactic acid undrawn yarn having a crystal size of less than 6 nm is drawn to obtain a drawn yarn having a strength at 25 ° C. of 4.0 cN / dtex or more , the drawing temperature is 130 ° C. or more, the heat treatment temperature Is achieved by a method for producing polylactic acid fibers, characterized in that the stretching ratio (DR) is in the following range.
0.90+ (Undrawn yarn elongation / 100%) ≦ DR ≦ 2.0 + (Undrawn yarn elongation / 100%)

  The polylactic acid fiber having a novel structure of the present invention can greatly improve the high-temperature mechanical properties, solve problems in false twisting and weaving processes, and greatly expand the application development of polylactic acid fiber. be able to.

  The polylactic acid referred to in the present invention refers to a polymerized lactic acid, and the optical purity of the L-form or D-form is preferably 90% or higher because of its high melting point. In the present invention, L-form or D-form having an optical purity of 97% or more is called homopolylactic acid. Moreover, in the range which does not impair the property of polylactic acid, you may copolymerize components other than lactic acid, or may contain additives, such as a polymer other than polylactic acid, particle | grains, a flame retardant, and an antistatic agent. However, from the viewpoint of biomass utilization and biodegradability, it is important that the lactic acid monomer is 50% by weight or more as a polymer. The lactic acid monomer is preferably 75% by weight or more, more preferably 96% by weight or more. Further, the molecular weight of the polylactic acid polymer is preferably 50,000 to 500,000 in terms of weight average molecular weight, because the balance between mechanical properties and yarn-making property is good.

  In the present invention, it is preferable to use one-stage stretching / heat treatment from the viewpoint of suppressing equipment costs and energy consumption, but it is of course possible to perform multi-stage stretching as necessary. However, it is important to adopt the following drawing conditions in view of the quality and performance of the yarn obtained.

  In the first method of the present invention, when a polylactic acid undrawn yarn having a crystal size of 6 nm or more is drawn, the drawing temperature is 85 ° C. or more, the heat treatment temperature is 120 ° C. or more, and the draw ratio (DR) is 0.90+ (not yet). A method of producing polylactic acid fibers, characterized in that the range of drawn yarn elongation / 100%) ≦ DR ≦ 2.0 + (undrawn yarn elongation / 100%).

  In the first method, it is important to subject the polylactic acid undrawn yarn having a crystal size of 6 nm or more to drawing and heat treatment. By using undrawn yarn having a crystal size of 6 nm or more, yarn breakage and yarn unevenness can be suppressed even when high-magnification drawing as described later is performed. The crystal size of the undrawn yarn is preferably 7 nm or more, more preferably 9 nm or more. Further, when the crystal orientation degree of the undrawn yarn is 0.90 or more, the molecular chain can be stably drawn from the crystal as will be described later. In order to obtain such a crystallized undrawn yarn, it is preferable to melt-spin polylactic acid and set the spinning speed of the undrawn yarn to 4000 m / min or more. The spinning speed of the undrawn yarn is more preferably 5000 m / min or more.

  In addition, it is important that the stretching temperature is 85 ° C. or higher, so that even if high-strength stretching is performed, the yarn unevenness can be reduced. The stretching temperature is preferably 130 ° C. or higher. However, since ordinary polylactic acid has a melting point of about 170 ° C., the stretching temperature is preferably 160 ° C. or lower.

  In addition, it is important that the heat treatment temperature is 120 ° C. or higher, so that the fiber structure of the drawn yarn obtained can be stabilized, and sufficient strength can be obtained and the yield can be lowered. Furthermore, by increasing the heat treatment temperature, stretching and heat treatment can be stabilized, and yarn breakage and yarn unevenness can be suppressed. The heat treatment temperature is preferably 140 ° C. or higher. However, since normal polylactic acid has a melting point of about 170 ° C., the heat treatment temperature is preferably 165 ° C. or lower.

  It is important that the draw ratio (DR) is 0.90+ (undrawn yarn elongation / 100%) ≦ DR ≦ 2.0 + (undrawn yarn elongation / 100%). By setting (drawing yarn elongation / 100%) ≦ DR, not only can the strength at 25 ° C. be sufficiently high, but also the high-temperature mechanical properties can be greatly improved. On the other hand, by setting DR ≦ 2.0 + (undrawn yarn elongation / 100%), excessive deformation of the fiber can be suppressed, and yarn breakage and yarn unevenness can be significantly suppressed. DR is preferably 0.95+ (undrawn yarn elongation / 100%) ≦ DR ≦ 1.5 + (undrawn yarn elongation / 100%), more preferably 1.1+ (undrawn yarn elongation / 100%). ≦ DR ≦ 1.4 + (undrawn yarn elongation / 100%).

