Polyethylene blown film with ultralow sealing temperature and high toughness

Abstract

The invention discloses a polyethylene blown film with ultralow initial sealing temperature and high toughness, and relates to the technical field of polyethylene films. The film comprises a composite layer, a middle layer and a heat sealing layer which are arranged in sequence. Wherein the composite layer and the middle layer are made of linear low-density polyethylene; the heat sealing layer is prepared from the following raw materials in parts by mass: 50 to 70 parts of ethylene-vinyl acetate copolymer, 30 to 50 parts of metallocene polyethylene, 5 to 10 parts of low-density polyethylene, 1 to 3 parts of open master batch, 1 to 3 parts of smooth master batch, 3 to 5 parts of modified cellulose whisker and 2 to 3 parts of maleic anhydride grafted polyethylene; the opening master batch is prepared from metallocene low-density polyethylene, an ethylene-vinyl acetate copolymer, maleic anhydride grafted polyethylene, modified nano silicon dioxide and an antioxidant. The modified cellulose whisker, the opening master batch and other components are introduced, so that the low temperature resistance of the film is effectively improved while the film has ultra-low initial sealing temperature. Therefore, the method has a wider application prospect.

Description

Technical Field

[0001] This invention relates to the field of polyethylene film technology, and specifically to a high-toughness polyethylene blown film with ultra-low sealing temperature. Background Technology

[0002] Polyethylene film, a thermoplastic, is widely used in the packaging industry due to its high tensile strength, lightweight, non-toxic and odorless properties, and ability to prevent product leakage or damage. With the rapid development of the flexible packaging industry, the quality requirements for packaging materials are constantly increasing, and traditional polyethylene and PP films can no longer meet the needs of specialized customers.

[0003] However, in practical applications, polyethylene blown films still have several performance shortcomings: First, their low-temperature toughness is insufficient. At low temperatures, the molecular chain mobility of conventional polyethylene blown films decreases, leading to a sharp decline in toughness and making them prone to brittleness and cracking, failing to meet the packaging requirements of cold chain transportation and low-temperature storage. Second, their heat-sealing performance is poor. Existing films have relatively high initial sealing temperatures and narrow heat-sealing windows, increasing energy consumption and easily causing problems such as incomplete sealing, leaks, or over-sealing leading to film damage, affecting packaging airtightness. Therefore, the low-temperature resistance of existing polyethylene blown films still needs improvement, and the initial sealing temperature needs to be reduced. Summary of the Invention

[0004] The purpose of this invention is to provide a polyethylene blown film with ultra-low sealing temperature and high toughness, thereby solving the following technical problems: Existing polyethylene blown films still suffer from poor low-temperature resistance and relatively high initial sealing temperature.

[0005] The objective of this invention can be achieved through the following technical solutions: A high-toughness polyethylene blown film with ultra-low sealing temperature includes a composite layer, an intermediate layer, and a heat-sealing layer arranged sequentially. The composite layer and the intermediate layer are made of linear low-density polyethylene; The heat-sealing layer comprises the following raw materials in parts by weight: 50-70 parts of ethylene-vinyl acetate copolymer, 30-50 parts of metallocene polyethylene, 5-10 parts of low-density polyethylene, 1-3 parts of open-cell masterbatch, 1-3 parts of slip masterbatch, 3-5 parts of modified cellulose whiskers, and 2-3 parts of maleic anhydride-grafted polyethylene. The open-cell masterbatch is made of metallocene low-density polyethylene, ethylene-vinyl acetate copolymer, maleic anhydride grafted polyethylene, modified nano-silica, antioxidant 1010, and antioxidant 168. The modified nano-silica is nano-silica that has been first coated with polycaprolactone and then grafted with silane coupling agent KH-550. The slip masterbatch is made of low-density polyethylene and erucamide; The modified cellulose whiskers are nano-cellulose whiskers that are first compounded with β-cyclodextrin and then cross-linked with epichlorohydrin.

