Multilayer film for agriculture and method for manufacturing thereof

Abstract

An agricultural multilayer film and a method for manufacturing the same are provided. According to the present invention, the agricultural multilayer film exhibits excellent thermal insulation and heat shielding effects even in the event of abnormal high temperatures, thereby minimizing the increase in the surface temperature of the multilayer film and reducing crop damage caused by high heat. Furthermore, since the implemented multilayer film is made into a thin film, it maintains low costs while ensuring good manufacturing stability. Additionally, as the mechanical strength can be equivalent to or improved compared to conventional agricultural films, it is possible to maintain suitable growing conditions for crops or effectively alleviate high-temperature stress on crops even in the event of abnormal high temperatures, thus allowing for widespread application in agriculture.

Description

Technology Field

[0001] The present invention relates to an agricultural multilayer film and a method for manufacturing the same, and more specifically, to an agricultural multilayer film capable of responding to abnormal high-temperature climate changes and a method for manufacturing the same. Background Technology

[0002] Recently, climate change caused by global warming has been accelerating worldwide, leading to a continuous rise in temperatures. This climate change is having a direct and widespread impact on the agricultural sector. In particular, the northward shift of suitable cultivation areas due to global warming is causing serious problems with existing crop cultivation methods and variety selection. Furthermore, as major crops that have long been grown in specific regions become vulnerable to high-temperature stress or the duration of periods exceeding optimal growth temperatures increases, issues such as quality degradation and reduced yields are arising. In addition to financial losses for farmers, this triggers rising crop costs, forcing them to switch crops or relocate to areas where they can cultivate the same crops.

[0003] Consequently, in order to ensure stable crop growth even amidst abnormal high-temperature climate change, effectively controlling the optimal microenvironment for crop growth—particularly soil and surface temperatures—is emerging as a key challenge in agricultural technology.

[0004] Meanwhile, in conventional agriculture, various types of mulching films have been habitually used to maintain soil moisture, control weeds, and regulate the early growth environment. However, there are fundamental limitations to temperature control in response to abnormal high temperatures caused by climate change, as common transparent films cause excessive soil temperature increases, inducing heat stress, and common black films often harm crops due to their high heat absorption rates leading to excessively high surface temperatures.

[0005] In addition, there have recently been attempts to use black films thicker than usual for agricultural purposes to provide physical insulation against abnormally high external environments. However, if the film is excessively thick, it is difficult to manufacture a film of uniform thickness during the production process, and there are problems in ensuring technical stability during rolling and handling. Furthermore, the increased amount of raw materials required for film manufacturing leads to a dramatic rise in production costs, which in turn passes on a high economic burden to farmers.

[0006] Accordingly, there is an urgent need for research on agricultural films that can maintain optimal growing conditions for crops or effectively alleviate high-temperature stress in the rapidly changing climate environment caused by global warming, while ensuring manufacturing stability and preventing cost increases. Prior art literature

[0007] Republic of Korea Registered Patent Publication No. 10-1481705 The problem to be solved

[0008] The present invention has been derived in consideration of the above points and aims to provide an agricultural multilayer film and a method for manufacturing the same, which can maintain a suitable growing environment for crops or effectively alleviate high-temperature stress despite rapidly changing climate environments, specifically abnormal high-temperature phenomena, while ensuring manufacturing stability and preventing cost increases, and which has mechanical strength equivalent to or improved compared to conventional agricultural films even when made into a thin film. means of solving the problem

[0009] To solve the above-mentioned problem, the present invention provides an agricultural multilayer film having a total thickness of 18 to 25 μm, comprising: a first layer comprising 3 to 10 parts by weight of a black pigment comprising carbon black per 100 parts by weight of a first resin comprising polyethylene; and a second layer disposed on the first layer comprising 3 to 8 parts by weight of a white pigment comprising titanium dioxide per 100 parts by weight of a second resin comprising polyethylene.

[0010] According to one embodiment of the present invention, the carbon black and titanium dioxide may each have an average particle size of 1 to 10 μm independently.

[0011] According to another embodiment of the present invention, the first layer and the second layer may each independently further comprise 100 to 150 parts by weight of calcium carbonate surface-treated with a saturated fatty acid having 12 to 18 carbon atoms and 2 to 5 parts by weight of polyethylene graft maleic anhydride with respect to 100 parts by weight of the first resin or the second resin.

[0012] According to another embodiment of the present invention, the titanium dioxide may further comprise an alkylsulfinate having 12 to 16 carbon atoms treated on the surface at a weight of 0.5 to 1.2 parts by weight based on the weight of the titanium dioxide.

