JP2005007610A - Biodegradable multilayered heat-shrinkable film and package - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biodegradable multilayered heat-shrinkable film having biodegradability and excellent in heat shrinkability, easy cutting properties, impact resistance, heat sealability and transparency, and a shrink package tensioned in close contact with an article to be packaged by the heat shrinkage of the packaging film, which is sealed using the heat-shrinkable film, adapted to the covering of the article to be packaged. <P>SOLUTION: The biodegradable multilayered heat-shrinkable film comprises a polylactic acid resin (A) and a biodegradable polyester (B) with a glass transition temperature Tg of 10°C or below other than the resin (A) and is characterized in that the heat shrinkage factor of the film is 20% or above in both of the longitudinal direction (MD direction) and width direction (TD direction) of the film, the tear strength of the film is 10-200 mN in both of the longitudinal direction (MD direction) and width direction (TD direction) of the film, the impact strength of the film per a unit thickness is 20 mJ/μm or above, the seal strength of the film is 10 N/15 mm width and the haze of the film is below 30%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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【発明の効果】
本発明の生分解多層性熱収縮フィルムは、ポリ乳酸系樹脂（Ａ）と、ガラス転移温度が１０℃以下である（Ａ）以外の生分解性ポリエステル（Ｂ）とからなるため、生分解性を有し、熱収縮性、易カット性、耐衝撃性、ヒートシール性と透明性に優れるので、生分解性多層熱収縮性フィルムとして有用である。また、このフィルムを用いてシールした包装フィルムで被包装物を覆い、熱収縮によって被包装物に密着して緊張されたシュリンク包装体は、ＭＤ方向、ＴＤ方向の両方に十分な収縮率を有し、フィルムが十分に被包装物の形状に追随して収縮し美麗なシュリンク包装体となる。
【図面の簡単な説明】
【図１】フィルム断面写真の撮影位置を説明した図
【図２】実施例８のフィルムのＴＤ断面の第二層部分の電子顕微鏡写真
【図３】実施例８のフィルムのＭＤ断面の第二層部分の電子顕微鏡写真[0001]
BACKGROUND OF THE INVENTION
The present invention provides a biodegradable multilayer heat-shrinkable film comprising a polylactic acid resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature of 10 ° C. or less, and thereby More specifically, the present invention relates to a packaged shrink package, and more specifically, a heat-shrinkable, easy-cut, impact-resistant, heat-sealable and transparent multi-layer heat-shrinkable film and The present invention relates to a shrink wrapping body that is covered and sealed with a wrapping film that has been used and is tightly adhered to and tensed by heat shrinkage.
[0002]
[Prior art]
Shrink wrapping is a container with lids for lunch containers and sugar beet containers, for example, because the packaging film is not bulky in close contact with the object to be packaged, and can be packaged beautifully without wrinkles in various shapes. It is used as a package in a wide range of fields such as trays without lids for meat, fresh meat, fresh vegetables, etc., food packaging such as cup ramen, and toys and daily goods.
[0003]
Moreover, as a packaging film used for this shrink package, a polyolefin resin film is generally used. Further, these shrink wrapping films and shrink wrapping bodies using the same are disclosed in JP-A-9-216956 and the like. However, these conventionally used polyolefin resin films are films that do not have biodegradability.
Synthetic polymer compounds have been widely used as plastics due to their excellent properties, but the amount of waste has increased with the increase in the amount of use, and how to treat this waste plastic is a big society. It is a problem. When incinerated, there is a problem that the incinerator is likely to be damaged because it generates a large amount of heat, and there is a risk that harmful substances may be generated. Furthermore, it is difficult to quickly disseminate recycling considering the cost of separation / collection and regeneration.
[0004]
Amid these growing environmental problems, biodegradable plastics that decompose in the natural environment after disposal are being demanded in order to reduce environmental impact and make society sustainable. Yes.
Biodegradable plastics known so far include starch polymers, aliphatic polyester resins produced by microorganisms, aliphatic polyester resins by chemical synthesis, and types of chemical structures that have been partially modified. Resins, biodegradable aliphatic aromatic polyester resins and the like are known.
[0005]
Among these biodegradable plastics, polylactic acid resin is superior in transparency and rigidity compared to other biodegradable plastics, but the stretched film is particularly stiff and excellent in transparency. Although it is suitable as various packaging films, a film suitable for shrink wrapping, which is in close contact with a packaged object due to heat shrinkage and has been tensioned, has not yet been obtained. In particular, in order to be able to wrap packages with different shapes in a beautiful manner without wrinkles, heat shrinkage is sufficient in both the longitudinal direction (hereinafter abbreviated as MD direction) and the width direction (hereinafter abbreviated as TD direction) of the film. Otherwise, the film cannot sufficiently shrink following the shape of the object to be packaged, and the remaining beautiful packaging cannot be performed.
[0006]
Regarding a heat-shrinkable film having biodegradability, JP-A-5-212790 discloses a film made of a polylactic acid-based resin composition, which is a shrink film for a label and is 38% in a uniaxial direction. The shrinkage is ˜83%, and the shrinkage rate is 13% or less in the direction perpendicular thereto, which is not suitable for the shrink packaging intended in the present invention.
Japanese Patent Application Laid-Open No. 7-267553 discloses a heat-shrinkable polylactic acid film having a specific degree of plane orientation and a difference between the heat of crystal fusion and the heat of crystallization of less than 20 J / g. With high shrinkage in both the TD directions, the film sufficiently shrinks following the shape of the object to be packaged. It does not break strongly against external impacts during packaging, and has an easy-cut property that can be easily opened when opened. In addition, a film that can be packaged beautifully so that the packaged article can be clearly seen has not yet been obtained.
[0007]
In addition, when a film is used in a bag shape, heat sealing is generally used in an ordinary bag making machine, and the heat sealability of the film is very important. Further, heat sealing properties are essential for sealing a packaged general packaging film. In the case of a pneumatic cushion bag, the seal strength directly affects the buffer performance, so that the seal strength is required simultaneously with the film strength.
JP-A-8-323946 discloses that the sealing property can be improved by using a biodegradable resin having a melting point of 10 ° C. or more lower than the melting point of the polylactic acid film as the sealing layer. There is no disclosure of a film excellent in shrinkage, easy cutability, impact strength, and transparency. Japanese Patent Application Laid-Open No. 10-1003003 is excellent in transparency and heat sealability by laminating a non-stretched biodegradable aliphatic polyester film different from a polylactic acid polymer on a polylactic acid stretched film. Although providing a film is disclosed, it does not disclose a film that is excellent in heat shrinkability, easy cutability, and impact resistance strength as well as sealing properties and transparency.
[0008]
In addition, what is disclosed in the examples of the above publication is a heat shrink film made of a biaxially stretched film by a flat method, and a polylactic acid resin heat shrink film by a tubular method is not disclosed.
In addition, the film formation technique by the flat method has less unevenness of film thickness compared to the tubular method, can increase the production amount per unit time, and if the film thickness is thick, it cannot be formed without the flat method. This is advantageous compared to the tubular method, but the construction cost is several times higher than that of the tubular method, and is suitable for mass production of small varieties, but the film market is relatively small. The tubular method becomes economically advantageous when it is necessary to produce a variety of products in small quantities and when the thickness is reduced and the tubular method can be applied.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-216956
[Patent Document 2]
JP-A-5-212790
[Patent Document 3]
JP-A-7-256653
[Patent Document 4]
JP-A-8-323946
[Patent Document 5]
JP-A-10-1003003
[0010]
[Problems to be solved by the invention]
The present invention provides a biodegradable multilayer heat-shrinkable film comprising a polylactic acid resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature of 10 ° C. or less, and thereby The purpose of the present invention is to provide a packaged shrink package, and more specifically, a heat-shrinkable, easy-cut, impact-resistant, heat-sealable and transparent multi-layer with biodegradability. It is an object of the present invention to provide a shrink wrapping body in which a package is covered with a heat-shrinkable film and a packaging film sealed using the film, and is tightly adhered to the package by heat shrinkage.
