JP2005336666A - Lactic acid fiber having low heat shrinkability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To bring it a theme to provide a polylactic acid fiber having a low shrink rate in boiling water, giving a fabric having sufficient dimensional stability to heat treatment in processing and bringing to a product and uniform appearance with moderate bulkiness and without irregularities caused by wrinkles and stripes. <P>SOLUTION: The polylactic acid fiber having low heat shrinkability uses a polylactic acid containing a syndiotactic polystyrene at least in a part of the fiber. The polylactic acid fiber uses the polylactic acid containing the syndiotactic polystyrene at least a part of the fiber and has ≤10% shrink rate in boiling water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fiber made of polylactic acid containing syndiotactic polystyrene.

  As awareness of the global environment increases, global warming due to carbon dioxide and the depletion of limited petroleum resources are regarded as problems. From such a background, polylactic acid, which is made of plant-derived materials and can be mass-produced, has attracted attention as a synthetic polymer having a low environmental load. Polylactic acid is a polymer made from lactic acid obtained by fermenting starch extracted from plants, and is excellent in terms of mechanical properties, heat resistance, and cost. Currently, development of resin products, fibers, films, and the like using polylactic acid is actively performed. In the textile industry, melt spinning is possible, and the development of polylactic acid fibers is actively carried out as a fiber that is low on the environment and friendly to the earth (see, for example, Patent Documents 1 and 2).

  Thus, polylactic acid fiber is a very powerful material that can cope with environmental problems. However, when polylactic acid fiber is actually used as a fabric (for example, non-woven fabric, woven fabric, knitted fabric, etc.), the melting point of polylactic acid is low. Various problems due to low (about 170 ° C.) are likely to occur. As one of them, there is a problem that it is difficult to reduce the boiling water shrinkage of the fiber because it is difficult to perform melt spinning and heat setting after drawing at a high temperature. In such a fiber having a high boiling water shrinkage rate, the shrinkage when subjected to hot water treatment such as dyeing is large when it is made into a fabric, the dimensional stability of the resulting product is deteriorated, and the product is inferior in quality. There's a problem.

  Therefore, a method for reducing the boiling water shrinkage of polylactic acid fibers has also been proposed. For example, Patent Document 3 proposes a biodegradable polylactic acid fiber having practically sufficient elastic modulus and dimensional stability and a method for industrially producing the fiber with high productivity. By using poly-L-lactic acid having a specific average molecular weight and optical purity, the polylactic acid fiber has an elastic modulus at 10% elongation of 7 g / d or more and a boiling water shrinkage of 13% or less. It is something that can be done.

  This fiber was excellent in a certain degree of dimensional stability, but according to this fiber, the type and production method of polylactic acid are preferably specific, more general-purpose, and further excellent in dimensional stability. Things were requested.

In general, when the fiber is a woven or knitted fabric, the boiling water shrinkage of the fiber is preferably less than 10%. When the boiling water shrinkage rate is 10% or more, the surface of the knitted or knitted fabric will be uneven due to wrinkles or streaks during hot water treatment such as scouring or dyeing when it is made into a fabric such as woven or knitted fabric. Is difficult to obtain. In order to obtain an appropriate swelling and uniform appearance, it is preferable that the boiling water shrinkage is in the range of 4 to 8%.
Japanese Patent No. 3462777 JP 2001-40527 A JP 11-293517 A

  Therefore, the present invention solves the above problems, has low boiling water shrinkage, has sufficient dimensional stability against heat treatment during processing and products, and has moderate swelling and unevenness due to wrinkles and lines. An object of the present invention is to provide a polylactic acid fiber capable of obtaining a fabric having a uniform appearance.

  As a result of investigations to solve the above problems, the present inventors have mixed polylactic acid with syndiotactic polystyrene, so that boiling water shrinkage of polylactic acid fibers can be achieved without performing heat treatment with a special apparatus or the like in the production process. The inventors have found that the rate can be lowered and have reached the present invention.

  That is, the gist of the present invention is a low heat-shrinkable polylactic acid fiber using at least a part of polylactic acid containing syndiotactic polystyrene.

  The low heat-shrinkable polylactic acid fiber of the present invention has low boiling water shrinkage, has sufficient dimensional stability against heat treatment during processing and product, and has a uniform appearance without irregularities due to moderate swelling and wrinkles and lines This fabric can be obtained. Moreover, since it is a fiber using polylactic acid, it is biodegradable and is a fiber friendly to the earth.

Hereinafter, the present invention will be described in detail.
The polylactic acid fiber of the present invention is a fiber using at least part of polylactic acid containing syndiotactic polystyrene (hereinafter referred to as SPS). In other words, it may be a fiber (single-type fiber) composed only of polylactic acid containing SPS, or a composite fiber using polylactic acid containing SPS as one component and another thermoplastic polymer as the other component. There may be.