In the second method of the present invention, when a polylactic acid undrawn yarn having a crystal size of less than 6 nm is drawn to obtain a drawn yarn having a strength at 25 ° C. of 4.0 cN / dtex or higher , the drawing temperature is 130 ° C. or higher. The temperature is 120 ° C. or more, and the draw ratio (DR) is in the range of 0.90+ (undrawn yarn elongation / 100%) ≦ DR ≦ 2.0 + (undrawn yarn elongation / 100%). It is a manufacturing method of a polylactic acid fiber.

In the second method, since a polylactic acid undrawn yarn that is not crystallized, that is, amorphous or insufficiently crystallized, is used, selection of a drawing temperature is particularly important, and the drawing temperature is set to 130 ° C. or higher. This is very important. As a result, the undrawn yarn is oriented and crystallized by preheating before drawing, and the crystal is sufficiently grown, and the drawing uniformity is improved even when high-magnification drawing is performed as in the first method of the present invention .

  It is also important to set the heat treatment temperature to 120 ° C. or higher, which can stabilize the fiber structure of the drawn yarn obtained, and can provide sufficient strength and lower boiling yield. . Furthermore, by increasing the heat treatment temperature, the drawing / heat treatment is stabilized and yarn breakage and yarn unevenness can be suppressed. The heat treatment temperature is preferably 140 ° C. or higher. However, since normal polylactic acid has a melting point of about 170 ° C., the heat treatment temperature is preferably 165 ° C. or lower.

  It is important that the draw ratio (DR) is 0.90+ (undrawn yarn elongation / 100%) ≦ DR ≦ 2.0 + (undrawn yarn elongation / 100%). By setting (drawing yarn elongation / 100%) ≦ DR, not only can the strength at 25 ° C. be sufficiently high, but also the high-temperature mechanical properties can be greatly improved. On the other hand, by setting DR ≦ 2.0 + (undrawn yarn elongation / 100%), excessive deformation of the fiber can be suppressed, and yarn breakage and yarn unevenness can be significantly suppressed. DR is preferably 0.95+ (undrawn yarn elongation / 100%) ≦ DR ≦ 1.5 + (undrawn yarn elongation / 100%), more preferably 1.1+ (undrawn yarn elongation / 100%). ≦ DR ≦ 1.4 + (undrawn yarn elongation / 100%).

  The undrawn yarn in the present invention refers to a fiber that can be stably drawn even when the above-described drawing conditions are adopted. For this reason, the elongation of the undrawn yarn is preferably 25% or more. Moreover, it is preferable to use the yarn as spun from the viewpoint of improving production efficiency.

  By the way, when the yarn spots of the obtained polylactic acid fiber are large, not only the quality of the fiber product is inferior, but also various problems are likely to occur, such as fluff and looseness in a high-order processing step. In particular, dyeing and functional materials are often post-processed in applications used for multifilaments, but if the thread spots are large, staining spots and processed spots are likely to occur. For this reason, in the polylactic acid fiber obtained by the production method of the present invention, it is important to determine the stretching and heat treatment conditions so that the Wooster spot which is an index of the thread spot is 2.0% or less. For this reason, it is preferable that the Worcester spots of undrawn yarns are also small because the drawing and heat treatment steps are stabilized and the yarn spots of the resulting fibers can be suppressed. The Worcester spot of the undrawn yarn is preferably 2.0% or less, more preferably 1.5% or less, and still more preferably 1.2% or less. In addition, the Worcester spots of the polylactic acid fiber obtained by the production method of the present invention are preferably 2.0% or less, more preferably 1.5% or less, and even more preferably 1.2% or less. It is important to adjust various stretching conditions such as magnification.

  Polylactic acid fibers have a high coefficient of friction, and are therefore prone to fluff during high-speed spinning processes, yarn processing processes such as false twisting and fluid processing, and cloth manufacturing processes such as beaming, weaving, and knitting. There is. For this reason, as a fiber oil agent, avoiding polyether-based ones, and using ones mainly composed of smoothing agents such as fatty acid esters and mineral oils, the friction coefficient of polylactic acid fibers can be reduced, and the above process It is preferable because fluff can be greatly suppressed.

