JP4265944B2 - Biodegradable multilayer film and airbag cushioning material using the same - Google Patents

Description

  The present invention is a multilayer film comprising a polylactic acid resin (A) and a layer comprising a biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or less, and (B) More specifically, the present invention relates to a biodegradable multilayer film composed of a layer composed of a biodegradable multilayer film excellent in dimensional stability, impact resistance, and heat sealability, and the use thereof. The present invention relates to an air bag cushioning material.

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.
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.
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. Suitable for various packaging films.

  However, the polylactic acid resin is a brittle resin in an unstretched state and is a resin lacking in mechanical strength as a film. Therefore, it is possible to improve the mechanical strength by biaxial stretching and become a physical property that can be used as a film, and as it is, it becomes a heat-shrinkable film and can be given dimensional stability by heat treatment thereafter. (Patent Document 1), Matsumoto et al. “Materials” Vol. 43, No. 495, pp. 1520-1524, Dec. 1994 (Non-Patent Document 1), Japanese Patent Application Laid-Open No. 7-207041 (Patent) Document 2) and Japanese Patent Application Laid-Open No. 7-256753 (Patent Document 3). However, the films disclosed in the examples and papers of these publications are biaxially stretched films by the flat method, and only films with improved heat-sealability but improved tensile break strength and tensile break elongation are obtained. It is not done.

  The biodegradable film is effectively used as a bag for garbage, for example, because it is decomposed by the action of microorganisms in nature. For example, a garbage bag, a film for a general bag, a film for an air bag cushioning material, and a general packaging For handling the film, the bag containing the contents, the package may be thrown or dropped, and the air bag cushioning material in the air may be compressed with impact force, so impact strength is also necessary. At the same time, in order to reduce costs, the impact strength per unit thickness is required to be strong. 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 an air bag cushioning material, the sealing strength directly affects the cushioning performance, so that the sealing strength is required simultaneously with the film strength. Airbag cushioning material here is a bag-like material that seals the film in a bag shape and encloses gas such as air inside to exhibit the buffering performance. Although there is a type in which air is injected during use with a check valve, the air bag cushioning material mentioned here includes both.

  JP-A-8-323946 (Patent Document 4) 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 that is excellent in impact strength as well as sealing properties. JP-A-10-1003003 (Patent Document 5) discloses transparency and heat by laminating a polylactic acid-based stretched film with a biodegradable aliphatic polyester unstretched film different from the polylactic acid-based polymer. Although providing a film having excellent sealing properties is disclosed, a film having excellent impact strength is not disclosed. In addition, films with poor dimensional stability can be sealed when heat-sealed, but there are problems that the film shrinks after sealing and the appearance is damaged, and the strength of the sealed portion is weakened. No film is disclosed.

  In addition, the stretched film by the flat method has less unevenness in thickness than the stretched film by the tubular method, and the production per unit time can be increased. 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.

JP-A-6-23836 JP-A-7-207041 JP-A-7-256653 JP-A-8-323946 JP-A-10-1003003 Matsumoto et al. “Materials” Vol.43, No.495, pp.1520-1524, Dec. 1994

  The present invention is a biodegradable multilayer film suitable as a garbage bag, a film for a general bag, a film for an air bag cushioning material and a film for a general packaging, and is sufficient even when used in the form of a bag as described above. Biodegradable multilayer film with improved impact strength that does not break even when a compression impact force is applied when it is used as an air bag cushioning material even when subjected to impact such as dropping, even if it has a sealing strength and is difficult to tear The object of the present invention is to provide a biodegradable multilayer film that is dimensionally stable even with heat at the time of heat sealing and does not impair the appearance after sealing, and an airbag cushioning material using the same.

  As a result of intensive studies to solve the above problems, the present inventors have surprisingly found that the film is a multilayer film, and has a polylactic acid resin (A) and a glass transition temperature Tg of 10 ° C. or less (A And a biodegradable polyester other than (B) in a specific ratio and a layer made of (B), and the layer made of (B) is formed on at least one surface of the multilayer film, and It has been found that a biodegradable multilayer film having excellent dimensional stability, impact strength, and heat sealability can be obtained by stretching and heat treatment, and the present invention has been completed.

