Heat-resistant polyethylene composite packaging film and preparation method thereof

Abstract

The invention relates to the technical field of packaging films, and particularly discloses a heat-resistant polyethylene composite packaging film and a preparation method thereof.The polyethylene composite packaging film comprises an inner layer, a middle layer and an outer layer, the inner layer is prepared from, by mass, 100 parts of linear low-density polyethylene, 28-32 parts of polypropylene and 8-10 parts of hydrotalcite modified blending materials, the middle layer comprises the following raw materials in parts by weight: 100 parts of low-density polyethylene, 40-60 parts of linear low-density polyethylene, 3-5 parts of a coupling agent and 0.5-1 part of an antioxidant, the outer layer comprises the following raw materials in parts by weight: 100 parts of modified PA6, 20-30 parts of metallocene polyethylene and 5-8 parts of a compatilizer, functional gradient distribution is realized by adopting layered extrusion of three-layer co-extrusion, and PA6 and polypropylene have a synergistic effect, so that the composite film has excellent heat resistance, and the service life of the composite film is prolonged. The hydrotalcite and the graphene oxide have a synergistic effect, the layered structure effectively obstructs oxygen and water vapor, and the obtained polyethylene composite packaging film is good in barrier property and has excellent mechanical property and heat resistance.

Description

Technical Field

[0001] The invention relates to the technical field of packaging films, in particular to a heat-resistant polyethylene composite packaging film and a preparation method thereof. Background Art

[0002] Polyethylene resin (PE) is a thermoplastic with abundant resources, low price, safety and non-toxicity, and excellent chemical stability and processability. Among them, polyethylene film made of polyethylene resin as the main raw material occupies an important position in the packaging industry, especially in the fields of food packaging, pharmaceutical packaging, and flexible packaging of industrial products. Polyethylene film has excellent toughness and moisture resistance, but ordinary polyethylene film has poor heat resistance and is prone to softening, deformation, or even melting under high temperature conditions, which not only greatly reduces the performance of the packaging material, but also may contaminate the packaged items. With the continuous advancement of modern food processing technology, high-temperature sterilization is widely used, and the demand for high-temperature packaging in the field of industrial packaging is also increasing. The disadvantages of poor heat resistance of traditional polyethylene film are gradually exposed, which to a certain extent limits the application scope of polyethylene film.

[0003] Chinese patent application CN111333991A discloses a high temperature resistant composite packaging film, which is made of the following raw materials in parts by weight: 50-60 parts of modified polyethylene resin, 6-8 parts of modified talc, and 1.5-2 parts of liquid paraffin. The modified polyethylene resin is used as the packaging film matrix, and heat-resistant filler talc is added to modify the talc, which reduces the agglomeration of talc and has excellent heat resistance. The components of the packaging film are not easy to precipitate under high temperature conditions. However, in the preparation process of the modified polyethylene resin in the packaging film, cobalt source irradiation is used, and the preparation cost is high, which limits its application. Chinese patent application CN110330717A discloses a high temperature resistant PE film modified by organic-inorganic hybrid materials and a preparation method thereof, wherein the high temperature resistant PE film is composed of the following components in mass ratio: 10-15 parts of modified plant cellulose, 4-6 parts of porous organic-inorganic hybrid materials, 1-3 parts of natural antioxidants, 1-3 parts of natural antibacterial agents, 70-80 parts of polyethylene matrix, and 3-5 parts of acrylic acid. The PE film has high safety and excellent antibacterial efficacy. However, under high temperature conditions, the natural antioxidants and natural antibacterial agents in the PE film are easily decomposed or oxidized, and precipitated from the PE film, affecting the mechanical properties of the PE film, and the compatibility between the raw materials is general, and problems such as stratification and cracking occur during processing and use, affecting the service life.

[0004] Therefore, there is an urgent need to develop a low-cost, heat-resistant polyethylene composite packaging film with excellent mechanical properties to overcome the shortcomings of traditional polyethylene films in high temperature environments and meet the market demand for high-performance packaging materials.

[0005] ‌ Summary of the invention 1. Technical issues to be resolved In view of the deficiencies in the prior art, the present invention provides a heat-resistant polyethylene composite packaging film and a preparation method thereof, which solves the problems of poor heat resistance and general mechanical properties of the polyethylene packaging film.

[0006] (II) Technical solution In order to achieve the above-mentioned object, the present invention discloses a heat-resistant polyethylene composite packaging film, comprising an inner layer, a middle layer, and an outer layer; The raw materials of the inner layer include, by weight: 100 parts of linear low-density polyethylene, 28-32 parts of polypropylene, and 8-10 parts of hydrotalcite-modified blend; The raw materials of the middle layer include, by weight: 100 parts of low-density polyethylene, 40-60 parts of linear low-density polyethylene, 3-5 parts of coupling agent, and 0.5-1 part of antioxidant; Calculated by weight, the raw materials of the outer layer include: 100 parts of modified PA6, 20-30 parts of metallocene polyethylene, and 5-8 parts of compatibilizer.

