JP4922232B2 - Polylactic acid fiber and fiber product using the same - Google Patents

Description

  The present invention relates to a polylactic acid fiber excellent in heat resistance and a fiber product using the fiber.

  A technique for fiberizing polylactic acid, which is a thermoplastic, by melt spinning is known. In particular, poly-L-lactic acid having a high L-form content is crystalline and has a melting point of about 170 ° C. and has biodegradability. Among thermoplastics, it has a relatively high melting point and is expected to be widely used for clothing or industrial fibers.

  However, when used as clothing fibers, for example, when ironing is performed in the same manner as synthetic fibers such as general-purpose polyester and polyamide, there is a problem that the texture becomes hard even if the fibers are not melted. For this reason, when ironing a fabric made of polylactic acid fibers, special care is required, such as requiring a particularly low temperature setting and a batter, and development in the clothing field is extremely limited. In addition, in the manufacturing process and processing process of textile products such as woven and knitted fabrics and nonwoven fabrics, there is a problem that troubles such as entanglement with the roll are likely to occur when the heat treatment zone or the heat roll passes.

On the other hand, a polylactic acid stereocomplex in which poly-L-lactic acid and poly-D-lactic acid are spatially arranged in a stereospecific manner and fibers thereof are known as those made of polylactic acid and having a higher melting point. For example, Patent Document 1 discloses a polylactic acid stereocomplex composition obtained by melt blending an amorphous polymer containing poly-L-lactic acid as a main component and an amorphous polymer containing poly-D-lactic acid as a main component. Articles and molded articles are disclosed. The melting point of the polylactic acid stereocomplex composition is 10 to 60 ° C. higher than that of ordinary poly-L-lactic acid. However, even a fiber composed of such a stereocomplex with a high melting point does not necessarily greatly improve the retention of physical properties in a high-temperature atmosphere.
JP 2000-17163 A

  The present invention solves the above-mentioned problem, and can be satisfactorily heat-treated in the manufacturing and processing steps of textile products such as woven and knitted fabrics and nonwoven fabrics made of polylactic acid fibers. It is an object of the present invention to provide a polylactic acid-based fiber that does not harden the texture when ironing the fiber product made of the above at a temperature lower than the melting point, and a fiber product made of the same.

  In order to achieve the above-mentioned problems, the present inventor has intensively studied about the thorough investigation and countermeasures for the cause of hardening of the texture when ironing polylactic acid fibers. In the course of the study, the present inventor indicated that the glass transition temperature is equivalent to that of conventional poly-L-lactic acid fiber, as the reason why the fiber with a high-melting point stereocomplex does not necessarily improve the physical property retention under a high temperature atmosphere. It was thought that this was due to the fact that the degree of crystallinity of the fibers was not significantly different from that of conventional poly-L-lactic acid fibers.

  Therefore, paying attention to the degree of crystallinity, the cause of hardening of the texture when ironing the polylactic acid fiber was investigated. In the polylactic acid fiber, it is important to increase the crystallinity at the same time as the melting point itself is high. I found out. That is, the phenomenon that polylactic acid fibers are hardened by heat treatment is largely due to the non-crystalline region softening above the glass transition temperature, and there is a close relationship between the crystallinity of polylactic acid fibers and the texture hardening during ironing. I found out. In order to increase the melting point and increase the crystallinity, the D-form content is extremely low rather than the poly-L lactic acid having a D-form content of 1 mol% or more that is readily available on the market. Thus, the problem could be achieved by obtaining the fiber by hot drawing using the purified poly-L lactic acid as a raw material.

  That is, the present invention is a polylactic acid fiber composed of poly-L lactic acid having a D-form content of 0.15 mol% or less, and has a melting point of 175 ° C. or higher and a crystal melting enthalpy of 50 J when the fiber is subjected to DSC analysis. The gist of the polylactic acid fiber is characterized by being / g or more.

  Hereinafter, the present invention will be described in detail.

  The polylactic acid fiber of the present invention is composed of poly-L-lactic acid mainly composed of L-form having a D-form content of 0.15 mol% or less, and is not a copolymer of other components, but homopolylactic acid. By the fiber. The poly-L lactic acid in the present invention has a D-form content reduced to the utmost limit, but it is industrially difficult to polymerize so as not to contain the D-form at all. And 0.15 mol% or less.

