A low shrinkage protective film and a method for preparing the same

Abstract

This invention discloses a low-shrinkage protective film and its preparation method, relating to the field of film material technology. A low-shrinkage protective film comprises a surface functional layer, a PET substrate layer, a pressure-sensitive adhesive layer, and a release layer sequentially disposed therefrom. The PET substrate layer comprises the following raw materials in parts by weight: 65-80 parts polyethylene terephthalate; 18-25 parts polycarbonate; 4-8 parts compatibilizer; 3-6 parts styrene-sodium methacrylate ionomer; 1-2.5 parts rare earth oxides; 1-3 parts talc; and 2-5 parts nano-silica. The low-shrinkage protective film provided in this application, as an electronic screen protector, can effectively prevent shrinkage and edge curling.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, and in particular to a low-shrinkage protective film and its preparation method. Background Technology

[0002] Screen protectors are applied to the surface of electronic screens as a surface protection material, providing functions such as scratch resistance, dust protection, and stain protection. The mainstream structure of screen protectors is a multi-layer composite design, typically consisting of:

[0003] Surface functional layers: such as scratch-resistant hardening coating, antistatic coating, anti-UV coating, anti-blue light coating, privacy coating, etc.;

[0004] Substrate layer: As the main material of the protective film, it determines the mechanical and optical properties of the protective film;

[0005] Adhesive layer: Acrylic pressure-sensitive adhesive layer or silicone pressure-sensitive adhesive layer are commonly used for attaching electronic screens;

[0006] Release layer: Used to protect the adhesive layer, it needs to be removed before use.

[0007] The substrate layer of existing protective films is often made of PET material, which has the advantages of high light transmittance, hard texture, and scratch resistance. However, during the manufacturing process of PET protective films, the film material undergoes a "stretching-cooling and shaping" process, which causes the macromolecular chains to align in a specific direction. This results in a memory effect in the material. When the protective film is heated or placed in a high-temperature environment, the "frozen" molecular chains begin to relax and retract to their unstretched natural state. At this time, the protective film will exhibit phenomena such as shrinkage and edge curling, affecting the normal use of the protective film. Summary of the Invention

[0008] To avoid shrinkage and edge curling of electronic screen protectors, this application provides a low-shrinkage protective film and its preparation method.

[0009] This application provides a low-shrinkage protective film and its preparation method, which adopts the following technical solution:

[0010] In a first aspect, a low-shrinkage protective film comprises a surface functional layer, a PET substrate layer, a pressure-sensitive adhesive layer, and a release layer disposed sequentially, wherein the PET substrate layer comprises the following raw materials in parts by weight:

[0011] 65-80 parts of polyethylene terephthalate;

[0012] 18-25 parts polycarbonate;

[0013] 4-8 parts compatibilizer;

[0014] 3-6 parts of styrene-sodium methacrylate ionomer;

[0015] Rare earth oxides 1-2.5 parts;

[0016] 1-3 parts talcum powder;

[0017] 2-5 parts of nano-silica.

[0018] Through the above technical solutions, the shrinkage of PET protective film is mainly caused by the relaxation and retraction of molecular chains in the PET substrate (polymer material) after heating, resulting in shrinkage and edge curling of the protective film. Therefore, the PET substrate layer in this application is modified with polyethylene terephthalate. Polycarbonate and compatibilizer are selected and compounded with PET. Rigid or flexible chain segments are introduced through blending, which disrupts the regularity of PET, increases the crystallization induction points, and improves crystallization performance and toughness. Styrene-sodium methacrylate ionomer can coordinate with the ester groups of PET, thereby playing a nucleation and toughening role and reducing post-crystallization shrinkage of PET after cooling. Rare earth oxides inhibit the thermal motion of molecular chains through lattice anchoring effect. Under heating conditions, the retraction of molecular chains is hindered, so that the protective film does not curl. At the same time, the addition of the above raw materials will not adversely affect the transparency and optical properties of the protective film. The presence of talc and nano-silica can act as anisotropic nucleating agents to further guide and control the crystallization process, while improving the heat resistance, wear resistance and anti-adhesion of the protective film. The crystallization behavior of polyethylene terephthalate can be controlled by adjusting the raw materials to improve the dimensional stability of the protective film.

