JP7543478B2 - Polyolefin resin film for agriculture - Google Patents

Description

The present invention relates to an agricultural polyolefin resin film used in agricultural facilities such as agricultural greenhouses and agricultural tunnels, and a method for producing the same.

In recent years, agricultural films made of olefin-based resins have come into use, but in agricultural greenhouses and tunnels, there is a demand for agricultural films that have heat retention properties so that the indoor air temperature and ground temperature, which rise during the day due to exposure to sunlight, do not drop too much at night.

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.

JP 2007-125001 A JP 2009-45060 A

To impart an anti-fogging function to agricultural polyolefin resin films, it is generally necessary to apply an anti-fogging agent to the agricultural polyolefin resin films. However, in the above-mentioned conventional agricultural films, the surface to which the anti-fogging agent is applied has large irregularities, making it difficult to apply the anti-fogging agent evenly.

Instead of applying an anti-fogging agent, it is also possible to knead the anti-fogging agent into the film. However, in this case, the anti-fogging agent applied to the inner surface of the film is a surfactant with a hydrophilic group. Once the anti-fogging agent is sprayed onto the film surface and washed away by moisture, the anti-fogging properties disappear, and the anti-fogging effect cannot be maintained for a long period of time. This makes it difficult to apply agricultural polyolefin resin films to interior ceiling linings, which require high anti-fogging properties.

The present invention was made in consideration of the above problems, and aims to provide an agricultural polyolefin resin film that can be used for interior ceiling linings, which require high anti-fogging properties, and can apply the anti-fogging agent evenly by suppressing the formation of irregularities on the surface to which the anti-fogging agent is applied.

In order to achieve the above object, the agricultural polyolefin resin film of the present invention comprises an outer layer made of a resin material (a) containing a polyolefin resin, an inner layer made of a resin material (c) containing a polyolefin resin, one or more intermediate layers made of a resin material (b) containing a polyolefin resin provided between the outer layer and the inner layer, and an anti-fogging layer provided on the surface of the inner layer opposite the outer layer side, wherein at least one intermediate layer is a foamed layer formed by foaming the resin material (b), the distance between the surface of the inner layer opposite the outer layer side and the surface of the foamed layer located on the innermost side of the foamed layers is 40 μm or more, and the maximum height Rz of the surface of the inner layer opposite the outer layer side is 95 μm or less.

The present invention makes it possible to provide an agricultural polyolefin resin film that can be uniformly coated with an anti-fogging agent and can be used for interior ceiling linings, which require high anti-fogging properties.

1 is a cross-sectional view showing an agricultural polyolefin resin film according to an embodiment of the present invention.

The agricultural polyolefin resin film of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiments, and can be modified as appropriate within the scope of the present invention.

<Polyolefin resin film for agricultural use>
As shown in FIG. 1, the agricultural polyolefin resin film 1 of the present invention comprises an outer layer 2 which is the layer on the side where sunlight is incident, an inner layer 3 which is the layer on the opposite side to the side where sunlight is incident, an intermediate layer 4 provided between the outer layer 2 and the inner layer 3, and an anti-fogging layer (anti-fogging coating film) 8 provided on the surface 3a of the inner layer 3 (the surface opposite to the outer layer 2), and has a multilayer structure in which these layers are laminated.

From the viewpoint of strength and ease of handling, the thickness of the agricultural polyolefin resin film 1 is preferably 50 to 400 μm, and more preferably 100 to 300 μm.

<Outer layer>
The outer layer 2 is the outermost layer facing the outside of the agricultural facility when the film is laid out in the agricultural facility. The outer layer 2 is a layer that reinforces the intermediate layer 3, which is lacking in strength because it contains a large amount of various pigments and is made of foamed resin material, and also prevents air from escaping from the inside to expand the tubular molten resin when the agricultural polyolefin resin film 1 is produced by the inflation method. Therefore, the outer layer 2 is made a non-foamed layer.

In addition, the outer layer 2 is a layer that protects the various pigments in the intermediate layer 4 from deterioration without interfering with the functions of the intermediate layer 4 (reflection, light blocking, etc.), so it is made a light-transmitting layer.

This outer layer 2 is a layer made of a resin material (a) containing a polyolefin-based resin, and as the polyolefin-based resin, linear low-density polyethylene is preferred from the viewpoint of improving the strength of the agricultural polyolefin-based resin film 1.

