JP3182077B2 - Biodegradable film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a film which decomposes in a natural environment and has excellent flexibility and transparency.

[0002]

2. Description of the Related Art Many conventional plastic products, especially 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 incineration. Furthermore, polyvinyl chloride, which is still used in large quantities, cannot be burned due to its self-extinguishing properties. In addition, plastic products including such non-combustible materials are often landfilled. However, they remain without being decomposed for chemical and biological safety and shorten the life of landfills. I'm offended. Therefore, the calorific value is low, it decomposes in soil,
What is desired is safe and much research has been done.

One example is polylactic acid. Polylactic acid has a heat of combustion less than half that of polyethylene, and hydrolyzes spontaneously in soil and water, and then becomes harmless degradation products by microorganisms. At present, studies are being made to obtain molded articles using polylactic acid, specifically, containers such as films, sheets and bottles. Polylactic acid is a polymer obtained by condensation polymerization of 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 having a ratio of L-lactic acid to D-lactic acid of about 80:20 to 20:80 does not have crystallinity, but becomes a transparent completely amorphous polymer that softens at a glass transition point of around 60 ° C. On the other hand, L-lactic acid alone or D-lactic acid
A homopolymer composed of only lactic acid has a glass transition point of about 60 ° C., but is a semicrystalline polymer having a melting point of 180 ° C. or higher. This semi-crystalline polylactic acid becomes an amorphous material having excellent transparency by being rapidly cooled immediately after being melt-extruded.

Polylactic acid is oriented uniaxially or biaxially to orient molecules, and then heat-treated to crystallize while suppressing 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 combining both used in the production of 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 cannot always be a suitable material. For example, even if the unstretched polylactic acid film or biaxially oriented polylactic acid film is formed into a bag and used as a bag, it is inferior in flexibility and easy to use as compared with existing plastic film bags such as polyethylene bags and polypropylene bags. Is bad.

On the other hand, a flexible biodegradable film includes 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 composed of a dicarboxylic acid component composed of succinic acid or adipic acid, or both, and an aliphatic polyester whose main structural unit is eletin glycol or butanediol, or a diol component composed of both. Such an aliphatic polyester has a glass transition point 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 quenched after melt extrusion and becomes opaque. The opacity of this film is high. Even when compared to polyethylene film and polypropylene film of similar thickness, even if the product is put in such an aliphatic polyester bag, the display effect such as the contents are not clear and the color of the contents become unclear Will be lost. Studies have been made to reduce the crystallinity by adjusting the dicarboxylic acid component and the diol component, and to slightly improve the transparency.However, if the crystallinity is too low, after extrusion, it is difficult to solidify even when cooled, and cast. Sticks to rolls, making it difficult to take off 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 a drawback of poor transparency, and improvement has been desired in any case. An object of the present invention has been made in consideration of the above problems, and an object of the present invention is to provide a biodegradable film which is easily decomposed in a natural environment, and has excellent flexibility and transparency.

[0007]

In order to solve the above-mentioned problems, a biodegradable film of the present invention comprises a polylactic acid-based polymer and an aliphatic polyester other than polylactic acid at 75:25 to 20: 8.
A film mixed at a weight ratio in the range of 0,
Tensile modulus of 250 kg / mm ² or less, light transmittance of 6
The aliphatic polyester has a number average molecular weight of about 10,000 to 150,000 and has the following structure. (Wherein R ¹ and R ² are an alkylene group having 2 to 10 carbon atoms,
It is a cyclocyclic group or a cycloalkylene group. Further, n is a degree of polymerization necessary for obtaining a number average molecular weight of about 10,000 to 150,000. If 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 is characterized in that a polylactic acid-based polymer and an aliphatic polyester other than polylactic acid are mixed in the above ratio, and a chelating agent and / or an acidic phosphate is not used. Further, the film of the present invention is an inflation film, and is characterized in that the blow ratio is formed in the range of 2.4 to 2.7.

