JP2007314899A - Polylactic acid monofilament, method for producing the same, and application of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide biodegradable polylactic acid monofilament having a combination of both high heat resistance and mechanical strength having been difficult to be attained by prior art, to provide a method for producing the same, and to provide industrial fabrics using the same. <P>SOLUTION: The polylactic acid monofilament is made from a resin composition composed of poly-L-lactic acid and poly-D-lactic acid, wherein the poly-L-lactic acid and poly-D-lactic acid form a stereocomplex structure. The monofilament is 0.05-1.0 mm in diameter, 200-235°C in melting point, and 3.0 cN/dtex or higher in tensile strength determined in accordance with JIS L-1013:1999-8.5. The method for producing the polylactic acid monofilament is also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polylactic acid monofilament having excellent heat resistance and high strength, a method for producing the same, and an industrial fabric using the polylactic acid monofilament.

  In recent years, with respect to environmental problems on a global scale, development of polymer materials that can be decomposed in a natural environment has been expected, and in particular, biodegradable polymers that are decomposed by microorganisms have attracted attention. Most of the conventional general-purpose resins such as polyethylene terephthalate and nylon are made from petroleum resources, but these general-purpose resins emit carbon dioxide when incinerated after use. A large amount of carbon dioxide is released into the atmosphere, which is one of the causes of abnormal weather such as global warming.

  In recent years, in addition to the global warming problem, the depletion of petroleum resources and the rise in the price of crude oil have become problems, and there is a need for technological development that can solve these problems all at once.

  Therefore, in recent years, as an alternative to conventional general-purpose resins made from petroleum resources, resins using biomass made from plant resources, such as biodegradable resins such as polylactic acid and polycaprolactone, have attracted a great deal of attention. .

  Since these biodegradable resins use plants that perform photosynthesis using carbon dioxide in the air as raw materials, they can circulate carbon dioxide, suppress global warming, deplete resources, etc. It has the potential to solve the problem.

  However, products using biodegradable resins such as polylactic acid and polycaprolactone generally have inferior mechanical properties and heat resistance compared to products using conventional general-purpose resins such as polyethylene terephthalate and nylon. Since products using resin are expensive, the use of biodegradable resins for various products has not yet been practically used.

  The use of biodegradable resins for products is currently expected for various industrial materials using monofilaments, especially papermaking fabrics such as press felt for papermaking and dryer canvas for papermaking, conveyor belts for conveyance and Since various industrial fabrics such as various filters may be used under severe conditions, monofilaments used in these industrial fabrics are required to have high mechanical properties and heat resistance.

  In response to this requirement, the polylactic acid resin having a molecular weight of 10,000 to 50,000 consists of 5 to 50% by weight and the polylactic acid resin having a molecular weight of 50,000 to 200,000 in weight ratio of 50 to 95% by weight. Monofilaments of 150 ° C. or higher (for example, see Patent Document 1) are known. Although this monofilament has sufficient strength because it is mainly used for fishing nets and offshore structures, it has a melting point as low as 180 ° C and can be used for purposes other than fishing nets and offshore structures. It wasn't.

  As a technique for improving the melting point, polylactic acid obtained by melt-spinning a blend of poly-L lactic acid and poly-D lactic acid under a spinning speed of 3500 to 12000 m / min to form a stereocomplex structure on the spinning line. A fiber (for example, refer to Patent Document 2) is known.

This polylactic acid fiber production method is a method particularly suitable for the production of multifilaments in which polylactic acid is crystallized on a spinning line by high-speed spinning, and further a stereocomplex structure is formed in the drawing and heat treatment steps. is there. However, if this method is applied to the production of monofilaments, the monofilament has a larger yarn diameter than a multifilament and must be spun at a low speed, so that polylactic acid cannot be sufficiently crystallized on the spinning line. And even if it extended | stretched and heat-set in such a crystal state, since the stereocomplex structure was not fully formed, only the monofilament lacking heat resistance was obtained.
JP 2005-146425 A Japanese Patent No. 2003-293220

  The object of the present invention is a polylactic acid monofilament having high heat resistance and strength, which is difficult to achieve with the prior art, and having biodegradability, a method for producing the same, and industrial use using the polylactic acid monofilament To provide a woven fabric.

