JP5652089B2 - Process for producing short fibers of polylactic acid - Google Patents

Description

  The present invention relates to a method for producing a polylactic acid precursor short fiber and a nonwoven fabric product. More specifically, the present invention relates to a method for producing a polylactic acid original short fiber for producing a high-performance nonwoven product.

  In recent years, polylactic acid having biodegradability has been attracting attention as environmental awareness on a global scale is increasing. Polylactic acid is a polymer made from lactic acid obtained by fermenting starch extracted from a plant, and as a biodegradable polymer using biomass, the balance of mechanical properties, heat resistance, and cost is most excellent. The development of polylactic acid fibers is preceded by agricultural materials and civil engineering materials that make use of biodegradability, but the application of various uses such as clothing and industrial materials has been studied as the next large-scale use. It has been broken.

  In Patent Document 1, before and after dyeing, the aliphatic polyester fiber is selected by selecting the dyeing temperature, dyeing pH, and dyeing time so that the reduction rate of the weight average molecular weight of the aliphatic polyester fiber used for dyeing is 20% or less. There is a study of dyeing with a disperse dye. However, the dyeing process has a problem that the molecular weight is lowered and the quality is deteriorated because high temperature treatment is essential. In addition, there is a problem that the profitability is not met when the textile product is made by the dyeing process.

  Because of such problems, studies have been made on the original yarn of polylactic acid fiber. Patent Document 2 describes a production method of an original continuous filament that is drawn by a heated drawing roller as an original polylactic acid crimped yarn for providing a nonwoven fabric excellent in texture and abrasion resistance and a method for producing the same. ing. However, this method cannot be applied to the production of short fibers that are drawn with tow. Further, in Patent Document 3, it is necessary to add a fatty acid bisamide and / or an alkyl-substituted monoamide to reduce devitrification yarn in providing a polylactic acid short fiber excellent in abrasion resistance and hydrolysis resistance. It is described.

JP-A-8-311781 Japanese Patent No. 4481907 JP 2009-167539 A

  An object of the present invention is to provide a high-quality polylactic acid-coated short fiber having hydrolysis resistance and having no color unevenness.

In order to achieve the above object, the method for producing a polylactic acid-based fiber of the present invention melts a polylactic acid-based resin composition in which a polylactic acid-based resin contains a trifunctional or higher functional epoxy group compound and an original component. Spinning to produce a tow having a total fineness of 10 to 100 ktex, and the tow containing a smoothing agent component comprising at least one alkyl ether surfactant at a concentration of 0.01 to 1.0 wt% The film is stretched in a hot water bath at ˜95 ° C., then mechanically crimped so that the degree of crimp is 5 to 18%, and cut into a predetermined fiber length.

  Moreover, the polylactic acid precursor fiber of the present invention is a polylactic acid precursor short fiber produced by the above production method, wherein the number of crimps is 5 pieces / 25 mm or more and the amount of terminal carboxyl groups is 10 equivalents / ton or less. The devitrification yarn is present in an amount of 0 to 10%, and the color unevenness (ΔE) is 1 or less.

  According to the method of the present invention, it is possible to produce an original raw cotton having no devitrification yarn, which has hydrolysis resistance and is suitable for producing a high-quality nonwoven fabric product having no color unevenness. It is possible to produce short fibers. Furthermore, the nonwoven fabric product which can fully exhibit the characteristic of this polylactic acid original fiber can be obtained.

  The polylactic acid used in the present invention refers to a polymerized lactic acid oligomer such as lactic acid or lactide. When the optical purity of the L-form or D-form is 90% or higher, the melting point is preferably high. The optical purity of the L-form or D-form is more preferably 97% or more. Moreover, you may use the polylactic acid-type resin which copolymerized components other than lactic acid in the range which does not impair the property of polylactic acid. The components to be copolymerized include polyethers such as polyethylene glycol, aliphatic polyesters such as polybutylene succinate and polyglycolic acid, aromatic polyesters such as polyethylene isophthalate, and hydroxycarboxylic acids, lactones, dicarboxylic acids and diols. Examples thereof include an ester bond-forming monomer.

  The polylactic acid used in the present invention preferably has a melting point of 130 ° C. or higher. When the melting point is lower than 130 ° C., fusion between single yarns is remarkable at the time of spinning, particularly spinning, and troubles such as poor drawing are likely to occur, and the quality of the product may be impaired. The melting point is preferably 140 ° C. or higher, more preferably 150 ° C. or higher.

  The production method of the polylactic acid fiber according to the present invention will be described in detail.

