JP2003247140A - Film string composed of polylactic acid slit yarn - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible and easily tieable film string made of a polylactic acid polymer having biodegradability and retaining excellent strength characteristics over a long period. <P>SOLUTION: The film string is composed of a polylactic acid slit yarn comprising a polylactic acid polymer consisting essentially of polylactic acid and an aliphatic-aromatic copolyester having ≤0°C glass transition temperature. The compounding ratio of the polylactic acid to the aliphatic-aromatic copolyester having ≤0°C glass transition temperature is within the range of (95/5) to (50/50) (mass%) of the (polylactic acid)/(aliphatic-aromatic copolyester). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film string, and more particularly to a film string made of a polylactic acid type slit yarn which is biodegradable and can be used for a long period of time.

[0002]

2. Description of the Related Art Conventionally, slit yarns obtained by slitting and stretching a film molded from petroleum-based synthetic resin such as polyethylene and polypropylene have been widely used for various industries. Among them, a string made of slit yarn is called a film string, which has excellent mechanical properties and is inexpensive, so a large amount of string is used as a binding string for packing and a handle for bag-like containers such as paper bags. It is used.

However, since the conventional film string is formed of a petroleum-based synthetic resin material, if it is discarded in the natural environment after its use, it will not decompose due to the scientific stability of the material, and it will be incinerated. Due to the high calorific value of its disposal, it may damage the incinerator or generate harmful gas.Therefore, with the recent increase in social demand for environmental protection, the film string will not be burdened with the environment. It is essential that the use of materials is required.

[0004]

In view of such a recent situation, a slit yarn made of a biodegradable aliphatic polyester such as polylactic acid having excellent mechanical strength and less deteriorated by aging is provided. Although proposed, since polylactic acid is hard and brittle, there is a problem that it is difficult to form a film itself, or a cracking phenomenon occurs when slitting, and it is difficult to form a yarn. Furthermore, in the case of a film string, it is necessary to make it easy to tie it, and not only a film string consisting of one slit yarn but also a film string formed by twisting a plurality of slit yarns is required. Getting a string was extremely difficult.

Therefore, the present invention provides a film string formed by using a biodegradable polylactic acid polymer, which is flexible and easy to tie, and which can be used for a long period of time while maintaining excellent strength characteristics. This is an issue.

[0006]

[Means for Solving the Problems] The present inventors have accomplished the present invention as a result of intensive research to solve the above problems. That is, the present invention includes a polylactic acid-based polymer mainly composed of polylactic acid and an aliphatic-aromatic copolyester having a glass transition temperature of 0 ° C or less, and polylactic acid and a fat having a glass transition temperature of 0 ° C or less. A polylactic acid-based slit yarn having a blending ratio of the group-aromatic copolyester of (polylactic acid) / (aliphatic-aromatic copolyester) = 95/5 to 50/50 (mass%) The gist is a film string characterized by the above.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The film string of the present invention is a film string made of polylactic acid type slit yarn. The polylactic acid slit yarn constituting the film string is a resin containing a polylactic acid copolymer in which polylactic acid and an aliphatic-aromatic copolyester having a glass transition temperature of 0 ° C. or less are blended in a specific ratio. It must consist of a composition.

As a method for producing the slit yarn,
A method of forming an unstretched film by melting the resin composition, cutting the obtained unstretched film along the longitudinal direction at predetermined intervals, and then performing a stretching treatment to form a slit yarn, or After melting and molding the resin composition,
A method may be adopted in which the stretched film obtained by stretching is cut along the longitudinal direction at predetermined intervals to form slit yarn.

The film yarn of the present invention can be obtained by twisting a plurality of slit yarns obtained as described above, if necessary, or by making them as a braid. The twisting step and the braiding step at this time may be performed by a known method in the same manner as in the case of the conventional polypropylene thread, and the polylactic acid-based slit yarn forming the film thread of the present invention has flexibility. Therefore, it can be performed without causing cracks or the like. Further, if there is no particular problem in use, a film string composed of one slit yarn may be used without twisting a plurality of them, and the film string of the present invention includes a plurality of slits as described above. It refers to both a film string from a yarn and a film string composed of one slit yarn.