[0019] Furthermore, the polyethylene terephthalate is prepared by in-situ polymerization of nano-alumina through the following steps:

[0020] The alumina sol was diluted with ethylene glycol to obtain a diluted solution. The diluted solution was stirred and heated to 60-80℃. The coupling agent KH-560 was dissolved in an ethylene glycol / water mixed solvent to obtain a mixed solution. The mixed solution was slowly added dropwise to the diluted solution, and the reaction was continued for 2-4 hours. Water and a small amount of alcohol were removed by vacuum distillation to obtain a modified alumina-ethylene glycol dispersion.

[0021] Terephthalic acid, ethylene glycol, and antimony-based catalyst were mixed and esterified at 220-250℃ and 0.25-0.3MPa. After the reaction was completed, a modified alumina-ethylene glycol dispersion was added under nitrogen protection, and the mixture was stirred for 30-40 minutes while maintaining the temperature.

[0022] Then, the temperature is raised to 270-285℃ and a vacuum is drawn to carry out a polycondensation reaction until the predetermined viscosity is reached, and the product is discharged to obtain polyethylene terephthalate.

[0023] The above technical solution modifies the surface functional groups of alumina using silane coupling agent KH-550, dispersing it in ethylene glycol to form a stable organic nano-dispersion. Ethylene glycol, as one of the reaction raw materials, does not introduce other impurities. The silane coupling agent bridges the nano-alumina and PET, improving the system's compatibility and ensuring that the nano-alumina is uniformly dispersed within the PET molecules. Adding modified alumina during the polycondensation stage avoids the adverse effects of moisture interference on the synthesis of PET molecular chains. By dispersing nano-alumina within the PET molecular chains, it promotes the formation of a finer and more stable crystal structure in PET. By acting as a rigid anchor point, it physically restricts the thermal shrinkage of the PET molecular chains, improving the thermal and dimensional stability of the protective film.

[0024] Furthermore, the talc powder is selected from modified talc powder and prepared through the following steps:

[0025] The talc powder was soaked in a 0.5-1 mol / L acetic acid solution for 5-10 minutes, filtered, washed and dried to obtain pretreated talc powder.

[0026] Phosphoric acid was dissolved in 0.2-0.5 mol / L dichloromethane. Carbonyl diimidazole was added under ice bath and stirred for 20-30 min. 1,3-diepoxypentan-5,5-methanol was added dropwise. After the reaction was completed, the temperature was raised to 20-25℃ and the reaction was carried out for 4-6 h. After the reaction was completed, water was added and stirred. The organic phase was separated and washed with water, dried with anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation to obtain diepoxy phosphate.

[0027] Diepoxyphosphate was mixed with pretreated talc powder and ball-milled to obtain modified talc powder.

[0028] Through the above technical solution, the phosphate groups in the diepoxyphosphate ester molecule can chemically bond or physically adsorb with the hydroxyl groups on the surface of talc, thereby improving the interfacial compatibility and dispersibility of talc with PET. Modified talc can further enhance the impact resistance of the protective film and reduce the shrinkage rate.

[0029] Furthermore, the compatibilizer is selected from one or more of the following: ethylene-acrylonitrile-butadiene-glycidyl methacrylate copolymer, styrene-acrylonitrile-glycidyl methacrylate terpolymer, and ethylene-octene elastomer grafted with glycidyl methacrylate.

[0030] The above technical solution uses the addition of compatibilizer to improve the interfacial compatibility between PET and polycarbonate, thereby better exerting the toughening effect.

[0031] Furthermore, the rare earth oxide is selected from one or more of lanthanum oxide, yttrium oxide, and ytterbium oxide.

[0032] Furthermore, the alumina sol has a solid content of 20%-30% and a particle size of 10-20 nm.

[0033] The above technical solution controls the content of nano-alumina to avoid affecting the transparency of PET.

[0034] Furthermore, the weight ratio of ethylene glycol, terephthalic acid, antimony catalyst and alumina sol is (5-8):(10-15):(0.005-0.02):(0.8-1.2), and the weight of coupling agent KH-560 is 3%-6% of the weight of alumina sol.

[0035] Further, the weight ratio of phosphoric acid, carbonyl diimidazole, and 1,3-diepoxypent-5,5-methanol is (9-12):(0.01-0.03):(14-18), and the weight of diepoxy phosphate is 0.8%-2% of the weight of talc.