[0006] Preferably, the preparation method of the open-face masterbatch is as follows: A1: Add deionized water and silane coupling agent KH-550 to anhydrous ethanol and stir for 20-30 minutes to obtain a diluted coupling agent solution; A2: Add 60℃ polycaprolactone to 60℃ nano silica and stir for 10-20 min. Then, while stirring, add the coupling agent dilution and stir for 15-20 min. Then, dry at 60-80℃ for 1-2 h to obtain modified nano silica. A3: Ethylene-vinyl acetate copolymer, maleic anhydride-grafted polyethylene, modified nano-silica, antioxidant 1010, and antioxidant 168 are added to metallocene low-density polyethylene and mixed evenly. Then, the mixture is melt-extruded, cooled with water, and pelletized to obtain open-face masterbatch.

[0007] Preferably, the mass ratio of anhydrous ethanol, deionized water, and silane coupling agent KH-550 in A1 is 5-6:1-2:1-1.5; The mass ratio of nano-silica, polycaprolactone, and coupling agent diluent in A2 is 15-20:3-5:7-9.

[0008] Preferably, the mass ratio of the metallocene low-density polyethylene, ethylene-vinyl acetate copolymer, maleic anhydride grafted polyethylene, modified nano-silica, antioxidant 1010, and antioxidant 168 in A3 is 45-55: 20-25: 2-3: 10-20: 0.2-0.3: 0.1-0.2; The twin-screw extruder used in the melt extrusion process described in A3 has a length-to-diameter ratio of 40:1, a zone 1 temperature of 120-125℃, a zone 2 temperature of 135-145℃, a zone 3 temperature of 150-155℃, a zone 4 temperature of 155-160℃, a die head temperature of 150-155℃, a screw speed of 300 r / min, and a feeding rate of 20 kg / h.

[0009] Preferably, the preparation method of the slip masterbatch is as follows: Erucamide is added to low-density polyethylene and melt-extruded, then cooled with water and pelletized to obtain a smooth masterbatch.

[0010] Preferably, the mass ratio of the low-density polyethylene to erucamide is 8-9:0.5-1; During the melt extrusion process, the twin-screw extruder has an aspect ratio of 40:1, a zone 1 temperature of 120-125℃, a zone 2 temperature of 135-145℃, a zone 3 temperature of 150-155℃, a zone 4 temperature of 155-160℃, a die head temperature of 150-155℃, a screw speed of 300 r / min, and a feeding rate of 20 kg / h.

[0011] Preferably, the modified cellulose whiskers are prepared by the following method: Nanocellulose whiskers were added to deionized water and ultrasonically dispersed. Then, β-cyclodextrin was added and stirred at 60°C for 30-40 min. Epichlorohydrin was then added dropwise and the pH was adjusted to 10-11. The mixture was then reacted at 65°C under a nitrogen atmosphere for 6-7 h. After cooling, the mixture was purified by dialyzing and finally freeze-dried to obtain modified cellulose whiskers.

[0012] Preferably, the mass ratio of deionized water, nanocellulose whiskers, β-cyclodextrin, and epichlorohydrin is 98-100:2:0.5-1:0.1-0.2.

[0013] Preferably, the preparation method of the ultra-low sealing temperature and high toughness polyethylene blown film is as follows: S1: Mix ethylene-vinyl acetate copolymer, metallocene polyethylene, low-density polyethylene, open-face masterbatch, slip masterbatch, modified cellulose whiskers, and maleic anhydride grafted polyethylene evenly at 45-50℃ to obtain heat-sealing layer mixture. S2: Mix linear low-density polyethylene XP7052ML, linear low-density polyethylene DOWLEX2045, and antistatic agent evenly at 45-50℃ to obtain a composite layer and intermediate layer mixture. S3: The composite layer mixture, intermediate layer mixture, and heat-sealing layer mixture are blown into film using a three-layer co-extrusion rotary blown film machine. After that, the composite layer is corona treated to obtain a polyethylene blown film with ultra-low sealing temperature and high toughness.

