Multilayer polyethylene film for soil solarization

Abstract

This invention relates to a multilayer polyethylene film for soil sun drying, the multilayer polyethylene film comprising two linear low-density polyethylenes, a soil sun drying system comprising the multilayer polyethylene film, and the use of the multilayer polyethylene film in soil sun drying.

Description

Technical Field

[0001] This invention relates to a multilayer polyethylene film for soil sun drying, the multilayer polyethylene film comprising two types of linear low-density polyethylene, a soil sun drying system including the multilayer polyethylene film, and the use of the multilayer polyethylene film in soil sun drying. Background Technology

[0002] Soil sun drying is an environmentally friendly, non-chemical method for eliminating pests, weeds, and diseases, and it has been used in various agricultural production systems. It involves covering a weed-free surface with a transparent, airtight material (usually a polyethylene (PE) film) so that solar energy can heat the soil and its rhizosphere. Under the PE film, temperatures at the top 0 to 10 cm of the ground can reach 42 to 60°C, depending on local climatic conditions.

[0003] The primary purpose of using this heat for soil sun-drying is to eradicate weeds and pests.

[0004] This treatment improves the chemical properties of the soil profile, leading to increased fertility. Furthermore, the soil is protected from erosion because the film prevents degradation by water and wind.

[0005] Although soil sun drying is a highly beneficial method and has been widely used worldwide, the requirements for available films are quite demanding, resulting in films with high thickness and narrow width being used only once.

[0006] It has now been surprisingly discovered that multilayer polyethylene films, comprising two types of linear low-density polyethylene (LLDPE), exhibit excellent properties for use in soil sun exposure. Summary of the Invention

[0007] This invention relates to a multilayer polyethylene film for soil sun drying, the multilayer polyethylene film comprising an inner layer (IL), an outer layer (OL), and a core layer (CL) located between the inner layer and the outer layer, characterized in that...

[0008] -Based on the total weight of the core layer, the core layer comprises at least 80% by weight, preferably 85 to 99% by weight, of a first linear low-density polyethylene (LLDPE) LLDPE-A and a second linear low-density polyethylene (LLDPE) LLDPE-B, wherein the first LLDPE-A has an MFR2 (190°, 2.16 kg) of 0.1 to 0.5 g / 10 min, preferably 0.1 to 0.3 g / 10 min, as determined according to ISO 1133, and the second LLDPE-B has an MFR2 (190°, 2.16 kg) of 0.9 to 2.2 g / 10 min, preferably 1.1 to 1.9 g / 10 min, as determined according to ISO 1133; and

[0009] - The inner layer (IL) comprises the second linear low-density polyethylene (LLDPE)-B, wherein the amount of the second LLDPE-B is at least 60% by weight, preferably 65 to 95% by weight, based on the total weight of the inner layer; and

[0010] - The outer layer (OL) comprises the second linear low-density polyethylene LLDPE-B, wherein the amount of the second linear low-density polyethylene LLDPE-B is at least 60% by weight, preferably 65 to 95% by weight, based on the total weight of the outer layer.

[0011] In another aspect, the present invention relates to a soil sun-drying system, the soil sun-drying system comprising:

[0012] i) Soil without crops;

[0013] ii) A multi-layered polyethylene film, as described above or below, placed on top of the soil; and

[0014] iii) A drip irrigation system located between the film and the soil.

[0015] In another respect, the present invention relates to the use of multilayer polyethylene films, as described above or below, for soil sun exposure.

[0016] definition

[0017] For the purposes of this invention, the term "composes of" is considered a preferred embodiment of the term "comprising". If a group is defined below as containing at least a certain number of elements, this should also be understood as disclosing a group preferably consisting only of those elements.

[0018] Unless otherwise specified, when referring to a singular noun, the plural form of the noun is included by using the indefinite or definite articles “a,” “a,” or “the.”

[0019] The polyethylene disclosed herein is an ethylene-based polymer containing at least 50% by weight of ethylene monomer. Detailed Implementation

[0020] The multilayer polyethylene film of the present invention for use in soil sun drying comprises an inner layer (IL), an outer layer (OL), and a core layer (CL).

[0021] Core Layer (CL)

[0022] The multilayer polyethylene film of the present invention includes a core layer (CL).

[0023] The core layer (CL) comprises a first linear low-density polyethylene (LLDPE)-A, the first LLDPE-A having an MFR2 (190°, 2.16 kg) of 0.1 to 0.5 g / 10 min as determined according to ISO 1133. Preferably, the LLDPE-A has an MFR2 (190°, 2.16 kg) of 0.1 to 0.3 g / 10 min as determined according to ISO 1133.

[0024] The core layer (CL) further comprises a second linear low-density polyethylene (LLDPE-B) having an MFR2 (190°, 2.16 kg) of 0.9 to 2.2 g / 10 min as determined according to ISO 1133. Preferably, the MFR2 (190°, 2.16 kg) of the LLDPE-B is 1.1 to 1.9 g / 10 min as determined according to ISO 1133.

[0025] LLDPE-A and LLDPE-B are the main components of the core layer. Therefore, the core layer contains at least 80% by weight, preferably 85 to 99% by weight, of LLDPE-A and LLDPE-B by weight, based on the total weight of the core layer.

[0026] In the core layer (CL), the weight ratio between LLDPE-A and LLDPE-B is preferably 15:1 to 5:1, more preferably 12:1 to 7:1.

[0027] In a particularly preferred embodiment, the total weight of LLDPE-A and LLDPE-B in the core layer is at least 92% by weight, more preferably 95.0 to 99.9% by weight.

