JP5656543B2 - Multi-layer film with biodegradability - Google Patents

Description

  The present invention relates to a multilayer film. More particularly, the present invention relates to a multilayer film having improved biodegradability, such as compost bags, agricultural films, and packaging materials, which have improved moldability, mechanical properties, water vapor permeability and biodegradability. In particular, the multilayer film of the present invention has moderately controlled water vapor permeability and biodegradability, and is useful for compost bags and agricultural films.

Biodegradable resins are known to decompose relatively easily without producing harmful substances in water or soil. For this reason, it is attracting worldwide attention from the viewpoint of environmental conservation such as the problem of waste disposal. Among these, the aliphatic polyester resin may have physical properties close to that of polyethylene, and the film obtained by molding the resin may be used for films such as agricultural materials, civil engineering materials, vegetation materials, and packaging materials. It is expected (see, for example, Patent Documents 1 and 2).
However, all of the conventional biodegradable films have a problem in practical use because the tear strength, particularly the tear strength in the machine (stretching) direction of the film is not sufficient.

  On the other hand, building a recycling-oriented society by switching from depleted resources to renewable resources has attracted attention, not only biodegradability but also materials derived from natural products, not materials synthesized from petroleum. There is growing interest. Biodegradable materials derived from natural products include starch, polylactic acid resin, and aliphatic polyester using biomass raw materials. Among them, especially starch is “produced most abundantly among natural resources, and can be re-produced every year, separation and purification technology from plant tissue has been established as a modern starch industry, and the price is stable and inexpensive. Therefore, it is considered as the most promising raw material for the production of biodegradable plastics, and research and development, industrialization, and market development are being promoted ”(Non-patent Document 1). .

  In recent years, many films and sheets having biodegradability utilizing the properties of the above-described biodegradable resins and biodegradable materials have been developed. In order to improve the transparency and water vapor permeability of a film containing a composition containing oxidized starch and a biodegradable resin in an intermediate layer, the present inventor consists of layers each containing a biodegradable resin. A multilayer film was developed (Patent Document 3). It was found that moldability and physical properties can be improved by this method. However, since it is desired that agricultural multi-films do not break in the field until harvesting is completed, it is necessary to delay the progress of biodegradation depending on the crop. Moreover, the progress of biodegradation may be accelerated due to factors such as temperature, humidity, soil properties, soil moisture content, and this method may be problematic.

It has been proposed that a modified polyvinyl alcohol-based polymer alloy containing starch is used for the intermediate layer, and a biodegradable resin is used for the outer layer and the inner layer (Patent Document 4). Physical properties cannot be obtained. It has also been proposed to use a starch containing moisture in the intermediate layer and use a biodegradable resin for the outer layer and inner layer (Patent Document 5). Since holes may be formed in the film, it is not preferable. In order to suppress this, it was necessary to add a compatibilizer with extremely low biodegradability.
While it is desirable for biodegradation to be moderately slow, in the applications such as agricultural multi-films and compost bags, it becomes a problem if a residue is generated, so it must eventually be completely biodegraded. In addition, it is conceivable to use a polylactic acid-based resin having a slow biodegradation and high rigidity, and a flexible biodegradable polyester-based resin for the intermediate layer. Patent Document 6 proposes a sheet and a molded body using polylactic acid for the inner layer and the outer layer and a biodegradable polyester resin for the intermediate layer, and Patent Document 7 uses polylactic acid for the surface layer and is flexible for the intermediate layer. A film using a biodegradable polyester resin has been proposed. However, since polylactic acid has high rigidity and low elongation at break at tensile break, the film is less flexible and easily breaks. Therefore, a combination of only polylactic acid and a biodegradable polyester resin may not be sufficient when film flexibility is required.

Further, it has been proposed to increase mechanical strength by stretching a film composed of a layer mainly composed of a polylactic acid-based polymer and a layer mainly composed of a biodegradable resin different from polylactic acid (Patent Document 8). , 9, 10). In this case, the tensile strength and the elongation are greatly improved, but there is a problem that a stretching process is required, and if the heat treatment is not performed, the film shrinks due to temperature rise (Non-patent Document 2). It becomes difficult to use for a multi-film in which the temperature of the film increases.
Moreover, since the melting point of polylactic acid-based resin exceeds 150 ° C., the temperature for forming a general film is 170 to 235 ° C. (Non-patent Document 3). It is difficult to co-extrude a polylactic acid resin together with a composition containing oxidized starch that easily decomposes and burns in an extruder at a processing temperature of 170 ° C. or higher under general molding conditions. Coextruding with lactic acid was difficult to imagine.

Japanese Patent Laid-Open No. 5-271377 Japanese Patent Laid-Open No. 6-170941 JP 2008-296482 A JP 7-285192 A JP-T-2006-508830 JP 2003-127711 A International Publication No. 2004/069535 JP 2007-320290 A JP 2001-47583 A JP 2005-047138 A

Biodegradable Plastic Handbook, edited by Biodegradable Plastics Research Group, 1995, p.122 All of bioplastic materials, Japan Bioplastics Association, 2008, p96 All of bioplastic materials, Japan Bioplastics Association, 2008, p85

  In view of the above-mentioned problems of the prior art, the object of the present invention is to improve the transparency and water vapor permeability of the film, to have high tear strength, to introduce natural product-derived components and to be biodegradable. An object of the present invention is to provide a multilayer film having high biodegradability that is highly stable in a natural environment, suitable for compost bags, agricultural films, packaging materials, and the like, and excellent in economic efficiency.

  As a result of intensive studies to solve the above problems, the present inventors have controlled the moisture content of the intermediate layer and specified the outer layer and the inner layer in the multilayer film containing oxidized starch and biodegradable resin in the intermediate layer. It has been found that the above-mentioned problems can be solved by using a composition containing polylactic acid in a proportion of 5%, and the present invention has been completed.

