Anti-aging PET protective film and preparation method thereof

Abstract

The invention relates to the technical field of functional polymer films, and particularly discloses an anti-aging PET (Polyethylene Terephthalate) protective film and a preparation method thereof. The anti-aging PET protective film comprises a PET base film layer and a weather-resistant coating, and the weather-resistant coating is obtained by coating the surface of the PET base film layer with a coating liquid; the PET base film layer is prepared from the following raw materials in parts by weight: first PET resin and anti-aging PET master batch; the anti-aging PET master batch is prepared from the following raw materials: second PET resin, a shielding agent, an ultraviolet light absorber, a stabilizer and an antioxidant; the mass ratio of the second PET resin to the screening agent to the ultraviolet light absorber to the stabilizer to the antioxidant is (55-65): (2-4): (0.7-1): (1-2): (0.1-0.2); the coating liquid is prepared from the following raw materials in parts by weight: fluorosilicone modified acrylic resin, modified filler, a composite cross-linking agent, a flatting agent and a solvent. The anti-aging performance of the PET protective film can be durable and stable.

Description

Technical Field

[0001] This invention relates to the field of functional polymer film technology, and in particular to an aging-resistant PET protective film and its preparation method. Background Technology

[0002] PET protective film, as a functional polymer film material, is widely used in long-term protection applications in outdoor or high-light environments due to its excellent mechanical strength, transparency, and chemical stability. Examples include solar panel backsheets, outdoor advertising light boxes, building exterior wall decorative films, automotive body wraps, and electronic device screen protectors. However, under long-term exposure to environmental stresses such as ultraviolet radiation, high temperatures, oxygen, and moisture, ordinary PET materials are prone to photo-oxidative degradation and thermo-oxidative aging of the molecular chains. This leads to problems such as yellowing, embrittlement, significant decreases in mechanical properties (tensile strength and elongation at break), and surface powdering.

[0003] To improve the aging resistance of PET materials, existing technologies typically employ the addition of aging-resistant additives. For example, small-molecule additives such as UV absorbers and antioxidants are incorporated into the PET substrate to inhibit photo-oxidation and thermo-oxidative aging processes, thereby extending the material's lifespan. However, due to their small molecular weight, these aging-resistant additives are prone to migration, volatilization, or precipitation during film processing and long-term use. This leads to a rapid decline in their stabilizing effect over time, failing to provide long-term protection. Furthermore, the precipitated additives may contaminate the substrate or the surrounding environment. Summary of the Invention

[0004] In order to achieve long-lasting and stable anti-aging performance of PET protective film, this application provides an anti-aging PET protective film and its preparation method.

[0005] Firstly, this application provides an aging-resistant PET protective film, which adopts the following technical solution: An aging-resistant PET protective film includes a PET base film layer and a weather-resistant coating, wherein the weather-resistant coating is obtained by coating the surface of the PET base film layer with a coating liquid. The PET base film layer comprises the following raw materials in parts by weight: 70-80 parts of first PET resin and 20-30 parts of aging-resistant PET masterbatch; The raw materials for preparing the aging-resistant PET masterbatch include a second PET resin, a shielding agent, an ultraviolet absorber, a stabilizer, and an antioxidant; the mass ratio of the second PET resin, the shielding agent, the ultraviolet absorber, the stabilizer, and the antioxidant is (55-65):(2-4):(0.7-1):(1-2):(0.1-0.2). The coating liquid comprises the following raw materials in parts by weight: 40-50 parts of fluorosilicone modified acrylic resin, 3-5 parts of modified filler, 4-6 parts of composite crosslinking agent, 1-2 parts of leveling agent, and 45-55 parts of solvent.

[0006] By adopting the above technical solution, aging-resistant PET masterbatch is added to the PET base film layer. Through the shielding agent, ultraviolet absorber, stabilizer and antioxidant contained in the masterbatch, the photo-oxidation and thermo-oxidative aging process of PET material can be inhibited, thereby improving the aging resistance of the PET base film layer.

[0007] The coating solution uses fluorosilicone-modified acrylic resin as the film-forming agent. This resin possesses excellent UV resistance and chemical stability, effectively improving the aging performance of the coating, preventing hot-stickiness and cold-brittleness, and enhancing weather resistance while also providing better mechanical properties. The fluorosilicone-modified acrylic resin molecular chain contains Si-O and CF bonds with high bond energy, and the CF bond energy forms a "shielding protection" on the CC backbone, resulting in good stability. The fillers in the coating solution, after modification, are uniformly dispersed in the resin system. Under the action of the composite crosslinking agent, they are tightly bound to the resin molecular chain, forming a "maze" effect within the coating. This significantly extends the penetration paths of ultraviolet light, oxygen, and moisture, thereby further improving the coating's aging resistance. Furthermore, the composite crosslinking agent reacts with the carboxyl and hydroxyl groups in the resin molecules, transforming the linear molecular chains into a molecular network structure. Simultaneously, the composite crosslinking agent, combined with a gradient curing process, controls the curing temperature and time in stages, which can avoid stress concentration inside the coating caused by excessively fast curing rates, reduce the generation of microcracks, and promote a more complete crosslinking reaction, making the molecular network structure more uniform and dense, thereby further improving the impact resistance and weather resistance of the coating.