[0007] Preferably, the preparation method of the hydrotalcite-modified blend comprises the following steps: S1. Ultrasonic dispersion of hydrotalcite in a mixed solvent. After uniform dispersion, use glacial acetic acid to adjust the pH to 4, stir and mix, dropwise add γ-methacryloxypropyltrimethoxysilane, stir and react. After the reaction is completed, filter, wash with anhydrous ethanol and deionized water, and dry in a vacuum drying oven at 80° C. for 12 h to obtain olefinated hydrotalcite; S2. Evenly mix acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite and initiator, and after the acetone is volatilized, transfer to a twin-screw extruder for melt blending, extrusion and cooling to obtain a hydrotalcite-modified blend.

[0008] Preferably, the mass ratio of hydrotalcite, mixed solvent and γ-methacryloxypropyltrimethoxysilane in S1 is 100:3000-4000:12-25.

[0009] Preferably, the reaction temperature in S1 is 55-65° C., and the reaction time is 1-2 h.

[0010] Preferably, the mixed solvent in S1 is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 9:1.

[0011] Preferably, the mass ratio of acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite and initiator in S2 is 400-450:10-14:20-30:100:5-8:2-5.

[0012] Preferably, the temperature of melt blending in S2 is 195-220° C., and the time of melt blending is 8-12 min.

[0013] Preferably, the initiator in S2 is dicumyl peroxide.

[0014] Preferably, the preparation method of the modified PA6 comprises the following steps: Step (1), ultrasonically dispersing graphene oxide in N,N-dimethylformamide, after uniform dispersion, adding triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, heating, stirring and mixing, reacting, and after the reaction is completed, centrifuging at a rate of 6000 r / min for 8 min, washing with deionized water, and vacuum drying at 60° C. for 12 h to obtain amino-modified graphene oxide; Step (2), mixing the nanocellulose and deionized water evenly, adding sodium periodate, stirring and mixing, heating, reacting in the dark, adding ethylene glycol to terminate the reaction, and after the reaction is completed, filtering, washing with deionized water, and freeze-drying to obtain aldehyded cellulose; Step (3), vacuum drying PA6 in an oven at 90° C. for 12 h, stirring and mixing the dried PA6, amino-modified graphene oxide, and formaldehyde-modified cellulose, adding the mixture to a twin-screw extruder, melt blending, extruding, and cooling to obtain modified PA6.

[0015] Preferably, in step (1), the mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide and 4-dimethylaminopyridine is 100:9500-10500:400-500:42-50:4-5.

[0016] Preferably, the reaction temperature in step (1) is 55-65° C., and the reaction time is 10-15 h.

[0017] Preferably, in step (2), the mass ratio of nanocellulose, deionized water and sodium periodate is 100:6000-7000:120-150.

[0018] Preferably, the reaction temperature in step (2) is 45-50° C., and the reaction time is 18-20 h.

[0019] Preferably, in the step (3), the mass ratio of the dried PA6, amino-modified graphene oxide and formaldehyde-modified cellulose is 100:4-7:3-5, and the temperature in the twin-screw extruder is set at 210-240°C.

[0020] Preferably, the PA6 is a nylon 6 resin having a melt index of 8-12 g / 10 min (test conditions: 230° C. / 2.16 kg).

[0021] Preferably, the coupling agent is a silane coupling agent.

[0022] Furthermore, the silane coupling agent is preferably vinyltrimethoxysilane.

[0023] Preferably, the antioxidant consists of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0024] Preferably, the compatibilizer is maleic anhydride grafted POE.

[0025] A method for preparing a heat-resistant polyethylene composite packaging film comprises the following steps: Step 1: weigh the raw materials of the inner layer, the middle layer and the outer layer by mass, and perform batching, mixing and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively, process them into melts, transmit through pipelines, filter through filters, extrude into sheet-like fluids out through the three-layer co-extrusion composite die head, cool through chilled rollers, and then perform biaxial stretching. After the stretching is completed, pull, roll, and slit to obtain a heat-resistant polyethylene composite packaging film.

[0026] Preferably, in the step 2, the heating temperatures in the extruder barrel are 180-220°C for the inner layer, 160-200°C for the middle layer, and 240-280°C for the outer layer, and the temperature of the three-layer co-extrusion composite die is 210-240°C.

[0027] Preferably, in the step 2, during the biaxial stretching process, the transverse stretching ratio is 2-4 times, and the longitudinal stretching ratio is 1.5-3 times.

[0028] 3. Beneficial technical effects In the present invention, γ-methacryloxypropyl trimethoxysilane is used to modify hydrotalcite, and a carbon-carbon double bond is introduced on the surface of hydrotalcite to obtain olefinic hydrotalcite, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite, and initiator dicumyl peroxide are mixed, and dicumyl peroxide produces free radicals during decomposition, and under the action of dicumyl peroxide, polymerization occurs to obtain a hydrotalcite modified mixed material, which improves the compatibility of hydrotalcite with a polyolefin matrix, forms a chemical bond, enhances interfacial bonding, and inhibits hydrotalcite agglomeration. Graphene oxide is modified using triethylenetetramine, and amidation reaction occurs between the amino group on triethylenetetramine and the carboxyl group on the surface of graphene oxide under the action of dicyclohexylcarbodiimide and 4-dimethylaminopyridine to obtain amino graphene oxide. Nanocellulose is oxidatively modified using sodium periodate to obtain aldehyde-modified cellulose. The dried PA6, amino-modified graphene oxide and aldehyde-modified cellulose are mixed and melt-blended in a twin-screw extruder to obtain modified PA6.

