JP5012141B2 - Polylactic acid raw cotton - Google Patents

Description

The present invention relates to a raw cotton made of short polylactic acid fibers that are biodegradable and exhibit high strength, but also have excellent quality due to the effect of inorganic oxides mixed in the fibers.

  Conventionally, polyethylene, polypropylene, polyester, polyamide, and the like have been used as materials for fibers and molded products, and consumption has been increasing year by year. Along with this, the amount of waste after use has also increased. Since these wastes are currently disposed of by incineration or landfill, various environmental problems and problems such as securing a disposal site have occurred, and the development of new treatment methods is urgently needed.

  As one of new processing methods, there is a method of collecting a recyclable resin and reusing it after separation. However, in reality, it is difficult to recover, and advanced technology and expensive equipment are required to separate the resin. Furthermore, the current technology has a limit on the number of reuses, and after 2 to 3 times of recycling, it is also disposed of by incineration or landfill.

  Therefore, recently, from the viewpoint of global environmental conservation, various biodegradable polymers have been developed that separate resins in the natural environment by the action of microorganisms present in soil and water. Among them, polylactic acid is attracting attention because of its high melting point and ease of handling.

  The development of polylactic acid fibers has expanded to include agricultural materials, civil engineering materials, clothing, interiors, vehicle interior materials, and industrial materials. Under such expansion, the strength and elasticity of polylactic acid fibers are expanding. There is an increasing demand for mechanical properties such as rate. For example, when producing spun yarns and fabrics from polylactic acid short fibers in clothing applications, yarn breakage and fluff frequently occur due to the strength of the short fibers, and stable and efficient production is not possible at present. is there. In order to increase the strength, it is necessary to draw at a high magnification. However, when the polylactic acid fiber is drawn at a high magnification, abnormally stretched yarn called devitrified yarn that loses its transparency is generated. This devitrified yarn is known to have lower strength than normal fibers. That is, when drawing at a high magnification in order to obtain a high-strength polylactic acid fiber, devitrified yarn is mixed in, so it was difficult to obtain a high-grade high-strength polylactic acid fiber.

In recent years, various attempts have been made to solve such problems. For example, Patent Document 1 and Patent Document 2 disclose techniques for increasing the strength of multifilaments by multistage drawing, but these are techniques limited to the production process of long fibers, and are sufficient for the production of short fibers. The effect cannot be obtained. Patent Document 3 discloses a technique for producing a high-quality and high-strength polylactic acid fiber by increasing the stretching temperature. However, in the short fiber that is stretched in a tow state, the heating by the roller has significant heat unevenness. Therefore, liquid bath stretching is generally employed. Therefore, in order to obtain the stretching temperature described in Patent Document 3, it is necessary to use an organic solvent instead of water, and this has many problems in various aspects such as safety, environment and cost.
Patent Document 4 discloses a method in which steam having a melting point or higher is blown at the time of drawing. However, in a method for producing a short fiber drawn in a tow shape, heat unevenness between the surface of the tow blown with steam and the inside of the tow is large. Cuts and devitrified yarns occur on the contrary. As described above, these technologies are designed based on the manufacturing technology of long fibers that are drawn in the form of filaments. Even if the same technology is applied to short fibers that are drawn in the shape of tows, high-quality and high-strength polymers are used. It is impossible to obtain lactic acid short fibers. In short fibers that are drawn in a tow shape, devitrification yarns occur due to complex overlap of factors such as fiber entanglement and concentration of drawing stress due to friction, but no effective countermeasures have been taken. Is the current situation.
JP 2000-248426 A (Claims) Japanese Patent Laying-Open No. 2005-113334 (Claims) JP 2000-136435 A (Claims) JP 2003-138423 A (Claims)

The object of the present invention is to provide a polylactic acid raw cotton which has solved both the above-mentioned problems and has both excellent quality and strength without fuzz and yarn breakage, which could not be solved by the prior art.

The inventors of the present invention have reached the present invention as a result of intensive studies in order to solve the above problems. That is, the polylactic acid raw cotton according to the present invention is as follows.
(1) It is obtained by stretching after stretching in a tow state, containing 0.5 to 3.0% by weight of titanium oxide particles having a particle size of 0.1 to 1.0 μm, and a strength of 3.0 to 5. A raw cotton composed of polylactic acid short fibers having a fiber-fiber static friction coefficient of 0.2 to 0.35, and having a devitrification yarn content of 10% or less. Polylactic acid raw cotton,
(2) The polylactic acid raw cotton described in (1) above, which is a raw cotton for spun yarn.

According to the present invention, it is possible to provide a polylactic acid raw cotton which is also biodegradable and has excellent strength without fuzz and yarn breakage due to the effect of an inorganic oxide kneaded in fibers while exhibiting high strength. Can do.

  Hereinafter, the present invention will be described in detail.

