JPH11293517A - Polylactic acid fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polylactic acid fiber having biodegradability, excellent in elastic modulus and dimension stability, and useful for a sanitary material, by spinning a poly(L-lactic acid) having a preferred average molecular weight and a preferred optical purity under a specific spinning condition. SOLUTION: This polylactic acid fiber having an elastic modulus of >=7 g/d in a stretched state of 10% and the coefficient of contraction of <=13% in boiling water is produced by the following steps: (1) melt spinning of poly(L- lactic acid) having an average molecular weight of 50,000-100,000 and an optical purity of 95.0-99.5% through extruding from a spinneret 1; (2) passing extruded fibers through a cylindrical heater 3 at the inner wall temperature of 120-170 deg.C after once cooled and solidified; (3) converging the fibers and giving them an oiling agent; (4) taking them up with the first roller 5 at the surface speed of >=3,000 m/min, followed by stretching them or relaxation treatment between the roller 5 and the second roller 6; (5) heat treatment with heated gas or heated steam just before winding with a winding apparatus 8, followed by winding the fibers at a speed of >=3,000 m/min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polylactic acid fiber having biodegradability and practically sufficient elastic modulus and dimensional stability, and a method for producing the same.

[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 natural degradable) materials. Sexual fibers are drawing attention.

[0003] Biodegradable fibers are particularly demanded in the fields of living materials such as garbage drain nets and compost bags, and sanitary materials such as disposable diapers and sanitary products.
Although development is desired, biodegradable fibers composed of aliphatic polyester generally have low strength and elastic modulus and are inferior in heat resistance, and are often limited in use. 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 polylactic acid polymerized by a special method, and has been practiced only in a low productivity method in which spinning and drawing are performed in separate steps. Further, polylactic acid fiber has a problem that it lacks dimensional stability at high heat because it is difficult to heat-treat at the time of winding.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and provides a polylactic acid fiber having biodegradability and sufficient elastic modulus and dimensional stability while being practically used. It is an object of the present invention to provide a method of manufacturing with high productivity.

[0007]

SUMMARY OF THE INVENTION The present invention has the following structure to achieve the above object. (1) Average molecular weight of 50,000 to 100,000, optical purity of 95.0 to 9
Consisting of 9.5% poly-L-lactic acid, speed 3000 m /
Fiber obtained by a method of winding in 10 minutes or more,
% Elasticity at the time of elongation is 7 g / d or more, boiling water shrinkage is 13%
A polylactic acid fiber characterized by the following. (2) 50,000 to 100,000 average molecular weight, 95.0 to 9 optical purity
After melt-spinning 9.5% poly-L-lactic acid and once cooling and solidifying the spun fibers, the fiber is passed through a cylindrical heating device having an inner wall temperature of 120 to 170 ° C. to converge and apply an oil agent. , Taken up by a first roller having a surface speed of 3000 m / min or more,
A polylactic acid which is stretched or relaxed with a subsequent second roller, heated immediately before a winding device with a heated gas or a heated steam, and then wound at a speed of 3000 m / min or more. Fiber manufacturing method.

[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 that affects the heat resistance and biodegradability. If the purity of the L-form is lower than this range, the biodegradation rate increases, but the melting point is low and the heat resistance is poor. Fiber. 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.

The average molecular weight of polylactic acid is from 50,000 to 1
It must be in the range of 10,000. 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, biodegradability will decrease.

The characteristics of the polylactic acid fiber of the present invention are that the elastic modulus at 10% elongation is 7 g / d or more and the boiling water shrinkage is 13% or less. By satisfying these physical properties,
It can be used for a wide range of applications, for example, it can be used for industrial material applications where the required performance of the mechanical properties in the initial stage of use is high. Polylactic acid fibers are usually
Since the elastic modulus after the primary yield point is low, stress unevenness occurs in the processing step, which causes strength, elongation variation and staining unevenness after processing.In the present invention, this point is improved, and the initial elasticity is improved. In addition to the modulus, it has an elastic modulus that does not cause any problem at the time of 10% elongation beyond the primary yield point. In addition, polylactic acid fibers have conventionally had poor dimensional stability at high heat,
Although there was a problem that the dimensional stability was poor due to the large shrinkage due to the heat applied during processing, the heat shrinkage characteristics of the present invention can be significantly improved by setting the boiling water shrinkage to 13% or less. And a product having good dimensional stability can be obtained.

