JP2008088570A - Sheath-core conjugated polyester fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conjugated fiber which is composed of polylactic acid and polyethylene terephthalate and has good durability and good spinning operability. <P>SOLUTION: This sheath-core conjugated polyester fiber whose core portion is composed of polylactic acid, a sheath portion is formed from polyethylene terephthalate having an intrinsic viscosity of 0.41-0.59 and the polyethylene terephthalate in the sheath portion is dope-dyed. Preferably, The number-average molecular weight of the polylactic acid composing the core portion is 70,000-150,000, and the eccentricity of the core portion is ≤3.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polyester core-sheath composite fiber containing polylactic acid and having excellent durability and spinning operability.

  Conventional synthetic fibers are hardly decomposed in the natural environment, and disposal is a problem. Therefore, recently, biodegradable fibers such as polylactic acid fibers have attracted attention and are being actively developed. However, biodegradable fibers such as polylactic acid fibers are biodegradable, so they have poor weather resistance and moist heat resistance and are durable for clothing, civil engineering materials, marine materials, automotive materials, etc. Use is limited in required areas.

  Therefore, in order to increase the durability of polylactic acid, it has been proposed to improve the hydrolysis resistance by blocking the ends of the polymer with a terminal blocking agent such as carbodiimide (see, for example, Patent Document 1). However, this method only reduces the number of terminal groups that promote hydrolysis after the polymerization, and it is insufficient to suppress the hydrolysis itself.

Further, as another means, composite fiber formation with an aromatic polyester having crystallinity has been proposed (see, for example, Patent Document 2), but since these polyesters have a large melting point difference from polylactic acid, composite fiber formation is performed. It is difficult. In particular, in the case of compounding with polyethylene terephthalate having a high melting point, it is necessary to set the spinning temperature to 270 ° C. or higher, which is considerably higher than the spinning temperature suitable for polylactic acid of 200 to 230 ° C. Therefore, when spinning at a temperature suitable for polyethylene terephthalate, the melt viscosity of polylactic acid becomes very low, so the difference in melt viscosity between polyethylene terephthalate and polylactic acid increases, resulting in a decrease in spinning operability and physical properties. Etc. happen. For this reason, the composite fiber of polyethylene terephthalate and polylactic acid has not been satisfactory in terms of both operability and fiber properties.
JP2001-261797 JP 2005-187950 A

  In addition, JP 2004-353161 A discloses a composite fiber using polylactic acid as a core and polyethylene terephthalate as a sheath, and an improvement effect on strength, wear resistance, and wet heat decomposition resistance is recognized. ing. However, when these composite fibers are dyed, dyeing at a high temperature is necessary, so that the polylactic acid in the core portion is deteriorated by heat, and the original durability may not be maintained.

  Therefore, the present invention solves the above problems and provides a polyester core-sheath composite fiber composed of polylactic acid and polyethylene terephthalate, which has durability and good operability in spinning.

The inventors of the present invention have arrived at the present invention as a result of intensive studies in order to solve the above problems.
That is, the gist of the present invention is as follows.
(1) A polyester core-sheath composite fiber having a core part made of polylactic acid, wherein polyethylene terephthalate having an intrinsic viscosity of 0.41 to 0.59 is used as the sheath part, and the polyethylene terephthalate in the sheath part is colored. A polyester core-sheath composite fiber characterized by having
(2) The polyester core-sheath conjugate fiber according to claim 1, wherein the polylactic acid constituting the core part has a number average molecular weight of 70,000 to 150,000, and the core part has an eccentricity of 3.0 or less. .

Since the polyester core-sheath composite fiber of the present invention is polyethylene terephthalate, which is a sheath component, is colored in advance, the polylactic acid component is not deteriorated due to the dyeing of the fiber and maintains excellent durability. In addition, the polyester core-sheath conjugate fiber of the present invention is not colored with polylactic acid in the core, and therefore, in spinning, it has excellent releasability from the nozzle and has excellent spinning operability without yarn breakage. is doing.
Furthermore, the polyester core-sheath composite fiber of the present invention is excellent in strength and moisture-heat-decomposability, although it is composed of polylactic acid, which is relatively inferior in thermal stability and mechanical properties compared to petroleum-derived general-purpose plastics. It can be used widely for clothing, industrial materials and the like.

