WO2005087988A1

WO2005087988A1 - Extremely fine polylactic acid fiber, fibrous structure and process for producing these

Info

Publication number: WO2005087988A1
Application number: PCT/JP2005/004165
Authority: WO
Inventors: Takanori Miyoshi; Kiyotsuna Toyohara; Hiroyoshi Minematsu
Original assignee: Teijin Limited
Priority date: 2004-03-16
Filing date: 2005-03-03
Publication date: 2005-09-22
Also published as: EP1731633A1; JPWO2005087988A1; CN1985032A; CA2560363A1; EP1731633A4; KR20060130732A; JP4243292B2; US20070172651A1

Abstract

A fibrous structure obtained by spinning a solution of L-lactic acid condensation product and D-lactic acid condensation product in accordance with an electrostatic spinning technique. There can be provided a fibrous structure containing fibers that have an extremely small fiber diameter, exhibiting excellent heat resistance and biodegradability.

Description

Specification

Ultrafine polylactic acid-based fibers, fiber structures, and methods for producing them

TECHNICAL FIELD The present invention relates to a fiber containing polylactic acid having a biological separation angle of 10 minutes as a component, and more particularly to an ultrafine polylactic acid-based fiber, a fibrous structure, and a method for producing them. Background art

Ultra-fine fibers are converted into woven or knitted or artificial leather from their soft texture and used for clothing and interior purposes. It is also used in the form of paper and non-woven fabric for filters, insulating paper, wipers, packaging materials, sanitary agents, etc.

In recent years, from the viewpoint of global environmental protection, reduction of environmental burden has been required. However, conventional nylon 6 nylon-polyethylene terephthalate, polypropylene, etc. used in microfibers do not decompose in soil or compost, so they must be incinerated or landfilled after use. The environmental load caused by leaving the landfill was large.

Therefore, ultrafine fibers that decompose in soil and compost are required. For example, ultrafine fibers made of a biodegradable thermoplastic aliphatic polyester having a single fiber fineness of 0.5 decitex or less have been proposed (see, for example, Patent Document 1).

See 1. ). Further, a fiber made of poly-L-lactic acid having a fiber diameter of 100 nm to 4 m has been proposed (for example, see Patent Document 2).

However, the ultrafine fibers obtained by the above proposal have poor heat resistance, and their uses are limited. As a method for improving the heat resistance of polylactic acid, formation of a stereo complex of poly (L-lactic acid) and poly (D-lactic acid) has recently attracted attention (for example, see Patent Document 3).

It is known that blending poly-lactic acid and poly-D-lactic acid in equal amounts can form a racemic crystal having a higher melting point than ordinary polylactic acid.

However, the polylactic acid stereocomplex fibers obtained so far contain both poly (L-lactic acid) single crystals and poly (D-lactic acid) single crystals, and the heat resistance is still insufficient. In addition, these fibers have a large fiber diameter, and a fiber structure formed from the fibers has insufficient flexibility (for example, see Patent Documents 3 and 4).

[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-192932

[Patent Document 2] International Publication No. 02/16680 Pamphlet [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-30523

[Patent Document 4] Japanese Patent Application Laid-Open No. 2003-138437 Disclosure of the Invention

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a fiber having an extremely small fiber diameter, excellent heat resistance and biodegradability.

Another object of the present invention is to provide a fibrous structure containing the fiber.

Still another object of the present invention is to provide a method for producing the above fiber structure by a very simple method. Brief Description of Drawings FIG. 1 is a diagram schematically showing one embodiment of an apparatus configuration for producing the fiber structure of the present invention.

FIG. 2 is a diagram schematically showing one embodiment of an apparatus configuration for producing the fibrous structure of the present invention.

FIG. 3 is a photographic diagram obtained by photographing the surface of the fibrous structure obtained in Example 1 with a scanning electron microscope (200 × magnification).

FIG. 4 is a photographic diagram obtained by photographing the surface of the fibrous structure obtained in Example 1 with a scanning electron microscope (× 800).

