JP2013011033A - Polylactic acid fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid fiber that is good in runnability for fibrillization, excellent in heat resistance, and excellent in flexibility.SOLUTION: The polylactic acid fiber is formed of polylactic acid-based polymer. The polylactic acid-based polymer comprises 95 mol% or more of L-lactic acid or D-lactic acid. The polylactic acid-based polymer includes polyglycerol fatty acid ester or polyglycerol condensed hydroxy fatty acid ester. The polyglycerol fatty acid ester or polyglycerol condensed hydroxy fatty acid ester is included in an amount of 0.5-5.0 pts.mass with respect to 100 pts.mass of the polylactic acid.

Description

  The present invention relates to a polylactic acid fiber.

  From the standpoint of protecting the natural environment, products using biodegradable polymers that decompose in nature are required. Under such circumstances, development of fibers using a biodegradable thermoplastic polymer has been actively conducted. This representative biodegradable thermoplastic polymer is a polylactic acid polymer.

Polylactic acid-based polymers are produced from crops represented by corn, and have a high effect of suppressing CO ² generation, which is one of the causes of global warming, which has been regarded as a problem in recent years. In addition, unlike polymers that are made from fossil fuels such as polyethylene terephthalate, polyethylene, and polypropylene, which have been used in the past, they are made from renewable resources, so there is less concern about the depletion of raw materials, and more and more in the future. That demand is expected to grow.

  However, since fibers and nonwoven fabrics using this polylactic acid polymer are hard and inferior in flexibility, it has been difficult to use for hygiene materials and other uses that require flexibility.

  As a method of imparting flexibility to a polylactic acid polymer having such a hard property, a specific aliphatic polyester having a low glass transition point is used as a plasticizer, and a mixed composition of the aliphatic polyester and polylactic acid is used. There is a method of obtaining a flexible polylactic acid fiber by using a molded product such as a fiber (Patent Document 1). However, in a mixed composition of polylactic acid and this specific aliphatic polyester, if a large amount of aliphatic polyester is mixed to improve flexibility, there is a difference in compatibility and flow characteristics between polylactic acid and aliphatic polyester. Therefore, there is a problem that the yarn tends to be broken during fiber formation and the heat resistance tends to be inferior, and on the other hand, when the mixing amount is reduced, the flexibility is also lowered.

JP-A-8-245866

  An object of the present invention is to solve the above-described problems, and to provide a polylactic acid fiber having good operability for fiberization, excellent heat resistance, and excellent flexibility.

  The inventors of the present invention have investigated the characteristics of polylactic acid strictly and have intensively studied to solve the above problems. As a result, by adding a specific fatty acid ester to the polylactic acid, it is possible to impart flexibility to the polylactic acid with a small amount of addition without impairing heat resistance, and it is difficult to cause yarn breakage during melt spinning. As a result, the present invention has been found.

  The present invention is a fiber comprising a polylactic acid polymer, wherein the polylactic acid polymer comprises 95 mol% or more of L-lactic acid or D-lactic acid, and the polylactic acid polymer is a polyglycerin fatty acid. It contains an ester or polyglycerin condensed hydroxy fatty acid ester, and the polyglycerin fatty acid ester or polyglycerin condensed hydroxy fatty acid is contained in an amount of 0.5 to 5.0 parts by mass with respect to 100 parts by mass of polylactic acid. The gist is polylactic acid fiber.

  Since the fiber of the present invention is composed of a polylactic acid-based polymer, it is almost completely decomposed by microorganisms, so that it is possible to save time and effort for waste disposal when it is no longer needed, and to contaminate the natural environment. .