[0011]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have surprisingly found that the biodegradable polyester other than the polylactic acid resin (A) and (A) having a glass transition temperature of 10 ° C. or less. (B) is blended so as to have a specific composition, and is coextruded and stretched so as to have at least one sealing layer, thereby being excellent in heat shrinkage rate, tear strength, impact strength, transparency, and A beautiful shrink wrapping where it was found that a biodegradable multilayer heat-shrinkable film having excellent heat-sealability could be obtained, and the package packaged with this film was tightly attached to the package by heat shrinkage. The present invention was completed by finding the body.
[0012]
That is, the present invention is as follows.
(1) A film comprising a polylactic acid-based resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or less, which is heated at 140 ° C. for 30 minutes. The thermal shrinkage is 20% or more in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, and the tear strength measured by JIS K 7128 (Method B) is the longitudinal direction (MD direction) and width of the film. The direction (TD direction) is in the range of 10 to 200 mN, the impact strength measured in accordance with ASTM D 1709-91 (A method) is 20 mJ / μm or more per unit thickness, and the seal is in accordance with JIS Z-1707 method Haze measured by a turbidimeter (ASTM D 1003-95) when the seal strength is 10 N / 15 mm width or more when heat sealed under conditions of a pressure of 0.5 MPa and a sealing time of 0.2 seconds Biodegradable multi-layer heat-shrinkable film Haze) is equal to or less than 30%.
[0013]
(2) Tear strength measured by JIS K 7128 (Method B), in which the thermal shrinkage ratio at the time of heating at 140 ° C. for 30 minutes is 30% or more in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film. Is in the range of 10 to 150 mN in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, and the impact strength measured in accordance with ASTM D 1709-91 (Method A) is 30 mJ / μm per unit thickness. Above, the seal strength when heat-sealed under the conditions of seal pressure 0.5 MPa and seal time 0.2 seconds in accordance with JISZ-1707 method is 15 N / 15 mm width or more and a turbidimeter (ASTM D 1003-95) The biodegradable multilayer heat-shrinkable film according to (1), wherein the haze measured in (1) is less than 25%.
[0014]
(3) The thermal shrinkage rate during heating at 140 ° C. for 30 minutes is 40% or more in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, and conforms to ASTM D 1709-91 (A method). The measured impact strength is 40 mJ / μm or more per unit thickness, and the seal strength is 20 N / 15 mm width or more when heat-sealed under the conditions of a seal pressure of 0.5 MPa and a seal time of 0.2 seconds in accordance with JIS Z-1707 method. And the haze measured by a turbidimeter (ASTM D 1003-95) is less than 20%, the biodegradable multilayer heat-shrinkable film according to (2).
[0015]
(4) Weight ratio (A) :( B) of polylactic acid resin (A) and biodegradable polyester (B) other than (A) whose glass transition temperature Tg is 10 ° C. or less is 95: 5 The biodegradable multilayer heat-shrinkable film according to any one of (1) to (3), which is within a range of 40:60.
(5) In the polylactic acid resin (A) phase matrix, 90% or more of the biodegradable polyester (B) phase domain other than (A) having a glass transition temperature Tg of 10 ° C. or less is in the form of a plate There are a large number of phase-separated layers, the plate-like domains are substantially parallel to the film surface, and the plate domain has an average thickness of 5 nm to 100 nm. The biodegradable multilayer heat-shrinkable film according to any one of (1) to (4), comprising at least one.
[0016]
(6) Extruded from a cylindrical multilayer die containing at least one mixed resin of polylactic acid resin (A) and biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or lower. A first bubble is formed with a multilayer molten resin, the resin is cooled to a glass transition temperature Tg + 20 ° C. or lower of the polylactic acid resin (A), and then the resin is melted again to a melting point higher than Tg of the polylactic acid resin (A). A method for producing a biodegradable multilayer heat-shrinkable film, wherein the film is heated to a temperature of Tm or less to form a second bubble and is subjected to tubular stretching.
(7) Use of the biodegradable multilayer heat-shrinkable film according to any one of (1) to (5) for a shrink package.
[0017]
[Embodiments of the Invention]
The present invention will be specifically described below.
An example of the process for obtaining the shrink package of the present invention from the biodegradable multilayer heat-shrinkable film of the present invention is as follows.
First, the article to be packaged is covered with a sealed packaging film having a margin of 5 to 50% with respect to the length in the vertical and horizontal directions of the article to be packaged. Either a pillow shrink or an L-shaped package may be used as a method of covering an object to be packaged with a packaging film. Here, the length in the vertical direction of the package is the length of one half of the circumference of the package in the flow direction when the package is passed through the packaging machine. Is the length of the circumference of the packaged object in the direction perpendicular to the vertical direction, and the margin of 5-50% means that the film length between the seals is the aforementioned packaged object 5 to 50% longer than the length.
[0018]
The reason why the margin is set to 5 to 50% is that there are various shapes such as a conical shape, a truncated cone shape, and an irregular shape with protrusions in addition to a rectangular parallelepiped shape or a cubic shape. If the margin ratio is less than 5%, the stress concentrates on the seal portion and the air vent small holes at the time of contraction, and seal peeling or tearing may occur. On the other hand, if it is larger than 50%, it tends to be difficult to obtain a tensioned shrink wrapping body that is in close contact with the object to be packaged, so that it does not become a beautiful shrink wrapping body. Easy to wake up.
The seal may be selected from ordinary sealing methods such as impulse sealing, heat sealing, and fusing sealing according to the packaging film to be used, and these sealing methods may be combined.
[0019]
Secondly, when packaging the entire package, the air inside is trapped in the packaging film during heat shrinkage, preventing the shrinkage. A shrink package that is in close contact with the object and is tensed. The air vent small hole can be opened using a needle, a hot needle, a laser, or the like, but this step may be performed before the first sealing step. Moreover, when not wrapping a to-be-packaged object completely, for example, when winding a packaging film in a strip shape, it is not necessary to make a small hole for removing air. For heat shrinkage, hot air, steam or the like can be used, but hot air which does not require post-treatment is preferable.
[0020]
Next, the film of the present invention will be described.
The film of this invention consists of polylactic acid-type resin (A) and biodegradable polyester (B) other than (A) whose glass transition temperature is 10 degrees C or less. The polylactic acid-based resin is a polylactic acid homopolymer and a copolymer containing 50% by weight or more of lactic acid monomer units. The polylactic acid homopolymer, lactic acid, and other hydroxycarboxylic acids and lactones are used. It is a copolymer with a compound selected from the group consisting of When the content of the lactic acid monomer unit is less than 50% by weight, the heat resistance and transparency of the film tend to be lowered. Preferably, it is a copolymer containing 80% by weight or more of lactic acid monomer units or a mixture thereof, more preferably a copolymer containing 90% by weight or more of lactic acid monomer units or a copolymer thereof. It is a mixture.
