Biodegradable resin film

Abstract

The present invention aims to provide a biodegradable resin film that, even as a thin film, exhibits excellent tear resistance in both the longitudinal and transverse directions, moderate biodegradability, and also possesses excellent bleed resistance and film-forming properties. [Solution] The present invention relates to a biodegradable resin film comprising an aliphatic aromatic polyester resin and a polylactic acid resin as a biodegradable resin, further comprising talc and an unsaturated fatty acid monoamide, wherein the film contains 2% to 15% by mass of the polylactic acid resin, 40% to 93% by mass of the aliphatic aromatic polyester resin, 5% to 30% by mass of the talc, and 0.05% to 0.5% by mass of the unsaturated fatty acid monoamide, with a thickness of 5 μm to 30 μm, and is suitable as an agricultural mulch film.

Description

Technical Field

[0001] The present invention relates to a biodegradable resin film having excellent tear resistance.

Background Art

[0002] An agricultural mulch film (hereinafter also referred to as a mulch film) is a film that covers ridges for growing crops and is used for the purpose of promoting stable growth of crops such as heat retention, weed suppression, and suppression of evaporation of soil moisture.

[0003] As the resin constituting the agricultural mulch film, general-purpose resins such as polyolefin-based resins and vinyl chloride-based resins are mainly used. However, there is a growing trend towards switching to biodegradable resins that are decomposed into water and carbon dioxide by the action of microorganisms present in the soil and do not remain in the natural environment. In the case of conventional mulch films using polyolefin-based resins or vinyl chloride-based resins, it was necessary to collect and dispose of them by recycling or incineration after use. However, if a biodegradable resin film is used, the resin component can be decomposed in the soil simply by plowing it into the soil after use, so the above-mentioned collection and disposal operations can be omitted, and the burden of agricultural work can be greatly reduced.

[0004] An agricultural mulch film needs to have excellent tear strength so as not to tear during operations such as mechanical stretching with a mulcher or opening planting holes. Generally, however, biodegradable resin films are inferior in physical properties such as tear strength compared to vinyl chloride-based resin films or olefin-based resin films.

[0005] Therefore, the present applicant has studied to improve the tear strength of biodegradable resins and found that by containing a specific amount of a polylactic acid-based resin in an aliphatic aromatic polyester-based resin, it is possible to improve the tear strength in the longitudinal direction (flow direction) of the film, that is, to suppress tearing in the longitudinal direction (tear resistance), and has already filed a patent application (Patent Document 1).

[0006] Furthermore, with the enactment of the "Act on Promotion of Resource Recycling Related to Plastics" in Japan in June 2021, there is a growing demand for lightweight and inexpensive biodegradable resin films to promote the use of biodegradable plastics. In an investigation to meet this demand, it was found that thinning the film is effective because biodegradable resins have a higher specific gravity and are more expensive than polyethylene. However, when biodegradable resin films are made into thin films, they decompose too quickly, making it difficult for them to function as a multi-layer film. Not only do they become unstable during film formation, but they are also prone to holes caused by foreign matter, making film formation itself difficult. Additives such as lubricants included to improve film formation are also prone to bleeding. Moreover, it was newly discovered that even films with improved longitudinal tear strength tend to tear easily in the transverse direction. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent application No. 2024-045743 [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, the present invention aims to provide a biodegradable resin film that, even as a thin film, exhibits excellent tear resistance in both the longitudinal and transverse directions, moderate biodegradability, and also possesses excellent bleed resistance and film-forming properties. [Means for solving the problem]

[0009] The present invention relates, in first aspect, to a biodegradable resin film comprising an aliphatic aromatic polyester resin and a polylactic acid resin as a biodegradable resin, further comprising talc and an unsaturated fatty acid monoamide, wherein the film contains 2% to 15% by mass of the polylactic acid resin, 40% to 93% by mass of the aliphatic aromatic polyester resin, 5% to 30% by mass of the talc, and 0.05% to 0.5% by mass of the unsaturated fatty acid monoamide, with a thickness of 5 μm to 30 μm, and is suitable as an agricultural mulch film.