[0014] In addition, the present invention relates to a method for manufacturing an agricultural multilayer film having a total thickness of 18 to 25 μm, wherein

[0015] The present invention provides a method for manufacturing an agricultural multilayer film comprising: a first step of melting a first layer forming composition comprising 3 to 10 parts by weight of a black pigment comprising carbon black per 100 parts by weight of a first resin comprising polyethylene, and a second layer forming composition comprising 3 to 8 parts by weight of a white pigment comprising titanium dioxide per 100 parts by weight of a second resin comprising polyethylene; and a second step of co-extruding the melted first layer forming composition and the second layer forming composition through an annular die, and manufacturing a multilayer film by injecting compressed air into the extruded tube-shaped film to expand and cool, and then compressing.

[0016] According to one embodiment of the present invention, the temperature during extrusion in the second step is 175 to 185°C, the expansion ratio (BUR) is 2.7 to 3.0, and the height of the freezing line can be formed at 35 to 45 cm from the annular die.

[0017] Additionally, the cooling may be a two-stage cooling system configured such that the cooling rate of the second cooling section is greater than the cooling rate of the first cooling section. It may include: a first cooling section from an annular die to a freezing line, where the outer surface of a tube-shaped film is isolated from the outside air and cooled by compressed air injected into the interior; and a second cooling section from the freezing line to a point where compression is performed, where the outer surface of the tube-shaped film is exposed to the outside air and cooled together with compressed air injected into the interior. Effects of the invention

[0018] According to the present invention, the agricultural multilayer film exhibits excellent thermal insulation and heat shielding effects despite abnormal high temperatures, thereby minimizing the increase in the surface temperature of the multilayer film and reducing crop damage caused by high heat. Furthermore, since the implemented multilayer film is made into a thin film, it ensures manufacturing stability while maintaining low costs, and its mechanical strength is equivalent to or improved compared to conventional agricultural films. Consequently, it can maintain suitable growing conditions for crops or effectively alleviate high-temperature stress on crops despite abnormal high temperatures, allowing for its widespread application in agriculture. Brief explanation of the drawing

[0019] FIG. 1 is a schematic cross-sectional view of an agricultural multilayer film according to one embodiment of the present invention. FIG. 2 is a graph of wavelength-dependent transmittance for an agricultural film according to one embodiment and a comparative example of the present invention. Figure 3 is a photograph of an agricultural film installed on soil according to one embodiment and a comparative example of the present invention. Figures 4 and 5 are photographs taken of the temperature of the film surface from 12:00 to 1:00 on a cloudless sunny day with an external temperature of 31℃, with respect to Figure 3. Specific details for implementing the invention

[0020] Hereinafter, embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention.

[0022] Referring to FIG. 1, an agricultural multilayer film (100) according to one embodiment of the present invention comprises a first layer (10) containing a black pigment and a second layer (20) disposed on the first layer (10) containing a white pigment.

[0024] The above agricultural multilayer film (100) has a first layer (10) containing a black pigment that becomes the inner surface in contact with the soil where crops are grown, and a second layer (20) containing a white pigment that becomes the outer surface in contact with the outside. The first layer (10) and the second layer (20) have greatly improved dispersion of the black pigment, white pigment, and optionally additionally included calcium carbonate filler material provided inside the agricultural multilayer film (100) compared to a conventional black agricultural film, so the scattering of incident light is greatly increased, and furthermore, light transmission in the visible light wavelength range and the near-infrared region wavelength range (800 nm ~ 1200 nm) is greatly reduced (see FIG. 2), so that the transmitted light in the corresponding wavelength range for light incident on the surface of the second layer (20) can be realized at 5% or less, more preferably 3% or less, and more preferably 2% or less. In addition, by absorbing some of the light in the wavelength range that can cause a rise in soil temperature and scattering the rest, it may be advantageous to ultimately suppress the increase in the surface temperature of the outer surface of the agricultural multilayer film, i.e., the second layer (20), to the maximum extent.

[0026] Meanwhile, referring to Fig. 2, in the case of Example 1, light transmission hardly occurs in the visible light wavelength range and the near-infrared wavelength range (800 nm to 1200 nm). In addition, along with these optical characteristics, the fact that it has highly enhanced scattering characteristics due to the high dispersibility of various particles provided inside the multilayer film can be indirectly observed through the level at which the surface temperature of the multilayer film increases after exposure to solar radiation for a certain period of time.