  In order to achieve the above object, according to the present invention, a monofilament comprising a fat composition comprising poly-L lactic acid and poly-D lactic acid, wherein poly-L lactic acid and poly-D lactic acid form a stereocomplex structure, and having a diameter Is 0.05 to 1.0 mm, the melting point is in the range of 200 to 235 ° C., and the tensile strength measured according to JIS L-1013: 1999-8.5 is 3.0 cN / dtex or more. A polylactic acid monofilament is provided.

  In the present invention, the resin composition is composed of 30 to 70% by weight of poly-L lactic acid and 70 to 30% by weight of poly-D lactic acid, and the boiling water shrinkage measured according to JIS 1013: 1999-8.18. 4% or less is mentioned as a more preferable condition, and by satisfying these conditions, a further excellent effect can be obtained.

  The method for producing a polylactic acid monofilament according to the present invention comprises at least the first stage of the multi-stage drawing when melt-spinning a mixture of poly-L lactic acid and poly-D lactic acid and then performing multi-stage drawing and heat setting of two or more stages. The stretching temperature is in the range of 60 to 150 ° C., the total stretching ratio is 4.0 to 10.0 times, and the heat setting temperature is in the range of 160 to 230 ° C.

  Furthermore, the industrial material of the present invention, particularly the industrial fabric, is characterized in that the polylactic acid monofilament is used at least in part.

  According to the present invention, as will be described below, the polylactic acid monofilament having high heat resistance and strength, which were difficult to achieve with the prior art, and having biodegradability, and high heat resistance and durability are combined. Industrial textiles can be obtained.

  Hereinafter, the polylactic acid monofilament of the present invention, the production method thereof, and the industrial fabric will be described.

  The polylactic acid monofilament of the present invention is a monofilament comprising a resin composition comprising poly L lactic acid and poly D lactic acid, wherein the poly L lactic acid and poly D lactic acid form a stereocomplex structure, and has a diameter of 0.05 to The tensile strength measured according to JIS L-1013: 1999-8.5 is 3.0 cN / dtex or more, while being 1.0 mm, melting | fusing point is in the range of 200-235 degreeC.

  The polylactic acid monofilament of the present invention requires that the PLLA and PDLA constituting it have a stereocomplex structure by a production method described later. When the polylactic acid monofilament does not have a stereocomplex structure, the melting point is 200 to It becomes difficult to obtain a polylactic acid monofilament excellent in heat resistance of 235 ° C.

  The diameter of the polylactic acid monofilament of the present invention needs to be 0.05 to 1.0 mm, and more preferably 0.08 to 0.7 mm.

  This is because, when the diameter is below the above range, troubles such as thread breakage are likely to occur when melt spinning the polylactic acid monofilament, and the operability tends to be difficult. If the range is exceeded, the polylactic acid monofilament will not be sufficiently crystallized during melt spinning, making it difficult for the stereocomplex structure to be sufficiently formed in the stretching and heat setting processes, resulting in a polylactic acid monofilament lacking heat resistance. It is because it is easy to be done.

  Furthermore, the polylactic acid monofilament of the present invention is required to have a tensile strength of 3.0 cN / dtex or more according to JIS L-1013: 1999-8.5 by a production method described later. Is preferably 5.0 cN / dtex or more.

  This is because when the tensile strength falls below the above range, a product with low durability is easily obtained when used for industrial materials, particularly industrial fabrics.

  The higher the tensile strength of the polylactic acid monofilament of the present invention, the more preferable it is for various industrial materials such as industrial fabrics. However, as the tensile strength increases, the elongation decreases and the polylactic acid lacks impact properties. Since the monofilament is easily obtained, the upper limit of the tensile strength is preferably 8.0 cN / dtex.

  Here, PLLA and PDLA referred to in the present invention are those obtained by polymerizing lactic acid that is a monomer, dimer thereof, and further oligomers. PLLA and PDLA used in the present invention are polylactic acid having a high melting point. It is preferable that the L-form optical purity and the D-form optical purity are 90% or more because a monofilament is easily obtained.

  Moreover, the composition ratio of PLLA and PDLA constituting the polylactic acid monofilament of the present invention is such that the PLLA is 30 to 70% by weight with respect to the PLLA of 30 to 70% by weight because it is easy to form a stereocomplex structure. More preferably, the PLLA is 45 to 55% by weight, and the PDLA is more preferably 55 to 45% by weight.