[0028] LLDPE-A

[0029] When the density of linear polyethylene is 910 to 940 kg / m³ 3 At that time, it was characterized as linear low-density polyethylene (LLDPE).

[0030] Preferably, the density of LLDPE-A in the core layer of the multilayer film of the present invention, as determined according to ISO 1183, is 915 to 930 kg / m³. 3 More preferably 918 to 925 kg / m 3 .

[0031] Unlike low-density polyethylene (LDPE), which is a homopolymer of polyethylene, linear low-density polyethylene (LLDPE) is a copolymer of ethylene and at least one other comonomer.

[0032] Preferably, LLDPE-A is a copolymer of ethylene and a comonomer selected from α-olefins having 4 to 6 carbon atoms. More preferably, LLDPE-A is a copolymer of ethylene and 1-butene or 1-hexene, and most preferably a copolymer of ethylene and 1-butene.

[0033] Preferably, the total amount of comonomers present in LLDPE-A is 2.0 to 7.0 mol%, more preferably 2.5 to 6.5 mol%, and most preferably 3.0 to 6.0 mol%, based on the total amount of monomers in LLDPE-A.

[0034] A higher molecular weight distribution (MWD) value indicates higher polydispersity of the polymer.

[0035] In this invention, preferably, the MWD of LLDPE-A is 10 to 30, more preferably 15 to 21.

[0036] Such a high MWD can be achieved, for example, when the corresponding polymer contains at least two polymer fractions with different molecular weights.

[0037] Therefore, in a preferred embodiment, based on the total amount of LLDPE-A, LLDPE-A contains two polyethylene fractions, A and B, in a total amount of at least 95% by weight, preferably 96 to 100% by weight.

[0038] In this embodiment, the MFR2 (190°, 2.16 kg) of polyethylene fraction A, as determined according to ISO 1133, is 100 to 500 g / 10 min, preferably 200 to 400 g / 10 min.

[0039] Given that LLDPE-A has a relatively low MFR2 value (0.1 to 0.5 g / 10 min), in this embodiment, polyethylene fraction B must have a substantially lower MFR2 than polyethylene fraction A, so that LLDPE-A is bimodal in molecular weight.

[0040] Furthermore, in this embodiment, the weight ratio between polyethylene fraction A and polyethylene fraction B is preferably 30:70 to 50:50.

[0041] This type of bimodal LLDPE and its production are described, for example, in WO 2004 / 000933 A1, pages 9 to 12.

[0042] As LLDPE-A, Borstar FB1200 resin manufactured by Borouge can be used.

[0043] Preferably, LLDPE-A is present in the core layer of the multilayer polyethylene film in an amount of 85 to 95% by weight, more preferably 86 to 91% by weight, based on the total weight of the core layer.

[0044] LLDPE-B

[0045] The core layer of the multilayer polyethylene film of the present invention further comprises LLDPE-B.

[0046] Preferably, LLDPE-B has a density of 912 to 925 kg / m³ as determined by ISO 1183. 3 More preferably, it is 915 to 921 kg / m³. 3 .

[0047] Preferably, LLDPE-B is a terpolymer of ethylene and two comonomers selected from α-olefins having 4 to 8 carbon atoms, more preferably a terpolymer of ethylene, 1-butene and 1-hexene.

[0048] Preferably, the MWD of LLDPE-B is 6 or less, typically greater than 1, and more preferably 3 to 5.

[0049] Preferably, the total amount of comonomers present in LLDPE-B is 0.5 to 10 mol%, more preferably 1 to 8 mol%, more preferably 1 to 5 mol%, even more preferably 1.5 to 5 mol%, and most preferably 2.5 to 4 mol%.

[0050] LLDPE-B can also be multi-peaked, preferably bi-peaked LLDPE.

[0051] Preferably, the MWD of LLDPE-B is 1 to 6, more preferably 3 to 5.

[0052] Suitable multimodal ethylene terpolymers are disclosed, for example, in WO2016 / 083208.

[0053] For definitions (e.g., the "multimodality" of the polymer) and production methods of these ethylene terpolymers, refer to WO2016 / 083208. Furthermore, all embodiments and preferred embodiments of these ethylene terpolymers described in WO2016 / 083208 (having 912 to 925 kg / m³) are also described. 3 The density and MFR2 of 0.9 to 2.2 g / 10 min are also preferred embodiments of LLDPE-B in this disclosure, whether or not explicitly described herein.

[0054] As an LLDPE-B, commercially available products with the performance required herein can be used, such as Borealis or Borouge's Anteo™, for example, Anteo™ FK1828.

[0055] Preferably, LLDPE-B is present in the core layer of the multilayer polyethylene film in an amount of 5 to 15% by weight, more preferably 7 to 13% by weight, based on the total weight of the core layer.

[0056] Inner and outer layers

[0057] In addition to the core layer (CL), the multilayer polyethylene film of the present invention also includes an inner layer and an outer layer.

[0058] The inner layer (IL) of a multilayer polyethylene film used for soil sun exposure is the soil-facing layer.

[0059] Therefore, the outer layer (OL) of the multilayer polyethylene film used for soil sun exposure is the sun-facing layer.

[0060] As mentioned above, the core layer (CL) is located between the inner and outer layers.

[0061] Although the multilayer polyethylene film for soil sun drying of the present invention may include other layers, such as bonding layers, the film is preferably composed of three layers as described above or below: an inner layer, an outer layer, and a core layer.

[0062] The inner layer (IL) contains at least 60% by weight, preferably 65 to 95% by weight, of the LLDPE-B described above, based on the total weight of the inner layer.