[0010] As a second aspect of the present invention, the present invention relates to a biodegradable resin film as described in the first aspect, wherein the product of the longitudinal tear strength (Elmendorf method) and transverse elongation at the breaking point is 100 N·% or more, and the product of the transverse tear strength (Elmendorf method) and longitudinal elongation at the breaking point is 30 N·% or more.

[0011] A third aspect of the present invention further relates to a biodegradable resin film according to the first or second aspect, comprising a saturated fatty acid monoamide. [Effects of the Invention]

[0012] The present invention provides a biodegradable resin film that, even as a thin film, exhibits excellent tear resistance in both the longitudinal and transverse directions, moderate biodegradability, and also possesses excellent bleed resistance and film-forming properties. [Modes for carrying out the invention]

[0013] The present invention relates to a biodegradable resin film comprising an aliphatic aromatic polyester resin and a polylactic acid resin as biodegradable resins, and further comprising talc and an unsaturated fatty acid monoamide.

[0014] Examples of aliphatic aromatic polyester resins of the present invention include polybutylene adipate terephthalate resins, polybutylene terephthalate alkylate resins, and polybutylene succinate terephthalate resins. Polybutylene adipate terephthalate (PBAT) is particularly preferred. Polybutylene adipate terephthalate (PBAT) is formed by a polycondensation reaction between a dicarboxylic acid component consisting of adipic acid and terephthalic acid and a diol component consisting of 1,4-butanediol, but other components may be included. For example, other diol components may be included. Examples of other diol components include 2,3-butanediol, 1,3-butanediol, 1,4-pentanediol, 2,4-pentanediol, 1,6-hexanediol, neopentyl glycol, ethylene glycol, and diethylene glycol.

[0015] The polylactic acid resin of the present invention is not particularly limited as long as it is a condensate of lactic acid (polylactic acid (PLA)), and may be a poly-L-lactic acid resin, a poly-D-lactic acid resin, or a mixture thereof (for example, a stereocomplex type polylactic acid resin obtained by mixing poly-L-lactic acid resin and poly-D-lactic acid resin).

[0016] In particular, when the aliphatic aromatic polyester resin is PBAT, it is preferable that the PLA contains 1% by mass or more of poly-D-lactic acid resin, and more preferably 10% by mass or less. The melting point of polylactic acid resins with a poly-D-lactic acid resin content of less than 1% by mass is about 170-180°C, but the melting point tends to decrease as the poly-D-lactic acid resin content increases. For example, when the content is 5%, it drops to about 150-160°C. Therefore, by using a polylactic acid resin containing 1% by mass or more of poly-D-lactic acid resin, it becomes easier to mold even at processing temperatures equivalent to PBAT with a melting point of 110-120°C, the generation of foreign matter due to unmelted polylactic acid resin can be suppressed, and film-forming properties can be improved.

[0017] The biodegradable resin used in this invention may be further blended with known biodegradable resins, etc., without departing from the purpose of the invention. Examples include aliphatic polyester resins such as polybutylene succinate (PBS), polyethylene succinate (PES), polybutylene succinate adipate (PBSA), and polycaprolactone (PCL), as well as polyhydroxyalkanoic acid (PHA) resins such as polyhydroxybutyric acid, and natural polymers such as starch and cellulose.

[0018] In this invention, the biodegradable resin film contains 2% to 15% by mass of polylactic acid resin per 100% by mass. If the amount of polylactic acid resin added is less than 2% by mass, the film exhibits excellent tear resistance in the transverse direction but poor tear resistance in the longitudinal direction. If the amount added is more than 15% by mass, the film exhibits excellent tear resistance in the longitudinal direction but poor tear resistance in the transverse direction. The tear resistance in this invention will be described later.

