High-density pe base film, preparation method and application

Abstract

The application discloses a high-density PE base film, a preparation method and application. The high-density PE base film comprises the following raw materials in parts by mass: 3-5 parts of maleic anhydride-vinyl triethoxysilane copolymer resin, 20-50 parts of low-density PE resin, and 35-75 parts of filling master batch; wherein the filling master batch is modified nano calcium carbonate master batch and / or modified nano barium sulfate master batch. The maleic anhydride-vinyl triethoxysilane copolymer resin contains siloxane groups which are inorganic powder-philic and long-chain maleic anhydride segments which are PE resin-philic. The macromolecular coupling agent effectively improves the bonding performance between nano calcium carbonate and nano barium sulfate in the filling master batch and the low-density PE resin. The PE base film prepared by using a high proportion of the filling master batch not only improves the density, but also greatly improves the tensile strength and elongation at break of the PE base film, and meets the performance requirements of the protective film.

Description

Technical Field

[0001] This invention relates to the field of PE film technology, and more specifically, to high-density PE base film, its preparation method, and its application. Background Technology

[0002] Protective films made by coating pressure-sensitive adhesives of different chemical compositions onto polyethylene (PE) film as the base film are widely used in surface protection of various decorative and finishing materials, surface protection of thermally broken aluminum profiles and fluorocarbon-coated aluminum profiles, and some industrial packaging materials due to their excellent adhesion performance, low-temperature resistance, and relatively low price. With the continuous expansion of the application scope and rapid growth in usage, my country consumes millions of tons of PE resin raw materials annually, resulting in a huge consumption of fossil fuels. How to minimize the consumption of fossil fuels and fully utilize widely available and inexpensive mineral powders as fillers to replace part of the PE resin, thereby reducing PE resin consumption, has become an inevitable requirement for the development of modern society. However, various mineral powders, such as calcium carbonate powder and barium sulfate powder, have hydrophilic and oleophobic properties, resulting in poor compatibility with PE resin. After film formation, the mechanical properties of the PE film decrease significantly, the appearance deteriorates, and agglomerates, bubbles, rough film surfaces, and poor aging resistance are present, rendering the PE film unusable. In current technology, to ensure that the tensile strength, elongation at break, high-temperature and high-humidity aging performance, and ultraviolet aging performance of the protective film meet the requirements, calcium carbonate masterbatch and barium sulfate masterbatch are used with caution to modify PE base film. Otherwise, the tensile strength and elongation at break of PE base film prepared with conventional masterbatch will decrease to varying degrees, the high-temperature and high-humidity aging performance will be unstable, and ultraviolet aging may result in powdering and cracking, which can easily lead to quality accidents and limit the application range of the protective film.

[0003] How to improve the compatibility and adhesion of calcium carbonate powder and barium sulfate powder with PE resin through modification technology, improve the dispersion uniformity of powder in PE resin, avoid agglomeration and grain formation, improve the mechanical properties and surface smoothness of PE film, especially after coating with pressure-sensitive adhesives of different chemical compositions, and after high temperature and high humidity aging, when the protective film is peeled off from the surface of the protected material, no residue or shadows appear, and after ultraviolet light aging, no powdering or cracking occurs, is a technical problem that researchers in this field need to solve.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a high-density PE-based film, its preparation method, and its application, which improves the mechanical properties of the film while using mineral powder as a filler.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a high-density PE-based film comprising the following raw materials in parts by weight: 3-5 parts of maleic anhydride-vinyltriethoxysilane copolymer resin, 20-50 parts of low-density PE resin, and 35-75 parts of filler masterbatch; wherein the filler masterbatch is modified nano-calcium carbonate masterbatch and / or modified nano-barium sulfate masterbatch.

[0008] In an optional embodiment, the filler masterbatch comprises the following raw materials in parts by weight: 4-6 parts of maleic anhydride-grafted ethylene-vinyl acetate resin, 18-22 parts of linear low-density PE resin, 68-72 parts of aluminate coupling agent-modified nano-inorganic salt powder, 2.5-3.5 parts of maleic anhydride-grafted oxidized polyethylene wax, and 1.8-2.2 parts of antioxidant pentaerythritol diphosphite; wherein the aluminate coupling agent-modified nano-inorganic salt powder is aluminate coupling agent-modified nano-calcium carbonate powder and / or aluminate coupling agent-modified nano-barium sulfate powder.

[0009] In an optional embodiment, the preparation of the filler masterbatch includes the following steps:

[0010] A first mixture is obtained by mixing aluminate coupling agent modified nano-inorganic salt powder, maleic anhydride grafted oxidized polyethylene wax and antioxidant pentaerythritol diphosphite. The first mixture is then mixed with maleic anhydride grafted ethylene-vinyl acetate resin and linear low-density PE resin to obtain a second mixture. The second mixture is then transferred to a twin-screw extruder for extrusion granulation.

[0011] Preferably, the mixing temperature of the raw materials for the filler masterbatch is 60–70°C;

[0012] Preferably, the temperature of the twin-screw extruder is 155±2℃ in zone one, 170±2℃ in zone two, 170±2℃ in zone three, and 165±2℃ in the die head.

[0013] In an optional embodiment, maleic anhydride and vinyltriethoxysilane are used as raw materials, ethyl acetate is used as solvent, and azobisisobutyronitrile is used as initiator to undergo a free radical copolymerization reaction to obtain maleic anhydride-vinyltriethoxysilane copolymer resin.

[0014] Preferably, the molar ratio of maleic anhydride, vinyltriethoxysilane, and ethyl acetate is 2.5–3.5:1:2.5–3.5;

[0015] Preferably, the amount of the initiator is 0.45 wt% to 0.55 wt% of the total weight of maleic anhydride and vinyltriethoxysilane;

[0016] Preferably, maleic anhydride, vinyltriethoxysilane, ethyl acetate and azobisisobutyronitrile are mixed and divided into a first reactant and a second reactant. The first reactant is placed in a water bath at 75±2℃. When the viscosity and temperature of the first reactant begin to increase, the second reactant is added dropwise and the dropwise addition time is controlled to be 50min~70min. After the dropwise addition is completed, the reaction continues for 4h~6h. The solvent is evaporated to obtain maleic anhydride-vinyltriethoxysilane copolymer resin.

[0017] Preferably, the volume ratio of the first reactant to the second reactant is 2.8-3.2:7.

[0018] In an optional embodiment, a first PE layer, a second PE layer, and a third PE layer are sequentially disposed, and the thickness ratio of the first PE layer, the second PE layer, and the third PE layer is 23-27:46-54:23-27, wherein:

[0019] The first PE layer comprises the following parts by weight of raw materials:

[0020]

[0021] The second PE layer comprises the following parts by weight of raw materials:

[0022] 3-5 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0023] 20-25 parts of low-density PE resin;

[0024] 70-75 parts of modified nano-barium sulfate masterbatch;

[0025] The third PE layer comprises the following parts by weight of raw materials:

[0026]

[0027]

[0028] In an optional embodiment, the density is ≥1.40 g / cm³. 3 The transverse tensile strength is ≥10.5MPa, and the transverse elongation at break is ≥450%; the longitudinal tensile strength is ≥12.5MPa, and the longitudinal elongation at break is ≥550%; the surface tension of the third PE layer after being placed at room temperature for 180 days is ≥42mN / m.

[0029] Secondly, the present invention provides a method for preparing the high-density PE base film described in the foregoing embodiments, comprising: obtaining the high-density PE base film by melt co-extrusion blown film preparation of the first PE layer, the second PE layer and the third PE layer.

[0030] In an optional embodiment, the temperatures of each zone of the screw extruder corresponding to the first PE layer are set as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 30±2r / min.

[0031] And / or, the temperature settings for each zone of the screw extruder corresponding to the second PE layer are as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 60±2r / min;

[0032] And / or, the temperatures of each zone of the screw extruder corresponding to the third PE layer are set as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 30±2r / min.

[0033] Thirdly, the present invention provides a protective film comprising an acrylic pressure-sensitive adhesive layer, a high-density PE base film as described in the foregoing embodiments, a printed composite adhesive layer, and a transparent PE film arranged sequentially.

[0034] Preferably, the high-density PE base film has a thickness of 140±2μm, the printed composite adhesive layer has a thickness of 2±0.5μm, the transparent PE film has a thickness of 25±1μm, and the acrylic pressure-sensitive adhesive layer has a thickness of 33±3μm.

