JP2006015723A - Biaxially stretched biodegradable film - Google Patents

Abstract

【Task】
To provide a polyester-based biaxially stretched biodegradable film that is excellent in stretch processability and low-temperature shrinkability, and further excellent in shrink packaging, such as packaging finish when a product is shrink-wrapped.
[Solution]
A polylactic acid polymer (A) is formed on both outer layers of the biodegradable laminated film, and a lactone is opened on the aliphatic-aromatic copolymer polyester resin (B) adjacent to the polylactic acid polymer (A) layer. By arranging a resin composition containing a cyclopolymerized aliphatic polyester-based resin (C), biaxial stretching that is excellent in stretch processability and low-temperature shrinkage, and that produces a beautiful package without the occurrence of corners and wrinkles. A biodegradable film can be obtained. Furthermore, an intermediate layer composed of a mixture (D) of an aliphatic polyester resin (C) obtained by ring-opening polymerization of an aliphatic-aromatic copolymer polyester resin (B) and a lactone is used as a polylactic acid polymer (A). Providing adjacent to the layer also has the effect of improving interlayer adhesion.
[Selection figure] None

Description

  The present invention relates to a heat-shrinkable polyester biaxially stretched film having biodegradability.

  Conventionally, a large amount of heat-shrinkable film has been used for shrink wrapping in the packaging field. Examples of the synthetic resin used for the heat-shrinkable film include polypropylene resins, polyethylene resins, vinyl chloride resins, and polystyrene resins. However, when heat-shrinkable films made of these synthetic resins are disposed in the natural environment after being used as a packaging material, they are not decomposed due to their chemical stability, and do not decompose in the natural environment for a long time. It remains and contributes to environmental pollution. In recent years, composting of garbage has been promoted from the viewpoint of reducing the amount of garbage, and shrink packaging using heat shrink films is frequently used for packaging food containers. However, when the film that has been broken to take out the packaged food container is thin and mixed with garbage, it is difficult to separate the garbage, which prevents the garbage from being composted.

Under such circumstances, a heat-shrinkable film is obtained from a biodegradable aliphatic polyester resin obtained by ring-opening polymerization of polylactic acid polymers or lactones or polycondensation of dicarboxylic acid and diol. An attempt is being made.
By using a polylactic acid polymer having suitable crystallinity, it is possible to obtain a heat-shrinkable film excellent in stretch processability, shrinkage and transparency, but the film is not flexible and is brittle and torn. There was a problem that it was easy. Although it is possible to add flexibility to the film by adding a plasticizer to the polylactic acid polymer, there is a problem that the packaged product is contaminated by the bleed-out plasticizer.
On the other hand, aliphatic polyester resins obtained by ring-opening polymerization of lactones or polycondensation of dicarboxylic acids and diols are more flexible than polylactic acid polymers, but have stretchability and transparency. There was a problem of being inferior.

Therefore, Patent Document 1 has both outer layers composed of polylactic acid (a) in which the composition ratio of L-lactic acid and D-lactic acid is 94: 6 to 79:21, and is mainly composed of an aliphatic polyhydric alcohol and an aliphatic group. At least one layer comprising an aliphatic polyester (b) synthesized from a dicarboxylic acid or a derivative thereof, or a mixture (c) of the polylactic acid (a) and the aliphatic polyester (b), Biodegradable heat obtained by stretching a multilayer film in which the weight ratio of (a) and aliphatic polyester (b) is (a) :( b) = 30: 70 to 75:25 in at least one direction A shrink laminate film is described. The biodegradable heat-shrinkable laminated film obtained by this configuration is excellent in transparency and heat-sealability, but the flexibility of the film is still not sufficient, and the corner part of the film is sufficient when shrink-wrapped. There is a problem that the so-called corners that are projected without being shrunk are left hard and a beautiful package cannot be obtained. Furthermore, the condition range that can be stretched is narrow and the low temperature shrinkability is poor, so the corners remain large, and if the corners are shrunk small, the film must be shrunk at a high temperature and the film is melted and whitened. There was also a problem of end.
JP 2001-47583 A

  The present invention has been made in view of such a situation, and is a polyester-based biaxially stretched biodegradable film that is excellent in stretch processability and low-temperature shrinkability, and further excellent in shrink packaging such as packaging finish when a product is shrink-wrapped. It is an issue to provide.