[0036] Furthermore, the ball milling speed is 250-300 r / min, and the ball milling time is 40-60 min.

[0037] The above technical solution controls the particle size of modified talc powder through ball milling, promoting uniform dispersion in the PET system.

[0038] Furthermore, the surface functional layer is selected from one or more of the following: antistatic coating, anti-blue light coating, and anti-scratch hardening coating.

[0039] Furthermore, the thickness of the surface functional layer is 5μm-15μm, the thickness of the PET substrate layer is 100μm-200μm, and the thickness of the pressure-sensitive adhesive layer is 5μm-10μm.

[0040] Secondly, a method for preparing a low-shrinkage protective film includes the following steps:

[0041] The raw materials for the PET substrate layer are mixed evenly and then extruded through an extruder to obtain the PET substrate layer;

[0042] The raw materials for the surface functional layer are mixed evenly and coated onto the upper surface of the PET substrate layer. After curing, the surface functional layer is formed.

[0043] Mix the pressure-sensitive adhesive material evenly, coat it onto the lower surface of the PET substrate layer, and dry it.

[0044] A release layer is bonded to the lower surface of the pressure-sensitive adhesive layer to obtain a low-shrinkage PET protective film.

[0045] By using the above technical solution, a PET protective film with low shrinkage, good transparency, and good heat resistance is obtained by sequentially laminating a surface functional layer, a PET substrate layer, a pressure-sensitive adhesive layer, and a release layer.

[0046] Furthermore, the PET substrate layer is prepared by the following steps:

[0047] S1. Polyethylene terephthalate, polycarbonate, compatibilizer, styrene-sodium methacrylate ionomer and rare earth oxides are added to a mixer and stirred at 65-70°C until a uniform mixture is obtained.

[0048] S2. Add talc powder and nano silica together to the mixture, control the stirring speed at 380-420 r / min, mix for 10-20 min to obtain the mixture;

[0049] S3. The mixture is fed into a twin-screw extruder and extruded to obtain the desired PET substrate layer.

[0050] In summary, this application has the following beneficial effects:

[0051] 1. The shrinkage of PET protective films is mainly caused by the relaxation and retraction of molecular chains in the PET substrate (polymer material) after heating, leading to edge curling. Therefore, the PET substrate layer in this application is modified with polyethylene terephthalate. Polycarbonate and compatibilizers are blended with PET to introduce rigid or flexible chain segments, disrupting the regularity of PET, increasing crystallization induction points, and improving crystallization performance and toughness. Styrene-sodium methacrylate ionomer can coordinate with the ester groups of PET, thereby playing a nucleation and toughening role and reducing post-crystallization shrinkage after PET cooling. Rare earth oxides inhibit the thermal motion of molecular chains through lattice anchoring effect, hindering the retraction of molecular chains under heating, thus preventing edge curling of the protective film. At the same time, the addition of the above raw materials will not adversely affect the transparency and optical properties of the protective film. The presence of talc and nano-silica can act as anisotropic nucleating agents to further guide and control the crystallization process, while also improving the heat resistance, wear resistance, and anti-blocking properties of the protective film. The crystallization behavior of polyethylene terephthalate can be controlled by adjusting the raw materials to improve the dimensional stability of the protective film.

[0052] 2. Silane coupling agent KH-550 was selected to modify the surface functional groups of alumina, which was then dispersed in ethylene glycol to form a stable organic nano-dispersion. Ethylene glycol, as one of the reaction raw materials, does not introduce other impurities. The silane coupling agent bridges the nano-alumina and PET, improving the system's compatibility and ensuring that the nano-alumina is uniformly dispersed within the PET molecules. The modified alumina was added during the polycondensation stage to avoid the adverse effects of moisture interference on the synthesis of the PET molecular chain. By dispersing the nano-alumina within the PET molecular chain, a finer and more stable crystal structure is formed in PET. By acting as a rigid anchor point, it physically restricts the thermal shrinkage of the PET molecular chain, improving the thermal and dimensional stability of the protective film. Detailed Implementation

[0053] Preparation Example

[0054] Preparation Example 1

[0055] Preparation of polyethylene terephthalate

[0056] 1.5 kg of ethylene glycol was used to dilute 0.8 kg of alumina sol with a solid content of 20% and a particle size of 10-20 mm to obtain a diluted solution. The diluted solution was stirred and heated to 60°C. 0.024 kg of coupling agent KH-560 was dissolved in a mixed solvent of 0.5 kg of ethylene glycol and 0.5 kg of water to obtain a mixed solution. The mixed solution was slowly added dropwise to the diluted solution, and the reaction was continued to be stirred for 2 hours. Water and a small amount of alcohol were removed by vacuum distillation to obtain a modified alumina-ethylene glycol dispersion.