[0019] In this invention, the biodegradable resin film contains 40% to 93% by mass of aliphatic aromatic polyester resin, preferably 54% to 90% by mass, relative to 100% by mass of the biodegradable resin film. When the amount of aliphatic aromatic polyester resin added is within this range, the resulting film exhibits excellent tear resistance and film-forming properties.

[0020] In the present invention, talc is added, for example, to stabilize the film during film formation by improving the crystallization rate of the resin composition, and is not particularly limited as long as it can be used as a filler for biodegradable resins. For example, the average particle size of talc is preferably 0.5 to 10 μm, more preferably 1 to 8 μm, and particularly preferably 4 to 6 μm. If it is too small, it tends to aggregate in the resin and become foreign matter, which can easily cause porosity during film formation, and if it is too large, it tends to cause surface roughness and a decrease in strength.

[0021] In the present invention, talc is contained in an amount of 5% by mass or more and 30% by mass or less based on 100% by mass of the biodegradable resin film. When the addition amount of talc is less than 5% by mass, the crystallization rate is slow and the resin is difficult to solidify by cooling, so it tends to become unstable during film formation of the film. When it is more than 30% by mass, it tends to aggregate in the resin and becomes a foreign substance, easily causing holes during film formation. The addition amount of talc is preferably 10% by mass or more and 20% by mass or less. The stability (film-forming property) during film formation of the film in the present invention will be described later.

[0022] As a filler added to the biodegradable resin, calcium carbonate is known in addition to talc. By adding calcium carbonate, it is possible to improve the crystallization rate of, for example, a resin composition in the same manner as talc. On the other hand, since calcium carbonate has an effect of promoting biodegradability, it is difficult to obtain appropriate biodegradability in the present invention. Therefore, it is preferable not to add it or to add it in an amount that does not excessively promote biodegradability.

[0023] In the present invention, the unsaturated fatty acid monoamide is added for the purpose of, for example, imparting lubricity and improving the dispersibility of talc. Specifically, examples include unsaturated fatty acid monoamides such as oleic acid amide, erucic acid amide, and ricinoleic acid amide, and erucic acid amide is particularly preferable.

[0024] In the present invention, the biodegradable resin film contains 0.05% by mass or more and 0.5% by mass or less of the unsaturated fatty acid monoamide based on 100% by mass. When the addition amount of the unsaturated fatty acid monoamide is less than 0.05% by mass, the dispersibility of talc in the biodegradable resin is poor, and holes are likely to occur during film formation due to aggregates of talc. When it is more than 0.5% by mass, it is likely to bleed, and there is a risk that powder will blow out on the film surface. The addition amount of the unsaturated fatty acid monoamide is preferably 0.1% by mass or more and 0.3% by mass or less.

[0025] In this invention, saturated fatty acid monoamides may be used in combination with unsaturated fatty acid monoamides. By adding saturated fatty acid monoamides, the water permeability can be lowered, resulting in excellent moisture retention. Examples of saturated fatty acid monoamides include lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, and hydroxystearic acid amide. Among these, stearic acid amide can be suitably used in terms of cost and performance.

[0026] In the present invention, it is preferable that the biodegradable resin film contains 0.3% to 0.6% by mass of saturated fatty monoamide per 100% by mass.

[0027] Furthermore, other additives may be added to the composition of the biodegradable resin film of the present invention as needed, provided that they do not impair the effects of the present invention. Examples include light stabilizers, heat stabilizers, lubricants, ultraviolet absorbers, photodegradation accelerators, biodegradation accelerators, biodegradation inhibitors, fillers, and pigments.

[0028] The thickness of the biodegradable resin film of the present invention is 5 μm or more and 30 μm or less, preferably 5 μm or more and less than 20 μm. If the thickness is less than 5 μm, the film will not have sufficient strength and may tear easily, especially when used in agricultural applications, such as as a mulch film. On the other hand, if the thickness exceeds 30 μm, the film will be heavy and may take too long to decompose.