[0021]
Lactic acid has L-lactic acid and D-lactic acid as optical isomers, and polylactic acid obtained by polymerizing them contains about 10% or less of D-lactic acid unit and about 90% or more of L-lactic acid unit, Or a polylactic acid having an L-lactic acid unit of about 10% or less and a D-lactic acid unit of about 90% or more, an optical purity of about 80% or more, and a D-lactic acid unit of 10% to 90% It is known that there are polylactic acid having an L-lactic acid unit of 90% to 10% and amorphous polylactic acid having an optical purity of about 80% or less. The polylactic acid resin (A) used in the present invention is particularly preferably a crystalline polylactic acid having an optical purity of 85% or higher alone, or a crystalline polylactic acid having an optical purity of 85% or higher and a non-crystalline liquid having an optical purity of 80% or lower. A mixture comprising crystalline polylactic acid.
[0022]
As a monomer used as a copolymerization component with lactic acid, as hydroxycarboxylic acid, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid Etc. Examples of the aliphatic cyclic ester include glycolide, lactide, β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, and lactones substituted with various groups such as a methyl group. Dicarboxylic acids include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, isophthalic acid, etc., and polyhydric alcohols include aromatic polyhydric alcohols such as bisphenol / ethylene oxide addition products, ethylene Glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, neopentyl glycol and other aliphatic polyhydric alcohols, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol and other ether glycols, etc. Can be mentioned.
[0023]
As a polymerization method of the polylactic acid resin (A), known methods such as a condensation polymerization method and a ring-opening polymerization method can be employed. Moreover, the method of increasing molecular weight using binders, such as a polyisocyanate, a polyepoxy compound, an acid anhydride, and polyfunctional acid chloride, can also be used.
The weight average molecular weight of the polylactic acid resin (A) is preferably in the range of 10,000 to 1,000,000. If the molecular weight is less than 10,000, the mechanical properties of the film tend to decrease. If it exceeds 1,000,000, the melt viscosity becomes high, and it becomes difficult to obtain a film having stable physical properties by a normal processing machine.
[0024]
The biodegradable polyester (B) other than (A) having a glass transition temperature of 10 ° C. or less used in the present invention is an aliphatic polyester or cyclic lactone obtained by polycondensation of an aliphatic dicarboxylic acid and an aliphatic diol as main components. Polyesters, ring-opening-polymerized aliphatic polyesters, synthetic aliphatic polyesters, aliphatic polyesters such as poly (hydroxyalkanoic acid) biosynthesized in bacterial cells, and some of these biodegradable polyesters are biodegradable. It is at least one selected from aliphatic aromatic polyesters having a structure substituted with an aromatic compound within a range not lost, and has a glass transition temperature Tg of 10 ° C. or less in differential scanning calorimetry (JIS-K-7121). A polymer composition comprising one or more biodegradable polyesters of preferably 0 ° C. or lower, more preferably −20 ° C. or lower. That. When the Tg of the biodegradable polyester (B) exceeds 10 ° C., the effect of improving the impact resistance of the obtained film is often not exhibited.
[0025]
Aliphatic polyesters obtained by polycondensation of aliphatic dicarboxylic acid and aliphatic diol as main components include aliphatic carboxylic acids such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid and dodecanedioic acid (raw (Aromatic carboxylic acids such as terephthalic acid and isophthalic acid may be included as long as the degradability is not hindered)), ethylene glycol, 1,3-propion glycol, 1,4-butanediol, 1,4-cyclohexanedimethano An example is polycondensation selected from one or more aliphatic diols such as Examples of aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones include ring-opening polymers selected from one or more cyclic monomers such as ε-caprolactone, δ-valerolactone, and β-methyl-δ-valerolactone. Can be mentioned. Examples of synthetic aliphatic polyesters include copolymers of succinic anhydride, cyclic acid anhydrides such as ethylene oxide and propylene oxide, and oxiranes.
[0026]
In addition, as poly (hydroxyalkanoic acid) biosynthesized in the microbial cells, poly (3-hydroxybutyric acid), poly (3-hydroxypropionic acid), poly (3-hydroxyvaleric acid), poly (3-hydroxybutyric acid) -3-hydroxyvaleric acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxyhexanoic acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxypropionic acid) copolymer, poly (3-hydroxy Examples include butyric acid-4-hydroxybutyric acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxyoctanoic acid) copolymer, poly (3-hydroxybutyric acid-3-hydroxydecanoic acid) copolymer, and the like. .
[0027]
Examples of the aliphatic aromatic polyester include polybutylene succinic acid phthalic acid copolymer, polyethylene succinic acid phthalic acid copolymer, polybutylene adipic acid phthalic acid copolymer, polyethylene adipic acid phthalic acid copolymer, and polyethylene glutar. Examples include acid terephthalic acid copolymer, polybutylene glutaric acid terephthalic acid copolymer, polybutylene succinic acid adipic acid phthalic acid copolymer, and the like.
What is particularly preferably used as the biodegradable polyester (B) having a glass transition temperature Tg of 10 ° C. or less used in the present invention is one having 2 to 10 carbon atoms, which is considered to have relatively good transparency. An aliphatic polyester obtained by polycondensation of an aliphatic dicarboxylic acid and an aliphatic diol having 2 to 10 carbon atoms as main components. Specific examples thereof include polyethylene adipate, polypropylene adipate, polybutylene adipate, polyhexene adipate, poly Examples include butylene glutarate, polybutylene succinate, polybutylene succinate adipate, and the like.
[0028]
As a polymerization method of the biodegradable polyester (B), known methods such as a direct method and an indirect method can be employed. In the direct method, for example, polycondensation is performed by selecting the dicarboxylic acid compound anhydride or derivative thereof as the aliphatic dicarboxylic acid component, and selecting the diol compound or derivative thereof as the aliphatic diol component and performing polycondensation. A high molecular weight product can be obtained while removing the water generated at the time. The indirect method can be obtained by adding a small amount of chain extender, for example, a diisocyanate compound such as hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate to the oligomer polycondensed by the direct method to obtain a high molecular weight. . The weight average molecular weight of the biodegradable polyester (B) is preferably in the range of 20,000 to 500,000, more preferably in the range of 50,000 to 250,000.
[0029]
When the molecular weight is less than 20,000, it is difficult to improve the physical properties such as mechanical strength and impact strength in the film obtained by blending and stretching with the polylactic acid resin (A). When the molecular weight exceeds 500,000, molding is performed. It tends to be inferior in workability. Moreover, in order to influence the microphase-separation structure in the film from which the balance of the viscosity of polylactic acid-type resin (A) and biodegradable polyester (B) at the time of melt extrusion is obtained, it affects the molecular weight of polylactic acid-type resin (A). In addition, it is preferable to select the molecular weight of the biodegradable polyester (B).
[0030]
The biodegradable multilayer heat-shrinkable film of the present invention comprises at least one seal layer, at least one polylactic acid resin (A) and a biodegradable polyester (A) other than (A) having a glass transition temperature Tg of 10 ° C. or lower. B) is a multilayer heat-shrinkable film having a layer made of a mixture with B), and the sealing layer is a layer made of a biodegradable polyester (B) resin alone other than (A) having a glass transition temperature Tg of 10 ° C. or lower. , A layer made of an amorphous polylactic acid resin (A) alone, or a resin layer made of a mixture of amorphous polylactic acid resins (A) and (B), and a system further containing a plasticizer A layer made of a biodegradable polyester (B) resin alone, a layer made of an amorphous polylactic acid resin (A) alone, and an amorphous polylactic acid resin ( Is it a layer consisting of A) and a plasticizer? Those selected are exemplified, more preferably a layer made of a biodegradable polyester (B) resin alone. Moreover, in the resin layer which consists of a mixture of an amorphous polylactic acid-type resin (A) and (B), a sealing property improves, so that the component of (B) increases, and it is preferable.
