Agricultural polyolefin-based resin film

Abstract

To provide an agricultural polyolefin-based resin film having high total light transmittance and light scattering property while maintaining excellent thermal insulation property.SOLUTION: An agricultural polyolefin-based resin film 1 comprises: one or more foam layers 2 having a plurality of pores in which a resin material (a) containing a polyolefin-based resin is foamed; one or more unfoamed outer layers 3 which are provided on surfaces of the foam layers 2, and are made of a resin material (b) containing a polyolefin-based resin; and one or more unfoamed inner layers 4 which are provided on surfaces on the opposite side of the outer layers 3 side of the foam layers 2, and are made of a resin material (c) containing a polyolefin-based resin, wherein a thickness of the foam layer 2 is 0.07 mm or more and 0.15 mm or less, and the total amount of thicknesses of the foam layer 2, the outer layer 3 and the inner layer 4 is 0.18 mm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polyolefin resin film for agricultural use used in agricultural facilities such as agricultural greenhouses and agricultural tunnels, and a method for producing the same. [Background technology]

[0002] In recent years, agricultural films made of olefin-based resins have been used, but agricultural films are required to have heat-retaining properties so that the indoor air temperature and soil temperature, which rise during the day due to exposure to sunlight, do not drop too much at night in agricultural greenhouses and agricultural tunnels.

[0003] For example, a polyolefin-based agricultural film containing a heat-retaining agent containing a complex hydroxide condensed silicate as an active ingredient (see Patent Document 1) and an agricultural film laminated with a cap film having excellent heat-insulating properties and numerous cap-shaped protrusions (see Patent Document 2) have been proposed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-125001 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-45060 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although the above-mentioned conventional agricultural films have improved heat retention, they have low total light transmittance and light scattering properties, which causes problems such as sunlight not evenly reaching the undersides of plant leaves, and the amount of light that passes through is low and insufficient.

[0006] Therefore, the present invention has been made in consideration of the above problems, and aims to provide an agricultural polyolefin resin film that has high total light transmittance and light scattering properties while maintaining excellent heat retention properties. [Means for solving the problem]

[0007] In order to achieve the above object, the agricultural polyolefin resin film of the present invention comprises: One or more foam layers each having a plurality of pores formed by foaming a resin material (a) containing a polyolefin resin; one or more non-foamed outer layers formed on the surface of the foamed layer and made of a resin material (b) containing a polyolefin-based resin; one or more non-foamed inner layers formed on the surface of the foamed layer opposite to the outer layer side and made of a resin material (c) containing a polyolefin-based resin, The thickness of the foam layer is 0.07 mm or more and 0.15 mm or less, The total thickness of the foam layer, the outer layer, and the inner layer is 0.18 mm or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a polyolefin resin film for agricultural use that has high total light transmittance and light scattering properties while maintaining excellent heat retention properties. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an agricultural polyolefin resin film according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The agricultural polyolefin resin film of the present invention will be specifically described below. The present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention. Each of the following components may be used alone or in combination of two or more types. Each component may be a commercially available product or a synthetic product.

[0011] <Polyolefin resin film for agricultural use> As shown in Figure 1, the agricultural polyolefin resin film 1 of the present invention (hereinafter also simply referred to as "film 1") has an outer layer 3 which is the layer on the side where sunlight is incident, an inner layer 4 which is the layer on the side opposite to the side where sunlight is incident, and a foam layer 2 provided between the outer layer 3 and the inner layer 4, and has a multilayer structure in which these layers are laminated. The film 1 is configured to have a structure of at least three layers. In other words, the film 1 may have a structure of four layers, five layers, or more layers.

[0012] The foam layer 2, outer layer 3, and inner layer 4 are each formed from a resin material containing a polyolefin resin as a main component. From the viewpoints of film strength, ease of handling, and flexibility, the polyolefin resin is preferably polyethylene, polypropylene, or ethylene-vinyl acetate copolymer. Examples of polyethylene include linear low-density polyethylene, low-density polyethylene, and high-pressure low-density polyethylene. The main component refers to the component that is present in the largest amount among the components contained in the resin material.

[0013] Here, in the agricultural polyolefin resin film 1, the total thickness of the foam layer 2, outer layer 3, and inner layer 4 is 0.18 mm or less. Because the thickness (total thickness) of the film 1 is specified within the above range, the film 1 has improved total light transmittance and light scattering properties while ensuring heat retention. The thickness of the film 1 is 0.18 mm or less, preferably 0.10 mm or more and 0.18 mm or less, and more preferably 0.12 mm or more and 0.18 mm or less. When the thickness of the film 1 is within the above range, the strength and handleability of the film 1 are also improved.