As a result of intensive studies, the inventors of the present application have found that both outer layers comprising a polylactic acid polymer (A) and an aliphatic polyester obtained by ring-opening polymerization of a lactone to the aliphatic-aromatic copolymer polyester resin (B). The present inventors have found that a biaxially stretched biodegradable film in which the above-mentioned problems are solved can be obtained by providing an intermediate layer composed of a resin composition blended with a system resin (C).
That is, the present invention
(1) The weight ratio of both outer layers composed of a polylactic acid polymer (A) and an aliphatic polyester resin (C) obtained by ring-opening polymerization of an aliphatic-aromatic copolymer polyester resin (B) and a lactone (B) :( C) = 90: 10-70: 30 biaxially stretched laminated film having an intermediate layer made of mixture (D),
A biaxially stretched biodegradable film characterized in that the shrinkage in the longitudinal direction and the transverse direction in glycerin is 30% or more at 90 ° C. and 50% or more at 110 ° C.,
(2) The biaxially stretched biodegradable film as described in (1) is provided, wherein the total thickness of the polylactic acid polymer (A) is 20 to 50% of the total thickness. The

  The biaxially stretched biodegradable film of the present invention is not only excellent in stretchability but also excellent in low temperature shrinkability and flexibility, so that when used for shrink wrapping, a beautiful package can be obtained in a wide range of packaging conditions. There is an effect that it is. Furthermore, an intermediate layer composed of a mixture (D) of an aliphatic polyester resin (C) obtained by ring-opening polymerization of an aliphatic-aromatic copolymer polyester resin (B) and a lactone is used as a polylactic acid polymer (A). Providing adjacent to the layer also has the effect of improving interlayer adhesion.

Hereinafter, the contents of the present invention will be described in detail.
In the present invention, a polylactic acid polymer (A) which is a homopolymer or copolymer of L-lactic acid or D-lactic acid, or a mixture of homopolymers is used. For example, poly L-lactic acid whose structural unit is L-lactic acid, poly D-lactic acid whose structural unit is D-lactic acid, poly LD-lactic acid which is a copolymer of L-lactic acid and D-lactic acid, and the like. .

Moreover, what was manufactured by conventionally well-known methods, such as a polycondensation method and a ring-opening polymerization method, can be used for the said polylactic acid-type polymer (A). For example, a polylactic acid polymer (A) having an arbitrary composition can be obtained by directly dehydrating polycondensation of L-lactic acid, D-lactic acid or a mixture thereof. In addition, in the ring-opening polymerization method, lactide, which is a cyclic dimer of lactic acid, is subjected to ring-opening polymerization in the presence of a predetermined catalyst and using a polylactic acid-based polymer having an arbitrary composition while using a polymerization regulator as necessary. A coalescence (A) is obtained. The lactide includes L-lactide, which is a dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid, and LD-lactide, which is a dimer of L-lactic acid and D-lactic acid, A polymer having any composition, that is, various crystallinity can be obtained by mixing them as necessary.
Poly LD-lactic acid occupies 90% or more of either one of the structural units constituting the main structure of L-lactic acid or D-lactic acid, and has crystallinity for expressing suitable stretch processability and heat shrinkability. Since it has, it is preferable. When either one of the structural units constituting the main structure of L-lactic acid or D-lactic acid is less than 90%, the heat resistance is inferior due to low crystallinity, and excessive heat is applied to the package when heat shrinks. , Because the film melts and whitens.

On the other hand, the aliphatic-aromatic copolymer polyester resin (B) used in the present invention is obtained by polycondensation of an aliphatic dicarboxylic acid and an aromatic dicarboxylic acid as a dicarboxylic acid component and an aliphatic diol as a diol component. Aliphatic-aromatic copolymer polyester resins can be mentioned. For example, an aliphatic-aromatic copolymer polyester resin obtained by polycondensation of adipic acid as an aliphatic dicarboxylic acid, terephthalic acid as an aromatic dicarboxylic acid, and 1,4-butanediol as an aliphatic diol is preferably used. The Furthermore, what has the ratio of a terephthalic acid as a dicarboxylic acid component of 30-60 mol% is utilized more suitably. When the proportion of terephthalic acid is more than 60 mol%, flexibility and biodegradability are deteriorated. On the other hand, when it is less than 30 mol%, film forming properties are deteriorated, which is not preferable.
Examples of the resin as described above include “Ecoflex” (trade name) commercially available from BASF.

