Aliphatic polyester film, package, agricultural and forestry and fishery materials, biodegradation method, and agricultural and forestry and fishery raw materials

Abstract

To provide a film having superior biodegradability while ensuring a balance between strength and flexibility.SOLUTION: An aliphatic polyester film has a structure in which A layers comprising polylactic acid as a main component and B layers comprising polyhydroxyalkanoate as a main component are alternately disposed in the thickness direction, with the combined number of the A and B layers being at least 5.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aliphatic polyester film, particularly to an aliphatic polyester film used for packaging and agriculture, forestry and fisheries. [Background technology]

[0002] In recent years, the separate collection and composting of food waste has been promoted, particularly in Europe, creating a demand for biodegradable plastic products and packaging materials that can be composted along with food waste. Among biodegradable plastics, aliphatic polyester resins have attracted attention due to their high biodegradability, and their application as packaging materials has been explored. However, polylactic acid, which is generally considered to be easy to form into films and has excellent strength, biodegrades slowly in soil under low-temperature conditions. In contrast, polyhydroxyalkanoates, which are highly biodegradable, are difficult to stretch and suffer from poor mechanical strength and thermal dimensional stability.

[0003] As a measure to improve films containing polylactic acid, a method of forming a laminate structure of polylactic acid and another resin is known. Patent Document 1 proposes a method of overcoming the brittleness of crystalline polylactic acid by laminating polylactic acid with a backbone resin layer such as acrylic, and obtaining a film with high transparency and excellent decorative properties. Patent Document 2 proposes a method of obtaining a film with high strength and excellent dimensional stability by laminating polylactic acid with another biodegradable resin. Patent Document 3 proposes a method of obtaining a film for food product packaging with excellent barrier properties by using a biodegradable resin such as polylactic acid or polyhydroxyalkanoic acid as a substrate and forming a structure with a metal oxide on the adhesive layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-245710 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-47138 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-521161 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the films obtained by the methods described in Patent Documents 1 to 3 all have a problem in that they are biodegraded slowly in soil under low temperature conditions because they are mainly composed of polylactic acid.

[0006] Therefore, an object of the present invention is to provide an aliphatic polyester film that has the properties of polylactic acid, which allows for a small heat shrinkage rate at 120°C, and also has excellent biodegradability. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have arrived at the following invention. That is, a preferred embodiment of the present invention is as follows. (1) An aliphatic polyester film having a structure in which layers A, primarily composed of polylactic acid, and layers B, primarily composed of polyhydroxyalkanoic acid, are alternately arranged in the thickness direction, and the total number of layers A and B is 5 or more. (2) The aliphatic polyester film according to (1), wherein the layer A mainly composed of polylactic acid further contains polyhydroxyalkanoic acid. (3) The aliphatic polyester film according to (1) or (2), wherein the ratio of polylactic acid to the total mass of the aliphatic polyester film is 30% by mass or more. (4) The aliphatic polyester film according to (2), wherein in at least one layer A, the domains made of polyhydroxyalkanoic acid have an average aspect ratio of 1.1 or more and 20 or less. (5) The aliphatic polyester film according to any one of (1) to (4), wherein the thickness of each of the inner layers A and B is 0.01 μm or more and 18 μm or less. (6) The aliphatic polyester film according to any one of (1) to (5), wherein F1 (%) is the heat shrinkage at 120°C in the main orientation axis direction and F2 (%) is the heat shrinkage at 120°C in the direction perpendicular to the main orientation axis direction, and both F1 and F2 are 15% or less. (7) The aliphatic polyester film according to any one of (1) to (6), wherein S1 (MPa) is the breaking strength in the main orientation axis direction and S2 (MPa) is the breaking strength in the direction perpendicular to the main orientation axis, and both S1 and S2 are 50 MPa or more and 280 MPa or less. (8) The aliphatic polyester film according to (2) or (4), which has a continuous phase of polyhydroxyalkanoic acid in the thickness direction. (9) The aliphatic polyester film according to any one of (1) to (8), further comprising a functional layer on at least one surface thereof. (10) The aliphatic polyester film according to any one of (1) to (9), which is used for packaging purposes. (11) The aliphatic polyester film according to any one of (1) to (9), which is used for agricultural, forestry and fisheries applications. (12) A package comprising the aliphatic polyester film according to any one of (1) to (9). (13) A material for agriculture, forestry and fisheries, comprising the aliphatic polyester film according to any one of (1) to (9). (14) A biodegradation method for decomposing the aliphatic polyester film according to any one of (1) to (9) above using composting equipment. (15) A biodegradation method in which the packaging material according to (12) is decomposed using composting equipment. (16) A biodegradation method for decomposing the agricultural, forestry and fishery materials described in (13) above using composting equipment. (17) The aliphatic polyester film according to any one of (1) to (9), which is used to cover agricultural, forestry and fishery materials, wherein the agricultural, forestry and fishery materials include one or more selected from fertilizers, feeds, seeds and seedlings, and chemicals. (18) An agricultural, forestry and fishery material, characterized by being covered with the aliphatic polyester film according to any one of (1) to (9). [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an aliphatic polyester film that has the properties of polylactic acid, which allows for a small heat shrinkage rate at 120°C, and also has excellent biodegradability. DETAILED DESCRIPTION OF THE INVENTION

[0009] The aliphatic polyester film of the present invention will be described in detail below. Hereinafter, when the upper and lower limits of a preferred range are separately stated, they can be combined arbitrarily. In addition, in this specification, the aliphatic polyester film may be simply referred to as "film." In addition, in the aliphatic polyester film of the present invention, the "thickness direction" refers to the direction perpendicular to the film surface. The "longitudinal direction" refers to the direction corresponding to the flow direction in the film production process (hereinafter, also referred to as "MD"), and the "width direction" refers to the direction perpendicular to the flow direction in the film production process within the film surface (hereinafter, also referred to as "TD"). When a film sample is in the form of a reel or roll, the film winding direction can be said to be the longitudinal direction. In addition, the main orientation axis direction in the present invention is defined as follows. First, a sample is cut into a rectangle of 150 mm long x 10 mm wide with an arbitrary direction facing upward. <1> Then, the sample <1> The direction of the long side of the sample is defined as 0°. Next, a sample of the same size is placed so that the long side direction is rotated 15° to the right from the 0° direction. <2> Similarly, rotate the rectangular sample by 15° in the long side direction and collect the sample. <3> ~ <12> Next, each rectangular sample is placed in a tensile tester (A&D's "Tensilon Universal Tester" RTG-1210) with an initial chuck distance of 30 mm so that the long side is the tensile direction, and a tensile test is performed at a tensile speed of 300 mm / min in an atmosphere of 25±5°C and 65±10% RH. The load at which the sample breaks is divided by the cross-sectional area of ​​the sample before the test (thickness x width of the film sample) to calculate the breaking strength (unit: MPa), and the strain at break is calculated as the breaking elongation (unit: %). Similar measurements are performed five times for each sample, and the average values ​​are used. In the present invention, the measurement direction in which the breaking strength obtained by this method is greatest is defined as the main orientation axis direction, and the direction perpendicular to this is defined as the direction perpendicular to the main orientation axis direction.

[0010] The aliphatic polyester film of the present invention has a structure in which A layers mainly composed of polylactic acid and B layers mainly composed of polyhydroxyalkanoic acid are alternately arranged in the thickness direction, i.e., a laminated structure, and the total number of A layers and B layers is 5 or more. Here, an A layer mainly composed of polylactic acid means that the layer contains 50% by mass or more of polylactic acid in 100% by mass of the layer, and a B layer mainly composed of polyhydroxyalkanoic acid means that the layer contains 60% by mass or more of polyhydroxyalkanoic acid in 100% by mass of the layer.