  Examples of the polylactic acid-based polymer used in the present invention include poly-D-lactic acid, poly-L-lactic acid, a copolymer of D-lactic acid and L-lactic acid, a copolymer of D-lactic acid and hydroxycarboxylic acid, Examples thereof include a copolymer of L-lactic acid and hydroxycarboxylic acid, a polymer selected from the group consisting of a copolymer of D-lactic acid, L-lactic acid and hydroxycarboxylic acid, or a blend thereof. Examples of the hydroxycarboxylic acid for copolymerizing the hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid, hydroxycaproic acid, hydroxyoctanoic acid, etc. Hydroxycaproic acid and glycolic acid are preferable from the viewpoint of cost reduction.

  In the present invention, the polylactic acid-based polymer needs to have a content of L-lactic acid or D-lactic acid of 95% or more. Preferably, it is 98% or more, more preferably 99% or more. By setting it as 95% or more, crystallinity becomes high, operativity is favorable, and heat resistance becomes favorable.

  The polyglycerin fatty acid ester used in the present invention is an ester obtained by reacting polyglycerin with a fatty acid. Specific examples of the polyglycerin that is a constituent of the polyglycerin fatty acid ester used in the present invention include diglycerin, triglycerin, tetraglycerin, pentaglycerin, hexaglycerin, heptaglycerin, octaglycerin, nonaglycerin, deca Glycerin etc. are mentioned, Preferably it is diglycerin and decaglycerin, and these 1 type, or 2 or more types of mixtures are utilized.

  The fatty acid constituting the polyglycerol fatty acid ester used in the present invention is preferably a saturated fatty acid in consideration of imparting flexibility and preventing the glass transition temperature from being lowered. Furthermore, it is preferable to use a fatty acid having 12 or more carbon atoms. This is because the polyglycerol fatty acid ester from the fiber can be prevented from bleeding. Preferred fatty acids are lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, nonadecanoic acid, arachidic acid, gadleyic acid, eicosadienoic acid, arachidonic acid, behenic acid, elca Acid, docosadienoic acid, lignoceric acid, isostearic acid, ricinoleic acid, 12-hydroxystearic acid, 9-hydroxystearic acid, 10-hydroxystearic acid, hydrogenated castor oil fatty acid (12-hydroxystearic acid plus a small amount of stearic acid And fatty acids containing palmitic acid), preferably palmitic acid, stearic acid, and oleic acid, which are used as one or a mixture of two or more thereof.

  Examples of the polyglycerol fatty acid ester preferably used in the present invention include diglycerol palmitate, diglycerol stearate, diglycerol oleate, decaglycerol palmitate, decaglycerol stearate, decaglycerol oleate, These 1 type or 2 or more types of mixtures are utilized. Of these, diglycerin stearic acid ester and decaglycerin oleic acid ester are particularly preferably used.

  The polyglycerol condensed hydroxy fatty acid ester used in the present invention is an ester obtained by reacting polyglycerol and condensed hydroxy fatty acid. As described above, polyglycerin that is a constituent of polyglycerin-condensed hydroxy fatty acid ester includes diglycerin, triglycerin, tetraglycerin, pentaglycerin, xaglycerin, heptaglycerin, octaglycerin, nonaglycerin, decagrin and the like. Preferably it is hexaglycerin and these 1 type, or 2 or more types of mixtures are utilized.

  A condensed hydroxy fatty acid is a condensate of hydroxy fatty acids. Hydroxy fatty acid is a fatty acid having one or more hydroxyl groups in the molecule. Specifically, for example, ricinoleic acid, 12-hydroxystearic acid, hydrogenated castor oil fatty acid (in addition to 12-hydroxystearic acid) Fatty acids containing small amounts of stearic acid and palmitic acid), sabinic acid, 2-hydroxytetradecanoic acid, isopouric acid, 2-hydroxyhexadecanoic acid, yarapinolic acid, uniperic acid, ambrettlic acid, alleutriic acid, 2- Examples thereof include hydroxyoctadecanoic acid, 18-hydroxyoctadecanoic acid, 9,10-dihydroxyoctadecanoic acid, camlolenic acid, ferronic acid, cerebronic acid, 9-hydroxystearic acid, and 10-hydroxystearic acid, and preferably ricinoleic acid. .

