JP2008057057A - Polylactic acid-based fiber and polylactic acid-based non-woven fabric - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid-based fiber showing a good fiber-forming property, without accompanying the generation of uncomfortable irritating smell in its production process, and also having hydrolytic decomposition resistance and strength-holding rate after passing a definite period, capable of being provided for a practical use, and a poly lactic acid-non-woven fabric. <P>SOLUTION: This polylactic acid-based fiber and the non-woven fabric constituted by the fiber are provided. The fiber is provided by having a first polylactic acid-based polymer of which at least a part of carboxyl group terminals is sealed by an anti-hydrolysis agent, and a second polylactic acid-based polymer in which the carboxyl group terminals are not sealed by the anti-hydrolysis agent, as constituting components, and at the cross section of the fiber, forming the inside part by the first polylactic acid-based polymer and the outside part covering the first polylactic acid-based polymer by the second polylactic acid-based polymer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polylactic acid fiber and a polylactic acid nonwoven fabric.

(Introduction)
Most of the conventional polymers are made from petroleum. However, by consuming large amounts of petroleum resources, carbon dioxide stored in the ground since the geological era is released into the atmosphere, and global warming is further reduced. There are concerns that it will become more serious. In addition, while mass production, mass consumption, and mass disposal of chemical products using petroleum as raw materials in the high-growth period of the 20th century have enriched our lives so far, environmental problems and fossil resource depletion problems, etc. Has come to be raised.

  On the other hand, if a polymer can be synthesized using plant resources that grow by taking in carbon dioxide from the atmosphere, it is possible not only to suppress global warming by carbon dioxide circulation, but also to solve the problem of resource depletion at the same time. There is. For this reason, attention has been focused on polymers made from plant resources, that is, biomass polymers. In addition, the development of polymer materials that can be decomposed in the natural environment is eagerly desired, and research and development of various polymers such as aliphatic polyesters and attempts to put them into practical use have become active. In particular, attention is focused on polymers that are degraded by microorganisms, that is, biodegradable polymers.

  In view of the above, biodegradable polymers using biomass attract great attention, and are expected to replace conventional polymers made from petroleum resources. However, biodegradable polymers using biomass generally have problems such as low mechanical properties and heat resistance and high cost. As a biodegradable polymer using biomass that can solve these problems, polylactic acid is currently attracting the most attention.

(Polylactic acid)
Polylactic acid is a polymer made from lactic acid obtained by fermenting starch extracted from plants. Among biodegradable polymers using biomass, it has the best balance of mechanical properties, heat resistance, and cost. . And various development of the fiber using this is performed.

(Uses and disadvantages of polylactic acid)
The development of polylactic acid fibers is preceded by agricultural materials and civil engineering materials that make use of biodegradability, but the following large-scale uses include clothing, curtains, carpets, interiors, vehicle interiors, and industrial materials. Application to applications is also expected. However, when it is applied to clothing and industrial materials, polylactic acid has a high hydrolyzability. For example, when the polylactic acid fiber is used for clothing, it is dyed in most cases, but it is difficult to dye it in a dark color. Therefore, a dyeing temperature of 110 ° C. or higher is essential to increase the exhaustion rate of the dye. However, when dyeing at a temperature of 110 ° C. or higher, polylactic acid is rapidly hydrolyzed to cause a decrease in molecular weight, so that there is a problem that the tear strength of the fabric does not satisfy the practical level.

  In addition, since hydrolysis proceeds even in a use environment, there is a problem that the product life is short particularly in industrial materials that require a high strength retention.

(Addition of hydrolysis resistance and side effects caused by it)
In order to solve this problem, polylactic acid fibers having improved hydrolysis resistance by adding a hydrolysis-resistant agent such as a carbodiimide compound have been developed (Patent Documents 1 to 4). However, carbodiimide compounds have poor heat resistance, and as a result, when a polymer added with a carbodiimide compound is melt-spun, a so-called unreacted carbodiimide compound that has not reacted with a reactive terminal in polylactic acid is converted to polylactic acid. Pyrolysis occurs rapidly at a melt spinning temperature of 200 to 250 ° C. This causes a problem that an irritating pyrolysis gas is generated and the working environment is deteriorated (Patent Document 3 [0009]).
Japanese Patent Laid-Open No. 11-80522 JP 2002-180328 A JP 2004-332166 A JP 2005-350829 A

  The present invention is a polylactic acid-based polylactic acid that has good yarn-making properties, does not cause unpleasant pungent odors during the production process, and has hydrolysis resistance and strength retention after a certain period of time that can be put to practical use. It is a technical problem to provide fibers and a polylactic acid-based nonwoven fabric.

The inventors of the present invention have arrived at the present invention as a result of intensive studies to solve the above problems.
That is, the means for solving the problems in the present invention are as follows.