  In the present invention, an aliphatic polyester obtained by ring-opening polymerization of a lactone is used. Examples of the cyclic monomer include ε-caprolactone, p-dioxanone, β-propiolactone, δ-valerolactone, α, α-dimethyl-β-propionlactone, β-ethyl-δ-valerolactone, α-methyl- ε-caprolactone, β-methyl-ε-caprolactone, γ-methyl-ε-caprolactone, 3,3,5-trimethyl-ε-caprolactone and the like, and aliphatic polyesters obtained by ring-opening polymerization of these are used. It is done. Among these, poly-ε-caprolactone obtained by ring-opening polymerization of ε-caprolactone is preferably used.

The biaxially stretched biodegradable film of the present invention has layers made of a polylactic acid polymer (A) on both outer layers. By using the polylactic acid polymer (A) for both outer layers, a biaxially stretched biodegradable film excellent in transparency and gloss can be obtained.
In the intermediate layer, the weight ratio of the aliphatic-polyester copolymer resin (B) and the aliphatic polyester resin (C) obtained by ring-opening polymerization of lactones is (B) :( C) = 90. The layer which consists of a mixture (D) which is: 10-70: 30 is provided.
When the proportion of the aliphatic polyester resin (C) obtained by ring-opening polymerization of the lactone compounded in the aliphatic-aromatic copolymerized polyester resin (B) is more than 30% by weight, stretch processability, low temperature shrinkage and flexibility When shrinkage packaging is performed, the corners become hard and a beautiful package cannot be obtained, and the transparency is also lowered, which is not preferable. On the other hand, if it is less than 10% by weight, peeling between the polylactic acid polymer (A) layer and the mixture (D) layer occurs when shrinking, which is not preferable.

Next, the layer structure of the biaxially stretched biodegradable film of the present invention will be described.
Both outer layers comprising a polylactic acid polymer (A), and a mixture (D) of an aliphatic-aromatic copolymerized polyester resin (B) and an aliphatic polyester resin (C) obtained by ring-opening polymerization of lactones. As long as the intermediate layer is provided, the layer structure is not particularly limited. For example, a three-layer structure of (A) / (D) / (A) may be used, or (A) / (D) / (B) / (D) / (A) or (A) / (D) / ( A five-layer structure such as A) / (D) / (A) may be used.
A mixture (D) of an aliphatic-aromatic copolymer polyester resin (B) and an aliphatic polyester resin (C) obtained by ring-opening polymerization of lactones is used as the outer layer, and a polylactic acid polymer (A) is used as the intermediate layer. When the layer structure of (D) / (A) / (D) provided in is used, transparency and gloss are deteriorated. The biaxially stretched film of the present invention is used for shrinkage packaging of products, and prevents the product from being contaminated by dust and the like, and has the purpose of enhancing display effect by performing shrinkage packaging, and is inferior in transparency and gloss. Since a sufficient display effect cannot be obtained with a film, a layer structure such as (D) / (A) / (D) is not preferable.

In addition, the intermediate layer composed of the mixture (D) of the aliphatic-aromatic copolymer polyester resin (B) and the aliphatic polyester resin (C) obtained by ring-opening polymerization of lactones is a polylactic acid polymer ( A) is preferably provided so as to be adjacent to both outer layers.
A polylactic acid polymer (A) and an aliphatic group are formed on an intermediate layer mainly composed of an aliphatic-aromatic copolymer polyester resin (B) provided adjacent to the polylactic acid polymer (A) layer. A polylactic acid polymer which originally has poor compatibility by blending an aliphatic polyester resin (C) obtained by ring-opening polymerization of a lactone having good compatibility with the aromatic copolymer polyester resin (B). Interlayer adhesion between (A) and aliphatic-aromatic copolymer polyester resin (B) is improved, and when the biaxially stretched biodegradable film is shrunk, it peels due to strain between the layers due to the difference in shrinkage behavior of the two Does not occur.
When an aliphatic polyester resin having biodegradability other than the aliphatic polyester resin (C) obtained by ring-opening polymerization of lactones is blended, the interlayer adhesiveness with the polylactic acid polymer (A) layer is improved. No improvement was found.

