JP4352843B2 - Polylactic acid fiber and method for producing the same - Google Patents

Description

  The present invention relates to a polylactic acid fiber suitable for industrial materials and a method for producing the same. Specifically, high-quality polylactic acid fibers for industrial materials that have sufficient strength and toughness when used, but have low environmental impact even after disposal due to their biodegradable characteristics after use, and make them efficient and stable It relates to a method of manufacturing.

  Since polylactic acid fibers are fibers that are biodegradable and obtained from non-petroleum-based raw materials, they have attracted attention in recent years as fibers having a small environmental load even when discarded, and their application development has been widely promoted. For example, draining garbage bags, seedling mats, civil engineering bags, herbicidal sheets for vegetation, tea bags, towels, gloves, napkins, etc. are applications that take advantage of the characteristics of biodegradable and non-petroleum-based fibers. It is. In addition, polylactic acid fiber has a unique luster, good color development when dyed, and has a smooth touch and texture. Development is progressing for use. Furthermore, it is being put to practical use in interior applications such as car option mats, household roll carpets and rugs.

  On the other hand, for industrial material use, after using polylactic acid fiber as a product, many uses have been proposed taking advantage of the biodegradable feature that the load at the time of disposal is low. Few things succeeded. Industrial material applications such as building construction nets, building construction sheets, land nets, tents, tarpaulins, etc. are required to have particularly high energy absorption, that is, high toughness, and are used as products. Since durability is required, it is a fact that conventional polylactic acid fibers have been overwhelmed by the risk of ensuring safety.

  In order to be able to apply polylactic acid fibers to industrial material applications with peace of mind, polylactic acid fibers having physical properties at the level of polyester fibers, which have a sufficient track record as industrial material applications, are necessary, and their development has been expected.

  Among the prior arts, those proposed to obtain particularly high strength and highly oriented polylactic acid fibers include Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Non-Patent Document 1, and the like. .

  Patent Document 1 states that “If left in a natural environment, it is gradually decomposed by microorganisms and eventually disappears, and there is no concern about environmental destruction, but it has good stability over time (strength retention) and strength. For the purpose of providing a biodegradable fiber having a low molecular weight compound content of 1% by weight, comprising a thermoplastic resin comprising polylactic acid and / or a copolymer mainly composed of polylactic acid. It is said that this is achieved by a biodegradable fiber characterized by the following: and a nonwoven fabric using the same.

  Patent Document 2 provides “a polylactic acid fiber having sufficient strength and elastic modulus that can be used for industrial materials while having biodegradability, and a method for producing this fiber industrially with high productivity. As a solution to this problem, “it is made of poly-L-lactic acid having an average molecular weight of 30,000 to 100,000 and an optical purity of 95 to 99.5%, and is obtained at a winding speed of 3000 m / min or more. A polylactic acid fiber having a strength of 4 g / d or more, an initial modulus of 60 g / d or more, and an elastic modulus of 10 g elongation at 7 g / d or more.

  Patent Document 3 has an object of “providing a method for stably and efficiently producing an aliphatic polyester multifilament having high strength and excellent mechanical strength and excellent quality”. In the method for producing an aliphatic polyester multifilament, a polymer mainly composed of an aliphatic polyester having a melting point of 130 ° C. or higher and a weight average molecular weight of 100,000 or higher is melt-spun and taken up at a take-up speed of 1200 m / min or more, and then two or more stages A method for producing an aliphatic polyester multifilament characterized in that the drawing is performed and the draw ratio Mn of the n-th stage (1 ≦ n ≦ N) satisfies the following formula (1) (: omitted). ” Yes.

  Patent Document 4 “provides a polylactic acid-based long fiber nonwoven fabric and a polylactic acid-based long fiber that can be favorably subjected to partial thermocompression bonding even when a polylactic acid-based polymer is used, and hardly peel in the thickness direction.” As a solution to this problem, “a non-woven fabric composed of long fibers of a single-phase cross section made of a polylactic acid-based polymer, and the long fibers are partially thermocompression bonded together. Is a temperature drop crystallization temperature Tcc, and the temperature drop crystallization temperature Tcc is 90 ° C. or more and less than 110 ° C., and the crystallization heat amount ΔHexo is 10 L / mg or more. Is disclosed.

  Non-Patent Document 1 discloses the results of measured values and theoretical calculation values of intrinsic birefringence for the purpose of estimating the intrinsic birefringence of the sample by subjecting polylactic acid fibers to a laboratory heat treatment to the limit. ing.

  The above prior art discloses polylactic acid fibers that have achieved high strength or high orientation, but none of them is at a sufficient level and is not satisfactory for widely deploying polylactic acid fibers in industrial material applications. . In other words, it was different from the highly oriented and high strength polylactic acid fiber aimed at and achieved by the present invention, and its production method was also different. The details will be described below.

  According to Patent Document 1, in Examples 1 to 4, polylactic acid fibers having a strength of 5.6 to 6.3 g / d, that is, 4.8 to 5.6 cN / dtex, are obtained. However, the technique does not describe birefringence. In addition, the production method is performed in a two-step method in which spinning and stretching are separated in all the examples, and it is difficult to stably realize the physical properties obtained by the direct spinning and stretching method of the present invention. is there. In addition, the high-strength, highly-oriented polylactic acid fibers of the present invention are characterized by being not devitrified or being obtained with little production, but nothing is said about these.

  According to Patent Document 2, in Examples 1 to 7, it is said that a polylactic acid fiber having a strength of 4.1 to 5 g / d, that is, 3.6 to 4.4 cN / dtex is obtained. A strong polylactic acid fiber has not been obtained. There is no mention of suppression of devitrification. The production method also employs a very simple method for drawing following spinning, and further, this technique is based on a method in which the spun yarn is cooled and solidified and then drawn through a high-temperature heating zone. The method of the present invention is significantly different from the multistage thermal stretching method.

