JP2006200085A - Polylactic acid short fiber, method for producing the same and nonwoven fabric - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid short fiber having an excellent mechanical strength and also showing less deformation caused by heat, a method for producing the same, and a nonwoven fabric using the polylactic acid short fiber as a main fiber and having a good dimensional stability. <P>SOLUTION: This polylactic acid short fiber is characterized by constituted with the polylactic acid having ≥(99/1) ratio of the L-lactic acid/D-lactic acid (copolymerization molar ratio), ≤30% dry shrinkage at 140°C and ≥3.0 cN/dtex single fiber strength. Also, the polylactic acid short fiber is produced by melt-spinning the polylactic acid having ≥(99/1) ratio of the L-lactic acid/D-lactic acid (copolymerization molar ratio) and ≤0.08 mass% monomer amount, then drawing the obtained undrawn yarn and performing a heat treatment under a tension. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a polylactic acid short fiber having excellent mechanical strength and less deformation due to heat, a method for producing the same, and a non-woven fabric having good dimensional stability using the polylactic acid short fiber as a main fiber. is there.

In recent years, since conventional synthetic resins such as polyethylene terephthalate use petroleum as a raw material, the use of conventional synthetic resins causes a problem of promoting the depletion of petroleum. Therefore, plant-derived polylactic acid resins are attracting attention. Therefore, polylactic acid fibers and nonwoven fabrics using these fibers have also been proposed (for example, Patent Document 1).

  However, non-woven fabrics using these polylactic acid fibers as main fibers and binder fibers have a problem that when the heat-sealing treatment is performed with hot air or the like, the non-woven fabric shrinks and the texture becomes stiff.

Therefore, in order to solve this problem, Patent Document 2 proposes a non-woven fabric using polylactic acid stereocomplex fibers having high heat resistance, which is a blend of poly L-lactic acid and poly D-lactic acid as polylactic acid fibers. ing. However, since it is difficult to produce poly-D lactic acid industrially at present, the cost is so high that it is impossible to industrially produce a nonwoven fabric using polylactic acid stereocomplex fibers. is there.
Japanese Patent No. 3329350 JP 2003-286640 A

  The present invention solves the problem that a nonwoven fabric using the above-mentioned conventional polylactic acid fiber as a main fiber or binder fiber tends to shrink and deform at the time of heat-sealing, has excellent mechanical strength, and It is an object of the present invention to provide a polylactic acid short fiber that is less deformed by heat, a method for producing the same, and a non-woven fabric having good dimensional stability using the polylactic acid short fiber as a main fiber.

The inventor of the present invention has arrived at the present invention as a result of intensive studies to solve the above-mentioned problems.
That is, the gist of the present invention is as follows.
(1) A polylactic acid short fiber, which is composed of polylactic acid having an L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99/1 or more and a dry heat shrinkage at 140 ° C. of 3. 2. The polylactic acid short fiber characterized by being a polylactic acid according to claim 1, having a single yarn strength of 0 c or less and a single yarn strength of 3.0 cN / dtex or more.
(2) Polylactic acid having an L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99/1 or more and a monomer amount of 0.08% by mass or less was melt-spun, and then the obtained undrawn yarn was drawn. After that, a tension heat treatment is performed, The method for producing polylactic acid short fibers according to (1) above.
(3) 50-90% by mass of polylactic acid short fibers described in (1) above and aliphatic polyester having a melting point of 100-140 ° C. as a sheath component, L-lactic acid / D-lactic acid (copolymerization molar ratio) is A short fiber nonwoven fabric comprising 50 to 10% by mass of a polylactic acid-based binder fiber having 99/1 or more polylactic acid as a core component.

  The polylactic acid short fiber of the present invention is a fiber that is hardly deformed by heat and has excellent mechanical strength. Therefore, the nonwoven fabric using this polylactic acid short fiber as a main fiber is small in shrinkage deformation at the time of heat-sealing and has excellent dimensional stability.

  Hereinafter, the present invention will be described in detail.