  The fiber of the present invention is composed of the polylactic acid-based polymer, and the polylactic acid-based polymer contains a polyglycerol fatty acid ester or a polyglycerol condensed hydroxy fatty acid ester, and is based on 100 parts by mass of the polylactic acid. The polyglycerol fatty acid ester or the polyglycerol condensed hydroxy fatty acid ester is contained in an amount of 0.5 to 5.0 parts by mass, and more preferably 1.0 to 3.0 parts by mass.

  When the amount containing the polyglycerol fatty acid ester or the polyglycerol condensed hydroxy fatty acid ester is less than 0.5 parts by mass, the flexibility of the obtained polylactic acid fiber becomes insufficient, and the object of the present invention cannot be achieved. On the other hand, when the amount exceeds 5.0 parts by mass, the quality is excessive in terms of flexibility, the bleed-out is easy, and the cost is increased.

  Even after the polylactic acid fiber of the present invention is heat-treated at 150 ° C. for 5 minutes, the polyglycerin fatty acid ester or polyglycerin condensed hydroxy fatty acid ester contained in the polylactic acid polymer constituting the fiber bleeds on the fiber surface. It is preferable not to go out. When bleed-out occurs, the bleed-out polyglycerin fatty acid ester or polyglycerin-condensed hydroxy fatty acid ester adheres to the fiber and cannot be preferably used depending on the application.

  The polylactic acid polymer may contain an additive as long as the object of the present invention is achieved. For example, it is preferable to add inert fine particles for promoting crystallization of the polylactic acid polymer. As such inert fine particles, talc, calcium carbonate, titanium oxide and the like can be suitably used.

  The addition amount of such inert fine particles is preferably 0.1 to 2.0% by mass. If the addition of the inert fine particles is less than 0.1% by mass, a sufficient crystallization promoting effect cannot be obtained, and if the addition amount of the inert fine particles exceeds 2.0% by mass, the yarn breaks during melt spinning. Is likely to occur frequently. Moreover, it is good to use the particle diameter (D50 laser diffraction method) of such an inert fine particle of 0.1-5 micrometers. When the thickness is 5 μm or more, it is liable to cause thread breakage during fiberization, which is not preferable. On the other hand, when the particle size is 0.1 μm or less, the particles are likely to aggregate and inferior in dispersibility.

  Additives added to polylactic acid-based polymers include pigments, heat stabilizers, antioxidants, weathering agents, flame retardants, endblockers, release agents, antistatic agents, fillers, etc. Is mentioned.

  The glass transition temperature (Tg) of the polylactic acid fiber of the present invention is preferably 50 ° C. or higher. When the temperature is lower than 50 ° C., the heat resistance is inferior, and the decomposition rate of the polylactic acid polymer is dramatically increased.

  What is necessary is just to select the single yarn fineness of the polylactic acid fiber of this invention suitably according to a use. In consideration of forming a nonwoven fabric using polylactic acid fibers, about 1 to 10 dtex is preferable. If the single yarn fineness is less than 1 dtex, the operability is impaired in the yarn making process. When the single yarn fineness exceeds 10 dtex, the flexibility of the resulting nonwoven fabric tends to be impaired.

  The cross section of the polylactic acid fiber is not limited to the usual circular cross section, but also its purpose and application, such as hollow cross section, irregular cross section, parallel composite cross section, multilayer composite cross section, core-sheath composite cross section, and split composite cross section. Depending on the, any fiber cross-sectional configuration can be employed.

  The form of the polylactic acid fiber of the present invention may be a continuous fiber, a short fiber or a shortcut fiber having a specific length, and may be appropriately selected depending on the application.

