High-barrier polyethylene composite material for heavy-duty packaging film and preparation method thereof

Abstract

The present application relates to the technical field of polyolefin composite material, in particular to a kind of high-barrier polyethylene composite material for heavy load packaging film and a preparation method thereof.The composite material contains 3.5%~5.5% functional materials, maleic anhydride grafted polyethylene and organic nucleating agent, and the balance is metallocene linear low density polyethylene, high density polyethylene, ethylene-octene copolymer and antioxidant.Functional materials are made by flaking kaolin successively through stearic acid spreading anchoring organic nucleating agent, maleic anhydride grafted polyethylene coating;The composite material is prepared by two-stage melt compounding, first by functional materials and high density polyethylene to prepare barrier masterbatch with 25%~40% functional materials, then under low shear, short residence time, the remaining components are blended and granulated.The water vapor transmission rate of the obtained film is reduced, and the falling weight impact damage mass is maintained.

Description

Technical Field

[0001] This invention relates to the field of polyolefin composite materials technology, specifically to a high-barrier polyethylene composite material for heavy-duty packaging films and its preparation method. Background Technology

[0002] Powdered and granular materials such as fertilizers and resin granules weighing 25 kg or more are mostly packaged in bags made of polyethylene heavy-duty packaging film. These films must both block moisture to prevent the contents from becoming damp and clumping, and remain intact during full-load drops and stacking. Therefore, requirements are placed on both water vapor permeability and dart impact strength. A commonly used resin system in this field is one that uses metallocene polyolefins as the continuous phase, combined with high-density polyethylene for water resistance and ethylene-octene copolymers for impact energy dissipation.

[0003] To reduce water vapor transmission, patent CN110713647A discloses a polyethylene composition with improved water vapor barrier properties, comprising a composition with a density of 0.93~0.96 g / cm³. 3 Polyethylene, low-density polyethylene, and ethylene-propylene copolymers are combined according to their respective crystallization temperatures, and nucleating agents may be added. The mixture is obtained through a single melt blending process. Patent CN113754949A discloses a barrier masterbatch for preparing polyethylene film, which is produced by mixing carrier resin, compatibilizer, and barrier filler through internal mixing and twin-screw extrusion. Patent CN111117041A discloses an oxygen-barrier polyethylene masterbatch, which uses graphene combined with kaolin, mica powder, and other flake minerals as oxygen-barrier components, obtained through pre-dispersion and two-stage melt blending.

[0004] Increasing the density of crystals and introducing platy minerals can both prolong the diffusion path of water molecules. However, the former reduces the continuity of the amorphous phase that can undergo plastic deformation, while the latter, as described in CN110713647A, often reduces the elongation at break of the material. Both of these approaches involve a single batching of the components or multiple batchings under the same conditions. The platy minerals are distributed according to the volume and interfacial properties of each phase. The portion that enters the flexible dispersed phase weakens the energy-consuming effect of that phase, making it difficult to reduce water vapor permeability without sacrificing impact resistance. Summary of the Invention

[0005] The purpose of this invention is to provide a high-barrier polyethylene composite material for heavy-duty packaging films and its preparation method, so as to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a high-barrier polyethylene composite material for heavy-duty packaging films, characterized in that, based on the total mass of the composite material, it comprises 3.5%~5.5% functional materials, 1.1%~1.9% maleic anhydride-grafted polyethylene, and 0.05%~0.09% organic nucleating agent, with the balance being metallocene linear low-density polyethylene, film-grade high-density polyethylene, ethylene-octene copolymer, and antioxidants. The content of the maleic anhydride-grafted polyethylene and the organic nucleating agent are not included in the contents already contained in the functional materials. The functional materials are prepared by the following steps: heating peeled kaolin to 95~110°C, spraying in molten stearic acid at 2%~3% of the mass of the peeled kaolin, mixing for 5~8 minutes, and adding a certain amount of molten stearic acid at a certain mass of the peeled kaolin. 1.7%~2.6% by mass of organic nucleating agent is mixed for 8~12 min, cooled to 55~65℃, and 10%~14% by mass of maleic anhydride-grafted polyethylene micro powder is added. The mixture is heated to 140~150℃, mixed for 6~10 min, cooled, discharged, and sieved. The composite material is obtained by melt composite in two stages: the first stage involves melt composite and granulation of the functional material, maleic anhydride-grafted polyethylene, and film-grade high-density polyethylene to obtain a barrier masterbatch, wherein the functional material accounts for 25%~40% by mass of the barrier masterbatch; the second stage involves melt blending and granulation of the barrier masterbatch and other components under the conditions of melt temperature 185~200℃, main machine speed 100~130 r / min, and average residence time 60~100 s.