[0011] By composing the A and B layers as described above, it is possible to achieve both the strength inherent in polylactic acid and the biodegradability inherent in polyhydroxyalkanoic acid. Furthermore, by alternately stacking them to form a laminate structure, the A layer, which is primarily composed of polylactic acid, has the effect of preventing dimensional changes in the adjacent B layer (hereinafter sometimes referred to as the "tensioning effect"), thereby reducing the thermal shrinkage rate at 120°C. In addition, increasing the number of B layers, which are primarily composed of polyhydroxyalkanoic acid, and increasing the surface area of ​​the A layer upon decomposition further improves biodegradability.

[0012] To further improve the balance between film strength and biodegradability, it is necessary to increase the number of layers, preferably 30 or more, and more preferably 250 or more. There is no particular upper limit to the number of layers, but if it significantly exceeds 250, the thickness per layer relative to the total film thickness will be thin, which may weaken the tensioning effect of the layer mainly composed of polylactic acid and impair dimensional stability. Therefore, from the perspective of being able to achieve both effects, the upper limit is considered to be around 780 layers. This laminate can be produced by the manufacturing method described below.

[0013] The aliphatic polyester film of the present invention preferably further contains a polyhydroxyalkanoic acid in Layer A, which is mainly composed of polylactic acid, thereby increasing the interfacial surface area of ​​the dispersed resin phase mainly composed of polyhydroxyalkanoic acid and achieving higher biodegradability.

[0014] Here, the polyhydroxyalkanoic acid is a polymer containing hydroxyalkanoic acid as a constituent component, and for example, a 3-hydroxyalkanoate repeating unit represented by the general formula [—CHR—CH—CO—O—] (wherein R is C n H 2n+1 where n is an integer of 1 to 15.) and poly(3-hydroxyalkanoates) (hereinafter sometimes referred to as "P3HA") containing the alkyl group represented by the formula:

[0015] Examples of P3HA include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxyhexanoate) (P3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (P3HB3HO), and poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (P3HBP3HD).

[0016] P3HA may be either chemically synthesized (for example, obtained by ring-opening polymerization of the corresponding lactone) or produced by a microorganism, but P3HA produced by a microorganism is preferred from the viewpoint of ease of production using biomass raw materials such as vegetable oil. Among P3HA produced by a microorganism, P3HB, P3HB3HH, P3HB3HV, P3HB3HV3HH, and P3HB4HB are preferably used from the viewpoint of ease of industrial production.

[0017] The melting point and crystallinity of polyhydroxyalkanoates, including P3HA, can be adjusted by changing the composition ratio of the repeating units. Although polyhydroxyalkanoates are generally known to be prone to thermal decomposition, by designing a copolymer structure of two or more hydroxyalkanoates with a low melting point, it is possible to create a sufficient temperature difference between the temperature range where melt extrusion processing is possible and the thermal decomposition temperature range.

[0018] The aliphatic polyester film of the present invention preferably has a polylactic acid content of 30% by mass or more relative to the total mass of the film, which increases the strength of the film and improves its stretchability, thereby improving film formability. The ratio of polylactic acid to the total mass of the film being 30% by mass or more herein refers to the ratio (% by mass) of the mass of polylactic acid to 100% by mass of the film.

[0019] Since the strength of the film improves and the dimensional stability improves as the proportion of polylactic acid in the total mass of the film increases, the polylactic acid content is more preferably 45% by mass or more, and even more preferably 60% by mass or more. There is no particular upper limit for the proportion of polylactic acid, but if it exceeds 60% by mass, the proportion of polyhydroxyalkanoic acid components in the film decreases, which may impair biodegradability. Therefore, from the perspective of achieving both effects, the upper limit is considered to be around 60% by mass.

[0020] In the aliphatic polyester film of the present invention, the average aspect ratio of the domains composed of polyhydroxyalkanoic acid is preferably 1.1 to 20 in at least one of the multiple A layers. Having an average aspect ratio of the domains (resin-dispersed phase) primarily composed of polyhydroxyalkanoic acid in the A layer is 1.1 to 20, which increases the diameter of the polyhydroxyalkanoic acid domains in the A layer and increases the interfacial surface area with the B layer containing polyhydroxyalkanoic acid, thereby improving biodegradability. From the above viewpoint, the average aspect ratio of the domains composed of polyhydroxyalkanoic acid in at least one of the A layers is more preferably 1.1 to 10, and even more preferably 1.1 to 5. From the same viewpoint, it is more preferable that the aspect ratio is within the above range in at least 50% of the multiple A layers, and even more preferable that the aspect ratio is within the above range in at least 80% of the multiple A layers. The average aspect ratio of the domains is determined by the method described in the Examples.

[0021] In the aliphatic polyester film of the present invention, the thickness of each of the inner layers, Layer A and Layer B, is preferably 0.01 μm or more and 18 μm or less. The inner layer here refers to the layers excluding the outermost layers on both sides of the film. By setting the thickness of each layer to 0.01 μm or more and 18 μm or less, the effect of improving dimensional stability due to tensioning of the layer containing polylactic acid as the main component can be more effectively achieved. Since the thicker the layer containing polylactic acid as the main component, the greater the tensioning effect, the thickness of each layer is more preferably 0.03 μm or more and 10 μm or less, and even more preferably 0.05 μm or more and 5 μm or less.

[0022] The thickness of the aliphatic polyester film of the present invention can be set depending on the application, but for example, for applications in the form of a film, such as general packaging, release agents, and agricultural, forestry, and fisheries applications, it is preferably 6 μm to 200 μm, and from the viewpoint of handling during processing and use, the upper limit is more preferably 100 μm, even more preferably 50 μm, and the lower limit is more preferably 8 μm, even more preferably 10 μm. Furthermore, for applications including a molding process such as tray molding or applications requiring self-supporting properties, the thickness is preferably 10 μm to 300 μm from the viewpoint of processability and handleability, and from the viewpoint of cost and film formability, the upper limit is more preferably 250 μm, even more preferably 220 μm, and the lower limit is more preferably 30 μm, even more preferably 50 μm.

[0023] In the aliphatic polyester film of the present invention, when the breaking strength in the main orientation axis direction measured by the method described below is S1 (MPa) and the breaking strength in the direction perpendicular to the main orientation axis is S2 (MPa), it is preferable that S1 and S2 are both 50 MPa or more and 280 MPa or less.

[0024] By having both S1 and S2 be 50 MPa or more, it is possible to prevent a decrease in the barrier properties and biodegradability of the aliphatic polyester film. Furthermore, by having both S1 and S2 be 280 MPa or less, it is possible to prevent a decrease in the processability of the aliphatic polyester film. From the same viewpoint as above, it is more preferable that both S1 and S2 be 100 MPa or more. From the same viewpoint as above, it is more preferable that both S1 and S2 be 240 MPa or less, and even more preferable that both S1 and S2 be 200 MPa or less.

[0025] The method for controlling S1 and S2 within the above ranges is not particularly limited, but examples include a method of controlling the content ratio of polylactic acid and / or polyhydroxyalkanoic acid within a preferred range. Other examples include a method of using a resin with a low water content during film formation, and a method of further slightly stretching after biaxial stretching.

[0026] In the aliphatic polyester film of the present invention, when the heat shrinkage in the main orientation axis direction measured by the method described below is F1 (%) and the heat shrinkage in the direction perpendicular to the main orientation axis direction is F2 (%), it is preferable that both F1 and F2 are 15% or less. By making both F1 and F2 15% or less, the dimensional stability of the aliphatic polyester film can be improved. To improve dimensional stability, the smaller the heat shrinkage due to heating, the better, so both F1 and F2 are more preferably 10% or less, and even more preferably 5% or less.

[0027] The method for controlling F1 and F2 within the above ranges is not particularly limited, but examples include a method for controlling the polyhydroxyalkanoic acid content and the heat setting temperature in the production method to fall within preferred ranges, as described below.