[0008] Preferably, the composite crosslinking agent comprises diisocyanate and etherified melamine-formaldehyde resin in a mass ratio of 1:(0.3-0.6).

[0009] Preferably, the etherified melamine-formaldehyde resin includes one or two of methyl etherified hexamethyl hydroxymethyl melamine resin and isobutyl etherified melamine-formaldehyde resin; the diisocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0010] By employing the above technical solution, diisocyanate can rapidly crosslink with the resin to form a preliminary network structure. The etherified melamine-formaldehyde resin contains hydroxymethyl, methoxy, and triazine ring structures, which are introduced as crosslinking agents. During the subsequent high-temperature drying and curing process, these agents further undergo crosslinking and polycondensation reactions with the polar groups -OH and -COOH in the resin molecules. The synergistic effect of both increases the crosslinking density of the coating and simultaneously imparts excellent weather resistance to the coating.

[0011] Preferably, the method for preparing the modified filler includes the following steps: (1) Disperse the nanofiller in water and add long-chain alkylammonium salt. Heat the mixture to react. After the reaction is complete, filter and collect the precipitate. Wash and dry the precipitate to obtain the intercalated modified filler. The mass ratio of the nanofiller to the long-chain alkylammonium salt is 1: (0.6-0.8). (2) After adding anhydrous ethanol and mercaptosilane to the intercalated modified filler, heating and stirring, filtering to remove the filtrate, washing, and drying, the surface modified filler is obtained; the mass ratio of the intercalated modified filler to mercaptosilane is (2-4):(4-6). (3) Add anhydrous ethanol, cashew phenol and photoinitiator to the surface modified filler, stir under ultraviolet irradiation, filter to remove filtrate, wash and dry to obtain modified filler; the mass ratio of the surface modified filler, cashew phenol and photoinitiator is (5-6): (2-3): (0.3-0.5).

[0012] By employing the above technical solution, firstly, the cation exchange of long-chain alkylammonium salts is used to insert them between the filler layers, which can expand the interlayer spacing of the nanofillers and improve dispersibility. Then, mercaptosilanes are introduced onto the filler surface, and through a click reaction between the mercaptosilanes and the carbon-carbon double bonds in cashew nut shell phenol, cashew nut shell phenol is introduced onto the filler particle surface, enhancing the compatibility of the filler in the resin system. Under the action of a composite crosslinking agent, chemical bridging between the inorganic filler and the organic resin is achieved, effectively improving the interfacial bonding strength. Furthermore, the grafting of cashew nut shell phenol introduces flexible long chains, improving the elongation at break of the coating.

[0013] Preferably, the nanofiller includes one or both of nano-mica powder and graphene nanosheets.

[0014] By adopting the above technical solution, the sheet-like structure of nano-mica powder and graphene nanosheets can form a multi-layer physical barrier in the coating, effectively improving the reflectivity of ultraviolet rays and significantly delaying the photoaging process.

[0015] Preferably, the ultraviolet absorber includes one or two of benzotriazole ultraviolet absorbers and triazine ultraviolet absorbers.

[0016] Preferably, the stabilizer is a hindered amine light stabilizer.

[0017] By employing the above technical solution, the ultraviolet absorber acts in the photoinitiation stage, reducing the energy of ultraviolet light entering the material by absorbing it; the hindered amine light stabilizer acts in the chain oxidation stage, transforming into active nitroxide free radicals under the action of a small amount of free radicals or oxidizing substances. This effectively captures destructive free radicals in the material, interrupting the oxidation chain reaction, while the reaction intermediates react with other free radicals to regenerate active nitroxide free radicals, forming a cycle. The free radicals scavenged by the hindered amine light stabilizer include active free radicals that could attack the ultraviolet absorber, delaying its photodegradation. Meanwhile, the ultraviolet absorber reduces the formation of hydrogen peroxide, lowering the oxidative burden on the hindered amine light stabilizer and extending its function and lifespan. Through synergistic action, both achieve highly efficient protection of the material.

