Scratch-resistant PET (polyethylene terephthalate) protective film and preparation method thereof

Abstract

The invention relates to the technical field of polymer functional film materials, and particularly discloses an anti-scraping PET (Polyethylene Terephthalate) protective film and a preparation method thereof. The scratch-resistant PET protective film comprises a PET base film layer, a bottom layer and a surface layer, the bottom layer is obtained by coating the PET base film layer with a bottom layer coating liquid, and the surface layer is obtained by coating the bottom layer with a surface layer coating liquid; the bottom layer coating liquid is prepared from the following raw materials in parts by weight: modified polyurethane acrylate, a silane coupling agent, a first photoinitiator and ethyl acetate; the surface layer coating liquid is prepared from the following raw materials in parts by weight: aliphatic polyurethane acrylate, glycidyl methacrylate, modified nano silicon dioxide, a second photoinitiator, a flatting agent and ethyl acetate. The adhesive force and the scratch resistance of the PET protective film can be effectively enhanced.

Description

Technical Field

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

[0002] PET protective film is widely used as a surface protection material due to its excellent transparency, mechanical strength, dimensional stability, and cost advantages. Applications include screen protection for high-end electronic products, panels for precision instruments, automotive interior surfaces, and temporary protection for architectural glass. However, traditional PET films have limited surface hardness (typically pencil hardness ≤2H) and scratch resistance, making them highly susceptible to scratches from hard objects (such as keys, grit) or cleaning cloths during use and transportation. These scratches not only affect the appearance but can also, in severe cases, reduce the display clarity or optical performance of the protected product.

[0003] To address the insufficient surface hardness of traditional PET films, existing technologies typically involve coating a hard coating onto the PET base film, leveraging the inherent hardness of the coating to enhance the scratch resistance of the PET protective film. However, due to poor adhesion between the hard coating and the PET substrate, cracking and peeling easily occur after bending or temperature changes. Furthermore, simply increasing the coating hardness often leads to increased brittleness and decreased flexibility. Summary of the Invention

[0004] To enhance the adhesion and scratch resistance of PET protective films, this application provides a scratch-resistant PET protective film and its preparation method.

[0005] Firstly, this application provides a scratch-resistant PET protective film, which adopts the following technical solution: A scratch-resistant PET protective film includes a PET base film layer, a bottom layer, and a top layer. The bottom layer is obtained by coating the PET base film layer with a bottom layer coating liquid, and the top layer is obtained by coating the bottom layer with a top layer coating liquid. The underlying coating liquid comprises the following raw materials in parts by weight: 35-45 parts modified polyurethane acrylate, 3-5 parts silane coupling agent, 1-3 parts first photoinitiator, and 40-50 parts ethyl acetate. The surface coating liquid comprises the following raw materials in parts by weight: 40-50 parts aliphatic polyurethane acrylate, 6-10 parts glycidyl methacrylate, 4-6 parts modified nano silica, 1-3 parts second photoinitiator, 1-2 parts leveling agent, and 45-55 parts ethyl acetate.

[0006] By adopting the above technical solution, the modified polyurethane acrylate in the undercoating solution exhibits good flexibility and reactivity, while the silane coupling agent contains groups that can react with both inorganic and organic materials. One end of the silane coupling agent can chemically react with the modified polyurethane acrylate to form a chemical bond, while the other end can react with hydroxyl groups and other groups on the surface of the PET base film, thereby enhancing the adhesion between the undercoat and the PET base film. This improves the problem of poor adhesion between the traditional PET film hard coating and the PET substrate, which easily leads to cracking and peeling after bending or temperature changes.

[0007] In the topcoat solution, glycidyl methacrylate contains epoxy groups, exhibiting high reactivity. It can react with the active groups of aliphatic polyurethane acrylate to form a cross-linked structure, thereby improving the hardness and strength of the coating. Simultaneously, the modified nano-silica surface possesses excellent dispersibility and reactivity, enabling it to disperse uniformly in the resin with strong interfacial bonding. It undergoes physical or chemical reactions with polyurethane acrylate and glycidyl methacrylate, further enhancing the coating's hardness and scratch resistance.

[0008] The PET protective film of this application adopts a structure with strong adhesion at the bottom layer and nanoparticle reinforcement at the top layer, which can effectively resist the scratches of everyday sharp objects and is suitable for scenarios requiring high surface durability.

[0009] Preferably, the modified polyurethane acrylate is prepared by the following method: Diisocyanate, catalyst, diluent and polymerization inhibitor are mixed and stirred evenly. The mixture is heated and polycaprolactone triol is added. The mixture is stirred evenly and heated to react, resulting in a polyurethane prepolymer. The mixture is cooled and 2-acryloyloxyethyl 6-hydroxyhexanoate is added. The mixture is stirred evenly and heated to react, resulting in a polyurethane acrylate prepolymer. The mixture is cooled and saturated fatty alcohol is added. The mixture is heated to react, and after the reaction is complete, modified polyurethane acrylate is obtained.