[0029] The biodegradable resin film of the present invention is manufactured by mixing a biodegradable resin, additives, and other components as needed, provided that the effects of the present invention are not impaired, and then molding the mixture using a generally accepted method for manufacturing resin films. Examples of such resin film manufacturing methods include T-die molding, inflation molding, and calendering. The film can also be produced without stretching, or by uniaxial or biaxial stretching. For producing thin films, inflation molding is preferred.

[0030] The biodegradable resin film of the present invention, even as a thin film, exhibits excellent tear resistance in both the longitudinal and transverse directions, moderate biodegradability, and also has excellent bleed resistance and film-forming properties. Here, the longitudinal direction of the film refers to the length (flow) direction during film formation, and the transverse direction refers to the width direction during film formation.

[0031] The inventors have found that the tear resistance of biodegradable resin films can be evaluated by the balance between tear strength and elongation at the breaking point. Specifically, it was found that while a film is less likely to tear if its tear strength is strong in the longitudinal and transverse directions, it also tends to be less likely to tear if the elongation at the breaking point is large in the direction perpendicular to the tearing direction, even if the tear strength is weak. More precisely, if the film has strong tear strength in the longitudinal direction and low elongation at the breaking point in the transverse direction, if it has strong tear strength in the longitudinal direction and high elongation at the breaking point in the transverse direction, or if it has weak tear strength in the longitudinal direction and high elongation at the breaking point in the transverse direction, it will be less likely to tear in the longitudinal direction. Similarly, if the film has strong tear strength in the transverse direction and low elongation at the breaking point in the longitudinal direction, if it has strong tear strength in the transverse direction and high elongation at the breaking point in the longitudinal direction, or if it has weak tear strength in the transverse direction and high elongation at the breaking point in the longitudinal direction, it will be less likely to tear in the transverse direction.

[0032] Therefore, in this invention, the product of the tear strength (N) and the elongation at the breaking point (%) of the film (N·%) is used as an indicator of the tear resistance of the film. A larger value indicates better tear resistance. In this invention, the tear strength (N) is a value measured according to JIS K 6732 (Elmendorf method), and the elongation at the breaking point (%) is a value measured according to JIS K 7127 under the condition of a tensile speed of 500 mm / min.

[0033] The biodegradable resin film of the present invention has a product of the longitudinal tear strength (N) and transverse elongation at the breaking point (%) of 100 N·% or more, and a product of the transverse tear strength (N) and longitudinal elongation at the breaking point (%) of 30 N·% or more, exhibiting excellent tear resistance. In this invention, a larger value for the product of the film's tear strength (N) and elongation at the breaking point (%) (N·%) is preferable, but it is preferable that both the longitudinal and transverse directions have a product of 1600 (N·%) or less.

[0034] In the present invention, having moderate biodegradability means that the film can exist for the period required for crop growth, that is, it does not decompose too quickly and can fulfill the role of a mulch film, and this is evaluated as described in the examples below. The biodegradable resin film of the present invention meets these evaluation criteria.

[0035] In the present invention, excellent bleed resistance means that there is no risk of lubricants such as unsaturated fatty acid monoamides bleeding and causing powder to appear on the film surface, and this is evaluated as described in the examples below. The biodegradable resin film of the present invention can meet these evaluation criteria.

[0036] In this invention, film-forming ability is determined by bubble stability and bubble appearance as follows.

[0037] Bubble stability is evaluated by visually checking, for example, whether the bubbles blown out of the die during inflation molding are undulating. While it's not always the case, if the crystallization rate of the resin composition is slow and the resin does not cool and solidify easily, the bubbles are more susceptible to the effects of cooling air and tend to undulate and wave. This undulating state of the bubbles is called an unstable state, and if this is significantly pronounced, the length accuracy in the width direction tends to deteriorate, making it difficult to obtain good quality products.