[0014] (Foam layer) As shown in FIG. 1, the foam layer 2 is interposed between the outer layer 3 and the inner layer 4, and can therefore also be considered an intermediate layer. The foam layer 2 has the effect and function of imparting heat retention and heat insulation to the agricultural polyolefin resin film 1 used outdoors. The foam layer 2 has a plurality of pores formed by foaming a resin material (a) containing a polyolefin resin. The pore size is not particularly limited. The pores can be confirmed, for example, using a scanning electron microscope (SEM).

[0015] The foam layer 2 is composed of one or more layers. That is, the foam layer 2 may be one layer, or two or more layers (multi-layer).

[0016] In the agricultural polyolefin resin film 1, the thickness of the foam layer 2 (when the foam layer 2 is multi-layered, the total thickness of each foam layer 2) is 0.07 mm or more and 0.15 mm or less. Because the thickness of the foam layer 2 is specified within the above range, the film 1 has improved total light transmittance and light scattering properties while ensuring heat retention. The thickness of the foam layer 2 is 0.07 mm or more and 0.15 mm or less, preferably 0.075 mm or more and 0.13 mm or less, and more preferably 0.08 mm or more and 0.12 mm or less. From the viewpoint of ensuring good physical properties of the film 1, when the total thickness of the film 1 is taken as 100%, the thickness of the foam layer 2 is preferably in the range of 50 to 80%, more preferably 55 to 80%.

[0017] The foamed layer 2 is a layer formed by foaming a resin material (a) containing a polyolefin resin. From the viewpoints of film strength, handling, and flexibility, the resin material (a) forming the foamed layer 2 preferably contains an ethylene-vinyl acetate copolymer as the polyolefin resin.

[0018] The ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of 5 to 30% by mass, more preferably 10 to 25% by mass. If the vinyl acetate content is 5% by mass or more, good adhesion to the anti-fogging layer (not shown) described below is achieved. Furthermore, if the content is 30% by mass or less, the film has sufficient strength and good transparency.

[0019] Furthermore, the ethylene-vinyl acetate copolymer preferably has a melt mass flow rate of 1.2 to 10 g / 10 min. If the melt mass flow rate is 1.2 g / 10 min or more, a low-density polyethylene with a high melt mass flow rate can be used, and the molding speed can be increased, making it possible to efficiently produce a film. On the other hand, if the melt mass flow rate exceeds 10 g / 10 min, it becomes difficult to maintain the shape of the film, resulting in poor film formability. The melt mass flow rate is measured in accordance with the provisions of JIS K 7210:1999.

[0020] The resin material (a) forming the foam layer 2 is foamed by a foaming agent. In other words, the resin material (a) contains a foaming agent.

[0021] The foaming agent may be any known foaming agent for polyolefin resins, such as sodium bicarbonate, azodicarbonamide, p,p'-oxybisbenzenesulfonylhydrazide, hydrazodicarbonamide, N,N'-dinitrosopentamethylenetetramine, etc. Commercially available foaming agents include Polythrene EV306G, Polythrene EE405F, and Polythrene EE2275F (manufactured by Eiwa Chemical Industry Co., Ltd.), Cellmike 3031T, Cellmike MB1061-7, and Cellmike Cellmike MB1023 (manufactured by Sankyo Kasei Co., Ltd.), etc.

[0022] The amount of foaming agent (the total amount of each foaming agent when two or more foaming agents are included) is preferably 0.05 to 5 parts by mass, more preferably 0.3 to 3 parts by mass, per 100 parts by mass of polyolefin resin (the total amount of each foaming agent when two or more foaming agents are included; the same applies below).

[0023] The resin material (a) may contain other polyolefin resins, other known additives, etc., within the range that does not impair the strength, handleability, and flexibility (within the range that does not impair the object of the present invention).

[0024] (outer layer) The outer layer 3 is provided on the surface of the foamed layer 2. When the agricultural facility is installed, the outer layer 3 becomes the outermost layer facing the outside of the facility. The outer layer 3 is a layer that reinforces the foamed layer 2, which lacks strength due to the foaming of the resin material (a). The outer layer 3 also prevents air from escaping from the inside when the agricultural polyolefin resin film 1 is produced by the inflation method, which causes the expansion of the tubular molten resin. For these reasons, the outer layer 3 is a non-foamed layer.