In the film string of the present invention, the polylactic acid as the constituent material and the aliphatic-aromatic copolyester having a glass transition temperature of 0 ° C. or less are both biodegradable, so that the film after use is The string can be almost completely decomposed by hydrolysis or microbial decomposition, and even if incineration is performed, there is almost no danger of damaging the incinerator because the calorific value at the time of incineration is low and no harmful substances are generated. Good disposal can be done without polluting the natural environment. By blending polylactic acid, which is hard and brittle at room temperature, with a low-crystalline biodegradable aliphatic-aromatic polyester having a glass transition temperature of 0 ° C. or less, the crystallinity of polylactic acid is relaxed. Since it has an appropriate viscosity, it is flexible and easy to tie, and has excellent knot strength while ensuring the necessary tensile strength for the film string, and it can be easily made into a twisted string or braid using the existing twisting machine. It does not cause twisting and cracking. Further, the degree of mechanical deterioration due to aging is small.

The details will be described below. The polylactic acid-based polymer of the present invention has a polylactic acid and glass transition temperature of 0.
And an aliphatic-aromatic copolyester having a temperature of not higher than 0 ° C. are mixed in a mass ratio of (polylactic acid) / aliphatic-aromatic copolyester) = 95/6 to 50/50 (mass%). Need to be When the blending ratio of the aliphatic-aromatic copolyester is less than 5% by mass, the crystallinity of polylactic acid is not sufficiently relaxed, so that not only the viscosity is low and the convergence is poor, but also the film is formed. Vertical slits tend to occur when slitting. On the other hand, when the blending ratio of the aliphatic-aromatic copolyester exceeds 50% by mass, the film string becomes too soft and the required strength becomes insufficient. From the above reason and from the viewpoint of preventing the occurrence of twist cracks, the compounding ratio of the aliphatic-aromatic copolyester is preferably 10 to 40% by mass, and 15
It is more preferable that the content is ˜35% by mass.

As the polylactic acid in the present invention, poly L-lactic acid whose structural unit is lactic acid is L-lactic acid, and the structural unit is D
-Poly D-lactic acid which is lactic acid, poly DL-lactic acid which is a copolymer of L-lactic acid and D-lactic acid, or a mixture thereof can be used and has a number average molecular weight of 30,000 to 150,000. Are preferable, and those in the range of 90,000 to 120,000 are more preferable. When the number average molecular weight is less than 30,000, not only is it difficult to form a film by melt extrusion, but also the mechanical strength of the film string tends to decrease, which is not preferable. On the other hand, even if the number average molecular weight exceeds 150,000, melt extrusion becomes difficult. The polylactic acid of the present invention may contain a small amount of a chain extender such as an organic peroxide, a bisoxazoline compound, a diisocyanate compound, an epoxy compound or an acid anhydride for the purpose of increasing the molecular weight. Good.

The aliphatic-aromatic copolyester in the present invention is a copolyester having at least an aliphatic dicarboxylic acid, an aromatic carboxylic acid, and an aliphatic diol as its constituents, and its glass transition temperature is 0. It is necessary that the temperature is not higher than ℃, more preferably -20 ℃ or less. When the glass transition temperature exceeds 0 ° C, the crystallinity of polylactic acid cannot be sufficiently relaxed, and viscosity is imparted to the polylactic acid-based polymer to improve the converging property, and the slit yarn and the film string formed thereof are longitudinally cracked. The effect of suppressing is not obtained. Examples of the aliphatic dicarboxylic acid constituting such an aliphatic-aromatic copolyester include succinic acid, adipic acid, suberic acid, sebacic acid,
Dodecanedioic acid and the like can be mentioned. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and the like. Further, examples of the aliphatic diol include ethylene glycol, propylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Then, the desired aliphatic-aromatic copolyester is obtained by polycondensing at least one selected from these and, if necessary, an isocyanate, an acid anhydride, an epoxy compound, an organic peroxide. It is also possible to provide jump-up and long-chain branching structurally by using, for example. Moreover, you may introduce a urethane bond, an amide bond, an ether bond, etc. in the range which does not affect biodegradability.

The relative viscosity of the polylactic acid polymer in the present invention is preferably at least 1.8 or more,
It is more preferably 1.85 or more. Relative viscosity here means phenol, 1,1,2,2-
The solution viscosity is measured by using a mixed solvent with tetrachloroethane (mass ratio 1/1) at a temperature of 20 ° C. and a concentration of 0.5 g / dl. Polylactic acid-based polymer has a relative viscosity of 1.8
If it does not satisfy, the tensile strength of the film string tends to be insufficient, which is not preferable. However, if the viscosity becomes too high, extremely high pressure will be required for film formation, so that the relative viscosity is preferably about 2.5 at the most.