  The polylactic acid fiber of the present invention has a melting point of 175 ° C. or higher and a crystal melting enthalpy of 50 J / g or higher when subjected to differential scanning calorimetry (DSC analysis: Differential Scanning Calorimetry analysis). Since the polylactic acid fiber of the present invention is composed of poly-L lactic acid with the D-form content reduced to the limit (0.15 mol% or less), the melting point is 175 ° C. or higher and the crystal melting enthalpy is 50 J / g. A highly crystalline fiber as described above can be obtained. In the present invention, by using the poly-L lactic acid as described above, by appropriately selecting the spinning conditions for obtaining the fibers, a highly crystalline fiber having a high melting point of about 185 ° C. and a crystal melting enthalpy of about 68 J / g is obtained. Can also be obtained. In general, poly-L lactic acid mainly composed of L-form which can be easily obtained on the market contains about 1.2 mol% even if the D-form content is low. The melting point is at most 167 to 170 ° C., and the crystal melting enthalpy is at most about 40 to 45 J / g.

  The melting endothermic curve (DSC curve) when the polylactic acid fiber of the present invention (polylactic acid fiber of Example 1 described later) is subjected to DSC analysis is shown in FIG. 1 and is composed of poly-L lactic acid having a D-form content of 1.4 mol%. FIG. 2 shows a DSC curve when the polylactic acid fiber (polylactic acid fiber of Comparative Example 1 described later) is subjected to DSC analysis. In the DSC analysis, it was determined from the DSC curve when automatically measured at a heating rate of 20 ° C./min using an input compensated differential scanning calorimeter (Diamond DSC manufactured by PerkinElmer). In the DSC curve, the calorific value of the endothermic peak (crystal melting enthalpy) indicates the amount of the crystalline phase of the polymer constituting the fiber, and this crystal melting enthalpy is the area surrounded by the baseline and peak lines of the DSC curve. expressed. The DSC curve when the polylactic acid fiber of the present invention is subjected to DSC analysis has a high endothermic peak temperature (melting point), and the peak shape is very sharp.

  The polylactic acid fiber of the present invention can be obtained by the following method.

  First, fibers are formed by melt spinning using poly-L lactic acid having a D-form content of 0.15 mol% or less as a raw material and mainly L-form. Next, the obtained fiber is heat-set at a temperature lower than the crystal melting start temperature and in a temperature range that promotes crystallization, that is, 110 to 150 ° C. By this heat setting, crystallization of poly-L lactic acid constituting the fiber can be promoted. Moreover, the crystal melting enthalpy by DSC analysis of the obtained fiber can be 50 J / g or more, and the thermal shrinkage rate of the fiber can be suppressed, and a stable fiber at high temperature can be obtained. This heat setting is performed when the polylactic acid fiber is drawn or false twisted or after. What is necessary is just to heat-set by making a fiber contact the heat plate set to the said temperature.

  The polylactic acid fiber of the present invention can be used, for example, in the form of a monofilament, a multifilament, a shortcut fiber, a staple or the like. Since the poly-L lactic acid in the present invention has a high crystallization rate, it is possible to keep the thermal contraction rate of the fibers low when trying to obtain long fibers (monofilaments and multifilaments) that are difficult to take a long heat setting time especially during yarn production. it can. For example, a long fiber made of poly-L lactic acid having a D-form content of 1.4 mol% that is readily available on the market has a dry heat shrinkage of 36% or more at 150 ° C., but can be obtained under the same spinning conditions. In the polylactic acid fiber of the present invention, the dry heat shrinkage rate is suppressed to about 9 to 13%.

  The cross-sectional form of the polylactic acid fiber of the present invention is not particularly limited, and may be a circular cross section or an atypical cross section, and may be hollow or non-hollow.

  Further, the fineness of the polylactic acid fiber is not particularly limited, and may be appropriately determined according to the required characteristics depending on the application, but is about 0.5 to 200 dtex. Moreover, the form of the fiber may be one having mechanical crimps or one having three-dimensional three-dimensional crimps. For example, for a cushioning material or the like, a material having a conjugate type steric crimp in which two types of polylactic acids having different degrees of polymerization are bonded together is preferable.

  What is necessary is just to give to a polylactic acid fiber according to a use, such as the oil agent for dry nonwoven fabrics for normal polyester fibers, the oil agent for wet nonwoven fabrics, the oil agent for spinning, the oil agent for filaments, and the oil agent for false twisting. A slippery silicone-based or non-silicone-based slippery oil may be applied.

  Since the polylactic acid fiber of the present invention has a specific melting point and a specific crystal melting enthalpy as described above, it has a low thermal shrinkage rate and is stable at high temperatures. Therefore, textile products such as woven and knitted fabrics and nonwoven fabrics using the polylactic acid fiber of the present invention, the fibers shrink in the processing step, the texture is inferior, and when making a textile product, especially when ironing When ironing with steam, the heat shrinks the fiber, losing moderate play (displacement) in the structure and structure of the fiber product, reducing the drape and the like, and making the texture harder Such problems are unlikely to occur.