[0010] By adopting the above technical solution, the molecular structure of 6-hydroxyhexanoic acid 2-acryloyloxyethyl ester is characterized by a highly reactive primary hydroxyl group at the end of its side chain, far from the main chain. Using it as an acrylate monomer for curing with diisocyanate significantly enhances its reactivity, allowing for a more complete cross-linking reaction. The resulting cured substrate exhibits superior hardness, elasticity, and processability. Furthermore, since both 6-hydroxyhexanoic acid 2-acryloyloxyethyl ester and saturated fatty alcohols have relatively long molecular chains, their synergistic effect imparts better flexibility to the coating, making it denser without increasing its brittleness. In addition, polyurethane acrylates modified with saturated fatty alcohols possess higher double bond conversion rates, adhesion, and lower volume shrinkage.

[0011] Preferably, the molar ratio of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol is 1:(2.6-3.2):(1.5-2):(1.2-1.6).

[0012] By adopting the above technical solution, controlling the molar ratio of each raw material in the modified polyurethane acrylate can enable the prepared modified polyurethane acrylate to have suitable functionality and molecular structure, thereby ensuring good adhesion between the bottom layer formed by the bottom coating liquid and the PET base film layer and the top layer. At the same time, it helps to improve the flexibility and scratch resistance of the scratch-resistant PET protective film.

[0013] Preferably, the molecular structural formula of the 6-hydroxyhexanoic acid 2-acryloyloxyethyl ester is as follows: .

[0014] Preferably, the saturated fatty alcohol includes one or more of lauryl alcohol, cetearyl alcohol, and stearyl alcohol.

[0015] By adopting the above technical solution, the saturated fatty alcohol, with its relatively long carbon chain and good flexibility, is incorporated into the polyurethane acrylate molecular chain, providing excellent flexibility and a flexible buffer interface for the surface layer. Simultaneously, the addition of the saturated fatty alcohol increases the molecular weight of the polyurethane acrylate, reduces the double bond density, and decreases volume shrinkage to a certain extent, thus improving adhesion.

[0016] Preferably, the diisocyanate includes one or more of dicyclohexylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0017] Preferably, the catalyst is dibutyltin dilaurate; the diluent is HDDA; and the polymerization inhibitor is p-hydroxyanisole.

[0018] Preferably, the silane coupling agent includes one or more of 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-methacryloxypropyltriisopropoxysilane.

[0019] By adopting the above technical solution, the silane coupling agent contains double bonds that can participate in the photocuring reaction, thereby improving the bonding strength between the nanoparticles and the resin interface.

[0020] Preferably, the method for preparing the modified nano-silica includes the following steps: Nano-silica was mixed with a dispersing solvent, stirred thoroughly and heated, vinylsilane was added, and the reaction was maintained at this temperature. After the reaction was completed, the mixture was filtered, washed and dried to obtain modified nano-silica.

[0021] Preferably, the mass ratio of the nano-silica to vinylsilane is 1:(0.1-0.2).

[0022] By employing the above technical solution, vinyl silane can react with the active groups on the surface of nano-silica, grafting vinyl and other organic groups onto its surface, thus modifying the nano-silica. When the modified nano-silica is applied to the topcoat solution, the improved compatibility with other raw materials due to the organic groups on its surface allows for better dispersion in the topcoat, thereby enhancing the surface hardness and scratch resistance of the scratch-resistant PET protective film.

[0023] Preferably, the vinyl silane includes one or more of vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriisopropoxysilane.

[0024] Preferably, the leveling agent includes one or more of BYK-3481, BYK-381, and BYK-333.

[0025] By adopting the above technical solution, the leveling agent is added to promote the wetting of the substrate by the topcoat liquid and the leveling of the paint surface.

[0026] Preferably, the first photoinitiator comprises one or more of α-hydroxy ketones, acetophenone and its derivatives, and acylphosphine oxides; the second photoinitiator comprises one or more of α-hydroxy ketones, acetophenone and its derivatives, and acylphosphine oxides.

[0027] By adopting the above technical solution, the first photoinitiator and the second photoinitiator can generate active free radicals or cations under light irradiation, which can initiate the polymerization reaction of unsaturated double bonds in the bottom coating liquid and the top coating liquid, promote the curing and molding of the bottom and top layers, and improve the film quality and performance of the bottom and top layers of the scratch-resistant PET protective film.