  According to Patent Document 3, in Examples 1 to 9, strengths of 4.7 to 7.2 cN / dtex are achieved. In addition, in order to obtain a high-strength polylactic acid fiber without causing the whitening phenomenon of the filaments as shown in FIGS. 2 and 3, that is, devitrification, a multistage hot drawing method is adopted, and the drawing ratio in each drawing step is set. It is disclosed that the specific ratio can be obtained.

  Certainly, although the polylactic acid fiber obtained by this technique has not been devitrified and has achieved high strength, the polylactic acid fiber of the present invention having high strength and extremely small strength variation is obtained. I can't say that. The polylactic acid fiber of the present invention is characterized by high orientation and high strength, as well as little variation in strength and excellent uniformity.

  On the other hand, the strength of the polylactic acid fiber which has caused devitrification is only 2.5 to 4 cN / dtex. The polylactic acid fiber of the present invention can provide extremely high strength even when slight devitrification occurs, but this point is also different.

  Although the degree of orientation (birefringence) achieved by this technique is not described, it is unknown, but according to the example, all the spinning and drawing are performed in a two-step method, It is presumed that the level of the invention has not been reached.

  Patent Document 4 discloses a double peak or shoulder expression of the melting curve of DSC, which is one of the characteristics of the polylactic acid fiber of the present invention. That is, the melting curve of the polylactic acid fiber to which the crystal nucleating agent is added shows a single peak, but the non-added polylactic acid fiber is exemplified as showing a clear shoulder. It can be seen that the polylactic acid fiber of the present invention has a DSC melting curve with a single peak even when no nucleating agent is added, and is significantly sharper than the DSC curve of this document, which is different from the technique of the present invention.

Non-Patent Document 1 measures the birefringence of a sample obtained by performing limit stretching and heat treatment by a laboratory method in order to determine the intrinsic birefringence of poly L-lactic acid fiber. The devitrified polylactic acid fiber achieves high birefringence of 36.8 × 10 ⁻³ and 37.0 × 10 ⁻³ , but the non-devitrified polylactic acid fiber has a maximum of 28.4. Only a birefringence of × 10 ⁻³ is obtained.

The polylactic acid fiber of the present invention is characterized by obtaining a high birefringence exceeding the literature value without devitrification. Moreover, the birefringence value obtained by this technique is the birefringence of the sample obtained by the limit treatment performed in the laboratory, and the polylactic acid fiber obtained by the industrial method as in the present invention. Different from the value of.
JP 9-21018 A JP-A-11-131323 JP 2000-248426 A JP 2003-64569 A Ogoshi, Shirai, Goto, Nakura; 55, (1), 21-27, 1999

  An object of the present invention is a polylactic acid fiber suitable for industrial material use, which has sufficient strength and toughness at the time of use. Polylactic acid fiber and a method for producing the same efficiently and stably.

In order to solve the above problems, the present invention employs the following means. That is, the polylactic acid fiber of the present invention is a polylactic acid multifilament fiber having a birefringence of 23 × 10 ⁻³ to 40 × 10 ⁻³ and a strength of 3.5 to 8 cN / dtex, and includes a devitrified filament. Or devitrified filaments are present in a proportion of 15% or less.

In addition, the polylactic acid fiber production method of the present invention is a method of producing a polylactic acid fiber by melting a polylactic acid polymer, extruding it from a die, applying an oil agent to a cooled and solidified yarn, and then hot-drawing without winding up once. In this method, the drawing is performed at a spinning speed of 300 to 1000 m / min, and in at least the first stage of the thermal drawing, the draw ratio is set to 20 to 70% of the total draw ratio, and the draw point is on the yarn supply roll. It extends | stretches so that it may be located in.

  The polylactic acid fiber obtained by the present invention is suitable for industrial materials and has sufficient strength, toughness and durability when used, but has a low environmental impact even after disposal due to its biodegradable characteristics after use. Polylactic acid fiber.

  In particular, since it is excellent in strength, toughness, weather resistance, etc., it can be applied to industrial materials that have severe use conditions such as building nets, building sheets, land nets, tarpaulins, and tents.

  In addition, according to the production method of the present invention, the high-quality polylactic acid fiber can be efficiently produced by a high-speed direct spinning and drawing method, and since there are few yarn breakage and fluff, it can be produced stably with high yield. be able to.

  The polylactic acid polymer used as a raw material for the polylactic acid fiber of the present invention is a polylactic acid obtained by polymerizing lactic acid mainly composed of L-lactic acid and / or D-lactic acid. Here, L-lactic acid as a main component means that 60% by weight or more of the constituent components is composed of L-lactic acid, and is a polyester containing D-lactic acid within a range not exceeding 40% by weight. is there. The same applies to L-lactic acid. Furthermore, it is polylactic acid in which 80% by weight or more, particularly 90% by weight or more, more preferably 95% by weight or more of all repeating units of the molecular chain of the constituent polymer is lactic acid, which impairs the constituent requirements and purpose of the present invention. Other polymer blends, copolymers, and additives may be included as long as they are not included.

  The polylactic acid used in the present invention may be a copolymerized polylactic acid obtained by copolymerizing other components having ester forming ability in addition to L-lactic acid and D-lactic acid. Alternatively, aliphatic polyester polymers such as polycaprolactone, polybutylene succinate, and polyethylene succinate can be used as plasticizers to reduce melt viscosity. Furthermore, inorganic fine particles and organic compounds can be added as necessary as matting agents, flame retardants, heat resistance agents, light resistance agents, ultraviolet absorbers, color pigments and the like that are usually used for synthetic fibers. However, the polylactic acid fiber of the present invention is a biodegradable and non-petroleum-based raw material, and is used as a product with a low environmental impact even when discarded. Therefore, a blend of petroleum-based polymers, copolymerization of the components, etc. In addition, it is preferable that various additives should not use any of the compounds that are expected to be of concern at this time, as well as heavy metal compounds and environmental hormone substances.