[0008]

Embodiments of the present invention will be described below. As described above, polylactic acid has a structural unit of L
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 and a ring-opening polymerization method may be employed. For example, in the polycondensation method, L-lactic acid or D-lactic acid or a mixture thereof can be directly subjected to dehydration polycondensation to obtain polylactic acid having an arbitrary composition. In the ring-opening polymerization method, lactide, which is a cyclic dimer of lactic acid, can be used to obtain polylactic acid by using a selected catalyst while using a polymerization regulator and the like as necessary. 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 composed of L-lactic acid and D-lactic acid. Polylactic acid having any composition and crystallinity can be obtained by mixing and polymerizing accordingly. or,
Other hydroxycarboxylic acids 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 exhibited, and if it is more than this, the melt viscosity is too high and molding processability is poor.

Polymers comprising an aliphatic carboxylic acid component and an aliphatic alcohol component (hereinafter simply referred to as "aliphatic polyesters") can be obtained by directly polymerizing them to obtain a high molecular weight product, There is an indirect production 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 and dodecanoic acid, and anhydrides and derivatives thereof. On the other hand, as the aliphatic diol, glycol compounds such as ethylene glycol, butanediol, hexanediol, octanediol, and cyclohexanedimethanol, and derivatives thereof are generally used. Each is a compound having an alkylene group, a cyclocyclic group or a cycloalkylene group having 2 to 10 carbon atoms, and is produced by condensation polymerization. Two or more carboxylic acid components or alcohol components may be used. Further, for the purpose of providing a branch in the polymer for improving the melt viscosity, a carboxylic acid, alcohol or hydroxycarboxylic acid having three or more functionalities may be used. If these components are used in large amounts, the resulting polymer will have a crosslinked structure and will no longer be thermoplastic, or even if it is thermoplastic, a microgel with a partially highly crosslinked structure will be formed. There is a possibility that. Therefore, the proportion of these trifunctional or higher functional components in the polymer is very small, and is contained to such an extent that the chemical and physical properties of the polymer are not largely affected. 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 selecting the above compound and obtaining a high molecular weight substance while removing water contained in the compound or generated during the polymerization. As an indirect production method, similarly to 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.

The conditions for forming a film will be described. First, the mixing of the polylactic acid-based polymer and the aliphatic polyester other than polylactic acid is performed by charging the respective raw materials into the same extruder. There is a method in which the film is directly extruded from a die to directly produce a film, or a method in which the film is extruded into a strand shape to produce a pellet, and the film is again produced by an extruder. In any case, the reduction 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 by an extruder. The melt extrusion temperature 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 mixing ratio of the polylactic acid-based polymer and the aliphatic polyester other than polylactic acid is 75:25 to 20:80 by weight.
Is an important point in the present invention. In the film obtained when the content of the aliphatic polyester is less than 25%, the thickness of the plastic film used for the existing bag-like material is due to the hardness and brittleness derived from polylactic acid,
There is a problem that cracks and tears are likely to occur at the fold. Also, it is too hard to be practically used. The flexibility can be imparted by mixing the aliphatic polyester with the polylactic acid-based polymer. As a measure of flexibility, the tensile modulus is preferably set to about 250 kg / mm ² or less, more preferably about 200 kg / mm ² or less. Incidentally, in the existing general-purpose plastic bags, even a biaxially oriented polypropylene belonging to a hard class has a tensile modulus of about 250 kg / mm ² . Such flexibility can be achieved by mixing about 25% or more, depending on the type of aliphatic polyester other than polylactic acid.

Usually, aliphatic polyesters, particularly those having a glass transition point and a crystallization point below room temperature, have high crystallinity, crystallize at room temperature, develop spherulites inside, become cloudy, and become opaque. Become. However, the transparency can be improved at least to the extent of existing polyethylene and polypropylene films by mixing polylactic acid. Generally, when polymers with low compatibility are mixed,
Although the resulting molded article becomes more opaque, 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 is not improved, depending on the degree of dispersion of both polymers. This may be due to the intermolecular interaction of the two polymers, but is currently unknown. Although the transparency of the film depends on its use, the light transmittance is 65%.
% Is preferable. More preferably, when the content is 75% or more, further transparency can be provided. Depending on the thickness, the mixing ratio of the aliphatic polyester is 80%.
%, 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 obtained in a 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 rapidly cooled and solidified while being taken up by a rotating casting drum. Alternatively, the molten polymer is pulled up in a cylindrical shape from a round die, and air-cooled simultaneously with a balloon. A known method such as a so-called inflation method of forming a film by inflating the film may be used. In general, the latter has a slower cooling rate, tends to crystallize, and is disadvantageous to the transparency of the film. Water can be used instead of air to increase cooling efficiency.