That is, the present invention includes the following:
(1) Gelatinized starch and biodegradable resin having a structure in which C-2 and C-3 in some glucose units are cleaved and carboxyl groups are formed in C-2 and C-3 In the intermediate layer, the outer layer and the inner layer are each composed of a layer containing a biodegradable resin, and the composition (A) containing oxidized starch and biodegradable resin in the intermediate layer has a moisture content of 5000 ppm by mass or less. And based on the total amount of gelatinized starch and biodegradable resin of oxidized starch, 25 to 60% by mass of gelatinized starch of oxidized starch and 75 to 40% by mass of biodegradable resin, Each of the inner layers is based on the total amount of the biodegradable resin, 30 to 45 % by mass of the polylactic acid resin (B), and 55 to 70 % by weight of the biodegradable resin (C) excluding the polylactic acid resin. Including multilayer film,
(2) The multilayer film according to (1), wherein the thickness ratio of the outer layer, the intermediate layer, and the inner layer is 1: 1: 1 to 1: 16: 1.
(3) The multilayer film according to (1) or (2), wherein the polylactic acid resin (B) has a melting point of 160 ° C. or higher.
(4) the outer layer, polylactic acid biodegradable resin except the resin (C) and that contained in the intermediate layer biodegradable resin contained in the inner layer is an aliphatic polyester, ethylene glycol and / or 1,4 The multilayer film according to any one of (1) to (3) above, which is a condensation polymer of butanediol and succinic acid and / or adipic acid,
(5) The biodegradable resins are aliphatic polyesters that are contained in the intermediate layer, an ethylene glycol and / or 1,4-butanediol and condensation polymers of succinic acid and adipic acid, succinic acid and adipic The multilayer film according to any one of (1) to (4), wherein succinic acid is 40 to 80 mol% and adipic acid is 20 to 60 mol%, based on the total amount of the acid,
(6) the outer layer is a biodegradable resin (C) and the biodegradable resin is an aliphatic aromatic polyester that is included in the intermediate layer excluding the polylactic acid resin contained in the inner layer, the aromatic polycarboxylic acid and fatty The multilayer film according to any one of (1) to (3) above, which is a condensation polymer with an aliphatic polyol and / or a condensation polymer of an aliphatic polycarboxylic acid and an aromatic polycarboxylic acid with an aliphatic polyol, and (7) The multilayer film according to (6), wherein the aliphatic polycarboxylic acid is adipic acid, the aromatic polycarboxylic acid is terephthalic acid, and the aliphatic polyol is butanediol,
(8) A compost bag comprising the multilayer film according to any one of (1) to (7) and an agricultural film comprising the multilayer film according to any one of (9) (1) to (7) are provided. Is.

  ADVANTAGE OF THE INVENTION According to this invention, the multilayer film which has the biodegradability which was improved in stability in natural environment while having practical transparency, water vapor | steam barrier property, mechanical physical property, and biodegradability is provided. In particular, since water vapor permeability and biodegradability are appropriately controlled, it is useful for compost bags and agricultural films.

  The layer structure in the multilayer film of the present invention is 3 layers or more. The inner layer and the outer layer are layers on the surface of the film, and the remainder is an intermediate layer. In the case of a three-layer blown film, the bubbles correspond to the inside and the outside, respectively. In the case of a T-die film, the side that contacts the cooling roll is the inner layer, and the side that contacts the nip roll is the outer layer.

  In order to obtain a gelatinized product of oxidized starch as one component in the composition of oxidized starch and biodegradable resin used for the intermediate layer in the multilayer film of the present invention, first, the following structure, that is, in starch It is necessary to produce oxidized starch having a structure in which C-2 and C-3 in some of the glucose units are cleaved and carboxyl groups are formed in C-2 and C-3.

In order to convert the glucose unit in the starch into the structure as described above, for example, it is usually performed by oxidizing the starch with sodium hypochlorite. When starch is oxidized with an oxidizing agent such as a peroxide, open polymerization occurs due to cleavage of the C—C bond and glycosidic bond, and the cleavage between C-2 and C-3 is not sufficiently performed. The amount formed is insufficient.
Oxidation of starch with sodium hypochlorite is about 40 to 50% by mass of starch concentration, preferably about 45% by mass of aqueous suspension is adjusted to pH 8 to 11 and chlorine concentration of about 8 to 12% by mass, Preferably, about 10 mass% sodium hypochlorite aqueous solution is added and it reacts at about 40-50 degreeC for about 1 to 2 hours. The reaction is preferably carried out with stirring in a corrosion-resistant reaction vessel under normal pressure. After completion of the reaction, the desired product can be obtained by separating using a centrifugal dehydrator or the like, thoroughly washing with water and drying.
The amount of the carboxyl group is represented by the degree of carboxyl group substitution, and the normal one has a value of the degree of carboxyl group substitution (neutralization titration method) of about 0.001 to 0.100, preferably 0.01 to 0.035. is there.

Commercially available starch can be used as the oxidized starch.
The method for oxidizing starch with sodium hypochlorite is, for example, Eiji Fuwa “Dictionary of Starch Science” (Asakura Shoten Co., Ltd., March 20, 2003) p408 and Jiro Jiro Kuni “Starch Science Handbook”. (Asakura Shoten Co., Ltd., July 20, 1977), p501 and the like.

  There is no restriction | limiting in particular about the starch used as the raw material of an oxidized starch, Any starch can be used. For example, potato starch, corn starch, sweet potato starch, tapioca starch, sago palm starch, rice starch, wheat starch, and other unmodified starches, and various esterified starches, etherified starches, and the like can be exemplified.

  The biodegradable resin of the multilayer film of the present invention and the biodegradable resin (C) excluding the inner and outer polylactic acid resins are not particularly limited. The resin itself may be a biodegradable resin, and is preferably thermoplastic considering moldability. Resins belonging to any of chemically synthesized resins, microbial resins, natural product utilizing resins, and the like may be used. For example, aliphatic polyester (for example, polybutylene succinate, polybutylene succinate-adipate, polyethylene succinate, polycaprolactone, polylactic acid, polyhydroxybutyrate / valerate copolymer, etc.), aliphatic aromatic polyester (polybutylene, etc.) Terephthalate-adipate copolymer, etc.), polyvinyl alcohol, acetyl cellulose and the like. These may be used alone or in combination of two or more. Among these, when considering film moldability and physical properties, an aliphatic polyester or aromatic aliphatic polyester having a melting point of 50 to 180 ° C. and a weight average molecular weight of 50000 or more is preferable for obtaining a good molded product.

  Here, the aliphatic polyester is usually obtained by dehydration cocondensation of glycols and an aliphatic dibasic acid. Examples of the glycol include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, decamethylene glycol, neopentyl glycol and the like. Examples of the aliphatic dibasic acid include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and anhydrides thereof. In order to obtain an aliphatic polyester having a practical melting point, it is preferable to use ethylene glycol and / or 1,4-butanediol as the glycol and succinic acid and / or adipic acid as the aliphatic dibasic acid.