[0007] Furthermore, the anchored organic nucleating agent in the functional material accounts for 42% to 66% of the sum of itself and the organic nucleating agent.

[0008] Furthermore, the mass ratio of the metallocene linear low-density polyethylene, the film-grade high-density polyethylene, and the ethylene-octene copolymer is 55:28:10.6.

[0009] Furthermore, the sum of the pre-anchored organic nucleating agent and the separately added organic nucleating agent in the functional material is 0.15% of the total mass of the composite material.

[0010] Furthermore, the median particle size of the exfoliated kaolin is 1.5 μm, and the aspect ratio is 20~30.

[0011] Furthermore, the organic nucleating agent is composed of calcium 1,2-cyclohexanedicarboxylate and zinc stearate.

[0012] Furthermore, the residual amount of the functional material after calcination at 600°C to constant weight is 72%~76%.

[0013] This invention also provides a method for preparing the above-mentioned high-barrier polyethylene composite material for heavy-duty packaging films, comprising the following steps: S1, heating peeled kaolin to 95-110°C, spraying in molten stearic acid, mixing for 5-8 min, adding an organic nucleating agent, mixing for 8-12 min, cooling to 55-65°C, adding maleic anhydride-grafted polyethylene micro powder, heating to 140-150°C, mixing for 6-10 min, cooling, discharging, and sieving to obtain the functional material; S2, combining the functional material obtained in S1 with maleic anhydride... Grafted polyethylene and film-grade high-density polyethylene are mixed, melt-composite, and granulated to obtain a barrier masterbatch with a functional material mass fraction of 25%~40%; S3, the barrier masterbatch obtained in S2 is mixed with metallocene linear low-density polyethylene, film-grade high-density polyethylene, ethylene-octene copolymer, organic nucleating agent and antioxidant, and melt-blended and granulated under the conditions of melt temperature of 185~200℃, main machine speed of 100~130r / min and average residence time of 60~100s to obtain the composite material.

[0014] Furthermore, the melt temperature of the molten composite in S2 is 195~215℃, and the specific energy input is 0.14~0.17kWh / kg.

[0015] Furthermore, after S3, the process includes a step of blow molding the resulting composite material at 180~195°C, a blow ratio of 2.5~3, and a draw ratio of 8~12.

[0016] The ethylene-octene copolymer exists as a dispersed phase in the composite material, thereby allowing the functional material to remain in the continuous phase; its amount is limited to maintaining it as a dispersed phase in the system without undergoing phase inversion.

[0017] The beneficial effects of this invention are: (1) The present invention uses a functional material obtained by spreading and anchoring organic nucleating agent with molten stearic acid on peeled kaolin and then coating it with maleic anhydride-grafted polyethylene as a barrier component. This functional material has both a sheet-like morphology and an outer surface that can entangle with the polyethylene matrix. In heavy packaging film material with metallocene polyolefin as the main continuous phase, it reduces the water vapor permeation of the film and increases the 1% secant modulus of the film.

[0018] (2) The composite material is prepared by two-stage melt composite. The functional material is first made into a barrier masterbatch with film-grade high-density polyethylene, and then blended and diluted with ethylene-octene copolymer under low shear and short residence conditions. Compared with materials with the same composition but blended in one batch, the resulting membrane maintains the quality of dart impact damage while reducing water vapor permeability.

[0019] (3) The functional material is first wetted and wrapped by film-grade high-density polyethylene in the first stage, and then diluted under low shear and short residence conditions in the second stage. As a result, the sheet mainly remains in the continuous phase and does not enter the ethylene-octene copolymer phase. In the film material with metallocene polyolefin as the main continuous phase, these two conditions together determine the destination of the functional material between the two phases.

[0020] (4) When the functional material accounts for 25% to 40% of the mass of the barrier masterbatch, the filling degree and melt viscosity of the first stage are suitable, and the functional material can be fully wetted and wrapped by the continuous phase resin. When the mass is below this range, the quality of the resulting membrane is reduced by dart impact damage, and when the mass is above this range, the amount of selective extract ignition residue increases.