[0025] The outer layer 3 is a light-transmitting layer that protects the various pigments in the foamed layer 2 from deterioration without interfering with the functions (reflection, light blocking, etc.) of the foamed layer 2. In other words, the outer layer 3 is a non-foamed and light-transmitting layer.

[0026] The outer layer 3 is composed of one or more layers. That is, the outer layer 3 may be one layer, or two or more layers (multi-layer). Of these, from the viewpoint of film strength and flexibility, the outer layer 3 is preferably two or more layers. When the outer layer 3 is two or more layers, the polyolefin resins (main components) constituting the respective layers may be the same or different.

[0027] The thickness of the outer layer 3 (the sum of the thicknesses of the individual outer layers if the outer layer 3 is a multi-layer) is not particularly limited and may be adjusted appropriately depending on the thickness (total thickness) of the agricultural polyolefin resin film 1, the thickness of the foamed layer 2, the thickness of the inner layer 4 (described later), etc., but is, for example, about 0.01 mm to 0.05 mm. Within this range, a sufficient dustproof effect can be obtained and light transmittance can be improved.

[0028] The outer layer 3 is a layer made of a resin material (b) containing a polyolefin resin. From the viewpoint of improving the strength of the film, the resin material (b) forming the outer layer 3 preferably contains linear low-density polyethylene as the polyolefin resin.

[0029] The resin material (b) may be, for example, a composition containing linear low-density polyethylene as the main component and high-pressure low-density polyethylene as a minor component, each having a melt mass-flow rate (MRF) differing by approximately 0.5 to 2.0 g / 10 min. By blending resins having melt mass-flow rates differing by approximately 0.5 to 2.0 g / 10 min, the matte finish of the multilayer film can be further improved.

[0030] The outer layer 3 having two or more layers made of resin material (b) containing different polyolefin resins preferably has a laminated structure including, from the surface of the foam layer 2, a first outer layer made of resin material (b) containing ethylene-vinyl acetate copolymer as a main component and a second outer layer made of resin material (b) containing linear low-density polyethylene as a main component.

[0031] The resin material (b) may contain other polyolefin resins or known additives within the range that does not impair the strength or light transmittance (within the range that does not impair the object of the present invention).

[0032] (inner layer) The inner layer 4 is provided on the surface of the foamed layer 2 opposite to the outer layer 3. When the foamed layer 2 is installed in an agricultural facility, the inner layer 4 becomes the innermost layer facing the inside of the facility. Like the outer layer 3 described above, the inner layer 4 is a layer that reinforces the foamed layer 2 and is a non-foamed, light-transmitting layer.

[0033] The inner layer 4 is composed of one or more layers. That is, the inner layer 4 may be one layer, or two or more layers (multi-layer). Of these, from the viewpoint of film strength and flexibility, the inner layer 4 is preferably two or more layers. When the inner layer 4 is two or more layers, the polyolefin resins (main components) constituting the layers may be the same or different.

[0034] The thickness of the inner layer 4 (the sum of the thicknesses of the individual inner layers when the inner layer 4 is a multi-layered layer) is not particularly limited and may be adjusted appropriately depending on the thickness (total thickness) of the agricultural polyolefin resin film 1, the thickness of the foamed layer 2, the thickness of the outer layer 3, etc., but is preferably 0.01 mm or more and 0.06 mm or less. If the thickness is within the above range, the inner layer 4 will have good processability when subjected to a surface coating process, as described below, if necessary.

[0035] The inner layer 4 is a layer made of a resin material (c) containing a polyolefin resin. From the viewpoint of improving the strength of the film, the resin material (c) forming the inner layer 4 preferably contains linear low-density polyethylene as the polyolefin resin.

[0036] The density of the polyolefin resin contained in the resin material (c) is 0.900 to 0.930 g / cm from the viewpoint of ensuring strength. 3 The melt mass flow rate (MRF) is preferably 0.5 to 3.0 g / 10 min.

[0037] In addition, if a resin material containing a conventional ethylene-vinyl acetate copolymer is used as the resin material for forming the inner layer 4, irregularities are likely to form on the surface of the inner layer 4 opposite the foamed layer 2 (outer layer 3), making it difficult to perform surface coating processing on that surface, which is not preferable.