  A large number of polylactic acid fibers of the present invention can be deposited to obtain a nonwoven fabric or a fiber sheet. At this time, when the polylactic acid fiber is a continuous fiber, it becomes a continuous fiber nonwoven fabric. When the polylactic acid fiber is a short fiber, it becomes a short fiber nonwoven fabric. When the polylactic acid fiber is a shortcut fiber, papermaking can be obtained. Moreover, a multifilament yarn can be obtained by aligning or twisting polylactic acid fibers, and a spun yarn can be obtained by spinning polylactic acid short fiber groups.

The basis weight of the nonwoven fabric in which a large number of polylactic acid fibers that are continuous fibers are deposited is preferably in the range of 5 to 200 g / m ² . If the basis weight is less than 5 g / m ² , the mechanical properties are weak and a sufficient function cannot be exhibited. When the basis weight exceeds 200 g / m ² , the flexibility tends to be inferior. As an index of the flexibility of the nonwoven fabric, it is preferable that the compression bending resistance of the nonwoven fabric is 5.0 cN / (g / m ² ) or less. More preferably, it is 3.0 cN / (g / m < ² >) or less, More preferably, it is 2.0 cN / (g / m < ² >) or less. When it is 2.0 cN / (g / m ² ) or less, for example, when the nonwoven fabric is used as a sanitary material that is used for touching the skin, there is no harsh feel and it can be suitably used. Further, for example, when used as an agricultural material, it can be suitably used because it has good followability to the ground and a house and is easy to handle.

  It is preferable that the dry heat shrinkage rate of the non-woven fabric composed of polylactic acid fibers which are continuous fibers is 10% or less at 150 ° C. More preferably, it is 8% or less, and most preferably 5% or less. If the dry heat shrinkage exceeds 10%, for example, when bonding with another material by heat sealing, the shrinkage becomes too large.

  The polylactic acid fiber of the present invention is obtained by melt spinning using a polylactic acid-based polymer containing the above-described polyglycerol fatty acid ester or polyglycerol condensed hydroxy fatty acid ester by a known method.

  For example, when obtaining a nonwoven fabric composed of continuous fibers, it can be efficiently produced by a so-called spunbond method. That is, a polylactic acid-based polymer containing the above-mentioned polyglycerin fatty acid ester or polyglycerin-condensed hydroxy fatty acid ester is heated and melted and discharged from a spinneret. Cooling is performed using a cooling device such as an annular spray, and then it is pulled and thinned by a suction device such as an air soccer. Subsequently, after the yarn group discharged from the suction device is opened, it is deposited on a moving deposition device such as a conveyor comprising a screen to form a web. Next, the web formed on the moving deposition apparatus is partially subjected to thermocompression bonding using a partial thermocompression bonding apparatus such as a heated embossing roll or an ultrasonic fusing apparatus to obtain a nonwoven fabric. The traction thinning may be performed at a high speed of 1000 to 6000 m / min. When pulling the spun yarn, if the pulling speed is less than 1000 m / min, the oriented crystallization of the polymer does not proceed, the mechanical strength of the resulting nonwoven fabric is reduced, and the biodegradation rate is excessively accelerated. On the other hand, if the pulling speed exceeds 6000 m / min, the yarn-making property is abruptly deteriorated and yarn breakage is not preferable.

  According to the present invention, a polylactic acid fiber excellent in flexibility, heat resistance, and operability can be obtained.

  EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by these Examples. In the examples, each characteristic value was measured by the following method.

(1) Weight per unit area (g / m ² ): Ten sample pieces of 10 cm × 10 cm were prepared, the mass (g) of each sample piece in the standard state was weighed, and the average value of the obtained values per unit area In conversion, the basis weight (g / m ² ) of the nonwoven fabric was obtained.

(2) Thickness (mm): Measured based on JIS L 1906.

(3) MFR (g / 10 min): Measured at 210 ° C. and 20.2 N based on ASTM-D1238 (L).