FIG. 5 is a photographic view ′ obtained by photographing the surface of the fiber structure obtained in Example 2 with a scanning electron microscope (200 × magnification).

FIG. 6 is a photographic diagram obtained by photographing the surface of the fiber structure obtained in Example 2 with a scanning electron microscope (magnification: 800,000).

FIG. 7 is a photographic diagram obtained by photographing the surface of the fibrous structure obtained in Comparative Example 1 with a scanning electron microscope (200 × magnification).

FIG. 8 is a photographic diagram obtained by photographing (800 × magnification) the surface of the fiber structure obtained in Comparative Example 1 with a scanning electron microscope.

FIG. 9 is a photographic diagram obtained by photographing the surface of the fibrous structure obtained in Comparative Example 2 with a scanning electron microscope (200 × magnification).

FIG. 10 is a photographic diagram obtained by photographing the surface of the fiber structure obtained in Comparative Example 2 with a scanning electron microscope (× 800).

FIG. 11 is a photographic diagram obtained by photographing the surface of the fiber structure obtained in Comparative Example 3 with a scanning electron microscope (200 × magnification).

FIG. 12 is a photographic diagram obtained by photographing (800 × magnification) the surface of the fiber structure obtained in Comparative Example 3 with a scanning electron microscope.

FIG. 13 is a scanning electron microscope showing the surface of the fibrous structure obtained in Example 3. It is a photograph figure obtained by taking a picture with a mirror (20000 times).

FIG. 14 is a photograph obtained by photographing the surface of the fibrous structure obtained in Example 3 with a scanning electron microscope (× 800).

FIG. 15 is a photographic diagram obtained by photographing the surface of the fiber structure obtained in Example 4 with a scanning electron microscope (200 × magnification).

FIG. 16 is a photographic diagram obtained by photographing (800 × magnification) the surface of the fiber structure obtained in Example 4 with a scanning electron microscope.

FIG. 17 is a photograph obtained by photographing the surface of the fibrous structure obtained in Comparative Example 4 with a scanning electron microscope (200 × magnification).

FIG. 18 is a photograph obtained by photographing (800 × magnification) the surface of the fiber structure obtained in Comparative Example 4 with a scanning electron microscope.

FIG. 19 is a photographic diagram obtained by photographing the surface of the fibrous structure obtained in Comparative Example 5 with a scanning electron microscope (200 × magnification).

FIG. 20 is a photographic diagram obtained by photographing (800 × magnification) the surface of the fiber structure obtained in Comparative Example 5 with a scanning electron microscope.

FIG. 21 is a photographic diagram obtained by photographing the surface of the fiber structure obtained in Comparative Example 6 with a scanning electron microscope (200 × magnification).

FIG. 22 is a photographic diagram obtained by photographing (800 × magnification) the surface of the fiber structure obtained in Comparative Example 6 with a scanning electron microscope. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.

The fiber of the present invention needs to have an average fiber diameter of 10 μπι or less. When the average fiber diameter of the fibers exceeds 10, the flexibility of the resulting fiber structure becomes poor, which is not preferable. The average fiber diameter of the fibers is 0. 0 is in the range of 1 to 5 μm.

The fiber of the present invention needs to have a fiber length of 20 μπι or more. If the fiber length is less than 20 μπι, the mechanical strength of the resulting fibrous structure will be insufficient. The fiber length is preferably at least 40 μπι, more preferably at least 1 mm.

Fibers of the present invention, it is necessary to the polylactic acid component Ru 1 90 ° have a C or higher melting point 1 "as the main component, the melting point is substantive free of components of less than 1 0 ^Q C Is preferred.

Here, the term “substantially free of components having a melting point of less than 190 ° C.” means that the obtained fiber has a melting endothermic curve (DSC curve) of 190 when subjected to differential scanning calorimetry. It means not showing an endothermic peak below ° C.

It is not preferable to have a component having a melting point of less than 190 ° C. because of poor heat resistance. The more preferable melting point of the fiber component is from 195 ° C to 250 ° C. Further, as described above, the fiber of the present invention is mainly composed of a polylactic acid component having a melting point of 190 ° C. or more.