[0031]
The weight ratio (total 100%) of the polylactic acid resin (A) of the present invention and the biodegradable polyester (B) other than (A) other than (A) having a glass transition temperature Tg of 10 ° C. or less is preferably (A) :( B) = 95: 5 to 40:60. If the biodegradable polyester (B) is less than 5%, the impact resistance improving effect tends to decrease, and if the total weight of the biodegradable polyester (B) exceeds 60%, the transparency of the entire film is increased. It tends to decrease. A more preferred weight ratio is (A) :( B) = 90: 10 to 50:50, and particularly preferably (A) :( B) = 85: 15 to 55:45.
[0032]
In the biodegradable multilayer heat-shrinkable film of the present invention, the weight ratio of (A) and (B) in the layer composed of a mixture of the polylactic acid resin (A) and the biodegradable polyester (B) is preferably ( A) :( B) = 95: 5 to 50:50, more preferably (A) :( B) = 90: 10 to 60:40, particularly preferably (A) :( B ) = 85: 15-60: 40.
Further, when the cut surface of the layer composed of the mixture of the polylactic acid resin (A) and the biodegradable polyester (B) in the biodegradable multilayer heat-shrinkable film of the present invention is observed, (A) dispersed in the phase matrix It is preferable that 90% or more of the (B) phase domain present in the present is present in a plate-like form and present in large numbers by microphase separation, and the (B) phase plate-like domain exists substantially parallel to the film surface, and What is microphase-separated so that the average thickness of the plate domain is 5 nm or more and 100 nm or less, more preferably the average thickness of the plate domain exists in the range of 5 nm to 80 nm, Particularly preferred is a microphase separation structure within a range of 10 to 60 nm.
[0033]
Here, the plate-like domain includes not only a flat plate-like domain but also a curved plate-like domain, a curved plate-like domain twisted three-dimensionally, and a plate-like domain in which these plate-like domains are partially bent. . When the cut surface is observed with an electron micrograph by the method described later, for example, the portion that looks linear as shown in FIGS. 2 and 3 is a plate-like domain, and the white portion surrounding this is the (A) phase matrix. is there.
By adopting such a microphase separation structure, the (A) thin plate-like (B) phase domain in the phase matrix effectively increases the impact strength of the film and does not impair transparency. Therefore, the film has excellent impact resistance and transparency. When the average thickness of the plate-like domain on the cut surface of the film exceeds 100 nm, for example, the crystal size of the aliphatic polyester as a factor that impairs the permeability becomes larger than the visible light wavelength (about 400 to 800 nm). The transparency tends to be inferior. Further, when the average thickness of the plate domain is less than 5 nm, the effect of improving physical properties such as impact strength is reduced. The length of the plate-like domain at the cut surface in any one of the MD direction and the TD direction of the film is preferably about 1 μm or more, more preferably about 5 μm or more.
[0034]
The biodegradable multilayer heat-shrinkable film of the present invention needs to have a heat shrinkage ratio of not less than 20% in both the MD direction and the TD direction when heated at 140 ° C. for 30 minutes. The thermal shrinkage is measured according to ASTM D-2732. In order to obtain a film having a heat shrinkage rate of 20% or more at 140 ° C. for 30 minutes, the second MD direction speed ratio and the second blow-up ratio are preferably set to 2.0 or more. When the heat shrinkage rate is less than 20%, it becomes difficult to obtain a tensioned shrink package closely adhered to a package when used as a heat shrink film. Preferably, the thermal shrinkage in both the MD direction and the TD direction is 30% or more and 90% or less, more preferably 35% or more and 85% or less, and particularly preferably 40% or more and 80% or less. It is difficult to stably form a film having a shrinkage ratio exceeding 90%.
[0035]
The biodegradable multilayer heat-shrinkable film of the present invention has a tear strength measured by JIS K 7128 (Method B) in the range of 10 to 200 mN in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film. It is necessary. Preferably, the tear strength is in the range of 10 to 150 mN, more preferably in the range of 10 to 130 mN, and particularly preferably in the range of 10 to 100 mN. When the tear strength is less than 10 mN, the film breaks frequently when the film is slit. Moreover, in the film where tear strength exceeds 200 mN, the cut property at the time of opening a packaged article is inferior. In order to obtain a film having a tear strength in the range of 10 to 200 mN in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, the second MD direction speed ratio and the second blow-up ratio are set to 2.0. The value of (second blow-up ratio) / (second MD direction speed ratio) is preferably in the range of 0.6 to 2.0.
[0036]
The biodegradable multilayer heat-shrinkable film of the present invention needs to have an impact strength measured in accordance with ASTM D 1709-91 (Method A) of 20 mJ / μm or more per unit thickness. The impact strength required for use varies depending on the application, but if the impact strength is less than 20 mJ / μm per unit thickness, the impact strength is about 2 J, which is about the same as a commonly used polyethylene-based shrink film or PVC-based shrink film. The film thickness necessary to obtain the film thickness exceeds 100 μm, and even if the impact resistance is obtained, the transparency is inferior and the film cost is increased.
[0037]
The impact strength per unit thickness is preferably 30 mJ / μm or more and 300 mJ / μm or less, more preferably 40 mJ / μm or more and 300 mJ / μm or less, and particularly preferably 50 mJ / μm or more and 300 mJ / μm or less. A film having an impact strength exceeding 300 mJ / μm per unit thickness is difficult to obtain stably. In order to obtain a film having an impact strength of 20 mJ / μm or more per unit thickness, the second MD direction speed ratio and the second blow-up ratio are preferably set to 2.0 or more.
[0038]
In addition, the biodegradable multilayer heat-shrinkable film of the present invention has a seal strength of 10 N / 15 mm width or more when heat-sealed under the conditions of a seal pressure of 0.5 MPa and a seal time of 0.2 seconds according to JIS Z-1707 method. It is necessary to be. Preferably, the film has a seal strength of 15 N / 15 mm width to 80 N / 15 mm width, and more preferably a film having a seal strength of 20 N / 15 mm width to 80 N / 15 mm width. If the seal strength is less than 10 N / 15 mm, the heat seal strength may be insufficient and the function as a packaging film may not be achieved. Moreover, it is difficult to stably obtain a film having a seal strength exceeding 80 N / 15 mm width.
[0039]
In order to improve the sealing strength, the ratio of the biodegradable polyester (B) other than (A) whose glass transition temperature Tg in the polylactic acid resin (A) is 10 ° C. or less is increased, and at least the film It is a multilayer film having a seal layer on one surface. At this time, the sealing layer is made of a film stretched so as to follow the layer composed of the polylactic acid resin (A) and the biodegradable polyester (B) so as not to inhibit the heat shrinkability of the film. A seal layer is preferred. More preferably, a sheet obtained by multilayer coextrusion of a layer composed of a polylactic acid-based tree (A) and a biodegradable polyester (B) and a sealing layer is a glass transition temperature Tg or more and a melting point Tm or less of the polylactic acid-based tree (A). It is a multilayer coextrusion stretched film obtained by stretching at the following temperature.
[0040]
The biodegradable multilayer heat-shrinkable film of the present invention needs to have a haze (Haze) of less than 30% as measured with a turbidimeter (ASTM D 1003-95). The haze is preferably 0.1% or more and less than 25%, more preferably 0.1% or more and less than 20%, and particularly preferably 0.1% or more and less than 10%. When it is 30% or more, the transparency is inferior and the packaged article cannot be clearly seen through the film, deteriorating the aesthetic appearance and reducing the commercial value. In order to obtain a film having a haze of less than 30%, a biodegradable polyester other than the polylactic acid resin (A) used in the present invention and (A) having a glass transition temperature Tg of 10 ° C. or lower. It is preferable that the weight ratio with (B) is within the range where the ratio of (A) is 40% or more and the ratio of (B) is 60% or less in the whole film.