[0057] 10 kg of terephthalic acid, 3 kg of ethylene glycol, and 0.005 kg of antimony-based catalyst were mixed and esterified at 220 °C and 0.25 MPa. After the reaction was completed, a modified alumina-ethylene glycol dispersion was added under nitrogen protection, and the mixture was stirred for 30 min while maintaining the temperature.

[0058] Then, the temperature is raised to 270°C and a vacuum is drawn to carry out a polycondensation reaction until the predetermined viscosity is reached, and the product is discharged to obtain polyethylene terephthalate.

[0059] Preparation Example 2

[0060] 3 kg of ethylene glycol was used to dilute 1.2 kg of alumina sol with a solid content of 30% and a particle size of 10-20 mm to obtain a diluted solution. The diluted solution was stirred and heated to 80°C. 0.072 kg of coupling agent KH-560 was dissolved in a mixed solvent of 0.5 kg of ethylene glycol and 0.5 kg of water to obtain a mixed solution. The mixed solution was slowly added dropwise to the diluted solution, and the reaction was continued to be stirred for 4 hours. Water and a small amount of alcohol were removed by vacuum distillation to obtain a modified alumina-ethylene glycol dispersion.

[0061] 15 kg of terephthalic acid, 4.5 kg of ethylene glycol, and 0.02 kg of antimony-based catalyst were mixed and esterified at 250 °C and 0.3 MPa. After the reaction was completed, a modified alumina-ethylene glycol dispersion was added under nitrogen protection, and the mixture was stirred for 40 min while maintaining the temperature.

[0062] Then, the temperature is raised to 285°C and a vacuum is drawn to carry out a polycondensation reaction until the predetermined viscosity is reached, and the product is discharged to obtain polyethylene terephthalate.

[0063] Preparation Example 3

[0064] Preparation of modified talc

[0065] Talc powder was soaked in 0.5 mol / L acetic acid solution for 10 min, filtered, washed and dried to obtain pretreated talc powder;

[0066] 9 g of phosphoric acid was dissolved in 0.5 mol / L dichloromethane. 0.01 g of carbonyl diimidazole was added under ice bath conditions and stirred for 20 min. 14 g of 1,3-diepoxypent-5,5-methanol was added dropwise. After the reaction was completed, the temperature was raised to 20 °C and the reaction was carried out for 6 h. After the reaction was completed, water was added and stirred. The organic phase was separated by liquid separation, washed with water, dried with anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation to obtain diepoxy phosphate.

[0067] Diepoxyphosphate was mixed with pretreated talc powder and ball-milled. The weight of the diepoxyphosphate was 0.8% of the weight of the talc powder. The ball milling speed was 250 r / min and the ball milling time was 60 min to obtain modified talc powder.

[0068] Preparation Example 4

[0069] Preparation of modified talc

[0070] Talc powder was soaked in 1 mol / L acetic acid solution for 5 min, filtered, washed and dried to obtain pretreated talc powder.

[0071] 12 g of phosphoric acid was dissolved in 0.2 mol / L dichloromethane. 0.03 g of carbonyl diimidazole was added under ice bath conditions and stirred for 30 min. 18 g of 1,3-diepoxypentyl-5,5-methanol was added dropwise. After the reaction was completed, the temperature was raised to 25 °C and the reaction was carried out for 4 h. After the reaction was completed, water was added and stirred. The organic phase was separated by liquid-liquid extraction. The organic phase was washed with water, dried with anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation to obtain diepoxy phosphate.