  First, the polylactic acid short fiber of the present invention is polylactic acid mainly composed of L-lactic acid, and is composed of polylactic acid having L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99/1 or more. That is, it is composed of polylactic acid having L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99/1 to 100/0. Polylactic acid that deviates from the copolymerization molar ratio has a low melting point, and the object of the present invention is not achieved.

  The polylactic acid short fiber of the present invention has a characteristic that the dry heat shrinkage at 140 ° C. is 3.0% or less. When the dry heat shrinkage rate at 140 ° C. is higher than 3.0%, the fiber structure having a desired size and texture can be obtained because it is thermally deformed during heat fusion treatment during the production of a fiber structure such as a nonwoven fabric. It becomes difficult to be. By setting the dry heat shrinkage at 140 ° C. to 3.0% or less, deformation due to heat treatment in producing the fiber structure is small, and the obtained fiber structure is also difficult to be thermally deformed. Furthermore, it is preferable that the dry heat shrinkage at 150 ° C. of the polylactic acid short fiber is 5.0% or less.

  Furthermore, the polylactic acid short fiber of the present invention has a single yarn strength of 3.0 cN / dtex or more. If the single yarn strength is less than 3.0 cN / dtex, the mechanical strength of the fiber structure formed by the polylactic acid short fibers tends to decrease, and this tends to occur. Furthermore, it is common knowledge of those skilled in the art that the single yarn strength is preferably 3.3 cN / dtex or higher, and the higher the single yarn strength is, it is common knowledge of those skilled in the art, but the upper limit is 5.0 cN / dtex. The object of the present invention is fully achieved.

  Mechanical crimps may be imparted to the polylactic acid short fibers of the present invention. The mechanical crimp is a crimp that is mechanically applied by a push-type crimper or the like, and the number of crimps is preferably in the range of 5 to 20 pieces / 25 mm, particularly preferably 8. -15 pieces / 25 mm, more preferably 10-13 pieces / 25 mm, and the crimp rate is in the range of 5-30%, particularly preferably 7-20%, and more preferably 9-15%. If the number of crimps is less than 5/25 mm or the crimp rate is lower than 5%, the card passing property tends to be inferior at the time of web creation. Further, when the number of crimps is greater than 20/25 mm, or when the crimp rate is higher than 30%, the fibers are strongly entangled, and nep and the like are likely to occur.

  Next, the manufacturing method of the polylactic acid short fiber of this invention which has the said characteristic is demonstrated.

  In the present invention, it is important that L-lactic acid / D-lactic acid (copolymerization molar ratio) of polylactic acid used as a raw material, the amount of monomer, and heat setting (heat treatment) of fibers are performed under tension.

  First, polylactic acid having L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99/1 or more and a monomer amount of 0.08% by mass or less is prepared. L-lactic acid / D-lactic acid (copolymerization molar ratio) is less than 99/1, that is, L-lactic acid / D-lactic acid deviates from 99/1 to 100/1, and the monomer amount is 0.08% by mass. When polylactic acid exceeding the amount is used as a raw material, the dry heat shrinkage rate of the fiber is remarkably increased, and it becomes difficult to set the dry heat shrinkage rate of the fiber to 3.0% or less.

  Moreover, it is preferable that the moisture content of the polylactic acid used as a raw material is 100 ppm or less. If the water content exceeds 100 ppm, polylactic acid tends to be hydrolyzed during melt spinning, which is not preferable.

  The number average molecular weight of polylactic acid is preferably 60000-90000.

  In the present invention, the above-described polylactic acid is melt-spun first, and the spinning temperature is preferably set to 235 ° C. or lower. Next, the undrawn yarn obtained by melt spinning is drawn. The stretching conditions are preferably a stretching temperature of 50 to 70 ° C. and a stretching ratio (DR) of 3.0 to 5.0 in consideration of stretchability and physical properties (strength and the like).