[0038] The two or more inner layers 4 made of resin materials (c) containing different polyolefin resins preferably have a laminate structure including, in order from the surface of the foam layer 2 (the surface opposite to the outer layer 3), a first inner layer made of resin material (c) containing ethylene-vinyl acetate copolymer as a main component and a second inner layer made of resin material (c) containing linear low-density polyethylene as a main component.

[0039] The resin material (c) may contain other polyolefin resins or known additives within the range that does not impair flexibility, transparency, etc. (within the range that does not impair the object of the present invention).

[0040] For example, the resin material (c) may contain an anti-fogging agent to impart anti-fogging properties to the agricultural polyolefin resin film 1. Examples of anti-fogging agents include partial esters of polyhydric alcohols (sorbitan, glycerin, diglycerin, etc.) with fatty acids, or condensates of these with alkylene glycols. The amount of anti-fogging agent added is preferably 1 to 5 parts by mass, more preferably 1.2 to 3 parts by mass, per 100 parts by mass of the polyolefin resin.

[0041] Furthermore, the resin material (c) may contain a fluorine-based surfactant or a silicone-based surfactant in addition to the antifogging agent in order to impart antifogging properties to the agricultural polyolefin-based resin film 1.

[0042] (Outer and inner layers) From the viewpoints of strength, handleability, and flexibility of the film, it is preferable that at least one of the resin material (b) forming the outer layer 3 and the resin material (c) forming the inner layer 4 contains a linear low-density polyethylene resin as a polyolefin-based resin, and it is more preferable that both the resin material (b) and the resin material (c) contain a linear low-density polyethylene resin.

[0043] From the viewpoint of film strength, handling, and flexibility, it is preferable that at least one of the outer layer 3 and the inner layer 4 is formed into two or more layers, and it is more preferable that both the outer layer 3 and the inner layer 4 are formed into two or more layers.

[0044] (Other layers) The agricultural polyolefin resin film 1 may have layers other than the foamed layer 2, outer layer 3, and inner layer 4, as long as the object of the present invention is not impaired. For example, the film 1 may have an anti-fogging layer (not shown) that provides anti-fogging properties on the surface of the inner layer 4 opposite to the foamed layer 2 (outer layer 3) side.

[0045] The anti-fog layer has the effect and function of maintaining the surface condition of the film (i.e., preventing smoothing due to fogging (moisture)) and maintaining scattering performance. The anti-fog layer is, for example, a layer made of a resin material containing a thermoplastic resin binder and an anti-fog agent such as an inorganic colloidal sol.

[0046] There are no particular limitations on the thermoplastic resin binder, as long as it is a thermoplastic resin that exhibits good adhesion to the inner layer 4. Examples of thermoplastic resin binders include acrylic resins, urethane resins, vinyl acetate resins, vinyl chloride-vinyl acetate resins, and polyester resins. These thermoplastic resin binders are usually used as aqueous emulsions dispersed in water or an aqueous solvent such as water and alcohol.

[0047] Examples of inorganic colloidal sols include colloidal silica particles and colloidal alumina particles. The colloidal silica particles may be spherical or have a large aspect ratio, such as an elongated shape. In addition to the above, colloidal lithium silicate particles may also be used.

[0048] The ratio of the thermoplastic resin binder to the inorganic colloidal sol, in terms of solids weight ratio, is preferably in the range of 1:9 to 7:3. When the ratio is in this range, sufficient adhesion between the anti-fogging layer and the inner layer 4 can be obtained, and good anti-fogging properties can be exhibited.

[0049] (Other ingredients) Each of the above resin materials may contain various additives, such as conventionally used emulsifiers, dispersants, stabilizers, and crosslinking agents, to the extent that the object of the present invention is not impaired. Furthermore, to improve the weather resistance of the coating film, hindered amine-based light stabilizers and ultraviolet absorbers may be contained. The incorporation of a crosslinking agent is particularly effective in improving the water resistance of the coating film. Examples of crosslinking agents include epoxy-based and aziridine-based agents.

[0050] <Method of manufacturing agricultural polyolefin resin film> The agricultural polyolefin resin film 1 of the present invention is preferably produced by an inflation method.

[0051] Specifically, the molten resin materials (a) to (c) forming the foam layer 2, outer layer 3, and inner layer 4 are first co-extruded through a die into a tubular shape, expanded from the inside by air pressure, and then cooled. At this time, the above-mentioned foaming agent is added in advance to the molten resin material (a) forming the foam layer 2.