[0018] Preferably, the shielding agent includes one or two of nano-cerium oxide and zinc oxide; the antioxidant includes one or more of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0019] By adopting the above technical solutions, the shielding agent has broadband characteristics and can physically reflect or scatter ultraviolet rays; the antioxidant can effectively capture the free radicals generated by PET materials during photo-oxidation and thermo-oxidative aging, terminate the free radical chain reaction, inhibit the breakage and degradation of PET molecular chains, thereby slowing down the aging rate of PET materials and improving the aging resistance of PET protective films.

[0020] Preferably, the leveling agent includes one or more of BYK-3481, BYK-381, and BYK-333.

[0021] By adopting the above technical solutions, BYK series leveling agents can reduce the surface tension of the coating liquid, promote the uniform spreading of the coating on the base film surface, and avoid defects such as pinholes and orange peel.

[0022] Secondly, this application provides a method for preparing an aging-resistant PET protective film, which adopts the following technical solution: A method for preparing an aging-resistant PET protective film includes the following steps: S1. The second PET resin is thoroughly mixed with a shielding agent, an ultraviolet absorber, a stabilizer, and an antioxidant, and then extruded and granulated to obtain an aging-resistant PET masterbatch; the aging-resistant PET masterbatch is mixed with the first PET resin, and then dried, melt-extruded, cast, stretched longitudinally, stretched transversely, heat-set, and wound to obtain a PET base film layer. S2. Mix the fluorosilicone modified acrylic resin, modified filler, composite crosslinking agent, leveling agent and solvent according to the weight parts, and store in the dark after mixing to obtain the coating liquid; S3. The PET base film layer is subjected to corona treatment, and the coating liquid is uniformly coated on the surface of the PET base film layer. After gradient curing, a weather-resistant coating is formed, resulting in an aging-resistant PET protective film.

[0023] By adopting the above technical solutions, the step-by-step preparation of aging-resistant PET masterbatch can ensure that functional additives such as shielding agents and ultraviolet absorbers are uniformly dispersed in the base film, avoiding agglomeration; corona treatment can increase the surface tension of the base film and significantly enhance the coating adhesion; the coating adopts a gradient curing process for segmented control, which improves the coating crosslinking degree and reduces internal stress, thereby reducing the phenomenon of coating cracking.

[0024] This application has the following beneficial effects: Adding aging-resistant PET masterbatch to the PET base film layer can inhibit the photo-oxidation and thermo-oxidative aging process of PET materials and improve the aging resistance of the PET base film layer through the shielding agents, ultraviolet absorbers, stabilizers and antioxidants contained in the masterbatch.

[0025] The coating solution uses fluorosilicone-modified acrylic resin as the film-forming agent. This resin possesses excellent UV resistance and chemical stability, effectively improving the aging performance of the coating, preventing hot-stickiness and cold-brittleness, and enhancing weather resistance while also providing better mechanical properties. The fluorosilicone-modified acrylic resin molecular chain contains Si-O and CF bonds with high bond energy, and the CF bond energy forms a "shielding protection" on the CC backbone, resulting in good stability. The fillers in the coating solution, after modification, are uniformly dispersed in the resin system. Under the action of the composite crosslinking agent, they are tightly bound to the resin molecular chain, forming a "maze" effect within the coating. This significantly extends the penetration paths of ultraviolet light, oxygen, and moisture, thereby further improving the coating's aging resistance. Furthermore, the composite crosslinking agent reacts with the carboxyl and hydroxyl groups in the resin molecules, transforming the linear molecular chains into a molecular network structure. Simultaneously, the composite crosslinking agent, combined with a gradient curing process, controls the curing temperature and time in stages, which can avoid stress concentration inside the coating caused by excessively fast curing rates, reduce the generation of microcracks, and promote a more complete crosslinking reaction, making the molecular network structure more uniform and dense, thereby further improving the impact resistance and weather resistance of the coating. Detailed Implementation

[0026] The present application will be further described in detail below with reference to the embodiments.

[0027] Both the first PET resin and the second PET resin are commercially available PET resins; the distinction between the two is merely that the first and the second are not related.

[0028] Preparation Example 1 The preparation method of the modified filler includes the following steps: (1) Weigh the nanofiller and long-chain alkylammonium salt at a mass ratio of 1:0.6; the nanofiller is specifically selected as nanomica powder; weigh deionized water at 20 times the mass of nanomica powder; the long-chain alkylammonium salt is specifically selected as hexadecyltrimethylammonium bromide.

[0029] Nano-mica powder was dispersed in deionized water, and hexadecyltrimethylammonium bromide was added. The mixture was heated to 85°C and reacted for 3 hours. After the reaction was completed, the filtrate was removed by filtration, washed, and dried to obtain the intercalated modified filler.