  The method for producing polylactic acid according to the present invention has an advantage that the production efficiency is very high, which will be described below. It is described in JP-A-8-246247 and JP-A-2000-89938 that the discharge amount per unit time during spinning can be used as one index of production efficiency. That is, it can be said that the larger the product of the spinning speed and the draw ratio until obtaining a fiber with a desired fineness, the larger the discharge amount per unit time and the higher the production efficiency per unit time. When the present invention is viewed from this point of view, the production method of the present invention has a very high production efficiency because the draw ratio can be increased as compared with the conventional method of producing polylactic acid fibers. For example, in the case of using undrawn yarn with a spinning speed of 3000 m / min, in the present invention, spinning speed × drawing ratio = 6150 (Example 7) and spinning speed of the conventional production method × drawing ratio = 4950 (Comparative Example 3) Compared with, productivity per unit time is significantly high. Further, when a high-speed spinning fiber is used for the undrawn yarn, the productivity per unit time can be further increased. In Example 4, the spinning speed × the draw ratio = 10500.

The polylactic acid fiber obtained by the production method of the present invention preferably has a high strength in consideration of keeping the process passability and the mechanical strength of the product sufficiently high. The strength of the resulting fiber at 25 ° C. is 4 .0cN / dtex Ru der more. The strength at 25 ° C. of the polylactic acid fiber is more preferably 5.5 cN / dtex or more. Moreover, when the elongation at 25 ° C. of the polylactic acid fiber is 15 to 70%, the process passability when the polylactic acid fiber is made into a fiber product is improved, which is preferable.

  Furthermore, when the production method of the present invention is used, it is possible to greatly improve the high-temperature mechanical properties of the resulting polylactic acid fiber. Considering processability of fibers and fiber products, the strength of polylactic acid fibers at 90 ° C. is preferably 1.0 cN / dtex or more. The strength at 90 ° C. is more preferably 1.3 cN / dtex or more, and still more preferably 1.5 cN / dtex or more. Further, in the polylactic acid fiber obtained by the production method of the present invention, the elongation under 0.7 cN / dtex stress at 90 ° C. can be 15% or less, and the mechanical dimensional stability at high temperature can be reduced. It can also be greatly improved. Here, the elongation under 0.7 cN / dtex stress at 90 ° C. means that a fiber tensile test is performed at 90 ° C., and the elongation at a stress of 0.7 cN / dtex is read in the strong elongation curve diagram. Can be sought. If the elongation under 0.7 cN / dtex stress at 90 ° C. is 15% or less, the dimensional stability at high temperature can be improved, the elongation of the polylactic acid fiber by gluing and drying can be suppressed, and the false twist Therefore, process passability and crimping characteristics can be improved. The elongation under 0.7 cN / dtex stress at 90 ° C. is preferably 10% or less, more preferably 6% or less.

  In the polylactic acid fiber obtained by the production method of the present invention, the Wooster spot (U%), which is an index of the thickness spot of the thread, can be 2% or less, and the quality of the fiber or the fiber product can be improved. Can do. U% is preferably 1.5% or less, more preferably 1.2% or less.

  Moreover, the polylactic acid fiber obtained by the production method of the present invention preferably has good dimensional stability of the fiber and the fiber product if the boiling yield is 0 to 20%. The boiling yield is preferably 2 to 10%.

  Regarding the cross-sectional shape of the polylactic acid fiber obtained by the production method of the present invention, it is possible to freely select a round cross-section, a hollow cross-section, a multi-leaf cross-section such as a trilobal cross-section, and other irregular cross-sections. The form of the fiber is not particularly limited, such as long fiber or short fiber, and in the case of long fiber, it may be multifilament or monofilament.

In the polylactic acid fiber obtained by the production method of the present invention, the reason why the high-temperature mechanical properties are improved is not well understood as described above. However, as described below, a 3 ₁ helical structure that does not exist in normal polylactic acid fiber is present. This is presumably due to the formation of the molecular chain to be taken. The 3 ₁ helical structure is described in detail below.