[0035] Preferably, the protective film has a peel strength of ≥8N / 25mm on SUS304 mirror steel plate, and after 96 hours of heating aging at 70℃ and 95% relative humidity, it leaves no residual adhesive or spots on the surface of the thermally broken aluminum profile. After 20 days of ultraviolet aging, it shows no powdering or cracking.

[0036] Fourthly, the present invention provides a method for preparing the protective film described in the foregoing embodiments, comprising: printing and laminating a high-density PE base film, coating the high-density PE base film with acrylic pressure-sensitive adhesive, and curing the protective film;

[0037] Preferably, the printing and lamination of the high-density PE base film includes: coating a composite adhesive on the surface of the first PE layer of the high-density PE base film and drying it, and laminating the transparent PE film with the printed composite adhesive surface during winding.

[0038] More preferably, before coating the composite adhesive on the high-density PE base film, the surface of the first PE layer of the high-density PE base film is first printed with ink and dried. The ink is diluted with ethyl acetate and isopropanol, wherein the mass ratio of ethyl acetate to isopropanol is 94-96:5. After ink printing, the high-density PE base film is dried at 80±3℃.

[0039] More preferably, a 200-mesh anilox roller is used to coat the polyurethane composite adhesive onto the surface of the first PE layer of the high-density PE base film, wherein the polyurethane composite adhesive is diluted with ethyl acetate to a solid content of 20±3% before being coated onto the high-density PE base film.

[0040] More preferably, a composite adhesive drying oven is used to dry the composite adhesive, wherein the temperature of the first zone of the composite adhesive drying oven is set to 60±3℃ and the temperature of the second zone is set to 75±3℃.

[0041] More preferably, the speed at which the transparent PE film is laminated with the printed adhesive surface is 80m / min to 100m / min;

[0042] Preferably, the high-density PE base film coated with acrylic pressure-sensitive adhesive includes: coating the surface of the third PE layer of the PE base film with acrylic pressure-sensitive adhesive, drying it in a coating oven, and then winding it up;

[0043] More preferably, the temperature setting of the coating oven is 70±3℃ for zone one, 90±3℃ for zone two, 110±3℃ for zone three, 110±3℃ for zone four, and 85±3℃ for zone five.

[0044] More preferably, the acrylic pressure-sensitive adhesive is first diluted with deionized water to a solid content of 50±2% before coating, and then the adhesive is filtered through a 300-mesh nylon mesh and coated with a 10-20 mesh anilox roller.

[0045] More preferably, the acrylic pressure-sensitive adhesive is applied at a speed of 35±5 m / min;

[0046] Preferably, the curing temperature is 45±5℃ and the curing time is 48±2h.

[0047] The present invention has the following beneficial effects:

[0048] This application introduces maleic anhydride-vinyltriethoxysilane copolymer resin into the high-density PE-based film raw material components. Maleic anhydride-vinyltriethoxysilane copolymer resin is a macromolecular coupling agent containing both lipophilic and hydrophilic groups in its molecular structure. One type consists of siloxane groups that are hydrophilic to inorganic powders, readily reacting with them; the other type consists of long-chain maleic anhydride segments that are hydrophilic to PE resins, easily forming hydrogen bonds with them. This macromolecular coupling agent effectively improves the adhesion between nano-calcium carbonate and nano-barium sulfate in the filler masterbatch and the low-density PE resin. PE-based films prepared using a high proportion of filler masterbatch not only increase density but also significantly improve tensile strength and elongation at break, meeting the performance requirements of protective films. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a schematic diagram of the structure of a high-density PE-based film.

[0051] Figure 2 This is a schematic diagram of the protective film structure.

[0052] Diagram: 1-First PE layer; 2-Second PE layer; 3-Third PE layer; 11-High-density PE base film; 12-Printed composite adhesive layer; 13-Transparent PE film; 14-Acrylic pressure-sensitive adhesive layer. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0054] In a first aspect, the present invention provides a high-density PE base film 11, comprising the following raw materials in parts by weight: 3-5 parts of maleic anhydride-vinyltriethoxysilane copolymer resin, 20-50 parts of low-density PE resin, and 35-75 parts of filler masterbatch; wherein the filler masterbatch is modified nano-calcium carbonate masterbatch and / or modified nano-barium sulfate masterbatch.

[0055] The high-density PE base film 11 of this application incorporates maleic anhydride-vinyltriethoxysilane copolymer resin. This is because maleic anhydride-vinyltriethoxysilane copolymer resin is a macromolecular coupling agent. Its molecular structure contains both lipophilic and hydrophilic groups. One type consists of siloxane groups that are affinity for inorganic powders, readily reacting chemically with them; the other type consists of long-chain maleic anhydride segments that are affinity for PE resin, easily forming hydrogen bonds with the PE resin. This macromolecular coupling agent effectively improves the adhesion between nano-calcium carbonate and nano-barium sulfate in the filler masterbatch and the low-density PE resin. The PE base film prepared using a high proportion of filler masterbatch not only increases density but also significantly improves the tensile strength and elongation at break of the PE base film, meeting the performance requirements of the protective film.

[0056] In an optional embodiment, the filler masterbatch comprises the following raw materials in parts by weight: 4-6 parts of maleic anhydride-grafted ethylene-vinyl acetate resin, 18-22 parts of linear low-density PE resin, 68-72 parts of aluminate coupling agent-modified nano-inorganic salt powder, 2.5-3.5 parts of maleic anhydride-grafted oxidized polyethylene wax, and 1.8-2.2 parts of antioxidant pentaerythritol diphosphite; wherein the aluminate coupling agent-modified nano-inorganic salt powder is aluminate coupling agent-modified nano-calcium carbonate powder and / or aluminate coupling agent-modified nano-barium sulfate powder.

[0057] In this embodiment, the filler masterbatch can be modified nano-calcium carbonate masterbatch and modified nano-barium sulfate masterbatch, which helps to further increase the proportion of filler masterbatch in the high-density PE base film 11, and at the same time helps to improve tensile strength and elongation at break, thereby improving the protective film's resistance to high temperature and high humidity aging and UV aging.

[0058] The filler masterbatch of this application contains maleic anhydride-grafted ethylene-vinyl acetate resin, which can be used as a toughening agent to improve the tensile strength and elongation at break of the high-density PE base film 11.

[0059] In an optional embodiment, the preparation of the filler masterbatch includes the following steps:

[0060] A first mixture is obtained by mixing aluminate coupling agent modified nano-inorganic salt powder, maleic anhydride grafted oxidized polyethylene wax and antioxidant pentaerythritol diphosphite. The first mixture is then mixed with maleic anhydride grafted ethylene-vinyl acetate resin and linear low-density PE resin to obtain a second mixture. The second mixture is then transferred to a twin-screw extruder for extrusion granulation.

[0061] Preferably, the mixing temperature of the raw materials for the filler masterbatch is 60–70°C;

[0062] Preferably, the temperature of the twin-screw extruder is 155±2℃ in zone one, 170±2℃ in zone two, 170±2℃ in zone three, and 165±2℃ in the die head.

[0063] Specifically, in some embodiments, the preparation method of modified nano-calcium carbonate masterbatch includes the following steps: Aluminate coupling agent modified nano-calcium carbonate powder, maleic anhydride-grafted oxidized polyethylene wax, and antioxidant pentaerythritol diphosphite are added to a mixer equipped with a high-speed stirrer. The mixer is covered, heated to 60–70°C, and the stirring motor is started, with the speed controlled at 700–800 r / min for 50–60 min. Then, maleic anhydride-grafted ethylene-vinyl acetate resin and linear low-density PE resin are added, and stirring continues for 30 min. The mixture is then kept warm for later use. The twin-screw extruder is then heated, with zone one temperature at 155±2°C, zone two at 170±2°C, zone three at 170±2°C, and the die head temperature at 165±2°C. Once the set temperature is reached, the mixture is transferred to the extruder hopper, the twin-screw extruder is started, and the melt is extruded and shaped into round bars with a diameter of 3±0.5mm using a special die. The bars are cooled by blowing air and cut into particles with a length of 3±0.5mm. After metering, they are packaged to complete the preparation of modified nano calcium carbonate masterbatch.