  The method of incorporating the trifunctional or higher functional epoxy compound and the original component into the polylactic acid is not particularly limited. For example, the polylactic acid chip and the epoxy compound and the original component are individually dried and then kneaded. A master method is preferred in which a master chip is prepared by a machine, and this master chip and polylactic acid chip are chip blended and melt-spun, and a predetermined amount of the above-mentioned epoxy compound and original component is converted to polylactic acid during melt spinning. You may employ | adopt the addition method etc. which add directly.

  The content of the original component in the original polylactic acid resin composition to be used for melt spinning may be an appropriate amount according to the original component so as to obtain a desired coloration. It is preferable that it is 0.01-5.0 wt% with respect to. Further, the content of the epoxy compound may be an appropriate amount at which the carboxyl end group concentration of the polylactic acid becomes a predetermined level, but is generally 0.1 to 5.0 wt% with respect to the polylactic acid. Is preferred.

  In order to suppress oxidative decomposition of polylactic acid during kneading and melt spinning, the inside of the apparatus is preferably sealed with nitrogen. Further, the yarn discharged from the die is applied with an oil agent, converged, stored in an undrawn yarn and then drawn. When drawing, the stored yarn is bundled and supplied as a tow shape.

  The total fineness of the tow subjected to stretching is 10 to 100 ktex, preferably 20 to 80 ktex. If it is less than 10 ktex, the production efficiency is poor, and if it exceeds 100 ktex, the interfiber interaction becomes strong and the devitrification yarn improvement effect is not sufficient.

  The liquid bath at the time of tow drawing needs to be a hot water bath containing a smoothing agent component in order to reduce interaction between fibers of tow. Specifically, at least one component having a smoothing action selected from an anionic surfactant having a smoothing action, a cationic surfactant, a zwitterionic surfactant, a nonionic surfactant and the like is 0.01 to It is necessary to use hot water contained at a concentration of 0.5 wt%. When the level of the smoothing agent component in the liquid bath is less than 0.01 wt%, the interaction between the fibers of the tow becomes strong, and the devitrification yarn improving effect is not sufficient. Also, if the level of the leveling agent in the liquid bath exceeds 0.5 wt%, the level of leveling agent adhering to the tow becomes too high, and when the crimp is applied, the friction with the roller of the stuffer box is too low, Slipping causes a crimp failure. The temperature of the liquid bath is 80 to 95 ° C, preferably 85 to 90 ° C. If the temperature is less than 80 ° C., the stress applied at the time of drawing is large, and thus devitrification occurs in the entire fiber. If it exceeds 95 ° C., it is difficult to control the temperature because it is close to the boiling point of water used in the bath liquid, and bubbles due to partial boiling are generated in the liquid bath, thereby inhibiting uniform stretching.

  As the smoothing agent component added to the stretching bath, an oil agent component having a smoothing action used as one component in the oiling agent may be used, and is not particularly limited. For example, an anionic interface having a smoothing action is used. As activators, fatty acid salts, alphasulfo fatty acid ester salts, alkylbenzene sulfonates, linear alkylbenzene sulfonates, alkyl sulfates, alkyl ether sulfate esters, alkyl phosphate esters, alkyl phosphate esters, alkyl sulfate triethanol Amines: Alkyl dimethylamine oxide, alkyl carboxybetaines as smoothing zwitterionic surfactants; Fatty acid diethanolamides, polyoxy (ethylene / propylene) alkyl ethers, polyoxy (ethylenes) as nonionic surfactants having smoothing action Propylene) alkyl esters, polyoxy (ethylene / propylene) alkylamines, polyoxy (ethylene / propylene) alkylphenyl ethers, sorbitan alkyl esters; higher amine halogenates, alkyltrimethylammonium salts, dialkyls as cationic surfactants with a smoothing action Examples thereof include dimethylammonium chloride and alkylpyridinium chloride.

  After stretching, mechanical crimps are applied using a stuffer box or the like so that the number of crimps is 5 to 18 pieces / 25 mm and the degree of crimp is 5 to 18%. A polylactic acid original short fiber is produced by cutting with an EC cutter or the like so that the fiber length becomes.

  The polylactic acid original short fiber obtained by the method of the present invention is mixed with at least one short fiber selected from synthetic fibers such as aromatic polyester, aliphatic polyester, polyethylene, polyolefin and polyamide at an arbitrary ratio. A non-woven fabric product is manufactured.

  The polylactic acid-origin short fibers of the present invention are suitable for use in non-woven fabric products such as non-woven carpets, and their use locations are not particularly limited for home use, interior use, vehicle use, and the like.