In particular, as the aliphatic polyester used in the intermediate layer, succinic acid and adipic acid are used as the aliphatic dibasic acid, and the succinic acid is 40 to 80 mol%, preferably 30 to 70, based on the total amount of succinic acid and adipic acid. In order to obtain good moldability and tear strength, it is preferable to use an aliphatic polyester having a mol% and adipic acid content of 20 to 60 mol%, preferably 30 to 50 mol%. If the succinic acid content is less than 40 mol%, the crystallization rate is slow, so that molding is difficult. If it exceeds 80 mol%, the tear strength decreases.
Moreover, what added a small amount of trihydric or tetrafunctional polyhydric alcohol, oxycarboxylic acid, or polyhydric carboxylic acid as another component may be used.

  The aliphatic aromatic polyester is a condensation polymer of an aromatic polycarboxylic acid and an aliphatic polyol or an aliphatic polycarboxylic acid and a condensation polymer of an aromatic polycarboxylic acid and an aliphatic polyol. It is desirable that the carboxylic acid is adipic acid, the aromatic polycarboxylic acid is terephthalic acid, and the aliphatic polyol is butanediol from the viewpoint of sufficient biodegradability and good physical properties.

Furthermore, there are commercially available aliphatic polyesters, for example, “Bionore” (registered trademark) series manufactured by Showa Polymer Co., Ltd. is well known.
As the aliphatic polyester, it is preferable to use “Bionore” series. As the aliphatic aromatic polyester, there are commercially available products, for example, “Ecoflex” (registered trademark) manufactured by BASF is well known.
In order to adjust the softening temperature of the biodegradable film finally obtained and the flexibility of the film, a polylactic acid resin can be used in combination.

  The gelatinized product of oxidized starch in the composition (A) used for forming the intermediate layer in the multilayer film of the present invention (for gelatinization reaction, the gelatinized product of oxidized starch and biodegradable resin are mixed to biodegradable. The content ratio of the biodegradable resin and the content ratio of the biodegradable resin is described in particular in terms of the moldability when the intermediate composition is produced by molding the composition and the physical properties of the resulting intermediate layer. From the viewpoint, based on the total amount of the gelatinized product of oxidized starch and the biodegradable resin, 25 to 60% by mass of gelatinized product of oxidized starch (75 to 40% by mass of biodegradable resin) is contained, preferably 30 to 30%. 50 mass% (biodegradable resin is 70-50 mass%). By making the gelatinized product of oxidized starch 25% by mass or more, economic efficiency is exhibited, and an improvement effect of moldability when producing the intermediate layer and an improvement in tear strength of the obtained intermediate layer are obtained. Moreover, the gelatinization thing of an oxidized starch shall be 60 mass% or less, and the fall of the film moldability by the dispersion | distribution of starch and the physical property of an intermediate | middle layer are prevented from falling.

As a method for producing a composition containing oxidized starch and a biodegradable resin used for forming an intermediate layer in the multilayer film of the present invention, an extruder that is usually used when melt-mixing a thermoplastic resin is used. It is preferable.
Specifically, it is equipped with a vent for dehydration with a twin screw system in order to simultaneously gelatinize, dehydrate, and melt-mix the gelatinized oxidized starch and biodegradable resin. is important. Furthermore, in order to ensure a sufficient production amount, sufficient L / D is an important factor, and usually L / D is 32 or more. As a more efficient method of dehydration and mixing, in the first step, the backflow due to the pressure increase in the extruder is prevented with an open vent at the completion of gelatinization of the oxidized starch by heating and mixing, and further in the second step, oxidized starch is used. The dehydration is performed with a vacuum vent while further mixing the gelatinized product and the biodegradable resin.

  In order to complete these two steps with a single extruder, it is important that the L / D is 32 at the minimum, and it is possible to increase the discharge amount with an apparatus having a larger L / D. The manufacturing cost can be reduced. In the first step, the set temperature is set to about 60 to 160 ° C., preferably 80 to 140 ° C. according to the softening temperature (or melting point) of the biodegradable resin. Since many biodegradable resins soften (melt) in this temperature range, gelatinized oxidized starch and biodegradable resin are mixed in a molten state simultaneously with gelatinization of the oxidized starch. The residence time in the first step is usually 30 to 180 seconds, preferably 60 to 120 seconds. By setting the residence time to 30 seconds or longer, gelatinization of the oxidized starch proceeds sufficiently, and by setting it to 180 seconds or shorter, decomposition can be suppressed and productivity can be ensured.

  In the second step, the set temperature is about 130 to 180 ° C, preferably 150 to 170 ° C. Thereby, the gelatinized product of oxidized starch and the biodegradable resin composition are completely melt-mixed. The residence time in the second step is usually 30 to 120 seconds, preferably 60 to 90 seconds. By setting the residence time to 30 seconds or longer, the gelatinized oxidized starch and the biodegradable resin are sufficiently mixed, and by setting the residence time to 120 seconds or shorter, decomposition can be suppressed and productivity can be secured. it can.

For the gelatinization of oxidized starch in the first step, it may be possible only with the moisture retained by the oxidized starch itself, depending on the temperature, residence time, shearing force, etc., but necessary to complete gelatinization Water and / or polar high-boiling solvents can be added. Examples of the high boiling polar solvent include ethylene glycol, propylene glycol, glycerin, sorbitol, polyethylene glycol, and polypropylene glycol.
Among these, glycerin is preferably used from the viewpoint of compatibility with starch and biodegradable resin, gelatinization ability and cost balance.
The composition containing the oxidized starch used for the intermediate layer of the present invention and the biodegradable resin is obtained by the procedure as described above.

  In the composition (A) containing the obtained oxidized starch and biodegradable resin, the water contained in the oxidized starch, the water for completing gelatinization, or the moisture in the air during storage If a large amount of moisture absorbed by touching is contained, foaming may occur at the time of film formation, the surface of the film becomes inhomogeneous, and pores may be generated when the surface gets worse. In particular, the composition (A) containing oxidized starch and biodegradable resin used for the intermediate layer is unlikely to dissipate moisture that is volatilized during molding by the surface layer, and thus easily becomes air bubbles and easily causes the above-mentioned problems. Therefore, the moisture content of the obtained composition (A) containing oxidized starch and biodegradable resin is 5,000 mass ppm or less, preferably 4,000 mass ppm or less. Although there is no limitation in particular as a method of removing a water | moisture content, the heat drying at 50-100 degreeC is preferable. In heat drying, the air may not be circulated in the apparatus. However, in order to perform quick drying, a dehumidified air circulation dryer or a fluidized bed dryer in which the generated hot air circulates in the apparatus is preferable. Alternatively, one or a plurality of vent holes may be provided in the second step in which the gelatinized product of oxidized starch and the biodegradable resin composition are melt-mixed to sufficiently remove moisture.