The outer layer 2 may be a composition that contains, for example, linear low-density polyethylene as the main component and high-pressure low-density polyethylene with melt mass flow rates (MRF) differing by approximately 0.5 to 2.0 g/10 min as a secondary component. By blending resins with 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.

The melt mass flow rate is obtained by measuring in accordance with the provisions of JIS K 7210:1999.

The resin material may also contain other polyolefin resins or known additives, etc., as long as the strength and light transmittance are not impaired.

The thickness of the outer layer 2 is preferably 10 to 40 μm, and more preferably 15 to 30 μm. If the thickness is 10 μm or more, the dustproof effect is sufficient, and if it is 40 μm or less, the light transmittance is good.

<Inner layer>
The inner layer 3 becomes the innermost layer facing the inside of the agricultural facility when the agricultural facility is laid out. This inner layer 3, like the outer layer 2 described above, is a layer that reinforces the intermediate layer 3 and is a non-foamed layer that is optically transparent.

This inner layer 3 is a layer made of a resin material (c) containing a polyolefin-based resin. Examples of polyolefin-based resins include linear low-density polyethylene and low-density polyethylene, but linear low-density polyethylene is preferred from the viewpoint of improving the strength of the agricultural polyolefin-based resin film 1.

From the viewpoint of ensuring strength, the density of the polyolefin resin is preferably 0.900 to 0.930 g/cm ³ , and the melt mass flow rate (MRF) is preferably 0.5 to 3.0 g/10 min.

When a resin material containing a conventional ethylene-vinyl acetate copolymer is used, irregularities tend to form on the surface 3a of the inner layer 3 opposite the outer layer 2, making it difficult to provide an anti-fogging layer 8 on that surface 3a, which is not preferable.

It may also contain other polyolefin resins and other known additives, etc., as long as they do not impair flexibility, transparency, etc.

For example, the resin material (c) forming the inner layer 3 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.) and fatty acids, or condensates of these with alkylene glycols.

The amount of anti-fogging agent is preferably 1 to 5 parts by mass, and more preferably 1.2 to 3 parts by mass, per 100 parts by mass of polyolefin resin.

In addition, the resin material (c) may contain a fluorine-based surfactant or a silicone-based surfactant together with the antifogging agent to impart antifogging properties to the agricultural polyolefin-based resin film 1.

The thickness of the inner layer 3 is preferably 10 to 40 μm, and more preferably 15 to 30 μm.

<Middle class>
The intermediate layer 4 has, from the outer layer 2 side, a first intermediate layer 5, a second intermediate layer 6, and a third intermediate layer 7, and from the viewpoint of imparting heat retention and insulation properties to the agricultural polyolefin-based resin film 1, at least one of these first to third intermediate layers 5 to 7 is composed of a foamed layer formed by foaming a resin material (b) containing a polyolefin-based resin.

The first to third intermediate layers 5 to 7 are layers made of a resin material (b) containing a polyolefin-based resin such as linear low-density polyethylene or ethylene-vinyl acetate copolymer, and from the viewpoints of film strength, handling, and flexibility, it is preferable to use ethylene-vinyl acetate copolymer as the polyolefin-based resin.

The ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of 5 to 30% by mass, and more preferably 10 to 25% by mass. If the vinyl acetate content is 5% by mass or more, the adhesion to the anti-fog layer described below will be good. Furthermore, if the content is 30% by mass or less, the strength of the resulting film will be sufficient and the transparency will also be good.

In addition, it is preferable to use an ethylene-vinyl acetate copolymer with 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, and film formability deteriorates.

When foaming the first to third intermediate layers 5 to 7, the resin material (b) containing the polyolefin resin is foamed with a foaming agent.

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. For example, commercially available products such as Polythrene EV306G (manufactured by Sankyo Kasei Co., Ltd.), Cellmike 3031T (manufactured by Eiwa Kasei Co., Ltd.), and Cellmike MB1061-7 (manufactured by Eiwa Kasei Co., Ltd.) can be used.

The amount of foaming agent is preferably 0.05 to 5 parts by mass, and more preferably 0.3 to 3 parts by mass, per 100 parts by mass of polyolefin resin.

From the viewpoint of further improving the smoothness of the surface 3a of the inner layer 3, it is preferable that in the agricultural polyolefin resin film 1 of the present invention, at least one of the first intermediate layer 5 and the second intermediate layer 6 is a foamed layer, and the layer of the intermediate layer 4 on the inner layer 3 side (i.e., the third intermediate layer 7) is a non-foamed layer.