  (1) A first polylactic acid-based polymer in which at least a part of carboxyl group ends are blocked with a hydrolysis-resistant agent, and a second polylactic acid-based polymer in which carboxyl group ends are not blocked with a hydrolysis-resistant agent And a first polylactic acid-based polymer forming an inner portion and a second polylactic acid-based polymer covering the first polylactic acid-based polymer in a cross section of the fiber. A polylactic acid fiber characterized by being formed.

  (2) The cross section of the fiber includes a core-sheath composite type cross section in which the first polylactic acid polymer forms a core and the second polylactic acid polymer forms a sheath, and the first polylactic acid heavy The combined body forms a core portion, and the second polylactic acid-based polymer is one of a multi-leaf composite type cross section in which a plurality of protruding leaf portions are formed so as to surround the outer periphery of the core portion. The polylactic acid fiber according to (1).

  (3) The composite ratio of the first polylactic acid polymer and the second polylactic acid polymer is a mass ratio of (first polylactic acid polymer) / (second polylactic acid polymer). ) = 3/1 to 1/1, and the first polylactic acid polymer is obtained using a polylactic acid polymer having a hydrolysis-resistant concentration of 1.0 to 3.0% by mass as a raw material. (1) or (2) polylactic acid-based fiber,

  (4) A polylactic acid-based nonwoven fabric characterized in that any of the above-mentioned polylactic acid-based fibers (1) to (3) is a constituent fiber.

  (5) The polylactic acid-based nonwoven fabric according to (4), which is a long-fiber nonwoven fabric, wherein the constituent fibers are integrated into a nonwoven fabric by being partially thermocompression bonded.

  The polylactic acid-based fiber of the present invention has good yarn-making properties, is not accompanied by the generation of unpleasant irritating odors during the manufacturing process, and has hydrolysis resistance that can be put to practical use. Excellent strength retention. For this reason, it can be used for various uses such as for clothing and industrial materials. Further, there is no risk of strength reduction during product storage and transportation, and high quality can be maintained.

  Hereinafter, the present invention will be described in detail.

(Polylactic acid polymer)
First, the polylactic acid polymer will be described.

  Examples of the polylactic acid polymer used in the present invention include poly-D-lactic acid, poly-L-lactic acid, a copolymer of D-lactic acid and L-lactic acid, and a copolymer of D-lactic acid and hydroxycarboxylic acid. And a polymer selected from the group consisting of a polymer, a copolymer of L-lactic acid and hydroxycarboxylic acid, and a copolymer of D-lactic acid, L-lactic acid and hydroxycarboxylic acid, or a blend thereof. It is done. Examples of the hydroxycarboxylic acid for copolymerizing the hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid, hydroxyheptanoic acid, hydroxyoctanoic acid, and the like. In particular, hydroxycaproic acid and glycolic acid are preferable from the viewpoint of decomposition performance and low cost.

  In the present invention, it is preferable to use a polylactic acid polymer having a melting point of 150 ° C. or higher or a blend thereof. When the melting point of the polylactic acid-based polymer is 150 ° C. or higher, since it has high crystallinity, shrinkage during heat treatment is less likely to occur, and heat treatment can be performed stably. The resulting fibers and nonwoven fabrics are excellent in heat resistance.

  The melting point of poly-L-lactic acid and poly-D-lactic acid, which are homopolymers of polylactic acid, is about 180 ° C. When a copolymer is used as the polylactic acid polymer, not a homopolymer, it is preferable to determine the copolymerization ratio of the monomer components so that the melting point of the copolymer is 150 ° C. or higher. In the case of a copolymer of L-lactic acid and D-lactic acid, the copolymerization ratio of L-lactic acid and D-lactic acid is (L-lactic acid) / (D-lactic acid) = 5 / 95 to 0/100 or (L-lactic acid) / (D-lactic acid) = 95/5 to 100/0 is used.

  By using polylactic acid having crystallinity, the ratio of L-form of polylactic acid (L-lactic acid) is preferably 95% or more for the purpose of increasing the tensile strength and decreasing the dry heat shrinkage rate. More preferably, it is 98% or more. This is because when the ratio of the L-form (L-lactic acid) decreases, an amorphous structure is formed, and oriented crystals do not advance in the spinning and drawing process, resulting in poor physical properties of the obtained fiber. When polylactic acid has an amorphous structure, particularly, the tensile strength is remarkably reduced and the dry heat shrinkage rate is excessive, which makes it difficult to use as a fabric.

(Hydrolysis-resistant agent)
Next, the hydrolysis-resistant agent blended in the polylactic acid polymer in the present invention will be described.

  The degradation of polylactic acid starts at the initial stage and is degraded by microorganisms after becoming low molecular weight by hydrolysis. As a technique for suppressing hydrolysis, a method of adding a hydrolysis-resistant agent is widely known.

