JPH11131323A - Polylactic acid fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly biodegradable polylactic acid fiber having such high mechanical strength and elastic modulus as to be also usable as an industrial material by subjecting poly-L-lactic acid having each specific average molecular weight and optical purity to fiber manufacturing under specified conditions. SOLUTION: Poly-L-lactic acid with an average molecular weight of 50,000-100,000 and optical purity of 95.5-99.5% is put to melt spinning and then cooled and solidified once, the resulting fiber Y is passed through a cylindrical heating device 3 with an inner wall temperature of 120-170 deg.C, gathered together, oiled, and then taken up with takeup rollers 5, 6 with a surface velocity of >=3,000 m/min and wound, thus obtaining the objective polylactic acid fiber Y with a tenacity of >=4.0 g/d, initial modulus of >=60 g/d, and the elastic modulus at 10% extension of >=7 g/d.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber having biodegradability and practically sufficient strength and elastic modulus.

[0002]

2. Description of the Related Art In recent years, in order to prevent industrial waste from polluting the environment, attention has been paid to the use of biodegradable (microbial or spontaneously degradable) materials. Biodegradable fibers made of polyester have attracted attention.

[0003] Biodegradable fibers are strongly demanded in the fields of living materials such as garbage draining nets and composting bags, and sanitary materials such as disposable diapers and sanitary articles. In general, biodegradable fibers made of polyester often have low strength and low elastic modulus and are inferior in heat resistance, and have a drawback that their applications are limited.
Further, the cost of the raw material polymer is high, and it is often difficult to produce it industrially at low cost.

Polylactic acid is a biodegradable resin from which a polymer can be obtained at relatively low cost and a molded article having practical strength and heat resistance can be produced. In order to produce a fiber, it is necessary to use a raw material having a high degree of polymerization, and in order to produce a stable operation, it is necessary to employ a low-productivity low-speed spinning method.

For example, Japanese Patent Application Laid-Open No. 7-305227 discloses a method for obtaining a high-strength polylactic acid fiber by preventing a decrease in the degree of polymerization at the time of melting and maintaining a high molecular weight to form a yarn. However, this method requires copolymerization of polyethylene glycol, and has been practiced only with a low productivity method in which spinning and drawing are performed in separate steps.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and a polylactic acid fiber having sufficient strength and elastic modulus, which is biodegradable and can be used for industrial materials, An object of the present invention is to provide a method for industrially producing this fiber with high productivity.

[0007]

The present invention has the following structure to solve the above-mentioned problems. (1) Average molecular weight of 50,000 to 100,000, optical purity of 95.0 to 9
The fiber is composed of 9.5% poly-L-lactic acid and obtained at a winding speed of 3000 m / min or more, and has a strength of 4.0.
g / d or more, an initial elastic modulus is 60 g / d or more, and a 10% elongation elastic modulus is 7 g / d or more. (2) 50,000 to 100,000 average molecular weight, 95.0 to 9 optical purity
9.5% of poly-L-lactic acid is melt-spun, once cooled and solidified, passed through a cylindrical heating device having an inner wall temperature of 120 to 170 ° C. to bundle fibers, apply an oil agent, and A method for producing polylactic acid fibers, wherein the fiber is taken up and taken up by a take-up roller having a speed of 3000 m / min or more.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polylactic acid fiber of the present invention comprises L-lactic acid and D-lactic acid.
The main component is a copolymer of lactic acid optical isomers.
It is necessary that the optical purity of L-lactic acid is 95.0 to 99.5%. The ratio between the L-form and the D-form is a factor affecting heat resistance and biodegradability. If the purity of the L-form is lower than this range, the crystallinity is reduced, the melting point is reduced, and the fiber having poor heat resistance is deteriorated. And the biodegradation rate increases at the same time. On the other hand, if the purity of the L-form is higher than this range, the crystallization is high and the decomposition rate is low, resulting in fibers with poor biodegradability.

It is necessary that the average molecular weight of polylactic acid is in the range of 50,000 to 100,000. If the average molecular weight is lower than this range, sufficient strength and elastic modulus will not be exhibited, and if the average molecular weight is higher than this range, the biodegradability will decrease, which is not preferable.

The fiber of the present invention is a fiber obtained at a winding speed of 3000 m / min or more, and is a fiber obtained with high industrial productivity. Moreover, its physical properties are as follows: strength is 4.0 g / d or more, and initial elastic modulus is 60 g / d or more.
The elastic modulus at% elongation is as excellent as 7 g / d or more.
By satisfying these physical properties at the same time, it can be used for a wide range of applications. For example, it can be used for industrial materials where the required performance of mechanical properties in the initial stage of use is high.