[0014] Preferably, the mass ratio of linear low-density polyethylene XP7052ML, linear low-density polyethylene DOWLEX2045, and antistatic agent in S2 is 60-80:20-40:0.5-1; In the blown film processing described in S3, the screw length-to-diameter ratio of the three-layer co-extrusion rotary blown film machine is 38:1, the screw speed of the composite layer and intermediate layer is 50-60 r / min, the screw speed of the heat-sealing layer is 45-55 r / min, the screw temperature of the composite layer and intermediate layer is 140-150℃ in zone 1, 155-160℃ in zone 2, and 165-170℃ in zones 3 and 4, the screw temperature of the heat-sealing layer is 130-135℃ in zone 1, 140-145℃ in zone 2, and 150-155℃ in zones 3 and 4, the die head temperature is 155-165℃, the blow-up ratio is 1.8-2.2, the traction speed is 8-12 m / min, the traction roller temperature is 30-40℃, and the winding tension is 50-80 N. In the ultra-low sealing temperature and high toughness polyethylene blown film described in S3, the thickness ratio of the composite layer, intermediate layer, and heat-sealing layer is 1:1:1.

[0015] The beneficial effects of this invention are: This invention provides a polyethylene blown film with ultra-low sealing temperature and high toughness. The invention achieves ultra-low sealing temperature while effectively improving the tensile strength, elongation at break and low temperature resistance of the polyethylene blown film through the following method.

[0016] (1) The modified cellulose whiskers of this invention can form a rigid support network in the heat-sealing layer, which can disperse external forces through stress transmission and avoid local stress concentration leading to fracture. The grafting of β-cyclodextrin and crosslinking with epichlorohydrin can give the whiskers good interfacial compatibility. In conjunction with the compatibility of maleic anhydride grafted polyethylene, the whiskers can be tightly bonded to the resin molecular chains such as ethylene-vinyl acetate copolymer and metallocene polyethylene, reducing interfacial defects and improving the energy absorption capacity during stretching. The rigid structure of nanocellulose whiskers can prevent the cold crystallization and aggregation of resin molecular chains at low temperature, maintain some mobility of molecular chains, and reduce the tendency of brittle fracture. The hydrophobic cavity and flexible segments of β-cyclodextrin can play a molecular buffering role at low temperature, alleviate the rigidity enhancement of resin molecular chains caused by low temperature curing, and improve the interfacial bonding stability at low temperature.

[0017] (2) The modified nano-silica of this invention can form stable chemical bonds with resins such as polyethylene and ethylene-vinyl acetate copolymer, thereby improving interfacial compatibility. The filler can be uniformly dispersed in the matrix to bear stress, avoiding stress concentration and strength reduction, and improving tensile strength. As a stress dispersion point, the modified nano-silica can prevent the generation and propagation of microcracks at low temperatures. At the same time, polycaprolactone itself has excellent low-temperature resistance, which can enhance the flexibility of the system at low temperatures and improve low-temperature resistance.

[0018] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. The embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the following information pertains to some of the raw materials used in the following embodiments and comparative examples of this invention: The linear low-density polyethylene XP7052ML is ExxonMobil's Exceed XP7052ML, with a melt index of 0.5 g / 10 min; the linear low-density polyethylene DOWLEX2045 is Dow Chemical's DOWLEX2045, with a melt index of 1.0 g / 10 min; the ethylene-vinyl acetate copolymer is DuPont's Appeel 53009, with a melt index of 5.5 g / 10 min; the metallocene polyethylene is Dow's AFFINITY PL 1881G; the antistatic agent was purchased from Wuhan Jiyesheng Chemical Co., Ltd., item number: A00297.