More preferably, the fiber of the present invention has a depression having a diameter of 0.01 to 1 / ^ m on its surface, and the depression occupies 10 to 95 ° of the fiber surface. By having such a surface structure, the surface area of the fiber structure formed from the fiber is increased, and the decomposition rate in soil or in a composite is improved. The diameter of the recess is more preferably 0.02 to 0.5 μπι, and the ratio of the recess occupying the fiber surface is 40 to 95 ° /. Is more preferred.

In the present invention, the polylactic acid component is a polymer composed of a condensate of lactic acid in which 80% by mole or more based on all repeating units is used, and other components are used together within a range that does not impair the features of the present invention. It may be polymerized.

The term “main constituent” refers to all constituents of the fiber of the present invention. As 75% by weight or more, preferably 80% by weight. / ₀ or more, more preferably 90% by weight or more, especially 95% by weight or more. In the present invention, the polylactic acid component is preferably a condensate of L-lactic acid with 80 mol% or more based on all repeating units and a condensate of D-lactic acid with 80 mol% or more based on all repeating units. Here, a condensate of L-lactic acid in which 80 mol% or more based on all repeating units is 80 to 100 mol% of L-lactic acid and D-lactic acid or D-lactic acid. It is composed of 0 to 20 mol% of a copolymer component other than lactic acid. On the other hand, a condensate of D-lactic acid in which 80 mol% or more based on all repeating units is 80 to 100 mol% of D-lactic acid and L-lactic acid or a copolymer component other than L-lactic acid 0 ~ 20 mol%.

Other than the above-mentioned D-lactic acid and L-lactic acid, examples of the copolymerization component include oxyacid, ratatone, dicarboxylic acid, and polyhydric alcohol. Further, various polyesters, polyethers, polycarbonates, and the like, which are composed of these components and have a functional group capable of forming an ester bond, may also be mentioned. In the present invention, the polylactic acid component is composed of a condensate of L-lactic acid with 80 mol% or more based on all repeating units and a condensate of D-lactic acid with 80 mol% or more based on all repeating units. More preferably, the mixture has a weight ratio of (6: 4) to (4: 6).

More preferably, at least 80 mol% of the condensate of L-lactic acid and at least 80 mol% of the condensate of D-lactic acid based on all repeating units are substantially (5 : 5) It is more preferable to mix them.

In the present invention, the weight average molecular weight of the polylactic acid component is 100,000 or more The mechanical strength of the obtained fiber structure is improved, which is more preferable.

The fibrous structure of the present invention contains at least the above-mentioned ultrafine polylactic acid-based fibers. In the present invention, the term “fibrous structure” refers to a fiber formed by subjecting fibers to operations such as weaving, knitting, and lamination. The non-woven fabric is a preferred example.

In the fibrous structure of the present invention, the content of the ultrafine polylactic acid-based fiber is not particularly limited. However, when the content is 50% by weight or more, the characteristics of the ultrafine polylactic acid-based fiber can be utilized, which is preferable. The content is more preferably 80% by weight or more, and a fiber structure substantially composed of only the polylactic acid-based fiber is further preferable.

In particular, it is preferable that the fibers forming the fibrous structure have an average diameter of 10 Im or less, and further contain substantially no fiber having a fiber length of 20 µm or less.

In order to produce the fiber structure of the present invention, any method can be employed as long as the above-mentioned fibers can be obtained. However, 80 mol% or more of L- A condensate of lactic acid and a condensate of D-lactic acid, of which at least 80 mol%, based on all repeating units, are mixed in a weight ratio of (6: 4) to (4: 6), and then the solvent is added. A step of producing a solution by dissolving the solution in an aqueous solution, a step of spinning the solution by an electrostatic spinning method, and a step of accumulating the solution on a collecting substrate by the spinning. be able to.

Further, a step of preparing a solution by dissolving a condensate of L-l-lactic acid in a solvent in which at least 80 mol% based on all repeating units is used, and a step in which at least 80 mol% of D-lactic acid is based on all repeating units. Dissolving the condensate in a solvent to prepare a solution, and the weight ratio of the two solutions is (6: 4) to (4: 6). Mixing, a step of spinning the mixed solution by an electrostatic spinning method, and a step of accumulating the mixed solution on a collecting substrate by the spinning. .