It is preferable to add a lubricant to the polylactic acid polymer in the present invention as long as the characteristics of the film string are not significantly impaired. By blending a lubricant, it is possible to prevent wrinkles from being produced during the production of the film in the production process of the film string, and further, the slipperiness of the film is further improved, and the flat yarn in the twisting machine when forming the twisted string. Can be sent more smoothly. The blending ratio of the lubricant to the polylactic acid-based polymer is 0.3
〜8.0 mass% is preferred. When the blending ratio of the lubricant is less than 0.3% by mass, the effect as the lubricant is not substantially obtained,
On the other hand, if it exceeds 8.0% by mass, manufacturing problems such as an increase in pack pressure during film formation are unfavorable. The mixing ratio of the lubricant is 0.35 to 7.
0 mass% is more preferable, and 0.4 to 6.0 mass% is particularly preferable.

The lubricant to be added is not particularly limited, but examples thereof include inorganic lubricants such as silica, talc, calcium carbonate, liquid paraffin, microcrystalline wax, natural paraffin, synthetic paraffin, and aliphatic such as polyethylene. Hydrocarbon lubricant, stearic acid,
Lauric acid, hydroxystearic acid, fatty acid lubricants such as hydrogenated castor oil, stearic acid amide, oleic acid amide, erucic acid amide, lauric acid amide, ethylenebisstearic acid amide, ethylenebisoleic acid amide,
Fatty acid amide lubricants such as ethylene bislauric acid amide, metal soap lubricants which are fatty acid metal salts having 12 to 30 carbon atoms such as aluminum stearate, lead stearate, calcium stearate and magnesium stearate,
Fatty acid (partial) ester lubricants of polyhydric alcohols such as glycerin fatty acid ester and sorbitan fatty acid ester,
Butyl stearate, fatty acid ester-based lubricants such as long-chain ester waxes such as montan wax, or composite lubricants in which these are compounded, and the like, particularly, the combined use of an inorganic lubricant and an organic lubricant is preferable, and specifically, silica and A combination of erucic acid amide or silica, erucic acid amide and aluminum stearate is preferred.

The lubricant may be added by a masterbatch method, a direct addition method, or a lubricant which is dispersed in advance in an aliphatic-aromatic copolyester substantially incompatible with polylactic acid. Is added to polylactic acid, and these methods can be used together.
In particular, when a lubricant is added by using both of these methods in combination, in addition to the sliding effect given by the lubricant dispersed in the polylactic acid matrix, the lubricant in the incompatible resin microdispersed in the polylactic acid is further slippery. It is preferable because it improves the property. The lubricant added to the polylactic acid by a masterbatch or directly and the lubricant previously dispersed in the aliphatic-aromatic copolyester substantially incompatible with the polylactic acid are of the same kind. May also be different.

The polylactic acid-based polymer of the present invention contains an anti-blocking agent, an anti-UV agent, a light-proofing agent, an antistatic agent, an antistatic agent, an antifouling agent, as long as the characteristics of the film string are not significantly impaired. A flame retardant, an antioxidant, a matting agent, a pigment and the like may be added, and these can be added directly or in a masterbatch. In the case of forming a colored film string, it is preferable to add the pigment in the range of 2% by mass or less.

In the present invention, the slit yarn constituting the film string has a fineness of 5,000 to 33,000.
It is preferably 0 decitex. If the fineness of the slit yarn is less than 5,000 decitex, the absolute strength is insufficient, and it becomes necessary to twist a very large number of slit yarns to produce a film string, which is extremely inefficient, which is not preferable. On the other hand, if it exceeds 33,000 decitex, it may not be possible to commercialize it because it does not meet the standard of the commonly used blown film machine and twisting machine. Although the thickness and width of the slit yarn are not particularly limited, workability in various steps and necessary strength may be taken into consideration so that the slit yarn may be designed to fall within the above range of fineness. When manufacturing a film string by twisting a plurality of slit yarns,
If the number of slit yarns twisted together is too large, the tenacity factor tends to decrease, so 5 or less is preferable, and 3 is particularly preferable.

The slit yarn of the present invention preferably has a tensile strength of 1.0 cN / dtex or more and a knot strength of 1.0 cN / dtex or more. Tensile strength of slit yarn is 1.0 cN / d
When it is less than tex, the strength of the film string is insufficient.