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a three-layer co-extrusion and biaxial stretching process to prepare a polyethylene composite packaging film. The inner layer uses linear low-density polyethylene as the main body, and polypropylene and hydrotalcite modified blends are added. The linear molecular structure and short branching characteristics of linear low-density polyethylene give it excellent tensile and tear resistance, which can significantly improve the mechanical properties of the packaging film, and the density is good, which can also improve the barrier performance. The polypropylene molecular chain has high rigidity, high melting point, good heat resistance and chemical resistance, and excellent mechanical properties, which can improve the heat resistance of the inner layer and prevent the composite film from softening and deforming. At the same time, it can also improve the mechanical properties, puncture resistance and tear resistance of the polyethylene composite film. Hydrotalcite has a layered structure, which can effectively block water vapor and oxygen, improve the barrier performance and thermal stability of the composite film, and effectively reduce high-temperature thermal shrinkage. After hydrotalcite modification, agglomeration is avoided, and the toughness and mechanical properties of the polyolefin composition are comprehensively improved. The hydrotalcite modified blend can enhance the barrier property and thermal stability.

[0030] (2) The middle layer structure of the present invention uses low-density polyethylene as the main body. Low-density polyethylene has good softness and extensibility, good impact resistance, and excellent processing fluidity. As the middle layer matrix, it can balance the overall flexibility and strength. Low-density polyethylene is mixed with linear low-density polyethylene. Under the action of a coupling agent, it has excellent toughness, can play a role in structural support, promotes the interface bonding of polymers, improves the uniformity of the middle layer, reduces stress concentration, and increases the interlayer force. The resulting composite film has excellent mechanical properties and heat resistance.

[0031] (3) In the present invention, modified PA6 is used as the main body in the outer layer, wherein PA6 has a high melting point and excellent mechanical strength, and can improve the high temperature resistance and puncture resistance of the outer layer. Graphene oxide has excellent heat resistance and mechanical properties. After modification, it effectively avoids agglomeration and can be evenly dispersed in the PA6 matrix. Nanocellulose has an extremely low thermal expansion coefficient, which can reduce the thermal expansion rate of the composite film. By enhancing the interaction between molecular chains, it delays the softening and deformation of polyethylene at high temperatures. It is evenly dispersed in the matrix to form a reinforced skeleton, which significantly improves the tensile strength and elastic modulus of the composite film. At the same time, the cross-linked network structure can also absorb external stress and reduce the risk of film tearing. Furthermore, the dense structure of nanocellulose can effectively improve the barrier properties of the composite film. The amino groups on the amino graphene oxide in the modified PA6 and the amino groups on PA6 can react with the aldehyde groups on the aldehyde-modified cellulose to construct a three-dimensional network structure, avoid phase separation problems, have excellent compatibility, improve the mechanical properties and barrier properties of the composite film, and improve heat resistance. Metallocene polyethylene has the characteristics of high heat resistance, excellent mechanical properties and chemical stability, which can improve the toughness of the outer layer and effectively prevent brittle cracking. The compatibilizer maleic anhydride grafted POE has good compatibility with non-polar polyolefins, can promote the compatibility of PA6 and polyethylene, and evenly disperse, effectively avoiding stratification.

[0032] (4) In the present invention, functional gradient distribution is achieved through layered extrusion of three-layer co-extrusion, avoiding problems such as crystallization, cracking, uneven thickness or inability to form a film. Biaxial stretching can induce molecular chain orientation crystallization and improve mechanical properties and heat resistance. PA6 and PP work synergistically to make the composite film have excellent heat resistance and can withstand high temperature environments. Hydrotalcite and graphene oxide work synergistically, and the layered structure effectively blocks oxygen and water vapor, and as a filler, it can significantly improve the tensile strength and puncture resistance of the composite film. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Example 1

[0034] A method for preparing a heat-resistant polyethylene composite packaging film comprises the following steps: Step 1, weigh the raw materials of the inner layer, the middle layer, and the outer layer by mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 28 parts of polypropylene, and 8 parts of hydrotalcite modified blends, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 40 parts of linear low-density polyethylene, 3 parts of coupling agent vinyltrimethoxysilane, 0.5 parts of antioxidant, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the raw materials of the outer layer include: 100 parts of modified PA6, 20 parts of metallocene polyethylene, and 5 parts of compatibilizer maleic anhydride grafted POE, and perform batching, mixing, and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 180°C for the inner layer, 160°C for the middle layer, and 240°C for the outer layer. Process them into a melt, transmit through a pipeline, filter, and then extrude them into a sheet-like fluid flowing out from a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 210°C. After cooling with a chilled roller, biaxial stretching is performed. During the biaxial stretching process, the transverse stretching ratio is 4 times, and the longitudinal stretching ratio is 3 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a heat-resistant polyethylene composite packaging film.