The resin material (b) may also contain other polyolefin resins, other known additives, etc., to the extent that the strength, ease of handling, and flexibility are not impaired.

The thickness of the intermediate layer 4 is preferably 30 to 100 μm, and more preferably 40 to 80 μm. If the thickness of the intermediate layer 4 is 30 μm or more, the physical properties such as tensile strength and stiffness of the agricultural polyolefin resin film 1 can be sufficiently obtained, and if the thickness is 100 μm or less, sufficient light transmittance can be obtained. From the viewpoint of ensuring good physical properties in the agricultural polyolefin resin film 1, the thickness of the intermediate layer 4 is preferably in the range of 50 to 80%, and more preferably in the range of 55 to 75%, assuming that the total thickness of the agricultural polyolefin resin film 1 is 100%.

<Anti-fogging layer>
The anti-fog layer 8 is intended to maintain the surface condition of the film (i.e., to prevent smoothing due to fogging (moisture)) and to maintain scattering performance, and is composed of a thermoplastic resin binder and an anti-fog agent such as an inorganic colloidal sol.

The thermoplastic resin binder used in the anti-fog layer 8 is not particularly limited as long as it exhibits good adhesion with the inner layer 3. Examples 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.

Among thermoplastic resin binders, aqueous urethane resins, particularly aqueous acrylic-modified urethane resins, are preferred. As the aqueous acrylic-modified urethane resin, polyester-based anionic ones are preferred, and for example, they can be produced by polymerizing (ii) a hydroxyl group-containing acrylic compound in the presence of (i) a polyester-based anionic aqueous urethane resin, followed by reacting (iii) an active isocyanate compound.

On the other hand, examples of inorganic colloidal sols used as other components of the anti-fogging layer 8 include colloidal silica particles and colloidal alumina particles. The colloidal silica particles may be spherical or have a large aspect ratio, for example, elongated. As spherical colloidal silica particles, colloidal silica particles having an average particle size of 5 to 90 nm, preferably 20 to 80 nm, can be used. As elongated colloidal silica particles, it is possible to use particles having a ratio D1/D2 of the particle size measured by dynamic light scattering (D1 millimicrons) to the particle size measured by nitrogen gas adsorption (D2 millimicrons) of 5 or more, D1 of 40 to 500 nm, and a minor axis of 5 to 40 nm as measured by electron microscope observation. Such elongated colloidal silica particles are known (JP Patent Publication 4-65314) and are available commercially.

In addition to the above, colloidal lithium silicate particles and the like can also be used. On the other hand, colloidal alumina particles having an average particle size of 5 to 70 nm, preferably 20 to 60 nm, are suitable. These inorganic colloidal sols may be used alone or in combination of two or more kinds.

The ratio of the thermoplastic resin binder to the inorganic colloid sol is preferably in the range of 1:9 to 7:3 by weight of solids. If the ratio of the thermoplastic resin binder to the inorganic colloid sol is in this range, sufficient adhesion between the anti-fogging layer 8 and the inner layer 3 can be obtained, and good anti-fogging properties can be exhibited.

To form the anti-fogging layer 8 on the surface 3a of the inner layer 3, the following method is preferably used. First, an aqueous emulsion composition (anti-fogging agent) containing a thermoplastic resin binder and an inorganic colloidal sol in a specified ratio is prepared, and the composition is applied to the surface 3a of the inner layer 3 using a coating method such as a gravure coater, reverse roll coater, or air knife coater. Then, the composition is dried with hot air at a temperature of about 50 to 150°C to form a coating film with a thickness of 0.2 to 5 μm, preferably about 0.5 to 2 μm. If the film thickness is 0.2 μm or more, the anti-fogging effect is fully exhibited, and if it is 5 μm or less, the light transmittance is good.

When forming a coating film, the aqueous emulsion composition may contain a silicone surfactant or a fluorosurfactant, if desired, to improve application properties. For example, polyether-modified silicone oil is preferred as a silicone surfactant, and for example, a surfactant containing a fluoroalkyl group or a fluoroalkenyl group is used as a fluorosurfactant. The amount of these surfactants is usually selected in the range of 0.01 to 1% by mass based on the total amount of the aqueous emulsion composition.