The polylactic acid fiber of the present invention has high orientation and high strength, a birefringence of 23 × 10 ⁻³ to 40 × 10 ⁻³ , and a strength of 3.5 to 8 cN / dtex, preferably 4.5 to 8 cN / It is a dtex polylactic acid fiber, and is characterized in that it does not include a devitrified filament among the filaments constituting the fiber, or the devitrified filament is present in a ratio of 15% or less. The polylactic acid fiber of the present invention is highly oriented and high strength fiber to achieve high toughness suitable for industrial materials. Although the degree of orientation can be expressed by birefringence, it is 23 × 10 ⁻³ to 40 × 10 ⁻³ , preferably 29 × 10 ⁻³ to 40 × 10 ⁻³ in terms of birefringence. When the birefringence is less than 23 × 10 ⁻³ , the orientation of the molecular chain is not sufficient, and a high strength of 3.5 cN / dtex or more may not be obtained. You may not be able to get it. On the other hand, the higher the birefringence and strength, the better. However, polylactic acid fibers having a high birefringence exceeding 40 × 10 ⁻³ and high-strength polylactic acid fibers exceeding 8 cN / dtex can be achieved with the current technology. Have difficulty.

  Further, among the filaments constituting the polylactic acid fiber having such a high birefringence and high strength, it does not include a devitrified filament or the devitrified filament is present at a ratio of 15% or less. . Patent Document 3 describes that polylactic acid multifilaments are whitened, that is, devitrified, so that the physical properties of the fibers are remarkably lowered. However, when the devitrified filament satisfies the above-mentioned scope of the present invention, the present inventors can obtain a polylactic acid fiber that can be used practically with good spinning performance, and the fiber properties are not deteriorated. A method for producing a polylactic acid fiber has been found. When the ratio of the devitrified filament exceeds 15%, it becomes difficult to obtain a polylactic acid fiber having high strength and good yarn forming properties as described in Patent Document 3.

  Further, the polylactic acid fiber of the present invention is a fiber having a very high toughness value corresponding to the energy absorption amount, which is a very important value when an industrial material product such as a net, a rope, or a belt is used.

  Further preferred embodiments of the present invention are roughly classified into the following two embodiments.

As one of the more preferable embodiments of the present invention, in order to further improve the spinning property and the quality of the polylactic acid fiber while the polylactic acid fiber maintains high strength and high toughness, the birefringence is 25 × 10 ⁻³ to 40 ×. 10 ⁻³ , strength is 4.5 to 7.5 cN / dtex, and the proportion of the devitrified filament among the filaments constituting the polylactic acid fiber is preferably less than 1%. The degree of orientation is 25 × 10 ⁻³ to 40 × 10 ⁻³ , preferably 29 × 10 ⁻³ to 40 × 10 ⁻³ in terms of birefringence. The strength is 4.5 to 7.5 cN / dtex, preferably 5 to 7.5 cN / dtex. According to Non-Patent Document 1, the birefringence achieved without causing devitrification is 28.4 × 10 ⁻³ at the maximum, and the birefringence value of the polylactic acid fiber of the present invention is the conventional value. This means that unreported levels could be achieved with industrial manufacturing methods. When the birefringence is 25 × 10 ⁻³ or more, the orientation of the molecular chain is at a sufficient level, so that a high strength of 4.5 cN / dtex or more can be obtained, and a desired high-toughness polylactic acid fiber can be obtained. . On the other hand, polylactic acid fibers having a high birefringence exceeding 40 × 10 ⁻³ are difficult to achieve with the current technology. Further, less than 1% of non-devitrified filaments means that substantially no devitrifying filaments are included, which means that uniform spinning and drawing are performed. Fibers substantially free of devitrifying filaments can be obtained with very good spinning properties.

  And the polylactic acid fiber comprised from the highly oriented, high-strength and substantially non-devitrified filament of this embodiment has a standard deviation of strength of 0.01 to 0.45 cN / dtex, preferably 0.01. It is characterized by being extremely uniform at ˜0.35 cN / dtex, more preferably from 0.01 to 0.3 cN / dtex. Polylactic acid fibers with a standard deviation of less than 0.01 are difficult to achieve with current technology, whereas when taking a standard deviation of more than 0.45 cN / dtex, filaments that are not substantially devitrified as in this embodiment However, it is not a high-strength polylactic acid fiber specified by the present invention. A method for measuring the standard deviation will be described later.

Further, another more preferable embodiment of the polylactic acid fiber of the present invention is a highly oriented, high-strength polylactic acid fiber containing some devitrified filaments, that is, 1 to 15%. That is, the birefringence is 23 × 10 ⁻³ to 40 × 10 ⁻³ , preferably 25 × 10 ⁻³ to 40 × 10 ⁻³ , and the intensity is 3.5 to 8 cN / dtex, preferably 4 to 7.5 cN. / Dtex polylactic acid fiber, characterized in that, among the filaments constituting the fiber, devitrified filaments are present in a proportion of 1 to 15%, preferably 1 to 10%. As described above, when the devitrified filament satisfies the scope of the present invention, the fiber physical properties are slightly inferior to the case where each filament is not substantially devitrified. Was found to be a polylactic acid fiber having a good balance of physical properties that can be used practically.

  Further, according to the knowledge of the present inventors, the devitrification phenomenon causes the polylactic acid fiber to be stretched close to the limit under specific stretching conditions (stretching means, number of stretching stages, stretching temperature, fiber height before stretching, etc.). Occurs. That is, it can be said that the polylactic acid fiber containing 1 to 15% of the devitrified filaments of the present invention is a fiber whose molecular orientation is increased to the limit without impairing the fiber properties under specific stretching conditions.

In the polylactic acid fiber of the present invention containing some devitrified filaments, when the birefringence is less than 23 × 10 ⁻³ , a high strength of 3.5 cN / dtex or more cannot be obtained, and the high toughness targeted by the present invention is achieved. In some cases, polylactic acid fibers cannot be obtained. Also, birefringence exceeding 40 × 10 ⁻³ and high strength yarn exceeding 8 cN / dtex are difficult to achieve with current technology.