First, the structure of the molecular chain in a normal polylactic acid fiber will be described. In polylactic acid fiber, a crystal form called α crystal is usually formed, but the molecular chain in α crystal has a 10 ₃ helical structure. J. Biopolym., Vol. 6, 299 ( 1968). Here, the 10 ₃ helical structure means a helical structure that rotates 3 times per 10 monomer units as shown in FIG. On the other hand, a fiber obtained by solution spinning (spinning speed: 1 to 7 m / min) of an ultrahigh molecular weight polylactic acid (viscosity average molecular weight of 560,000 to 1,000,000) from a chloroform / toluene mixed solvent is used at an ultrahigh temperature (204 ° C. or higher). ), A polylactic acid fiber obtained by ultrahigh magnification stretching (12 to 19 times, stretching speed of 1.2 m / min or less) produces crystals different from normal α crystals called β crystals. , vol.23, 642 (1990). Here β crystal and the helical structure (3 ₁ helical structure, Fig. 4) which rotates once per three monomer units that are formed from have been described in the literature. By the way, this 3 ₁ helical structure is a helical structure that rotates 3 times per 9 monomer units from a different point of view, and can be said to be a tension type form in which the 10 ₃ helical structure is slightly stretched.

In addition, in the analysis by the inventors' solid ¹³ C-NMR, only a peak around 170.2 ppm corresponding to the 10 ₃ helical structure is observed in the conventional polylactic acid fiber, whereas the fiber of the present invention has a lower magnetic field of 171. It was found that a peak was observed around .6 ppm (Fig. 1). This is considered to be a conformation, that is, a helical structure having a structure different from that of the conventional polylactic acid fiber 10 ₃ helical structure. Then, a pattern similar to a β crystal was observed from wide-angle X-ray diffraction (WAXD) measurement (FIG. 3), and it was confirmed that a 3 ₁ helical structure was formed. That is, the inventors have found that if a peak is observed in the vicinity of 171.6 ppm in solid ¹³ C-NMR, it means that a 3 ₁ helical structure is formed.

The polylactic acid fiber of the present invention has a 3 ₁ helical structure that is a tension type, and thus exhibits a strong resistance to pulling, and has sufficient mechanical properties not only at room temperature but also at a high temperature of 90 ° C. or higher. It is thought to show.

The 3 ₁ helix structure may be contained in at least a part of the fiber, but in the solid ¹³ C-NMR spectrum, the peak area intensity (3 ₁ ratio) corresponding to the 3 ₁ helix structure is observed at 165 to 175 ppm. When the area intensity is 5% or more of the peak area intensity, the intensity at 90 ° C. can be preferably 1.0 cN / dtex or more. In addition, the 3 ₁ helical structure does not necessarily have to be crystallized, but if it is crystallized so as to be confirmed by WAXD as shown in FIG. 3, the strength at 90 ° C. can be preferably 1.5 cN / dtex or more. .

Further, the production method of the present invention, the reason why the above-mentioned fiber structure (3 ₁ helical structure) is expressed is estimated as follows.

In the present invention is to a high draw ratio than the polylactic acid undrawn yarn to normal stretching, thereby polylactic acid chains are pulled out, 3 ₁ to 10 ₃ helical structure by high stress is applied to more molecular chains It is thought that the transition to the helical structure. And it is thought that this structure is stabilized by heat treatment. That is, it is considered that a structure different from that of the conventional polylactic acid fiber and the undrawn yarn is expressed by restructuring the fiber structure of the undrawn yarn while being broken by drawing.

The draw ratio of ordinary polylactic acid fibers is 0.75+ (undrawn yarn elongation / 100%) or less (Comparative Examples 2 and 3) for clothing use, and even for industrial use, for example, In No. 248426, the draw ratio in the first stage is 0.75+ (undrawn yarn elongation / 100%) or less, much more than 0.90+ (undrawn yarn elongation / 100%) of the present invention. It is a low magnification stretching. For this reason, the polylactic acid fibers obtained by these production methods did not have a 3 ₁ helical structure, and had low high-temperature mechanical properties.

Thus, although the present invention is the first time 3 ₁ helical structure by high magnification stretching can be formed, the previously arranged aligned drawn polylactic acid chains prior to stretching, can be uniformly stretched even at high magnification stretching Thus, it is possible to suppress the occurrence of whitening of fibers and stretched spots. As a specific method of aligning and arranging polylactic acid molecular chains before stretching, processes such as pre-stretching and pre-heat treatment can be performed using an oriented crystallization structure by high-speed spinning as in the first method of the present invention. There is no need to add, high efficiency and low cost can be achieved. In addition, as in the second method of the present invention, the undrawn yarn obtained at a spinning speed of about 3000 m / min has a molecular orientation that has progressed to some extent, but is often non-crystallized. By increasing the temperature to 110 ° C. or higher, orientation crystallization is sufficiently performed at a preheated portion such as the first hot roller, and high-stretching is possible.