That is, the present invention is as follows.
1) A multilayer coextrusion stretched film, which is a layer made of a mixture of a polylactic acid resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or less; ), The layer consisting of (B) forms at least one surface of the multilayer film, and the biodegradable polyester (B) contained in any layer is the same, at 120 ° C., 1 The heat shrinkage rate at the time of minute heating is 15% or less 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 (A method) is a unit. A biodegradable multilayer film having a thickness of 30 mJ / μm or more per thickness.

  2) The thermal shrinkage rate during heating at 120 ° C. for 1 minute is 10% or less 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, the seal strength measured according to JIS Z-1707 is 10 N / 15 mm width or more, and the haze measured with a turbidimeter (ASTM D 1003-95) ( The biodegradable multilayer film according to 1), wherein Haze) is less than 30%.

  3) The thermal shrinkage rate during heating at 120 ° C. for 1 minute is 5% or less in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, in accordance with ASTM D 1709-91 (A method). The measured impact strength is 50 mJ / μm or more per unit thickness, the seal strength measured according to JIS Z-1707 is 15 N / 15 mm width or more, and the haze measured with a turbidimeter (ASTM D 1003-95) ( The biodegradable multilayer film according to 1), wherein Haze) is less than 20%.

4) Weight ratio of (A) and (B) in a layer composed of a mixture of polylactic acid resin (A) and biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or less. The biodegradable multilayer film according to any one of 1) to 3), wherein (A) :( B) is in the range of 95: 5 to 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. Any one of 1) to 4), wherein a large number of phase-separated domains are present, the plate-like domains are 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. A biodegradable multilayer film according to claim 1.
6) Gas-filled air bag cushioning material using the biodegradable multilayer film according to any one of 1) to 5)

The biodegradable multilayer film of the present invention has a polylactic acid resin (A) and a glass transition temperature Tg of 1.
It is composed of a layer composed of a mixture of biodegradable polyester (B) other than (A) other than 0 ° C. and a layer composed of (B), and the layer composed of (B) forms at least one surface of the multilayer film. Therefore, it is a biodegradable film with excellent dimensional stability, heat sealability, and impact resistance, so it is useful as a garbage bag, general bag film, general packaging film, and air bag cushioning film. It is a good film. In addition, since the air bag cushioning material obtained has excellent sealing strength, it has sufficient cushioning performance, and after use, it is easy to reduce the volume by breaking the bag and is a biodegradable film, so it is a compost facility It is a useful air bag cushioning material that can be used for garbage disposal.

Hereinafter, the present invention will be specifically described focusing on its preferred form.
The film of the present invention is a multilayer film comprising a layer of a polylactic acid resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or lower; It is necessary that the layer composed of the layer (B) and the layer (B) form at least one surface of the multilayer film. The thickness of the layer made of (B) is preferably 2 μm or more, more preferably 3 μm or more, and particularly preferably 4 μm or more. (B) If the thickness of the layer is less than 2 μm, the seal strength tends to become unstable.

  The polylactic acid-based resin of the present invention is a polylactic acid homopolymer and a copolymer containing 50% by weight or more of lactic acid monomer units, and the polylactic acid homopolymer, lactic acid and other hydroxycarboxylic acids and lactones 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 polylactic acid homopolymer and a copolymer containing 80% by weight or more of lactic acid monomer units, or a mixture of these copolymers, more preferably 90% by weight of polylactic acid homopolymer and lactic acid monomer units. % Of a copolymer or a mixture of these copolymers.

  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.

  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. Examples of the dicarboxylic acid include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the polyhydric alcohol include aromatic polyhydric alcohols such as bisphenol / ethylene oxide addition reaction products, Aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, neopentyl glycol, ether glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, etc. Is mentioned.

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, it is difficult to obtain only a film having poor mechanical properties, and if it exceeds 1,000,000, the melt viscosity becomes high, and it is difficult to obtain a film having stable physical properties by an ordinary processing machine.

  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.

  Aliphatic polyesters obtained by polycondensation of aliphatic dicarboxylic acids and aliphatic diols 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. 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. . 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.

  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.

  When the molecular weight is less than 20,000, it is difficult to sufficiently improve the practical properties such as mechanical strength and impact strength in the film obtained by blending and stretching with the polylactic acid resin (A), and the molecular weight exceeds 500,000. And may be inferior in moldability. Moreover, since the balance of the viscosity of the polylactic acid resin (A) and the biodegradable polyester (B) at the time of melt extrusion affects the microphase separation structure in the obtained film, the molecular weight of the polylactic acid resin (A) It is preferable to select the molecular weight of the biodegradable polyester (B) according to the above.