  The standard deviation of the strength of the polylactic acid fiber of the present invention containing some devitrifying filaments is 0.05 to 1 cN / dtex, preferably 0.05 to 0.75 cN / dtex. Less than 0.05 cN / dtex is difficult to achieve as long as it contains 1 to 15% devitrified filaments. On the other hand, if it exceeds 1 cN / dtex, the physical property variation is so large that it is difficult to put it to practical use as an industrial application, and the strength of the polylactic acid fiber of the present invention may not be achieved.

  The polylactic acid fiber of the present invention is also characterized by a low thermal shrinkage and excellent thermal dimensional stability. The dry heat shrinkage measured at 120 ° C. is 1 to 13%, preferably 2 to 10%, more preferably 2 to 6%. This feature has the advantage that uniform heat setting can be achieved and a uniform product can be obtained when heat treatment such as laminating a fabric or net manufacturing process or a film is performed.

  Next, the polylactic acid fiber of the present invention has a sharp melting curve and a single peak when heat measurement is performed at a heating rate of 5 ° C./min using a DSC (differential scanning calorimeter). It is also characterized by not showing double peaks or shoulders. The cause of the DSC melting curve being broad or the appearance of double peaks and shoulders is, for example, a copolymer polymer or a polymer with a wide molecular weight distribution, or depending on the spinning cooling process and the drawing heat treatment conditions in the spinning process. This often occurs when the crystal size distribution is significantly widened. Therefore, using a uniform polymer, the higher the strength and the higher the strength, the more uniform the fiber structure. As shown in FIG. 4A, the DSC melting curve shows a sharp single peak pattern. However, polylactic acid fibers having a shoulder as shown in FIGS. 4B and 4C and polylactic acid fibers having a double peak often cannot achieve the birefringence and / or high strength of the present invention.

  The devitrification in the present invention means a phenomenon that occurs mainly in the drawing process and is caused by micro unevenness formed on the surface of the polylactic acid fiber filament, and as it is said, it loses transparency and becomes whitened. Is. Here, the size of the irregularities on the surface is on the order of sub-μ to μ. If it is less than sub-μ, it does not devitrify. On the other hand, if it is on the order of several tens of μ, the portion usually causes thread breakage or fluff, and is therefore rarely recognized as devitrification. That devitrification occurs due to the unevenness of the surface formed on the filament during stretching means that smooth thermal stretching has not been performed and excessive stretching has been performed. Smooth thermal stretching means that, for example, in a multi-stage thermal stretching process, each filament is preheated at a temperature suitable for the level of orientation before stretching, and is stretched at a stretching ratio suitable for the mobility of the molecular chain. Is to be stretched. If the preheating temperature is too high for the degree of orientation before stretching, the molecular chain will crystallize before orientation, making it difficult to stretch, resulting in surface irregularities. If it is too high, molecular chain flow occurs, so-called superdraw phenomenon without molecular chain orientation occurs, and effective stretching is not performed. In this case, although the unevenness is not generated on the filament surface, the strength cannot be obtained. On the other hand, if the preheating before stretching is not sufficient, the molecular chain will be stretched with low mobility, resulting in the formation of irregularities on the filament surface and devitrification.

  Polylactic acid has a glass transition temperature (Tg) at which molecular chain mobility occurs of about 60 ° C., and the melting temperature (melting point: Tm) of the fiber structure crystal is about 170 ° C. The temperature difference between Tm and Tg is As small as about 110 ° C. Incidentally, polyethylene terephthalate has Tg = 80 ° C. and Tm = 260 ° C., respectively, and the difference between Tm and Tg is 180 ° C.

  Therefore, since the optimum temperature range when heat-stretching the polylactic acid fiber is narrow, it is easy to deviate from smooth stretching conditions, the surface irregularities and the like are easily generated, and devitrification is likely to occur.

  The polylactic acid fiber of the present invention is established in consideration of the above-described heat-drawing behavior unique to the polylactic acid fiber, and can be produced by the following method.

That is, the polylactic acid fiber production method of the present invention is a method of producing a polylactic acid fiber by melting a polylactic acid polymer, extruding it from a die, applying an oil agent to a cooled and solidified yarn, and then hot-drawing without winding once. In this method, the drawing is performed at a spinning speed of 300 to 1000 m / min, and in at least the first stage of the thermal drawing, the draw ratio is set to 20 to 70% of the total draw ratio, and the draw point is on the yarn supply roll. It extends | stretches so that it may be located in.

  In order to describe the production method of the polylactic acid fiber of the present invention in detail, an example of a typical direct spinning drawing process for carrying out the method is shown in FIG. The process of FIG. 1 is a “pre-stretch-three-stage stretch-relax” method, but, of course, the process is not limited to this process as long as the above requirements are satisfied.

  Although the polylactic acid polymer used for the production of the polylactic acid fiber of the present invention has the above-described characteristics, it is preferable to use a high viscosity polymer having a relative viscosity of 2.6 to 4.5, more preferably 3 to 4.5. More preferably, it is in the range of 3.5 to 4.5. When a polymer having a relative viscosity of less than 2.6 is used, the highly oriented and high strength polylactic acid fiber of the present invention cannot be stably obtained. On the other hand, use of a polymer having a high viscosity exceeding 4.5 is not preferable because it is difficult to produce a stable yarn, and a devitrified filament is likely to be generated. The water content of the polylactic acid polymer used for melt spinning is preferably 0 to 0.05% in order to suppress hydrolysis of the polymer.

  The spinning temperature is preferably 190 to 250 ° C, more preferably 200 to 240 ° C. When spinning at less than 190 ° C., sufficient fluidity cannot be obtained when the polymer is melted, and devitrified filaments may be generated at the stage of undrawn yarn, and devitrification filaments frequently occur due to drawing. On the other hand, at temperatures exceeding 250 ° C., highly oriented and high strength polylactic acid fibers are difficult to obtain stably.