  Next, the drawn yarn is subjected to heat treatment. By performing the heat treatment, a fiber having low heat shrinkage can be obtained. In the present invention, it is important to perform this heat treatment under tension (tensile heat treatment). The polylactic acid fiber has a strong tendency to decrease the single yarn strength by heat treatment, and the single yarn strength is remarkably lowered when heat treatment (relaxation heat treatment) is performed in a non-tensioned state, that is, in a relaxed state, not under tension. In order to maintain the single yarn strength, it is necessary to perform tension heat treatment. In general, the effect of suppressing thermal shrinkage of the fiber obtained is higher in the relaxation heat treatment, but the polylactic acid fiber of the present invention uses polylactic acid having a specific copolymerization ratio and very high crystallinity. Therefore, even if relaxation heat treatment is not performed, the desired low shrinkage can be achieved and high strength can be maintained. As the tension heat treatment, heat treatment may be performed in a state where tension is applied to the yarn with a heat drum or a heater plate, and the temperature is preferably 140 to 155 ° C.

  Next, crimps are imparted to the yarn after the tension heat treatment as necessary. As a method for imparting crimps, any known method may be used, and it may be a push-in type crimper or the like, preferably by providing mechanical crimps having a crimp number of 5 to 20/25 mm and a crimp rate of 5 to 30%. Good.

  Next, a finishing oil is applied to the yarn. After applying the finishing oil, it may be dried with hot air or the like, but since it is under non-tension, the drying temperature may be set to a low temperature of 50 to 80 ° C.

  Finally, it is cut into a predetermined fiber length to obtain polylactic acid short fibers having a dry heat shrinkage at 140 ° C. of 3.0% or less and a single yarn strength of 3.0 dN / dtex or more.

  Next, the nonwoven fabric which consists of the polylactic acid-type short fiber of this invention is demonstrated.

  The nonwoven fabric of the present invention is composed of a main fiber composed of the above-described short polylactic acid fibers, and a polylactic acid-based binder fiber having an aliphatic polyester having a specific melting point as a sheath component and a specific polylactic acid as a core component. . The binder component (sheath component) of the binder fiber is melted or softened, and the constituent fibers are heat-fused, heat-fixed, thermocompression bonded, etc., and integrated as a nonwoven fabric.

  In the present invention, the mixing ratio of the polylactic acid short fibers as the main fibers is 50 to 90% by mass, preferably 65 to 90% by mass. When the blending ratio of the polylactic acid short fibers is less than 50% by mass, the blending ratio of the polylactic acid short fibers having a low dry heat shrinkage ratio is decreased, and therefore, the nonwoven fabric is likely to shrink or deform due to heat, which is not preferable. On the other hand, when the mixing ratio of the polylactic acid short fibers exceeds 90% by mass, the mixing ratio of the binder fibers decreases and the strength of the nonwoven fabric tends to decrease.

  The polylactic acid-based binder fiber constituting the nonwoven fabric of the present invention contains polylactic acid having L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99/1 or more as a core component. That is, L-lactic acid / D-lactic acid (copolymerization molar ratio) is L-lactic acid-based polylactic acid having a ratio of 99/1 to 100/0. In general, the binder fiber has a low melting point of the sheath component and cannot be sufficiently heat-set in the stretching process or the like, and thus tends to be highly shrunk. However, in the present invention, L-lactic acid / D-lactic acid ( Since highly crystalline polylactic acid having a copolymerization molar ratio) of 99/1 or more is used as a core component, shrinkage due to heat can be suppressed. When L-lactic acid / D-lactic acid (copolymerization molar ratio) is less than 99/1, the crystallinity of polylactic acid is not sufficiently high, so that the shrinkage due to heat increases and the effects of the present invention are hardly obtained.

  Moreover, polylactic acid-type binder fiber uses aliphatic polyester whose melting | fusing point is 100-140 degreeC as a sheath component. When the melting point of the aliphatic polyester serving as the sheath component is less than 100 ° C., the heat resistance of the non-woven fabric is deteriorated, and softening or deformation due to heat during use tends to occur. On the other hand, when the melting point of the aliphatic polyester exceeds 140 ° C., the melting point difference from the polylactic acid short fiber as the main fiber becomes small, the heat treatment temperature is limited, and the desired physical properties and texture tend to be hardly obtained.