[0030] (2) Weigh the intercalation modified filler and mercaptosilane at a mass ratio of 2:4; and weigh anhydrous ethanol at 25 times the mass of the intercalation modified filler; the mercaptosilane to be selected is γ-mercaptopropyltrimethoxysilane.

[0031] Anhydrous ethanol and γ-mercaptopropyltrimethoxysilane were added to the intercalation modified filler, heated to 70°C and stirred for 5 hours. The filtrate was removed by filtration, washed, and dried to obtain the surface modified filler.

[0032] (3) Weigh the surface-modified filler, cashew phenol and photoinitiator in a mass ratio of 5:2:0.3; and weigh anhydrous ethanol in a mass ratio of 20 times that of the surface-modified filler; the photoinitiator is specifically α,α-dimethoxy-α-phenylacetophenone.

[0033] Anhydrous ethanol, cashew phenol, and α,α-dimethoxy-α-phenylacetophenone were added to the surface-modified filler. The mixture was stirred at 30°C for 1.5 h under ultraviolet irradiation. The filtrate was removed by filtration, washed, and dried to obtain the modified filler.

[0034] Preparation Example 2 The preparation method of the modified filler includes the following steps: (1) Weigh the nanofiller and long-chain alkylammonium salt at a mass ratio of 1:0.7; the nanofiller is specifically selected as nanomica powder; weigh deionized water at 20 times the mass of nanomica powder; the long-chain alkylammonium salt is specifically selected as octadecyltrimethylammonium bromide.

[0035] Nano-mica powder was dispersed in deionized water, and octadecyltrimethylammonium bromide was added. The mixture was heated to 85°C and reacted for 3 hours. After the reaction was completed, the filtrate was removed by filtration, washed, and dried to obtain the intercalated modified filler.

[0036] (2) Weigh the intercalation modified filler and mercaptosilane at a mass ratio of 3:5; and weigh anhydrous ethanol at 25 times the mass of the intercalation modified filler; the mercaptosilane to be selected is γ-mercaptopropyltriethoxysilane.

[0037] Anhydrous ethanol and γ-mercaptopropyltriethoxysilane were added to the intercalation modified filler, heated to 72°C and stirred for 5.5 h, the filtrate was removed by filtration, washed and dried to obtain the surface modified filler.

[0038] (3) Weigh the surface-modified filler, cashew phenol and photoinitiator in a mass ratio of 5.5:2.5:0.4; and weigh anhydrous ethanol at 20 times the mass of the surface-modified filler; the photoinitiator is specifically α,α-dimethoxy-α-phenylacetophenone.

[0039] Anhydrous ethanol, cashew phenol, and α,α-dimethoxy-α-phenylacetophenone were added to the surface-modified filler. The mixture was stirred at 32°C for 1.8 h under ultraviolet irradiation. The filtrate was removed by filtration, washed, and dried to obtain the modified filler.

[0040] Preparation Example 3 The preparation method of the modified filler includes the following steps: (1) Weigh the nanofiller and long-chain alkylammonium salt at a mass ratio of 1:0.8; the nanofiller is specifically selected as nanomica powder; weigh deionized water at 20 times the mass of nanomica powder; the long-chain alkylammonium salt is specifically selected as octadecyltrimethylammonium bromide.

[0041] Nano-mica powder was dispersed in deionized water, and octadecyltrimethylammonium bromide was added. The mixture was heated to 85°C and reacted for 3 hours. After the reaction was completed, the filtrate was removed by filtration, washed, and dried to obtain the intercalated modified filler.

[0042] (2) Weigh the intercalation modified filler and mercaptosilane at a mass ratio of 4:6; and weigh anhydrous ethanol at 25 times the mass of the intercalation modified filler; the mercaptosilane to be selected is γ-mercaptopropyltrimethoxysilane.

[0043] Anhydrous ethanol and γ-mercaptopropyltrimethoxysilane were added to the intercalation modified filler, heated to 75°C and stirred for 6 hours. The filtrate was removed by filtration, washed, and dried to obtain the surface modified filler.

[0044] (3) Weigh the surface-modified filler, cashew phenol and photoinitiator in a mass ratio of 6:3:0.5; and weigh anhydrous ethanol at 20 times the mass of the surface-modified filler; the photoinitiator is specifically α,α-dimethoxy-α-phenylacetophenone.

[0045] Anhydrous ethanol, cashew phenol, and α,α-dimethoxy-α-phenylacetophenone were added to the surface-modified filler. The mixture was stirred at 35°C for 2 hours under ultraviolet irradiation. The filtrate was removed by filtration, and the filler was washed and dried to obtain the modified filler.

