Biodegradable resin film

Abstract

To provide a biodegradable resin film which is excellent in film formation property, gas barrier property and film strength even when the biodegradable resin film is thin, and is early decomposable.SOLUTION: A biodegradable resin film is a laminate of two or more layers of a biodegradable resin layer (layer A) and a biodegradable resin layer (layer B), wherein a percentage content of a poly(3-hydroxyalkanoate)-based resin is more than 90 mass% and 100 mass% or less, in 100 mass% of a biodegradable resin constituting the layer A, a percentage content of an aliphatic aromatic polyester-based resin is 70 mass% or more and 100 mass% or lessin 100 mass% of a biodegradable resin constituting the layer B, a thickness ratio of the layer A to the layer B is 1 / 4 or more and 2 / 1 or less, the layer A is positioned on at least one outermost surface, thickness is 10 μm or more and 100 μm or less, and the film is molded by simultaneous multilayer molding.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biodegradable resin film that is preferably used as an agricultural mulch film for covering the surface of soil, for example, when disinfecting soil by injecting and spraying a chemical solution into the soil in a farm field. [Background technology]

[0002] Traditionally, soil disinfection has been carried out in farm fields to protect crops from pathogens and pests. To prevent the disinfectant from scattering around, the disinfectant is first injected into the soil, and then the soil surface is covered with agricultural mulch film using a machine such as a mulcher.

[0003] Polyethylene film and polyvinyl chloride film are used as such agricultural mulch films. Usually, after use, films are collected and incinerated. However, in consideration of today's environmental concerns, there is a growing demand for biodegradable resin films that do not require incineration. Biodegradable resins are resins that can be decomposed by microorganisms in the soil or water of nature over a certain period of time, ultimately breaking down into water and carbon dioxide.

[0004] For example, Patent Document 1 discloses a biodegradable resin film that can be used as an agricultural mulch film. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-185793

[0006] Agricultural mulch films that can be used for soil disinfection must have gas barrier properties to retain disinfectants in the soil and film strength that can withstand spreading with a mulcher. In addition, when biodegradable resin films are used, they must maintain their shape for the disinfection period of about four weeks, and after that period, they must decompose to the point where they can be immediately incorporated into the soil.

[0007] The biodegradable resin film of Patent Document 1 uses a mixture of poly(3-hydroxyalkanoate) resin, which is known to be easily degradable and capable of improving gas barrier properties, and commonly used biodegradable resins such as PBAT and PBS. Generally, poly(3-hydroxyalkanoate) resins decompose quickly but have weak film strength, while PBAT and PBS decompose slowly but have excellent film strength. Therefore, it is difficult to achieve both rapid decomposition and film strength by mixing these, and the biodegradable resin film of Patent Document 1 does not easily achieve the rapid decomposition required for soil disinfection.

[0008] Furthermore, a method of reducing the film thickness to achieve rapid decomposition is known, but this not only reduces the gas barrier properties but also the film strength, such as tear strength, required for agricultural mulch films.

[0009] On the other hand, when a poly(3-hydroxyalkanoate) resin is mixed with other biodegradable resins to form a single-layer film, if the content of the poly(3-hydroxyalkanoate) resin is high, the film-forming properties may be poor, for example, during inflation molding. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, an object of the present invention is to provide a biodegradable resin film that is thin but has excellent film-forming properties, gas barrier properties, and film strength, and is rapidly decomposable. [Means for solving the problem]

[0011] As a result of intensive research conducted by the inventors to achieve the above object, it was discovered that by specifying the thickness ratio and forming a laminated film by simultaneous multilayer molding, a biodegradable resin film that is excellent in film formability, gas barrier properties, and film strength and is capable of decomposing quickly can be obtained, leading to the present invention.

[0012] That is, the biodegradable resin film of the present invention is a biodegradable resin film that is a laminate of two or more layers including a biodegradable resin layer (A layer) and a biodegradable resin layer (B layer), wherein, of the 100% by mass of biodegradable resin that constitutes the A layer, the content of poly(3-hydroxyalkanoate)-based resin is more than 90% by mass and 100% by mass or less, and of the 100% by mass of biodegradable resin that constitutes the B layer, the content of aliphatic aromatic polyester-based resin is 70% by mass or more and 100% by mass or less, the thickness ratio of the A layer to the B layer is A layer / B layer = 1 / 4 or more and 2 / 1 or less, the A layer is located on at least one of the outermost surfaces, has a thickness of 10 μm or more and 100 μm or less, and is characterized by being formed by simultaneous multilayer molding.