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

The polylactic acid used in the present invention is mainly composed of a copolymer of optical isomers of L-lactic acid and D-lactic acid,
It is necessary that the optical purity of lactic acid is 95.0 to 99.5%. If the purity of the L-form is lower than this range, only fibers having inferior heat resistance will be obtained, and if the purity of the L-form is higher than this range, high-speed spinning properties will be poor, which is not suitable for the present invention.

Further, the average molecular weight of 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, it is not possible to obtain fibers having sufficient strength and elastic modulus, and if the average molecular weight is higher than this range, when spinning at high speed, yarn breakage is likely to occur, and the present invention Not suitable. 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 the polylactic acid once melt-spun and once cooled and solidified is reheated and taken up after imparting air resistance, thereby promoting orientation and crystallization, thereby improving the ordinary high-speed spinning and drawing method. An object of the present invention is to obtain a polylactic acid fiber having a strength and an elastic modulus which cannot be obtained by the above method.

FIG. 1 is a schematic process diagram showing one embodiment of the present invention. 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 heating device are naturally cooled, the fibers are bundled together with the application of the oil agent by the oil agent application device 4, are taken up by the first roller (take-off roller) 5, and are passed through the second roller 6 to the heating fluid treatment device 7.
After being subjected to a relaxation heat treatment, it is supplied to the winding device 8.

In the above steps, the inner wall temperature of the cylindrical heating device 3 needs to be in the range of 120 to 170 ° C. When the temperature is lower than 120 ° C., the effect of promoting orientation and crystallization is low, and a fiber having sufficient strength and elastic modulus cannot be obtained. 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 about 0.6-2.5m
Is appropriate. If the heating length is shorter than this range, the effect of accelerating the orientation and crystallization is reduced. If the heating length is longer than this range, the yarn sway in the heating device becomes large, and it is not preferable because the yarn unevenness is induced.

The take-up speed (ie, the surface speed of the first roller 5) needs to be 3000 m / min or more. The higher the stress applied to the yarn in the heating device, the greater the effect of promoting the orientation and crystallization. Therefore, the higher the take-up speed, the more desirable it is. If it is less than 3000 m / min, the effect is lacking. On the other hand, if it exceeds 7000 m / min, the passage time in the heating device becomes short, and the stress applied to the yarn becomes too high, which may cause cutting, which is not preferable.

By continuously supplying the taken fiber to the second roller 6 and subjecting it to a slight stretching or relaxation treatment, it is possible to finely adjust the physical properties according to the intended use and to form a good winding form. Can also. At that time, the surface speed ratio between the second roller 6 and the first roller 5 is preferably 0.95 to 1.20. If the surface speed ratio is lower than this range, the tension at the time of winding is low and the winding form is poor. If it is higher than this range, the elongation becomes low, which may lead to cutting, which is not preferable.

It is also possible to carry out heat treatment on an arbitrary roller. However, if the surface temperature of the roller is too high, the swaying of the fiber on the roller becomes large, causing thread spots and cutting. It is difficult to obtain a fiber having good dimensional stability, which is the object of the present invention. Therefore, in the present invention,
By performing a heat treatment with a heated gas or heated steam immediately before the winding device 8, it is possible to simultaneously satisfy both the operation stability at the time of spinning and the dimensional stability of the obtained fiber. The type of the heating gas is not particularly limited as long as it is air, nitrogen, or a material having a density and thermal conductivity close to those of air, nitrogen, and the use of pressurized steam enables more efficient heat treatment. At that time, the temperature of the heating gas or the heating steam is preferably set to 100 to 160 ° C. If the temperature is lower than 100 ° C., it is difficult to stably control the temperature of the steam, which causes fibrillation.
If the temperature exceeds 0 ° C., fusion between fibers is likely to occur.

Although the production method of the present invention can handle a wide range of brands, it is particularly preferable that the single yarn fineness is in the range of 0.5 to 8.0 d and the number of filaments is in the range of 10 to 250 filaments.

[0022]

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) Boiling water shrinkage rate The sample was immersed in boiling water for 15 minutes, air-dried, and the rate of change in length before and after that was determined. (3) Average molecular weight The number average value of dispersion by GPC analysis of a 0.4 wt% solution of chloroform of the sample was determined. (4) Biodegradability The sample was buried in soil for 12 months, taken out, measured for tensile strength, and evaluated based on the strength retention with respect to the initial tensile strength.