[0028] Secondly, this application provides a method for preparing an anti-scratch PET protective film, which adopts the following technical solution: A method for preparing a scratch-resistant PET protective film includes the following steps: S1. Under light-protected conditions, the modified polyurethane acrylate, silane coupling agent, first photoinitiator, and ethyl acetate are stirred and mixed according to the weight parts. After mixing, the mixture is stored in the dark to obtain the bottom coating liquid. Under light-protected conditions, the aliphatic polyurethane acrylate, glycidyl methacrylate, modified nano silica, second photoinitiator, leveling agent, and ethyl acetate are stirred and mixed according to the weight parts. After mixing, the mixture is stored in the dark to obtain the top coating liquid. S2. Perform corona treatment on the cleaned PET base film layer; S3. Apply the base coating liquid onto the PET base film layer, and after preliminary curing, form a solid base layer; S4. Apply the topcoat liquid to the bottom layer, and after gradient curing, form the topcoat to obtain a scratch-resistant PET protective film.

[0029] By adopting the above technical solution, the bottom layer formed by the base coating liquid has strong adhesion, and the top layer formed by the top coating liquid is reinforced by nanoparticles. The two work together to effectively resist scratches from everyday sharp objects. At the same time, the two-step coating and gradient curing process offers high controllability and can effectively solve industrialization problems such as nanoparticle dispersion and coating internal stress control, resulting in high production efficiency.

[0030] Preferably, the PET base film layer has a thickness of 50μm-188μm, the bottom layer has a thickness of 1μm-5μm, and the top layer has a thickness of 2μm-8μm.

[0031] By adopting the above technical solution, the thickness of the bottom layer is controlled at 1μm-5μm and the thickness of the top layer is controlled at 2μm-8μm. This ensures that the scratch-resistant PET protective film has good scratch resistance while avoiding the decrease in flexibility due to excessive coating thickness, thus reducing cracking and peeling after bending or temperature changes. At the same time, combined with the PET base film layer thickness of 50μm-188μm, the overall structure of the protective film is more reasonable and the overall performance is better.

[0032] This application has the following beneficial effects: 1. The modified polyurethane acrylate in the base coat solution exhibits good flexibility and reactivity, while the silane coupling agent contains groups capable of reacting with both inorganic and organic materials. One end of the silane coupling agent can chemically react with the modified polyurethane acrylate to form a chemical bond, while the other end can react with hydroxyl groups and other groups on the surface of the PET base film, thereby enhancing the adhesion between the base coat and the PET base film and improving the poor adhesion between the traditional PET film hard coating and the PET substrate, which is prone to cracking and peeling after bending or temperature changes. In the top coat solution, glycidyl methacrylate contains epoxy groups and has high reactivity. It can react with the active groups of aliphatic polyurethane acrylate to form a cross-linked structure, improving the hardness and strength of the coating. Simultaneously, the modified nano-silica surface exhibits good dispersibility and reactivity, enabling it to disperse uniformly in the resin and form a strong interfacial bond. It reacts physically or chemically with the polyurethane acrylate and glycidyl methacrylate, further enhancing the coating's hardness and scratch resistance. The PET protective film of this application adopts a structure with strong adhesion at the bottom layer and nanoparticle reinforcement at the top layer, which can effectively resist the scratches of everyday sharp objects and is suitable for scenarios requiring high surface durability.

[0033] The molecular structure of 2,6-hydroxyhexanoic acid 2-acryloyloxyethyl ester is characterized by a highly reactive primary hydroxyl group at the end of its side chain, far from the main chain. Using it as an acrylate monomer in curing with diisocyanates significantly enhances its reactivity, allowing for a more complete cross-linking reaction. The resulting cured substrate exhibits superior hardness, elasticity, and processability. Furthermore, since both 2-hydroxyhexanoic acid 2-acryloyloxyethyl ester and saturated fatty alcohols have relatively long molecular chains, their synergistic effect imparts better flexibility to the coating, making it denser without increasing brittleness. In addition, polyurethane acrylates modified with saturated fatty alcohols possess higher double bond conversion rates, adhesion, and lower volume shrinkage. Detailed Implementation

[0034] The present application will be further described in detail below with reference to the embodiments.

[0035] Preparation Example 1 The preparation method of modified polyurethane acrylate includes the following steps: Weigh out polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol according to a molar ratio of 1:2.6:1.5:1.2. Polycaprolactone triol was purchased from Hubei Shishun Biotechnology Co., Ltd., CAS No. 37625-56-2. The diisocyanate used was dicyclohexylmethane diisocyanate. The saturated fatty alcohol used was lauryl alcohol. The catalyst is weighed at 1.5% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the catalyst is specifically selected as dibutyltin dilaurate; the diluent is weighed at 20% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the diluent is specifically selected as HDDA; the polymerization inhibitor is weighed at 0.8% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the polymerization inhibitor is specifically selected as p-hydroxyanisole. Dicyclohexylmethane diisocyanate, dibutyltin dilaurate, HDDA, and p-hydroxyanisole were mixed and stirred until homogeneous. The mixture was heated to 35°C and polycaprolactone triol was added. The mixture was stirred until homogeneous and then heated to 45°C for 1 hour to obtain a polyurethane prepolymer. The mixture was then cooled to 35°C and 2-acryloyloxyethyl 6-hydroxyhexanoate was added. The mixture was stirred until homogeneous and then heated to 65°C for 1 hour to obtain a polyurethane acrylate prepolymer. The mixture was then cooled to 35°C and lauryl alcohol was added. The mixture was heated to 65°C for 2 hours to obtain a modified polyurethane acrylate.