  In the multilayer film of the present invention, each of the outer layer and the inner layer is based on the total amount of the biodegradable resin, and the polylactic acid resin (B) is 5 to 50% by mass, desirably 5 to 40% by mass, and more desirably 7 to The proportion of the biodegradable resin (C) excluding the polylactic acid resin is 28 to 95% by mass, desirably 60 to 95% by mass, and more desirably 72 to 93% by mass. When the component (B) is less than 5% by mass, biodegradation is fast, so that durability in the field is deteriorated and rigidity is lowered. On the other hand, if the amount is more than 50% by mass, the tear strength is lowered and no practical strength is exhibited.

  As a manufacturing method of the resin composition used for the outer layer and the inner layer of the present invention, the polylactic acid resin (B) and the biodegradable resin (C) excluding the polylactic acid resin are melt-mixed using an extruder, and the composition There is a method of making a product pellet. When forming into a film or the like, the polylactic acid resin (B) and the biodegradable resin (C) excluding the polylactic acid resin may be mixed in a pellet state and directly molded.

  The polylactic acid resin (B) used in the present invention may be one obtained by polymerizing a lactic acid monomer as an essential component. For example, poly L-lactic acid whose structural unit is L-lactic acid, poly D-lactic acid whose structural unit is D-lactic acid, poly DL-lactic acid whose structural units are L-lactic acid and D-lactic acid, and mixtures thereof It can be a polymer containing as a main component. Moreover, as a structure of the above-mentioned polylactic acid-type resin, it is preferable that it is D-lactic acid: L-lactic acid = 100: 0-85: 15 or 0: 100-15: 85 as molar ratio.

  It is also possible to blend other polylactic acid resins having different constituent ratios of D-lactic acid and L-lactic acid. A polylactic acid resin having only D-lactic acid or L-lactic acid as a structural unit is a crystalline resin, has a high melting point, and tends to be excellent in heat resistance and mechanical properties. Furthermore, the polylactic acid-based resin may be a copolymer of the above-mentioned polylactic acid-based resin and other hydroxycarboxylic acid units described later, or may contain a small amount of a chain extender residue. As other hydroxycarboxylic acid units, optical isomers of lactic acid (D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid), glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid 2-functional aliphatic hydroxycarboxylic acids such as 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, 2-hydroxycaproic acid, and the like, and Examples include lactones such as caprolactone, butyrolactone, and valerolactone. Such other hydroxycarboxylic acid units are preferably used in an amount of less than 15 mol% in the component (B).

  As a polymerization method of the polylactic acid resin (B), a known method such as a condensation polymerization method or a ring-opening polymerization method can be employed. For example, in the condensation polymerization method, polylactic acid resin having an arbitrary composition and crystallinity can be obtained by directly dehydrating condensation polymerization of L-lactic acid, D-lactic acid, or a mixture thereof. Further, in the ring-opening polymerization method (lactide method), a lactate which is a cyclic dimer of lactic acid can be used to obtain a polylactic acid resin using an appropriate catalyst while using a polymerization regulator or the like as necessary. it can. The lactide includes L-lactide which is a dimer of L-lactic acid, D-lactide which is a dimer of D-lactic acid, DL-lactide which is a dimer of D-lactic acid and L-lactic acid. These are mixed as necessary and polymerized to obtain a polylactic acid resin having an arbitrary composition and crystallinity. The polylactic acid resin used in the present invention preferably has a weight average molecular weight of 60,000 to 700,000, more preferably 80,000 to 400,000, and particularly preferably 100,000 to 300,000. When the molecular weight is less than 60,000, practical physical properties such as mechanical properties and heat resistance are hardly expressed, and when it is more than 700,000, the melt viscosity is too high and the molding processability is poor. The melting point is preferably 160 ° C. or more and 170 ° C. or less. When the melting point is less than 160 ° C., biodegradation and hydrolysis are fast. The problem is that it cannot be stored for a long time because it is easy to occur. When the temperature exceeds 170 ° C., the molding temperature must be increased, so that it may be difficult to co-extrusion with starch that tends to burn at high temperatures.

Next, the biodegradable multilayer film of the present invention will be described.
As a method for producing a biodegradable multilayer film of the present invention, for example, as described above, a gelatinized product of oxidized starch and a biodegradable resin are melt-mixed using an extruder to form an intermediate layer. A composition for forming an outer layer and an inner layer by melting and mixing the polylactic acid resin (B) and the biodegradable resin (C) excluding the polylactic acid resin with an extruder as the composition (A) The extruder outlet may be connected to a known water-cooled or air-cooled multilayer inflation molding or a T-die multilayer film molding machine and continuously produced by a co-extrusion method together with a biodegradable resin that becomes an outer layer and an inner layer. The intermediate layer and the composition for forming the outer layer and the inner layer are once pelletized or flaked, and separately known water-cooled or air-cooled multilayer inflation molding, T-die multilayer film extrusion molding It may be formed by co-extrusion method together with the biodegradable resin to be the outer layer and the inner layer as well be used.
Further, after a film to be an intermediate layer is prepared, a solution of a biodegradable resin may be applied to both surfaces of the film, or a film to be an outer layer and an inner layer may be formed by lamination.

  When forming into the biodegradable multilayer film of the present invention, each of the intermediate layer, outer layer and inner layer may further contain a plasticizer. The effect of adding a plasticizer is exhibited when the biodegradable resin further contains a polylactic acid resin. As the plasticizer to be used, a glycerin derivative is preferable, and polyglycerin acetate or a derivative thereof or adipic acid diester is particularly preferable. The addition amount is usually about 1 to 10% by mass, preferably 2 to 8% by mass. By setting the content to 1% by mass or more, film properties, particularly tensile elongation and film impact strength are improved, and by setting the content to less than 10% by mass, the plasticizer bleeds to prevent appearance defects.

  In addition, for each layer of the intermediate layer, outer layer or inner layer of the biodegradable multilayer film of the present invention, additives usually used in the technical field as desired, for example, antioxidants, heat stabilizers, UV protection An agent, an antistatic agent, a flame retardant, a crystallization accelerator, a pigment, and the like may be added as long as the characteristics of the present invention are not impaired.