  In the present invention, the hydrolysis-resistant agent blended in the polylactic acid polymer is preferably at least one selected from the group consisting of a carbodiimide compound, an isocyanate compound, and an oxazoline compound.

  By adding such a specific hydrolysis-resistant agent, the residual monomer and the carboxyl group end produced by the decomposition are blocked, and the chain reaction of hydrolysis is sufficiently suppressed, so that the heat and moisture resistance and heat resistance are improved. Will be improved. Of these hydrolysis resistance agents, carbodiimide compounds are preferred. The carbodiimide compound is excellent in the blocking property of the carboxyl group, and more excellent in the melt-kneading property with the aliphatic polyester, and tends to be able to further suppress the hydrolysis with a small amount of addition.

(Carbodiimide compound)
The carbodiimide compound used as a hydrolysis-resistant agent in the present invention is preferably a carbodiimide compound having one or more carbodiimide groups in its molecule (such as a monocarbodiimide compound and a polycarbodiimide compound), and is a generally well-known method. The one synthesized with can be used.

(Addition concentration of hydrolysis resistance)
In this invention, it is suitable that the addition amount of the hydrolysis-resistant agent (carbodiimide compound) with respect to a polylactic acid-type polymer is 0.1-3.0 mass%. When the addition amount of the hydrolysis inhibitor is less than 0.1% by mass, no effect is seen in the hydrolysis resistance. On the other hand, if the amount is more than 3.0% by mass, the effect is sufficient, but the amount of unreacted carbodiimide compound becomes excessive, and as the melt viscosity decreases or increases, the yarn-making property tends to be remarkably deteriorated. In general, the hydrolysis-resistant agent is expensive and not good in terms of cost. For this reason, the more preferable range of addition amount is 1.0-3.0 mass%.

  However, the addition concentration of the hydrolysis-resistant agent refers to the content concentration in a mass ratio with respect to the polylactic acid polymer at the time of chip blending and before melt kneading in the melt extruder. In practice, the added hydrolysis-resistant agent does not necessarily exist as a reaction component, but is divided into (1) a reaction component, (2) an unreacted component, and (3) a thermal decomposition component.

(Mixing method of hydrolysis resistance and polylactic acid polymer chip)
As a method of mixing a hydrolysis resistant agent such as a carbodiimide compound into a polylactic acid polymer chip, a polylactic acid polymer chip and a carbodiimide compound are separately dried, and then a master chip is once created by a kneader. Alternatively, a master chip and a polylactic acid polymer chip may be melt-spun by chip blending (master batch method), or a dry powdered carbodiimide compound may be added directly to a polylactic acid chip and mixed (dry). Blend spinning) may be followed by melt spinning. Alternatively, a polylactic acid polymer chip and a carbodiimide compound mixed in advance by melt kneading to prepare a chip may be prepared and then melted (compound method).

(Composite form of fiber)
In the polylactic acid fiber of the present invention, in the fiber cross section, the first polylactic acid polymer containing a hydrolysis-resistant agent forms an inner portion, and the second polylactic acid-based weight not containing the hydrolysis-resistant agent is used. The combined structure forms the outer portion. As such a composite form, the first polylactic acid-based polymer containing a hydrolysis-resistant agent forms a core portion, and the second polylactic acid-based polymer not containing a hydrolysis-resistant agent forms a sheath portion. The core-sheath composite form or the first polylactic acid-based polymer containing the hydrolysis-resistant agent forms the core, and the second polylactic acid-based polymer not containing the hydrolysis-resistant agent covers the outer periphery of the core. A multi-leaf composite form in which a plurality of protruding leaf portions are formed so as to surround them can be exemplified.

  As described above, the first polylactic acid-based polymer in which at least a part of the carboxyl group ends is blocked by the hydrolysis-resistant agent is arranged at the center of the fiber cross section, and it contains the hydrolysis-resistant agent. By enclosing with the second polylactic acid polymer that does not, when the first polylactic acid polymer is melt-spun at a high temperature for fiber production, An irritating decomposition gas generated from a hydrolysis-resistant agent such as a carbodiimide compound is contained outside the fiber, that is, outside the second polylactic acid polymer surrounding the first polylactic acid polymer. It can be made into the form which is hard to discharge | release to a part. As a result, it is possible to cover the disadvantage that the working environment deteriorates due to the irritating odor from the spun yarn just below the base of the melt spinning nozzle, the irritation to the eyes, the irritating odor in the vicinity of the hot press roll, etc. .

(Detailed explanation about multi-leaf composite type cross section)
FIG. 1 shows an example of a fiber cross section of a multileaf composite form. Here, 1 is a core part, which is formed of a first polylactic acid-based polymer containing a hydrolysis-resistant agent. A plurality of leaf portions 2 are provided along the outer periphery of the core portion 1 and are formed of a second polylactic acid-based polymer that does not contain a hydrolysis-resistant agent. It is necessary that the outer periphery of the core part 1 is completely covered with a plurality of leaf parts 2. For example, if the outer surface of the core portion 1 is partially exposed between a pair of leaf portions 2 and 2 adjacent to each other in the circumferential direction, the effect of the present invention is halved.