  In the biodegradable multilayer film of the present invention, (A) and (B) in a layer comprising a mixture of a polylactic acid resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or less. ) The weight ratio is preferably in the range of (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: 10-50: 50, and particularly preferably (A) :( B) = 85: 15-60: 40.

  In the biodegradable multilayer film of the present invention, when the cut surface of the layer composed of the mixture of the polylactic acid resin (A) and the biodegradable polyester (B) is observed, it is dispersed in the phase matrix (A). (B) It is preferable that 90% or more of the phase domains are present in a plate-like form in a large number after microphase separation, and the (B) phase plate-like domains are present almost in parallel to the film surface, and the plate-like domains Are preferably microphase-separated so that the average thickness is 5 nm or more and 100 nm or less, more preferably the average thickness of the plate-like domain is in the range of 5 nm to 80 nm, and particularly preferably 10 nm. It takes a microphase separation structure within a range of ˜60 nm. 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. .

  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 at the cut surface of the film exceeds 100 nm, for example, the crystal size of the biodegradable polyester (B) as a factor that impairs permeability is larger than the visible light wavelength (about 400 to 800 nm). As a result, transparency is 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.

The biodegradable multilayer film of the present invention has a thermal shrinkage ratio of 120% when heated at 120 ° C. for the MD of the film.
The direction and the TD direction must be 15% or less. The thermal shrinkage is measured according to ASTM D-2732. A film having a heat shrinkage rate of 15% or less at 120 ° C. for 1 minute can be obtained by heat-treating the film at a temperature not lower than the glass transition temperature Tg and not higher than the melting point Tm of the polylactic acid resin (A). When a film with a thermal shrinkage rate exceeding 15% is used, in the case of a packaging film, the heat seal part shrinks and the appearance is impaired. In the case of an air bag cushioning material, the seal part shrinks and the appearance is impaired. Strength may decrease. Preferably, in both the MD direction and the TD direction, the thermal shrinkage rate when heated at 120 ° C. for 1 minute is 10% or less, more preferably 5% or less.

  The biodegradable multilayer film of the present invention needs to have an impact strength measured in accordance with ASTM D 1709-91 (Method A) of 30 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 30 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 required to obtain the film thickness exceeds 60 μm, and even if the impact resistance is obtained, the transparency is inferior and the film cost is increased. Preferably, the impact strength per unit thickness is 40 mJ / μm or more, more preferably 50 mJ / μm or more, and particularly preferably 60 mJ / μm or more. In order to obtain a film having an impact strength of 30 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.

In addition, the biodegradable multilayer film of the present invention preferably has a seal strength of 10 N / 15 mm width or more when heat sealed according to JIS Z-1707. More preferred is a film having a seal strength of 15 N / 15 mm width or more, and particularly preferred is a film having a seal strength of 20 N / 15 mm width or more. When the seal strength is less than 10 N / 15 mm width, the heat seal strength is insufficient, and the function when used as a packaging film may not be achieved, or sufficient buffer performance may not be obtained when used as an air bag cushioning material. .
In order to improve the sealing strength, a multilayer film having a layer made of biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or lower on at least one surface of the multilayer film is used. . Preferably, a sheet obtained by multilayer coextrusion of a layer composed of a mixture of polylactic acid tree (A) and biodegradable polyester (B) and a layer composed of (B) is a glass transition of polylactic acid tree (A). It is a multilayer coextrusion stretched film obtained by stretching at a temperature not lower than the temperature Tg and not higher than the melting point Tm, followed by heat treatment.

  The biodegradable multilayer film of the present invention preferably has a haze measured by a turbidimeter (ASTM D 1003-95) of less than 30%. More preferably, the haze is less than 20%, particularly preferably less than 15%. When the haze 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. Further, in the air bag cushioning material, when the transparency of the film is lowered, when the article protected by the air bag cushioning is small, the airbag cushioning material is hidden behind the cushioning material and is likely to forget to take the article. 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. In the layer consisting of (B), the weight ratio of (A) is preferably 40% or more.

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 biodegradable multilayer film of the present invention preferably has a tensile breaking strength measured according to ASTM D-882 of 50 MPa or more. More preferably, the film has a tensile strength at break of 60 MPa or more, and particularly preferably a film of 70 MPa or more. Films with a tensile strength at break of less than 50 MPa will have insufficient film strength even if the seal strength is improved. For example, when used as an air bag cushioning material, the film will break before the seal part peels off, resulting in sufficient buffering. Performance may not be obtained.