  The polylactic acid fiber obtained by the production method of the present invention can take various forms of fiber products such as woven fabrics, knitted fabrics, nonwoven fabrics, molded articles such as cups and the like.

  The polylactic acid fiber obtained by the production method of the present invention is not only used for crimped yarns such as false twisting, but for clothing such as shirts, blousons and pants, as well as for clothing materials such as cups and pads, curtains and carpets. , Mats, furniture and other interior uses, vehicle interior uses, belts, nets, ropes, heavy cloth, bags, sewing materials, and other industrial materials, as well as felt, non-woven fabrics, filters, artificial turf, etc. it can. It is also possible to obtain ultrahigh strength polylactic acid fibers by further stretching and heat-treating the polylactic acid fibers obtained by the production method of the present invention.

  Hereinafter, the present invention will be described in detail with reference to examples. In addition, the measuring method in an Example used the following method.

A. Weight average molecular weight of polylactic acid A chloroform solution of a sample was mixed with THF (tetrohithrofuran) to obtain a measurement solution. This was measured at 25 ° C. using water permeation chromatography (GPC) Waters 2690 manufactured by Waters, and the weight average molecular weight was determined in terms of polystyrene.

B. Strength and elongation at 25 ° C. At room temperature (25 ° C.), an initial sample length = 200 mm, a pulling rate = 200 mm / min, and a load-elongation curve was obtained under the conditions shown in JISL1013. Next, the load value at break was divided by the initial fineness, which was used as the strength, and the elongation at break was divided by the initial sample length to obtain a strong elongation curve.

C. Strength at 90 ° C. At a measurement temperature of 90 ° C., a strong elongation curve was obtained in the same manner as C, and the load value was divided by the initial fineness to obtain the strength at 90 ° C.

D. Elongation at 90 ° C. under 0.7 cN / dtex stress In the strong elongation curve at 90 ° C. obtained in D above, the elongation under 0.7 cN / dtex stress is read, and 0.7 cN at 90 ° C. / Elongation under dtex stress.

E. Boiling yield The yarn was scraped and treated in boiling water, and the boiling yield was obtained from the following formula from the dimensional change before and after that.
Boiling yield (%) = [(L0−L1) / L0)] × 100 (%)
L0: Original length of skein measured under initial load 0.09cN / dtex after skein of drawn yarn L1: Skein measured L0 was treated in boiling water for 15 minutes in a substantially load-free state, and after initial drying after air drying Skein length under 0.09cN / dtex

F. Worcester spots (U%)
Using a USTER TESTER 4 manufactured by zellweger uster, measurement was performed in a normal mode at a yarn feeding speed of 200 m / min.

G. Solid ¹³ C-NMR
A CP / MAS NMR spectrum of ¹³ C nuclei was measured using a CMX-300 infinity type NMR apparatus manufactured by Chemagnetics under the following conditions, and the carbonyl carbon portion of the ester bond was analyzed. Then, by curve fitting, the peak near 170.2 ppm attributed to the 10 ₃ helical structure and the peak near 171.6 ppm attributed to the 3 ₁ helical structure are divided into peaks, and the peak observed at 165 to 175 ppm is divided. The area intensity ratio (3 ₁ ratio) of the peak near 171.6 ppm relative to the entire area intensity was determined.
Equipment: CMX-300 infinity manufactured by Chemagnetics
Measurement temperature: Room temperature reference material: Si rubber (internal reference: 1.56 ppm)
Measurement nucleus: 75.1910 MHz
Pulse width: 4.0 μsec
Pulse repetition time: ACQTM = 0.06826sec PD = 5sec
Data points: POINT = 8192 SAMPO = 2048
Spectral width: 30.003 kHz
Pulse mode: Relaxation time measurement mode Contact time: 5000 μsec

H. Wide-angle X-ray diffraction (WAXD)
Using a 4036A2 type X-ray diffractometer manufactured by Rigaku Corporation, a WAXD plate photograph was taken under the following conditions.
X-ray source: Cu-Kα ray (Ni filter)
Output: 40kV x 20mA
Slit: 1mmφ pinhole collimator Camera radius: 40mm
Exposure time: 8 minutes Film: Kodak DEF-5

I. Crystal Size Using a 4036A2 type X-ray diffractometer manufactured by Rigaku Corporation, the diffraction intensity in the equator direction was measured under the following conditions.
X-ray source: Cu-Kα ray (Ni filter)
Output: 40kV x 20mA
Slit: 2mmφ-1 ° -1 ° Detector: Scintillation counter counting recording device: RAD-C type step scan manufactured by Rigaku Corporation: 0.05 ° step integration time: 2 seconds
The (200) plane direction crystal size L was calculated using the following Scherrer equation.
L = Kλ / (β0 cos θB)
L: Crystal size (nm)
K: Constant = 1.0
λ: X-ray wavelength = 0.15418 nm
θB: Bragg angle β0 = (βE2-βI2) 1/2
βE: Apparent half width (measured value)
βI: device constant = 1.046 × 10 −2 rad.