  Further, in the fiber cross-sectional structure shown in FIG. 1, since the leaf portion 2 protrudes in a protruding shape, the degree of atypicality becomes high, so that the fiber that has been melt-spun in the fiber production process is easy to cool, and the spreadability is high. There is also an effect of improvement.

  From the above, the number of leaf parts 2 in the multileaf composite type is preferably 3 to 10. If the number of protruding leaf parts 2 is small, depending on the size of each leaf part 2, the first polylactic acid-based polymer containing the hydrolysis-resistant agent that is the core part 1 is exposed on the fiber surface. The coating effect (decomposition gas suppression effect) by the second polylactic acid polymer that is the object of the present invention tends to be difficult to achieve. In addition, when the number of the leaf parts 2 increases, the leaf parts 2 come into contact with each other, so that a so-called core-sheath cross-sectional shape that completely covers the core part 1 tends to be formed, and the degree of variation tends to decrease.

(Composite ratio)
The composite ratio (mass ratio) of the first polylactic acid-based polymer containing the inner hydrolysis-resistant agent and the second polylactic acid-based polymer not containing the outer hydrolysis-resistant agent is the inner part / outer side. Part = 3/1 to 1/1 is preferable.

  When the ratio of the inner part exceeds 3/1, the proportion of the hydrolysis-resistant agent (carbodiimide compound) in the entire fiber increases, and as a result, in the melt spinning process, stimulation derived from hydrolysis-resistant agents such as carbodiimide compounds. Tend to generate volatile decomposition gas. In addition, an irritating odor tends to be generated in the thermal bonding step when the nonwoven fabric is produced using the obtained fiber. On the other hand, when the ratio of the inner part is less than 1/1, the amount of terminal carboxyl groups of the polylactic acid polymer end-capped with a hydrolysis-resistant agent (carbodiimide compound) with respect to the entire fiber is lowered. As a result, the hydrolysis resistance tends to decrease.

  By setting the composite ratio and the concentration of the above-mentioned hydrolysis-resistant agent within the above-mentioned ranges, respectively, it is possible to maintain the same hydrolysis resistance as in the case of a single-phase fiber that is not a composite structure. Can be obtained and good spinning properties can be obtained, and the operability can be improved by suppressing smoke generation.

(First and second polylactic acid polymers)
As the first and second polylactic acid-based polymers, the same polylactic acid-based polymer may be used, or polylactic acid-based polymers having the same type and different viscosity may be used, or copolymerization may be performed. Polylactic acid polymers having different melting points due to different ratios may be used. By making the first polylactic acid polymer having a high melting point and the second polylactic acid polymer having a low melting point, thermal adhesiveness can be imparted to the resulting fiber.

(Fiber single yarn fineness)
In the present invention, the single yarn fineness of the polylactic acid fiber having a composite structure is preferably about 0.5 dtex to 11 dtex. When the single yarn fineness is less than 0.5 dtex, yarn breakage is likely to occur frequently in the spinning / drawing process, so that the operability tends to deteriorate, and the mechanical strength of the obtained long fiber nonwoven fabric tends to be inferior. Therefore, it becomes easy to become impractical. On the other hand, when the single yarn fineness exceeds 11 decitex, the cooling property of the spun yarn is likely to be inferior, and the yarns are easily adhered to each other. For these reasons, the single yarn fineness is more preferably 1 to 8 dtex.

  The polylactic acid fiber of the present invention can be used as either a multifilament or a monofilament.

(Nonwoven fabric weight)
According to this invention, a nonwoven fabric can be comprised using the obtained polylactic acid-type fiber. Basis weight of the nonwoven fabric may be appropriately selected depending on the nonwoven applications, it is not particularly limited, is generally preferably in the range of 10 to 300 g / m ^2. More preferably, it is the range of 15-200 g / m < ² >. If the basis weight is less than 10 g / m ² , the formation and mechanical strength are inferior, and it becomes difficult to be practical. Conversely, if the basis weight exceeds 300 g / m ² , it tends to be disadvantageous in terms of cost.

(Additive)
The polymer for forming the fiber of the present invention and the polymer for forming the fiber constituting the nonwoven fabric of the present invention include a pigment, a heat stabilizer, and a matting agent, as long as the object of the present invention is not greatly impaired. It is also possible to add antioxidants, weathering agents, flame retardants, plasticizers, lubricants, mold release agents, antistatic agents, crystal nucleating agents, fillers, and the like. In particular, a crystal nucleating agent such as talc, titanium oxide, calcium carbonate, and magnesium carbonate is used to form a first polylactic acid-based polymer that forms the inner part of the fiber and a second polylactic acid-based polymer that forms the outer part of the fiber. It is preferable to mix with both of them in order to prevent fusion (blocking) between yarns in the spinning / cooling step. This crystal nucleating agent is preferably used in the range of 0.1 to 3% by mass.