  The biodegradable multilayer film of the present invention preferably has a tensile modulus measured according to ASTM D-882 of 2500 MPa or less. More preferred is a film having a tensile modulus of 2000 MPa or less, and particularly preferred is a film having 1500 MPa or less. A film having a tensile modulus of elasticity exceeding 2500 MPa becomes a hard film, and when an air bag cushioning material is used, the sound generated from the film during handling becomes loud and annoying. In order to reduce the tensile modulus of the film to 2500 MPa or less, a layer comprising a mixture of a polylactic acid resin (A) and a biodegradable polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or less. (B) in the weight ratio of 5% or more, or a plasticizer is blended in this layer, and in the multilayer film, the ratio of the thickness of the layer consisting of (B) to the total layer is increased. preferable.

The thickness of the biodegradable multilayer film of the present invention is preferably 5 to 100 μm, more preferably 6 to 70 μm, still more preferably 7 to 50 μm, but is not particularly limited in the present invention.
The biodegradable multilayer film mainly composed of the polylactic acid-based resin of the present invention is preferably used after coating with an antistatic agent, a slip 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, but the biodegradable heat-shrinkable film of the present invention is used as an antistatic agent, a slip agent, and an anti-blocking agent. 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. In this case, the surface tension is preferably in the range of 400 μN / cm to 600 μN / cm.

In addition to the above resins, the biodegradable multilayer film of the present invention includes known additions such as plasticizers, heat stabilizers, antioxidants, and UV absorbers, antifogging agents, antistatic agents, and rust inhibitors. It is possible to mix | blend an agent in the range which does not impair the requirements and characteristics of this invention. In particular, when flexibility is required when used as an airbag cushioning material, it is preferable to add flexibility to the film by adding a plasticizer or the like as necessary.
In addition, the biodegradable multilayer film of the present invention has an intermediate layer added with an additive that exhibits a function only on the surface layer of the film, particularly when only improving the surface properties of the film while maintaining the physical properties of the film body. Is preferably a multilayer film having a composition that maintains the physical properties of the film, since the desired surface properties 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.

Next, the manufacturing method of the film of this invention is described.
The biodegradable multilayer film of the present invention can be formed by any method of a tubular method, a flat method as a classification according to the form, and a sequential stretching method and a simultaneous stretching method as a classification according to the method. Simultaneous biaxial stretching is preferred. The tubular stretching method is, for example, a method described in pages 374 to 377 of “Practical Plastic Molding Encyclopedia” issued on March 24, 1997 by the Encyclopedia Publishing Center, Inc.

  Specifically, the raw material resin is supplied to a single-screw or twin-screw extruder, melted and mixed, and a first bubble is formed with a multilayer molten resin extruded in a tube shape from a cylindrical multilayer die as it is. The glass is rapidly cooled to a temperature of glass transition temperature (Tg) + 20 ° C. or less, pinched with a pinch roll, the tubular resin is flattened, and then the resin is again treated by infrared heater heating or hot air heating. Is heated to a temperature not lower than Tg and not higher than Tm and then a second bubble is formed by using a gas such as air or a liquid such as water, so that the MD direction and the TD direction are simultaneously tubular stretched, and then the temperature not higher than Tg. Until the tube is stretched, pinched with a pinch roll, the tubular stretched film is flattened, and then wound up to obtain a multilayer biaxially stretched film. That.

  In the production of the biodegradable multilayer film of the present invention, it is necessary to improve the dimensional stability by additionally heat-treating the stretched film at a temperature not lower than Tg and not higher than Tm of the polylactic acid resin (A). is there. As the method, if the tubular method is used, the second bubble is formed, the tube is stretched, pinched with a pinch roll, the third bubble is formed, the gas is sealed inside, and the pressure is maintained. A method of heat-treating the tube-like film at a temperature not lower than the glass transition temperature Tg and not higher than the melting point Tm of the polylactic acid resin (A) used by using a heat source such as hot air or infrared rays from the outside while the film is in a tension state, or once flat There are a method of passing through a heat treatment zone in a state where both ends are gripped by a clip after being cut into a film, or a method of heat treatment by contacting with a hot roll. Preferable heat treatment conditions are a method of heat treatment for 1 second or more in a temperature range of the glass transition temperature Tg or more and a melting point Tm or less of the film, particularly preferably a method of heat treatment for 2 seconds or more in a temperature range of Tg + 5 ° C. or more and the melting point or less. It is. In order to reduce the heat shrinkage rate, it is also effective to reduce the heat shrinkage rate by heat treatment by relaxing the tension in the TD direction and / or the MD direction.