[0064] Specifically, in some embodiments, the preparation method of modified nano-barium sulfate masterbatch includes the following steps:

[0065] Aluminate coupling agent-modified nano-barium sulfate powder, maleic anhydride-grafted oxidized polyethylene wax, and antioxidant pentaerythritol diphosphite were added to a mixer equipped with a high-speed stirrer. The mixer was covered, heated to 60–70°C, and the stirring motor was started, with the speed controlled at 700–800 r / min for 50–60 min. Maleic anhydride-grafted ethylene-vinyl acetate resin and linear low-density PE resin were then added, and stirring continued for 30 min. The mixture was then kept at this temperature until ready for use. The twin-screw extruder was then heated, with zone 1 at 155±2°C, zone 2 at 170±2°C, zone 3 at 170±2°C, and the die head at 165±2°C. Once the set temperature is reached, the mixture is transferred to the extruder hopper, the twin-screw extruder is started, and the melt is extruded and shaped into round bars with a diameter of 3±0.5mm using a special die. The bars are cooled by blowing air and cut into particles with a length of 3±0.5mm. After metering, they are packaged to complete the preparation of modified nano barium sulfate masterbatch.

[0066] In an optional embodiment, maleic anhydride and vinyltriethoxysilane are used as raw materials, ethyl acetate is used as solvent, and azobisisobutyronitrile is used as initiator to undergo a free radical copolymerization reaction to obtain maleic anhydride-vinyltriethoxysilane copolymer resin.

[0067] Preferably, the molar ratio of maleic anhydride, vinyltriethoxysilane, and ethyl acetate is 2.5–3.5:1:2.5–3.5;

[0068] Preferably, the amount of the initiator is 0.45 wt% to 0.55 wt% of the total weight of maleic anhydride and vinyltriethoxysilane;

[0069] Preferably, maleic anhydride, vinyltriethoxysilane, ethyl acetate and azobisisobutyronitrile are mixed and divided into a first reactant and a second reactant. The first reactant is placed in a water bath at 75±2℃. When the viscosity and temperature of the first reactant begin to increase, the second reactant is added dropwise and the dropwise addition time is controlled to be 50min~70min. After the dropwise addition is completed, the reaction continues for 4h~6h. The solvent is evaporated to obtain maleic anhydride-vinyltriethoxysilane copolymer resin.

[0070] Preferably, the volume ratio of the first reactant to the second reactant is 2.8-3.2:7.

[0071] Specifically, in some embodiments, the preparation method of maleic anhydride-vinyltriethoxysilane copolymer resin includes the following steps:

[0072] Maleic anhydride, vinyltriethoxysilane, and ethyl acetate were added to a four-necked flask in a molar ratio of 3:1:3, along with 0.5% (by weight) of azobisisobutyronitrile (AIBN) as an initiator. After the mixture was thoroughly dissolved and homogenized by stirring, 70% of the reactants by weight was added to a constant-pressure dropping funnel. A stirrer, reflux condenser, and thermometer were installed. The four-necked flask was purged with nitrogen to remove oxygen. The flask was heated in a water bath, and the stirrer was turned on. Once the water bath temperature reached 75±2℃, the mixture was stirred at a constant temperature. The reaction began after 20–30 minutes, with the viscosity increasing and the temperature rising. The reactants were then added dropwise, controlling the dropping rate. The addition was completed in approximately 1 hour, and the reaction was continued with stirring for another 5 hours. Stop heating, cool down, remove the dropping funnel and reflux condenser, install the vacuum distillation apparatus, heat with an electric heating mantle, and distill off ethyl acetate from the synthesized product at atmospheric pressure. Perform vacuum distillation for 30 minutes, then stop distillation. While still hot, pour the synthesized product into a suitable container, cool, and then granulate using a twin-screw extruder. Store in a sealed container for later use.

[0073] In an optional embodiment, the system includes a first PE layer 1, a second PE layer 2, and a third PE layer 3 disposed sequentially, wherein the thickness ratio of the first PE layer 1, the second PE layer 2, and the third PE layer 3 is 23-27:46-54:23-27, wherein:

[0074] The first PE layer 1 comprises the following parts by weight of raw materials:

[0075]

[0076] The second PE layer 2 comprises the following parts by weight of raw materials:

[0077] 3-5 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0078] 20-25 parts of low-density PE resin;

[0079] 70-75 parts of modified nano-barium sulfate masterbatch;

[0080] The third PE layer 3 comprises the following raw materials in parts by weight:

[0081]

[0082]

[0083] The high-density PE film in this embodiment comprises three layers. The first PE layer is used for ink printing. Therefore, the first PE layer needs to maintain certain mechanical properties while ensuring surface smoothness to avoid blurry or unclear patterns in the ink printing. The second PE layer is located in the middle and has relatively lower requirements for its mechanical properties, surface smoothness, and surface tension. Therefore, a large amount of modified nano-barium sulfate masterbatch is added to the second PE layer to effectively improve the density of the product. The third PE layer needs to have its composition adjusted to maintain certain mechanical properties while keeping the surface tension stable.

[0084] Specifically, in this embodiment, the PE resin in the high-density PE film is a combination of low-density PE resin and metallocene-catalyzed linear low-density PE resin. Low-density PE resin has a lower cost but lower strength and higher elongation. Therefore, it is used in combination with metallocene-catalyzed linear low-density PE resin, which has higher strength and lower elongation, to achieve complementary advantages. The maleic anhydride-vinyltriethoxysilane copolymer resin improves the compatibility between the PE resin and the inorganic powder in the filler masterbatch. Furthermore, as those skilled in the art know, low-density PE resin and other raw materials contain small molecules such as opening agents and slip agents. As the high-density PE film is used for an extended period, some of these small molecules gradually migrate to the film surface, potentially reducing the surface tension of the high-density PE film and causing coating layer transfer. The maleic anhydride-vinyltriethoxysilane copolymer resin in this embodiment can inhibit the migration of small molecules, thereby mitigating or preventing coating layer transfer.

[0085] In an optional embodiment, the density is ≥1.40 g / cm³. 3 The transverse tensile strength is ≥10.5MPa, and the transverse elongation at break is ≥450%; the longitudinal tensile strength is ≥12.5MPa, and the longitudinal elongation at break is ≥550%; the surface tension of the third PE layer after being placed at room temperature for 180 days is ≥42mN / m.

[0086] Secondly, the present invention provides a method for preparing the high-density PE base film 11 described in the foregoing embodiments, comprising: obtaining the high-density PE base film 11 by melt co-extrusion blown film of the first PE layer 1, the second PE layer 2 and the third PE layer 3.

[0087] In an optional embodiment, the temperature of each zone of the screw extruder corresponding to the first PE layer 1 is set as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 30±2r / min.

[0088] And / or, the temperature settings of each zone of the screw extruder corresponding to the second PE layer 2 are as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 60±2r / min;

[0089] And / or, the temperature settings of each zone of the screw extruder corresponding to the third PE layer 3 are as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 30±2r / min.

[0090] Specifically, in some embodiments, the preparation method of the high-density PE base film 11 includes the following steps:

[0091] 1) Maleic anhydride-vinyltriethoxysilane copolymer resin, metallocene-catalyzed linear low-density PE resin, low-density PE resin, modified nano-calcium carbonate masterbatch, and colored masterbatch are added to the screw extruder hopper corresponding to the first PE layer 1 according to the designed raw material ratio. The temperature of each zone of the screw extruder is set as follows: zone 1 148±2℃, zone 2 155±2℃, zone 3 160±2℃, zone 4 165±2℃, zone 5 160±2℃, flow channel 160±2℃, and die head 160±2℃. The screw speed is set to 30±2r / min.

[0092] 2) Add maleic anhydride-vinyltriethoxysilane copolymer resin, low-density PE resin, and modified nano barium sulfate masterbatch to the screw extruder hopper corresponding to the second PE layer 2 according to the designed raw material ratio. Set the temperature of each zone of the screw extruder as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃. Set the screw speed to 60±2r / min.

[0093] 3) Maleic anhydride-vinyltriethoxysilane copolymer resin, metallocene-catalyzed linear low-density PE resin, low-density PE resin, modified nano-calcium carbonate masterbatch, and black masterbatch are added to the screw extruder hopper corresponding to the third PE layer 3 according to the designed raw material ratio. The temperature of each zone of the screw extruder is set as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃. The screw speed is set to 30±2r / min.

[0094] 4) After the temperature reaches the set temperature and stabilizes for 30 minutes, start the three screw extruders at the same time. Control the speed ratio of the screw extruders through the AC frequency converter to be: first PE layer 1 screw extruder : second PE layer 2 screw extruder : third PE layer 3 screw extruder = 1:2:1. The melt extruded through the die goes through processes such as film drawing, blowing, stretching, traction, corona treatment, edge trimming and winding to prepare a high-density PE base film 11.