In the biaxially stretched biodegradable film of the present invention, the total thickness of the layers made of the polylactic acid polymer (A) is preferably 20 to 50% of the total thickness. If the thickness of the layer made of the polylactic acid polymer (A) is greater than 50%, the Young's modulus of the obtained film becomes 1600 MPa or more, the flexibility is lowered, and the film does not shrink when shrink-wrapping is performed. This is not preferable because the remaining corner portion becomes harder. On the other hand, when the thickness of the layer made of the polylactic acid polymer (A) is less than 20%, the flexibility of the film is increased, but the slipping property is deteriorated, the hand link at the time of film formation is poor, and the productivity is remarkably reduced. Absent.
The thickness of the biaxially stretched biodegradable film of the present invention is preferably 5 to 300 μm. When used for soft packaging applications, the thickness is more preferably 10 to 50 μm.

In addition, the biodegradable biaxially stretched film of the present invention has a stretching temperature, a stretching ratio, etc. so that the shrinkage in the longitudinal direction and the transverse direction in glycerin is 30% or more at 90 ° C. and 50% or more at 110 ° C. It is necessary to select the stretching process conditions.
If the shrinkage rate in glycerin is 30% or higher at 90 ° C., that is, excellent in low-temperature shrinkability, the film shrinkage temperature can be set low during shrink wrapping, and the heating time can be set short, so it is easily altered by heat. It is suitably used for packaging an article to be packaged. The shrinkage rate in glycerin at 110 ° C. shows a value close to the final shrinkage rate of the film. If this value is less than 50%, the corner portion of the film does not shrink sufficiently when it is shrink-wrapped, and it forms a hard protrusion. A so-called corner is formed, or a portion in contact with the package body is not sufficiently contracted and wrinkles are generated, so that a beautiful package body cannot be obtained.

  In addition, the biaxially stretched biodegradable film of the present invention has an antioxidant, an ultraviolet absorber, a light stabilizer, a lubricant, an antiblocking agent, a tackifier, an antifogging agent as long as the object of the present invention is not impaired. Conventional additives such as an agent, an antistatic agent and various fillers may be blended.

  The biaxially stretched biodegradable film of the present invention is produced by a conventionally known method. For example, it can be manufactured by simultaneously biaxially stretching a tube-shaped unstretched film obtained by extruding each resin from a plurality of extruders equipped with a circular die. It can also be produced by simultaneously biaxially or sequentially biaxially stretching a flat unstretched film obtained by extruding each resin from a plurality of extruders equipped with T-shaped dies with a tenter stretching machine. it can.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited by the matter described below. In addition, the evaluation method in this invention is as follows.

[Heat shrinkage]
The film is cut to produce a 100 mm square test piece for both MD (longitudinal direction) and TD (lateral direction). After immersing this test piece in glycerin set at 90 ° C. and 110 ° C. for 30 seconds, the MD and TD dimensions (L) of the test piece are measured, and the shrinkage is calculated using the following equation.
Shrinkage rate (%) = 100 × (100−L) / 100 [L: length of test piece after being immersed in glycerin set to a predetermined temperature for 30 seconds (mm)]
[Transparency (haze)]
Based on ASTM D 1003, measurement is performed with HM-150 manufactured by Murakami Color Research Laboratory.
[Glossy]
Measured with GM-26PRO manufactured by Murakami Color Research Laboratory Co., Ltd. according to ASTM D 2457.
[Young's modulus]
Measurement is performed at a tensile speed of 50 mm / min according to ASTM D882.
[Film forming properties]
Stretch processability and productivity when producing a biaxially stretched biodegradable film were comprehensively evaluated based on the following criteria.
○: Good
×: Defect
[Packing finish]
Cylinder-shaped adhesive tape 11cm in diameter and 5cm in height wrapped with various films is heated and shrunk in a hot air tunnel set at 130 ° C for 5 seconds. Was evaluated sensuously.
○: Good
×: Defect
[Peelability]
The state of delamination of the test piece after being immersed in glycerin at 90 ° C. for 10 seconds was evaluated based on the following criteria.
○: No peeling △: Some peeling
X: Completely peeled between layers

The following resins were used in Examples and Comparative Examples.
<Polylactic acid polymer>
Polylactic acid composed of L-lactic acid: 96% and D-lactic acid: 4% (trade name: Lacia H440, density: 1.25 g / cm3, manufactured by Mitsui Chemicals, Inc.).
<Aliphatic-aromatic polyester resin>
Polybutylene adipate terephthalate copolymer (BASF, trade name: Ecoflex FBX7011, density: 1.26 g / cm3), which is a copolymer of 1,4-butanediol, adipic acid and terephthalic acid. Abbreviated.
<Aliphatic polyester obtained by ring-opening polymerization of lactones>
Poly-ε-caprolactone (manufactured by Dow Chemical Co., Ltd., trade name: TONE-P-767, density: 1.15 g / cm 3).
<Aliphatic polyester resin>
Polybutylene succinate adipate copolymer which is a copolymer of 1,4-butanediol, adipic acid and succinic acid (manufactured by Showa Kogyo Co., Ltd., trade name: Bionore # 3001, density: 1.26 g / cm 3 ··· Abbreviated as PBSA.