[0072] Diepoxyphosphate was mixed with pretreated talc powder and ball-milled. The weight of the diepoxyphosphate was 2% of the weight of the talc powder. The ball milling speed was 300 r / min and the ball milling time was 40 min to obtain modified talc powder. Example

[0073] Example 1

[0074] A low-shrinkage protective film includes a surface functional layer, a PET substrate layer, a pressure-sensitive adhesive layer, and a release layer arranged sequentially. In this embodiment, the surface functional layer is an antistatic coating with a thickness of 5 μm; the pressure-sensitive adhesive layer is an acrylic pressure-sensitive adhesive layer with a thickness of 5 μm; the release layer is a PET release layer; and the PET substrate layer has a thickness of 100 μm. The film comprises the following raw materials:

[0075] 65 kg of polyethylene terephthalate, the polyethylene terephthalate prepared in Preparation Example 1 was selected;

[0076] 18 kg of polycarbonate, brand name Mitsubishi S-3000UR, purchased from Guanhe Plastics Technology (Shanghai) Co., Ltd.

[0077] 4 kg of compatibilizer, selected from ethylene-acrylonitrile-butadiene-glycidyl methacrylate copolymer;

[0078] 3 kg of sodium styrene-methacrylate ionomer;

[0079] 1 kg of rare earth oxides, yttrium oxide is selected;

[0080] 1 kg of talc powder, purchased from Lingshou County Xudong Mineral Products Processing Plant, with a mesh size of 800 mesh;

[0081] 2 kg of nano-silica.

[0082] In this embodiment, the surface functional layer includes the following raw materials: 1 kg of antistatic agent, which is an organolithium-based antistatic agent of model EF-N115; 7 kg of UV-curable resin, model CB-2707, from Lida Chemical; 15 parts of propylene glycol methyl ether; and 15 parts of ethyl acetate.

[0083] The pressure-sensitive adhesive layer comprises the following raw materials: 100kg polyacrylate resin with a weight-average molecular weight of 500,000 and a glass transition temperature of -50℃; 3kg isocyanate curing agent, brand name D-100K, manufactured by DIC Japan; 0.5kg antioxidant 1010; and 35kg ethyl acetate.

[0084] The release layer is made of PET release film, purchased from Shenzhen Xinweisheng Adhesive Products Co., Ltd.

[0085] The method for preparing a low-shrinkage protective film includes the following steps:

[0086] Preparation of PET substrate layer: Polyethylene terephthalate, polycarbonate, compatibilizer, styrene-sodium methacrylate ionomer and rare earth oxides are added to a mixer and stirred at 65°C until homogeneous to obtain a mixture; talc powder and nano-silica are added to the mixture, and the stirring speed is controlled at 380 r / min for 20 min to obtain a mixture; the mixture is fed into a twin-screw extruder for extrusion to obtain the desired PET substrate layer;

[0087] Preparation of surface functional layer: The raw materials of surface functional layer are mixed evenly and coated on the upper surface of PET substrate layer. After curing, surface functional layer is formed.

[0088] Preparation of pressure-sensitive adhesive layer: Mix the pressure-sensitive adhesive layer raw materials evenly, coat them on the lower surface of the PET substrate layer, and dry;

[0089] Preparation of release layer: The release layer is attached to the lower surface of the pressure-sensitive adhesive layer;

[0090] A low-shrinkage PET protective film was obtained.

[0091] Example 2

[0092] A low-shrinkage protective film includes a surface functional layer, a PET substrate layer, a pressure-sensitive adhesive layer, and a release layer arranged sequentially. In this embodiment, the surface functional layer is a blue light blocking coating with a thickness of 15 μm; the pressure-sensitive adhesive layer is a silicone pressure-sensitive adhesive layer with a thickness of 10 μm; the release layer is a PET release layer; and the PET substrate layer has a thickness of 200 μm. The film comprises the following raw materials:

[0093] 80 kg of polyethylene terephthalate, the polyethylene terephthalate prepared in Preparation Example 2 was selected;

[0094] 25kg of polycarbonate, brand name Mitsubishi S-3000UR, purchased from Guanhe Plastics Technology (Shanghai) Co., Ltd.

[0095] 8 kg of compatibilizer, selected as styrene-acrylonitrile-glycidyl methacrylate terpolymer;

[0096] 6 kg of sodium styrene-methacrylate ionomer;

[0097] 2.5 kg of rare earth oxides, lanthanum oxide was selected;

[0098] 3 kg of talc powder, purchased from Xudong Mineral Products Processing Plant in Lingshou County, with a mesh size of 800 mesh;

[0099] 5 kg of nano-silica.