[0027] Specifically, referring to FIGS. 4 and FIGS. 5, when an agricultural multilayer film according to one embodiment of the present invention is installed on the soil (see FIG. 4), the external temperature was 31°C and the temperature measured from 12:00 to 1:00, when the amount of sunlight is greatest on a cloudless day, was 38.6 to 46.1°C. However, when a conventional black film is installed on the soil (see FIG. 5), the temperature measured from 12:00 to 1:00 on the same day as the case in FIG. 4 was 62.5 to 69°C. Through this, it can be anticipated that the agricultural multilayer film according to one embodiment of the present invention may be more advantageous in an environment where abnormally high temperatures persist.

[0029] To describe each layer in the above agricultural multilayer film (100) in detail, the first layer (10) contains 3 to 10 parts by weight of a black pigment containing carbon black with respect to 100 parts by weight of a first resin containing polyethylene, and the second layer (20) contains 3 to 8 parts by weight of a white pigment containing titanium dioxide with respect to 100 parts by weight of a second resin containing polyethylene.

[0031] The first resin and the second resin comprising polyethylene of the first layer (10) and the second layer (20) above contain polyethylene as the main component as a polymer component for forming a film, and the polyethylene may include, for example, one or more types of low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE). In addition, the first resin and the second resin may each independently include other film-forming resins in addition to polyethylene, and the other resins may be polyolefin-based resins such as high-density polyethylene and polypropylene, for example. Furthermore, the meaning of including polyethylene as the main component in the first resin and the second resin is, for example, more than 50% by weight, and for other examples, more than 60% by weight, more than 70% by weight, more than 80% by weight, more than 90% by weight, or more than 95% by weight. Alternatively, the first resin and the second resin may be made of polyethylene.

[0033] In addition, the first layer (10) includes a black pigment containing carbon black.

[0034] The carbon black above may preferably have an average particle size of 1 to 10 μm, more preferably an average particle size of 1 to 5 μm. If the average particle size of the carbon black is 1 μm or less, there is a risk that the dispersibility within the first resin will be reduced, and if it exceeds 10 μm, it is difficult to make the thickness of the first layer thin, the surface quality will be degraded such as some carbon black particles protruding from the surface, there is a risk that the carbon black will frequently detach, and there is a risk that coarse particles may be included, which will significantly reduce the film-forming ability.

[0036] In addition, the carbon black may preferably have a particle size dispersion coefficient corresponding to the percentage of the standard deviation of the particle size relative to the average particle size of 30% or less, more preferably 20% or less, and thereby increase the dispersibility of the carbon black particles and make it advantageous to manufacture a multilayer film with uniform thickness.

[0038] In addition, the black pigment may comprise carbon black as a main component, for example, 80% by weight or more, or for other examples, 90% by weight or more, 95% by weight or more, 99% by weight or more, or 100% by weight. In addition, the black pigment may further comprise known black pigments in addition to carbon black, and although the present invention does not particularly limit the types thereof, a material with high hydrophobicity may be more advantageous for achieving the purpose of the present invention.

[0040] In addition, the black pigment containing the carbon black is included in an amount of 3 to 10 parts by weight, preferably 3 to 8 parts by weight, per 100 parts by weight of the second resin, which may be advantageous for achieving a uniform thickness while improving the blocking characteristics against external light that causes abnormal high temperatures.

[0042] In addition, the second layer (20) contains a white pigment containing titanium dioxide.

[0043] The titanium dioxide above may preferably have an average particle size of 1 to 10 μm, more preferably an average particle size of 1 to 5 μm. If the average particle size of the titanium dioxide is 1 μm or less, there is a risk that the dispersibility within the second resin will be reduced, and if it exceeds 10 μm, it is difficult to make the thickness of the second layer thin, and the surface quality may be degraded such as some titanium dioxide particles protruding from the surface, and there is a risk that the detachment of titanium dioxide may occur frequently, and there is a risk that the film-forming ability may be significantly reduced as coarse particles may be included.

[0045] In addition, the titanium dioxide may preferably have a particle size dispersion coefficient corresponding to the percentage of the standard deviation of the particle size relative to the average particle size of 40% or less, more preferably 15% or more, and even more preferably 35% or more, which is advantageous for achieving the objectives of the present invention, such as improving light reflection characteristics in near-infrared light while increasing the dispersibility of titanium dioxide particles.

[0047] In addition, the white pigment may contain titanium dioxide as the main component, for example, 80% by weight or more, or for other examples, 90% by weight or more, 95% by weight or more, 99% by weight or more, or 100% by weight. In addition, the white pigment may further include known white pigments in addition to titanium dioxide, and although the present invention does not particularly limit the types thereof, non-limiting examples thereof may include zinc oxide, zinc sulfide, barium sulfate, etc.

