Biodegradable mulch film

Abstract

To provide a biodegradable agricultural mulch film that resists being lifted or peeled off from the ridges.SOLUTION: A biodegradable mulch film 1 is a band-like film with a fixed width and thickness. The biodegradable mulch film 1 includes a first edge 10, a second edge 20, and a center 30. The first edge 10, the center 30 and the second edge 20 are all shaped liked bands and arranged in the stated order across the width of the film. The degradation rates of the first edge 10 and the second edge 20 are slower than that of the center 30.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a biodegradable multi-film, and particularly to a biodegradable multi-film for agricultural use.

Background Art

[0002] When cultivating crops such as tobacco, vegetables, and fruits, it is common practice to cover the ridges with agricultural multi-films made of polyethylene. By covering the ridges with agricultural multi-films, effects such as heat preservation, moisture retention, weed prevention, aphid prevention, early cultivation, suppression cultivation, ground temperature suppression, and prevention of ridge runoff due to rain can be obtained. The agricultural multi-film is installed to cover the ridges while holding down both ends in the soil, and then the seedlings of the crops are planted or sown.

[0003] For such agricultural multi-films made of polyethylene, a recovery operation is required after harvesting the crops. Therefore, for example, Patent Document 1 discloses a biodegradable multi-film that eliminates the need for the operation of recovering the agricultural multi-film. The biodegradable multi-film of Patent Document 1 can be plowed into the soil together when plowing the field after harvesting the crops and decomposed in the soil.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Figure 9 shows an example of covering a ridge with biodegradable mulch film. Figure 10 schematically shows a cross-section of the biodegradable mulch film covering the ridge. Conventional biodegradable mulch films have a central section with openings that covers the ridge, while both ends are buried in the soil. Often, the ends underground decompose before the central section above ground. As a result, the decomposition of the ends can cause the agricultural mulch film to be blown away from the ridge by the wind, damaging crops growing through the openings, exposing the ridge and reducing its heat retention and moisture retention effects, and allowing weeds to grow on the ridge.

[0006] Therefore, the present invention aims to provide a biodegradable agricultural mulch film that can prevent it from peeling off the ridges. [Means for solving the problem]

[0007] To achieve the above objective, the biodegradable mulch film according to the present invention is a strip-shaped biodegradable mulch film characterized in that the decomposition rate at both ends in the width direction is slower than the decomposition rate at the center in the width direction.

[0008] In the present invention, it is preferable that both ends and the central part are composed of one or more layers, the central part is composed of only the first biodegradable layer, and both ends are composed of only the second biodegradable layer, or a combination of the first biodegradable layer and the second biodegradable layer, wherein the decomposition rate of the second biodegradable layer is slower than the decomposition rate of the first biodegradable layer.

[0009] In the present invention, it is preferable that the first biodegradable layer and the second biodegradable layer contain polybutylene adipate terephthalate, polylactic acid, and polybutylene succinate.

[0010] In the present invention, it is preferable that the amount of hydrolysis inhibitor contained in each of the two ends is greater than the amount of hydrolysis inhibitor contained in the central part.

[0011] In the present invention, it is preferable that the width of the central portion is 10% to 80% of the width of the biodegradable mulch film. [Effects of the Invention]

[0012] According to the present invention, the biodegradable mulch film is formed in a strip shape, and the decomposition rate at both ends in the width direction is slower than that at the center in the width direction. This allows the ends to remain in place by the soil for a longer period of time. Furthermore, the time difference between the decomposition of the center and the decomposition of the ends can be reduced. Therefore, the biodegradable mulch film can be effectively prevented from peeling away from the ridges. [Brief explanation of the drawing]

