Weather-resistant flame-retardant PE composite film and preparation method thereof

Abstract

The invention relates to the technical field of polyethylene film materials, in particular to a weather-resistant flame-retardant PE composite film and a preparation method thereof.The preparation method comprises the following steps that S1, a PE-based copolymer, an antioxidant and a light stabilizer are mixed and then discharged; s2, mixing LDPE resin, magnesium hydroxide, a silane coupling agent and zinc stearate, and discharging; s3, the outer-layer mixture and the core-layer mixture are put into a double-screw extruder for melt extrusion granulation and drying, and outer-layer master batches and core-layer master batches are obtained; and S4, respectively putting the outer-layer master batch and the core-layer master batch into an extruder for extrusion, and carrying out three-layer co-extrusion casting film forming, cooling shaping and rolling to obtain the weather-resistant flame-retardant PE composite film. The weather-resistant flame-retardant PE composite film obtained by the preparation method disclosed by the invention has relatively good weather resistance and flame retardance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyethylene film materials, and particularly relates to a weather-resistant flame-retardant PE composite film and a preparation method thereof. BACKGROUND

[0002] As one of the most widely used plastic film materials in modern industry and daily life, polyethylene (PE) film has long dominated the fields of packaging, agriculture, building materials, electronics, etc. due to its low cost, excellent processing performance, good chemical stability, etc. According to the search, the patent with the publication number CN109880222A discloses a white graphene composite PE material, a film and a preparation method thereof, which comprises modified white graphene 0.1-15 parts, PE resin 60-99.7 parts, white oil 0.1-10 parts and compatibilizer 0.1-20 parts. The film has high strength and high barrier property, and does not need to add antioxidants and other additives to improve the anti-aging property. The patent with the publication number CN115625956A discloses a PE multi-layer barrier composite film and a preparation method thereof. The preparation comprises a composite film with PE polyethylene layers as outer and inner layers and an EVOH layer as an intermediate barrier layer, which has excellent oxygen and water vapor barrier properties.

[0003] However, in the prior art, the molecular chain structure of ordinary PE film is sensitive to ultraviolet light, and long-term exposure to outdoor environment can cause photo-oxidative degradation, resulting in surface yellowing, brittleness and a sharp drop in mechanical properties. In agricultural mulch, the service life of traditional PE film is usually not more than 1 year, and frequent replacement not only increases the cost, but also causes resource waste. PE, as a hydrocarbon, has a limiting oxygen index (LOI) of only about 17%, and is a flammable material. In the fields of building, electronics, new energy, etc. with extremely high safety requirements, the flame retardancy of traditional PE film becomes a major hidden danger. For example, in power battery packaging, if the film has insufficient flame retardancy, it may cause battery thermal runaway diffusion and cause serious safety accidents. Although halogen-based flame retardants can significantly improve the flame retardancy, they will produce toxic gases during combustion, which does not meet the environmental protection trend; and halogen-free flame retardants have the contradiction of large addition amount and influence on film transparency and mechanical properties. SUMMARY

[0004] In order to solve the problems mentioned in the background, the present application provides a weather-resistant flame-retardant PE composite film and a preparation method thereof.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: A preparation method of a weather-resistant flame-retardant PE composite film, comprising the following steps: S1, put the PE-based copolymer into a mixer, add antioxidants and light stabilizers under stirring, set the temperature, mix for 5-7 min, and then discharge to obtain an outer layer mixture; S2, put the LDPE resin into the mixer, add magnesium hydroxide, silane coupling agent and zinc stearate under stirring, set the temperature, mix for 10-12 min, and then discharge to obtain the core layer mixture; S3, put the outer layer mixture and the core layer mixture into the double screw extruder respectively for melt extrusion and granulation, and dry to obtain the outer layer master batch and the core layer master batch; S4, put the outer layer master batch and the core layer master batch into the extruder respectively for extrusion, three-layer co-extrusion and film forming, the three layers are outer layer, core layer and outer layer in sequence, cool and shape, pass through the corona treatment roller, pass through the traction roller and the flattening roller, and wind to obtain the weather-resistant and flame-retardant PE composite film.