The above embodiment is a non-stretched film excellent in transparency and heat resistance, but can be stretched if necessary. For example, when 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]

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

(Example 1) A polylactic acid (manufactured by Shimadzu Corp., trade name: Lacty) shown in Table 1 and an aliphatic polyester other than polylactic acid were mainly used by using a 25 mmφ coaxial small twin screw extruder. Polybutylene succinate (manufactured by Showa Polymer Co., Ltd., trade name: Bionole # 1001), which is a condensation polymer of 4-butanediol and succinic acid, was added in a ratio of 70: 3.
After mixing and melting at a ratio of 0, the mixture was extruded into a strand at 210 ° C. to produce a pellet. Next, using a 30 mmφ small single-screw extruder, melt-extrude from a 30 mmφ round die at 200 ° C., air-cool, and blow at 20μ with a blow ratio of 2.4.
An m-thick blown film was produced. The evaluation of the obtained film is shown in Table 1. (Example 2) Instead of the polybutylene succinate used in Example 1, polybutylene succinate / adipate obtained by copolymerizing mainly 1,4-butanediol, succinic acid and adipic acid (Showa Kogaku Co., Ltd.) It is shown in Table 1 in the same manner as in Example 1 except that the mixture was melted at a ratio of 70:30 using a company, trade name: Bionore # 3001), and then extruded into a strand shape at 200 ° C. to produce a pellet. A 20 μm thick blown film having a blow ratio of 2.5 was produced. (Examples 3 and 4) The mixing ratio of polylactic acid and polybutylene succinate / adipate was 50:50, 2 and 2, respectively.
Except that the ratio was 5:75, a film having a blow ratio of 2.7 in both cases was obtained in the same manner as in Example 2.

(Comparative Example 1) An inflation film shown in Table 1 was prepared in the same manner as in Example 2 except that only 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,
A blown film having a blow ratio of 3.1 and a thickness of 20 μm was produced. (Comparative Examples 3 and 4) Table 1 was prepared 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.
Was obtained.

[0018]

[Table 1]

In Examples 1 and 2, although it is slightly harder,
A film having flexibility and excellent transparency was obtained. The film obtained in Example 3 was excellent in transparency and obtained a flexible film. In addition, in Example 4, a film which was slightly inferior in transparency but excellent in flexibility was obtained. The films of these examples in which the blow ratio was in the range of 2.4 to 2.7 had a light transmittance of 68 to 85%, and all had no practical problems. On the other hand, Comparative Examples 1 and 3
Is excellent in transparency, but lacks flexibility.
Sample No. 4 was excellent in flexibility but insufficient in transparency.

[0020]

According to the present invention, it is possible to obtain a film having decomposability in a natural environment and having excellent flexibility and transparency.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 67/00-67/04

Claims (3)

(57) [Claims] 1. A film obtained by mixing a polylactic acid-based polymer and an aliphatic polyester other than polylactic acid in a weight ratio of 75:25 to 20:80, and having a tensile modulus of 25.
0 kg / mm ² or less, the light transmittance is in the range of 65 to 85%, and the aliphatic polyester other than the polylactic acid has the following structure having a number average molecular weight of about 10,000 to 150,000. Biodegradable film. (Wherein R ¹ and R ² are an alkylene group having 2 to 10 carbon atoms,
It is a cyclocyclic group or a cycloalkylene group. Further, n is a degree of polymerization necessary for obtaining a number average molecular weight of about 10,000 to 150,000. ) 2. The biodegradable film according to claim 1, wherein the film is produced without using a chelating agent and / or an acidic phosphate. 3. The film according to claim 1, wherein the film is a blown film having a blow ratio of 2.4 to 2.
7. A biodegradable film formed as the range of 7.