[0063] The outer layer (OL) also contains at least 60% by weight, preferably 65 to 95% by weight, of LLDPE-B as described above, based on the total weight of the outer layer.

[0064] All the embodiments and preferred features of LLDPE-B described above for the core layer are also preferred embodiments and features of LLDPE-B for the inner or outer layer.

[0065] Low-density polyethylene can improve the processability of LLDPE films.

[0066] In addition to LLDPE-B, the inner layer (IL) may also contain low-density polyethylene (LDPE).

[0067] In the inner layer, the weight ratio between LLDPE-B and LDPE is preferably 15:1 to 5:1, more preferably 10:1 to 6:1.

[0068] Preferably, the total weight of LLDPE-B and LDPE in the inner layer (IL) is at least 87% by weight, more preferably 89 to 99% by weight, based on the total weight of the inner layer.

[0069] The amount of LDPE in the inner layer (IL) is preferably 5 to 15% by weight, and more preferably 7 to 13% by weight, based on the total weight of the inner layer.

[0070] Similar to the inner layer of the multilayer polyethylene film of the present invention, the outer layer may also contain low-density polyethylene (LDPE).

[0071] In the outer layer, the weight ratio between LLDPE-B and LDPE is preferably 15:1 to 5:1, more preferably 10:1 to 6:1.

[0072] Preferably, the total amount of LLDPE-B and LDPE in the outer layer (OL) is at least 90% by weight, more preferably 92 to 99% by weight, based on the total weight of the outer layer.

[0073] Based on the total weight of the outer layer, the amount of LDPE in the outer layer (OL) is preferably 5 to 15% by weight, and more preferably 7 to 13% by weight.

[0074] LDPE

[0075] Preferably, the LDPE present in the outer and / or inner layers has an MFR2 (190°, 2.16 kg) of 0.2 to 1.0 g / 10 min as determined by ISO 1133, more preferably 0.3 to 0.7 g / 10 min.

[0076] Preferably, the density of LDPE, as determined according to ISO 1183, is 917 to 930 kg / m³. 3 More preferably, it is 920 to 926 kg / m 3 .

[0077] additive

[0078] In addition to polyethylene, as mentioned above, multilayer polyethylene films may also contain additives (Ad).

[0079] The additive (Ad) is selected from the following: antioxidants, stabilizers, nucleating agents, antistatic agents, polymer processing aids, UV stabilizers, antiblocking agents, antidrip agents, and mixtures thereof, preferably selected from antioxidants, stabilizers, slip agents, antiblocking agents, antioxidants, polymer processing aids, UV stabilizers, and antidrip agents.

[0080] Such additives are generally commercially available and are described, for example, in Hans Zweifel's "Plastic Additives Handbook" 5th edition (2001), pages 871-873.

[0081] Since the multilayer polyethylene film of the present invention was developed for soil sun exposure, it is beneficial to stabilize the film to resist ultraviolet light from the sun.

[0082] Therefore, preferably, at least one of the inner layer, outer layer and core layer, and more preferably all layers, contains an ultraviolet stabilizer.

[0083] The amount of ultraviolet stabilizer in the at least one layer is preferably 0.5 to 5.0% by weight, more preferably 1.0 to 3.0% by weight, based on the total weight of the layers containing the ultraviolet stabilizer.

[0084] In a preferred embodiment of the multilayer polyethylene film of the present invention, the inner layer (IL) further comprises an anti-drip agent as an additive, preferably in an amount of 2 to 10% by weight, more preferably 4 to 8% by weight, based on the total weight of the inner layer.

[0085] Preferably, the multilayer polyethylene film contains additives other than UV stabilizers and anti-drip agents, with a total amount of less than 7% by weight in each layer.

[0086] Since the multilayer polyethylene film of the present invention is developed for soil sun exposure, it is beneficial to allow as much sunlight as possible to reach the soil and heat it.

[0087] Colorants significantly reduce the amount of sunlight reaching the soil.

[0088] Therefore, preferably, the multilayer polyethylene film of the present invention does not contain colorants as additives.

[0089] Colorants are known to those skilled in the art and are described, for example, in Hans Zweifel’s Handbook of Plastic Additives, 5th Edition (2001), pp. 840-869.

[0090] Multilayer thin films

[0091] The multilayer polyethylene film of the present invention comprises (preferably composed of) an inner layer, an outer layer, and a core layer as described above.

[0092] Preferably, the thickness ratio (OL:CL:IL) between the three layers is 0.8-1.2:1.8-2.2:0.8-1.2, and more preferably 1:2:1.

[0093] Ideally, as much sunlight as possible should reach the soil. Therefore, it is beneficial if the multilayer polyethylene film has a high total light transmittance.

[0094] Preferably, the total light transmittance of the multilayer polyethylene film of the present invention, as measured by ASTM D1003, is greater than 85%, more preferably 88 to 99%.

[0095] Ideally, sunlight should reach the soil as directly as possible. Therefore, it is beneficial if the multilayer polyethylene film has low haze.

[0096] Preferably, the haze of the multilayer polyethylene film of the present invention, as measured according to ASTM D1003, is less than 15%, more preferably 1 to 14%.

[0097] Preferably, the multilayer polyethylene film for soil sun drying of the present invention has one or more of the following mechanical properties, more preferably all of them.

[0098] Preferably, the multilayer polyethylene film has a dart impact strength (DDI) of 5 to 20 g / µm as determined by ASTM D 1709 / A, more preferably 8 to 15 g / µm.

[0099] Preferably, the longitudinal (MD) tear strength (elmendorf) of the multilayer polyethylene film, as determined according to ASTM D1922, is 2 to 15 gf / µm, more preferably 4 to 12 gf / µm.