[0006] Further, the PE-based copolymer is prepared by the following steps: Put the vinyl isobutyl ether and 9-vinyl anthracene into the reaction kettle pre-charged with cyclohexane, add bis (triphenylphosphine) palladium dichloride and methylaluminoxane, preheat for 10-20 min, pass in ethylene to control the pressure, and heat for 4-6 h. After the reaction is completed, cool and precipitate to obtain the PE-based copolymer.

[0007] Further, the mass ratio of the PE-based copolymer, the antioxidant and the light stabilizer in step S1 is 10: (0.04-0.06): (0.04-0.08).

[0008] Further, the antioxidant in step S1 is at least one of antioxidant 1010, antioxidant 1076, antioxidant BHT, antioxidant 168 or antioxidant 626.

[0009] Further, the light stabilizer in step S1 is at least one of light stabilizer 770, light stabilizer 622 or light stabilizer 944.

[0010] Further, the temperature in step S1 is set to 50-60°C, and the stirring speed is 500-600 rpm.

[0011] Further, the temperature in step S2 is set to 60-70°C, and the stirring speed is 500-600 rpm.

[0012] Further, the mass ratio of the LDPE resin, magnesium hydroxide, silane coupling agent and zinc stearate in step S2 is 10: (2.5-3.5): (0.2-0.5): (0.03-0.1).

[0013] Further, the LDPE resin in step S2 is a low-density polyethylene resin with a melt index (190°C / 2.16 kg) of 5-10 g / 10 min and a density of 0.920-0.928 g / cm³. Optionally, the LDPE resin contains 2-5% of vinyl acetate (VA) units by mass fraction.

[0014] Further, the silane coupling agent in step S2 is at least one selected from silane coupling agent KH-570, silane coupling agent KH-550 or silane coupling agent A-151.

[0015] Further, the specific process parameters of melt extrusion granulation in step S3 are as follows: The twin-screw extruder is divided into five temperature zones, for the outer layer mixture, the temperature of the first zone is 145-155℃, the temperature of the second zone is 160-170℃, the temperature of the third zone is 170-180℃, the temperature of the fourth zone is 175-185℃, the temperature of the fifth zone is 175-185℃, and the temperature of the die head is 170-180℃; For the core layer mixture, the temperature of the first zone is 140-150℃, the temperature of the second zone is 155-165℃, the temperature of the third zone is 170-180℃, the temperature of the fourth zone is 180-190℃, the temperature of the fifth zone is 180-190℃, and the temperature of the die head is 175-185℃; Further, the screw speed in step S3 is 180-280 rpm, and the vacuum exhaust system is turned on when the core layer mixture is granulated, with a vacuum degree of (-0.04) - (-0.08) MPa.

[0016] Further, the process parameters of three-layer co-extrusion flow casting in step S4 are as follows: The temperature control of the outer layer extruder is as follows: the first zone 150-160℃, the second zone 165-175℃, the third zone 170-180℃, and the die head 175-185℃; The temperature control of the core layer extruder is as follows: the first zone 145-155℃, the second zone 165-175℃, the third zone 175-185℃, and the die head 180-190℃; Further, the co-extrusion die head temperature in step S4 is 180-190℃.

[0017] Further, the quenching roller temperature is controlled at 20-30℃ during cooling and shaping in step S4.

[0018] Further, the power density of the corona treatment in step S4 is 6-10 W·min / m²; The winding tension is controlled at 70-110 N, and the taper tension control is used with a taper coefficient set at 10-30%.

[0019] Further, the mass ratio of vinyl isobutyl ether, 9-vinylanthracene, cyclohexane, bis(triphenylphosphine)palladium dichloride and methylaluminoxane is 1: (0.5-0.7): (20-30): (0.004-0.006): (0.9-1.1); The preheating temperature is 40-45℃, the temperature for heating up is 65-70℃, and the control pressure is 0.8-1.0 MPa.

[0020] According to another aspect of the present application, there is provided a weather-resistant flame-retardant PE composite film prepared by the above preparation method.