[0036] Preparation Example 2 The preparation method of modified polyurethane acrylate includes the following steps: Weigh out polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol according to a molar ratio of 1:2.9:1.8:1.4. Polycaprolactone triol was purchased from Hubei Shishun Biotechnology Co., Ltd., CAS No. 37625-56-2. Isophorone diisocyanate was selected. Cetearyl alcohol was selected. The catalyst is weighed at 1.8% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the catalyst is specifically selected as dibutyltin dilaurate; the diluent is weighed at 23% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the diluent is specifically selected as HDDA; the polymerization inhibitor is weighed at 0.9% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the polymerization inhibitor is specifically selected as p-hydroxyanisole. Isophorone diisocyanate, dibutyltin dilaurate, HDDA, and p-hydroxyanisole were mixed and stirred until homogeneous. The mixture was heated to 38°C and polycaprolactone triol was added. The mixture was stirred until homogeneous and then heated to 48°C for 1.5 hours to obtain a polyurethane prepolymer. The mixture was then cooled to 38°C and 2-acryloyloxyethyl 6-hydroxyhexanoate was added. The mixture was stirred until homogeneous and then heated to 68°C for 1.5 hours to obtain a polyurethane acrylate prepolymer. The mixture was then cooled to 38°C and cetearyl alcohol was added. The mixture was heated to 68°C for 2.5 hours to obtain a modified polyurethane acrylate.

[0037] Preparation Example 3 The preparation method of modified polyurethane acrylate includes the following steps: Weigh out polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol according to a molar ratio of 1:3.2:2:1.6. Polycaprolactone triol was purchased from Hubei Shishun Biotechnology Co., Ltd., CAS No. 37625-56-2. Hexamethylene diisocyanate was selected as the diisocyanate. Stearyl alcohol was selected as the saturated fatty alcohol. The catalyst is weighed at 2% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the catalyst is specifically selected as dibutyltin dilaurate; the diluent is weighed at 25% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the diluent is specifically selected as HDDA; the polymerization inhibitor is weighed at 1% of the total mass of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol, and the polymerization inhibitor is specifically selected as p-hydroxyanisole. Hexamethylene diisocyanate, dibutyltin dilaurate, HDDA, and p-hydroxyanisole were mixed and stirred until homogeneous. The mixture was heated to 40°C and polycaprolactone triol was added. The mixture was stirred until homogeneous and then heated to 50°C for 2 hours to obtain a polyurethane prepolymer. The mixture was then cooled to 40°C and 2-acryloyloxyethyl 6-hydroxyhexanoate was added. The mixture was stirred until homogeneous and then heated to 70°C for 2 hours to obtain a polyurethane acrylate prepolymer. The mixture was then cooled to 40°C and stearyl alcohol was added. The mixture was heated to 70°C for 3 hours to obtain a modified polyurethane acrylate.

[0038] Preparation Example 4 The difference between this preparation example and preparation example 3 is that stearyl alcohol is replaced by n-octanol by mass.

[0039] Preparation Example 5 The difference between this preparation example and preparation example 3 is that stearyl alcohol is replaced by n-butanol by mass.

[0040] Preparation Example 6 The difference between this preparation example and Preparation Example 3 is that stearyl alcohol was not added. Therefore, the preparation method of the modified polyurethane acrylate includes the following steps: Hexamethylene diisocyanate, dibutyltin dilaurate, HDDA, and p-hydroxyanisole were mixed and stirred until homogeneous. The mixture was heated to 40°C and polycaprolactone triol was added. The mixture was stirred until homogeneous and then heated to 50°C for 2 hours to obtain a polyurethane prepolymer. The mixture was then cooled to 40°C and 2-acryloyloxyethyl 6-hydroxyhexanoate was added. The mixture was stirred until homogeneous and then heated to 70°C for 2 hours to obtain a modified polyurethane acrylate.

[0041] Preparation Example 7 The difference between this preparation example and preparation example 3 is that 6-hydroxyhexanoic acid 2-acryloyloxyethyl ester is replaced by an equal mass of hydroxyethyl acrylate.