In addition, various additives such as emulsifiers, dispersants, stabilizers, and crosslinking agents that are commonly used in the past can be added to the extent that the object of the present invention is not impaired. Furthermore, in order to improve the weather resistance of the coating film, hindered amine-based light stabilizers and ultraviolet absorbers can be added. The incorporation of a crosslinking agent can have the effect of improving the water resistance of the coating film in particular. Examples of crosslinking agents include epoxy-based and aziridine-based agents.

Here, the inventors have investigated the conditions for ensuring the smoothness of the surface 3a of the inner layer 3 in the agricultural polyolefin resin film 1, and have found that controlling the surface roughness (maximum height Rz) of the surface 3a of the inner layer 3 can improve the applicability of the anti-fogging agent on said surface 3a.

More specifically, by setting the maximum height Rz of the surface 3a of the inner layer 3 to 95 μm or less, it is possible to suppress the formation of irregularities on the surface 3a of the inner layer 3, making it possible to uniformly apply the antifogging agent to the surface 3a. As a result, it becomes easier to provide the antifogging layer 8 on the surface 3a of the inner layer 3.

In addition, since the anti-fogging agent can be applied uniformly to the surface 3a of the inner layer 3, unlike the above-mentioned conventional technology, kneading the anti-fogging agent or applying an anti-drip agent is not necessary. As a result, the anti-fogging properties of the agricultural polyolefin resin film 1 are improved, and it can be used for interior ceilings, which require high anti-fogging properties.

In this specification, "maximum height Rz" is measured in accordance with JIS B 0601:2001 and refers to the sum of the height of the highest peak and the depth of the deepest valley on the roughness curve.

In addition, from the viewpoint of improving the heat retention of the agricultural polyolefin resin film 1, it is preferable that the porosity calculated by the following formula (1) is 5% or more.

[Equation 1]
Porosity [%] = 1 - (ρ/ρ ₀ ) (1)
(Here, ρ is the apparent specific gravity including pores, and ρ ₀ is the true specific gravity without pores.)

In this specification, "porosity" refers to that measured in accordance with JIS R 2205 (method of measurement of apparent porosity, water absorption, and specific gravity of firebricks).

In addition, the "apparent specific gravity including pores" and the "true specific gravity excluding pores" are specific gravities measured in accordance with JIS K 7222. However, since the foam layer of the agricultural polyolefin resin film of the present invention is not visible on the outside and can be considered to have closed pores, the specific gravity measured in accordance with the underwater displacement method of JIS K 7222 is used.

From the viewpoint of maintaining strength, the porosity is preferably 60% or less, more preferably 50% or less, and even more preferably 30% or less.

In addition, it is preferable that the agricultural polyolefin resin film 1 has a breaking strength of 10 N or more and 30 N or less in the mechanical axis (longitudinal) direction of the film (hereinafter referred to as the "MD direction"), and an Elmendorf strength of 10 N or more and 38 N or less.

In this specification, "breaking strength" refers to the tensile breaking strength measured by the method described in the Examples below, and "Elmendorf strength" refers to the tear strength measured in accordance with JIS K 7128-2.

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

Specifically, first, the molten resin materials (a) to (c) forming the outer layer 2, inner layer 3, and intermediate layer 4 are co-extruded from a die into a tube shape, expanded from the inside by air pressure, and then cooled. At this time, at least one of the molten resin materials (b) forming the first to third intermediate layers 5 to 7 must already contain the foam layer described above.

Methods for co-extrusion of the molten resins that make up each layer include the pre-die lamination method, in which the molten resins come into contact with each other before the die, the in-die lamination method, in which the molten resins come into contact with each other inside the die, and the out-die lamination method, in which the molten resins come into contact with each other after being discharged from multiple concentric lips of the die.

Next, the above-mentioned anti-fogging agent is applied to the surface 3a of the inner layer 3 using a coating method such as a gravure coater, reverse roll coater, or air knife coater, and then dried to form an anti-fogging layer 8 on the surface 3a of the inner layer 3, thereby producing the agricultural polyolefin resin film 1 of the present invention.

<Other forms>
The agricultural polyolefin resin film of the present invention is not limited to the illustrated example. For example, in the agricultural polyolefin resin film 1 in the above embodiment, the intermediate layer 4 is three layers, but the intermediate layer 4 may be one or more layers, may be two layers, or may be four or more layers.