[0021] (5) The organic nucleating agent in the formulation consists of two parts: the part already anchored on the surface of the functional material and the separately added powder. The sum of the two remains constant, and the additional powder makes up for any changes in the amount of functional material. Under the condition of the same total amount of nucleating agent, the 1% secant modulus of the film obtained by anchoring it to the surface of the sheet is 307 MPa, which is higher than the 297 MPa when it is all added as powder, thus improving the stiffness of the film. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments. These embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0023] The flaked kaolin used in the preparation examples, embodiments, and comparative examples was sourced from China Kaolin Co., Ltd. It was flaked type, with a median particle size of 1.5 μm, an aspect ratio of 20–30, and a moisture content not exceeding 1%. The organic nucleating agent was sourced from Milliken Chemicals, traded under the name Hyperform, brand name HPN-20E, composed of calcium 1,2-cyclohexanedicarboxylate and zinc stearate, with calcium 1,2-cyclohexanedicarboxylate accounting for approximately 66%. The maleic anhydride-grafted polyethylene was sourced from Nanjing Genus New Materials Co., Ltd., and was of high grafting rate grade, with a grafting rate of 0.8%–1.2%, and the powder passed through 80 mesh. The metallocene linear low-density polyethylene was sourced from ExxonMobil Chemicals, brand name Exceed m 1018CA, an ethylene-hexene copolymer with a density of 0.918 g / cm³. 3 The melt flow rate is 1 g / 10 min; the film-grade high-density polyethylene is sourced from China Petroleum & Chemical Corporation (Sinopec), grade 5000S, with a density of 0.954 g / cm³. 3 The melt flow rate is 0.9 g / 10 min; the ethylene-octene copolymer is from Dow Chemical, traded under the name ENGAGE, grade 8100, with a density of 0.870 g / cm³. 3 The melt flow rate was 1 g / 10 min; the antioxidant was a compound of BASF's Irganox 1010 and Irgafos 168 in a mass ratio of 1:2.

[0024] Preparation Example 1: 5000g of exfoliated kaolin was added to a high-speed mixer, stirred at 1000 rpm, and heated to 100°C. 125g of molten stearic acid was sprayed in and mixed at 100°C for 6 minutes to spread it into layers on the flake surface. 105g of organic nucleating agent was added, and mixing continued at 100°C for 10 minutes. The mixture was cooled to 60°C, and 600g of maleic anhydride-grafted polyethylene micropowder was added. The mixture was heated to 145°C and mixed at 1350 rpm for 8 minutes. The mixture was cooled to below 50°C and discharged, passing through a 200-mesh sieve to obtain the functional material. Two batches were prepared according to the above proportions and conditions, and the combined batches yielded 11368g of functional material. The residual weight after ignition at 600°C to constant weight was 74.2%.

[0025] Preparation Example 2: 5000g of exfoliated kaolin was added to a high-speed mixer, stirred at 1000 rpm, and heated to 100°C. 125g of molten stearic acid was sprayed in, and mixed at 100°C for 6 min. The mixture was then cooled to 60°C, and 600g of maleic anhydride-grafted polyethylene micropowder was added. The mixture was heated to 145°C and mixed at 1350 rpm for 8 min. The mixture was cooled to below 50°C and discharged, then passed through a 200-mesh sieve to obtain 5582g of the control functional material, of which the residue after ignition at 600°C to constant weight was 75.2%.

[0026] Preparation Example 3: 5000g of exfoliated kaolin was added to a high-speed mixer, stirred at 1000r / min and heated to 100℃; 125g of molten stearic acid was sprayed in, and mixed at 100℃ for 6min; 105g of organic nucleating agent was added, and mixing continued at 100℃ for 10min. The mixture was cooled to below 50℃ and discharged, then passed through a 200-mesh sieve to obtain 5099g of control functional material, of which the residual weight after ignition at 600℃ to constant weight was 82.8%.

[0027] Preparation Example 4: 1500g of the functional material obtained in Preparation Example 1, 500g of maleic anhydride-grafted polyethylene, and 3000g of film-grade high-density polyethylene were mixed evenly and fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1. The temperature of each section of the barrel from the feeding section to the die head was 190℃, the melt temperature was 205℃, the main extruder speed was 280r / min, and the specific energy input was 0.155kWh / kg. The mixture was pelletized in a water ring and dried to obtain a barrier masterbatch. Two batches were prepared according to the above ratio and conditions, and the combined batches yielded 9700g of barrier masterbatch.