  Immediately below the spinneret, the upper end is 0 to 15 cm from the spinneret surface, and a range of 5 to 100 cm from the upper end is surrounded by a heating tube and / or a heat insulating tube, and the spinning yarn is placed in a high temperature atmosphere of 200 to 280 ° C. Passing is a preferred form of the production method of the present invention.

  The spinning filament is not cooled immediately, but is gradually cooled through a high-temperature atmosphere surrounded by the heating tube and / or the heat insulating tube, thereby relaxing the orientation of the spun filament and uniformity among the filaments. Can be increased. On the other hand, when cooled immediately without passing through a high-temperature atmosphere, the orientation of the undrawn yarn is increased and the orientation degree distribution between the filaments is increased. When such undrawn yarn is hot drawn, as a result, highly oriented and high strength polylactic acid fibers cannot be obtained. In particular, the intensity variation between the filaments increases, and the uniform polylactic acid fiber intended by the present invention may not be obtained.

  The unstretched filament that has passed through the high-temperature atmosphere is then preferably cooled and solidified by blowing air at 10 to 80 ° C., preferably 15 to 75 ° C. When the cooling air is less than 10 ° C., a large cooling device is required separately from the normal device, which is not preferable. Further, when the cooling air exceeds 80 ° C., the swing of the filament during spinning becomes large, so that the filaments collide with each other, and it becomes difficult to manufacture the fiber with good spinning property. The air cooling device may be a horizontal blowing type or an annular blowing type.

  The unstretched filament that has been cooled and solidified is then applied with an oil agent.

  The oil agent contains a smoothing agent as a main component and includes a surfactant, an antistatic agent, an extreme pressure agent component, and the like, but it is necessary to have an oil agent composition excluding components active on polylactic acid fibers. For example, the emulsified component contained in the water emulsion has an action of changing the fiber structure of the polylactic acid fiber, and easily works to generate surface irregularities during stretching. Therefore, it is preferable to use a non-aqueous oil agent. Further, a preferred oil agent composition is, for example, a non-aqueous oil agent obtained by diluting an alkyl ether ester as a smoothing agent component, an alkylene oxide adduct of a higher alcohol as a surfactant component, and an organic phosphate salt as an extreme pressure agent component with a mineral oil. .

The unstretched filament yarn provided with the oil agent is wound around a take-up roll (1FR) and taken up. Take-up roll speed, i.e. spinning speed 300 to 1000 m / min, preferably 5 00~ 1000 m / min. Although the physical properties of the polylactic acid fiber of the present invention can be obtained even at a spinning speed of less than 300 m / min, it is difficult to employ because the production efficiency is low. On the other hand, when the spinning speed exceeds 1000 m / min, high orientation and high strength of the polylactic acid fiber of the present invention cannot be obtained.

The undrawn yarn taken up at the spinning speed is drawn continuously without being wound once. Similar to the take-up roll (1FR), a Nelson type roll having two rolls as one unit is a yarn feeding roll (2FR), a first drawing roll (1DR), a second drawing roll (2DR), a third It arrange | positions along with a extending | stretching roll (3DR) and a relaxation | loosening roll (RR), and winds a thread | yarn sequentially and performs an extending | stretching heat processing. Usually, stretching is performed between 1FR and 2FR to focus the yarn. A preferred stretch ratio is in the range of 1 to 7%, more preferably 1 to 5%. 1FR is heated to 50 to 80 ° C., preferably 50 to 70 ° C., and the take-up yarn is preheated and sent to the next drawing step. The first stage of stretching is performed between 2FR and 1DR, but at least the draw point at the time of the first stage stretching, that is, the necking point, is positioned stably on the 2FR roll, preferably within a few centimeters immediately before leaving the roll. Thus, it is preferable to set the temperatures of 2FR and 1DR and the first draw ratio. However, these conditions need to be changed in consideration of the degree of orientation of the undrawn yarn. Usually, the temperature of 2FR is 80 to 120 ° C., preferably 80 to 110 ° C., the temperature of 1DR is 90 to 120 ° C., preferably 100 to 120 ° C., and the first stage draw ratio is 20 as the total draw ratio. -70 %, preferably 20-50%. Within the range of the above conditions, the draw point is set so as to be positioned in the vicinity of the 2FR roll upper exit. Furthermore, in order to set the draw point so as to be positioned at the upper outlet of the 2FR roll, the roll is preferably a satin roll with low friction. Usually, a chrome-plated one having a roll surface roughness Ra = 0.3-5 μm, preferably Ra = 0.5-3 μm is used.

  The second stage stretching is performed between 1DR and 2DR, and 2DR is 110 to 160 ° C, preferably 115 to 145 ° C. In the case of two-stage stretching, the remaining stretching of the first-stage stretching ratio is performed between the total stretching ratios. In the case of three-stage stretching, the remaining stretching ratio is divided into two stages. The temperature of 3DR when performing three-stage stretching is 120 to 160 ° C, preferably 130 to 150 ° C. The yarn that has finished two-stage drawing or three-stage drawing is subjected to a relaxation treatment of 0 to 10%, preferably 0 to 7%, more preferably 0.5 to 5% with RR, and is generated by hot drawing. In addition to taking the strain, the highly oriented structure achieved by stretching can be fixed, the orientation of the amorphous region can be relaxed, and the thermal shrinkage rate can be lowered. RR uses an unheated roll or a roll heated to 160 ° C. or lower. Usually, RR becomes a temperature of 90 to 150 ° C. regardless of the presence or absence of heating due to the heat brought in by the yarn heated at the time of hot drawing.

  Moreover, in the manufacturing method of the polylactic acid fiber of this invention, it is necessary to make it the multistage extending | stretching of 2-5 steps of extending | stretching steps, Preferably it is 3-5 steps. When the number of stretching stages is one, it is difficult to stretch at a high magnification while suppressing the occurrence of devitrification. As the number of stretching stages increases, it becomes possible to stretch at a higher magnification. However, when the number of stretching stages is 5 or more, the equipment is enlarged and the manufacturing process becomes complicated.