[0100] The transverse (TD) tear strength (elmendorf) of the multilayer polyethylene film, as determined by ASTM D1922, is 5 to 25 gf / µm, more preferably 10 to 20 gf / µm.

[0101] Preferably, the multilayer polyethylene film has a longitudinal (MD) tensile modulus (1% secant) of 100 to 300 MPa, more preferably 150 to 250 MPa, and / or a transverse (TD) tensile modulus (1% secant) of 110 to 310 MPa, more preferably 160 to 260 MPa, as determined by ASTM D882.

[0102] Preferably, the multilayer polyethylene film has a longitudinal (MD) tensile stress at break of 30 to 60 MPa and / or a transverse (TD) tensile stress at break of 10 to 40 MPa, as determined according to ISO 527-3.

[0103] Preferably, the multilayer polyethylene film has a longitudinal (MD) nominal tensile strain at break of 350 to 800% and / or a transverse (TD) nominal tensile strain at break of 250 to 700% as determined by ISO 527-3.

[0104] The bonding of LLDPE-A and LLDPE in the film of the present invention improves the mechanical properties of the film. Therefore, the thickness of the film can be reduced and the width of the film can be increased.

[0105] Preferably, the thickness of the multilayer polyethylene film of the present invention is 10 to 100 µm, more preferably 12 to 50 µm, and even more preferably 15 to 35 µm.

[0106] Preferably, the width of the film is at least 2 m, more preferably 3 to 5 m.

[0107] In a particularly preferred embodiment of the multilayer polyethylene film, the film comprises an inner layer, an outer layer, and a core layer, and

[0108] - The inner layer (IL) consists of 79 to 85% LLDPE-B, 7 to 13% LDPE, 1 to 3% UV stabilizer as an additive, 4 to 8% anti-drip agent as an additive, and other additives in total less than 7% by weight.

[0109] - The core layer (CL) consists of: 85 to 91 wt% LLDPE-A, 7 to 13 wt% LLDPE-B, 1 to 3 wt% UV stabilizer as an additive, and other additives in a total amount of less than 7 wt%; and

[0110] - The outer layer (OL) consists of 85 to 91% LLDPE-B, 7 to 13% LDPE, 1 to 3% UV stabilizer as an additive, and other additives in total less than 7% by weight.

[0111] The weight percentages are based on the total weight of each layer; the total amount of polyethylene and additives in each layer is added up to 100% by weight, and the other additives are selected from slip agents, anti-blocking agents, antioxidants and polymer processing aids.

[0112] Soil solar evaporation system

[0113] The properties of the multilayer polyethylene film of the present invention, as described above, make it ideal for use as a soil sun film (SSF).

[0114] This soil sun-drying film can be used in soil sun-drying systems.

[0115] Therefore, the present invention also relates to a soil sun-drying system, the soil sun-drying system comprising:

[0116] i) Soil without crops;

[0117] ii) A multilayer polyethylene film as described above, placed on top of the soil; and

[0118] iii) A drip irrigation system located between the film and the soil.

[0119] Cropless soil describes soil that is essentially devoid of crop plants, such as after the harvest of the previous crop plant and before the sowing of seeds for the next crop plant.

[0120] It is beneficial to prepare the soil before placing SSF on uncultivated soil.

[0121] Therefore, preferably, the soil without crops is prepared by at least one of the following methods before it is exposed to sunlight:

[0122] • Clear weeds and debris from fields (uncultivated soil);

[0123] • Till the soil to break up larger clods;

[0124] • Selectively aerate the soil to reduce compaction;

[0125] • Prepare the seedbed (flat or raised);

[0126] • Raise the center of the cover strip to allow rainwater to flow away from the SSF.

[0127] To prevent heat, air, and / or moisture from leaking out from under the SSF, it is preferable to bury the edges of the SSF in the soil.

[0128] Drip irrigation systems ensure that soil moisture content remains sufficiently high during periods of soil exposure to sunlight.

[0129] As described above, the multilayer polyethylene film of the present invention has high puncture and tear resistance, and therefore can be used more than once. Preferably, the multilayer polyethylene film is used in at least two soil sun exposure cycles.

[0130] Experimental Section

[0131] A. Measurement Method

[0132] Unless otherwise defined, the following terms and measurement methods apply to the general description of the invention above and the embodiments described below.

[0133] a) Measurement of melt flow rate (MFR)

[0134] Melt flow rate (MFR) is determined according to ISO 1133 and expressed in g / 10 min. A higher melt flow rate corresponds to a lower polymer viscosity. For polyethylene, the MFR at 190 °C is defined as 2.16 kg (MFR2), 5.00 kg (MFR5), or 21.6 kg (MFR6). 21 The load was measured.

[0135] The quantity FRR (Flow Rate Ratio) indicates the molecular weight distribution and represents the ratio of flow rates under different loads. Therefore, FRR... 21 / 5 MFR 21 The value of / MFR5.

[0136] b) Density

[0137] The density of the polymer was determined according to ISO 1183-1:2004 (Method A) on compression-molded specimens prepared according to ISO 17855-2, and expressed in kg / m³. 3 express.

[0138] c) GPC standard methods

[0139] Average molecular weight (M) z M w and M n Molecular weight distribution (MWD) and its polydispersity index PDI = M w / M n The described molecular weight width (where M) n M is the number average molecular weight. w (Weight-average molecular weight) is determined by gel permeation chromatography (GPC) according to ISO 16014-1:2003, ISO 16014-2:2003, ISO 16014-4:2003 and ASTM D 6474-12 using the following formula:

[0140] (1)

[0141] (2)

[0142] (3)

[0143] For a constant elution volume interval ΔV i In the formula A i and M i These are respectively related to the elution volume V i The relevant chromatographic peak slice area and polyolefin molecular weight (MW) are used, where N equals the number of data points obtained in the chromatogram between the integration limits.