[0021] Advantages of the present application: 1、The present application introduces 9-vinyl anthracene units into the polyethylene main chain through catalytic copolymerization, forming stable covalent bonds, which helps to build an efficient ultraviolet absorption and conversion mechanism, effectively reducing the aging effect of ultraviolet radiation on materials. In combination with the synergistic effect of hindered amine light stabilizers and antioxidants, a multi-level protection system is formed, which is beneficial to prolong the service life of the film in outdoor environment and maintain its mechanical properties and appearance stability.

[0022] 2、By improving the compatibility of fillers and polymer matrix, it is beneficial to achieve uniform dispersion of flame retardants and promote the formation of a dense and strong carbon layer structure during combustion, thereby improving the flame retardant properties of the material. At the same time, good interfacial bonding also helps to reduce performance defects caused by filler agglomeration, allowing the material to maintain good physical properties.

[0023] 3、The A-B-A three-layer co-extrusion structure is used in the film structure, realizing the spatial rational distribution of functional components, concentrating the weather-resistant function in the outer layer and the flame-retardant system in the core layer, which not only plays the functional characteristics of each layer, but also improves the overall performance through the synergistic effect between layers. The protective effect of the outer layer on the core layer helps to maintain the long-term stability of the flame-retardant properties, and the interaction between the interfaces is also beneficial to improve the mechanical behavior of the material and reduce the brittleness problem commonly seen in high-filled systems. DETAILED DESCRIPTION

[0024] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0025] Unless otherwise specified, the raw materials used in the present application are all purchased from the market and are conventional products.

[0026] Example 1 The PE-based copolymer is prepared by the following steps: Into a reactor pre-charged with 2000 g of cyclohexane, 100 g of vinyl isobutyl ether and 50 g of 9-vinyl anthracene were added, followed by 0.4 g of palladium dichloride bis(triphenylphosphine) and 90 g of methylaluminoxane, preheated at 40℃ for 10 min, ethylene was introduced to control the pressure at 0.8 MPa, the temperature was raised to 65℃, and the reaction was carried out for 4 h. After the reaction was completed, the temperature was lowered to 10℃, the remaining pressure was released to the tail gas treatment system, the reaction was poured into ethanol, stirred and precipitated, stood for 12 h, filtered, washed with ethanol for 3 times, and dried at 50℃ to constant weight to obtain a PE-based copolymer.

[0027] Example 2 The PE-based copolymer was prepared by the following steps: Into a reactor pre-charged with 2500 g of cyclohexane, 100 g of vinyl isobutyl ether and 60 g of 9-vinyl anthracene were added, followed by 0.5 g of palladium dichloride bis(triphenylphosphine) and 100 g of methylaluminoxane, preheated at 42℃ for 15 min, ethylene was introduced to control the pressure at 0.9 MPa, the temperature was raised to 67℃, and the reaction was carried out for 5 h. After the reaction was completed, the temperature was lowered to 10℃, the remaining pressure was released to the tail gas treatment system, the reaction was poured into ethanol, stirred and precipitated, stood for 12 h, filtered, washed with ethanol for 3 times, and dried at 50℃ to constant weight to obtain a PE-based copolymer.

[0028] Example 3 The PE-based copolymer was prepared by the following steps: Into a reactor pre-charged with 3000 g of cyclohexane, 100 g of vinyl isobutyl ether and 70 g of 9-vinyl anthracene were added, followed by 0.6 g of palladium dichloride bis(triphenylphosphine) and 110 g of methylaluminoxane, preheated at 45℃ for 20 min, ethylene was introduced to control the pressure at 1.0 MPa, the temperature was raised to 70℃, and the reaction was carried out for 6 h. After the reaction was completed, the temperature was lowered to 10℃, the remaining pressure was released to the tail gas treatment system, the reaction was poured into ethanol, stirred and precipitated, stood for 12 h, filtered, washed with ethanol for 3 times, and dried at 50℃ to constant weight to obtain a PE-based copolymer.