  The polylactic acid fiber of the present invention preferably has a boiling water shrinkage of 10% or less, and more preferably a boiling water shrinkage of 8 to 4%.

  Although the mechanism by which SPS lowers the boiling water shrinkage of fibers is not clearly understood, SPS, which has better thermal dimensional stability than polylactic acid fibers, is in a substantially uniform state along the longitudinal direction of the fibers by a drawing process. It is considered that the boiling water shrinkage of the polylactic acid fiber can be reduced by dispersing it inside and acting as an anchor that links the polylactic acid molecules.

The boiling water shrinkage in the present invention is measured as follows. The polylactic acid fiber of the present invention is wound 10 times, and the original length L0 is measured under a load of 0.1 cN / dtex. After removing the load to make it unloaded, the polylactic acid fiber cocoon is removed for 15 minutes in a boiling water bath adjusted to 100 ° C. After this is air-dried, the post-treatment length L1 is measured under a load of 0.1 cN / dtex. And let the value obtained by following Formula be a boiling-water shrinkage | contraction rate.
Boiling water shrinkage (S0) (%) = {(L0−L1) / L0} × 100

  In the polylactic acid fiber of the present invention, the content of SPS in the polylactic acid is preferably 3 to 15% by mass, and preferably 5 to 12% by mass in both the single type fiber and the composite fiber. When the SPS content is less than 3% by mass, the effect of lowering the boiling water shrinkage becomes poor. On the other hand, when the content exceeds 15% by mass, the spinnability is deteriorated, and spinning and stretching tend to be difficult.

  The polylactic acid fiber of the present invention is preferably a single type fiber in consideration of the boiling water shrinkage and biodegradability as described above.

  When it is set as a composite fiber, it is preferable that the ratio of the polylactic acid containing SPS is 50 mass% or more of the whole fiber. Further, the other components are not particularly limited, and a thermoplastic polymer such as polyester or polyamide can be used. However, in consideration of biodegradability, a biodegradable polymer such as aliphatic polyester may be used. Among them, polylactic acid is preferably used.

SPS is different from ordinary polystyrene in that the three-dimensional structure is different. The repeating units of the structural unit have a chiral atom in the main chain, and the repeating units that are in an enantiomeric relationship with each other are arranged alternately along the main chain. It is what you are doing.
Specifically, “Zalek (trade name)” manufactured by Idemitsu Petrochemical Co., Ltd. is preferably used.

  The polylactic acid containing SPS in the fiber of the present invention includes poly-D-lactic acid, poly-L-lactic acid, poly-DL-lactic acid that is a copolymer of poly-D-lactic acid and poly-L-lactic acid, and poly-D. -Lactic acid and poly L-lactic acid mixture (stereo complex), poly D-lactic acid and hydroxycarboxylic acid copolymer, poly L-lactic acid and hydroxycarboxylic acid copolymer, poly D-lactic acid or poly L -It is preferable to use a copolymer of lactic acid, aliphatic dicarboxylic acid and aliphatic diol, or a blend thereof.

  The polylactic acid is one in which L-lactic acid and D-lactic acid are used alone or in combination as described above. Among them, the melting point is 120 ° C. or more, and the heat of fusion is 10 J / g or more. It is preferable that

  The melting point of L-lactic acid and D-lactic acid, which are homopolymers of polylactic acid, is about 180 ° C., but in the case of a copolymer of D-lactic acid and L-lactic acid, the proportion of any component is about 10 mol%. Then, the melting point is about 130 ° C. Furthermore, when the proportion of any of the components is 18 mol% or more, the melting point is less than 120 ° C. and the heat of fusion is less than 10 J / g, which is almost completely amorphous. When such an amorphous polymer is used, it becomes difficult to heat-stretch particularly in the production process, and it becomes difficult to obtain high-strength fibers. Even if fibers are obtained, the boiling water shrinkage rate is high. It is not preferable because it becomes inferior or has poor heat resistance and wear resistance.

  Therefore, as polylactic acid, L / D or D / which is the content ratio (molar ratio) of L-lactic acid and D-lactic acid indicated by the content ratio of L-lactic acid or D-lactic acid when polymerizing using lactide as a raw material. L is preferably 82/18 or more, more preferably 90/10 or more, and even more preferably 95/15 or more. By setting it as such a copolymerization ratio, there exists a tendency for it to become a fiber with low boiling-water shrinkage and excellent heat resistance.

  In addition, the molecular weight of polylactic acid is 1 to 100 (g / 10 min) as measured by a temperature of 210 ° C. and a load of 2160 g according to the ASTM D-1238 method used as an index of molecular weight. More preferably, it is 5-50 (g / 10min). By setting the melt flow rate within this range, strength, wet heat decomposability, and wear resistance are improved.