Here, in the electrostatic spinning method, a solution in which a fiber-forming compound is dissolved is discharged into an electrostatic field formed between the electrodes, the solution is drawn toward the electrodes, and the formed fibrous substance is removed. A method for obtaining a fibrous structure by accumulating on a collecting substrate, wherein the fibrous substance includes not only a state in which a solvent in which a fiber-forming compound is dissolved is distilled off, but also a state in which the solvent is dissolved. The state contained in fibrous substances is also shown.

Usually, to produce a stereocomplex fiber composed of poly L-lactic acid and poly D-lactic acid, a melt-kneading and melt spinning force or a condensate of L-lactic acid and poly D-lactic acid is used. Dry spinning is performed from a solution in which the condensate is dissolved, but in any case, it is impossible to completely eliminate the melting point of 190 ° C or lower. However, it has surprisingly been found that the fiber obtained by the electrospinning method has substantially no melting point of 190 ° C. or less.

Next, an apparatus used in the electrostatic spinning method in the production method of the present invention will be described.

The above-mentioned electrode can be used as long as it shows conductivity of any metal, inorganic substance or organic substance, and has a thin film of conductive metal, inorganic substance or organic substance on an insulator. May be.

Further, the electrostatic field is formed between a pair or a plurality of electrodes, and a high voltage may be applied to any of the electrodes. This includes, for example, the use of two high-voltage electrodes with different voltage values (for example, 15 kV and 10 kV) and three electrodes connected to earth, or more than three electrodes. Number of electrodes It includes the case of using.

Next, a method for producing the fibers constituting the fiber structure of the present invention by the electrospinning method will be described step by step.

First, a solution in which the above-mentioned polylactic acid component is dissolved in a solvent is produced. Here, the concentration of the polylactic acid component in the solution is preferably 1 to 30% by weight. If the concentration is less than 1% by weight, it is difficult to form a fiber structure because the concentration is too low, which is not preferable. On the other hand, if it is larger than 30% by weight, the average diameter of the obtained fiber is undesirably large. A more preferred concentration is 2 to 25% by weight.

The solvent for dissolving the polylactic acid component is not particularly limited as long as it can dissolve the polylactic acid component and evaporate at the stage of spinning by the electrostatic spinning method to form a fiber. .

The use of a volatile solvent as the solvent facilitates the formation of the dents on the fiber surface described above, which is preferable. The volatile solvent in the present invention is a substance having a boiling point of 200 ° C. or less under atmospheric pressure and being liquid at room temperature (for example, 27 ° C.). Specific volatile solvents include, for example, methylene chloride, chlorophonorem, dichloroethane, tetrachloroethane, and trichloroethane.

, Dibromomethane, bromohonolem, tetrahydrofuran, 1,4-dioxane, 1,1,1,3,3,3-hexafluoroisopropanol, toluene, xylene, dimethylformamide, etc. Preferred are dimethylene chloride, chlorophonorem, dichloroethane, tetrachloroethane, trichloroethane, dibromomethane, bromophonolem, tetrahydrofuran and 1,4-dioxane, and most preferred is methylene chloride. These solvents may be used alone or as a mixed solvent obtained by combining a plurality of solvents. Next, the step of spinning the solution by the electrostatic spinning method will be described. Any method can be used to discharge the solution into the electrostatic field. For example, by supplying the solution to a nozzle, the solution is placed at an appropriate position in the electrostatic field, and the solution is discharged from the nozzle. What is necessary is just to string by an electric field and to make it a fiber.

Hereinafter, a preferred embodiment for producing the fibrous structure of the present invention will be described more specifically with reference to FIG.