[0095] Thirdly, the present invention provides a protective film comprising an acrylic pressure-sensitive adhesive layer 14, a high-density PE base film 11 as described in the foregoing embodiments, a printed composite adhesive layer 12, and a transparent PE film 13 arranged sequentially.

[0096] Preferably, the high-density PE base film 11 has a thickness of 140±2μm, the printed composite adhesive layer 12 has a thickness of 2±0.5μm, the transparent PE film 13 has a thickness of 25±1μm, and the acrylic pressure-sensitive adhesive layer 14 has a thickness of 33±3μm.

[0097] Preferably, the protective film has a peel strength of ≥8N / 25mm against SUS304 mirror steel plate, and after 96 hours of heating aging at 70℃ and 95% relative humidity, it leaves no residual adhesive or spots on the surface of the thermally broken aluminum profile. After 20 days of ultraviolet aging, it shows no powdering or cracking.

[0098] The protective film provided in this application mainly consists of a high-density PE base film 11, a printed composite adhesive layer 12, a transparent PE film 13, and an acrylic pressure-sensitive adhesive layer 14, satisfying the requirements for protective films used in decorative and finishing materials, thermally broken aluminum profiles, and various aluminum profiles. The high-density PE base film 11 is ±2μm, the printed composite adhesive layer 12 is ±0.5μm, the transparent PE film 13 is ±1μm, and the acrylic pressure-sensitive adhesive layer 14 is ±3μm.

[0099] Fourthly, the present invention provides a method for preparing the protective film described in the foregoing embodiments, comprising: printing and laminating a high-density PE base film 11, coating the high-density PE base film 11 with acrylic pressure-sensitive adhesive, and curing the protective film.

[0100] Preferably, the printing and lamination of the high-density PE base film 11 includes: coating a composite adhesive on the surface of the first PE layer of the high-density PE base film 11 and drying it, and laminating the transparent PE film 13 with the printed composite adhesive surface during winding.

[0101] More preferably, before coating the high-density PE base film 11 with the composite adhesive, ink is first printed and dried on the surface of the first PE layer of the high-density PE base film 11, wherein the ink is diluted with ethyl acetate and isopropanol, and the mass ratio of ethyl acetate to isopropanol is 94-96:5; after ink printing, the high-density PE base film 11 is dried at 80±3℃.

[0102] More preferably, a 200-mesh anilox roller is used to coat the polyurethane composite adhesive onto the surface of the first PE layer of the high-density PE base film 11, wherein the polyurethane composite adhesive is diluted with ethyl acetate to a solid content of 20±3% before being coated onto the high-density PE base film 11.

[0103] More preferably, a composite adhesive drying oven is used to dry the composite adhesive, wherein the temperature of the first zone of the composite adhesive drying oven is set to 60±3℃ and the temperature of the second zone is set to 75±3℃.

[0104] More preferably, the speed at which the transparent PE film 13 is laminated with the printed composite adhesive is 80 m / min to 100 m / min;

[0105] Preferably, the high-density PE base film 11 is coated with acrylic pressure-sensitive adhesive, which includes: coating acrylic pressure-sensitive adhesive on the surface of the third PE layer of the PE base film, drying it in a coating oven, and then winding it up.

[0106] More preferably, the temperature setting of the coating oven is 70±3℃ for zone one, 90±3℃ for zone two, 110±3℃ for zone three, 110±3℃ for zone four, and 85±3℃ for zone five.

[0107] More preferably, the acrylic pressure-sensitive adhesive is first diluted with deionized water to a solid content of 50±2% before coating, and then the adhesive is filtered through a 300-mesh nylon mesh and coated with a 10-20 mesh anilox roller.

[0108] More preferably, the acrylic pressure-sensitive adhesive is applied at a speed of 35±5 m / min;

[0109] Preferably, the curing temperature is 45±5℃ and the curing time is 48±2h.

[0110] Specifically, in some embodiments, the method for preparing the protective film includes the following steps:

[0111] S1. Printing and Lamination of High-Density PE Base Film 11: The printing and lamination process of the high-density PE base film 11 is completed using a five-color gravure printing laminator. The specific steps are as follows: The printing oven is turned on and heated to a set temperature of 80±3℃; the lamination adhesive drying oven is turned on and heated, with the temperature set for zone one at 60±3℃ and zone two at 75±3℃. After reaching the set temperature, the temperature is maintained for 30 minutes. Five different colored inks are diluted with ethyl acetate and isopropanol at a mixing ratio of 95:5wt%. Corresponding gravure rollers are installed according to the designed color pattern, and the corresponding colored inks are added to the ink tank. Commercially available polyurethane lamination adhesive is added to the lamination adhesive tank and diluted with ethyl acetate to a solid content of 20±3%. The adhesive is then applied using a 200-mesh anilox roller. Place the high-density PE base film 11 on the unwinding rack, print on the surface of the first PE layer, draw the film, turn on the double-sided corona machine, turn on the printing drying fan and the composite adhesive drying fan, start the main motor, print the first PE layer surface with five-color ink, dry, apply the composite adhesive, dry in the coating oven, and when winding up, use the transparent PE film 13 to laminate the ink surface, and then wind up, controlling the printing and laminating speed to be 80-100m / min.

[0112] S2. Coating of High-Density PE Base Film 11 with Acrylic Pressure-Sensitive Adhesive: The process of coating high-density PE base film 11 with acrylic pressure-sensitive adhesive is completed using a thin film coating machine. The specific steps are as follows: The coating oven is turned on and heated. The set temperatures are 70±3℃ for zone 1, 90±3℃ for zone 2, 110±3℃ for zone 3, 110±3℃ for zone 4, and 85±3℃ for zone 5. After reaching the set temperatures, the temperature is maintained for 30 minutes. The high-density PE base film 11 prepared in step 1) is placed on the unwinding rack. Adhesive is applied to the black film surface. The film is drawn up. Commercially available two-component water-based acrylic pressure-sensitive adhesive is added to the adhesive tank and diluted with a small amount of deionized water to a solid content of 50±2%. The adhesive is filtered through a 300-mesh nylon mesh and coated using a 10-20 mesh anilox roller. Start the main motor, apply adhesive to the surface of the third PE layer of the PE base film, dry in a coating oven, and then roll it up, controlling the coating speed at 35±5m / min. The preparation of the protective film is complete.

[0113] S3. Curing and performance testing of the protective film: The protective film prepared in step S2 is placed in a curing chamber and heated to complete the curing reaction of the pressure-sensitive adhesive. It is placed at a curing temperature of 45±5℃ for 48 hours. After the curing process is completed, samples are taken for relevant performance testing.

[0114] The present invention uses the following specific embodiments and comparative examples to test the thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break of the high-density PE base film 11; the peel strength of the protective film; whether there is residual adhesive and speckle after high temperature and high humidity aging; and whether there is powdering and cracking after 20 days of ultraviolet light aging.

[0115] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0116] Example 1

[0117] 1. A method for preparing a high-density PE-based film 11, comprising the following steps:

[0118] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0119] The first PE layer 1 is composed of the following raw materials in parts by weight:

[0120]

[0121] The second PE layer 2 is composed of the following raw materials in parts by weight:

[0122] 4 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0123] 23 parts of low-density PE resin;

[0124] 73 parts of modified nano-barium sulfate masterbatch;

[0125] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0126]

[0127] Maleic anhydride-vinyltriethoxysilane copolymer resin, metallocene-catalyzed linear low-density PE resin, low-density PE resin, modified nano-calcium carbonate masterbatch, and colored masterbatch are added to the screw extruder hopper corresponding to the first PE layer 1 according to the designed raw material ratio. The temperature of each zone of the screw extruder is set as follows: zone 1 148±2℃, zone 2 155±2℃, zone 3 160±2℃, zone 4 165±2℃, zone 5 160±2℃, flow channel 160±2℃, and die head 160±2℃. The screw speed is set to 30±2 r / min.

[0128] Maleic anhydride-vinyltriethoxysilane copolymer resin, low-density PE resin, and modified nano-barium sulfate masterbatch are added to the screw extruder hopper corresponding to the second PE layer 2 according to the designed raw material ratio. The temperature of each zone of the screw extruder is set as follows: zone 1 148±2℃, zone 2 155±2℃, zone 3 160±2℃, zone 4 165±2℃, zone 5 160±2℃, flow channel 160±2℃, and die head 160±2℃. The screw speed is set to 60±2r / min.