[0144] A high-temperature GPC instrument equipped with an infrared (IR) detector (IR4 or IR5 from PolymerChar (Valencia, Spain), with 3 x Agilent-PLgel Olexis and 1 x Agilent-PLgel Olexis Guard columns) was used. 1,2,4-trichlorobenzene (TCB) stabilized with 250 mg / L 2,6-di-tert-butyl-4-methylphenol was used as the mobile phase. The chromatographic system was run at a constant flow rate of 1 mL / min at a column temperature of 160 °C and a detector temperature of 160 °C. 200 μL of sample solution was injected for each analysis. Data collection was performed using PolymerChar GPC-IR control software.

[0145] The column assembly was calibrated using a universal calibration (according to ISO 16014-2:2003) with 18 narrow MWD polystyrene (PS) standards ranging from 0.37 kg / mol to 11,000 kg / mol. The PS standards were dissolved at room temperature for several hours. The conversion of the polystyrene peak molecular weight to the polyolefin molecular weight was achieved using the Mark Houwink equation and the following Mark Houwink constant:

[0146] K PS = 19 x 10 -3 mL / g, α PS = 0.655

[0147] K PE = 39 x 10 -3 mL / g, α PE = 0.725

[0148] Third-order polynomial fitting was used to fit the calibration data.

[0149] All samples were prepared at concentrations ranging from approximately 1 mg / ml, and were dissolved by continuous gentle shaking for 3 (triple) hours at 160 °C in freshly distilled TCB stabilized with 250 ppm BHT to obtain PE. Sample vials were purged with N2 gas before the addition of solvent.

[0150] d) Comonomer content

[0151] The content of comonomers (wt% and mol%) was determined by quantitative nuclear magnetic resonance (NMR) spectroscopy.

[0152] Quantitative 13 C{ 1 ¹H NMR spectra were recorded using a Broker Avance III 500 NMR spectrometer in the molten state, targeting… 1 H and13 The operating frequencies of C are 500.13 and 125.76 MHz, respectively. All spectra were used at 150 °C. 13 Recording was performed using a C-optimized 7 mm magic angle rotation (MAS) probe, with all pneumatic devices using nitrogen.

[0153] Approximately 200 mg of material was loaded into a 7 mm outer diameter zirconia MAS rotor and rotated at 4 kHz. This setup was chosen primarily for the high sensitivity required for rapid identification and accurate quantification. Standard single-pulse excitation was employed with NOE at a short 3 s cyclic delay and RS-HEPT decoupling scheme. A total of 1024 (kJ) transient values ​​were acquired for each spectrum.

[0154] Quantitative 13 C{ 1 The ¹H NMR spectra were processed and integrated, and the relevant quantitative properties were determined based on the integration. All chemical shifts were referenced internally to the bulk methylene signal at 30.00 ppm. {randall89}. A characteristic signal {randall89} corresponding to 1-butene incorporation was observed, and the comonomer fraction was calculated as the fraction of 1-butene in the polymer relative to all monomers in the polymer.

[0155] The amount of isolated 1-butene incorporated into the EEBEE sequence was determined using a concentration of 39.9 ppm. The integral of the sites is quantified, which indicates the number of reporter sites for each comonomer:

[0156]

[0157] In the absence of observed signals indicating other comonomer sequences (i.e., continuous comonomer incorporation), the total 1-butene comonomer content is calculated solely based on the amount of isolated 1-butene sequences:

[0158] B 总 = B

[0159] The amount of 1-butene continuously incorporated into the EEBBEE sequence was quantified using the integral of the ααB2B2 site at 39.4 ppm, which indicates the number of reporter sites per comonomer.

[0160]

[0161] The amount of 1-butene discontinuously incorporated into the EEBEBEE sequence was quantified using the integral of the ββB2B2 site at 24.7 ppm, which indicates the number of reporter sites per comonomer:

[0162]

[0163] Due to isolated (EEBEE) and discontinuous (EEBEBEE)-doped 1-butene and The sites overlap, and the total amount of isolated 1-butene incorporation is corrected based on the amount of discontinuous 1-butene present:

[0164]

[0165] The total 1-butene content is calculated based on the sum of isolated, continuous, and discontinuous 1-butene incorporations:

[0166] B 总 = B + BB + BEB

[0167] Then, the total mole fraction of 1-butene in the polymer is calculated as follows:

[0168] fB = B 总 / (E) 总 + B 总 + H 总 )

[0169] The characteristic signal {randall89} corresponding to 1-hexene incorporation was observed, and the comonomer fraction was calculated as the fraction of 1-hexene in the polymer relative to all monomers in the polymer.

[0170] The amount of isolated 1-hexene incorporated into the EEHEE sequence was determined using a concentration of 38.3 ppm. The integral of the sites is quantified, which indicates the number of reporter sites for each comonomer:

[0171]

[0172] The amount of 1-hexene continuously incorporated into the EEHHEE sequence was quantified using the integral of the ααB4B4 site at 40.5 ppm, which indicates the number of reporter sites per comonomer.