[0028] Example 1: Step (1): 1500g of the barrier masterbatch obtained in Example 4, 1901g of film-grade high-density polyethylene, 5502g of metallocene linear low-density polyethylene, 1060g of ethylene-octene copolymer, 6.9g of organic nucleating agent, and 30g of antioxidant were mixed evenly and fed into a twin-screw extruder equipped with conveying elements and toothed mixing elements. The temperature of each section of the barrel was 185℃, the melt temperature was 192℃, the main engine speed was 120r / min, and the average residence time was 90s. The mixture was extruded and granulated to obtain 9700g of composite material. Step (2): The composite material obtained in Step (1) was blown into shape on a single-screw blown film unit at 188℃, a blow-up ratio of 2.8, and a traction ratio of 10 to obtain a single-layer film with a thickness of 50μm.

[0029] Example 2: Step (1): 1167g of the barrier masterbatch obtained in Example 4, 2140g of film-grade high-density polyethylene, 5579g of metallocene linear low-density polyethylene, 1075g of ethylene-octene copolymer, 8.7g of organic nucleating agent, and 30g of antioxidant were mixed evenly and fed into a twin-screw extruder equipped with conveying elements and toothed mixing elements. The temperature of each section of the barrel was 185℃, the melt temperature was 192℃, the main engine speed was 120r / min, and the average residence time was 90s. The mixture was extruded and granulated to obtain 9700g of composite material. Step (2): The composite material obtained in Step (1) was blown into shape on a single-screw blown film unit at 188℃, a blow-up ratio of 2.8, and a traction ratio of 10 to obtain a single-layer film with a thickness of 50μm.

[0030] Example 3: Step (1): 1833g of barrier masterbatch obtained in Example 4, 1662g of film-grade high-density polyethylene, 5425g of metallocene linear low-density polyethylene, 1045g of ethylene-octene copolymer, 5.1g of organic nucleating agent, and 30g of antioxidant were mixed evenly and fed into a twin-screw extruder equipped with conveying elements and toothed mixing elements. The temperature of each section of the barrel was 185℃, the melt temperature was 192℃, the main engine speed was 120r / min, and the average residence time was 90s. The mixture was extruded and granulated to obtain 9700g of composite material. Step (2): The composite material obtained in Step (1) was blown into shape on a single-screw blown film unit at 188℃, a blow-up ratio of 2.8, and a traction ratio of 10 to obtain a single-layer film with a thickness of 50μm.

[0031] Example 4: Step (1): Mix 1250g of the functional material obtained in Example 1, 500g of maleic anhydride grafted polyethylene and 3250g of film-grade high-density polyethylene evenly, and put them into a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1. The temperature of each section of the barrel is 190℃, the melt temperature is 205℃, the main engine speed is 280r / min, the specific energy input is 0.155kWh / kg, the water ring pellets and dry to obtain the barrier masterbatch. Step (2): Mix 1800g of barrier masterbatch, 1622g of film-grade high-density polyethylene, 5484g of metallocene linear low-density polyethylene, 1057g of ethylene-octene copolymer, 6.9g of organic nucleating agent and 30g of antioxidant obtained in step (1) evenly, and put it into a twin-screw extruder equipped with conveying elements and toothed mixing elements. The temperature of each section of the barrel is 185℃, the melt temperature is 192℃, the main engine speed is 120r / min, the average residence time is 90s, and the extrusion granulation is performed to obtain 9700g of composite material. Step (3): Blow the composite material obtained in step (2) on a single-screw blown film unit at 188℃, blow ratio 2.8 and traction ratio 10 to obtain a single-layer film with a thickness of 50μm.

[0032] Example 5: Step (1): 2000g of the functional material obtained in Example 1, 500g of maleic anhydride grafted polyethylene and 2500g of film-grade high-density polyethylene were mixed evenly and fed into a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1. The temperature of each section of the barrel was 190℃, the melt temperature was 205℃, the main engine speed was 280r / min, the specific energy input was 0.155kWh / kg, the water ring pellets were dried to obtain the barrier masterbatch. Step (2): Mix 1125g of barrier masterbatch, 2250g of film-grade high-density polyethylene, 5523g of metallocene linear low-density polyethylene, 1065g of ethylene-octene copolymer, 6.9g of organic nucleating agent, and 30g of antioxidant obtained in step (1) evenly, and put them into a twin-screw extruder equipped with conveying elements and toothed mixing elements. The temperature of each section of the barrel is 185℃, the melt temperature is 192℃, the main engine speed is 120r / min, the average residence time is 90s, and the extrusion granulation is performed to obtain 9700g of composite material. Step (3): Blow-mold the composite material obtained in step (2) on a single-screw blown film unit at 188℃, blow-up ratio 2.8, and traction ratio 10 to obtain a single-layer film with a thickness of 50μm.