  The high strength and high toughness polylactic acid fiber suitable for the industrial material of the present invention can have basic physical properties by the above method. However, in order to obtain a high-quality polylactic acid fiber by reducing the yarn breakage and improving the yield and reducing the occurrence of fuzz, between 2FR and 1DR where at least one-stage drawing is performed, Stretching may be performed while spraying a high-pressure fluid on the fiber yarn to impart entanglement between the filaments constituting the fiber and converging the yarn. The device for entanglement and focusing of the yarn can use an entanglement nozzle that is used for imparting entanglement to the yarn and concentrating the yarn just before winding the yarn. The entanglement device is effective when it is stretched in the first stage, but it may also be performed during the stretch of the second and third stages in addition to the first stage.

  The polylactic acid fiber of the present invention is characterized by high orientation and high strength, but no irregularities are formed on the surface of the filament, and therefore, devitrified filaments are not generated or only slightly generated. In particular, the manufacturing method for achieving this is to set the 2FR temperature, the 1DR temperature, and the one-stage draw ratio so that the draw point in the first-stage drawing is located in the vicinity of the outlet on the 2FR roll, This is achieved by providing entanglement between the filaments at the time of stretching and concentrating and stretching the second and subsequent stages.

  Thus, the polylactic acid fiber of the present invention having the above physical properties is obtained.

  Hereinafter, embodiments of the present invention will be described in more detail by way of examples. Definitions and measuring methods of characteristics used in the specification text and examples are as follows.

  [Birefractive index (Δn)]: Retardation and yarn diameter were measured by the Belek Compensator method using D-line as a light source, and determined according to the following formula.

Δn = (Retardation / Thread diameter)
Ten filaments were measured and the average value was taken as Δn.

  [Total Fineness and Fineness of Filament]: Measured according to JIS L1090.

  [Strength, strength, elongation]: Measured by the method of JIS L1013. The strength was measured using a Tensilon tensile tester manufactured by Orientec Corp. under the conditions of a test length of 250 mm and a tensile speed of 300 mm / min. The strength is a value obtained by dividing the strength by the total fineness of the sample.

[Toughness]: Using the strength and elongation values measured by the method of JIS L1013, the toughness was calculated according to the following formula.
Toughness = {strength x (elongation) ^1/2 }
[Standard deviation of filament strength]: The strength and elongation of polylactic acid fiber were measured 20 times in accordance with JIS L1013, and the standard deviation was determined from the obtained 20 strength data.

[Ratio of devitrification filament]: In this example, the determination of devitrification of each filament was confirmed by the method shown in (1) below. However, devitrified filaments can be observed with the naked eye as well as with a stereomicroscope and SEM as shown in the following (2) to (3), and when it is difficult to determine with the naked eye, the type of fiber to be observed (filament fineness) The observation method may be changed in a timely manner depending on the yarn and the original yarn.
(1) Confirmation with the naked eye Place the polylactic acid fiber on black drawing paper and observe. In the case of multifilament, each single yarn is arranged so as not to overlap. If a white region is present when the filament 0.5 m is observed, it is determined that the filament is devitrified.
(2) Confirmation with a stereomicroscope A polylactic acid fiber is observed with reflected light using a stereomicroscope (Nikon stereomicroscope HFX type), photographed with a color video camera (CCD-IRIS) manufactured by SONY, and observed with a monitor. Random 25 points are selected and observed in 0.3 m of the filament, and if there is a region where light is diffusely reflected by devitrification and appears white as shown in FIG. 2, it is determined that the filament is devitrified. The observation magnification can be changed as appropriate depending on the fineness of the fiber. FIG. 2 shows an example of observation of devitrified yarn and non-devitrified yarn by observation with a stereoscopic microscope.
(3) Confirmation with SEM All filaments at arbitrary points in the polylactic acid fiber were vapor-deposited using an ion coater (IB-3 manufactured by Eiko Engineering). The prepared sample was observed using SEM (ABT-55 manufactured by Topcon Corporation). If there exists a filament which has an unevenness | corrugation on the fiber surface as shown in FIG. 3, it will determine with the fiber having a devitrification area | region. In addition, what is necessary is just to change observation magnification suitably according to a filament fineness. FIG. 3 shows an example of observation of devitrified yarn and non-devitrified yarn by SEM observation.

The ratio of devitrified filaments is the following formula: Ratio of devitrified filaments (%) = (number of devitrified filaments) / (total number of filaments) × 100
Can appear.

  [Dry Heat Shrinkage]: Measured at 120 ° C. according to the method of JIS L1013. Two samples were collected from the same sample and measured, and the average value was obtained.

  [DSC Melting Curve] A DSC-7 differential scanning calorimeter manufactured by Perkin Elmer (USA) was used and measured at a heating rate of 5 ° C./min.

  [Relative viscosity]: 25 mL of chloroform was added to a 0.5 g sample, and the mixture was stirred for 5 hours to dissolve the polymer. Then, chloroform was added to dilute to 50 mL. The diluted solution was measured using a Scott AVS500 automatic viscometer at a test temperature of 30 ° C., and the relative viscosity ηr was determined based on the following formula. The measurement was performed twice and the average value was taken.

ηr = t / t ₀
t: Solution dropping seconds
t ₀ : The number of seconds that the solvent (chloroform only) falls [Draw point between 2FR-1DR]: Between 2FR-1DR, that is, the position of the draw point at the first stage of stretching is measured, and the draw point is on 2FR Was evaluated as x between 2FR-1DR, that is, outside the yarn feeding roller.

  In addition, the draw point measured the thread | yarn speed from 2FR to 1DR using the laser Doppler velocimeter (LS-50M made from TSI), and made the point where speed | velocity | rate rapidly rose to 1DR surface speed the draw point.

[Spinning stability]: The occurrence frequency of fluff was measured over a length of 1 million m with a fluff detection device installed at the outlet of the relaxation roll, and the number of fluff per 10,000 m was expressed by the following formula:
Number of fuzz per 10,000 m = number of fuzz per million m / 100
Sought according to.