[0173]

[0174] The amount of 1-hexene discontinuously incorporated into the EEHEHEE sequence was quantified using the integral of the ββB4B4 site at 24.7 ppm, which indicates the number of reporter sites per comonomer:

[0175]

[0176] Due to the presence of 1-hexene incorporated from isolated (EEHEE) and discontinuous (EEHEHEE) sources. and The signals from the sites overlapped, and the total amount of isolated 1-hexene incorporation was corrected based on the amount of discontinuous 1-hexene present:

[0177]

[0178] The total 1-hexene content is calculated based on the sum of isolated, continuous, and discontinuous incorporations of 1-hexene:

[0179] H 总 = H + HH + HEH

[0180] Then, the total mole fraction of 1-hexene in the polymer is calculated as follows:

[0181] fH = H 总 / (E) 总 + B 总 + H 总 )

[0182] The amount of ethylene used was based on bulk methylene at 30.00 ppm. The integral of the γ site is quantified. This integral includes the γ site and the 3B4 site from 1-hexene. The total ethylene content is calculated based on the bulk integral and compensated for by the observed 1-butene and 1-hexene sequences and end groups:

[0183]

[0184] Characteristic signals caused by saturated end groups were observed. The content of these saturated end groups was quantified using the average of the signal integrals assigned to 22.8 and 32.2 ppm at the 2s and 3s sites, respectively.

[0185]

[0186] The presence of isolated comonomer units is corrected based on the number of existing comonomer units and saturated end groups:

[0187]

[0188] The molar percentage of comonomer incorporation is calculated from the molar fraction:

[0189]

[0190] The weight percentage of comonomer incorporation is calculated from the mole fraction:

[0191]

[0192] randalI89: J. Randall, Macromol. Sci., Rev. Macromol. Chcm. Phys. 1989, C29, 201.

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[0194] parkinson07: Parkinson, M., Klimke, K., Spiess, H.W., Wilhelm, M., Macromol. Chem. Phys. 2007;208:2128.

[0195] pollard04: Pollard, M., Klimke, K., Graf, R., Spiess, H.W., Wilhelm, M., Sperber, O., Piel, C, Kaminsky, W., Macromolecules 2004;37:813.

[0196] filip05: Filip, X., Tripon, C, Filip, C, J. Mag. Resn. 2005, 176, 239

[0197] griffin07: Griffin, J.M., Tripon, C, Samoson, A., Filip, C, and Brown, S.P., Mag. Res. in Chem. 2007 45, SI, S198

[0198] castignolles09: Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373

[0199] e) Mechanical properties

[0200] The tensile properties of polyethylene resin were determined on molded specimens prepared from compression-molded sheets (with a sample thickness of 4 mm). The tensile modulus was determined at 1 mm / min and 23°C according to ISO 527-2 / 1 A. A test speed of 50 mm / min was used to determine the yield stress.

[0201] Tensile modulus and tensile stress at break of thin film

[0202] The tensile properties of the film were determined using a type 2 specimen at 23°C with blown film according to ISO 527-3. The longitudinal (MD) tensile modulus and transverse (TD) tensile modulus were determined according to ASTM D882 using a test speed of 5 mm / min and a gauge length of 50 mm at 1% secant modulus.

[0203] The tensile stress at break of the film was determined according to ISO 527-3 Type 2 specimens with a gauge length of 50 mm and a test speed of 500 mm / min. The film samples were prepared as described below in the "Examples" section.

[0204] Nominal tensile strain at break of the thin film

[0205] The longitudinal (MD) and transverse (TD) nominal tensile strain at break were measured according to ISO 527-3 on films having the specified thickness and prepared as described below in the “Examples”.

[0206] tear strength of film

[0207] Longitudinal (MD) and transverse (TD) Elmendorf tear strengths are determined according to ASTM D1922 or ISO 6383-2 and are expressed in grams per gram (gf).

[0208] The tear strength per unit thickness (gf / µm) is calculated by dividing the Elmendorf tear strength (in gf) by the film thickness (in µm).

[0209] Dart Impact

[0210] The dart impact (DDI) of the film was determined according to ASTM D1709 “Method A” on films having the specified thickness and prepared as described below in “Examples”, and is expressed in grams (g).

[0211] DDI per unit thickness (in g / µm) is calculated by dividing DDI (in grams) by the thickness of the film (in µm).

[0212] f) Haze and total transmittance

[0213] The total transmittance and haze of the plastic film were determined according to ASTM D 1003 using a Haze-Gard instrument (BYK-Gardner) on films of the specified thickness prepared as described below in the "Examples". Total transmittance was measured using a haze meter to determine the ratio of transmitted light to incident light. It is affected by absorption and reflection properties. Total transmitted light consists of a direct transmission component and a diffuse component. Film specimens with a minimum radius of 7 cm were used, and measurements were taken for five specimens of each sample and a reference sample.

[0214] B. Example

[0215] Manufacturing of an exemplary LLDPE-A1

[0216] a) Catalyst

[0217] The polymerization catalyst used for polymerizing LLDPE-A1 was prepared according to Example 1 of EP 1 378 528 A1.

[0218] b) Polymerization of LLDPE-A1

[0219] In the prepolymerization stage, a volume of 50 dm 3 The first loop reactor was operated at 70 °C and 64 bar pressure. Ethylene, 1-butene, and hydrogen were added to produce the prepolymer fraction. Furthermore, the polymerization catalyst prepared according to the above description and the triethylaluminum (TEA) co-catalyst were introduced into the reactor. The reactor conditions are shown in Table A.

[0220] The polymer slurry was removed from the first loop reactor and transferred to a 500 dm³ volumetric reactor. 3 The second loop reactor was operated at 85°C and 64 bar pressure. Ethylene, 1-butene, and hydrogen were introduced into the reactor. No additional catalyst was fed into the reactor. The reactor conditions are shown in Table A.