[0021] Example 1: A method for preparing a polyethylene blown film with ultra-low sealing temperature and high toughness is as follows: S1: Add 2g of nanocellulose whiskers (diameter 10-20nm, length 200-500nm) to 98g of deionized water and sonicate for 30min. Then add 0.5g of β-cyclodextrin and stir at 60℃ for 30min. Then add 0.1g of epichlorohydrin dropwise at 0.05g / min and adjust the pH to 10. Then react at 65℃ under nitrogen atmosphere for 6h. After cooling to room temperature, dialyze to purify (molecular weight cutoff 8000) to neutral. Finally freeze-dry to obtain modified cellulose whiskers. S2: Add 1g of deionized water and 1g of silane coupling agent KH-550 to 5g of anhydrous ethanol and stir for 20min to obtain a diluted coupling agent solution; S3: Add 3g of polycaprolactone at 60℃ to 15g of nano silica at 60℃ and stir for 10min. Then, while stirring, add 7g of coupling agent dilution and stir for 15min. Then dry at 80℃ for 1h to obtain modified nano silica. S4: Add 20g of ethylene-vinyl acetate copolymer, 2g of maleic anhydride grafted polyethylene, 10g of modified nano-silica, 0.2g of antioxidant 1010, and 0.1g of antioxidant 168 to 45g of metallocene low-density polyethylene. Mix at 400r / min for 5-7min at 40℃, then mix at 1000r / min for 15min. Then melt extrude the mixture using a twin-screw extruder with a length-to-diameter ratio of 40:1 at zone 1 temperature of 120℃, zone 2 temperature of 135℃, zone 3 temperature of 150℃, zone 4 temperature of 155℃, die head temperature of 150℃, screw speed of 300r / min, and feed rate of 20kg / h. After water cooling and pelletizing, open-face masterbatch is obtained. S5: Add 0.5g of erucamide to 8g of low-density polyethylene and melt extrude it using a twin-screw extruder with a length-to-diameter ratio of 40:1. The temperature of the first zone is 120℃, the temperature of the second zone is 135℃, the temperature of the third zone is 150℃, the temperature of the fourth zone is 155℃, the die head temperature is 150℃, the screw speed is 300r / min, and the feeding rate is 20kg / h. After water cooling and pelletizing, smooth masterbatch is obtained. S6: Mix 50g of ethylene-vinyl acetate copolymer, 30g of metallocene polyethylene, 5g of low-density polyethylene, 1g of open-face masterbatch, 1g of slip masterbatch, 3g of modified cellulose whiskers, and 2g of maleic anhydride-grafted polyethylene at 45°C and 600r / min for 30min to obtain a heat-sealing layer mixture. S7: Mix 60g of linear low-density polyethylene XP7052ML, 20g of linear low-density polyethylene DOWLEX2045, and 0.5g of antistatic agent at 45-50℃ and 600r / min for 30min to obtain a composite layer and intermediate layer mixture. S8: The composite layer mixture, intermediate layer mixture, and heat-sealing layer mixture are blown into shape using a three-layer co-extrusion rotary blown film extruder with a screw length-to-diameter ratio of 38:1. The screw speed for the composite layer and intermediate layer is 50 r / min, the screw speed for the heat-sealing layer is 45 r / min, the die temperature is 155℃, the blow-up ratio is 1.8, the traction speed is 8 m / min, the traction roller temperature is 30℃, and the winding tension is 50 N. Afterward, the composite layer undergoes corona treatment to obtain a high-toughness polyethylene blown film with an ultra-low sealing temperature. Specifically, the screw temperatures for the composite layer and intermediate layer are 140℃ in zone 1, 155℃ in zone 2, and 165℃ in zones 3 and 4; the screw temperatures for the heat-sealing layer are 130℃ in zone 1, 140℃ in zone 2, and 150℃ in zones 3 and 4; the thickness ratio of the composite layer, intermediate layer, and heat-sealing layer is 1:1:1; and the surface tension of the composite layer is 38 dynes.