  In order to use the polylactic acid-deposited short fibers produced by the method of the present invention for non-woven fabric products such as non-woven carpets, the single fiber fineness is preferably 3 to 20 dtex in view of wear resistance. In addition, the polylactic acid short fiber of the present invention may be a core-sheath composite or sea-island type composite fiber even if it has a circular cross section, a flat cross section, a triangular shape, a hollow shape, a star shape, or a different shape cross section. It may be.

  The polylactic acid precursor short fiber of the present invention requires a strength of 1.3 cN / dtex or more, preferably 1.5 cN / dtex, more preferably 1.8 cN / dtex or more. If it is less than 1.3 cN / dtex, the card-passing property is poor, and when it is made into a nonwoven fabric product, the abrasion resistance is inferior, and the polylactic acid fiber may be worn out during use.

  The number of crimps of the polylactic acid fiber of the present invention is required to be 5/25 mm or more, and preferably 8/25 mm or more. If the number of crimps is less than 5 pieces / 25 mm, the entanglement between the fibers is low, so that wrapping occurs in the card process and the operability is remarkably deteriorated. The upper limit of the number of crimps is not limited as long as the fibers are not fused when crimped by a stuffing box, but is preferably 18 pieces / 25 mm or less.

  Further, the degree of crimp is required to be 5 to 18%, preferably 6% to 15%. When the degree of crimp is less than 5%, the entanglement property between fibers when processing into a nonwoven fabric is low, so that wrapping occurs in the card process and the operability is remarkably deteriorated. On the other hand, if the degree of crimp is greater than 18%, the entanglement of the fibers becomes strong and the spreadability is poor, nep is generated in the card process, and the quality of the product is remarkably deteriorated.

  In order to improve the hydrolysis resistance, it is necessary to add a trifunctional or higher functional epoxy compound as a terminal reactant to the polylactic acid before spinning. In the prior art as described in JP-A-2009-167539, polycarbodiimide or the like is added as a terminal reactive substance. However, these substances increase the frequency of devitrification yarn by the addition thereof, This is inappropriate because the color unevenness of the fibers becomes large. By using a trifunctional or higher functional epoxy compound as the terminal reactant, local IV fluctuation can be reduced and the frequency of devitrification yarn can be suppressed. Furthermore, it is very important from the viewpoint of improving hydrolysis resistance to react a tri- or higher functional epoxy compound with at least a part of polylactic acid, preferably with at least a part of the carboxyl group terminal of polylactic acid. is there.

  The trifunctional or higher functional epoxy compound used in the present invention is a compound having 3 or more functional groups containing an epoxy group and / or an epoxy in one molecule, and is represented by the following general formula (1).

(Here, R1 to R3 are an epoxy group or a functional group containing an epoxy, and at least one of them is a glycidyl group)
Examples of the functional group containing an epoxy group include a glycidyl group, a glycidyl ether group, a glycidyl ester group, and a glycidylamine group.

  The epoxy compound represented by the general formula (1) is not particularly limited, but triglycidyl isocyanurate, trimethyl glycidyl isocyanurate, triethyl glycidyl isocyanurate, tripropyl glycidyl isocyanurate, diethyl glycidyl methyl glycidyl isocyanurate, Examples include ethyl glycidyl dimethyl glycidyl isocyanurate, diepoxycyclopentylmethyl glycidyl isocyanurate, epoxycyclopentylmethyl diglycidyl isocyanurate, diepoxycyclobutylmethyl glycidyl isocyanurate, and epoxycyclobutylmethyldiglycidyl isocyanurate. In addition, the trifunctional or higher functional epoxy compound used as the end-capping substance may be used alone or in combination.

  The content of the epoxy compound in the present invention with respect to the entire short fiber is not particularly limited, but if the amount of the epoxy compound is such that the carboxyl end group concentration of the polylactic acid polymer is 10 equivalents / ton or less, the resistance of the polylactic acid short fiber is reduced. The hydrolyzability can be drastically improved, which is preferable.

  The primary component used in the present invention is a metallic inorganic pigment excluding lead, chromium and cadmium, for example, an oxide-based inorganic pigment, a ferrocyanide inorganic pigment, a silicate inorganic pigment, a carbonate inorganic pigment, a phosphate inorganic Pigments, inorganic pigments such as carbon black, aluminum powder, bronze powder and titanium powder-coated mica, organic pigments such as phthalocyanine-based organic pigments, perylene-based organic pigments, isointoserinone-based organic pigments, and heterocyclic dyes , Helinone dyes, perylene dyes and thioindio dyes.