[0033] Comparative Example 1: 2978g of film-grade high-density polyethylene, 5850g of metallocene linear low-density polyethylene, 1127g of ethylene-octene copolymer, 15.0g of organic nucleating agent and 30g of antioxidant were mixed evenly in one batch and fed into a twin-screw extruder. The temperature of each section of the barrel was 190℃, the melt temperature was 200℃, the main machine speed was 400r / min, and the average residence time was 120s. The mixture was extruded and granulated to obtain 9700g of composite material, which was then blow-molded according to step (2) of Example 1.

[0034] Comparative Example 2: 450g of the functional material obtained in Preparation Example 1, 150g of maleic anhydride-grafted polyethylene, 2801g of film-grade high-density polyethylene, 5502g of metallocene linear low-density polyethylene, 1060g of ethylene-octene copolymer, 6.9g of organic nucleating agent and 30g of antioxidant were fed into a single batch and mixed evenly. The mixture was then fed into a twin-screw extruder with the barrel temperature at 190°C, the melt temperature at 200°C, the main extruder speed at 400r / min, and the average residence time at 120s. The mixture was extruded and granulated to obtain 9700g of composite material, which was then blow-molded according to step (2) of Example 1.

[0035] Comparative Example 3: Except that the barrier masterbatch obtained in Preparation Example 4 was replaced with the barrier masterbatch prepared according to the conditions of Preparation Example 4 by 1473g of control functional material, 500g of maleic anhydride grafted polyethylene and 3027g of film-grade high-density polyethylene obtained in Preparation Example 2, and the amount of organic nucleating agent added was changed to 15.0g, the other raw materials, amounts and preparation conditions were the same as in Example 1, and the composite material was obtained and blow-molded.

[0036] Comparative Example 4: Except that the barrier masterbatch obtained in Preparation Example 4 was replaced with the barrier masterbatch prepared according to the conditions of Preparation Example 4 by using 1346g of control functional material, 654g of maleic anhydride grafted polyethylene and 3000g of film-grade high-density polyethylene obtained in Preparation Example 3, the other raw materials, amounts and preparation conditions were the same as in Example 1, and the composite material was obtained and blow-molded.

[0037] Comparative Example 5: Except for changing the main engine speed in step (1) to 400 r / min and the average dwell time to 300 s, the other raw materials, dosages and preparation conditions were the same as in Example 1, and 9600 g of composite material was obtained and blow-molded.

[0038] Comparative Example 6: 714g of maleic anhydride-grafted polyethylene and 4286g of film-grade high-density polyethylene were melt-granulated according to the conditions of Preparation Example 4 to obtain a resin masterbatch. 1050g of the resin masterbatch was taken and mixed evenly with 450g of functional material obtained in Preparation Example 1, 1901g of film-grade high-density polyethylene, 5502g of metallocene linear low-density polyethylene, 1060g of ethylene-octene copolymer, 6.9g of organic nucleating agent and 30g of antioxidant. The mixture was extruded and granulated according to the conditions of step (1) of Example 1 to obtain 9700g of composite material, which was then blow-molded according to step (2) of Example 1.

[0039] Comparative Example 7: Except for changing the amount of barrier masterbatch obtained in Preparation Example 4 to 667g, film-grade high-density polyethylene to 2499g, metallocene linear low-density polyethylene to 5695g, ethylene-octene copolymer to 1098g, and organic nucleating agent to 11.4g, the other raw materials, dosages, and preparation conditions were the same as in Example 1, and the composite material was obtained and blow-molded.

[0040] Comparative Example 8: Except for changing the amount of barrier masterbatch obtained in Preparation Example 4 to 2333g, film-grade high-density polyethylene to 1303g, metallocene linear low-density polyethylene to 5309g, ethylene-octene copolymer to 1023g, and organic nucleating agent to 2.4g, the other raw materials, dosages, and preparation conditions were the same as in Example 1, and the composite material was obtained and blow-molded.

[0041] Comparative Example 9: Except that the barrier masterbatch was changed to be prepared according to the conditions of Preparation Example 4, consisting of 900g of functional material obtained in Preparation Example 1, 500g of maleic anhydride-grafted polyethylene, and 3600g of film-grade high-density polyethylene, with the addition amount changed to 2500g, film-grade high-density polyethylene changed to 971g, metallocene linear low-density polyethylene changed to 5443g, and ethylene-octene copolymer changed to 1049g, the other raw materials, dosages, and preparation conditions were the same as in Example 1, and the composite material was obtained and blow-molded.