  Examples of fiber products using the polylactic acid fiber of the present invention include woven fabrics, knitted fabrics, nets, spun yarns, braided cords, wet papermaking sheets made by dispersing shortcut fibers in water, spunbond nonwoven fabrics, staple staple fibers. A web in which staples are accumulated by opening with a card machine, etc., a short fiber nonwoven fabric in which the web is subjected to needling processing, spunlace processing, and fibers are entangled, and the web is heat embossed, thermocompression bonding equipment And a heat-bonded nonwoven fabric in which fibers are heat-bonded by heat treatment using a hot-air treatment apparatus or the like.

When using a short fiber nonwoven fabric as a cushioning material or a filter, the thickness is preferably 5 mm or more. The upper limit of the thickness is not particularly limited, but is preferably about 150 mm from the viewpoint of manufacturing equipment, manufacturing cost, and ease of use. The density of the cushion material is preferably 0.01 g / cm ³ or more. In order to regulate the thickness and density of the nonwoven fabric, the punch density by needling processing is appropriately selected, and thermal compression is performed at a temperature of about (melting point of polylactic acid−5) ° C.

  The fiber product in the present invention may be composed only of polylactic acid fibers, but polylactic acid fibers, natural fibers such as cotton, wool and hemp, regenerated fibers such as rayon and solvent-spun cellulose fibers, polyester and nylon Further, it may be mixed with synthetic fibers such as acrylic to obtain blended yarn, blended yarn, union knitted fabric, blended nonwoven fabric and the like.

  The polylactic acid fiber of the present invention has a melting point of 175 ° C. or higher and a crystal melting enthalpy by DSC analysis of a specific value or higher, so that the thermal stability at a high temperature is very good and the heat shrinkage rate is small. It is.

  Therefore, it is possible to perform heat treatment satisfactorily in the manufacturing process and processing process when manufacturing a textile product such as a woven or knitted fabric or a nonwoven fabric using the polylactic acid fiber of the present invention.

  In addition, when ironing a fiber product using the polylactic acid fiber of the present invention, ironing is performed at a set temperature of 150 ° C. without paying close attention to temperature setting and application of a patch. However, the texture does not harden.

  In addition, since the polylactic acid fiber of the present invention has the above-mentioned thermal characteristics, even when it is mixed with other natural fibers or synthetic fibers to obtain a fiber product, it is heat-treated in a processing step or the like. be able to.

  According to the polylactic acid fiber of the present invention, since it is not necessary to pay close attention to heat, it can be used in various fields. For example, in the non-woven fabric field, which is an example of textile products, a garment interlining for ironing, a filter for filtering high-temperature media, a shoulder pad for high-temperature washing and drying, stuffed cotton and beds for furniture, a mattress and a cushion It can be used satisfactorily for mats, cushioning materials such as cushions for automobiles and vehicle seats whose temperature rises around the engine during running, and ceilings, panel materials, sound-absorbing materials, and vibration-proofing materials.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by these.

Examples 1-5
Poly-L-lactic acid (L) with a relative viscosity mainly composed of L-lactic acid (measured at a sample concentration of 0.5 g / dl and a temperature of 20 ° C. using an equal mass mixture of phenol and ethane tetrachloride as a solvent at a temperature of 20.degree. Body: 99.90 mol%, D body: 0.10 mol%) at 225 ° C. or 235 ° C. at a spinning speed of 3000 m / min to obtain fibers, and the drawing heat set to the temperatures shown in Table 1 Using a roller and a heat plate set between the heat rollers and set to the temperature shown in Table 1, heat drawing and heat setting were performed at a draw ratio of 1.3 to obtain a multifilament of 84 dtex / 36 filaments. In Table 1, the stretching temperature represents the set temperature of the stretching heat roller.

Comparative Examples 1-3
Poly-L-lactic acid (L-form: 98. L.) having a relative viscosity mainly composed of L-lactic acid (measured at a sample concentration of 0.5 g / dl and a temperature of 20 ° C. using an equal mass mixture of phenol and ethane tetrachloride as a solvent) 60 mol%, D-form: 1.40 mol%) at 225 ° C. or 235 ° C. at a spinning speed of 3000 m / min to obtain fibers, and a drawing heat roller set at the temperature shown in Table 1, Using a heat plate set between the rollers and set to the temperature shown in Table 1, thermal stretching was performed with a stretching ratio of 1.3, which also served as heat setting, to obtain a multifilament of 84 dtex / 36 filaments.

  In Comparative Example 3, it was not possible to obtain a practical fiber because the fiber was cured at the time of hot drawing.