[0013] [Figure 1] This is a plan view of a biodegradable mulch film according to one embodiment of the present invention. [Figure 2] Figure 1 is a cross-sectional view of the biodegradable mulch film. [Figure 3] This is a cross-sectional view of a modified example of the biodegradable mulch film shown in Figure 1. [Figure 4] This diagram shows how the ridges are covered with biodegradable mulch film. [Figure 5] This diagram shows crops being grown in furrows covered with biodegradable mulch film. [Figure 6] This figure shows the decrease in strength and degradation status of biodegradable mulch film, as well as the evaluation results. [Figure 7] This figure shows an example of the decomposition status of the biodegradable mulch film according to the example. [Figure 8] This figure shows an example of the degradation status of a biodegradable mulch film in a comparative example. [Figure 9] This figure shows an example of covering a ridge with biodegradable mulch film. [Figure 10] This diagram schematically shows a cross-section of a biodegradable mulch film covering a ridge. [Modes for carrying out the invention]

[0014] Hereinafter, a biodegradable multilayer film according to an embodiment of the present invention will be described with reference to FIGS. 1 to 5.

[0015] FIG. 1 is a plan view of a biodegradable multilayer film according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the biodegradable multilayer film of FIG. 1. FIG. 3 is a cross-sectional view of a modified example of the biodegradable multilayer film of FIG. 1. In FIGS. 2 and 3, the thickness of the biodegradable multilayer film is schematically shown in an emphasized manner. FIG. 4 is a view showing a state in which ridges are covered with the biodegradable multilayer film. FIG. 5 is a view showing a state in which crops are growing in ridges covered with the biodegradable multilayer film.

[0016] The biodegradable multilayer film according to the present embodiment is used in agriculture. In this specification, "biodegradable" includes not only the property that a substance is decomposed by the action of microorganisms and finally becomes carbon dioxide and water, but also the property that a substance is decomposed by reacting with water (hydrolysis).

[0017] As shown in FIG. 1, the biodegradable multilayer film 1 is a strip-shaped film having a certain width and a certain thickness. The biodegradable multilayer film 1 has a first end portion 10, a second end portion 20, and a central portion 30. The first end portion 10, the central portion 30, and the second end portion 20 are each strip-shaped and arranged side by side in the width direction (the left-right direction in FIG. 1) in this order. The first end portion 10 and the central portion 30 are continuous, and the second end portion 20 and the central portion 30 are continuous.

[0018] The central portion 30 is provided with a plurality of apertures 35. The shape of the apertures 35 is circular, oval, rectangular, diamond-shaped, or the like. The plurality of apertures 35 are arranged at equal intervals in the length direction (the vertical direction in FIG. 1). The width of the central portion 30 is preferably 10% to 80% of the width of the biodegradable multifilm 1. The biodegradable multifilm 1 has the widths of the first end portion 10, the second end portion 20, and the central portion 30, the shape, size, and interval of the apertures 35 set according to the crop. Note that the central portion 30 may not be provided with the apertures 35. Instead of the apertures 35, the central portion 30 may be provided with perforations for forming holes.

[0019] The first end portion 10, the second end portion 20, and the central portion 30 are each composed of one layer or a plurality of layers. Specifically, the biodegradable multifilm 1 has a first biodegradable layer 40 and a second biodegradable layer 50, and the first end portion 10, the second end portion 20, and the central portion 30 are each composed of the first biodegradable layer 40, the second biodegradable layer 50, or a combination of these layers. Each layer is integrated. In the present embodiment, the first end portion 10 and the second end portion 20 have the same configuration.

[0020] The decomposition rate of the second biodegradable layer 50 is suppressed compared to that of the first biodegradable layer 40. For example, when buried in the soil or placed under the same conditions, the second biodegradable layer 50 has a slower decomposition rate than the first biodegradable layer 40. The first end portion 10 and the second end portion 20 each have at least one second biodegradable layer 50. The first end portion 10, the second end portion 20, and the central portion 30 are configured such that when placed under the same conditions, the decomposition rates of the first end portion 10 and the second end portion 20 are slower than the decomposition rate of the central portion 30.

[0021] The first biodegradable layer 40 and the second biodegradable layer 50 are mainly composed of a biodegradable resin. In the first biodegradable layer 40 and the second biodegradable layer 50, for example, polybutylene adipate terephthalate (PBAT) is used as the biodegradable resin. Other biodegradable resins may also be used. In the present embodiment, the first biodegradable layer 40 and the second biodegradable layer 50 contain PBAT, polylactic acid, and polybutylene succinate.