[0046] Preparation Example 4 The difference between this preparation example and preparation example 3 is that octadecyltrimethylammonium bromide was not added, i.e., step (1) is missing.

[0047] Preparation Example 5 The difference between this preparation example and preparation example 3 is that cashew phenol and other substances are replaced with phenol by mass.

[0048] Example 1 The preparation method of the aging-resistant PET protective film includes the following steps: S1. Weigh out PET resin, shielding agent, ultraviolet absorber, stabilizer, and antioxidant according to a mass ratio of 55:2:0.7:1:0.1; the PET resin is specifically DuPont 70G43L; the shielding agent is specifically nano-cerium oxide; the ultraviolet absorber is a benzotriazole ultraviolet absorber, specifically UV-P; the stabilizer is specifically hindered amine light stabilizer HALS; the antioxidant is specifically a mixture of antioxidant 1010 and antioxidant 168 at a mass ratio of 1:0.5.

[0049] PET resin is thoroughly mixed with nano-cerium oxide, UV-P, hindered amine light stabilizer HALS, and antioxidants 1010 and 168, and then extruded and granulated to obtain aging-resistant PET masterbatch; 20 parts of aging-resistant PET masterbatch are mixed with 70 parts of PET resin, and then dried, melt-extruded, cast, stretched longitudinally, stretched transversely, heat-set and wound to obtain PET base film layer.

[0050] S2. Weigh the raw materials according to the following weight proportions: 40 parts of fluorosilicone modified acrylic resin, 3 parts of modified filler, 4 parts of composite crosslinking agent, 1 part of leveling agent, and 45 parts of solvent; the modified filler is prepared by Preparation Example 1; the composite crosslinking agent is specifically toluene diisocyanate and methyl etherified hexamethyl melamine resin in a mass ratio of 1:0.3; the leveling agent is specifically BYK-3481; and the solvent is specifically ethyl acetate.

[0051] Fluorosilicone modified acrylic resin, modified filler, toluene diisocyanate, methyl etherified hexamethyl hydroxymethyl melamine resin, BYK-3481 and ethyl acetate were mixed according to the weight parts, and then subjected to high-speed shearing and sand milling. After mixing, the mixture was stored in a light-proof and sealed container to obtain the coating liquid.

[0052] S3. The PET base film layer is subjected to corona treatment. The coating liquid is uniformly coated on the surface of the PET base film layer using a micro-gravure coating method. The wet film thickness is controlled to be 5μm. After passing through a 70℃ preheating oven to remove residual solvent, it is then passed through a 110℃ oven and a 140℃ oven in sequence. After deep curing, a weather-resistant coating is formed, resulting in an aging-resistant PET protective film.

[0053] Example 2 The preparation method of the aging-resistant PET protective film includes the following steps: S1. Weigh out PET resin, shielding agent, ultraviolet absorber, stabilizer, and antioxidant according to a mass ratio of 60:3:0.8:1.5:0.15; the PET resin is specifically DuPont 70G43L; the shielding agent is specifically nano zinc oxide; the ultraviolet absorber is a triazine ultraviolet absorber, specifically UV1164; the stabilizer is specifically hindered amine light stabilizer HALS; the antioxidant is specifically a mixture of antioxidant 1076 and antioxidant 168 at a mass ratio of 1:0.5.

[0054] PET resin is thoroughly mixed with nano zinc oxide, UV1164, hindered amine light stabilizer HALS, and antioxidants 1076 and 168, and then extruded and granulated to obtain aging-resistant PET masterbatch. 25 parts of aging-resistant PET masterbatch are mixed with 75 parts of PET resin, and then dried, melt-extruded, cast, stretched longitudinally, stretched transversely, heat-set and wound to obtain PET base film layer.

[0055] S2. Weigh the raw materials according to the following weight proportions: 45 parts of fluorosilicone modified acrylic resin, 4 parts of modified filler, 5 parts of composite crosslinking agent, 1.5 parts of leveling agent, and 50 parts of solvent. The modified filler was prepared by Preparation Example 2. The composite crosslinking agent was specifically isophorone diisocyanate and isobutyl etherified melamine-formaldehyde resin in a mass ratio of 1:0.5. The isobutyl etherified melamine-formaldehyde resin was sourced from Mitsui Chemicals, Japan, and its model was U-VAN 261. The leveling agent was specifically BYK-381. The solvent was specifically ethyl acetate.

[0056] Fluorosilicone modified acrylic resin, modified filler, isophorone diisocyanate, isobutyl etherified melamine-formaldehyde resin, BYK-381 and ethyl acetate were mixed according to the weight parts, and then subjected to high-speed shearing and sand milling. After mixing, the mixture was stored in a light-proof and sealed container to obtain the coating liquid.