[0029] Example 4 A preparation method of a weather-resistant flame-retardant PE composite film, comprising the following steps: S1, 100 g of the PE-based copolymer prepared in Example 1 was put into a mixer, stirred at a speed of 500 rpm, 0.4 g of antioxidant 1010 and 0.4 g of light stabilizer 770 were added, the temperature was set to 50℃, and the mixture was discharged after mixing for 5 min to obtain an outer layer mixture; S2, 100g LDPE resin was put into the mixer, stirred at a speed of 500 rpm, 25g magnesium hydroxide, 2g silane coupling agent KH-570 and 0.3g zinc stearate were added, the temperature was set to 60℃, mixed for 10min, then discharged, the core layer mixture was obtained; S3, the outer layer mixture was put into a double screw extruder for melt extrusion and granulation, the temperature of the first zone was 145℃, the temperature of the second zone was 160℃, the temperature of the third zone was 170℃, the temperature of the fourth zone was 175℃, the temperature of the fifth zone was 175℃, and the temperature of the die head was 170℃, the core layer mixture was put into a double screw extruder for melt extrusion and granulation, the temperature of the first zone was 140℃, the temperature of the second zone was 155℃, the temperature of the third zone was 170℃, the temperature of the fourth zone was 180℃, the temperature of the fifth zone was 180℃, and the temperature of the die head was 175℃, wherein the screw speed was 180rpm, the core layer mixture was granulated with the vacuum exhaust system opened, the vacuum degree was (-0.04) MPa, and the mixture was dried to constant weight at 60℃, to obtain the outer layer masterbatch and the core layer masterbatch; S4, the outer layer masterbatch and the core layer masterbatch were respectively put into the extruder for extrusion, and three-layer co-extrusion flow casting was carried out, the temperature control of the outer layer extruder was: the first zone 150℃, the second zone 165℃, the third zone 170℃, and the die head 175℃, the temperature control of the core layer extruder was: the first zone 145℃, the second zone 165℃, the third zone 175℃, and the die head 180℃, the co-extrusion die head temperature was 180℃, the cooling and setting were carried out, the quenching roller temperature was controlled at 20℃, the roller was passed through the corona treatment, the power density of the corona treatment was 6W·min / m², the roller was passed through the traction roller and the flattening roller, and the film was wound, the winding tension was controlled at 70N, the taper tension control was used, and the taper coefficient was set to 10%, to obtain the weather-resistant and flame-retardant PE composite film.

[0030] Example 5 A preparation method of a weather-resistant and flame-retardant PE composite film, comprising the following steps: S1, 100g of the PE-based copolymer prepared in Example 2 was put into a mixer, stirred at a speed of 550 rpm, 0.5g of antioxidant 1076 and 0.6g of light stabilizer 622 were added, the temperature was set to 55℃, mixed for 6min, then discharged, to obtain an outer layer mixture; S2, 100g LDPE resin was put into the mixer, stirred at a speed of 550 rpm, 30g magnesium hydroxide, 4g silane coupling agent KH-550 and 0.7g zinc stearate were added, the temperature was set to 65℃, mixed for 11min, then discharged, to obtain a core layer mixture; S3, the outer layer mixture is put into a twin-screw extruder for melt extrusion granulation, the temperature of the first zone is 150℃, the temperature of the second zone is 165℃, the temperature of the third zone is 175℃, the temperature of the fourth zone is 180℃, the temperature of the fifth zone is 180℃, the temperature of the die head is 175℃, the core layer mixture is put into a twin-screw extruder for melt extrusion granulation, the temperature of the first zone is 145℃, the temperature of the second zone is 160℃, the temperature of the third zone is 175℃, the temperature of the fourth zone is 185℃, the temperature of the fifth zone is 185℃, the temperature of the die head is 180℃, wherein the screw speed is 220 rpm, the core layer mixture is granulated while the vacuum exhaust system is turned on, the vacuum degree is (-0.06) MPa, and the core layer mixture is dried at 60℃ until the weight is constant to obtain the outer layer master batch and the core layer master batch; S4, the outer layer master batch and the core layer master batch are respectively put into an extruder for extrusion, three-layer co-extrusion flow casting is carried out, the temperature control of the outer layer extruder is: the first zone 155℃, the second zone 170℃, the third zone 175℃, and the die head 180℃, the temperature control of the core layer extruder is: the first zone 150℃, the second zone 170℃, the third zone 180℃, and the die head 185℃, the co-extrusion die head temperature is 185℃, the cooling and shaping are carried out, the quenching roller temperature is controlled at 25℃, the power density of the corona treatment roller is 7W·min / m², the traction roller and the flattening roller are passed through, the winding is carried out, the winding tension control is 100N, the taper tension control is used, the taper coefficient is set to 20%, and a weather-resistant flame-retardant PE composite film is obtained.