[0100] In this embodiment, the surface functional layer includes the following raw materials: 20 kg of polyester acrylate; 80 kg of ethyl acetate; 2 kg of α-hydroxy ketone photoinitiator; and 5 kg of rare earth luminescent material, which is rare earth ion-doped molybdenum tungstate, purchased from Xi'an Qiyue Biotechnology Co., Ltd.

[0101] The pressure-sensitive adhesive layer comprises the following raw materials: 100kg polyacrylate resin with a weight-average molecular weight of 500,000 and a glass transition temperature of -50℃; 3kg isocyanate curing agent, brand name D-100K, manufactured by DIC Japan; 0.5kg antioxidant 1010; and 35kg ethyl acetate.

[0102] The release layer is made of PET release film, purchased from Shenzhen Xinweisheng Adhesive Products Co., Ltd.

[0103] The method for preparing a low-shrinkage protective film includes the following steps:

[0104] Preparation of PET substrate layer: Polyethylene terephthalate, polycarbonate, compatibilizer, styrene-sodium methacrylate ionomer and rare earth oxides are added to a mixer and stirred at 70°C to obtain a uniform mixture; talc powder and nano silica are added to the mixture, and the stirring speed is controlled at 420 r / min, and the mixture is mixed for 10 min to obtain a compound; the compound is fed into a twin-screw extruder for extrusion to obtain the desired PET substrate layer;

[0105] Preparation of surface functional layer: The raw materials of surface functional layer are mixed evenly and coated on the upper surface of PET substrate layer. After curing, surface functional layer is formed.

[0106] Preparation of pressure-sensitive adhesive layer: Mix the pressure-sensitive adhesive layer raw materials evenly, coat them on the lower surface of the PET substrate layer, and dry;

[0107] Preparation of release layer: The release layer is attached to the lower surface of the pressure-sensitive adhesive layer;

[0108] A low-shrinkage PET protective film was obtained.

[0109] Example 3

[0110] A low-shrinkage protective film includes a surface functional layer, a PET substrate layer, a pressure-sensitive adhesive layer, and a release layer arranged sequentially. In this embodiment, the surface functional layer is a scratch-resistant hardened coating with a thickness of 10 μm; the pressure-sensitive adhesive layer is a silicone pressure-sensitive adhesive layer with a thickness of 8 μm; the release layer is a PET release layer; and the PET substrate layer has a thickness of 150 μm. The film comprises the following raw materials:

[0111] 73 kg of polyethylene terephthalate, the polyethylene terephthalate prepared in Preparation Example 2 was selected;

[0112] 22kg of polycarbonate, brand name Lotte SC-1100R from South Korea, purchased from Dongguan Shenghao Plastic Raw Materials Co., Ltd.

[0113] 7 kg of compatibilizer, selected from ethylene-octene elastomer grafted with glycidyl methacrylate;

[0114] 5 kg of sodium styrene-methacrylate ionomer;

[0115] 1.7 kg of rare earth oxides, ytterbium oxide was selected;

[0116] 2 kg of talc powder, purchased from Shijiazhuang Chenghe New Material Technology Co., Ltd., China, with a mesh size of 1250;

[0117] 3 kg of nano-silica.

[0118] In this embodiment, the surface functional layer includes the following raw materials: 50 kg of polyurethane acrylic resin, Sartoma Corporation, grade CN8007NS; and 50 kg of nano-silica.

[0119] The pressure-sensitive adhesive layer comprises the following raw materials: 100kg polyacrylate resin with a weight-average molecular weight of 500,000 and a glass transition temperature of -50℃; 3kg isocyanate curing agent, brand name D-100K, manufactured by DIC Japan; 0.5kg antioxidant 1010; and 35kg ethyl acetate.

[0120] The release layer is made of PET release film, purchased from Shenzhen Xinweisheng Adhesive Products Co., Ltd.

[0121] The preparation method is the same as that in Example 1.

[0122] Example 4

[0123] The difference between this embodiment and Embodiment 1 is that the talc in the PET substrate layer is different.

[0124] In this embodiment, the talc powder used is the modified talc powder prepared in Preparation Example 3.

[0125] Example 5

[0126] The difference between this embodiment and Embodiment 1 is that the talc in the PET substrate layer is different.

[0127] In this embodiment, the talc powder used is the modified talc powder prepared in Preparation Example 4.

[0128] Example 6

[0129] The difference between this embodiment and Embodiment 1 is that the polyethylene terephthalate in the PET substrate layer is different.