[0052] Examples of methods for co-extrusion of the molten resins that make up each layer include a pre-die lamination method in which the molten resins are brought into contact before the die, an in-die lamination method in which the molten resins are brought into contact inside the die, and an out-die lamination method in which the molten resins are brought into contact after being discharged from multiple concentric lips of the die.

[0053] In this manner, the agricultural polyolefin resin film 1 of the present invention can be produced. When an anti-fogging layer is provided as needed, the anti-fogging layer can be formed by applying the above-mentioned anti-fogging agent to the surface of the inner layer 4 opposite to the foamed layer 2 (outer layer 3) using a coating method such as a gravure coater, a reverse roll coater, or an air knife coater, and then drying the anti-fogging agent.

[0054] <Physical properties of agricultural polyolefin resin films> The agricultural polyolefin resin film 1 constructed as described above has a specified overall thickness (total thickness) and the thickness of the foamed layer 2, which controls the foaming state of the foamed layer 2, thereby providing the same level of heat retention as conventional films, while also providing high total light transmittance and light scattering properties.

[0055] Total light transmittance refers to the transmittance of light that has completely passed through a substance (film) and is measured in accordance with JIS K 7136-1. Light scattering property is expressed as diffuse light transmittance, which is calculated using the following formula (I) based on the total light transmittance and haze measured in accordance with JIS K 7136-1. A higher diffuse light transmittance indicates higher light scattering property.

[0056] [Number 1] H = Td / Tt × 100 (I) In the formula (I), H is haze (%), Td is diffuse light transmittance (%), and Td is total light transmittance (%).

[0057] According to formula (I), the greater the diffuse light transmittance (Td), the greater the haze (H) (closer to 100%). Note that diffuse light transmittance is the total light transmittance minus parallel light transmittance. Parallel light transmittance refers to the transmittance of light that passes straight through a material, and the greater the parallel light transmittance, the higher the transparency.

[0058] From formula (I), in order to improve both the total light transmittance and the light scattering property, it is preferable to adjust the total light transmittance (Td) and the diffuse light transmittance (Td) [in other words, the haze (H)] to be within the following numerical ranges.

[0059] From the viewpoint of improving the total light transmittance, the agricultural polyolefin resin film 1 preferably has a total light transmittance of 86% or more, more preferably 88% or more, and even more preferably 90% or more.

[0060] The diffuse light transmittance of the agricultural polyolefin resin film 1 is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more, from the viewpoint of improving light scattering properties.

[0061] The haze (haze, cloudiness) of the agricultural polyolefin resin film 1 is preferably 30% or more and 55% or less, more preferably 35% or more and 55% or less, and even more preferably 40% or more and 55% or less, from the viewpoint of improving total light transmittance and light scattering properties.

[0062] The agricultural polyolefin resin film 1 preferably has a breaking strength of 8N or more and 30N or less in the mechanical axis (longitudinal, longitudinal) direction (hereinafter also referred to as "MD direction") of the film. The film 1 preferably has a breaking elongation of 350% or more and 600% or less in the MD direction. The film 1 preferably has an Elmendorf strength of 6N or more and 38N or less in the MD direction. The breaking strength refers to the tensile breaking strength measured by the method described in the Examples below. The breaking elongation refers to the breaking elongation measured in accordance with JIS K 7161-1 (and 7161-2):2014. The Elmendorf strength refers to the tear strength measured in accordance with JIS K 7128-2.

[0063] <Other embodiments> The agricultural polyolefin resin film of the present invention is not limited to the illustrated example (three types and three layers). The term "type" means that the resin materials (main component polyolefin resins) forming each layer are different. Examples of such films include: - 1 outer layer, 1 foam layer, and 2 inner layers (2 types, 4 layers in total) - 1 outer layer, 2 foam layers of 2 types, and 1 inner layer, for a total of 4 types and 4 layers. -2 types of outer layers (2 layers), 1 foam layer and 1 inner layer (4 types, 4 layers in total) - 2 types of outer layers, 2 layers, 1 foam layer, and 2 types of inner layers, for a total of 5 types and 5 layers. - 1 outer layer, 2 types of foam layers (2 layers), and 2 types of inner layers (2 layers) for a total of 5 types and 5 layers. The outer layer may be two layers of two kinds, the foam layer may be two layers of two kinds, and the inner layer may be one layer, for a total of five kinds and five layers, or six kinds and six layers or more. [Example]

[0064] The present invention will be described below based on examples. However, the present invention is not limited to these examples, and these examples can be modified or changed based on the spirit of the present invention, and such modifications are not excluded from the scope of the present invention.