[0031] Example 6 A preparation method of a weather-resistant flame-retardant PE composite film, comprising the following steps: S1, 100g of the PE-based copolymer prepared in Example 3 is put into a mixer, stirred at a speed of 600 rpm, 0.6g of antioxidant 168 and 0.8g of light stabilizer 944 are added, the temperature is set to 60℃, and the mixture is discharged after mixing for 7min to obtain an outer layer mixture; S2, 100g of LDPE resin is put into a mixer, stirred at a speed of 600 rpm, 35g of magnesium hydroxide, 5g of silane coupling agent A-151 and 1g of zinc stearate are added, the temperature is set to 70℃, and the mixture is discharged after mixing for 12min to obtain a core layer mixture; S3, the outer layer mixture is put into a twin-screw extruder for melt extrusion granulation, the temperature of the first zone is 155℃, the temperature of the second zone is 170℃, the temperature of the third zone is 180℃, the temperature of the fourth zone is 185℃, the temperature of the fifth zone is 185℃, and the temperature of the die head is 180℃, the core layer mixture is put into a twin-screw extruder for melt extrusion granulation, the temperature of the first zone is 150℃, the temperature of the second zone is 165℃, the temperature of the third zone is 180℃, the temperature of the fourth zone is 190℃, the temperature of the fifth zone is 190℃, and the temperature of the die head is 185℃, wherein the screw rotation speed is 280 rpm, the vacuum exhaust system is turned on when the core layer mixture is granulated, the vacuum degree is (-0.08) MPa, and the core layer mixture is dried at 60℃ until the weight is constant to obtain the outer layer master batch and the core layer master batch; S4, the outer layer master batch and the core layer master batch are respectively put into an extruder for extrusion, three-layer co-extrusion flow casting is carried out, the temperature control of the outer layer extruder is as follows: the first zone is 160℃, the second zone is 175℃, the third zone is 180℃, and the die head is 185℃, the temperature control of the core layer extruder is as follows: the first zone is 155℃, the second zone is 175℃, the third zone is 185℃, and the die head is 190℃, the co-extrusion die head temperature is 190℃, cooling and shaping, the quenching roller temperature is controlled at 30℃, the power density of the corona treatment roller is 10 W·min / m², the traction roller and the flattening roller are passed through, and the winding tension is controlled at 110 N, the taper tension control is used, the taper coefficient is set to 30%, and a weather-resistant flame-retardant PE composite film is obtained.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that no vinyl isobutyl ether is added, and the rest is the same as Example 1.

[0033] Comparative Example 2 The difference between this comparative example and Example 2 is that no 9-vinyl anthracene is added, and the rest is the same as Example 2.

[0034] Comparative Example 3 The difference between this comparative example and Example 4 is that the copolymer prepared in Comparative Example 1 is used instead of the PE-based copolymer prepared in Example 1, and the rest is the same as Example 4.

[0035] Comparative Example 4 The difference between this comparative example and Example 5 is that the copolymer prepared in Comparative Example 2 is used instead of the PE-based copolymer prepared in Example 2, and the rest is the same as Example 5.

[0036] Comparative Example 5 The difference between this comparative example and Example 6 is that no outer layer master batch is added, and the rest is the same as Example 6.

[0037] Comparative Example 6 The difference between this comparative example and Example 6 is that no core layer master batch is added, and the rest is the same as Example 6.

[0038] (I) Weather resistance test: Refer to GB / T 16422.3 “Plastics - Methods of exposure to laboratory light sources - Part 3: Fluorescent UV lamps” and GB / T 1040.3 “Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets”, uniformly cut at least 12 standard 1B dumbbell-shaped test samples and at least 3 square test samples with a size of 100 mm x 100 mm from each group of film roll from Examples 4-6 and Comparative Examples 3-6.

[0039] Take 5 dumbbell-shaped test samples and perform tensile test according to the standard on a universal material testing machine. Record the tensile strength (MPa) and elongation at break (%) of each test sample as the initial mechanical property value of the group of samples. Take 1 square test sample and use a color difference meter to measure its initial color coordinates (L*, a*, b*), and take the average value of 3 points.