  The polylactic acid referred to in the present invention refers to a polymer obtained by polymerizing lactic acid oligomers such as lactic acid and lactide. The optical purity of the L-form or D-form is 90% or higher, which is preferable because of its high melting point. The optical purity of the L-form or D-form is more preferably 97% or more. Moreover, you may copolymerize 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 method for producing polylactic acid used in the present invention is not particularly limited. Specifically, there is a manufacturing method disclosed in JP-A-6-65360. That is, a direct dehydration condensation method in which lactic acid is dehydrated and polymerized as it is in the presence of an organic solvent and a catalyst. Further, there is a method in which at least two types of homopolymers disclosed in JP-A-7-173266 are copolymerized and transesterified in the presence of a polymerization catalyst. Furthermore, there is a method disclosed in US Pat. No. 2,703,316. That is, an indirect polymerization method in which lactic acid is once dehydrated to form a cyclic dimer and then subjected to ring-opening polymerization.

  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., there is a risk that the quality of the product may be impaired, for example, the fusion between the single yarns may be remarkable during spinning, particularly spinning, and the drawing may be poor. The melting point is preferably 150 ° C. or higher, more preferably 160 ° C. or higher.

  In the present invention, it is important to reduce the coefficient of friction of the polylactic acid fiber.

  As a result of investigating in detail the generation mechanism of the devitrified yarn generated at the time of drawing the polylactic acid fiber, the fiber structure is destroyed by applying excessive stress at the time of drawing, the fiber surface becomes uneven, and the inside It was also found that when the voids are generated, the fiber loses transparency, that is, becomes devitrified. Further, it has been found that this structural breakage is also caused by a decrease in strength of the devitrified yarn. Accordingly, several methods have been proposed for reducing the stretching stress for filaments that can basically suppress the expression of devitrified yarn by relaxing the stretching stress. However, in short fibers that are drawn in a tow shape, it is necessary to consider factors such as fiber entanglement and concentration of drawing stress due to friction, and it was found that reducing the friction coefficient is important.

  As a method for reducing the coefficient of friction, it is preferable to use a lubricant. Lubricant application methods include kneading into fibers and surface treatment by dipping or showering the lubricant in liquid form, but both dipping and showering are at the toe stage before stretching. In order to treat all the single yarns forming the tow efficiently and uniformly, there is a drawback that the lubricant needs to be treated and the lubricant adheres only to the tow surface and cannot be treated to the inside of the tow. A crowding formula is preferred.

In addition, examples of the lubricant include inorganic and organic lubricants. However, organic lubricants have a drawback in that they react with polylactic acid or undergo thermal decomposition during spinning, resulting in deterioration of spinnability and smoke generation. Therefore, an inorganic lubricant is suitable. Also inorganic lubricant, those metal systems are difficult to align the grain size and shape, giving adverse effects on spinnability and fiber quality. In general, inorganic carbides are often black solids, and the fibers are also colored, thereby limiting the application. And above this, and titanium oxide is used from the viewpoint of steering industry, quality and cost handling.

The method for mixing titanium oxide is not particularly limited. For example, after drying polylactic acid and titanium oxide separately, a master chip is prepared with a kneader, the master chip and the polylactic acid chip are blended, dried, melt-spun, or melted. Titanium oxide may be added directly during spinning. Moreover, in order to suppress oxidative decomposition of polylactic acid during kneading and melt spinning, it is preferable to seal the inside of the apparatus with nitrogen.

The kneading amount of titanium oxide needs to be 0.5 to 3.0% by weight of the whole polylactic acid fiber. Preferably it is 1.0 to 1.5 weight%. When the kneading amount is less than 0.5% by weight, a sufficient effect for the purpose does not appear, and when it exceeds 3.0% by weight, the spinnability is remarkably deteriorated.

The particle size of titanium oxide is preferably 0.1 to 1.0 μm, more preferably 0.3 μm to 0.8 μm. When the particle diameter exceeds 1.0 μm, an increase in pack internal pressure during spinning and a decrease in strength of short fibers are caused. On the other hand, if the particle size is less than 0.1 μm, the particles aggregate at the time of melting and form a huge lump, which induces an increase in the pack internal pressure during yarns and decreases the strength of short fibers.

In the polylactic acid staple fiber according to the present invention, the intensity Ru 3.0~5.0cN / dtex der. Good Mashiku is 3.5~5.0cN / dtex. If it is less than 3.0 cN / dtex, the strength is low, and yarn breakage and fluff frequently occur in the spinning process, making it impossible to produce a stable spun yarn. If it exceeds 5.0 cN / dtex, devitrified yarn and yarn breakage occur frequently during stretching, and stable production cannot be performed.

Moreover, in the poly milk short fiber in this invention, a fiber-fiber static friction coefficient is 0.2-0.35 . Good Mashiku is 0.2 to 0.25. From the standpoint of preventing devitrification, the lower the static friction coefficient, the better. However, if the static friction coefficient is less than 0.2, the entanglement property of the short fibers deteriorates, and it becomes impossible to obtain a spun yarn of stable quality. .