  In order to suppress uneven color and increase the strength of the polylactic acid precursor short fibers of the present invention, it is necessary to reduce the abundance of devitrified yarn. Polylactic acid short fibers tend to generate abnormally stretched yarns called devitrified fibers in which the fibers lose transparency, and the devitrified fibers have lower strength and elongation than normal fibers. Moreover, even if it is an original yarn, a devitrification part will be whitened and will cause uneven color. Therefore, when the devitrified fibers are mixed, the color unevenness and quality of the polylactic acid original short fibers are remarkably lowered. Therefore, the abundance ratio of the devitrified yarn needs to be specifically 0 to 10%, preferably 0 to 5%. When the abundance of devitrified yarn exceeds 10%, thread breakage and fluff frequently occur in high-order processing, and stable processing becomes difficult. Further, when processed into a non-woven fabric, the fibers whitened due to devitrification have noticeable color unevenness and cannot be said to be a high-quality product.

  Since the polylactic acid original short fiber of the present invention is a high-quality nonwoven fabric product, it is necessary to minimize color unevenness. Therefore, it is necessary to set the color unevenness (ΔE) to 1 or less. Here, ΔE (color unevenness) being 1 or less means that ΔE (color unevenness) of fibers sampled at 10 g from 10 or more positions in 100 kg of the original short fibers is measured and all are 1 or less. is there. If the color unevenness (ΔE) is larger than 1, the nonwoven fabric has uneven color, and it cannot be said that the quality is high.

  The definition and measurement method of the characteristics used in the specification text and examples are as follows.

[Fineness]
The fineness (dtex) is measured by the method shown in JIS L-1015 (1999).

[Strength]
The strength (cN / dtex) is measured by the method shown in JIS L-1015 (1999).

[Crimped number]
The number of crimps (pieces / 25 mm) is measured by the method shown in JIS L-1015 (1999).

[Crimp]
The degree of crimp (%) is measured by the method shown in JIS L-1015 (1999).

[Terminal amount of carboxyl group]
The weighed sample is dissolved in o-cresol adjusted to a moisture content of 5%, and after adding an appropriate amount of dichloromethane, it is titrated with a 0.02 normal potassium hydroxide methanol solution to measure the carboxyl group terminal amount.

[Presence of devitrified yarn]
In this example, the presence or absence of devitrification of the original short fibers was determined by the method shown in (1) below (confirmation with the naked eye). However, the devitrified yarn can be observed with an electron microscope or the like in addition to the naked eye, and when it is difficult to determine with the naked eye because the raw cotton is white, the state of the short fibers to be observed (inorganic oxide amount, The presence or absence of devitrification may be determined by an observation method as shown in (2) below depending on the fineness, the original yarn, and the like.

(1) Confirmation with the naked eye Place the polylactic acid-coated short fibers on black or white drawing paper so that they do not overlap in the same direction. The criterion is devitrification if there is devitrification even in part of the short fiber. Regarding the level, 10 samples are randomly collected from the manufactured short fibers (raw cotton), and the presence or absence of devitrification is confirmed for 20 short fibers at each point. Determine (10 points × 20 lines = 200 levels).

Presence of devitrified yarn (%) = (number of devitrified yarn) / (total number of short fibers; 200) × 100
(2) Observation with an electron microscope Polylactic acid short fibers are arranged so as not to overlap in the same direction, and vapor deposition is performed with gold or silver. The produced sample is observed with SEM (ABT-55 manufactured by Topcon Corporation). Ten points are randomly observed for each short fiber, and if the fiber surface is uneven, it is a devitrified region, and the short fiber is determined to be devitrified yarn. The observation magnification can be changed as appropriate depending on the fineness of the fiber. Regarding the level, samples are randomly collected from the produced short fibers from 5 points, and the presence or absence of devitrification is confirmed for 20 short fibers at each point (10 points × 20 pieces = 200 level).

[Color unevenness (ΔE)]
The color of the original short fiber (raw cotton) is measured with a color meter, and ΔE (color difference) is calculated using the method of L * a * b * color system (JIS-Z8729). As a calculation method, ΔE for standard cotton is calculated using the values of lightness (L *), hue (a *), and saturation (b *).
ΔE = [(ΔL *) ² + (Δa *) ² + (Δb *) ² ] ^1/2
Calculate by the following formula.

[Card passability]
For 100 g of fiber, the fiber spinning state from the card when passing through the roller card was observed, and the determination was made according to the following criteria.
○: The web is discharged from the roller card without interruption.
(Triangle | delta): The entanglement of the web discharged | emitted from a roller card | curd is weak, and a web break occurs accidentally.
X: The web is not discharged from the roller card.