(Production method of polylactic acid fiber)
Next, the preferable manufacturing method of the polylactic acid-type fiber of this invention is demonstrated.

  First, a first polylactic acid-based polymer in which at least a part of carboxyl group ends is blocked with a hydrolysis-resistant agent, and a second polylactic acid-based polymer in which carboxyl group ends are not blocked with a hydrolysis-resistant agent. Prepare the merger. Each prepared polymer is individually weighed, for example, through a core-sheath compound spinneret in which the first polylactic acid polymer forms the core and the second polylactic acid polymer forms the sheath. Alternatively, the first polylactic acid-based polymer forms a core portion, and the second polylactic acid-based polymer melt-spins through a multi-leaf type composite spinneret that constitutes a leaf portion. After the strip is cooled using a conventionally known cooling device such as horizontal spraying or annular spraying, an oil agent is applied and wound on a winder as unstretched yarn through a take-up roller. When it is desired to obtain a short fiber as the fiber form, the wound undrawn yarn is drawn between a group of rollers having different peripheral speeds by a known drawing machine, and crimped by a push-type crimping machine or the like. After that, the target length may be cut with a cutter such as an EC cutter. When it is desired to obtain a long fiber as the form of the fiber, after drawing with a drawing machine, it may be wound, and if necessary, processing such as twisting and false twisting may be performed.

(Production method of polylactic acid nonwoven fabric)
The polylactic acid-based nonwoven fabric of the present invention can be efficiently produced by a spunbond method.

(Melt spinning, drawing, web formation)
First, in the same manner as described above, melt spinning and pulverization are performed to obtain polylactic acid-based long fibers. The traction speed at this time is preferably set to 4000 to 6000 m / min. When the pulling speed is less than 4000 m / min, molecular orientation is not sufficiently promoted in the yarn, and the dimensional stability of the resulting fiber tends to be poor. On the other hand, if the pulling speed is too high, the spinning stability tends to be poor. Then, the stretched long fibers are opened and spread on a movable collection surface such as a screen conveyor after opening with a known opening device, and a nonwoven web in which constituent fibers are randomly distributed and To do.

(Thermal bonding process)
Next, the obtained web is subjected to a heat treatment to melt or soften at least the second polylactic acid polymer on the fiber surface to thermally bond the fibers to obtain the polylactic acid long fiber nonwoven fabric of the present invention. .

  Examples of the heat treatment method include a method of blowing hot air, a method of passing through a hot embossing device, etc., but in the point that it is possible to obtain a nonwoven fabric excellent in both mechanical strength and flexibility, a heat embossing device is used. It is preferable to pass through. That is, a method in which a nonwoven web is partially thermocompression bonded using a heated embossing roll and a metal roll having a smooth surface, and the constituent fibers are integrated to form a nonwoven fabric is preferable.

The temperature during the heat treatment is preferably set to a temperature at which the second polylactic acid polymer on the fiber surface is melted or softened, but is appropriately selected according to the treatment time and the like.
For example, in the case of a partial thermocompression bonding part formed by passing the web through a hot embossing device, the polylactic acid polymer melts or softens to maintain the shape of the long fiber nonwoven fabric, and then passes through the hot embossing device. It is preferable to set the surface temperature of the heat treatment roll at a temperature lower by 10 to 50 ° C. than the melting point of the polylactic acid polymer. If the temperature is lower than the melting point of the polylactic acid polymer by 50 ° C., the polylactic acid polymer is not sufficiently melted or softened, so that the constituent fibers are not easily integrated with each other. The mechanical performance of the nonwoven fabric is inferior, and it becomes easy to fluff. On the other hand, when the temperature is set higher than the temperature lower by 10 ° C. than the melting point of the polylactic acid-based polymer, the melted product of the polymer is fixed to the roll and the operability tends to be impaired.

(Three-dimensional entanglement process and resin adhesion)
Moreover, as a form of the long-fiber nonwoven fabric, a nonwoven fabric that is entangled and integrated by a three-dimensional entanglement process such as a needle punch after a temporary thermocompression bonding process using a hot embossing device can also be adopted. When this three-dimensional entanglement treatment is performed, the fibers constituting the partial temporary thermocompression bonding part are partially or completely separated from the temporary thermocompression bonding part to be in a free state, whereby the fibers are sufficiently tertiary. It will be entangled originally.

