JPH09272794A - Biodegradable film - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a film that decomposes in a natural environment and has excellent flexibility and transparency. SOLUTION: A polylactic acid-based polymer and an aliphatic polyester composed of an aliphatic carboxylic acid component and an aliphatic alcohol component are mixed at a weight ratio of 75:25 to 20:80, and a tensile elastic modulus is 250 kg. / Mm ² or less and a light transmittance of 65% or more to form a film, which was a biodegradable film.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a film which is decomposed in a natural environment and is excellent in flexibility and transparency.

[0002]

2. Description of the Related Art Many conventional plastic products, particularly plastic packaging materials, are often discarded immediately after use, and their processing problems have been pointed out. Typical plastics for general packaging include polyethylene, polypropylene and PET.
However, these materials have a high calorific value during combustion and may damage the combustion furnace during the incineration process. Furthermore, even today, polyvinyl chloride, which is used in large amounts, cannot burn due to its self-extinguishing properties. In addition, plastic products, including materials that cannot be burned, are often landfilled, but due to chemical and biological safety, they hardly decompose and remain, which shortens the life of landfill sites. I am waking up. Therefore, the heat of combustion is low, it decomposes in the soil,
And what is safe is desired, and much research has been done.

One example is polylactic acid. Polylactic acid has a burning calorie less than half that of polyethylene, and hydrolysis naturally proceeds in soil and water, and then becomes a harmless decomposition product by microorganisms. Currently, research is being conducted to obtain molded products, specifically films, sheets, containers such as bottles, using polylactic acid. Polylactic acid is a polymer obtained by polycondensing lactic acid. Lactic acid includes two types of optical isomers, L-lactic acid and D-lactic acid, and the crystallinity differs depending on the ratio of these two types of structural units. For example, a random copolymer in which the ratio of L-lactic acid and D-lactic acid is approximately 80:20 to 20:80 does not have crystallinity and becomes a transparent completely amorphous polymer which softens at a glass transition temperature of around 60 ° C. On the other hand, L-lactic acid alone or D
A homopolymer consisting only of lactic acid has a glass transition temperature of about 60 ° C., but is a semi-crystalline polymer having a melting point of 180 ° C. or higher. This semi-crystalline polylactic acid is melt-extruded and then rapidly cooled to be an amorphous material having excellent transparency.

Further, polylactic acid is crystallized while uniaxially or biaxially stretched to orient the molecules and then heat-treated to suppress the growth of spherulites having a size larger than the wavelength of visible light. , There is a way to maintain transparency. As an industrial production method, a roll-type, a tenter-type or a biaxial stretching device in which both are used, which are used for producing a biaxially oriented polypropylene film or a biaxially oriented polyethylene terephthalate film, can be used. However,
Polylactic acid is a hard and brittle material. Depending on the application, it may not always be a suitable material. For example, even if these unstretched polylactic acid film or biaxially oriented polylactic acid film is used as a bag after being processed into a bag, it is inferior in flexibility and easy to use as compared with the existing plastic film bag such as a polyethylene bag or a polypropylene bag. Is bad.

On the other hand, examples of the flexible biodegradable film include a film made of a condensation polymer of an aliphatic polyfunctional carboxylic acid and an aliphatic polyfunctional alcohol. As an example, there is a film made of a succinic acid or adipic acid, or a dicarboxylic acid component composed of both of them, and an aliphatic polyester having a diol component composed of eletin glycol or butanediol or both of them as a main structural unit. Such an aliphatic polyester has a glass transition temperature of room temperature or lower, has high crystallinity, and is in a crystalline state at room temperature. It is difficult to suppress the growth of spherulites even if the polymer is melt-extruded and then rapidly cooled, and it becomes opaque. The opacity of this film is high. Compared with polyethylene film, polypropylene film, etc., which have similar thicknesses, it is high, and even if you put the product in such an aliphatic polyester bag, the contents are not clear, the shade of the contents becomes unclear, etc. It will be damaged. It has been studied to adjust the dicarboxylic acid component and the diol component to lower the crystallinity and slightly improve the transparency, but if the crystallinity is too low, it will be hard to solidify even after cooling after being extruded. It sticks to the roll, making it difficult to take it as a film.