  In particular, when the weight average molecular weight of PLLA is 1 and the weight average molecular weight of PDLA is d, the value of l / d or d / l is in the range of 1.5 to 20 to exhibit better heat resistance. It is more preferable for the reason.

  As a method for examining the formation state of the stereocomplex structure of polylactic acid monofilament, a method for determining the melting peak temperature and the heat of fusion using a differential scanning calorimeter (DSC) is conventionally known. In the present invention, polylactic acid is used. The monofilament was analyzed by wide-angle X-ray diffraction (hereinafter referred to as WAXD), and the presence or absence of X-ray peak intensity derived from the (100) plane of the stereocomplex crystal observed near θ = 12.0 ° on the equator line. A method of checking is adopted.

  In the present invention, the reason why the state of the stereocomplex structure of the polylactic acid monofilament is determined by WAXD is as follows.

  In the Textile Society Proceedings F-133 (1989), from the WAXD results of undrawn yarn, neither crystallization nor stereocomplex structure was observed, but thermal analysis showed a melting peak of stereocomplex structure around 225 ° C. It is described.

  This is because PLLA and PDLA crystallize independently at around 90 ° C in the temperature rising process of thermal analysis, and melt and recrystallize at around 180 ° C to form a stereocomplex structure, and further stereocomplex at around 225 ° C. This is thought to be due to the melting of the structure.

  Therefore, even if the stereo complex structure is not formed before the analysis, there is a problem that it is determined that the stereo complex structure was formed before the analysis when the thermal analysis is performed. In order to avoid the above problems caused by DSC, WAXD, which is a kind of nondestructive test, was adopted.

  Furthermore, the monofilament of the present invention has a boiling water shrinkage measured according to JIS1013: 1999-8.18 because it is difficult to cause a problem in dimensional change of the fabric, particularly when used as an industrial fabric. Is preferably 4% or less.

  The polylactic acid monofilament of the present invention can be produced by the following method.

  First, a PLLA chip and a PDLA chip are supplied to a known melt spinning machine, for example, an extruder type melt spinning machine, and both the chips are sufficiently melt-kneaded in the melt spinning machine. Extrude through hole.

  At this time, the temperature in the melt spinning machine is preferably 200 to 250 ° C. in order to suppress the generation of decomposition gas during melt spinning and to suppress the decrease in the molecular weight of polylactic acid. In addition, if PLLA and PDLA are finely dispersed with each other, it is more preferable to use a static kneader or a metal nonwoven filter in the spinning pack because a stereocomplex structure is easily formed.

  Thereafter, the extruded resin composition is cooled and solidified in a cooling bath, and further subjected to multistage stretching and heat setting treatment. In order to facilitate the formation of a stereocomplex structure in the stretching and heat setting process, First, it is necessary to promote crystallization of PLLA and PDLA. Therefore, in order to promote the crystallization of PLLA and PDLA in the stretching step before the multi-stage stretching, it is necessary to set the stretching temperature of at least the first stage to a range of 60 to 150 ° C, and further to 60 to 130 ° C. It is preferable to be in the range.

  This is because when at least the first stage stretching temperature is below the above range, PLLA and PDLA are not crystallized, so that a stereocomplex structure is hardly formed, and a polylactic acid monofilament with low heat resistance is easily obtained. In other words, since it is stretched in an amorphous state, it becomes easy to obtain a low-strength polylactic acid monofilament. On the contrary, when the stretching temperature exceeds the above range, the molecular orientation degree of PLLA and PDLA is overall. This is because a low-strength polylactic acid monofilament is easily obtained.

  In the present invention, in order to further promote crystallization, the stretching temperature after the second stage can also be set within the above range. However, if the number of stages in the stretching process is too large, there are problems in equipment and high costs. Since a problem may occur, the number of steps in the stretching process is preferably two or three.

  Furthermore, in order to obtain a high-strength polylactic acid monofilament, the total draw ratio in the drawing step needs to be 4.0 to 10.0 times, and more preferably 7.0 to 10.0 times. Is preferred.

  Next, PLLA and PDLA crystallized and molecularly oriented in the stretching process are formed into a stereocomplex structure in the heat setting process. Here, in order to form a stereo complex structure, the heat set temperature needs to be in the range of 160 to 230 ° C, and more preferably in the range of 200 to 220 ° C.