[0035] The preparation method of the hydrotalcite modified blend comprises the following steps: S1. Ultrasonic dispersion of hydrotalcite in a mixed solvent, wherein the mixed solvent is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 9:1. After uniform dispersion, the pH value is adjusted to 4 using glacial acetic acid, and the mixture is stirred and mixed. γ-methacryloxypropyltrimethoxysilane is added dropwise, wherein the mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:3000:12. The mixture is stirred and reacted at 55° C. for 1 h. After the reaction is completed, the mixture is filtered, washed with anhydrous ethanol and deionized water, and dried in a vacuum drying oven at 80° C. for 12 h to obtain olefinated hydrotalcite. S2. Evenly mix acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite and initiator dicumyl peroxide in a mass ratio of 400:10:20:100:5:2. After the acetone is volatilized, transfer the mixture to a twin-screw extruder for melt blending at a temperature of 195° C. for 12 min. Extrude and cool the mixture to obtain a hydrotalcite-modified blend.

[0036] The preparation method of modified PA6 comprises the following steps: (1) Ultrasonic dispersion of graphene oxide in N,N-dimethylformamide, after uniform dispersion, adding triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, wherein the mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:9500:400:42:4, heating, stirring and mixing, reacting, the reaction temperature is 55°C, the reaction time is 15h, after the reaction is completed, centrifuging, the centrifugal speed is 6000r / min, the centrifugal time is 8min, washing with deionized water, and vacuum drying at 60°C for 12h to obtain amino graphene oxide; (2) Mix the nanocellulose and deionized water evenly, add sodium periodate, wherein the mass ratio of nanocellulose, deionized water and sodium periodate is 100:6000:120, stir and mix, heat up, and react in the dark at a temperature of 45°C for 20 hours. Add ethylene glycol to terminate the reaction. After the reaction is completed, filter, wash with deionized water, and freeze-dry to obtain aldehyded cellulose; (3) The PA6 was vacuum dried in an oven at 90°C for 12 h, and the dried PA6, amino-modified graphene oxide, and aldehyde-modified cellulose in a mass ratio of 100:4:3 were stirred and mixed evenly, added to a twin-screw extruder, melt-blended at 210°C, extruded, and cooled to obtain modified PA6. Example 2

[0037] A method for preparing a heat-resistant polyethylene composite packaging film comprises the following steps: Step 1, weigh the raw materials of the inner layer, the middle layer, and the outer layer by mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 29 parts of polypropylene, and 8.5 parts of hydrotalcite modified blends, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 45 parts of linear low-density polyethylene, 3.5 parts of coupling agent vinyl trimethoxy silane, 0.6 parts of antioxidant, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the raw materials of the outer layer include: 100 parts of modified PA6, 24 parts of metallocene polyethylene, and 6 parts of compatibilizer maleic anhydride grafted POE, and perform batching, mixing, and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 200°C for the inner layer, 180°C for the middle layer, and 250°C for the outer layer. The raw materials are processed into a melt, and after being transmitted through a pipeline and filtered by a filter, they are extruded into a sheet-like fluid and flow out through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 220°C. After being cooled by a chilled roller, they are biaxially stretched. During the biaxial stretching process, the transverse stretching ratio is 3 times, and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a heat-resistant polyethylene composite packaging film.

[0038] The preparation method of the hydrotalcite modified blend comprises the following steps: S1. Ultrasonic dispersion of hydrotalcite in a mixed solvent, wherein the mixed solvent is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 9:1. After uniform dispersion, the pH value is adjusted to 4 using glacial acetic acid, and the mixture is stirred and mixed. γ-methacryloxypropyltrimethoxysilane is added dropwise, wherein the mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:3500:18. The mixture is stirred and reacted at 60° C. for 1.5 h. After the reaction is completed, the mixture is filtered, washed with anhydrous ethanol and deionized water, and dried in a vacuum drying oven at 80° C. for 12 h to obtain olefinated hydrotalcite. S2. Evenly mix acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite and initiator dicumyl peroxide in a mass ratio of 420:12:24:100:6:3. After the acetone is volatilized, transfer the mixture to a twin-screw extruder for melt blending at a temperature of 205° C. for 9 min. Extrude and cool the mixture to obtain a hydrotalcite-modified blend.

[0039] The preparation method of modified PA6 comprises the following steps: (1) Ultrasonic dispersion of graphene oxide in N,N-dimethylformamide, after uniform dispersion, adding triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, wherein the mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:10000:480:48:4.6, heating, stirring and mixing, reacting, the reaction temperature is 60°C, the reaction time is 14h, after the reaction is completed, centrifuging, the centrifugal speed is 6000r / min, the centrifugal time is 8min, washing with deionized water, and vacuum drying at 60°C for 12h to obtain amino graphene oxide; (2) Mix the nanocellulose and deionized water evenly, add sodium periodate, wherein the mass ratio of nanocellulose, deionized water and sodium periodate is 100:6500:135, stir and mix, heat up, and react in the dark at a temperature of 48°C for 19 hours. Add ethylene glycol to terminate the reaction. After the reaction is completed, filter, wash with deionized water, and freeze-dry to obtain aldehyded cellulose; (3) The PA6 was vacuum dried in an oven at 90°C for 12 h, and the dried PA6, amino-modified graphene oxide, and formaldehyde-modified cellulose in a mass ratio of 100:5:3.5 were stirred and mixed evenly, added to a twin-screw extruder, melt-blended at 225°C, extruded, and cooled to obtain modified PA6. Example 3