Comparative Example 4
In Example 3, a multifilament was obtained in the same manner as in Example 3 except that the heat plate temperature in the heat setting was 80 ° C.

  The obtained polylactic acid fibers of Examples 1 to 5 and Comparative Examples 1, 2 and 5 were evaluated for thermal properties (melting point, crystal melting enthalpy), yarn physical properties, and the following methods. Moreover, the fiber product was obtained using the obtained polylactic acid fiber, and the iron characteristic was evaluated.

(Thermal characteristics) It was determined from the DSC curve when the input compensation differential scanning calorimeter (Diamond DSC, manufactured by Perkin Elmer) was automatically measured at a heating rate of 20 ° C / min.

(Yarn physical properties) Based on JIS L 1013 8.5.1 tensile strength and elongation rate (standard time test), measurement was performed using a constant speed extension type tester at a grip interval of 20 cm and a tensile speed of 20 cm / min.

(Iron characteristics) Using the polylactic acid fibers obtained in Examples 1 to 5 and Comparative Examples 1, 2, and 5, knitting was performed by a cylindrical knitting machine having 270 needles to prepare cylindrical knitted samples. Water was sprayed so that the entire tubular knitted sample was uniformly moistened, and the texture after ironing with an iron set at a surface temperature of 150 ° C. was evaluated according to the following criteria.
A: Very good with no texture hardening.
B: There is almost no texture hardening and it is good.
C: The texture is clearly cured.

  Table 1 shows the evaluation of polylactic acid fibers obtained in Examples and Comparative Examples.

Example 6
The poly-L lactic acid used in Example 1 was melt-spun using a normal melt spinning apparatus at a spinning temperature of 235 ° C. and a total discharge rate of 313 g / min. After cooling the spun yarn, it was drawn at a take-up speed of 1000 m / min to obtain an undrawn fiber yarn. The resulting yarns are bundled, made into a 110,000 dtex tow, drawn at a draw ratio of 2.9, drawn at a temperature of 80 ° C., heat-set with a 130 ° C. heat drum, and then using a push-in crimper. After crimping, it was cut to a length of 51 mm, melting point 181 ° C., crystal melting enthalpy 61.3 J / g, single yarn fineness 4.4 dtex, strength 2.8 cN / dtex, elongation 37% (JIS L 1015 8.7.1 using a constant speed extension type tester with a grip interval of 20 mm and a tensile speed of 20 mm / min), 120 ° C. dry heat shrinkage of 1.8% (according to JIS L 1015 8.15b) Measurement) polylactic acid short fibers were obtained.

The obtained polylactic acid short fibers were passed through a carding machine and then laminated with a cross lapper to form a web having a basis weight of 120 g / m ² . Further, this web was subjected to a needling process at a punch density of 192 punch / cm ² to obtain a nonwoven fabric having a thickness of 2 mm.

  When the obtained nonwoven fabric was cut into 30 cm × 30 cm and ironed with an iron set at a surface temperature of 150 ° C., it was not cured and the texture was very good.

Comparative Example 5
In Example 6, a polylactic acid short fiber was obtained in the same manner as in Example 6 except that the resin used in Comparative Example 1 was used as the polylactic acid resin.

  The resulting polylactic acid short fiber has a melting point of 169 ° C., crystal melting enthalpy of 45.3 J / g, single yarn fineness of 4.4 dtex, strength of 2.7 cN / dtex, elongation of 35%, 120 ° C. dry heat shrinkage ratio of 2. It was 6%.

  A nonwoven fabric was prepared in the same manner as in Example 6 using the obtained polylactic acid short fibers. When the obtained non-woven fabric was ironed in the same manner as in Example 6, the texture was clearly cured.

Example 7
The polylactic acid short fibers obtained in Example 6 were passed through a carding machine and then laminated with a cross lapper to obtain a web having a basis weight of 50 g / m ^2. Then, the roll surface temperature was set to 200 ° C. It was embossed through a hot embossing device to obtain a partially heat-bonded nonwoven fabric.

  The obtained nonwoven fabric of Example 7 was ironed in the same manner as in Example 6. As a result, there was no curing and the texture was very good.

Melting endothermic curve when polylactic acid fiber of the present invention (polylactic acid fiber of Example 1) was subjected to DSC analysis Melting endothermic curve when the polylactic acid fiber of Comparative Example 1 was subjected to DSC analysis

Claims (2)

It is a polylactic acid fiber composed of poly-L lactic acid having a D-form content of 0.15 mol% or less, a melting point when the fiber is subjected to DSC analysis is 175 ° C. or higher, and a crystal melting enthalpy is 50 J / g or higher. Polylactic acid fiber characterized by 2. A fiber product using the polylactic acid fiber according to claim 1.