[0065] The materials used to prepare the agricultural polyolefin resin film are listed below. LLDPE: Linear low-density polyethylene, density: 0.915 g / cm 3 , MFR: 2.0 g / 10 min (manufactured by Prime Polymer Co., Ltd., product name: SP2020). EVA: Ethylene-vinyl acetate copolymer with a vinyl acetate unit content of 15% by mass, MFR: 1.1 g / 10 min (NUC Corporation, product name: NUC-8452D). Foaming agent 1: Manufactured by Eiwa Chemical Industry Co., Ltd., product name: Polyslen EE405F. Foaming agent 2: Manufactured by Eiwa Chemical Industry Co., Ltd., product name: Polyslen EE2275F.

[0066] <Production of agricultural polyolefin resin film> (Each Example and Comparative Examples 1, 2, and 7) First, the materials shown in Tables 1 to 3 were blended to prepare resin materials having the compositions (parts by mass) shown in Tables 1 to 3. The foam layer resin material was then foamed with the foaming agent shown in Tables 1 to 3. Next, using a 1-type 1-layer, 3-type 3-layer, 4-type 4-layer, or 5-type 5-layer inflation machine, the resin materials were co-extruded in a molten state from multiple concentric lips of a die to form, in order from the outside, the resin material for the inner layer, the resin material for the foam layer, and the resin material for the outer layer. The extrusion was expanded from the inside by air pressure, cooled, and wound up to produce 1-type 1-layer, 3-type 3-layer, 4-type 4-layer, or 5-type 5-layer agricultural polyolefin resin films having the thicknesses shown in Tables 1 to 3. In the "Layer Number" column for each outer layer, foam layer, and inner layer in the table, for example, "Layer 1 / 2" means a two-layer structure including Layer 1 and Layer 2, and "Layer 1-2" means a single layer (single-layer structure) in which Layer 1 and Layer 2 are integrated (having the total thickness of Layer 1 and Layer 2). As a specific example, the outer layer layer number "Layer 1 / 2-3" means a two-layer structure including Layer 1 and an integrated layer (single layer) of Layer 2 and Layer 3.

[0067] (Comparative Example 3) We used "Batsugun 5" (5-layer structure), an agricultural polyolefin resin film manufactured by Takiron C.I. Co., Ltd. Note that "Batsugun 5" does not have a foam layer.

[0068] Comparative Example 4 We used "Eco Poka Puti" (three-layer structure, air cap), a bubble wrap for greenhouse cultivation manufactured by Kawakami Sangyo Co., Ltd. Note that "Eco Poka Puti" does not have a foam layer. The thickness of "Eco Poka Puti" (total thickness of the film) is approximately 3.2 mm (outside the range of 0.18 mm or less).

[0069] (Comparative Example 5) We used "Sunny Coat," an agricultural greenhouse insulation film (a hollow double-structure film with an air layer in the middle) manufactured by Ube Exsymo Co., Ltd. Note that "Sunny Coat" does not have a foam layer.

[0070] (Comparative Example 6) We used Skycoat Air Plus, an agricultural polyolefin resin film manufactured by Takiron C.I. Co., Ltd. (a five-layer film made specifically for interior lining sides with air bubbles added to the inner layer). The thickness of Skycoat Air Plus (total film thickness) is approximately 0.2 mm (outside the range of 0.18 mm or less).

[0071] <Evaluation of agricultural polyolefin resin films> The agricultural polyolefin resin films of the Examples and Comparative Examples were evaluated as follows, and the results are shown in Tables 1 to 3.

[0072] (Moldability) Regarding the formability of the resin film, those that could be formed into a resin film according to the above procedure were marked "Good", and those that could not be formed were marked "Poor".

[0073] (HAZE) The haze of the agricultural polyolefin resin film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., trade name: NDH2000) in accordance with JIS K 7136-1.

[0074] (Total light transmittance) The total light transmittance of the agricultural polyolefin resin film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., trade name: NDH2000) in accordance with JIS K 7136-1.

[0075] (Diffuse light transmittance) Using the haze and total light transmittance measured above, the diffuse light transmittance was calculated according to the above formula (I).