  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. For example, two films can be formed, and the film width and thickness can be changed over a wide range by adjusting the amount of air blown.

  As the film forming conditions of the biodegradable multilayer 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 less, more preferably. It is to cool the glass transition temperature (Tg) of the polylactic acid resin (A) to 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 heat-treated biaxially stretched film is obtained by heat-treating at a temperature of Tm or less and then cooling to a temperature of Tg or less.

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) ÷ (Calculated from the extrusion amount and die lip opening area)
(MD direction speed at which molten resin flows out at the die outlet)
First blow-up ratio = (Cut the tubular resin after forming the first bubble and cooling it,
The total width of the resin tube when it is made to be a toroid) ÷ (outer die lip circumference and
(Average value with inner die lip circumference)

The second MD direction speed ratio and the second blow-up ratio when forming the second bubble are large in the thermal shrinkage rate, impact strength, tensile strength, and haze of the biodegradable multilayer film of the present invention finally obtained. Affect. A preferred film forming method is a method in which 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 2.5 or more, particularly preferably the second MD direction speed ratio is in the range of 2.5 to 5.0 and the second blow-up ratio is 3.0 to 5.0. It is the method of forming into a film in the range. 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) ÷ (Second bubble
MD direction line speed before stretching)
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)

The present invention will be described with reference to Examples, Reference Examples and Comparative Examples .
The evaluation methods used in the examples, reference examples and comparative examples are described below.
(1) D, L lactic acid composition and optical purity of polylactic acid polymer The optical purity of the polylactic acid polymer is the composition of L-lactic acid and / or D-lactic acid monomer units constituting the polylactic acid polymer as described above. It is calculated from the ratio by the following formula.
Optical purity (%) = | [L] − [D] |, where [L] + [D] = 100
(| [L]-[D] | represents the absolute value of [L]-[D].)

  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.

(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

(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 (μm)
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.

(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 slice was cut perpendicular to the plane of the film using an ultramicrotome, LKB2088, and used as a microscopic sample. 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. 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.

(6) Thermal contraction rate (%)
The heat shrinkage rate at 120 ° C. for 1 minute heating was measured according to ASTM D-2732.
(7) Impact strength (mJ), impact strength / total layer thickness (mJ / μm)
Thirty 225 mm × 250 mm square films were cut out as a test piece from a polylactic acid-based resin film that was conditioned in a standard state (23 ° C. and 65% RH) (left at 23 ° C. for 1 week). -Based on D1709-91 (Method A), a 50% fracture energy (Dart strength: unit mJ) was measured under standard conditions using a dirt impact test apparatus manufactured by Toyo Seiki (2 significant digits). 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).

(8) Tensile breaking strength (MPa), tensile breaking elongation (%), tensile elastic modulus (MPa)
The tensile strength at break, tensile elongation at break and tensile modulus of the film were measured according to ASTM D882.
(9) Haze (Haze,%)
After cutting into a square film of 50 mm square as a test piece from a film sample that was conditioned (left at 23 ° C. for 1 week) under standard conditions (23 ° C. and 65% RH), ASTM D1003
-95, a haze (unit:%) was measured under standard conditions using a turbidimeter (haze meter) manufactured by Nippon Denshoku Industries Co., Ltd., NDH-1001DP type. The arithmetic average value of the points (2 significant digits) was taken as the measured value.

(10) 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). For films with different resin compositions on the front and back of the film, the biodegradable polyester (B) layer (first layer or third layer in the examples and comparative examples described later) and the (B) layer are measured together. The sealing strength obtained was taken as the sealing strength of the film.
(11) Appearance of heat-sealed part The appearance of the sealed part heat-sealed by the method of (10) was evaluated as follows.
◯: A film having a good appearance in which the heat seal part does not shrink after sealing.
X: A film in which the heat seal part shrinks after sealing and the appearance is impaired.