[0221] The polymer slurry was removed from the second loop reactor and transferred to a flash vessel operating at 3 bar pressure and 70 °C, where hydrocarbons were substantially removed from the polymer. The polymer was then introduced into a gas-phase reactor, which was operated at 78.5 °C and 19.6 bar pressure. Ethylene, 1-butene, and hydrogen were also introduced into the reactor. Conditions are shown in Table A.

[0222] The resulting polymer was purged with nitrogen (approximately 50 kg / h) for one hour, stabilized with 1000 ppm of Irganox 1010 and Irgafos 168 and 1000 ppm of calcium stearate, and then extruded into granules in a counter-rotating twin-screw extruder CIM90P (manufactured by Nippon Steel Works) to achieve a throughput of 223 kg / h and a screw speed of 323 rpm.

[0223] Table A: Polymerization conditions for LLDPE-A1.

[0224]

[0225] The soil sun-dried film (SSF) of the present invention is a three-layer film, wherein each layer is a polyethylene layer containing suitable additives (see Table 1). The outer layer, core layer, and inner layer exist in a thickness ratio of 1:2:1 (OL:CL:IL). The composition of each layer is given in Table 1:

[0226] Table 1: SSF formulation of the present invention.

[0227]

[0228] As a comparison with SSF, a commercially available three-layer SSF was used, each layer being a polyethylene layer containing suitable additives (see Table 2). The outer, core, and inner layers are aluminum in a 1:2:1 (OL:CL:IL) thickness ratio. The composition of each layer is given in Table 2:

[0229] Table 2: Comparison of SSF formulations.

[0230]

[0231] The properties of other polymers used in SSF are given in Table 3:

[0232] Table 3: Base polymers of SSF.

[0233]

[0234] The additives used in thin film preparation are as follows:

[0235] UV masterbatch 20, purchased from Polmann India Ltd., was used as a UV stabilizer.

[0236] The anti-drip agent was purchased from Ray Color in India.

[0237] The SSF of this invention is produced using a 3-layer W&H blown film equipment with an output of 600 kg / hr and an internal bubble cooling system, with a cooling air temperature of 12 to 16°C. Detailed parameters and temperature distributions used to prepare the SSF of this invention are listed in Tables 4 and 5 below.

[0238] Table 4: Parameters of blown film production line.

[0239]

[0240] Table 5 lists the temperature distribution of the blown film line, that is, the temperature of different layers at different locations on the blown film extruder of the blown film line.

[0241] Table 5: Temperature distribution (°C) of blown film production line.

[0242]

[0243] The mechanical / optical properties of the SSF of this invention are shown in Table 6:

[0244] Table 6: Mechanical and optical properties of the SSF of this invention.

[0245]

[0246] Due to the high puncture resistance (DDI) and tear resistance of SSF, it is possible to increase the width of the film to 4 μm.

[0247] In contrast, the SSF has a thickness of 40 µm and a width of 2 m.

[0248] During field use, the outer layer of the SSF is exposed to direct sunlight (i.e., facing the atmosphere), while the inner layer of the SSF is exposed to the soil (i.e., facing the ground).

[0249] Field trials of the SSF of this invention and the comparative SSF were conducted using protected cultivated fields (i.e. greenhouses) in India.

[0250] Prepare the field for soil sunning before placing the soil sun-drying film on the field.

[0251] Field preparation includes:

[0252] • Clear weeds and debris from the field to avoid damaging the SSF, and also because vegetation cover can hinder heat penetration;

[0253] • Till the soil to break up large clods that may damage or elevate the SSF cover;

[0254] • Selectively aerate the soil to reduce compaction, as large soil masses can negatively impact water retention capacity;

[0255] • Prepare the seedbed (flat or raised);

[0256] • Set a center elevation for the cover strip so that rainwater flows off the plastic without cooling it;

[0257] • Install drip irrigation lines to ensure that the soil moisture remains high enough during periods of sun exposure.

[0258] After land preparation and installation of drip irrigation lines to ensure sufficient soil moisture before laying the SSF in the greenhouse, place the SSF on top of the soil in an airtight manner, ensuring no leakage. Bury the edges of the SSF into the soil. Maintain adequate moisture levels using the drip irrigation lines during the trial.

[0259] SSF was left in the field for 4 to 6 weeks, and soil temperature was measured at different depths. The average temperatures obtained are shown in Table 7.

[0260] Table 7: Average temperature at different soil depths.

[0261]

[0262] As can be seen, compared with commercially available SSF, the SSF of the present invention can store more heat and increase the average temperature by more than 1°C at various soil depths.

[0263] The increased temperature reduces weed growth, decreases nematode impact (i.e., pests and diseases), lowers seedling mortality, and leads to better overall yields for subsequent crops.

[0264] The increased width of the SSF of the present invention also facilitates its installation, thereby saving time and money.

Claims

1. A multilayer polyethylene film for soil sun drying, the multilayer polyethylene film comprising an inner layer (IL), an outer layer (OL), and a core layer (CL), the core layer (CL) being located between the inner layer and the outer layer, characterized in that... -Based on the total weight of the core layer, the core layer (CL) comprises at least 80% by weight, preferably 85 to 99% by weight, of a first linear low-density polyethylene (LLDPE) LLDPE-A and a second linear low-density polyethylene (LLDPE) LLDPE-B, wherein the first LLDPE-A has an MFR2 (190°, 2.16 kg) of 0.1 to 0.5 g / 10 min, preferably 0.1 to 0.3 g / 10 min, as determined according to ISO 1133, and the second LLDPE-B has an MFR2 (190°, 2.16 kg) of 0.9 to 2.2 g / 10 min, preferably 1.1 to 1.9 g / 10 min, as determined according to ISO 1133. - The inner layer (IL) comprises the second linear low-density polyethylene (LLDPE)-B, wherein the amount of the second LLDPE-B is at least 60% by weight, preferably 65 to 95% by weight, based on the total weight of the inner layer; and - The outer layer (OL) comprises the second linear low-density polyethylene LLDPE-B, wherein the amount of the second linear low-density polyethylene LLDPE-B is at least 60% by weight, preferably 65 to 95% by weight, based on the total weight of the outer layer.