[0022] Example 2: A method for preparing a polyethylene blown film with ultra-low sealing temperature and high toughness is as follows: S1: Add 2g of nanocellulose whiskers (diameter 10-20nm, length 200-500nm) to 99g of deionized water and sonicate for 30min. Then add 0.8g of β-cyclodextrin and stir at 60℃ for 35min. Then add 0.15g of epichlorohydrin dropwise at 0.08g / min and adjust the pH to 10.5. React at 65℃ under a nitrogen atmosphere for 6.5h. After cooling to room temperature, dialyze to purify (molecular weight cutoff 8000) to neutral. Finally, freeze dry to obtain modified cellulose whiskers. S2: Add 1.5g of deionized water and 1.3g of silane coupling agent KH-550 to 5.5g of anhydrous ethanol and stir for 25min to obtain a diluted coupling agent solution; S3: Add 4g of polycaprolactone at 60℃ to 18g of nano silica at 60℃ and stir for 15min. Then, while stirring, add 8g of coupling agent dilution and stir for 18min. Then dry at 70℃ for 1.5h to obtain modified nano silica. S4: Add 23g of ethylene-vinyl acetate copolymer, 2.5g of maleic anhydride grafted polyethylene, 15g of modified nano-silica, 0.25g of antioxidant 1010, and 0.15g of antioxidant 168 to 50g of metallocene low-density polyethylene. Mix at 400r / min for 6min at 45℃, then mix at 1000r / min for 18min. Then melt extrude the mixture using a twin-screw extruder with a length-to-diameter ratio of 40:1. The temperature of the first zone is 123℃, the second zone is 140℃, the third zone is 153℃, the fourth zone is 158℃, the die head temperature is 153℃, the screw speed is 300r / min, and the feeding rate is 20kg / h. After water cooling and pelletizing, open-face masterbatch is obtained. S5: Add 0.8g of erucamide to 8.5g of low-density polyethylene and melt extrude it using a twin-screw extruder with a length-to-diameter ratio of 40:1. The temperature of zone 1 is 123℃, zone 2 is 138℃, zone 3 is 153℃, zone 4 is 158℃, the die head temperature is 153℃, the screw speed is 300r / min, and the feeding rate is 20kg / h. After water cooling and pelletizing, smooth masterbatch is obtained. S6: Mix 60g of ethylene-vinyl acetate copolymer, 40g of metallocene polyethylene, 8g of low-density polyethylene, 2g of open-face masterbatch, 2g of slip masterbatch, 4g of modified cellulose whiskers, and 2.5g of maleic anhydride-grafted polyethylene at 48°C and 800r / min for 25min to obtain a heat-sealing layer mixture. S7: Mix 70g of linear low-density polyethylene XP7052ML, 30g of linear low-density polyethylene DOWLEX2045, and 0.8g of antistatic agent at 48℃ and 8000r / min for 20-30min to obtain a composite layer and intermediate layer mixture. S8: The composite layer mixture, intermediate layer mixture, and heat-sealing layer mixture are blown into shape using a three-layer co-extrusion rotary blown film extruder with a screw length-to-diameter ratio of 38:1. The screw speed for the composite layer and intermediate layer is 55 r / min, the screw speed for the heat-sealing layer is 48 r / min, the die temperature is 160℃, the blow-up ratio is 2, the traction speed is 10 m / min, the traction roller temperature is 35℃, and the winding tension is 65 N. Afterward, the composite layer is corona treated to obtain a high-toughness polyethylene blown film with an ultra-low sealing temperature. Specifically, the screw temperatures for the composite layer and intermediate layer are 145℃ in zone 1, 158℃ in zone 2, and 168℃ in zones 3 and 4; the screw temperatures for the heat-sealing layer are 133℃ in zone 1, 143℃ in zone 2, and 153℃ in zones 3 and 4; the thickness ratio of the composite layer, intermediate layer, and heat-sealing layer is 1:1:1; and the surface tension of the composite layer is 40 dynes.