[0040] A method for preparing a heat-resistant polyethylene composite packaging film comprises the following steps: Step 1, weigh the raw materials of the inner layer, the middle layer, and the outer layer by mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 29 parts of polypropylene, and 8.5 parts of hydrotalcite modified blends, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 45 parts of linear low-density polyethylene, 3.5 parts of coupling agent vinyl trimethoxy silane, 0.6 parts of antioxidant, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the raw materials of the outer layer include: 100 parts of modified PA6, 24 parts of metallocene polyethylene, and 6 parts of compatibilizer maleic anhydride grafted POE, and perform batching, mixing, and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 200°C for the inner layer, 180°C for the middle layer, and 250°C for the outer layer. The raw materials are processed into a melt, and after being transmitted through a pipeline and filtered by a filter, they are extruded into a sheet-like fluid and flow out through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 220°C. After being cooled by a chilled roller, they are biaxially stretched. During the biaxial stretching process, the transverse stretching ratio is 3 times, and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a heat-resistant polyethylene composite packaging film.

[0041] The preparation method of the hydrotalcite modified blend comprises the following steps: S1. Ultrasonic dispersion of hydrotalcite in a mixed solvent, wherein the mixed solvent is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 9:1. After uniform dispersion, the pH value is adjusted to 4 using glacial acetic acid, and the mixture is stirred and mixed. γ-methacryloxypropyltrimethoxysilane is added dropwise, wherein the mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:3500:24. The mixture is stirred and reacted at 60° C. for 1.5 h. After the reaction is completed, the mixture is filtered, washed with anhydrous ethanol and deionized water, and dried in a vacuum drying oven at 80° C. for 12 h to obtain olefinated hydrotalcite. S2. Evenly mix acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite and initiator dicumyl peroxide in a mass ratio of 420:13:24:100:6:4. After the acetone is volatilized, transfer the mixture to a twin-screw extruder for melt blending at a temperature of 215° C. for 10 min. Extrude and cool the mixture to obtain a hydrotalcite-modified blend.

[0042] The preparation method of modified PA6 comprises the following steps: (1) Ultrasonic dispersion of graphene oxide in N,N-dimethylformamide, after uniform dispersion, adding triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, wherein the mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:10000:480:48:4.6, heating, stirring and mixing, reacting, the reaction temperature is 60°C, the reaction time is 14h, after the reaction is completed, centrifuging, the centrifugal speed is 6000r / min, the centrifugal time is 8min, washing with deionized water, and vacuum drying at 60°C for 12h to obtain amino graphene oxide; (2) Mix the nanocellulose and deionized water evenly, add sodium periodate, wherein the mass ratio of nanocellulose, deionized water and sodium periodate is 100:6500:135, stir and mix, heat up, and react in the dark at a temperature of 48°C for 19 hours. Add ethylene glycol to terminate the reaction. After the reaction is completed, filter, wash with deionized water, and freeze-dry to obtain aldehyded cellulose; (3) PA6 was vacuum dried in an oven at 90°C for 12 h, and the dried PA6, amino-modified graphene oxide, and aldehyde-modified cellulose in a mass ratio of 100:6:4.5 were stirred and mixed evenly, added to a twin-screw extruder, melt-blended at 235°C, extruded, and cooled to obtain modified PA6. Example 4

[0043] A method for preparing a heat-resistant polyethylene composite packaging film comprises the following steps: Step 1, weigh the raw materials of the inner layer, the middle layer, and the outer layer by mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 31 parts of polypropylene, and 9.5 parts of hydrotalcite modified blends, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 55 parts of linear low-density polyethylene, 4 parts of coupling agent vinyl trimethoxy silane, 0.8 parts of antioxidant, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the raw materials of the outer layer include: 100 parts of modified PA6, 28 parts of metallocene polyethylene, and 7 parts of compatibilizer maleic anhydride grafted POE, and perform batching, mixing, and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 215°C for the inner layer, 190°C for the middle layer, and 265°C for the outer layer. Process them into a melt, transmit through a pipeline, filter, and then extrude them into a sheet-like fluid out of a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 230°C. After cooling with a chilled roller, biaxial stretching is performed. During the biaxial stretching process, the transverse stretching ratio is 3 times, and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a heat-resistant polyethylene composite packaging film.

[0044] The preparation method of the hydrotalcite-modified blend and the modified PA6 is the same as the preparation method of the hydrotalcite-modified blend and the modified PA6 in Example 3. Example 5

[0045] A method for preparing a heat-resistant polyethylene composite packaging film comprises the following steps: Step 1, weigh the raw materials of the inner layer, the middle layer, and the outer layer by mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 32 parts of polypropylene, and 10 parts of hydrotalcite-modified blends, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 60 parts of linear low-density polyethylene, 5 parts of coupling agent vinyl trimethoxy silane, and 1 part of antioxidant, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the raw materials of the outer layer include: 100 parts of modified PA6, 30 parts of metallocene polyethylene, and 8 parts of compatibilizer maleic anhydride grafted POE, and perform batching, mixing, and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 220°C for the inner layer, 200°C for the middle layer, and 280°C for the outer layer. The raw materials are processed into a melt, and after being transmitted through a pipeline and filtered by a filter, they are extruded into a sheet-like fluid and flow out through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 240°C. After being cooled by a chilled roller, they are biaxially stretched. During the biaxial stretching process, the transverse stretching ratio is 2 times, and the longitudinal stretching ratio is 1.5 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a heat-resistant polyethylene composite packaging film.