[0057] S3. The PET base film layer is subjected to corona treatment. The coating liquid is uniformly coated on the surface of the PET base film layer using a micro-gravure coating method. The wet film thickness is controlled to be 5μm. After passing through a 75℃ preheating oven to remove residual solvent, it is then passed through a 115℃ oven and a 145℃ oven in sequence. After deep curing, a weather-resistant coating is formed, resulting in an aging-resistant PET protective film.

[0058] Example 3 The preparation method of the aging-resistant PET protective film includes the following steps: S1. Weigh out PET resin, shielding agent, ultraviolet absorber, stabilizer, and antioxidant according to a mass ratio of 65:4:1:2:0.2; the PET resin is specifically DuPont 70G43L; the shielding agent is specifically nano-cerium oxide; the ultraviolet absorber is a benzotriazole ultraviolet absorber, specifically UV-327; the stabilizer is specifically hindered amine light stabilizer HALS; the antioxidant is specifically a mixture of antioxidant 1010 and antioxidant 168 at a mass ratio of 1:0.5.

[0059] PET resin is thoroughly mixed with nano-cerium oxide, UV-327, hindered amine light stabilizer HALS, and antioxidants 1010 and 168, and then extruded and granulated to obtain aging-resistant PET masterbatch; 30 parts of aging-resistant PET masterbatch are mixed with 80 parts of PET resin, and then dried, melt-extruded, cast, stretched longitudinally, stretched transversely, heat-set and wound to obtain PET base film layer.

[0060] S2. Weigh out the raw materials according to the following weight proportions: 50 parts of fluorosilicone modified acrylic resin, 5 parts of modified filler, 6 parts of composite crosslinking agent, 2 parts of leveling agent, and 55 parts of solvent; the modified filler is prepared by Preparation Example 3; the composite crosslinking agent is specifically hexamethylene diisocyanate and methyl etherified hexamethyl melamine resin in a mass ratio of 1:0.6; the leveling agent is specifically BYK-333; and the solvent is specifically ethyl acetate.

[0061] Fluorosilicone modified acrylic resin, modified filler, hexamethylene diisocyanate, methyl etherified hexamethylol melamine resin, BYK-333 and ethyl acetate were mixed according to the weight parts, and then subjected to high-speed shearing and sand milling. After mixing, the mixture was stored in a light-proof and sealed container to obtain the coating liquid.

[0062] S3. The PET base film layer is subjected to corona treatment. The coating liquid is uniformly coated on the surface of the PET base film layer using a micro-gravure coating method. The wet film thickness is controlled to be 5μm. After passing through an 80℃ preheating oven to remove residual solvent, it is then passed through a 120℃ oven and a 150℃ oven in sequence. After deep curing, a weather-resistant coating is formed, resulting in an aging-resistant PET protective film.

[0063] Example 4 The difference between this embodiment and Example 3 is that the modified filler prepared in Example 4 is used.

[0064] Example 5 The difference between this embodiment and Example 3 is that the modified filler prepared in Example 5 is used.

[0065] Example 6 The difference between this embodiment and Embodiment 3 is that the etherified melamine-formaldehyde resin is replaced by an aziridine crosslinking agent, that is, the methyl etherified hexamethylol melamine resin is replaced by the aziridine crosslinking agent CX-100.

[0066] Comparative Example 1 The method for preparing the aging-resistant PET protective film differs from that in Example 3 in that the modified filler is replaced with nano-mica powder.

[0067] Comparative Example 2 The preparation method of the aging-resistant PET protective film differs from that in Example 3 in that no modified filler is added.

[0068] Comparative Example 3 The preparation method of the aging-resistant PET protective film differs from that in Example 3 in that the fluorosilicone-modified acrylic resin is replaced by an organosilicon-modified acrylic resin. The organosilicon-modified acrylic resin was purchased from Jufeng Chemical, model J-611.

[0069] Comparative Example 4 The method for preparing the aging-resistant PET protective film differs from that in Example 3 in that the composite crosslinking agent is replaced by hexamethylene diisocyanate in equal mass.

[0070] Comparative Example 5 The method for preparing the aging-resistant PET protective film differs from that in Example 3 in that the composite crosslinking agent is replaced by an equal amount of methyl etherified hexamethylol melamine resin.