J. Crystal orientation
The degree of crystal orientation in the (200) plane direction was determined as follows.
The peak corresponding to the (200) plane was calculated from the half value width of the intensity distribution obtained by scanning in the circumferential direction by the following formula.
Crystal orientation degree (π) = (180−H) / 180
H: Half width (deg.)
Measurement range: 0 to 180 °
Step scan: 0.5 ° Step integration time: 2 seconds

K. Crimp characteristics of false twisted yarn, CR value The false twisted yarn was scraped, treated in boiling water for 15 minutes in a substantially load-free state, and air-dried for 24 hours. The sample was immersed in water under a load equivalent to 0.088 cN / dtex (0.1 gf / d), and the skein length L′ 0 after 2 minutes was measured. Next, the skein length corresponding to 0.088 cN / dtex was removed in water and replaced with a fine load equivalent to 0.0019 cN / dtex (2 mgf / d), and the skein length L′ 1 after 2 minutes was measured. And CR value was calculated by the following formula.
CR (%) = [(L′ 0−L′1) / L′ 0] × 100 (%)

Reference examples 1 and 2
Polymerization of lactide produced from L-lactic acid with an optical purity of 99.5% in the presence of bis (2-ethylhexanoate) tin catalyst (lactide to catalyst molar ratio = 10000: 1) at 180 ° C. for 180 minutes in a nitrogen atmosphere. went. The resulting homopoly L lactic acid had a weight average molecular weight of 190,000 and an optical purity of 99% L lactic acid. This was melt-spun at 240 ° C., and the yarn was cooled and solidified by a chimney 4 with a cooling air of 25 ° C., then a fiber oil agent mainly composed of a fatty acid ester was applied by the converged oil supply guide 6, and the yarn was formed by the entanglement guide 7. Confounding was applied (FIG. 7). Thereafter, the undrawn yarn 10 was wound up through the non-heated second take-up roller 9 after being taken up by the non-heated first take-up roller 8 having a peripheral speed of 5000 m / min (spinning speed 5000 m / min). The homopoly L-lactic acid undrawn yarn wound up had a crystal size in the (200) plane direction of 9.2 nm, a crystal orientation degree of 0.96, an elongation of 56%, and U% of 0.8%. The undrawn yarn 10 is subjected to one-stage drawing and heat treatment under the conditions shown in Table 1 at a drawing speed (peripheral speed of the second hot roller 13) of 800 m / min using the apparatus shown in FIG. Of drawn yarn was obtained. No yarn breakage occurred during spinning and drawing, and the process stability was good.

Although a solid state NMR spectra of these drawn yarn 1, the fibers of Example 1 are observed peak near 171.6ppm attributed to 3 ₁ helical structure clearly observed as a shoulder peak in the reference example 2 Fiber It was done. Then, make these peaks division were determined in the peak area intensity ratio of around 171.6ppm the (3 ₁ ratio), 29% in Reference Example 1, was 17% in Reference Example 2 (Figure 2). Further, the fibers of Reference Example 1 was subjected to WAXD measurement, Macromolecules, vol.23, 642 (1990 ). Β crystal similar pattern was obtained according, the crystal having a 3 ₁ helical structure is generated Was confirmed (FIG. 3). On the other hand, the fiber of Reference Example 2 did not have a WAXD pattern of crystals having a 3 ₁ helical structure. The strong elongation curve at 90 ° C. of Reference Example 1 is shown in FIG. 6 and the physical properties are shown in Table 2. Mechanical properties at 90 ° C. are greatly improved as compared with the conventional high strength polylactic acid fiber (Comparative Example 1). Was.