[0046] The preparation method of the hydrotalcite modified blend comprises the following steps: S1. Ultrasonic dispersion of hydrotalcite in a mixed solvent, wherein the mixed solvent is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 9:1. After uniform dispersion, the pH value is adjusted to 4 using glacial acetic acid, and the mixture is stirred and mixed. γ-methacryloxypropyltrimethoxysilane is added dropwise, wherein the mass ratio of hydrotalcite, mixed solvent, and γ-methacryloxypropyltrimethoxysilane is 100:4000:25. The mixture is stirred and reacted at 65° C. for 1 h. After the reaction is completed, the mixture is filtered, washed with anhydrous ethanol and deionized water, and dried in a vacuum drying oven at 80° C. for 12 h to obtain olefinated hydrotalcite. S2. Acetone, maleic anhydride, polypropylene, polyethylene, olefinated hydrotalcite and initiator dicumyl peroxide in a mass ratio of 450:14:30:100:8:5 are mixed evenly, and after the acetone is volatilized, the mixture is transferred to a twin-screw extruder for melt blending at a temperature of 220° C. for 8 min, extruded, and cooled to obtain a hydrotalcite-modified blend.

[0047] The preparation method of modified PA6 comprises the following steps: (1) Ultrasonic dispersion of graphene oxide in N,N-dimethylformamide, after uniform dispersion, adding triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, wherein the mass ratio of graphene oxide, N,N-dimethylformamide, triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 100:10500:500:50:5, heating, stirring and mixing, reacting, the reaction temperature is 65°C, the reaction time is 10 hours, after the reaction is completed, centrifugation, the centrifugation speed is 6000 r / min, the centrifugation time is 8 minutes, washing with deionized water, and vacuum drying at 60°C for 12 hours to obtain amino graphene oxide; (2) Mix the nanocellulose and deionized water evenly, add sodium periodate, wherein the mass ratio of nanocellulose, deionized water and sodium periodate is 100:7000:150, stir and mix, heat up, and react in the dark at a temperature of 50°C for 18 hours. Add ethylene glycol to terminate the reaction. After the reaction is completed, filter, wash with deionized water, and freeze-dry to obtain aldehyded cellulose; (3) The PA6 was vacuum dried in an oven at 90°C for 12 h, and the dried PA6, amino-modified graphene oxide, and aldehyde-modified cellulose in a mass ratio of 100:7:5 were stirred and mixed evenly, added to a twin-screw extruder, melt-blended at 240°C, extruded, and cooled to obtain modified PA6. Comparative Example 1

[0048] A method for preparing a polyethylene composite packaging film comprises the following steps: Step 1, weigh the raw materials of the inner layer, the middle layer, and the outer layer by mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 31 parts of polypropylene, 0.5 parts of hydrotalcite, and 9 parts of modified blends, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 55 parts of linear low-density polyethylene, 4 parts of coupling agent vinyltrimethoxysilane, 0.8 parts of antioxidant, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the raw materials of the outer layer include: 100 parts of modified PA6, 28 parts of metallocene polyethylene, and 7 parts of compatibilizer maleic anhydride grafted POE, and perform batching, mixing, and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 215°C for the inner layer, 190°C for the middle layer, and 265°C for the outer layer. Process them into a melt, transmit through a pipeline, filter, and then extrude them into a sheet-like fluid through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 230°C. After cooling with a chilled roller, biaxial stretching is performed. During the biaxial stretching process, the transverse stretching ratio is 3 times, and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a polyethylene composite packaging film.

[0049] The preparation method of the modified blend comprises the following steps: Acetone, maleic anhydride, polypropylene, polyethylene and initiator dicumyl peroxide in a mass ratio of 420:13:24:106:4 were mixed evenly, and after the acetone was volatilized, they were transferred to a twin-screw extruder for melt blending. The melt blending temperature was 215° C., the melt blending time was 10 min, extruded, and cooled to obtain a modified blend.

[0050] The preparation method of the modified PA6 is the same as the preparation method of the modified PA6 in Example 3. Comparative Example 2

[0051] A method for preparing a polyethylene composite packaging film comprises the following steps: Step 1, weigh the raw materials of the inner layer, the middle layer, and the outer layer by mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 31 parts of polypropylene, and 9.5 parts of hydrotalcite-modified blends, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 55 parts of linear low-density polyethylene, 4 parts of coupling agent vinyltrimethoxysilane, and 0.8 parts of antioxidant, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the raw materials of the outer layer include: 90.5 parts of PA6, 5.5 parts of graphene oxide, 4 parts of nanocellulose, 28 parts of metallocene polyethylene, and 7 parts of compatibilizer maleic anhydride grafted POE, and perform batching, mixing, and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 215°C for the inner layer, 190°C for the middle layer, and 265°C for the outer layer. Process them into a melt, transmit through a pipeline, filter, and then extrude them into a sheet-like fluid through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 230°C. After cooling with a chilled roller, biaxial stretching is performed. During the biaxial stretching process, the transverse stretching ratio is 3 times, and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a polyethylene composite packaging film.