  This is because when the heat setting temperature is below the above range, it becomes difficult to form a stereocomplex structure, and it becomes easier to obtain polylactic acid monofilaments lacking heat resistance. When the above range is exceeded, the stereocomplex structure is melted and low-strength polylactic acid monofilaments are easily obtained.

  The heat setting step can be performed in two or more stages as in the stretching step, and is more preferable for forming a stereo complex structure.

  Here, the spinning speed at the time of melt spinning the polylactic acid monofilament of the present invention is preferably 10 to 1000 m / min, more preferably 50 to 300 m / min. .

  This is because when the spinning speed falls below the above range, the yarn partially melts in the drawing and heat setting processes, and the yarn is not only hard-set, but also a polylactic acid monofilament with low strength is easily obtained. On the contrary, if the spinning speed exceeds the above range, the stereocomplex structure cannot be sufficiently formed in the stretching and heat setting processes, and it becomes easy to obtain polylactic acid monofilaments lacking heat resistance. It is.

  When the polylactic acid monofilament thus obtained is actually analyzed by WAXD, a peak derived from a stereocomplex crystal is observed in the vicinity of θ = 12.0, so that it can be seen that it has a stereocomplex structure.

  And since this polylactic acid monofilament has higher heat resistance and strength than conventional polylactic acid monofilaments, various industrial materials such as fishery materials such as fishing lines and fishing nets, toothbrushes, makeup brushes, body brushes It can be used in the field of brushes such as industrial brushes, guts, musical instrument strings, electrical components, horticultural materials, and in particular, paper fabrics such as paper felt press felts and paper dryer drier canvas, conveyor belts for transport and various filters. When used for various industrial fabrics, such as industrial fabrics excellent in heat resistance and durability can be obtained.

  Hereinafter, the polylactic acid monofilament of the present invention will be described in more detail based on examples.

  The diameter, melting point, tensile strength, boiling water shrinkage, stereocomplex structure confirmation and operability evaluation were performed by the following methods.

[diameter]
Measurement was performed using a micrometer manufactured by MITUTOYO.

[Melting point]
DSC (DSC-7 manufactured by PERKIN ELMER) was used to obtain the melting point Tm of 1 st run as the melting point (° C.) of the polylactic acid monofilament.

[Tensile strength]
In accordance with JIS L1013: 1999-8.5, a polylactic acid monofilament having a yarn length of 250 mm was measured under a tensile speed of 300 mm / min, and the tensile strength (N) at break was determined. Then, the tensile strength (cN / dtex) was calculated by dividing the tensile strength (N) by the fineness (dtex) of the polylactic acid monofilament. This measurement and calculation were performed on ten polylactic acid monofilaments, and the average value was taken as the tensile strength (cN / dtex).

[Boiling water shrinkage]
Measured according to JIS L1013: 1999-8.18.

[Confirmation of stereo complex structure]
The obtained polylactic acid monofilament was analyzed using WAXD (4036A2 type X-ray diffractometer manufactured by Rigaku Corporation), and the (100) plane of the stereocomplex crystal observed at θ = 12.0 ° around the equator line. from derived peak heights of the X-ray _{H 12} and theta = 16.0 ° peak heights of homo PLLA or homo PDLA observed near _{H 16 Prefecture,} the ratio of _{H 12} and _{H 16 H} 12 _{/ H 16} Asked.

And the formation state of the stereocomplex structure was evaluated from the obtained H ₁₂ / H ₁₆ value according to the following two criteria.
○: 0.1 or more
X: Less than 0.1.

[Operability]
Melt spinning was performed continuously for 4 days, and the occurrence frequency of yarn breakage in the drawing process was evaluated in the following three stages.
○: No problem at all, very good,
Δ: Some yarn breakage occurred, but operation was possible sufficiently.
X: Yarn breakage occurred frequently, and operation was extremely difficult.

[Preparation of PLLA chip]
Using a bis (2-ethylhexanoate) tin catalyst (lactide to catalyst molar ratio = 10000: 1) in a nitrogen atmosphere at a temperature of 180 ° C., a lactide composed of L lactic acid having an optical purity of 99.5% was obtained. Polymerization was performed for minutes, and a PLLA chip having a weight average molecular weight of 190,000 and an L-form optical purity of 99% was obtained.