  Furthermore, in the polylactic acid fiber of the present invention, both the polylactic acid and the polymer of other components when making a composite fiber are within a range that does not impair the effect, such as a lubricant such as a higher fatty acid metal salt, an antiblocking agent, and an inorganic filler. Further, various additives such as a reinforcing agent, an antioxidant, a plasticizer, a flame retardant, a matting agent, and a pigment may be contained.

  The polylactic acid fiber of the present invention may be a monofilament or a multifilament, and may be either a short fiber or a long fiber. The fineness, strength, elongation, cross-sectional shape, and number of filaments can be set according to the application and purpose. Further, twisting or crimping may be applied by post-processing, and in this case as well, the number of twists, the number of crimps, and the crimping rate may be set as appropriate according to the application.

  Next, a method for producing the polylactic acid fiber (single type) of the present invention will be described using an example. First, as means for incorporating SPS into polylactic acid, chip-shaped polylactic acid and SPS may be directly mixed and then extruded by a melt extruder, or polylactic acid premixed with SPS may be melt-kneaded to obtain a master batch. And it may be extruded with a melt extruder. Among them, the method of directly mixing SPS with chip-like polylactic acid is preferable because the decrease in molecular weight due to the thermal history of polylactic acid is reduced.

  Then, such SPS-containing polylactic acid is supplied to a normal melt spinning apparatus and melt-spun at a spinning temperature of 260 to 290 ° C. After the fiber obtained by spinning is cooled and solidified, a spinning oil agent is applied, and the fiber is once wound or continuously stretched and heat-treated without being wound. At this time, the draw ratio is about 1.5 to 4.5 times, the film is stretched at about 80 to 130 ° C., and heat treatment is performed at about 120 to 150 ° C. Thereafter, the low heat shrinkable polylactic acid fiber of the present invention can be obtained by winding.

  In the present invention, a polylactic acid fiber having a low boiling water shrinkage rate can be obtained by such a normal production method. However, when polylactic acid not containing SPS is used, the boiling water shrinkage rate is 10%. In order to reduce the boiling water shrinkage rate, it is necessary to further heat-treat at the time of stretching or after stretching, which complicates the process and reduces other characteristic values such as the strength of the polylactic acid fiber obtained. It becomes easy.

Next, the polylactic acid fiber of the present invention will be specifically described with reference to examples.
Various values in the examples were measured as follows. The boiling water shrinkage rate and the melt flow rate are measured by the above methods.
[Melting point of polylactic acid (° C), heat of fusion (J / g)]
A differential scanning calorimeter DSC-2 manufactured by Perkin Elmer was used, and the measurement was performed under the condition of a heating rate of 20 ° C./min.
[Content ratio (molar ratio) of L-lactic acid and D-lactic acid in polylactic acid]
It measured by the high performance liquid chromatography (HPLC) method by using the equal mass mixed solution of the ultrapure water and the methanol solution of 1N sodium hydroxide as a solvent. The column used was sumichiral OA6100, and was detected by a UV absorption measuring device.

Example 1
Polylactic acid has a melting point of 170 ° C., a heat of fusion of 38 J / g, an L / D content ratio (molar ratio) between L-lactic acid and D-lactic acid of 98.5 / 1.5, a melt flow rate value (hereinafter referred to as MFR). And a relative viscosity of 3.10 was used. As SPS, product number 142AF of “Zalek (trade name)” manufactured by Idemitsu Petrochemical Co., Ltd. was used. And SPS was mixed so that it might become 5 mass% in polylactic acid.
This mixed polymer was supplied to a normal melt spinning apparatus and melt-proofed from a spinneret with 24 holes under the conditions of a spinning temperature of 270 ° C. and a discharge rate of 29.1 g / min. Next, after cooling the spun yarn with a cooling device, and applying a spinning oil agent (an oil agent containing 20% by mass of polyethylene glycol monooleate having a molecular weight of 600) to an amount of 0.6% by mass, It was wound up once at 550 m / min. After that, preheat with the first roller (90 ℃), provide a 130 ℃ hot plate between the second roller (130 ℃) and heat stretch 3.8 times at a stretching speed of 450m / min. Heat set at 130 ° C.) and wound up.
The obtained polylactic acid fiber had 140 dtex / 24f and a boiling water shrinkage (S0) of 5.3%.

Example 2
The same procedure as in Example 1 was conducted except that SPS was changed to a content of 8% by mass in polylactic acid.
The obtained polylactic acid fiber had 140 dtex / 24f and a boiling water shrinkage (S0) of 4.2%.

Comparative Example 1
Except having used polylactic acid which does not contain SPS, it carried out like Example 1 and obtained polylactic acid fiber.
The obtained polylactic acid fiber had 140 dtex / 24f and a boiling water shrinkage (S0) of 12.0%.

Claims (2)

Low heat-shrinkable polylactic acid fiber using at least part of polylactic acid containing syndiotactic polystyrene. 2. The low heat shrinkable polylactic acid fiber according to claim 1, wherein the boiling water shrinkage is 10% or less.