[0052] The preparation method of the hydrotalcite-modified blend is the same as the preparation method of the hydrotalcite-modified blend in Example 3. Comparative Example 3

[0053] A method for preparing a polyethylene composite packaging film comprises the following steps: Step 1, weigh the raw materials of the inner layer, the middle layer, and the outer layer by mass, the raw materials of the inner layer include 100 parts of linear low-density polyethylene, 31 parts of polypropylene, and 9.5 parts of modified blends, the raw materials of the middle layer include: 100 parts of low-density polyethylene, 55 parts of linear low-density polyethylene, 4 parts of coupling agent vinyltrimethoxysilane, 0.8 parts of antioxidant, wherein the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, and the raw materials of the outer layer include: 100 parts of PA6, 28 parts of metallocene polyethylene, and 7 parts of compatibilizer maleic anhydride grafted POE, and perform batching, mixing, and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively. The heating temperatures in the extruder barrel are 215°C for the inner layer, 190°C for the middle layer, and 265°C for the outer layer. Process them into a melt, transmit through a pipeline, filter, and then extrude them into a sheet-like fluid through a three-layer co-extrusion composite die head. The temperature of the three-layer co-extrusion composite die head is 230°C. After cooling with a chilled roller, biaxial stretching is performed. During the biaxial stretching process, the transverse stretching ratio is 3 times, and the longitudinal stretching ratio is 2.5 times. After the stretching is completed, the film is pulled, rolled, and slit to obtain a polyethylene composite packaging film.

[0054] The preparation method of the modified blend comprises the following steps: Acetone, maleic anhydride, polypropylene, polyethylene and initiator dicumyl peroxide in a mass ratio of 420:13:24:106:4 were mixed evenly, and after the acetone was volatilized, they were transferred to a twin-screw extruder for melt blending. The melt blending temperature was 215° C., the melt blending time was 10 min, extruded, and cooled to obtain a modified blend.

[0055] The linear low-density polyethylene used in the embodiments of the present invention and the comparative examples was purchased from Shanghai Qianyi Plastic Technology Co., Ltd. with the item number px-21; polypropylene was purchased from PetroChina Daqing Petrochemical Company with the model number T30S; hydrotalcite was purchased from Tai'an Boyang Chemical Technology Co., Ltd.; low-density polyethylene was purchased from Sinopec Maoming Petrochemical Co., Ltd. with the model number LDPE2426H; graphene oxide was purchased from Suzhou Carbon Graphite Technology Co., Ltd.; nanocellulose was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. with a particle size of ≤25 μm; PA6 was purchased from Sinopec Baling Petrochemical Co., Ltd. with the model number YH800; metallocene polyethylene was purchased from Dongguan Mingyuan Plastic Co., Ltd. with the brand name Dow NG5401B; maleic anhydride grafted POE was purchased from Jiayirong Polymer (Shanghai) Co., Ltd. with the model number CMG5805-L; other reagents are all commercially available.

[0056] The polyethylene composite packaging films prepared in Examples 1-5 and Comparative Examples 1-3 were used as samples to conduct relevant performance tests, and the test results are as follows: (1) Heat resistance test: Cut the sample into 100 mm × 100 mm, record it as the original size, place it in a 120°C oven for 30 min, cool it down, measure the size after heating, and calculate the thermal shrinkage rate, thermal shrinkage rate = (original size - size after heating) / original size × 100%; use the test standard GB / T 19466.1-2004 "Plastics Differential Scanning Calorimetry (DSC) Part 1: General Rules" to test the melting peak temperature of the sample; the test results are shown in Table 1: Table 1

[0057] According to the test results in Table 1, it can be seen that the polyethylene composite packaging films corresponding to Examples 1-5 have excellent heat resistance, low heat shrinkage, and high melting temperature. In Comparative Example 1, hydrotalcite and modified blends are added instead of hydrotalcite modified blends as the raw materials for the inner film, and the hydrotalcite is not modified. The dispersibility of hydrotalcite in the composite packaging film becomes poor, and the compatibility is greatly reduced, resulting in thermal stress concentration and increased heat shrinkage. In Comparative Example 2, PA6, graphene oxide, and nanocellulose are added instead of modified PA6 as the raw materials for the outer film, and the heat shrinkage of the composite packaging film is reduced, and the melting temperature is reduced. In Comparative Example 3, modified blends are added instead of hydrotalcite modified blends, and PA6 is added instead of modified PA6. The thermal stability is poor and the heat resistance is greatly reduced.

[0058] (2) Mechanical property test: The tensile strength and elongation at break of the samples were tested according to the test standard GB / T 1040.3-2006 "Determination of tensile properties of plastics Part 3: Test conditions for films and sheets". The puncture resistance of the samples was tested according to the test standard ASTM F1306. The diameter of the puncture needle used was 1 mm, the puncture speed was 50 mm / min, and the maximum force value was recorded. Each group of the above tests was tested three times, and the test results were averaged. The above test results are shown in Table 2: Table 2

[0059] According to the test results in Table 2, it can be seen that the polyethylene packaging composite films corresponding to Examples 1-5 have excellent mechanical properties, high tensile strength, are not easy to break, and have good puncture resistance. The polyethylene composite packaging films corresponding to Comparative Examples 1 and 2 have interface defects and reduced mechanical properties. The tensile strength, elongation at break, and puncture resistance of the polyethylene composite packaging film in Comparative Example 3 are all greatly reduced.