[0040] Stress-free install the remaining dumbbell-shaped and square test samples on the sample holder of the aging test box, ensuring that the sample surface is uniformly exposed to ultraviolet light. Set the parameters as follows: lamp type UVB-313, irradiation intensity 0.76 W / m²@340 nm, cycle period light stage 60°C for 4 h; condensation stage 50°C for 4 h, total duration 500 h. When the cumulative running time of the equipment reaches 500 h, the test is suspended. The removed samples need to be conditioned for 24 h in a standard environment (23°C, 50% RH), and the mechanical properties (tensile strength retention rate and elongation at break retention rate) and yellow index change (Δb) of the samples after 500 h of aging are tested. Among them, the tensile strength retention rate (%) = (average tensile strength after aging / initial average tensile strength) x 100%, and the elongation at break retention rate (%) = (average elongation at break after aging / initial average elongation at break) x 100%. The results are shown in Table 1: Table 1. Performance changes of each sample after 500 h of ultraviolet accelerated aging

[0041] (II) Refer to GB / T 2406.2 “Plastics - Determination of the burning behavior of plastics - Part 2: Test methods at room temperature”, cut at least 10 effective test samples from each group of film from Examples 4-6 and Comparative Examples 3-6, with a size of 120 mm x 6.5 mm.

[0042] The initial oxygen concentration was selected as 17.5%, and whether the burning time of the sample at this concentration exceeded 3 min or the burning length exceeded 50 mm was recorded. If the burning time of the sample at this concentration exceeded 3 min or the burning length exceeded 50 mm, it was recorded as "O" (burning). Or vice versa, recorded as "X" (non-burning). If the previous sample was "O", the oxygen concentration was reduced, and if the previous sample was "X", the oxygen concentration was increased. The change amount (step size d) of the oxygen concentration was 0.2%. The LOI value was calculated as LOI = C f + K x d, wherein C f is the oxygen concentration value (%) used in the last test, d is the step size (0.2%), and K is determined according to the table in the standard appendix. The results are shown in Table 2: Table 2. Limiting Oxygen Index (LOI) test results of each sample

[0043] As can be seen from Table 1, after 500 h of ultraviolet accelerated aging, the tensile strength retention rate, elongation at break retention rate of Examples 4-6 are higher, and the change in yellow index is smaller. The PE-based copolymer prepared in the specific example is used in the outer layer mixture, which is prepared by polymerizing monomers such as vinyl isobutyl ether and 9-vinyl anthracene under specific conditions, and its molecular structure may have certain stability and weather resistance. At the same time, the antioxidants and light stabilizers added can effectively inhibit oxidation and photodegradation reactions, reduce the damage of ultraviolet light to the film, thereby maintaining good mechanical properties and smaller color change.

[0044] The LDPE resin in the core layer mixture is used in combination with magnesium hydroxide, silane coupling agent and zinc stearate, etc. Magnesium hydroxide acts as a flame retardant, silane coupling agent can improve the interfacial bonding between inorganic fillers and resins, and zinc stearate plays a role in lubrication, etc., which helps to maintain the overall performance of the film and has a positive effect on the retention of mechanical properties during the aging process.

[0045] Comparative Examples 3 and 4 compared with Examples 4 and 5, Comparative Example 3 uses the copolymer prepared in Comparative Example 1 instead of the PE-based copolymer prepared in Example 1, and Comparative Example 4 uses the copolymer prepared in Comparative Example 2 instead of the PE-based copolymer prepared in Example 2. The tensile strength retention rate and elongation at break retention rate of these two groups of samples after aging are significantly reduced, and the change in yellow index is increased. This indicates that vinyl isobutyl ether and 9-vinyl anthracene play a key role in the preparation of PE-based copolymer, which may change the molecular structure of the copolymer, making it less resistant to weathering, more susceptible to damage by ultraviolet light, and more prone to oxidation and degradation reactions, resulting in decreased mechanical properties and increased color change.