An appropriate means, for example, a needle-like solution jet nozzle (3 in FIG. 1), to which a voltage is applied by means of a high-voltage generator (6 in FIG. 1), is applied to the tip of the cylindrical solution holding tank (3 in FIG. 1) of the syringe. Install 1) in Fig. 1 and guide the solution (2 in Fig. 1) to the tip of the nozzle that ejects the solution. The tip of the solution ejection nozzle (1 in FIG. 1) is arranged at an appropriate distance from the grounded fibrous substance collecting electrode (5 in FIG. 1), and the solution (2 in FIG. 1) is discharged from the solution ejection nozzle. A fibrous substance can be formed between the tip of the nozzle (1 in FIG. 1) and the fibrous substance collecting electrode (5 in FIG. 1).

As another embodiment, referring to FIG. 2, fine droplets (not shown) of the solution can be introduced into an electrostatic field, and the only requirement in that case is the solution (FIG. 2). 2) is to be placed in an electrostatic field and held away from the fibrous substance collecting electrode (5 in FIG. 2) at such a distance that fibrillation can occur. For example, the electrode (2 in FIG. 2) in the solution holding tank (3 in FIG. 2) having the solution ejection nozzle (1 in FIG. 2) directly opposes the fibrous substance collecting electrode (2 in FIG. 2). 4) in the figure can also be inserted.

When the solution is supplied from a nozzle into an electrostatic field, several nozzles can be used in parallel to increase the production rate of the fibrous substance. The distance between the electrodes depends on the amount of charge, nozzle size, amount of solution ejected from the nozzle, solution concentration, etc. However, when the voltage was about 10 kV, a distance of 5 to 20 cm was appropriate. The applied electrostatic potential is generally 3 to 100 kV, preferably 5 to 50 kV, and more preferably 5 to 30 kV. The desired potential may be created by any suitable method known in the art.

In the above two embodiments, the electrodes also serve as the collecting substrate, but by installing a potential collecting substrate between the electrodes, a collecting substrate is provided separately from the electrodes, and the fiber laminate is collected there. You can do it. In this case, for example, continuous production is possible by placing a belt-like substance between the electrodes and using this as a collecting substrate.

Next, a step of obtaining a fiber structure accumulated on the collecting substrate will be described. In the present invention, during the spinning of the solution toward the collecting substrate, the solvent evaporates according to the conditions to form a fibrous substance. At normal room temperature, the solvent evaporates completely before being collected on the collecting substrate. However, if the solvent evaporation is insufficient, spinning may be performed under reduced pressure. At the time of collection on the collection substrate, a fiber structure satisfying at least the fiber average diameter and the fiber length is formed. The spinning temperature may be adjusted according to the evaporation behavior of the solvent and the viscosity of the spinning solution, which is usually in the range of 0 to 10 ° C. Preferably, the relative humidity is between 20 and 80% RH. If the relative humidity is out of the above range, it becomes difficult to perform stable spinning for a long time. A more preferred relative humidity is 30 to 70% RH.

The fibrous structure obtained by the production method of the present invention may be used alone, or may be used in combination with other members according to handleability and other requirements. For example, a non-woven fabric that can serve as a support By forming a fiber laminate on a cloth, a woven fabric, a film, or the like, a member combining the support base material and the fiber laminate can be produced.

The obtained fiber structure may be subjected to a heat treatment or a chemical treatment. Further, at any stage before the spinning, the above-mentioned polylactic acid is mixed with an emulsion, an organic or inorganic powder, a filler or the like. You may.

For example, by supporting various catalysts on the fiber structure of the present invention, it can be used as a catalyst-carrying substrate. Example

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. The evaluation items in each of the following examples and comparative examples were implemented by the following methods. Average fiber diameter:

The surface of the obtained fibrous structure was photographed with a scanning electron microscope (S-240, manufactured by Hitachi, Ltd.) (magnification: 20000 times). Was selected, the diameter of the fiber was measured, and the average value of all the fiber diameters (η = 20) was determined to be the average diameter of the fiber. Confirmation of the presence of fibers with a fiber length of 20 μm or less:

The surface of the obtained fiber structure was photographed with a scanning electron microscope (S-240, manufactured by Hitachi, Ltd.) (magnification: 200,000), and a photograph obtained was observed. It was checked whether fibers of less than m existed. Depression of fiber surface structure A scanning electron micrograph (magnification: 8000 times) of the surface of the obtained fiber structure was taken. Using general-purpose image processing software (NanoHunter NS 2K ~ Pro / LtVer 5.2, manufactured by Nanosystems Co., Ltd.), select one of the sharpest fibers in the photograph, An imaginary line A passing through the central axis of the selected fiber and imaginary lines B and B 'along both outer edges of the selected fiber are set, and then the center of the imaginary line A and the imaginary lines B and B' is set. Set two virtual lines C and C 'that pass through.

