JPH10138433A - Gas barrier biaxially oriented poly-lactic acid film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide with a high degree of gas barrier characteristics, necessary for a packaging material, retaining transparency, tensile strength, thermal stability and the like, tender to environment while prominent in utility, by a method wherein the transparent thin film layer of silicon oxide is laminated on one side of a poly-lactic acid based polymer film, oriented biaxially with a specified magnification. SOLUTION: A gas barrier biaxially oriented film is formed by laminating the transparent thin film layer of silicon oxide on one side of poly lactic acid based polymer film, biaxially oriented into longitudinal and lateral directions with the magnification of 1.5 or more respectively. Poly-lactic acid based polymer includes polylactic acid homopolymer, copolymer composed primarily of poly-lactic acid having biodegradability and a mixture while copolymerizing constituents, forming the copolymer, are glycolic acid, 3-hydroxy butyric acid, 3-hydroxy valeric acid and the like. Either one of vacuum deposition method, spattering method and ion plating can be adopted as the method of forming the thin film layer of silicon oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched polylactic acid film having excellent transparency, tensile strength, thermal dimensional stability and gas barrier properties and suitable as a packaging material.

[0002]

2. Description of the Related Art At present, many plastic films including a biaxially stretched polyethylene terephthalate film are known as films excellent in transparency, tensile strength and thermal dimensional stability, and are widely used in the industrial world. Have been. However, when these films are discarded in a natural environment, they remain without being decomposed due to their stability, impair the landscape, and pollute the living environment of fish, wild birds and the like.

[0003] Therefore, there is a demand for a material made of a degradable polymer which does not cause these problems, and much research and development has been carried out. One example is polylactic acid. It is known that polylactic acid naturally undergoes hydrolysis in soil, does not remain in its original form in soil, and then becomes a harmless degradation product by microorganisms.

Therefore, a film made of polylactic acid, which is excellent in transparency, tensile strength and dimensional stability and which does not damage the environment at the time of disposal, has been proposed (Japanese Patent Laid-Open No. 7-207041).
No.) However, as a result of the study by the present inventors, it has been found that this film is inferior in gas barrier properties and cannot be used for packaging foods, pharmaceuticals, chemicals, and the like that require prevention of deterioration of the packaged contents.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a packaging material which imparts a high gas barrier property to a polylactic acid-based film having excellent transparency, tensile strength and thermal dimensional stability, and is environmentally friendly and excellent in practical use. The purpose of the present invention is to provide a film which is suitable for the following.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and the gist of the present invention is to provide a biaxial stretching method comprising a polylactic acid-based polymer, which is stretched 1.5 times or more in each of a longitudinal direction and a transverse direction. A gas-barrier biaxially stretched film, wherein a transparent thin film layer of silicon oxide is formed on one surface.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the present invention, the polylactic acid-based polymer is
In addition to polylactic acid (homopolymer), it includes copolymers and mixtures mainly composed of biodegradable polylactic acid. Lactic acid that forms polylactic acid includes L-lactic acid and D-lactic acid.
Either lactic acid or a mixture of both may be used. In addition, glycolic acid, 3
And hydroxycarboxylic acids such as -hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid and 6-hydroxycaproic acid.

As a polymerization method for obtaining polylactic acid, any of a condensation polymerization method and a ring-opening polymerization method can be adopted, and a small amount of a chain extender such as a diisocyanate compound is used for the purpose of increasing the molecular weight. , Diepoxy compounds, acid anhydrides and the like may be used.

The polylactic acid polymer has a weight average molecular weight of 1
If the molecular weight is too small, a film having a practically usable tensile strength cannot be obtained, and if the molecular weight is too large, the melt viscosity increases, making film formation difficult. Become.

In the present invention, the biaxially stretched film is obtained by forming a polylactic acid-based polymer into a flat unstretched sheet by a common melt molding method such as an extrusion method, and then forming this into a tenter-type simultaneous biaxial stretching method. Alternatively, it is obtained by biaxial stretching by a tenter-type sequential biaxial stretching method. Further, a biaxially stretched film can be formed by a tubular method in which an unstretched tube obtained by extruding a polylactic acid-based polymer into a cylindrical shape is simultaneously biaxially stretched.

[0012] The stretching ratio is determined in the longitudinal and transverse directions respectively.
It is necessary to make it 1.5 times or more, and if it is less than this range, the tensile strength becomes insufficient and the material becomes unsuitable as a packaging material.

After the stretching, the film is heat-treated at a temperature higher than the glass transition temperature and lower than the melting point to improve the dimensional stability of the film.

When used as a flexible packaging material, the thickness of the film may be generally selected from the range of 5 to 300 μm, and particularly preferably from the range of 10 to 50 μm.