As described above, a film made of polylactic acid is hard, brittle and lacks flexibility. On the other hand, a film made of an aliphatic polyester has the drawback of being poor in transparency, and in any case, improvement has been desired. An object of the present invention is to solve the above-mentioned problems, and to provide a biodegradable film which is easily decomposed in a natural environment and is excellent in flexibility and transparency.

[0007]

The present invention for solving the above-mentioned problems is achieved by mixing a polylactic acid-based polymer and an aliphatic polyester other than polylactic acid in a weight ratio in the range of 75:25 to 20:80. It is in a biodegradable film. When the above ratio is in the range of about 60:40 to 35:65, the balance between flexibility and transparency can be made even more preferable. Further, the present invention provides a polylactic acid-based polymer and a polylactic acid other than polylactic acid. A film obtained by mixing an aliphatic polyester is characterized by having a tensile elastic modulus of 250 kg / mm ² or less and a light transmittance of 65% or more.
The aliphatic polyester has a number average molecular weight of about 10,000 to 15
It is preferable to have the following structure. (In the formula, R ¹ and R ² are alkylene groups having 2 to 10 carbon atoms,
It is a cyclo ring group or a cycloalkylene group. Further, n is the degree of polymerization required to have a number average molecular weight of about 10,000 to 150,000. )

[0008]

Embodiments of the present invention will be described below. As described above, polylactic acid has a structural unit of lactic acid of L
There are poly (L-lactic acid) which is lactic acid, poly (D-lactic acid) whose structural unit is D-lactic acid, and poly (DL-lactic acid) which is a copolymer of L-lactic acid and D-lactic acid. There are also mixtures of these. As the polymerization method, any known method such as a condensation polymerization method or a ring-opening polymerization method may be adopted. For example, in the polycondensation method, L-lactic acid, D-lactic acid, or a mixture thereof can be directly dehydrated and polycondensed to obtain polylactic acid having an arbitrary composition. In the ring-opening polymerization method, polylactic acid can be obtained by using lactide, which is a cyclic dimer of lactic acid, and a catalyst selected while using a polymerization modifier and the like as required. Lactide includes L-lactide which is a dimer of L-lactic acid, D-lactide which is a dimer of D-lactic acid, and DL-lactide which is composed of L-lactic acid and D-lactic acid, and these are required. Polylactic acid having an arbitrary composition and crystallinity can be obtained by appropriately mixing and polymerizing. or,
Other hydroxycarboxylic acids and the like may be copolymerized to the extent that the properties of polylactic acid are not impaired. Further, a small amount of a chain extender such as a diisocyanate compound, an epoxy compound or an acid anhydride can be used for the purpose of increasing the molecular weight. The preferred range of the weight average molecular weight of the polymer is 6
If it is less than this range, practical physical properties are hardly expressed, and if it exceeds this range, the melt viscosity is too high and the moldability is poor.

A polymer comprising an aliphatic carboxylic acid component and an aliphatic alcohol component (hereinafter, simply referred to as "aliphatic polyester") is a method of directly polymerizing them to obtain a high molecular weight substance, and after polymerizing to an oligomer level, There is an indirect manufacturing method for obtaining a high molecular weight substance with a chain extender or the like. The aliphatic polyester other than polylactic acid used in the present invention preferably comprises a dicarboxylic acid and a diol. Examples of the aliphatic dicarboxylic acid include compounds such as succinic acid, adipic acid, suberic acid, sebacic acid, dodecanoic acid, and their anhydrides and derivatives. On the other hand, as the aliphatic diol, glycol-based compounds such as ethylene glycol, butanediol, hexanediol, octanediol, cyclohexanedimethanol, and derivatives thereof are generally used. All are compounds having an alkylene group having 2 to 10 carbon atoms, a cyclo ring group or a cycloalkylene group, and are produced by condensation polymerization. Two or more kinds may be used in both the carboxylic acid component and the alcohol component. Further, a trifunctional or higher functional carboxylic acid, alcohol or hydroxycarboxylic acid may be used for the purpose of providing a branch in the polymer in order to improve the melt viscosity. When these components are used in a large amount, the resulting polymer has a crosslinked structure and is not thermoplastic, or even if it is thermoplastic, a microgel with a partially highly crosslinked structure is produced, and when it is made into a film, fisheye is formed. There is a risk that Therefore, these tri- or higher-functional components are contained in the polymer in a very small proportion, and are contained to such an extent that they do not greatly affect the chemical and physical properties of the polymer. As the polyfunctional component, malic acid, tartaric acid, citric acid, trimellitic acid, pyromellitic acid, pentaerythritol, trimethylolpropane or the like can be used.
The direct polymerization method is a method of obtaining the high molecular weight compound by selecting the above-mentioned compound and removing the water contained in the compound or generated during the polymerization. In addition, as an indirect manufacturing method, like the above-mentioned polylactic acid, a small amount of a chain extender is used to increase the molecular weight. Examples of the main chain extender include diisocyanate compounds such as hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate and diphenylmethane diisocyanate.