  The aliphatic polyester as the sheath component is not particularly limited as long as the peak temperature of the melting peak obtained by DSC measurement using a differential scanning calorimeter is 110 to 140 ° C., and polylactic acid, polyethylene succinate, polybutylene succinate Polycaprolactam, poly-3-hydroxypropionate, poly-3-hydroxybutyrate, poly-3-hydroxybutyrate valerate and the like can be used. In addition, cyclic lactones such as L-lactic acid, D-lactic acid, and ε-caprolactone, and α-oxy such as α-hydroxybutyric acid, α-hydroxyisobutyric acid, α-hydroxyvaleric acid, and the like may be used as long as the effects of the present invention are not impaired. Acids, glycols such as ethylene glycol and 1,4-butanediol, and dicarboxylic acids such as succinic acid, sebacic acid and adipic acid may be contained.

  Here, in the present invention, the aliphatic polyester constituting the sheath component is polylactic acid mainly composed of L-lactic acid having an L-lactic acid / D-lactic acid (copolymerization molar ratio) of 94/6 to 90/10. Preferably there is. Polylactic acid is a plant-derived resin, and it is preferable to use it as a sheath component of the binder fiber because the ratio of the plant-derived resin of the nonwoven fabric of the present invention can be increased. By setting L-lactic acid / D-lactic acid (copolymerization molar ratio) to 94/6 to 90/10, the melting point can be about 100 to 140 ° C.

  Moreover, in this invention, it is preferable that the aliphatic polyester which comprises a sheath component is polybutylene succinate. By using polybutylene succinate as the sheath component, it is preferable to use the resulting binder fiber because a nonwoven fabric having a very soft texture can be obtained.

  In the present invention, the aliphatic polyester constituting the sheath component is preferably a copolymer obtained by copolymerizing 1 to 10 mol% of lactic acid with polybutylene succinate. By using, as a sheath component, a copolymer obtained by copolymerizing lactic acid with polybutylene succinate in an amount of 1 to 10 mol%, the resulting binder fiber has a soft texture and high compatibility with polylactic acid. Therefore, the adhesiveness with the polylactic acid short fiber as the main fiber is improved, which is preferable. The lactic acid copolymerized with polybutylene succinate may be either L-lactic acid or D-lactic acid. When the amount of lactic acid to be copolymerized is less than 1 mol%, the compatibility with polylactic acid is not sufficiently improved, and the effect of improving adhesiveness cannot be expected. On the other hand, when it is more than 10 mol%, the inherent flexibility of polybutylene succinate tends to be impaired.

  The composite ratio of the core component and the sheath component of the binder fiber is not particularly limited, but is preferably 30/70 to 70/30 in terms of the mass ratio of the core / sheath from the viewpoint of adhesiveness, yarn production, and the like.

  The fineness of the polylactic acid short fibers and the polylactic acid-based binder fibers constituting the nonwoven fabric of the present invention is preferably about 1.0 to 80 dtex, more preferably 1.7 to 50 dtex in consideration of texture, adhesion performance, and the like. Moreover, as a cut length, 5-100 mm is preferable and 25-70 mm is more preferable. Further, the cross-sectional shape of both fibers is not limited to a circular cross section, and may be a flat cross section, a polygon, a multi-leaf shape, a gourd shape, an alphabet shape, and other various non-circular shapes (an irregular shape). .

  Furthermore, the end fibers such as aliphatic alcohols, carbodiimide compounds, oxazoline compounds, oxazine compounds, and epoxy compounds are added to the polylactic acid for the purpose of enhancing the durability of the polylactic acid, to both the fibers constituting the nonwoven fabric of the present invention. You may have done.

  Furthermore, the two fibers constituting the nonwoven fabric of the present invention include various pigments, dyes, water repellents, water absorbents, flame retardants, stabilizers, antioxidants, ultraviolet absorbers, metal particles, crystal nucleating agents, lubricants, You may mix a plasticizer, an antibacterial agent, a fragrance | flavor, and other additives.