In particular, a feature of the fiber of the present invention resides in the elastic modulus at 10% elongation. Polylactic acid fibers usually have a low modulus of elasticity after the primary yield point during tensile strain, and thus have a problem that stress unevenness is likely to occur in the processing step.
Since the elastic modulus at% elongation is as high as 7 g / d or more, this defect is improved, and the fiber has no problem in processing not only at the initial elastic modulus but also at 10% elongation exceeding the primary yield point.

Next, a method for producing the polylactic acid fiber of the present invention will be described.

The polylactic acid used in the present invention comprises a copolymer of optical isomers of L-lactic acid and D-lactic acid as a main component.
It is necessary that the optical purity of lactic acid is 95.0 to 99.5%. When the purity of the L-form is lower than this range, only fibers having poor heat resistance can be obtained, and when the purity of the L-form is higher than this range, high-speed spinning properties are poor and the fiber is not suitable for the production method employed in the present invention. Absent.

The average molecular weight of the polylactic acid must be in the range of 50,000 to 100,000 at the time of melting and discharging. If the average molecular weight is lower than this range, fibers having sufficient strength and elastic modulus cannot be obtained.If the average molecular weight is higher than this range, yarn breakage is likely to occur when spinning at high speed, and is employed in the present invention. Not suitable for the production method. In the present invention, a small amount of an inorganic substance or another thermoplastic biodegradable component can be added as long as the basic characteristics of each component are not impaired.

The feature of the present invention is that polylactic acid, which has been melt-spun and cooled and solidified once, is reheated and taken up after giving air resistance, thereby promoting orientation and crystallization. An object of the present invention is to obtain a polylactic acid fiber having an unobtainable strength and elastic modulus.

FIG. 1 is a schematic process diagram showing one embodiment of the method for producing a polylactic acid fiber of the present invention. In FIG. 1, a polylactic acid fiber Y is melt-spun from a spinneret 1, cooled and solidified by a cooling air blowing device 2, and passed through a cylindrical heating device 3. After the fibers that have passed through the cylindrical heating device 3 are naturally cooled, they are bundled together with the application of the oil agent by the oil agent application device 4, taken up by the take-up roller (first roller) 5, and taken up via the second roller 6. It is wound by the device 7.

In the above step, the inner wall temperature of the cylindrical heating device 3 needs to be in the range of 120 to 170 ° C. If the temperature is lower than 120 ° C., the effect of promoting orientation and crystallization is low, and it is not possible to obtain a fiber having sufficient strength and elastic modulus. On the other hand, if the temperature exceeds 170 ° C., the fibers may be fused when they come into contact with the inner wall of the apparatus, which is not preferable. The effective heating length of the heating device is approximately 0.6 to 2.5
m is appropriate. If the heating length is shorter than this range, the effect of accelerating the orientation and crystallization tends to be reduced. If the heating length is longer than this range, the yarn sway in the heating device becomes large and yarn spots are easily induced.

Further, the take-up speed (ie, the surface speed of the take-up roller 5) needs to be 3000 m / min or more. The higher the stress applied to the fibers in the heating device,
Since the effect of accelerating the orientation and crystallization is large, it is desirable that the take-up speed is high, and if the speed is less than 3000 m / min, the above effect is lacking. Further, the upper limit of the take-up speed is preferably about 7000 m / min, and if it exceeds 7000 m / min, the passage time in the heating device becomes short, and the stress applied to the fiber becomes too high, which is not preferable because the fiber may be cut.

Although the fiber having the physical properties specified in the present invention can be obtained by winding the fiber taken up by the take-up roller 5 as it is, it is supplied to the second roller and subjected to a slight stretching or relaxation treatment. If it is, fine adjustment of the physical properties according to the use is possible, and a good roll form can be formed. At this time, the surface speed ratio between the second roller and the take-up roller is set to be 0.1.
It is preferably from 95 to 1.20, and if it is lower than this range, the tension at the time of winding is low, and the winding form is deteriorated. If it is higher than this range, the elongation becomes too low, which may lead to cutting, which is not preferable.

It is also possible to carry out heat treatment on any roller, between rollers, between a roller and a winding device, etc. Is more preferable for stabilizing the winding form. At this time, the surface temperature of the second roller is set to 70 to 140 ° C.
If the surface temperature is lower than this range, the effect of heating is poor, and if the surface temperature is higher than this range, the fiber sway on the roller is large, causing thread spots and cutting, which is not preferable.

The production method of the present invention can be applied to a wide range of brands, but preferably has a single yarn fineness of 0.5 to 8.0 d and a number of filaments of 10 to 250 filaments. The fiber obtained by the above-described production method has a strength of 4.0 g / d or more despite the high-speed spinning method of 3000 m / min or more.
Initial elastic modulus is 60 g / d or more, elastic modulus at 10% elongation is 7 g
/ D or higher polylactic acid fibers having high strength and high elastic modulus.