Hereinafter, the present invention will be described in detail.
The polyester core-sheath composite fiber of the present invention (hereinafter sometimes abbreviated as the composite fiber of the present invention) is a core-sheath composite fiber composed of polyethylene terephthalate and polylactic acid, the sheath part is polyethylene terephthalate, and the core part is It is composed of polylactic acid.

  The polylactic acid constituting the core of the conjugate fiber of the present invention includes poly-L-lactic acid, poly-D-lactic acid, a copolymer of L-lactic acid and D-lactic acid, or poly-L-lactic acid. Examples thereof include a mixture (stereo complex) with poly-D-lactic acid.

  Here, when the polylactic acid in the present invention is a copolymer of L-lactic acid and D-lactic acid, the main component is either poly-L-lactic acid or poly-D-lactic acid, The content of the polylactic acid component not to be used is preferably 5% by mass or less, and more preferably 2% by mass or less. When the content of the polylactic acid component which is not the main component is more than 5% by mass, the crystallinity of the polylactic acid copolymer is lowered, and heat resistance and durability may be lowered.

  Moreover, as a number average molecular weight of the polylactic acid in this invention, what is 70,000-150,000 is preferable, and what is in the range of 80,000-130,000 is more preferable. When the number average molecular weight is less than 70,000, melt extrusion becomes difficult, and the mechanical strength of the fiber tends to decrease. Further, when the number average molecular weight exceeds 150,000, melt extrusion becomes difficult, and the balance of melt viscosity with polyethylene terephthalate which is a sheath component is not appropriate, and it tends to be difficult to obtain a durable composite fiber. Therefore, it is not preferable.

  In the conjugate fiber of the present invention, the polyethylene terephthalate constituting the sheath part is mainly composed of polyethylene terephthalate obtained from terephthalic acid and ethylene glycol using a conventional method, but the characteristics of the present invention are not impaired. Other carboxylic acid components and diol components may be copolymerized within the range.

Examples of carboxylic acid components include aromatic dicarboxylic acids such as isophthalic acid and 5-sulfoisophthalic acid, aliphatic dicarboxylic acids such as adipic acid, succinic acid, suberic acid, sebacic acid, and dodecanedioic acid, glycolic acid, and hydroxybutyric acid. Hydroxyvaleric acid, hydroxycaproic acid, hydroxypentanoic acid, hydroxyheptanoic acid, hydroxyoctanoic acid and other hydroxycarboxylic acids, and ε-caprolactone and other aliphatic lactones.
Examples of the diol component include aliphatic diols such as propylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol.

  In the conjugate fiber of the present invention, it is necessary that the intrinsic viscosity of polyethylene terephthalate used for the sheath is 0.41 to 0.59, preferably 0.45 to 0.57, more preferably. Is 0.50 to 0.57. This intrinsic viscosity value is considerably lower than the viscosity of polyethylene terephthalate (0.62 to 0.68) commonly used for fibers, but the viscosity of polyethylene terephthalate should be low. Thus, since the difference in melt viscosity between polylactic acid and polyethylene terephthalate during composite spinning can be reduced, the effect of improving spinning operability and physical properties (particularly strength) can be obtained.

  When the intrinsic viscosity value of polyethylene terephthalate is larger than 0.59, the difference in melt viscosity from polylactic acid increases, the operability such as thread breakage decreases, and the orientation difference between the two polymers increases due to stretching. Therefore, the obtained composite yarn has low strength. On the other hand, when the intrinsic viscosity is less than 0.41, the melt viscosity of polyethylene terephthalate becomes too low, making melt extrusion difficult, and the target composite fiber of the present invention cannot be obtained.

  In the composite fiber of the present invention, it is necessary that the polyethylene terephthalate constituting the sheath is colored. Usually, the raw material coloring of the composite fiber includes (1) coloring the core part as raw material, (2) coloring the sheath part as raw material, and (3) coloring the raw material at both the core part and the sheath part. Although there are two methods, in the present invention, it is necessary to color the sheath portion as a raw material. When the core of (1) is colored with the raw material, and when both the core and the sheath of (3) are colored with the raw material, polylactic acid will be colored with the raw material, When polylactic acid is colored as a raw material, the extrudability of the composite fiber from the spinning nozzle is significantly deteriorated during spinning, and the polymer adheres to the nozzle surface, which makes spinning difficult.