(12) Rupture resistance test of airbag cushioning material A film cut into a width of 150 mm is heat-sealed in a longitudinal direction (MD direction) with biodegradable polyester (B) layers bonded to each other, and air is passed through the resulting tube. The top and bottom were heat-sealed so as to form a pillow type air bag with a vertical length of 130 mm. The heat seal conditions were the temperature at which the highest seal strength was recorded in (10), the seal pressure was 0.5 MPa, and the seal time was 0.2 seconds. The air bag thus formed was sandwiched between rectangular pressure plates having a length of 120 mm and a width of 50 mm (area 60 cm ² ). The load was applied by pressing the pressure plate at a speed of 10 mm / min from the top, and the load at the time of rupture was measured. . The results were evaluated as follows.
◎: or load 160 Kg (breakage pressure 26N / cm ² or higher) breakage films with ○: more load 80 Kg (breakage pressure 13N / cm ² or higher) breakage films × in: less than load 80 Kg (breakage pressure 13N / Cm ² )

(13) Quietness of airbag cushioning material The quietness of the cushioning material was evaluated as follows based on the magnitude of noise generated from the film when the airbag created in (12) was grasped by hand and loosened.
○: Generated sound is relatively small, low sound and not harsh.
X: The generated sound is relatively loud, high-pitched, and harsh.

The polylactic acid resins used in the following examples, reference examples and comparative examples are controlled in catalyst amount, polymerization conditions, monomer composition and the like according to the methods described in Examples 1B to 7B of JP-T-4-5044731. And 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. In addition, biodegradable polyesters (B1), (B2), and (B3) other than polylactic acid resins having a glass transition temperature Tg of 10 ° C. or less are Bionore # 3001 and Bionore # 3010MB manufactured by Showa Polymer Co., Ltd. Ecoflex, ATBC (tributyl acetyl citrate) manufactured by Nissei Chemical Industry Co., Ltd. was used as the plasticizer (C). However, the composition of the resin in the present invention is not limited to this.

[ Examples 1-4, 6, 8-10, Reference Examples 1 and 2 ]
In Examples 1 to 4 , 6, 8 to 10, and Reference Examples 1 and 2 , the crystalline polylactic acid (A1), (A2) and amorphous polylactic acid (A3) in Table 1 and the biodegradable polyester (B1) ), (B2), and (B3) pellets were dry blended to the compositions shown in Tables 2 and 3 and then melt blended for each layer using the same direction twin screw extruder, and the molten resin was extruded at a resin temperature of 190 ° C. did. However, in Example 4, 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. While blowing the cooling water of the temperature shown in Table 2 and Table 3 from the water cooling ring to the molten resin extruded in a tube shape, air is injected into the tube to form the first bubble, while cooling the obtained bubble The tube-shaped resin was led to a pinch roll and wound up with a roll as a flat sheet. 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 second pre-bubble stretching sheet thus obtained was heated to the temperatures shown in Tables 2 and 3, and the air injection amount and the take-up speed of the pinch rolls before and after the bubble were adjusted. Then, second bubbles were formed so as to have a second MD direction speed ratio and a second blow-up ratio, and then heat treatment was performed under the conditions shown in Tables 2 and 3 to obtain a 30 μm film. Tables 2 and 3 show the physical property evaluation results of the films obtained in Examples 1 to 4, 6, 8 to 10, and Reference Examples 1 and 2.

[Comparative Examples 1 and 2]
In Comparative Example 1, as shown in Table 3, the first layer is formed using biodegradable polyesters (B1) and (B2), 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 a first bubble, and a sheet before stretching the second bubble having a thickness of about 180 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.

[Comparative Examples 3 to 5]
In Comparative Example 3, the polylactic acid (A2) and biodegradable polyesters (B1) and (B2) shown in Table 1 were used, and after dry blending to form the composition and layer structure of Table 3, the same direction Melt blended using a twin screw extruder and extruded at a resin temperature of 190 ° C from a two-layer cylindrical die with 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. While blowing cold air from the cooling air ring to the extruded molten resin, air is injected into the tube to form bubbles, the resulting film is guided to a pinch roll, and the tubular film is rolled into two flat films. Winded up. In this way, after the bubble is stabilized, fine adjustment of the resin extrusion speed, the amount of air injected into the bubble, the film winding speed in the pinch roll, and then winding with the pinch roll, without forming the second bubble, without heat treatment 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, as in Example 1, a single layer film having the composition shown in Table 3 was extruded, stretched, and heat-treated to obtain a final film. In Comparative Example 5, a two-layer film having the composition and layer structure shown in Table 3 was extruded and stretched in the same manner as in Example 1 to obtain a final film without heat treatment.