[0023]

Next, the present invention will be described in detail with reference to examples. In addition, the measurement and evaluation methods are as follows. (1) Tensile strength and elongation properties Measured according to JIS L 1013. (2) Shrinkage of boiling water After immersion in boiling water for 15 minutes, air-dry and 1/30
(g / d) was applied to determine the ratio of change in length before and after the load. (3) Average molecular weight The number average value of the dispersion by GPC analysis of a 0.4% by weight solution of chloroform of the sample was determined. (4) Biodegradability The sample was buried in the soil for 6 months and then taken out. The tensile strength was measured and evaluated by the strength retention rate with respect to the initial tensile strength.

Examples 1 to 6 and Comparative Examples 1 to 6 Poly-L-lactic acid having an optical purity of 99.0% was supplied to an extruder type melt spinning machine, melted at a spinning temperature of 210 ° C., and spun at a diameter of 0.3 mm. After spinning out from a die having 36 holes and blowing cooling air at 15 ° C to solidify the fiber, it was passed through a cylindrical heating device with an effective heating length of 130 cm with various inner wall temperatures set and naturally cooled. Thereafter, the oil is applied simultaneously with the convergence by the oil applying device, and the oil is applied by a take-off roller having various surface velocities. Subsequently, the oil is applied via a second roller having a surface temperature of 110 ° C. and various surface velocities. Winding was performed by a winding device having variously set speeds to obtain a 75d / 36f multifilament yarn. The production conditions and the characteristic values of the obtained multifilament yarn are shown in Tables 1 and 2.

[0025]

[Table 1]

[0026]

[Table 2]

As is apparent from Table 1, the multifilament yarns obtained in Examples 1 to 6 were fibers having strength and elastic modulus which were both sufficiently usable for industrial materials.

On the other hand, as is apparent from Table 2, Comparative Example 1 has a low heating cylinder temperature, Comparative Example 3 has a low take-off speed, and Comparative Example 5 has a low average molecular weight. None of the yarns had sufficient strength and elastic modulus. In Comparative Example 2, fibers were fused because the heating cylinder temperature was too high, and in Comparative Example 6, yarn breakage occurred frequently during spinning due to high average molecular weight. Comparative Example 4 is a conventional drawing method without using a heating tube, and thus the obtained multifilament yarn was insufficient in both strength and elastic modulus.

Examples 7 and 8, Comparative Examples 7 and 8 Using poly-L-lactic acid having an optical purity shown in Table 3, a multifilament yarn of 75d / 36f was obtained in the same production method as in Example 1. The average molecular weight at the time of discharge is 64000
Met. Table 3 shows the characteristic values and biodegradability of the obtained multifilament yarn.

[0030]

[Table 3]

As is clear from Table 3, the multifilament yarns obtained in Examples 7 and 8 have sufficient strength and elastic modulus for practical use, and also have good biodegradability after 6 months in soil. Met. On the other hand, in Comparative Example 7, the heat resistance of the fiber was poor due to the low ratio of the L-form, and the fiber was fused in boiling water. In Comparative Example 8, the biodegradability of the fiber was inferior because the ratio of the L-form was high, and the decrease in strength was small.

[0032]

According to the present invention, an inexpensive biodegradable fiber having strength and elastic modulus which can be used for industrial materials is provided. The polylactic acid fiber of the present invention can be used as a clothing material, as well as a marine material, an agricultural and horticultural material, a living material, a sanitary material, and other general industrial materials, and is left in an environment where microorganisms are present after use. If the fibers are decomposed completely after a certain period of time, the use of this fiber makes it possible to prevent pollution due to waste treatment without requiring special waste treatment.

[Brief description of the drawings]

FIG. 1 is a schematic process chart showing one embodiment of a method for producing a polylactic acid fiber of the present invention.

[Explanation of symbols]

 Y Polylactic acid fiber 1 Spinneret 2 Cooling air blowing device 3 Cylindrical heating device 4 Oil applying device 5 Take-up roller (first roller) 6 Second roller 7 Winding device

Claims (2)

[Claims] An average molecular weight of 50,000 to 100,000 and an optical purity of 9
Consisting of 5.0-99.5% poly-L-lactic acid, 300
A fiber obtained at a winding speed of 0 m / min or more, having a strength of 4.0 g / d or more, an initial elastic modulus of 60 g / d or more,
A polylactic acid fiber having an elastic modulus at 10% elongation of 7 g / d or more. 2. An average molecular weight of 50,000 to 100,000 and an optical purity of 9
5.0 to 99.5% of poly-L-lactic acid is melt-spun and once cooled and solidified, passed through a cylindrical heating device having an inner wall temperature of 120 to 170 ° C. to bundle fibers and apply an oil agent. And then taking up and winding up with a take-up roller having a surface speed of 3000 m / min or more.