[0028] The aliphatic polyester film of the present invention preferably has a continuous phase of polyhydroxyalkanoic acid in the thickness direction. Here, "thickness direction" refers to the direction perpendicular to the film surface. Furthermore, the continuous phase of polyhydroxyalkanoic acid in the thickness direction refers to a form in which the polyhydroxyalkanoic acid phase is continuous in adjacent layers A and B. Having a continuous phase in the thickness direction increases the interfacial surface area of ​​the polyhydroxyalkanoic acid, accelerating the progress of biodegradation and improving biodegradability.

[0029] In order to have a continuous phase consisting of polyhydroxyalkanoic acid in the thickness direction, for example, a method can be used in which polylactic acid and polyhydroxyalkanoic acid are not completely mixed with each other, and some of them exist as coarse domains.One way to achieve this is to have a viscosity difference between polylactic acid and polyhydroxyalkanoic acid.

[0030] In order to meet the requirements of various applications, the aliphatic polyester film according to an embodiment of the present invention preferably has a functional layer on at least one side of the film. Hereinafter, an aliphatic polyester film having a functional layer will be described. The aliphatic polyester film of the present invention having a functional layer may be simply referred to as a "laminate." Examples of functional layers that can be formed on the aliphatic polyester film include a gas barrier layer, an adhesive layer, a heat-sealing layer, an easy-adhesion layer, a colored layer, a printed layer, an easy-peel layer, a release layer, an easy-slip layer, a porous layer, and a nonwoven fabric. The method for forming the functional layer may be selected depending on the functional layer. For example, the functional layer may be formed by vapor deposition, sputtering, coating, various printing methods such as gravure printing and offset printing, thermal bonding, lamination via an adhesive layer, or the like. For example, when the aliphatic polyester film of the present invention is used for packaging applications, a coating layer, a vapor deposition layer, or a heat-sealing layer that imparts gas barrier properties is preferably selected as the functional layer. For example, when the aliphatic polyester film of the present invention is used to cover agricultural, forestry, and fishery materials such as fertilizers, feed, seeds, and medicines, a pressure-sensitive adhesive layer that imparts pressure-sensitive adhesiveness or a heat-sealing layer that imparts thermal pressure-sensitive adhesiveness is preferably selected as the functional layer that imparts adhesiveness. Note that, from the viewpoint of not impairing the effects of the present invention, it is preferable that the functional layer be biodegradable or have low toxicity.

[0031] As a gas barrier layer that can be used in the functional layer of the present invention, a vapor-deposited layer is particularly preferred from the viewpoint of exhibiting high barrier performance. A vapor-deposited layer preferably contains a metal and an inorganic compound in a total amount of more than 50% by mass but not more than 100% by mass. Here, a layer containing a metal and an inorganic compound in a total amount of more than 50% by mass but not more than 100% by mass may refer to any of the following structures, where the total amount of all components constituting the vapor-deposited layer is taken as 100% by mass: a layer containing more than 50% by mass of a metal alone; a layer containing more than 50% by mass of an inorganic compound alone; or a layer containing both a metal and an inorganic compound, the total amount of which exceeds 50% by mass. As the metal and / or inorganic compound in the vapor-deposited layer, from the viewpoints of improving adhesion to a film, improving gas barrier properties when laminated to a film, and reducing environmental impact, for example, aluminum, aluminum oxide, silicon oxide, germanium oxide, magnesium oxide, cerium oxide, calcium oxide, diamond-like carbon film, or a mixture thereof is preferably used. Furthermore, from the viewpoint of visibility of contents, it is more preferable to use an inorganic compound, particularly aluminum oxide, silicon oxide, or a mixture containing these. The thickness of the vapor-deposited layer in the laminate is preferably 200 nm or less, more preferably 110 nm or less, even more preferably 50 nm or less, and particularly preferably 30 nm or less, from the viewpoints of recyclability when the laminate is reused as a resin or film, suppressing deterioration of gas barrier properties due to cracks, and ensuring visibility of the contents when used as a packaging material. There is no particular lower limit, but 1 nm or more is preferred from the viewpoint of exhibiting barrier properties.

[0032] As a method for forming a vapor deposition layer on the aliphatic polyester film of the present invention to form a laminate, physical vapor deposition methods such as vacuum vapor deposition, EB vapor deposition, sputtering, and ion plating, and various chemical vapor deposition methods such as plasma CVD can be used, but from the viewpoint of productivity, vacuum vapor deposition is particularly preferred.

[0033] In the laminate of the aliphatic polyester film and the functional layer according to the present invention, a resin layer may be provided between the vapor-deposited layer and the surface of the aliphatic polyester film by coating or the like. The provision of such a resin layer may have the effect of improving the adhesion between the vapor-deposited layer and the aliphatic polyester film. However, from the viewpoint of production costs, an embodiment without such a resin layer (i.e., an embodiment in which the vapor-deposited layer is directly laminated on the outermost surface of the aliphatic polyester film) is preferred, and an embodiment in which the vapor-deposited layer is provided on the surface of the aliphatic polyester film is more preferred.

[0034] In addition, in the laminate of the present invention, from the viewpoint of improving the gas barrier property and suppressing a decrease in the gas barrier property due to deposition defects in the deposition layer or damage such as cracks during use, an overcoat layer may be provided on the surface of the deposition layer facing the aliphatic polyester film.

[0035] When a layer that provides adhesiveness, such as a pressure-sensitive adhesive layer or a heat-sealing layer, is laminated on the aliphatic polyester film of the present invention as a functional layer, it is preferable that the layer be laminated on at least one side of the film. Resin components that can be used for the adhesive layer, from the viewpoint of high heat-sealing strength, are preferably, for example, polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-methacrylic acid copolymer, etc., or mixtures thereof. When multiple films are laminated, from the viewpoint of reducing the thickness of the final product, it is more preferable to use, for example, ethylene-vinyl acetate copolymer (EVA)-based hot melt adhesives, olefin-based hot melt adhesives, rubber-based hot melt adhesives, polyester-based hot melt adhesives, polyamide-based hot melt adhesives, polyurethane-based hot melt adhesives, etc., or mixtures thereof. From the viewpoint of increasing the biodegradability of the entire laminate, it is even more preferable to use, for example, resin components obtained by adjusting the copolymerization components of the polyhydroxyalkanoic acids exemplified above, or biodegradable resins such as polylactic acid, polyglycolic acid, and polybutylene succinate, which have a softening point or melting point lower than that of the aliphatic polyester film of the present invention, or mixtures thereof.

[0036] The thickness of the adhesive layer in the laminate is preferably 0.5 μm or more, more preferably 1 μm or more, and even more preferably 3 μm or more, from the viewpoint of exhibiting high adhesive strength. Also, from the viewpoint of suppressing a decrease in the biodegradability of the laminate and suppressing the thickness of the final product when multiple films are laminated, the thickness of the adhesive layer in the laminate is preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less.

[0037] Furthermore, in the laminate, a resin layer having a thickness of 1 μm or less may be provided between the adhesive layer and the surface of the aliphatic polyester film by coating or the like. The provision of such a resin layer may have the effect of improving the adhesion between the adhesive layer and the aliphatic polyester film. However, from the viewpoint of production costs, an embodiment without such a resin layer (i.e., an embodiment in which the adhesive layer is laminated directly on the outermost surface of the aliphatic polyester film) is preferred, and an embodiment in which the adhesive layer is provided on the surface of the aliphatic polyester film is more preferred.