[0071] Comparative Example 6 The method for preparing the aging-resistant PET protective film differs from that in Example 3 in that the aging-resistant PET masterbatch is replaced with PET resin in equal quantities. Performance testing

[0072] Accelerated aging test: The prepared aging-resistant PET protective film was cut into rectangular strips of 150mm × 10mm. Tensile strength was tested using a universal testing machine at a tensile speed of 200mm / min, a test temperature of 23℃, and a relative humidity of 50%RH. Five measurements were taken, and the average value was recorded. The aging-resistant PET protective film was then placed in an accelerated aging chamber and irradiated with a UVA-340 lamp for 3000 hours. Tensile strength was then tested again, and the tensile strength retention rate was calculated. Simultaneously, according to the national standard GB / T 39822-2021, the degree of yellowing was assessed by calculating the change in the yellowing index of the aging-resistant PET protective film before and after aging (ΔYI = YI after aging - YI before aging).

[0073] Moisture permeability test: According to GB / T 1037-2021 "Determination of water vapor permeability of plastic films and sheets by cup weight gain and weight loss method", the moisture permeability of the aging resistant PET protective films in Examples 1-6 and Comparative Examples 1-5 was tested using the weight gain method.

[0074] Flexibility test: According to the ASTM D4145 test standard, fix one end of the specimen, slowly bend the free end to 180°, with the coating on the outside, and check for cracks through a magnifying glass (5-10x).

[0075] Table 1

[0076] Based on the comparison between Examples 3 and 4-5, and the data in Table 1, it can be seen that: the filler in Example 4 was not modified by intercalation, resulting in poor particle dispersion, which in turn affects the uniformity and density of the coating, reducing the resistance of the aging-resistant PET protective film to environmental stresses such as ultraviolet radiation and heat and oxygen; Example 5 used phenol grafting, which degrades the performance of the modified filler. Because cashew nut shell phenol has a long-chain alkyl structure, it can give the material better flexibility. Using phenol to replace cashew nut shell phenol will lead to a decrease in the flexibility of the coating.

[0077] Based on the comparison between Example 3 and Example 6 and the data in Table 1, it can be seen that Example 6 uses aziridine crosslinking agent, which will change the crosslinking structure of the weather-resistant coating, reduce its crosslinking density and stability, weaken the protective effect of the weather-resistant coating on the PET base film layer, and reduce the aging resistance of the aging-resistant PET protective film. Under long-term exposure to environmental stresses such as ultraviolet rays, high temperature, oxygen and moisture, it is more likely to suffer from problems such as yellowing, embrittlement, decreased mechanical properties and surface powdering.

[0078] Based on the comparison between Example 3 and Comparative Example 1, and the data in Table 1, it can be seen that: Comparative Example 1 did not modify the filler, and the filler agglomeration in the coating led to an increase in ultraviolet transmittance. In contrast, the modified filler in Example 3 achieved uniform dispersion through intercalation-grafting process, which greatly extended the penetration path of ultraviolet rays and water vapor, and effectively improved the tensile strength. This indicates that the modification treatment can effectively exert the physical barrier and toughening effect of the filler.

[0079] Based on the comparison between Example 3 and Comparative Example 2, and the data in Table 1, it can be seen that: Comparative Example 2 did not add modified filler, which resulted in a significant increase in the ultraviolet transmittance of the coating and a significant decrease in the barrier performance against water vapor; Example 3, by adding modified filler to the coating liquid, effectively blocked ultraviolet rays and water vapor, and combined with the aging-resistant PET masterbatch of the PET base film layer, formed double protection inside and out, and the anti-aging performance was long-lasting and stable.

[0080] Based on the comparison between Example 3 and Comparative Example 3 and the data in Table 1, it can be seen that: the use of organosilicon-modified acrylic resin as a film-forming agent in the coating liquid of Comparative Example 3 resulted in a significant decrease in the tensile strength of the coating after UV aging; the fluorosilicone-modified acrylic resin of Example 3 has excellent weather resistance and stability due to the high bond energy characteristics of Si-O and CF bonds.

[0081] Based on the comparison between Example 3 and Comparative Examples 4-5 and the data in Table 1, it can be seen that: Comparative Example 4 uses a single diisocyanate crosslinking agent, and Comparative Example 5 uses a single etherified melamine-formaldehyde resin. Both of these will lead to insufficient or excessive crosslinking of the resin molecular chains, resulting in a significant decrease in the tensile strength retention rate of the aging-resistant PET protective film after aging; The composite crosslinking agent in Example 3 increases the crosslinking density and has excellent barrier properties, proving that the combination of diisocyanate and etherified melamine-formaldehyde resin can synergistically enhance the chemical stability of the coating.