[0049] In addition, the white pigment containing titanium dioxide is included in an amount of 3 to 8 parts by weight, preferably 3 to 5 parts by weight, per 100 parts by weight of the second resin, which may be advantageous for achieving a uniform thickness while improving the blocking characteristics against external light that causes abnormal high temperatures.

[0051] In addition, according to one embodiment of the present invention, the titanium dioxide may have a surface modified to increase dispersibility within the second layer (20) and compatibility with the polyethylene resin, and to prevent damage caused by active oxygen resulting from the reaction between the titanium dioxide and moisture permeating under high temperature and high humidity conditions and ultraviolet rays. Specifically, the surface may be modified with an alkyl sulfinate having 12 to 16 carbon atoms. This is advantageous for realizing a uniform and thin film second layer and can guarantee the surface quality of the second layer. If titanium dioxide is introduced as is without surface modification, it becomes easy for titanium dioxide particles to form secondary and tertiary particles within the polyethylene resin, which may result in non-uniform thickness and a decrease in the dispersibility of titanium dioxide. Meanwhile, the alkyl sulfinate used as a surface modifier may be a sodium salt, for example, but is not limited thereto. In addition, the alkyl sulfinate may have 12 to 16 carbon atoms. If the carbon atoms are less than 12, the effect of improving dispersibility may be minimal, and there is a risk that some decomposition may occur at the extrusion temperature during the extrusion process described later, thereby forming voids between the particles and the polyethylene interface. Furthermore, if the alkyl sulfinate has more than 16 carbon atoms, the amount of alkyl sulfinate placed on the titanium dioxide particles may decrease, which may lead to a decrease in the dispersibility of the titanium dioxide and cause thickness non-uniformity.

[0052] Meanwhile, even when the sulfinate has 12 or more carbon atoms, if it includes a structure other than an alkyl group, such as a phenyl group, it is not sufficient to achieve the purpose of the present invention, and in particular, it is difficult to perform an antioxidant function to remove generated active oxygen, so it cannot prevent infringement of the second resin and may be undesirable in terms of durability.

[0054] In addition, according to one embodiment of the present invention, the first layer (10) and the second layer (20) may each independently further include calcium carbonate as a filler.

[0055] The calcium carbonate, which is the filler mentioned above, can perform the function of an extender and improve physical properties. For example, the calcium carbonate can improve characteristics such as dimensional stability and mechanical strength.

[0056] The above calcium carbonate may be included in an amount of 100 to 150 parts by weight per 100 parts by weight of the first resin or the second resin, for example, and this may be advantageous for achieving the objective of the present invention.

[0057] Meanwhile, the calcium carbonate may have a surface modified to improve dispersibility, compatibility, and processability within the first resin or second resin containing polyethylene.

[0058] For example, the calcium carbonate may be treated with a saturated fatty acid having 12 to 18 carbon atoms in an amount of 0.5 to 3 weight percent based on the weight of the calcium carbonate, and it may be difficult to achieve the objective of the present invention through this.

[0059] In addition, preferably, 2 to 5 parts by weight of polyethylene graft maleic anhydride may be further included to improve the dispersibility of calcium carbonate and the processability of each layer, and more preferably, the polyethylene graft maleic anhydride may include a first polyethylene graft maleic anhydride in which maleic anhydride is grafted onto polyethylene having a number average molecular weight of 2000 to 2200, and a second polyethylene graft maleic anhydride in which maleic anhydride is grafted onto polyethylene having a number average molecular weight of 5600 to 6000. In addition, as an example, the first polyethylene graft maleic anhydride and the second polyethylene graft maleic anhydride may be included in a weight ratio of 1:3 to 4, and this may be advantageous for manufacturing a multilayer film of more uniform thickness by improving the dispersibility and fluidity of calcium carbonate at an extrusion temperature higher than the usual temperature in the manufacturing process described later.

[0061] In addition, the first layer (10) and the second layer (20) may further include other additives typically included in agricultural films in addition to the components described above. As a non-limiting example, the other additives may further include light stabilizers, antioxidants, slip agents, UV blockers, heat stabilizers, etc., and a description of specific examples of each of these is omitted. The other additives may be included in an amount of 4% by weight or less based on the weight of each layer, but are not limited thereto.