[0038] As a method for forming an adhesive layer on the aliphatic polyester film of the present invention to form a laminate, coating or lamination is particularly preferred. As a coating method, bar coating, gravure coating, calendar coating, die coating, etc. can be used. As a laminating method, dry lamination, solventless lamination, extrusion lamination, coextrusion, etc. can be used. From the viewpoint of productivity, gravure coating, die coating, extrusion lamination, and coextrusion are more preferably used.

[0039] The aliphatic polyester film of the present invention can be used for a wide variety of purposes, such as packaging applications, release applications, and process films for producing packaging materials, packaging materials, sanitary products, agricultural products, agricultural, forestry and fishery products, construction products, medical products, and various other products. In particular, when used for packaging materials and agricultural, forestry and fishery materials, the aliphatic polyester film can be suitably used as an aliphatic polyester film that has excellent biodegradability and can be used without breaking or deforming during processing and use.

[0040] The aliphatic polyester film according to an embodiment of the present invention is preferably used for packaging applications due to its excellent biodegradability, quality, and various processability. Packages containing the aliphatic polyester film according to an embodiment of the present invention can protect various contents, including food, and the manner in which they are used is not particularly limited. Examples of such packages include a bag-shaped product formed from the film or laminate of the present invention by heat sealing, and a tray-shaped container filled with or arranged with the contents, which is then sealed with the film or laminate of the present invention.

[0041] The aliphatic polyester film according to the embodiment of the present invention is favorably used as an agricultural, forestry, and fishery material because it has good biodegradability in various environments, including the marine environment, and is excellent in quality and various processability. For example, the film is favorably used for materials where biodegradability after use is preferred, such as soil mulch film, vegetation film, fumigation film, water retention film, fertilizer coating material, feed coating material, aquaculture support film, marine organism adhesion prevention film, and environmental conservation material.

[0042] The aliphatic polyester film of the present invention, and packaging and agricultural, forestry, and fishery materials containing the aliphatic polyester film of the present invention, can be biodegraded using composting equipment. Examples of composting equipment that can be used include industrial composting, which is heated or maintained at around 60°C to enhance biodegradability, simple composting made by digging holes in the soil, composting containers that are partially or completely buried in the soil, small composting such as compost bags, and biological composting such as earthworm composting and zoocomposting using flies. When the aliphatic polyester film of the present invention, packaging, or agricultural, forestry, and fishery materials containing the aliphatic polyester film of the present invention does not have a functional layer or when the functional layer is a biodegradable or low-toxicity vapor-deposited layer, they can be decomposed by placing them in composting equipment and subjecting them to a typical process, such as mixing with decomposition materials such as soil or a microorganism-containing fermentation promoter. Furthermore, when a non-biodegradable functional layer or other layer is used in combination, the functional layer may be peeled off and then placed in composting equipment, or a layer with low environmental toxicity, human toxicity, etc. may be placed in composting equipment even if it is not biodegradable, and the residue may be collected after the aliphatic polyester film of the present invention has been decomposed. The purposes of composting include waste reduction through volume reduction, composting, and biogas generation, and the aliphatic polyester film, packaging, and agricultural, forestry, and fisheries material of the present invention are suitable for composting equipment for any purpose.

[0043] The present invention relates to an aliphatic polyester film. Aliphatic polyesters are polymeric compounds that do not have an aromatic ring structure and are classified as polyhydroxy acids, polyhydroxyalkanoic acids, or polyalkylenedicarboxylic acids. The aliphatic polyester film of the present invention contains at least 50% by mass, preferably at least 95% by mass, of aliphatic polyesters. Layers A and B constituting the aliphatic polyester film of the present invention can contain, in addition to polylactic acid and polyhydroxyalkanoic acid, polyhydroxy acids such as polyglycolic acid, and polyalkylenedicarboxylic acids such as polyethylene succinate, polybutylene succinate, and polybutylene succinate adipate. The aliphatic polyesters are not limited to these.

[0044] The aliphatic polyester film of the present invention may contain various additives, such as organic particles, inorganic particles, antioxidants, heat stabilizers, slipping agents, antistatic agents, antiblocking agents, fillers, viscosity modifiers, colorants, color inhibitors, and crystal nucleating agents, as long as the additives do not impair the object of the present invention.

[0045] <Packaging materials, packaging> The packaging material and package of the present invention are described below. The packaging material of the present invention is characterized by using at least one of the aliphatic polyester film of the present invention and the laminate of the present invention. The packaging material of the present invention is excellent in handleability, not breaking or deforming even during post-processing such as printing or the conveying tension during the vapor deposition process of the vapor deposition layer provided as a gas barrier layer, and therefore can be suitably used as a packaging material. Furthermore, since it can suppress deterioration of gas barrier properties due to cracks in the vapor deposition layer, it can be suitably used for packaging items that are susceptible to deterioration by water vapor or oxygen.

[0046] The package of the present invention is characterized in that the contents are packaged using the packaging material of the present invention. The form of the package is not particularly limited. For example, a package obtained by processing the packaging material of the present invention into a bag shape by heat sealing and placing the contents inside, or a package obtained by filling or placing the contents in a tray-shaped container and then sealing it with the packaging material of the present invention, etc., can be mentioned.

[0047] <Agriculture, forestry and fisheries materials> The agricultural, forestry, and fishery material of the present invention will be described below. The agricultural, forestry, and fishery material of the present invention is characterized by using at least one of the aliphatic polyester film of the present invention and the laminate of the present invention. The agricultural, forestry, and fishery material of the present invention is characterized by combining excellent biodegradability with strength and flexibility, and is suitable for use in applications where biodegradation after use is an advantage, such as soil mulch film, vegetation film, fumigation film, water retention film, fertilizer coating material, feed coating material, seed and seedling coating material, pesticide coating material, aquaculture support film, marine organism adhesion prevention film, and environmental conservation material.

[0048] <Covering film for agricultural, forestry and fishery materials> The aliphatic polyester film of the present invention can be used to coat agricultural, forestry, and fishery materials, including one or more selected from fertilizers, feed, seeds, and chemicals. This protects the coated agricultural, forestry, and fishery materials, preventing deterioration and environmental pollution due to leakage. Furthermore, the film biodegrades in soil or the ocean, allowing the fertilizer, feed, or chemical to diffuse and disperse at the appropriate time. It also protects the seeds and seedlings from settling and settling, and then biodegrades to prevent impediments to their growth. Here, agricultural, forestry, and fishery materials refer to materials and components contained in agricultural, forestry, and fishery materials. These materials are not particularly limited as long as they do not impair the effects of the present invention, and a wide range of known materials can be used. As described above, the aliphatic polyester film of the present invention, which has excellent biodegradability, high strength, and moderate flexibility, can be used for this application to prevent leakage of the agricultural, forestry, and fishery materials contained therein through pinholes, cracks, and uneven coating thickness. The thickness of the aliphatic polyester film of the present invention can also control the rate of diffusion and dispersal in soil or the ocean. In addition, two or more agricultural, forestry, and fishery materials such as fertilizer, feed, seeds, and chemicals can be coated together. For example, coating seeds with the desired fertilizer or chemicals together is preferable because it enables germination and growth of the crop to be enhanced at the same time.

[0049] From the above viewpoint, the thickness of the aliphatic polyester film is preferably selected within the above-mentioned preferred range according to the diffusion and scattering speed in the soil or ocean. If the thickness of the aliphatic polyester film is too thin, the strength may be insufficient, which may reduce the protection of the contents or cause tearing during processing. Furthermore, if the thickness of the aliphatic polyester film is too thick, the flexibility may be insufficient, which may make it difficult to process into the desired shape described below. For example, by selecting a thin film for fast-acting fertilizers that will diffuse and scatter quickly after biodegradation and a thick film for slow-acting fertilizers that will diffuse and scatter slowly after biodegradation, and spreading these coated fertilizers together, the work of farmers can be reduced.