[0013] Furthermore, the present invention is preferably a laminate of three or more layers in which the layer A is located on both surfaces. [Effects of the Invention]

[0014] The present invention can provide a biodegradable resin film that is excellent in film-forming properties, gas barrier properties, and film strength, and is capable of decomposing quickly, even when the film thickness is thin. DETAILED DESCRIPTION OF THE INVENTION

[0015] The biodegradable resin film of the present invention is a biodegradable resin film that is a laminate of two or more layers including a biodegradable resin layer (layer A) mainly containing a poly(3-hydroxyalkanoate)-based resin and a biodegradable resin layer (layer B) mainly containing an aliphatic aromatic polyester-based resin.

[0016] [A layer] In the present invention, layer A contains a poly(3-hydroxyalkanoate)-based resin. The poly(3-hydroxyalkanoate)-based resin is not particularly limited as long as it is a copolymerized polyhydroxyalkanoate containing a 3-hydroxyhexanoate unit, but a copolymerized polyhydroxyalkanoate obtained by polymerizing 3-hydroxyhexanoate with one or more monomers selected from 3-hydroxyalkanoic acids having 4 to 16 carbon atoms (excluding 3-hydroxyhexanoate) is preferred, and a copolymer of 3-hydroxyhexanoate units and 3-hydroxybutyrate units (PHBH) is more preferred.

[0017] Of the 100% by mass of biodegradable resins constituting Layer A of the present invention, the content of poly(3-hydroxyalkanoate) resin is more than 90% by mass and 100% by mass or less, preferably 100% by mass. If the content is 90% by mass or less, film formability tends to be poor even when Layer B, which will be described later, is laminated thereon.

[0018] Agricultural mulch films that can be used for soil disinfection are required to have gas barrier properties and rapid decomposition properties, so in this invention, poly(3-hydroxyalkanoate) resins are used. However, poly(3-hydroxyalkanoate) resins have poor film strength, and improvements have been made by blending them with other biodegradable resins or adding various additives. However, blending them with other biodegradable resins that decompose more slowly than poly(3-hydroxyalkanoate) resins makes it difficult to achieve the rapid decomposition required for biodegradable films used in soil disinfection. Generally, poly(3-hydroxyalkanoate) resins decompose quickly but have poor film strength, while PBAT and PBS decompose slowly but have excellent film strength. Therefore, it is difficult to achieve both rapid decomposition and film strength by blending these resins. Furthermore, when poly(3-hydroxyalkanoate) resins are blended with other biodegradable resins to form a single-layer film, if the poly(3-hydroxyalkanoate) resin content is high, poor film formability can occur, for example, during inflation molding. In the present invention, by laminating Layer B, which will be described later, by simultaneous multilayer molding, excellent film strength and improved film formability can be achieved even when the content of poly(3-hydroxyalkanoate) resin in Layer A is high. As a result, a biodegradable resin film can be obtained that can easily exhibit the gas barrier properties and biodegradability of poly(3-hydroxyalkanoate) resin even when the film is thin.

[0019] Here, in the present invention, film-forming properties are judged by bubble stability and opening properties during inflation molding. Bubble stability is evaluated by visually observing the bubble shape when blown out of the die, and it is preferable that the bubble shape is stable and not shaking. If the bubble is unstable, it is difficult to obtain a good film. Furthermore, opening properties are evaluated by cutting out a tubular film after inflation molding and determining whether the inner surfaces of the film can be opened, and it is preferable that the film can be opened by rubbing with a finger or using adhesive tape. In the present invention, a film that is excellent in both bubble stability and opening properties is judged to have excellent film-forming properties.

[0020] The layer A of the present invention may contain a biodegradable resin other than a poly(3-hydroxyalkanoate)-based resin, provided that the effect of the present invention is not impaired, and the content of such a resin is 10% by mass or less. Examples of such a resin include the aliphatic aromatic polyester-based resin constituting the layer B described below and other known biodegradable resins, and polybutylene adipate terephthalate (PBAT) is preferred.

[0021] [B layer] In the present invention, the layer B contains an aliphatic aromatic polyester resin. The aliphatic aromatic polyester resin of the present invention is a polymerized condensation product of an aliphatic dicarboxylic acid such as succinic acid, adipic acid, suberic acid, sebacic acid, dodecanoic acid, succinic anhydride, or adipic anhydride, an aromatic dicarboxylic acid such as terephthalic acid, and an aliphatic diol. Examples of the aliphatic diol include 1,4-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-pentanediol, 2,4-pentanediol, 1,6-hexanediol, neopentyl glycol, ethylene glycol, and diethylene glycol, and one or more of these may be used.

[0022] More specifically, examples of aliphatic aromatic polyester resins include polybutylene adipate terephthalate (PBAT), polybutylene succinate terephthalate, and polytetramethylene adipate terephthalate, and among these, polybutylene adipate terephthalate (PBAT) is particularly suitable.