2. The multilayer polyethylene film according to claim 1, wherein... The density of the LLDPE-A, as determined according to ISO 1183, is 915 to 930 kg / m³. 3 More preferably, 918 to 925 kg / m 3 ,and The density of the LLDPE-B, as determined according to ISO 1183, is 912 to 925 kg / m³. 3 More preferably, 915 to 921 kg / m 3 .

3. The multilayer polyethylene film according to any one of the preceding claims, wherein... - The LLDPE-A is a copolymer of ethylene and a comonomer selected from α-olefins having 4 to 6 carbon atoms, wherein the comonomer selected from α-olefins having 4 to 6 carbon atoms is preferably 1-butene; and / or - The LLDPE-B is a terpolymer of ethylene and two comonomers selected from α-olefins having 4 to 8 carbon atoms, preferably 1-butene and 1-hexene.

4. The multilayer polyethylene film according to any one of the preceding claims, wherein, The molecular weight distribution (MWD) of the LLDPE-A is 10 to 30, preferably 15 to 21.

5. The multilayer polyethylene film according to any one of the preceding claims, wherein, Based on the total amount of LLDPE-A, the LLDPE-A in the core layer contains at least 95% by weight, preferably 96 to 100% by weight, of two polyethylene fractions A and B, wherein polyethylene fraction A has an MFR2 (190°, 2.16 kg) of 100 to 500 g / 10 min, preferably 200 to 400 g / 10 min, as determined according to ISO 1133; and The weight ratio between polyethylene fraction A and polyethylene fraction B is 30:70 to 50:

50.

6. The multilayer polyethylene film according to any one of the preceding claims, wherein, The weight ratio between LLDPE-A and LLDPE-B in the core layer (CL) is 15:1 to 5:1, and the total weight of LLDPE-A and LLDPE-B is at least 92% by weight, preferably, the weight ratio is 12:1 to 7:1, and the total weight is 95.0% to 99.9% by weight.

7. The multilayer polyethylene film according to any one of the preceding claims, wherein, The thickness ratio (OL:CL:IL) between the three layers is 0.8-1.2:1.8-2.2:0.8-1.2, preferably 1:2:

1.

8. The multilayer polyethylene film according to any one of the preceding claims, wherein, At least one of the inner layer and the outer layer, preferably both, further comprises low-density polyethylene (LDPE), with a weight ratio of LLDPE-B to LDPE of 15:1 to 5:1, and the total weight of LLDPE-B and LDPE is at least 88% by weight based on the total weight of the respective inner or outer layer. Preferably, the weight ratio is 10:1 to 6:1, and the total weight is 90 to 99% by weight.

9. The multilayer polyethylene film according to any one of the preceding claims, wherein, At least one of the inner layer, the outer layer, and the core layer, preferably all of the layers, further comprises an ultraviolet stabilizer as an additive, and the film optionally further comprises an additive selected from slip agents, anti-blocking agents, antioxidants, polymer processing aids, and anti-drip agents.

10. The multilayer polyethylene film according to any one of the preceding claims, wherein, The film does not contain colorants as additives.

11. The multilayer polyethylene film according to any one of the preceding claims, wherein, The thin film is composed of the inner layer, the outer layer, and the core layer, and - The inner layer (IL) consists of: 79 to 85% by weight of the LLDPE-B, 7 to 13% by weight of the LDPE, 1 to 3% by weight of a UV stabilizer as an additive, 4 to 8% by weight of an anti-drip agent as an additive, and other additives in a total amount of less than 7% by weight. - The core layer (CL) comprises: 85 to 91 wt% of the LLDPE-A, 7 to 13 wt% of the LLDPE-B, 1 to 3 wt% of a UV stabilizer as an additive, and other additives in a total amount of less than 7 wt%; and - The outer layer (OL) consists of: 85 to 91% by weight of the LLDPE-B, 7 to 13% by weight of the LDPE, 1 to 3% by weight of a UV stabilizer as an additive, and other additives in a total amount of less than 7% by weight. The weight percentages are based on the total weight of each layer; the total amount of polyethylene and additives in each layer is added up to 100% by weight, and the other additives are selected from slip agents, anti-blocking agents, antioxidants and polymer processing aids.

12. The multilayer polyethylene film according to any one of the preceding claims, wherein, The thin film has the following properties - Total light transmittance, as measured by ASTM D 1003, is greater than 85%, more preferably 88 to 99%; as well as - The haze, as measured by ASTM D 1003, is less than 15%, preferably 1 to 14%.

13. The multilayer polyethylene film according to any one of the preceding claims, wherein, The thin film has the following properties - A thickness of 10 to 100 µm, preferably 12 to 50 µm, more preferably 15 to 35 µm; and / or - The width is at least 2 m, preferably 3 to 5 m.

14. A soil sun-drying system, the soil sun-drying system comprising: i) Soil without crops; ii) A multilayer polyethylene film as described in any of the preceding claims placed on top of the soil; as well as iii) A drip irrigation system located between the film and the soil.

15. Use of the multilayer polyethylene film according to any one of claims 1 to 13 for soil sun exposure, preferably for at least two soil sun exposure cycles.

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