[0050] Furthermore, by taking advantage of the characteristics of the aliphatic polyester film of the present invention, the coating can be made into a multilayer structure. Specifically, by coating a slow-release fertilizer with the aliphatic polyester film of the present invention and then coating the surrounding area with a fast-release fertilizer and the aliphatic polyester film of the present invention, it is possible to produce a fertilizer in which the slow-release fertilizer and the fast-release fertilizer are sequentially coated with the aliphatic polyester film of the present invention. Furthermore, by coating seeds and seedlings with fertilizer, feed, and chemicals in that order in a similar manner, it is expected that the fertilizer, feed, and chemicals will be applied to the grown agricultural and marine products at the appropriate time.

[0051] As described above, agricultural, forestry, and fishery materials coated with the aliphatic polyester film of the present invention can enhance the effectiveness of agricultural, forestry, and fishery materials selected from fertilizers, feeds, seeds and seedlings, and chemicals, while preventing environmental pollution due to unintended leakage. By diffusing and scattering in the soil or ocean at the appropriate time, the efficacy can be improved and the workload of workers can be reduced, making the film particularly suitable for use in the agriculture, forestry, and fishery fields.

[0052] The form of the fertilizer, feed, seeds and chemicals coated with the aliphatic polyester film of the present invention is not particularly limited as long as it does not impair the effects of the present invention, and various forms such as pellets, granules, blocks, pouches, ropes, sheets, etc. Specifically, for coated fertilizers for agricultural use, block, pellet or granular forms that are compatible with spreaders are preferred, while for coated seeds and chemicals, rope or sheet forms that are expected to reduce work are preferred.

[0053] <Manufacturing method> The method for producing the aliphatic polyester film of the present invention will be described below. A preferred embodiment of the method for producing an aliphatic polyester film of the present invention involves the following steps in this order: a melting step of melting a resin raw material mainly composed of an aliphatic polyester, a casting step of discharging the melted resin into a film form from a die and cooling and solidifying it on a support, a stretching step of stretching the resulting film in two perpendicular directions, and a heat treatment step of subjecting the film obtained in the stretching step to a heat treatment and relaxation treatment. The aliphatic polyester film of the present invention employs a structure in which five or more layers of two types of resin are laminated alternately, such as layer A and layer B.

[0054] The production method thereof will be explained in more detail below, but the aliphatic polyester film of the present invention and the production method thereof are not necessarily limited thereto.

[0055] First, the raw material resin constituting Layer A, which is primarily composed of polylactic acid, is referred to as "Resin A," and the raw material resin constituting Layer B, which is primarily composed of polyhydroxyalkanoic acid, is referred to as "Resin B." Resin A and Resin B are melted in separate single-screw extruders. The melt is extruded from each single-screw extruder, with the extrusion temperature set to 150°C to 220°C, and passed through a filtration filter to remove foreign matter. The molten resins are then merged using a lamination device so that they are arranged alternately in the thickness direction, and extruded through a slit die to form a molten resin film laminated with five or more layers. At this time, from the viewpoint of preventing deterioration of resin A and resin B and increasing the strength of the film, it is preferable to control the oxygen concentration in the raw material charging hopper to 0.10% by volume or less.

[0056] Next, the molten resin film extruded from the slit die is cooled and solidified on a casting drum whose surface temperature is controlled to 10° C. to 40° C. to obtain an unstretched film. The molten film may be adhered to the casting drum by any of the following methods: electrostatic application, adhesion using the surface tension of water, air knife method, press roll method, underwater casting method, air chamber method, etc., or a combination of two or more methods may be used.

[0057] In the present invention, it is preferable to impart orientation to the unstretched film obtained by the above method by sequential biaxial stretching or simultaneous biaxial stretching in the longitudinal direction and the width direction.

[0058] First, when performing sequential biaxial stretching or simultaneous biaxial stretching, the unstretched film is preheated by being introduced into a group of rolls or a continuous oven before stretching. In the present invention, the crystals formed in the preheating step before stretching are pre-oriented by applying a certain range of conveyance speed difference, and then stretching is performed, thereby enabling the aforementioned degree of crystal orientation and crystallite size to be controlled with high precision. More specifically, it is preferable that the difference in conveyance speed before and after passing through a group of rolls or a continuous oven controlled at a temperature of (the melting point of the aliphatic polyester - 100°C) to (the melting point of the aliphatic polyester - 10°C) be 100.2% or more and 130% or less.

[0059] From the viewpoint of increasing the degree of crystalline orientation of the aliphatic polyester film and preventing the crystallite size from becoming excessively small, the lower limit of the above-mentioned conveying speed difference is more preferably 101%, and even more preferably 105%. Furthermore, from the viewpoint of preventing an excessive increase in the degree of crystalline orientation and preventing excessive growth in crystallite size, the upper limit is more preferably 120%, and even more preferably 115%. The above-mentioned conveying speed difference can be achieved by the difference in the rotation speed of the group of rolls supporting the unstretched film or the difference in the movement speed of the clips that grip the film edges when introducing it into the continuous oven. The time required for the preheating step is preferably 0.1 seconds or more and 100 seconds or less. Here, when multiple rolls are used in succession, the conveying speed difference is the total value of the group of rolls controlled to a temperature of (the melting point of the aliphatic polyester - 100°C) to (the melting point of the aliphatic polyester - 10°C).

[0060] The preheated unstretched film is then introduced, without cooling, into a group of rolls or a continuous oven maintained at a temperature below the melting point of the aliphatic polyester, where it is uniaxially stretched in the longitudinal direction or simultaneously biaxially stretched in the longitudinal and width directions. The degree of crystal orientation and crystallite size can be controlled by applying a certain range of stretching stress to the pre-oriented crystals B produced in the preheating step. More specifically, the uniaxial stretching ratio in the longitudinal direction or the stretching ratios in the longitudinal and width directions in simultaneous biaxial stretching are preferably 2.3 to 5 times. From the viewpoint of suppressing the growth of the crystallite size of the aliphatic polyester film, the lower limit is more preferably 2.8 times, and even more preferably 3.0 times. Furthermore, from the viewpoint of suppressing excessive reduction in the degree of crystal orientation, the upper limit is more preferably 4.5 times, and even more preferably 4.0 times. The time required to pass through the stretching section in the longitudinal uniaxial stretching or simultaneous biaxial stretching is preferably 0.1 seconds to 100 seconds.

[0061] After uniaxial stretching in the longitudinal direction, the resulting stretched film is preferably held at its edges with clips and then introduced into a continuous oven controlled at a temperature below the melting point of the aliphatic polyester, where it is stretched in the width direction. The degree of crystal orientation and crystallite size can be controlled by applying a certain range of deformation stress to the crystals B generated and oriented in the uniaxial stretching process. More specifically, the stretching ratio in the width direction is preferably 2.3 to 5 times, with a lower limit of 2.8 times being more preferable, and a lower limit of 3.0 times being even more preferable, from the viewpoint of preventing excessive increases in the degree of crystal orientation of the aliphatic polyester film. Furthermore, an upper limit of 4.5 times being more preferable, and a higher limit of 4.0 times being even more preferable, from the viewpoint of preventing excessive decreases in crystallite size. The process time in the width direction stretching step is preferably 1 second to 1,000 seconds in the preheating section and 0.1 seconds to 100 seconds in the stretching section.

[0062] The areal magnification of the film is preferably 5.3 to 25. From the viewpoint of controlling the crystal orientation and crystallite size of the aliphatic polyester film within a preferred range, the lower limit is more preferably 7, and more preferably 9. From the same viewpoint, the upper limit is more preferably 20, and more preferably 16.