[Examples 1 to 4]
PLA containing 200 ppm of erucic acid amide (lubricant) was used as both outer layers, and a resin composition in which PCL was blended with PBAT was used as an intermediate layer. The above composition was supplied to a multilayer tubular stretching machine equipped with three extruders and a downward circular die, and after extrusion, the composition was immediately cooled with 20 ° C. water to obtain a tubular three-layer unstretched film. Next, the unstretched film was heated to 80 ° C. in a preheating furnace, and then simultaneously biaxially stretched at a magnification of 4.0 times in both the longitudinal and horizontal directions in a stretching furnace maintained at 80 ° C. The stretched film thus obtained is as shown in Table 1. The performance evaluation results of the obtained biaxially stretched biodegradable film are also shown in Table 1.

[Comparative Example 1]
A biaxially stretched biodegradable film was obtained in the same manner as in Example 2 except that the intermediate layer was PBAT.
[Comparative Example 2]
A biaxially stretched biodegradable film was obtained in the same manner as in Example 2 except that the resin blended in the intermediate layer PBAT was PBSA.
[Comparative Example 3]
A stretched film was obtained in the same manner as in Example 2 except that the resin composition in which PCL was blended with PBAT was used as both outer layers, and PLA containing 200 ppm of erucic acid amide (lubricant) was used as the intermediate layer.
[Comparative Examples 4 and 5]
A biaxially stretched biodegradable film was obtained in the same manner as in Examples 1 to 3 except that the ratio of PCL to be blended with PBAT was changed.
[Comparative Examples 6 and 7]
A biaxially stretched biodegradable film was obtained in the same manner as in Example 2 except that the thickness ratios of both outer layers were changed.
About the obtained stretched film, performance evaluation was performed similarly to the Example, and the result is shown in Table 2.

  In Examples 1 to 4, a biaxially stretched biodegradable film that is excellent in transparency, gloss, flexibility, shrinkage properties, film-forming properties, packaging finish of shrink-wrapping, and does not cause delamination when shrunk is obtained. However, Comparative Examples 1, 2 and 4 were inferior in interlayer adhesion, Comparative Example 3 was inferior in transparency, gloss and film forming property, and Comparative Examples 5 and 6 were in film forming property and packaging. Only inferior finish and comparative example 7 were inferior in flexibility.

  In the above examples and comparative examples, attention was paid to the transparency, gloss, heat shrinkability, film-forming property, and packaging finish of the obtained samples, but the biodegradability and heat sealability were not mentioned. In view of the characteristics of the two synthetic resins used in the present invention, it is obvious that the biaxially stretched biodegradable film has complete biodegradability and heat sealability.

  The biaxially stretched biodegradable film of the present invention not only has excellent stretchability and low-temperature shrinkability, but also has no flexibility and flexibility, which is a defect of a film made of a polylactic acid-based polymer. Therefore, if used for shrink wrapping, the corners of the film will not be sufficiently shrunk when shrink wrapping, so that they become hard protrusions, so that the film does not break from the corners and pinholes for air venting. It becomes possible to obtain a beautiful package in the packaging condition range.

Claims (2)

The weight ratio of the outer layer made of the polylactic acid polymer (A), the aliphatic polyester resin (C) obtained by ring-opening polymerization of the aliphatic-aromatic copolymer polyester resin (B) and the lactone is (B ): (C) = 90: 10 to 70:30 Biaxially stretched laminated film having an intermediate layer made of the mixture (D),
A biaxially stretched biodegradable film characterized by having a shrinkage in the longitudinal and transverse directions in glycerin of 30% or more at 90 ° C and 50% or more at 110 ° C.   2. The biaxially stretched biodegradable film according to claim 1, wherein the total thickness of the layers made of the polylactic acid polymer (A) is 20 to 50% of the total thickness.