[0042] Comparative Example 10: Except that the barrier masterbatch was changed to be prepared according to the conditions of Preparation Example 4 using 2500g of functional material obtained in Preparation Example 1, 500g of maleic anhydride-grafted polyethylene and 2000g of film-grade high-density polyethylene, with the addition amount changed to 900g, the film-grade high-density polyethylene changed to 2459g, the metallocene linear low-density polyethylene changed to 5537g and the ethylene-octene copolymer changed to 1067g, the other raw materials, dosages and preparation conditions were the same as in Example 1, and the composite material was obtained and blow-molded.

[0043] Application example: The composite material obtained in Example 1 is used as the core layer material, and together with the polyethylene heat-sealing layer material and the polyethylene outer layer material, it is blown into shape at 180~195°C on a three-layer co-extrusion blown film unit. The thickness ratio of the three layers is 1:3:1, resulting in a three-layer co-extrusion heavy packaging film with a total thickness of 160μm, which is used for bag making and filling of 25kg of powdery and granular materials.

[0044] Performance testing: The composite materials obtained in each example and comparative example were independently formed into 3 batches. A single layer film with a thickness of 50 μm was used as the test material, and the arithmetic mean was taken after each test.

[0045] Water vapor transmission rate: determined by cup weight gain method according to GB / T 1037-2021, under test conditions of 38℃ and 90% relative humidity.

[0046] Dart impact breakage quality: determined by the step method according to GB / T 9639.1-2008, with a dart head diameter of 38mm and a drop height of 0.66m. Each batch of film shall complete one step test according to the number of samples specified in the standard.

[0047] Longitudinal tensile nominal strain at break and 1% secant modulus: determined according to GB / T 1040.3-2006, type 2 specimens with a width of 15 mm and a gauge length of 50 mm were cut along the longitudinal direction of the membrane; the tensile speed was 500 mm / min when determining the nominal strain at break, and the tensile speed was 1 mm / min when determining the modulus. The 1% secant modulus was calculated as the ratio of the stress at 1% strain on the stress-strain curve to that strain.

[0048] Selective extract mass fraction and ignition residue: Take the above 50 μm monolayer membrane, cut it into pieces with sides of approximately 5 mm, weigh 20 g and place it in a three-necked flask equipped with a reflux condenser. Add 800 mL of n-heptane and extract by stirring in an 80℃ constant temperature oil bath for 12 h, replacing the n-heptane every 2 h to preferentially dissolve the ethylene-octene copolymer phase. At this temperature, the ethylene-octene copolymer is completely melted and highly swollen, while the crystalline network of metallocene linear low-density polyethylene has not yet disintegrated. Combine the extracts, evaporate to dryness, and vacuum dry to constant weight at 60℃. The selective extract mass fraction is calculated as the percentage of the extract mass to the sample mass. Then, ignite the extract at 600℃ to constant weight, and the selective extract ignition residue is calculated as the percentage of the extract mass. The results are shown in Tables 1 and 2.

[0049] Table 1. Main properties of the membranes obtained in each embodiment and comparative example. ; Table 2 Selective extraction results of composite materials obtained in each embodiment and comparative example ; Results Analysis As shown in Table 1, the water vapor permeation rate of Examples 1 to 5 was 4.20~4.65 g / (m²). 2 ·d), all were lower than the 5.55 g / (m²) of Comparative Example 1 without sheet filler. 2 (d) The 1% secant modulus increased from 254 MPa to 289-314 MPa. This indicates that introducing the functional material into the polyethylene matrix reduced the water vapor permeation of the membrane and improved the membrane stiffness.

[0050] Example 1 and Comparative Example 2 have identical compositions, differing only in their formation processes. The dart impact failure mass of Example 1 was 410g, while that of Comparative Example 2 was 340g; the selective extract residues on ignition for both were 1.47% and 10.46%, respectively (see Table 2). This indicates that by first preparing a masterbatch from the functional material and the continuous phase resin, and then introducing the elastomer phase under low shear conditions, the impact resistance of the membrane is maintained.

[0051] Comparative Example 5 increased the main engine speed in the second stage to 400 r / min and extended the average residence time to 300 s. The impact mass of the falling dart decreased to 355 g, while the water vapor permeability increased to 4.70 g / (m³). 2 •d) The residual amount of selectively extracted material on ignition increased to 9.40%. This indicates that the excessive shearing force in the second stage cancels out the distribution formed by the combination of the two stages.