[0130] In this embodiment, the polyethylene terephthalate is DuPont RE15022 from Japan, purchased from Dongguan Xuanyuan Plastics Co., Ltd. Comparative Example

[0131] Comparative Example 1

[0132] The difference between this comparative example and Example 1 is that the raw materials in the PET substrate are different.

[0133] In this comparative example, no polycarbonate or compatibilizer was added to the raw materials of the PET substrate.

[0134] Comparative Example 2

[0135] The difference between this comparative example and Example 1 is that the raw materials in the PET substrate are different.

[0136] In this comparative example, no styrene-sodium methacrylate ionomer was added to the raw materials of the PET substrate.

[0137] Performance testing

[0138] The properties of the PET substrate layer of the protective films prepared in Examples 1-6 and Comparative Examples 1-2, such as heat shrinkage rate and light transmittance, were tested. The test results are shown in Table 1.

[0139] The heat shrinkage rate was tested in the following way:

[0140] Rectangular strips measuring 15mm × 100mm were cut from the PET substrate layer along both the MD and TD directions and marked. The strips were then placed in a constant temperature water bath at 150℃ for 30 minutes for heat treatment. The heat shrinkage rate S was calculated as follows:

[0141] S = (L0 - L) / L0 × 100%, where L0 is the original length of the sample (mm); L is the length of the sample after shrinkage (mm).

[0142] The light transmittance was tested according to the method in GB / T 2410-2008 "Test Method for Light Transmittance and Haze of Transparent Plastics".

[0143] Table 1

[0144] MD heat shrinkage rate (%) TD heat shrinkage rate (%) Light transmittance (%) Example 1 0.87 0.54 92.3 Example 2 0.91 0.59 91.8 Example 3 0.83 0.51 92.1 Example 4 0.68 0.43 93.4 Example 5 0.72 0.46 93.2 Example 6 1.12 0.7 92.7 Comparative Example 1 1.75 1.32 92 Comparative Example 2 1.57 1.08 90.5

[0145] According to the data in Table 1, the light transmittance of the PET substrate layer prepared by this application using specific raw materials is >90%, and the heat shrinkage rate is <1% in both the transverse and longitudinal directions. This indicates that the PET substrate layer prepared by this application optimizes dimensional stability and improves high-temperature resistance while maintaining good transparency and light transmittance.

[0146] The protective film obtained by compositing the PET substrate layer, surface functional layer, pressure-sensitive adhesive layer, and release layer of this application has a low thermal shrinkage rate. When applied to the protective film of electronic screens, it can adapt to high-temperature environments and reduce edge curling and shrinkage.

[0147] This application regulates the crystallization behavior of PET molecular chains through the synergy of raw materials. By promoting the formation of smaller and finer crystals in PET and increasing physical anchor points to restrict the thermal contraction movement of molecular chains, the structure of the PET substrate layer is fundamentally changed, thereby improving the dimensional stability of the protective film.

[0148] By comparing the data from Example 6, Comparative Example 1, and Comparative Example 2, it was found that the heat shrinkage rate increased when any one of the raw materials was missing, demonstrating the synergistic effect of the raw materials in this application on low shrinkage performance.

[0149] 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 low shrinkage protective film comprising, in order, a surface functional layer, a PET substrate layer, a pressure sensitive adhesive layer, and a release layer, characterized in that: The PET substrate layer comprises the following raw materials in parts by weight: 65-80 parts of polyethylene terephthalate; 18-25 parts polycarbonate; 4-8 parts compatibilizer; 3-6 parts of styrene-sodium methacrylate ionomer; Rare earth oxides 1-2.5 parts; 1-3 parts talcum powder; 2-5 parts of nano-silica; The polyethylene terephthalate is prepared by in-situ polymerization of nano-alumina through the following steps: The alumina sol was diluted with ethylene glycol to obtain a diluted solution. The diluted solution was stirred and heated to 60-80℃. The coupling agent KH-560 was dissolved in an ethylene glycol / water mixed solvent to obtain a mixed solution. The mixed solution was slowly added dropwise to the diluted solution, and the reaction was continued for 2-4 hours. Water and a small amount of alcohol were removed by vacuum distillation to obtain a modified alumina-ethylene glycol dispersion. Terephthalic acid, ethylene glycol, and antimony-based catalyst were mixed and esterified at 220-250℃ and 0.25-0.3MPa. After the reaction was completed, a modified alumina-ethylene glycol dispersion was added under nitrogen protection, and the mixture was stirred for 30-40 minutes while maintaining the temperature. Then the temperature is raised to 270-285℃ and a vacuum is drawn to carry out a polycondensation reaction until the predetermined viscosity is reached, and the product is discharged to obtain polyethylene terephthalate. The talc powder used is bis(epoxyphosphate) modified talc powder.