Example 1
Spinning and drawing were performed under the conditions shown in Table 1 in the same manner as in Reference Example 1 at a spinning speed of 3000 m / min to obtain a drawn yarn of 84 dtex and 24 filaments. The physical properties of the undrawn yarn are shown in Table 1. Unlike the undrawn yarn used in Reference Examples 1 and 2, a crystalline pattern was not obtained with WAXD, and the yarn was amorphous. For this reason, although it does not become a problem, the yarn swing on the 1st hot roller was a little large.

From solid state NMR spectrum of the stretched filament it was confirmed the formation of 3 ₁ helical structure. The physical property values are shown in Table 2. The mechanical properties at 90 ° C. were greatly improved as compared with the conventional high-strength polylactic acid fiber (Comparative Example 1).

Comparative Example 1
Polymerization of lactide prepared from L-lactic acid having an optical purity of 99.5% in the presence of bis (2-ethylhexanoate) tin catalyst (lactide to catalyst molar ratio = 10000: 1) at 180 ° C. for 140 minutes in a nitrogen atmosphere. went. The resulting homopoly L lactic acid had a weight average molecular weight of 150,000 and an optical purity of 99% L lactic acid. Using this, high-strength polylactic acid fibers were obtained by three-stage stretching and heat treatment according to Example 9 of JP 2000-248426 A. At this time, the undrawn yarn spinning speed is 2200 m / min, the first stage stretching temperature is 82 ° C., the second stage stretching temperature is 130 ° C., the third stage stretching temperature is 160 ° C., and the first stage stretching ratio is 1. The draw ratio of 53 times and the second stage was 1.55 times, the draw ratio of the third stage was 1.55 times, and the final heat treatment temperature was 155 ° C.

When solid-state NMR was measured, no peak corresponding to the 3 ₁ helical structure in the vicinity of 171.6 ppm was observed (FIG. 1). Further, when WAXD measurement was performed, only a pattern corresponding to a normal α crystal (10 ₃ helical structure) was obtained although it was highly crystallized. Further, the physical properties are shown in Table 2. The strength at room temperature was high, but the mechanical properties at 90 ° C. were low.

  When all the draw ratios were 1.0, the hot plate temperature, and the heat treatment temperature were room temperature, the undrawn yarn was measured for winding properties of a spinning speed of 2200 m / min. The undrawn yarn was not crystallized and stretched. The degree was 120%. From this, the draw ratio of the first-stage drawing in this comparative example was 0.33+ (undrawn yarn elongation / 100%).

Comparative Examples 2 and 3
Polylactic acid undrawn yarn was obtained in the same manner as in Reference Example 1 as the spinning speed shown in Table 1. The obtained undrawn yarn was amorphous, and the crystal size could not be measured. The undrawn yarn was drawn and heat-treated in the same manner as in Reference Example 1 under the conditions shown in Table 1 to obtain a drawn yarn having 84 dtex, 24 filaments and a round cross section.

When solid-state NMR of this was measured, no peak corresponding to the 3 ₁ helical structure in the vicinity of 171.6 ppm was observed. Further, when WAXD measurement was performed, only a pattern corresponding to the α crystal (10 ₃ helical structure) was obtained although it was highly crystallized. Further, the physical properties are shown in Table 2. The mechanical properties at 90 ° C. were low.

Reference example 3
The polylactic acid fibers obtained in Reference Examples 1 and 2 were stretched false twisted under the conditions shown in Table 3 using the apparatus shown in FIG. The processing speed, which is the speed of the stretching roller 20, was 400 m / min, and the second heater 21 was not used. A triaxial twister was used as the false twist rotor 19. The yarn physical properties are shown in Table 3, and a false twisted yarn exhibiting sufficient crimp characteristics of CR ≧ 25% was obtained. Further, the boiling point was 20% or less, which was sufficient.

Reference example 4
Using the undrawn yarn of Reference Example 2, the temperature of the second heater 21 was 150 ° C., the relaxation rate between the drawing roller 20 and the delivery roller 22 was 8%, and false twisted yarn was obtained. The yarn physical properties are shown in Table 3. The yield of the boiling point was reduced to 4% by the effect of the second heater.

Comparative Example 4
The conventional polylactic acid fiber obtained in Comparative Example 3 was subjected to a friction disk false twisting process in the same manner as in Reference Example 3 at a draw ratio of 1.35 times and a heater temperature of 130 ° C. It was impossible to apply. Next, when the heater temperature was lowered to 110 ° C. and processing was performed, there was still a problem with threading, but it was possible to wind the thread. The CR value, which is an index of crimp characteristics, was 20%, but the boiling point was too high at 25% because the heater temperature was too low.