[0129] Maleic anhydride-vinyltriethoxysilane copolymer resin, metallocene-catalyzed linear low-density PE resin, low-density PE resin, modified nano-calcium carbonate masterbatch, and black masterbatch were added to the screw extruder hopper corresponding to the third PE layer 3 according to the designed raw material ratio. The temperature of each zone of the screw extruder was set as follows: zone 1 148±2℃, zone 2 155±2℃, zone 3 160±2℃, zone 4 165±2℃, zone 5 160±2℃, flow channel 160±2℃, and die head 160±2℃. The screw speed was set to 30±2 r / min.

[0130] After the temperature reaches the set temperature and stabilizes for 30 minutes, three screw extruders are started simultaneously. The speed ratio of the screw extruders is controlled by an AC frequency converter as follows: first PE layer 1 screw extruder : second PE layer 2 screw extruder : third PE layer 3 screw extruder = 1 : 2 : 1. The melt extruded through the die undergoes processes such as film drawing, blowing, stretching, traction, corona treatment, edge trimming, and winding to prepare a high-density PE base film 11, such as... Figure 1 As shown.

[0131] 2. A method for preparing a protective film, comprising the following steps:

[0132] S1. Printing and Lamination of High-Density PE Base Film 11: The printing and lamination process of the high-density PE base film 11 is completed using a five-color gravure printing laminator. The specific steps are as follows: The printing oven is turned on and heated to a set temperature of 80±3℃; the lamination adhesive drying oven is turned on and heated, with the temperature set for zone one at 60±3℃ and zone two at 75±3℃. After reaching the set temperature, the temperature is maintained for 30 minutes. Five different colored inks are diluted with ethyl acetate and isopropanol at a mixing ratio of 95:5wt%. Corresponding gravure rollers are installed according to the designed color pattern, and the corresponding colored inks are added to the ink tank. Commercially available polyurethane lamination adhesive is added to the lamination adhesive tank and diluted with ethyl acetate to a solid content of 20±3%. The adhesive is then applied using a 200-mesh anilox roller. Place the high-density PE base film 11 onto the unwinding rack, print on the surface of the first PE layer, draw the film, turn on the double-sided corona machine, turn on the printing drying fan and the composite adhesive drying fan, start the main motor, print five-color inks on the colored film surface, dry, apply composite adhesive, dry in the coating oven, and when rewinding, use transparent PE film 13 to laminate the ink surface, rewind, and control the printing and laminating speed to 90m / min.

[0133] S2. Coating of High-Density PE Base Film 11 with Acrylic Pressure-Sensitive Adhesive: The process of coating high-density PE base film 11 with acrylic pressure-sensitive adhesive is completed using a thin film coating machine. The specific steps are as follows: The coating oven is turned on and heated. The set temperatures are 70±3℃ for zone 1, 90±3℃ for zone 2, 110±3℃ for zone 3, 110±3℃ for zone 4, and 85±3℃ for zone 5. After reaching the set temperatures, the temperature is maintained for 30 minutes. The high-density PE base film 11 prepared in step 1) is placed on the unwinding rack. Adhesive is applied to the surface of the third PE layer. The film is drawn up, and commercially available two-component water-based acrylic pressure-sensitive adhesive is added to the adhesive tank. It is diluted with a small amount of deionized water to a solid content of 50±2%. The adhesive is filtered through a 300-mesh nylon mesh and coated using a 10-mesh anilox roller. The main motor is started, and adhesive is applied to the black surface of the PE base film. After drying in the coating oven, the film is wound up, and the coating speed is controlled at 35±5 m / min. Complete the preparation of the protective film.

[0134] S3. Curing and Performance Testing of the Protective Film: The protective film prepared in step S2 was placed in a curing chamber and heated to complete the curing reaction of the pressure-sensitive adhesive. It was then placed at a curing temperature of 45±5℃ for 48 hours to obtain the protective film as shown below. Figure 2 As shown, samples were taken after the curing process was completed for relevant performance testing.

[0135] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0136] Example 2

[0137] 1. A method for preparing a high-density PE-based film 11, differing from Example 1 only in the raw materials:

[0138] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0139] The first PE layer 1 is composed of the following raw materials in parts by weight:

[0140]

[0141] The second PE layer 2 is composed of the following raw materials in parts by weight:

[0142] 3 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0143] 22 parts of low-density PE resin;

[0144] 75 parts of modified nano-barium sulfate masterbatch;

[0145] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0146]

[0147] 2. A method for preparing a protective film, comprising the following steps:

[0148] S1. Printing and Lamination of High-Density PE Base Film 11: The printing and lamination process of the high-density PE base film 11 is completed using a five-color gravure printing laminator. The specific steps are as follows: The printing oven is turned on and heated to a set temperature of 80±3℃; the lamination adhesive drying oven is turned on and heated, with the temperature set for zone one at 60±3℃ and zone two at 75±3℃. After reaching the set temperature, the temperature is maintained for 30 minutes. Five different colored inks are diluted with ethyl acetate and isopropanol at a mixing ratio of 95:5wt%. Corresponding gravure rollers are installed according to the designed color pattern, and the corresponding colored inks are added to the ink tank. Commercially available polyurethane lamination adhesive is added to the lamination adhesive tank and diluted with ethyl acetate to a solid content of 20±3%. The adhesive is then applied using a 200-mesh anilox roller. Place the high-density PE base film 11 on the unwinding rack, print on the colored film side, draw the film, turn on the double-sided corona machine, turn on the printing drying fan and the composite adhesive drying fan, start the main motor, print ink on the surface of the first PE layer, dry, apply composite adhesive, dry in the coating oven, and when rewinding, use transparent PE film 13 to laminate the ink side, rewind, and control the printing and laminating speed to 80m / min.

[0149] S2. Coating of High-Density PE Base Film 11 with Acrylic Pressure-Sensitive Adhesive: The process of coating high-density PE base film 11 with acrylic pressure-sensitive adhesive is completed using a thin film coating machine. The specific steps are as follows: The coating oven is turned on and heated. The set temperatures are 70±3℃ for zone 1, 90±3℃ for zone 2, 110±3℃ for zone 3, 110±3℃ for zone 4, and 85±3℃ for zone 5. After reaching the set temperatures, the temperature is maintained for 30 minutes. The high-density PE base film 11 prepared in step 1) is placed on the unwinding rack. Adhesive is applied to the black film surface. The film is drawn up, and commercially available two-component water-based acrylic pressure-sensitive adhesive is added to the adhesive tank. It is diluted with a small amount of deionized water to a solid content of 50±2%. The adhesive is filtered through a 300-mesh nylon mesh and coated using a 20-mesh anilox roller. The main motor is started, and adhesive is applied to the surface of the third PE layer of the PE base film. After drying in the coating oven, the film is wound up, and the coating speed is controlled at 35±5 m / min. Complete the preparation of the protective film.

[0150] S3. Curing and performance testing of the protective film: The protective film prepared in step S2 is placed in a curing chamber and heated to complete the curing reaction of the pressure-sensitive adhesive. It is placed at a curing temperature of 45±5℃ for 48 hours. After the curing process is completed, samples are taken for relevant performance testing.

[0151] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0152] Example 3

[0153] 1. A method for preparing a high-density PE-based film 11, differing from Example 1 only in the raw materials:

[0154] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0155] The first PE layer 1 is composed of the following raw materials in parts by weight:

[0156]

[0157] The second PE layer 2 is composed of the following raw materials in parts by weight:

[0158] 5 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0159] 25 parts of low-density PE resin;

[0160] 70 parts of modified nano-barium sulfate masterbatch;

[0161] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0162]

[0163] 2. A method for preparing a protective film, comprising the following steps:

[0164] S1. Printing and Lamination of High-Density PE Base Film 11: The printing and lamination process of the high-density PE base film 11 is completed using a five-color gravure printing laminator. The specific steps are as follows: The printing oven is turned on and heated to a set temperature of 80±3℃; the lamination adhesive drying oven is turned on and heated, with the temperature set for zone one at 60±3℃ and zone two at 75±3℃. After reaching the set temperature, the temperature is maintained for 30 minutes. Five different colored inks are diluted with ethyl acetate and isopropanol at a mixing ratio of 95:5wt%. Corresponding gravure rollers are installed according to the designed color pattern, and the corresponding colored inks are added to the ink tank. Commercially available polyurethane lamination adhesive is added to the lamination adhesive tank and diluted with ethyl acetate to a solid content of 20±3%. The adhesive is then applied using a 200-mesh anilox roller. Place the high-density PE base film 11 on the unwinding rack, print on the surface of the first PE layer, draw the film, turn on the double-sided corona machine, turn on the printing drying fan and the composite adhesive drying fan, start the main motor, print five-color inks on the colored film surface, dry, apply composite adhesive, dry in the coating oven, and when rewinding, use transparent PE film 13 to laminate the ink surface, rewind, and control the printing and laminating speed to 100m / min.