[0063] Next, the resulting stretched film is preferably introduced into a continuous oven while the edges are held with clips, and subjected to heat treatment and relaxation treatment. In the heat treatment and relaxation treatment steps, the crystalline structure obtained by stretching is subjected to heat treatment within a certain temperature range, thereby controlling the crystallite size while suppressing heat shrinkage. More specifically, the film is preferably subjected to a relaxation treatment of 2% to 20% in the longitudinal and / or transverse directions while passing through a continuous oven controlled at a temperature of (the melting point of the aliphatic polyester -100°C) to (the melting point of the aliphatic polyester -5°C). From the viewpoint of controlling the crystallite size of the aliphatic polyester film within a preferred range, the lower limit of the heat treatment and relaxation treatment temperature is more preferably (the melting point of the aliphatic polyester -70°C) or higher, and even more preferably (the melting point of the aliphatic polyester -50°C) or higher. From the same viewpoint, the upper limit of the heat treatment and relaxation treatment temperature is more preferably a temperature not higher than (the melting point of the aliphatic polyester - 10°C), and even more preferably a temperature not higher than (the melting point of the aliphatic polyester - 20°C). The process time in the heat treatment and relaxation treatment steps is preferably 0.1 seconds or more and 100 seconds or less.

[0064] To control the heat shrinkage of the aliphatic polyester film within a preferred range, it is preferable to perform a heat treatment and relaxation treatment according to the treatment temperature, specifically, the heat treatment and relaxation treatment are preferably performed at a temperature of 50° C. or higher and 150° C. or lower for 1 second or longer. The lower limit of the heat treatment and relaxation treatment temperature is preferably 100° C., more preferably 120° C., while the upper limit is preferably 145° C., more preferably 135° C. The upper limit of the process time in the heat treatment and relaxation treatment steps is preferably 60 seconds, more preferably 45 seconds, while the lower limit is preferably 4 seconds, more preferably 8 seconds.

[0065] The clips are then released in a room temperature atmosphere, and the film is slit at both ends in the width direction to obtain an aliphatic polyester film. The unstretched film formation, stretching, heat treatment, and relaxation treatment described above may be performed continuously or individually in a batch process. Furthermore, additional stretching, heat treatment, relaxation, surface treatment, coating, etc. may be performed within a range that does not impair the object of the present invention. According to the present invention, by controlling the crystal structure and heat shrinkage rate using such a production method, an aliphatic polyester film having excellent biodegradability, strength, and flexibility can be obtained.

[0066] Next, the method for producing fertilizers, feeds, seeds and seedlings, and drugs coated with the aliphatic polyester film of the present invention will be described in more detail using examples, but the present invention is not necessarily limited to these.

[0067] In the method for producing the fertilizer coated with the aliphatic polyester film of the present invention, the aliphatic polyester film obtained by the above method is introduced into upper and lower molds each having a pellet-shaped depression, and the film is then adhered to the molds by suction. Next, the fertilizer to be coated is spread on the film in the lower mold, and the upper mold is lowered and heated to bond the upper and lower films together.

[0068] The fertilizer to be coated with the aliphatic polyester film of the present invention may be in the form of pellets, granules, powder, paste, or liquid. Among these, from the viewpoints of ease of protection with the film and conformability to the shape of a mold, the form of the fertilizer is preferably any of granules, powder, paste, and liquid.

[0069] Furthermore, from the viewpoint of adhesiveness, it is preferable to provide the aliphatic polyester film of the present invention with the aforementioned heat seal layer as an adhesive layer. In this case, it is more preferable to arrange the film in a mold so that the adhesive layer is located on at least one of the surfaces where the films contact each other. Next, the fertilizer-coated film is removed from the mold, and the excess film-bonded portion is cut and removed to obtain coated fertilizer processed into pellets. Here, the cutting method preferably uses a cutter equipped with a blade. Examples of the cutting method include a batch-type sheet-by-sheet processing method using a mold equipped with a blade, a method in which the film is continuously cut in one direction using a rotary blade to form a rope and then periodically cut in the perpendicular direction, and a method in which the above-mentioned mold is equipped with a blade to perform heat-compression bonding and cutting simultaneously.

[0070] Other methods for coating agricultural, forestry, and fishery materials include a method in which two rolls of the aliphatic polyester film of the present invention are prepared and the agricultural, forestry, and fishery material is inserted between them at regular intervals while laminating them; a method in which the agricultural, forestry, and fishery material is held on the film and heated to cause thermal shrinkage, thereby coating; and a method in which the film is reduced pressure to cause shrinkage and coating. According to the present invention, the production method can provide fertilizers, feeds, seeds and seedlings, and medicines coated with the aliphatic polyester film of the present invention, which has excellent biodegradability, strength and flexibility.

[0071] <Biodegradation method> The aliphatic polyester film of the present invention, and the packaging and agricultural, forestry, and fishery materials containing the aliphatic polyester film of the present invention can be biodegraded using composting equipment. Examples of composting equipment that can be used include industrial composting, which is heated or maintained at around 60°C to enhance biodegradability, simple composting made by digging holes in the soil, composting containers that are partially or completely buried in the soil, small composting such as compost bags, and biological composting such as earthworm composting and zoocomposting using flies. When the aliphatic polyester film of the present invention, the packaging and agricultural, forestry, and fishery materials containing the aliphatic polyester film of the present invention do not have a functional layer or when the functional layer is a biodegradable or low-toxicity vapor-deposited layer, they can be decomposed by placing them in composting equipment and subjecting them to a typical process, such as mixing with decomposition materials such as soil or a microorganism-containing fermentation promoter. Furthermore, when a non-biodegradable functional layer or other layer is used in combination, the functional layer may be peeled off and then placed in composting equipment, or a layer with low environmental toxicity, human toxicity, etc., may be placed in composting equipment even if it is non-biodegradable, and the residue may be collected after the aliphatic polyester film of the present invention has been decomposed. The purposes of composting include waste reduction through volume reduction, composting, and biogas generation, and the aliphatic polyester film, packaging, and agricultural, forestry, and fisheries material of the present invention are suitable for composting equipment for any purpose. [Example]

[0072] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the embodiments shown below. Each item was evaluated by the following methods. <Film evaluation and method for determining the effect of the present invention> The film evaluation method and the method for determining the effects of the present invention are as follows: Unless otherwise specified, the film is evaluated after being left for 24 hours in a temperature and humidity environment of 25±5°C and 65±10% RH.

[0073] (1) Film thickness The thickness of the film was measured at five random locations using a contact-type high-precision digital length measuring instrument, "Litematic" (registered trademark) VL50B, manufactured by Mitutoyo Corporation. The arithmetic mean value of the thicknesses at the five locations was taken as the film thickness (unit: μm).

[0074] (2) Determining the direction of the main orientation axis and the direction perpendicular to the main orientation axis The machine direction (MD) in the film manufacturing process was defined as the main orientation axis direction, and the direction perpendicular to the machine direction in the film manufacturing process (TD) in the film plane was defined as the direction perpendicular to the main orientation axis direction. For films with an unknown machine direction, the main orientation axis direction was determined by the following method. First, a sample was cut into a rectangle 150 mm long x 10 mm wide with the long side in an arbitrary direction. <1> Then, the sample <1> The direction of the long side of the sample is defined as 0°. Next, a sample of the same size is placed so that the long side direction is rotated 15° to the right from the 0° direction. <2> Similarly, the rectangular sample was rotated 15° in the long side direction, and the sample was <3> ~ <12> Next, each rectangular sample was placed in a tensile tester (A&D's "Tensilon" (registered trademark) universal testing machine RTG-1210) with an initial chuck distance of 30 mm so that the long side was the tensile direction, and a tensile test was performed at a tension speed of 300 mm / min under a temperature and humidity atmosphere of 25±5°C and 65±10% RH. The breaking strength (unit: MPa) was calculated by dividing the load at which the sample broke by the cross-sectional area of ​​the sample before the test (film thickness × width calculated in (3)). The strain at which the sample broke was calculated as the breaking elongation (unit: %). Similar measurements were performed five times for each sample, and the average value was used. In the present invention, the main orientation axis direction was defined as the measurement direction in which the breaking strength obtained by this method was maximum, and the direction perpendicular to this was defined as the direction perpendicular to the main orientation axis direction.