[0041]
In addition, in the polylactic acid resin (A) phase matrix, 90% or more of the biodegradable polyester (B) phase other than (A) having a glass transition temperature Tg of 10 ° C. or less is a plate-like domain and is microphase-separated. Thus, it is preferable that the plate-like domains exist almost in parallel with the film surface, and the average thickness of the plate-like domains is 5 nm or more and 100 nm or less.
The film thickness after stretching is preferably 5 to 100 μm, more preferably 6 to 70 μm, and further preferably 7 to 50 μm, but is not particularly limited in the present invention.
[0042]
The biodegradable multilayer heat-shrinkable film mainly composed of the polylactic acid resin of the present invention is preferably used after coating with an antistatic agent, a slipping agent, an antiblocking agent or the like depending on applications. In this case, the polylactic acid-based resin film is more hydrophilic than the polyolefin-based resin film or the polystyrene-based resin film. In order to apply uniformly to the surface, it is preferable to further hydrophilize the film surface to be the application surface by corona treatment. By this hydrophilic treatment, the uniformity of the coating film is improved, and antistatic properties and slipperiness are efficiently exhibited. The surface tension at that time is preferably in the range of 400 μN / cm to 600 μN / cm.
[0043]
Since the biodegradable multilayer heat-shrinkable film of the present invention comprises a polylactic acid resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature of 10 ° C. or lower, it is biodegradable. The film is excellent as a shrink wrapping film because it has excellent heat shrinkability, easy cutability, impact resistance, heat sealability and transparency. Further, a shrink package that is sealed using this film to cover an object to be packaged and is tightly adhered to the object to be packaged by heat shrinkage becomes a beautiful shrink package.
[0044]
The biodegradable multilayer heat-shrinkable film of the present invention includes, in addition to the above resins, plasticizers, heat stabilizers, antioxidants, ultraviolet absorbers, antifogging agents, antistatic agents, rust inhibitors, etc. Known additives can be blended within a range that does not impair the requirements and characteristics of the present invention. Especially when the shrink film has protrusions at the corners and edges of the shrink wrapping after shrink wrapping, the film may need to be flexible because the operator may injure the hands at the protrusions. It is preferable to add flexibility to the film by adding a plasticizer or the like as necessary.
[0045]
The plasticizer can be selected from those generally used in the industry, and preferably does not bleed out even when added to the resin composition by about 10% by weight. For example, aliphatic polycarboxylic acid ester, fatty acid polyhydric alcohol ester, oxy acid ester, epoxy plasticizer and the like are included. Specific examples include triacetin (TA), tributyrin (TB), butylphthalyl butyl glycolate (BPBG), acetyl tributyl citrate (ATBC), dioctyl sebacate (DBS), triethylene glycol diacetate, glycerin esters, Examples include butyl oleate (BO), adipic acid ether ester, epoxidized soybean oil (ESO), and the like.
[0046]
In addition, in the case of improving only the surface properties of the film while maintaining the physical properties of the film, an additive that exhibits a function is added only to the surface layer of the film, and the intermediate layer is a multilayer film having a composition that maintains the physical properties of the film. It is preferable that the desired surface characteristics can be imparted while minimizing changes in the physical properties of the film body. Particularly preferred is a multilayer film having a surface layer containing an organic and / or inorganic slip agent, antistatic agent, antifogging agent, and the like on the surface layer. Moreover, it is preferable to use a layer structure having a layer containing an anti-blocking agent on the surface layer because blocking and wrinkling of the resin before stretching and the film after stretching can be prevented and processability is improved.
[0047]
Next, the manufacturing method of the film of this invention is described.
The biodegradable multilayer heat-shrinkable film of the present invention can be formed by any method of the tubular method, the flat method as the classification according to the form, and the sequential stretching method and the simultaneous stretching method as the classification according to the method. It is preferable to perform simultaneous biaxial stretching by a stretching method. The tubular stretching method is, for example, a method described on pages 374 to 377 of “Practical Plastic Molding Encyclopedia” issued on March 24, 1997 by the Encyclopedia Publishing Center, Inc.
[0048]
Specifically, the raw resin is supplied to a plurality of single-screw or twin-screw extruders, melted and mixed, and a first bubble is formed with a multilayer molten resin extruded in a tube shape from a cylindrical multilayer die, and water-cooled or The resin is rapidly cooled to a temperature of glass transition temperature (Tg) + 20 ° C. or less by air cooling, pinched with a pinch roll, the tubular resin is flattened, and then again by a method such as infrared heater heating or hot air heating, After the resin is heated to a temperature not lower than Tg and not higher than Tm, the MD and TD directions are simultaneously stretched by forming a second bubble using a gas such as air or a liquid such as water, and then to a temperature equal to or lower than Tg. The biaxially stretched film is obtained by cooling, pinching with a pinch roll, flattening the tubular stretched film, and then winding it.
[0049]
The advantages of this tubular stretching method compared to the flat stretching method are that the equipment cost is relatively low and the operation is easy, the range of applicable resins is wide, and it is not suitable for mass production. Suitable for production and production of various products, and by controlling the molding conditions, it is possible to obtain a film with a balance in the longitudinal direction (MD direction) and lateral direction (TD direction). Ear loss compared to the flat method Since it can be obtained in a tube shape, a seamless bag can be obtained, and it is convenient only with the bottom seal. It can be cut wide at one end to make a wide film. It is possible to make two films, and the width of the film can be changed over a wide range by adjusting the amount of air blown.
[0050]
As the film forming conditions of the biodegradable multilayer heat-shrinkable film of the present invention, it is preferable to cool the first bubble to a glass transition temperature (Tg) of the polylactic acid resin (A) used in the present invention + 20 ° C. or lower. Preferably, the polylactic acid resin (A) is cooled to a glass transition temperature (Tg) + 10 ° C. or lower. The temperature of the resin at the start of the second bubble stretching is preferably a temperature of Tg to Tm of the polylactic acid resin (A) used in the present invention, more preferably a temperature in the range of Tg + 5 ° C. to Tg + 50 ° C. Is preferred. Thereafter, the second bubble is formed using a gas such as air or a liquid such as water to simultaneously stretch the MD direction and the TD direction, and then the Tg of the polylactic acid resin (A) used in the present invention. A biaxially stretched film is obtained by cooling to the following temperature.
[0051]
The first MD direction speed ratio in forming the first bubble is preferably 1.5 or more, and the first blow-up ratio is preferably 1.1 or more. More preferably, the first MD direction speed ratio is 2.5 or more, and the first blow-up ratio is 1.2 or more, and particularly preferably, the first MD direction speed ratio is 4.0 or more, and The up ratio is 1.4 or more. These values are obtained by the following formula.
First MD direction speed ratio = (speed at which the first bubble is formed and the tube-shaped resin after cooling is picked up by a pinch roll) / (MD direction in which the molten resin flows out from the die outlet calculated from the extrusion amount and die lip opening area) Speed)
First blow-up ratio = (the total width of the resin tube when the first bubble is formed and the tube-shaped resin after cooling is opened and flattened) ÷ (average value of outer die lip circumference and inner die lip circumference)
[0052]
The second MD direction speed ratio and the second blow-up ratio in forming the second bubble are the heat shrinkage rate, tear strength, impact strength, haze of the biodegradable multilayer heat-shrinkable film of the present invention finally obtained. Greatly affects the degree. Preferably the second MD direction speed ratio is 2.0 or more and the second blow-up ratio is 2.0 or more, more preferably the second MD direction speed ratio is 2.2 or more and the second blow-up ratio is More preferably, the second MD direction speed ratio is in the range of 2.5 to 5.0, and the second blow-up ratio is in the range of 3.0 to 5.0. Further, the value of (second blow-up ratio) / (second MD direction speed ratio) is preferably in the range of 0.6 to 2.0, particularly preferably in the range of 0.8 to 1.4. The second MD direction speed ratio and the second blow-up ratio used here are values obtained by the following equations.