[0165] S2. Coating of High-Density PE Base Film 11 with Acrylic Pressure-Sensitive Adhesive: The process of coating high-density PE base film 11 with acrylic pressure-sensitive adhesive is completed using a thin film coating machine. The specific steps are as follows: The coating oven is turned on and heated. The set temperatures are 70±3℃ for zone 1, 90±3℃ for zone 2, 110±3℃ for zone 3, 110±3℃ for zone 4, and 85±3℃ for zone 5. After reaching the set temperatures, the temperature is maintained for 30 minutes. The high-density PE base film 11 prepared in step 1) is placed on the unwinding rack. Adhesive is applied to the surface of the third PE layer. The film is drawn up, and commercially available two-component water-based acrylic pressure-sensitive adhesive is added to the adhesive tank. It is diluted with a small amount of deionized water to a solid content of 50±2%. The adhesive is filtered through a 300-mesh nylon mesh and coated using a 10-mesh anilox roller. The main motor is started, and adhesive is applied to the black surface of the PE base film. After drying in the coating oven, the film is wound up, and the coating speed is controlled at 35±5 m / min. Complete the preparation of the protective film.

[0166] S3. Curing and performance testing of the protective film: The protective film prepared in step S2 is placed in a curing chamber and heated to complete the curing reaction of the pressure-sensitive adhesive. It is placed at a curing temperature of 45±5℃ for 48 hours. After the curing process is completed, samples are taken for relevant performance testing.

[0167] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0168] Example 4

[0169] 1. A method for preparing a high-density PE-based film 11, differing from Example 1 only in the raw materials:

[0170] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0171] The first PE layer 1 is composed of the following raw materials in parts by weight:

[0172]

[0173] The second PE layer 2 is composed of the following raw materials in parts by weight:

[0174] 4 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0175] 24 parts of low-density PE resin;

[0176] 72 parts of modified nano-barium sulfate masterbatch;

[0177] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0178]

[0179] 2. A method for preparing a protective film, comprising the following steps:

[0180] S1. Printing and Lamination of High-Density PE Base Film 11: The printing and lamination process of the high-density PE base film 11 is completed using a five-color gravure printing laminator. The specific steps are as follows: The printing oven is turned on and heated to a set temperature of 80±3℃; the lamination adhesive drying oven is turned on and heated, with the temperature set for zone one at 60±3℃ and zone two at 75±3℃. After reaching the set temperature, the temperature is maintained for 30 minutes. Five different colored inks are diluted with ethyl acetate and isopropanol at a mixing ratio of 95:5wt%. Corresponding gravure rollers are installed according to the designed color pattern, and the corresponding colored inks are added to the ink tank. Commercially available polyurethane lamination adhesive is added to the lamination adhesive tank and diluted with ethyl acetate to a solid content of 20±3%. The adhesive is then applied using a 200-mesh anilox roller. Place the high-density PE base film 11 on the unwinding rack, print on the surface of the first PE layer, draw the film, turn on the double-sided corona machine, turn on the printing drying fan and the composite adhesive drying fan, start the main motor, print five-color inks on the colored film surface, dry, apply composite adhesive, dry in the coating oven, and when rewinding, use transparent PE film 13 to laminate the ink surface, rewind, and control the printing and laminating speed to 85m / min.

[0181] S2. Coating of High-Density PE Base Film 11 with Acrylic Pressure-Sensitive Adhesive: The process of coating high-density PE base film 11 with acrylic pressure-sensitive adhesive is completed using a thin film coating machine. The specific steps are as follows: The coating oven is turned on for heating. The set temperatures are 70±3℃ for zone 1, 90±3℃ for zone 2, 110±3℃ for zone 3, 110±3℃ for zone 4, and 85±3℃ for zone 5. After reaching the set temperatures, the temperature is maintained for 30 minutes. The high-density PE base film 11 prepared in step 1) is placed on the unwinding rack. Adhesive is applied to the surface of the third PE layer. The film is drawn up, and commercially available two-component water-based acrylic pressure-sensitive adhesive is added to the adhesive tank. It is diluted with a small amount of deionized water to a solid content of 50±2%. The adhesive is filtered through a 300-mesh nylon mesh and coated using a 10-mesh anilox roller. The main motor is started, and adhesive is applied to the surface of the third PE layer of the PE base film. After drying in the coating oven, the film is wound up, and the coating speed is controlled at 35±5 m / min. Complete the preparation of the protective film.

[0182] S3. Curing and performance testing of the protective film: The protective film prepared in step S2 is placed in a curing chamber and heated to complete the curing reaction of the pressure-sensitive adhesive. It is placed at a curing temperature of 45±5℃ for 48 hours. After the curing process is completed, samples are taken for relevant performance testing.

[0183] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0184] Comparative Example 1

[0185] 1. A method for preparing a high-density PE base film 11, differing from Example 1 only in the raw materials: the first PE layer 1 of the PE base film does not contain filler masterbatch, and the raw materials are specifically:

[0186] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0187] The first PE layer 1 is composed of the following parts by weight of raw materials:

[0188]

[0189] The second PE layer 2 is composed of the following parts by weight of raw materials:

[0190] 4 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0191] 23 parts of low-density PE resin;

[0192] 73 parts of modified nano-barium sulfate masterbatch;

[0193] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0194]

[0195]

[0196] 2. The preparation method of a protective film is the same as in Example 1.

[0197] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0198] Comparative Example 2

[0199] 1. A method for preparing a high-density PE base film 11, differing from Example 1 only in the raw materials: the second PE layer 2 of the PE base film does not contain filler masterbatch; specifically, the raw materials are:

[0200] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0201] The first PE layer 1 is composed of the following parts by weight of raw materials:

[0202]

[0203] The second PE layer 2 is composed of the following parts by weight of raw materials:

[0204] 4 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0205] 96 parts of low-density PE resin;

[0206] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0207]

[0208] 2. The preparation method of a protective film is the same as in Example 1.

[0209] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0210] Comparative Example 3

[0211] 1. A method for preparing a high-density PE-based film 11, differing from Example 1 only in the raw materials: the third PE layer 3 of the PE-based film does not contain filler masterbatch; specifically, the raw materials are:

[0212] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0213] The first PE layer 1 is composed of the following parts by weight of raw materials:

[0214]

[0215] The second PE layer 2 is composed of the following parts by weight of raw materials:

[0216] 4 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0217] 23 parts of low-density PE resin;

[0218] 73 parts of modified nano-barium sulfate masterbatch;

[0219] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0220]

[0221] 2. The preparation method of a protective film is the same as in Example 1.

[0222] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0223] Comparative Example 4

[0224] 1. A method for preparing a high-density PE base film 11, differing from Example 1 only in the raw materials: the first PE layer 1, the second PE layer 2, and the third PE layer 3 of the PE base film do not contain maleic anhydride-vinyltriethoxysilane copolymer resin. Specifically, the raw materials are:

[0225] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0226] The first PE layer 1 is composed of the following parts by weight of raw materials:

[0227]

[0228] The second PE layer 2 is composed of the following parts by weight of raw materials:

[0229] 27 parts of low-density PE resin;

[0230] 73 parts of modified nano-barium sulfate masterbatch;

[0231] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0232]

[0233]

[0234] 2. The preparation method of a protective film is the same as in Example 1.

[0235] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0236] Comparative Example 5

[0237] 1. A method for preparing a high-density PE-based film 11, differing from Example 1 only in the raw materials: the maleic anhydride-vinyltriethoxysilane copolymer resin in the PE-based film is replaced with an equal mass of 3-(2,3-epoxypropane)propyltrimethoxysilane (KH-560). Specifically, the raw materials are:

[0238] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0239] The first PE layer 1 is composed of the following parts by weight of raw materials:

[0240]

[0241] The second PE layer 2 is composed of the following parts by weight of raw materials:

[0242] 4 parts of 3-(2,3-epoxypropoxy)propyltrimethoxysilane;

[0243] 23 parts of low-density PE resin;

[0244] 73 parts of modified nano-barium sulfate masterbatch;

[0245] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0246]

[0247] 2. The preparation method of a protective film is the same as in Example 1.