[0063] In addition, the agricultural multilayer film (100) has a total thickness of 18 to 25 μm despite being implemented as a multilayer film, which allows for a significant reduction in cost and further improvement in ease of installation. At the same time, the tensile strength in the TD direction is 4000 MPa or more, the tensile strength in the MD direction is 3700 MPa or more, more preferably 3800 MPa or more, and the tear strength is 900 MPa or more in the MD direction and 1000 MPa or more in the TD direction, so that it can have mechanical strength and durability equivalent to that of a conventional agricultural film relative to the thinned thickness. In addition, as an example, in the agricultural multilayer film (100), the first layer (10) may have a thickness of 6 to 10 μm and the second layer (20) may have a thickness of 10 to 15 μm, and the thicknesses of the first layer (10) and the second layer (20) may be formed asymmetrically.

[0064] In addition, the multilayer film may have a thickness dispersion of 5% or less, more preferably 3% or less, and more preferably 2.5% or less, which is the percentage of the standard deviation of the thickness relative to the average thickness of a total of 10 points measured at intervals of 10 cm in the MD direction from the center line in the width direction (TD direction) of the film, thereby enabling the realization of a multilayer film with a very uniform and thin thickness.

[0066] An agricultural multilayer film (100) according to one embodiment of the present invention described above can be manufactured by including a first step of melting a first layer forming composition containing 3 to 10 parts by weight of a black pigment containing carbon black for 100 parts by weight of a first resin containing polyethylene, and a second layer forming composition containing 3 to 8 parts by weight of a white pigment containing titanium dioxide for 100 parts by weight of a second resin containing polyethylene, respectively, and a second step of co-extruding the melted first layer forming composition and second layer forming composition through a ring die, and manufacturing a multilayer film by injecting compressed air into the discharged tube-shaped film to expand and cool, and then compressing.

[0068] First, step 1 includes melting each of a first layer forming composition comprising a first resin comprising polyethylene and a black pigment comprising carbon black, and a second layer forming composition comprising a second resin comprising polyethylene and a white pigment comprising titanium dioxide.

[0069] The melting temperature of each of the first layer forming composition and the second layer forming composition may be subjected to heat greater than the melting point, taking into account the melting point of the first resin included, for example, heat greater than 120°C may be applied.

[0070] In addition, each of the first layer forming composition and the second layer forming composition can be introduced into a mixer and sufficiently mixed and stirred before melting, thereby further increasing the dispersibility of each component and making it advantageous to manufacture a layer having a uniform thin film thickness.

[0071] In addition, each of the first layer forming composition and the second layer forming composition can be melted in an extruder that manufactures conventional agricultural films, and, for example, said extruder may be a blow film extruder.

[0073] Subsequently, as a second step of the present invention, the method may include a step of co-extruding the molten first layer forming composition and the second layer forming composition through a ring die, and injecting compressed air into the discharged tube-shaped film to expand and cool it, and then compressing it to produce a multilayer film.

[0074] Each of the molten first layer forming composition and the second layer forming composition may be extruded through the die gap in the annular die without mixing with each other and forming layers. At this time, the temperature of each of the molten first layer forming composition and the second layer forming composition in the extruder before extrusion may be 175 to 185°C, which may be advantageous for further improving the dispersibility of the components included in each of the first layer forming composition and the second layer forming composition, specifically components such as black pigment, white pigment, and calcium carbonate. If the temperature before extrusion is less than 175°C, there is a risk that the variation in the thickness of each layer being implemented will increase, and if it exceeds 185°C, thermal damage to the first resin or the second resin may occur, or partial thermal decomposition of the modified component provided on the surface of titanium dioxide and / or calcium carbonate may be induced, resulting in reduced dispersibility and a risk that the variation in thickness will increase.

[0076] In addition, compressed air is injected into the extruder discharged through the annular die, thereby allowing the extruder to be cooled while forming a tubular film shape. At this time, the compressed air is supplied such that the tube expansion ratio is 2.7 to 3.0 and the height of the freezing line is formed at 35 to 45 cm from the annular die, thereby expanding and cooling the tube. This is advantageous for realizing a multilayer film with a more uniform thickness of thin film layers. Here, the expansion ratio (BUR) refers to the diameter of the tube (or bubble) divided by the diameter of the die. Furthermore, the freezing line (frost line) refers to the freezing line typically defined in the blow film process; specifically, it refers to the starting point within the tube where the molten resin is cooled and crystallization begins, connected to the neck portion discharged from the annular die. If any one of the aforementioned extrusion temperature, tube expansion ratio, or freezing line height is unsatisfactory, it may not be easy to manufacture a multilayer film composed of thin film layers of uniform thickness.