Second MD direction speed ratio = (MD direction line speed after stretching in second bubble) ÷ (MD direction line speed before stretching in second bubble)
Second blow-up ratio = (stretching in the second bubble, folding width in the TD direction of the cooled film) / (folding width in the TD direction of the resin tube before stretching in the second bubble)
[0053]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be explained by examples and comparative examples.
The evaluation methods used in the examples and comparative examples are described below.
(1) D and L lactic acid composition and optical purity of polylactic acid polymer
The optical purity of the polylactic acid polymer is calculated by the following formula from the constituent ratio of L-lactic acid and / or D-lactic acid monomer units constituting the polylactic acid polymer as described above.
Optical purity (%) = | [L] − [D] |, where [L] + [D] = 100
(| [L]-[D] | represents the absolute value of [L]-[D].)
[0054]
The composition ratio of L-lactic acid and / or D-lactic acid monomer units constituting the polylactic acid polymer is determined by hydrolysis of the sample with 1N-NaOH, neutralized with 1N-HCl, and then adjusted with distilled water. About the sample (liquid), the detection peak area ratio of L-lactic acid and D-lactic acid at UV UV 254 nm by Shimadzu high performance liquid chromatography (HPLC: LC-10A-VP) equipped with an optical isomer separation column From (area measurement by perpendicular method), the weight ratio [L] (unit%) of L-lactic acid constituting the polylactic acid polymer, the weight ratio [D] (unit%) of D-lactic acid constituting the polylactic acid polymer The three-point arithmetic average (rounded off) per polymer was taken as the measured value.
[0055]
(2) Weight average molecular weight Mw of polylactic acid polymer
Using a gel permeation chromatography device (GPC: data processing unit GPC-8020, detector RI-8020) manufactured by Tosoh, the polystyrene-converted standard polystyrene is used under the following measurement conditions to calculate the weight average molecular weight Mw. The measured value was determined as the arithmetic average (rounded off) of 3 points per polymer.
Column: Connected column of Shodex K-805 and K-801 manufactured by Showa Denko [7.8 mm length × 60 cm length]
Eluent: Chloroform
Sample solution concentration: 0.2 wt / vol%
Sample solution injection volume: 200 μL
Solvent flow rate: 1 ml / min
Column / detector temperature: 40 ° C
[0056]
(3) Glass transition point (Tg), melting point (Tm)
Based on JIS-K7121 and JIS-K7122, the temperature was raised from −100 ° C. to 200 ° C. with a differential scanning calorimeter (DSC), and Tg and Tm were measured. That is, after cutting out about 10 mg from a sample that was conditioned at 23 ° C. and 65% RH (left at 23 ° C. for 1 week), a differential scanning calorimeter (thermal flow rate DSC manufactured by Perkin-Elmer) was used. ), Using DSC-7 model, raise the temperature from −100 ° C. to 200 ° C. at a nitrogen gas flow rate of 25 ml / min, 10 ° C./min, and melt the melting (endothermic) peak from the peak of the drawn DSC curve. Tm (° C), the intersection (midpoint glass transition temperature) of the stepwise change partial curve at the time of temperature rise and a straight line equidistant in the vertical axis direction from each baseline extension line is measured as Tg (unit ° C), The measured value was the arithmetic average (rounded off) of 4 points per product.
(4) Total film thickness, each layer thickness (m)
The total thickness of the film was measured according to JIS-K-7130 using a micrometer, and the thickness of each layer was measured by observing the cross section of the multilayer film with a microscope.
[0057]
(5) Measurement of average thickness of plate-like domain of biodegradable polyester (B) subjected to microphase separation (nm)
A 10 mm square film was cut out as a test piece from a film conditioned at 23 ° C. and 65% RH (left at 23 ° C. for 1 week), then double-stained with osmium tetroxide and ruthenium tetroxide, and epoxy-based After embedding in the resin, an ultra-thin piece was cut out perpendicular to the plane of the film using an ultramicrotome, LKB2088, as shown in FIG. With respect to the microscopic sample, a transmission electron microscope (TEM) manufactured by Hitachi, Ltd. and H7100 type (MD and TD direction cross sections are observation surfaces) were obtained, and a measurement photograph with a magnification of 40,000 times was obtained.
[0058]
Among the domains of the biodegradable polyester (B) phase dyed from the obtained measurement photograph, it exists as a main form (90% or more) excluding less than 10% spherical (elliptical) gel-like foreign matters. The thickness measurement was performed on the plate-like domain as follows. That is, in the total of 25 divided sections obtained by dividing the measurement photograph into 5 parts vertically and horizontally, a plate domain is selected by selecting one point of the relatively clear and non-overlapping plate phase of the dyeing interface. The average value of the thicknesses of the 25 plate-like domains obtained from these 25 divisions was defined as the average thickness (nm) of the plate-like domains of the film.
[0059]
(6) Thermal contraction rate (%)
The thermal shrinkage rate at the time of heating at 140 ° C. for 30 minutes was measured according to ASTM D-2732.
(7) Impact strength (mJ), impact strength / total layer thickness (mJ / μm)
After cutting out a rectangular film having a thickness of 25 μm × 225 mm × 250 mm square as a test piece from a polylactic acid-based resin film that has been conditioned (left at 23 ° C. for 1 week) in a standard state (23 ° C. and 65% RH). In accordance with ASTM-D 1709-91 (Method A), a 50% fracture energy (Dart strength: mJ) was measured under standard conditions using a dirt impact test apparatus manufactured by Toyo Seiki (2 significant figures) ). The impact strength per unit thickness (mJ / μm) was determined by dividing the impact strength (mJ) determined in (7) by the total film thickness (μm) determined in (4).
[0060]
(8) Tensile breaking strength (MPa), tensile breaking elongation (%), tensile elastic modulus (MPa) The tensile breaking strength, tensile breaking elongation and tensile elastic modulus of the film were measured according to ASTM D882.
(9) Tear strength (mN)
The tear strength (mN) of the film was measured according to JIS K7128 (Method B).
(10) Haze (Haze,%)
A film sample that has been conditioned at 23 ° C. and 65% RH (left at 23 ° C. for 1 week) is cut into a 25 μm thick × 50 mm square film as a test piece, and in accordance with ASTM D1003-95. Using a turbidimeter (haze meter) manufactured by Denshoku Industries Co., Ltd., NDH-1001DP type, the haze (Haze: unit%) was measured under standard conditions, and an arithmetic average value (significant figures) of 6 points per kind of film. The measured value was 2 digits).
[0061]
(11) Heat seal strength (N / 15mm)
The heat seal strength is measured according to JIS Z1707, the seal pressure is 0.5 MPa, the seal time is 0.2 seconds, and the seal strength is measured every 10 ° C. in the temperature range from 80 ° C. until the film is melted. It was set as the sealing strength of the film. The seal strength was measured in both the MD direction (film longitudinal direction) and the TD direction (film width direction). In the measurement of the seal strength, when the seal strength is equal to or greater than the strength of the film and the film breaks first, the expression that the seal strength is equal to or greater than the strength at the time of the film break is given. For films with different resin compositions on the front and back of the film, the seal strength measured by bonding the seal layer (first layer or third layer in Examples and Comparative Examples described later) and the seal layer together is measured. Seal strength.