  The non-woven fabric of the present invention is composed of polylactic acid short fibers and polylactic acid-based binder fibers, which are main fibers, but may be mixed with other fibers within a range not impairing the effects of the present invention. . Examples of other fibers include synthetic fibers such as polyester fibers, nylon fibers, acrylic fibers, and polypropylene fibers, recycled fibers such as rayon fibers, and natural fibers such as wool, cotton, hemp, and pulp.

  The nonwoven fabric of the present invention can be obtained by the following method.

  First, composed of polylactic acid short fibers, which are the main fibers, and polylactic acid-based binder fibers in a desired ratio, and after forming a web using a card machine or the like, the binder component is melted or softened by heat treatment. The fibers are fused and integrated as a nonwoven fabric.

  For heat treatment, a method of fusion bonding with a heat fusion treatment device using heated air such as a continuous heat treatment machine (thermal through), or a device comprising a pair of heat rolls such as a heat embossing device and a heat calender device. Examples thereof include a method in which the binder fiber is melt-pressed through and the constituent fibers are integrated by fusing the binder components. Note that before the heat treatment, needling processing or spunlace processing may be performed.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these.

In addition, the measuring methods, such as a characteristic value in an Example, are as follows.
(1) Number average molecular weight and monomer amount of resin The resin was dissolved in chloroform to a concentration of 10 mg / mL, and measured by gel permeation chromatography (GPC) using chloroform as a solvent. The detector used was a refractometer, and polystyrene was used as a molecular weight standard. Moreover, the monomer amount (mass%) in resin was computed from the ratio of the component of molecular weight 1000 or less.

(2) L-lactic acid / D-lactic acid (copolymerization molar ratio)
The copolymer molar ratio of L-lactic acid and D-lactic acid was measured by a high performance liquid chromatography (HPLC) method using a mixed solution of equal mass of ultrapure water and 1N sodium hydroxide in methanol as a solvent. The column used was sumichiral OA6100 and was detected by a UV absorption measurement device.

(3) Moisture content of polylactic acid It was measured using a moisture vaporizer VA-06 type manufactured by Mitsubishi Chemical Corporation and a company moisture analyzer CA-06 type.

(4) Melting point (° C)
Using a differential scanning calorimeter DSC-2 manufactured by Perkin Elma Co., Ltd., measurement was performed under the condition of a heating rate of 20 ° C./min, and the temperature giving an extreme value in the obtained melting endotherm curve was defined as the melting point.

(5) Single yarn fineness (dtex)
It measured by the method of JIS L-1015 7-5-1A.

(6) Single yarn strength (cN / dtex)
It measured by the method of JIS L-1015 8-7-1.

(7) Dry heat shrinkage (%)
It measured by the method of JIS L-1015 7-15-2. The treatment temperature was set at two points of 140 ° C. and 150 ° C.

Production Example 1 of Polylactic Acid Short Fiber (Main Fiber)
Mainly L-lactic acid having a number average molecular weight of 85100, L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99.2 / 0.8, monomer amount of 0.05% by mass and moisture content of 38 ppm. Polylactic acid to be melt melt spun at a discharge rate of 320 g / min and a spinning temperature of 220 ° C. using a normal single component fiber nozzle having a pore number of 720, and taken out at a take-up speed of 900 m / min. Obtained. At this time, there was no spun yarn and the tone of the process was very good.

  The obtained undrawn yarn was drawn at a drawing temperature of 60 ° C. and a draw ratio of 3.50 times, and then subjected to tension heat treatment with a 150 ° C. heat drum, and the number of crimps was 10/25 mm with an indentation type crimper. After applying mechanical crimping with a crimp rate of 10%, a finishing oil is applied, dried at 70 ° C. (relaxation heat treatment), cut to a fiber length of 51 mm, and a polylactic acid short fiber having a fineness of 1.7 dtex is obtained. It was. Table 1 shows the physical properties of this polylactic acid short fiber.

Example 2 and Comparative Example 1
Polylactic acid short fibers were obtained in the same manner as in Example 1, except that the heat setting temperature at the time of producing the polylactic acid short fibers was changed to 140 ° C. (Example 2) and 130 ° C. (Comparative Example 1). Table 1 shows the physical properties of the obtained polylactic acid short fibers.