[0023] Of the 100% by mass of biodegradable resins constituting Layer B of the present invention, the content of aliphatic aromatic polyester resins is 70% by mass or more and 100% by mass or less, preferably 80% by mass or more and 100% by mass or less, and more preferably 100% by mass. If the content of the aliphatic aromatic polyester resin is less than 70% by mass, lamination with Layer A having a high content of poly(3-hydroxyalkanoate) resin will result in poor film formability.

[0024] Layer B of the present invention may contain a biodegradable resin other than the aliphatic aromatic polyester resin to the extent that the effects of the present invention are not impaired, and the content of the biodegradable resin is less than 20% by mass. Examples include the poly(3-hydroxyalkanoate) resin constituting Layer A described above and other known biodegradable resins. A copolymer of 3-hydroxyhexanoate units and 3-hydroxybutyrate units (PHBH) is preferred.

[0025] Any additives may be added to Layer A and Layer B of the present invention within the range that does not impair the effects of the present invention, such as plasticizers, heat stabilizers, lubricants, antiblocking agents, nucleating agents, biodegradation accelerators, biodegradation inhibitors, antioxidants, UV stabilizers, light stabilizers, antibacterial agents, fillers, colorants, antistatic agents, and starch.

[0026] The present invention provides a biodegradable resin film that is thin but has excellent film-forming properties, gas barrier properties, and strength, and is rapidly degradable, by laminating an A layer having a high content of poly(3-hydroxyalkanoate) resin with a B layer containing an aliphatic aromatic polyester resin, where the thickness ratio of A layer to B layer is 1 / 4 or more and 2 / 1 or less. If the thickness ratio of layer A is too small, i.e., if the thickness ratio of layer B is too large, the degradability will be poor, and if the thickness ratio of layer A is too large, i.e., if the thickness ratio of layer B is too small, the film strength will be poor. In the present invention, in the case of a two-kind three-layer structure, for example, layer A / layer B / layer A, the thickness of layer A refers to the combined thickness of the outer and inner layers. In addition, in the case of a layer A' having a different composition, as described below, the thickness of layer A refers to the combined thickness of layer A and layer A'.

[0027] The layer structure of the present invention has two or more layers, with Layer A positioned on the outermost surface of at least one of the layers. Examples include two layers of two kinds (Layer A / Layer B), two layers of three kinds (Layer A / Layer B / Layer A), three layers formed by laminating Layer A' and Layer B' of different compositions (Layer A / Layer B / Layer A', Layer A / Layer A' / Layer B, Layer A / Layer B / Layer B'), and five layers (Layer A / Layer B / Layer A / Layer B / Layer A, Layer A / Layer B / Layer A' / Layer B / Layer A). Since layer A is located on the outermost surface, when the present invention is used for soil disinfection, it is easy to decompose quickly by using it so that layer A comes into contact with the soil. Preferably, it is a laminate of three or more layers in which layer A is located on both surfaces.

[0028] The thickness of the film of the present invention is preferably 10 μm or more and 100 μm or less. If the film thickness is less than 10 μm, the gas barrier property and film strength tend to be poor, and if it exceeds 100 μm, it becomes difficult to handle during transportation or when spreading with a mulcher.

[0029] The biodegradable resin film of the present invention is produced by simultaneous multilayer molding. Examples of methods for producing such a resin film include T-die molding, inflation molding, and calendar molding. In addition, the film may be unstretched or may be uniaxially or biaxially stretched.

[0030] The present invention provides a biodegradable resin film that is excellent in film-forming properties, gas barrier properties, and film strength, and is rapidly decomposable, even when the film thickness is thin. In the present invention, the film thickness, film-forming properties, gas barrier properties, film strength, and biodegradability are evaluated as described in the examples below.

[0031] It is ideal for agricultural mulch films that can be used for soil disinfection, and can also be used for other purposes, such as ordinary agricultural mulch films and forestry fumigation films. [Example]

[0032] The present invention will be described in more detail below with reference to examples, but is not limited to these examples.

[0033] Examples 1 to 10, Comparative Examples 1 to 6, Reference Examples 1 to 4 The components were blended in the blending ratios shown in Tables 1 to 3 below, and films of Examples 1 to 10, Comparative Examples 1 to 6, and Reference Examples 1 to 4 were formed by inflation molding. Examples 1 to 6 and Comparative Examples 1 to 4 were two-kind, two-layer films formed by simultaneous multilayer molding, Examples 7 to 10 and Comparative Examples 5 and 6 were two-kind, three-layer films formed by simultaneous multilayer molding, and Reference Examples 1 to 4 were single-layer films. The total thickness of each film was 20 μm, and the thickness ratio (layer ratio) of Layer A to Layer B was as shown in Tables 1 to 3. The blending ratios in the tables are expressed in mass%.