[0052] Comparative Example 6, where the functional material was added together with the elastomer in the second stage, showed a dart impact breaking mass of 345g and a water vapor permeability of 4.85g / (m²). 2 •d) The residual amount of selectively extracted material on ignition was 11.69%, the highest among all samples. This indicates that the functional material must enter in the first stage and be wetted and encapsulated by the continuous phase resin before it is added; otherwise, the same distribution cannot be obtained.

[0053] Comparative Example 3 changed the nucleating agent to be added entirely as free powder, and its water vapor permeation rate was 4.60 g / (m²). 2 ·d) The impact breakage mass of the dart was 415g, compared with 4.40g / (m) in Example 1. 2 •d) Equivalent to 410g; 1% secant modulus decreased from 307MPa in Example 1 to 297MPa, and the selective extract residue on ignition was 2.33%. It can be seen that whether the nucleating agent is anchored on the surface of the sheet does not change the fact that the sheet mainly remains in the continuous phase, but it affects the stiffness of the membrane.

[0054] Comparative Example 4, by omitting the maleic anhydride-grafted polyethylene coating layer and adding an equal amount of this component directly with the masterbatch, reduced its dart impact breaking mass to 360g and increased its water vapor permeability to 4.85g / (m³). 2 •d) The residual amount of selectively extracted material on ignition increased to 7.01%. The coating layer must be pre-formed on the particle surface; simply adding an equal amount of compatibilizer to the melt cannot make the lamellar layer stably reside in the continuous phase.

[0055] Comparative Example 7, with 2% functional material, had a 1% secant modulus of 275 MPa, lower than the 289 MPa of Example 2 with 3.5% functional material; its water vapor permeability was 4.95 g / (m²). 2 ·d), higher than the 4.40 g / (m²) of Example 1 with a dosage of 4.5%. 2 •d). In Comparative Example 8, where the dosage was increased to 7%, the water vapor permeation decreased to 3.80 g / (m²). 2 •d) The nominal strain at longitudinal tensile fracture decreased to 585%, lower than 600% of that in Example 3 with a dosage of 5.5%. This indicates that when the dosage is too low, the improvement in both barrier and stiffness is insufficient, and when the dosage is too high, the film's elongation capacity decreases.

[0056] Comparative Example 9, with a functional material mass fraction of 18%, had a dart impact fracture mass of 380g, lower than the 410-430g of Examples 1, 4, and 5 (25%-40% mass fraction). The selective extractable residues on ignition of Comparative Examples 9 and 10 were 5.67% and 4.30%, respectively, both higher than the 2.11%, 1.47%, and 1.82% of Examples 4, 1, and 5 in the same range. This indicates that below this range, the shear transfer in the first stage is insufficient, leading to a decrease in the dart impact fracture mass; above this range, the melt is difficult to plasticize uniformly under high filling conditions, and in both cases, the functional material is not sufficiently encapsulated by the continuous phase.

[0057] The selective extractable mass fraction of each sample ranged from 10.9% to 12.9%, and the organic fraction after deducting the residue on ignition was 10.6% to 11.6%, which was 0.31 to 0.79 percentage points higher than the ethylene-octene copolymer content of 10.2% to 11.3% in the formulation. This excess came from the 0.3% antioxidant in the formulation, as well as the organic matter carried by the functional materials dissolved along with the sheets and the structural water lost during ignition. Comparative Example 1, which had the highest content of metallocene linear low-density polyethylene without sheet fillers, had an excess of 0.32 percentage points, comparable to the amount of antioxidant. Comparative Examples 6, 2, and 5, which had the highest residue on ignition, also had the highest excesses, at 0.79, 0.77, and 0.63 percentage points, respectively. It can be seen that the matrix did not co-dissolve significantly under these extraction conditions, and the difference in residue on ignition reflects the amount of sheets dissolved along with the ethylene-octene copolymer.

[0058] The nominal longitudinal tensile fracture strain of Examples 1 to 5 is 600%~615%, which is lower than 650% of Comparative Example 1 without sheet filler, and its dart impact fracture mass is still not less than 410g.

[0059] The maleic anhydride-grafted polyethylene coating on the surface of the functional material allows it to be wetted and wrapped by film-grade high-density polyethylene in the first stage. The low shear and short residence conditions in the second stage are insufficient for it to re-migrate into the subsequently added ethylene-octene copolymer phase. As a result, the sheet mainly remains in the continuous phase. This may be the reason why the residual amount of selective extracts on ignition and the dart impact damage quality change synchronously in the above examples.