Comparative Example 2
In the same manner as in Example 1, except that the heat setting at the time of producing the polylactic acid short fibers was changed to 150 ° C. tension heat treatment, and the heat treatment was 150 ° C. relaxation heat treatment (heat treatment under non-tension). Fiber was obtained. Table 1 shows the physical properties of the obtained polylactic acid short fibers.

Comparative Example 3
The polylactic acid has a number average molecular weight of 85,800, L-lactic acid / D-lactic acid (copolymerization molar ratio) of 98.8 / 1.2, a monomer amount of 0.05% by mass, and a moisture content of 33 ppm. Polylactic acid short fibers were obtained in the same manner as in Example 1 except that polylactic acid mainly composed of lactic acid was used. Table 1 shows the physical properties of the obtained polylactic acid short fibers.

Comparative Example 4
The polylactic acid has a number average molecular weight of 86100, L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99.2 / 0.8, a monomer amount of 0.10% by mass, and a moisture content of 31 ppm. Polylactic acid short fibers were obtained in the same manner as in Example 1 except that polylactic acid mainly composed of lactic acid was used. Table 1 shows the physical properties of the obtained polylactic acid short fibers.

Manufacture of polylactic acid binder fiber Binder fiber A
Mainly L-lactic acid having a number average molecular weight of 85100, L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99.2 / 0.8, monomer amount of 0.05% by mass and moisture content of 38 ppm. Polylactic acid as a core component, number average molecular weight is 82800, L-lactic acid / D-lactic acid (copolymerization molar ratio) is 91.2 / 8.8 (melting point is 132 ° C.), monomer amount is 0.13 mass %, A polylactic acid mainly composed of L-lactic acid having a moisture content of 31 ppm as a sheath component, and using a nozzle for a normal concentric core-sheath composite fiber having a pore number of 560, a discharge rate of 290 g / min, a spinning temperature Composite spinning was carried out at 220 ° C. (composite ratio 50/50) and taken up at a take-up speed of 800 m / min to obtain undrawn yarn. At this time, there was no spun yarn and the tone of the process was very good.

  The obtained undrawn yarn was drawn at a drawing temperature of 60 ° C. and a draw ratio of 4.00 times, and then a mechanical crimp with a crimping number of 10 pieces / 25 mm and a crimping rate of 10% was imparted by an indentation type crimper. Then, a finishing oil was applied, dried at 70 ° C., and cut to a fiber length of 51 mm to obtain a polylactic acid-based binder fiber (binder fiber A) having a fineness of 2.2 dtex.

Binder fiber B
As a sheath component of the binder fiber, a polylactic acid-based binder fiber (in the same manner as the production method of the binder fiber A) except that polybutylene succinate (PBS) having a melting point of 114 ° C. and a number average molecular weight of 45300 was used. Binder fiber B) was obtained.

Binder fiber C
Production of binder fiber A described above, except that a polybutylene succinate copolymer of 4 mol% of L-lactic acid (melting point: 114 ° C., number average molecular weight: 49800) was used as the sheath component of the binder fiber. A polylactic acid-based binder fiber (binder fiber C) was obtained by the same method.

Binder fiber D
As a core component of the binder fiber, the number average molecular weight is 86300, L-lactic acid / D-lactic acid (copolymerization molar ratio) is 98.4 / 1.6, the monomer amount is 0.14% by mass, and the moisture content is 36 ppm. A polylactic acid-based binder fiber (binder fiber D) was obtained by the same method as the method for producing the binder fiber A except that polylactic acid mainly composed of L-lactic acid was used.

Binder fiber E
As a core component of the binder fiber, the number average molecular weight is 86300, L-lactic acid / D-lactic acid (copolymerization molar ratio) is 98.4 / 1.6, the monomer amount is 0.14% by mass, and the moisture content is 36 ppm. Of the binder fiber A except that polylactic acid mainly composed of L-lactic acid was used, and polybutylene succinate (PBS) having a melting point of 114 ° C. and a number average molecular weight of 45300 was used as the sheath component. A polylactic acid-based binder fiber (binder fiber E) was obtained by the same method as the production method.