Film forming conditions will be described. First, the polylactic acid-based polymer and the aliphatic polyester other than polylactic acid are mixed by putting the respective raw materials into the same extruder. There is a method of directly extruding from a die to directly produce a film, or a method of extruding into a strand shape to produce pellets, and then again producing a film with an extruder. In both cases, the decrease in molecular weight due to decomposition must be taken into consideration, but it is better to select the latter for uniform mixing. The polylactic acid-based polymer and the aliphatic polyester other than polylactic acid are sufficiently dried to remove water, and then melted in an extruder. The melting point of polylactic acid is appropriately selected in consideration of the fact that the melting point changes depending on the composition ratio of the L-lactic acid structure and the D-lactic acid structure and the melting point of the aliphatic polyester and the mixing ratio. In practice, a temperature range of about 100-250 ° C is usually chosen.

The polylactic acid polymer and the aliphatic polyester other than polylactic acid are mixed in a weight ratio of 75:25 to 20:80.
It is an important point in the present invention that the range is set to. In the film obtained when the aliphatic polyester content is less than 25%, the thickness of the plastic film used for the existing bag-like product is due to the hardness and brittleness derived from polylactic acid,
There arises a problem that cracks and tears are likely to occur at the fold points. Also, it is too hard to be practically used. By mixing the aliphatic polyester with the polylactic acid-based polymer, flexibility can be imparted. As a measure of flexibility, the tensile modulus is preferably about 250 kg / mm ² or less, and more preferably about 200 kg / mm ² or less. Incidentally, in the existing general-purpose plastic bag, even the biaxially oriented polypropylene belonging to the hard class has a tensile elastic modulus of about 250 kg / mm ² . These flexibility can be achieved by mixing about 25% or more depending on the kind of aliphatic polyester other than polylactic acid.

Usually, aliphatic polyesters, especially those having glass transition points and crystallization points below room temperature have high crystallinity and are crystallized at room temperature, and spherulites develop inside to become cloudy and opaque. Become. However, by mixing polylactic acid, the transparency can be improved at least to the extent of existing polyethylene and polypropylene films. Generally, when polymers with low compatibility are mixed,
The obtained molded product becomes more opaque, but such a phenomenon is not observed in the present invention. That is, polylactic acid and aliphatic polyester are relatively excellent in compatibility. The effect can be obtained by making the mixing ratio of the aliphatic polyester less than 80% and making the polylactic acid more than 20%. Above this range, the transparency of the resulting film will not be improved, depending on the degree of dispersion of both polymers. This is thought to be due to the intermolecular interaction of both polymers, but it is currently unknown. The transparency of the film depends on its use, but the light transmittance is 65%.
% Is preferable. Even more preferably, if it is 75% or more, a more transparent feeling can be given. Depending on the thickness, the mixing ratio of aliphatic polyester is 80
If it exceeds%, it is difficult to increase the light transmittance to 65% or more. By mixing two kinds of polymers within the above range, excellent properties can be brought out in the balance between flexibility and transparency of the film.

The film forming method is a method in which the molten polymer is extruded from a T-die and is rapidly cooled and solidified while being taken by a rotating casting drum, or the molten polymer is pulled up in a cylindrical shape from a round die and air-cooled at the same time. A known method such as a so-called inflation method in which the film is expanded and formed into a film may be used. Generally, the latter has a slower cooling rate, is more likely to be crystallized, and is a disadvantageous condition for the transparency of the film. It is also possible to improve the cooling efficiency by using water instead of air.

The above-mentioned form is a non-stretched film which is excellent in transparency and heat resistance, but it can be stretched if necessary. For example, when it is used as a film for shrink wrapping, it can be obtained by producing a stretched oriented film by a tenter method or a tubular method.