  Specifically, 1,1,3-tris (2-methyl-4hydroxy-5-t-butylphenyl) butane and n-octadecyl-3- (3,5-di-t-butyl) are used as antioxidants. -4-hydroxyphenyl) propionate, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane, triethylene glycol bis [3- (3-t-butyl-4- Hindered phenolic antioxidants such as hydroxy-5-methylphenyl) propionate] and tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate; triphenyl phosphite as the thermal stabilizer; Trisnonylphenyl phosphite and the like; UV absorbers include pt-butylphenyl salicylate, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2, -carboxybe Zophenone, 2,4,5-trihydroxybutyrophenone, etc .; N, N-bis (hydroxyethyl) alkylamine, alkylamine, alkylarylsulfonate, alkylsulfonate, etc. as antistatic agent; hexabromocyclododecane as flame retardant, Tris- (2,3-dichloropropyl) phosphate, pentabromophenyl allyl ether and the like; Examples of the crystallization accelerator include talc, holon nitride, polyethylene terephthalate, poly-transcyclohexanedimethanol terephthalate and the like. As the pigment, known pigments can be used alone or in combination. Specifically, carbon black, titanium white, titanium yellow, disazo yellow, isoindolinone yellow, polyazo yellow, polyazo red, quinacridone red, Examples include DPP red, perylene red, phthalocyanine green, phthalocyanine blue, dial, ultramarine, dioxazine violet, iron black, and the like.

  The above additives can be added and dispersed in the production process of each biodegradable resin raw material used in the outer layer, the intermediate layer, and the inner layer. Melting and mixing the degradable resin with an extruder, in the outer layer and the inner layer, melting the polylactic acid resin (B) and the biodegradable resin (C) excluding the polylactic acid resin with an extruder It is also possible to add and disperse the material in the mixing stage. Further, when film forming is performed using a water-cooled or air-cooled multi-layer inflation molding or a T-die multi-layer film extrusion molding machine, it can be introduced into a hopper together with the material and dispersed. Can be added as a masterbatch to prevent agglomeration and improve dispersibility, in which case aliphatic polyesters, aliphatic aromatics in order to be compatible with the material and not remain as a residue after biodegradation It is desirable to add an additive to a biodegradable resin such as polyester or polylactic acid resin to form a masterbatch. In the master batch, a known dispersant suitable for each additive and resin can be used. For example, low molecular weight resin waxes such as ethylene bisamide, polyethylene wax and polypropylene wax, fatty acid metal salts such as calcium stearate and magnesium stearate, water and the like can be used.

As described above, the starch and biodegradable resin once pelletized or flaked instead of continuously producing a film following the preparation of the composition of oxidized starch and biodegradable resin used for the intermediate layer In the case of producing a multilayer film using a composition containing, the preset temperature of the intermediate layer extruder of the multilayer inflation molding, T-die type multilayer film extruder is the same as that of the second step, that is, 130 to About 180 ° C., preferably 145 to 170 ° C. Below 130 ° C., plasticization becomes insufficient and cannot be extruded, or unmelted material is extruded into the film, so that the film is perforated or gel is formed, resulting in a non-uniform film. Above 180 ° C., the starch component begins to oxidize, causing problems such as film coloration and black spots due to scorching. As for the set temperature of the outer layer and inner layer extruders, the barrel temperature is preferably set to 180 ° C. to 230 ° C., and the temperature settings of the extruder and die adapter and the die are preferably set to 130 to 180 ° C. When the barrel set temperature is 180 ° C. or lower, polylactic acid does not melt, and when it is 230 ° C. or higher, the material deteriorates, the molecular weight decreases, and the moldability deteriorates. If the set temperature of the adapter and the die is 130 ° C. or less, plasticization becomes insufficient and cannot be extruded, or unmelted material is extruded into the film, so that the film is perforated or gel is formed, resulting in unevenness. Become a film. Above 180 ° C., the starch component in the intermediate layer begins to oxidize, causing problems such as film coloring and black spots due to scorching.
The biodegradable multilayer film of the present invention may be further uniaxially or biaxially stretched.

The ratio of the outer layer: intermediate layer: inner layer thickness in the layer structure of the biodegradable multilayer film of the present invention is preferably 1: 1: 1 to 1: 16: 1, more preferably 1: 2: 1. 1: 8: 1. However, the thickness of the outer layer and inner layer does not necessarily have to be the same. Considering the stability, flexibility, biodegradability, cost, etc. when forming different films depending on the application of the multilayer film and the type of biodegradable resin used And can be appropriately changed.
If the thickness of the intermediate layer is significantly smaller than the thickness of the outer layer or the inner layer, the mechanical properties and low cost characteristic of the composition containing oxidized starch and biodegradable resin used for the intermediate layer cannot be utilized. When the thickness of the intermediate layer is 16 times or more of the thickness of the outer layer or the inner layer, the outer layer and the inner layer become too thin and molding stability cannot be obtained. Even if molding can be performed, the surface haze does not improve and It cannot be improved.
The total thickness of the multilayer film is preferably 10 to 100 μm, more preferably 15 to 50 μm, from the viewpoints of ease of handling, flexibility, film strength, cost, and the like.

  The composition containing oxidized starch and biodegradable resin used for forming the intermediate layer in the multilayer film of the present invention has improved moldability when it is formed into a film, so that productivity is improved, In addition, the multilayer film obtained by using a composition containing polylactic acid and a biodegradable resin on the surface layer has improved mechanical properties, particularly the impact strength of the multilayer film. Film, plastic bag, folder, protective film, adhesive tape, gloves, and packaging material. In particular, although it is biodegradable, it is excellent in stability in a natural environment and its water vapor permeability is appropriately controlled, so it is excellent in use in compost bags and agricultural films.

The present invention will be described in more detail with reference to examples and comparative examples below, but the present invention is not limited to the following examples.
[Examples 1 to 11 and Comparative Examples 1 to 8]
The resin materials used in each example are shown in Table 1, and the measured values of each characteristic are shown in Table 2. In Table 1, numerical values other than the example number, the comparative example number, and the thickness ratio in the layer structure all represent mass%.
Example 3 is a reference example.