  In the case of performing the treatment for obtaining such a nonwoven fabric, the surface temperature of the roll when passing the web through a hot embossing device for temporary thermocompression bonding is a temperature lower by 60 to 100 ° C. than the melting point of the polylactic acid polymer. It is preferable to set to. If the temperature is set to a temperature lower than 100 ° C. lower than the melting point of the polylactic acid-based polymer, temporary thermocompression bonding is not performed to the necessary extent. Therefore, in the web transport process for producing the long fiber nonwoven fabric, Inability to withstand the tension of the fibers, the fibers are easily removed from the web, and the problem that the web form cannot be maintained tends to occur. On the other hand, if the temperature is set to a temperature that is not 60 ° C. lower than the melting point of the polylactic acid-based polymer, the fibers in the thermocompression bonding part are excessively fused, and even if a three-dimensional entanglement treatment such as a needle punch is performed It becomes difficult to be in a free fiber state due to peeling. On the other hand, when a three-dimensional entanglement process is performed, the fiber is cut from the pressure-bonding portion by the force, and it tends to cause the occurrence of fuzz and a decrease in mechanical strength.

  Thereafter, if a desired amount of a binder resin is attached to the polylactic acid fibers entangled and integrated by needle punching as required, a nonwoven fabric in which the constituent fibers are firmly attached at the contact portions can be obtained. Such a nonwoven fabric can be applied to carpet primary base fabrics, automobile interior materials, and other industrial materials.

  Next, based on an Example, this invention is demonstrated concretely. However, the present invention is not limited to only these examples. In addition, the various physical-property values in a following example and a comparative example were measured with the following method.

(1) Melt flow rate (g / 10 min):
According to the method described in ASTM-D-1238 (E), the temperature was 210 ° C. and the load was 21.2 N (2160 gf). Hereinafter, the melt flow rate is abbreviated as “MFR”.

(2) Melting point (° C):
Using a differential scanning calorimeter (Perkin Elma, DSC-2 type), the sample mass was measured at 5 mg and the rate of temperature increase was 10 ° C./min, and the temperature giving the maximum value of the obtained melting endotherm curve was the melting point. (° C).

(3) Fineness (Decitex, hereinafter abbreviated as “dtex”):
The fiber diameter of 50 fibers in the web state was measured with an optical microscope, and the average value obtained by correcting the density was defined as the fineness.

(4) Weight per unit area (g / m ² ):
After preparing 10 sample pieces with a sample length of 10 cm and a sample width of 5 cm from the sample in the standard state, and making the equilibrium moisture, weigh the mass (g) of each sample piece and measure the average value of the obtained values in units In terms of area, the weight per unit area (g / m ² ) was used.

(5) Spinnability:
The melt-spun spun yarn was cooled by a cooling device, and then evaluated by the degree of yarn breakage during pulling (stretching) by air soccer provided below the spinneret as follows. Among these, if the level is “good” or “slightly good”, it can be operated without any problem, and the yarn quality is also good.

Good: Stable towing thinning is possible with almost no thread breakage.
Slightly good ... Breakage of yarn sometimes occurs, but it is difficult for undrawn yarn to be mixed into the accumulated web, and stable pulling can be achieved.

    Defects: Many yarn breaks occur, and undrawn yarns are mixed in the accumulated web, resulting in defects or difficult continuous and fine pulling.

(6) Initial tensile strength (N / 5 cm width), initial tensile elongation (%):
Before carrying out the hydrolysis treatment described later, 10 strip-shaped test pieces having a width of 5 cm and a length of 20 cm are prepared in the longitudinal direction (MD) and the transverse direction (TD) of the nonwoven fabric, and the constant speed is obtained in a normal temperature atmosphere. Using an extension type tensile tester (Tensilon UTM-4-1-100 manufactured by Orientec Co., Ltd.), a tensile test was performed at a grip interval of 10 cm and a tensile speed of 20 cm / min, and the measurement was performed according to JIS-L-1906. And the average value about 10 measured values was made into tensile strength (N / 5cm width). Further, the elongation at break in the tensile test under the above conditions was defined as the tensile elongation (%).

(7) Hydrolysis resistance:
The obtained polylactic acid-based long-fiber nonwoven fabric was put in a thermo-hygrostat at a temperature of 60 ° C. and a humidity of 80% for 1000 hours, and at each exposure time, the tensile strength and tensile strength were the same as in (6) above. The elongation was determined.

Moreover, the tensile strength after 1000 hours was measured and evaluated in the following four stages.
A: The strength equal to the initial tensile strength is maintained even after 1000 hours.
◯: After 1000 hours, the strength is slightly inferior to the initial tensile strength.

Δ: After 1000 hours, the strength is reduced to about half compared to the initial tensile strength, but the form is maintained.
X: After 1000 hours, the deterioration is so large that the form is not maintained.

(8) Strength retention (%), elongation retention (%):
From the values of tensile strength and tensile elongation obtained for each exposure time in (7) above, calculation was performed according to the following formula.