[0038] Furthermore, if foreign matter such as unmelted resin or aggregates of additives (talc) is present, holes may form in the bubbles, preventing film formation. Therefore, the appearance of the bubbles is evaluated as described in the examples below.

[0039] Thin films tend to have unstable bubbles during film formation and are prone to punctures caused by foreign matter. However, the thin biodegradable resin film of the present invention can prevent such problems during film formation and can meet the evaluation criteria for film formation described in the examples below.

[0040] The biodegradable resin film of the present invention, even as a thin film, exhibits excellent tear resistance in both the longitudinal and transverse directions, possesses moderate biodegradability, and also has excellent bleed resistance and film-forming properties. Therefore, it does not tear during operations such as mechanical deployment with a mulcher or when creating planting holes, and can be suitably used as an agricultural mulch film. [Examples]

[0041] The present invention will be described in more detail below with reference to examples, but is not limited to these examples.

[0042] [Examples 1-11, Comparative Examples 1-7] Each component was blended according to the mixing ratios shown in Tables 1 and 2 below, and films with a thickness of 10 μm, Examples 1 to 11 and Comparative Examples 1 to 7, were formed by inflation molding. Components other than the biodegradable resin were blended in the form of a masterbatch prepared by pre-mixing a fixed amount of PBAT with a twin-screw extruder and then melt-kneading it. The various conditions for the inflation molding were as follows. Note that the mixing ratios in the tables are expressed in mass%. Cylinder temperature: 160~190℃ Die temperature: 165℃ Die diameter: 100mmφ Pickup speed: 5-15 m / min Blow ratio: 2-3

[0043] For each obtained film, the tear resistance in the longitudinal and transverse directions (product of tear strength and elongation at the break), bleed resistance, biodegradability, moisture permeability, and film-forming properties were evaluated using the following methods. The results are shown in Tables 1 and 2. Note that for Comparative Example 3, the bubbles were unstable during film formation and no good product was obtained, and for Comparative Examples 4 and 5, film formation was not possible, so evaluations for Comparative Examples 3 to 5 were not performed.

[0044] PBAT: Polybutylene adipate terephthalate resin (manufactured by BASF, trade name "Ecoflex®") PLA1: Polylactic acid (D-isomer content: 2.5% by mass, manufactured by Kaisei Seibutsu Co., Ltd., product name: "REVODE110") PLA2: Polylactic acid (D-isomer content: 0.5% by mass, manufactured by Kaisei Seibutsu Co., Ltd., product name: "REVODE190") Talc (manufactured by Takehara Chemical Industry Co., Ltd., product name "Hytron", average particle size 5 μm) Calcium carbonate (manufactured by Nitto Funka Kogyo Co., Ltd., product name "NN500", average particle size 4 μm) Unsaturated fatty acid monoamide: Erucic acid amide (manufactured by NOF Corporation, product name "Alflow P-10") Saturated fatty acid monoamide: Stearic acid amide (manufactured by Mitsubishi Chemical Corporation, product name "AP-1")

[0045] (tear resistance) The tear strength (N) of the film in the longitudinal and transverse directions was measured according to JIS K 6732 (Elmendorf method). Based on JIS K 7127, the elongation at the break point in the longitudinal and transverse directions of the film was measured at a tensile speed of 500 mm / min. For longitudinal tear resistance, a product of longitudinal tear strength and transverse elongation at fracture point of 100 N·% or more was rated as ○, and a product of less than 100 N·% was rated as ×. For lateral tear resistance, a product of the lateral tear strength and longitudinal elongation at the fracture point of 30 N·% or more was rated as ○, and a product of less than 30 N·% was rated as ×.