  The column of the intermediate layer in Table 1 shows the types of oxidized starch and biodegradable resin used in the intermediate layer, and the blending amounts (mass%). The raw materials and additives in each example were mixed with a super mixer and melt-kneaded using a 65 mm screw twin-screw extruder (L / D is 35) equipped with a vent for dehydration. ) Was obtained. The set temperature is 80 to 140 ° C. for the first step, 120 to 160 ° C. for the second step, the residence time is 60 to 90 seconds for the first step, and 60 to 90 seconds for the second step.

  Each of the obtained pellets was dried at a temperature of 80 ° C. for 20 hours with a dehumidifying air circulation dryer. However, only Comparative Example 7 was 15 hours. Table 1 shows the moisture content after drying. (The numerical values in parentheses of the resin and starch in the intermediate layer in Table 1 indicate the mass% in the composition (A) after drying.) Tomy Machinery Co., Ltd. 3-type 3-layer inflation molding machine (extruder 40 mmφ, Using a die diameter of 100 mm and a lip spacing of 1.5 mm, a multilayer film having a thickness of 20 μm (outer and inner layer thickness of 5 μm, intermediate layer thickness of 10 μm) and a folding width of 350 mm (equivalent to a blow-up ratio of 2.2) is coextruded. Molded. When two types of resins were mixed and used for the outer layer and the inner layer, the pellets were mixed in advance with a tumbler, and then charged into the hopper of each extruder to perform molding.

The measuring method of each characteristic is shown below.
<Young's modulus>
The Young's modulus was Tensilon RTM-1T (manufactured by Orientec Co., Ltd.), and a sample piece having a width of 20 mm and a length of 300 mm was prepared in the MD direction and TD direction, and the tensile speed was 5 mm / min according to ASTM D-822. Min, measured at a grip interval of 250 mm.
<Tear strength>
The tear strength was determined by dividing the tear strength (N) measured according to JIS P-8116 by the film thickness (mm) using a pendulum Elmendorf tear tester (manufactured by Toyo Seiki Co., Ltd.).
<Transparency (haze)>
The haze was measured according to JIS K-7105 using a haze meter HM-150 type (manufactured by Murakami Color Research Laboratory Co., Ltd.).
<Biodegradability>
Using the soil of the field of SDS Biotech Co., Ltd. “Minori Agricultural Experiment Station”, the water content was adjusted to 50% of the maximum water capacity. The soil was adjusted by acclimatization by exposing it in advance for one month with a 20 μm film made from “Bionore 3001G” manufactured by Showa Denko K.K.
The multilayer film obtained in each example cut to 5 cm square was sandwiched between nylon meshes and embedded for one month, and then the mass loss was measured, and the degree of biodegradation was evaluated in% from the reduction ratio. That is, the larger the value, the easier the biodegradation proceeds. The soil in which the test sample of the multilayer film is embedded is managed under constant temperature and humidity at a temperature of 23 ° C. and a relative humidity of 50%, and the moisture in the soil is determined from the decrease in the total mass (sample plus soil) every week. Calculated, added and controlled to retain 50% of maximum volume.

<Water vapor permeability>
For water vapor permeability, using a molded 20 μm thick film according to JIS K 7129 (Method A) (40 ° C., 90% RH), using a water vapor permeability tester L80-4000 manufactured by LYSSY, g / m ² · 24 hour).
<Film formability>
The case where a film having a predetermined size was obtained by the molding machine was indicated by ◯, and the case where the film could not be formed was indicated by ×.
Among the above properties, mechanical properties were measured for each film only when the film formability was evaluated as ◯ and a film was obtained. The mechanical properties were measured in both the vertical direction (film take-up direction, MD) and the horizontal direction (TD).
<Melting point>
The melting point of polylactic acid was measured by using a differential scanning calorimeter (DSC, SSC5200 manufactured by Seiko Instruments Inc.), melted at 200 ° C., cooled to 0 ° C. at 10 ° C./min, held for 5 minutes, and then at 10 ° C./min. The temperature was raised to 200 ° C. and the melting point was measured.
<MFR>
MFR (melt flow rate) was measured in accordance with JIS K7210 under conditions of a temperature of 190 ° C. and a load of 21.18N.
<Moisture content measurement method>
About 2 g of the sample was precisely weighed and measured at a vaporization temperature of 180 ° C. using a Karl Fischer moisture meter (MKC-210) with a moisture vaporizer (ADP-351) manufactured by Kyoto Electronics Industry Co., Ltd.
<Method for measuring weight average molecular weight>
The weight average molecular weight (hereinafter referred to as “Mw”) was measured under the following conditions using gel permeation chromatography (manufactured by Showa Denko, Shodex GPC System-11).
Solvent: Hexafluoroisopropyl alcohol solution containing 15 mmol / L of ammonium acetate Resin concentration: 0.1% by mass Calibration curve: PMMA standard sample (Showa Denko, Shodex Standard M-75)

<Materials used>
(1) Resin A: After replacing a 700 L reactor with nitrogen, 183 kg of 1,4-butanediol and 224 kg of succinic acid were charged. Subsequently, 34 g of catalyst tetraisopropoxytitanium was added under a nitrogen flow at normal pressure. The temperature was raised in a nitrogen stream, and the esterification reaction by dehydration condensation was carried out for 3.5 hours at 192 to 220 ° C. for 3.5 hours and further for 3.5 hours under a reduced pressure of 260 to 2600 Pa. Thereafter, the temperature was raised, and a deglycolization reaction was carried out at a temperature of 215 to 220 ° C. under a reduced pressure of 26 to 1940 Pa for 5.5 hours. After the deglycolization reaction, 170 g of Irganox 1010 (manufactured by Ciba Geigy) as an antioxidant and 170 g of calcium stearate as a lubricant were added, and stirring was further continued for 30 minutes. The yield of the obtained polyester was 339 kg when condensed water was removed.
In a reactor containing 339 kg of the obtained polyester, 57 g of phosphorous acid was added at 160 ° C., and stirring was further continued for 30 minutes. Subsequently, 5420 g of hexamethylene diisocyanate was added, and a coupling reaction was performed at 180 to 200 ° C. for 1 hour. The viscosity increased rapidly, but no gelation occurred. The reaction product was extruded into water with a gear pump and cut into a pellet by a cutter. The yield of polyester (B1) after vacuum drying at 90 ° C. for 6 hours was 300 kg.
The obtained polyester was slightly ivory-like white wax-like crystal having a melting point of 110 ° C., a weight average molecular weight (Mw) of 170,000, and an MFR (190 ° C.) of 1.0 g / 10 min.