Further, in the raw cotton made of the polylactic acid short fiber in the present invention, it is necessary that the abundance of the devitrified yarn is 10% or less. It may not exist at all, i.e. 0. Preferably it is 5% or less. If the abundance of devitrified yarn exceeds 10%, yarn breakage and fluff due to devitrified yarn frequently occur in the spinning process, and stable production cannot be performed. The abundance of devitrified yarn is defined by (1) visual confirmation of [abundance of devitrified yarn] in the examples described later.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these specific examples.

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

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

[Inorganic oxide particle size]
Titanium oxide to be used is deposited as gold or silver as a pretreatment. The produced sample was observed with SEM (ABT-55 manufactured by Topcon Corporation). 100 particles were observed, and the average particle size was defined as the particle size.

[Presence of devitrified yarn]
In the polylactic acid raw cotton, whether or not the short fiber corresponds to the devitrified yarn was confirmed by the method by the naked eye shown in the following (1). Incidentally, ShitsuToruito other macroscopic, following (2), (3) stereomicroscope as shown in, Ru observable der in an electron microscope or the like.

(1) Confirmation with the naked eye Place polylactic acid short fibers on black 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, 5 raw cotton samples are randomly collected from the manufactured raw cotton , and 20 short fibers in the sample at each point are confirmed (5 points × 20 fibers = 100 level).

(2) Confirmation with a stereomicroscope The polylactic acid short fibers are placed on a sample stage so as not to overlap in the same direction, and observed using a stereomicroscope (Nikon stereomicroscope HFX type). For each short fiber, 10 points are observed at random, and it is observed whether there is a devitrified (whitened) region. If there is a devitrified part even at one point, the devitrified yarn is used. The observation magnification can be changed as appropriate depending on the fineness of the fiber. Regarding the level, 5 raw cotton samples are randomly collected from the manufactured raw cotton , and 20 short fibers in the sample at each point are confirmed (5 points × 20 fibers = 100 level).

(3) 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 was 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, 5 raw cotton samples are randomly collected from the manufactured raw cotton , and 20 short fibers in the sample at each point are confirmed (5 points × 20 fibers = 100 level).

Abundance of ShitsuToruito (%) = (ShitsuToruito number) / (total short fiber number; 100) × 10 0

[Fiber-fiber friction coefficient]
The fiber-fiber static friction coefficient was measured by the method shown in JIS L-1015.

[Spinnability]
As for the spinnability, the yarn breakage at the guide for converging the yarn and the state of winding of the roller were visually confirmed.

[Extensible]
When the yarn breaks due to drawing, the yarn breakage single yarn is wound around the roller.

Example 1
Polylactic acid chips having a melting point of 170 ° C. (Nature Works; grade 6201D) and titanium oxide particles having a particle diameter of 0.5 μm as inorganic oxide particles are separately dried and mixed so as to have a weight ratio of 90:10. A master chip was prepared by melting and kneading at 220 ° C. and forming a chip. Master chip 10 parts by weight to prepare a polylactic acid chips 90 parts by weight and (acid titanium 1.0 part by weight containing) were mixed at an extruder type spinning machine, and melt-spun at a spinning temperature of 230 ° C., the spinning yarn was allowed to cool, and oiling, after collecting bundles, taken up at 1000m / min to obtain an undrawn 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 obtained undrawn yarn is converged to obtain a 80 ktex tow , drawn 4.0 times in a 90 ° C. liquid bath, mechanically crimped with a stuffer box, heat treated at 145 ° C. for 10 minutes, and then an oil agent Was applied by a spray method so as to be 0.5% by weight with respect to the fibers, and cut into 51 mm to obtain raw cotton of short polylactic acid fibers. The results of measuring the physical properties of the obtained fiber are shown in Table 1.

(Example 2)
Polylactic acid short fibers were obtained in the same manner as in Example 1 except that the content of titanium oxide was changed to 3.0 parts by weight. The results of measuring the physical properties of the obtained fiber are shown in Table 1.

( Comparative Example 1 )
Polylactic acid short fibers were obtained in the same manner as in Example 1 except that the inorganic oxide particles were changed to alumina oxide. The results of measuring the physical properties of the obtained fiber are shown in Table 1.

(Comparative Example 2 )
A polylactic acid short fiber was obtained in the same manner as in Example 1 except that no titanium oxide was added. The results of measuring the physical properties of the obtained fiber are shown in Table 1.

(Comparative Example 3)
Polylactic acid short fibers were obtained in the same manner as in Example 1 except that the content of titanium oxide was changed to 0.2 parts by weight. The results of measuring the physical properties of the obtained fiber are shown in Table 1.

Claims (2)

It is obtained by stretching after stretching in a tow state, containing 0.5 to 3.0% by weight of titanium oxide particles having a particle size of 0.1 to 1.0 μm, and a strength of 3.0 to 5.0 cN / dtex. Polylactic acid raw cotton comprising a polylactic acid short fiber having a fiber-fiber static coefficient of friction of 0.2 to 0.35, wherein the abundance of devitrified yarn is 10% or less . 2. The polylactic acid raw cotton according to claim 1, which is a raw cotton for spun yarn.