[0022] The second biodegradable layer 50 has a hydrolysis inhibitor added to it. The first biodegradable layer 40 does not have a hydrolysis inhibitor added to it. However, the first biodegradable layer 40 may also have a hydrolysis inhibitor added to it, but the degradation rate should not be slower than that of the second biodegradable layer 50 (the degradation rate should not be suppressed too much). In the first biodegradable layer 40 and the second biodegradable layer 50, for example, a carbodiimide compound can be used as the hydrolysis inhibitor. Other types of hydrolysis inhibitors may also be used.

[0023] Let a (a≧0) be the total amount of hydrolysis inhibitors contained in each layer constituting the central part 30, and let b be the total amount of hydrolysis inhibitors contained in each layer constituting the first end part 10 (the same applies to the second end part 20). The first end part 10, the second end part 20, and the central part 30 are configured such that b>a.

[0024] As shown in Figure 2, in this embodiment, the first end 10 and the second end 20 are composed of two layers, a first biodegradable layer 40 and a second biodegradable layer 50, which are stacked in order, and the central portion 30 is composed of one first biodegradable layer 40 having the same thickness as the first end 10 and the second end 20.

[0025] The biodegradable mulch film according to the present invention may have, for example, the configuration shown in Figures 3(a) to 3(c). The biodegradable mulch film 1A shown in Figure 3(a) has one first biodegradable layer 40 added to the configuration shown in Figure 2, with the first end 10 and the second end 20 being composed of three layers: a first biodegradable layer 40, a second biodegradable layer 50, and a first biodegradable layer 40 stacked in order, and the central part 30 being composed of two first biodegradable layers 40. The biodegradable mulch film 1B shown in Figure 3(b) has the first end 10 and the second end 20 being composed of one second biodegradable layer 50, and the central part 30 being composed of one first biodegradable layer 40 having the same thickness as the first end 10 and the second end 20. The biodegradable mulch film 1C shown in Figure 3(c) has two additional first biodegradable layers 40 compared to the configuration shown in Figure 3(b). The first end 10 and the second end 20 are composed of three layers: the first biodegradable layer 40, the second biodegradable layer 50, and the first biodegradable layer 40, which are stacked in order. The central part 30 is composed of three first biodegradable layers 40. In these biodegradable mulch films 1A to 1C, the first end 10, the central part 30, and the second end 20 have the same thickness. In addition to these configurations, for example, the first end 10 and the second end 20 may include multiple second biodegradable layers 50.

[0026] The biodegradable mulch film 1 is rolled up, and during the covering work, one end of the rolled biodegradable mulch film 1 in the length direction is buried in the soil to secure it, and the mulch film laying machine B attached to the tractor A is used to cover the ridges, and at the same time, soil C which acts as a weight is placed on both ends in the width direction to prevent it from being blown away by the wind, etc., and the biodegradable mulch film 1 is installed on the ridges. The biodegradable mulch film 1 is provided with openings 35 in advance, and after the ridges are covered, crop seedlings are planted or seeds are sown in the ridges through the openings 35.

[0027] As explained above, the biodegradable mulch film 1 is formed in a strip shape, and the decomposition rate of the first end 10 and second end 20, which are the ends in the width direction, is slower than the decomposition rate of the central part 30 in the width direction. In this way, the state in which the first end 10 and second end 20 are held down by the soil can be maintained for a longer period of time. In addition, the difference in the timing of decomposition between the central part 30 and the ends can be reduced. Therefore, the biodegradable mulch film 1 can be effectively prevented from peeling off the ridges.

[0028] Furthermore, the first end 10, the second end 20, and the central part 30 are composed of one or more layers. The central part 30 is composed of only the first biodegradable layer 40. The first end 10 and the second end 20 are composed of a combination of the first biodegradable layer 40 and the second biodegradable layer 50, or are composed of only the second biodegradable layer 50. The decomposition rate of the second biodegradable layer 50 is slower than the decomposition rate of the first biodegradable layer 40. In this way, the decomposition rates of the first end 10 and the second end 20 relative to the central part 30 can be adjusted relatively easily in the biodegradable mulch film 1. Note that if the decomposition rates of the first end 10 and the second end 20 are slower than the decomposition rate of the central part 30 in the width direction, the central part 30 may be composed of a combination of the first biodegradable layer 40 and the second biodegradable layer 50.