[0078] In addition, according to one embodiment of the present invention, the cooling may be performed in a two-stage cooling method in which the section from the annular die to the point where compression is performed is divided and cooling is performed at different cooling rates.

[0079] Specifically, the cooling comprises a first cooling section from an annular die to a freezing line, where the outer surface of the tube-shaped film is isolated from the outside air and cooled by compressed air injected into the interior, and a second cooling section from the freezing line to a point where compression is performed, where the outer surface of the tube-shaped film is exposed to the outside air and cooled together with compressed air injected into the interior. The cooling rate of the second cooling section may be configured to be greater than the cooling rate of the first cooling section, thereby enabling the realization of a multilayer film having a very thin and uniform thickness in which various particles provided within the first and second layers are very uniformly dispersed. Here, the outside air is the air atmosphere within the workplace, and may be, for example, room temperature of 20 to 25°C.

[0081] In addition, the tube-shaped film can subsequently be compressed by a nip roll or the like to form a multilayer, and can be drawn out and wound.

[0083] The present invention will be explained more specifically through the following examples, but the following examples are not intended to limit the scope of the invention and should be interpreted as being for the purpose of aiding understanding of the invention.

[0085] <Example 1>

[0086] For the first layer forming composition, 7 parts by weight of carbon black powder having an average particle size of 4.8 μm and a particle size dispersion coefficient of 18.7% was mixed with 100 parts by weight of linear low-density polyethylene resin (MI 1.0 g / 10 min), 120 parts by weight of surface-modified calcium carbonate prepared in Preparation Example 1 below, and 3 parts by weight of polyethylene graft maleic anhydride A prepared in Preparation Example 2 below.

[0087] In addition, for the second layer forming composition, 4.6 parts by weight of rutile titanium dioxide powder having an average particle size of 4.5 μm and a particle size dispersion coefficient of 32.4% was mixed with 100 parts by weight of linear low-density polyethylene resin (MI 1.0 g / 10 min), 120 parts by weight of modified calcium carbonate having tetradecanoic acid on its surface at 1% by weight based on the total weight of the modified calcium carbonate, and 3 parts by weight of polyethylene graft maleic anhydride A prepared in Preparation Example 1 below.

[0088] Subsequently, the first layer forming composition and the second layer forming composition were each introduced into a mixer and thoroughly stirred, then introduced into a blow film extruder. After melting, the extruded materials were extruded through an annular die at a temperature of 178°C. Compressed air was introduced into the center of the extruded material, with a strength and cooling rate such that the tube-shaped film expansion ratio (BUR) was 2.8 and the height of the freezing line was formed at 40.5 cm from the annular die. Additionally, the area from the annular die to the freezing line (frost line) was designated as the first cooling section, and the equipment was set so that the exterior of the discharged tube-shaped film was isolated from the outside air of the workplace, allowing cooling to be achieved by the compressed air injected into the interior of the tube-shaped film. The area from the freezing line to the lip roll where compression occurs was designated as the second cooling section, and the equipment was set so that the exterior of the discharged tube-shaped film was exposed to the outside air (23°C) of the workplace, allowing cooling to be performed in two stages, with the interior and exterior cooling occurring together with the compressed air injected into the interior of the tube-shaped film. In addition, a cooled tube-shaped film was compressed with a lip roll and then wound to produce an agricultural multilayer film with a final thickness of 7㎛ for the first layer, 13㎛ for the second layer, and a total average thickness of 20㎛.

[0090] Preparation Example 1

[0091] 100g of polyethylene with a number average molecular weight of approximately 5800 and 3g of maleic anhydride were mixed and added to an o-dichlorobenzene solvent, and heated at 140°C to swell. Subsequently, tert-butyl peroxybenzoate was added as an initiator, and the reaction was carried out for 3 hours at 130°C under argon gas with stirring. The synthesized reaction product was washed with boiling acetone until the maleic anhydride derivative was removed, and then washed three times with distilled water. The washed mixture was then filtered to obtain dried polyethylene grafted maleic anhydride A, and the grafted maleic anhydride content in the polyethylene grafted maleic anhydride A was 1.05 wt%.

[0093] <Comparative Example 1>

[0094] We prepared a commercially available black agricultural polyethylene film from Company A, which has a thickness of 40㎛ and contains carbon black as a black pigment.

[0096] <Comparative Example 2>

[0097] We prepared the applicant's commercially available black agricultural polyethylene film with a thickness of 30㎛ containing carbon black as a black pigment.