[0046] (Bleed resistance) The film surface was visually inspected after being left at room temperature for one week and evaluated according to the following criteria. ○: No change △: There is a slight amount of powder on the surface, but this does not affect its use. ×: Powder has surfaced, spoiling the appearance.

[0047] (biodegradable) 60g of culture medium (manufactured by Takii Seed Co., Ltd., product name "Planter Soil") was weighed into a plastic petri dish (90mm in diameter), and each test piece, cut from molded film to a size of 5cm x 5cm, was embedded in it. The moisture content of the culture medium was adjusted by adding deionized water to approximately 20-30% by mass. The petri dish was left standing at a constant temperature and humidity of 25°C and 95% RH, and the mass of each test piece was measured before and after the test. The mass change rate after 4 weeks was calculated using the formula shown below (Equation 1). A mass change rate of 5% or less was evaluated as ○, and a rate exceeding 5% was evaluated as ×. Mass change rate (%) = 100 × (Mass of test specimen before test - Mass of test specimen after test) / Mass of test specimen before test ... (Equation 1)

[0048] (moisturizing) Based on JIS Z 0208, the amount of moisture absorbed by the desiccant after being placed in a constant temperature and humidity chamber at 40°C and 90% relative humidity for 72 hours was used to determine the moisture permeability (g / m³). 2 We calculated the value of 24 hours. Moisture permeability A (g / m³) in Example 2 2 Based on 24 hours, the moisture permeability X (g / m³) for each example and comparative example is used. 2 When the interval is set to 24 hours, the difference Δ(moisture permeability X - moisture permeability A) was calculated and evaluated as follows. ◎: Superior to Example 2, Δ<-500 ○: Equivalent to Example 2, -500 ≤ Δ ≤ 300 △: Inferior to Example 2, Δ>300

[0049] (Film-forming properties: Bubble stability) During inflation molding, the stability of the bubbles blown out of the die was visually inspected and evaluated as follows. ○: The bubble was stable with no fluctuations, and good quality products were obtained. △: There is some slight fluctuation in the bubble, but the film was obtained. ×: The bubble was unstable and volatile, resulting in no good quality products being obtained.

[0050] (Film-forming properties: Bubble appearance) During inflation molding, the state of the bubbles blown out of the die was visually inspected and evaluated as follows. ○: No foreign matter was found, and a good film was obtained. △: Although foreign matter was detected, no holes were created in the film, and the film was obtained. ×: The film was perforated by foreign matter, and the film could not be obtained.

[0051] [Table 1]

[0052] [Table 2]

[0053] Table 1 shows that, according to Examples 1 to 11 of the present invention, even with a thin film thickness of 10 μm, it is possible to provide a biodegradable resin film that has excellent tear resistance in the longitudinal and transverse directions, moderate biodegradability, and also excellent bleed resistance and film-forming properties.

Claims

1. A biodegradable resin film comprising an aliphatic aromatic polyester resin and a polylactic acid resin as biodegradable resins, Furthermore, it contains talc and unsaturated fatty acid monoamide, For 100% by mass of biodegradable resin film, The aforementioned polylactic acid resin contains 2% by mass or more and 15% by mass or less, The aliphatic aromatic polyester resin contains 40% by mass or more and 93% by mass or less, The above talc contains 5% by mass or more and 30% by mass or less, The above unsaturated fatty acid monoamide is contained in an amount of 0.05% by mass or more and 0.5% by mass or less. The thickness is between 5 μm and 30 μm. A biodegradable resin film suitable for use as agricultural mulch film.

2. The biodegradable resin film according to claim 1, wherein the product of the longitudinal tear strength (Elmendorf method) and transverse elongation at the breaking point of the biodegradable resin film is 100 N・% or more, and the product of the transverse tear strength (Elmendorf method) and longitudinal elongation at the breaking point of the biodegradable resin film is 30 N・% or more.

3. Furthermore, the biodegradable resin film according to claim 1 or claim 2, comprising a saturated fatty acid monoamide.

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