[0062]
(12) Easy cut (no notch)
A 300 mm square film piece was cut out parallel to the MD direction, and the central part of the film piece was torn by hand. The results were evaluated as follows.
A: The film was easily torn by hand.
○: A little resistance when tearing, but tearing by hand.
X: There is a great resistance when tearing, and it is difficult to tear by hand.
[0063]
(13) Packaging evaluation
The finish of the shrink package was evaluated according to the following criteria.
1) Wrinkles
○: The packaging film is tightly attached to the package without wrinkles and is in tension
Δ: Wrinkles are not on the package, but small wrinkles remain around
X: Wrinkles remain on the top and surroundings of the package
2) Air vent hole and seal break
○: Neither air vent hole nor seal part is broken
△: Some air vent hole or seal break
×: The air vent hole and the seal part are both broken
3) Transparency of film taken out from shrink package
A: The haze is less than 20%
○: Haze of 20% or more and less than 30%
×: Haze of 30% or more
[0064]
The polylactic acid resins used in the following examples and comparative examples are polymerized by controlling the catalyst amount, polymerization conditions, monomer composition, and the like according to the methods described in Examples 1B to 7B of JP-T-4-5044731. Crystalline polylactic acid (A1), (A2) and amorphous polylactic acid (A3) having the weight average molecular weight, optical purity, Tg, and Tm shown in Table 1 were obtained. Bionore polyesters (B1), (B2), (B3), and (B4) other than polylactic acid-based resins having a glass transition temperature Tg of 10 ° C. or less are Bionore # 3001 (trade name) manufactured by Showa Polymer Co., Ltd. Bionore # 3020 (trade name), Bionore # 3010MB (trade name), Ecoflex (trade name) manufactured by BASF, and ATBC (tributyl acetylcitrate) manufactured by Nissei Chemical Industry Co., Ltd. were used as the plasticizer (C). However, the composition of the resin in the present invention is not limited to this.
[0065]
Examples 1 to 11
In Examples 1 to 11, the crystalline polylactic acid (A1), (A2) and the amorphous polylactic acid (A3) and the biodegradable polyester (B1), (B2), (B3), (B4) in Table 1 ) Was dry blended to the composition shown in Table 2 and then melt blended using the same-direction twin screw extruder, and the molten resin was extruded at a resin temperature of 190 ° C. However, in Example 4 and Example 11, the plasticizer (C) in Table 1 was added and blended in a twin-screw extruder so as to have the composition in Table 2. The outer die lip diameter is fixed at 110 mm using a cylindrical multilayer die, and the inner die lip diameter is changed within the range of 105 mm to 108.5 mm according to the film forming conditions. It selected so that it might be set to 30 micrometers, and extruded from the die | dye with a lip clearance of about 0.75-2.5 mm.
[0066]
Air is injected into the tube while blowing the cooling water at the temperature shown in Table 2 from the water-cooled ring to the molten resin extruded in a tube shape to form the first bubble, and to the pinch roll while cooling the obtained bubble The guiding tube-shaped resin was wound up as a flat sheet with a winding roll. Next, after the bubble is stabilized, the resin extrusion speed, the amount of air injected into the bubble, and the sheet take-up speed in the pinch roll are finely adjusted, and then wound with the pinch roll, and the second bubble stretching having a thickness of about 150 to 420 μm. A front sheet was obtained. Next, the sheet before second bubble stretching thus obtained was heated to the temperature shown in Table 2 and Table 3, and the air injection amount and the take-up speed of the pinch roll before and after the bubble were adjusted. The second bubble was formed so that the second MD direction speed ratio and the second blow-up ratio were obtained, and a 30 μm film was obtained. The physical property evaluation results of the films obtained in Examples 1 to 11 are shown in Table 2 and Table 3.
[0067]
Using the obtained film, a shrink wrap was produced by a commercially available horizontal pillow shrink wrapping machine. As a packaged item, a lunch box with a polystyrene foam sheet lid on a polystyrene foam tray is used. The film is sent around the lunch box in a cylindrical shape, and the seam of the film at the bottom of the package is heat sealed. Subsequently, both ends of the cylindrical film are fused and sealed. Sealing was performed with a margin rate of 15% in both the vertical and horizontal directions. A small hole for venting air was generated by a needle-like protrusion on the bottom of the package. Subsequently, it was conveyed to a heating tunnel, and the tunnel residence time was shrunk in 5 seconds to obtain a shrink package. Packaging was performed by changing the temperature of the heating tunnel from 80 ° C. to 160 ° C. Table 4 shows the results.
[0068]
[Comparative Examples 1 and 2]
In Comparative Example 1, as shown in Table 1, the first layer is formed using biodegradable polyesters (B2) and (B3), the second layer is formed using polylactic acid (A1), the first layer and the first layer Extrusion was controlled so that the thickness ratio with the two layers was 1: 5, and extrusion was performed at a resin temperature of 190 ° C. in the same manner as in Example 1. In Comparative Example 2, only (A2) was used, and the resin temperature was 190 ° C. Then, extrusion was performed in the same manner as in Example 1 to form the first bubble, and a sheet before stretching the second bubble having a thickness of about 150 μm was obtained. Next, air was injected to form a second bubble in the same manner as in Example 1. However, the resin tube burst at the end when air was injected, and the second bubble was stably formed. It was not possible to stretch.
[0069]
[Comparative Examples 3 to 5]
In Comparative Example 3, the polylactic acid (A2) shown in Table 1 and the biodegradable polyesters (B1), (B2), and (B3) were used and dry blended so as to have the composition and layer structure shown in Table 3. After that, melt blending is performed using a twin screw extruder in the same direction, and the molten resin is extruded from a two-layer cylindrical die having an outer die lip diameter of 110 mm, an inner die lip diameter of 109.4 mm, and a lip clearance of 0.3 mm at a resin temperature of 190 ° C. In the same manner as in Example 1, the molten resin extruded into a tube shape was injected with air into the tube while blowing cooling water having the temperature shown in Table 3 from the water-cooled ring to form bubbles, and the resulting film was obtained. It led to the pinch roll, and the tubular film was wound up with a winding roll as two flat films.
[0070]
Next, after the bubble is stabilized, finely adjust the resin extrusion speed, the amount of air injected into the bubble, and the film winding speed in the pinch roll, and then wind up with the pinch roll, without forming the second bubble and stretching. A film having a final thickness of 30 μm was obtained. Table 3 shows the physical properties of the obtained film.
In Comparative Example 4, a monolayer film having the composition shown in Table 3 was extruded and stretched in the same manner as in Example 1. In Comparative Example 5, the composition and layers shown in Table 3 were obtained in the same manner as in Example 1. A three-layer film of construction was obtained.
Using the obtained film, a shrink package was produced by a commercially available horizontal pillow shrink wrapping machine in the same manner as in Examples 1-11. The results are shown in Table 4.