[0023] Example 3: A method for preparing a polyethylene blown film with ultra-low sealing temperature and high toughness is as follows: S1: Add 2g of nanocellulose whiskers (diameter 10-20nm, length 200-500nm) to 100g of deionized water and sonicate for 30min. Then add 1g of β-cyclodextrin and stir at 60℃ for 40min. Then add 0.2g of epichlorohydrin dropwise at 0.1g / min and adjust the pH to 11. React at 65℃ under nitrogen atmosphere for 7h. After cooling to room temperature, dialyze to purify (molecular weight cutoff 8000) to neutral. Finally freeze-dry to obtain modified cellulose whiskers. S2: Add 2g of deionized water and 1.5g of silane coupling agent KH-550 to 6g of anhydrous ethanol and stir for 30min to obtain a diluted coupling agent solution; S3: Add 5g of polycaprolactone at 60℃ to 20g of nano silica at 60℃ and stir for 20min. Then, while stirring, add 9g of coupling agent dilution and stir for 20min. Then dry at 60℃ for 2h to obtain modified nano silica. S4: Add 25g of ethylene-vinyl acetate copolymer, 3g of maleic anhydride grafted polyethylene, 20g of modified nano-silica, 0.3g of antioxidant 1010, and 0.2g of antioxidant 168 to 55g of metallocene low-density polyethylene. Mix at 400r / min for 5-7min at 50℃, then mix at 1000r / min for 20min. Then melt extrude the mixture using a twin-screw extruder with a length-to-diameter ratio of 40:1. The temperature of the first zone is 125℃, the second zone is 145℃, the third zone is 155℃, the fourth zone is 160℃, the die head temperature is 155℃, the screw speed is 300r / min, and the feeding rate is 20kg / h. After water cooling and pelletizing, open-face masterbatch is obtained. S5: Add 1g of erucamide to 9g of low-density polyethylene and melt extrude it using a twin-screw extruder with a length-to-diameter ratio of 40:1. The temperature of the first zone is 125℃, the temperature of the second zone is 145℃, the temperature of the third zone is 155℃, the temperature of the fourth zone is 160℃, the die head temperature is 155℃, the screw speed is 300r / min, and the feeding rate is 20kg / h. After water cooling and pelletizing, smooth masterbatch is obtained. S6: Mix 70g of ethylene-vinyl acetate copolymer, 50g of metallocene polyethylene, 10g of low-density polyethylene, 3g of open-face masterbatch, 3g of slip masterbatch, 5g of modified cellulose whiskers, and 3g of maleic anhydride-grafted polyethylene at 50°C and 1000r / min for 20min to obtain a heat-sealing layer mixture. S7: Mix 80g of linear low-density polyethylene XP7052ML, 40g of linear low-density polyethylene DOWLEX2045 and 1g of antistatic agent at 50℃ and 1000r / min for 20min to obtain a composite layer and intermediate layer mixture. S8: The composite layer mixture, intermediate layer mixture, and heat-sealing layer mixture are blown into a film using a three-layer co-extrusion rotary blown film machine with a screw length-to-diameter ratio of 38:1. The screw speed for the composite layer and intermediate layer is 60 r / min, the screw speed for the heat-sealing layer is 55 r / min, the die temperature is 165℃, the blow-up ratio is 2.2, the traction speed is 12 m / min, the traction roller temperature is 30-40℃, and the winding tension is 80 N. After that, the composite layer is corona treated to obtain a 60 μm thick polyethylene blown film with ultra-low sealing temperature and high toughness. The screw temperatures for the composite layer and intermediate layer are 150℃ in zone 1, 160℃ in zone 2, and 170℃ in zones 3 and 4; the screw temperatures for the heat-sealing layer are 135℃ in zone 1, 145℃ in zone 2, and 155℃ in zones 3 and 4; the thickness ratio of the composite layer, intermediate layer, and heat-sealing layer is 1:1:1; and the surface tension of the composite layer is 42 dynes.

[0024] Comparative Example 1: Compared with Example 1, this comparative example only replaces the "modified cellulose whiskers" added in the preparation process of S6 with "nanocellulose whiskers (diameter of 10-20nm, length of 200-500nm)". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a polyethylene blown film with ultra-low sealing temperature and high toughness is obtained.

[0025] Comparative Example 2: Compared with Example 1, this comparative example only did not add "modified cellulose whiskers" in the preparation process of S6. All other steps and parameters were the same, and will not be repeated here. Finally, a polyethylene blown film with ultra-low sealing temperature and high toughness was obtained.