(Example 1)
A polylactic acid chip having a relative viscosity of 4 was melt-spun at 220 ° C. using an extruder-type spinning machine. The molten polymer was filtered through a 20 μ nonwoven fabric filter in a spin pack, and then spun from a 192-hole die with a hole diameter of 0.6φ.

  A 15 cm heating cylinder and a 15 cm heat insulation cylinder were attached 3 cm below the base surface, and heated so that the in-cylinder atmosphere temperature was 250 ° C. Here, the in-cylinder atmosphere temperature is an air layer temperature in a central portion of the heating cylinder length and a portion 1 cm away from the inner wall.

  An annular blow-off chimney was attached immediately below the heating cylinder, and cold air of 30 ° C. was blown onto the yarn at a speed of 30 m / min to solidify by cooling. An oil was applied to the solidified yarn. Oils include iso-C24 alcohol / thiodipropionic acid ester (40% by weight), C11-15 alcohol AOA / thiodipropionic acid ester (30% by weight), trimethylolpropane AOA distearate (10% by weight), C8 alcohol AOA ( 10% by weight) hydrogenated castor oil (7% by weight) and stearylamine EO15 (3% by weight) diluted to 20% with mineral oil were used.

The unstretched yarn provided with the oil agent was wound around a take-up roll (1FR) rotating at a speed of 500 m / min. Next, the take-up yarn was continuously stretched by 1.5% between the take-up roll and the yarn feeding roll (2FR) without being wound once, and subsequently subjected to three-stage hot drawing. Then, after giving 1.5% relaxation, it was wound up at a speed of 3000 m / min. Direct spinning drawing was performed using the process shown in FIG. 1FR is 60 ° C, 2FR is 100 ° C, the first stretching roll (1DR) is 115 ° C, the second stretching roll (2DR) is 140 ° C, the third stretching roll is 140 ° C, and the relaxation roll (RR) is unheated. did. The number of windings of the yarn on the roll was set to 3, 5, 5, 5, 9, and 4.5 times, respectively. An entanglement imparting nozzle was installed between the relaxing roll and the winder to impart entanglement to the fibers. Entangling was performed by injecting 4 kg / cm ² of high-pressure air in a direction substantially perpendicular to the running yarn in the entanglement imparting device.

  The first stage draw ratio was 34% of the overall draw ratio, the second stage draw ratio was 33%, and the third stage draw ratio was set to 33%.

  The obtained fiber properties, the ratio of devitrified filaments in the fiber yarn, the occurrence frequency of fluff, etc. were evaluated and shown in Table 1.

(Examples 2 to 8)
Table 1 shows the results of evaluating the spinning conditions, the fiber properties, the ratio of devitrifying filaments, and the fluff, using the same winding speed as in Example 1 and changing the spinning and drawing conditions. Moreover, regarding the oil agent of Example 2, iso C24 alcohol / thiodipropionic acid ester (40% by weight), C11-15 alcohol AOA / thiodipropionic acid ester (30% by weight), trimethylolpropane AOA distearate (10% by weight). %), C8 alcohol AOA (10% by weight) hydrogenated castor oil (7% by weight), stearylamine EO15 (3% by weight) to 20% with hot water at 50 ° C., and stirring the aqueous emulsion obtained. Using.

Example 9
After spinning, the yarn to which the oil is applied is wound around a take-up roll (1FR) that rotates at a speed of 1000 m / min. ), Followed by two-stage hot stretching, and after giving 1.5% relaxation, the film was wound at a speed of 4500 m / min. 1FR is 70 ° C, 2FR is 80 ° C, the first draw roll (1DR) is 120 ° C, and the second draw roll (2DR) is 140 ° C. The number of laps was 3 times, 6 times, 6 times, 9 times, and 4.5 times, respectively. However, the first stage draw ratio was set to 70% of the overall draw ratio, and the second stage draw ratio was set to 30%. Table 1 shows the results of evaluating the spinning conditions, fiber properties, the ratio of devitrified filaments and fluff.

(Comparative Examples 1 and 2)
As a basic process, Example 1 was used, and the spinning and drawing conditions were changed, and the yarn was produced. Table 2 shows the results of the spinning, the fiber properties, the ratio of devitrified filaments, and the fluff.
(Comparative Example 3) After spinning, the yarn provided with the oil agent is wound around the take-up roll (1FR) and taken up, and the take-up roll and the yarn feed roll (2FR) are continuously taken up without being wound up once. After stretching 1.5% between the layers, the film was subsequently stretched by one step, and then it was wound at a speed of 3000 m / min after giving 1.5% relaxation. The same procedure as in Example 1 was performed except that 1FR was 60 ° C, 2FR was 100 ° C, and the first stretching roll (1DR) was 140 ° C. The number of windings of the yarn on the roll was set to 3, 6, 9, and 4.5 times, respectively. The total magnification was 3.5 times. Table 2 shows the results of evaluating the spinning conditions, fiber properties, the ratio of devitrified filaments and fluff.

(Comparative Example 4)
The same procedure as in Example 1 was performed except that a polylactic acid chip having a relative viscosity of 2.5 was used.

(Comparative Example 5)
The same procedure as in Example 1 was performed except that the spinning temperature was 260 ° C.

(Comparative Example 6)
It carried out like Example 1 except not having used a heating cylinder and a heat insulation cylinder.

As a result, as shown in Table 1, the polylactic acid fiber of the present invention had high strength and high toughness, and could be obtained with good yarn production.

In addition, as shown in Examples 1 to 5, the polylactic acid fiber of the present invention substantially free of devitrified filaments, which is one of the aspects of the present invention, has high strength, high orientation, and high toughness. It was possible to obtain a very good spinning property.
In addition, as shown in Examples 6 to 9, the polylactic acid fiber slightly including a devitrified filament according to another aspect of the present invention is a polylactic acid substantially not containing the devitrified filament. Although it was inferior to the fiber as compared with the fiber, it was a polylactic acid fiber that had sufficient strength and toughness for practical use and good yarn production.