Claims

1. A high-barrier polyethylene composite material for heavy-duty packaging films, characterized in that, The composite material comprises, by total mass, 3.5%–5.5% functional materials, 1.1%–1.9% maleic anhydride-grafted polyethylene, and 0.05%–0.09% organic nucleating agent, with the balance being metallocene linear low-density polyethylene, film-grade high-density polyethylene, ethylene-octene copolymer, and antioxidants. The content of the maleic anhydride-grafted polyethylene and the organic nucleating agent is not included in the content already present in the functional materials. The functional materials are prepared by the following steps: heating exfoliated kaolin to 95–110°C, spraying in 2%–3% molten stearic acid (by mass of the exfoliated kaolin), mixing for 5–8 minutes, adding 1.7%–2.6% organic nucleating agent (by mass of the exfoliated kaolin), and mixing for 8 minutes. After 12 minutes, the temperature is lowered to 55-65℃, and maleic anhydride-grafted polyethylene micropowder (10%-14% of the mass of the peeled kaolin) is added. The temperature is then raised to 140-150℃, and the mixture is stirred for 6-10 minutes. The mixture is then cooled, discharged, and sieved. The composite material is obtained by melt compounding in two stages: the first stage involves melt compounding and granulation of the functional material, maleic anhydride-grafted polyethylene, and film-grade high-density polyethylene to obtain a barrier masterbatch, wherein the functional material accounts for 25%-40% of the mass of the barrier masterbatch; the second stage involves melt blending and granulation of the barrier masterbatch and other components under the conditions of melt temperature 185-200℃, main machine speed 100-130 r / min, and average residence time 60-100 s.

2. The high-barrier polyethylene composite material for heavy-duty packaging film according to claim 1, characterized in that, The anchored organic nucleating agent in the functional material accounts for 42% to 66% of the sum of itself and the organic nucleating agent.

3. The high-barrier polyethylene composite material for heavy-duty packaging film according to claim 1, characterized in that, The mass ratio of the metallocene linear low-density polyethylene, film-grade high-density polyethylene, and ethylene-octene copolymer is 55:28:10.

6.

4. The high-barrier polyethylene composite material for heavy-duty packaging film according to claim 1, characterized in that, The sum of the pre-anchored organic nucleating agent and the separately added organic nucleating agent in the functional material is 0.15% of the total mass of the composite material.

5. The high-barrier polyethylene composite material for heavy-duty packaging film according to claim 1, characterized in that, The median particle size of the exfoliated kaolin is 1.5 μm, and the aspect ratio is 20~30.

6. The high-barrier polyethylene composite material for heavy-duty packaging film according to claim 1, characterized in that, The organic nucleating agent is composed of calcium 1,2-cyclohexanedicarboxylate and zinc stearate.

7. The high-barrier polyethylene composite material for heavy-duty packaging film according to claim 1, characterized in that, The residual amount of the functional material after calcination at 600°C to constant weight is 72%~76%.

8. A method for preparing a high-barrier polyethylene composite material for heavy-duty packaging film as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Heat the peeled kaolin to 95-110℃, spray in molten stearic acid, mix for 5-8 min, add an organic nucleating agent, mix for 8-12 min, cool to 55-65℃, add maleic anhydride-grafted polyethylene micro powder, heat to 140-150℃, mix for 6-10 min, cool, discharge, and sieve to obtain the functional material; S2. Mix the functional material obtained in S1, maleic anhydride-grafted polyethylene, and film-grade high-density polyethylene, then melt-blend and granulate to obtain a barrier masterbatch with a functional material mass fraction of 25%-40%; S3. Mix the barrier masterbatch obtained in S2 with metallocene linear low-density polyethylene, film-grade high-density polyethylene, ethylene-octene copolymer, organic nucleating agent, and antioxidant, melt-blend and granulate under the conditions of melt temperature 185-200℃, main machine speed 100-130 r / min, and average residence time 60-100 s to obtain the composite material.

9. The preparation method according to claim 8, characterized in that, The melt temperature of S2 in the molten composite is 195~215℃, and the specific energy input is 0.14~0.17kWh / kg.

10. The preparation method according to claim 8, characterized in that, S3 is followed by a step of blow molding the resulting composite material at 180-195°C, a blow-up ratio of 2.5-3, and a draw ratio of 8-12.