The imaginary lines C and C set above and the part surrounded by both edges of the photograph were extracted using image processing software, and the proportion of the area of the dent in that range was calculated.

The measurement was performed by averaging the area ratios obtained from electron micrographs at arbitrary 10 locations of the fiber structure.

Weight average molecular weight:

The weight-average molecular weight was measured by GPC-11 (manufactured by Showa Denko KK) (column SH ODEX LF-804, solvent port form, detector RI, styrene conversion). Melting point:

The DSC curve of the obtained fiber structure was measured by differential scanning calorimetry (DSC-2920, manufactured by Texas Instruments), and the melting point was determined from the endothermic peak. Example 1 500 ppm of tin octylate is mixed with D-lactide, and polymerized in a reaction vessel equipped with a stirrer at 200 ° C for 60 minutes under a nitrogen atmosphere to obtain a poly (D-lactic acid) having a weight average molecular weight of 120,000. A homopolymer was obtained.

A solution obtained by dissolving 1 part by weight of the obtained poly D-lactic acid in 9 parts by weight of methylene chloride, and poly L-lactic acid (manufactured by Shimadzu Corporation: trade name “L acty 93 1”, weight average molecular weight 16) 8,000) A solution was prepared by dissolving 1 part by weight in 9 parts by weight of methylene chloride, and both parts were mixed by 5 parts by weight.

Next, the solution was discharged to the fibrous substance collecting electrode 5 for 5 minutes using the apparatus shown in FIG. The inner diameter of the ejection nozzle (1 in Fig. 2) is 0.8 mm, the voltage is 12 kV, and the distance from the ejection nozzle (1 in Fig. 2) to the fibrous material collecting electrode (5 in Fig. 2) is 1 The relative humidity was 2 cm and the relative humidity was 35% RH. When the obtained fiber structure was measured with a scanning electron microscope (S-240, manufactured by Hitachi, Ltd.), the average fiber diameter was 3 m, and fibers with a fiber length of 20 / zm or less were present. Did not. The average diameter of the depressions on the fiber surface was 0.2 βm, and the ratio of the area of the depressions to the fiber surface was 23%. Scanning electron micrographs of the fiber structure are shown in Figs.

As a result of DSC measurement of the obtained fiber structure, the melting point was 2 16 ° C, and no endothermic peak was observed below 190 ° C. Example 2

6 parts by weight of a solution in which 1 part by weight of poly D-lactic acid is dissolved in 9 parts by weight of methylene chloride and 4 parts by weight of a solution in which 1 part by weight of poly L-l-lactic acid is dissolved in 9 parts by weight of methylene chloride are mixed. A fibrous structure was obtained in the same manner as in Example 1, except that the distance to the particulate matter collecting electrode was 10 cm.

The average fiber diameter of the obtained fiber structure is 4 μm, and the fiber length is 20 μm or less. The lower fiber was not present. The average diameter of the depressions on the fiber surface was 0.2 μm, and the area of the depressions on the fiber surface was 22%. Figs. 5 and 6 show scanning electron micrographs of the fiber structure.

As a result of DSC measurement of the obtained fiber structure, the melting point was 218 ° C, and no endothermic peak was observed below 190 ° C. Comparative Example 1

Example 1 was repeated except that 7 parts by weight of a solution in which 1 part by weight of poly D-lactic acid was dissolved in 9 parts by weight of methylene chloride and 3 parts by weight of a solution in which 1 part by weight of poly L-monolactic acid was dissolved in 9 parts by weight of methylene chloride. A fiber structure was obtained in the same manner as in 2.