The method for producing the film string of the present invention will be described below with reference to an example. First, the polylactic acid and the aliphatic-aromatic copolyester are directly charged into the extruder at the blending ratio of the present invention, or raw materials pre-compounded at the blending ratio of the present invention are charged to the extruder. Melt and knead. The melting temperature of the polymer in the extruder is appropriately selected in consideration of the composition ratio of L-lactic acid and D-lactic acid constituting polylactic acid, but is usually 190 to 240 ° C.
Temperature range.

As a method for forming a film from the melt-kneaded polylactic acid-based polymer, for example, a melt casting method,
Although a melt extrusion method, a calendar method and the like can be used, the melt extrusion method is generally used industrially.

As the melt extrusion method, known T-die method, inflation method and the like can be applied. The extrusion temperature is 170 to 250 ° C., preferably 190 to 230 ° C.
Is the range. If the molding temperature is too low, the film molding becomes unstable, and if it is too high, the polylactic acid is decomposed and the strength of the obtained film is lowered, and problems such as yellowing occur. The shape of the die used for melt extrusion by the inflation method may be flat, but an embossed die is preferable because it makes it easy to tie a film string.

The extruded unstretched film is stretched and then slit to obtain a slit yarn having a desired width. Alternatively, a slit yarn having a desired width can be obtained by slitting an unstretched film into a predetermined width and then subjecting it to a stretching treatment. As the stretching treatment,
The uniaxial stretching is preferable. When biaxial stretching is performed,
In the obtained film, the molecules are oriented in the vertical and horizontal directions, so even if there are a few cracks in the horizontal direction, they tend to be easily cut, which is not preferable.

In the case of uniaxial stretching, it is preferable that the stretching ratio in the machine direction be 1.5 to 9.0. If the draw ratio is too low, not only stretching unevenness occurs, but it is difficult to obtain a film having a sufficiently satisfactory strength, while if the draw ratio is too high, not only frequent cutting during stretching, but also molecular orientation However, vertical cracking (fibrillation) is likely to occur due to traverse. Therefore, the stretching ratio in the machine direction is more preferably 2.5 to 8.0 times.
It is particularly preferable to set it to 0 to 7.0 times.

The stretching temperature is preferably in the range of not lower than the glass transition temperature (Tg) of the polylactic acid used and not higher than (Tg + 65) ° C. If the stretching temperature is less than Tg, stretching is difficult, and if it exceeds (Tg + 65) ° C., the strength improvement due to stretching may not be recognized. Further, in order to increase heat resistance and dimensional stability, after stretching, heat treatment may be performed under tension at a temperature of 70 ° C. or higher and lower than the melting point.

The slit yarn obtained as described above can be rolled into a single roll and used as the film string of the present invention. Further, by twisting a plurality of slit yarns with a known twisting machine or the like, the film string of the present invention in the form of a twisted string can be manufactured.

When the film string of the present invention is disposed of after use, it is decomposed by microorganisms by leaving the waste in the soil or on the surface of the soil or in the compost, and accumulated in the natural environment. Disposal can be performed satisfactorily without At this time, the decomposition can be promoted by performing an artificial treatment such as using steam in a high temperature and high humidity environment or by spraying an alkaline substance for hydrolysis. In addition, it is preferable that the film string is not easily decomposed and deteriorated during use and can be used while maintaining its strength for a long period of time, and is rapidly biodegraded after use.
This strong holding period can be adjusted by adjusting the blending ratio of the polylactic acid polymer.

[0029]

EXAMPLES Next, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In addition, the measuring method of the physical-property value of the slit yarn in the following Examples and Comparative Examples is as follows. (1) Tensile strength: JI of the slit yarn immediately after production and after 6 months of being left in river water
The measurement was performed according to the method described in SZ-1533. (2) Knot strength: JI of each of the slit yarns immediately after production and 6 months after being left in river water
The measurement was performed according to the method described in SZ-1533.