[0034] The obtained films were evaluated for film thickness, film-forming properties (bubble stability, opening properties), gas barrier properties (moisture permeability), film strength (tear strength, elongation at break), and biodegradability using the following methods. The results are shown in Tables 1 to 3. However, for Comparative Examples 1 and 2 and Reference Examples 3 and 4, films could not be obtained and therefore could not be evaluated.

[0035] [Ingredients in Tables 1 to 3] biodegradable resin PBAT: Polybutylene adipate terephthalate (manufactured by BASF, trade name "Ecoflex (registered trademark)") PHBH: Polyhydroxybutyrate hexanoate (manufactured by Kaneka Corporation, "GreenPlanet (registered trademark)")

[0036] [Film thickness] The total thickness of each film was measured using a dial gauge with a minimum scale of 0.001 mm. The thicknesses of Layer A and Layer B were measured by observing the cross section of each film using a scanning electron microscope (SEM: JSM-6700F manufactured by JEOL Ltd.).

[0037] [Film forming property] The evaluation was based on bubble stability and mouth opening property in inflation molding as shown below. In the present invention, when bubble stability is rated as ◯ or △ and mouth opening property is rated as ◯, it is judged that the film formability is excellent. Bubble stability: During inflation molding, the stability of the bubbles blown up from the die was visually confirmed and evaluated as follows. ◯: The bubbles were stable with no shaking, and a good film was obtained. △: The bubbles were slightly wobbly, but a film was obtained. ×: The bubbles were unstable and swayed, and no film was obtained. Openability: After inflation molding, the tubular film was cut out, and whether the inner surfaces of the film (layers A) could open was evaluated as follows. ◯: Can be opened by rubbing with a finger or using adhesive tape (manufactured by Nitto Denko Corporation, product "NO. 31B"). ×: The inner surfaces of the film are in close contact with each other, and the film cannot be opened even with adhesive tape (manufactured by Nitto Denko Corporation, product "NO. 31B").

[0038] [Gas barrier properties] With reference to JIS Z 0208, the moisture permeability was calculated from the amount of moisture absorbed by the moisture absorbent after placing it in a thermo-hygrostat at a temperature of 40°C and a relative humidity of 90% (condition B) for 72 hours. 2 24 hours or less: 〇 rating, 650g / m 2 -More than 24 hours was rated as ×.

[0039] [Tear strength: Elmendorf method] This is the value obtained by dividing the tear strength (N) in the TD direction measured in accordance with JIS K 6732 by the film thickness (20 μm), with 100 N / mm or more being rated as ◯ and less than 100 N / mm being rated as ×.

[0040] [Elongation at break] In a tensile test performed in accordance with JIS K 7127, the elongation at break in the TD direction was measured at a tensile speed of 500 mm / min. An elongation at break of 200% or more was evaluated as ◯, and an elongation at break of less than 200% was evaluated as ×.

[0041] [Biodegradable] Sixty grams of culture soil (manufactured by Takii Seed Co., Ltd., product name "Planter's Soil") was weighed out and placed in a plastic petri dish (diameter 90 mm), and each test piece, made by cutting the formed film into a 5 cm x 5 cm size, was buried in the culture soil. The moisture content of the culture soil was adjusted to approximately 20-30 mass% by adding ion-exchange water. The petri dish was left to stand under a constant temperature and humidity of 25°C and 95% RH. The mass of each test piece was measured before and after the test, and the mass change rate after 4 weeks was calculated using the following formula (Equation 1). A mass change rate of 20% or more was evaluated as ◯, and a mass change rate of less than 20% was evaluated as ×. Mass change rate (%) = 100 × (mass of test piece before test − mass of test piece after test) / mass of test piece before test (Equation 1)

[0042] [Table 1]

[0043] [Table 2]

[0044] [Table 3]

[0045] Tables 1 and 2 show that by using a laminated film with a specific thickness ratio, as in Examples 1 to 10 of the present invention, it is possible to obtain a biodegradable resin film that is excellent in film-forming properties, gas barrier properties, and film physical properties and is capable of decomposing quickly, even if the film thickness is thin.

Claims

1. A biodegradable resin film that is a laminate of two or more layers including a biodegradable resin layer (layer A) and a biodegradable resin layer (layer B), the content of poly(3-hydroxyalkanoate) resin is more than 90% by mass and 100% by mass or less of the biodegradable resin constituting the layer A, the content of aliphatic aromatic polyester resin is 70% by mass or more and 100% by mass or less out of 100% by mass of the biodegradable resin constituting the layer B, a thickness ratio of the A layer to the B layer of A layer / B layer=1 / 4 or more and 2 / 1 or less; Layer A is located on at least one outermost surface, The thickness is 10 μm or more and 100 μm or less, A biodegradable resin film characterized by being formed by simultaneous multilayer molding.

2. 2. The biodegradable resin film according to claim 1, wherein the layer A is a laminate of three or more layers located on both surfaces.

Images