Tensile strength retention (%) = (tensile strength after hydrolysis / initial tensile strength) × 100
Elongation retention (%) = (tensile elongation after hydrolysis / initial tensile elongation) × 100

(9) Comprehensive evaluation: Comprehensive evaluation was performed in the following three stages from hydrolyzability and the working environment of the manufacturing process.

◯: Excellent hydrolysis resistance and manufacturing process (working environment).
(Triangle | delta): Although a manufacturing process (working environment) is excellent, it is somewhat inferior to hydrolysis resistance.
X: Work environment deteriorates.

Example 1
<Melt spinning process>
As the second polylactic acid polymer for forming the sheath, L-lactic acid / D having a melting point of 168 ° C., MFR 65 g / 10 min, L-lactic acid / D-lactic acid = 98.6 / 1.4 mol%. -A lactic acid copolymer was prepared. As the first polylactic acid-based polymer for forming the core portion, the same polylactic acid-based polymer as the sheath portion, powdered carbodiimide compound as a hydrolysis-resistant agent (manufactured by Matsumoto Yushi Co., Ltd., product number EN-160) Prepared by a dry blend method so as to have a content of 2.0% by mass with respect to the polylactic acid polymer.

  With the first polylactic acid copolymer as the core and the second polylactic acid copolymer as the sheath, the core-sheath composite cross section with core / sheath = 1/1 (mass ratio) is obtained. In addition, after individually weighing so that the talc is 0.5% by mass in the molten polylactic acid polymer in both the core and the sheath, each polymer is used with an individual extruder-type melt extruder. The melt was melted at a temperature of 210 ° C. and melt-spun at a single-hole discharge rate of 1.38 g / min.

<Stretching and opening process>
Next, the spun yarn is cooled by a known cooling device, and subsequently, it is pulled and thinned at a pulling speed of 5000 m / min by an air soccer provided below the spinneret, and opened using a known opening device. Then, it was collected and deposited as a composite long fiber web on a moving screen conveyor. The single fiber fineness of the long-fiber nonwoven web made of the deposited polylactic acid-based polymer long fibers was 2.7 dtex. At this time, no irritating odor or eye irritation was felt from the spun yarn immediately under the base. Further, there was no yarn breakage during spinning, and the yarn-making property was good.

<Thermal bonding process>
The obtained long fiber web was passed through a partial thermocompression bonding device composed of an embossing roll and a smooth metal roll, the roll temperature was 135 ° C., the crimping area ratio was 14.9%, and the crimping point density was 21.9 / cm ² . thermocompression bonding at a linear pressure of 60 kg / cm conditions, to obtain a long-fiber nonwoven fabric having a mass per unit area of 50 g / ^{m 2.} There was no pungent odor near the roll at this time.

  The physical properties and the like of the obtained long fiber nonwoven fabric are shown in Table 1. When this long-fiber non-woven fabric was placed in a thermo-hygrostat for 1000 hours, it showed good hydrolysis resistance to such an extent that the strength and elongation were reduced but the form was maintained.

Example 2
Compared to Example 1, the core-sheath ratio was set to core / sheath part = 2/1 (mass ratio). Other than that, a long fiber nonwoven fabric was obtained through the same spinning, stretching, fiber opening, and thermal bonding steps as in Example 1.

  At this time, there was a slight irritating odor near the hot press roll. However, as in the case of Example 1, no irritating odor or eye irritation from the spun yarn just under the base was felt, and there was no yarn breakage during spinning, and the yarn production was good.

  The physical properties and the like of the obtained long fiber nonwoven fabric are shown in Table 1. This long fiber nonwoven fabric showed excellent hydrolysis resistance.

Example 3
Compared to Example 1, the core-sheath ratio was set to core / sheath part = 3/1 (mass ratio). Other than that, a long fiber nonwoven fabric was obtained through the same spinning, stretching, fiber opening, and thermal bonding steps as in Example 1. However, the pulling speed by air soccer was 4900 m / min, and the single yarn fineness of the long fibers was 2.8 dtex.

  At this time, there was some yarn breakage at the time of spinning, but it was not to the extent that it could not be made into a nonwoven web or nonwoven fabric. Although there was a slight irritating odor in the vicinity of the hot pressing roll, as in Example 1, there was no irritation to the eyes just below the base, and there was a slight irritating odor from the spun yarn. It was not so much.

  The physical properties and the like of the obtained long fiber nonwoven fabric are shown in Table 1. This long fiber nonwoven fabric exhibited particularly excellent hydrolysis resistance.

Comparative Example 1
<Melt spinning process>
A nonwoven fabric was produced only from a nonwoven web made of a polylactic acid polymer. That is, L-lactic acid / D-lactic acid = 98.6 / 1.4 mol% L-lactic acid / D-lactic acid copolymer having a melting point of 168 ° C. and MFR of 65 g / 10 min was added with talc as an additive. 0.5% by mass was blended and melt-spun in a single phase from a round spinneret at a spinning temperature of 210 ° C. and a single-hole discharge rate of 1.67 g / min.