(4) Single yarn fineness (decitex): The fiber web is observed using a microscope, the fiber diameters of 50 fibers are measured, and the average value of the fineness obtained by density correction is defined as the single yarn fineness (decitex). did.

(5) Compression bending resistance (cN / (g / m ² )): Five sample pieces each having a sample length of 10 cm and a sample width of 5 cm are prepared so that the machine direction of the nonwoven fabric is the sample length. A cylindrical measurement sample having a height of 10 cm was prepared by bending the plate in the lateral direction to form a cylindrical shape and joining the ends thereof. Next, with respect to the axial direction of each measurement sample, the maximum load obtained by compressing the measurement sample at a compression rate of 5 cm / min using a constant speed extension type tensile tester (Tensilon UTM-4-100 manufactured by Toyo Baldwin). The average value of the values (cN) was determined, and the value obtained by dividing the value by the basis weight (g / m ² ) of the sample was taken as the compression bending resistance (cN / (g / m ² )).

(6) Dry heat shrinkage rate (%): A sample of 15 cm (machine direction) × 15 cm (direction perpendicular to the machine direction) is put into a constant temperature dryer set at a temperature of 150 ° C., left for 5 minutes, and taken out. The length of the sample in the machine direction and the length in the direction perpendicular to the machine direction were measured, and the respective shrinkage rates were calculated by the following formula. The number of samples was 5 points, and the average value of all the calculated shrinkage rates was defined as the dry heat shrinkage rate. In the following formula, L is the length (cm) of the sample after standing at a temperature of 150 ° C. for 5 minutes.
Thermal contraction rate (%) = [(15−L) / 15] × 100

(7) Bleed-out property: The sample (nonwoven fabric) was put into a constant temperature dryer set at a temperature of 150 ° C., left for 5 minutes and then taken out and cooled in air for 1 minute. Thereafter, when the sample was touched with a finger, it was evaluated whether or not the finger had a sticky feeling.
○: There is no stickiness.
Δ: Slightly sticky.
X: There is a sticky feeling.

(8) Biodegradability: A sample (nonwoven fabric) is buried in an aged compost maintained at about 58 ° C., taken out after 3 months, and if the nonwoven fabric does not retain its form, or retains its form However, when the tensile strength was 50% or less with respect to the initial strength value before burying, the biodegradability was good, and when the tensile strength exceeded 50%, the biodegradability was evaluated as poor.
○: The biodegradability of the non-woven fabric is recognized. ×: The biodegradability of the non-woven fabric is not recognized.

Example 1
An L-lactic acid / D-lactic acid copolymer (L-lactic acid / D-lactic acid = 98.6 / 1.4 mol%) having a melting point of 168 ° C. and an MFR of 60 g / 10 min was prepared as a polylactic acid polymer.
In addition, as a polyglycerin fatty acid ester, a polylactic acid polymer in which tirabazole VR-08 (manufactured by Taiyo Kagaku Co., Ltd.) was metered and blended so as to be 1.0 part by mass with respect to 100 parts by mass of the polylactic acid polymer was melted. Then, melt spinning was performed using a spinneret.
On the screen conveyor, after the discharged yarn is cooled by a cooling device, it is continuously refined with an air football provided below the spinneret at a pulling speed of 5000 m / min, opened using a known spreader, and moved. And collected as a web. In the polylactic acid polymer, inert fine particles for promoting crystallization were not added, but melt spinning and fiber opening could be carried out without any problem, so that Tirabazole VR- used as a polyglycerol fatty acid ester was used. It can be presumed that it was functioning as a crystallization accelerator in 08 (manufactured by Taiyo Kagaku Co.).
Subsequently, this web was partially thermocompression-bonded through a partial thermocompression bonding apparatus composed of an embossing roll having a pressure contact area ratio of 15% and a roll temperature of 130 ° C., and a basis weight composed of continuous fibers having a single yarn fineness of 3.3 dtex was obtained. A nonwoven fabric of 50 g / m ² was obtained.