Binder fiber F
As a core component of the binder fiber, the number average molecular weight is 86300, L-lactic acid / D-lactic acid (copolymerization molar ratio) is 98.4 / 1.6, the monomer amount is 0.14% by mass, and the moisture content is 36 ppm. Polylactic acid mainly composed of L-lactic acid was used, and as a sheath component, a copolymer (melting point: 114 ° C., number average molecular weight: 49800) obtained by copolymerizing 4 mol% of L-lactic acid with polybutylene succinate. A polylactic acid-based binder fiber (binder fiber F) was obtained in the same manner as the method for producing the binder fiber A except that it was used.

Nonwoven Fabric Production Example 11
The polylactic acid short fiber of Example 1 and the polylactic acid-based binder fiber (binder fiber A) were mixed so that the mixed cotton mass ratio was main fiber / binder fiber = 80/20, and 50 g / m 2 by a card machine. After creating the web, needle punching was performed at a needle density of 192 / cm 2 to obtain a needle punched nonwoven fabric.

  This nonwoven fabric was cut into 30 cm × 30 cm and heat-treated at 150 ° C. for 2 minutes with a continuous heat treatment machine to obtain the nonwoven fabric of the present invention.

In addition, with respect to the needle punched nonwoven fabric (30 cm × 30 cm) subjected to the needle punch processing in the above manufacturing process, the longitudinal and lateral of the nonwoven fabric obtained after the heat treatment by the continuous heat treatment machine (150 ° C. × 2 minutes) Table 2 shows the values obtained by measuring the length and calculating the thermal shrinkage rate by the following equation.
Thermal contraction rate (%) = (1− (vertical length) × (horizontal length) / 900) × 100

Moreover, the following evaluation was performed about the physical property of the obtained nonwoven fabric. The results are also shown in Table 2.
(Tensile strength of nonwoven fabric)
The obtained nonwoven fabric was cut into strips of 25 mm in the CD direction (direction perpendicular to the machine direction) and 150 mm in the MD direction (machine direction) to prepare a sample. This sample was stretched and cut in the MD direction with a tensile speed of 100 mm / min using UTM-4 type Tensilon manufactured by Orientec, and the maximum strength was read. The number of samples was 20 points, and the average value of these was the tensile strength. In addition, in this invention, the thing more than 1500cN / 25mm width was set as the pass.
(Nonwoven texture)
The softness of the texture was sensorially evaluated by touching the nonwoven fabric with 10 panelists. The number of people evaluated that the texture is soft is ◎ for 9 or more of 10 people, ○ for 5 to 8 people, △ for 2 to 4 people, × for 0 to 1 people .

Example 12
A nonwoven fabric was obtained in the same manner as in Example 11 except that the polylactic acid short fibers of Example 2 were used.

Comparative Example 11
A nonwoven fabric was obtained in the same manner as in Example 11 except that the polylactic acid short fibers of Comparative Example 1 were used.

Comparative Example 12
A nonwoven fabric was obtained in the same manner as in Example 11 except that the polylactic acid short fibers of Comparative Example 2 were used.

Examples 13 to 16 and Comparative Examples 13 and 14
The mixing ratio of the polylactic acid short fiber and the binder fiber is as follows: main fiber / binder fiber = 90/10 (Example 13), main fiber / binder fiber = 70/30 (Example 14), main fiber / binder fiber = 60/40 (Example 15), main fiber / binder fiber = 50/50 (Example 16), main fiber / binder fiber = 40/60 (Comparative Example 13), main fiber / binder fiber = 95/5 (Comparative Example 14) A nonwoven fabric was obtained in the same manner as in Example 11 except that.

Example 17
A nonwoven fabric was obtained in the same manner as in Example 11 except that binder fiber B was used as the binder fiber.

Example 18
A nonwoven fabric was obtained in the same manner as in Example 11 except that binder fiber C was used as the binder fiber.

Comparative Example 15
A nonwoven fabric was obtained in the same manner as in Example 11 except that binder fiber D was used as the binder fiber.