In addition, if light-blocking properties are required, it is preferable that the intermediate layer 4 contains various pigments, but if light-blocking properties are not required, it is not necessary to contain various pigments.

The present invention will be described below based on examples. Note that 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 are not excluded from the scope of the present invention.

The materials used to make the agricultural polyolefin resin film are listed below.

(1) 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)
(2) EVA: ethylene-vinyl acetate copolymer with a vinyl acetate unit content of 15% by mass, MFR: 1.1 g/10 min (manufactured by NUC Corporation, product name: NUC-8452D)
(3) Foaming agent 1: Azodicarbonamide (manufactured by Eiwa Chemical Industry Co., Ltd., product name: Polythren EE405F)
(4) Foaming agent 2: Azodicarbonamide (manufactured by Eiwa Chemical Industry Co., Ltd., product name: Polythren EE2275F)
(5) Foaming agent 3: Azodicarbonamide (manufactured by Sankyo Kasei Co., Ltd., product name: Cellmike Cellmike MB1023)

Example 1
<Preparation of agricultural polyolefin resin film>
First, the materials shown in Table 1 were blended to prepare a resin material of Example 1 having the composition (parts by mass) shown in Table 1. Next, using a five-kind, five-layer inflation device, resin materials were co-extruded in a molten state from multiple concentric lips of a die so as to become, from the outside, the resin material of the inner layer, the resin material of the first intermediate layer, the resin material of the second intermediate layer, the resin material of the third intermediate layer, and the resin material of the outer layer, and then expanded from the inside by air pressure, followed by cooling and winding to produce a five-kind, five-layer film having an outer layer thickness of 20 μm, an intermediate layer thickness of 100 to 170 μm, and an inner layer thickness of 20 μm.

Next, a coating liquid (anti-fogging agent) for forming an anti-fogging layer was prepared, consisting of 50 parts by weight of an acrylic resin emulsion, 50 parts by weight of alumina sol, and 0.5 parts by weight of a polyether-modified silicone surfactant. This was applied to the outer surface of the film (the surface of the inner layer opposite the outer layer) using a bar coater #7, and dried at 50°C for 5 minutes to form an anti-fogging layer with a thickness of 2 μm, thereby producing the agricultural polyolefin resin film of this example.

<Measurement of surface roughness (maximum height Rz) of the inner layer surface>
The surface roughness (maximum height Rz) of the surface of the inner layer (the surface of the inner layer opposite to the outer layer side) before the anti-fog layer was formed was measured in accordance with JIS B 0601:2001. More specifically, the surface roughness was measured three times in an area of 2000 μm × 2756 μm using a shape analysis laser microscope (manufactured by Keyence, product name: VK-X1000), and the average value was taken as Rz. The results are shown in Table 1.

<Evaluation of Coating Properties>
The coating solution for forming the anti-fogging layer was dried at 50° C. for 5 minutes, and the state of the coated surface was evaluated according to the following evaluation criteria. The results are shown in Table 1.
The coated surface is dry and the coating properties are excellent: ○
The coated surface is not dry and the coating properties are poor: ×

<Porosity Measurement>
The porosity of the produced agricultural polyolefin resin film was measured using the above formula (1) in accordance with JIS R 2205. More specifically, the apparent specific gravity ρ including pores and the true specific gravity ρ ₀ not including pores were measured using an automatic pycnometer (manufactured by Toyo Seiki, product name: high precision type D-H100) by the underwater displacement method in accordance with JIS K 7222 to obtain the porosity. The results are shown in Table 1.

<Measurement of breaking strength>
The breaking strength of the prepared agricultural polyolefin resin film in the longitudinal direction was measured using a precision universal testing machine (Shimadzu Corporation, product name: Autograph AG-500D). The test piece had a measurement width of 5 mm, and a mark was made at a position exactly 10 mm from the center of the test piece toward both ends, with a distance between the markings of 20 mm, and the test piece was accurately attached to the tensile tester. The test speed was 200±20 mm/min, and the force at which the test piece broke was taken as the tensile breaking strength (breaking strength in the longitudinal direction). The results are shown in Table 1.