[0075] (3) Tensile evaluation From the measurement results obtained in the same tensile test as in (2) for the main orientation axis direction and the direction perpendicular to the main orientation axis, the breaking strength in the main orientation axis direction S1 (unit: MPa) and the breaking strength in the direction perpendicular to the main orientation axis direction S2 (unit: MPa) were determined. The obtained breaking strengths S1 and S2 were evaluated according to the following criteria. A: Breaking strength is 100 MPa or more and 280 MPa or less B: Breaking strength is 50 MPa or more and less than 100 MPa C: Breaking strength is less than 50 MPa The breaking strength of the film is preferably B or higher, and more preferably A.

[0076] (4) The total number of layers A and B, the thickness of each layer, and whether or not there are continuous layers The layer structure of the aliphatic polyester film was confirmed by observing a cross-section of a sample cut by cryo-ultrathin sectioning using a microtome with a transmission electron microscope (TEM) to determine the number of layers in the aliphatic polyester film, the thickness of the surface layers, the thickness of each layer, and the presence or absence of a continuous phase. Specifically, a transmission electron microscope H-7100FA (manufactured by Hitachi, Ltd.) was used to take cross-sectional photographs of the film at an accelerating voltage of 75 kV and a magnification of 20,000x to confirm the number of layers, the average thickness of each inner layer excluding the outermost layers on both sides, and the presence or absence of a continuous phase. The continuous phase here refers to a state in which the polyhydroxyalkanoic acid (PHA) domains in layer A are in contact with layer B, which is primarily composed of polyhydroxyalkanoic acid (PHA). The continuous phase does not need to be in a straight line with the main orientation axis direction, as long as they are in contact. In this case, being in a straight line does not mean that the PHA domains of the A layers on both sides of one B layer need to completely overlap in the thickness direction, and it is also acceptable for the PHA domains to only partially overlap.

[0077] (5) Average aspect ratio of the domains composed of polyhydroxyalkanoic acid in the A layer The domain diameter of the aliphatic polyester film was confirmed by observing the entire thickness of a sample cut out of a cross section by cryo-ultrathin sectioning using a microtome under a transmission electron microscope (TEM). Specifically, a transmission electron microscope H-7100FA (Hitachi, Ltd.) was used to take cross-sectional photographs of the film at an accelerating voltage of 75 kV and a magnification of 20,000 times to confirm the domain diameter. The domain diameter here refers to the circle-equivalent diameter based on the domain area. Several A layers were observed under a transmission electron microscope to determine the average thickness and the average domain diameter of the polyhydroxyalkanoic acid, and then the average aspect ratio was calculated using the following formula. Average aspect ratio = average domain diameter (μm) determined from multiple A layers / average thickness (μm) determined from multiple A layers.

[0078] (6) Heat shrinkage rate The thermal shrinkage (F1, F2) was determined after 15 minutes of heating at 120°C. The film was cut into 150mm long x 10mm wide rectangles along the main orientation axis and perpendicular to the main orientation axis. A mark was made in the center 100mm of the film using an oil-based marker. The length was measured using a universal projector to determine the initial length (I0). The measured sample was then placed in a gear-type hot air oven adjusted to 120°C. A 2.1g load was attached to the bottom of the hanging film, and the gear was rotated while the oven was heated for 15 minutes. The film was then removed and cooled to room temperature. The length between the marks was measured using a universal projector to determine the thermal shrinkage (IH). The 120°C thermal shrinkage (unit: %) was calculated from the measured I0 and IH values ​​using the following formula. The same measurements were performed five times for each sample along the main orientation axis and perpendicular to the main orientation axis. The average value along the main orientation axis was F1 (%), and the average value perpendicular to the main orientation axis was F2 (%). 120℃ heat shrinkage rate (%) = (I0-IH) / I0×100 The obtained heat shrinkage was evaluated according to the following criteria. A: Heat shrinkage rate is 10% or less B: Heat shrinkage rate is over 10% and 15% or less C: Heat shrinkage rate is over 15% The heat shrinkage rate of the film is preferably B or higher, and A is more preferable.

[0079] (7) Biodegradability of the film 1 L of wet synthetic compost was prepared according to JIS K6954 (2008) and placed in a 10 L polypropylene container. Next, a 5 cm x 5 cm piece of evaluation film was cut out and placed in a polyethylene holder with a 2 cm square cutout on the inside, leaving the film inside the holder exposed to the outside.

[0080] The film sample, fixed in a holder, was then placed in a polypropylene container and placed in an oven controlled at 28±2°C for 60 days, following a method in accordance with JIS K6954 (2008). When placing the film sample, the entire 2cm square exposed film area in the holder was covered with the wet synthetic compost. After the initial placement, the film sample was removed every two days, the wet synthetic compost was stirred with a scoop, and the film sample was then placed again. This process was repeated.

[0081] Sixty days after initial addition, the film samples were removed from the container and photographed with a digital camera at a resolution of 1200 dpi (2 million pixels) or higher. From the photograph, the area of ​​the sample remaining within a 2 cm square frame inside the holder was determined, and the collapsed area ratio (%) was calculated using the formula (initial area of ​​the sample within the holder - remaining area of ​​the sample within the holder) / (initial area of ​​the sample within the holder) x 100. A total of three holders were evaluated in the same compost, and the arithmetic mean of the three measurements was taken as the collapsed area ratio (%) of the film sample. The biodegradability of the film was assessed according to the following criteria: A: Collapse area ratio is 60% or more B: Collapse area ratio is 30% or more but less than 60% C: Collapse area ratio is 5% or more but less than 30% D: Collapse area ratio is less than 5% The biodegradability of the film is preferably C or higher, more preferably B or higher, and even more preferably A.

[0082] (8) Film recovery rate The yield rate during film formation was defined as the recovery rate, and was calculated using the following formula. The recovery rate (%) was calculated as follows: (amount of sample collected (g) / amount of raw material input (g))×100. The obtained recovery rate was judged according to the following criteria. A: Recovery rate is 85% or more B: Recovery rate is between 70% and 85% C: Recovery rate is 50% or more but less than 70% D: Recovery rate is less than 50% The recovery rate of the film is preferably C or higher, more preferably B or higher, and even more preferably A.

[0083] (9) Content of polyhydroxyalkanoic acid resin and resin components other than polyhydroxyalkanoic acid The aliphatic polyester film was dissolved in hexafluoroisopropanol (HFIP), 1 H-NMR and 13 The content (mass%) of polyhydroxyalkanoic acid resin was measured using C-NMR. The content (mass%) of resin components other than polyhydroxyalkanoic acid was calculated by subtracting the content (mass%) of polyhydroxyalkanoic acid resin from the entire film, which was set to 100 (mass%). In the case of laminated films, each layer of the film was scraped off according to the laminate thickness to collect and evaluate the components constituting each layer alone. In the examples and comparative examples, the composition was calculated from the raw material mixing ratio during film production.

[0084] [Aliphatic polyester resin] The following resins were used to produce the aliphatic polyester films in each of the Examples and Comparative Examples. Note that polylactic acid may be referred to as "PLA" and polyhydroxyalkanoic acid may be referred to as "PHA." PHA: Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) BP350-05 manufactured by Blue Crystal Microorganisms. PLA: Polylactic acid LX175 manufactured by TotalEnergiesCorbion.