Example 1 The melting point was 167 ° C., and the molar ratio of D-lactic acid to L-lactic acid was D / L.
= 1.2 / 98.8, polylactic acid with a number average molecular weight of 99,600 (Nature Works, Cargill Dow)
0 parts by mass and polybutylene adipate terephthalate (BASF Corp., Ecoflex F), which is an aliphatic-aromatic copolyester having a glass transition temperature of -35 ° C. 19
Part by mass and 0.5 part by mass of erucic acid amide as a lubricant and 0.5 part by mass of silica were dry blended to obtain a raw material polymer. This raw material polymer was melt-kneaded at 210 ° C., and a film was formed by an inflation method using an extruder equipped with an embossed round die. After slitting this film, it was uniaxially stretched 7.0 times along the above extrusion direction at 120 ° C. by a roll method to have a width of 55 m.
A slit yarn having m and fineness of 11,000 dtex was obtained. One of the obtained slit yarns was rolled into a roll to obtain the film string of the present invention. Further, the film string of the present invention was obtained as a twisted string by putting three of the above slit yarns together and twisting them in the S direction at 30 T / m.

Examples 2 to 4 A film string composed of one slit yarn and three slit yarns were prepared in the same manner as in Example 1 except that the raw material composition and the draw ratio were as shown in Table 1 below. A twisted film string was obtained. At this time, width 55m after stretching
The extrusion rate of the molten polymer in the inflation method was adjusted so that a slit yarn having a m and fineness of 11,000 dtex was obtained. The production conditions of the film string and the characteristics of the flat yarn in Examples 1 to 4 are shown in Table 1 below.

[0032]

[Table 1]

As shown in Table 1 above, the film strings obtained in Examples 1 to 4 have the constitution of the present invention and can maintain good mechanical properties for a long period of time.
Both the film string composed of three slit yarns and the film string obtained by twisting three slit yarns could be used as a film string without any problem. Further, there were no troubles such as fibrillation in the manufacturing process. Furthermore, it could be rapidly biodegraded using compost.

Comparative Example 1 An attempt was made to manufacture a film string in the same manner as in Example 1 except that the raw material composition and the draw ratio were as shown in Table 2 below. However, since the blending ratio of the aliphatic-aromatic copolyester was too small, fibrillation occurred severely, and the slit yarn could not be obtained.

Comparative Example 2 A film string consisting of one slit yarn and three slit yarns were twisted together in the same manner as in Example 1 except that the raw material composition and the draw ratio were as shown in Table 2 below. Got a film string. However, since the blending ratio of the aliphatic-aromatic copolyester was too large, both the film string consisting of one slit yarn and the film string obtained by twisting three slit yarns had weak strength and was practically used as a film string. It was unbearable.

Comparative Example 3 99 parts by weight of polybutylene succinate (PBS), 0.5 part by weight of erucamide as a lubricant and 0.
A film string consisting of one slit yarn and three slit yarns were used in the same manner as in Example 1 except that 5 parts by mass of dry blend was used as the raw material polymer and the draw ratio was 4.0 times. The film string which twisted together was obtained. However, the strength was drastically reduced over time, and it was not practical. Table 2 below shows the manufacturing conditions of the film string and the characteristics of the flat yarn in Comparative Examples 1 to 3.

[0037]

[Table 2]

[0038]

The film string of the present invention solves the drawback of biodegradable polylactic acid resin, which is hard and brittle. Therefore, it is possible to prevent vertical cracking at the time of manufacturing, etc., and not only when it is made of one slit yarn but also when it is manufactured by twisting a plurality of slit yarns.
It can be manufactured without any problem using existing equipment, retains the good characteristics of being flexible and excellent in strength over a long period of time, and when it is discarded, it should be left in the soil, or a positive method using compost etc. Can be biodegraded. Therefore, the film string of the present invention is suitable as a film string that does not give an environmental load in a wide range of fields including agricultural applications such as a binding string for packing, a handle for a paper bag, or a hanging string for melon cultivation. Available for

Claims (3)

[Claims] 1. A polylactic acid-based polymer comprising polylactic acid and an aliphatic-aromatic copolyester having a glass transition temperature of 0 ° C. or lower as main components, wherein the polylactic acid and the glass transition temperature are 0.
A polylactic acid-based composition in which the blending ratio of the aliphatic-aromatic copolyester at a temperature of ℃ or less is (polylactic acid) / (aliphatic-aromatic copolyester) = 95/5 to 50/50 (mass%) A film string that is made of slit yarn. 2. The fineness of the polylactic acid type slit yarn is 5,
000-33,000 dtex, tensile strength 1.0 cN
/ Dtex or more and knot strength of 1.0 cN / dte
It is x or more, The film string of Claim 1 characterized by the above-mentioned. 3. A fineness of 5,000 to 33,000 dte
The film string according to claim 1 or 2, wherein a plurality of polylactic acid type slit yarns of x are twisted together.