  When the degree of orientation of the polylactic acid fiber is low as described in Comparative Example 1, the obtained fiber does not have a devitrifying filament, but has a DSC shoulder, that is, the fiber internal structure is non-uniform and low. It had high strength and low orientation and high dry heat shrinkage.

  As described in Comparative Example 2, when the first-stage draw point is not on the yarn feeding roller, not only the yarn forming property is bad, but also the obtained polylactic acid fiber has many devitrifying filaments and large strength variation. Met.

  As described in Comparative Example 3, when trying to increase the molecular orientation to the range of the present invention by using the one-step stretching method, the ratio of devitrified filaments is increased and the variation in strength is increased. Only a fiber having a shoulder at the melting peak was obtained.

  Even when a low-viscosity polymer is used as a raw material as described in Comparative Example 4, when the molecular orientation is increased to the range of the present invention, the obtained fiber has high toughness but increases devitrification filaments. In addition to an increase in strength variation, only fibers having a shoulder at the DSC melting peak could be obtained.

  When spinning at a temperature exceeding the range of the present invention as described in Comparative Example 5, the obtained fiber has high toughness, but the spinning yarn is insufficiently cooled, and the polylactic acid fiber with less fluff It was difficult to stably obtain.

  As described in Comparative Example 6, when an attempt is made to obtain a polylactic acid fiber having a strength that falls within the scope of the present invention without providing a cooling zone under the die, the orientation degree distribution between the filaments becomes large and the loss is lost. The ratio of the permeable filaments and the strength variation were large, and uniform polylactic acid fibers could not be obtained.

(Comparative Example 7)
The same procedure as in Example 1 was conducted except that the spinning temperature was 190 ° C. However, since the spinning temperature was low, the melt viscosity of the polymer was high, and the spinning pressure was remarkably increased, so that spinning was impossible.

(Comparative Example 8)
The same procedure as in Example 1 was performed except that a polylactic acid chip having a relative viscosity of 5 was used. However, spinning was impossible because the melt viscosity was high and the spinning pressure was remarkably increased.

(Comparative Example 9)
The same procedure as in Example 1 was performed except that a 90 cm heating cylinder and a 30 cm heat insulating cylinder were used. However, the yarn swaying after spinning is intense and collisions between filaments occur, making it difficult to continue spinning with good spinning properties.

It is an extending process figure of an example of an embodiment of the present invention. It is an example of the stereoscopic microscope observation image of a devitrification and non-devitrification polylactic acid fiber. It is an example of the SEM observation image of devitrification and non-devitrification polylactic acid fiber. (A): It is the DSC curve at the time of temperature rising of the polylactic acid fiber in embodiment of this invention. (B) and (c): DSC curves at the time of temperature rise of the polylactic acid fiber different from the embodiment of the present invention for comparison with (a).

Explanation of symbols

1: Spinneret 2: Cooling zone 3: Cooling device 4: Oiling device 5: Take-up roller 6: Yarn feeding roller 7: First stretching roller 8: Second stretching roller 9: Third stretching roller 10: Relaxing roller 11: Entangling device 12: winding device

Claims (9)

A polylactic acid fiber which is a multifilament having a birefringence of 23 × 10 ⁻³ to 40 × 10 ⁻³ and an intensity of 3.5 to 8 cN / dtex, and the ratio of the devitrified filament is less than 1%, A polylactic acid fiber having a standard deviation of strength of 0.01 to 0.45 cN / dtex . Polylactic acid fiber according to claim 1, wherein the birefringence and wherein the ^{25 × 10 -3 ~40 × 10 -3} , the strength is 4.5~7.5cN / dte x. Birefringence is 23 × 10 ^-3 ~ 40x10 ^-3 A polylactic acid fiber which is a multifilament having a strength of 3.5 to 8 cN / dtex, wherein devitrified filaments are present at a ratio of 1 to 15%, and a standard deviation of the strength is 0.05 to 1 cN / dtex Polylactic acid fiber characterized by being. The melting peak in a melting curve measured by a DSC (differential scanning calorimeter) at a heating rate of 5 ° C./min shows a single peak and does not show a double peak or a shoulder. The polylactic acid fiber in any one of 1-3 . The polylactic acid fiber according to any one of claims 1 to 4 , wherein the dry heat shrinkage measured at 120 ° C is 1 to 13%. The polylactic acid fiber according to any one of claims 1 to 4 , wherein the dry heat shrinkage measured at 120 ° C is 2 to 6%. In a method in which polylactic acid polymer is melted and extruded from the die, and an oil agent is applied to the cooled and solidified yarn, and then heat-stretched without winding once to produce polylactic acid fiber, it is taken up at a spinning speed of 300 to 1000 m / min. In addition, in at least the first stage of the thermal drawing, the draw ratio is set to 20 to 70% of the overall draw ratio, and the draw point is positioned on the yarn supply roll. A method for producing polylactic acid fibers. The method for producing a polylactic acid fiber according to claim 7 , wherein the following requirements (1) to (4) are satisfied.
(1) The relative viscosity of the raw material polymer is 2.6 to 4.5.
(2) The upper end is 0 to 15 cm immediately below the spinneret, the range from 5 to 100 cm from the upper end is surrounded by a heating cylinder and / or a heat insulating cylinder, and the spinning yarn is passed through a high temperature atmosphere of 200 to 280 ° C. .
(3 ) The number of hot-drawing stages is 2-5.
(4) The yarn feeding roll is a satin roll, and the roughness of the roll surface is Ra = 0.3 to 5 µm. Oil agent, alkyl ether ester as a smoothing agent component, alkylene oxide adducts of a higher alcohol as a surfactant ingredient, claim 6 or 7, characterized in that a non-aqueous oil containing an organic phosphate salt as an extreme pressure agent component The manufacturing method of the polylactic acid fiber as described in 1 ..