(2) Resin B: After replacing a 700 L reactor with nitrogen, 194.3 kg of 1,4-butanediol, 173 kg of succinic acid, 91.8 kg of adipic acid (succinic acid: adipic acid = 70: 30 (molar ratio)) ). Subsequently, 46 g of catalyst tetraisopropoxytitanium was added. The temperature was raised in a nitrogen stream, and the esterification reaction by dehydration condensation was carried out for 3.5 hours at 192 to 220 ° C. for 3.5 hours and further for 3.5 hours under a reduced pressure of 260 to 2600 Pa. Thereafter, the temperature was raised, and a deglycolization reaction was carried out at a temperature of 215 to 220 ° C. under a reduced pressure of 26 to 1940 Pa for 5.5 hours. After the deglycolization reaction, 190 g of Irganox 1010 (manufactured by Ciba Specialty Chemicals) as an antioxidant and 190 g of calcium stearate as a lubricant were added, and stirring was continued for another 30 minutes.
The yield of the obtained polyester was 380 kg when condensed water was removed. In a reactor containing 380 kg of the obtained polyester, 57 g of phosphorous acid was added at 160 ° C., and stirring was further continued for 30 minutes. Next, 4180 g of hexamethylene diisocyanate was added to the reactor under stirring, and a coupling reaction was performed at 160 to 190 ° C. for 1 hour. The viscosity increased rapidly, but no gelation occurred. The reaction product was extruded into water with a gear pump and cut into a pellet by a cutter. The polyester yield after drying in a dehumidifying air circulation dryer at 70 ° C. for 3 hours was 350 kg.
The obtained polyester was in the form of white pellets, the melting point was 76 ° C., the weight average molecular weight (Mw) was 210000, and the MFR was 2.3 g / 10 min.

(3) Resin C: After replacing the 700 L reactor with nitrogen, 174 kg of 1,4-butanediol, 173 kg of succinic acid, and 54 kg of adipic acid (succinic acid: adipic acid = 80: 20 (molar ratio)) were charged. . Subsequently, 46 g of catalyst tetraisopropoxytitanium was added. The temperature was raised in a nitrogen stream, and the esterification reaction by dehydration condensation was carried out for 3.5 hours at 192 to 220 ° C. for 3.5 hours and further for 3.5 hours under a reduced pressure of 260 to 2600 Pa. Thereafter, the temperature was raised, and a deglycolization reaction was carried out at a temperature of 215 to 220 ° C. under a reduced pressure of 26 to 1940 Pa for 5.5 hours. After the deglycolization reaction, 190 g of Irganox 1010 (manufactured by Ciba Specialty Chemicals) as an antioxidant and 190 g of calcium stearate as a lubricant were added, and stirring was continued for another 30 minutes. The obtained polyester had a yield of 325 kg, excluding condensed water.
Into a reactor containing 325 kg of the obtained polyester, 57 g of phosphorous acid was added as a coloring inhibitor at 160 ° C., and stirring was further continued for 30 minutes. Next, 3600 g of hexamethylene diisocyanate was added to the reactor with stirring, and a coupling reaction was performed at 160 to 190 ° C. for 1 hour. The viscosity increased rapidly, but no gelation occurred. The reaction product was extruded into water with a gear pump and cut into a pellet by a cutter. The polyester yield after drying with a dehumidifying air circulation dryer at 70 ° C. for 3 hours was 300 kg.
The obtained polyester was in the form of white pellets, the melting point was 92 ° C., the weight average molecular weight (Mw) was 230000, and the MFR was 1.2 g / 10 minutes.

(4) Resin D: A 700 L reactor was purged with nitrogen, and then charged with 172 kg of 1,4-butanediol, 130 kg of succinic acid, and 107 kg of adipic acid (succinic acid: adipic acid = 60: 40 (molar ratio)). . Subsequently, 46 g of catalyst tetraisopropoxytitanium was added. The temperature was raised in a nitrogen stream, and the esterification reaction by dehydration condensation was carried out for 3.5 hours at 192 to 220 ° C. for 3.5 hours and further for 3.5 hours under a reduced pressure of 260 to 2600 Pa. The temperature was raised, and the deglycolization reaction was performed at a temperature of 215 to 220 ° C. under a reduced pressure of 26 to 1940 MPa for 5.5 hours. After the deglycolization reaction, 190 g of Irganox 1010 (manufactured by Ciba Specialty Chemicals) as an antioxidant and 190 g of calcium stearate as a lubricant were added, and stirring was continued for another 30 minutes. The yield of the obtained polyester was 336 kg when condensed water was removed.
In a reactor containing 336 kg of the obtained polyester, 57 g of phosphorous acid was added as a coloring inhibitor at 160 ° C., and stirring was further continued for 30 minutes. Next, 3700 g of hexamethylene diisocyanate was added to the reactor with stirring, and a coupling reaction was performed at 160 to 190 ° C. for 1 hour. The viscosity increased rapidly, but no gelation occurred. The reaction product was extruded into water with a gear pump and cut into a pellet by a cutter. The polyester yield after drying in a dehumidifying air circulation dryer at 70 ° C. for 3 hours was 307 kg.
The obtained polyester was in the form of white pellets, the melting point was 92 ° C., the weight average molecular weight (Mw) was 240000, and the MFR was 1.0 g / 10 min.

(5) Resin E: Dehydration condensation type aliphatic aromatic polyester manufactured by BASF Corporation [Ecoflex (melting point: 120 ° C., MFR; 4.0 g / 10 min)]
(6) Resin F: After replacing the 700 L reactor with nitrogen, 180 kg of 1,4-butanediol, 213 kg of succinic acid, and 17 kg of adipic acid (succinic acid: adipic acid = 94: 6 (molar ratio)) were charged. . Subsequently, 46 g of catalyst tetraisopropoxytitanium was added. The temperature was raised in a nitrogen stream, and the esterification reaction by dehydration condensation was carried out for 3.5 hours at 192 to 220 ° C. for 3.5 hours and further for 3.5 hours under a reduced pressure of 260 to 2600 Pa. The temperature was raised, and the deglycolization reaction was performed at a temperature of 215 to 220 ° C. under a reduced pressure of 26 to 1940 Pa for 5.5 hours. After the deglycolization reaction, 190 g of Irganox 1010 (manufactured by Ciba Specialty Chemicals) as an antioxidant and 190 g of calcium stearate as a lubricant were added, and stirring was continued for another 30 minutes. The collected polyester had a yield of 336 kg excluding condensed water.
In a reactor containing 336 kg of the obtained polyester, 57 g of phosphorous acid was added as a coloring inhibitor at 160 ° C., and stirring was further continued for 30 minutes. Next, 3600 g of hexamethylene diisocyanate was added to the reactor with stirring, and a coupling reaction was performed at 160 to 190 ° C. for 1 hour. The viscosity increased rapidly, but no gelation occurred. The reaction product was extruded into water with a gear pump and cut into a pellet by a cutter. The polyester yield after drying in a dehumidifying air circulation dryer at 70 ° C. for 3 hours was 307 kg.
The obtained polyester was in the form of white pellets, the melting point was 92 ° C., the weight average molecular weight (Mw) was 230000, and the MFR was 1.3 g / 10 minutes.