[0042] Preliminary Example 1 The preparation method of modified nano-silica includes the following steps: Weigh nano-silica and vinyl silane at a mass ratio of 1:0.1, and weigh out a dispersion solvent at 15 times the mass of nano-silica, specifically toluene; for vinyl silane, specifically vinyltrimethoxysilane, and weigh out toluene at 10 times the mass of vinyltrimethoxysilane. Dissolve vinyltrimethoxysilane in toluene to obtain a vinyl silane solution.

[0043] First, the nano-silica was vacuum dried. The dried nano-silica was then mixed with toluene, stirred thoroughly, heated to 60°C, and a vinylsilane solution was added. The mixture was kept at this temperature for 2 hours. The resulting product was filtered, washed twice, and then vacuum dried to obtain modified nano-silica.

[0044] Preliminary Example 2 The preparation method of modified nano-silica includes the following steps: Weigh nano-silica and vinyl silane at a mass ratio of 1:0.2, and weigh out a dispersion solvent at 15 times the mass of nano-silica, specifically toluene; for vinyl silane, specifically vinyltriisopropoxysilane, and weigh out toluene at 10 times the mass of vinyltriisopropoxysilane. Dissolve vinyltriisopropoxysilane in toluene to obtain a vinyl silane solution.

[0045] First, the nano-silica was vacuum dried. The dried nano-silica was then mixed with toluene, stirred thoroughly, heated to 70°C, and a vinylsilane solution was added. The mixture was kept at this temperature for 3 hours. The resulting product was filtered, washed three times, and then vacuum dried to obtain modified nano-silica.

[0046] Example 1 A method for preparing a scratch-resistant PET protective film includes the following steps: S1. Weigh the raw materials according to the following weight proportions: 35 parts modified polyurethane acrylate, 3 parts silane coupling agent, 1 part first photoinitiator, and 40 parts ethyl acetate; the modified polyurethane acrylate is prepared from Preparation Example 1; the silane coupling agent is specifically 3-methacryloyloxypropyltrimethoxysilane; the first photoinitiator is specifically 3-hydroxy-3-methyl-2-butanone.

[0047] Under light-protected conditions, modified polyurethane acrylate, 3-methacryloyloxypropyltrimethoxysilane, 3-hydroxy-3-methyl-2-butanone, and ethyl acetate were stirred and mixed. After mixing, the mixture was stored in the dark to obtain the bottom coating solution.

[0048] The raw materials were weighed according to the following proportions by weight: 40 parts aliphatic polyurethane acrylate, 6 parts glycidyl methacrylate, 4 parts modified nano silica, 1 part second photoinitiator, 1 part leveling agent, and 45 parts ethyl acetate. The aliphatic polyurethane acrylate with a viscosity of 20000-35000 Pa.s / 25℃ was purchased from Dongguan Jing Shang New Material Development Co., Ltd. The modified nano silica was prepared from Preliminary Example 1. The second photoinitiator was specifically 3-hydroxy-3-methyl-2-butanone. The leveling agent was specifically BYK-3481.

[0049] Under light-protected conditions, aliphatic polyurethane acrylate, glycidyl methacrylate, modified nano silica, 3-hydroxy-3-methyl-2-butanone, BYK-3481, and ethyl acetate were stirred and mixed. After mixing, the mixture was stored in the dark to obtain the topcoat solution.

[0050] S2. The cleaned PET base film layer is subjected to corona treatment, and the thickness of the PET base film layer is 100μm.

[0051] S3. The bottom coating liquid is coated onto the PET base film layer using a micro-gravure coating method. After being preheated in a 60°C oven, most of the solvent is evaporated. Then, under nitrogen protection, it is initially cured by an ultraviolet light source to form a solid bottom layer with a thickness of 2μm.

[0052] S4. The topcoat liquid is coated onto the bottom layer using a micro-gravure coating method. After preheating in a 60°C oven to remove residual solvent, the topcoat is initially gelled under nitrogen protection using a low-intensity ultraviolet light source, then deeply cured using a medium-intensity ultraviolet light source, and finally stress-freeed using a high-intensity ultraviolet light source to form a 5μm thick topcoat, resulting in a scratch-resistant PET protective film.

[0053] Example 2 A method for preparing a scratch-resistant PET protective film includes the following steps: S1. Weigh out the raw materials according to the following weight proportions: 40 parts modified polyurethane acrylate, 4 parts silane coupling agent, 2 parts first photoinitiator, and 45 parts ethyl acetate; the modified polyurethane acrylate is prepared from Preparation Example 2; the silane coupling agent is specifically 3-methacryloyloxypropyltriethoxysilane; the first photoinitiator is specifically dimethoxyphenylacetophenone.

[0054] Under light-protected conditions, modified polyurethane acrylate, 3-methacryloyloxypropyltriethoxysilane, dimethoxyphenylacetophenone, and ethyl acetate were stirred and mixed. After mixing, the mixture was stored in the dark to obtain the bottom coating solution.