The average fiber diameter of the obtained fiber structure was 3 m, and there was no fiber having a fiber length of 20 μm or less. The average diameter of the concave portion on the fiber surface was 0.2 μπι, and the ratio of the area of the concave portion to the fiber surface was 31%. Scanning electron micrographs of the fiber structure are shown in FIGS. 7 and 8.

As a result of DSC measurement of the obtained fiber structure, the main melting point was 219 ° C, and a small endothermic peak was observed at 165 ° C. Comparative Example 2

A fiber structure was obtained in the same manner as in Example 2, except that only a solution in which 1 part by weight of poly D-lactic acid was dissolved in 9 parts by weight of methylene chloride was used.

The average fiber diameter of the obtained fiber structure was 2 μm, and there was no fiber having a fiber length of 20 μm or less. The average diameter of the concave portion on the fiber surface was 0.2 m, and the ratio of the area of the concave portion to the fiber surface was 21%. Scanning electron micrographs of the fiber structure are shown in FIGS. 9 and 10.

As a result of DSC measurement of the obtained fiber structure, the melting point was 1.4 ° C. Comparative Example 3

A fiber structure was obtained in the same manner as in Example 2, except that only a solution obtained by dissolving 0.7 part by weight of poly L-monolactic acid in 9.3 parts by weight of methylene chloride was used.

The average fiber diameter of the obtained fiber structure was 3 μm, and there was no fiber having a fiber length of 20 m or less. The average diameter of the depressions on the fiber surface was 0.2 Aim, and the ratio of the area of the depressions to the fiber surface was 27%. Scanning electron micrographs of the fibrous structure are shown in FIGS. 11 and 12.

As a result of DSC measurement of the obtained fiber structure, the melting point was 1722 ° C. Example 3

A fibrous structure was obtained in the same manner as in Example 2, except that a mixed solvent of methylene chloride and ZDMF (8/2; weight ratio) was used instead of methylene chloride. The average fiber diameter of the obtained fiber structure was 2 μm, and there was no fiber having a fiber length of 20 μm or less. No dents were observed on the fiber surface. Scanning electron micrographs of the fiber structure are shown in FIGS. 13 and 14.

As a result of DSC measurement of the obtained fiber structure, the melting point was 220 ° C., and no endothermic peak was observed below 190 ° C. '' Example 4

4 parts by weight of a solution prepared by dissolving 1 part by weight of poly D-lactic acid in 9 parts by weight of a mixed solvent of methylene chloride and ZDMF (8/2; weight ratio) and 1 part by weight of poly L-lactic acid in a mixed solvent of 8 parts of A fiber structure was obtained in the same manner as in Example 2 except that 6 parts by weight of the solution dissolved in 9 parts by weight was mixed. The average fiber diameter of the obtained fiber structure was 2 m, and there was no fiber having a fiber length of 20 μm or less. No dents were observed on the fiber surface. Scanning electron micrographs of the fiber structure are shown in FIGS. 15 and 16.

As a result of DSC measurement of the obtained fiber structure, the melting point was 222 ° C., and no endothermic peak was observed below 190 ° C. Comparative Example 4

3 parts by weight of a solution prepared by dissolving 1 part by weight of poly D-lactic acid in 9 parts by weight of a mixed solvent of methylene chloride / DMF (8 to 2; weight ratio) and 1 part by weight of poly L-lactic acid in a mixed solvent of methylene chloride and ZDMF ( A fiber structure was obtained in the same manner as in Example 2 except that 7 parts by weight of the solution dissolved in 9 parts by weight was mixed. The average fiber diameter of the obtained fiber structure was 2/2. / m, and no fiber with a fiber length of 20 μππ or less was present. No dents were observed on the fiber surface. Scanning electron micrographs of the fiber structure are shown in Fig. 17 and Fig. 18.