(7) Polylactic acid A: Polylactic acid Revoda 110, manufactured by Zhejiang Haisheng Biological Materials Co., Ltd. Melting point: 160 ° C., MFR: 5 g / 10 min. 3 g / 10 min (9) Starch A: Oxidized starch manufactured by Oji Corn Starch Co., Ltd. [Ace A; carboxyl group substitution degree 0.01, viscosity 300 plus or minus 50 BU (Brabender viscosity, concentration 20% by mass, 1 hour after 50 ° C.) Measurement), moisture 12 mass% (normal pressure heating method 105 ° C., 4 hours)
(10) Starch B: Corn Starch manufactured by Oji Corn Starch Co., Ltd. [Raw starch; Carboxyl group substitution degree 0, Viscosity 1100 plus or minus 50 BU (Brabender viscosity, concentration 8% by mass, measured after 1 hour at 50 ° C.), moisture 12% by mass (Normal pressure heating method 105 ° C, 4 hours)
(11) Water: Deionized water (12) High boiling polar solvent: Sakamoto Yakuhin Kogyo Co., Ltd., purified glycerin (13) Plasticizer A: Riken Vitamin Co., Ltd. polyglycerin acetate [Riquemar PL-710]
(14) Plasticizer B: Adipic acid diester [Adeka Sizer RS-107] manufactured by Asahi Denka Co., Ltd.

From the measurement results of each characteristic shown in Table 2, the multilayer film of the present invention is superior in balance of mechanical strength, transparency and film formability, water vapor permeability, and biodegradability as compared with the comparative example. I understand that.
In Examples 1 to 11, films having practical rigidity and tear strength, high transparency, moderate biodegradability, and moderate water vapor permeability were obtained.

In Comparative Example 1, when raw starch was used instead of oxidized starch, starch agglomerated, holes were opened from that portion, and a film could not be formed.
In Comparative Example 2, the tear strength was greatly reduced because 60% by mass of polylactic acid was added to the surface layer.
In Comparative Example 3, since polylactic acid was not added to the surface layer, biodegradation was fast, and when used as a multifilm, it could not be used due to deterioration depending on the climate and crops.
In Comparative Example 4, oxidized starch was used, but because the amount of starch was too much, the starch aggregated, and holes were opened from that portion, making it impossible to form a film.
In Comparative Example 5, the tear strength was greatly reduced because the amount of starch was too small.
In Comparative Example 6, since the surface layer was not provided, the water vapor permeability was high and the biodegradation was accelerated.
In Comparative Example 7, the drying time of the pellets used for the intermediate layer was set to 15 hours, so there was a lot of moisture, foamed at the die exit, and a hole was formed at the time of film formation, and the film could not be formed.
In Comparative Example 8, since no starch was used for the intermediate layer, the tear strength was reduced.

  As described above in detail, the present invention relates to a multilayer film having a high proportion of plant-derived raw materials, good physical properties, and economical biodegradability, and according to the present invention, it is necessary to recover after use. The present invention is useful as a film suitable for use in agricultural films and compost bags that can be put into compost production facilities as they are, and plastic bags that decompose and disappear in the natural environment even if discarded.

Claims (9)

An intermediate layer of gelatinized oxide starch and biodegradable resin having a structure in which C-2 and C-3 in some glucose units are cleaved and carboxyl groups are formed in C-2 and C-3 And the outer layer and the inner layer are each composed of a layer containing a biodegradable resin, and the composition (A) containing oxidized starch and biodegradable resin of the intermediate layer has a moisture content of 5000 ppm by mass or less, and Based on the total amount of the gelatinized product of oxidized starch and biodegradable resin, the gelatinized product of oxidized starch is contained in a proportion of 25 to 60% by mass and biodegradable resin in a proportion of 75 to 40% by mass, each of the outer layer and the inner layer Is a multilayer film containing 30 to 45 mass% of the polylactic acid resin (B) and 55 to 70 wt% of the biodegradable resin (C) excluding the polylactic acid resin, based on the total amount of the biodegradable resin. .   The multilayer film according to claim 1, wherein the thickness ratio of the outer layer, the intermediate layer, and the inner layer is 1: 1: 1 to 1: 16: 1.   The multilayer film according to claim 1 or 2, wherein the polylactic acid resin (B) has a melting point of 160 ° C or higher. The outer layer, polylactic acid biodegradable resin except the resin (C) and biodegradable resin that contained in the intermediate layer contained in the inner layer is an aliphatic polyester, and ethylene glycol and / or 1,4-butanediol The multilayer film according to any one of claims 1 to 3, which is a condensation polymer of succinic acid and / or adipic acid. The biodegradable resins are aliphatic polyesters that are contained in the intermediate layer, an ethylene glycol and / or 1,4-butanediol and condensation polymers of succinic acid and adipic acid, the sum of succinic acid and adipic acid The multilayer film according to any one of claims 1 to 4, wherein succinic acid is 40 to 80 mol% and adipic acid is 20 to 60 mol% based on the amount. The outer layer, a biodegradable resin (C) and the biodegradable resin is an aliphatic aromatic polyester that is included in the intermediate layer excluding the polylactic acid resin contained in the inner layer, the aromatic polycarboxylic acid and an aliphatic polyol The multilayer film according to any one of claims 1 to 3, which is a condensation polymer of an aliphatic polycarboxylic acid and / or an aromatic polycarboxylic acid and an aliphatic polyol.   The multilayer film according to claim 6, wherein the aliphatic polycarboxylic acid is adipic acid, the aromatic polycarboxylic acid is terephthalic acid, and the aliphatic polyol is butanediol.   The compost bag which consists of a multilayer film of any one of Claims 1-7.   The agricultural film which consists of a multilayer film of any one of Claims 1-7.