[0099] <Comparative Example 3>

[0100] We prepared the applicant's commercially available black agricultural biodegradable film, which contains carbon black as a black pigment and has a thickness of 20㎛.

[0102] <Comparative Example 4>

[0103] We prepared the applicant's commercially available white agricultural film, which is 20㎛ thick and contains titanium dioxide as a white pigment.

[0105] <Experimental Example 1>

[0106] Tensile strength, tear strength, and elongation were measured for the agricultural films of Example 1 and Comparative Examples 1 to 4 using a universal testing machine in accordance with KS M 3001, and the results are shown in Table 1 below.

[0108] Thickness (㎛) tensile strength Growth rate Tear strength TD MD TD MD TD MD Comparative Example 1 40 4150 3900 790 580 840 750 Bagyoye 2 30 3800 3500 760 550 950 900 Comparative Example 3 20 3795 3650 770 450 890 800 Comparative Example 4 20 3750 3600 740 530 940 870 Example 1 20 4100 3820 800 594 1020 950

[0109] As can be seen from Table 1,

[0110] In the case of Example 1, it can be seen that even though the thickness is implemented thinner compared to Comparative Examples 1 and 2, it is superior in terms of tensile strength, tear strength, and elongation.

[0112] <Experimental Example 2>

[0113] The light transmittance by wavelength was measured for the multilayer film according to Example 1 and the black film according to Comparative Example 2 using a UV-Vis device, and the results are shown in Fig. 2.

[0114] In addition, as shown in Fig. 3, the temperature was measured from 12:00 to 1:00 on a sunny, cloudless day with an external temperature of 31°C after installation on the soil, and the results are shown in Fig. 4 (Example 1) and Fig. 5 (Comparative Example 2).

[0116] As can be seen from Figure 2, Example 1 shows a significant decrease in light transmittance from visible light to near-infrared light compared to Comparative Example 2.

[0117] As can be seen from FIGS. 4 and 5, the measured film surface temperature of Example 1 was 38.6 to 46.1°C, whereas the measured film surface temperature of Comparative Example 2 was 62.5 to 69°C. This indicates that Example 1 has significantly larger light scattering characteristics compared to Comparative Example 2, and thus it can be anticipated that Example 1 may be more advantageous in an environment where abnormally high temperatures persist.

[0119] <Examples 2 ~ 7>

[0120] An agricultural multilayer film was manufactured by carrying out the same procedure as in Example 1, but using a titanium dioxide surface included in the second layer modified with the modification component of Table 1 below. At this time, the modification of the titanium dioxide was prepared by dissolving the modification component in acetone, mixing it with titanium dioxide powder, and drying it. The content of the modification component was determined by measuring the weight before and after modification, and the modification was performed so that it was 1% by weight based on the total modified weight.

[0122] <Example 8>

[0123] An agricultural multilayer film was manufactured by carrying out the same procedure as in Example 2, but without modifying titanium dioxide as a modifying component, and by mixing it in equal weight with the second layer forming composition.

[0125] <Experimental Example 3>

[0126] The following physical properties were evaluated for the multilayer films according to Examples 1 to 8, and the results are shown in Table 2.

[0128] 1. Thickness uniformity evaluation

[0129] During the manufacturing process of a multilayer film, the thickness of the film being transported on the production line was measured using a capacitive method at 10 cm intervals in the MD direction for a 10 m long multilayer film, and the average thickness and standard deviation of the thickness were calculated. Additionally, the thickness dispersion coefficient, which is the percentage of the standard deviation of the thickness relative to the average thickness, was calculated. A smaller thickness dispersion coefficient indicates higher thickness uniformity.

[0131] 2. Durability Evaluation

[0132] In order to evaluate whether the multilayer film was damaged by ultraviolet rays in a high temperature and high humidity environment, specimens according to each example were placed in a constant temperature and humidity chamber at 55°C and 90 RH% for 10 days, then an ultraviolet lamp was installed in the chamber and the specimens were placed again for 5 days, after which the tensile strength was measured using the method according to Experimental Example 1, and the MD direction tensile strength of Example 2 was set as 100 as the standard, and the MD direction tensile strengths of the remaining examples were converted into relative percentages.