[0026] Comparative Example 3: Compared with Example 1, this comparative example only replaces the "modified nano silica" added in the preparation process of S4 with "nano silica". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, a polyethylene blown film with ultra-low sealing temperature and high toughness is obtained.

[0027] Performance testing: Determination of tensile strength: Referring to GB / T 1040.3-2006 standard, the longitudinal and transverse average tensile strengths (MPa) of the ultra-low sealing temperature and high toughness polyethylene blown films prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were determined at a tensile rate of 2 mm / min. The test results are shown in Table 1. Determination of elongation at break: Referring to GB / T 1040.3-2006 standard, the longitudinal and transverse average elongation at break (%) of the ultra-low sealing temperature and high toughness polyethylene blown films prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were determined at a tensile rate of 2 mm / min. The test results are shown in Table 1. Determination of heat seal strength: Referring to the QB / T 2358-1998 standard, the sealing temperature and sealing temperature (°C) of the ultra-low sealing temperature and high toughness polyethylene blown films prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were determined, and the test results are shown in Table 1. Determination of low temperature resistance: Referring to GB / T 1040.3-2006 standard, the elongation at break retention (%) of the ultra-low sealing temperature and high toughness polyethylene blown films prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention at a tensile rate of 2 mm / min was determined at -20℃. The test results are shown in Table 1. Table 1: Performance test results of Examples 1-3 and Comparative Examples 1-3

[0028] Data Analysis: As can be seen from Table 1, the polyethylene blown film with ultra-low sealing temperature and high toughness prepared in the embodiments of the present invention has excellent tensile strength, elongation at break, low temperature resistance and ultra-low sealing temperature.

[0029] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A polyethylene blown film with ultra-low sealing temperature and high toughness, characterized in that, It includes a composite layer, an intermediate layer, and a heat-sealing layer arranged sequentially; The composite layer and the intermediate layer are made of linear low-density polyethylene; The heat-sealing layer comprises the following raw materials in parts by weight: 50-70 parts of ethylene-vinyl acetate copolymer, 30-50 parts of metallocene polyethylene, 5-10 parts of low-density polyethylene, 1-3 parts of open-cell masterbatch, 1-3 parts of slip masterbatch, 3-5 parts of modified cellulose whiskers, and 2-3 parts of maleic anhydride-grafted polyethylene. The open-cell masterbatch is made of metallocene low-density polyethylene, ethylene-vinyl acetate copolymer, maleic anhydride grafted polyethylene, modified nano-silica, antioxidant 1010, and antioxidant 168. The modified nano silica is nano silica that has been first coated with polycaprolactone and then grafted with silane coupling agent KH-550. The slip masterbatch is made of low-density polyethylene and erucamide; The modified cellulose whiskers are nano-cellulose whiskers that are first compounded with β-cyclodextrin and then crosslinked with epichlorohydrin.

2. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 1, characterized in that, The preparation method of the open-face masterbatch is as follows: A1: Add deionized water and silane coupling agent KH-550 to anhydrous ethanol and stir for 20-30 minutes to obtain a diluted coupling agent solution; A2: Add 60℃ polycaprolactone to 60℃ nano silica and stir for 10-20 min. Then, while stirring, add the coupling agent dilution and stir for 15-20 min. Then, dry at 60-80℃ for 1-2 h to obtain modified nano silica. A3: Ethylene-vinyl acetate copolymer, maleic anhydride-grafted polyethylene, modified nano-silica, antioxidant 1010, and antioxidant 168 are added to metallocene low-density polyethylene and mixed evenly. Then, the mixture is melt-extruded, cooled with water, and pelletized to obtain open-face masterbatch.

3. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 2, characterized in that, The mass ratio of anhydrous ethanol, deionized water, and silane coupling agent KH-550 in A1 is 5-6:1-2:1-1.5; The mass ratio of nano-silica, polycaprolactone, and coupling agent diluent in A2 is 15-20:3-5:7-9.

4. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 2, characterized in that, The mass ratio of metallocene low-density polyethylene, ethylene-vinyl acetate copolymer, maleic anhydride grafted polyethylene, modified nano-silica, antioxidant 1010, and antioxidant 168 in A3 is 45-55: 20-25: 2-3: 10-20: 0.2-0.3: 0.1-0.