[0046] Comparative Example 5 did not add the outer layer masterbatch, and the initial tensile strength and elongation at break were lower, the retention rate after aging was worse, and the yellow index change was also large. Because the outer layer masterbatch contains PE-based copolymer and antioxidant and light stabilizer and other components, it plays a major protective role in the weather resistance of the film. Without the outer layer masterbatch, the film is directly exposed to ultraviolet light, and is more susceptible to aging and degradation, with a significant decrease in mechanical properties and a significant change in color.

[0047] Comparative Example 6 did not add the core layer masterbatch, although the initial tensile strength was higher, the tensile strength retention rate and elongation at break retention rate after aging decreased, and the yellow index change was also large. Although the components in the core layer masterbatch do not directly provide weather resistance, they work synergistically with the outer layer masterbatch to maintain the structure and properties of the film. Without the core layer masterbatch, the overall structural integrity of the film is affected, and the performance decreases more obviously during the aging process.

[0048] As can be seen from Table 2, the limiting oxygen index (LOI) values of Examples 4-6 are higher, indicating better flame retardant performance. Magnesium hydroxide is added to the core layer mixture as a flame retardant. Magnesium hydroxide will decompose and absorb heat when heated, reducing the surface temperature of the material, and releasing water vapor to dilute the concentration of combustible gas, thereby playing a flame-retardant role. In addition, the silane coupling agent improves the interfacial bonding between magnesium hydroxide and LDPE resin, allowing the flame retardant to be better dispersed in the resin, fully exerting the flame-retardant effect, and thus increasing the limiting oxygen index of the film.

[0049] Comparative Examples 3 and 4 have slightly lower LOI values compared to Examples 4 and 5. It may be because the structure of the copolymer used in the comparative examples changes, affecting the overall performance of the film, including the interaction with other components such as flame retardants, resulting in a decrease in flame retardant effect, but overall still maintaining a certain degree of flame retardancy.

[0050] Comparative Example 5 does not add the outer layer masterbatch, and the LOI value of the two groups is significantly reduced. The lack of the outer layer masterbatch in Comparative Example 5 may affect the overall structure and performance of the film, indirectly affecting the flame retardant effect; Comparative Example 6 does not add the core layer masterbatch, which directly lacks the main flame-retardant component magnesium hydroxide, resulting in a significant decrease in the flame-retardant performance of the film and a significant decrease in the limiting oxygen index.

[0051] In summary, the preparation method of Examples 4-6 produces a weather-resistant and flame-retardant PE composite film with good weather resistance and flame retardancy. The use of vinyl isobutyl ether and 9-vinyl anthracene in the preparation of PE-based copolymer improves the weather resistance of the film; antioxidants and light stabilizers in the outer layer masterbatch effectively protect the film from ultraviolet damage; and components such as magnesium hydroxide in the core layer masterbatch give the film good flame retardant properties.

[0052] In the description, reference to terms such as "making", "implementing", "embodiments", and the like means that the particular feature, structure, material, or characteristic being referred to is included in at least one embodiment of the present application. The illustrative examples described in this specification are not meant to be limiting. Also, well-known steps along with their

[0053] The above descriptions are only the preferred embodiments of the present application, not intended to limit the protection scope of the present application. Any modification, equivalent replacement or change made by any person skilled in the art within the technical scope disclosed by the present application and the inventive concept thereof should be covered within the protection scope of the present application.

Claims

1. A method for preparing a weather-resistant flame-retardant PE composite film, characterized in that, The method comprises the following steps: S1, put the PE-based copolymer into the mixer, add the antioxidant and light stabilizer under stirring, set the temperature, mix for 5-7 min, and then discharge to obtain the outer layer mixture; S2, put the LDPE resin into the mixer, add the magnesium hydroxide, silane coupling agent and zinc stearate under stirring, set the temperature, mix for 10-12 min, and then discharge to obtain the core layer mixture; S3, put the outer layer mixture and the core layer mixture into the double screw extruder respectively for melt extrusion and granulation, and then dry to obtain the outer layer master batch and the core layer master batch; S4, put the outer layer master batch and the core layer master batch into the extruder respectively for extrusion, three-layer co-extrusion flow casting film forming, cooling and shaping, passing through the corona treatment roller, passing through the traction roller and the flattening roller, and then winding to obtain the weather-resistant and flame-retardant PE composite film.