  In the conjugate fiber of the present invention, when polylactic acid is colored as a raw material, the extrudability of the conjugate fiber from the spinning nozzle is remarkably deteriorated because the spinning temperature of the conjugate fiber needs to be the spinning temperature of polyethylene terephthalate. Therefore, it is considered that the thermal decomposition reaction of polylactic acid occurs, and that the polylactic acid is further colored to promote the thermal decomposition reaction of polylactic acid.

  In general, when dyeing a composite fiber composed of polylactic acid and polyethylene terephthalate, a temperature condition suitable for polyethylene terephthalate is selected, so that the polylactic acid component deteriorates due to wet heat treatment in the dyeing process, and the durability of the composite fiber. Occurs. In the composite fiber of the present invention, pre-coloring ethylene terephthalate is effective in avoiding this.

  Therefore, in the composite fiber of the present invention, since the polyethylene terephthalate constituting the sheath is colored as a raw material, the spinnability of the composite fiber is not impaired and the deterioration of the durability of the composite fiber due to the dyeing process is avoided. be able to.

  As a method for coloring ethylene terephthalate in the present invention, a conventional method may be used. For example, it may be a method of directly adding a pigment or dye at any stage from the production of the polymer to fiberization, or after adding the following dye or pigment to the polymer and mixing with a kneader such as an extruder, A method using master pellets obtained by re-pelletizing may also be used.

  The master pellet is dried before spinning and diluted with an uncolored polymer. When used as a master pellet, one or more raw colored pellets and uncolored pellets may be mixed with an appropriate mixing device such as a V-type blender or a double cone type blender. Alternatively, two or more kinds of raw material colored pellets and uncolored pellets are melted separately, and then a kneading device having a driving unit such as an extruder or a static kneading device having no driving unit such as a static mixer is used. May be mixed.

  Examples of the pigment or dye used for coloring the raw material in the present invention include conventionally known inorganic pigments such as carbon black, titanium oxide, cadmium sulfide, iron oxide, and chromium oxide, azo-based, phthalocyanine-based, quinacridone-based, Examples thereof include organic pigments such as dioxane, anthraquinone, and perylene / perinone. In addition, known dyes having good heat resistance and light resistance that can be used for coloring polyethylene terephthalate resin, or mixtures thereof can also be used.

  In addition, in order to improve the dispersibility, heat resistance, light resistance, etc. of the above-mentioned pigments and dyes, an appropriate amount of an additive such as a dispersant, a surfactant, an ultraviolet adsorbent, or an antioxidant may be added as necessary. it can. Further, the ratio of the above-described pigment or dye to be contained in the composite fiber of the present invention is preferably 0.01 to 5% by mass, and can be appropriately adjusted depending on the kind of the pigment or dye used. For example, in the case of carbon black, 0.5 to 3% by mass, in the case of inorganic pigment, 0.5 to 5% by mass, and in the case of organic pigment, 0.3 to 3% by mass are preferable.

  The conjugate fiber of the present invention preferably has an eccentricity of 3.0 or less, more preferably 2.0 or less. The degree of eccentricity in the present invention is a value indicating how much the center point of the core part of the composite fiber is deviated from the center point of the entire composite fiber in the cross section of the fiber. The center has shifted | deviated from the center of the whole composite fiber, and it has shown that the thickness of a sheath part is not uniform. That is, the degree of eccentricity in the present invention is the degree of eccentricity when the thickness of the thickest part of the sheath is a and the thickness of the thinnest part is b in the cross section cut perpendicular to the fiber direction of the composite fiber. It can be obtained as a / b.