[Uneven color on the web]
The web obtained by the roller card was visually observed for color unevenness.
○: No color unevenness ×: Color unevenness

Example 1
Polylactic acid chips having a melting point of 170 ° C. [manufactured by Natureworks; 6201D], triglycidyl isocyanurate (TGIC) [manufactured by Nissan Chemical Co., Ltd .; TEPIC-S] and carbon black as an original pigment are individually dried. Then, they were mixed at a weight ratio of 88: 10: 2, melted and kneaded at 220 ° C. to form chips, and master chips were produced. The same polylactic acid chip as described above and the prepared master chip were mixed at a weight ratio of 90:10, melt-spun at an spinning temperature of 230 ° C. with an extruder-type spinning machine, the spun yarn was cooled, and an oil agent After applying and converging, it was taken up at 1000 m / min to produce an undrawn yarn. The resulting undrawn yarn is further converged to form a 25 ktex tow and a liquid bath (temperature 90 ° C., polyoxyethylene / polyoxypropylene alkyl ether (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) containing 0.2% concentration) After stretching 3.0 times in water), mechanical crimps are applied in the stuffer box so that the target crimp number is 12 pieces / 25 mm and the target crimp degree is 10%. Refueling was applied at 0.6% by weight, and heat treatment was performed at 145 ° C. for 15 minutes. Thereafter, it was cut to 51 mm to produce a polylactic acid original short fiber (6.6 dtex).

  The obtained raw short fiber cotton and polyethylene terephthalate black raw short fiber (6.6 dtex) raw cotton were mixed at a weight ratio of 50:50, and a web was obtained by carding. evaluated. The results are shown in Table 1.

Example 2
Polylactic acid original short fibers were produced in the same manner as in Example 1 except that the oil agent concentration in the liquid bath used for stretching was changed to 0.4% and the oil bath was stretched 3.0 times in this liquid bath. .

Comparative Example 1
The polylactic acid primary short fibers were prepared in the same manner as in Example 1 except that the liquid bath used for stretching was changed to 90 ° C. hot water containing no oil and stretched 3.0 times in this liquid bath. Manufactured.

Comparative Example 2
A polylactic acid precursor fiber was produced in the same manner as in Example 1 except that the temperature of the liquid bath used for stretching was changed to 70 ° C. and the liquid bath was stretched 3.0 times in this liquid bath.

Comparative Example 3
The polylactic acid precursor fiber was prepared in the same manner as in Example 1 except that the stuffer box conditions were set so that the number of crimps was 20 pieces / 25 mm and the target degree of crimp was 20%. Manufactured.

Comparative Example 4
A polylactic acid original short fiber was produced in the same manner as in Example 1 except that triglycidyl isocyanurate (TGIC), which is an additive for blocking the terminal carboxyl group of polylactic acid, was not added.

  As is apparent from Table 1, Examples 1 and 2 both satisfy the characteristics specified in the present invention and can be excellent.

  In Comparative Examples 1 and 2, devitrified yarn was generated in the drawing process, and white fibers were mixed in the entire fiber. Even in the non-woven fabric, white fibers were conspicuous, and color unevenness could be confirmed visually.

  In Comparative Example 3, the tow was fused at the time of crimping, resulting in fiber deterioration and poor fiber opening. Along with this, the card passage was poor and the web was not discharged at all. Even in the visual confirmation of the slightly obtained non-woven fabric, the color unevenness was conspicuous due to the mixture of the fused yarns, and the quality was not high.

  In Comparative Example 4, the same card process passability and uneven color were obtained as in Examples 1 and 2, but the amount of terminal carboxyl groups was as high as 24.5 and lacking hydrolysis resistance. It was not suitable for use.

  The polylactic acid precursor short fibers produced by the method of the present invention are particularly useful as raw cotton for nonwoven carpets.

Claims (3)

A polylactic acid resin composition containing a polylactic acid resin containing a trifunctional or higher functional epoxy group compound and an original component is melt-spun to produce a tow having a total fineness of 10 to 100 ktex. Stretching was carried out in a hot water bath at 80 to 95 ° C. containing a smoothing agent component of various alkyl ether surfactants at a concentration of 0.01 to 0.5 wt%, and then the degree of crimp was 5 to 18%. A process for producing a polylactic acid-based short fiber, characterized in that mechanical crimping is applied so that the fiber is cut into a predetermined fiber length.   A polylactic acid original short fiber manufactured by the method for producing a polylactic acid original short fiber according to claim 1, wherein the number of crimps is 5/25 mm or more and the terminal carboxyl group amount is 10 equivalent / ton or less. A polylactic acid primary short fiber characterized by having an abundance of devitrified yarn of 0 to 10% and color unevenness (ΔE) of 1 or less.   A non-woven product comprising the lactic acid precursor short fibers according to claim 2.