Comparative Example 5
In the conventional polylactic acid fiber obtained in Comparative Example 3, the temperature of the second heater 21 is 150 ° C., the relaxation rate between the drawing roller 20 and the delivery roller 22 is 8%, and false twisted yarn is obtained in the same manner as in Comparative Example 4. It was. The yarn physical properties are shown in Table 3. Although the yield was reduced by 8% due to the effect of the second heater, the CR value was 3% and almost no crimp.

Reference Example 5
A plain weave was prepared by using the yarn obtained in Reference Example 1 as a warp and a weft. Although warp sizing and drying were performed at 110 ° C., there was no occurrence of fluff or trouble of yarn elongation. The obtained plain weave was scoured at 60 ° C. according to a conventional method, and then an intermediate set was applied at 140 ° C. Furthermore, it dye | stained at 110 degreeC according to the conventional method. The obtained fabric had a squeaky feeling and a soft feeling, and had an excellent texture for clothing.

  Weaving and fabric evaluation of the yarns obtained in Reference Example 2 and Example 1 were conducted in the same manner. However, the occurrence of fluff and the trouble of yarn elongation did not occur, and the obtained fabric had a squeaky feeling and a soft feeling. There was an excellent texture for clothing.

Comparative Example 6
A plain weave was prepared in the same manner as in Reference Example 5 using the yarn obtained in Comparative Example 3 as warp and weft. The warp paste was dried at 110 ° C., but the yarn was stretched and could not be dried. Therefore, a tubular knitting was produced using the yarn obtained in Comparative Example 3 and dyed at 110 ° C. according to a conventional method, but the dyeing spots were large and the quality was poor.

Reference Example 6
The polylactic acid fiber obtained in Reference Example 2 was subjected to redrawing and heat treatment at a drawing temperature of 150 ° C., a draw ratio of 1.15 times, and a heat treatment temperature of 155 ° C. The resulting polylactic acid fiber has a room temperature strength of 8.0 cN / dtex, a room temperature elongation of 15%, a 90 ° C. strength of 3.0 cN / dtex, a 90 ° C., an elongation of 0.7 cN / dtex of 3%, a boiling yield of 2%, U % = 1.2% high-strength polylactic acid fiber. Moreover, the production | generation of 3 ₁ helical structure was confirmed from the solid state NMR spectrum.

It is a figure which shows the solid NMR spectrum of this invention and the conventional high intensity | strength polylactic acid fiber. It is a figure which shows the peak splitting of a solid state NMR spectrum. 6 is a diagram showing a wide-angle X-ray diffraction pattern of Reference Example 1. FIG. It is a figure which shows the helical structure of a polylactic acid molecular chain. It is a figure which shows the strong elongation curve of the conventional polylactic acid fiber (comparative example 3) and nylon 6 fiber. It is a figure which shows the strong elongation curve in 90 degreeC of the reference example 1 and the conventional high intensity | strength polylactic acid fiber (comparative example 1). It is a figure which shows a spinning apparatus. It is a figure which shows an extending | stretching apparatus. It is a figure which shows an extending | stretching false twist apparatus.

Explanation of symbols

1: Spin block 2: Spin pack 3: Base 4: Chimney 5: Yarn 6: Converging oiling guide 7: Entangling guide 8: First take-up roller 9: Second take-up roller 10: Undrawn yarn 11: Feed roller 12: 1st hot roller 13: 2nd hot roller 14: 3rd roller (room temperature)
15: drawn yarn 16: feed roller 17: heater 18: cooling plate 19: false twist rotor 20: drawn roller 21: second heater 22: delivery roller 23: false twisted yarn

Claims (3)

When a polylactic acid undrawn yarn having a crystal size of less than 6 nm is drawn to obtain a drawn yarn having a strength at 25 ° C. of 4.0 cN / dtex or more , the drawing temperature is 130 ° C. or more, the heat treatment temperature is 120 ° C. or more, and the draw ratio (DR) is the following range, The manufacturing method of the polylactic acid fiber characterized by the above-mentioned.
0.90+ (Undrawn yarn elongation / 100%) ≦ DR ≦ 2.0 + (Undrawn yarn elongation / 100%)   2. The method for producing polylactic acid fiber according to claim 1, wherein Worcester spots of the polylactic acid undrawn yarn are 2.0% or less.   The method for producing a polylactic acid fiber according to claim 1 or 2, wherein the drawing is one-stage drawing.

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