  When the eccentricity is greater than 3.0 in the conjugate fiber of the present invention, the difference between the thick part and the thin part of the polyethylene terephthalate in the sheath is large, and the effect of improving durability, which is the effect of the present invention. Is not preferred because it is difficult to obtain. That is, when the degree of eccentricity is larger than 3.0, the thick part becomes thicker, while the thin part becomes thinner, and the thin part of the sheath part is stored or stored during use of the composite fiber. Is likely to be eroded due to wear, wet heat, etc., and the polylactic acid component in the core is exposed to the surface. As a result, the deterioration of the polylactic acid component as the core is promoted, and the durability of the entire composite fiber becomes poor. As the eccentricity in the present invention, 1.0 is the lower limit when the sheath has a uniform thickness.

  The composite fiber of the present invention can be obtained by composite spinning using a conventional method. That is, the polyethylene terephthalate component and the polylactic acid component are spun by a conventionally known melt compound spinning method, cooled using a conventionally known cooling device such as a horizontal spray or an annular spray, and then provided with an oil agent, and a take-up roller Is wound on a winder as undrawn yarn. The wound undrawn yarn is drawn between a group of rollers having different peripheral speeds by a known drawing machine, and an oil agent is applied as necessary. When the target fiber is a short fiber, mechanical crimping with a crimper or the like may be performed as necessary, and the target fiber may be cut into a target length with a cutter such as an EC cutter or a guillotine cutter. When the target fiber is a long fiber, it can be scraped off as it is, and processing such as twisting and false twisting can be performed as necessary.

  Further, the shape of the conjugate fiber of the present invention is not particularly limited, but in order to maximize the effects of the present invention, polyethylene terephthalate (sheath part) is made of polylactic acid (core part). It is important to cover with a uniform thickness, and a round cross section is preferred, since it is relatively easy to make the sheath polymer uniform in thickness.

  The composite ratio of the core-sheath component in the conjugate fiber of the present invention is preferably a volume ratio of core: sheath = 30: 70-70: 30, and more preferably in the range of core: sheath = 40: 60-60: 40.

  In the composite fiber of the present invention, in order to further enhance the durability of the polylactic acid, the aliphatic alcohol, the carbodiimide compound, the oxazoline compound, the oxazine compound, and the epoxy compound are added to the polylactic acid as long as the effects of the present invention are not impaired. You may add terminal blockers, such as. Further, the composite fiber of the present invention includes pigments, dyes, water repellents, water absorbents, flame retardants, stabilizers, antioxidants, ultraviolet absorbers, crystal nucleating agents, lubricants, plasticizers, antibacterial agents, fragrances and the like. Additives and metal particles can be mixed.

Hereinafter, the present invention will be described in detail by way of examples, but is not limited thereto.
In addition, the measuring methods, such as a characteristic value in an Example, are as follows.
(1) Intrinsic viscosity of polyethylene terephthalate It measured based on the conventional method at 20 degreeC using the Ubbelohde viscometer using the equal mass mixed solution of phenol / ethane tetrachloride as a solvent.
(2) Number average molecular weight of polylactic acid It was measured by a gel permeation chromatography (GPC) method using tetrahydrofuran as a solvent and a refractometer.
(3) Content of L-lactic acid and D-lactic acid (%)
It was measured by a high performance liquid chromatography (HPLC) method using a 1N sodium hydroxide methanol solution and an equal mass mixed solution of ultrapure water as a solvent. The column used was sumichiral OA6100, and was detected by a UV absorption measuring device.
(4) Spinning operability Spinning was performed with two spindles for 8 hours, the yarn breakage was 0 times, 、 １, 1 to 2 times, ○, 3 to 5 times, Δ, and 6 times or more. In the present invention, thread breakage of 2 times or less was regarded as acceptable.
(5) Eccentricity Calculated by the above formula. In addition, the thickness of a sheath part image | photographed with the optical microscope (500 times) the cross section cut | disconnected perpendicularly | vertically with respect to the length direction of a fiber, it measured from the microscope picture, and was taken as the average value of n = 20.
(6) Single yarn strength (cN / dtex)
In evaluating the durability of the obtained composite fiber, the single fiber strength of the composite fiber was used. The strength measurement was performed by the method of JIS L-1015 8-7-1.
In the present invention, a single yarn strength of 3.0 cN / dtex or more was regarded as acceptable.