[0248] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0249] Comparative Example 6

[0250] 1. A method for preparing a high-density PE-based film 11, differing from Example 1 only in the raw materials: the modified nano-calcium carbonate masterbatch in the PE-based film is replaced with an equal mass of commercially available general-purpose nano-calcium carbonate masterbatch; the modified nano-barium sulfate masterbatch in the PE-based film is replaced with an equal mass of commercially available general-purpose nano-barium sulfate masterbatch. Specifically, the raw materials are:

[0251] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0252] The first PE layer 1 is composed of the following parts by weight of raw materials:

[0253]

[0254] The second PE layer 2 is composed of the following parts by weight of raw materials:

[0255] 4 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0256] 23 parts of low-density PE resin;

[0257] 73 parts of nano barium sulfate masterbatch;

[0258] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0259]

[0260] 2. The preparation method of a protective film is the same as in Example 1.

[0261] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0262] Comparative Example 7

[0263] 1. A method for preparing a high-density PE-based film 11, differing from Example 1 only in the amount of maleic anhydride-vinyltriethoxysilane copolymer resin used; the specific raw materials are as follows:

[0264] The raw material components of the first PE layer 1, the second PE layer 2, and the third PE layer 3 are weighed out according to the following parts by weight, mixed evenly, and added to the corresponding hoppers. A composite film is then prepared using a three-layer melt co-extrusion blown film process:

[0265] The first PE layer 1 is composed of the following parts by weight of raw materials:

[0266]

[0267]

[0268] The second PE layer 2 is composed of the following parts by weight of raw materials:

[0269] 2 parts of maleic anhydride-vinyltriethoxysilane copolymer resin;

[0270] 23 parts of low-density PE resin;

[0271] 73 parts of modified nano-barium sulfate masterbatch;

[0272] The third PE layer 3 is composed of the following raw materials in parts by weight:

[0273]

[0274] 2. The preparation method of a protective film is the same as in Example 1.

[0275] The prepared high-density PE film and protective film were tested for PE base film thickness, density, transverse tensile strength, transverse elongation at break, longitudinal tensile strength, and longitudinal elongation at break; the protective film was tested for peel strength, presence of residual adhesive and speckles after high-temperature and high-humidity aging, and presence of powdering and cracking after 20 days of ultraviolet aging. The test results are shown in Table 1.

[0276] Table 1. Summary of performance test results for each embodiment and comparative example.

[0277]

[0278]

[0279] Thickness test: The thickness of the PE film was tested according to GB / T7125-2014 "Test method for thickness of adhesive tape". The thickness was measured 5 times at different locations and the average value was taken.

[0280] Density test: The density of PE film was tested according to GB / T36053-2018 "X-ray reflection method for measuring the thickness, density and interface width of thin films". The density was measured 5 times at different locations and the average value was taken.

[0281] Mechanical property testing: Mechanical property testing was conducted according to GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", with an ambient temperature of 23±1℃ and a relative humidity of 55±5%. PE film was cut into 10mm wide strips, and tensile strength and elongation at break were tested using a material tensile testing machine. The tests were performed in three parallel trials, and the average value was taken.

[0282] Peel strength test: The peel strength performance was tested according to GB / T2792-2014 "Test Method for Peel Strength of Adhesive Tapes" at an ambient temperature of 23±1℃ and a relative humidity of 55±5%. The protective film was cut into strips 25mm wide and 250mm long. The mirror steel plate was cleaned with anhydrous alcohol and left for 30 minutes. The protective film was then attached to the steel plate and rolled back and forth three times with a 1kg roller. After leaving for 20 minutes, the peel strength was measured three times in parallel, and the average value was taken.

[0283] Damp heat aging test: The damp heat aging test was conducted according to GB / T2423.3-2014 "Basic Environmental Testing Procedures for Electrical and Electronic Products - Test Ca: Constant Damp Heat Test Method". The protective film sample was cut into 50mm*200mm strips. After wiping the surface of the thermally broken aluminum profile clean with anhydrous alcohol and letting it stand for 30 minutes, the protective film was attached to the surface of the aluminum profile. A 1kg roller was used to roll the strips back and forth three times. After standing for 20 minutes, the damp heat aging performance test was started at 70℃ and 95% relative humidity for 96 hours.

[0284] Ultraviolet (UV) Aging Test: The UV aging test was conducted according to GB / T16422.3-2014 "Laboratory Light Source Exposure Test Methods for Plastics - Part 3: Fluorescent UV Lamps". The protective film sample was cut into 50mm*200mm strips, fixed on a glass slide using clamps, and the UV lamp was turned on for the aging performance test. The UVA340 UV light wavelength was 295–365nm, and the light intensity was 0.68w / m². 2Irradiation time: 20 days, temperature: 50±5℃.

[0285] As shown in Table 1, the high-density PE film prepared using the method of the present invention exhibits a relatively high density in Examples 1, 2, 3, and 4, with density values ​​ranging from 1.43 to 1.52 g / cm³. 3 The longitudinal tensile strength is 13.5–14.6 MPa, the transverse tensile strength is 10.9–11.9 MPa, the longitudinal elongation at break is 590–670%, and the transverse elongation at break is 450–528%. Both tensile strength and elongation at break exhibit good mechanical properties, meeting application requirements. After coating the protective film prepared from this high-density PE base film 11 with pressure-sensitive adhesive, a series of protective films with different peel strengths can be prepared under the cohesive strength of the pressure-sensitive adhesive and the interfacial adhesion. After aging at 70℃ and 95% relative humidity for 96 hours, no adhesive residue or bleed-like phenomena were observed. Under ultraviolet light with a wavelength of 295–365 nm and an irradiation intensity of 0.68 W / m², the protective film showed good performance. 2 After 20 days of irradiation, no pulverization or cracking was observed.

[0286] In Comparative Example 1, the first PE layer 1 of the PE base film did not contain modified nano-calcium carbonate masterbatch; in Comparative Example 2, the second PE layer 2 did not contain modified nano-barium sulfate masterbatch; in Comparative Example 3, the third PE layer 3 did not contain modified nano-calcium carbonate masterbatch; and in Comparative Example 4, the first PE layer 1, the second PE layer 2, and the third PE layer 3 did not contain maleic anhydride-vinyltriethoxysilane copolymer resin. Due to the reduction in modified masterbatch in Comparative Examples 1, 2, and 3, the density of the corresponding PE base films decreased, but the tensile strength and elongation at break did not increase significantly. This indicates that the modified nano-calcium carbonate masterbatch and the modified nano-barium sulfate masterbatch have a certain reinforcing effect on the PE base film. The protective films prepared from the PE base films of Comparative Examples 1 and 2 did not exhibit residual adhesive or speckling after high-temperature and high-humidity aging performance testing. No powdering or cracking was observed after UV aging. However, the protective film of Comparative Example 3 exhibited residual adhesive and speckling after high-temperature and high-humidity aging. Comparative Example 4, lacking maleic anhydride-vinyltriethoxysilane copolymer resin, showed a significant decrease in tensile strength and elongation at break, rendering it unusable. The protective film prepared with this resin exhibited residual adhesive and speckling after high-temperature and high-humidity aging, and showed powdering and cracking after UV aging. Comparative Example 5 used the conventional coupling agent 3-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560) instead of the maleic anhydride-vinyltriethoxysilane copolymer resin. Comparative Example 6 used general-purpose calcium carbonate masterbatch and general-purpose barium sulfate masterbatch instead of the modified nano-calcium carbonate masterbatch and modified nano-barium sulfate masterbatch, respectively. Comparative Example 7 reduced the amount of maleic anhydride-vinyltriethoxysilane copolymer resin. The mechanical properties of the prepared PE film, as well as the high-temperature and high-humidity aging performance and UV aging resistance of the protective film, all showed varying degrees of decline, with mechanical properties and aging resistance inferior to Examples 1-4.