2. The low shrinkage protective film according to claim 1, characterized in that: The diepoxyphosphate modified talc powder is prepared through the following steps: The talc powder was soaked in a 0.5-1 mol / L acetic acid solution for 5-10 minutes, filtered, washed and dried to obtain pretreated talc powder. Phosphoric acid was dissolved in 0.2-0.5 mol / L dichloromethane. Carbonyl diimidazole was added under ice bath and stirred for 20-30 min. 1,3-diepoxypentan-5,5-methanol was added dropwise. After the reaction was completed, the temperature was raised to 20-25℃ and the reaction was carried out for 4-6 h. After the reaction was completed, water was added and stirred. The organic phase was separated and washed with water, dried with anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation to obtain diepoxy phosphate. Modified talc powder was obtained by ball milling a mixture of diepoxyphosphate and talc.

3. The low shrinkage protective film according to claim 1, characterized in that: The compatibilizer is selected from one or more of the following: ethylene-acrylonitrile-butadiene-glycidyl methacrylate copolymer, styrene-acrylonitrile-glycidyl methacrylate terpolymer, and ethylene-octene elastomer grafted with glycidyl methacrylate.

4. The low shrinkage protective film according to claim 1, characterized in that: The rare earth oxide is selected from one or more of lanthanum oxide, yttrium oxide, and ytterbium oxide.

5. The low shrinkage protective film according to claim 1, wherein: The alumina sol has a solid content of 20%-30% and a particle size of 10-20 nm.

6. The low shrinkage protective film according to claim 1, wherein: The weight ratio of ethylene glycol, terephthalic acid, antimony catalyst and alumina sol is (5-8):(10-15):(0.005-0.02):(0.8-1.2), and the weight of coupling agent KH-560 is 3%-6% of the weight of alumina sol.

7. The low shrinkage protective film according to claim 2, wherein: The weight ratio of phosphoric acid, carbonyl diimidazole, and 1,3-diepoxypentyl-5,5-methanol is (9-12):(0.01-0.03):(14-18), and the weight of diepoxy phosphate is 0.8%-2% of the weight of talc.

8. The low shrinkage protective film according to claim 2, wherein: The ball milling speed is 250-300 r / min, and the ball milling time is 40-60 min.

9. The low shrinkage protective film according to claim 1, wherein: The surface functional layer is selected from one or more of the following: antistatic coating, anti-blue light coating, and anti-scratch hardening coating.

10. The low shrinkage protective film according to claim 1, wherein: The thickness of the surface functional layer is 5μm-15μm, the thickness of the PET substrate layer is 100μm-200μm, and the thickness of the pressure-sensitive adhesive layer is 5μm-10μm.

11. A method of producing a low shrinkage protective film according to any one of claims 1 to 10, characterized in that, Includes the following steps: The raw materials for the PET substrate layer are mixed evenly and then extruded through an extruder to obtain the PET substrate layer; The raw materials for the surface functional layer are mixed evenly and coated onto the upper surface of the PET substrate layer. After curing, the surface functional layer is formed. Mix the pressure-sensitive adhesive material evenly, coat it onto the lower surface of the PET substrate layer, and dry it. A release layer is bonded to the lower surface of the pressure-sensitive adhesive layer to obtain a low-shrinkage PET protective film.

12. The method of claim 11, wherein: The PET substrate layer is prepared by the following steps: S1. Polyethylene terephthalate, polycarbonate, compatibilizer, styrene-sodium methacrylate ionomer and rare earth oxides are added to a mixer and stirred at 65-70°C until a uniform mixture is obtained. S2. Add talc powder and nano silica together to the mixture, control the stirring speed at 380-420 r / min, mix for 10-20 min to obtain the mixture; S3. The mixture is fed into a twin-screw extruder and extruded to obtain the desired PET substrate layer.