[0134] Titanium dioxide in the second layer multilayer film Whether surface modified Modification component Thickness dispersion coefficient (%) Tensile strength (%) after exposure to high temperature and humidity / UV Example 1 Unmodified - 12.3 60.5 Example 2 Modification C12 alkylsulfinic acid 2.5 100 Example 3 Modification C16 alkylsulfinic acid 2 103.8 Example 4 Modification C10 alkylsulfinic acid 5.2 82.5 Example 5 Modification C18 alkylsulfinic acid 3.2 89.7 Example 6 Modification C12 alkylbenzene sulfinic acid 2.1 73.4 Example 7 Modification C14 saturated fatty acids 9.4 61.2 Example 8 Unmodified C12 alkylsulfinic acid (simple mixture within two layers) 12.2 60.0

[0135] As can be seen from Table 2,

[0136] Compared to Example 1, which contains unmodified titanium dioxide, Examples 2 to 6, which contain modified titanium dioxide, show improved dispersibility of titanium dioxide and reduced thickness variation. However, in the case of Example 7, it can be seen that the thickness uniformity is lower compared to Examples 2 to 6.

[0138] Meanwhile, in Examples 2 to 6, it can be seen that Examples 2 to 3 exhibited superior tensile strength and less polyethylene damage under high temperature, high humidity, and UV exposure environments compared to the remaining examples. Through this, it can be seen that Examples 2 to 3 demonstrated a significant antioxidant effect against active oxygen resulting from the reaction between titanium dioxide and absorbed moisture through modification.

[0140] In addition, in the case of Example 8, the modified component from Example 2 is simply mixed in the second layer, and it can be seen that it is difficult to improve the dispersibility of titanium dioxide or improve durability with simple mixing.

[0142] Although an embodiment of the present invention has been described above, the concept of the present invention is not limited to the embodiments presented in this specification. Those skilled in the art who understand the concept of the present invention may easily propose other embodiments within the scope of the same concept by adding, changing, deleting, or adding components, and such embodiments shall also be considered to fall within the scope of the concept of the present invention. Explanation of the symbols

[0143] 100: Agricultural multilayer film 10: 1st floor 20: 2nd floor

Claims

Claim 1 An agricultural multilayer film comprising: a first layer comprising 3 to 10 parts by weight of a black pigment comprising carbon black per 100 parts by weight of a first resin comprising polyethylene; and a second layer disposed on the first layer comprising 3 to 8 parts by weight of a white pigment comprising titanium dioxide per 100 parts by weight of a second resin comprising polyethylene; wherein the total thickness is 18 to 25 μm, and the titanium dioxide further comprises an alkyl sulfinate having 12 to 16 carbon atoms treated on the surface at 0.5 to 1.2 parts by weight based on the weight of the titanium dioxide. Claim 2 In claim 1, the carbon black and titanium dioxide are agricultural multilayer films having an average particle size of 1 to 10 μm, respectively, independently. Claim 3 An agricultural multilayer film according to claim 1, wherein the first layer and the second layer each independently further comprise 100 to 150 parts by weight of calcium carbonate surface-treated with a saturated fatty acid having 12 to 18 carbon atoms and 2 to 5 parts by weight of polyethylene grafted maleic anhydride, with respect to 100 parts by weight of the first resin or the second resin. Claim 4 delete Claim 5 A method for manufacturing an agricultural multilayer film having a total thickness of 18 to 25 μm, comprising: a first step of melting a first layer forming composition comprising 3 to 10 parts by weight of a black pigment comprising carbon black per 100 parts by weight of a first resin comprising polyethylene, and a second layer forming composition comprising 3 to 8 parts by weight of a white pigment comprising titanium dioxide per 100 parts by weight of a second resin comprising polyethylene; and a second step of co-extruding the melted first layer forming composition and the second layer forming composition through a ring die, injecting compressed air into the extruded tube-shaped film to expand and cool it, and then compressing it to manufacture a multilayer film; wherein the titanium dioxide further comprises an alkyl sulfinate having 12 to 16 carbon atoms treated on the surface at a weight of 0.5 to 1.2 parts by weight based on the weight of the titanium dioxide. Claim 6 A method for manufacturing an agricultural multilayer film according to claim 5, wherein the temperature during extrusion in the above 2nd step is 175 to 185℃, the expansion ratio (BUR) is 2.7 to 3.0, and the height of the freezing line is formed at 35 to 45 cm from the annular die. Claim 7 A method for manufacturing a multilayer agricultural film according to claim 5, wherein the cooling comprises: a first cooling section from an annular die to a freezing line in which the outer surface of a tube-shaped film is isolated from the outside air and cooled by compressed air injected into the inside; and a second cooling section from the freezing line to a point where compression is performed in which the outer surface of the tube-shaped film is exposed to the outside air and cooled together with compressed air injected into the inside, wherein the cooling rate of the second cooling section is greater than the cooling rate of the first cooling section.

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