(Example 1)
16.5 parts by mass of polyethylene terephthalate having a number average molecular weight of 89,500 and a polylactic acid mainly composed of L-lactic acid having a D-lactic acid content of 1.3% by mass and having an intrinsic viscosity of 0.42. In addition, by mixing 1 part by mass of master pellets (polyethylene terephthalate, intrinsic viscosity 0.59) obtained by kneading 35% by mass of carbon black having an average primary particle size of 43 μm, the carbon black concentration becomes 2.0% by mass. The raw material-colored polyethylene terephthalate is used as a sheath, the number of holes is 560, a round cross-section composite spinneret is used, the core-sheath ratio is the melt volume ratio, the core: sheath = 50: 50, and the eccentricity is 1.5. In this way, melt spinning was performed at a spinning temperature of 280 ° C. and a spinning speed of 800 m / min to obtain an undrawn yarn of a polyester core-sheath composite fiber. Next, the obtained undrawn yarn was drawn at a drawing temperature of 60 ° C. and a draw ratio of 4.50 times, and then subjected to tension heat treatment at 140 ° C. to obtain a polyester core-sheath composite fiber having a fineness of 3.3 dtex. . The results are shown in Table 1.

(Examples 2-3, Comparative Example 1)
A polyester core-sheath composite fiber was obtained in the same manner as in Example 1, except that the intrinsic viscosity and the eccentricity of polyethylene terephthalate in Example 1 were changed as shown in Table 1. The results are shown in Table 1.

(Comparative Example 2)
Carbon black having an average primary particle size of 43 μm is obtained with respect to 16.5 parts by mass of polylactic acid mainly composed of L-lactic acid having a number average molecular weight of 89,500 and a D-lactic acid content of 1.3% by mass. By mixing 1 part by mass of master pellets (number average molecular weight 85300) made of 35% by mass kneaded polylactic acid, the core is made of polylactic acid that is colored so that the carbon black concentration is 2.0% by mass. The polyester core-sheath composite fiber was spun in the same manner as in Example 1 except that the sheath was made of ethylene terephthalate (inherent viscosity 0.56) that was not colored. The results are shown in Table 1.

(Comparative Example 3)
The master pellet made of polyethylene terephthalate prepared in Example 1 is used for the sheath part, the master pellet made of polylactic acid prepared in Comparative Example 2 is used for the core part, and the pigment concentration is 1.5 mass for both the core part and the sheath part. The polyester core-sheath composite fiber was spun in the same manner as in Example 1 except that the raw material was colored in%. The results are shown in Table 1.
(Comparative Example 4)
A polyester core-sheath composite fiber was spun in the same manner as in Example 1 except that the intrinsic viscosity of polyethylene terephthalate in Example 1 was changed to 0.38. The results are shown in Table 1.

  As can be seen from Table 1, in Examples 1 to 3 that satisfy the requirements of the present invention, the spinnability is good, and the strength of the obtained composite fiber is also good, which is a composite made of polyethylene terephthalate and polylactic acid. Fiber was obtained.

On the other hand, in Comparative Example 1, since the intrinsic viscosity of the polyethylene terephthalate in the sheath portion was high and the difference in melt viscosity from polylactic acid was large, the spinning operability was poor and the single yarn strength was also lowered.
Further, in Comparative Examples 2 and 3, since the polylactic acid was colored as a raw material, the extrudability of the composite fiber from the spinning nozzle was remarkably deteriorated, the polymer adhered to the nozzle surface, and spinning could not be performed. Furthermore, in Comparative Example 4, since the intrinsic viscosity of the polyethylene terephthalate in the sheath was low, the melt viscosity was low, the spinning operability was poor, and the intended core-sheath composite yarn could not be obtained.

Claims (2)

It is a polyester core-sheath composite fiber whose core part is composed of polylactic acid, and polyethylene terephthalate having an intrinsic viscosity of 0.41 to 0.59 is used as the sheath part, and the polyethylene terephthalate in the sheath part is colored as a raw material Polyester core-sheath composite fiber characterized by 2. The polyester core-sheath composite fiber according to claim 1, wherein the polylactic acid constituting the core part has a number average molecular weight of 70,000 to 150,000 and an eccentricity of the core part of 3.0 or less.