2. The twin-screw extruder used in the melt extrusion process described in A3 has a length-to-diameter ratio of 40:1, a zone 1 temperature of 120-125℃, a zone 2 temperature of 135-145℃, a zone 3 temperature of 150-155℃, a zone 4 temperature of 155-160℃, a die head temperature of 150-155℃, a screw speed of 300 r / min, and a feeding rate of 20 kg / h.

5. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 1, characterized in that, The preparation method of the slip masterbatch is as follows: Erucamide is added to low-density polyethylene and melt-extruded, then cooled with water and pelletized to obtain a smooth masterbatch.

6. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 5, characterized in that, The mass ratio of the low-density polyethylene to erucamide is 8-9:0.5-1; During the melt extrusion process, the twin-screw extruder has an aspect ratio of 40:1, a zone 1 temperature of 120-125℃, a zone 2 temperature of 135-145℃, a zone 3 temperature of 150-155℃, a zone 4 temperature of 155-160℃, a die head temperature of 150-155℃, a screw speed of 300 r / min, and a feeding rate of 20 kg / h.

7. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 1, characterized in that, The method for preparing the modified cellulose whiskers is as follows: Nanocellulose whiskers were added to deionized water and ultrasonically dispersed. Then, β-cyclodextrin was added and stirred at 60°C for 30-40 min. Epichlorohydrin was then added dropwise and the pH was adjusted to 10-11. The mixture was then reacted at 65°C under a nitrogen atmosphere for 6-7 h. After cooling, the mixture was purified by dialyzing and finally freeze-dried to obtain modified cellulose whiskers.

8. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 7, characterized in that, The mass ratio of deionized water, nanocellulose whiskers, β-cyclodextrin, and epichlorohydrin is 98-100:2:0.5-1:0.1-0.

2.

9. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 1, characterized in that, The preparation method of the ultra-low sealing temperature and high toughness polyethylene blown film is as follows: S1: Mix ethylene-vinyl acetate copolymer, metallocene polyethylene, low-density polyethylene, open-face masterbatch, slip masterbatch, modified cellulose whiskers, and maleic anhydride grafted polyethylene evenly at 45-50℃ to obtain heat-sealing layer mixture. S2: Mix linear low-density polyethylene XP7052ML, linear low-density polyethylene DOWLEX2045, and antistatic agent evenly at 45-50℃ to obtain a composite layer and intermediate layer mixture. S3: The composite layer mixture, intermediate layer mixture, and heat-sealing layer mixture are blown into film using a three-layer co-extrusion rotary blown film machine. After that, the composite layer is corona treated to obtain a polyethylene blown film with ultra-low sealing temperature and high toughness.

10. The ultra-low sealing temperature and high toughness polyethylene blown film according to claim 9, characterized in that, The mass ratio of linear low-density polyethylene XP7052ML, linear low-density polyethylene DOWLEX2045, and antistatic agent in S2 is 60-80:20-40:0.5-1; In the blown film processing described in S3, the screw length-to-diameter ratio of the three-layer co-extrusion rotary blown film machine is 38:1, the screw speed of the composite layer and intermediate layer is 50-60 r / min, the screw speed of the heat-sealing layer is 45-55 r / min, the screw temperature of the composite layer and intermediate layer is 140-150℃ in zone 1, 155-160℃ in zone 2, and 165-170℃ in zones 3 and 4, the screw temperature of the heat-sealing layer is 130-135℃ in zone 1, 140-145℃ in zone 2, and 150-155℃ in zones 3 and 4, the die head temperature is 155-165℃, the blow-up ratio is 1.8-2.2, the traction speed is 8-12 m / min, the traction roller temperature is 30-40℃, and the winding tension is 50-80 N. In the ultra-low sealing temperature and high toughness polyethylene blown film described in S3, the thickness ratio of the composite layer, intermediate layer, and heat-sealing layer is 1:1:1.

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