[0076] (breaking strength) The breaking strength of agricultural polyolefin resin films was measured in the longitudinal (machine direction) and transverse (transverse) directions (transverse) using a precision universal testing machine (Shimadzu Corporation, product name: Autograph AG-500D). The test specimens were 5 mm wide, with marks placed exactly 10 mm from the center of the specimen toward both ends, with a distance of 20 mm between the marks. The specimens were accurately attached to the tensile testing machine. The test speed was 200 ± 20 mm / min, and the force at which the specimen broke was taken as the tensile breaking strength (breaking strength).

[0077] (Elongation at break) The breaking elongation in the MD and TD directions of agricultural polyolefin resin films was measured using a precision universal testing machine (Shimadzu Corporation, product name: Autograph AG-500D) in accordance with JIS K 7161-1 (and 7161-2):2014.

[0078] (Elmendorf Strength) In accordance with JIS K 6732, test pieces for Elmendorf tear strength tests (MD: 76 mm, TD: 63 mm) were prepared from agricultural polyolefin resin films. Next, an Elmendorf tear strength test was conducted on the test pieces in accordance with JIS K 7128-2 using a digital Elmendorf tear tester (Toyo Seiki Seisakusho Co., Ltd., product number: SA-WP). The strength of the film was evaluated based on the following criteria. More specifically, nine test pieces were prepared, the test temperature was set to 23°C, and the test pieces were kept in the test location for at least one hour. The tear strength of the test pieces was then measured using the digital Elmendorf tear tester. Two large and two small values ​​were removed from the nine measurements, and the average of the remaining five was calculated to determine the Elmendorf tear strength.

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] <Considerations on Tables 1 to 3> Comparing each example with each comparative example, it was confirmed that the films of each example have a foam layer thickness of 0.07 mm or more and 0.15 mm or less, and a total film thickness (total thickness) of 0.18 mm or less, and therefore have a total light transmittance of 86% or more and a diffuse light transmittance of 30% or more; in other words, both the total light transmittance and light scattering properties are high. On the other hand, it was confirmed that the films of Comparative Examples 1 and 3 to 6, in which at least one of the thicknesses of the film was outside the above range, were inferior in either total light transmittance or light scattering property. In Comparative Example 2, in which an attempt was made to add a foaming agent to all of the resin materials forming each layer and to construct an all-foamed layer, it was not possible to form it into a film. In Comparative Example 7, where the foam layer thickness was outside the above range, it was not possible to form the foam into a film. It was confirmed that the films of Comparative Examples 3 to 5, which did not have a foam layer, had poor light scattering properties. The films of each example have one or more foam layers between the outer and inner layers, so they have the same heat retention as conventional films. Furthermore, the films of each example have high strength, with a breaking strength of 8N or more in the MD direction, a breaking elongation of 350% or more, and an Elmendorf strength of 6N or more in the MD direction. [Industrial Applicability]

[0083] As described above, the present invention is suitable for agricultural polyolefin resin films. [Explanation of symbols]

[0084] 1. Polyolefin resin film for agricultural use 2 Foam layer 3 Outer layer 4 Inner layer

Claims

1. one or more foam layers each having a plurality of pores formed by foaming a resin material (a) containing a polyolefin-based resin; one or more non-foamed outer layers provided on the surface of the foamed layer and made of a resin material (b) containing a polyolefin-based resin; one or more non-foamed inner layers formed on a surface of the foamed layer opposite to the outer layer side and made of a resin material (c) containing a polyolefin-based resin; The thickness of the foam layer is 0.07 mm or more and 0.15 mm or less, A polyolefin resin film for agricultural use, characterized in that the total thickness of the foam layer, the outer layer, and the inner layer is 0.18 mm or less.

2. 2. The agricultural polyolefin resin film according to claim 1, wherein the thickness of the inner layer is 0.01 mm or more and 0.06 mm or less.

3. 3. The agricultural polyolefin resin film according to claim 1, wherein the polyolefin resin is at least one selected from the group consisting of polyethylene, polypropylene, and ethylene-vinyl acetate copolymer.

4. 3. The agricultural polyolefin resin film according to claim 1, wherein the resin material (a) contains an ethylene-vinyl acetate copolymer.

5. 3. The agricultural polyolefin resin film according to claim 1, wherein at least one of the resin material (b) and the resin material (c) contains a linear low-density polyethylene resin.

6. 3. The agricultural polyolefin resin film according to claim 1, wherein at least one of the outer layer and the inner layer is formed of two or more layers.

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