[0055] The raw materials were weighed according to the following proportions by weight: 45 parts aliphatic polyurethane acrylate, 8 parts glycidyl methacrylate, 5 parts modified nano silica, 2 parts second photoinitiator, 1.5 parts leveling agent, and 50 parts ethyl acetate. The aliphatic polyurethane acrylate with a viscosity of 20000-35000 Pa.s / 25℃ was purchased from Dongguan Jing Shang New Material Development Co., Ltd. The modified nano silica was prepared from Preliminary Example 2. The second photoinitiator was specifically selected as dimethoxyphenyl acetophenone. The leveling agent was specifically selected as BYK-381.

[0056] Under light-protected conditions, aliphatic polyurethane acrylate, glycidyl methacrylate, modified nano silica, dimethoxyphenyl acetophenone, BYK-381, and ethyl acetate were stirred and mixed. After mixing, the mixture was stored in the dark to obtain the topcoat solution.

[0057] S2. The cleaned PET base film layer is subjected to corona treatment, and the thickness of the PET base film layer is 100μm.

[0058] S3. The bottom coating liquid is coated onto the PET base film layer using a micro-gravure coating method. After being preheated in a 70°C oven, most of the solvent is evaporated. Then, under nitrogen protection, it is initially cured by an ultraviolet light source to form a solid bottom layer with a thickness of 2μm.

[0059] S4. The topcoat liquid is coated onto the bottom layer using a micro-gravure coating method. After preheating in a 65°C oven to remove residual solvent, the topcoat is initially gelled under nitrogen protection using a low-intensity ultraviolet light source, then deeply cured using a medium-intensity ultraviolet light source, and finally stress-freeed using a high-intensity ultraviolet light source to form a 5μm thick topcoat, resulting in a scratch-resistant PET protective film.

[0060] Example 3 A method for preparing a scratch-resistant PET protective film includes the following steps: S1. Weigh the raw materials according to the following weight proportions: 45 parts modified polyurethane acrylate, 5 parts silane coupling agent, 3 parts first photoinitiator, and 50 parts ethyl acetate; the modified polyurethane acrylate is prepared from Preparation Example 3; the silane coupling agent is specifically 3-methacryloyloxypropyltriisopropoxysilane; the first photoinitiator is specifically BAPO.

[0061] Under light-protected conditions, modified polyurethane acrylate, 3-methacryloyloxypropyltriisopropoxysilane, BAPO, and ethyl acetate were stirred and mixed. After mixing, the mixture was stored in the dark to obtain the bottom coating solution.

[0062] The raw materials were weighed according to the following proportions by weight: 50 parts aliphatic polyurethane acrylate, 10 parts glycidyl methacrylate, 6 parts modified nano silica, 3 parts second photoinitiator, 2 parts leveling agent, and 55 parts ethyl acetate. The aliphatic polyurethane acrylate with a viscosity of 20000-35000 Pa.s / 25℃ was purchased from Dongguan Jing Shang New Material Development Co., Ltd. The modified nano silica was prepared from Preliminary Example 2. BAPO was specifically selected as the second photoinitiator. BYK-333 was specifically selected as the leveling agent.

[0063] Under light-protected conditions, aliphatic polyurethane acrylate, glycidyl methacrylate, modified nano silica, BAPO, BYK-333, and ethyl acetate were stirred and mixed. After mixing, the mixture was stored in the dark to obtain the topcoat solution.

[0064] S2. The cleaned PET base film layer is subjected to corona treatment, and the thickness of the PET base film layer is 100μm.

[0065] S3. The bottom coating liquid is coated onto the PET base film layer using a micro-gravure coating method. After being preheated in an 80°C oven, most of the solvent is evaporated. Then, under nitrogen protection, it is initially cured by an ultraviolet light source to form a solid bottom layer with a thickness of 2μm.

[0066] S4. The topcoat liquid is coated onto the bottom layer using a micro-gravure coating method. After preheating in a 70°C oven to remove residual solvent, the topcoat is initially gelled under nitrogen protection using a low-intensity ultraviolet light source, then deeply cured using a medium-intensity ultraviolet light source, and finally stress-freeed using a high-intensity ultraviolet light source to form a 5μm thick topcoat, resulting in a scratch-resistant PET protective film.

[0067] Example 4 The difference between this embodiment and Example 3 is that the modified polyurethane acrylate obtained in Preparation Example 4 is used.

[0068] Example 5 The difference between this embodiment and Example 3 is that the modified polyurethane acrylate obtained in Preparation Example 5 is used.

[0069] Example 6 The difference between this embodiment and Example 3 is that the modified polyurethane acrylate obtained in Preparation Example 6 is used.