As a result of DSC measurement of the obtained fiber structure, the main melting point was 21 ° C and a small endothermic peak was observed at 156 ° C. Comparative Example 5

A fibrous structure was obtained in the same manner as in Example 2 except that only a solution in which 1 part by weight of poly D-lactic acid was dissolved in 9 parts by weight of a mixed solvent of methylene chloride and ZDMF (8 to 2; weight ratio) was used. Was.

The average fiber diameter of the obtained fiber structure was 1 μm, and there was no fiber having a fiber length of 20 m or less. No dents were observed on the fiber surface. Scanning electron micrographs of the fiber structure are shown in FIGS. 19 and 20. As a result of DSC measurement of the obtained fiber structure, the melting point was 172 ° C. Comparative Example 6

A fibrous structure was obtained in the same manner as in Example 2, except that only a solution in which 1 part by weight of poly L-monolactic acid was dissolved in 9 parts by weight of a mixed solvent of methylene chloride / DMF (8Z2; weight ratio) was used. Was.

The average fiber diameter of the obtained fiber structure was 3 μm, and there was no fiber having a fiber length of 20 μm or less. Some wrinkles were observed on the fiber surface, but no dents were observed. Scanning electron micrographs of the fiber structure are shown in FIGS. 21 and 22.

As a result of DSC measurement of the obtained fiber structure, the melting point was 170 ° C.

Claims

1. An ultrafine polylactic acid-based fiber having a polylactic acid component having a melting point of 190 ° C. or more as a main constituent and having an average fiber diameter of 10 μm or less and a fiber length of 20 μm or more.

2. The fiber according to claim 1, wherein the fiber has substantially no component having a melting point of less than 190 ° C.

3. The fiber surface according to claim 1, wherein the surface of the fiber has a depression having a diameter of 0.01 to 1 μπ having an Sι diameter, and the depression occupies 10 to 95% of the fiber surface. Fiber. Enclosure

4. The polylactic acid component is a mixture of a condensate of L-lactic acid with 80 mol% or more based on all repeating units and a condensate of D-lactic acid with 80 mol% or more based on all repeating units. The fiber according to claim 1.

5. The fiber according to claim 4, wherein the weight ratio of the condensate of L-lactic acid to the condensate of D-lactic acid is (6: 4) to (4: 6).

6. A fiber structure comprising at least the ultrafine polylactic acid-based fiber according to claim 1.

7. The fiber structure according to claim 6, wherein the fibers forming the fiber structure have an average diameter of 10 µm or less, and further substantially do not include fibers having a fiber length of 20 m or less.

8. At least 80 mol% of the condensate of L-lactic acid and at least 80 mol% of the condensate of D-lactic acid based on the total repeating units, based on the total repeating units, have a weight ratio of (6: 4 ) To (4: 6), and then dissolving in a solvent to produce a solution; spinning the solution by an electrostatic spinning method; To obtain a fibrous structure to be used A method for producing a fibrous structure, comprising:

9. The production method according to claim 8, wherein the solvent is a volatile solvent.

10. The production according to claim 8, wherein the relative humidity between the nozzle on which the fibrous material is formed and the collecting substrate is in the range of 20 to 80% RH in the step of spinning by the electrostatic spinning method. Method.

1 1. At least 80 mol% of L-lactic acid condensate is dissolved in a solvent to prepare a solution, based on all repeating units, and at least 80 mol% of D-lactic acid is condensed based on all repeating units. Dissolving the body in a solvent to produce a solution; mixing the two solutions so that the weight ratio thereof is (6: 4) to (4: 6); A method for producing a fiber structure, comprising: spinning by an electrospinning method; and obtaining a fiber structure accumulated on a collecting substrate by the spinning.

1 2. The production method according to claim 11, wherein the solvent is a volatile solvent.

1 3. The volatile solvent is at least one selected from the group consisting of methylene chloride, chloroform, dichloroethane, tetrachloroethane, trichloromethane, dibromomethane, bromoform, tetrahydrofuran, and 1,4-dioxane. 13. The production method according to claim 12, wherein:

14. The method according to claim 11, wherein the relative humidity between the nozzle on which the fibrous substance is formed and the collecting substrate in the step of spinning by the electrostatic spinning method is in the range of 20 to 80% RH. Method.