Example 2
Under the same conditions as in Example 1, a nonwoven fabric having a basis weight of 100 g / m ² was obtained.

Example 3
In Example 1, the single yarn fineness was set to 3. in the same manner as in Example 1 except that the polyglycerin fatty acid ester was metered and blended so as to be 2.0 parts by mass with respect to 100 parts by mass of the polylactic acid polymer. A nonwoven fabric having a basis weight of 50 g / m ² made of 3 dtex continuous fibers was obtained.

Example 4
A nonwoven fabric having a basis weight of 100 g / m ² was obtained under the same conditions as in Example 2.

Comparative Example 1
In Example 1, no polyglycerin fatty acid ester was used, and when the polylactic acid polymer was melt-spun, 0.5% by mass of talc having an average particle diameter of 1.5 μm as inert fine particles was added to the melt polymer. A nonwoven fabric having a basis weight of 50 g / m ² made of continuous fibers having a single yarn fineness of 3.3 dtex was obtained in the same manner as in Example 1 except that the amount was blended.

Comparative Example 2
Under the same conditions as in Comparative Example 1, a nonwoven fabric having a basis weight of 100 g / m ² was obtained.

Comparative Example 3
In Example 1, no polyglycerin fatty acid ester was used, and when the polylactic acid polymer was melt-spun, an aliphatic polyester composed of succinic acid and 1,2-propylene glycol was used as a plasticizer in the melt polymer. A non-woven fabric having a basis weight of 50 g / m ² made of continuous fibers having a single yarn fineness of 3.3 dtex was obtained in the same manner as in Example 1 except that it was metered to 2.0% by mass.

Comparative Example 4
A nonwoven fabric having a basis weight of 100 g / m ² was obtained under the same conditions as in Comparative Example 3.

Comparative Example 5
In Comparative Example 3, the same as Comparative Example 3 except that an aliphatic polyester composed of succinic acid as a plasticizer and 1,2-propylene glycol was metered into the molten polymer so as to be 8.75% by mass. Thus, a nonwoven fabric having a basis weight of 50 g / m ² made of continuous fibers having a single yarn fineness of 3.3 dtex was obtained.

Comparative Example 6
A nonwoven fabric having a basis weight of 100 g / m ² was obtained under the same conditions as in Comparative Example 5.

  The evaluation results of Examples 1 to 4 and Comparative Examples 1 to 6 are shown in Table 1. The dry heat shrinkage was measured for Example 1, Example 3, Comparative Example 1, Comparative Example 3, and Comparative Example 5.

Examples 1-4 of the present invention have good operability, and the obtained ones were Comparative Examples 1 and 2 in which no plasticizer was added, and Comparative Examples in which aliphatic polyester was added as a plasticizer Compared with 3-6, it had a softness | flexibility, and the value of the compression bending resistance of the nonwoven fabric was also small, and the softness | flexibility improved. In addition, it has little heat shrinkage and heat resistance, and there is almost no bleed-out after heat treatment, and it can be applied to various uses such as hygiene materials that directly touch the skin.

Claims (3)

A fiber comprising a polylactic acid polymer, wherein the polylactic acid polymer comprises 95 mol% or more of L-lactic acid or D-lactic acid, and the polylactic acid polymer is a polyglycerin fatty acid ester or polyglycerin. A polylactic acid fiber containing a condensed hydroxy fatty acid ester and containing 0.5 to 5.0 parts by mass of polyglycerol fatty acid ester or polyglycerol condensed hydroxy fatty acid with respect to 100 parts by mass of polylactic acid . The polylactic acid fiber according to claim 1, wherein the fatty acid is a saturated fatty acid having 12 or more carbon atoms. A polylactic acid nonwoven fabric comprising a plurality of the polylactic acid fibers according to claim 1, wherein the polylactic acid fibers are continuous fibers.