Examples 1 to 6 and Comparative Examples 1 to 7 According to the process shown in FIG. 1, poly-L having an optical purity of 99.0% was used.
-Lactic acid is supplied to an extruder-type melt spinning machine, melted at a temperature of 210 ° C, spun out from a die having 36 spinning holes of 0.3 mm in diameter, and then cooled with a cooling air at a temperature of 15 ° C to solidify the fiber. did. Continuously, effective heating length 130cm
After passing the fiber through the cylindrical heating device and allowing it to cool naturally,
The oil was applied at the same time as the bundle was condensed by the oil applying device, and the oil was applied, and the oil was applied to the first roller.

Subsequently, the fiber was heat-treated with heated steam through a second roller, and then wound up by a winding device to obtain a 75d / 36f polylactic acid fiber. Tables 1 and 2 show the above production conditions and characteristic values of the obtained polylactic acid fibers.

[0025]

[Table 1]

[0026]

[Table 2]

As is clear from Table 1, the polylactic acid fibers obtained in Examples 1 to 6 can be put to practical use in all of the strength, the elastic modulus at the initial stage and at 10% elongation, and the boiling water shrinkage ratio. Value.

On the other hand, as is clear from Table 2, Comparative Example 1 has a low heating cylinder temperature, Comparative Example 5 has a low average molecular weight, and all of the obtained fibers have sufficient strength and elastic modulus. It was not something. In Comparative Example 3, since the take-up speed was low and the fiber orientation was low, fusion was performed with heated steam. In Comparative Example 2, the fibers were fused together because the heating cylinder temperature was too high, and in Comparative Example 6, the yarn breakage occurred frequently during spinning due to the high average molecular weight. Next, Comparative Example 4 was a conventional stretching method that did not use a heating cylinder, and thus had insufficient strength and elastic modulus. In Comparative Example 7, the boiling water shrinkage was high and the dimensional stability was poor because no heated steam was used.

Examples 7 and 8 and Comparative Examples 8 and 9 Using poly-L-lactic acid having an optical purity shown in Table 2, polylactic acid fibers of 75d / 36f were obtained in the same manner as in Example 1. The average molecular weight at the time of ejection was 64,000 in all cases. Table 3 shows the characteristic values and biodegradability of the obtained polylactic acid fibers.

[0030]

[Table 3]

As is evident from Table 3, the polylactic acid fibers obtained in Examples 7 and 8 can be put to practical use in all of the strength, the initial elastic modulus at 10% elongation, and the boiling water shrinkage. The biodegradability was good 12 months after burying the soil. On the other hand, Comparative Example 8
Since the ratio of the L-form was low, the heat resistance was inferior and it was fused in boiling water. Further, Comparative Example 9 was inferior in biodegradability due to a high ratio of L-forms, and had little decrease in strength.

[0032]

According to the present invention, an inexpensive biodegradable polylactic acid fiber having practically sufficient elastic modulus and dimensional stability 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 this fiber is used, it will be completely decomposed after a certain period of time, so that if this fiber is used, it is 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]

 DESCRIPTION OF SYMBOLS 1 Spinneret 2 Cooling air blowing device 3 Cylindrical heating device 4 Oil supply device 5 First roller (take-off roller) 6 Second roller 7 Heated fluid processing device 8 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, speed 3
A polylactic acid fiber obtained by a method of winding at 000 m / min or more, wherein the elasticity at 10% elongation is 7 g / d or more and the boiling water shrinkage is 13% or less. 2. An average molecular weight of 50,000 to 100,000 and an optical purity of 9
After melt-spinning 5.0 to 99.5% of poly-L-lactic acid and once cooling and solidifying the spun fibers, the inner wall temperature is 120 to 17%.
After passing through a cylindrical heating device at 0 ° C., converging and applying an oil agent, the surface is taken up by a first roller having a surface speed of 3000 m / min or more, and stretched or relaxed with a subsequent second roller. A method of producing a polylactic acid fiber, comprising: immediately before a winding device, performing a heat treatment with a heated gas or heated steam, and then winding at a speed of 3000 m / min or more.