[0029] Furthermore, the amount of hydrolysis inhibitor contained in the first end portion 10 and the second end portion 20 is greater than the amount of hydrolysis inhibitor contained in the central portion 30. In this way, the decomposition rate of the first end portion 10 and the second end portion 20 relative to the central portion 30 can be adjusted relatively easily in the biodegradable mulch film 1.

[0030] To confirm the effect of suppressing the decomposition rate of biodegradable mulch films, the inventors prepared the following biodegradable mulch films as Examples 1, 2 and Comparative Example 1 and conducted evaluation tests. Examples 1, 2 and Comparative Example 1 have the same configuration in the central and both ends in the width direction.

[0031] Example 1: A biodegradable mulch film with a thickness of 0.018 mm was prepared using PBAT as the main component, with 6% by weight of a black pigment masterbatch and 1% by weight of a hydrolysis inhibitor masterbatch added. In Example 1, the amount of black pigment was 2.1% by weight. Example 1 assumes a second biodegradable layer 50 with a relatively small amount of hydrolysis inhibitor.

[0032] Example 2: A biodegradable mulch film with a thickness of 0.018 mm was prepared using PBAT as the main component, with 6% by weight of a black pigment masterbatch and 3% by weight of a hydrolysis inhibitor masterbatch added. In Example 2, the amount of black pigment was 2.1% by weight. The weight percentage of the hydrolysis inhibitor in Example 2 is higher than the weight percentage of the hydrolysis inhibitor in Example 1. Example 2 assumes a second biodegradable layer 50 with a relatively large amount of hydrolysis inhibitor.

[0033] Comparative Example 1: A biodegradable mulch film with a thickness of 0.018 mm was prepared using PBAT as the main component, with 6% by weight of a black pigment masterbatch added, and without the addition of a hydrolysis inhibitor. In Comparative Example 1, the amount of black pigment was 2.1% by weight. Comparative Example 1 assumes a first biodegradable layer 40 without a hydrolysis inhibitor.

[0034] In Example 1, Example 2, and Comparative Example 1, the same PBAT, black pigment masterbatch, and hydrolysis inhibitor masterbatch were used.

[0035] Furrows in an open environment were covered with Example 1, Example 2, and Comparative Example 1, and both ends of each were buried in the soil to secure them. The decrease in tensile strength (strength reduction) and the state of decomposition at both ends were checked at 2 months, 3 months, and 4 months after covering. The goal of this evaluation test is to maintain tensile strength and decomposition suppression for 4 months.

[0036] The decrease in tensile strength was evaluated on a three-point scale based on the feel when the evaluator pulled the material in a tearing direction with both hands. ◎...There is no decrease in tensile strength, or there is only a slight decrease. ○...Although the tensile strength has decreased, it still maintains the tensile strength necessary to protect the ridges. △...The tensile strength has decreased, and it cannot protect the ridges.

[0037] The disassembly status was evaluated by the evaluator through visual inspection, using the following three-stage system. ◎...No decomposition, or only slight decomposition. ○...It is decomposing, but the decomposition has not progressed to the point where it can no longer protect the furrows. △...It has broken down and cannot protect the furrows.

[0038] The overall evaluation was based on the following criteria. Good... Does not include "△" in the evaluation of tensile strength reduction and decomposition status. Defective... Includes "△" in the evaluation of reduced tensile strength and degree of decomposition.

[0039] Figure 6 shows the evaluation results for the decrease in tensile strength and the degree of decomposition for Example 1, Example 2, and Comparative Example 1, as well as the overall evaluation results.