[0082] Based on the comparison between Example 3 and Comparative Example 6, and the data in Table 1, it can be seen that: Comparative Example 6, without the addition of aging-resistant PET masterbatch, had a light transmittance and tensile strength retention rate of only 70% after accelerated aging for 3000 hours, and a yellowing index of 5.4. In contrast, Example 3, due to the synergistic effect of the shielding agent and ultraviolet absorber in the masterbatch, had a light transmittance retention rate of over 85% and a yellowing index of 2, indicating that the aging-resistant PET masterbatch can significantly inhibit the photo-oxidative degradation of the base film.

[0083] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this specific embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An aging-resistant PET protective film, characterized in that, It includes a PET base film layer and a weather-resistant coating, wherein the weather-resistant coating is obtained by coating the surface of the PET base film layer with a coating liquid; The PET base film layer comprises the following raw materials in parts by weight: 70-80 parts of first PET resin and 20-30 parts of aging-resistant PET masterbatch; The raw materials for preparing the aging-resistant PET masterbatch include a second PET resin, a shielding agent, an ultraviolet absorber, a stabilizer, and an antioxidant; the mass ratio of the second PET resin, the shielding agent, the ultraviolet absorber, the stabilizer, and the antioxidant is (55-65):(2-4):(0.7-1):(1-2):(0.1-0.2). The coating liquid comprises the following raw materials in parts by weight: 40-50 parts of fluorosilicone modified acrylic resin, 3-5 parts of modified filler, 4-6 parts of composite crosslinking agent, 1-2 parts of leveling agent, and 45-55 parts of solvent.

2. The aging-resistant PET protective film according to claim 1, characterized in that, The composite crosslinking agent comprises diisocyanate and etherified melamine-formaldehyde resin in a mass ratio of 1:(0.3-0.6).

3. The aging-resistant PET protective film according to claim 1, characterized in that, The etherified melamine-formaldehyde resin includes one or two of methyl etherified hexamethyl hydroxymethyl melamine resin and isobutyl etherified melamine-formaldehyde resin; the diisocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

4. The aging-resistant PET protective film according to claim 1, characterized in that, The method for preparing the modified filler includes the following steps: (1) Disperse the nanofiller in water and add long-chain alkylammonium salt. Heat the mixture to react. After the reaction is complete, filter and collect the precipitate. Wash and dry the precipitate to obtain the intercalated modified filler. The mass ratio of the nanofiller to the long-chain alkylammonium salt is 1: (0.6-0.8). (2) After adding anhydrous ethanol and mercaptosilane to the intercalated modified filler, heating and stirring, filtering to remove the filtrate, washing, and drying, the surface modified filler is obtained; the mass ratio of the intercalated modified filler to mercaptosilane is (2-4):(4-6). (3) Add anhydrous ethanol, cashew phenol and photoinitiator to the surface modified filler, stir under ultraviolet irradiation, filter to remove filtrate, wash and dry to obtain modified filler; the mass ratio of the surface modified filler, cashew phenol and photoinitiator is (5-6): (2-3): (0.3-0.5).

5. The aging-resistant PET protective film according to claim 4, characterized in that, The nanofiller includes one or both of the following: mica nanoparticles and graphene nanosheets.

6. The aging-resistant PET protective film according to claim 1, characterized in that, The ultraviolet absorber includes one or both of benzotriazole ultraviolet absorbers and triazine ultraviolet absorbers.

7. The aging-resistant PET protective film according to claim 1, characterized in that, The stabilizer is a hindered amine light stabilizer.

8. The aging-resistant PET protective film according to claim 1, characterized in that, The shielding agent includes one or two of nano-cerium oxide and zinc oxide; the antioxidant includes one or more of antioxidant 1010, antioxidant 1076, and antioxidant 168.

9. The aging-resistant PET protective film according to claim 1, characterized in that, The leveling agent includes one or more of BYK-3481, BYK-381, and BYK-333.

10. A method for preparing an aging-resistant PET protective film according to any one of claims 1-9, characterized in that, Includes the following steps: S1. The second PET resin is thoroughly mixed with a shielding agent, an ultraviolet absorber, a stabilizer, and an antioxidant, and then extruded and granulated to obtain an aging-resistant PET masterbatch; the aging-resistant PET masterbatch is mixed with the first PET resin, and then dried, melt-extruded, cast, stretched longitudinally, stretched transversely, heat-set, and wound to obtain a PET base film layer. S2. Mix the fluorosilicone modified acrylic resin, modified filler, composite crosslinking agent, leveling agent and solvent according to the weight parts, and store in the dark after mixing to obtain the coating liquid; S3. The PET base film layer is subjected to corona treatment, and the coating liquid is uniformly coated on the surface of the PET base film layer. After gradient curing, a weather-resistant coating is formed, resulting in an aging-resistant PET protective film.

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