2. The preparation method of the weather-resistant flame-retardant PE composite film according to claim 1, characterized in that, The PE-based copolymer is prepared by the following steps: Put the vinyl isobutyl ether and 9-vinyl anthracene into a reaction kettle pre-loaded with cyclohexane, add the bis(triphenylphosphine)palladium dichloride and methylaluminoxane, preheat for 10-20 min, introduce ethylene to control the pressure, and then heat for 4-6 h; after the reaction is completed, cool, and then precipitate to obtain the PE-based copolymer.

3. The preparation method of the weather-resistant flame-retardant PE composite film according to claim 1, characterized in that, The mass ratio of the PE-based copolymer, the antioxidant and the light stabilizer in step S1 is 10: (0.04-0.06): (0.04-0.08); The antioxidant is at least one selected from antioxidant 1010, antioxidant 1076, antioxidant BHT, antioxidant 168 or antioxidant 626; The light stabilizer is at least one selected from light stabilizer 770, light stabilizer 622 or light stabilizer 944.

4. The preparation method of the weather-resistant flame-retardant PE composite film according to claim 1, characterized in that, The temperature in step S1 is set to 50-60°C, and the stirring speed is 500-600 rpm; The temperature in step S2 is set to 60-70°C, and the stirring speed is 500-600 rpm.

5. The preparation method of the weather-resistant flame-retardant PE composite film according to claim 1, characterized in that, The mass ratio of the LDPE resin, the magnesium hydroxide, the silane coupling agent and the zinc stearate in step S2 is 10: (2.5-3.5): (0.2-0.5): (0.03-0.1). The silane coupling agent is at least one selected from silane coupling agent KH-570, silane coupling agent KH-550 or silane coupling agent A-151.

6. The preparation method of the weather-resistant flame-retardant PE composite film according to claim 1, characterized in that, The specific process parameters for melt extrusion and granulation in step S3 are as follows: The double screw extruder is divided into five temperature zones; for the outer layer mixture, the temperature of the first zone is 145-155°C, the temperature of the second zone is 160-170°C, the temperature of the third zone is 170-180°C, the temperature of the fourth zone is 175-185°C, the temperature of the fifth zone is 175-185°C, and the temperature of the die head is 170-180°C; For the core layer mixture, the temperature of the first zone is 140-150°C, the temperature of the second zone is 155-165°C, the temperature of the third zone is 170-180°C, the temperature of the fourth zone is 180-190°C, the temperature of the fifth zone is 180-190°C, and the temperature of the die head is 175-185°C; The screw rotation speed is 180-280 rpm, and the vacuum exhaust system is opened when the core layer mixture is granulated, and the vacuum degree is (-0.04) - (-0.08) MPa.

7. The preparation method of the weather-resistant flame-retardant PE composite film according to claim 1, characterized in that, The process parameters for three-layer co-extrusion flow casting film forming in step S4 are as follows: The temperature control of the outer layer extruder is: zone 1 150-160℃, zone 2 165-175℃, zone 3 170-180℃, and the head 175-185℃; The temperature control of the core layer extruder is: zone 1 145-155℃, zone 2 165-175℃, zone 3 175-185℃, and the head 180-190℃; The temperature of the co-extrusion die is 180-190℃; The temperature of the quenching roller is controlled at 20-30℃ during the cooling and setting.

8. The preparation method of the weather-resistant flame-retardant PE composite film according to claim 1, characterized in that, The power density of the corona treatment in step S4 is 6-10 W·min / m²; The winding tension is controlled at 70-110 N, and the taper tension control is adopted, and the taper coefficient is set to 10-30%.

9. The preparation method of the weather-resistant flame-retardant PE composite film according to claim 2, characterized in that, The mass ratio of vinyl isobutyl ether, 9-vinyl anthracene, cyclohexane, bis(triphenylphosphine)palladium dichloride and methylaluminoxane is 1:(0.5-0.7):(20-30):(0.004-0.006):(0.9-1.1); The preheating temperature is 40-45℃, the temperature during the temperature rise is 65-70℃, and the control pressure is 0.8-1.0 MPa.

10. A weather-resistant flame-retardant PE composite film prepared by the preparation method according to any one of claims 1-9.

Images