[0085] Example 1 PHA and a 3:7 blend of PHA and PLA were fed into separate single-screw extruders. The oxygen concentration in the extruder feed hoppers was controlled to 0.05% by volume. Each extruder was melt-extruded at 170°C, and the extruded molten resin was then passed through a 250 μm mesh filter to remove foreign matter. The streams were then merged in a lamination device designed to have 251 slits and a thickness of the outermost layer of 5% of the film thickness, resulting in a laminate of 251 layers stacked alternately in the thickness direction. The laminate was fabricated according to the method described in paragraphs

[0053] to

[0056] of JP 2007-307893 A. The slit length and spacing were all constant. The resulting laminate had a thickness-wise alternating laminate structure of 126 layers of PHA (layer B) and 125 layers of the PHA and PLA blend (layer A). Thereafter, the extruded laminate (molten film) was cooled and solidified on a casting drum maintained at 30° C. to obtain an unstretched film.

[0086] Next, the unstretched film was introduced into a longitudinal stretching machine consisting of a series of roll groups 1 maintained at 30°C, roll groups 2 and 3 maintained at 60°C, and roll group 4 maintained at 30°C. The difference in conveying speed from roll group 2 to roll group 3 was 110%, the passing time was 90 seconds, and the difference in conveying speed from roll group 3 to roll group 4 was 330%, the passing time was 0.5 seconds, and the unstretched film was uniaxially stretched 3.0 times in the longitudinal direction.

[0087] Next, the film passed through roll group 4 and was introduced into a tenter, where, while both widthwise ends were held with clips, it was preheated and stretched 3.0 times in the width direction in an oven controlled at 75°C, and then heat-treated at 120°C while giving 10% relaxation in the width direction. The passage times were 3 seconds in the preheating section, 3 seconds in the stretching section, and 10 seconds in the heat-treatment section.

[0088] Thereafter, while the widthwise ends were still held taut with clips, the film was cooled to 30°C and guided to the outside of the tenter, the clips on both widthwise ends were released, and a 20 μm thick aliphatic polyester film was obtained on a winding machine.

[0089] The film evaluation results and properties of the aliphatic polyester film obtained are shown in Tables 2 and 3. The film was found to have excellent biodegradability and dimensional stability, derived from polyhydroxyalkanoic acid and polylactic acid. The thickness of each of the inner layers, A and B, was 0.07 μm. Furthermore, by using a blend of polylactic acid and polyhydroxyalkanoic acid for Layer A, the film could be stretched to the edges without rupturing, resulting in an excellent recovery rate.

[0090] Examples 2 to 4 Aliphatic polyester films were obtained in the same manner as in Example 1, except that the production method was changed as shown in Table 1. The evaluation results of the obtained films and the properties of the aliphatic polyester films are shown in Tables 2 and 3. The thickness per inner layer of the A layer and the B layer was 6.00 μm in Example 2, 0.62 μm in Example 3, and 0.02 μm in Example 4.

[0091] Examples 5 to 7 Aliphatic polyester films were obtained in the same manner as in Example 1, except that the raw material compositions and production methods of Layer A and Layer B were changed as shown in Table 1. The evaluation results of the obtained films and the properties of the aliphatic polyester films are shown in Tables 2 and 3. The thickness per inner layer of Layer A and Layer B was 0.07 μm in Examples 5 to 7.

[0092] (Comparative Example 1) Aliphatic polyester films were obtained in the same manner as in Example 1, except that the raw material composition was changed and the production method was changed to a single film, as shown in Table 1. Evaluation results of the obtained films showed that although the biodegradability was excellent, the dimensional stability was deteriorated, and the recovery rate was poor because the film was broken during film formation and it was difficult to collect the film unless the edges were cut.

[0093] (Comparative Example 2) As shown in Table 1, an aliphatic polyester film was obtained in the same manner as in Example 1, except that the raw material composition was changed and the production method was changed to a single film. Evaluation results of the obtained film showed that although the dimensional stability was excellent, the biodegradability was significantly deteriorated.

[0094] (Comparative Example 3) Aliphatic polyester films were obtained in the same manner as in Example 1, except that the raw material composition was changed and the production method was changed to a single film, as shown in Table 1. Evaluation results of the obtained films showed that the biodegradability was improved by the addition of polyhydroxyalkanoic acid compared to Comparative Example 2, but the dimensional stability was slightly worsened due to the reduced polylactic acid ratio.

[0095] Comparative Example 4 As shown in Table 1, an aliphatic polyester film was obtained in the same manner as in Example 1, except that the raw material composition and manufacturing method were changed. Evaluation results of the obtained film showed that the laminated structure improved biodegradability and dimensional stability compared to Comparative Example 3, but the breaking strength did not reach the target. The thickness of each of the inner layers, Layer A and Layer B, was 18.00 μm.

[0096] [Table 1]

[0097] [Table 2]

[0098] [Table 3] [Industrial Applicability]

[0099] The present invention provides an aliphatic polyester film that has excellent biodegradability while also achieving both strength and flexibility. Because the aliphatic polyester film of the present invention has the above properties, it can be suitably used for packaging applications and agricultural, forestry, and fisheries applications that require biodegradability and strength and flexibility during processing and use.

Claims

1. An aliphatic polyester film having a structure in which A layers mainly composed of polylactic acid and B layers mainly composed of polyhydroxyalkanoic acid are alternately arranged in the thickness direction, and the total number of A layers and B layers is 5 or more.

2. The aliphatic polyester film according to claim 1 , wherein the layer A mainly composed of polylactic acid further contains a polyhydroxyalkanoic acid.

3. 3. The aliphatic polyester film according to claim 1, wherein the ratio of polylactic acid to the total mass of the aliphatic polyester film is 30 mass% or more.

4. 3. The aliphatic polyester film according to claim 2, wherein in at least one A layer, the domains comprising the polyhydroxyalkanoic acid have an average aspect ratio of 1.1 or more and 20 or less.

5. 3. The aliphatic polyester film according to claim 1, wherein the thickness of each of the inner layers A and B is from 0.01 μm to 18 μm.

6. 3. The aliphatic polyester film according to claim 1, wherein F1 (%) is the heat shrinkage at 120°C in the main orientation axis direction and F2 (%) is the heat shrinkage at 120°C in the direction perpendicular to the main orientation axis direction, and both F1 and F2 are 15% or less.

7. 3. The aliphatic polyester film according to claim 1, wherein S1 (MPa) is the breaking strength in the main orientation axis direction and S2 (MPa) is the breaking strength in the direction perpendicular to the main orientation axis direction, and both S1 and S2 are 50 MPa or more and 280 MPa or less.

8. 5. The aliphatic polyester film according to claim 2, which has a continuous phase comprising a polyhydroxyalkanoic acid in the thickness direction.

9. The aliphatic polyester film according to claim 1 or 2, further comprising a functional layer on at least one surface thereof.

10. The aliphatic polyester film according to claim 1 or 2, which is used for packaging purposes.

11. The aliphatic polyester film according to claim 1 or 2, which is used for agriculture, forestry and fisheries.

12. A packaging material comprising the aliphatic polyester film according to claim 1 or 2.

13. A material for agriculture, forestry and fisheries, comprising the aliphatic polyester film according to claim 1 or 2.

14. A biodegradation method comprising decomposing the aliphatic polyester film according to claim 1 or 2 with composting equipment.

15. A biodegradation method comprising decomposing the packaging material according to claim 12 using composting equipment.

16. A biodegradation method comprising decomposing the agricultural, forestry and fishery material according to claim 13 using composting equipment.

17. 3. The aliphatic polyester film according to claim 1, which is used to cover agricultural, forestry, and fishery materials, wherein the agricultural, forestry, and fishery materials include at least one selected from the group consisting of fertilizers, feeds, seeds and seedlings, and chemicals.

18. 3. A material for agricultural, forestry and fisheries products, characterized by being covered with the aliphatic polyester film according to claim 1 or 2.

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