[Comparative Example 6]
In Comparative Example 6, the polylactic acid (A1) shown in Table 1 was extruded into a central layer (core layer) using a three-layer T die with a single-screw extruder so that it would be 80% by weight of the entire film, and both outer layers (skins) Layer) was dry blended with biodegradable polyesters (B1) and (B2) to the composition shown in Table 3, 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. Then, the film was stretched 1.5 times at 75 ° C. with a tenter in the TD direction (width direction), and further heat-treated under the conditions shown in Table 3 to obtain a 30 μm three-layer coextruded film. The physical properties of the film thus obtained are shown in Table 3.

  From Table 2 and Table 3, it is a multilayer film, and consists of a mixture of a polylactic acid resin (A) and a biodegradable aliphatic polyester (B) other than (A) having a glass transition temperature Tg of 10 ° C. or lower. The biodegradable multilayer film of this example, which is composed of a layer and a layer consisting of (B) and the layer (B) forms at least one surface, has a thermal shrinkage rate of 120 ° C. for 1 minute when heated. The longitudinal direction (MD direction) and the width direction (TD direction) are both 15% or less, and the impact strength measured in accordance with ASTM D 1709-91 (Method A) is 20 mJ / μm or more per unit thickness. -Multilayer excellent in dimensional stability, impact resistance, and heat sealability, with a seal strength of 10N / 15mm width or more when heat sealed under conditions of seal pressure 0.5MPa and seal time 0.2sec in accordance with the 1707 method fill It can be seen that is. Moreover, it turns out that the airbag cushioning material produced from the obtained film is a biodegradable airbag cushioning material which has the outstanding cushioning performance.

The biodegradable multilayer film of the present invention has a polylactic acid resin (A) and a glass transition temperature Tg of 1.
It is composed of a layer composed of a mixture of biodegradable polyester (B) other than (A) other than 0 ° C. and a layer composed of (B), and the layer composed of (B) forms at least one surface of the multilayer film. Therefore, since it is a biodegradable film with excellent dimensional stability, heat sealability, and impact resistance, it can be used for garbage bags, general bag films, general packaging films, and air bag cushioning films. It can be suitably used in the field. In addition, since the air bag cushioning material obtained has excellent sealing strength, it has sufficient cushioning performance, and after use, it is easy to reduce the volume by breaking the bag and is a biodegradable film, so it is a compost facility It can be suitably used in the field of cushioning material as an air bag cushioning material that can also handle garbage.

Claims (6)

A multilayer coextrusion stretched film comprising a polylactic acid resin (A) and a biodegradable polyester (B) mixture other than (A) having a glass transition temperature Tg of 10 ° C. or less; The layer made of (B) forms at least one surface of the multilayer film, and the biodegradable polyester (B) contained in any layer is the same, and is heated at 120 ° C. for 1 minute. The heat shrinkage rate at the time is 15% or less 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 (A method) is per unit thickness. A biodegradable multilayer film characterized by being 30 mJ / μm or more. The thermal shrinkage rate during heating at 120 ° C. for 1 minute is 10% or less in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, and the impact measured according to ASTM D1709-91 (A method) The strength is 40 mJ / μm or more per unit thickness, the seal strength measured according to JIS Z-1707 is 10 N / 15 mm width or more, and the haze measured by a turbidimeter (ASTM D1003-95) is 30. The biodegradable multilayer film according to claim 1, wherein the biodegradable multilayer film is less than%. The thermal shrinkage rate during heating at 120 ° C. for 1 minute is 5% or less in both the longitudinal direction (MD direction) and the width direction (TD direction) of the film, and the impact measured according to ASTM D1709-91 (A method) The strength is 50 mJ / μm or more per unit thickness, the seal strength measured according to JIS Z-1707 is 15 N / 15 mm width or more, and the haze measured by a turbidimeter (ASTM D1003-95) is 20 The biodegradable multilayer film according to claim 1, wherein the biodegradable multilayer film is less than%. 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. The plate-like domains are present 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. Biodegradable multilayer film. 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. 5. The plate-like domain exists substantially in parallel with the film surface, and the average thickness of the plate-like domain is 5 nm or more and 100 nm or less. Biodegradable multilayer film. A gas-filled air bag cushioning material using the biodegradable multilayer film according to claim 1.