In the present invention, the biaxially stretched film is
A transparent thin film layer of silicon oxide is formed on one side. As a method of forming the silicon oxide thin film layer, any of a vacuum deposition method, a sputtering method, and an ion plating method can be adopted. For example, in the case of a vacuum deposition method, using silicon monoxide or silicon dioxide as a deposition substance, under a vacuum of 10 ^-3 to 10 ^-5 Torr, an electron beam, high-frequency induction heating, heating and evaporating by a resistance heating method to perform evaporation. Just do it. Alternatively, a reactive evaporation method performed while supplying oxygen gas can be employed. In this case, metal silicon may be used as an evaporation material.

The silicon oxide may be one containing about 10% by weight or less of calcium, magnesium, or an oxide thereof as an impurity. It is not allowed.

The thickness of the silicon oxide thin film layer is 5 to 50 nm.
It is preferable to select within the range. If the thickness of this thin film layer is less than 5 nm, the gas barrier properties are insufficient, while
If it exceeds, curling occurs in the film or cracks or peeling occurs in the thin film layer, which is not preferable.

The film of the present invention may contain additives and modifiers such as plasticizers, lubricants, inorganic fillers and ultraviolet absorbers for the purpose of adjusting the formability and film properties. is there.

The film of the present invention is used as a packaging material or the like, if necessary, by coating or laminating a substance for improving heat sealability. Examples of the substance that improves the heat sealing property include low-density polyethylene, polypropylene, iomonomer, and ethylene-vinyl acetate copolymer.

[0020]

Next, the present invention will be described specifically with reference to examples. The measurement and evaluation were performed by the following methods. (1) Tensile strength The tensile strength was measured on a sample having a width of 10 mm and a length of 10 cm according to the measurement method of ASTM-D882. (2) Hot water shrinkage (dimensional stability) A 10 mm wide and 10 cm long sample was immersed in hot water at 80 ° C for 5 minutes.
The dimensional change before and after the treatment was measured and determined as a percentage of the original length. (3) Transparency Transparency was judged by the naked eye. (4) Oxygen permeability Using OX-TRAN 10-50A manufactured by Mordern Control, temperature
It was measured under the conditions of 20 ° C. and 65% RH. (5) Moisture permeability Measured under the conditions of a temperature of 40 ° C. and a humidity of 90% RH according to JIS Z 0208.

Example 1 Poly-L-lactic acid having a weight-average molecular weight of 100,000 was melted using a 50 mmφ extruder, extruded from a T-die into a sheet, and rapidly cooled with a casting roll to obtain an unstretched sheet having a thickness of 200 μm. Was. The end of this unstretched sheet is placed in a tenter-type
Hold the clips of the axial stretching machine, preheat at 50 ° C, and
After the simultaneous biaxial stretching at a stretching ratio of 3.0 times in the longitudinal direction and a 3.3 times in the transverse direction, the relaxation ratio in the transverse direction was set to 5%, and the temperature was 140 ° C.
After heat treatment for 10 seconds, the film was cooled and wound up by a winder to obtain a biaxially stretched film having a thickness of 200 μm. Next, the obtained biaxially stretched film is supplied to a vacuum evaporation apparatus, and 99.9% purity silicon monoxide (SiO) is heated and evaporated under a vacuum of 5 × 10 ⁻⁵ Torr by an electron beam heating method of 10 kw. On one side of the biaxially stretched film, a transparent thin film layer of silicon oxide having a thickness of 50 nm was formed.

Example 2 In Example 1, the stretching ratio was 2.0 times in the machine direction and 2.0 times in the transverse direction.
Except having made 2.0 times, it carried out similarly to Example 1.

Example 3 Example 1 was carried out in the same manner as in Example 1 except that the thickness of the silicon oxide thin film layer deposited on one side of the biaxially stretched film was 20 nm.

Example 4 Example 4 was carried out in the same manner as in Example 1 except that silicon dioxide (SiO ₂ ) was used instead of SiO as a deposition material.

Comparative Example 1 In Example 1, the stretching ratio was 1.2 times in the longitudinal direction,
Except having made it 1.2 times, it carried out similarly to Example 1.

Comparative Example 2 The procedure of Example 1 was repeated, except that aluminum (Al) was used instead of SiO as the deposition material.

Table 1 shows the results of evaluating the properties of the vapor-deposited biaxially stretched films obtained in the above Examples and Comparative Examples. In addition, the reference example shows the evaluation result of the biaxially stretched film in which the silicon oxide thin film layer is not formed in Example 1.

[0028]

[Table 1]

[0029]

According to the present invention, a polylactic acid-based film having excellent transparency, tensile strength and thermal dimensional stability can be provided with a high gas barrier property, and is environmentally friendly and excellent in practical use. A film suitable for the material can be obtained.

Claims (1)

[Claims] 1. A biaxially stretched film comprising a polylactic acid-based polymer and stretched 1.5 times or more in each of a longitudinal direction and a transverse direction, wherein a transparent thin film layer of silicon oxide is formed on one surface. A biaxially stretched gas barrier film characterized by the following.