[0071]
[Comparative Example 6]
In Comparative Example 6, crystalline polylactic acid (A1) was extruded from a T-die at 210 ° C. with a single-screw extruder and quenched with a casting roll to prepare a 150 μm unstretched sheet. Subsequently, this unstretched sheet was roll-stretched 3 times at 75 ° C. in the MD direction (longitudinal direction), subsequently stretched 3.5 times at 75 ° C. with a tenter in the TD direction (width direction), and then 5 times at 130 ° C. Second, heat treatment was performed to obtain a 15 μm biaxially stretched polylactic acid film. In addition, the biodegradable polyesters (B2) and (B3) were dry blended to the composition shown in Table 3 and then melt blended using a same-direction twin screw extruder and extruded from a T-die at a resin temperature of 190 ° C. The film was quenched with a casting roll to obtain a 15 μm unstretched film. The two types of films thus obtained were both coated on the corona-treated surface of the biaxially stretched polylactic acid film so that the polyurethane solvent-based adhesive was approximately 1 μm after both sides were subjected to a single-side corona treatment. The corona-treated surface of the sheet of film was bonded with a roller, followed by pressing with a roller, followed by drying for several seconds in a drying oven, and further aging at 40 ° C. for 3 days. Table 3 shows the physical properties of the dry laminated film thus obtained.
Using the film obtained in Comparative Example 6, a shrink package was produced in the same manner as in Examples 1 to 11 using a commercially available horizontal pillow shrink wrapping machine. The results are shown in Table 4.
[0072]
[Comparative Example 7]
In Comparative Example 7, using a three-layer die, the polylactic acid (A1) shown in Table 1 was extruded into a central layer (core layer) with a single screw extruder so as to be 80% by weight of the entire film, and both outer layers (skin layers) ), The biodegradable polyesters (B2) and (B3) were dry blended to the composition shown in Table 3 and then melt blended using the same-direction twin screw extruder, and coextruded so that each layer was 10% by weight. Extrusion is performed at a molten resin temperature of 200 ° C through a T-die, quenched with a 45 ° C casting roll to produce a 68 µm unstretched film, and then rolled in the MD direction (longitudinal direction) at 70 ° C by 1.5 times. The film was stretched and subsequently stretched 1.5 times at 75 ° C. with a tenter in the TD direction (width direction) to obtain a 30 μm three-layer coextruded film. The physical properties of the film thus obtained are shown in Table 3.
Using the film obtained in Comparative Example 7, a shrink package was produced by a commercially available horizontal pillow shrink wrapping machine in the same manner as in Examples 1-11. The results are shown in Table 4.
[0073]
From Table 2 and Table 3, the biodegradability of the present Example which consists of polylactic acid-type resin (A) and biodegradable aliphatic polyester (B) other than (A) whose glass transition temperature Tg is 10 degrees C or less. The multilayer heat-shrinkable film has a heat shrinkage ratio of not less than 20% in both the longitudinal direction (MD direction) and the width direction (TD direction) when heated at 140 ° C. for 30 minutes, according to JIS K 7128 (Method B). The measured tear strength is in the range of 10 to 200 mN in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, and the impact strength measured according to ASTM D1709-91 (Method A) is per unit thickness. It is 20 mJ / μm or more, has a seal strength of 10 N / 15 mm width or more when heat-sealed under conditions of a sealing pressure of 0.5 MPa and a sealing time of 0.2 seconds in accordance with JIS Z-1707 method, and a turbidimeter ( Haze measured by STM D 1003-95) is less than 30%, and it is a multilayer heat-shrinkable film excellent in heat shrinkability, easy cutability, impact resistance, heat sealability and transparency. I understand. Further, it can be seen from Table 4 that the shrink wrapping body made of the film of this example has a good finish in a wide temperature range, has few tears at the air vent holes and the seal portion, and is excellent in transparency.
[0074]
[Table 1]

[0075]
[Table 2]

[0076]
[Table 3]

[0077]
[Table 4]

[0078]
【The invention's effect】
The biodegradable multilayer heat-shrinkable film of the present invention is composed of a polylactic acid resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature of 10 ° C. or lower. It is useful as a biodegradable multilayer heat-shrinkable film because it has excellent heat shrinkability, easy cutability, impact resistance, heat sealability and transparency. In addition, a shrink wrapping body covered with a wrapping film sealed with this film and tightly adhered to and tensed by heat shrinkage has a sufficient shrinkage ratio in both the MD and TD directions. Then, the film sufficiently follows the shape of the object to be packaged and shrinks to form a beautiful shrink package.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a film cross-sectional photograph shooting position.
2 is an electron micrograph of the second layer portion of the TD cross section of the film of Example 8. FIG.
3 is an electron micrograph of the second layer portion of the MD cross section of the film of Example 8. FIG.

Claims (7)

A film comprising a polylactic acid-based resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or lower, and a heat shrinkage rate upon heating at 140 ° C. for 30 minutes However, both the longitudinal direction (MD direction) and the width direction (TD direction) of the film are 20% or more, and the tear strength measured by JIS K 7128 (Method B) is the longitudinal direction (MD direction) of the film and the width direction (TD). Direction) both within the range of 10 to 200 mN, the impact strength measured in accordance with ASTM D 1709-91 (Method A) is 20 mJ / μm or more per unit thickness, and the seal pressure is 0. 0 according to JIS Z-1707 method. The haze measured by a turbidimeter (ASTM D 1003-95) when the seal strength is 10 N / 15 mm width or more when heat sealed under conditions of 5 MPa and a seal time of 0.2 seconds. A biodegradable multilayer heat-shrinkable film characterized in that Haze) is less than 30%. The heat shrinkage rate during heating at 140 ° C. for 30 minutes is 30% or more in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, and the tear strength measured by JIS K 7128 (Method B) is The longitudinal direction (MD direction) and the width direction (TD direction) are both in the range of 10 to 150 mN, and the impact strength measured in accordance with ASTM D 1709-91 (A method) is 30 mJ / μm or more per unit thickness. , Measured with a turbidimeter (ASTM D 1003-95) when the seal strength is 15 N / 15 mm width or more when heat sealed in accordance with JIS Z-1707 method under conditions of seal pressure 0.5 MPa and seal time 0.2 seconds. The biodegradable multilayer heat-shrinkable film of claim 1, wherein the haze is less than 25%. The heat shrinkage rate during heating at 140 ° C. for 30 minutes was 40% or more in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, and was measured according to ASTM D 1709-91 (Method A). The impact strength is 40 mJ / μm or more per unit thickness, the seal strength is 20 N / 15 mm width or more when heat-sealed under the conditions of a seal pressure of 0.5 MPa and a seal time of 0.2 seconds according to JIS Z-1707 method, and The biodegradable multilayer heat-shrinkable film according to claim 2, wherein the haze (Haze) measured with a turbidimeter (ASTM D 1003-95) is less than 20%. Weight ratio (A) :( B) of polylactic acid resin (A) and biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or lower is 95: 5 to 40:60. The biodegradable multilayer heat-shrinkable film according to claim 1, wherein the film is in the range of In the polylactic acid resin (A) phase matrix, 90% or more of the biodegradable polyester (B) phase domain other than (A) having a glass transition temperature Tg of 10 ° C. or less is microphase-separated in a plate-like form. At least one layer composed of (A) and (B), wherein the plate-like domains are present substantially parallel to the film surface, and the average thickness of the plate-like domains is 5 nm or more and 100 nm or less. The biodegradable multilayer heat-shrinkable film according to any one of claims 1 to 4, which is contained. Multi-layer melt extruded from a cylindrical multilayer die containing at least one mixed resin of polylactic acid resin (A) and biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or lower A first bubble is formed with the resin, and the resin is cooled to a glass transition temperature Tg + 20 ° C. or lower of the polylactic acid resin (A), and then the resin is again Tg of the polylactic acid resin (A) to a melting point Tm or less. A method for producing a biodegradable multilayer heat-shrinkable film, wherein the film is heated to a temperature to form a second bubble and subjected to tubular stretching. Use of the biodegradable multilayer heat-shrinkable film according to any one of claims 1 to 5 for a shrink package.

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