Comparative Example 16
A nonwoven fabric was obtained in the same manner as in Example 11, except that the binder fiber D was used as the binder fiber, and the mixing ratio of the polylactic acid short fibers and the binder fibers was changed to main fiber / binder fiber = 90/10.

Comparative Example 17
A nonwoven fabric was obtained in the same manner as in Example 11 except that binder fiber E was used as the binder fiber.

Comparative Example 18
A nonwoven fabric was obtained in the same manner as in Example 11 except that binder fiber F was used as the binder fiber.

Tables 2 and 3 show the evaluation results of the heat shrinkage rate and physical properties of the obtained nonwoven fabrics of Examples 13 to 17 and Comparative Examples 13 to 18, respectively.

As is clear from Table 1, Examples 1 and 2 were able to obtain short polylactic acid fibers having a low dry heat shrinkage ratio and excellent single yarn strength. Nonwoven fabrics (Examples 11 to 18) using these polylactic acid short fibers as main fibers at a blending ratio of 50 to 90% by mass have low shrinkage when forming the nonwoven fabric, soft texture, and sufficient mechanical properties. It had strength.

  On the other hand, since the polylactic acid short fiber of Comparative Example 1 had a heat setting temperature of 130, the effect of heat treatment was small and the dry heat shrinkage ratio was large. The heat shrinkage of the also increased.

  Since the polylactic acid short fiber of Comparative Example 2 was not subjected to tension heat treatment, the single yarn strength did not reach the target range, and the nonwoven fabric of Comparative Example 12 using this as a main fiber also had low nonwoven fabric strength. .

  Since the polylactic acid short fiber of Comparative Example 3 had a copolymerization molar ratio outside the range of the present invention, the desired dry heat shrinkage rate could not be obtained.

  As for the polylactic acid short fiber of Comparative Example 4, since the amount of the polylactic acid monomer used as a raw material was outside the range of the present invention, the desired dry heat shrinkage rate could not be obtained.

  The nonwoven fabrics of Comparative Examples 13 and 14 were inferior in the shrinkage rate and strength of the nonwoven fabric because the mixing ratio of the polylactic acid short fibers and the binder fibers did not satisfy the requirements of the present invention.

The nonwoven fabrics of Comparative Examples 15 to 18 are those in which L-lactic acid / D-lactic acid (copolymerization molar ratio) of polylactic acid constituting the core component of the binder fiber is out of the range of 99/1 to 100/0. Thermal shrinkage during production was large.

Claims (6)

  Polylactic acid short fiber, which is composed of polylactic acid having L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99/1 or more, and has a dry heat shrinkage at 140 ° C. of 3.0% or less. 2. The polylactic acid short fiber according to claim 1, wherein the single yarn strength is 3.0 cN / dtex or more.   Polylactic acid having an L-lactic acid / D-lactic acid (copolymerization molar ratio) of 99/1 or more and a monomer amount of 0.08% by mass or less is melt-spun, and then the obtained undrawn yarn is drawn and then tensioned. The method for producing a polylactic acid short fiber according to claim 1, wherein heat treatment is performed.   A polylactic acid short fiber according to claim 1 of 50 to 90% by mass and an aliphatic polyester having a melting point of 100 to 140 ° C as a sheath component, L-lactic acid / D-lactic acid (copolymerization molar ratio) is 99/1 or more. A short fiber nonwoven fabric comprising 50 to 10% by mass of a polylactic acid-based binder fiber having a polylactic acid as a core component.   The aliphatic polyester constituting the sheath component of the polylactic acid-based binder fiber is polylactic acid having an L-lactic acid / D-lactic acid (copolymerization molar ratio) of 94/6 to 90/10. The short fiber nonwoven fabric described.   4. The short fiber nonwoven fabric according to claim 3, wherein the aliphatic polyester constituting the sheath component of the polylactic acid-based binder fiber is polybutylene succinate. The short fiber nonwoven fabric according to claim 3, wherein the aliphatic polyester constituting the sheath component of the polylactic acid-based binder fiber is a copolymer obtained by copolymerizing 1 to 10 mol% of lactic acid with polybutylene succinate.