[0015]

EXAMPLES Examples will be shown below, but the present invention is not limited thereto. The measurement and evaluation shown in the examples were performed under the following conditions. (1) Light transmittance The measurement was performed according to JIS K 7105. The larger the value, the better the transparency. (2) Tensile elastic modulus Using a Toyo Seiki Tensilon type II tensile tester, a temperature of 23
The measurement was performed at a temperature of 50 ° C. and a relative humidity of 50%. 5m film
It was cut into a strip having an m width and a length of 300 mm, and a tensile test was performed at a chuck distance of 250 mm and a pulling speed of 5 mm / min, and the strength and strain of 1/2 of the yield strength were calculated. It can be seen that the lower the value, the more flexible the film.
The longitudinal direction of the film was represented as MD and the width direction was represented as TD.

(Example 1) Using a 25 mmφ same-direction small twin-screw extruder, polylactic acid shown in Table 1 (manufactured by Shimadzu Corporation, trade name: Lacty), and an aliphatic polyester other than polylactic acid were mainly used. 70: 3 polybutylene succinate (produced by Showa Highpolymer Co., Ltd., trade name Bionole # 1001), which is a condensation polymer of 4-butanediol and succinic acid, is used.
After mixing and melting at a ratio of 0, it was extruded at 210 ° C. into a strand shape to prepare pellets. Next, using a small 30 mmφ single-screw extruder, melt extrusion was performed from a 30 mmφ round die at 200 ° C., air-cooled, and a blow ratio of 2.4 was 20 μ.
An m-thick blown film was produced. The evaluation of the obtained film is shown in Table 1. (Example 2) Instead of the polypropylene succinate used in Example 1, a copolymer of mainly 1,4-butanediol, succinic acid, and adipic acid was used for the poly (styrene succinate / adipate (Showa Polymer Co., Ltd. Table 1 is shown in the same manner as in Example 1 except that the pellets were produced by extruding into a strand shape at 200 ° C. after mixing and melting at a ratio of 70:30 using a company-made product name: Bionole # 3001). A 20 μm thick blown film having a blow ratio of 2.5 was produced. (Examples 3 and 4) The mixing ratios of polylactic acid and polybutylene succinate / adipate were 50:50 and 2 respectively.
A film having a blow ratio shown in Table 1 of 2.7 was obtained in the same manner as in Example 2 except that the film ratio was set to 5:75.

Comparative Example 1 An inflation film shown in Table 1 was prepared in the same manner as in Example 2 except that polylactic acid was used. However, the blow ratio is 1.9. Comparative Example 2 Only polybutylene succinate / adipate was melt extruded at 180 ° C. in the same manner as in Example 2,
An inflation film having a blow ratio of 3.1 and a thickness of 20 μm was produced. (Comparative Examples 3 and 4) Table 1 was conducted in the same manner as in Example 2 except that the mixing ratios of polylactic acid and polybutylene succinate / adipate were 80:20 and 15:85, respectively.
The film shown in was obtained.

[0018]

[Table 1]

In Examples 1 and 2, although slightly hard, a film having flexibility and excellent transparency could be obtained. The film obtained in Example 3 was excellent in transparency and had flexibility and flexibility. In addition, in Example 4, a film having a slightly poor transparency but an excellent flexibility was obtained. There is no problem in practical use. On the other hand, Comparative Examples 1 and 3 were excellent in transparency and lacked in flexibility, and Comparative Examples 2 and 4 were excellent in flexibility but insufficient in transparency.

[0020]

According to the present invention, a film having degradability in a natural environment and having excellent flexibility and transparency can be obtained.

Claims (3)

[Claims] 1. A biodegradable film comprising a polylactic acid-based polymer and an aliphatic polyester other than polylactic acid mixed in a weight ratio of 75:25 to 20:80. 2. A film obtained by mixing a polylactic acid polymer and an aliphatic polyester other than polylactic acid, which has a tensile elastic modulus of 250 kg / mm ² or less and a light transmittance of 65% or more. Biodegradable film. 3. The biodegradable film according to claim 1, wherein the aliphatic polyester other than polylactic acid has the following structure having a number average molecular weight of about 10,000 to 150,000. (In the formula, R ¹ and R ² are alkylene groups having 2 to 10 carbon atoms,
It is a cyclo ring group or a cycloalkylene group. Further, n is the degree of polymerization required to have a number average molecular weight of about 10,000 to 150,000. )