[0070] Example 7 The difference between this embodiment and Example 3 is that the modified polyurethane acrylate obtained in Preparation Example 7 is used.

[0071] Comparative Example 1 The method for preparing the scratch-resistant PET protective film differs from that in Example 3 in that the modified polyurethane acrylate in the bottom coating liquid is replaced by an aliphatic polyurethane acrylate in the top coating liquid.

[0072] Comparative Example 2 The method for preparing the scratch-resistant PET protective film differs from that in Example 3 in that glycidyl methacrylate and other components in the surface coating solution are replaced with methyl methacrylate.

[0073] Comparative Example 3 The method for preparing the scratch-resistant PET protective film differs from that in Example 3 in that the modified nano-silica is replaced with nano-silica.

[0074] Comparative Example 4 The method for preparing the scratch-resistant PET protective film differs from that in Example 3 in that modified nano-silica is not added to the surface coating liquid.

[0075] Comparative Example 5 The method for preparing the scratch-resistant PET protective film differs from that in Example 3 in that the aliphatic polyurethane acrylate in the topcoat solution is replaced by an aromatic polyurethane acrylate. The aromatic polyurethane acrylate was purchased from Hubei Xinjiecheng Chemical Technology Co., Ltd. Performance testing

[0076] Adhesion test: The adhesion of the samples in each example and comparative example was determined by cross-cut test according to the national standard GB / T 9286-2021.

[0077] Pencil Hardness: The scratch resistance of the samples was tested using a pencil hardness tester, in accordance with the standard ASTM D3363-2005, "Standard Test Method for Film Hardness by Pencil Test". The scratching speed was 1 cm / s, and the load was 1 kg.

[0078] 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).

[0079] Transmittance and Haze: Using a Tiber abrasion tester, a CS-10 wheel was used to rotate and rub the coating surface under a 500g load at 500 revolutions. A spectrophotometer was used, referring to ASTM D1003-2013 Transmittance and Haze of Transparent Plastics, at a wavelength of 550nm, to measure the transmittance of the samples after the abrasion test and the increase in haze before and after the abrasion test.

[0080] Table 1

[0081] Based on the comparison between Examples 3 and 4-6, and the data in Table 1, it can be seen that the adhesion and flexibility of the substrate are related to the length of the saturated fatty alcohol molecular chain. Polyurethane acrylate modified with saturated fatty alcohols with longer carbon chains exhibits higher adhesion and lower volume shrinkage. Example 4 used n-octanol, Example 5 used n-butanol, while Example 3 used long-chain stearyl alcohol. It is speculated that as the introduced fatty alcohol chain length increases, the surface tension of the cured film tends to decrease, thus reducing the surface tension of the coating and improving adhesion. In Example 6, since no saturated fatty alcohol was introduced, its various properties showed a deterioration trend compared to Example 5. It is speculated that this is because the volume shrinkage during the coating curing process was greater than in Example 5, leading to reduced adhesion.

[0082] Based on the comparison between Examples 3 and 7 and the data in Table 1, it can be seen that 6-hydroxyhexanoic acid 2-acryloyloxyethyl ester has a longer molecular chain than hydroxyethyl acrylate in Example 7. Because the hydroxyethyl acrylate molecular chain is shorter, the flexibility of the modified polyurethane acrylate may decrease, leading to a weakening of the bond between the bottom layer and the PET base film when the scratch-resistant PET protective film is bent or subjected to temperature changes. This makes it more prone to cracking and even peeling, and the scratch resistance of the protective film may also be affected.

[0083] 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 uses aliphatic polyurethane acrylate, which has not undergone the synergistic modification between saturated long-chain fatty acids and 6-hydroxyhexanoic acid 2-acryloyloxyethyl ester, resulting in a significant deterioration in the adhesion, flexibility and other properties of the underlying coating.

[0084] Based on the comparison between Example 3 and Comparative Example 2, and the data in Table 1, it can be seen that the methyl methacrylate (MMA) molecule in Comparative Example 2 does not contain epoxy groups, which reduces the adhesion between the bottom and top layers of the scratch-resistant PET protective film. This is because the epoxy groups in glycidyl methacrylate help enhance the reaction and bonding ability with other components. Simultaneously, the flexibility of the protective film may decrease, as glycidyl methacrylate plays a role in improving flexibility and impact resistance. Furthermore, the scratch resistance of the protective film may also deteriorate, making it less effective at resisting scratches from hard objects during use and transportation.