[0287] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-density PE-based film, characterized in that, The high-density PE base film comprises a first PE layer, a second PE layer, and a third PE layer arranged sequentially, wherein: The first PE layer comprises the following parts by weight of raw materials: 3-4 parts of maleic anhydride-vinyltriethoxysilane copolymer resin; 15-16 parts of metallocene-catalyzed linear low-density PE resin; 24-26 parts of low-density PE resin; 50-53 parts of modified nano-calcium carbonate masterbatch; 5-6 parts of colored masterbatch; The second PE layer comprises the following parts by weight of raw materials: 3-5 parts of maleic anhydride-vinyltriethoxysilane copolymer resin; 20-25 parts of low-density PE resin; 70-75 parts of modified nano-barium sulfate masterbatch; The third PE layer comprises the following parts by weight of raw materials: 3-4 parts of maleic anhydride-vinyltriethoxysilane copolymer resin; 10-12 parts of metallocene-catalyzed linear low-density PE resin; 46-48 parts of low-density PE resin; 30-33 parts of modified nano-calcium carbonate masterbatch; 5-6 parts of black masterbatch; The thickness ratio of the first PE layer, the second PE layer, and the third PE layer is 23-27:46-54:23-27; The modified nano-calcium carbonate masterbatch and / or modified nano-barium sulfate masterbatch are filler masterbatches; The filler masterbatch comprises the following raw materials in parts by weight: 4-6 parts maleic anhydride-grafted ethylene-vinyl acetate resin, 18-22 parts linear low-density PE resin, 68-72 parts aluminate coupling agent modified nano-inorganic salt powder, 2.5-3.5 parts maleic anhydride-grafted oxidized polyethylene wax, and 1.8-2.2 parts antioxidant pentaerythritol diphosphite; wherein the aluminate coupling agent modified nano-inorganic salt powder is aluminate coupling agent modified nano-calcium carbonate powder and / or aluminate coupling agent modified nano-barium sulfate powder; The preparation of the filler masterbatch includes the following steps: mixing aluminate coupling agent modified nano-inorganic salt powder, maleic anhydride grafted oxidized polyethylene wax and antioxidant bis(octadecyl alcohol) pentaerythritol diphosphite to obtain a first mixture; mixing the first mixture with maleic anhydride grafted ethylene-vinyl acetate resin and linear low-density PE resin to obtain a second mixture; and then transferring the second mixture to a twin-screw extruder for extrusion granulation.

2. The high-density PE-based film according to claim 1, characterized in that, The mixing temperature of the raw materials for the filler masterbatch is 60~70℃.

3. The high-density PE-based film according to claim 1, characterized in that, The twin-screw extruder has a zone temperature of 155±2℃, a zone temperature of 170±2℃, a zone temperature of 170±2℃, and a die temperature of 165±2℃.

4. The high-density PE-based film according to claim 1, characterized in that, Maleic anhydride and vinyltriethoxysilane were used as raw materials, ethyl acetate was used as solvent, and azobisisobutyronitrile was used as initiator to undergo a free radical copolymerization reaction to obtain maleic anhydride-vinyltriethoxysilane copolymer resin.

5. The high-density PE-based film according to claim 4, characterized in that, The molar ratio of maleic anhydride, vinyltriethoxysilane and ethyl acetate is 2.5~3.5:1:2.5~3.

5.

6. The high-density PE-based film according to claim 4, characterized in that, The amount of the initiator is 0.45 wt% to 0.55 wt% of the total weight of maleic anhydride and vinyltriethoxysilane.

7. The high-density PE-based film according to claim 4, characterized in that, Maleic anhydride, vinyltriethoxysilane, ethyl acetate, and azobisisobutyronitrile were mixed and separated into a first reactant and a second reactant. The first reactant was placed in a water bath at 75±2℃. When the viscosity and temperature of the first reactant began to increase, the second reactant was added dropwise, and the addition time of the second reactant was controlled to be 50min~70min. After the addition was completed, the reaction continued for 4h~6h. The solvent was then evaporated to obtain a copolymer resin of maleic anhydride and vinyltriethoxysilane.

8. The high-density PE-based film according to claim 7, characterized in that, The volume ratio of the first reactant to the second reactant is 2.8-3.2:

7.

9. The high-density PE-based film according to claim 1, characterized in that, Density ≥ 1.40 g / cm³ 3 The transverse tensile strength is ≥10.5MPa, and the transverse elongation at break is ≥450%; the longitudinal tensile strength is ≥12.5MPa, and the longitudinal elongation at break is ≥550%; the surface tension of the third PE layer after being placed at room temperature for 180 days is ≥42mN / m.

10. A method for preparing a high-density PE-based film according to any one of claims 1-9, characterized in that, include: The high-density PE base film is obtained by melt co-extrusion blown film of the first PE layer, the second PE layer and the third PE layer.

11. The method for preparing a high-density PE-based film according to claim 10, characterized in that, The temperature settings for each zone of the screw extruder corresponding to the first PE layer are as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 30±2r / min. And / or, the temperature settings for each zone of the screw extruder corresponding to the second PE layer are as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 60±2r / min; And / or, the temperatures of each zone of the screw extruder corresponding to the third PE layer are set as follows: Zone 1 148±2℃, Zone 2 155±2℃, Zone 3 160±2℃, Zone 4 165±2℃, Zone 5 160±2℃, Runner 160±2℃, Die 160±2℃, and the screw speed is set to 30±2r / min.

12. A protective film, characterized in that, It includes an acrylic pressure-sensitive adhesive layer, a high-density PE base film as described in any one of claims 1-9, a printed composite adhesive layer, and a transparent PE film arranged sequentially.

13. The protective film according to claim 12, characterized in that, The high-density PE base film has a thickness of 140±2μm, the printed composite adhesive layer has a thickness of 2±0.5μm, the transparent PE film has a thickness of 25±1μm, and the acrylic pressure-sensitive adhesive layer has a thickness of 33±3μm.

14. The protective film according to claim 12, characterized in that, The protective film exhibits a peel strength of ≥8N / 25mm on SUS304 mirror steel plate. After 96 hours of heating at 70℃ and 95% relative humidity, it leaves no residual adhesive or blemishes on the surface of the thermally broken aluminum profile. After 20 days of ultraviolet aging, it shows no powdering or cracking.

15. A method for preparing the protective film according to any one of claims 12-14, characterized in that, include: Printing and laminating of high-density PE base film, coating of high-density PE base film with acrylic pressure-sensitive adhesive and curing of protective film.

16. The method for preparing the protective film according to claim 15, characterized in that, The printing and lamination of the high-density PE base film includes: coating a composite adhesive on the surface of the first PE layer of the high-density PE base film and drying it, and then laminating it with the composite adhesive surface of the transparent PE film during winding.

17. The method for preparing the protective film according to claim 16, characterized in that, Before coating the composite adhesive onto the high-density PE base film, ink printing and drying are performed on the surface of the first PE layer of the high-density PE base film. The ink is diluted with ethyl acetate and isopropanol, and the mass ratio of ethyl acetate to isopropanol is 94~96:

5. After ink printing, the high-density PE base film is dried at 80±3℃.

18. The method for preparing the protective film according to claim 16, characterized in that, A 200-mesh anilox roller is used to coat the surface of the first PE layer of the high-density PE base film with polyurethane composite adhesive. The polyurethane composite adhesive is diluted with ethyl acetate to a solid content of 20±3% before being coated onto the high-density PE base film.

19. The method for preparing the protective film according to claim 16, characterized in that, The composite adhesive is dried using a composite adhesive drying oven, wherein the temperature of zone one is set at 60±3℃ and the temperature of zone two is set at 75±3℃.

20. The method for preparing the protective film according to claim 16, characterized in that, The speed at which transparent PE film is laminated with printed adhesive is 80 m / min ~ 100 m / min.

21. The method for preparing the protective film according to claim 15, characterized in that, The high-density PE base film coated with acrylic pressure-sensitive adhesive includes: coating the surface of the third PE layer of the PE base film with acrylic pressure-sensitive adhesive, drying it in a coating oven, and then winding it up.

22. The method for preparing the protective film according to claim 21, characterized in that, The coating oven is set to a temperature of 70±3℃ for zone 1, 90±3℃ for zone 2, 110±3℃ for zone 3, 110±3℃ for zone 4, and 85±3℃ for zone 5.

23. The method for preparing the protective film according to claim 21, characterized in that, Before coating, the acrylic pressure-sensitive adhesive is first diluted with deionized water to a solid content of 50±2%, then the adhesive is filtered through a 300-mesh nylon mesh and coated with a 10-20 mesh anilox roller.

24. The method for preparing the protective film according to claim 21, characterized in that, The acrylic pressure-sensitive adhesive is applied at a speed of 35±5m / min.

25. The method for preparing the protective film according to claim 15, characterized in that, The curing temperature is 45±5℃ and the curing time is 48±2h.

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