[Production of PDLA chip]
Using a bis (2-ethylhexanoate) tin catalyst (lactide to catalyst molar ratio = 10000: 1) in a nitrogen atmosphere at a temperature of 180 ° C., lactide consisting of D-lactic acid with an optical purity of 99.5% was converted to 100 Polymerization was carried out for a minute to obtain a PDLA chip having a weight average molecular weight of 100,000 and a D-form optical purity of 99%.

[Example 1]
After supplying a mixture of 40% by weight of PLLA chips and 60% by weight of PDLA chips to an extruder-type melt spinning machine, the resin composition melt-kneaded at 240 ° C. is extruded from the mouthpiece hole, led to a cooling bath and solidified by cooling. Thus, an undrawn yarn was obtained.

  Thereafter, the undrawn yarn is stretched at the first stage under conditions of 100 ° C. and 4.0 times under the condition of spinning speed of 150 m / min, and further stretched at the second stage under conditions of 190 ° C. and 2.0 times. A total of 8.0 times stretching was performed. Further, a polylactic acid monofilament having a diameter of 0.4 mm was produced by heat setting under the conditions of 200 ° C. and 0.90 times.

[Examples 2 to 9]
A polylactic acid monofilament was produced in the same manner as in Example 1 except that the spinning speed, stretching, and heat setting conditions were changed as shown in Table 1.

[Examples 10 to 12]
A polylactic acid monofilament was produced by the same method as in Example 1 except that the blending amounts of the PLLA chip and the PDLA chip were changed as shown in Table 1.

[Comparative Examples 1-8]
A polylactic acid monofilament was produced by the same method as in Example 1 except that the spinning speed, the drawing temperature, and the heat setting temperature were changed as shown in Table 1.

[Comparative Examples 9 to 10]
A polylactic acid monofilament was produced by the same method as in Example 1 except that the diameter was changed as shown in Table 1.

  Various physical properties and evaluation results of the polylactic acid monofilaments obtained in Examples and Comparative Examples are listed in Tables 1-4.

  As is clear from the results in Tables 1 to 4, it can be seen that the polylactic acid monofilaments (Examples 1 to 11) obtained under the production conditions of the present invention have a high melting point and sufficient strength.

  On the other hand, it turns out that the polylactic acid monofilaments (Comparative Examples 1 to 11) obtained without satisfying the production conditions of the present invention have a low melting point and strength.

  Therefore, from this result, the polylactic acid monofilaments of Examples 1 to 11 have a sufficient crystal state and a stereocomplex structure, and can be used as various industrial materials in the same manner as conventional general-purpose resins. I understand.

  The polylactic acid monofilament of the present invention not only has biodegradability, but also has a high melting point and sufficient strength compared to conventional polylactic acid monofilaments, so various industries that require heat resistance and durability are required. When used for various industrial fabrics such as papermaking fabrics such as press felt for papermaking and paper dryer drier canvas, conveyor belts for conveyance and various filters, etc., obtain industrial fabrics with excellent heat resistance and durability. be able to.

Claims (6)

A monofilament comprising a resin composition comprising poly-L lactic acid and poly-D lactic acid, wherein poly-L lactic acid and poly-D lactic acid form a stereocomplex structure, having a diameter of 0.05 to 1.0 mm and a melting point of 200 to A polylactic acid monofilament characterized by being in a range of 235 ° C. and having a tensile strength of 3.0 cN / dtex or more measured according to JIS L-1013: 1999-8.5. 2. The polylactic acid monofilament according to claim 1, wherein the resin composition comprises 30 to 70% by weight of poly L lactic acid and 70 to 30% by weight of poly D lactic acid. The polylactic acid monofilament according to any one of claims 1 to 2, wherein the boiling water shrinkage measured according to JIS 1013: 1999-8.18 is 4% or less. The industrial material characterized by using the polylactic acid monofilament according to any one of claims 1 to 3 in at least one part. The industrial material according to claim 4, which is an industrial fabric. After melt spinning a mixture of poly-L lactic acid and poly-D lactic acid, when performing two-stage or more multi-stage stretching and heat setting, at least the first stage of the multi-stage stretching has a stretching temperature in the range of 60 to 150 ° C., The polylactic acid according to any one of claims 1 to 3, wherein the total draw ratio is 4.0 to 10.0 and the heat setting temperature is in the range of 160 to 230 ° C. Monofilament manufacturing method.