<Elmendorf strength measurement>
A test piece for an Elmendorf tear strength test (MD direction: 76 mm, TD direction: 63 mm) was taken from the film obtained in Example 1 in accordance with JIS K 6732. Next, an Elmendorf tear strength test was performed on the test piece in accordance with JIS K 7128-2 using a digital Elmendorf tear tester (Toyo Seiki Seisakusho Co., Ltd., product number: SA-WP), and the strength of the film was evaluated based on the following evaluation criteria.

More specifically, nine of the above test pieces were taken, 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. Of the nine measured values, two large and two small values were removed, and the average of the remaining five values was calculated to determine the Elmendorf tear strength. The results are shown in Table 1.

(Examples 2 to 8)
A polyolefin-based resin film for agricultural use was produced in the same manner as in Example 1 above, except that the composition of the resin material was changed to the composition (parts by mass) shown in Table 1.

Then, in the same manner as in Example 1 described above, the surface roughness (maximum height Rz) of the inner layer surface was measured, the coatability was evaluated, the porosity was measured, the breaking strength was measured, and the Elmendorf strength was measured. The results are shown in Tables 1 to 3.

(Comparative Examples 1 to 2)
A polyolefin-based resin film for agricultural use was produced in the same manner as in Example 1 above, except that the composition of the resin material was changed to the composition (parts by mass) shown in Table 2.

Then, in the same manner as in Example 1 described above, the surface roughness (maximum height Rz) of the inner layer surface was measured, the coatability was evaluated, the porosity was measured, the breaking strength was measured, and the Elmendorf strength was measured. The results are shown in Table 4.

As shown in Tables 1 to 3, in the films of Examples 1 to 8, the maximum height Rz of the surface of the inner layer (the surface coated with the anti-fog agent) is 95 μm or less, and the formation of irregularities on the surface of the inner layer is suppressed, which shows that the anti-fog agent is excellent in applicability (i.e., the anti-fog agent can be applied uniformly).

In addition, the films of Examples 1 to 8 have excellent moisture retention because the porosity is 5% or more, and the breaking strength and Elmendorf strength are both 10 N or more, so they also have excellent strength.

On the other hand, as shown in Table 4, in the films of Comparative Examples 1 and 2, the maximum height Rz of the surface of the inner layer (the surface coated with the anti-fog agent) is greater than 95 μm, and large irregularities are formed on the surface of the inner layer, which shows that the applicability of the anti-fog agent is poor (i.e., the anti-fog agent cannot be applied uniformly). In particular, in Comparative Example 2, the second and third intermediate layers are foam layers, and the inner layer is formed from a resin material containing an ethylene-vinyl acetate copolymer, which shows that large irregularities are formed on the surface of the inner layer to which the anti-fog agent is applied, which shows that the applicability of the anti-fog agent on this surface is poor.

In addition, in Comparative Example 2, the breaking strength and Elmendorf strength are both less than 10 N, indicating that the strength is poor.

As explained above, the present invention is suitable for agricultural polyolefin resin films.

REFERENCE SIGNS LIST 1 Agricultural polyolefin resin film 2 Outer layer 3 Inner layer 3a Surface of inner layer opposite to outer layer 4 Intermediate layer 5 First intermediate layer 6 Second intermediate layer 7 Third intermediate layer 8 Anti-fog layer

Claims (3)

An outer layer made of a resin material (a) containing a polyolefin-based resin;
An inner layer made of a resin material (c) containing a polyolefin-based resin;
one or more intermediate layers provided between the outer layer and the inner layer and made of a resin material (b) containing a polyolefin-based resin;
an anti-fogging layer provided on a surface of the inner layer opposite to the outer layer side,
At least one of the intermediate layers is a foamed layer formed by foaming the resin material (b),
a distance between a surface of the inner layer opposite to the outer layer side and a surface of the foamed layer located closest to the inner layer side among the foamed layers, the surface being on the inner layer side, is 40 μm or more;
The maximum height Rz of the surface of the inner layer opposite to the outer layer side is 95 μm or less,
1. A polyolefin resin film for agricultural use , characterized in that the foam layer is in contact with the outer layer made of the resin material (a) containing linear low density polyethylene . 2. The agricultural polyolefin resin film according to claim 1, characterized in that the porosity calculated by the following formula (1) is 5% or more.
Porosity [%] = 1 - (ρ/ρ ₀ ) (1)
(Here, ρ is the apparent specific gravity including pores, and ρ ₀ is the true specific gravity without pores.) 3. The agricultural polyolefin resin film according to claim 2, wherein the porosity is 7.3 to 22%.

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