[0060] Although the embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that all equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A heat-resistant polyethylene composite packaging film, characterized in that: Including inner layer, middle layer and outer layer; In parts by mass, the raw materials of the inner layer include: 100 parts of linear low-density polyethylene, 28-32 parts of polypropylene, and 8-10 parts of hydrotalcite modified blend; The raw materials of the middle layer include, by weight: 100 parts of low-density polyethylene, 40-60 parts of linear low-density polyethylene, 3-5 parts of coupling agent, and 0.5-1 part of antioxidant; Calculated by weight, the raw materials of the outer layer include: 100 parts of modified PA6, 20-30 parts of metallocene polyethylene, and 5-8 parts of compatibilizer.

2. The heat-resistant polyethylene composite packaging film according to claim 1, characterized in that: The preparation method of the hydrotalcite modified blend comprises the following steps: S1. Ultrasonic dispersion of hydrotalcite in a mixed solvent. After uniform dispersion, use glacial acetic acid to adjust the pH to 4, stir and mix, dropwise add γ-methacryloxypropyltrimethoxysilane, stir and react. After the reaction is completed, filter, wash with anhydrous ethanol and deionized water, and dry in a vacuum drying oven at 80° C. for 12 h to obtain olefinated hydrotalcite; S2. Evenly mix acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite and initiator, and after the acetone is volatilized, transfer to a twin-screw extruder for melt blending, extrusion and cooling to obtain a hydrotalcite-modified blend.

3. The heat-resistant polyethylene composite packaging film according to claim 2, characterized in that: The mass ratio of hydrotalcite, mixed solvent and γ-methacryloxypropyltrimethoxysilane in S1 is 100:3000-4000:12-25, the reaction temperature is 55-65° C., and the reaction time is 1-2 h.

4. The heat-resistant polyethylene composite packaging film according to claim 2, characterized in that: The mass ratio of acetone, maleic anhydride, polypropylene, polyethylene, olefinic hydrotalcite and initiator in S2 is 400-450:10-14:20-30:100:5-8:2-5, the temperature of melt blending is 195-220°C, and the time of melt blending is 8-12min.

5. The heat-resistant polyethylene composite packaging film according to claim 1, characterized in that: The preparation method of the modified PA6 comprises the following steps: Step (1), ultrasonically dispersing graphene oxide in N,N-dimethylformamide, after uniform dispersion, adding triethylenetetramine, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine, heating, stirring and mixing, reacting, and after the reaction is completed, centrifuging at a rate of 6000 r / min for 8 min, washing with deionized water, and vacuum drying at 60° C. for 12 h to obtain amino-modified graphene oxide; Step (2), mixing the nanocellulose and deionized water evenly, adding sodium periodate, stirring and mixing, heating, reacting in the dark, adding ethylene glycol to terminate the reaction, and after the reaction is completed, filtering, washing with deionized water, and freeze-drying to obtain aldehyded cellulose; Step (3), vacuum drying PA6 in an oven at 90° C. for 12 h, stirring and mixing the dried PA6, amino-modified graphene oxide, and formaldehyde-modified cellulose, adding the mixture to a twin-screw extruder, melt blending, extruding, and cooling to obtain modified PA6.

6. The heat-resistant polyethylene composite packaging film according to claim 5, characterized in that: In the step (3), the mass ratio of the dried PA6, amino-modified graphene oxide, and formaldehyde-modified cellulose is 100:4-7:3-5, and the temperature in the twin-screw extruder is set at 210-240°C.

7. The heat-resistant polyethylene composite packaging film according to claim 1, characterized in that: The coupling agent is a silane coupling agent; the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; and the compatibilizer is maleic anhydride grafted POE.

8. A method for preparing the heat-resistant polyethylene composite packaging film according to any one of claims 1 to 7, characterized in that: The steps include: Step 1: weigh the raw materials of the inner layer, the middle layer and the outer layer by mass, and perform batching, mixing and drying pretreatment respectively; Step 2: Heat the inner layer raw material, the middle layer raw material, and the outer layer raw material in the extruder barrel respectively, process them into melts, transmit through pipelines, filter through filters, extrude into sheet-like fluids out through the three-layer co-extrusion composite die head, cool through chilled rollers, and then perform biaxial stretching. After the stretching is completed, pull, roll, and slit to obtain a heat-resistant polyethylene composite packaging film.

9. The method for preparing a heat-resistant polyethylene composite packaging film according to claim 8, characterized in that: In the step 2, the heating temperatures in the extruder barrel are 180-220°C for the inner layer, 160-200°C for the middle layer, and 240-280°C for the outer layer, and the temperature of the three-layer co-extrusion composite die is 210-240°C.

10. The method for preparing a heat-resistant polyethylene composite packaging film according to claim 8, characterized in that: In the step 2, during the biaxial stretching process, the transverse stretching ratio is 2-4 times, and the longitudinal stretching ratio is 1.5-3 times.

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