<Stretching and opening process>
Next, the spun yarn is cooled by a known cooling device, and subsequently, it is pulled and thinned at a pulling speed of 5000 m / min by an air soccer provided below the spinneret, and opened using a known opening device. Then, it was collected and deposited as a composite long fiber web on a moving screen conveyor. The single yarn fineness of this long fiber nonwoven web was 3.3 dtex. There was no irritating odor or eye irritation from the spun yarn directly under the base, no yarn breakage during spinning, and the yarn production was good.

<Thermal bonding process>
The obtained long fiber web was passed through a partial thermocompression bonding apparatus composed of an embossing roll and a smooth metal roll, the roll temperature was 135 ° C., the crimping area ratio was 14.9%, the crimping point density was 21.9 / cm ² , the wire thermocompression bonding under conditions of pressure of 60 kg / cm, to obtain a long-fiber nonwoven fabric having a mass per unit area of 50 g / ^{m 2.}

At this time, no irritating gas was observed in the vicinity of the hot pressing roll.
However, the obtained long-fiber non-woven fabric was so inferior that it broke down and deteriorated in 600 hours when measuring the hydrolysis resistance.

  The physical properties and the like of the obtained long fiber nonwoven fabric are shown in Table 1.

Comparative Example 2
Not only the polylactic acid polymer as in Comparative Example 1, but also the polylactic acid polymer was mixed with a powdered carbodiimide compound (manufactured by Matsumoto Yushi Co., product number EN-160) as a hydrolysis-resistant agent. What was mixed by the dry blend method so that it might become 1.0 mass% in inside was used. Other than that, a long fiber nonwoven fabric was obtained through the same spinning, stretching, opening, and thermal bonding steps as in Comparative Example 1.

  At this time, there was no yarn breakage at the time of spinning, and the yarn-making property was good, but there was some irritating odor and eye irritation from the spun yarn just below the base, and the working environment was poor. There was a little pungent odor near the hot press roll.

  The physical properties and the like of the obtained long fiber nonwoven fabric are shown in Table 1. This long-fiber non-woven fabric was slightly inferior to the extent that it was broken by tattering at 800 hr when measuring hydrolysis resistance, and was somewhat inferior.

Comparative Example 3
Compared to Comparative Example 2, the content of the carbodiimide compound in the polylactic acid polymer was 2.0% by mass. Other than that, a long fiber nonwoven fabric was obtained through the same spinning, stretching, opening, and thermal bonding steps as in Comparative Example 2.

  At this time, there was no yarn breakage at the time of spinning, and the spinning property was good. However, generation of irritating gas directly under the die was severe, and the working environment in the melt spinning process was extremely bad. Also, a large amount of irritating gas was generated near the hot press roll.

  The physical properties and the like of the obtained long fiber nonwoven fabric are shown in Table 1. This long fiber nonwoven fabric showed excellent hydrolysis resistance.

It is a figure which shows the example of the fiber cross section of the multileaf composite form based on this invention.

Claims (5)

  A first polylactic acid-based polymer in which at least a part of the carboxyl group ends are blocked by a hydrolysis-resistant agent; and a second polylactic acid-based polymer in which the carboxyl group ends are not blocked by a hydrolysis-resistant agent; And the first polylactic acid-based polymer forms an inner part in the fiber cross section, and the second polylactic acid-based polymer forms an outer part that covers the first polylactic acid-based polymer. A polylactic acid fiber characterized by having   The cross-section of the fiber is a core-sheath composite type cross section in which the first polylactic acid polymer forms a core and the second polylactic acid polymer forms a sheath, and the first polylactic acid polymer is a core. The multi-leaf composite type cross section in which a plurality of projecting leaf portions are formed so that the second polylactic acid polymer surrounds the outer periphery of the core portion. The polylactic acid fiber according to 1.   The composite ratio of the first polylactic acid polymer and the second polylactic acid polymer is, by mass ratio, (first polylactic acid polymer) / (second polylactic acid polymer) = 3. The first polylactic acid polymer is obtained using a polylactic acid polymer having a hydrolysis-resistant agent concentration of 1.0 to 3.0% by mass as a raw material. The polylactic acid fiber according to claim 1, wherein the polylactic acid fiber is present.   A polylactic acid-based nonwoven fabric comprising the polylactic acid-based fiber according to any one of claims 1 to 3 as a constituent fiber.   5. The polylactic acid-based nonwoven fabric according to claim 4, wherein the polylactic acid-based nonwoven fabric is a long-fiber nonwoven fabric, and the constituent fibers are integrated into a nonwoven fabric by being partially thermocompression bonded.

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