[0040] As shown in Figure 6, in Example 1, the decrease in tensile strength and the progression of decomposition were slow at each elapsed period, and there was no impact on the protection of the ridges. Similarly, in Example 2, the decrease in tensile strength and the progression of decomposition were very slow at each elapsed period, and there was no impact on the protection of the ridges. On the other hand, in Comparative Example 1, the decrease in tensile strength progressed at each elapsed period, which may affect the protection of the ridges. Furthermore, Comparative Example 1 decomposed after 4 months, which may affect the protection of the ridges.

[0041] From these evaluation results, it became clear that by including Example 1 or Example 2 as the second biodegradable layer 50 at both ends of the biodegradable mulch film, the ridges can be adequately protected for a predetermined period (e.g., 4 months) after covering. In contrast, Comparative Example 1 showed a decrease in tensile strength and decomposition more rapidly than Examples 1 and 2, potentially causing it to peel away from the ridges and failing to protect them for the predetermined period. Therefore, by configuring both ends of the biodegradable mulch film with either Example 1 or Example 2 alone, or a combination of Example 1 or Example 2 and Comparative Example 1, a biodegradable mulch film capable of protecting the ridges for a predetermined period can be obtained. In the evaluation test, the target period for protecting the ridges was 4 months, but it is possible to adjust the period of protection by changing the configuration of both ends of the biodegradable mulch film (layer configuration, amount of hydrolysis inhibitor added, etc.).

[0042] Figure 7 is a diagram (photograph) showing an example of the decomposition in Example 2. Figure 8 is a diagram (photograph) showing an example of the decomposition in Comparative Example 1. Figures 7(a) and 8(a) were taken two months after the ridges were covered. Figures 7(b) and 8(b) were taken four months after the ridges were covered. As shown in Figures 7(a) and (b), in Example 2, the edges maintain their shape even after the predetermined period has elapsed, indicating that the material remains in a state capable of protecting the ridges for the predetermined period. On the other hand, as shown in Figures 8(a) and (b), in Comparative Example 1, relatively large cracks appear everywhere at the edges after two months, and after four months, most of the edges have decomposed and no longer retain their original shape. Therefore, in Comparative Example 1, the edges may decompose and peel away from the ridges before the predetermined period has elapsed, and there is a risk that the material will not be able to protect the ridges for the predetermined period.

[0043] Although embodiments of the present invention have been described above, the present invention is not limited to the configurations of these embodiments. Additions, deletions, design modifications, and combinations of features of the embodiments, as appropriate by those skilled in the art, are also included within the scope of the present invention, as long as they do not contradict the spirit of the invention. [Explanation of Symbols]

[0044] 1, 1A, 1B, 1C… Biodegradable mulch film 10...First end 20…Second end 30...Central part 35...Opening hole 40...First biodegradable layer 50…Second biodegradable layer

Claims

1. A strip-shaped biodegradable multi-film, when both end portions in the width direction and the central portion in the width direction are placed under the same conditions, the decomposition rate of the both end portions is slower than the decomposition rate of the central portion, and the biodegradable multi-film is characterized by this.

2. The both end portions and the central portion are composed of one layer or a plurality of layers, the central portion is composed of only the first biodegradable layer, the both end portions are composed of only the second biodegradable layer, or are composed of a combination of the first biodegradable layer and the second biodegradable layer, The biodegradable multi-film according to claim 1, wherein the decomposition rate of the second biodegradable layer is slower than the decomposition rate of the first biodegradable layer.

3. The biodegradable multi-film according to claim 2, wherein the first biodegradable layer and the second biodegradable layer contain polybutylene adipate terephthalate, polylactic acid, and polybutylene succinate.

4. The biodegradable multi-film according to any one of claims 1 to 3, wherein the amount of the hydrolysis inhibitor contained in each of the both end portions is more than the amount of the hydrolysis inhibitor contained in the central portion.

5. The biodegradable multi-film according to any one of claims 1 to 3, wherein the width of the central portion is 10% to 80% of the width of the biodegradable multi-film.

6. The biodegradable multi-film according to claim 4, wherein a hydrolysis inhibitor is kneaded into at least the both end portions among the central portion and the both end portions.

Images