[0085] Based on the comparison between Example 3 and Comparative Examples 3-4, and the data in Table 1, it can be seen that in Comparative Example 3, the nano-silica was not modified. Because it was not modified with vinyl silane, the dispersibility of the nano-silica in the surface coating liquid was poor, making it prone to agglomeration. This resulted in a decrease in the surface hardness and scratch resistance of the scratch-resistant PET protective film, and a weakening of its bonding with other components. After bending or temperature changes, the surface layer was more prone to cracking and peeling, reducing the service life and stability of the protective film. In Comparative Example 4, the surface layer lacked modified nano-silica, significantly reducing the scratch resistance of the protective film. This is because modified nano-silica effectively enhances the hardness and wear resistance of the surface layer; its absence makes the protective film more susceptible to scratches when subjected to hard objects.

[0086] Based on the comparison between Example 3 and Comparative Example 5 and the data in Table 1, it can be seen that the surface coating liquid of Comparative Example 5 uses aromatic polyurethane acrylate. Since aromatic polyurethane acrylate has relatively poor flexibility, it may reduce the flexibility of the protective film and make it more prone to cracking when bent or subjected to external impact.

[0087] 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. A scratch-resistant PET protective film, characterized in that, It includes a PET base film layer, a bottom layer, and a top layer. The bottom layer is obtained by coating the PET base film layer with a bottom layer coating liquid, and the top layer is obtained by coating the bottom layer with a top layer coating liquid. The underlying coating liquid comprises the following raw materials in parts by weight: 35-45 parts modified polyurethane acrylate, 3-5 parts silane coupling agent, 1-3 parts first photoinitiator, and 40-50 parts ethyl acetate. The surface coating liquid comprises the following raw materials in parts by weight: 40-50 parts aliphatic polyurethane acrylate, 6-10 parts glycidyl methacrylate, 4-6 parts modified nano silica, 1-3 parts second photoinitiator, 1-2 parts leveling agent, and 45-55 parts ethyl acetate.

2. The scratch-resistant PET protective film according to claim 1, characterized in that, The modified polyurethane acrylate is prepared by the following method: Diisocyanate, catalyst, diluent and polymerization inhibitor are mixed and stirred evenly. The mixture is heated and polycaprolactone triol is added. The mixture is stirred evenly and heated to react, resulting in a polyurethane prepolymer. The mixture is cooled and 2-acryloyloxyethyl 6-hydroxyhexanoate is added. The mixture is stirred evenly and heated to react, resulting in a polyurethane acrylate prepolymer. The mixture is cooled and saturated fatty alcohol is added. The mixture is heated to react, and after the reaction is complete, modified polyurethane acrylate is obtained.

3. The scratch-resistant PET protective film according to claim 2, characterized in that, The molar ratio of polycaprolactone triol, diisocyanate, 2-acryloyloxyethyl 6-hydroxyhexanoate, and saturated fatty alcohol is 1:(2.6-3.2):(1.5-2):(1.2-1.6).

4. The scratch-resistant PET protective film according to claim 2, characterized in that, The saturated fatty alcohols include one or more of lauryl alcohol, cetearyl alcohol, and stearyl alcohol.

5. The scratch-resistant PET protective film according to claim 1, characterized in that, The method for preparing the modified nano-silica includes the following steps: Nano-silica was mixed with a dispersing solvent, stirred thoroughly and heated, vinylsilane was added, and the reaction was maintained at this temperature. After the reaction was completed, the mixture was filtered, washed and dried to obtain modified nano-silica.

6. The scratch-resistant PET protective film according to claim 5, characterized in that, The mass ratio of the nano-silica to vinylsilane is 1:(0.1-0.2).

7. The scratch-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.

8. The scratch-resistant PET protective film according to claim 1, characterized in that, The first photoinitiator includes one or more of α-hydroxy ketones, acetophenone and its derivatives, and acylphosphine oxides; the second photoinitiator includes one or more of α-hydroxy ketones, acetophenone and its derivatives, and acylphosphine oxides.

9. A method for preparing a scratch-resistant PET protective film according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Under light-protected conditions, the modified polyurethane acrylate, silane coupling agent, first photoinitiator, and ethyl acetate are stirred and mixed according to the weight parts. After mixing, the mixture is stored in the dark to obtain the bottom coating liquid. Under light-protected conditions, the aliphatic polyurethane acrylate, glycidyl methacrylate, modified nano silica, second photoinitiator, leveling agent, and ethyl acetate are stirred and mixed according to the weight parts. After mixing, the mixture is stored in the dark to obtain the top coating liquid. S2. Perform corona treatment on the cleaned PET base film layer; S3. Apply the base coating liquid onto the PET base film layer, and after preliminary curing, form a solid base layer; S4. Apply the topcoat liquid to the bottom layer, and after gradient curing, form the topcoat to obtain a scratch-resistant PET protective film.

10. The method for preparing a scratch-resistant PET protective film according to claim 9, characterized in that, The thickness of the PET base film layer is 50μm-188μm, the thickness of the bottom layer is 1μm-5μm, and the thickness of the top layer is 2μm-8μm.

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